US20080179011A1 - Plasma reactor with wide process window employing plural vhf sources - Google Patents
Plasma reactor with wide process window employing plural vhf sources Download PDFInfo
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- US20080179011A1 US20080179011A1 US11/734,040 US73404007A US2008179011A1 US 20080179011 A1 US20080179011 A1 US 20080179011A1 US 73404007 A US73404007 A US 73404007A US 2008179011 A1 US2008179011 A1 US 2008179011A1
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- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
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- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
- C23C16/45563—Gas nozzles
- C23C16/45574—Nozzles for more than one gas
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- C—CHEMISTRY; METALLURGY
- C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
- C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
- C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
- C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
- C23C16/50—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges
- C23C16/505—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges using radio frequency discharges
- C23C16/509—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating using electric discharges using radio frequency discharges using internal electrodes
- C23C16/5096—Flat-bed apparatus
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/32—Gas-filled discharge tubes
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/32—Gas-filled discharge tubes
- H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
- H01J37/32082—Radio frequency generated discharge
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- H01J37/32155—Frequency modulation
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
- H01J37/32—Gas-filled discharge tubes
- H01J37/32009—Arrangements for generation of plasma specially adapted for examination or treatment of objects, e.g. plasma sources
- H01J37/32082—Radio frequency generated discharge
- H01J37/32174—Circuits specially adapted for controlling the RF discharge
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/67005—Apparatus not specifically provided for elsewhere
- H01L21/67011—Apparatus for manufacture or treatment
- H01L21/67017—Apparatus for fluid treatment
- H01L21/67063—Apparatus for fluid treatment for etching
- H01L21/67069—Apparatus for fluid treatment for etching for drying etching
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
- H01L21/67—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere
- H01L21/683—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping
- H01L21/6831—Apparatus specially adapted for handling semiconductor or electric solid state devices during manufacture or treatment thereof; Apparatus specially adapted for handling wafers during manufacture or treatment of semiconductor or electric solid state devices or components ; Apparatus not specifically provided for elsewhere for supporting or gripping using electrostatic chucks
Abstract
A plasma reactor includes an electrostatic chuck in the chamber for supporting the workpiece, a ceiling electrode facing the electrostatic chuck and an ESC electrode in the electrostatic chuck with an electrostatic clamping voltage supply coupled to the ESC electrode. The reactor further includes at least a first RF bias source of an LF or HF frequency coupled to the pedestal electrode, and first and second VHF power sources of different frequencies coupled to the same or to different ones of the electrodes. The first and second VHF power sources are of sufficiently high and sufficiently low frequencies, respectively, to produce center-high and center-low plasma distribution non-uniformities, respectively, in the chamber.
Description
- This application claims the benefit of U.S. Provisional Application Ser. No. 60/898,632, filed Jan. 30, 2007.
- Embodiments of the present invention concern a capacitively coupled plasma source for processing a workpiece such as a semiconductor wafer. A capacitively coupled plasma source comprises a ceiling electrode that is driven at a very high frequency (VHF) frequency over 110 MHz which can produce a high density plasma at a relatively low voltage. A capacitively coupled plasma source can further produce a low electrode potential for low electrode erosion, and permits the ion energy at the wafer surface to be limited to a low level if desired, while operating over a wide range of plasma density (very low to very high plasma ion density). One problem inherent in such a plasma source is that the ceiling electrode exhibits radial transmission line effects and loading due to the effective dielectric constant of the plasma. For example, at 150 MHz, a free-space quarter wavelength is about 20 inches, which is on the order of the diameter of the ceiling electrode (about 15 inches). Therefore, the RF field varies significantly across the surface of the ceiling electrode, giving rise to process non-uniformities at the wafer surface. For a plasma with an effective dielectric constant greater than 1, the effective wavelength is reduced to less than the ceiling electrode diameter, worsening the non-uniformity of the RF field, making processing non-uniformities across the wafer surface worse. For an etch process, this may produce a non-uniform edge low etch rate distribution across the wafer surface.
- Various approaches are employed to reduce such undesirable effects. In one approach, magnetic steering may be employed to alter the plasma ion distribution, e.g., to reduce its center-high non-uniformity to produce a somewhat flatter distribution. One problem with this approach is that a center-high non-uniformity of the source may be beyond the corrective capability of magnetic steering. Another problem with this approach can be electrical charging damage of the workpiece if the magnetic flux density is too high. In another approach, the plasma sheath (or bias) voltage is increased by applying more plasma RF bias power to the wafer. This has the effect of increasing the plasma sheath thickness which in turn typically decreases the capacitance across the ceiling-plasma sheath as well as the capacitance across the wafer-plasma sheath, thereby forming three capacitors in series, including the ceiling sheath capacitance, the plasma capacitance and the wafer sheath capacitance. The net effect is to reduce the effect of the dielectric constant of the plasma, thereby reducing the non-uniformity of the RF field. The high bias voltage required in some oxide etch plasma process recipes is compatible with this latter approach. However, a high plasma bias voltage is not desirable in some other types of plasma processes. The worst non-uniformities appear in processes employing the lowest plasma bias voltage.
- Such approaches are complicated by the fact that other process conditions dictated by the process recipe have as great an effect upon plasma distribution as either magnetic steering or bias (sheath) voltage. For example, increasing chamber pressure produces a less center high and a more center low plasma ion distribution, while decreasing the chamber pressure produces a more center high distribution. Other changes in plasma distribution are caused by source power (plasma density), gas chemistry, electronegativity of the gas mixture, pumping rate, gas flow rate and other parameters dictated by the process recipe.
- A plasma reactor is provided for processing a workpiece within a chamber of the reactor. The reactor includes an electrostatic chuck in the chamber for supporting the workpiece, a ceiling electrode facing the electrostatic chuck and an ESC electrode in the electrostatic chuck with an electrostatic clamping voltage supply coupled to the ESC electrode. The reactor further includes at least a first RF bias source of an LF or HF frequency coupled to the pedestal electrode, and first and second VHF power sources of different frequencies coupled to the same or to different ones of the electrodes. The first and second VHF power sources are of sufficiently high and sufficiently low frequencies, respectively, to produce center-high and center-low plasma distribution non-uniformities, respectively, in the chamber.
- In one embodiment, the reactor further includes a turbo pump capable having a sufficient capacity to maintain the chamber in a pressure range including a minimum pressure as low as a few mT. In a related embodiment, the reactor further includes a workpiece lift mechanism for varying a workpiece-to-ceiling gap. In a related embodiment, the ceiling electrode includes a gas distribution showerhead, the reactor further including a process gas supply coupled to the gas distribution showerhead. In one embodiment, the workpiece-to-ceiling gap defines a process region of the chamber, the reactor further including a confinement annulus between the process region and non-symmetrical elements of the chamber, the confinement annulus having a peripheral edge separated from the side wall by a side gap restriction. In one embodiment, the confinement annulus includes a planar ring extending radially from a periphery of the electrostatic chuck. In one embodiment, the confinement annulus is conductive and is coupled to an RF ground potential so as to shield the process region from electrical effects of the non-symmetrical elements in the chamber.
- So that the manner in which the above recited embodiments of the invention are attained and can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.
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FIG. 1A illustrates a plasma reactor having multiple VHF source power frequencies applied to a ceiling electrode. -
FIG. 1B depicts elements of a variable reactance or bandpass filter controlling the impedance of an RF ground return path in the reactor ofFIG. 1A . -
FIG. 2 illustrates a plasma reactor having different VHF frequencies applied to opposing electrodes. -
FIGS. 3A and 3B illustrate a plasma reactor with different VHF frequencies applied to respective concentric electrodes. -
FIG. 4 illustrates a plasma reactor with different VHF frequencies applied to the cathode electrode. -
FIG. 5 illustrates a plasma reactor with two VHF source power frequencies, in which the high VHF source power frequency is produced using a low VHF frequency generator and a third harmonic resonator. -
FIG. 6 illustrates a plasma reactor with a single VHF variable frequency generator in the low portion (e.g., 50-60 MHz) of the VHF band with a third harmonic resonator to produce a VHF frequency component in the high portion (e.g., over 100 MHz) of the VHF band at a power level determined by varying the generator output frequency. -
FIG. 7 illustrates a process that can be carried out using the reactor ofFIG. 1 . -
FIG. 8 illustrates a process that can be carried out using the reactor ofFIG. 2 . -
FIG. 9 illustrates a process that can be carried out using the reactor ofFIG. 3A . -
FIG. 10 illustrates a process that can be carried out in the reactor ofFIG. 2 by setting the two VHF frequencies f1 and f2 ofFIG. 2 equal to one another. -
FIG. 11 illustrates a process that may be carried out using the reactor ofFIG. 5 . -
FIG. 12 illustrates a process that can be carried out in a modification of the reactor ofFIG. 5 in which the locations of thef2 bandpass filter 254 and the f2 generator andmatch -
FIG. 13 illustrates a process that may be carried out in the reactor ofFIG. 6 , using only a single lower VHF frequency generator. - To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The drawings in the figures are all schematic and not to scale.
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FIG. 1A is a simplified schematic diagram of a plasma reactor capable of controlling radial distribution of plasma ion density by apportioning capacitively coupled plasma source power among different source power frequencies. The reactor has avacuum chamber 200 enclosed by acylindrical side wall 202 and a disk-shaped ceiling 204. Theceiling 204 is both a conductive ceiling electrode as well as a gas distribution showerhead or plate, and will be referred to herein as theceiling electrode 204. The ceiling electrode may optionally be covered with a conducting, semiconducting or insulating material. Theceiling electrode 204 includes inner andouter zones bottom surface 204 c coupled to respective inner and outerinternal gas manifolds outer manifolds wafer support pedestal 218 can support a workpiece such as asemiconductor wafer 220. Thepedestal 218 may have the features of an electrostatic chuck, including aconductive base layer 222 and an insulatingtop layer 224 that encloses aninternal electrode 226. Avacuum pump 228 is coupled through thefloor 230 of thechamber 200. Thepedestal 218 is supported on aleg 232 that is coupled to alift mechanism 234 that can elevate or depress the level of thepedestal 218. In one implementation, thelift mechanism 234 provides a wafer-to-ceiling gap range from about 0.3 inch to about 6 inches. The wafer is clamped onto the pedestal by applying a D.C. clamping voltage from aD.C. supply 236 to theelectrode 226.D.C. supply 236 typically includes a low-pass filter to isolate the DC supply from the RF voltage present on theelectrode 226. RF bias power may be coupled directly to theinternal electrode 226, or indirectly through theconductive base layer 222.Pedestal 218 typically includes aconductive ground housing 217 that is typically isolated fromconductive base layer 222 andinternal electrode 226 by an insulating material such as quartz, ceramic or plastic. Alternatively,conductive base layer 218 may be grounded. - The uniformity of the plasma ion radial distribution across the
chamber 200 is controlled by providing a pair of VHF plasmasource power generators RF generator 240 has a frequency in the upper portion of the VHF range, on the order of between 110 and 250 MHz, and nominally about 162 MHz, while the other RF generator has a frequency in the lower portion of the VHF range, on the order of about 40-90 MHz, and nominally about 60 MHz. We have discovered that the higher VHF frequency from the generator 240 (if applied alone) tends to produce a plasma ion density radial distribution that is center high and edge low, while the lower VHF frequency from the generator 242 (if applied alone) tends to produce a plasma ion density radial distribution that is center low and edge high. In this respect, the two generators complement one another when used simultaneously. In one embodiment, the output power of one of thegenerators generators - In one embodiment, the higher
VHF frequency generator 240 is coupled to theceiling electrode 204 through animpedance match network 244 that may be either fixed or dynamic and may be either formed of lumped or distributed elements. The lowerVHF frequency generator 242 is coupled to theceiling electrode 204 through animpedance match network 246 that is formed of either lumped or distributed elements and may be either fixed or dynamic. The output of thehigh VHF match 244 is protected from the output of thelow VHF generator 242 by anotch filter 248 tuned to block a narrow band centered around the frequency f2 of thelow VHF generator 242, or alternatively by a high-pass filter tuned to block the frequency f2 of thelow VHF generator 242. The output of thelow VHF match 246 is protected from the output of thehigh VHF generator 240 by anotch filter 250 tuned to block a narrow band centered around the frequency f1 of thehigh VHF generator 240, or alternatively by a low-pass filter tuned to block the frequency f1 of thehigh VHF generator 240. The filter circuits are designed in accordance with conventional practice in conjunction with the matching networks so as to achieve the desired matching range with the required frequency isolation. - Two RF ground return paths are provided for each of the VHF frequencies f1, f2. A path along the side of the
chamber 200 is provided by grounding theside wall 202, as indicated in the drawing. VHF current along this path promotes an edge-high center low plasma ion radial distribution, or at least a less center-high plasma ion radial distribution relative to an RF ground return path through the center of the chamber. A path through the center of thechamber 200 is optionally provided by coupling the pedestal electrode 226 (or the base layer 222) to ground through respective tunable (variable)bandpass filters variable bandpass filter 252 has a narrow pass band that includes (or is centered at least approximately on) the frequency f1 of thehigher VHF generator 240. Thevariable bandpass filter 254 has a narrow pass band that includes (or is centered at least approximately on) the frequency f2 of thelower VHF generator 242. Bothbandpass filters controller 270 to determine the division of RF current from eachgenerator pedestal electrode 226 and theside wall 202. The apportionment of this current is controlled by varying the reactance of eachbandpass filter FIG. 1B is a simplified schematic diagram of a variable bandpass filter of the type that can be employed in the reactor ofFIG. 1A . The variable bandpass filter ofFIG. 1B can include ashunt capacitor 256, aninductor 258 and aload capacitor 260, either or bothcapacitors filters filters chamber 200 may be provided by grounding thepedestal electrode 226. This may be through a high-pass filter to permit effective isolation of the RF bias. - RF bias power is applied to the
ESC electrode 226, including LF power (e.g., about 2 MHz) from a low frequencyRF power generator 262 through anLF impedance match 264, and HF power (e.g., about 13.56 MHz) from a high frequencyRF power generator 266 through anHF impedance match 268. Typically, the RF bias frequencies are selected such that the LF power level controls the peak ion energy, while the HF power level controls the central width of the ion energy distribution. An RF current ground path may be provided for each of the RF bias sources applied to theESC electrode 226. A path through theceiling 204 is optionally provided by coupling the ceiling through a bandpass or low-pass filter to ground. Furthermore, a variable reactance may be inserted in the path to allow control of the bias return current to the ceiling relative to bias return current to other surfaces, namely current to thewall 202 andring 219. The insertion reactance or impedance may be increased to force more bias return current to the edge (ring 219 or wall 202), which tends to favor an edge high plasma ion density uniformity condition. Alternatively, the insertion reactance or impedance may be decreased to force less bias return current to the edge (ring 219 or wall 202), which tends to favor a center high plasma ion density uniformity condition. - The two VHF
source power generators bias power generators bias generators source power generators - Uniformity of gas flow across the surface of the
wafer 220 and uniformity of the RF field near the wafer edge can be improved by providing a below-wafer ground return 219 extending radially outwardly from the side of thepedestal 218 at a level that is below the wafer support surface of thepedestal 218. The below-wafer ground return 219 is typically shaped as a cylinder or a flat annular ring that extends toward theside wall 202 to form agap 203 that partly constricts gas flow from the process region above the wafer into the pumping annulus below the wafer evacuated by thevacuum pump 228. The level of the below-wafer ground return is above features such as thewafer slit valve 229 or pumping port that produces undesirable asymmetries in the plasma distribution arising from asymmetries in gas flow pattern or electrostatic or electromagnetic fields. The narrow gap between the side wall and the outer edge of the below-wafer ground return 219 partially constricts gas flow, such that the region above thewafer 220 is fairly immune to such asymmetries, thereby improving process uniformity. In one implementation, the below-wafer ground plane 219 is formed of a conductive material and is connected to ground. It therefore provides a more uniform ground reference at the wafer edge that renders the electric field more uniform there and less susceptible to asymmetries in the distribution of conductive surfaces in the chamber interior. Thering 219 may also serve as a plasma boundary to help confine the plasma volume to the chamber region above thering 219. In an alternative implementation, thering 219 does not serve as a ground plane, and is instead formed of a non-conductive material. In another alternative implementation, the ground return ring (or cylinder) 219 is at the workpiece or wafer level or above workpiece level. It may be at or near the ceiling level and concentrically surround theceiling electrode 204. In another embodiment, the level of theground return ring 219 may be selectively adjusted relative to the workpiece level with a lift mechanism. For example, by attaching thering 219 to the outside of thepedestal 218, thering 219 is lifted up and down by the pedestal lift mechanism. Theground return ring 219 may be insulated from other grounded surfaces in the chamber (such as the ESC base layer 224) so as to not be directly coupled to ground, and instead be coupled to ground through a variable reactive element (e.g., the variable filter 252). In this case, theground return ring 219 serves as the edge ground return path for the VHF frequency f2. The height of this edge ground return path is therefore variable and serves as one of the adjustable parameters of the reactor. - A
uniformity controller 270 controls the relative power output levels of the twoVHF generators controller 270 can set the impedance of the high VHF frequency (f1) bandpass filter so as to provide a lower impedance return path to ground through thewafer 220 than the through theside wall 202 at the higher VHF frequency f1, so that the power from thef1 generator 240 produces a more pronounced center high radial distribution. Furthermore, thecontroller 270 can set the impedance of the low VHF frequency (f2) bandpass filter so as to provide a higher impedance return path to ground through thewafer 220 than through theside wall 202 at the lower VHF frequency f2, so that power from thef2 generator 242 produces a more pronounced center low and edge high radial distribution. Thecontroller 270 apportions the relative power output levels of the high and lowVHF frequency generators controller 270 may make such adjustments in response to non-uniformity patterns measured on a previously-processed wafer by a downstream or in-line metrology tool 272. During the processing of successive wafers, standard feedback control corrective techniques, implemented as programmed algorithms in thecontroller 270, may be employed to enact successive corrections by theuniformity controller 270 to minimize non-uniformities in etch rate distribution sensed by themetrology tool 272. Themetrology tool 272 may be programmed to inform thecontroller 270 whether plasma ion density distribution has a predominantly center-high non-uniformity or a predominantly edge-high non-uniformity. Alternatively, themetrology tool 272 may embody in-situ sensors may provide real-time signals to thecontroller 270. OES (optical emission spectroscopy) sensors may be placed on theceiling 204 at various radii, providing an indication of radial plasma excited species density. The plasma itself may be used as the light source, or external light sources may be used. Alternatively, interferometry sensors may be placed on theceiling 204 at various radii, providing an indication of workpiece film thickness rate of change as a function of radius. Alternatively, ion flux sensors may be placed on theceiling 204 at various radii, providing an indication of radial plasma ion density. Alternatively, voltage sensors may be placed on theceiling 204 at various radii, providing an indication of radial electrode voltage. Alternatively, isolated voltage sensors may be placed on theceiling 204 at various radii, providing an indication of radial plasma floating potential. Real-time control of plasma uniformity may be performed bycontroller 270 using sensor input and conventional techniques. - The uniformity controller can also control the
lift mechanism 234, in order to provide another control dimension for improving uniformity of plasma ion distribution (or uniformity of etch rate distribution). By raising thepedestal 218 toward theceiling electrode 204, the wafer-to-ceiling gap is decreased, which suppresses plasma ion density near the center of the wafer and promotes plasma ion density near the wafer edge. Conversely, by lowering thepedestal 218 away from theceiling electrode 204, the wafer-to-ceiling gap is increased, which promotes plasma ion density over the wafer center while detracting from plasma ion density at the wafer edge. Thus, the plasma distribution may be rendered more center-high or more center-low by raising or lowering thepedestal 218, respectively. As discussed above, the plasma distribution may be rendered more center-high or more center-low by increasing or decreasing, respectively, the ratio of the higher VHF frequency power to lower VHF frequency power. Thus, the pedestal height and the VHF power ratio are two different controls that affect the plasma ion distribution. Theuniformity controller 270 can employ both of these controls simultaneously to optimize plasma ion distribution uniformity. For example, an edge-high plasma non-uniformity may be reduced by increasing the output power of the higherVHF frequency generator 240, which may tend to increase a center-high peak in plasma ion distribution. This increase in the center-high peak may be suppressed, without requiring further change in the VHF power apportionment, by raising thepedestal 218 to decrease the wafer-ceiling gap until an optimum plasma distribution is realized. This may be useful for process recipes calling for a low RF bias and a low chamber pressure, in which case the center-high peak in plasma ion distribution is particularly pronounced. The control of both VHF frequency apportionment together with control of the wafer-ceiling gap extends the range of non-uniformity that thecontroller 270 is capable of counteracting. For a severe center-high nonuniformity, for example, thecontroller 270 may call for both an increase in the higher-versus-lower VHF frequency power apportionment as well as a narrower wafer-ceiling gap. - The variable wafer-to-ceiling gap affects where a particular VHF frequency (e.g., f1 or f2) has a peak in non-uniform plasma ion density distribution. Therefore, the
controller 270 can set the gap to optimize the choice of f1 to produce a predominantly center-high non-uniform plasma ion density distribution and the choice of f2 to produce a predominantly edge-high non-uniform plasma ion density distribution. For example, thecontroller 270 sets the wafer-ceiling gap to optimize the choice of f1 and f2 to produce the different non-uniformity patterns, and thecontroller 270 varies the ratio of RF power (or current or voltage) at the different frequencies f1, f2 to control the plasma ion distribution and reduce its non-uniformities. - The
controller 270 may respond to an indication from themetrology tool 272 of a predominantly center-high or edge-high non-uniformity in plasma ion density distribution by measuring and controlling (changing) any one of the following so as to tend to reduce that non-uniformity: (a) the ratio of RF voltages at the frequencies f1, f2; (b) the ratio of RF currents at the frequencies f1, f2; or (c) the ratio of RF power at the frequencies f1, f2. Such measurements may be made at the respective electrodes, for example, or another suitable location. - In one alternate mode, the
controller 270 varies plasma ion density distribution without necessarily changing the apportionment of power among the higher (f1) and lower (f2)VHF generators controller 270 by varying the impedances to the center ground return paths presented by the f1 and f2 variablebandpass filters variable bandpass filter 252. Likewise, the tendency of the lower frequency (f2) VHF power to create an edge peak or suppress a center peak in plasma ion density distribution may be increased or decreased by changing the impedance presented to the f2 power by thevariable bandpass filter 254. Such changes affect the apportionment of VHF current at each of the frequencies f1, f2 between the center ground return path (ceiling-to-wafer) and the side ground return path (through the side wall 202). By directing more of the f1 power to the center ground return path, the tendency of the higher VHF frequency (f1) power to create a center-high distribution is increased. By directing more of the f2 power to the side ground return path, the tendency of the lower VHF frequency (f2) power to create an edge-high distribution is increased. In some cases, the controller may change the ground return path apportionment for only one of the two frequencies f1, f2. - In a further alternate mode of the reactor of
FIG. 1 , only one of the VHF generators (e.g., only the generator 240) provides RF power, the other generator (e.g., the generator 242) not being used or else being eliminated. Theuniformity controller 270 changes the plasma ion radial distribution by varying thef1 bandpass filter 252 so as to control the impedance of the ground return path through theESC electrode 226. This apportions the ground return currents between the center path through theESC electrode 226 and the side path through theside wall 202. As a result, this feature of thecontroller 270 varies the center-high and center-low non-uniformities in plasma ion distribution (or equivalently in etch rate distribution) to optimize uniformity. - While only two
VHF generators FIG. 1A , more VHF generators may be employed of different frequencies. For example, a third VHF generator may be employed having a frequency higher than either of the twoVHF generators - The reactor of
FIG. 1A may be used to reproduce plasma process conditions characteristic of a very low density bias-only plasma conventionally produced with a single HF (13.56 MHz) frequency source to both generate plasma ions and control the bias voltage on the wafer. This simulation may be realized by applying only an LF (e.g., 2 MHz) bias power from thegenerator 264, and setting the output power of each of the twoVHF generators generators -
FIG. 2 depicts a modification of the reactor ofFIG. 1A , in which the lower VHF frequency (f2)generator 242 and itsmatch 246 andnotch filter 250 are coupled to theESC electrode 226 rather than theceiling electrode 204. In this case, the f2 ground return path is through theceiling electrode 204. Therefore, the f2variable bandpass filter 254 is coupled to theceiling electrode 204 rather than theESC electrode 226. Anotch filter 255 tuned to block RF current from the higher VHF frequency (f1)generator 240 may be connected to thef2 bandpass filter 254. Likewise, anotch filter 253 tuned to block RF current from the lower VHF frequency (f2)generator 242 may be connected to thef1 bandpass filter 252. - In one alternative mode of the reactor of
FIG. 2 , the VHF frequencies f1 and f2 applied to the top (ceiling electrode 204) and bottom (ESC electrode 226) respectively are the same frequency (f1=f2). In this case, thecontroller 270 varies radial distribution of ion density (or etch rate) by varying the phase between the voltages (or currents) at theceiling electrode 204 and theESC electrode 226. The phase between the currents at theceiling electrode 204 and theESC electrode 226 may be controlled, for example, by varying the reactance of thebandpass filters generators bandpass filters ESC electrodes ceiling electrode 204 and theESC electrode 226, generating a center-high distribution of plasma ion density or etch rate. At a phase of zero degrees, essentially all of the current flows from either theceiling electrode 204 or theESC electrode 226 to theside wall 202, generating a center-low edge-high distribution. Therefore, thecontroller 270 can vary the phase angle between 0 and 180 degrees to attain a wide range of results. - In another alternate mode of the reactor of
FIG. 2 , only one of the VHF generators (i.e., only the f2 generator 242) provides RF power, theother generator 240 not being used or else being eliminated. Theuniformity controller 270 changes the plasma ion radial distribution by varying thef2 bandpass filter 254 so as to control the impedance of the ground return path through theceiling electrode 204, so that it increases or decreases relative to the (fixed) impedance of the ground return path through theside wall 202. This apportions the ground return current between the center path through theceiling electrode 204 and the side path through theside wall 202. As a result, this feature of thecontroller 270 varies the center-high and center-low non-uniformities in plasma ion distribution (or equivalently in etch rate distribution) to optimize uniformity. - In yet another alternate mode of the reactor of
FIG. 2 , only one of the VHF generators (i.e., only the f1 generator 240) provides RF power, theother generator 242 not being used or else being eliminated. Theuniformity controller 270 changes the plasma ion radial distribution by varying thef2 bandpass filter 252 so as to control the impedance of the ground return path through theESC electrode 226, so that it increases or decreases relative to the (fixed) impedance of the ground return path through theside wall 202. This apportions the ground return current between the center path through theESC electrode 226 and the side path through theside wall 202. As a result, this feature of thecontroller 270 varies the center-high and center-low non-uniformities in plasma ion distribution (or equivalently in etch rate distribution) to optimize uniformity. -
FIGS. 3A and 3B depict a modification of the reactor ofFIG. 1 in which theceiling electrode 204 is divided into radially inner andouter sections generators inner electrode 204 a leaving the other to drive theouter electrode 204 b, it is preferred that the higherVHF frequency generator 240 be coupled to theinner electrode 204 a and the lowerVHF frequency generator 242 be coupled to theouter electrode 204 b, in order to enhance the tendency of the higher frequency to develop a center-high ion distribution and enhance the tendency of the lower frequency to develop a center-low ion distribution. -
FIG. 4 depicts a modification of the reactor ofFIG. 1 in which both theVHF generators ESC electrode 226 while the ground return bandpass filters 252, 254 are coupled to theceiling electrode 204. -
FIG. 5 depicts a modification of the reactor ofFIG. 2 , in which the two frequencies f1 and f2 are both in the lower portion of the VHF band. For example, f1 and f2 may be 54 MHz and 60 MHz, respectively. This represents a significant cost savings by eliminating the need for a high VHF frequency generator having an output frequency near 200 MHz or over 150 MHz. In the reactor ofFIG. 5 , the missing high VHF frequency (e.g., 162 MHz), that provides the center-high response, is produced with a high VHF frequency (e.g., 162 MHz)resonator 274 coupled to the ceiling electrode 204 (or alternatively to the output of the f1 generator 240). Preferably, theresonator 274 is tuned to resonate at an odd harmonic of f1, such as the third harmonic. For example, if f1=54 MHz, then the third harmonic generated in theresonator 274 would be 162 MHz. Production of the higher harmonic is facilitated by the non-linear response of the plasma in the reactor chamber that functions as a frequency multiplier in cooperation with theresonator 274. Thevariable bandpass filter 252 is tuned to the third harmonic of f1 so that some of the RF power at f1 from thegenerator 240 is converted to the third harmonic of f1. - In another alternate mode of the reactor of
FIG. 5 , only one of the VHF generators (i.e., only the generator 240) provides RF power, theother generator 242 not being used or else being eliminated. Theuniformity controller 270 changes the plasma ion radial distribution by varying thef1 bandpass filter 252 so as to control the impedance of the ground return path through theceiling electrode 204, so that it increases or decreases relative to the (fixed) impedance of the ground return path through theside wall 202. This apportions the ground return currents between the center path through theceiling electrode 204 and the side path through theside wall 202. As a result, this feature of thecontroller 270 varies the center-high and center-low non-uniformities in plasma ion distribution (or equivalently in etch rate distribution) to optimize uniformity. -
FIG. 6 depicts a modification of the reactor employing simultaneous high and low VHF frequencies but employing only a single low VHF frequency generator to achieve a great cost savings. Thelow VHF generator 240 is a variable frequency oscillator (VFO) whose frequency is varied by thecontroller 270 between a fundamental frequency f and f±Δf, where Δf is a small deviation from f. Theresonator 274 is tuned to the third harmonic, F=3·f, of the fundamental frequency f. By changing the frequency of thegenerator 240, the proportion of the output power of the generator that is converted to the third harmonic F is increased or decreased in inverse proportion to the difference between the generator output frequency f±Δf and the fundamental frequency f whose third harmonic is the resonant frequency of theresonator 274. The result is that both frequencies, i.e., the generator output frequency f±Δf and the harmonic frequency F, are coupled to the plasma, and their relative power levels are controlled by varying the output frequency of thegenerator 240. By decreasing the difference between the generator output frequency and the fundamental frequency f, the power coupled to the plasma at the third harmonic increases while the power at the fundamental, f, decreases, thereby increasing the center-high non-uniformity or decreasing the edge-high non-uniformity. Conversely, by increasing the difference between the generator output frequency and the fundamental frequency f, the power coupled to the plasma at the third harmonic decreases while the power at the fundamental, f, increases, thereby increasing the edge-high non-uniformity or decreasing the center-high non-uniformity. Therefore, plasma uniformity is regulated by thecontroller 270 by varying the frequency of the VFO orgenerator 240. The two variable bandpass filters 252, 254 have passbands centered at, respectively, the fundamental, f, and the third harmonic, F. - In one aspect, the interior chamber elements are formed of a metal such as aluminum. In order to prevent or minimize metal contamination during plasma processing, the surfaces of the metal chamber elements that can be exposed to plasma, such as the interior surface of the
side wall 202 and the exposed surfaces of thepedestal 218, are coated with a film of a process-compatible material, such as yttira, for example. The film may be a plasma-spray-coated yttria. Alternatively, bulk ceramic material such as yttria may be bonded to underlying metal interior chamber elements. For example, theceiling 204 may have a bonded ceramic plate on the side exposed to plasma. Thesidewall 202 may include a bonded ceramic cylinder on the side exposed to plasma, or thering 219 may include a bonded ceramic ring on the side exposed to plasma. Ceramic materials may be doped or otherwise fabricated such that their electrical resistivity is in the semiconducting range (e.g., resistivity in the range 10̂8 to 10̂12 ohm*cm) to provide a DC current return path for the ESC clamping voltage applied to theESC electrode 226. These chamber surfaces may be heated in order to minimize undesired deposition or accumulation of materials such as polymers, for example, or cooled to minimize or eliminate etching, or temperature controlled employing both heating and cooling. The interior surfaces of the chamber may be cleaned in a plasma etch process by employing an appropriate chemistry. For example, in a dry cleaning step, oxygen or oxygen-containing, or chlorine or chlorine-containing gas may be introduced into the chamber and a plasma may generated using the VHFsource power generators bias power generators -
FIG. 7 illustrates a process that can be carried out using the reactor ofFIG. 1 . Inblock 300 ofFIG. 7 , RF plasma source power is capacitively coupled through an electrode (ceiling or wafer) at two different VHF frequencies f1 and f2 simultaneously, where f1 is in the higher range of the VHF band (e.g., 162 MHz) and f2 is in the lower region of the VHF band (e.g., 50-60 MHz). In block 302, an individual center ground return path is provided through a counter electrode (wafer or ceiling) for each of the frequencies f1 and f2, by providing thebandpass filters FIG. 1 . Inblock 304 ofFIG. 7 , an edge return path is provided through the side wall for each of the frequencies f1 and f2 by grounding theside wall 202 as shown inFIG. 1 . Inblock 306, the impedance of the f1 center return path is adjusted relative to the impedance of the f1 edge return path to promote current flow at the f1 frequency to the center return path, by adjusting thebandpass filter 252. Inblock 308, the impedance of the f2 edge return path is adjusted relative to the impedance of the f2 center return path to promote current flow at the f2 frequency to the side wall, by adjusting thebandpass filter 254. Inblock 310, theuniformity controller 270 improves the uniformity of the radial plasma ion density distribution by selecting a ratio of VHF power at the f1 frequency to VHF power at the f2 frequency. The step ofblock 310 may be carried out to reduce a center-high plasma ion density distribution by decreasing the ratio of VHF power at the f1 frequency relative to VHF power at the f2 frequency (block 312). Or, the step ofblock 310 may be carried out to reduce an edge-high plasma ion density distribution nonuniformity by decreasing the ratio of VHF power at the f2 frequency relative to VHF power at the f1 frequency (block 314). As another way of affecting or improving ion density distribution, thecontroller 270 may adjust the impedances of the center and edge return paths of either or both f1 and f2 (by adjusting therespective bandpass filters 252, 254) to either: (a) channel more current toward the edge in order to suppress a center-high non-uniformity or (b) channel more current toward the center to suppress an edge-high non-uniformity (block 316). - In this description, uniformity may be referred to with respect to radial plasma ion density distribution. It is understood that such a distribution is inferred from or is equivalent to etch rate radial distribution that can be measured across the surface of a wafer that has been processed by a plasma etch process in the reactor.
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FIG. 8 illustrates a process that can be carried out using the reactor ofFIG. 2 . In the step ofblock 318 ofFIG. 8 , RF plasma source power is capacitively coupled through one electrode (ceiling or wafer) at an upper VHF frequency f1 (e.g., about 162 MHz) while RF plasma source power is capacitively coupled through the counterelectrode (wafer or ceiling) at a lower VHF frequency f2 (e.g., about 50-60 MHz). Inblock 320, a center return path is provided through the counterelectrode for the frequency f1. Inblock 322, a center return path is provided through the electrode for the frequency f2. In the step ofblock 324, an edge return path through the side wall for each of the frequencies f1 and f2. In the step ofblock 326, the impedance of the f1 center return path is adjusted relative to the impedance of the f1 edge return path to promote current flow at the f1 frequency to the center return path, by adjusting thevariable bandpass filter 252. In the step ofblock 328, the impedance of the f2 side return path is adjusted relative to the impedance of the f2 center return path to promote current flow at the f2 frequency to the side wall, by adjusting thevariable bandpass filter 254. In the step ofblock 330, thecontroller 270 improves the uniformity of the radial plasma ion density distribution by selecting a ratio of VHF power at the f1 frequency to VHF power at the f2 frequency. This step may be carried out to reduce center-high plasma ion density distribution by decreasing the ratio of VHF power at the f1 frequency relative to VHF power at the f2 frequency (block 332). This step may be carried out to reduce edge-high plasma ion density distribution nonuniformity by decreasing the ratio of VHF power at the f2 frequency relative to VHF power at the f1 frequency (block 334). Alternatively or in addition to the step ofblock 330, thecontroller 270 may improve uniformity by adjusting the impedances of the center and edge return paths of either or both f1 and f2 (by adjusting therespective bandpass filters 252, 254) to either: (a) channel more current toward the edge in order to suppress a center-high non-uniformity or (b) channel more current toward the center to suppress an edge-high non-uniformity (block 336 ofFIG. 8 ). -
FIG. 9 illustrates a process that can be carried out using the reactor ofFIG. 3A . In the process ofFIG. 9 , RF plasma source power through an inner ceiling electrode at an upper VHF frequency f1 RF plasma source power is capacitively coupled through an outer ceiling electrode at lower VHF frequency f2 (block 338 ofFIG. 9 ). Inblock 340, a center return path is provided through the wafer for the frequency f1 by providing thebandpass filter 252 coupled to ground. Inblock 342, a center return path through the wafer is provided for the frequency f2 by providing thebandpass filter 254 coupled to ground. Inblock 344 ofFIG. 9 , an edge return path through theside wall 202 for each of the frequencies f1 and f2 by grounding theside wall 202, as shown inFIG. 3A . In the step ofblock 346, the impedance of the f1 center return path is adjusted relative to the impedance of the f1 edge return path to promote current flow at the f1 frequency to the center return path, by adjusting the reactance of thebandpass filter 252. In the step ofblock 348, the impedance of the f2 edge return path is adjusted relative to the impedance of the f2 center return path to promote larger current flow at the f2 frequency to the side wall, by adjusting the reactance of thebandpass filter 254. Inblock 350, thecontroller 270 improves the uniformity of the radial plasma ion density distribution (or of etch rate distribution on the wafer) by selecting a ratio of VHF power at the f1 frequency to VHF power at the f2 frequency. This step may be carried out to reduce a center-high plasma ion density distribution by decreasing the ratio of VHF power at the f1 frequency relative to VHF power at the f2 frequency (block 352). Or, this step may be carried out to reduce edge-high plasma ion density distribution nonuniformity by decreasing the ratio of VHF power at the f2 frequency relative to VHF power at the f1 frequency (block 354). Alternatively, or in addition to the step ofblock 350, thecontroller 270 may improve uniformity of plasma ion density distribution (or etch rate distribution on the wafer) by adjusting the impedances of the center and edge return paths of either or both f1 and f2 to either: (a) channel more current toward the edge in order to suppress a center-high non-uniformity or (b) channel more current toward the center to suppress an edge-high non-uniformity (block 356 ofFIG. 9 ). -
FIG. 10 illustrates a process that can be carried out in the reactor ofFIG. 2 by setting the two VHF frequencies f1 and f2 ofFIG. 2 equal to one another (or at least nearly equal to one another). The bandpass filters 252, 254 are used in this case as variable reactances that can control or vary the phase between the VHF voltages (or currents) at the ceiling and wafer. In the step ofblock 358 ofFIG. 10 , RF plasma source power is capacitively coupled through one electrode (ceiling or wafer) at a VHF frequency while capacitively coupling RF plasma source power through the counterelectrode (wafer or ceiling) at the same VHF frequency. Inblock 360, a control element such as a variable reactance (e.g., the variable bandpass filter 252) is provided at thecounterelectrode 226 ofFIG. 2 for controlling phase. Inblock 362, a control element such as a variable reactance (e.g., the variable bandpass filter 254) is provided at theelectrode 204 for controlling phase. In the step ofblock 364, an edge return path is provided by grounding theside wall 202. In the step ofblock 366, thecontroller 270 improves the uniformity of the radial plasma ion density distribution by controlling the phase difference between the VHF currents at the electrode and the counterelectrode. This step may be carried out to reduce a center-high plasma ion density distribution by moving the phase difference toward 180 degrees (block 367 ofFIG. 10 ). Or, the step ofblock 368 may be carried out to reduce an edge-high plasma ion density distribution nonuniformity by moving the phase difference towards 0 degrees. -
FIG. 11 illustrates a process that may be carried out using the reactor ofFIG. 5 . Inblock 370 ofFIG. 11 , RF plasma source power at two similar VHF frequencies f1 and f2, both in the lower region of the VHF band, to an electrode (204 ofFIG. 5 ) and to a counterelectrode (226 ofFIG. 5 ), respectively. This represents a significant cost savings by eliminating the cost of a high VHF frequency (e.g., 160-200 MHz) generator. Inblock 372 ofFIG. 11 , theelectrode 204 is coupled to a resonator (274 ofFIG. 5 ) having a resonant frequency which is an odd (e.g., third) harmonic of f1, and lies in the higher region of the VHF band, so as to produce VHF power at the odd (e.g., third) harmonic (e.g., 162 MHz). Inblock 374, an individual center return path is provided through the counter electrode (266 ofFIG. 5 ) for the third harmonic of f1, for example by providing thebandpass filter 252. Inblock 376, an individual center return path is provided through theelectrode 204 for the VHF frequency f2, for example by providing thebandpass filter 254. Inblock 378, an edge return path is provided through the side wall for f2 and for the odd harmonic of f1, by grounding the side wall (202 ofFIG. 5 ). In the step ofblock 380, thecontroller 270 adjusts the impedance of the f1 harmonic center return path relative to the impedance of the f1 harmonic edge return path to promote current flow at the f1 harmonic to the center return path, by adjusting the reactance of thebandpass filter 252. In the step ofblock 382, thecontroller 270 adjusts the impedance of the f2 edge return path relative to the impedance of the f2 center return path to promote current flow at the f2 frequency to the side wall, by adjusting the reactance of thebandpass filter 254. Thecontroller 270 improves the uniformity of the radial plasma ion density distribution by selecting a ratio of VHF power between the f1 and f2 generators to control the ratio between the f1 harmonic power and f2 power coupled to the plasma (block 384). This step may be carried out to reduce a center-high plasma ion density distribution by decreasing the ratio of VHF power generated at the f1 frequency relative to VHF power at the f2 frequency (block 386). Or, this step may be carried out to reduce edge-high plasma ion density distribution nonuniformity by decreasing the ratio of VHF power at the f2 frequency relative to VHF power generated at the f1 frequency (block 388 ofFIG. 11 ). Alternatively or in addition to the step ofblock 384, thecontroller 270 may improve uniformity of plasma ion density distribution by adjusting the impedances of the center and edge return paths of either or both f2 and the harmonic of f1 to either: (a) channel more current toward the edge in order to suppress a center-high non-uniformity or (b) channel more current toward the center to suppress an edge-high non-uniformity (block 390). -
FIG. 12 illustrates a process that can be carried out in a modification of the reactor ofFIG. 5 in which the locations of thef2 bandpass filter 254 and the f2 generator andmatch ceiling electrode 204. Atblock 392, RF plasma source power at two similar lower VHF frequencies f1 and f2 simultaneously to an electrode (e.g., theceiling electrode 204 ofFIG. 5 ). Atblock 394, a resonator (274 ofFIG. 5 ) is coupled theelectrode 204, the resonator having a resonant frequency which is an odd harmonic of f1, so as to produce VHF power at the odd harmonic. This frequency up-conversion is facilitated by the non-linear response of the plasma that provides a frequency-multiplying effect. Inblock 396 ofFIG. 12 , an individual center return path is provided through a counter electrode (226 ofFIG. 5 ) for the harmonic of f1, by providing thebandpass filter 252 coupled to ground. Inblock 398 ofFIG. 12 , an individual center ground return path is provided through the counterelectrode for the VHF frequency f2 by providing thebandpass filter 254 ofFIG. 5 coupled to ground. Inblock 400, edge return paths are provided through the side wall for f2 and the harmonic of f1, by grounding theside wall 202 ofFIG. 5 . Inblock 402, thecontroller 270 adjusts the impedance of the f1 harmonic center return path relative to the impedance of the f1 harmonic edge return path to promote current flow at the f1 harmonic through the center return path, by adjusting thebandpass filter 252 ofFIG. 5 . Inblock 404 ofFIG. 12 , thecontroller 270 adjusts the impedance of the f2 edge return path relative to the impedance of the f2 center return path to promote current flow at the f2 frequency to the side wall, by adjusting the reactance of thebandpass filter 254 ofFIG. 5 . Inblock 406, thecontroller 270 improve the uniformity of the radial plasma ion density distribution by selecting a ratio of VHF power between the f1 and f2 generators to control the ratio between the f1 harmonic power and f2 power coupled to the plasma. This step may be carried out to reduce center-high plasma ion density distribution by decreasing the ratio of VHF power at the f1 harmonic relative to VHF power at the f2 frequency (block 408). Or, this step may be carried out to reduce edge-high plasma ion density distribution nonuniformity by decreasing the ratio of VHF power at the f2 frequency relative to VHF power at the f1 harmonic (block 410). Alternatively or in addition to the process atblock 408, thecontroller 270 may improve uniformity by adjusting the impedances of the center and edge return paths of either or both the f1 harmonic and f2, to either: (a) channel more current toward the edge in order to suppress a center-high non-uniformity or (b) channel more current toward the center to suppress an edge-high non-uniformity (block 412 ofFIG. 12 ). -
FIG. 13 illustrates a process that may be carried out in the reactor ofFIG. 6 , using only a single lower VHF frequency generator (between about 50-60 MHz) to realize the functionality that requires two generators in the reactors described previously herein. Inblock 414 ofFIG. 13 , RF plasma source power is capacitively coupled through an electrode (e.g., theceiling electrode 204 ofFIG. 6 ) from a variablefrequency VHF generator 240 having a frequency range that includes a fundamental lower VHF frequency f. Inblock 416, aresonator 274 is coupled to theelectrode 204, the resonator having a resonant frequency F which is an odd harmonic of the fundamental frequency f, so as to produce VHF power at the odd harmonic, using the plasma in the chamber as a non-linear mixing element. Inblock 418, an individual center return path is provided through a counterelectrode (e.g., theESC electrode 226 ofFIG. 6 ) for the harmonic frequency F, by providing thebandpass filter 252 coupled to ground. Inblock 420, an individual center return path is provided through the counterelectrode (226 of FIG, 6) for the fundamental VHF frequency f, by providing thebandpass filter 254 coupled to ground. Inblock 422 ofFIG. 12 , edge return paths through the side wall for both frequencies f and F by grounding theside wall 202 ofFIG. 6 . Inblock 424 ofFIG. 12 , thecontroller 270 adjusts the impedance of the F center return path relative to the impedance of the F edge return path to promote current flow at F to the center return path, by adjusting thevariable bandpass filter 252. Inblock 426, thecontroller 270 adjusts the impedance of the f edge return path relative to the impedance of the f center return path to promote current flow at the f frequency to the side wall, by adjusting thevariable bandpass filter 254. Inblock 428, thecontroller 270 improve plasma ion density distribution uniformity, by controlling the ratio of VHF power at (or near) the fundamental f to VHF power at harmonic F. This is accomplished by controlling the proportion of power up-converted from f to F. This proportion is controlled by controlling the difference between the variable output frequency of the VHF generator and the fundamental frequency f. As the generator output frequency approaches closer to the fundamental, the proportion of VHF power produced by thevariable frequency generator 240 converted to the (third) harmonic F increases, for example. The maximum ratio VHF power at F to VHF power at f is attained when the generator frequency equals the fundamental f. The step ofblock 428 may be carried out in order to reduce a center-high plasma ion density distribution by decreasing the ratio of VHF power at F relative to VHF power at f (block 430 ofFIG. 13 ). Or, the step ofblock 428 may be carried out to reduce an edge-high plasma ion density distribution nonuniformity by decreasing the ratio of VHF power at the f frequency relative to VHF power at F (block 432 ofFIG. 13 ). Alternatively or in addition to the step ofblock 428, thecontroller 270 may improve uniformity by adjusting the impedances of the center and edge return paths of either or both F and f to either: (a) channel more current toward the edge in order to suppress a center-high non-uniformity or (b) channel more current toward the center to suppress an edge-high non-uniformity, by adjusting therespective bandpass filters - The use of an
electrostatic chuck 218 facilitates high rates of heat transfer to or from thewafer 220, even at very low (mT) chamber pressures where heat transfer is poor without an electrostatic chuck. This feature enables thevacuum pump 228 to be a very powerful turbo pump to run chamber recipes calling for extremely low chamber pressures. These features, in combination with theVHF power sources FIGS. 1-6 , fulfill the needs of certain processes such as dielectric etch plasma processes and plasma immersion ion implantation processes that impose high heat load while requiring low chamber pressure and high plasma ion density. However, these reactors are capable of performing across a wide range of chamber pressure (mT to Torr), a wide range of wafer heat load and a wide range of plasma ion density (e.g., 10̂9 to 10̂11 ions/cc). Therefore, the reactors ofFIGS. 1-6 may also be employed in carrying out other processes at either high or low chamber pressure and at either high or low plasma ion density, such as plasma enhanced chemical vapor deposition (PECVD), plasma enhanced physical vapor deposition (PEPVD), plasma doping and plasma enhanced materials modification. - While the foregoing is directed to embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
Claims (24)
1. A plasma reactor for processing a workpiece within a chamber of the reactor, comprising:
an electrostatic chuck in the chamber for supporting the workpiece;
a ceiling electrode facing the electrostatic chuck and an ESC electrode in said electrostatic chuck;
an electrostatic clamping voltage supply coupled to said ESC electrode;
at least a first RF bias source of an LF or HF frequency coupled to said pedestal electrode; and
first and second VHF power sources of different frequencies coupled to the same or to different ones of said electrodes, said first and second VHF power sources being of sufficiently high and sufficiently low frequencies, respectively, to produce center-high and center-low plasma distribution non-uniformities, respectively, in said chamber.
2. The reactor of claim 1 further comprising:
a turbo pump capable having a sufficient capacity to maintain said chamber in a pressure range including a minimum pressure as low as a few mT.
3. The reactor of claim 2 further comprising a workpiece lift mechanism for varying a workpiece-to-ceiling gap.
4. The reactor of claim 3 wherein said ceiling electrode comprises a gas distribution showerhead, said reactor further comprising a process gas supply coupled to said gas distribution showerhead.
5. The reactor of claim 4 wherein the workpiece-to-ceiling gap comprises a process region of said chamber, said reactor further comprising:
a side wall of said chamber;
non-symmetrical elements in said chamber;
a confinement annulus between said process region and said non-symmetrical elements and having a peripheral edge separated from said side wall by a side gap restriction.
6. The reactor of claim 5 wherein said confinement annulus comprises a planar ring extending radially from a periphery of said electrostatic chuck.
7. The reactor of claim 5 wherein said confinement annulus is conductive and is coupled to an RF ground potential so as to shield said process region from electrical effects of said non-symmetrical elements in said chamber.
8. The reactor of claim 7 wherein said non-symmetrical elements comprises at least one of: (a) a wafer slit valve, (b) a pumping port of said turbo pump.
9. The reactor of claim 1 further comprising:
a first variable reactance coupled between RF ground and one of said pedestal and ceiling electrodes which is opposite the one to which said first VHF power source is coupled.
10. The reactor of claim 9 further comprising one of: (a) a confinement annulus coupled to RF ground, (b) a side wall of said chamber coupled to RF ground.
11. The reactor of claim 9 further comprising:
a second variable reactance coupled between RF ground and one of said pedestal and ceiling electrodes which is opposite the one to which said second VHF power source is coupled.
12. The reactor of claim 1 wherein said first VHF power source comprises a resonator coupled to plasma in said chamber for up-converting a fundamental frequency to said frequency sufficiently high to produce a center-high non-uniformity in plasma ion density distribution.
13. The reactor of claim 1 wherein said ceiling electrode comprises separate concentric electrode sections isolated from one another, said first and second VHF power sources being coupled to respective ones of said electrode sections of said ceiling electrode.
14. The reactor of claim 1 wherein said chamber further comprises:
a side wall;
a layer on at least one of: (a) said side wall, (b) said electrostatic chuck, (c) said ceiling electrode, said layer comprising one of: (a) a bulk ceramic material, (b) a yttria-containing material.
15. A plasma reactor for processing a workpiece within a chamber of the reactor, comprising:
an electrostatic chuck in the chamber for supporting the workpiece;
an ESC electrode within the electrostatic chuck;
an electrostatic clamping voltage supply coupled to said ESC electrode;
a ceiling electrode facing the electrostatic chuck;
a VHF power source coupled to one of the electrodes;
a variable reactance coupled between RF ground and the other one of the electrodes; and
at least a first RF bias source of an LF or HF frequency coupled to said ESC electrode.
16. The reactor of claim 15 further comprising:
a turbo pump capable having a sufficient capacity to maintain said chamber in a pressure range including a minimum pressure as low as a few mT.
17. The reactor of claim 16 further comprising a workpiece lift mechanism for varying a workpiece-to-ceiling gap.
18. The reactor of claim 17 wherein said ceiling electrode comprises a gas distribution showerhead, said reactor further comprising a process gas supplier coupled to said gas distribution showerhead.
19. The reactor of claim 18 wherein the workpiece-to-ceiling gap comprises a process region of said chamber, said reactor further comprising:
a side wall of said chamber;
non-symmetrical elements in said chamber; and
a confinement annulus between said process region and said non-symmetrical elements and having a peripheral edge separated from said side wall by a side gap restriction.
20. The reactor of claim 19 wherein said confinement annulus comprises a planar ring extending radially from a periphery of said electrostatic chuck.
21. The reactor of claim 19 wherein said confinement annulus is conductive and is coupled to an RF ground potential so as to shield said process region from electrical effects of said non-symmetrical elements in said chamber.
22. The reactor of claim 15 wherein said VHF power source comprises:
a variable frequency generator having a frequency range that includes a fundamental frequency of which said VHF frequency is a harmonic;
a resonator coupled to plasma in said chamber for up-converting a proportion of the RF power at said fundamental frequency to said VHF frequency, whereby to couple RF power of both said fundamental frequency and said harmonic frequency to said plasma.
23. The reactor of claim 22 wherein said proportion is a function of the difference between the output of said variable frequency generator and said fundamental frequency.
24. The reactor of claim 15 wherein said chamber further comprises:
a side wall;
a layer on at least one of: (a) said side wall, (b) said electrostatic chuck, (c) said ceiling electrode, said layer comprising one of: (a) a bulk ceramic material, (b) a yttria-containing material.
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US11/734,040 US20080179011A1 (en) | 2007-01-30 | 2007-04-11 | Plasma reactor with wide process window employing plural vhf sources |
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US89863207P | 2007-01-30 | 2007-01-30 | |
US11/734,040 US20080179011A1 (en) | 2007-01-30 | 2007-04-11 | Plasma reactor with wide process window employing plural vhf sources |
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US11/733,767 Expired - Fee Related US7884025B2 (en) | 2007-01-30 | 2007-04-11 | Plasma process uniformity across a wafer by apportioning ground return path impedances among plural VHF sources |
US11/733,770 Expired - Fee Related US8076247B2 (en) | 2007-01-30 | 2007-04-11 | Plasma process uniformity across a wafer by controlling RF phase between opposing electrodes |
US11/734,040 Abandoned US20080179011A1 (en) | 2007-01-30 | 2007-04-11 | Plasma reactor with wide process window employing plural vhf sources |
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US11/733,770 Expired - Fee Related US8076247B2 (en) | 2007-01-30 | 2007-04-11 | Plasma process uniformity across a wafer by controlling RF phase between opposing electrodes |
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Also Published As
Publication number | Publication date |
---|---|
CN101242702B (en) | 2013-01-16 |
CN101242702A (en) | 2008-08-13 |
US20080182417A1 (en) | 2008-07-31 |
CN101242703A (en) | 2008-08-13 |
CN101242704A (en) | 2008-08-13 |
US7884025B2 (en) | 2011-02-08 |
US8080479B2 (en) | 2011-12-20 |
US20080182418A1 (en) | 2008-07-31 |
US20080180028A1 (en) | 2008-07-31 |
US8076247B2 (en) | 2011-12-13 |
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