WO2003058671A2

WO2003058671A2 - Target end station for the combinatory ion implantation and method of ion implantation

Info

Publication number: WO2003058671A2
Application number: PCT/EP2003/000293
Authority: WO
Inventors: Bernd Stritzker; Helmut Karl; Ingo Grosshans; Axel Wenzel
Original assignee: Universität Augsburg
Priority date: 2002-01-14
Filing date: 2003-01-14
Publication date: 2003-07-17
Also published as: WO2003058671A3

Abstract

The present invention is directed to a device (target end station) and method for the combinatory ion implantation into a sample. It generally comprises a defining section for spatially defining the dimension and shape of the ion beam, a sample chamber in which the sample to be irradiated is positioned, and a shutter assembly located between the defining section and the sample chamber. The shutter assembly typically comprises two individually controllable shutter systems each having a movable shutter that can be moved into and out of the ion beam in predetermined steps and/or intervals. The shutter itself is preferably a guillotine-type shutter, wherein the edges of the two shutters are preferably arranged perpendicularly with respect to one another. Alternatively, one or both of the shutters may be slit shutters or even more than two shutter systems may be provided in order to more freely define the dimension and shape of the ion beam. The particular advantage of the device and method of the present invention is that on one sample a plurality of areas can be irradiated under identical process conditions so that a considerable amount of time can be saved during the manufacture and development of materials, particularly semiconductors.

Description

Target End Station for the Combinatory Ion Implantation and Method of Ion Implantation

Technical Field

The present invention generally relates to ion implantation, and in particular to a device, a so-called target end station, for the combinatory ion implantation, and a method of combinatory ion implantation being useful, for instance, in the manufacturing of semiconductors.

Technical Background

While complex functional materials are often required nowadays, these materials are typically difficult to manufacture. For example, during the production of such materials a variety of parameters (e.g., pressure, temperature etc.) has to be controlled so as to obtain optimal material properties. This is even more difficult in the development of new materials. This is particularly true since it is typical initially not known how the various parameters have to be selected so that each of the parameters must be varied and correlated to the desired properties of the material in order to reach an optimum of the desired functionality.

The development of this type of materials becomes more and more difficult since the degree of complexity of the materials increases continuously which causes a rapid increase of the number of parameter combinations. This makes it necessary to develop manufacturing processes and investigation techniques allowing a fast screening or fast analysis of possible parameter combinations so as to get a grip on the plurality of variation possibilities.

In the technical field of ion beam technique such fast screening methods have so far not been considered. More precisely, in the ion beam technique either a single sample (i.e. one sample per process step) is produced or alternatively masks are used that have to be exchanged several times depending on the process so that a plurality of time consuming steps is necessary. For each exchange of the sample and/or masks the vacuum chamber has to be aired in order to remove the sample and/or mask from and to mount a new one in the vacuum chamber. Depending on the size of the vacuum chamber and the capacity of the vacuum pump this process may take up to 30 minutes until the next sample or mask can be implanted into the chamber. If the process is conducted at temperatures different from the ambient temperature, additional time for cooling and heating is required. In particular, if the process is conducted at very low or very high temperatures, the required time may be so long that on one day only one or at most two samples can be manufactured. Additionally, this single-piece production makes it difficult to ensure in case of the production of series of samples that all samples are manufactured under process conditions which are identical with the exception of the one parameter to be varied. Possible variations of other parameters may cause problems in the evaluation of the results of the analysis or may even lead to false results.

DE 41 08 404 C2 discloses an ion beam machining control process, particularly for surface correction in the finish machining of optical functional surfaces. The process comprises modifying an ion beam originating from broad beam ion source based on determined correction values by means of an aperture system. The ion beam is modified by variation of the position, shape and opening time of the aperture system comprising three or more apertures which are independently, linearly moved. The system is operated in accordance with simulation machining strategy by a digital computer control system. The strategy is derived from the correction data and comprises ion beam parameters, material properties, surface shape and the requisite precision. This process is particularly useful in the finish machining of lenses or mirrors for high performance optics or for shaping of (micro-)mechanical or electronic components. No further details of the structure and function of the aperture system are described in this document. Summary of the invention

It is an object of the present invention to provide a device or target end station for the combinatory ion implantation and an improved method for the combinatory ion implantation overcoming the deficiencies of the prior art. More precisely, it is an object of the present invention to provide an improved device and method for the development and manufacturing of materials (e.g., semiconductors) that is more reliable, better reproducible and faster than known ion implantation techniques. This object is achieved with the features of the claims.

The invention is based on the concept that a sample is mounted on a sample holder in the device (target end station), while at least two individually moveable shutters are provided so that any desired area of the sample can be masked or covered during ion implantation. This allows selective irradiation of individual areas of the sample with a variety of different process parameters on a single sample. This saves time and increases the productivity so that a greater variety of parameters or parameter combinations can be processed more efficiently. Because of the individual controlling of the shutters, that is preferably done by use of computer, a high degree of automation can be achieved so that the amount of process steps can be reduced to a minimum.

Brief Description of the Drawings

In the following preferred embodiments of the present invention will be described with reference to the drawings, in which:

Fig. 1 is a schematic cross-sectional view of the device (target end station) of the present invention; Fig. 2 is a front view of a first embodiment of a shutter assembly used in the device of the present invention shown in Fig. 1 ; Fig. 3A illustrates how individual fields or areas of a sample can be exposed to varying doses of ion radiation by the use of the device of the present invention with the shutter assembly of Fig. 2; Fig. 3B illustrates another example how individual fields or areas of a sample can be exposed to varying doses of ion radiation by the use of the device of the present invention with the shutter assembly of Fig. 2; Fig. 4A is a further embodiment of a shutter assembly that can be used in the device shown in Fig. 1 ; and Fig. 4B is another embodiment of a shutter assembly that can be used in the device of Fig. 1.

Detailed Description of Preferred Embodiments

The target end station or device 2 for the combinatory ion implantation of the present invention is schematically shown in the cross section of Fig. 1. The device 2 can generally be divided into three sections, namely a defining section I, a shutter section II, and a sample section III. In the illustration of Fig. 1 these sections are divided from each other by means of the dashed lines; however, these sections are not actually separated from each other but rather used for illustrative purposes only. Generally, in the defining section I a ion beam 4 introduced through an opening 6 into a housing 8 of the target end station 2 is spatially defined by means of a defining aperture 10 held in the housing 8 by means of a support member 12. The cross sectional area of the ion beam 4 is typically slightly larger than the area of the opening of the defining aperture 10 so that the defining aperture 10 limits or defines the ion beam 4 to a particular shape and size. For example, the ion beam 4 may have a diameter slightly larger than 4 inches (101.6 mm) so that by means of the defining aperture 10 a circular ion beam 4 is defined having a diameter of 4 inches (101.6 mm), while the rest of the ion beam 4 is blocked by the defining aperture 10.

Furthermore, the defining section I of the target end station 2 of the present invention is typically provided with a "corner cup system" 14 for measuring the ionic current so as to exactly determine the implanted dose of radiation. The corner cup system 14 is preferably also mounted to the support member 12. The functioning of the corner cup system 14 is generally known in the art so that no further explanation in this context appears necessary. Only generally it should be mentioned that in the target end station 2 of the present invention the corner cup system comprises four corner cups 14', 14", 14'" and 14"" that are arranged in the corners of a rectangle 16 circumscribing the defining aperture 10 as is shown in Fig. 2. Preferably, the defining aperture 10 and the corner cup system 14 are mounted to the support member 12 so that the whole arrangement is pluggably mountable in the housing 8 of the target end station 2.

The housing 8 of the target end station 2 furthermore comprises a sample compartment or chamber 18 in which a sample holder 20 is provided. Preferably, the sample chamber 18 is surrounded by a cooling shield 22 acting as a heat sink in order to eliminate the radiant heat of the sample holder 20. The cooling shield 22 may be water cooled, if necessary. By means of the cooling shield 22 it can be avoided that the electrical system, seals etc. are damaged due to the radiant heat produced during ion implantation.

The sample chamber 18 comprises an opening 24 in its upper portion through which different sample holders 20 can be inserted in the sample chamber 18 by means of a carrier plate 26. As shown in Fig. 1 , the carrier plate 26 is mounted to the housing 8 of the device 2 along its circumferential rim 28 that contacts a lid 30 of the sample chamber 18. For example, two different sample holders 20 may be used, one of which for the implantation of ions at low temperatures (e.g. < 100°C) and another sample holder 20 for high temperatures, e.g., up to about 1000°C.

The sample holder 20 for low temperature may be a tank or container made of stainless steel which is held in a vacuum. The container is connected to one or more tubes through which the container can be loaded with liquid nitrogen from the atmosphere side of the device. A stainless steel plate is connected, preferably adhesively bonded, to the container, for example by means of indium, so that a good heat transfer is achieved. The samples can than be applied onto this plate. With this type of sample holder 20, temperatures on the surface of the sample plate can be achieved that are only slightly above the temperature of the liquid oxygen (i.e. about -196°C). By means of an integrated heating element in the plate the temperature can be varied between -190°C and +100°C.

The sample holder 20 for high temperatures is preferably substantially made of molybdenum due to its high melting temperature. This sample holder comprises a sample plate having two rods that are mounted to the carrier plate 26 of the sample chamber 18. In the connection between the sample plate of the sample holder 20 and the carrier plate 26 a "weak link" of high temperature stainless steel is provided that provides for a low heat transfer so that as little as possible of the heat is led out of the sample chamber 18. Furthermore, it is preferred to provide one or more heat shields between the sample plate and the carrier plate

26 so that the carrier plate 26 and associated seals are not heated excessively.

The sample plate is heated by a radiation heater made of boron nitride so that depending on the power of the heater temperatures up to about 1000°C on the front surface of the sample plate can be realised.

In the following, the shutter section II shown in Fig. 1 will be described with reference to Figures 2 and 3. Generally, this section comprises at least two individually controllable mask or shutter systems 32 and 34. In the illustrated embodiments, the shutter systems 32 and 34 comprise guillotine-type shutters 36 and 38 that are individually vertically movable as indicated by arrows 40 and 42, respectively. The shutter systems 32 and 34 are mounted to a support frame 44 provided in the housing 8. Each of the shutter systems 32 and 34 comprises guiding and advancing means with which the shutters 36, 38 are guided and advanced into predetermined positions into the ion beam 4. The guiding means preferably comprises an axial thrust bearing for guiding the guillotine-type shutters 36, 38 as indicated by the arrows 40 and 42. The advancing means can be of any type allowing an axial displacement of the shutters 36, 38 relative to the housing 8. In the illustrated preferred embodiment of the present invention the advancing means of each shutter system 33, 34 comprises a stepping motor 46 and is connected to a rotatable spindle 48 defining a longitudinal axis. A carriage 50 carrying each guillotine-type shutter 36, 38 is mounted to the spindle 48 so as to be axially movable with respect to the spindle 48 upon activation of the stepping motor 46. The carriage 50 is axially guided by the axial thrust bearing in order to allow, in combination with the spindle drive, precise axial displacement of the shutters 36, 38 into the ion beam 4. Each of the shutter systems 32 and 34 is driven by individually controlling the stepping motors 46, preferably by use of an appropriate computer system.

As illustrated in Fig. 2, the two shutter systems 32 and 34 combined together form a shutter assembly 52 which allows a plurality of defined areas of the sample to be exposed to varying doses of ion radiation. To this end the shutters 36 and 38 are preferably guillotine-like shaped, i.e. each of the shutters has an upper substantially rectangular part 36a, 38a and a lower substantially triangular part 36b, 38b. In the illustrated embodiment shown in Fig. 2 the triangular parts 36b and 38b of the shutters 36 and 38 are isosceles triangles, wherein the hypotenuse forms an oblique edge 54 and 56 of the respective shutters 36 and 38. Preferably, the oblique edges 54 and 56 are formed under an angle of about 45° so that the two edges are perpendicular with respect to one another.

However, it is also possible to provide the shutters 36 and 38 with differently oriented edges as long as the edges of the two shutters are perpendicular with respect one another. For example, it would be possible to provide rectangular shutters that are movable into mutually perpendicular directions.

During the implantation the edges 54 and 56 of the shutters 36 and 38 are hit by the ion beam 4, whereby items may be knocked out of the shutters 36 and 38 which may deposit on the surface of the sample and contaminate it. Therefore, the edge regions and edges of the shutters 36, 38 are typically provided with substrate material that is identical to the sample material so that due to the atomisation no foreign matter deposits on the sample.

As already mentioned above, by means of individually controlling the stepping motors 46 the shutters 36 and 38 can be driven independently such that depending on the process requirements individual areas in the x- and y- direction can be exposed to the ion beam or can be covered or screened. This will be described in the following in connection with Fig. 3 by means of an exemplary implantation procedure. First, ions of the type "A" are to be implanted into the sample at predetermined process parameters (e.g., temperature, energy etc.). During this implantation of the ion type "A" a variation of the dose is to be realised in the form of a strip pattern on the sample. In this example, the dose variation is once, twice, three times, four times, and five times a base dose. After the sample is mounted onto a sample holder 20, the sample holder 20 is assembled into the target end station 2, and after the sample chamber 18 is evacuated, the implantation starts at the desired process parameters in that a first dose corresponding to the base dose of the ion type "A" is implanted into the sample. Thereafter, the total dose of the sample corresponds to the base dose. Then, one of the shutters 36 or 38 (x-shutter) is closed by one step so as to cover a first strip. The rest of the sample is then irradiated by the base dose, whereupon the x-shutter is again advanced by one step so as to cover a second strip. If this is repeated until the last strip, the sample comprises the above mentioned five strips irradiated with one, two, three, four and five base doses, respectively.

By means of the other of the two shutters 38 or 36 (y-shutter) a further strip pattern can be produced that is provided perpendicular to the first strip pattern. The ion type "B" can be implanted into the sample at the same or different process parameters. The procedure is the same as described above with respect to the x-shutter, i.e. the shutter is advanced step by step until the strips are exposed to once, twice, three times, four times, and five times the base dose. With this procedure an array or matrix of individually irradiated areas can be produced on the sample. With the above-mentioned example a 5x5-matrix can be achieved as shown in Fig. 3A with a different shading of the 25 defined areas. In this matrix two parameters have been varied, namely the stoichiometry and the dose. On the main diagonal 58 of this matrix a dose variation at a 1:1 stoichiometry is located, while on the auxiliary diagonals 60 the respective under or over stoichiometric doses are positioned.

This is further shown in Fig. 3B, where in the respective defined areas or fields of the matrix the respective doses of the ion types "A" and "B" are indicated.

The target end station 2 and the method of the present invention provides the possibility to produce a plurality of different areas on the sample under identical process conditions, i.e. under comparable conditions while saving a large amount of time. More precisely, in the above-described example for each ion type a total dose of five times the base dose is implanted. If the ions are individually implanted into the samples in the conventional manner, there is a total dose amounting to 15 times the base dose necessary (namely 1 + 2 + 3 + 4 + 5 times the base dose), i.e. the time necessary for the implantation is tripled. Additional time is necessary to air the vacuum chamber, to assemble and disassemble the samples and to evacuate the vacuum chamber. Accordingly, the device and the method of the present invention provides considerable advantages in the manufacture and in particular in the development of new materials.

It is also possible to provide an irradiation pattern with the respective doses in each defined area as shown in Fig. 3A by applying multiples of the base dose in each irradiation step and/or by changing the applied dose by a multiple of the base dose from one irradiation step to the next. For example, irradiation with a specific ion type can be carried out with the base dose in step 1 in x-direction and with 6 times, 11 times, 16 times and 21 times the base dose in steps 2, 3, 4 and 5, respectively. Subsequently, in y-direction in the first irradiation step using the base dose the first strip of defined areas is not irradiated, i.e. covered by the y-shutter, and then, with y-shutter movement in y-direction, irradiation is carried out again with the base dose in three further steps. With this method the 25 defined areas are irradiated with the base dose, twice the base dose etc. up to 25 times the base dose, respectively, i.e., each area receives a different dose. This method can also be combined with the above described method using two different ion types so that a plurality of variations with respect to stoichiometry and/or dose can be achieved.

In Figures 4A and 4B two alternative constructions for the shutter assembly 52 are illustrated. In the shutter assembly 52 shown in Fig. 4A the guillotine-type shutter 36 is replaced by a slit shutter 62. The slit shutter 62 comprises an obliquely extending slit 64. The slit 64 is at least as long as to extent over the total width of the defining aperture 10. The width of the slit 64 corresponds to the width of each line of the strip pattern of the matrix to be produced on the sample. The guiding and advancing means for the slit shutter described above with respect to Figures 1 to 3 can also be applied for the embodiment of the shutter assembly shown in Fig. 4A. The other shutter 38 is a guillotine-type shutter 38 as described above with reference to Figures 1 to 3.

The embodiment of the shutter assembly 52 shown in Fig. 4B differs from the previously described embodiment of Fig. 4A in that the guillotine-type shutter 38 is replaced by a second slit shutter 66 having an obliquely extending slit 68. The slits 64 and 68 of the shutters 62 and 66 are typically arranged perpendicularly with respect to one another as described above in the context of the guillotine- type shutters 36 and 38. The guiding and advancing means of the two slit shutters 62 and 66 may be the same as described above with reference to Figures 1 to 3.

In accordance with a further embodiment (not shown) the width of the slits 64 and 68 of the slit shutters 62 and 64 may be variable. The variation of the width of the slits is preferably performed in the evacuated vacuum chamber during the process. This provides an even broader spectrum of application for the shutter system. To this end, for example, four individually controllable shutter systems may be used.

With the use of one slit shutter (Fig. 4A) strips can be treated independently from one another, while with two slit shutters 62 and 66 (Fig. 4B) single areas or fields of the sample, e.g. elements or "dots" of a matrix, are freely addressable. These systems therefore allow more possibilities for combinations of the process parameters for the sample while reducing manufacturing and process time.

In summary, it can be seen that the present invention is directed to a new target end station or device for the combinatory ion implantation comprising a controllable shutter system by means of which a variation of different process parameters (e.g., elements, doses, energy etc.) onto a sample is possible under otherwise identical process conditions. This leads in comparison to conventional procedures to a considerable reduction of the time necessary for implantation. In combination with automated analysis procedures a large variety of parameters can be effectively evaluated in short time and with little work involved.

Possible applications of the device and the method of the present invention are in particular in the ion beam technique. More precisely, in the semiconductor technique in which the implantation process, e.g., for doping should be optimised in as little time as possible, this fast screening method can be used advantageously. In the synthesis of hard material layers by means of high dose ion implantation the time saving is particularly large due to the combinatorial analysis.

Furthermore, the device and method of the present invention may be useful in the production of calibration test pieces for diverse analysis procedures. In particular, in the SIMS (Secondary Ion Mass Spectrometry) such calibration test pieces having a similar known concentration distribution of the elements are required in order to calibrate unknown samples. The ion implantation is the basic procedure for the production of such calibrated test pieces since the concentration distribution of the elements in the sample can be adjusted very exactly. Furthermore, all elements can be incorporated in a large variety of substrates without any substantial problems. This is one of the particular advantages of the combinatory ion beam synthesis of the invention. For example, with this procedure calibrated test pieces can be manufactured that have on one surface a plurality of areas with different element concentrations. These test pieces may then be used as calibration matrix in a SIMS-device.

Generally, the above-described principle of covering different areas of a sample may also be applied to other applications that are not particularly related to the ion beam technique. For example, the principle and method of the present invention can be used for varying elimination of photo lacquers, coating or spraying tests onto surfaces to be coated, variation of the layer thickness in vapour deposition processes etc.

The device of the present invention may be used for a combinatorial approach for the synthesis of optically active ll-VI compound semiconductor nanocrystals. Due to the wide field of possible parameter combinations (e.g. dose, stoichiometry, implantation energy, temperature, etc.) to investigate, it is advantageous to apply a fast synthesis technique as well as a fast screening method.

The device or target end station of the invention is equipped with two crossed and movable computer controlled apertures in front of the substrate of 4 inches in diameter so that the wafer can be implanted with a lateral rectangular pattern of distinct dose combinations under identical conditions. Thermally grown Siθ2 on silicon is used as substrate material. The wafers are clamped on one or more sample holders, which allow implantation temperatures down to that of liquid nitrogen. The chemical reaction of the implanted components is initiated during a subsequent annealing step in a rapid thermal furnace. To study the photoluminescence (PL) properties, the whole wafer can be mounted in an optical cryostat. The implanted matrix can then be scanned by a computer controlled setup so that a database of the wafer is generated. By virtue of this database, samples with the best PL quality can then be investigated by SIMS, RBS, XRD and TEM.

Claims

1. A device for the combinatory ion implantation into a sample comprising: a) a defining section for spatially defining an ion beam; b) a sample chamber in which the sample to be irradiated by the ion beam is supported; and c) a shutter assembly arranged between the defining section and the sample chamber, the shutter assembly comprising at least two individually controllable shutter systems and being adapted to allow independent irradiation of individual areas of the sample with the ion beam.

2. The device of claim 1 , wherein each of the shutter systems comprises advancing means being mounted to a housing of the device, a shutter being movable relative to the housing and connected to the advancing means, and guiding means for guiding movement of the shutter.

3. The device of claim 2, wherein the advancing means comprises an electrical stepping motor and a spindle rotatably connected to the stepping motor, and the guiding means comprise a carriage receiving the spindle and supporting the shutter for movement of the shutter.

4. The device of claim 2 or 3, wherein each of the shutters is a guillotine-type shutter having an oblique edge.

5. The device of claim 4 comprising two shutters, wherein the oblique edges of the two shutters are arranged perpendicularly with respect to one another.

6. The device of claim 4 comprising two pairs of shutters, wherein each pair comprises parallel oblique edges and wherein the two pairs of oblique edges are arranged perpendicularly with respect to one another.

7. The device of claim 2 or 3, wherein one of the shutters is a guillotine-type shutter having an oblique edge and the other shutter is a slit shutter having an oblique slit, wherein the oblique edge and the oblique slit are preferably arranged perpendicularly with respect to one another.

8. The device of claim 2 or 3, wherein each of the shutters is a slit shutter having oblique slits that are preferably arranged perpendicularly with respect to one another.

9. The device of any of claims 1 to 8, wherein the defining section comprises a defining aperture, preferably a circular defining aperture.

10. The device of any of claims 1 to 9, wherein the defining section comprises a corner cup system for measuring the ionic current in order to determine the implanted dose.

11. The device of any of claims 1 to 10, wherein the sample chamber is provided in a vacuum chamber or is itself a vacuum chamber.

12. The device of any of claims 1 to 11 , wherein the sample chamber comprises an opening through which the sample can be inserted into and removed from the sample chamber, and a lid for closing the opening.

13. The device of any of claims 1 to 12, wherein the sample is supported in the sample chamber by means of a sample holder.

14. The device of any of claims 1 to 13, wherein the edge of each of the shutters is provided with a substrate material that is identical to the sample material so that due to the atomisation no foreign matter deposits on the sample.

15. A method for the combinatory ion implantation into a sample comprising the steps of: a) providing the sample into a sample chamber; b) directing a spatially defined ion beam into the sample chamber and onto the sample; and c) controlling at least two individually controllable shutter systems of a shutter assembly so as to allow independent irradiation of individual areas of the sample with the ion beam.

16. The method of claim 15, wherein the directing step b) comprises directing the ion beam through a defining aperture, preferably a circular defining aperture.

17. The method of claim 15 or 16, further comprising the step of measuring the ionic current in order to determine the implanted dose.

18. The method of any of claims 15 to 17, wherein the controlling step c) comprises controlling movement of one or more shutters of the shutter assembly.

19. The method of any of claims 15 to 18, wherein in the controlling step c) the ion beam is controlled such that individual areas of the sample are exposed to varying doses of radiation.

20. The method of claim 19, wherein the sample is exposed to varying doses of radiation in first and second strip patterns that are arranged perpendicularly with respect to one another so as to form a matrix of individually irradiated areas on the sample.

21. The method of claim 15, wherein the control of the shutter assembly is carried out stepwise, and the ion beam irradiation in each step is carried out with the same dose or different doses.