WO2000078654A1

WO2000078654A1 - Improved wafer handling apparatus

Info

Publication number: WO2000078654A1
Application number: PCT/US2000/016274
Authority: WO
Inventors: Jose R. Gonzalez-Martin
Original assignee: Speedfam-Ipec Corporation
Priority date: 1999-06-17
Filing date: 2000-06-14
Publication date: 2000-12-28
Also published as: WO2000078654A9

Abstract

Transfer arms (10) for the automated handling of semiconductor wafers have a single vacuum passageway (32) communicating with a wafer-contacting vacuum opening (28). The transfer arms may have an optional U-shaped wafer-engaging end (122, 124) with a part circular vacuum opening for acquiring the wafer. The transfer arms may be single-sided or double-sided, each side being capable of acquiring, moving and selectively releasing a wafer on demand.

Description

IMPROVED WAFER HANDLING APPARATUS

BACKGROUND OF THE INVENTION

1. Field of the Invention;

The present invention pertains to apparatus used in the surface finishing of relatively thin, flexible workpieces such as semiconductor wafers and in particular to such apparatus used in the polishing of wafers so as to attain a high degree of surface flatness. More particularly, the present invention pertains to automation for acquiring, transporting and releasing semiconductor wafers and for end effectors employed as robotic manipulators.

2. Description of the Related Art;

Wafer blanks are employed in the commercial production of many types of semiconductor devices.

Typically, wafers undergo layering operations in which a variety of structures are formed on the wafer blank, utilizing such techniques as ion implantation, metali- zation or sputtering. Such layers have a relatively small thickness, usually measured in terms of microns or micro inches. Nonetheless, the resulting layered suri-ace must be polished extremely flat in preparation for repeated subsequent layering operations.

Typically, the layer formation and polishing are conducted at work stations remote from one another, and thus wafer handling is involved to transport the wafer back and forth between layer forming and polishing operations. Additional wafer handling is also required when the wafers are scrubbed or otherwise cleaned after a polishing operation, so as to remove particulate from the wafer surface. The flatness dimensions required for the semiconductor wafers is such that even particles of residue remaining after cleaning may interfere with subsequent layering operations, and thus stringent controls are required to maintain the wafer surfaces in a desired condition. Various arrangements have been proposed to aid in transporting a wafer from one location to another. For example, apparatus may be employed to "flip" or invert a wafer surface. For example, wafers polished with a downwardly facing device side may be inverted prior to transport to a remote location so that the wafer can be conveniently supported from below. Various wafer handling equipment, in addition to the wafer inverting apparatus, is needed to complete a transfer operation. In general, the wafer surface must not be injured during transfer operations, and it is desirable to minimize the number of times a wafer is required to be transferred from one location to another. Manufacturers are considering employing robots and robotic equipment for wafer handling operations to help reduce labor costs. Japanese Patent No. 61-241060, for example, discloses a robot arm, at one end of which is located a circular carrier plate having a plurality of suction members. The carrier plate is lowered onto the wafer to be transported, and a vacuum signal applied to the vacuum members so as to acquire physical control over the wafer. The robot arm is then extended, retracted or elevated so as to move the wafer to a desired position. Despite advances in automated wafer handling, further improvements in the flexibility, capability and cost of ownership of wafer handling apparatus are being sought. SUMMARY OF THE INVENTION

It is an object of the present invention to provide apparatus for the automated transport of semi^¬ conductor wafers and other relatively thin flexible workpieces, from one location to another.

Another object of the present invention is to provide apparatus for transporting wafers from one location, to another, requiring a minimum of auxiliary apparatus . These and other objects according to principles of the present invention are provided in a transfer arm for acquiring, transporting and releasing a semiconductor wafer, comprising: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body of ceramic material defining a single vacuum passageway extending from the wafer- contacting portion to the mounting end of the body;^' the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; and a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end.

Other objects of the present invention are attained in a semiconductor wafer manipulating apparatus comprising the combination of a robotic manipulator having a mounting head and at least one transfer arm for acquiring, transporting and releasing a semiconductor wafer mounted to the mounting head, said transfer arm including: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body of ceramic material defining a single vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; and a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end. Further objects of the present invention are attained in a transfer arm for acquiring, transporting and releasing a semiconductor wafer, comprising: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body defining at least one vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end; and wherein the wafer- contacting portion is generally U-shaped and defines a curved recess communicating with the wafer- facing surface and the vacuum passageway. Still further objects of the present invention are attained in a wafer manipulating apparatus, including a robotic manipulator having a mounting head and a transfer arm for acquiring, transporting and releasing a semiconductor wafer, the transfer arm including: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end_ with a wafer- contacting portion; a body defining at least one vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end; and wherein the wafer- contacting portion is generally U-shaped and defines a curved recess communicating with the wafer- facing surface and the vacuum passageway.

BRIEF DESCRIPTION OF JTHE DRAWINGS

FIG. 1 is perspective view of a transfer arm according to the principles of the present invention;

FIG. 2 is a bottom plan view thereof;

FIG. 3 is a cross-sectional view taken along the line 3-3 of FIG. 2;

FIG. 4 is a top plan view thereof;

FIG. 5 is a cross-sectional view taken on an enlarged scale along the line 5-5 of FIG. 4; FIG. 6 is a side elevational view of the transfer arm mounted in a robotic manipulator;

FIG. 7 shows a portion of FIG. 6, on an enlarged scale; FIG. 8 is a bottom plan view of an alternative transfer arm;

FIG. S is a cross-sectional view taken along the line 9-9 of FIG. 8 ;

FIG. 10 is a bottom plan view of a further alternative transfer arm;

FIG. 11 is a cross -sectional view taken along the line 11-11 of FIG.10;

FIG. 12 shows the arms of FIGS. 8-11 mounted on a robotic end effector; FIG. 13 shows another alternative transfer arm according to the principles of the present invention;

FIG. 14 is a cross -sectional view taken along the line 14-14 of FIG. 13; FIG. 15 is a top plan view thereof;

FIG. 16 is a side elevational view of the transfer arms of FIGs . 8 and 13 mounted to a robotic end effector; and

FIG. 17 is a top plan view of a wafer treatment installation for use with transfer arms according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and initially to Figs. 1-5, a transfer arm generally indicated at 10 is shown in an inverted ("upside-down") position.

Transfer arm 10 is particularly adapted for acquiring, transporting and releasing semiconductor wafers, especially during wafer surface treatment operations such as polishing. In the wafer polishing art, for example, semiconductor wafers are repeatedly transferred between circuit forming stations such as those employing metal deposition techniques, and polishing stations in which the resulting wafer is polished flat in preparation for subsequent wafer- forming steps. Accordingly, it is necessary to transfer the wafers being processed from one physical location to another.

Transfer arm 10 has a first major surface 12 which faces toward the wafer to be manipulated (usually the bottom surface of the transfer arm, when placed in operation. The opposed major surface 14 (usually the upper surface) is shown in Fig. 4. Transfer arm 10 has a working end 18 and an imposed mounting end 20. As shown for example in Fig. 6, the mounting end 20 is affixed to a robotic manipulator while the working end 18 comprises a free end receiving cantilever support from the robotic manipulator. A series of mounting holes 22 are provided for the cantilever mounting to a robotic or other type of manipulator, while holes 24 are provided adjacent the mounting end 20 for coupling to a vacuum source (now shown) .

Transfer arm 10 represents an improvement over prior art transfer arms adapted for use in end effector assemblies of robotic manipulators. As can be seen, for example, in Figs. 1 and 2, .the working end 18 of transfer arm 10 includes an X-shaped opening 28 extending from surface 12 into the ^"thickness t of the transfer arm indicated in Fig. 3. As indicated in Fig. 3, the X-shaped opening 28 has a depth between one- third and one-half the thickness t. As will be seen herein, construction of the transfer arm 10 allows for a surprising reduction in overall thickness which allows the transfer arm to be employed, for example, in storage cassettes in which wafers are closely spaced to one another.

As those familiar with the art are aware, wafer-storing cassettes are employed to transfer a large number of wafers from one location to another. To acquire the wafers from the cassette, the transfer arm must be inserted within the cassette, in between wafers, and a vacuum signal is applied to acquire a single, selected wafer. The transfer arm, thus readied for withdrawal of the selected wafer from the cassette, is relocated along with the wafer. A problem has arisen in that wafers of different diameters have cassettes with differing inter-wafer spacings and, heretofore, specially configured transfer arms had to be developed for particular wafer sizes. With the transfer arm of the present invention, a single transfer arm can be employed for use with multiple wafer sizes, such as 150 mm, 200 mm and 300 mm wafers. The transfer arm according to the present invention, even though very thin, has been found to be sufficiently stiff, even for wafers having a 150 millimeter radius, and associated substantially increased mass. The material properties of the preferred ceramic material (flexural strength of 45,000 psi and compressive strength of 300,000 psi) allow a transfer arm of only 2.25 millimeter thickness to operate successfully throughout the range of motions required in conventional wafer-handling apparatus.

Opening 28 is characterized by a plurality of legs outwardly extending from a common center point. In the preferred embodiment, four outwardly extending legs are arranged in an X-shaped pattern, although other patterns may be employed, having varying numbers of legs generally oriented in what is referred to as a geometrical "star" configuration. As will be seen herein, transfer arm 10 provides a number of substantial advantages. Previously, transfer arms were commonly made of non- conductive plastic material or conductive aluminum or other lightweight metals. As will be appreciated by those skilled in the art, one important design requirement for transfer arms employed in the semiconductor industry, is the ability of the transfer arms to control unwanted electrical discharges. In general, since it is desirable to reduce the weight of the transfer arm as much as possible so as to avoid overburden to the robotic manipulator from which the transfer arm is cantilevered, transfer arms typically have a thin profile with relatively large opposed major surfaces, oriented generally parallel to areas of friction-generating activity. As a result, static electrical charges build up on the transfer arms. If such stored charges should be allowed to discharge to a wafer semiconductor surface, the electrical circuits built up on the wafer surface are likely^' to be damaged, and also, local surface flatness will be destroyed. Accordingly, substantial concerns have been raised with regard to the ability of certain materials to perform in a wafer polishing environment, when formed as transfer arms of the type to which the present invention is directed.

Transfer arms must also be able to selectively acquire and release semiconductor wafers by directly contacting the wafer surfaces. Arrangements for acquiring wafers in this manner involve applying a vacuum signal at the portion of the transfer arm in contact with the wafer surface. The vacuum source for such operations is ultimately located remote from the transfer arm and, accordingly, interconnecting conduits must be provided from the wafer- contacting end of the transfer arm. It is desirable that such conduits be formed directly in the transfer arm in the form of internal passageways. However, since it is desirable to reduce transfer arm overall weight, the vacuum passageways within the transfer arm body must reflect limitations of the structural strength of the transfer arm construction.

The ability of a particular material to meet the many conflicting requirements of a transfer arm employed with semiconductor wafers cannot be adequately predicted beforehand. In addition, semiconductor industry requirements are tending toward more massive wafer sizes, with each increasing wafer size presenting changes in shape and overall weight, necessitating design challenges which were not required to be addressed in previous designs. After an ongoing process of selecting various materials for consideration, attention was given to ceramic materials, and especially to filled ceramics. A material commercially available under the designation

"Alumina- 995 " was chosen for prototype constructions illustrated herein to accommodate large, 300 mm size wafers .

As can be seen, for example, in Fig. 1, a single continuous slot 32 extends between the X-shaped opening 28 and vacuum holes 24. Passageway 32 is enlarged adjacent mounting end 20 so as to communicate with both vacuum holes 24, the location of which is chosen to correspond to the vacuum holes of prior transfer arm constructions so as to accommodate established mounting patterns. Unlike prior transfer arms which employed two passageways, roughly centered on the vacuum holes 24, transfer arm 10 employs a single, wider passageway 32 terminating in a T-shaped configuration with the head of the "T" extending to vacuum holes 24. The passageway of the present invention can be enlarged to reduce the pressure drop at the X-shaped opening 28, despite an unprecedented reduction in transfer arm thickness and increase in wafer mass.

Although Alumina- 995 is the preferred material due to a variety of properties relating to its ability to manage static electricity, bending strength when cantilever mounted, surface smoothness, and overall weight, other ceramic materials, such as alumina A-479G (see Table 2 and related discussion, herein), DLC (diamond- like-carbon) and other aluminum oxide (A1,0 ) ceramics may be employed as well.

As can be seen, for example, in Fig. 3, transfer arm 10 is of generally constant thickness t (2.03 mm for the preferred alumina embodiment) except for a wafer contacting portion 36 of slightly increased thickness (2.26 mm for the same embodiment). Wafer contacting portion 36 extends from a step 38 to the free, working end 18. By slightly raising the wafer contact portion 36 from step 38 and beyond, only a centrally located portion of the wafer is contacted. In the preferred embodiment, the amount of increased thickness of wafer contact portion 36 is 0.23 milli- meter.

As those skilled in the art will appreciate, the overall thickness of the wafer-contacting portion of the transfer arm is an important design consideration. For example, it is sometimes required in producing batches of semiconductor wafers, that a batch of wafers be transferred from one location to another. Specialized cassettes, oftentimes with elaborate environmental controls, are employed for the purpose. For purposes of economy, the wafers are stored in compact, closely spaced intervals. As indicated above, it is important that transfer arms employed to insert and extract wafers from such storage modules have a minimal thickness so as to be able to enter the storage module and acquire a wafer, withdrawing the wafer from its slot -like storage space. Optional scribe marks 40, 42 indicate the desired alignment of transfer arm 10 with wafers of differing diameters. With reference to Fig. 2, in the preferred embodiment, circular wafers are centered at center point 44 of the X-shaped opening 28 while portions of the wafer outer periphery fall along scribe marks 40 or 42, depending upon wafer diameter. In a preferred embodiment, scribe mark 40 corresponds to a wafer diameter of 150 millimeters, while scribe mark 42 corresponds to a wafer diameter of 200 millimeters. As will now be seen, certain advantages in constructing transfer arm 10 are also made possible by the present invention. Referring to Fig. 5, transfer arm 10 is formed by one or two simple milling opera- tions to form a stepped slot in the surface 14. In

Fig. 5 the stepped slot is covered with a cover member 50 also formed of the same ceramic material as the body portion. Use of Alumina-995 allows the thin profile needed for the cover. Preferably, cover 50 is bonded or molded to the recess milled in the transfer arm, so as to form a vacuum- tight seal throughout the length of passageway 32. The preferred material for transfer arm 10 allows relatively thin cover to be formed as a separate member and fit into place, as shown, using commercially practical techniques. This represents a substantial advance over prior art transfer arms having vacuum- tight passageways formed by adhesive tape "covers". In general, the backing material of the adhesive tape is not found objectionable, but the adhesive material applied thereto has been found to attract dust and other contaminating particles and on occasion has been found to migrate to various mechanisms in the wafer vicinity. A portion of the slot forming passageway 32 is visible, for example, in Figs. 1 and 2. Finally, the X-shaped recess 28 is formed in surface 12.

As can be seen, for example, in Figs. 1-4, interior passageway 32 communicates with the center of X-shaped recess 28, being formed so as to extend across two legs 28a, 28b of slot 28. As indicated in Fig. 5, it is generally preferred that passageway 32 be milled at a depth such that the slot barely intersects the recess 28. The close spacing arrangement indicated in Fig. 5, the passageway 32 and the X-shaped opening, along with other features according to the present invention allows transfer arm 10 to have a reduced thickness t of approximately 2.25 millimeters.

As previously indicated, the thickness t of transfer arm 10 is substantially constant from mounting end 20 to step 38 whereas, in the prior art, the mounting end has a substantially increased thickness of 5 to 6 millimeters and at its thinnest part extending to the free end, has a thickness slightly more than 3.5 millimeters. The transfer arm according to the principles of the present invention has a 35% reduction in transfer arm thickness, and further eliminates the need for a massive, much thicker mounting end. The slotting cutter used to mill passageway 32 is approximately five times wider than the slotting cutter used on previous transfer arms, allowing the thickness of the internal passageway 32 to be reduced when necessary to accommodate the greatly reduced transfer arm thickness, and to allow the internal passageway to be formed in one, or at most two, milling operations. Transfer arms according to the principles of the present invention can be lengthened so as to accommodate popularly sized wafers having a 150 millimeter radius, without a substantial increase in transfer arm thickness. As opposed to prior art transfer arms having two much smaller parallel separated slots, the single slot forming passageway 32 has been found to provide an improved acquisition of wafers suspended from the transfer arm, even wafers of newly required 300 mm size. As can be seen, for example, in Fig. 2, the slot forming passageway 32 extends beyond the V-shaped apex formed where legs 28a, 28b intersect, thus further reducing vacuum restrictions formed by the V-shaped "corner" of recess 28 and assuring a more uniform distribution of the vacuum signal throughout the X-shaped recess, as the recess becomes closed upon contact with the center of a wafer being acquired.

Referring now to Fig. 6, a conventional "6-axis" robotic manipulator is generally indicated at 60. The robotic manipulator has a conventional chuck 62 for receiving a conventional end effector mounting 64. The end effector mounting 64 includes mounting arms 66 to which a conventional transfer arm 70 and a transfer arm 10 are mounted. A wrist action of the robotic manipulator indicated by arrow 72 and associated movements of the robotic manipulator allow either transfer arm to be "swung" into position for a desired wafer transfer operation. Fig. 7 is an enlarged view of transfer arms 10, 70, mounted in a slightly different end effector mounting 76. A vacuum connection line 78 connects the vacuum holes 24 of transfer ^'arm 10 to a vacuum source (not shown) . As indicated in Fig. 7, it is generally preferred that the wafer contacting side 12 of transfer arm 10 and the wafer contacting side 71 of transfer arm 70 have the same relative position with respect to a pivoting motion indicated by arrow 82. That is, assuming a rotation of the end effector assembly shown in Fig. 7, the wafer contacting the surfaces of transfer arms 10 and 70 will be located on the leading surfaces of their respective transfer arms.

Further, it has been found that the preferred ceramic material allows a smoother surface finish to be attained than conventional prior art plastic materials. Accordingly, a more effective vacuum seal can be formed upon contact with a wafer to be acquired. As those familiar with the semiconductor processing art are aware, commercially successful transfer arms must exhibit a low tendency to store static charge (i.e., must have sufficiently low surface electrical resistance) and must withstand elevated temperatures encountered in production of the transfer arm material, as well as subsequent machining operations. Turning now to Figs. 8-12, alternative transfer arms according to principles of the present invention are shown. For example, in Figs. 8 and 9 a transfer arm 90 has a U-shaped wafer contacting portion 92, generally resembling an electrical space lug connector. The opposed mounting end 94 of transfer arm 90 includes mounting holes 96 and vacuum holes 98. A pair of spaced apart parallel vacuum passageways 102 extent the full length of the transfer arm, terminating in a generally C- shaped vacuum recess 106. As can be seen, for example, in Fig. 8, vacuum recess 106 includes a centrally located finger- like extension 108. A step 112 is formed in the transfer arm to accommodate a substantially thicker portion adjacent the mounting end 94, to increase rigidity and load carrying capability for the transfer arm. A series of scribe marks 114, 116 and 118 locate the outer periphery of three different size wafers which can be accommodated by the transfer arm. In the preferred embodiment, the scribe marks 114, 116 and 118 correspond to outer peripheries of wafers having radii of 75 millimeters, 100 millimeters and 150 millimeters, respectively.

As can be seen in Fig. 8, the legs 122, 124 have beveled free ends 122a, 124a, respectively, located at the free end of the transfer arm. The preferred orientation for the wafer places the wafer center at center point 126.- The generally arcuate vacuum recess 106 subtends an angle of approximately 120 degrees, with the center of the arc-shaped recess 106 located at center point 126. Thus, with the arc- shaped recess 106 engaging the left-hand portion of the wafer, the legs 122, 124 extend into the right-hand portion of the wafer (with the left and right-hand portions of the wafer being defined with reference to a vertical line in Fig. 8 extending through center point 126). The U-shaped or "horseshoe" -shaped portion 92 is raised slightly above the wafer- facing surface 130, a feature associated with step 132 which preferably has a part circular shape with a center also located at center point 126. The cooperation of the raised wafer contacting portion 92, the arc-shaped slot 106, with projecting finger 108, and the legs 122 projecting beyond the center point 126 have been found to cooperate to produce improved wafer-handling stability, even when larger more massive 300 mm wafers are suspended from the transfer arm.

Referring now to Figs. 10 and 11, transfer arm 140 is substantially identical to transfer arm 90 described above, except for the formation of two pairs of notches 142 and a replacement of step 112 with a step 144 which is arranged at a non-normal angle to the axial center line 146 of transfer arm 140. The angled step 144 helps manage the passage of slurry, deionized water or other fluid media, traveling underneath the wafer- facing surface 130 of the transfer arm. Notches 142 are provided to locate auxiliary equipment, such as video cameras, on transfer arm 140.

Turning now to Fig. 12, transfer arms 90, 140 are shown mounted to mounting 76 to provide convenient securement to a robotic manipulator. It is generally preferred in such insulations, that transfer arm 90 be restricted to so-called "dry" wafer transfer operations whereas the wafer transfer arm 140 be limited to so- called "wet" and "non- clean" wafer operations. For example, at the conclusion of a polishing operation, wafer removal is accomplished using transfer arm 140. Transfer arm 140 would also be used for subsequent wafer handling operations. When surface treatment (e.g., polishing) of the wafer is completed, the wafer is transferred to a spin-dry station or the like facility whereupon the wafer attains a clean, dry condition. The transfer arm 90 is thereafter employed to transfer the clean, dry wafer preventing moisture or contamination from being re- introduced on the wafer surface.

Turning now to Figs. 13-15, an alternative wafer transfer arm is generally indicated at 200. As can be seen by comparison with Fig. 10, for example, the wafer surface illustrated in Fig. 13, the wafer surface shown in Fig. 13 is identical to that illustrated in Fig. 10. The opposed side of transfer arm 200 illustrated in Fig. 15 is a mirror image of the opposite side shown in Fig. 13, and the mirror image relationship is reflected in Fig. 14, as well. In effect, the functionality of two separate transfer arms is provided in a single transfer arm construction 200.

In Fig. 14, one side of wafer transfer arm 200 is generally indicated by the reference numeral 210, while the opposed side is indicated by reference numeral 212. With the provision of manipulators having a brisk motion, the sides 210, 212 of wafer transfer arm 200 may be interchanged one for the other, as desired. For example, in one preferred application, the side 210 of wafer transfer arm 200 is reserved for wet, clean use, for example in transferring a wafer from a cleaning station to a spin-dry station. The opposed side 212 is reserved for wet, non- clean use, such as transferring a wafer between intermediate polish steps, prior to cleaning.

After the wafer is cleaned, the opposed side 210 is used for further wet wafer transfer operations. With reference to Fig. 16, it has been found convenient to combine operation of transfer arm 200 with a transfer arm 90, the transfer arms being mounted to a common end-effector mounting unit 76. The transfer arm 90 in the preferred operation is reserved for dry, clean wafer transfer operations, in moving a wafer from a spin-dry station to a wafer storage cassette, for example.

Turning now to Fig. 17, a wafer treatment installation is generally indicated at 300. The robotic manipulator 60 shown in the lower portion of Fig. 17 is located adjacent storage cassettes 308 and a wafer cleaning module 310. A wafer transfer table 312 is located within an enclosure generally indicated at 314. A window 316 allows robotic manipulator 60 to communicate with the interior of enclosure 314 to transfer wafers back and forth through the window. The wafers are located in load cups 318 located on transfer table 312.

A polishing assembly (not shown) traveling on tracks 322 moves between transfer table 312 and polish wheel 326. Load cups 318 contain wafers which are about to be polished, as well as wafers which have already completed polishing operations. Both polished and unpolished wafers pass back and forth between window 316 under the operation of robotic manipulator 60. For example, at the beginning of an operation cycle, robotic manipulator 60 withdraws wafers from cassettes 308 and inserts the wafers through opening 316 to load cups on transfer table 312. The transfer arm of Figs. 1-5 or 8-9 and the end- effector of Figs. 7 or 12 could be used for this operation.

A gantry (not shown) traveling along rails 322 is positioned over transfer table 312 and wafers and load cups 318 are acquired by carriers and drive spindles mounted to the gantry. The gantry then moves over polish table 326 where the wafers are polished. Wafers are then removed from polish table 326 and the gantry again located over transfer table 312 where the polished wafers (in a wet, non- clean condition) are deposited on load cups 318. The transfer table is then indexed as required and polished wafers are extracted by the robotic manipulator through window 316, being transferred to clean module 310. The transfer arm of Figs. 10-11 or 13-15 and the end- effector arrangements of Figs. 12 and 16 could be employed for this purpose. Thereafter, the wafer travels through clean module 310 emerging at rinse ring 332, in a we -clean condition. Thereafter, the wafer is transferred to spin-dry station 334. Preferably, a separate wet transfer arm such as that described in Figs. 10-11 or 13-15 and mounted to end- effectors shown in Figs. 12 or 16 could be used for the purpose. It is preferred, however, that a transfer arm separate from that used to carry wet, non- clean wafers be used for this final wet transfer. After the spin-dry cycle is completed, a dry, clean wafer is present at the spin-dry station 334 and a dry transfer arm, such as that described in Figs. 1-5 or 8-9, carried on end- effector arrangements shown in Figs. 7 or 12 are employed to transfer the clean, dry wafer from spin-dry station 334 to a storage magazine 308, thus completing the dry- in, dry-out polish operation. It will be appreciated by those skilled in the art, that the transfer arms shown and described herein could be employed for other purposes, such as a wet- in, wet-out wafer operation associated, for example, with surface treatment of the wafer or wafer measurements. Further details concerning the polish station 300 may be found in United States patent application Serial No. 08/926,700, filed September 10, 1997, the disclosure of which is incorporated in this application as if fully set forth herein.

As mentioned, several criteria have been identified when selecting materials for end effectors according to the principles of the present invention. The so-called "mechanical" aspects of the material are important, especially for end effectors which are scaled in size to accommodate larger wafers. Traditionally, metallic materials were initially chosen for end effectors because of their desirable properties, such as good stiffness, strength and porosity. For a variety of reasons, some of which were enumerated above, metallic materials are unable to meet present requirements. These requirements are expected to extend into the near future, with a prospect of becoming even more stringent as time goes on.

Because of the high cost of wafers being handled, desirable "mechanical" properties considered here must be maintained in non-metallic substitute materials. In addition, today's stringent requirements were found to be best satisfied by a substantial increase in volume resistivity with similar or improved non-porous water resisting surface properties. More specifically, water absorption was found to be an important factor in meeting stringent fabrication requirements. Water trapped in the pores of various test materials were observed to accommodate bacterial growth, leading to a contamination mechanism in which bacteria is readily transferred to a wafer when conventional wafer handling procedures were followed.

Absorbed water resident on the surface of an end effector also substantially lowers the electrical resistivity, thus increasing the likelihood of an electrical discharge at or near the wafer surface. It is important also to take into account other environmental factors which are likely to affect end effector performarice . Wafer fabrication requires that certain operations be conducted at elevated tempera- tures . For example, chemical vapor deposition (CVD) takes place in a high temperature chamber. It is important that the end effector be able to maintain strength at high temperatures and one factor in successful performance at high temperatures is a relatively low thermal expansion rate.

Several important properties and acceptable ranges were identified, and will now be discussed. Table l shows the acceptable range for important properties that are to be found in successful end effector materials. TABLE 1

Property Acceptable Range

1. Young's Modulus (or Greater than 30,000,000 psi

Modulus of Elasticity) 2. Flexural (or Tensile) Greater than 35,000 psi Strength

3. Compressive Strength Greater than 150,000 psi

4. Rockwell Hardness Greater than 60

5. Chemical Resistance (mg/cm./day) : See Note 1

6. Water Absorption (or 0% Porosity

7. Volume Resistivity Greater than 10^":: Megohm- cm

NOTE 1: Equal or better than chrome steel when exposed to 95% sulfuric acid at 95 C, 60% nitric acid at 90^" C . and 30% caustic soda at 80^' C.

The first four properties listed in Table 1 are directed generally to the "mechanical" aspects of ceramic _t end- effector performance. The remaining properties, numbered 5-7, address the environment -related performance, with the last two properties, numbers 6 and 7, being directed to the electrical surface performance desired from a successful end-effector material . Rather than express the chemical resistance desired operating range, in numerical terms, it was preferred to express chemical resistance performance in comparison to that of chrome steel, upon exposure to a number of aggressive materials, such as sulfuric acid, nitric acid and caustic soda.

As indicated above, the most preferred material used to form end-effectors using conventional milling and other conventional tooling operations is alumina available from Kyocera, Material Numbers A-479G, A-480S and A-601D. Of these three materials, the most preferred is Kyocera Material Number A-479G which has the lowest alumina content of the three, 99.5%.

In addition, Kyocera alumina number A-479G exhibits a satisfactorily low co-efficient of linear thermal expansion of 8x10^"' per degrees centigrade as measured over temperature range of 400 and 800 degrees centigrade.

Table 2 shows the values for the most preferred material, Kyocera alumina number A-479G.

TABLE 2

Property Alumina Al.O-.. 99.% 1. Young's Modulus (or 55,000,000 psi

Modulus of Elasticity)

2. Flexural (or Tensile) 45, 000 psi Strength

3. Compressive Strength 320,000 psi

4. Rockwell Hardness 81 5. Chemical Resistance (mg/cmVday) : See Note 1

6. Water Absorption (or Porosity

Volume Resistivity 10^"-^ϋMegohm-cm at 300 C.

NOTE 1: Equal or better than chrome steel when exposed to 95% sulfuric acid at 95^: C, 60% nitric acid at 90^" C. and 30% caustic soda at 80^' C. Other favorable materials have also been identified. For example, a ceramic material number 997SG from LTD Ceramics has the following properties.

TABLE 3

Property Kyocera STEATITE S-210

1. Young's Modulus (or 17 x 10^' psi Modulus of Elasticity)

2. Flexural (or Tensile) 26,000 psi Strength 3. Vickers Hardness 5.9 (500 g load)

4. Water Absorption (or 0% Porosity

5. Volume Resistivity 10^"-° Megohm at 300^: C.

If desired, certain changes can be made to the above-described transfer arms when carrying out the present invention. For example, vacuum openings having an X- shape and a part circular shape have been described. Vacuum openings of other shapes could also be used. For example, the vacuum openings could comprise a series of holes or elongated slots formed in the wafer contacting surface of the transfer arm. Due to the material selection and shape of the transfer arms, as described above, double- sided transfer arms, such as those described above in Figs. 13-15, can be constructed to accommodate even those wafer cassettes having relatively close wafer spacings within. As explained above with reference to Figs. 17, certain commercially important wafer-processing operations require three or more different transfer arms to match to the wafer's surface conditions (e.g., dry, non-clean; wet, non-clean; wet, clean and dry, clean conditions) .

The drawings and the foregoing descriptions are not intended to represent the only forms of the invention in regard to the details of its construction and manner of operation. Changes in form and in the proportion of parts, as well as the substitution of equivalents, are contemplated as circumstances may suggest or render expedient; and although specific terms have been employed, they are intended in a generic and descriptive sense only and not for the purposes of limitation, the scope of the invention being delineated by the following claims.'

Claims

WHAT IS CLAIMED IS;

1. A transfer arm for acquiring, transporting and releasing a semiconductor wafer, comprising: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body of ceramic material defining a single vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; and a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end.

2. The transfer arm of claim 1 wherein the wafer-engaging portion includes an X-shaped recess communicating with the wafer- facing surface and the vacuum passageway.

3. The transfer arm of claim 1 wherein the recess receiving said cover member is formed in the back surface of said transfer arm.

4. The transfer arm of claim 1 wherein the wafer-engaging portion includes a recess having multiple outwardly extending legs, and the vacuum passageway extends to at least two of said legs.

5. The transfer arm of claim 1 wherein the vacuum passageway forms a generally T-shaped configura- tion adjacent the mounting end of the transfer arm, the T-shaped configuration extending to a pair of spaced apart holes formed in the transfer arm for vacuum connection to an external vacuum source.

6. A semiconductor wafer manipulating apparatus comprising the combination of a robotic manipulator having a mounting head and at least one transfer arm for acquiring, transporting and releasing a semiconductor wafer mounted to the mounting head, said transfer arm including: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body of ceramic material defining a single vacuum passageway extending from the wafer- contacting- portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; and a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end.

7. The transfer arm of claim 6 wherein the wafer- engaging portion includes an X-shaped recess communicating with the wafer- facing surface and the vacuum passageway.

8. The transfer arm of claim 6 wherein the transfer arm body has a generally constant width, and a generally constant thickness throughout a major portion of its longitudinal extent.

9. The transfer arm of claim 6 wherein the wafer-engaging portion includes a recess having multiple outwardly extending legs, and the vacuum passageway extend to at least two of said legs.

10. The transfer arm of claim 6 wherein the vacuum passageway forms a generally T-shaped configuration adjacent the mounting end of the transfer arm, the T-shaped configuration extending to a pair of spaced apart holes formed in the transfer arm for vacuum connection to an external vacuum source.

11. The transfer arm of claim 6 further comprising a second transfer arm mounted to said mounting head.

12. The transfer arm of claim 11 wherein said one transfer arm and said second transfer arm are spaced apart so as to form an angle of generally 90 degrees therebetween.

13. A transfer arm for acquiring, transporting and releasing a semiconductor wafer, comprising: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body defining at least one vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end; and wherein the wafer- contacting portion is generally U-shaped and defines a curved recess communicating with the wafer- facing surface and the vacuum passageway.

14. The transfer arm of claim 13 wherein the curved recess has a generally part circular configura- tion.

15. The transfer arm of claim 13 wherein the U-shaped wafer contacting portion includes a pair of spaced apart legs having free ends and the part circular recess has a center, with the free ends of the legs extending beyond the center of the part circular recess .

16. The transfer arm of claim 15 wherein the vacuum passageway includes a finger- like extension, extending from the part circular recess, toward the mounting end of the transfer arm.

17. The transfer arm of claim 13 wherein the transfer arm body has a generally constant width, and a generally constant thickness throughout a major portion of its longitudinal extent.

18. The transfer arm of claim 13 wherein the wafer-engaging portion includes a recess having multiple outwardly extending legs, and the vacuum passageway extend to at least two of said legs.

19. The transfer arm of claim 13 wherein the vacuum passageway forms a generally T-shaped configuration adjacent the mounting end of the transfer arm, the T-shaped configuration extending to a pair of spaced apart holes formed in the transfer arm for vacuum connection to an external vacuum source.

20. A double sided transfer arm for acquiring, transporting and releasing a semiconductor wafer, comprising: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body defining at least one vacuum passage- way extending from the wafer- contacting portion to the mounting end of the body; and the transfer arm body having opposed wafer- facing major surfaces, each of which has a vacuum passage associated therewith.

21. The double sided transfer arm of claim

20 wherein the curved recess has a generally part circular configuration.

22. The double sided transfer arm of claim 20 wherein the U-shaped wafer contacting portion includes a pair of spaced apart legs having free ends and the part circular recess has a center, with the free ends of the legs extending beyond the center of the part circular recess.

23. The double sided transfer arm of claim 20 wherein the vacuum passageway includes a finger- like extension, extending from the part circular recess, toward the mounting end of the transfer arm.

24. The double sided transfer arm of claim 20 wherein the transfer arm body has a generally constant width, and a generally constant thickness throughout a major portion of its longitudinal extent.

25. The double sided transfer arm of claim 20 wherein the wafer- engaging portion includes a recess having multiple outwardly extending legs, and the vacuum passageway extend to at least two of said legs.

26. The double sided transfer arm of claim 20 wherein the vacuum passageway forms a generally T-shaped configuration adjacent the mounting end of the transfer arm, the T-shaped configuration extending to a pair of spaced apart holes formed in the transfer arm for vacuum connection to an external vacuum source.

27. A wafer manipulating apparatus, including a robotic manipulator having a mounting head and a transfer arm for acquiring, transporting and releasing a semiconductor wafer, the transfer arm including: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body defining at least one vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed major surfaces including a wafer- facing surface and an opposed back surface, the transfer arm body defining a stepped recess formed in the back surface; a cover member received in the stepped recess to form a vacuum passageway extending from the wafer- contacting portion to the mounting end; and wherein the wafer- contacting portion is generally U-shaped and defines a curved recess communicating with the wafer- facing surface and the vacuum passageway.

28. The apparatus of claim 27 wherein the curved recess has a generally part circular configuration.

29. The apparatus of claim 27 wherein the

U-shaped wafer contacting portion includes a pair of spaced apart legs having free ends and the part circular recess has a center, with the free ends of the legs extending beyond the center of the part circular recess.

30. The apparatus of claim 27 wherein the vacuum passageway includes a finger- like extension, extending from the part circular recess, toward the mounting end of the transfer arm.

31. The apparatus of claim 27 wherein the transfer arm body has a generally constant width, and a generally constant thickness throughout a major portion of its longitudinal extent.

32. The apparatus of claim 27 wherein the wafer-engaging portion includes a recess having multiple outwardly extending legs, and the vacuum passageway extend to at least two of said legs.

33. The apparatus of claim 27 wherein the vacuum passageway forms a generally T-shaped configuration adjacent the mounting end of the transfer arm, the T-shaped configuration extending to a pair of spaced apart holes formed in the transfer arm for vacuum connection to an external vacuum source.

34. A wafer manipulating apparatus for use with semiconductor wafers, including a robotic manipulator having a mounting head and at least one transfer arm for acquiring, transporting and releasing a semiconductor wafer, the transfer arm including: an elongated transfer arm body having a mounting end with means for mounting to an external manipulator device, an opposed free end with a wafer- contacting portion; a body defining at least one vacuum passageway extending from the wafer- contacting portion to the mounting end of the body; the transfer arm body having opposed wafer- facing major surfaces; and wherein the wafer- contacting portion is generally U-shaped and defines a curved recess communicating with the wafer- facing surface and the vacuum passageway.

35. The apparatus of claim 34 wherein the curved recess has a generally part circular configuration.

36. The apparatus of claim 34 wherein the

37. The apparatus of claim 34 wherein the vacuum passageway includes a finger- like extension, extending from the part circular recess, toward the mounting end of the transfer arm.

38. The apparatus of claim 34 wherein the transfer arm body has a generally constant width, and a generally constant thickness throughout a major portion of its longitudinal extent.

39. The apparatus of claim 34 wherein the wafer-engaging portion includes a recess having multiple outwardly extending legs, and the vacuum passageway extend to at least two of said legs.

40. The apparatus of claim 34 wherein the vacuum passageway forms a generally T-shaped configuration adjacent the mounting end of the transfer arm, the T-shaped configuration extending to a pair of spaced apart holes formed in the transfer arm for vacuum connection to an external vacuum source.