US3661253A

US3661253A - Retaining trays for semiconductor wafers and the like

Info

Publication number: US3661253A
Application number: US882179A
Authority: US
Inventors: Paul W Cronkhite
Original assignee: Monsanto Co
Current assignee: SunEdison Inc
Priority date: 1969-12-04
Filing date: 1969-12-04
Publication date: 1972-05-09
Anticipated expiration: 1989-05-09

Abstract

A series of marginally registrable plastic trays having a plurality of wells for accommodating semiconductor wafers and similar elements. The retaining wells are provided with a wall having a surface configuration such that the critical surface of the wafer does not contact the well. A removable cap is disposed over each of the retaining wells and is provided with means for engaging the upwardly presented surface of the semiconductor wafer. Each of the trays is registrable with like trays so that a series of these trays can be stacked, wrapped, and shipped as a unit.

Description

I United States Patent [151 3,66 1 ,253

Cronkhite 1 May 9, 1972 [541 RETAINING TRAYS FOR 3,178,051 4/1965 Edwards ..229/43 SEMICONDUCTOR WAFERS AND THE 545,225 8/1895 Fitch et al.. ....206/18 LIKE 2,821,307 1/1958 Linsley ..206/72 3,311,229 3/1967 Troll et al... .220/60 R [72} Inventor: Paul W. Cronkhite, St. Charles, Mo. 1,331,263 2/1920 H m ..206/18 [73] Assignee: Monsanto Company, St. Louis, Mo. 2'947'459 8/1960 Pregem" C [22] Filed: Dec. 4, 1969 OTHER PUBLICATIONS 21 A I. No.: 882 179 IBM Technical Disclosure Bulletin Wafer Package, L. l 1 PP Hershoff, Vol. 8, No. 1 1 April 1966, page 1642. Related U.S. Application Data Prima Examiner-William T. Dixson Jr. [63] Continuation-in-part of Ser. No. 764,472, Oct. 2,

1968, Pat. No. 3,482,682, which is a continuation-in- UPham and Neal part of Ser, No. 644,966, June 9, 1967, abandoned.

[57] ABSTRACT [52] U.S. Cl ..206/65 R, 206/46 FR, 229/25 A series of marginally registrable plastic trays having a plura [5]] f "B65d8l/00B65d 85/30 ty of wells for accommodating semiconductor wafers and [58] Flew of Search "6 65 similar elements. The retaining wells are provided with a wall 206/45'14 4 4 220/60 9 having a surface configuration such that the critical surface of 229/25 14 C the wafer does not contact the well. A removable cap is disposed over each of the retaining wells and is provided with [56] References Cited means for engaging the upwardly presented surface of the UNITED STATES PATENTS semiconductor wafer. Each of the trays is registrable with like trays so that a senes of these trays can be stacked, wrapped, 3,256,975 6/1966 Puente ..220/60 R and Shipped as a unit. 2,166,616 7/1939 Wallace.... ....206/l.7 2,922,563 l/l960 Aldington ..229/43 10 Claims, 16 Drawing Figures PATENTEDMAY 9 I972 sum 1 UF 3 INVENTOR PAUL W. CRONKHITE ATTORNEY PATENTEDHAY 9l972 3,661,255

SHEET 2 UF 3 INVENTOR PAUL W. CRONKHITE BY firK6 LL% My? ATTORNEY PATENTEDMAY 9|97E 3,661,253

sum 3 OF 3 INVENTOR FIG. l6 PAUL W. CRONKHITE ATTOR NEY RETAINING TRAYS FOR SEMICONDUCTOR WAFERS AND THE LIKE This application is a continuation-in-part of my copending application Ser. No. 764,472, filed Oct. 2, 1968 (US. Pat. No. 3,482,682), which is in turn, a continuation-in-part of my copending application Ser. No. 644,966, filed June 9, 1967, now abandoned This invention relates in general to certain new and useful improvements in devices for storing and transporting semiconductor wafers, and more specifically to a plurality of registrable trays which are capable of accommodating a plurality of wafers.

In recent years, semiconductor devices such as silicon controlled rectifiers have found widespread use in the electronics industry. These semiconductor devices are made from semiconductor materials which may have a plurality of layers of semiconductor material having different conductivities and separated by a transition zone. Semiconductor materials of this type having at least two layers of difierent conductivities with a transition region therebetween are very suitable for use in the formation of electronic members such as diodes, transistors, switches and similar types of electronic structure. One very effective method of producing semiconductor materials is by the epitaxial deposition of silicon on a substrate wafer formed of like material. Generally, the wafers involved must be formed of single crystal silicon with precisely controlled concentrations of doping impurities.

Frequently, the semiconductor wafers have a highly polished surface which must remain free from contact with any foreign surface whatsoever during storage and transporting thereof. It has generally been found that when this polished surface contacts any foreign surface, the surface tends to become contaminated and marred. These slight marrings of the surface and the impurities often materially interfere with effective further processing of the wafers such as growth of epitaxial layers or fabrication of semiconductor devices. In the past, transporting of the wafer between steps in processing thereof has often caused serious problems since it was not always possible to maintain the wafers in a substantially clean atmospheric environment. Furthermore, accidental contact with the surface of the wafer often occurred through inadvertence which, in effect, made subsequent processing steps futile and destroyed the value of the semiconductor wafer.

These problems were even more severe during shipping of the wafers to the purchasers thereof. Generally, each of the wafers had to be enclosed in a specially designed bag of plastic or paper which was treated in order to eliminate impurities. Even in this type of container, it was impossible to prevent contact of the wafer surface with the bag, per se. It was necessary to wrap these wafers and stack them in such manner that a minimum of movement could be obtained. However, due to this technique, the surface of a number of wafers was often contaminated by the time they were received by the user thereof. Accordingly, the various methods heretofore employed for the handling, shipment and storage of semiconductor wafers have not been very effective.

It is, therefore, the primary object of the present invention to provide a series of marginally registrable nestable trays which are capable of carrying semiconductor wafers in such manner that the critical surfaces of the semiconductor wafers do not contact any foreign surface.

It is another object of the present invention to provide a series of retaining trays of the type stated which can be manufactured in a mass-production operation and are capable of being constructed with desired tolerance so that adverse surface conditions are not created on the semiconductor wafers carried therein.

It is also an object of the present invention to provide a retaining tray of the type stated for a plurality of wafer diameters.

It is a further object of the present invention to provide retaining trays of the type stated which are specifically designed so that inadvertent handling of the wafers will not cause injury thereof in the retaining trays.

It is an additional object of the present invention to provide retaining trays of the type stated which are disposable and which can be manufactured at a relatively low unit cost.

With the above and other objects in view, my invention resides in the novel features of form, construction, combination, and arrangement of parts presently described and pointed out in the claims.

In the accompanying drawings:

FIG. I is a perspective view of a retaining tray which is constructed in accordance with and embodies the present invention, and showing a plurality of wafers disposed therein and caps removably disposed over some of the retaining wells;

FIG. 2 is a fragmentary vertical sectional view taken along line 2-2 of FIG. 1;

FIG. 3 is a vertical sectional view similar to the sectional view of FIG. 2 and showing portions of one of the retaining wells with a cap disposed thereabove;

FIG. 4 is a fragmentary vertical sectional view similar to the sectional view of FIG. 2 and showing portions of the retaining wells of a pair of stacked trays with wafers disposed therein;

FIG. 5 is a fragmentary vertical sectional view similar to the sectional view of FIG. 2 and showing a modified form of wafer retaining tray constructed in accordance with an embodying the present invention;

FIG. 6 is a fragmentary vertical sectional view similar to the sectional view of FIG. 5 with a cap secured to the tray and engaging a wafer disposed in the retaining well;

FIG. 7 is a fragmentary vertical sectional view similar to the sectional view of FIG. 2 and showing a modified form of wafer retaining tray having a somewhat arcuate bottom wall constructed in accordance with and embodying the present invention;

FIG. 8 is a fragmentary vertical sectional view similar to the sectional view of FIG. 2 and showing another modified form of wafer retaining tray constructed in accordance with an embodying the present invention;

FIG. 9 is a fragmentary vertical sectional view of a wafer tray similar to the tray described in FIG. 8 and showing a wafer disposed therein in such manner that it is not parallel to the bottom wall of the retaining well;

FIG. 10 is a fragmentary vertical sectional view showing a wafer tray similar to that of FIG. 8 with a wafer disposed therein in another angulated position with respect to the bottom wall of the retaining tray;

FIG. 11 is a fragmentary vertical sectional view similar to the sectional view of FIG. 2 and showing another modified form of wafer retaining tray having an arcuate wafer retaining wall which is constructed in accordance with and embodies the present invention;

FIG. 12 is a perspective view of an insert provided for removable interposition between the cap and a wafer in the tray ofFIG. 1;

FIG. 13 is a side elevational view of the insert of FIG. 12;

FIG. 14 is a fragmentary vertical sectional view, similar to FIG. 2 and showing the employment of the insert of FIG. 12 in the wafer tray;

FIG. 15 is a vertical sectional view similar to the sectional view of FIG. 2 and showing a wafer tray with a modified form of cap used thereon; and

FIG. 16 is a perspective view of an insert which can be disposed between a cap and the wafer disposed in the tray.

GENERAL DESCRIPTION The present invention relates to a series of registrable retaining trays which are designed to carry semiconductor wafers having a highly polished or epitaxial surface. Each of the retaining trays is preferably made of a somewhat rigid but yet sufficiently flexible material to absorb shock loads during shipment. The trays are formed with a plurality of upstanding circular bosses which are substantially hollow in the provision of wafer retaining wells. In one embodiment of the tray of the present invention, the retaining wells include an inwardly extending shoulder which merges into an inwardly tapered wall section, which is designed in such manner that a wafer disposed within the well with the critical surface presented in a generally downward position does not contact any surface of the well. In essence, the tapered wall section is so-designed that only the peripheral margins of the wafer come into contact with any portion of the well. When the wafer is disposed in a substantially horizontal position, the peripheral margins of the entire surface of the wafer will frictionally engage the tapered wall section at the proper diametral cross section. In this position, the wafer is spaced from the bottom wall of the retaining well.

Each of the bosses is provided with an annular bead at its upper end and is adapted to receive a snap-fitting lid or cover member. Each of the lids is provided with a circular annular shoulder for engaging the boss and an inwardly struck engaging finger so that the lid may be snap-fitted over the bead of the boss in a fairly tight position. Furthermore, the lid is provided with a downwardly extending central portion which engages the upwardly presented surface of the wafer and, thereby holds the same in a substantially immobile position in the retaining well. The portions of the supporting surface extending between each of the retaining wells is sized to fit snugly between the upwardly extending bosses of a marginally registered tray disposed therebeneath. In this manner, it is possible to marginally align each of the trays during a vertical stacking operation. Furthermore, the portions of the trays which extend between adjacent bosses will fit snugly therein so that each of the trays can be stacked in marginal registration.

The present invention also provides a modified form of wafer retaining tray which includes a support plate and a plurality of upstanding bosses, each being hollowed in the form of a wafer retaining well. In this embodiment of the wafer retaining tray, the upstanding boss is provided with an annular bead which is somewhat rectangular in horizontal cross section. The upstanding boss is provided with an annular groove for engaging an inwardly extending annular finger formed on a removable cap.

The present invention also provides a modified form of wafer retaining tray which includes a tapered wall section and a somewhat arcuately shaped bottom wall as opposed to a flat bottom wall. Another embodiment of the wafer retaining tray of the present invention includes a pair of tapered walls for supporting semiconductor wafers of different diametral sizes. In this type of wafer retaining tray, the bottom wall may be either flat or arcuately shaped.

The wafer retaining tray of the present invention can also be constructed in a manner where the wall of the recess is hemispherical or arcuately shaped, there being no provision for a tapered wall. In this manner, the wafer is supported in the arcuately shaped wall. The only criterion for the type of wall is that the wafer must be supported with the critical surface presented downwardly and the wall must have a shape and size such that the critical surface of the wafer does not contact any portion of the retaining wall.

A number of cap systems can be used with wafer trays of the present invention. One of these cap systems provides for an insert removably disposed between the cap and the wafer so that the insert holds the wafer into contact with the wall of the recess. The insert may be fastened to the cap or removably interposed between the cap and the wafer.

DETAILED DESCRIPTION Referring now in more detail and by reference characters to the drawings, A designates a retaining tray constructed in accordance with the present invention. The retaining tray A generally comprises a relatively flat sheet or so-called support plate" 1 which is integrally formed with two rows of upstanding bosses 2 having a total of five bosses in the manner as illustrated in FIG. 1. It should be recognized, however, that bosses and the invention is not limited to the number of bosses illustrated or to the specific pattern in which they are formed in the retaining sheet 1.

Each of the bosses 2 is formed with an inwardly and upwardly extending annular side wall 3 which integrally merges into an enlarged annularly extending somewhat circular bead 4 at its upper end in the manner as illustrated in FIG, 2. The circular bead 4, in turn, merges into an inwardly presented annular shoulder .5, which is in turn integrally formed with a downwardly and inwardly extending tapered wall 6. By reference to F IG. 2, it can be seen that the tapered wall 6 is diametrally larger than a wafer W at its upper end and is diametrally smaller than the wafer W at its lower end. The tapered wall 6, in turn, merges at its lower end into a slightly convex bottom wall 7. Thus, it can be seen that the hollowed portion of the boss 2 serves as a retaining well 8 for accommodation of wafers W of a specific size.

The bottom wall 7 is slightly diametrally smaller than a semiconductor wafer W, which is to be disposed within the retaining well 8. Accordingly, it can be seen that a wafer W which is disposed therein in a position substantially parallel to the bottom wall 7 is supported on the tapered wall 6. It should also be understood that the bottom wall 7 could be hemispherical in shape in accordance with the present invention.

Generally, the retaining tray A of the present invention was designed for use with polished silicon semiconductor wafers. However, the invention is by no means limited to these types of wafers and the various applications thereof are set forth in more detail hereinafter. For purposes of illustration and description of the present invention, it may be assumed that the wafers are, for example, silicon wafers with an epitaxial silicon coating formed thereon. This epitaxial silicon surface is the critical surface which must be maintained in a dust-free atmosphere. The preparation of the epitaxial silicon surface involves a great deal of time-consuming preparations and is very costly. It has been found that even slight contact with this surface is often sufficient to abrade the surface to an extent where it is no longer usable for the manufacture of semiconductor devices. In addition, it has also been found that mere momentary touching of the wafer by a fingertip will also create sufiicient contamination on the surface thereof that it may be rendered unusable. The same problems hold true for semiconductor wafers with highly polished surfaces. These treated surfaces, which must be protected, are herein referred to as the critical surfaces." The retaining tray A of the present invention was designed to specifically overcome these problems.

By reference to FIG. 9, it can be seen that each of the retaining wells 8 is so constructed that a wafer W disposed therein can be oriented in substantially any position and the substantial position of the epitaxial surface thereof will still remain out of contact with any portion of the

walls

6 or 7 in the well 8. In essence, if the tray A should be inadvertently tipped slightly so that the wafer W is no longer supported on the tapered wall 6, it may shift to a position substantially as illustrated in FIG. 9. For example, it can -be seen that the peripheral margin of the wafer W is actually supported in the manner as illustrated in FIG. 7 and on the spaced points (labeled X"). It can be seen that the epitaxial surface of the wafer W will remain out of contact with any portion of the wall of the well 8 and only the peripheral margin of the wafer will contact any portion of the wall of the well 8 at any one time.

In FIG. 10, it can be seen that the wafer W may be oriented in a slightly different position and again, the wafer is supported on the spaced points (labeled X"). While the shape of the retaining trays illustrated in FIGS. 9 and 10 are slightly different than the other retaining trays described in connection with the present invention, it should be recognized that the wafer W can be oriented in substantially any position in any of the embodiments of the present invention in such manner that the critical surface does not contact any portion of the recessed walls.

In order to maintain brevity, only one of the retaining wells 8 has been described herein and only one has been illustrated in detail in the accompanying drawings. However, it should be recognized that each of the other retaining wells are substantially identical in construction and are, therefore, neither illustrated nor described in detail herein.

A removable cap C is provided for coverwise disposition over each of the retaining wells 8 in the manner as illustrated in FIG. 3. The cap C generally comprises a relatively flat top sheet 9, which is slightly frusto-conical or dish-shaped so that it forms a downwardly projecting central pressure point 10 which is designed to bear against the upper surface of the wafer W in the manner as illustrated in FIG. 3. Furthermore, the sheet 9 of the cap C may be hemispherically shaped in accordance with the present invention. The cap C is also provided with a somewhat circular annular peripheral shoulder 11 which integrally merges into the flat sheet 9 and is sized to extend over the annular bead 4. Furthermore, the cap C is formed of the same material as the tray A and is, therefore, sufficiently flexible to become snap-fitted over the bead 4 in the manner as illustrated in FIG. 3. The annular shoulder 11 merges into an inwardly extending annular finger 12 which engages the underside of the bead 4 at its point of integral merger with the side wall 3. Furthermore, the cap C is provided with an annular outwardly flaring flange 13 in the manner as illustrated in FIG. 3. Thus, it can be seen that the cap C can be engaged by the flange l3 and urged upwardly from its closurewise position on the boss 2 and can be easily reinserted thereon in tight-fitting coverwise disposition. Furthermore, when the cap C is disposed over the well 8 in coverwise disposition, it engages the wafer W and holds the same in a fairly immobile position in the retaining well 8, by urging the same against the tapered wall 6.

By further reference to FIGS. 1 and 2, it can be seen that the side walls 3 of each of the bosses 2 merge into the support plate 1 through an arcuate section 14. By reference to FIG. 4, it can be seen that a series of the trays can be stacked in marginal registration so that the arcuate sections 14 of one tray fit snugly between the annular beads 4 on a tray disposed immediately therebeneath. This is true even though cover members C are disposed over each of the retaining wells 8. This type of construction also serves to space the retaining wells of one tray from the bottom wall of the tray disposed immediately thereabove. Nevertheless, the trays A can be stacked in marginal registration in the manner as illustrated.

It is possible to provide a modified form of wafer tray B, substantially as illustrated in FIGS. 5 and 6, and which is substantially similar to the wafer retaining tray A. The wafer retaining tray B generally comprises a relatively flat sheet 20 with a plurality of upstanding bosses 21 having a relatively flat annular side wall 22. At its upper end, the annular side wall 22 integrally merges into an annular bead 23 which is substantially rectangular in horizontal cross section. The bead 23 is provided on its interior surface with a vertical shoulder 24, which in turn, merges into an inwardly and downwardly extending tapered side wall 25, for retaining a wafer W thereon. At its lower end, the side wall 25 integrally merges into a slightly convex bottom wall 26. The size and shape of the tapered wall 25 and the bottom wall 26 is substantially similar to the tapered wall 6 and bottom wall 7 respectively of the retaining tray A. However, it is to be noted that the upstanding bead 23 is not rounded in the same manner as the bead 4 in the wafer retaining tray A. Furthermore, each of the bosses 21 is provided with an annular groove 27 in the side wall 22 for reasons which will presently more fully appear. Thus, it can be seen that the recessed portion in each of the upstanding bosses 21 provides a wafer retaining well 28, which is substantially similar to the wafer retaining well 8 in the retaining tray A.

A cap C, which is substantially similar to the previously described cap C is provided for coverwise disposition over each of the retaining wells 28. The cover member C generally comprises a relatively flat sheet 29, which is slightly frustoconical in shape and provides a downwardly projecting center pressure point 30, which engages the central portion of the upper surface of the wafer W, in the manner as illustrated in FIG. 7. Furthermore, the flat sheet 29 integrally merges into a downwardly extending relatively vertical side wall 31, which is provided with a somewhat V-shaped annular finger 32, the latter being snap-fitted in the groove 27 in the manner as illustrated in FIG. 7. The vertical side wall 31 integrally merges into an outwardly extending annular flange 33. Thus, it can be seen that the cap C can be easily removed from the upstanding boss 21 by merely engaging the flange 33 and pulling the cap C from the boss 21. In like manner, the cap C can be easily disposed over the wafer retaining well 28 by snap-fitting the same so that the annular finger 32 extends into the annular groove 27 on the boss 21.

The wafer retaining tray B is substantially similar in all other respects to the wafer retaining tray A and is also nestable and marginally registrable with like trays.

It is possible to provide a modified form of wafer tray B, substantially as illustrated in FIG. 7 and which is similar to the wafer tray A, illustrated in FIG. 1. The wafer tray B differs from the wafer tray A in that an arcuately shaped bottom wall 34 is provided in place of the flat bottom wall 7 of the tray A. In all other respects, the wafer tray B, is similar to the tray A. In like manner, the cap C may also be used on the wafer tray B for retaining the wafer W therein.

It is also possible to provide another modified form of wafer tray B which is more fully illustrated in FIGS. 8 and 10. The wafer tray B generally comprises a support plate 35 having an upstanding boss 36 integrally formed thereon. The boss 36 is substantially identical to the boss 2 in the tray A and has a somewhat arcuate recess 37 formed by a vertical wall 38 integrally merging into a somewhat arcuately shaped tapered wall 39. The arcuately shaped tapered wall 39, in turn, merges into an arcuately shaped tapered wall 40 and thence into a relatively flat bottom wall 41. It can be seen that a wafer W can be supported on either of the tapered

wall

39,40. Thus, the wafer retaining tray B is sized to accommodate a number of wafers W having different diametral sizes. A cap C is also removably disposed over the boss 36 in the same manner as the cap C was used in the wafer tray A. The present invention also contemplates a wafer tray 8, substantially as illustrated in FIG. 9. The wafer tray 8, differs from the wafer tray B in that an arcuately shaped bottom wall 42 is used in place of the flat bottom wall 41. A removable cap C is also provided for use with each of the recesses in the tray 8,. Furthermore, the tray 8, is used in substantially the same manner as the tray B The present invention further provides for another modified form of wafer retaining tray B (FIG. 11) which is constructed in accordance with and embodying the present invention. The wafer tray B is similar to the wafer tray B and generally comprises a support plate 43 having an upstanding boss 44 integrally formed thereon. The boss 44 is substantially identical to the boss 2 in the tray A and has a recess 45 which is formed by an arcuately shaped recess forming wall 46. It can be observed that the arcuately shaped wall 46 may have any desired radius which is limited only in such manner that it is capable of retaining a wafer W in a position where the critical surface of the wafer is disposed in spaced relation to a bottom portion of the wall 46. Thus, the wafer W should be capable of being oriented in substantially any position, such as that illustrated in FIGS. 9 and 10, without having the critical surface thereof contact the upwardly presented surface of the arcuate wall 46. It should be observed, furthermore, that the wafer trays of the present invention are not necessarily limited by the shape of the wall which retains the wafer. The only important criterion is that the wall must be designed in such fashion that the critical surface of the wafer W does not contact the wall when oriented in substantially any position with respect to the wall. The removable cap C is also provided for coverwise disposition over the recess 45 in the manner as illustrated in FIG. 1 1.

It is possible to provide another modified form of wafer tray D, substantially as illustrated in FIG. 14. The wafer tray D is similar to the wafer tray A and generally comprises a support plate 50, having an upstanding boss 51 integrally formed thereon. The boss 51 is substantially identical to the boss 2 in the tray A and has a recess 52 which is formed by a tapered wall 53 and a bottom wall 54 which are substantially identical in all respects to the similar components in the tray A. In like manner, a removable cap C" is provided for coverwise disposition over each of the recesses 52 in the manner as illustrated in FIG. 14. The cap C" is substantially identical to the cap C and includes a top sheet 55 which is slightly frusto-conical or dish-shaped" so that it forms a downwardly projecting central pressure point 56. In like manner, the cover member C could have a flat top sheet with no downwardly projecting portion whatsoever.

Provided for interposition between the lower surface of the top sheet 55 and the upper surface of the wafer W which is disposed in the recess 52 is a disc-like insert 57. By reference to FIGS. 12 and 13, it can be seen that the insert is somewhat in the form of an'inverted cup and generally comprises a relatively flat top wall 58 formed with an annular downwardly and outwardly flaring skirt 59. The insert 57 is preferably formed of the same material as the tray D and, therefore, is slightly resilient. Thus, when the flat sheet 55 of the cap C bears against the top wall 58 of the disc-like insert 57, the lower peripheral margin of the skirt 59 will engage the upper surface of the wafer W and urge the same downwardly against the tapered wall 53 of the recess 52.

It is also possible to provide a wafer tray E as illustrated in FIG. which is similar to the wafer tray illustrated in FIG. 2.

' The tray E differs from the tray A in that a different type of cap F is provided. The cap F generally comprises a relatively flat top sheet 60 which is provided with a somewhat circular annular peripheral shoulder 61. The shoulder 61 integrally merges into the flat sheet 60 and is sized to extend over the annular bead 4. Furthermore, the cap F is formed of the same material as the tray E and is, therefore, sufficiently flexible to' be snap-fitted over the bead 4 in the manner as illustrated in FIG. 15. The annular shoulder 61 merges into an inwardly extending annular finger 62 which engages the underside of the bead 4 at its point of integral merger with the side wall 3. Furthermore, the cap C is provided with an annular outwardly flaring flange 63 in the manner as illustrated in FIG. 15. Thus, it can be seen that the cap C can be engaged by the flange 63 and urged upwardly from its closurewise position over the boss 2 on the tray E and can be easily reinserted thereon in a tight-fitting coverwise disposition.

Adhesively or otherwise secured to the underside of the flat sheet 60 is a downwardly projecting circular retaining flange 64 which engages the upper surface of the wafer W in order to hold the wafer into snug fitting position against the tapered wall of the tray E. The circular flange 64 is sized to extend near the peripheral margin of the wafer W. It should be observed that the cap F can be used with essentially any of the other wafer trays described herein. It should be recognized that the retaining flange 64 may be secured to the underside of the flat sheet 60 by means of a snap-fitting engagement. Furthermore, the flange 64 can be fabricated in the form of a ring as illustrated in FIG. 16 for removable interposition between the cap F and the wafer disposed in the wafer tray E.

The concept of using a cylindrical ring for engagement against a wafer has been found to be highly effective. While the employment of a disc 47 (FIG. 12) is indeed effective, the manufacture of the disc must be carefully controlled both with regard to critically of dimension and the composition of the material employed. When the disc is employed, there is a tendency for the disc to spread out from the resultant vertical forces imposed by the cap. This wiping action across the upwardly presented surface of the wafer W in many cases has undesirable effects. The concept of the ring obviates this particular problem. There is no wiping action whatsoever in connection with the ring and hence, the deleterious effects to the wafer W are thereby avoided.

Many of the various embodiments of caps and capping systems described herein can be used with any of the embodiments of the trays of the present invention. For example, the cap C can adequately be used with the tray 8,

This method of transporting each of the wafers W has been found to be highly successful and has substantially eliminated the problems of contacting the surfaces of the wafer W with any foreign matter, thereby maintaining a high degree of purity and eliminating any surface abrasion. While the trays of the present invention were specifically designed for use with polished silicon wafers and silicon wafers having epitaxial silicon or oxide coatings thereon, they are also successfully employed with other types of semiconductor wafers, such as gallium arsenide wafers and gallium arsenide phosphide wafers. Furthermore, the trays are equally suitable to hold and transport and store similar slice-shaped objects which have critical surfaces prepared by methods other than machine polishing, objects with critical surfaces which have been prepared by cleaning, chemically etching, vapor etching, deposition from the vapor phase, sputtering, or other thin film techniques, crystallization from the melt, chemical or electrolyticai precipitation from solution can also be successfully used in the retaining trays of the present invention. Furthermore, the tray is capable of handling slices of any regular shape, preferably in the form of a flat disc and may consist of materials other than semiconductor materials, such as solid metal and metal alloys and minerals. The wafers which may be used in the trays of the present invention may be formed of glass, quartz, ceramics, sapphire and other precious and semiprecious stones.

When transporting a series of marginally registered stacked trays, the trays may be stored in a hermetically sealable container or simply wrapped in a substantially self-sealing dustproof foil or plastic film. The trays may then be properly stacked and placed in a suitable shipping container as desired. It should be observed that the wafers W would not be damaged even if the trays A were inadvertently turned over. It can be observed that after the wafers W have been properly inserted into each of the wells 8, they are held in place by the cap C. This type of condition eliminates any possibility of contamination or abrasion to the critical surface of the wafer.

It should be understood that changes and modifications in the form, construction, arrangement and combination of parts presently described and pointed out may be made and substituted for those herein shown without departing from the nature and principle of my invention.

Having thus described my invention, what I desire to claim and secure by Letters Patent is:

l. A tray for retaining relatively thin flat semiconductor wafers which have a critical surface and a surface opposed to said critical surface, said tray comprising a supporting member having a boss thereon which forms a recess sized to accommodate semiconductor wafers, said recess having a wall which is operatively connected to said supporting member and forming a recess opening larger than the wafer to be supported in said recess, said wall being of such size and shape to support a wafer with the critical surface presented away from the opening and in such manner that-only the marginal edge portions of said wafer contact said wall when oriented in substantially any position with respect to said wall, cover means removably disposed over said recess, and means operatively associated with said cover means for engaging the surface of the wafer opposed to said critical surface.

2. The tray of claim 1 further characterized in that a plurality of recesses are operatively formed on said supporting member.

3. The tray of claim I further characterized in that an annular bead is operatively associated with the upper end of said boss and is sized to engage the cover means disposed thereon.

4. The tray of claim 3 further characterized in that each bead is somewhat circular in vertical cross section.

5. The tray of claim 1 wherein said cover means is a caplike cover member which has a dish-shaped wall including a downwardly projecting surface which engages the wafer at a point somewhat centrally thereof.

6. The tray of claim 1 further characterized in that said wall has a bottom portion which is substantially flat and that a wafer is disposed in substantially parallel relationship to said bottom wall portion when located in said recess.

7. The tray of claim 1 further characterized in that said wall is arcuately shaped.

8. The tray of claim 1 further characterized in that said wall has a pair of tapered wall sections for supporting the wafer and a bottom wall section, the latter being diametrally smaller than the tapered wall sections so that a wafer may be disposed in spaced relationship with respect to said bottom wall section.

9. A tray for retaining relatively thin flat semiconductor wafers which have a critical surface and a surface opposed to said critical surface, said tray comprising a supporting member having a boss thereon which forms a recess sized to accommodate a semiconductor wafer, said recess having a wall which is operatively connected to said supporting member and forming a recess opening larger than the wafer to be supported in said recess, a thin flat semiconductor wafer disposed in said recess with its critical surface presented away from the opening and having only its marginal edge portions in contact with said recess when oriented in substantially any position with respect to said wall, cover means removably disposed over said recess, and means operatively associated with said cover means for engaging the surface of the wafer opposed to said critical surface.

10. The tray of claim 9 further characterized in that said wall is arcuately shaped.

Claims

1. A tray for retaining relatively thin flat semiconductor wafers which have a critical surface and a surface opposed to said critical surface, said tray comprising a supporting member having a boss thereon which forms a recess sized to accommodate semiconductor wafers, said recess having a wall which is operatively connected to said supporting member and forming a recess opening larger than the wafer to be supported in said recess, said wall being of such size and shape to support a wafer with the critical surface presented away from the opening and in such manner that only the marginal edge portions of said wafer contact said wall when oriented in substantially any position with respect to said wall, cover means removably disposed over said recess, and means operatively associated with said cover means for engaging the surface of the wafer opposed to said critical surface.

3. The tray of claim 1 further characterized in that an annular bead is operatively associated with the upper end of said boss and is sized to engage the cover means disposed thereon.