Technical Field

The present invention relates, generally, to wafer cassette holding mechanisms, and more particularly to an adjustable platform for securely yet releasably holding a cassette containing a plurality of wafers.

Background Art and Technical Problems

Cassettes for holding stacks of wafers are generally well known in the semiconductor manufacturing industry More particularly, a wafer cassette comprises a lightweight, hand-carryable housing configured with a plurality of parallel, spaced-apart horizontal slots for storing a plurality of disks or wafers. In this context, the disks or wafers may compnse flat, circular silicon wafers used in the manufacture of integrated circuit components and the like. As the workpieces (wafers or disks) are processed, they often need to be transported from one operation to another within the same machine, or from one machine to another machine for further processing. A plastic or metal wafer cassette conveniently accommodates these needs.

A typical workpiece comprises a housing having a substantially open front-facing portion to allow the convenient loading and unloading of individual cassettes, either manually or more typically through the use of precision robotics. The bottom of the cassette housing often comprises a flat portion to allow the cassette to remain stable when placed on a flat surface. The top of the cassette typically includes a handle for convenient manual grasping to transport the cassette from one processing position to the next. In addition, the rear portion of the cassette often includes one or more thin, elongated vertical post for secunng engagement by a cassette holder, as described in greater detail below.

Cassettes for holding and transporting workpieces are often used in conjunction with Chemical Mechanical Planaπzation (CMP) machines. In particular, a fully loaded cassette, containing for example 25 wafers, may be placed in the unload compartment of a CMP machine, wafer cleaning machine, or the like. A robotic arm is configured to selectively retrieve wafers from the cassette, and transport the wafers one at a time to a processing station. When the

machine (CMP, wafer cleaner, or the like) has finished processing each wafer, an unloading robotic arm retrieves each wafer from the final processing position and sequentially stacks each wafer into a particular slot within an unload cassette. For economy and interchangeability, the same or similar cassette housings may be employed as load cassettes and as unload cassettes in a broad variety of machines, as is well known in the industry. Once an unload cassette is filled with processed wafers, the machine operator may grasp the fully loaded cassette by the handle and transport the cassette to a subsequent processing station or facility. In many processing environments, cassettes loaded with workpieces may be subject to vibration, which can cause wafers within a cassette to become dislodged. In view of the high cost of wafers, particularly silicon wafers in the latter stages of semiconductor fabrication, the cost of breakage should a wafer become dislodged from the cassette can be quite high. Accordingly, many wafer processing machines include tilting mechanisms configured to tilt the cassette rearwardly so that the wafers become gravity loaded against to the rear portion of the cassette housing, so even in the presence of vibrations the wafers cannot be dislodged from the cassette.

Presently known cassette holder platforms such as cassette holders used in CMP machines, wafer cleaning machines, and the like, are unsatisfactory in several regards. For example, often the stepper motors and other actuators used to tilt the wafer cassettes may dislodge the cassette housing from the cassette holder as the cassettes are tilted. This can cause misalignment of the individual wafers with respect to the robotic arms configured to load and unload wafers from the cassettes.

In addition, a broad range of cassette housing designs are available from a number of different manufacturers. While many CMP and other wafer processing machines include cassette platforms designed to accommodate many of these cassette housing designs, a universal cassette holder capable of accommodating a broad variety of cassette housing designs is still needed.

Presently known cassette platforms are further unsatisfactory in that they do not easily accommodate the leveling adjustments necessary to properly

position the cassettes. In particular, presently known leveling mechanisms are cumbersome and typically require a separate tightening screw for each adjustment screw.

A cassette holder which addresses the shortcomings of the prior art is thus needed.

Summary of the Invention

The present invention provides a new and improved cassette holder which addresses and resolves many of the shortcomings of the prior art.

In accordance with a preferred embodiment of the present invention, a cassette support platform includes a substantially flat, horizontal cassette support platform upon which virtually any cassette design may be stably placed. In accordance with a further aspect of the present invention, the cassette support surface has associated with it an adjustable cassette guide at the forward portion of the support platform, and two alignment posts disposed at the rearward portion of the support platform for securely receiving the vertical wings which typically project rearwardly from the back of the cassette housing. Both the alignment posts as well as the cassette guide are freely adjustable to accommodate virtually any cassette design.

In accordance with a further aspect of the present invention, the support platform may be adjusted to a level position (or to any desired position) using a plurality (e.g., 3) of adjustment screws to fine tune the level position of the support platform. In a particularly preferred embodiment of the present invention, a wing screw is employed at the center of gravity of the triangle defined by the three adjustment screws, such that the leveling position of the three adjustment screws may be rigidly fixed by a single wing screw.

Brief Description of the Drawing Figures

The subject invention will hereinafter be described in conjunction with the appended drawing figures, wherein like numerals denote like elements, and:

Figure 1 A is a side elevation view of a wafer cassette stand including

a tilt actuator, shown with an empty wafer cassette positioned on the support platform of the cassette stand;

Figure 1B shows the assembly of Figure 1A in a tilted position;

Figure 2 is a front elevation view of the wafer cassette housing shown in Figure 1;

Figure 3 is a bottom view of the cassette housing of Figure 2;

Figure 4 is a closeup view of an exemplary embodiment of the support platform, alignment posts, adjustment bracket, and tilting mechanism of the cassette stand of Figure 1 ; Figure 5 is a front view of the assembly of Figure 4;

Figure 6 is a detailed view of the cassette flange abutting the adjustment guide shown in Figure 1;

Figure 7 is a top plan view of an exemplary cassette platform, illustrating the configuration of the level adjustment screws and wing screw; and Figure 8 is a top plan view of the cassette platform of Figure 7, shown with an exemplary cassette housing emphantom atop the platform.

Detailed Description of Preferred Exemplary Embodiment

Referring now to Figures 1A and 1B, an exemplary wafer cassette housing 300 is shown secured within an exemplary wafer cassette stand 100. In accordance with a preferred embodiment of the present invention, wafer cassette stand 100 may be configured to accommodate a variety of different designs and configurations of cassette housings 300. In this regard, suitable cassettes 300 are available from a number of cassette housing manufacturers, including the XT200 manufactured by Empak, the A192-81M-0215 and A198-80M-47C02 available from Fluroware, and the like. The specifications and general design parameters for wafer cassette housings are generally defined by SEMATECH specification SEMI E1-86. In this regard, the present invention may be configured to accommodate virtually any type of workpiece cassette, including both plastic and metal wafer carriers used for 3 inch, 100 millimeter, 125 millimeter, 150 millimeter, 200 millimeter, and 300 millimeter diameter wafers, including wafer carriers useful both in a general usage and auto transport usage classifications.

With continued reference to Figure 1, cassette housing 300 suitably includes a handle 302 and respective wings 202A and 202B, described in greater detail in conjunction with Figures 3, 5, and 8. When it is desired to load a cassette 300 into cassette stand 100, the machine operator may grasp handle 302 and place the cassette housing onto the cassette platform associated with cassette stand 100. If the operator determines that the cassette platform does not conveniently accept cassette 300, the operator may adjust cassette stand 100 to thereby "tune" the cassette stand to the particular cassette configuration currently used by the operator in conjunction with cassette stand 100, as described in greater detail below.

With continued reference to Figures 1A and 1B, cassette stand 100 suitably comprises an actuator assembly 104, for example a linear stepper motor, servo motor, cam drive assembly, or the like configured to controllably tilt cassette 300 along arrow 191, as shown in Figure 1B. In this regard, cassette stand 100 suitably includes a datum platform 103 which is rigidly secured to a fixed panel 102 associated with the processing machine within which cassette stand 100 is embodied. See, for example, Arai, et al., U.S. Patent No. 5,099,614, issued March, 1992; Karlsrud, U.S. Patent No. 5,498,196, issued March, 1996; Arai, et al., U.S. Patent No.4, 805,348, issued February, 1989; Karlsrud etal., U.S. Patent No. 5,329,732, issued July, 1994; and Karlsrud et al., U.S. Patent No. 5,498,199, issued March, 1996, for a discussion of CMP and other machines within which cassette stand 100 may be conveniently employed.

Although the present invention is illustrated in the context of a tiltable cassette stand, the inventions described herein are not so limited. In particular, the various adjustment features may be employed in virtually any cassette stand, including non-tiltable, rotatable and rigid cassette stands and holders.

With momentary reference to Figures 2 and 3, cassette 300 suitably comprises an open front portion which permits the convenient loading and unloading of wafers into the cassette, a bottom portion 306, a left side panel 301 and a right side panel 303. In the illustrated embodiment, left side panel 301 and right side panel 303 each comprise a plurality of slots 304 within which individual wafers are stored.

With particular reference to Figure 3, bottom 306 of housing 300 suitably comprises a flange 206 which extends at least partially between left panel 301 and right panel 303. Flange 206 preferably includes a forward facing flange edge 207 and a ridge 210. Bottom surface 306 further includes respective ridges 208A and 208B which suitably comprise thin, elongated web features extending downwardly from the bottom of the cassette. As described in greater detail below, ridges 208 are convenient features of housing 300 for engaging the cassette present sense switch associated with cassette stand 1 0, as described in further detail below. With continued reference to Figure 3, cassette housing 100 further includes respective rearwardly extending wings 202A and 202B, which suitably comprise thin, flat, wings which extend rearwardly in parallel vertical planes from the backside of housing 300.

Referring now to Figures 1A, 4 and 5, cassette stand 100 further comprises respective pivot mounts 110 about which pivoting assembly 111 is configured to pivot.

More particularly, pivoting assembly 111 suitably comprises a cassette support platform 118, having a cassette adjustment guide 128 and respective cassette alignment posts 120A and 120B adjustably secured to support platform 118. A cassette presence switch button 140 suitably extends upwardly from the surface of platform 118, and is advantageously configured to deflect downwardly when a cassette 300 is placed on platform 118. In particular, as a cassette 300 is placed onto platform 118, switch 140 is pressed downwardly, indicating that a cassette is present on platform 118. When cassette 300 is removed from platform 118 or otherwise becomes dislodged from the platform, switch 140 is urged upwardly, for example, by an internal biasing spring, indicating that no cassette is present on platform 118. In this regard, a suitable switch housing 116, which may comprise the electronics associated with switch 140 may be secured (e.g., flush mounted) to the underside of platform 118. A suitable wire (not shown) or other communication facility may be employed in connection with switch 140 and switch housing 116 to transmit a cassette present/cassette not present signal to an appropriate operator screen.

Referring now to Figures 1 and 4-8, pivoting assembly 111 further comprises a leveling plate 114 which is substantially parallel to cassette support platform 118. Support platform 118 is suitably secured to leveling plate 114 through a plurality (e.g., 3) of leveling assemblies 124. Assemblies 124 may comprise a fixed nut into which a screw is threaded, on a fixed screw over which a nut is threaded, or another convenient mechanism for positioning platform 118 with respect to plate 114. In the illustrated embodiment, respective biasing springs 126, associated with respective leveling screws 124, are suitably interposed between support platform 118 and leveling plate 114 to bias platform 118 away from leveling plate 114. As described in greater detail below, wing adjustment 126 is suitably configured to fix the particular leveling position of platform 118 established by operator manipulation of respective leveling screws 124, and to maintain the adjustment in place even as cassette stand 100 is subject to vibrations and the like. With particular reference to Figures 1 and 4, Figures 1A and 4 show the subject cassette stand in the nominal, horizontal position. When it is desired to tilt pivoting assembly 111 and, hence, cassette 300 into the tilted position shown in Figure 1B, actuator assembly 104 extends upwardly (along arrow 193 in Figure 1B) such that a clevis 106 associated with actuation assembly 104 exerts an upward force on a shaft 109 extending between respective clevis brackets 108. Shaft 109 transmits the actuating force to plate 114, causing pivoting assembly 111 to pivot about a shaft 117 having a horizontal axis 112 associated therewith. More particularly, respective bearing brackets 119 are rigidly secured to the undersurface of leveling plate 114, such that pivoting shaft 117 is journaled through respective bearing brackets 119 and rotatably mounted within support arms 110. In this way, as actuator assembly 104 urges clevis assembly 108, 109 upwardly, leveling plate 114 rotates about shaft 117 supported by pivot arms 110. As leveling plate 114 pivots about axis 112, support platform 118 similarly pivots about axis 112, inasmuch as platform 118 is essentially rigidly secured to leveling plate 114 through the interaction of respective leveling screws 124 and wing screw 126.

With momentary reference to Figure 7, wing screw 126 is suitably positioned at the center of gravity defined by respective adjustment screws 124. Specifically, the center of gravity of the triangle defined by respective adjustment screws 124 may be determined by drawing an internal circle tangent to each of the three lags comprising the triangle; the center of gravity of the triangle corresponds to the center of the circle. Alternatively, the center of gravity of the triangle may be defined by the intersection of the three imaginary lines which respectively bisect the three internal angles of the triangle. With momentary reference to Figure 4, threaded shaft 132 of wing screw 126 suitably threadly engages plate 114, and bottoms out on the underside of platform 118. As a result, wing screw 126 may be tightened, forcibly urging plate 114 away from platform 118. In this way, the level position of platform 118, as determined by respective leveling screws 124 with respect to plate 114, may be maintained.

The manner in which cassette stand 100 may be adjusted to accommodate a plurality of different cassette housing designs will now be described in accordance with the present invention.

Referring now to Figures 1, 3, 5, and 7, the two principal cassette stand adjustment mechanisms in accordance with the illustrated embodiment surround a cassette adjustment guide 128 and respective alignment posts 120A and 120B. In particular, adjustment guide 128 is suitably positioned so that its rearward facing edge 129 (see Figure 7) abuts leading edge 207 of flange 206 (see Figure 3) when housing 300 is placed on support platform 118. At the same time, respective wings 202A and 202B (see Figure 3) are received within respective alignment posts 120A and 120B (see Figures 5, 7 and 8). In order to conveniently accommodate cassette housings having dimensional variations or different design configurations, the adjustability of adjustment guide 128 and alignment posts 120 exploits the fact that virtually all cassette housings have at least the following two features in common: (1) a bottom flange similar to flange 206 having a leading edge 207 which abuts against leading edge 129 of guide 128; and (2) respective vertical wings analogues to wings 202 of cassette 300 which are spaced apart in the range of 3 to 6 inches (and most preferably about 4.7 inches) for convenient receipt within alignment

post 120. For cassette housings which have wings 202 which are separated by a greater or lesser distance, respective alignment posts 120 may be adjusted along respective arrows 123 (see Figures 5 and 7) to ensure that alignment posts 120 optimally accommodate the wing configuration of the particular cassette housings being used. Moreover, the position of cassette guide 128 may be adjusted, for example, along arrow 128A (see Figure 7), to obtain an optimal "fit" between the housing and the support platform. With momentary reference to Figure 1A, the particular position of respective posts 120 along arrows 123 may be secured by any suitable mechanism, for example through the use of an adjustment screw 122. Similarly and with particular reference to Figure 7, the particular position of guide 128 along arrow 128A, as well as the extent to which guide 128A is aligned with or deviates from nominal position 128B, may be secured by suitable adjustment screws 131 which are configured to slide within respective oval recesses 133 as guide 128 is manually positioned along arrow 128A.

Referring now to Figures 6-8, when cassette 300 is properly placed on platform 118, underside 306 of cassette housing 300 suitably engages switch 140, actuating switch mechanism 116 indicating that a cassette is present on platform 118. More particularly, by properly aligning cassette 300 on platform 118 as described above in conjunction with the adjustment features of the present invention, a portion of ridge 208B (or alternatively ridge 208A), which suitably extends downwardly below the surface defined by flange 206, configured to contact switch 140 and depress the switch. In accordance with a particularly preferred embodiment, a region 141 (see Figure 3) of ridge 208 proximate the outer edge of flange 206 is positioned to contact switch 140.

In accordance with a further aspect of the present invention, various of the adjustable features described herein are optimally configured to facilitate the placement of cassette 300 onto platform 118. Referring now to Figures 4 and 5-7, cassette adjustment guide 128 suitably comprises a first angled surface 144 and a second angled surface 146 configured to guide leading edge 207 of flange 206 rearwardly (i.e., to the right in Figures 4 and 6) and downwardly as cassette 300 is being placed onto platform 118. This is particularly helpful when a cassette

filled with wafers is being placed on the platform, inasmuch as the presence of the wafers blocks the operator's view of adjustment guide 128. In effect, angled surfaces 144 and 146 guide leading edge 207 of flange 206 into position as the operator lowers the cassette onto the platform.

Referring now to Figures 4-5 and 7-8, respective alignment posts 120A and 120B each include a central slot 148 within which respective wings 202A and 202B are received. More particularly, each slot 148 suitably comprises a dove tail or bevel guide 149 which assist in the alignment of each wing 202 into slot 148. That is, if wing 202 is not properly aligned with th