Abstract:
A method for performing a batch spray comprises providing a substrate mounted upon a turntable, rotating the turntable to revolve the substrate around a center axis of the turntable, rotating the substrate independently of the turntable, wherein the rotating of the substrate occurs simultaneously with the rotating of the turntable, and spraying a chemical onto the substrate from at least one fixed location. Rotating the substrate independently of the turntable allows the entire circumference of the substrate to be exposed to the chemical spray. In one implementation, the substrate may be loaded into a process cassette, the process cassette may be mounted on the turntable, and the process cassette may rotate independently of the turntable while the turntable is rotating.

Description:
BACKGROUND  
       [0001]     In the field of semiconductor wafer processing, batch spray tools provide a way to efficiently dispense chemicals onto the surfaces of multiple wafers simultaneously. Batch spray tools offer the advantages of both batch immersion systems and wet cleaning systems in that batch spray tools enable users to process large batches with high throughput or batches with short cycle times. Batch spray tools can be used for a variety of semiconductor processes, including but not limited to photoresist stripping, electroless plating, and wafer cleaning. The chemicals used in batch spray processes can be re-circulated to reduce chemical consumption and can be heated or cooled as necessary for the particular semiconductor processing steps being carried out.  
         [0002]     One drawback to conventional batch spray tools is that an uneven distribution of chemicals often occurs on the surface of the semiconductor wafer. Within a batch spray tool chamber, the semiconductor wafers are generally mounted on a process cassette that has a fixed rotation relative to one or more spray posts used to dispense chemicals. The fixed rotation causes chemicals to be dispensed across the surface of the semiconductor wafer in a unidirectional fashion, thereby leading to a non-uniform distribution of chemicals on the wafer surface. Certain areas of the semiconductor wafer surface are exposed to large amounts of chemicals while other areas of the wafer surface are exposed to very small amounts of chemicals. This typically results in a high defect rate for integrated circuit dies cut from the semiconductor wafer as well as localized non-uniformity.  
         [0003]     Conventional batch spray tools have no viable options for reducing or eliminating this non-uniform distribution of chemicals on the wafer surface. Accordingly, improved batch spray tools are needed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a conventional batch spray tool.  
         [0005]      FIG. 2  shows how a semiconductor wafer is mounted to a process cassette.  
         [0006]      FIG. 3  is a batch spray tool constructed in accordance with the invention.  
         [0007]      FIG. 4  is a cross-section of a batch spray tool constructed in accordance with the invention.  
         [0008]      FIG. 5  is another batch spray tool constructed in accordance with the invention.  
         [0009]      FIG. 6  is a semiconductor wafer mount constructed in accordance with the invention.  
         [0010]      FIG. 7  is yet another batch spray tool constructed in accordance with the invention.  
     
    
     DETAILED DESCRIPTION  
       [0011]     Described herein are batch spray tool systems and methods that provide an improved distribution of chemicals across the surface of a semiconductor wafer. In the following description, various aspects of the illustrative implementations will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that the present invention may be practiced with only some of the described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the illustrative implementations. However, it will be apparent to one skilled in the art that the present invention may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative implementations.  
         [0012]     Various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention, however, the order of description should not be construed to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation.  
         [0013]      FIG. 1  illustrates a conventional batch spray tool  100 . Within a process chamber (not shown), two or more process cassettes  102  are mounted upon a turntable  104 . Each process cassette  102  holds one lot of semiconductor wafers  106  in a stacked formation.  FIG. 1  only shows the top semiconductor wafer  106  of the stack. Each lot may contain any reasonable number of semiconductor wafers  106 , for instance, twenty-five semiconductor wafers  106 . Of course, the process cassettes  102  may hold more or less than twenty-five wafers  106 . The batch spray tool  100  also includes one or more spray posts  108  from which one or more chemicals are dispensed (e.g., sprayed) onto the semiconductor wafers  106 . The spray posts  108  may include a side spray post  108 (A) and/or a center spray post  108 (B).  
         [0014]     The turntable  104  may rotate within the process chamber in either a counter-clockwise direction (as shown in  FIG. 1 ) or in a clockwise direction. The spray posts  108  do not rotate and remain in fixed positions within the process chamber as they dispense a chemical  110 . As the turntable  104  rotates, the semiconductor wafers  106  revolve around a center axis of the turntable  104  and pass by the spray posts  108  where they receive the chemical  110  being dispensed. In some known systems, only the side spray post  108 (A) is used. In other known systems, both the side spray post  108 (A) and the center spray post  108 (B) are used (as shown in  FIG. 1 ).  
         [0015]     The process cassettes  102  are affixed to the turntable  104  so there is no relative motion between the turntable  104  and the process cassettes  102 . As a result, an outward facing edge  112  of each semiconductor wafer  106  (i.e., the edge facing outward relative to the center of the turntable  104 ) will always face outward as the turntable  104  rotates, and an inward facing edge  114  of each semiconductor wafer  106  (i.e., the edge facing inward relative to the center of the turntable  104 ) will always face inward as the turntable  104  rotates. For example, if the semiconductor wafer  106  is loaded such that its wafer notch is facing the center of the turntable  104 , as the turntable  104  rotates, the wafer notch will continue to face the center of the turntable  104 .  
         [0016]     In systems using only the side spray post  108 (A), the rotation of the turntable  104  causes the outward facing edge  112  to continuously be the only portion of the semiconductor wafer  106  that is sprayed with the chemical  110 . The inward facing edge  114  receives the chemical  110  only after it has traveled across the entire surface of the semiconductor wafer  106 . Although the exact path of the chemical  110  across the surface of each semiconductor wafer  106  is dictated by variables such as spray force, rotation speed and the angle of the wafer  106  relative to normal, the chemical  110  as a whole may be described as primarily moving across the wafer  106  in a substantially single direction from the outward facing edge  112  to the inward facing edge  114 . This unidirectional movement tends to cause a non-uniform distribution of the chemical  110  across the surface of the semiconductor wafer  106 .  
         [0017]     In systems using both the side spray post  108 (A) and the center spray post  108 (B), the chemical  110  may move across the semiconductor wafer  106  in two directions. As the process cassette  102  moves past the side spray post  108 (A), the outward facing edge  112  is still the first portion of the semiconductor wafer  106  to receive the chemical  110 . And as the process cassette  102  moves past the center spray post  108 (B), the inward facing edge  114  is the first portion of the semiconductor wafer  106  to receive the chemical  110 . Although the chemical  110  is now distributed across the surface of the semiconductor wafer  106  in a bi-directional manner, non-uniformity issues still exist.  
         [0018]      FIG. 2  illustrates how the semiconductor wafer  106  is mounted to the process cassette  102 . As shown, the process cassette  102  uses several upright mounts  200  to secure the stack of semiconductor wafers  106 . As the turntable  104  rotates and each semiconductor wafer  106  receives a unidirectional or bidirectional application of the chemical  110 , it has been shown that the upright mounts  200  can cause leading and trailing edge effects that result in wafer non-uniformity at one or more areas  202  in proximity to the upright mounts  200 . This is yet another problem that arises with conventional batch spray tools.  
         [0019]     To mitigate these non-uniformity issues, the batch spray tools made in accordance with the invention provide batch spray processes in which the semiconductor wafers  106  are rotated independently of the turntable  104 . In other words, as the turntable  104  rotates during a batch spray process, the semiconductor wafers  106  rotate relative to and independent of the turntable  104 . This enables each semiconductor wafer  106  to expose its entire circumference to the spray posts  108  rather than just an outward facing edge  112  or an inward facing edge  114 .  
         [0020]      FIG. 3  illustrates a batch spray tool  300  according to one implementation of the invention. The batch spray tool  300  includes the turntable  104  mounted within a process chamber (not shown). The turntable  104  may rotate in either a clockwise or a counter-clockwise direction. The batch spray tool  300  also includes spray posts  308  to deliver chemicals  110 , including but not limited to a side spray post  308 (A) and a center spray post  308 (B).  
         [0021]     One or more process cassettes  302  are mounted on the turntable  104 . In accordance with the invention, the process cassettes  302  may rotate independently of the turntable  104 . The rotation may be in either a counter-clockwise direction as shown in  FIG. 3  or in a clockwise direction. In some implementations, the rotation of the process cassettes  302  may be in the same direction as the turntable  104 , while in other implementations the rotation of the process cassettes  302  may be in the opposite direction of the turntable  104 . In some implementations, each process cassette  302  may rotate independently of other process cassettes  302  mounted on the same turntable  104 .  
         [0022]     The process cassettes  302  may each hold one lot of semiconductor wafers  106 . The semiconductor wafers  106  are stationary to the process cassettes  302  and do not move relative to the process cassettes  302 . The independent rotation of the process cassettes  302 , however, causes the semiconductor wafers  106  to rotate relative to the turntable  104 . The semiconductor wafers  106  rotate about either their center axis or the center axis of the process cassette  302 . Unlike conventional systems where only the outward facing edge  112  or the inward facing edge  114  are directly sprayed, the rotation of the turntable  104  in combination with the rotation of the process cassettes  302  enables the entire circumference of each semiconductor wafer  106  to be directly sprayed by the spray posts  308 . Spraying the semiconductor wafer  106  along its entire circumference provides many benefits such as minimizing issues that arise from unidirectional or bidirectional applications of the chemical  110 , minimizing the effect of the upright mounts  200 , and improving uniformity across the surface of the semiconductor wafers  106 .  
         [0023]     In some implementations of the invention, the turntable  104  may rotate at speeds that range up to 300 rotations per minute (RPM). In some implementations, the process cassettes  302  may rotate at speeds that range up to 200 RPM. In other implementations, many other RPM ranges may be used for either the turntable  104  or the process cassettes  302 .  
         [0024]      FIG. 4  is a cross-section of one implementation of a batch spray tool  300  that includes a mechanism to rotate the process cassettes  302 . The batch spray tool  300  may include a process chamber  400  that houses the spray posts  308 (A) and  308 (B) and the process cassettes  302 . As shown, the process cassettes  302  each hold a stack of the semiconductor wafers  106 . Each process cassette  302  may be mounted on a central support post  402  that holds and rotates the process cassette  302 . In some implementations, the central support posts  402  may be attached to the process cassettes  302  by means of a keyed locking mechanism. In some implementations, the central support posts  402  may attach to motor units  404  used to induce a rotation in the central support posts  402 . The motor units  404  therefore rotate the process cassettes  302  by means of the central support posts  402 .  
         [0025]     In implementations of the invention, the motor units  404  may be mounted on the turntable  104 . The turntable  104  may then rotate about an axis  406 . The turntable  104  may rotate the motor units  404  while the motor units  404  rotate the process cassettes  302 . In some implementations, the turntable  104  and the motor units  404  may be housed within the process chamber  400 , as shown in  FIG. 4 . In some implementations, the motor units  404  may be mounted within the turntable  104  while the process cassettes  302  are mounted atop the turntable  104 .  
         [0026]     In another implementation of the invention, the process cassettes  302  may be rotated using rotating magnets. A bottom surface of each process cassette  302  may be magnetized and the rotating magnets may be mounted either within or outside the process chamber  400 . The rotating magnets may be rotated to induce a rotation in the process cassettes  302 . In this implementation, the process cassettes  302  may be mounted on the turntable  104  using a mechanism that allows the process cassettes  302  to freely rotate.  
         [0027]      FIG. 5  illustrates a batch spray tool  500 , formed according to the invention, in which the stack of semiconductor wafers  106  rotates independently of both a process cassette  502  upon which they are mounted and the turntable  104 . In this implementation, the process cassettes  502  are affixed to the turntable  104  and do not independently rotate. The stack of semiconductor wafers  106 , however, may rotate within the process cassettes  502 . Because the stack of semiconductor wafers  106  may rotate independent of both the process cassette  502  and the turntable  104 , each semiconductor wafer  106  again exposes its entire circumference to the chemical spray  110 . In some implementations, the semiconductor wafers  106  may rotate in a clockwise direction (as shown in  FIG. 5 ), while in some implementations the semiconductor wafers  106  may rotate in a counter-clockwise direction. The semiconductor wafers  106  may rotate in the same direction or in the opposite direction of the turntable  104 .  
         [0028]      FIG. 6  illustrates one implementation of the process cassette  502  where the stack of semiconductor wafers  106  may rotate independently. The process cassette  502  includes a plurality of rotating uprights  600  that secure and rotate the stack of semiconductor wafers  106 . The rotating uprights  600  must rotate in the same direction, either clockwise or counter-clockwise, to rotate the stack of semiconductor wafers  106 . Accordingly, although the process cassette  502  does not rotate relative to the turntable  104 , the stack of semiconductor wafers  106  does. In other implementations, alternate rotation mechanisms such as ball bearings may be used to secure and rotate the stack of semiconductor wafers  106 .  
         [0029]      FIG. 7  illustrates yet another implementation of a batch spray tool  700  in which both the process cassettes  702  and the semiconductor wafers  106  rotate independent of the turntable  104 . The rotations of the turntable  104 , the process cassettes  702 , and the semiconductor wafers  106  may all be in the same directions or in different directions, depending on the desired flow of chemicals  110  across the semiconductor wafers  106 .  
         [0030]     The systems and methods of the invention may be used for a variety of processes that include, but are not limited to, electroless plating (e.g., electroless cobalt plating), and metal etching. The batch spray tools of the invention may provide improved uniformity of chemical application across the surface of the semiconductor wafer, and may reduce streaking that often occurs on semiconductor wafers after photoresist stripping and improve the within-wafer uniformity of wet-cleaned or wafers plated using an electroless plating process.  
         [0031]     The above description of illustrated implementations of the invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. While specific implementations of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize.  
         [0032]     These modifications may be made to the invention in light of the above detailed description. The terms used in the following claims should not be construed to limit the invention to the specific implementations disclosed in the specification and the claims. Rather, the scope of the invention is to be determined entirely by the following claims, which are to be construed in accordance with established doctrines of claim interpretation.