Abstract:
A semiconductor wafer aligning system includes a table having a spray opening for upwardly spraying fluid to form a fluid surface on which a semiconductor wafer floats. A guide disposed on the table contacts the wafer at a circumferential edge to guide the wafer to a correct location. Thus, a wafer is aligned without generating particles that hinder semiconductor fabrication, and without directly scratching a front side during back side grinding.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a semiconductor wafer aligning system and method. More particularly, the present invention relates to a semiconductor wafer aligning system and method wherein a wafer floats on a fluid as the wafer is contacted by guides. 
     DESCRIPTION OF THE RELATED ART 
     Generally, in the semiconductor device fabrication process, wafers are processed in processing equipment after being moved by a transfer system for loading wafers, and then the wafers are moved to other processing equipment by a transfer system for unloading wafers. 
     A wafer aligning system is used to secure the wafer at a correct loading location on a stage of the processing equipment so that it may be moved within the processing equipment. If the wafer is not precisely aligned, the wafer may collide with fabrication equipment and may be broken, representing a malfunction of the wafer transfer system. 
     Generally, the aligning system for wafers can have various configurations and operating principles. Aligning systems can be divided into two different types, a wafer holding aligning system and a wafer guide aligning system. The first type holds the wafer securely by its edges and then moves it into alignment. The second type moves the wafer in contact with guides until alignment is achieved, and then holds the wafer securely by its edges. 
     The wafer holding aligning system and the wafer guide aligning system are normally operated such that the front surface of the wafer, which has a pattern thereon, faces upwardly and the back surface of the wafer faces downwardly, toward the aligning system. 
     While the wafer is aligned, any scratch occurring on the back surface of the wafer in contact with the system causes no direct difficulties. However, cleanliness of the cleanroom for semiconductor devices fabrication environment is important, and the ultrafine particles generated due to the scratches can affect the production yield and the reliability of the semiconductor device fabrication process. 
     In a wafer grinding process, the thickness of the wafer is reduced and the particles accumulated on the back side of the wafer are removed. During this process the back side of the wafer faces upwardly and the front side of the wafer, covered with tape, faces downwardly on the aligning system. Since the tape-covered front side of the wafer contacts the guide, any damage from the guide may penetrate the tape and cause scratches and direct damage to the front side. 
     In addition, to minimize damage from conventional alignment systems, the aligning operation is typically performed only one time. This makes it difficult to maintain a precise alignment throughout processing. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to provide a semiconductor wafer aligning system for aligning a wafer precisely without causing wafer damage or generation of particles. 
     It is another object of the present invention to use a fluid on which the wafer is made to float to prevent damage and generation of particles. 
     Another object of the present invention is to provide a semiconductor wafer aligning method using the semiconductor wafer aligning system of the present invention while minimizing the amount of fluid usage. 
     To achieve these and other advantages and in accordance with the purpose of the present invention as embodied and broadly described, a semiconductor wafer aligning system includes a table having a spray opening for upwardly spraying ultrapure water to form a water surface on which a semiconductor wafer floats. A guide disposed on the table contacts the wafer at a circumferential edge, to guide the wafer into a correct location. 
     In another aspect of the present invention, an upward extended member is disposed on the table outside a peripheral edge of the spray opening such that the water surface is wider than the spray opening. It includes a wall having an open section such that the wafer floating on the water surface moves horizontally in a drift direction toward the open section. 
     In another aspect of the present invention, each of a left guide and a right guide of the guide includes a horizontal plate for supporting the bottom of the wafer when the wafer is not floating, and an upward protruded part connected to the horizontal plate for contacting the circumferential edge of the wafer. The protruded part is a screw protrusion having a male screw part. The horizontal plate has a plurality of female screws, each corresponding to a respective one of a plurality of wafer diameters. 
     In another aspect of the invention, a method of aligning a semiconductor wafer using the semiconductor wafer aligning system includes spraying ultrapure water. The spraying includes opening a valve leading to the spray opening so as to spray ultrapure water through the spray opening upward toward a wafer. The wafer is guided, after the spraying, by moving the wafer to a correct position with the guide, and then closing the valve so as to stop the spray of the ultrapure water. 
     By contacting and aligning a wafer which floats on a water surface of ultrapure water, the present invention substantially obviates one or more of the problems due to the limitations and disadvantages of the related art 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a perspective view showing the wafer aligning system according to one embodiment of the present invention, wherein a wafer having a large diameter is mounted on the guide plates of the wafer aligning system; 
     FIG. 2 is a perspective view showing the wafer aligning system according to one embodiment of the present invention, wherein the wafer having a large diameter is contacted and aligned by the protruding parts on the guide plates of the wafer aligning system; 
     FIG. 3 is a partial sectional view showing the wafer aligning system of FIG. 2; 
     FIG. 4 is a top view showing the guide plates of the wafer aligning system of FIG. 2; 
     FIG. 5 is a perspective view showing the wafer aligning system according to one embodiment of the present invention, wherein a wafer having a small diameter is contacted and aligned by the guide plates of the wafer aligning system after the guide plates of FIG. 2 have been adjusted; 
     FIG. 6 is an enlarged sectional view showing how a protrusion of FIG. 1 is coupled to a guide plate; 
     FIG. 7 is a schematic representation showing the wafer aligning system according to one embodiment of the present invention; and 
     FIG. 8 is a schematic diagram showing the recirculation part of the wafer aligning system according to another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 1 is a perspective view showing the wafer aligning system according to one embodiment of the present invention, wherein a wafer having a large diameter is mounted so as to contact guide plates of the wafer aligning system. FIG. 2 is a perspective view showing the wafer aligning system according to one embodiment of the present invention, wherein the wafer having a large diameter is contacted at its edge and aligned, i.e., moved to a correct position by the guide plates of the wafer aligning system. FIG. 3 is a partial sectional view showing the wafer aligning system of FIG.  2 . 
     Referring to FIGS. 1-3, the wafer aligning system includes a table  14  having a spray opening  12  for spraying a fluid  10  supplied from a fluid source (not shown) at a spray pressure. In the embodiments described herein, the fluid  10  is ultrapure water. Other suitable fluids may be employed as well. A wafer  16  floats on a water surface formed by the spray pressure. Guides, such as left and right guide plates  18 , are mounted on the table  14  and contact the wafer on different portions of the wafer circumference so as to guide the wafer and move it to a correct horizontal location. 
     In the example embodiment of FIGS. 1-3, a drive part  20  is connected to the left or right guide plates, or both, for controlling the distance between the two guide plates  18  between wide and narrow limits. 
     The table  14  may include a vertically extended member  22 , such as a pool wall, which protrudes from the table at a location outside the peripheral edge sides of the spray opening  12 . The pool wall holds a certain amount of the ultrapure water  10  sprayed from the spray opening  12  such that the water surface is extended horizontally as wide as the pool wall. A part A of the wall of the extended member  22  is open so that the wafer  16  floating on the water surface drifts along the water surface of the ultrapure water  10  in a drift direction, as indicated by the horizontal arrows in FIG.  3 . 
     FIG.  3 . The ultrapure water  10  is sprayed through the spray opening  12  at a spray volume such that the water fills the area enclosed by the pool wall  22  and continuously overflows the pool wall at part A as shown in FIG.  3 . Due to the spray volume of the water and the surface tension on the surface of the water, the surface of the water enclosed within the pool wall is slightly higher than the top of the pool wall. 
     Alignment. This easy alignment is possible because the guide plates  18  are not in contact with the wafer during the alignment. The bottom of the wafer floats above the top of the guide plates due to the surface tension of the water, and the edges of the wafer do not contact the protrusions  24  on the guide plates, because the guides plates are spaced apart such that the protrusions are separated by a distance larger than the diameter of the wafer. Operation of the guide plates to align the wafer in a second alignment is discussed in detail below. 
     Therefore, the wafer  16  floats on the water surface formed by the upward water pressure sprayed through the spray opening  12  located on the table  14 . The extended member  22  formed around the spray opening  12  sets the width of the water surface to be large enough that the wafer  16  floats sufficiently to allow for easy alignment. 
     The water surface also functions to absorb the particles contained in the surrounding air and on the downwardly facing side of the wafer, and to discharge these particles through a discharge opening. Such absorption minimizes the undesirable effects of particles on the wafer  16 . 
     In addition, as shown in FIG. 1, enough of the sprayed ultrapure water flows in the direction of the open wall A of the extended member  22  as described above, that the wafer  16  drifts in the direction of the open wall A to complete a first aligning operation in which the wafer is displaced laterally toward the open wall. 
     After completing the first aligning operation, the laterally displaced wafer  16  is forced centerward as the guide plates  18  close. This continues until the wafer  16  is held securely by the protrusions  24  of the guide plates  18  at substantially directly opposing sides of the wafer edge, as shown in FIG.  2 . This completes a second aligning operation. Therefore, the precise aligning operation is substantially achieved by the two operations of the aligning process, i.e., the above first and second aligning operations. 
     The shape of the guide, such as the guide plates  18  with protrusions  24 , can be varied. Preferably, a two-pronged horizontal plate is formed of left and right guide plates  18 , as shown in FIG.  4 . These horizontal guide plates  18  support the wafer  16  on its lower side when the wafer  16  is mounted thereon. Protruded parts, such as the protrusions  24 , are provided on the guide plates  18  for contacting the peripheral edge of the wafer  16  such that the wafer  16  can be both guided and, ultimately, secured. 
     As shown in FIG. 6, each protrusion  24  may be formed by a male member, such as a partially threaded shaft, which is removably inserted into one of a plurality of female receptors, such as threaded holes  26 , formed in the upper surface of the guide plates  18 . The plurality of female receptors are located at different positions to accommodate various diameters of wafers to be aligned. For example, female receptor positions can correspond to 4 inch, 6 inch, 8 inch, and 12 inch to wafer diameters. As shown in FIG. 4, a plurality of female receptors having various positions corresponding to various wafer sizes are formed on the guide plates  18 . The plurality of female receptors may include, for example, 4-inch female receptors  34 , 6 inch female receptors  32 , 8 inch female receptors  30 , and 12-inch female receptors  28 . 
     An operator can assemble or disassemble the protrusion  24  on the guide plates  18  manually, with or without tools. Thus, protrusions can be adjusted to positions appropriate for various wafer diameters. 
     Other configurations of the protrusions  24  than the threaded versions shown in FIG. 6 are possible. As examples, the protrusion may comprise a member which is forcibly inserted and held by friction, or it may be an arc-shaped protrusion member having an insertion groove formed around the peripheral edge of the wafer. 
     As shown in FIG. 2, when a 12-inch wafer needs aligning, for example, the protrusions  24  are coupled with  12  inch-female receptors ( 28  in FIG. 4) previously formed on the guide plates  18 . In the case of a 4-inch wafer, as shown in FIG. 5, the protrusions  24  are coupled using the 4-inch female receptors ( 34  in FIG. 4) previously formed on the guide plates  18 . 
     In addition, as shown in FIG. 4, through holes  36  may be formed on the guide plates  18 . When the guide plates  18  are placed under the water surface, the ultrapure water  10  penetrates the through holes  36  and the water surface pushes the wafer  16  upwardly so that the wafer floats. The shapes of the through hole  36  are advantageously wide and symmetrical to allow for sufficient spray pressure to be applied uniformly under the wafer  16 . 
     As shown in FIGS. 1 and 2, the drive part  20  may comprise a horizontal double-acting cylinder  42 , with two pistons  38  which are each connected to one end of the left/right guide plates  18 . The pistons  38  are horizontally moved by the double-acting cylinder  42  receiving air pressure supplied through an air pressure line  40 . 
     As an alternative to the double-acting cylinder  42 , two single-acting cylinders can be connected to the right and left guide plates  18 , respectively. It is also possible to employ two double screws with each screw direction being different than the other. The double screws penetrate through a moving member connected to the guide plates, and are rotated by a motor so as to create a linear, reciprocating motion of the moving member. However, it is more desirable to use the double-acting cylinder because it is easier to handle, and it allows for more precise control. 
     In addition, as shown in FIG. 7, the cylinder  42  may have a speed control valve  44  to control the speed of the straight reciprocal piston movement driven by the cylinder  42 . The speed control valve  44  controls the flow amount of the air pressure supplied through the air pressure line  40  connected to the cylinder  42 . By using the speed control valve  44 , the speed is optimized so as to be high enough to align the wafer  16  but low enough to avoid a damaging impact on the wafer  16  by the guide plates  18 . 
     As shown in FIGS. 1 and 2, a shield member  46  is further installed between the drive part  20  and the extended member  22  in order to prevent the ultrapure water  10  from flowing over the extended member  22  and going into the drive part  20 . 
     As shown in FIG. 7, the semiconductor wafer aligning system of the present invention may include a sensor  48  installed on the guide plates  18  for sensing the mounting state of the wafer  16 . A controller  50  receives the wafer sensing signal from the sensor  48  and provides a control signal to the cylinder  42  in order to drive the cylinder  42 . The controller  50  controls the driving of the cylinder  42  through the air pressure line  40 . Also, the controller  50  sends a water control signal to a valve  52  on an ultrapure water line  71  connecting an ultrapure water source  11 . This water control signal makes the valve  52  open so as to spray the ultrapure water  10 , compressed at a certain pressure. This spray causes the wafer  16  to float on the water surface formed by the water pressure of the ultrapure water. 
     The aligning operation of one embodiment of the semiconductor wafer aligning system of the present invention is described in detail referring to FIGS. 5 and 7. The protrusions  24  secured on the guide plates  18  are matched to the size of the wafer to be aligned. If necessary, the protrusions are disassembled from the guide plates, and the protrusions  24  are reassembled on the female receptors matching the diameter of the wafer being selected, e.g., one diameter chosen among the 4-inch, 6-inch, 8-inch, and 12-inch female receptors  34 ,  32 ,  30  and  28 , respectively, which were previously formed on the guide plates  18 . 
     When the protrusions  24  are assembled in accordance with the diameter of the wafer to be aligned, a vacuum chuck for wafer transfer mounts the wafer on the guide plates  18 . 
     At this stage, the sensor  48  installed on the guide plates  18  senses the mounted wafer  16 , and transmits a wafer sensing signal to the controller  50 . The controller  50  then transmits a water control signal that opens the closed valve  52  connecting the ultrapure water source  11  so that ultrapure water  10  is sprayed on the lower surface of the wafer  16 . 
     When the wafer  16  floats on the water surface formed by the spray pressure of the ultrapure water  10 , as shown in FIG. 1, the floating wafer  16  first drifts along the water surface toward the direction of the open wall A in the extended member  22 . The wafer is then aligned when both the distance between the guide plates  18  is narrowed, e.g., moved to a narrow limit, as shown in FIG. 2, in response to the guide control signal transmitted from the controller  50 . 
     At this stage, the controller  50  closes the valve  52  to stop spraying the ultrapure water  10  from the source  11 . 
     Then, the aligned wafer  16  is suctioned onto the same vacuum chuck for intraprocessing wafer transfer, e.g., movement within the same equipment, or onto another vacuum chuck for other interprocessing wafer transfer, e.g., for moving to other processing equipment. The separation between the guide plates  18  is widened, e.g., moved to a wide limit, so that the wafer can be freely moved, before the vacuum chuck moves the suctioned wafer. 
     After that, other wafers to be aligned continue to be mounted on the guide plates and the aligning operation is performed for the new wafer. 
     Referring to FIG. 8, a discharge groove  62  can be further formed in the table  14  in order to collect the sprayed ultrapure water and cause it to flow into a desired discharge direction. The discharge direction is indicated by the arrows in FIG.  8 . The ultrapure water flowing along the discharge groove  62  goes into a discharge opening  64  and is stored in an ultrapure water storage container  66  which is installed below the surface of the table  14 . 
     An ultrapure water circulation assembly may also be installed in the table  14  such that the sprayed ultrapure water is discharged out of the table 14 and circulated to the ultrapure water source  11  for reusage. This saves valuable ultrapure water. The ultrapure water circulation assembly may include the discharge groove  62 , a ultrapure water purification apparatus  68 , for purifying the collected ultrapure water, and a ultrapure water supply apparatus  70  for supplying the purified ultrapure water to the ultrapure water source  11 . 
     The present invention provides a method for aligning wafers using the semiconductor wafer aligning system as described with reference to FIGS. 5 and 7. During guide adjustment, protrusions  24  assembled on the guide plates  18  are disassembled and reassembled on the female receptors according to the diameter of the wafer  16 , e.g., by matching the diameter of the wafer  16  among the female receptors  34 ,  32 ,  30 ,  28  previously formed on the guide plates  18 . During wafer mounting, a vacuum chuck for wafer transfer mounts the wafer  16  on the guide plates  18 . During ultrapure water spraying, when the wafer mounting is completed, the sensor  48  senses that a wafer has been mounted, and provides the wafer sensing signal to the controller  50 . Then the controller  50  opens the closed valve  52  to spray the ultrapure water onto the bottom of the wafer  16 . During wafer aligning, while the wafer  16  floats over the water surface formed by the spray pressure of the ultrapure water, the floated wafer first drifts along the water surface in a drift direction set by the open wall A of a part of the extended member  22 . Then, in a second aligning operation, the wafer  16  is pushed along the sides of the wafer circumference by the protrusions of both guide plates  18  while the separation distance of the plates narrows, according to the guide control signal from the controller  50 . At the narrow limit, the guide plates  18  securely hold the wafer  16  in alignment, and the controller  50  closes the valve  52  so as to stop the spray of the ultrapure water. During wafer transfer, the vacuum chuck for wafer transfer suctions the aligned wafer, and when the guide plates  18  are widened so as to free the wafer  16 , the vacuum chuck moves the wafer  16  within the equipment or to another piece of equipment. 
     Using this method, the wafer aligning operation starts only after the wafer is completely mounted. Also, the usage of ultrapure water is minimized because the spray of the ultrapure water starts only after the wafer mounting is confirmed, and the spray stops as soon as the wafer  16  is aligned. 
     In the case of wafer back side grinding, some steps precede mounting the wafer on the semiconductor wafer aligning system of the present invention. First, during laminating, an adhesive tape is applied on the front side of the wafer, which has a pattern formed thereon. The tape protects the front side while the back side grinding occurs. A vacuum chuck for wafer transfer attaches to the wafer and transfers the wafer with its back side upwardly directed, and its front side downwardly directed. Then, after the wafer transfer, wafer back side grinding is performed, wherein the wafer is placed in the correct location, and then, the back side of the wafer is cut or ground using a cutter or a grinder. 
     According to the semiconductor wafer aligning system and method of the present invention as described above, wafer damage is minimized, the generation of particles is prevented, precise aligning of the wafer can be provided, and usage of ultrapure water is minimized. 
     While example embodiments of the present invention have been described in detail above, it should be understood that various changes, substitutions and alterations can be made hereto by one of ordinary skill in the art without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.