Abstract:
The present invention provides a method of cleaning a wafer. The method comprises suspending the wafer beneath a vacuum chuck. The vacuum chuck contains an acoustic wave emitter. The acoustic wave emitter is positioned within the vacuum chuck to prevent the acoustic wave emitter from contacting the surface of the wafer. The method further comprises applying acoustic waves to the wafer.

Description:
TECHNICAL FIELD OF INVENTION 
     The present invention relates generally to the field of wafer production and, more particularly, to an apparatus and methods for cleaning a wafer. 
     BACKGROUND 
     The problem of wafer contamination has existed since the birth of wafer manufacturing. The yield on fully processed silicon wafers is inversely related to the defect density of the wafers. One way to decrease defect density is to use cleaning techniques that remove particle contaminants. 
     A problem faced by those working in the wafer manufacturing industry, however is to find an effective way to remove particles from wafers with efficiency and without damage to the wafers. Small particles are difficult to remove from wafers, for example, because, of the strong electrostatic forces between the particles and the substrate. 
     Modern wafer manufacturing facilities use stringent contamination control protocols. These protocols can include the use of clean room suits, latex gloves, highly purified ventilation systems, and the like. In combination with these protocols, modern manufacturing facilities use various methods of cleaning wafers. The most common methods used to clean contaminated wafers usually involve pressurized water jet scrubs, rotating wafer scrubbers, wet chemical baths and rinses and similar systems. These processes, however, are prone to damaging the wafer. Additionally, the chemical processes have inherent dangers associated with the use of chemicals such as sulfuric acid, ammonium hydroxide, isopropyl alcohol, and the like. 
     SUMMARY OF THE INVENTION 
     Other features and advantages of the present invention shall be apparent to those of ordinary skill in the art upon reference to the following detailed description taken in conjunction with the accompanying drawings. 
     The present invention-provides a method of cleaning a wafer. The method comprises suspending the wafer beneath a vacuum chuck. The vacuum chuck contains an acoustic wave emitter. The acoustic wave emitter is positioned within the vacuum chuck to prevent the acoustic wave emitter from contacting the surface of the wafer. The method further comprises applying acoustic waves to the wafer. 
     The present invention further provides a wafer cleaning apparatus. The apparatus can include a vacuum chuck and an acoustic wave emitter. The acoustic wave emitter can be contained within the vacuum chuck and positioned to prevent the acoustic wave emitter from contacting the surface of the wafer. 
     The present invention also provides a method of cleaning a wafer. The method can include the steps of suspending the wafer beneath a vacuum chuck. The vacuum chuck can contain an acoustic wave emitter. The acoustic wave emitter can be positioned within the vacuum chuck to prevent the acoustic wave emitter from contacting the surface of the wafer. The method can further include applying acoustic waves to the wafer. Additionally, the method can include directing a stream of cleaning liquid at a surface of the wafer, the stream of cleaning liquid having an angle of incidence of less than about 10 degrees. 
     The present invention can further provide a method of cleaning a wafer. The method can include the steps of mounting the wafer to a vacuum chuck. The vacuum chuck can contain an acoustic wave emitter. The acoustic wave emitter can be positioned within the vacuum chuck to prevent the acoustic wave emitter from contacting the surface of the wafer. The method can further include applying acoustic waves to the wafer. 
     The present invention may also provide a method of cleaning a wafer. The method can include the steps of mounting the wafer to a vacuum chuck. The vacuum chuck can contain an acoustic wave emitter. The acoustic wave emitter can be positioned within the vacuum chuck to prevent the acoustic wave emitter from contacting the surface of the wafer. The method can further include applying acoustic waves to the wafer. Additionally, the method can include directing a stream of water at a surface of the wafer, the stream of water having an angle of incidence of less than about 10 degrees. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures in which corresponding numerals in the different figures refer to corresponding parts and in which: 
     FIG. 1 is a schematic view of a typical embodiment of an apparatus of the present invention; 
     FIG. 2A is a schematic view, partially sectioned, of another embodiment of an apparatus of the present invention; 
     FIG.  2 B,is a view taken from line  2 B— 2 B of FIG. 2A; 
     FIG. 2C is a view taken from line  2 C— 2 C of FIG. 2A; and 
     FIG. 3 is a schematic view similar to FIG.  1  and also showing the liquid spray part of wafer cleaning apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that may be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention. 
     Referring now to FIG. 1, an apparatus of the present invention is shown as  10 . The apparatus  10  can include a vacuum chuck  15 . A vacuum chuck is a common device for holding a wafer, such as a silicon wafer, patterned wafer, or semiconductor wafer in place while the wafer is being spun and cleaned. A spindle  25  can be attached to the vacuum chuck  15 . The spindle  25  allows the vacuum chuck to be rotated 360° upon its center axis. Contained within the spindle  25  can be power lines, power supply wires and the internal vacuum line  20 . The internal vacuum line  20  allows the vacuum chuck  15  to form a vacuum seal between itself and the wafer  45  during the cleaning process. 
     An electric motor  30  can be attached to the spindle  25 . The electric motor  30  powers the spindle  25  and enables the vacuum chuck  15  to be rotated 360 degrees around its axis. A speed controller  35  can be attached to the electric motor  30 . The speed controller  35  allows the spindle  25  to be rotated at varying speeds. By allowing for varying cleaning speeds, a more efficient cleaning process can be attained. 
     An acoustic wave emitter  50  can be contained within the vacuum chuck  15 . The acoustic wave emitter  50  can lie beneath the surface of the vacuum chuck  15 . The placement of the acoustic wave emitter  50  can be such that the acoustic wave emitter  50  will not directly contact the surface of the wafer  45 . The acoustic wave emitter can be any commonly used piezoelectric element. An acoustic controller  55  can be attached to the acoustic wave emitter  50 . The acoustic controller  55  can automatically vary the frequency of the acoustic waves produced by the acoustic wave emitter  50 . This allows, for instance, during one cleaning cycle the frequency of the acoustic waves produced by the acoustic wave emitter  50  to vary, for example, from 0.1 MHz to 190 MHz. By allowing the acoustic wave emitter  50  to vary the frequency of the acoustic waves, maximum cleaning efficiency can be achieved. A greater cleaning efficiency occurs because some particle contaminants removed from the surface of the wafer  45  may vibrate resonately at a lower frequency and some may vibrate resonately at a higher frequency. 
     The apparatus  10  depicted in FIG. 1 shows the wafer  45  suspended beneath the vacuum chuck  15 . It will be appreciated, however, that the apparatus  10  can be positioned such that the wafer  45  is positioned above the vacuum chuck  15 . By positioning the wafer  45  beneath the vacuum chuck  15 , the apparatus  10  allows gravity to assist in the removal of particles from the wafer  45 . 
     The assembly of the vacuum chuck  15  and the acoustic wave emitter  50  can be seen more easily in FIG.  2 . As depicted in FIG. 2A, the acoustic wave emitter  50  can be contained fully with the vacuum chuck  15 . The spindle can be attached to upper surface  16  of the vacuum chuck  15 . The vacuum chuck  15  can include vacuum slots  17 . The vacuum slots  17  allow the vacuum chuck  15  to form a suction between the vacuum chuck  15  and the wafer. The suction holds the wafer in place during the cleaning process. It should be noted that the vacuum slots can be positioned to avoid going through the acoustic wave emitter  50 . 
     The vacuum chuck  15  can have openings  19  on the lower surface  18  of the vacuum chuck  15 . The openings  19 , as shown in FIG. 2B, allow the suction to form between the wafer and the vacuum chuck  15 . As shown in FIG. 2C, the spindle  25  can contain vacuum tubes  26  and power Lines  28 . The vacuum tubes  26  allow the suction to be present in the vacuum chuck  15 . The power lines  28  enable the acoustic wave emitter  50  to generate the appropriate acoustic waves. 
     Referring now to FIG. 3, another embodiment of the apparatus of the present invention is shown. The apparatus can contain the same components as depicted in FIG.  1 . As shown FIG. 3, however, a spray nozzle  60  can be positioned beneath the wafer  45 . The spray nozzle  60  can be attached to a rod  65 . The rod  65  can be attached to a roller shaft  70 . By attaching the spray nozzle  60  to the rod  65  and roller shaft  70 , the spray nozzle  60  can be pivoted from side to side. The motion caused by the roller shaft  70  allows the spray nozzle  60  to spray all points on the surface of the wafer  45 . The spray nozzle  60  can be positioned such that the angle of incidence of the spray from the nozzle with the surface of the wafer  45  would be less than about 10 degrees. It will be appreciated, however, that larger or smaller angles may be used depending upon the pattern on the wafer and the particles to be removed. Likewise, it will be appreciated that the spray nozzle  60  can be operated in a manner where the angle of incidence between the spray nozzle  60  and the surface of the wafer  45  could be automatically changed during the cleaning process. Thus, for example, during one cleaning cycle, the angle of the spray from the spray nozzle could vary between about 5 degrees to about 20 degrees. 
     A pressure control valve  75  can be attached to the spray nozzle  60 . The pressure control valve  75  controls the strength of the spray produced by the spray nozzle  60 . The pressure control valve  75  can contain a liquid reservoir  80 . The liquid reservoir  80  can hold either water or another suitable cleaning liquid used, for particle removal within the wafer industry. 
     Operator of the present invention may be understood by the following description. Referring to FIG. 3, a wafer  45  can be positioned beneath the vacuum chuck  15 . As mentioned previously, however, the wafer  45  can be positioned such that it lies on top of the vacuum chuck  15  rather than being suspended beneath the vacuum chuck. Such a configuration can be accomplished by rotating the apparatus, as depicted in FIG. 3, 180 degrees. 
     After positioning the wafer  45  beneath the vacuum chuck  15 , the vacuum line  20  can be energized causing a vacuum to form between the vacuum chuck  15  and the wafer  45 . The vacuum generated by the vacuum line causes the wafer  45  to be pulled into the vacuum chuck  40 , thereby holding the wafer  45  firmly in place. 
     After the wafer  45  has been properly positioned, the electric motor  30  can be engaged. The electric motor  30  allows the spindle  25  to rotate in a counterclockwise or clockwise direction. The speed with which the spindle  25  can rotate depends upon the programming of the speed controller  35 . By incorporating a speed controller as part of the invention, the speed with which the spindle  25  and the wafer  45  can be rotated, can vary. 
     After engaging the electric motor  30  causing the wafer to rotate, the acoustic wave emitter  50  can be energized. The acoustic wave emitter  50  then begins to transmit acoustic energy throughout the wafer  45 . The frequency with which the acoustic energy can be transmitted can vary. The variance can be accomplished by energizing the acoustic controller  55 . The acoustic controller  55  will automatically vary the acoustic waves being transmitted by the acoustic wave emitter  50  during any one cleaning cycle. By enabling the acoustic wave emitter  50  to vary the frequency of the waves it transmits, the invention obtains maximum cleaning efficiency. For example, during one cleaning cycle, the frequency could be programmed to vary from 0.1 MHz to 190 MHz. 
     Once the acoustic wave emitter  50  has been energized and the wafer  45  experiences the acoustic cleaning process, then the spray nozzle  60  can be engaged. The spray nozzle  60  can project a sharp stream of liquid onto the surface of the wafer  45 . By projecting the sharp stream of liquid onto the surface of the wafer  45 , the invention allows for maximum cleaning potential. Although gravity and the acoustic waves may cause most, if not all, the particles to be removed from the surface of the wafer  45 , there may be a need to assist in the removal of those particles with the use of a stream of cleaning liquid. It will be appreciated, that the smaller the angle that the stream is incident to the surface of the wafer  45 , the more efficient the cleaning process becomes. 
     Once the spray nozzle  60  has been engaged, the roller shaft  70  begins to rotate the rod  65  attached to the spray nozzle  60 . The rotation of the rod  65  causes the spray nozzle  60  to transgress the surface of the wafer  45 . As the acoustic waves dislodge the contaminants from the wafer  45 , the spray from the spray nozzle  60  assists in removing the contaminants and debris. Moreover, as the wafer  45  rotates all portions of the surface of the wafer  45  become exposed to both the acoustic wave energy and the spray stream from the spray nozzle. 
     The sequence described above can be varied to some extent without effecting the cleaning process. It should be noted that effective cleaning action is caused primarily by the combination of the variants in acoustic waves frequency applied throughout the wafer and the motion of the wafer. Due to the configuration of the apparatus, manual contact with the work pieces is avoided, thus providing superior results and precluding surface scratches and other materials to be introduced upon the delicate surface of the wafer, which is detrimental when the wafer becomes part of a delicate electronic circuit product. 
     While this invention has been described in reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Various modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to persons skilled in the art upon reference to the description. It is therefore intended that the appended claims encompass any such modifications or embodiments.