Abstract:
A bipolar electrostatic chuck refurbishing process in accordance with an aspect of the present invention does not require physical separation of the two electrodes of the electrostatic chuck. One aspect of the present invention is drawn to method of treating a bipolar electrostatic chuck having a front surface and a back surface and comprising a first electrode disposed at the front surface, a second electrode at the front surface and an anodized layer disposed on the front surface, the first electrode and the second electrode. The method comprises measuring a first parameter of the electrostatic chuck, discarding the electrostatic chuck if the first measured parameter is not within a first predetermined range, cleaning the electrostatic chuck if the first measured parameter is within the first predetermined range, sealing gaps between the first electrode and the second electrode at the front surface with a sealant, without displacing the first electrode relative to the second electrode, eliminating the anodized layer, and disposing a new anodized layer onto the front surface, the first electrode and the second electrode.

Description:
BACKGROUND 
     Bipolar electrostatic chucks are commonly used in semiconductor wafer fabrication. These chucks use electrostatic forces to hold a semiconductor wafer in place during the manufacturing process. Over time, the chucks develop wear from use and their performance degrades. 
     An exemplary electrostatic chuck will be described with reference to  FIGS. 1A-1B  and  FIGS. 2A-2B . 
       FIG. 1A  shows a plan view of front side  102  of exemplary electrostatic chuck  100 . Front side  102  has a mounting ledge  104  and a top surface  106 . Top surface  106  is elevated above mounting ledge  104  as seen in  FIG. 1B . Mounting ledge  104  is used to mount electrostatic chuck  100  during use. Mounting ledge  104  may have mounting holes (not shown) to secure electrostatic chuck  100  during use. Mounting ledge  104  may also be modified in any other known fashion to secure electrostatic chuck  100  during use. 
     Top surface  106  comprises a first electrode portion  108  and a second electrode portion  110 . First electrode portion  108  is further divided into an outer electrode ring  112  and an inner electrode portion  114 . Second electrode portion  110  is a ring of aluminum and is electrically separated from first electrode portion  108  via dielectric epoxy  116 . Dielectric epoxy  116  also retains second electrode portion  110  within first electrode portion  108 . 
     In  FIG. 1B , the uppermost portion of front side  102  is anodized to prevent unwanted oxidation and provide a dielectric surface of specific thickness between electrostatic chuck  100  and a semiconductor wafer when in use. Outer electrode ring  112  and mounting ledge  104  have associated anodized surface  118 , second electrode  110  has associated anodized surface  120 , and inner electrode portion  114  has associated anodized surface  122 . Also seen in  FIG. 1B  is access path  126 , a way of electrically connecting second electrode portion  110  through first electrode portion  108 . 
       FIG. 2A  shows a plan view of back side  200  of electrostatic chuck  100 . There are four sections shown on back side  200 . Two of these sections are anodized, outer anodized portion  208  and inner anodized portion  210 . The other two sections are bare aluminum, outer aluminum portion  206  and inner aluminum portion  204 . Before the anodization process, sections  204  and  206  are prevented from being anodized by coating sections  204  and  206  with a masking substance. After the anodization process, the mask is removed. On inner aluminum portion  204  access path  126  can be seen. 
     In operation, electrostatic chuck  100  uses electrostatic forces to hold a semiconductor wafer to its surface. As shown in  FIG. 1B , first electrode portion  108  and second electrode portion  110  are oppositely charged. First electrode portion  108  is positively charged and second electrode portion  110  is negatively charged. This charge is developed by applying a voltage difference between first electrode portion  108  and second electrode portion  110 . The charges of the two portions of electrostatic chuck  100  induce an opposite charge in a nearby portion of a semiconductor wafer, which creates an electrostatic attraction between the semiconductor wafer and electrostatic chuck  100 . 
     When processing of the semiconductor water is completed, the voltage applied to first electrode portion  108  and second electrode portion  110  may be removed or partially reversed to “dechuck” the wafer. Because of the fragility of the wafer and the precision required in all aspects of the fabrication process, very precise control of the electric fields produced by the electrostatic chuck is required. Accordingly, all parameters of the electrostatic chuck that may affect the electric fields produced, must be maintained within a precise range. Non-limiting examples of these intrinsic characteristics include resistance, inductance, capacitance, and impedance of the electrostatic chuck. 
     Use of electrostatic chuck  100  over time may degrade its performance. The degradation may occur as a result of surface affects that may develop with use, as shown in  FIG. 3 .  FIG. 3  shows a cross-sectional view of an exemplary electrostatic chuck  300 . Electrostatic chuck  300  shows various signs of wear. Electrostatic chuck  300  has front side  302 , which comprises mounting ledge  304  and top surface  306 . Top surface  306  has first electrode portion  312  and second electrode portion  310 . First electrode portion  312  is separated from second electrode portion  310  by a dielectric epoxy  316 . The upper portion of top surface  306  has an anodized layer  318  disposed thereon. 
     Several types of wear may develop on electrostatic chuck  300 . Particulate matter  320  and  322  may stick to top surface  306 . Scratches or marks  324  and  326  may occur in anodized layer  318 . Pits  328  and  330  may also develop in dielectric epoxy layer  316 . Deep scratches  332  may occur in top surface  306  such that the scratch penetrates anodized layer  318  and affects first electrode portion  312 . Particulate matter  320  and  322  may be removed from the surface of electrostatic chuck  300  by known methods of cleaning, but scratches  324  and  326 , pits  328  and  330 , and deep scratches  332  require more intensive repair. 
     When an electrostatic chuck becomes too worn to use, it may be refurbished to repair the wear developed in use. Conventionally, such a process requires separation of the two electrodes  402  and  404  of electrostatic chuck  400  as seen in  FIG. 4 . By separating electrodes  402  and  404 , the entire epoxy layer that separated the two electrodes may be removed and replaced. Disassembly of an electrostatic chuck is very difficult and may cause irreparable damage to the electrostatic chuck. When electrode  404  is removed from the recess in electrode  402 , the epoxy left as residue on both electrodes must be fully removed. This removal may damage one or both of electrodes  402  and  404 . Also, the epoxy is generally removed by means of scraping, which may damage either or both of electrodes  402  and  404 . 
     Further, improper reassembly after such a refurbishing process is also very likely to compromise the working parameters of an electrostatic chuck. Specifically, when second electrode  404  is placed back in recess  406  in electrostatic chuck  400 , it may scratch or be scratched by the edges of recess  406 . A point of contact may also be formed between the wall of recess  406  and second electrode  404 , causing a failure of the refurbishing process. Also, if the upper surface of second electrode  404  is not flush with the upper surface of first electrode  402 , the height mismatch may negatively affect the performance of electrostatic chuck  400  or may even render the resulting device unusable. 
     During reassembly, a new epoxy layer must be added to electrostatic chuck  400  to separate electrodes  402  and  404 . Improper application of this new epoxy layer is very difficult. If there is too little epoxy applied, the upper surface of second electrode  404  will end tip lower than the upper surface of electrode  402 , which may negatively affect the performance of electrostatic chuck  400 . If there is too much epoxy applied, the upper surface of electrode  404  will end tip higher than the upper surface of electrode  402 , which may negatively affect the performance of electrostatic chuck  400 . Also if the reassembly is not carefully controlled, air bubbles may form between electrodes  402  and  404  or the epoxy layer and either electrode  402  or electrode  404 . These air bubbles may negatively affect the performance of electrostatic chuck  400 . 
     In light of the various potential problems associated with the conventional techniques for refurbishing a bipolar electrostatic chuck discussed above, the typical yield of such techniques is only approximately 30%. 
     What is needed is a bipolar electrostatic chuck refurbishing process that is less likely to damage the bipolar electrostatic chuck. 
     What is additionally needed is a bipolar electrostatic chuck refurbishing process that provides a yield greater than 30%. 
     BRIEF SUMMARY 
     It is an object of the present invention to provide a bipolar electrostatic chuck refurbishing process that is less likely to damage the bipolar electrostatic chuck. 
     It is another object of the present invention to provide a bipolar electrostatic chuck refurbishing process that does not require physically separating the two electrodes of the bipolar electrostatic chuck. 
     It is another object of the present invention to provide a bipolar electrostatic chuck refurbishing process that provides a yield of close to 100%. 
     One aspect of the present invention is drawn to method of treating a bipolar electrostatic chuck having a front surface and a back surface and comprising a first electrode disposed at the front surface, a second electrode at the front surface and an anodized layer disposed on the front surface, the first electrode and the second electrode. The method comprises measuring a first parameter of the electrostatic chuck, discarding the electrostatic chuck if the first measured parameter is not within a first predetermined range, cleaning the electrostatic chuck if the first measured parameter is within the first predetermined range, sealing gaps between the first electrode and the second electrode at the front surface with a sealant, without displacing the first electrode relative to the second electrode, eliminating the anodized layer; and disposing a new anodized layer onto the front surface, the first electrode and the second electrode. Measuring the first parameter of the electrostatic chuck includes measuring a resistance. Measuring a resistance includes measuring a resistance between the first electrode and the second electrode. Measuring a resistance includes measuring a resistance between the back surface and one of the first electrode and the second electrode. Measuring a resistance between the back surface and one of the first electrode and the second electrode includes measuring a resistance between the back surface and the first electrode. Measuring a resistance between the surface and one of the first electrode and the second electrode includes measuring a resistance between the back surface and the second electrode. Measuring the first parameter of the electrostatic chuck includes measuring a capacitance. Measuring a capacitance includes measuring, a capacitance between the first electrode and the second electrode. Measuring a capacitance includes measuring a capacitance between the back surface and one of the first electrode and the second electrode. Measuring a capacitance between the back surface and one of the first electrode and the second electrode includes measuring a capacitance between the back surface and the first electrode. Measuring a capacitance between the back surface and one of the first electrode and the second electrode includes measuring a capacitance between the back surface and the second electrode. Measuring a first parameter of the electrostatic chuck includes measuring an impedance. Measuring an impedance includes measuring an impedance between the first electrode and the second electrode. Measuring an impedance includes measuring an impedance between the back surface and one of the first electrode and the second electrode. Measuring an impedance between the back surface and one of the first electrode and the second electrode includes measuring an impedance between the back surface and the first electrode. Measuring an impedance between the back surface and one of the first electrode and the second electrode includes measuring an impedance between the back surface and the second electrode. 
     Additional objects, advantages and novel features of the invention are set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. 
    
    
     
       BRIEF SUMMARY OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and form a part of the specification, illustrate an exemplary embodiment of the present invention and, together with the description, serve to explain the principles of the invention. In the drawings: 
         FIG. 1A  illustrates a plan view of the front side of an exemplary electrostatic chuck; 
         FIG. 1B  illustrates a cross-sectional view of the exemplary electrostatic chuck of  FIG. 1A  along line x-x; 
         FIG. 2A  illustrates a plan view of the back side of an exemplary electrostatic chuck; 
         FIG. 2B  illustrates a cross-sectional view of the exemplary electrostatic chuck of  FIG. 2A  along line y-y; 
         FIG. 3  illustrates a cross-sectional view of a portion of an exemplary electrostatic chuck showing wear from use: 
         FIG. 4  illustrates a conventional method for refurbishing an exemplary electrostatic chuck; 
         FIGS. 5A-5C  illustrate a logic flow diagram detailing an exemplary refurbishing process in accordance with the present invention; 
         FIG. 6  illustrates an exemplary method for sealing gaps between electrodes; and 
         FIG. 7  illustrates an exemplary process for removal of the anodized surface and reanodization of an exemplary electrostatic chuck. 
     
    
    
     DETAILED DESCRIPTION 
     An exemplary process for refurbishing bipolar electrostatic chucks will be described with reference to  FIGS. 1-3  and  5 - 7 . One of the beneficial aspects that differentiate the present invention over conventional bipolar electrostatic chucks refurbishing techniques is that the present invention does not separate the two electrodes in the refurbishing process. Another feature of the following exemplary process is a plurality of quality checks. The quality checks provide a way of greatly increasing the probability of the refurbishing process resulting in a working electrostatic chuck. 
     The exemplary process begins with the receiving of electrostatic chuck  100  (S 500 ) as seen in  FIG. 5A . Next, electrostatic chuck  100  is given an initial inspection (S 502 ) for physical defects including but not limited to cracks, dents, and deep scratches. One example of such damage would be deep scratch  332  on electrostatic chuck  300  as shown in  FIG. 3 . Resurfacing the aluminum of electrostatic chuck  300  may not be able to repair such a deep scratch, or similar defect, which would result in a failure of the refurbishing process. 
     After determining whether chuck  100  passes this pre-inspection (S 504 ), failure may result in returning chuck  100  to the customer (S 506 ) and passing of the pre-inspection may lead to an initial inspection of one or more parameters of electrostatic chuck  100  (S 508 ). Parameters that may be measured include, but are not limited to, resistance, capacitance, inductance, and impedance. These measurements may be measured between front side  102  and back side  200  of electrostatic chuck  100 , first electrode  108  and second electrode  110 , or any other set of points on electrostatic chuck  100 . The measured values for these parameters must be within a predetermined acceptable range. If the value is much higher or much lower, it may indicate the presence of various types of defects in electrostatic chuck  100  that cannot be repaired by the refurbishing process, including but not limited to a short circuit between first electrode  108  and second electrode  110 . 
     The measured values for the parameters of electrostatic chuck  100  are compared to a known baseline value, said value being known to be an acceptable for the parameter measured. The known baseline value may be obtained, for example, from manufacturer specifications or taking electrostatic chucks, known to be acceptable in performance, and measuring the parameter. A further method measures values the parameter using a plurality of electrostatic chucks, for example  100 , to create a range of data for comparison. This range of data may be used to create a bell curve of values and the acceptable value range obtained via this method would be values that fall within a specified number of standard deviations from the mean. 
     After determining whether chuck  100  passes this inspection (S 510 ), failure may result in returning chuck  100  to the customer (S 506 ) and passing may lead to decontamination and cleaning (S 512 ). Any known method of decontamination and cleaning may be used. In one exemplary embodiment, this procedure includes wiping with and soaking in isopropyl alcohol, an ultrasonic cleaning, and an oven baking. This cleaning process removes dirt particles such as particles  320  and  322  as shown in  FIG. 3 . If dirt particles  320  and  322  were not cleaned off, they may affect at least one of the physical parameters of electrostatic chuck  100 , including but not limited to resistance, capacitance, inductance, and impedance. Particles  320  and  322  may also interfere with other steps of the refurbishing process including reanodization of the surface (S 540 ). 
     Following step S 512 , electrostatic chuck  100  may be given a quality check (S 514 ). This quality check (S 514 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 514 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to the next step of scaling the gaps between electrodes (S 516 ). 
     As discussed previously, gaps in the sealant between electrodes of an electrostatic chuck may occur from use. A portion of front side  102  of an exemplary electrostatic chuck  100  is shown in  FIG. 6 . Outer electrode ring  112  and second electrode portion  110  are electrically separated by dielectric epoxy  116 , a portion of which has worn down over time to create gap  602 . Contrary to conventional techniques, the present invention does not separate the electrodes  108  and  110  of electrostatic chuck  100  to repair damage to front side  102 . Therefore, the present invention does not risk further damage to electrostatic chuck  100  that may be caused by disassembling and reassembling the electrostatic chuck. In one exemplary embodiment of the present invention, a microscope is used by a worker to guide syringe  604  into gap  602 . Syringe  604  is filled with epoxy  608  which is used to rill gap  602 . Other known methods may be used to seal gap  602  in other embodiments, including but not limited to an automated system. As discussed above, in accordance with the present invention, electrodes  108  and  110  are not separated to repair damage to electrostatic chuck  100 . As a result, the present invention does not risk damage to electrodes  108  and  110  that may arise due to disassembly and reassembly of electrostatic chuck  100 . 
     Returning to  FIG. 5A  and following step S 516 , electrostatic chuck  100  may be given a quality check (S 518 ). This quality check (S 518 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 518 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to masking of back side  200  of electrostatic chuck  100  (S 524 ) as continued in  FIG. 5B  along point A. 
     Returning to  FIG. 2A , bare aluminum sections  204  and  206  are coated with a known masking substance. Anodized sections  208  and  210  are not coated with the masking substance and will therefore be subjected to the following processes that etch and anodize any unmasked surfaces of electrostatic chuck  100 . 
     Following step S 524 , electrostatic chuck  100  may be given a quality check (S 526 ). Passing the check may lead to chemical stripping and cleaning of electrostatic chuck  100  (S 528 ). This quality check (S 526 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 526 ) may result in returning chuck  100  to the customer (S 506 ) by returning to  FIG. 5A  along point B. 
       FIG. 7  shows a blown-up cross-sectional portion of electrostatic chuck  100 . Section  700  shows a thin anodized layer  704  over an aluminum base  702 . Anodized layer  704  shows some damage or wear. Any known method may be used to strip the anodized surface from the raw aluminum. Once the anodized layer has been removed, the surface is cleaned using any known cleaning method. 
     Returning to  FIG. 5B  and following step S 528 , electrostatic chuck  100  may be given a quality check (S 530 ). This quality check (S 530 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 530 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to resurfacing of the bare aluminum (S 532 ). This resurfacing will allow for a more even and controlled reanodization of the surface. 
     Following step S 532 , electrostatic chuck  100  may be given a quality check (S 534 ). This quality check (S 534 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 534 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to a precision cleaning of electrostatic chuck  100  (S 536 ). Any known non-destructive method may be used to clean the surface. 
     Following step S 536 , electrostatic chuck  100  may be given a quality check (S 538 ). This quality check (S 538 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 538 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to anodization of the aluminum surface to develop a new anodized layer (S 540 ). This process is carefully monitored to obtain a precise predetermined thickness of new anodized layer  706  atop aluminum  702 . New anodized layer  706  returns the original operational parameters of electrostatic chuck  100 . 
     Returning to  FIG. 5B  and following step S 540 , electrostatic chuck  100  may be given a quality check (S 546 ) following point C into  FIG. 5C . This quality check (S 546 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 546 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to a final cleaning of electrostatic chuck  100  (S 548 ). The cleaning is accomplished by any known method, non-limiting examples of which include ultrasonic cleaning. 
     After step S 548 , electrostatic chuck  100  may be given a quality check (S 550 ). This quality check (S 550 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. Failure of quality check (S 550 ) may result in returning chuck  100  to the customer (S 506 ) following point D into  FIG. 5B . Passing the check may lead to an oven bake (S 552 ) to evaporate any moisture remaining from the cleaning process. 
     Following step S 552 , electrostatic chuck  100  may be given a quality check (S 554 ). This quality check (S 554 ) may measure a value of a parameter of electrostatic chuck  100 , as discussed above. 
     Failure of quality check (S 554 ) may result in returning chuck  100  to the customer (S 506 ) and passing the check may lead to a post-inspection of one or more additional parameters of electrostatic chuck  100  (S 556 ). Parameters that may be measured include, but are not limited to, resistance, capacitance, inductance, and impedance. These measurements may be measured between front side  102  and back side  200  of electrostatic chuck  100 , first electrode  108  and second electrode  110 , or any other set of points on electrostatic chuck  100 . The measured values for these parameters must be within a predetermined acceptable range, else electrostatic chuck  100  has failed the refurbishing process. 
     After the post-inspection (S 556 ), electrostatic chuck  100  has finished the refurbishing process (S 558 ) and may be packaged and resold. 
     The refurbishing-process described above includes a plurality of quality checks. Each quality check is based on at least one parameter of electrostatic chuck  100 . The parameter is compared to a predetermined value known from manufacturer specifications or known from previous measurements of electrostatic chucks known to be acceptable in their performance after undergoing the refurbishing process. These quality checks are performed without disassembly of electrostatic chuck  100 . 
     During the refurbishing process described above, electrode  108  is not separated from electrode  110  for repair. Therefore, the refurbishing process does not risk damage to electrodes  108  and  110  as a result of disassembly or reassembly of electrostatic chuck  100  during the refurbishing process. Further, methods in accordance with the present invention provide close to 100% yield of acceptable refurbished bipolar electrostatic chucks because the processes outlined of cleaning the electrostatic chuck if the first measured parameter is within the first predetermined range; sealing gaps between the first electrode and the second electrode at the front surface with a sealant, without displacing the first electrode relative to the second electrode; eliminating the anodized layer; and disposing a new anodized layer onto the front surface, the first electrode and the second electrode have proven to return electrostatic chucks to their original form almost 100% of the time. The only times that electrostatic chucks are not returned to their original form are those when the quality checks fail. 
     The foregoing description of various preferred embodiments of the invention have been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments, as described above, were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.