Abstract:
A method is provided for treating a bipolar ESC having a front surface and a back surface, the front surface including an anodized layer. The method includes eliminating the anodized layer, disposing a new anodized layer onto the front surface, and treating the new anodized layer with water to seal the new anodized layer.

Description:
BACKGROUND 
       [0001]    Bipolar electrostatic chucks (ESCs or ESC for singular) are commonly used in semiconductor wafer fabrication. These ESCs 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. 
         [0002]    Methods for refurbishing ESCs have been developed, however the known anodization process for refurbishment may present consistency issues associated with the dielectric constant for an anodized layer. 
         [0003]    What is needed is a method for ESC refurbishment enabling fabrication of an anodized layer with a consistent dielectric constant. 
       BRIEF SUMMARY 
       [0004]    The present invention provides a method for refurbishing an ESC with an anodized layer performed by application of a deionized water seal for supplying an anodized layer. 
         [0005]    In accordance with an aspect of the present invention, a method is provided for treating a bipolar ESC having a front surface and a back surface, the front surface including an anodized layer. The method includes eliminating the anodized layer, disposing a new anodized layer onto the front surface, and treating the new anodized layer with water to seal the new anodized layer. 
         [0006]    Additional 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 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 
         [0007]    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: 
           [0008]      FIG. 1  illustrates a cross-sectional view of an exemplary ESC, in accordance with an aspect of the present invention; 
           [0009]      FIG. 2  illustrates a cross-sectional view of an exemplary partial ESC as described with reference to  FIG. 1  where a layer portion has been removed, in accordance with an aspect of the present invention; 
           [0010]      FIG. 3  illustrates a cross-sectional view of an example partially refurbished ESC wherein a defective or deformed layer portion has been replaced with a new layer portion, in accordance with an aspect of the present invention; 
           [0011]      FIG. 4  illustrates a cross-sectional view of an example ESC, wherein a defective or deformed layer portion has been replaced with a functional layer portion, in accordance with an aspect of the present invention; and 
           [0012]      FIG. 5  illustrates an example method for refurbishing a semiconductor wafer, in accordance with an aspect of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    In accordance with aspects of the present invention, an anodized layer is removed from an ESC. A replacement anodized layer is then added to ESC. The new anodized layer is treated with hot water to eliminate pores therein. The hot water treated anodized layer is more resistant to corrosion and maintains consistent electromagnetic properties for longer periods than anodized layers that are not treated with hot water. 
         [0014]      FIG. 1  illustrates a cross-sectional view of a portion of an example ESC  100 , to be refurbished in accordance with an aspect of the present invention. 
         [0015]    As seen in the figure, ESC  100  includes an electrode  102  and an anodized layer  104 . ESC  100  is used to hold a semiconductor wafer (not shown) in place during the manufacturing process via electrostatic attraction between the semiconductor wafer and ESC  100 . Electrode  102  may be positively or negatively charged. The charge applied to electrode  102  is developed by applying a voltage difference between electrode  102  and a second electrode (not shown). Anodized layer  104  prevents unwanted oxidation of electrode  102 . 
         [0016]    Anodized layer  104  includes a porous layer  106  and a barrier layer  108 . As a non-limiting example, porous layer  106  and barrier layer  108  may be formed of Al 2 O 3 . Anodized layer  104  resides on a top surface  110  of electrode  102 . Barrier layer  108  resides between electrode  102  and porous layer  106  and resides on top surface  110 . Typically, the thickness of barrier layer  108  is smaller than the thickness of porous layer  106 . Furthermore, in general, the density of barrier layer  108  is greater than that of porous layer  106 . 
         [0017]    Anodizing an aluminum alloy such as Al 2 O 3  produces a porous layer (e.g. porous layer  106 ) containing a high density of microscopic pores with a sampling denoted as a pore  122 . As a result of the pores, the anodized aluminum alloy reacts readily or oxidizes with oxygen in air resulting in undesirable oxidation, i.e., corrosion. The resulting oxidation varies throughout the volume of the material producing variable electromagnetic properties (i.e. permittivity or ∈ 0  associated with electrical properties and permeability or μ 0  associated with magnetic properties) for the material. The variable electromagnetic properties results in inconsistent operation and negatively affects the performance of an ESC for fabricating semiconductor wafers. 
         [0018]    An ESC is used to hold wafers via an electrostatic attraction also known as chucking a wafer. Furthermore, wafers are released from an ESC via an electrostatic repulsion also known as de-chucking. As the electromagnetic properties (i.e. ∈ 0  and μ 0 ) of an ESC begin to vary as a result of unwanted oxidation, the parameters associated with chucking and de-chucking a wafer also vary. Furthermore, due to the precision required for fabricating a semiconductor, the efficiency, effectiveness and ability to chuck and de-chuck a wafer is negatively affected as a result of unwanted oxidation and the undesirable variance associated with the electromagnetic properties distributed throughout the volume of Al 2 O 3 . 
         [0019]    Furthermore, ESC  100  will wear over time by developing cracks, dents, pits, scratches and deep scratches. The degradation may occur as a result of surface conditions that may develop with use. Due to the physical defects associated with ESC  100 , the processing of semiconductor wafers may be not be performed correctly, may not be performed sufficiently and/or may not be performed efficiently. 
         [0020]    Several types of wear may develop for ESC  100 . Particulate matter may stick to a top surface  111 , with example particulate matter illustrated as a particulate matter  112  and a particulate matter  120 . Scratches or marks may occur in anodized layer  104  with example scratches illustrated as a scratch  114 , a scratch  116  and a scratch  118 . 
         [0021]    A wafer handling system, which uses ESC  100 , is operated under very precise conditions. When the electromagnetic properties of ESC  100  change, the efficiency of the operation of the entire wafer handling system degrades. As such, it is important to maintain the electromagnetic properties of ESC  100 . In order to maintain the electromagnetic properties of ESC  100 , the issues resulting from operational wear over time should be addressed. Particulate matter  112  and  120  may be removed from the surface of ESC  100  by known methods, however scratches  114 ,  116  and  118  require more intensive repair. 
         [0022]    ESC  100  with a damaged anodized layer  104  may be refurbished in order to restore its electromagnetic properties. The process of refurbishment of ESC  100  includes removal and replacement of anodized layer  104 . 
         [0023]      FIG. 1  illustrates a cross-sectional view of ESC  100 , wherein anodized layer  104  has become physically damages during operation. Anodized layer  104  may be removed and replaced in order to restore the electromagnetic properties of ESC  100 . Removal and replacement of an anodized layer will be described with reference to  FIGS. 2-3 . 
         [0024]      FIG. 2  illustrates a cross-sectional view of ESC  100  of  FIG. 1 , wherein anodized layer  104  has been removed. Removal of anodized layer  104  may be performed by any known method, non-limiting examples of which include lathing (stripping). 
         [0025]    Anodized layer  104  may be accurately stripped with a controlled resolution of 30 seconds or less, followed by deionized water rinsing and measurement. Stripping is controlled in order to cease material removal process when previous anodic material has been removed. Top surface  110  is then polished to remove 1 to 2 mils of electrode  102 . With the anodized layer removed, top surface  110  of electrode  102  is ready to receive a new anodized layer. 
         [0026]      FIG. 3  illustrates a cross-sectional view of an example partially refurbished ESC  300 , wherein a defective anodized layer has been replaced with a new anodized layer, in accordance with an aspect of the present invention. 
         [0027]    Partially refurbished ESC  300  includes electrode  102 , a barrier layer  302  and a layer  308 . The term “partially” is used in partially refurbished ESC  300  because the ESC will not be completely refurbished, in accordance with aspects of the present invention, until the new anodized layer is treated with hot water. This will be described later. 
         [0028]    Layer  308  forms on top of barrier layer  302 . Barrier layer  302  is formed with a thickness  304  and layer  308  is formed with a thickness  312 . As a non-limiting example, layer  308  may be fabricated with Al 2 O 3 . Layer  308  has been formed with thickness  312  above a top surface  306 . 
         [0029]    Barrier layer  302  and layer  308  form a layer portion  310 . 
         [0030]    When forming layer portion  310 , barrier layer  302  and layer  308  form simultaneously. Since the density of barrier layer  302  is greater than layer  308 , a thickness  408  of barrier layer  302  increases at a faster rate than thickness  304  of barrier layer  302 . The layer forming process initiates with zero electrical current and the current is increased. As the current is increased, the voltage on the surface of the newly forming layer portion  310  begins to increase. Surface nucleation operates to aid in generation of layer portion  310 . Surface nucleation is a process where components in a solution precipitate out and form nuclei that attracted additional precipitate. 
         [0031]    To maintain precise quality, many fabrication parameters may be controlled. In a non-limiting example, with a voltage potential of 75 Volts, thickness  304  is approximately 750 Angstroms to 800 Angstroms. Furthermore, the pH for application of layer portion  310  is controlled, wherein in an example embodiment, the pH is maintained between 5.6 and 6.2. Still further, the temperate for application of layer portion  310  is controlled, wherein in an example embodiment, the temperature is maintained between 96°-99° Celsius. With these example parameters, approximately 1 mil of layer portion  310  is formed fro every 75 minutes. Accordingly, with these parameters, the time for forming 2 mils of layer portion  310  is approximately 150 minutes. 
         [0032]    Following formation of layer portion  310 , an ESC may function to process wafers in accordance with conventional systems. However, unwanted effects associated with oxidation as described with reference to  FIG. 1  will be experienced as a result of the porous nature of layer  308 . To prevent oxidation and the unwanted negative performance associated with the oxidation, layer  308  is treated in accordance with aspects of the present invention as discussed below with reference to  FIG. 4 . 
         [0033]      FIG. 4  illustrates a cross-sectional view of an example ESC  400 , in accordance with an aspect of the present invention. 
         [0034]    Refurbished ESC  400  includes electrode  102 , barrier layer  302  and a layer  402 . 
         [0035]    Layer  402  has been formed by treating layer  308  ( FIG. 3 ) with a water seal. As a non-limiting example, a water seal may be performed via application of hot deionized water. 
         [0036]    Deionized water is produced by processing water to the point where the water is free of ions. A common method for producing deionized water is to pass a relatively pure source of water through a reverse osmosis filter. Reverse osmosis filtering may be performed by applying pressure to the water when it is located on one side of a selective membrane, resulting in solute being retained on pressurized side of membrane with deionized water passing to depressurized side of the membrane. The membrane allows small particles to pass, but larger particles, such as ions, to not pass. 
         [0037]    Layer  402  is created via a reaction of hot deionized water with the porous Al 2 O 3  of layer  308  ( FIG. 3 ). The reaction of the Al 2 O 3  with the deionized water creates AlO(OH). In some embodiments, the AlO(OH) takes the form of boehmite. 
         [0038]    Layer  402  with thickness  408  and includes properties of high corrosion resistance for preventing corrosion and/or oxidation. Furthermore, layer  402  includes a consistent dielectric constant for avoiding failures associated with chucking or de-chucking. As a non-limiting example, a dielectric constant of 10 may be attributed to layer  402 . 
         [0039]    Pores (e.g. pore  316 ) as described with reference to  FIG. 3  (which have the potential to cause unwanted oxidation) have been removed as illustrated by layer  402  of  FIG. 4 . In particular, the pores have been removed via treatment of the Al 2 O 3  with hot water. More specifically, the Al 2 O 3  reacts with the hot water and is converted into AlO(OH), as illustrated in  FIG. 4 . The AlO(OH) as illustrated in  FIG. 4  is much less porous than the Al 2 O 3  of  FIG. 3 , and as a result, is much less susceptible to unwanted oxidation. 
         [0040]    The AlO(OH) of  FIG. 4  retains consistent electromagnetic properties for a much longer period of time than the Al 2 O 3  described with reference to  FIG. 1 . 
         [0041]    Although the electromagnetic properties (i.e. those associated with ∈ 0  and μ 0 ) of the AlO(OH) layer of  FIG. 4  are slightly different than the electromagnetic properties of Al 2 O 3  of  FIG. 1 , refurbished ESC  400  adequately performs chucking and de-chucking operations. Furthermore, refurbished ESC  400  performs chucking and de-chucking for a longer period of time and operates more efficiently over time as compared to ESC  100 , which is more susceptible to oxidation. 
         [0042]    Thickness  408  for layer  402  is greater than the thickness  304  for barrier layer  302 . 
         [0043]    The density of barrier layer  302  is greater than the density of layer  402 . 
         [0044]    The chuck force for refurbished ESC  400  is characterized by Equation (1) shown below: 
         [0000]        F =(½)∈ o ∈ r   V   2   /D   2   (1)
 
         [0045]    The variable F represents the chuck force for refurbished ESC  400 , ∈ o =8.85×10 −12  F/m and represents the permittivity of free space, ∈ r , relative permittivity, represents the dielectric constant of layer  402 , variable V represents the applied chuck voltage and variable D represents the thickness of the anodic film or a thickness  410 . 
         [0046]    The consistent dielectric constant associated with layer  402  results in a reliable chucking/de-chucking force as the chucking/de-chucking force is proportional to the dielectric constant as illustrated with reference to Equation (1). The consistent dielectric constant associated with layer  402  prevents a too low dielectric constant and enables proper chucking. Furthermore, the consistent dielectric constant aids in preventing high helium flow from leakage during chamber testing and wafer production as a result of a too low chucking force. Furthermore, helium may be used for controlling temperature of semiconductor process and an insufficient chucking force may result if an excessive amount of helium applied for semiconductor manufacturing process, thereby resulting in defective wafers. 
         [0047]    For too large of a dielectric constant, water moisture becomes trapped inside pores of anodic film, resulting in poor de-chucking. 
         [0048]    A problem that arises with the use of an ESC is the difficulty of removing the residual electrostatic force between the wafer and the ESC during “de-chucking”. This residual force results from electric charges having accumulated at the interface between the wafer and the ESC support surface. One technique for de-chucking involves connecting the electrode and the wafer to ground. Another technique reverses the polarity of the DC chucking voltage applied to the electrodes to discharge the electrodes. However, these techniques are not completely effective at removing the charge on the electrodes and the wafer. Consequently, a mechanical force is often needed to overcome the remaining attractive electrostatic force due to residual charges on the electrodes and wafer. At times, the mechanical force used to release the wafer may cause the wafer to “pop”, i.e., to be released from the chuck in some unpredictable manner, which may cause either wafer damage or difficulty in retrieving the wafer from unintended position. Therefore, a successful de-chucking operation is one which leaves the wafer in a state subject to acceptably low residual electrostatic attractive force without “popping” the wafer. 
         [0049]    The voltage control of an ESC is used for the operation of the device, as the voltage differential created also generates an electric field used to attract and hold a wafer for processing. The capacitance of refurbished ESC  400  is a parameter which affects voltage control and therefore is maintained consistent in order to maintain a consistent voltage control. 
         [0050]    The capacitance of refurbished ESC  400  is characterized by Equation (2) as shown below: 
         [0000]        C=∈   o ∈ r   A/D   (2)
 
         [0051]    The variable C represents the capacitance of refurbished ESC  400  and variable A represents the surface area for the stop surface of the refurbished ESC  400 . Furthermore, refurbished ESC  400  receives a semiconductor wafer  412  on a top surface  414  of refurbished ESC  400 . 
         [0052]    As can be observed by Equation (2), the capacitance, C, is proportional to the dielectric constant, ∈ r , so in order to maintain a consistent capacitance, a consistent dielectric constant is maintained. 
         [0053]    The resistance of refurbished ESC  400  is a parameter which affects arcing and therefore is consistently maintained in order to prevent arcing. In some instances, it is possible for arcing to occur as a result of a low resistance point associated with an ESC. In order to prevent arcing, resistance is maintained at a consistently high value. The permittivity, ∈, of a material is given by Equation (3) shown below: 
         [0000]      ∈=∈ o ∈ r   (3)
 
         [0054]    Permittivity, ∈, is a measure of how much resistance is encountered when forming an electric field in a medium. Permittivity is a measure of how an electric field affects, and is affected by a dielectric medium. Permittivity is determined by the ability of a material to polarize in response to an electric field, and thereby reduce the total electric field inside the material. Permittivity describes a material&#39;s ability to transmit (i.e. permit) an electric field. Less electric flux exists in a medium with a high permittivity due to polarization effects. Processing of layer  402  via deionized water contributes to a permittivity such that arcing is reduced. 
         [0055]      FIG. 5  illustrates an example method for refurbishing a semiconductor wafer, in accordance with an aspect of the present invention. 
         [0056]    In the example embodiment, a method  500  starts (S 502 ) and a portion of a second layer (e.g. porous layer  106  ( FIG. 1 )) is removed if it exists or a portion of a barrier layer (e.g. barrier layer  108  ( FIG. 1 )) is removed if second layer does not exist for an ESC(S 504 ). 
         [0057]    Removal of layers may be performed via any know means or method for removal of layers. Non-limiting examples of means and methods for removal of layer includes, mechanical, chemical and electrical. 
         [0058]    A determination is performed as to whether the second layer and the barrier layer have been removed (S 506 ). 
         [0059]    Dimensions of ESC are measured using coordinate measurement machine. Based upon the measured dimensions, a determination is performed as to whether additional layer material is to be removed. 
         [0060]    Following a determination for adequate removal of layer material (S 506 ), ESC is configured as described with reference to  FIG. 2 . 
         [0061]    A new layer portion (e.g. layer portion  310  ( FIG. 3 )) is added to ESC (S 510 ). 
         [0062]    Layer portion may be added to ESC using any known means or method. 
         [0063]    A determination is performed as to whether addition of layer portion has been completed (S 512 ). 
         [0064]    Dimensions of ESC are measured using coordinate measurement machine. Based on the measured dimensions, a determination is performed as to whether additional layer material is to be added. 
         [0065]    Following a determination for adequate addition of layer material (S 512 ). ESC is configured as described with reference to  FIG. 3 . 
         [0066]    Deionized water seal is applied to layer portion  310  ( FIG. 3 ) (S 514 ). 
         [0067]    An anodic film (e.g. layer  402  ( FIG. 4 )) is created via a reaction of hot deionized water with the porous Al 2 O 3  of layer  308  ( FIG. 3 ). The reaction of the Al 2 O 3  with the deionized water creates AlO(OH) also known as boehmite. 
         [0068]    A determination is performed as to whether a multiplicity of wafers have been refurbished successfully (S 516 ). 
         [0069]    Measurements, testing and analysis are performed for determining whether refurbishment of a multiplicity of ESCs have been performed successfully. 
         [0070]    For a determination of not having processed a multiplicity of ESCs successfully, the process of refurbishing an ESC is initiated (S 518 ). 
         [0071]    An ESC previously refurbished unsuccessfully may be processed again, or an entirely different ESC which has not been attempted to be refurbished may be processed again. 
         [0072]    For a determination of having successfully processed a multiplicity of ESCs (S 516 ), a process specification is developed. 
         [0073]    Process specification is developed based upon the measurements and other associated information determined while successfully processing a multiplicity of ESCs (S 520 ). 
         [0074]    Method  500  ceases operation (S 522 ). 
         [0075]    An ESC is subject to wear and/or degradation from conditions associated with operation. ESC may be refurbished by replacing degraded anodized layer with a new anodized layer which has been subject to a water seal for realizing an anodized layer with properties conducive to the successful operation of refurbished ESC. 
         [0076]    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 example 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.