Abstract:
A cleaning wafer is used during the vaporization of particulate deposits that were previously deposited on the walls of a plasma chamber. The cleaning wafer includes a first dielectric layer, a conducting layer and a second dielectric layer covering the conducting layer.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a method of cleaning plasma chambers used for processing semiconductor wafers and, more particularly, a method of cleaning such plasma chambers utilizing a universal cleaning wafer suitable for use with an electrostatic clamping chuck or a mechanical clamping chuck. 
     Plasma processing of semiconductor wafers involves the performance of one or more plasma processes such as gas chemistry etching, or chemical vapor deposition on one or more semiconductor wafers within the plasma chamber. As the geometries of semiconductor devices become smaller, the ability to maintain the uniformity and accuracy of critical dimensions becomes strained. Many of the processes carried out within semiconductor processing reactors leave contaminant deposits throughout the process chamber which accumulate and become the source of particulate matter harmful to the creation of a semiconductor device. The non-volatile particulate matter tend to remain inside the plasma chamber in the form of loosely attached particles to the various element surfaces of the plasma chamber. As the dimension size of the semiconductor device has become smaller, the presence of particulate matter upon the surface of the semiconductor wafer has become more of a risk factor. Consequently, the cleanliness of plasma processing chambers (i.e., plasma etching, reactive ion etching (RIE), plasma enhanced chemical vapor deposition (PECVD), etc.) is critical. 
     Removal of contaminants from the various surfaces inside a plasma chamber has been accomplished by periodically cleaning the plasma chamber. Known cleaning methods have involved opening the plasma chamber, disassembling portions of the chamber, and removing the contaminant deposits by physical or chemical methods. Such cleaning methods are complicated, disruptive, time consuming and can be the source of additional contamination. 
     Recognizing the disadvantages of disassembling the plasma chamber for cleaning, it has been proposed in Law et al. U.S. Pat. Nos. 4,960,488, Cheung et al. 5,158,644, and Shufflebotham et al. 5,503,676, the disclosures of which are incorporated by reference herein, to use an etching plasma to self-clean the plasma chamber. The gas used in the self-cleaning is chosen so as to chemically react with the particulate matter and vaporize it but at the same time avoiding damage to the chamber hardware. Su et al. U.S. Pat. No. 5,507,874, the disclosure of which is incorporated by reference herein, is similar to the above references but the teaching is directed to the cleaning of an electrostatic chuck. 
     Kilburn et al. U.S. Pat. No. 5,240,555, the disclosure of which is incorporated by reference herein, discloses a cleaning wafer that is used during the self-cleaning of an etching machine. The purpose of the cleaning wafer is to activate the radio frequency power which is used to create the cleaning plasma. The cleaning wafer is made from the same material as the interior of the etching machine to avoid contamination by foreign elements. The cleaning wafer could be aluminum as disclosed by Kilburn et al. or any of a wide variety of unspecified materials. 
     Electrostatic chucks are devices for holding or clamping semiconductor wafers during plasma manufacturing processes. An electrostatic chuck secures the entire lower surface of a semiconductor wafer by Coulombic force and provides an alternative to mechanical clamping of the semiconductor wafer to the support platform or pedestal. A clear advantage in using an electrostatic chuck is that it eliminates the need for mechanical clamping mechanisms, which physically contact the front of the wafer inducing contamination on the surface of the wafer. Additionally, when a semiconductor wafer is secured to the electrostatic chuck, the flatness of the semiconductor wafer is improved, improving things like the across wafer thermal cooling. 
     While the Kilburn et al. aluminum cleaning wafer would work with an electrostatic chuck, it would not be inert to many cleaning plasmas. Assuming that Kilburn et al.s cleaning wafer could be made of a different material, such as ceramic, a ceramic cleaning wafer would not work with an electrostatic chuck although it would be inert to many cleaning plasmas. 
     Thus, a problem with the Kilburn et al. cleaning wafer is that it is not suitable for electrostatic chucks while also being resistant to the cleaning plasma. 
     It is accordingly a purpose of the present invention to have a universal cleaning wafer that is both inert to many cleaning plasmas and that is usable with an electrostatic chuck. 
     It is another purpose of the present invention to have a universal cleaning wafer that is suitable for use with both electrostatic chucks and mechanical chucks. 
     These and other purposes of the invention will become more apparent after referring to the following description of the invention in conjunction with the accompanying drawings. 
     BRIEF SUMMARY OF THE INVENTION 
     One aspect of the invention relates to a method of cleaning a plasma chamber having a chuck for holding a semiconductor wafer and particulate deposits remaining from a previous plasma utilizing operation, the method comprising the steps of: 
     a. obtaining a cleaning wafer comprising a first dielectric layer, conducting layer and a second dielectric layer covering the conducting layer; 
     b. placing the cleaning wafer on the chuck with the second dielectric layer in direct contact with the chuck; 
     c. generating a plasma in the plasma chamber for a predetermined interval of time to vaporize particulate deposits within the plasma chamber; and 
     d. removing the vaporized particulate deposits from the plasma chamber. 
     A second aspect of the invention relates to a method of operating a plasma chamber having a chuck for holding a semiconductor wafer the method comprising the steps of: 
     a. placing a semiconductor wafer on the chuck in the plasma chamber; 
     b. generating a plasma in the plasma chamber for a predetermined interval of time to process the semiconductor wafer, the processing causing particulate deposits to form in the plasma chamber; 
     c. removing the semiconductor wafer from the plasma chamber; 
     d. optionally processing additional semiconductor wafers; 
     e. placing on the chuck a cleaning wafer comprising a first dielectric layer, conducting layer and a second dielectric layer covering the conducting layer, the second dielectric layer being in direct contact with the chuck; 
     f. generating a plasma for a predetermined interval of time to vaporize the particulate deposits within the plasma chamber; and 
     g. removing the flowing gas and vaporized particulate deposits form the plasma chamber. 
     A third aspect of the invention relates to a plasma apparatus comprising a plasma chamber having a chuck for holding a semiconductor wafer and a cleaning wafer comprising a first dielectric layer, conducting layer and a second dielectric layer covering the conducting layer; wherein, in operation, the cleaning wafer is placed on the chuck and a plasma generated after a predetermined number of semiconductor wafers have been processed, the processing of the semiconductor wafers causing particulate deposits to form in the plasma chamber, the plasma generated while using the cleaning wafer causing the vaporization and removal of the particulate deposits. 
     A fourth aspect of the invention relates to a cleaning wafer for use in cleaning a plasma chamber of particulate matter comprising a first dielectric layer, a conducting layer and a second dielectric layer covering the conducting layer, wherein the first dielectric layer is substantially thicker than either of the conducting layer or the second dielectric layer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the invention believed to be novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The Figures are for illustration purposes only and are not drawn to scale. The invention itself, however, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematical view in cross section of a first type of plasma chamber apparatus and the cleaning wafer according to the present invention on an electrostatic chuck. 
     FIG. 2 is a schematical view in cross section of a second type of plasma chamber apparatus and the cleaning wafer according to the present invention on an electrostatic chuck. 
     FIG. 3 is a cross section of the cleaning wafer according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1, a first type of plasma chamber apparatus, generally indicated by  10 , is schematically shown in cross section. Plasma chamber apparatus  10  includes plasma chamber  12 , chuck  14  for holding a semiconductor wafer (not shown), plasma  16 , gas inlet  20  for the entry of a suitable gas, and gas outlet  22  for the exit of the gas and other volatiles. On top of chuck  14  is universal cleaning wafer  18 . 
     It should be understood that chuck  14  can be a mechanical chuck or an electrostatic chuck. Preferably, chuck  14  is an electrostatic chuck. However, since universal cleaning wafer  18  can be readily used with either kind of chuck, the universality of the universal cleaning wafer  18  can be appreciated. 
     Plasma  16  shown in plasma chamber  12  or produced in plasma chamber  12  of FIG. 1 may be generated by any known source including, but not limited to, RF source, multiple RF sources or microwave. 
     Some plasma chambers utilize a downstream plasma source where the plasma is actually formed outside of the plasma chamber by conventional means and then transported into the plasma chamber. 
     Referring now to FIG. 2, a second type of plasma chamber apparatus, generally indicated by  30 , is schematically shown in cross section. Plasma chamber apparatus  30  includes plasma chamber  32 , chuck  14  for holding a semiconductor wafer (not shown), plasma  38 , inlet  34  for the entry of the plasma  38  and outlet  36  for the exit of the reactant by-products and other volatiles. In plasma chamber apparatus  30 , the plasma  38  is actually formed in another chamber (not shown) and transported into plasma chamber  32 . Although not formed in plasma chamber  32 , plasma  38  shall nevertheless be considered for purposes of the present invention to be generated or produced in plasma chamber  32 . On top of chuck  14  is universal cleaning wafer  18 . 
     Referring now to FIG. 3, there is shown a cross sectional view of the universal cleaning wafer  18  which consists of a bulk ceramic (dielectric) portion  24  and conductive thin film  26  and dielectric thin film  28 . The bulk ceramic portion  24  is substantially thicker than the thin films  26  and  28 . By substantially thicker, it is meant that bulk ceramic portion  24  is at least several hundred times thicker than thin films  26  and  28 , as it is bulk ceramic portion  24  that will get exposed to any erosion from sputtering. While universal cleaning wafer  18  is shown in cross section, it should be understood that universal cleaning wafer  18  is generally circular in nature. 
     Universal cleaning wafer  18  should preferably be the same size and shape as the standard silicon wafer used for semiconductor device production. That is, universal cleaning wafer  18  can be a direct substitute for a silicon wafer during the operation of the cleaning plasma. It should be understood, however, that cleaning wafer  18  can be larger or smaller than the silicon wafer, depending on the equipment utilized and the location of the particulate matter remaining in the plasma chamber  12 . 
     Bulk ceramic portion  24  is preferably Al 2 O 3  but may also be SiC, Si 3 N 4  or SiO 2  Thin film  26  should be a conductive metal to provide operability of the universal cleaning wafer  18  with an electrostatic chuck. The conductive metal of the thin film  26  should preferably be silicon but could also be aluminum or copper. Lastly, thin film  28  is preferably Al 2 O 3  but could also be SiO 2 , SiC or Si 3 N 4 . Thin film  28  covers thin film  26  to protect thin film  26  from the cleaning plasma. Depending on the material of thin film  26  and the plasma application, complete encapsulation of thin film  26  by thin film  28  may be required. For example, where thin film  26  is copper, complete encapsulation would be required if copper contamination is a problem for the plasma application. 
     The back of the wafer is usually contacted by the cleaning plasma. By burying the conductive thin film  26 , contact with the cleaning plasma is thus avoided. If conductive thin film  26  is contacted by the cleaning plasma and ordinarily would be etched by the cleaning plasma, then by burying the conductive thin film  26  or completely encapsulating it as discussed above, thin film  26  will not be etched (i.e., removed) by the cleaning plasma, thereby avoiding recoating the universal cleaning wafer  18  periodically and, further, avoiding contamination in the plasma chamber  12 . Thin film  28  thus improves the life of universal clean wafer  18 . Moreover, because of the layered structure of universal clean wafer  18 , it can be used in any type of plasma chamber with any type of chuck. 
     The choice of materials, as well as their thickness, is dependent on the cleaning plasma utilized. For the most versatility, it is preferred that the universal cleaning wafer  18  comprise Al 2 O 3  bulk ceramic portion  24 , followed by thin film  26  of silicon and thin film  28  of Al 2 O 3 . The thickness of bulk ceramic portion  24  is nominally 750 microns, and the thickness of each of thin films  26  and  28  is nominally 1 microns. If thin film  28  were of a higher dielectric material, the thickness would have to be less than 1 micron so as to achieve an adequate clamp with the electrostatic chuck. 
     The universal cleaning wafer  18  according to the present invention was made in the following manner. A bulk Al 2 O 3  wafer, 740 microns in thickness, was purchased from LTD Ceramics, Inc., Menlo Park, Calif. 92025. Since the size and shape of the bulk ceramic is, in the preferred embodiment of the invention, equivalent to that of a typical silicon wafer as used in the semiconductor industry, thin films  26  and  28  may be formed by using conventional semiconductor deposition equipment. Thus, 1 micron of silicon was deposited on the bulk ceramic wafer by DC Magnetron sputtering followed by deposition of 1 micron of Al 2 O 3  by PECVD. 
     During the normal operation of a plasma chamber apparatus  10 , one or more silicon wafers would be processed. By processed, it is meant that the silicon wafer would undergo etching (e.g., by RIE) or deposition (e.g., by PECVD). As a result of this processing, particulate matter would be loosely deposited on the walls of the plasma chamber  12  or  32  as is well known to those skilled in the art. If this particulate matter is not removed, some of the particulates can fall on the semiconductor wafer, thereby adversely affecting the quality of the semiconductor wafer. Accordingly, after a predetermined number of semiconductor wafers are processed (the precise number being determined by the equipment, operator, type of plasma, materials, etc.), a universal cleaning wafer is inserted in the plasma chamber  12  or  32  and placed on the chuck  14 , with thin film  28  in direct contact with the chuck  14 . Thereafter, a cleaning plasma is generated in plasma chamber  12  or  32 . The universal cleaning wafer  18  is chosen so as to be relatively inert to the cleaning plasma, thereby avoiding sputtering of the universal cleaning wafer  18  and further contamination of the plasma chamber  12  or  32 . The universal cleaning wafer  18  does not actually participate in the cleaning of the plasma chamber  12  or  32  but rather protects the chuck  14  from the cleaning plasma and also activates the sensing switch (if one is present) to indicate that a wafer is on the chuck so that the plasma can be generated. The cleaning plasma causes the particulate matter in the plasma chamber  12  or  32  to be volatilized and removed from the plasma chamber  12  or  32  when the gases and volatiles are exhausted through outlet  22  or  36 . The universal cleaning wafer  18  may then be removed and replaced by a semiconductor wafer. 
     It will be apparent to those skilled in the art having regard to this disclosure that other modifications of this invention beyond those embodiments specifically described here may be made without departing from the spirit of the invention. Accordingly, such modifications are considered within the scope of the invention as limited solely by the appended claims.