Universal cleaning wafer for a plasma chamber

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.

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.

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.sub.2 O.sub.3 but may also be SiC,
 Si.sub.3 N.sub.4 or SiO.sub.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.sub.2 O.sub.3 but could also be SiO.sub.2, SiC or
 Si.sub.3 N.sub.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.sub.2 O.sub.3 bulk ceramic
 portion 24, followed by thin film 26 of silicon and thin film 28 of
 Al.sub.2 O.sub.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.sub.2 O.sub.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.sub.2 O.sub.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.