Abstract:
A replaceable upper chamber section of a plasma reaction chamber in which semiconductor substrates can be processed comprises a monolithic metal cylinder having a conical inner surface which is widest at a lower end thereof, an upper flange extending horizontally outward away from the conical inner surface and a lower flange extending horizontally away from the conical inner surface. The cylinder includes an upper annular vacuum sealing surface adapted to seal against a dielectric window of the plasma chamber and a lower annular vacuum sealing surface adapted to seal against a bottom section of the plasma chamber. A thermal mass at an upper portion of the cylinder is effective to provide azimuthal temperature uniformity of the conical inner surface. A thermal choke is located at a lower portion of the cylinder and is effective to minimize transfer of heat across the lower vacuum sealing surface.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/164,270 entitled REPLACEABLE UPPER CHAMBER SECTION OF PLASMA PROCESSING APPARATUS, filed Mar. 27, 2009, the entire content of which is hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates in general to semiconductor substrate manufacturing technologies and in particular to a replacement upper chamber section of a plasma chamber. 
     BACKGROUND OF THE INVENTION 
     In the processing of a substrate, e.g., a semiconductor substrate or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. As part of the processing of a substrate for example, the substrate is divided into a plurality of dies, or rectangular areas, each of which will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (etching) and deposited (deposition) in order to form electrical components thereon. 
     In an exemplary plasma process, a substrate is coated with a thin film of hardened emulsion (i.e., such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing components of the underlying layer to become exposed. The substrate is then placed in a plasma processing chamber on a substrate support structure comprising a mono-polar or bi-polar electrode, called a chuck or pedestal. Appropriate etchant source are then flowed into the chamber and struck to form a plasma to etch exposed areas of the substrate. 
     Referring now to  FIG. 1 , a simplified diagram of inductively coupled plasma processing system components is shown. Generally, the plasma chamber (chamber)  202  is comprised of a bottom chamber section  251  forming a sidewall of the chamber, an upper chamber section  244  also forming a sidewall of the chamber, and a cover  249 . An appropriate set of gases is flowed into chamber  202  from gas distribution system  222 . These plasma processing gases may be subsequently ionized to form a plasma  220 , in order to process (e.g., etch or deposition) exposed areas of substrate  224 , such as a semiconductor substrate or a glass pane, positioned with edge ring  215  on an electrostatic chuck (chuck)  216 . Gas distribution system  222  is commonly comprised of compressed gas cylinders (not shown) containing plasma processing gases (e.g., C 4 F 8 , C 4 F 6 , CHF 3 , CH 2 F 3 , CF 4 , HBr, CH 3 F, C 2 F 4 , N 2 , O 2 , Ar, Xe, He, H 2 , NH 3 , SF 6 , BCl 3 , Cl 2 , etc.). 
     Induction coil  231  is separated from the plasma by a dielectric window  204  forming the upper wall of the chamber, and generally induces a time-varying electric current in the plasma processing gases to create plasma  220 . The window both protects induction coil from plasma  220 , and allows the generated RF field  208  to generate an inductive current  211  within the plasma processing chamber. Further coupled to induction coil  231  is matching network  232  that may be further coupled to RF generator  234 . Matching network  232  attempts to match the impedance of RF generator  234 , which typically operates at about 13.56 MHz and about 50 ohms, to that of the plasma  220 . Additionally, a second RF energy source  238  may also be coupled through matching network  236  to the substrate  224  in order to create a bias with the plasma, and direct the plasma away from structures within the plasma processing system and toward the substrate. Gases and byproducts are removed from the chamber by a pump  299 . 
     Generally, some type of cooling system  240  is coupled to chuck  216  in order to achieve thermal equilibrium once the plasma is ignited. The cooling system itself is usually comprised of a chiller that pumps a coolant through cavities in within the chuck, and helium gas pumped between the chuck and the substrate. In addition to removing the generated heat, the helium gas also allows the cooling system to rapidly control heat dissipation. That is, increasing helium pressure subsequently also increases the heat transfer rate. Most plasma processing systems are also controlled by sophisticated computers comprising operating software programs. In a typical operating environment, manufacturing process parameters (e.g., voltage, gas flow mix, gas flow rate, pressure, etc.) are generally configured for a particular plasma processing system and a specific recipe. 
     In addition, a heating and cooling apparatus  246  may operate to control the temperature of the upper chamber section  244  of the plasma chamber  202  such that the inner surface of the upper chamber section  244 , which is exposed to the plasma during operation, is maintained at a controlled temperature. The heating and cooling apparatus  246  is formed by several different layers of material to provide both heating and cooling operations. 
     The upper chamber section itself is commonly constructed from plasma resistant materials that either will ground or are transparent to the generated RF field within the plasma processing system (e.g., coated or uncoated aluminum, ceramic, etc.). 
     For example, the upper chamber section can be a machined piece of aluminum which can be removed for cleaning or replacement thereof. The inner surface of the upper chamber section is preferably coated with a plasma resistant material such as a thermally sprayed yttria coating. Cleaning is problematic in that the ceramic coatings of this type are easily damaged and due to the sensitive processing of some plasma processes, it is sometimes preferred to replace the upper chamber section rather than remove it for cleaning. 
     In addition, correctly reseating the upper chamber section after maintenance is often difficult, since it must properly be aligned with the bottom chamber section such that a set of gaskets properly seal around the upper chamber section. A slight misalignment will preclude a proper mounting arrangement. 
     The volume of material in the upper chamber section also tends to add a substantial thermal mass to the plasma processing system. Thermal mass refers to materials have the capacity to store thermal energy for extended periods. In general, plasma processes tend to very sensitive to temperature variation. For example, a temperature variation outside the established process window can directly affect the etch rate or the deposition rate of polymeric films, such as poly-fluorocarbon, on the substrate surface. Temperature repeatability between substrates is often desired, since many plasma processing recipes may also require temperature variation to be on the order of a few tenths of degree C. Because of this, the upper chamber section is often heated or cooled in order to substantially maintain the plasma process within established parameters. 
     As the plasma is ignited, the substrate absorbs thermal energy, which is subsequently measured and then removed through the cooling system. Likewise., the upper chamber section can be thermally controlled. However, plasma processing may require temperature changes during multi-step processing and it may be necessary to heat the upper chamber section to temperatures above 100° C., e.g. 120, 130, 140, 150 or 160° C. or any temperature therebetween whereas the prior upper chamber sections were run at much lower temperatures on the order of 60° C. The higher temperatures can cause undesirable increases in temperature of adjacent components such as the bottom chamber section. For example, if it is desired to run the upper chamber section and overlying dielectric window at temperatures on the order of 130 to 150° C. and the bottom chamber section at ambient temperatures of about 30° C., heat from the much hotter upper chamber section can flow into the bottom chamber section and raise its temperature sufficiently to affect the plasma processing conditions seen by the semiconductor substrate. Thus, heat flow variations originating from the upper chamber section may cause the substrate temperature to vary outside narrow recipe parameters. 
     In view of the foregoing, a replaceable upper chamber section having improved thermal characteristics would be of interest for optimizing plasma processing in a plasma processing system. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, a replaceable upper chamber section of a plasma reaction chamber in which semiconductor substrates can be processed, comprises a monolithic metal cylinder having a conical inner surface which is widest at a lower end thereof, an upper flange extending horizontally outward away from the conical inner surface and a lower flange extending horizontally away from the conical inner surface; an upper annular vacuum sealing surface adapted to seal against a dielectric window of the plasma chamber; a lower annular vacuum sealing surface adapted to seal against a bottom section of the plasma chamber; a thermal mass at an upper portion of the cylinder, the thermal mass defined by a portion of the cylinder between the conical inner surface and an outer surface extending vertically from the upper flange, the thermal mass being effective to provide azimuthal temperature uniformity of the conical inner surface, and a thermal choke at a lower portion of the cylinder effective to minimize transfer of heat across the lower vacuum sealing surface, the thermal choke defined by a thin metal section having a thickness of less than 0.25 inch and extending at least 25% of the length of the conical inner surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  shows a simplified diagram of a plasma processing system. 
         FIG. 2  shows a cross section of a prior upper chamber section. 
         FIG. 3  shows a cross section of an upper chamber section according to one embodiment. 
         FIG. 4  shows a top view of the upper chamber section shown in  FIG. 2 . 
         FIG. 5  shows a side view of the upper chamber section shown in  FIG. 2 . 
         FIG. 6  shows a top view of the upper chamber section shown in  FIG. 3 . 
         FIG. 7  shows a side view of the upper chamber section shown in  FIG. 3 . 
         FIG. 8  shows a perspective cross-sectional view of an upper chamber section. 
         FIG. 9  is a cross section of the upper chamber section shown in  FIG. 8 . 
         FIG. 10  is a bottom view of the upper chamber section shown in  FIG. 8 . 
         FIG. 11  is a side view of the upper chamber section shown in  FIG. 8 . 
         FIG. 12  is a cross-sectional side view of the upper chamber section shown in  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described in detail with reference to a few preferred embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. As used herein, the term “about” should be construed to include values up to 10% above or below the values recited. 
     Compared to the previously designed upper chamber section shown in  FIGS. 2, 4 and 5 , the redesigned upper chamber section shown in  FIGS. 3, 6 and 7  has improved azimuthal temperature uniformity, improved thermal transfer to the overlying dielectric window and reduced thermal transfer to the underlying bottom chamber section. The prior upper chamber section shown in  FIGS. 2, 4 and 5  was designed for low mass and ease of service due to its reduced weight. The design of the upper chamber section was changed to achieve improved azimuthal thermal uniformity by increasing the contact area of the upper surface in contact with the overlying window, increasing mass to improve azimuthal uniformity, and decreasing wall thickness to minimize thermal transfer to the bottom chamber section. 
     In a preferred embodiment, the upper chamber section is a hard anodized aluminum cylinder that has features for mounting process support hardware (RF input coil, temperature controlled window, alignment features, chamber temperature control hardware, etc.), sealing vacuum, and conducting electrical current out of the part. The vacuum seals are preferably one or more O-rings at the top and bottom of the cylinder. Electrical conduction is preferably established through the use of a metallic spring RF gasket that fits into a groove on the cylinder and contacts a bare metal strip on an adjacent component. The weight and thermal mass are increased at the upper portion of the cylinder to achieve the desired temperature uniformity. The internal shape of the plasma exposed surface is the same as the prior upper chamber section to duplicate the electrical, gas flow and plasma containment features of the prior upper chamber section. The change in design can be seen by comparing the cross sections shown in  FIGS. 2 and 3 . 
     The upper chamber section shown in  FIG. 3  differs from the prior upper chamber section shown in  FIG. 2  with respect to features for mounting temperature control, mounting and alignment hardware. Such changes in design can be seen by comparing the views shown in  FIGS. 4-5  to the views shown in  FIGS. 6-7 . For example, the new design of the upper chamber section is at least 40% heavier than the prior upper chamber section and the new design has removable auxiliary hardware (alignment features, bumper features, etc) which minimize the potential contaminating materials from being run through a clean cycle with the upper chamber section. In contrast, the prior upper chamber section was designed to be cleaned with plastic and stainless steel components still attached. 
     With reference to  FIGS. 2 and 4-5 , the prior upper chamber section  244  includes an upper flange  250 , a lower flange  252 , an upper vacuum sealing surface  254  which includes an annular groove for receipt of an O-ring, a lower vacuum sealing surface  256  which includes an annular groove for receipt of an O-ring and another annular groove for receipt of an RF gasket, an inner conical surface  258 , an outer surface  260  for mounting the heating and cooling hardware  246 , and an upper recessed surface  262 . As can be seen in  FIG. 2 , the upper vacuum sealing surface  254  is smaller than the lower vacuum sealing surface  256  and the heat flow from the upper chamber section  244  favors heat transfer to the bottom chamber section  251  rather than to the window  204 . Also, the upper chamber section  244  is designed to be lightweight making control of thermal uniformity more reliant on the heating and cooling hardware and less dependent on the thermal mass of the upper chamber section itself. 
     With reference to  FIGS. 3 and 6-7 , the redesigned upper chamber section  300  includes an upper flange  302 , a lower flange  304 , an upper vacuum sealing surface  306  which includes an annular groove for receipt of an O-ring, a lower vacuum sealing surface  308  which includes an annular groove for receipt of an O-ring and another annular groove for receipt of an RF gasket, an inner conical surface  310 , an outer surface  312  for mounting the heating and cooling hardware  246 , and an upper recessed surface  315 . As can be seen in  FIG. 3 , the upper vacuum sealing surface  306  is larger than the upper vacuum sealing surface of the prior upper chamber section  244  and thus provides improved thermal transfer with the window  204 . To minimize thermal transfer to the bottom chamber section  251 , the upper chamber section  300  includes a thermal choke  314  formed by a thin walled section of the cylinder. Preferably, the thickness of thermal choke  314  is less than 0.25 inch and more preferably is about 0.125 inch in thickness. The length of the thermal choke is preferably at least 0.5 inch and more preferably at least 1 inch in length. The thermal choke preferably begins close to the vacuum sealing surface  308  and ends at a thermal mass section  316  of the cylinder. The flange  304  includes a vertical surface  318  forming a V-shaped groove  320  with an outer surface  322  of the thermal choke  314 . The thermal mass section  316  begins at a horizontal surface  324  which is spaced from the upper recessed surface  315  by at least 2 inches, preferably about 2.15 inches. 
     In the embodiment shown in  FIG. 3 , the outer surface  312  is recessed between the flange  302  and an annular rim  326  for receipt of the heating and cooling arrangement  246 . An alignment pin  330  located in a hole in the outer surface  312  can be used to position the heating and cooling arrangement  246 . A series of circumferentially spaced apart vertical mounting holes  332  in the upper flange  302  can be used to mount an RF coil assembly which includes RF coil  231 . Other holes and/or slots can be provided in the upper flange  302  to cooperate with other equipment such as a bumper to protect the window  204  from being damaged during mounting on the upper vacuum sealing surface  306  or a mechanism which locks into the upper chamber section for installation and removal thereof. One or more temperature probe mounting holes  334  can be provided in the outer surface  312  for single zone or multiple zone temperature control. 
     In a preferred embodiment, the upper chamber section  300  is a monolithic aluminum cylinder having an inner diameter of 18 inches at the inner edge of the vacuum sealing surface  306 , an outer diameter of 21.75 inches at the outer edge of the upper flange  302 , an inner diameter of 21.15 inches at the inner edge of the lower vacuum sealing surface  308  and an outer diameter of 22.48 inches at the outer edge of the lower flange  304 . The O-ring groove in the upper vacuum sealing surface is located on a diameter of 18.220 to 18.275 inches and the O-ring groove in the lower vacuum sealing surface is located on a diameter of about 21.45 inches and the groove for the RF gasket is located on a diameter of about 21.94 inches. The inner edge of the upper recessed surface has a diameter of 19.625 inches. 
     Another embodiment of the upper chamber section is shown in  FIGS. 8-12 . In this embodiment, the upper chamber section  400  includes an upper flange  402 , a lower flange  404 , an upper vacuum sealing surface  406  which includes an annular groove for receipt of an O-ring, a lower vacuum sealing surface  408  which includes an annular groove for receipt of an O-ring and another annular groove for receipt of an RF gasket, an inner conical surface  410  having a series of circumferentially spaced apart holes  409  for mounting gas injectors (not shown), an outer surface  412  for mounting the heating and cooling hardware  246 , and an upper recessed surface  415 . As can be seen in  FIG. 8 , the upper vacuum sealing surface  406  is larger than the upper vacuum sealing surface of the prior upper chamber section  244  and thus provides improved thermal transfer with the window  204 . To minimize thermal transfer to the bottom chamber section  251 , the upper chamber section  400  includes a thermal choke  414  formed by a thin walled section of the cylinder. Preferably, the thickness of thermal choke  414  is less than 0.25 inch and more preferably is about 0.10 to 0.125 inch in thickness. The length of the thermal choke can preferably at least 0.5 inch and more preferably at least 1 inch in length. The thermal choke preferably begins close to the vacuum sealing surface  408  and ends at a thermal mass section  416  of the cylinder. The flange  404  includes an angled surface  418  forming a V-shaped groove  420  with an outer surface  422  of the thermal choke  414 . The thermal mass section  416  begins at a horizontal surface  424  which is spaced from the upper recessed surface  415  by at least 2 inches, preferably about 2.3 inches. 
     In the embodiment shown in  FIGS. 8-12 , the outer surface  412  is recessed between the flange  402  and an annular rim  426  for receipt of the heating and cooling arrangement  246 . An alignment pin  430  located in a hole in the outer surface  412  can be used to position the heating and cooling arrangement  246 . A series of circumferentially spaced apart vertical mounting holes  432  in the upper flange  402  can be used to mount an RF coil assembly which includes RF coil  231 . Other holes and/or slots can be provided in the upper flange  402  to cooperate with other equipment such as a bumper to protect the window  204  from being damaged during mounting on the upper vacuum sealing surface  406  or a mechanism which locks into the upper chamber section for installation and removal thereof. One or more temperature probe mounting holes can be provided in the outer surface  412  for single zone or multiple zone temperature control. 
     In a preferred embodiment, the upper chamber section  400  is a monolithic aluminum cylinder having an inner diameter of 18 inches at the inner edge of the vacuum sealing surface  406 , an outer diameter of 21.75 inches at the outer edge of the upper flange  402 , an inner diameter of 21.15 inches at the inner edge of the lower vacuum sealing surface  408  and an outer diameter of 22.48 inches at the outer edge of the lower flange  404 . The O-ring groove in the upper vacuum sealing surface is located on a diameter of 18.220 to 18.275 inches and the O-ring groove in the lower vacuum sealing surface is located on a diameter of about 21.45 inches and the groove for the RF gasket is located on a diameter of about 21.94 inches. The inner edge of the upper recessed surface has a diameter of 19.625 inches. 
     While this invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents which fall within the scope of this invention. For example, although the present invention has been described in connection with plasma processing systems from Lam Research Corporation (e.g., Exelan™, Exelan™ HP, Exelan™ HPT, 2300™, Versys™ Star, etc.), other plasma processing systems may be used. This invention may also be used with substrates of various diameters (e.g., 200 mm, 300 mm, etc.). Also, materials other than aluminum may be used, such as ceramics. 
     Having disclosed exemplary embodiments and the best mode, modifications and variations may be made to the disclosed embodiments while remaining within the subject and spirit of the invention as defined by the following claims.