Abstract:
A system for processing substrates within a chamber and for cleaning accumulated material from chamber components is provided. The system includes a reactive species generator adapted to generate a reactive gas species for chemically etching accumulated material from chamber components, and a processing chamber having at least one fluoropolymer coated component which is exposed to the reactive species. Preferably to have the greatest impact on chamber cleaning efficiency, the fluoropolymer coated component(s) are large components such as a gas distribution plate or a backing plate, and/or a plurality of smaller components (e.g., a shadow frame, chamber wall liners, a susceptor, a gas conductance line) so as to constitute a large percentage of the surface area exposed to the reactive species. Most preferably all surfaces which the reactive species contacts are coated with fluoropolymer.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to an improved method and apparatus for enhancing chamber cleaning rates. More specifically, the present invention relates to a method and apparatus for enhancing the effective etch rate of a reactive chemical species which etches accumulated materials from process chamber components.  
         BACKGROUND OF THE INVENTION  
         [0002]    The manufacture of liquid crystal displays, flat panel displays, thin film transistors and other semiconductor devices occurs within a plurality of chambers, each of which is designed to perform a specific process on the substrate. Many of these processes can result in an accumulation of material (e.g., material deposited on the substrate in layers, such as by chemical vapor deposition, physical vapor deposition, thermal evaporation, material etched from substrate surfaces, and the like) on chamber surfaces. Such accumulated material can crumble from the chamber surfaces and contaminate the sensitive devices being processed therein. Accordingly, process chambers must be cleaned of accumulated materials frequently (e.g., every 1-6 substrates).  
           [0003]    To clean chamber surfaces, an in-situ dry cleaning process is preferred. In an in-situ dry cleaning process one or more gases are dissociated to form one or more reactive gas species (e.g., fluorine ions, radicals). The reactive species clean chamber surfaces by forming volatile compounds with the material accumulated on those surfaces. Unfortunately, as described further below, such chamber cleaning processes conventionally require considerable time and consume considerable amounts of cleaning gases, and thus undesirably increase the cost per substrate processed within a processing chamber. Further, large cleaning rate variations often are observed between processing chambers cleaned by identical cleaning processes. Accordingly, there is a need for an improved method and apparatus for etching accumulated material from chamber surfaces.  
         SUMMARY OF THE INVENTION  
         [0004]    The present inventors have discovered that chamber cleaning rates may be increased by as much as 20-100% when chamber surfaces exposed to reactive cleaning gas species are coated with a fluoropolymer (e.g., polytetrafluoroethylene (PTFE), a tetrafluoroethylene and hexafluoropropylene copolymer (FEP), a copolymer of tetrafluoroethylene and perfluoropropylvinyl ether (PFA)). The present invention therefore comprises a system for processing substrates within a chamber and for cleaning accumulated material from chamber components. The system includes a reactive species generator adapted to generate a reactive gas species for chemically etching accumulated material from chamber components, and a processing chamber having at least one flouropolymer coated component which is exposed to the reactive species. Preferably to have the greatest impact on chamber cleaning efficiency, the fluoropolymer coated component(s) include large components such as a gas distribution plate or a backing plate, and/or a plurality of smaller components (e.g., the chamber&#39;s shadow frame, wall liners, susceptor, gas conductance line, etc.) so as to constitute a large percentage of the surface area exposed to the reactive species. Most preferably all surfaces which the reactive species contacts are coated with a fluoropolymer.  
           [0005]    By coating exposed chamber components with PTFE, FEP or PFA, not only have cleaning rate enhancements been observed, cleaning rate variations between processing chambers can be virtually eliminated, process chamber throughput increased significantly and the amount of precursor gas required for cleaning reduced. Because of the high costs associated with precursor gases such as NF 3 , both monetarily and environmentally (e.g., global warming), any reduction in precursor gas consumption is beneficial.  
           [0006]    Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiments, the appended claims and the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is a side elevational view of a processing system configured in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0008]    [0008]FIG. 1 is a side elevational view of a processing system  10  configured in accordance with the present invention. Any suitable processing system may be modified as described herein such as a model AKT-1600 PECVD System manufactured by Applied Kamatsu Technology and described in U.S. Pat. No. 5,788,778, which is hereby incorporated by reference herein in its entirety, the GIGAFILL™ processing system manufactured by Applied Materials, Inc. and described in U.S. Pat. No. 5,812,403, which is hereby incorporated by reference herein in its entirety, thermal deposition chambers and the like. For convenience an AKT-1600 PECVD System configured in accordance with the present invention is shown in FIG. 1. The AKT-1600 PECVD System is designed for fabricating active-matrix liquid crystal displays and may be used to deposit amorphous silicon, silicon dioxide, silicon oxynitrides and silicon nitride as is known in the art.  
         [0009]    With reference to FIG. 1, the processing system  10  comprises a deposition chamber  11  having a gas distribution plate  12  having apertures  12   a - u  and a backing plate  13  adapted to deliver process gases and cleaning gases into the deposition chamber  11 , and a susceptor  14  for supporting a substrate  16  to be processed within the deposition chamber  11 . The susceptor  14  includes a heater element  18  (e.g., a resistive heater) coupled to a heater control  20  for elevating the temperature of the substrate  16  to a processing temperature and for maintaining the substrate  16  at the processing temperature during processing. A lift mechanism  22  is coupled to the susceptor  14  via a lift member  24  to allow the substrate  16  to be lifted from the susceptor  14 . Specifically, a plurality of lift pins  26  (fixedly held by a lift pin holder  28 ) penetrate the susceptor  14  (via a plurality of lift pin apertures  30 ) so as to contact and lift the substrate  16  from the susceptor  14  when the susceptor  14  is lowered by the lift mechanism  22 . The deposition chamber  11  further comprises a chamber wall liner  29  which blocks material from accumulating on the chamber wall and which can be removed and cleaned, and a shadow frame  31  which overhangs the substrate&#39;s edge and thereby prevents material from depositing or accumulating on the wafer&#39;s edge.  
         [0010]    In addition to their above described functions, the gas distribution plate  12  and the susceptor  14  also serve as parallel plate upper and lower electrodes, respectively, for generating a plasma within the deposition chamber  11 . For example, the susceptor  14  may be grounded and the gas distribution plate  12  coupled to an RF generator  32  via a matching network  34 . An RF plasma thereby may be generated between the gas distribution plate  12  and the susceptor  14  through application of RF power supplied thereto by the RF generator  32  via the matching network  34 . A vacuum pump  36  is coupled to the deposition chamber  11  for evacuating/pumping the same before, during or after processing as required.  
         [0011]    The processing system  10  further comprises a first gas supply system  38  coupled to an inlet  40  of the deposition chamber  11  for supplying process gases thereto through the backing plate  13  and the gas distribution plate  12 . The first gas supply system  38  comprises a valve controller system  42  (e.g., computer controlled mass flow controllers, flow meters, etc.) coupled to the inlet  40  of the deposition chamber  11 , and a plurality of process gas sources  44   a ,  44   b  coupled to the valve controller system  42 . The valve controller system  42  regulates the flow of process gases to the deposition chamber  11 . The specific process gases employed depend on the materials being deposited within the deposition chamber  11 .  
         [0012]    In addition to the first gas supply system  38 , the processing system  10  comprises a second gas supply system  46  coupled to the inlet  40  of the deposition chamber  11  (via a gas conductance line  48 ) for supplying cleaning gases thereto during cleaning of the deposition chamber  11  (e.g., to remove accumulated material from the various interior surfaces of the chamber  11 ). The second gas supply system  46  comprises a remote plasma chamber  50  coupled to the gas conductance line  48  and a precursor gas source  52  and a minor carrier gas source  54  coupled to the remote plasma chamber  50  via a valve controller system  56  and a valve controller system  58 , respectively. Typical precursor cleaning gases include NF 3 , CF 4 , SF 6 , C 2 F 6 , CCl 4 , C 2 Cl 6 , etc., as are well known in the art. The minor carrier gas, if employed, may comprise any non-reactive gas compatible with the cleaning process being employed (e.g., argon, helium, hydrogen, nitrogen, oxygen, etc.). The precursor and minor carrier gas sources  52 ,  54  may comprise a single gas source if desired.  
         [0013]    A high power microwave generator  60  supplies microwave power to the remote plasma chamber  50  to activate the precursor gas within the remote activation chamber (as described below). A flow restrictor  62  preferably is placed along the gas conductance line  48  to allow a pressure differential to be maintained between the remote plasma chamber  50  and the deposition chamber  11 .  
         [0014]    During cleaning of the deposition chamber  11 , a precursor gas is delivered to the remote plasma chamber  50  from the precursor gas source  52 . The flow rate of the precursor gas is set by the valve controller system  56 . The high power microwave generator  60  delivers microwave power to the remote plasma chamber  50  and activates the precursor gas to form one or more reactive species (e.g., fluorine radicals) which travel to the deposition chamber  11  through the gas conductance line  48 . The one or more reactive species then travel through the inlet  40 , through the backing plate  13 , through the gas distribution plate  12  and into the deposition chamber  11 . A minor carrier gas may be supplied to the remote plasma chamber  50  from the minor carrier gas source  54  to aid in transport of the one or more reactive species to the chamber  11  and/or to assist in chamber cleaning or plasma initiation/stabilization within the deposition chamber  11  if an RF plasma is employed during chamber cleaning.  
         [0015]    Exemplary cleaning process parameters for the deposition chamber  11  when an NF 3  precursor cleaning gas is employed include a precursor gas flow rate of about 2 liters per minute and a deposition chamber pressure of about 0.5 Torr. A microwave power of 3-12 kW, preferably 5 kW, is supplied to the remote plasma chamber  50  by the high power microwave generator  60  to activate the NF 3  precursor gas. Preferably the remote plasma chamber  50  is held at a pressure of at least 4.5 Torr and preferably about 6 Torr. Other cleaning process parameter ranges/chemistries are described in previously incorporated U.S. Pat. No. 5,788,778.  
         [0016]    As previously described, common problems with conventional cleaning processes include low cleaning rates and large variations in cleaning rates between process chambers. The present inventors have discovered that cleaning rates and cleaning rate variations between chambers are dependent on the internal chamber surface condition, and that all internal surfaces between a remote plasma source (e.g., remote plasma chamber  50 ) and a chamber (e.g., deposition chamber  11 ) (“downstream surfaces”) affect cleaning rates. Specifically, a surface controlled deactivation process is believed to cause reactive species employed during cleaning (e.g., active etchant species such as F radicals) to combine to form non-reactive species (e.g., F 2  in the case of F radicals) which do not assist in chamber cleaning. This surface controlled deactivation process appears to occur at many material surfaces including both bare and anodized aluminum surfaces.  
         [0017]    The present inventors have found that by coating one or more downstream components with PTFE, FEP or PFA, known generally as fluoropolymers, significantly higher cleaning rates are achieved and cleaning rate variations between chambers are virtually eliminated. Components found to have the most significant affect on cleaning performance include a chamber&#39;s gas distribution plate and backing plate. Components found to have a slight affect on cleaning performance include a chamber&#39;s shadow frame, wall liners, susceptor and gas conductance line. Components found to have little effect on cleaning performance include a chamber&#39;s microwave power supply, magnetron and microwave applicator. In order to affect an improvement in chamber cleaning rates, a certain percentage of the chamber components should be coated with a fluoropolymer. Although this percentage may vary, higher percentages are preferred to achieve faster cleaning rates, with 100% coating of exposed surfaces being most preferred. Note that an increase in cleaning rate (e.g., up to 15%) also can be achieved by using an RF plasma within a processing chamber in conjunction with a remote plasma source, i.e., by powering electrode  12  to form the radicalized gases entering from the remote plasma source, or secondarily introducing cleaning gases into a plasma. However, applied RF power should be limited to avoid damage to processing chamber components due to ion bombardment.  
         [0018]    With reference to the processing system  11  of FIG. 1, to affect increased cleaning rate and reduced cleaning rate variations between the deposition chamber  11  and other deposition chambers (not shown), one or more downstream components of the processing system  11  are coated with a polytetrafluoroethylene (PTFE), a tetrafluoroethylene and hexafluoropropylene copolymer (FEP), or a copolymer of tetrafluoroethylene and perfluoropropylvinyl ether coating (“fluoropolymer coating  64 ”). As shown in FIG. 1, the interior surfaces of the deposition chamber  11 , the gas distribution plate  12  the backing plate  13 , the susceptor  14 , the inlet  40 , the gas conductance line  48 , the chamber wall liner  29  and the shadow frame  31  are coated with the protective coating  64 . Fewer components may be coated with the fluoropolymer coating  64  if desired.  
         [0019]    With respect to the PECVD deposition chamber  11  of FIG. 1, the fluoropolymer coating  64  significantly increases the cleaning rate and significantly reduces chamber-to-chamber cleaning rate variations while neither producing process drift nor changes in the properties of PECVD films deposited within the deposition chamber  11 . The fluoropolymer coating  64  is believed to cover surface adsorption sites at which the surface controlled deactivation process is believed to occur (e.g., maintaining a high and a uniform F radical concentration) and is also believed to reduce the amount of material deposited on component surfaces of the deposition chamber  11  during processing therein (e.g., reducing the amount of material that must be cleaned from component surfaces and the time required for material removal during cleaning).  
         [0020]    The inventive fluoropolymer coating may be applied either in-situ or ex-situ. For in-situ application of PTFE coatings, a precursor gas such as CHF 3  may be employed to coat process chamber components using either a microwave or RF plasma. For example, within the processing system  10 , a CHF 3  precursor gas source  52  may feed CHF 3  to the remote plasma chamber  50  wherein microwave power applied via the high power microwave generator  60  dissociates the CHF 3  into CF 2  and HF. The CF 2  and HF travel to the deposition chamber  11 , and, en route, the CF 2  forms a fluoropolymer coating on the gas conductance line  48 , the flow restrictor  59 , the inlet  40 , the backing plate  13 , the gas distribution plate  12 , the susceptor  14  and the interior surfaces of the deposition chamber  11 . Alternatively, CHF 3  (and, if desired, CF 2  from the remote plasma chamber  50 ) may be flowed into the deposition chamber  11  while an RF plasma is generated within the deposition chamber  11  via the RF generator  32 . As with the microwave plasma of the remote plasma chamber  50 , the RF plasma within the deposition chamber  11  will dissociate CHF 3  into CF 2  which in turn will coat chamber components with a fluoropolymer coating. Thereafter, the chamber  11  may be heated (e.g., via the heater control  20  and the resistive heating element  18  or via any conventional heating mechanism capable of heating the entire chamber to the desired temperature) so as to melt/reflow the fluoropolymer coating. Preferably a heater temperature of about 500-800° F. is employed. In this manner, a uniform fluoropolymer coating, preferably about 0.5-10 μm in thickness, is formed on the chamber components.  
         [0021]    For ex-situ application of protective coatings, chamber components such as the gas distribution plate  12  and the backing plate  13  preferably are uniformly coated with a thin layer (e.g., about 0.5 to 10 microns) of a PTFE, a FEP- or a PFA-contained in a solution or suspension fluid such as water, isopropyl alcohol, etc. After a few minutes of air drying or after an oven bake at 500-800° F. heater temperature, the chamber components may be reinstalled within the processing chamber. Care should be taken to prevent clogging of the small gas injection holes of the gas distribution plate due to capillary effect.  
         [0022]    It should be noted that the inventive protective coating described herein differs from flouropolymers which undesirably accumulate over time on chamber surfaces as a result of flouropolymer deposition on a underlying substrate, or which are formed as a byproduct of certain CVD processes (i.e., are not continuously formed), in that such undesirably accumulated material is characteristically non-uniform, often exhibiting both areas of thick accumulation which can crumble from chamber surfaces, and areas where no material accumulates. Accordingly, such undesirable byproduct and deposited material accumulation must be cleaned from chamber surfaces. However, these undesirable fluoropolymer accumulations do not react with reactive fluorine gas species and therefore must be cleaned by other, less efficient means.  
         [0023]    By coating downstream chamber components with PTFE, FEP or PFA, cleaning rate enhancements of as much as 100% have been observed, and cleaning rate variations between processing chambers have been virtually eliminated. Accordingly, process chamber throughput increases significantly with use of the present invention, and the amount of precursor gas required for cleaning is reduced. Because of the high costs associated with precursor gases such as NF 3 , both monetarily (e.g. NF 3  presently costs $100/lb) and environmentally (e.g., NF 3  is a “global warming” gas,) reduction in precursor gas consumption is extremely beneficial. Moreover, flouropolymers are non-brittle, inexpensive and easy to apply, unlike coatings (e.g., AlF 3 ) which conventionally have been applied to prevent corrosion of chamber surfaces or to prevent accumulated material from crumbling therefrom.  
         [0024]    The foregoing description discloses only the preferred embodiments of the invention, modifications of the above disclosed apparatus and method which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, while the present invention has been described with reference to a PECVD chamber, it will be understood that the invention has applicability to a wide variety of process chambers including thermal deposition chambers. Additionally, cleaning processes employing reactive species (e.g., reactive species generated by an RF plasma within a process chamber, or remote plasma source generated reactive species etc.) may be improved by employing the fluoropolymer coatings described herein. Finally, although any fluoropolymer is believed to enhance cleaning when applied as described herein, the fluoropolymers PTFE, FEP and PFA have been found to significantly enhance cleaning and are preferred.  
         [0025]    Accordingly, while the present invention has been disclosed in connection with the preferred embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.