Abstract:
Embodiments of a gas distribution plate for distributing gas in a processing chamber for large area substrates are provided. The embodiments describe a gas distribution plate assembly for a plasma processing chamber having a cover plate comprises a diffuser plate having an upstream side, a downstream side facing a processing region, and a plurality of gas passages formed through the diffuser plate, and a baffle plate, placed between the cover plate of the process chamber and the diffuser plate, having a plurality of holes extending from the upper surface to the lower surface of the baffle plate, wherein the plurality of holes have at least two sizes. The small pinholes of the baffle plate are used to allow sufficient pass-through of gas mixture, while the large holes of the baffle plate are used to improve the process uniformity across the substrate.

Description:
BACKGROUND OF THE DISCLOSURE  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the invention generally relate to a baffle plate used to improve film deposition uniformity in a deposition processing chamber.  
         [0003]     2. Description of the Background Art  
         [0004]     Liquid crystal displays or flat panels are commonly used for active matrix displays such as computer and television monitors. Plasma enhanced chemical vapor deposition (PECVD) is generally employed to deposit thin films on a substrate such as a transparent substrate for flat panel display or semiconductor wafer. PECVD is generally accomplished by introducing a precursor gas or gas mixture into a vacuum chamber that contains a substrate. The precursor gas or gas mixture is typically directed downwardly through a distribution plate situated near the top of the chamber. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material on a surface of the substrate that is positioned on a temperature controlled substrate support. Volatile by-products produced during the reaction are pumped from the chamber through an exhaust system.  
         [0005]     Flat panels processed by PECVD techniques are typically large, often exceeding 370 mm×470 mm. Large area substrates approaching and exceeding 4 square meters are envisioned in the near future. Gas distribution plates (or gas diffuser plates) utilized to provide uniform process gas flow over flat panels are relatively large in size, particularly as compared to gas distribution plates utilized for 200 mm and 300 mm semiconductor wafer processing.  
         [0006]      FIG. 1  illustrates a cross-sectional schematic view of a thin film transistor structure. A common low temperature polysilicon TFT structure is the top gate TFT structure shown in  FIG. 1 . The substrate  101  may comprise a material that is essentially optically transparent in the visible spectrum, such as, for example, glass or clear plastic. The substrate may be of varying shapes or dimensions. Typically, for TFT applications, the substrate is a glass substrate with a surface area greater than about 500 mm 2 . The substrate may have an underlayer  102  thereon. The underlayer  102  may be an insulating material, such as, for example, silicon dioxide (SiO 2 ) or silicon nitride (SiN). An n-type doped silicon layer  104   n  is deposited on the underlayer  102 . Alternatively, the silicon layer may be a p-type doped layer. In one embodiment, the n-type doped silicon layer  104   n  is an amorphous silicon, which is melted and re-crystallized rapidly by an annealing process to form a polysilicon layer.  
         [0007]     After the n-type doped silicon layer  104   n  is formed, selected portions thereof are ion implanted to form p-type doped regions  104   p  adjacent to n-type doped regions  104   n.  The interfaces between n-type regions  104   n  and p-type regions  104   p  are semiconductor junctions that support the ability of the thin film transistor to act as a switching device. By ion doping portions of semiconductor layer  104 , one or more semiconductor junctions are formed, with an intrinsic electrical potential present across each junction.  
         [0008]     A gate dielectric layer  108  is deposited on the n-type doped regions  104   n  and the p-type doped regions  104   p.  The gate dielectric layer  108  may comprise, for example, silicon dioxide (SiO 2 ), silicon nitride (SiN), or silicon oxynitride (SiON), deposited using an embodiment of a PECVD system in accordance with this invention. In one embodiment, the gate dielectric layer  103  is a silicon dioxide (SiO 2 ) layer, deposited using TEOS (tetraethylorthosilicate) and oxygen. TEOS is a liquid source precursor and can be vaporized to be carried into the process chamber. TEOS oxide film is known to have better comformality than silane oxide in the semiconductor industry.  
         [0009]     A gate metal layer  110  is deposited on the gate dielectric layer  108 . The gate metal layer  110  comprises an electrically conductive layer that controls the movement of charge carriers within the thin film transistor. The gate metal layer  110  may comprise a metal such as, for example, aluminum (Al), tungsten (W), chromium (Cr), tantalum (Ta), or combinations thereof, among others. The gate metal layer  110  may be formed using conventional deposition techniques. After deposition, the gate metal layer  110  is patterned to define gates using conventional lithography and etching techniques. After the gate metal layer  110  is formed, an interlayer dielectric  112  is formed thereon. The interlayer dielectric  112  may comprise, for example, an oxide such as silicon dioxide. Interlayer dielectric  112  may be formed using conventional deposition processes. The interlayer dielectric  112  is patterned to expose the n-type doped regions  104   n.  The patterned regions of the interlayer dielectric  112  are filled with a conductive material to form contacts  120 . The contacts  120  may comprise a metal such as, for example, aluminum (Al), tungsten (W), molybdenum (Mo), chromium (Cr), tantalum (Ta), indium tin oxide (ITO), zinc oxide (ZnO) and combinations thereof, among others. The contacts  120  may be formed using conventional deposition techniques.  
         [0010]     Thereafter, a passivation layer  122  may be formed thereon in order to protect and encapsulate a completed thin film transistor  125 . The passivation layer  122  is generally an insulator and may comprise, for example, silicon oxide or silicon nitride. The passivation layer  122  may be formed using conventional deposition techniques. While  FIG. 1  as well as the supporting discussion provide an embodiment in which the doped silicon layer  104  is an n-type silicon layer with p-type dopant ions implanted therein, one skilled in the art will recognize that forming this and other configurations are within the scope of the invention described below. For example, one may deposit a p-type silicon layer and implant n-type dopant ions in regions thereof. The TFT structure described here is merely used as an example.  
         [0011]      FIG. 2A  is a schematic cross-sectional view of one embodiment of a prior art plasma enhanced chemical vapor deposition system  200 , available from AKT, a division of Applied Materials, Inc., Santa Clara, Calif. The system  200  generally includes a processing chamber  202  coupled to a gas source  204 . The processing chamber  202  has walls  206  and a bottom  208  that partially define a process volume  212 . The process volume  212  is typically accessed through a port (not shown) in the walls  206  that facilitates movement of a substrate  240  into and out of the processing chamber  202 . The walls  206  and bottom  208  are typically fabricated from a unitary block of aluminum or other material compatible with processing. The walls  206  support a lid assembly  210  that contains a pumping plenum  214  that couples the process volume  212  to an exhaust port (that includes various pumping components, not shown).  
         [0012]     A temperature controlled substrate support assembly  238  is centrally disposed within the processing chamber  202 . The support assembly  238  supports a glass substrate  240  during processing. In one embodiment, the substrate support assembly  238  comprises an aluminum body  224  that encapsulates at least one embedded heater  232 .  
         [0013]     Generally, the support assembly  238  has a lower side  226  and an upper side  234 . The upper side  234  supports the glass substrate  240 . The lower side  226  has a stem  242  coupled thereto. The stem  242  couples the support assembly  238  to a lift system (not shown) that moves the support assembly  238  between an elevated processing position (as shown) and a lowered position that facilitates substrate transfer to and from the processing chamber  202 . The stem  242  additionally provides a conduit for electrical and thermocouple leads between the support assembly  238  and other components of the system  200 .  
         [0014]     A bellows  246  is coupled between support assembly  238  (or the stem  242 ) and the bottom  208  of the processing chamber  202 . The bellows  246  provides a vacuum seal between the chamber volume  212  and the atmosphere outside the processing chamber  202  while facilitating vertical movement of the support assembly  238 .  
         [0015]     The support assembly  238  generally is grounded such that RF power supplied by a power source  222  to a gas distribution plate assembly  218  positioned between the lid assembly  210  and substrate support assembly  238  (or other electrode positioned within or near the lid assembly of the chamber) may excite gases present in the process volume  212  between the support assembly  238  and the distribution plate assembly  218 . The RF power from the power source  222  is generally selected commensurate with the size of the substrate to drive the chemical vapor deposition process. The precursor gas or gas mixture in the chamber is energized (e.g., excited) into a plasma by applying radio frequency (RF) power to the chamber from one or more RF sources coupled to the chamber. The excited gas or gas mixture reacts to form a layer of material on a surface of the substrate  240  that is positioned on a temperature controlled substrate support assembly  238 .  
         [0016]     The support assembly  238  additionally supports a circumscribing shadow frame  248 . Generally, the shadow frame  248  prevents deposition at the edge of the glass substrate  240  and support assembly  238  so that the substrate does not stick to the support assembly  238 . The support assembly  238  has a plurality of holes  228  disposed therethrough that accept a plurality of lift pins  250 . The lift pins  250  are typically comprised of ceramic or anodized aluminum.  
         [0017]     The lid assembly  210  provides an upper boundary to the process volume  212 . The lid assembly  210  typically can be removed or opened to service the processing chamber  202 . In one embodiment, the lid assembly  210  is fabricated from aluminum (Al). The lid assembly  210  includes a pumping plenum  214  formed therein coupled to an external pumping system (not shown). The pumping plenum  214  is utilized to channel gases and processing by-products uniformly from the process volume  212  and out of the processing chamber  202 .  
         [0018]     The lid assembly  210  typically includes an entry port  280  through which process gases provided by the gas source  204  are introduced into the processing chamber  202 . The entry port  280  is also coupled to a cleaning source  282 . The cleaning source  282  typically provides a cleaning agent, such as dissociated fluorine, that is introduced into the processing chamber  202  to remove deposition by-products and films from processing chamber hardware, including the gas distribution plate assembly  218 .  
         [0019]     The gas distribution plate assembly  218  is coupled to an interior side  220  of the lid assembly  210 . The gas distribution plate assembly  218  is typically configured to substantially follow the profile of the glass substrate  240 , for example, polygonal for large area flat panel substrates and circular for wafers. The gas distribution plate assembly  218  includes a perforated area  216  through which process and other gases supplied from the gas source  204  are delivered to the process volume  212 . The perforated area  216  of the gas distribution plate assembly  218  is configured to provide uniform distribution of gases passing through the gas distribution plate assembly  218  into the processing volume  212 .  
         [0020]     The gas distribution plate assembly  218  typically includes a diffuser plate (or distribution plate)  258  suspended from a hanger plate  260 . The diffuser plate  258  and hanger plate  260  may alternatively comprise a single unitary member. A plurality of gas passages  262  are formed through the diffuser plate  258  to allow a predetermined distribution of gas passing through the gas distribution plate assembly  218  and into the process volume  212 . The hanger plate  260  maintains the diffuser plate  258  and the interior surface  220  of the lid assembly  210  in a spaced-apart relation, thus defining a plenum  264  therebetween. The plenum  264  allows gases flowing through the lid assembly  210  to uniformly distribute across the width of the diffuser plate  258  so that gas is provided uniformly above the center perforated area  216  and flows with a uniform distribution through the gas passages  262 .  
         [0021]      FIG. 2B  is a partial sectional view of an exemplary diffuser plate  258  that is described in commonly assigned United States Patent Application Serial No. 10/824,347, titled “Gas Diffusion Shower Head Design For Large Area Plasma Enhanced Chemical Vapor Deposition”, filed on Apr. 14, 2004. For example, for a 696468 mm 2  (e.g. 762 mm×914 mm) diffuser plate, the diffuser plate  258  includes about 12,000 gas passages  262 . For larger diffuser plates used to process larger flat panels, the number of gas passages  262  could be as high as 100,000. The gas passages  262  are generally patterned to promote uniform deposition of material on the substrate  240  positioned below the diffuser plate  258 . Referring to  FIG. 2B , in one embodiment, the gas passage  262  is comprised of a restrictive section  422 , and a conical opening  406 . The restrictive section  422  passes from the first side  418  of the diffuser plate  258  and is coupled to the conical opening  406 . The conical opening  406  is coupled to the restrictive section  422  and flares radially outwards from the restrictive section  422  to the second side  420  of the diffuser plate  258 . The second side  420  faces the surface of the substrate. The flaring angle  416  of the conical opening  406  is between about 20 to about 35 degrees.  
         [0022]     The flared openings  406  promote plasma ionization of process gases flowing into the processing region  212 . Moreover, the flared openings  406  provide larger surface area for hollow cathode effect to enhance plasma discharge. In one embodiment, the diameter of the restrictive section  422  is 1.40 mm (or 0.055 inch). The length of the restrictive section  422  is 14.35 mm (or 0.565 inch). The conical opening  406  has a diameter of 7.67 mm (or 0.302 inch) on the second side  420  of the diffuser plate  258 . The flaring angle of the flared opening  406  is 22 degree. The length of the flared opening is 16.13 mm (or 0.635 inch).  
         [0023]     As the size of substrate continues to grow in the TFT-LCD industry, especially, when the substrate size is at least about 100 cm by about 100 cm (or about 10,000 cm 2 ), film thickness uniformity value of some films becomes too large to meet the stringent requirement of some device manufacturers for large area plasma-enhanced chemical vapor deposition (PECVD). For example, gate dielectric thickness uniformity requirement is below 2-3% for some manufacturers and could not be achieved by the existing designs of gas distribution plates.  
         [0024]     Therefore, there is a need for an improved gas distribution plate assembly that improves the control of film properties, such as film thickness uniformity.  
       SUMMARY OF THE INVENTION  
       [0025]     Embodiments of a gas distribution plate for distributing gas in a processing chamber are provided. In one embodiment, a gas distribution plate assembly for a plasma processing chamber having a cover plate comprises a diffuser plate having an upstream side, a downstream side facing a processing region, and a plurality of gas passages formed through the diffuser plate, and a baffle plate, placed between the cover plate of the process chamber and the diffuser plate, having a plurality of holes extending from the upper surface to the lower surface of the baffle plate, wherein the plurality of holes have at least two sizes.  
         [0026]     In another embodiment, a plasma processing chamber with a cover plate comprises a diffuser plate having an upstream side, a downstream side facing a processing region, and a plurality of gas passages formed through the diffuser plate, and a baffle plate, placed between the cover plate of the process chamber and the diffuser plate, having a plurality of holes extending from the upper surface to the lower surface of the baffle plate, wherein the plurality of holes have at least two sizes.  
         [0027]     In another embodiment, a method of depositing a thin film on a substrate comprises placing a substrate in a process chamber having a cover and with a diffuser plate having an upstream side, a downstream side facing a processing region, and a plurality of gas passages formed through it, and a baffle plate, placed between the cover plate of the process chamber and the diffuser plate, having a plurality of holes extending from the upper surface to the lower surface of the baffle plate, wherein the plurality of holes have at least two sizes, flowing process gas(es) through the baffle plate and the diffuser plate toward a substrate supported on a substrate support, creating a plasma between the diffuser plate and the substrate support, and depositing a thin film on the substrate in the process chamber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The teachings of the present invention can be readily understood by considering the following detailed description in conjunction with the accompanying drawings, in which:  
         [0029]      FIG. 1  (Prior Art) depicts a cross-sectional schematic view of a bottom gate thin film transistor.  
         [0030]      FIG. 2A  (Prior Art) is a schematic cross-sectional view of an illustrative processing chamber having a gas diffuser plate.  
         [0031]      FIG. 2B  (Prior Art) depicts a cross-sectional schematic view of the gas diffuser plate of  FIG. 2A .  
         [0032]      FIG. 3A  is a schematic cross-sectional view of an illustrative processing chamber having an exemplary gas diffuser plate and an exemplary baffle plate.  
         [0033]      FIG. 3B  depicts a cross-sectional schematic view of the exemplary baffle plate placed between a top plate and the exemplary diffuser plate.  
         [0034]      FIG. 4  shows the process flow of depositing a thin film on a substrate in a process chamber with a diffuser plate.  
         [0035]      FIG. 5A  shows the tetraethylorthosilicate (TEOS) oxide deposition rate measurement across a 920 mm by 730 mm substrate collected from deposition with a gas distribution assembly without a baffle plate.  
         [0036]      FIG. 5B  shows the TEOS oxide deposition rate measurement across a 920 mm by 730 mm substrate collected from deposition with a gas distribution assembly with a baffle plate with small pinholes.  
         [0037]      FIG. 5C  shows a top view of a baffle plate with symmetrically distributed small pinholes.  
         [0038]      FIG. 5D  shows the TEOS oxide deposition rate measurement across a 920 mm by 730 mm substrate collected from deposition with a gas distribution assembly with a baffle plate with small pinholes and large holes.  
         [0039]      FIG. 5E  shows a top view of a baffle plate with symmetrically distributed large holes.  
         [0040]      FIG. 6A  shows the SiN deposition rate measurement across a 920 mm by 730 mm substrate collected from deposition with a gas distribution assembly without a baffle plate.  
         [0041]      FIG. 6B  shows the SiN deposition rate measurement across a 920 mm by 730 mm substrate collected from deposition with a gas distribution assembly with a baffle plate with small pinholes and large holes. 
     
    
       [0042]     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures.  
       DETAILED DESCRIPTION  
       [0043]     The invention generally provides a gas distribution assembly for providing gas delivery within a processing chamber. The invention is illustratively described below in reference to a plasma enhanced chemical vapor deposition system configured to process large area substrates, such as a plasma enhanced chemical vapor deposition (PECVD) system, available from AKT, a division of Applied Materials, Inc., Santa Clara, Calif. However, it should be understood that the invention has utility in other system configurations such as etch systems, other chemical vapor deposition systems and any other system in which distributing gas within a process chamber is desired, including those systems configured to process round substrates.  
         [0044]     We have determined that the uniformity of reactive plasma distribution in the process chamber can be improved by adding a baffle plate  257  to the gas distribution plate assembly  218 , as shown in  FIG. 3A . The baffle plate  257  is placed between the cover plate  303  of the lid assembly  210  and the gas diffuser plate  258 . The baffle plate  257  is typically configured to substantially follow the profile of the gas distribution plate  258 , for example, polygonal for large area flat panel substrates and circular for wafers. The holes  253  across the baffle plate  257  and the gas passages  262  across the gas diffuser plate  258  together affect the gas distribution from the gas entry port  280 .  FIG. 3B  is a drawing that shows the relationship between the cover plate  303 , the baffle plate  257  and the diffuser plate  258 . The baffle plate  257  is typically fabricated from stainless steel, aluminum (Al), anodized aluminum, nickel (Ni) or other RF conductive material. The baffle plate  257  could be cast, brazed, forged, hot iso-statically pressed or sintered. The baffle plate  257  is configured with a thickness that maintains sufficient flatness across the aperture  266  as not to adversely affect substrate processing. The baffle plate  257  also should be kept relatively thin to prevent excessive drilling time to make holes  253 . In one embodiment, the thickness of the baffle plate  257  is between about 0.02 inch to about 0.20 inch. Since the baffle plate  257  works together with the gas diffuser plate  258  to affect the gas distribution uniformity, the distance “D” between the baffle plate  257  and the gas diffuser plate  258  should be kept small. In one embodiment, the distance “D” is below 0.6 inch. If the distance between the two plates is too large, the affect of the baffle plate  257  would diminish, since the gas or gas mixture would redistribute between the two plates.  
         [0045]     The holes  253  across the baffle plate  257  have more than one size. The holes  253  should distribute symmetrically across the baffle plate to increase the gas distribution uniformity. The holes  253  are typically cylindrical; however, other shapes of holes can also be used. Different sizes of holes could be placed across the baffle plate  257  symmetrically to control the gas distribution uniformity. In one embodiment, the baffle plate  257  has holes  253  with at least two sets of sizes, small pinholes and large holes. The small pinholes are needed to transport high-flow-rate gas mixture from upstream to downstream without building up pressure in the blocker plate upstream plenum  264 . Building up pressure in the blocker plate upstream plenum  264  could result in recombination of reactive radicals, such as the fluorine radicals from the remote plasma clean source. Large holes are used to adjust the film deposition thickness uniformity and profile across the substrate. These large holes alone are not enough for high gas flow, such as flow rate &gt;3000 sccm, to pass through. For example during remote plasma clean (RPS) clean, the cleaning gas flow rate is about 4000 sccm. Sufficient numbers of small pinholes would prevent the pressure build up in the block plate upstream plenum  264 . The small pinholes could be all at one size or at more than one size. In one embodiment, the diameters of the small pinholes are kept below 1.27 mm (or 0.05 inch). The large holes could also be at one size or at more than one size. In one embodiment, the diameters of these the large holes are between about 1.59 mm (or 1/16 inch) to about 6.35 mm (or ¼ inch).  
         [0046]     The total cross-sectional areas of the small pinholes should be kept to larger than 1 inch 2  to ensure enough pass-through for the gas mixture, such as cleaning gas species generated by a RPS (remote plasma source) unit. In one embodiment, the diameters of the large holes are kept greater than 1.56 mm (or 1/16 inch).  
         [0047]     The process of depositing a thin film in a process chamber is shown in  FIG. 4 . The process starts at step  401  by placing a substrate in a process chamber with a gas distribution assembly. Next at step  402 , flow process gas(es) through the gas distribution assembly toward a substrate supported on a substrate support. Then at step  403 , create a plasma between the gas distribution assembly and the substrate support. At step  404 , deposit a thin film on the substrate in the process chamber.  
         [0048]      FIG. 5A  shows a thickness profile of a TEOS oxide film across a glass substrate. The size of the substrate is 920 mm by 730 mm. The gas distribution assembly does not include a baffle plate. The diffuser plate has diffuser holes with design shown in  FIG. 2B . The diameter of the restrictive section  422  is 1.40 mm (or 0.055 inch). The length of the restrictive section  422  is 14.35 mm (or 0.565 inch). The conical opening  406  has a diameter of 7.67 mm (or 0.302 inch) on the second side  420  of the diffuser plate  258 . The flaring angle of the flared opening  406  is 22 degrees. The length of the flared opening is 16.13 mm (or 0.635 inch). The TEOS oxide film is deposited using 850 sccm TEOS, 300 sccm He, and 10000 sccm O 2 , under 0.95 Torr, and 2700 watts source power. The spacing between the diffuser plate  258  and the substrate support assembly  238  is 11.94 mm (or 0.47 inch). The process temperature is maintained at about 400° C. The deposition rate is averaged to be 1800 Å/min and the thickness uniformity (with 15 mm edge exclusion) is about 5.5%, which is higher than the 2-3% manufacturing specification for some manufacturers. The thickness profile shows a center thick and edge thick profile, or “W shape” profile.  
         [0049]      FIG. 5B  shows a thickness profile of a TEOS oxide film across a glass substrate. The size of the substrate is 920 mm by 730 mm. The gas distribution assembly includes a baffle plate, in addition to the diffuser plate used for  FIG. 5A  deposition. The baffle plate only has small, cylindrical pinholes. The diameter of the small pinholes is 0.41 mm (or 0.016 inch). They are totally 8426 holes across the baffle plate.  FIG. 5C  shows the pattern of the pinholes on the baffle plate. The pinholes are radially and symmetrically distributed from the center of the blocker plate to the edges of the blocker plate. In one embodiment, the density of the pinholes near the center of the blocker plate is higher than the density of pinholes near the edges of the blocker plate.  
         [0050]     The distance between the baffle plate and the diffuser plate is 12.55 mm (or 0.494 inch). The thickness of the baffle plate is 1.37 mm (or 0.054 inch). The diffuser plate is similar to the one used for  FIG. 5A  deposition. The spacing between the diffuser plate and the support assembly is 11.94 mm (or 0.47 inch). The deposition condition and process are the same as those of  FIG. 5A . The deposition rate is found to average about 1800 Å/min and the thickness uniformity (with 15 mm edge exclusion) is about 5.0%, which is still higher than the manufacturing specification. The thickness profile still shows a center thick and edge thick profile, or “W shape” profile. The results show that a baffle plate with small pinholes only does not improve the TEOS uniformity.  
         [0051]      FIG. 5D  shows a thickness profile of a TEOS oxide film across a glass substrate. The size of the substrate is 920 mm by 730 mm. The gas distribution assembly includes a baffle plate. The baffle plate only has small, cylindrical pinholes, and large, cylindrical holes. The diameter of the small pinholes is 0.41 mm (or 0.016 inch). There are 8426 pinholes across the baffle plate. The size and location of the small pinholes are similar to the small pinholes on the baffle plate used for  FIG. 5B  deposition.  FIG. 5C  shows the pattern of the small pinholes on the baffle plate. The baffle plate also has large holes with diameters 1.59 mm (or 1/16 inch), 3.18 mm (or ⅛ inch), and 4.76 mm (or 3/16 inch). There are 14 holes with diameter of 1.59 mm, 4 holes with diameter of 3.18 mm and 4 holes with diameter of 4.76 mm. Their distribution across the baffle plate is shown in  FIG. 5E . The distance between the baffle plate and the diffuser plate is 12.55 mm (or 0.494 inch). The thickness of the baffle plate is 1.37 mm (or 0.054 inch). The diffuser plate is similar to the one used for deposition in  FIGS. 5A and 5B . The spacing between the diffuser plate and the support assembly is 11.94 mm (or 0.47 inch). The deposition condition and process are the same as those of  FIG. 5A  and  FIG. 5B . The deposition rate is found to be averaged about 1800 Å/min and the thickness uniformity (with 15 mm edge exclusion) is about 1.8%, which is within the manufacturing specification. The thickness profile shows a smooth profile from center to edge. The results show that a baffle plate with small pinholes and large holes improve the TEOS uniformity.  
         [0052]     The addition of the baffle plate does not appear to affect other TEOS oxide film properties. Table 1 compares stress, refractive index (RI), Si—O peak position, and wet etch rate.  
                                     TABLE 1                           Comparison of film properties on substrates deposited with       TEOS Oxide film.                    Stress   Si—O   WER       Baffle Plate   RI   (E9Dynes/cm 2 )   Peak Position   (Å/min)               None   1.46   C0.7   1080   2043       small pinholes   1.46   C0.8   1080   2058       small pinholes + large   1.46   C0.6   1080   2093       holes                  
 
         [0053]     The refractive index (RI), film stress, Si—O peak position data and wet etch rate (WER) data all show similar values for three types of baffle plates. The Si—O peak position is measured by FTIR (Fourier Transform Infrared Spectroscopy). Wet etch rate is measured by immersing the samples in a BOE (buffered oxide etch) 6:1 solution.  
         [0054]     In addition to TEOS oxide film, the effect of the baffle plate on other types of dielectric film has also been investigated.  FIG. 6A  shows the SiN film deposition rate across the substrate surface, using a gas distribution assembly that is the same as the gas distribution assembly of  FIG. 5A  (without a baffle plate). The SiN film is deposited using 810 sccm SiH 4 , 6875 sccm NH 3 , and 9000 sccm N 2 , under 1.60 Torr, and 3400 watts source power. The spacing between the diffuser plate and the support assembly is 28.83 mm (or 1.135 inch). The process temperature is maintained at about 400° C. The deposition rate is averaged to be about 1850 Å/min and the thickness uniformity (with 15 mm edge exclusion) is about 2.5%, which is within the manufacturing specification. The thickness profile shows a smooth profile from center to edge.  
         [0055]      FIG. 6B  shows the SiN film deposition rate across the substrate surface, using a gas distribution assembly that is the same as the gas distribution assembly of  FIG. 5D  (with a baffle plate with small pinholes and large holes). The SiN film is deposited using 810 sccm SiH 4 , 6875 sccm NH 3 , and 9000 sccm N 2 , under 1.60 Torr, and 3400 watts source power. The spacing between the diffuser plate and the support assembly is 28.83 mm (or 1.135 inch). The process temperature is maintained at about 400° C. The deposition rate is averaged to be about 1850 Å/min and the thickness uniformity (with 15 mm edge exclusion) is about 2.5%, which is within the manufacturing specification. The thickness profile also shows a smooth profile from center to edge.  
         [0056]     The results show that SiN film thickness across the substrate is not affected by the addition of a baffle plate with small pinholes and large holes such as the one used for depositing TEOS film in  FIG. 5D  and described in  FIG. 5C  and  FIG. 5E . The addition of the baffle plate does not affect other SiN film properties. Table 2 compares stress, refractive index (RI), N—H/Si—H ratio, and wet etch rate.  
                                     TABLE 2                           Comparison of film properties on substrates deposited with SiN film.                    Stress       WER       Baffle Plate   RI   (E9Dynes/cm 2 )   N—H/Si—H   (Å/min)               None   1.87   T5.7   19.6/16.8   1878       small pinholes + large   1.87   T5.3   19.7/16.3   1849       holes                  
 
         [0057]     The refractive index (RI), film stress, N—H/Si—H ratio data and wet etch rate (WER) data all show similar values for substrates deposited with or without a baffle plate with small pinholes and large holes as used in  FIG. 5D  deposition and described in  FIG. 5C  and  FIG. 5E . The N—H/Si—H ratio is measured by FTIR. Wet etch rate is measured by immersing the samples in a BOE (buffered oxide etch) 6:1 solution.  
         [0058]     The results show that using a baffle plate with small pinholes and large holes improves the TEOS oxide thickness uniformity and does not affect the other film properties of the TEOS film. The results also show that using the same baffle plate with small pinholes and large holes does not affect the film thickness uniformity and other film properties of SiN film. The difference could be due to the fact that TEOS is a liquid source and also has a higher molecular weight.  
         [0059]     Gas distribution plates of gas distribution plate assembly that may be adapted to benefit from the invention described above are described in commonly assigned U.S. patent application Ser. No. 09/922,219, filed Aug. 8, 2001 by Keller et al., U.S. patent application Ser. No. 10/140,324, filed May 6, 2002 by Yim et al., and U.S. Ser. No. 10/337,483, filed Jan. 7, 2003 by Blonigan et al., U.S. Pat. No. 6,477,980, issued Nov. 12, 2002 to White et al., U.S. patent application Ser. No. 10/417,592, filed Apr. 16, 2003 by Choi et al., and U.S. patent application Ser. No. 10/823,347, filed on Apr. 12, 2004 by Choi et al., which are hereby incorporated by reference in their entireties.  
         [0060]     Although the processes and examples used are for making thin film transistor devices, the concept of the invention can be used for making OLED application, solar panel substrates and other applicable devices.  
         [0061]     Although several preferred embodiments which incorporate the teachings of the present invention have been shown and described in detail, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings.