Abstract:
Methods for bevel edge etching are provided. One example method is for etching a film on a bevel edge of a substrate in a plasma etching chamber. The method includes providing the substrate on a substrate support in the plasma etching chamber. The plasma etching chamber has a top edge electrode and a bottom edge electrode disposed to surround the substrate support. Then flowing an etching process gas through a plurality of edge gas feeds disposed along a periphery of the gas delivery plate. The periphery of the gas deliver plate is oriented above the substrate support and the bevel edge of the substrate, and the flowing is further directed to a space between the top edge electrode and bottom edge electrode. And, flowing a tuning gas through a center gas feed of the gas delivery plate.

Description:
CLAIM OF PRIORITY 
     This is a divisional application of U.S. patent application Ser. No. 12/021,177, filed on Jan. 28, 2008 now U.S. Pat. No. 8,083,890, entitled “Gas Modulation to Control Edge Exclusion in a Bevel Edge Etching Plasma Chamber,” which was continuation-in-part of application Ser. No. 11/440,561, filed May 24, 2006, now U.S. Pat. No. 7,909,960, and which claimed priority under 35 USC 120 as a continuation-in-part of application Ser. No. 11/237,327, filed on Sep. 27, 2005 now abandoned, each of which is herein incorporated by reference. 
    
    
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 11/758,576, filed on Jun. 5, 2007, entitled “Edge Electrodes with Variable Power,” U.S. patent application Ser. No. 11/758,584, filed on Jun. 5, 2007, entitled “Edge Electrodes with Dielectric Covers,” U.S. patent application Ser. No. 11/440,561, filed on May 24, 2006, entitled “Apparatus and Methods to Remove Films on Bevel Edge and Backside of Wafer,” U.S. patent application Ser. No. 11/355,458, filed on Feb. 15, 2006, entitled “Plasma Processing Reactor with Multiple Capacitive and Inductive Power Sources,” and U.S. patent application Ser. No. 11/363,703, filed on Feb. 27, 2006, entitled “Integrated Capacitive and Inductive Power Sources for a Plasma Etching Chamber.” The disclosure of each of the above-identified related applications is incorporated herein by reference. 
     FIELD OF INVENTION 
     The present invention relates in general to substrate manufacturing technologies and in particular to apparatus and methods for the removal of deposited films and/or etch byproducts from a bevel edge of a substrate. 
     BACKGROUND 
     In the processing of a substrate, e.g., a semiconductor substrate (or wafer) or a glass panel such as one used in flat panel display manufacturing, plasma is often employed. During substrate processing, the substrate (or wafer) is divided into a plurality of dies, or rectangular areas. Each of the plurality of dies will become an integrated circuit. The substrate is then processed in a series of steps in which materials are selectively removed (or etched) and deposited. 
     Typically, a substrate is coated with a thin film of hardened emulsion (such as a photoresist mask) prior to etching. Areas of the hardened emulsion are then selectively removed, causing parts of the underlying layer to become exposed. The substrate is then placed on a substrate support structure in a plasma processing chamber. An appropriate set of plasma gases is then introduced into the chamber and a plasma is generated to etch exposed areas of the substrate. 
     During an etch process, etch byproducts, for example polymers composed of Carbon (C), Oxygen (O), Nitrogen (N), Fluorine (F), etc., are often formed on the top and the bottom surfaces near a substrate edge (or bevel edge). Etch plasma density is normally lower near the edge of the substrate, which results in accumulation of polymer byproducts on the top and on the bottom surfaces of the substrate bevel edge. 
     Typically, there are no dies present near the edge of the substrate, for example between about 2 mm to about 15 mm from the substrate edge. However, as successive purposely deposited films and byproduct polymer layers are deposited on the top and bottom surfaces of the bevel edge as a result of several different deposition and etch processes, bonds that are normally strong and adhesive will eventually weaken during subsequent processing steps. The purposely deposited films and polymer layers formed near the bevel edge would then peel or flake off, often onto another substrate during substrate transport. For example, substrates are commonly moved in sets between plasma processing systems via substantially clean containers, often called cassettes. As a higher positioned substrate is repositioned in the container, particles (or flakes) of purposely deposited film and byproducts on the bevel edge may fall on a lower substrate where dies are present, potentially affecting device yield. 
     Dielectric films, such as SiN and SiO 2 , and metal films, such as Al and Cu, are examples of films that are purposely deposited on the substrates. These films can also be deposited on the bevel edge (including the top and bottom surfaces) and do not get removed during etching processes. Similar to etching byproducts, these films at bevel edge can accumulate and flake off during subsequent processing steps, thereby impacting device yield. 
     For advanced technologies, it is desirable to expand the usable areas on the substrate surface to the edge of wafer (or substrate). As mentioned above, there are typically no dies present near the edge of the substrate, for example between about 2 mm to about 15 mm from the substrate edge, which is also called the “edge exclusion zone.” Edge exclusion zone is a region, such as between about 2 mm to about 15 mm from the substrate edge, at the edge of the substrate that is not usable and does not have dies. For advanced technologies, the target is to have usable area expended to less than about 2 mm from the edge of the substrate to increase usable area on the substrate. Therefore, the edge exclusion zone is targeted to be less than 2 mm. 
     In view of the foregoing, there is a need for apparatus and methods that remove unwanted deposits on the bevel edge of substrates to reduce edge exclusion zone to be less than 2 mm from the edge of substrates. Such apparatus and methods would expand usable area and improve process yield on the substrate. 
     SUMMARY 
     The various embodiments provide apparatus and methods of removal of unwanted deposits near the bevel edge of substrates to improve process yield. The embodiments provide apparatus and methods with center and edge gas feeds as additional process knobs for selecting a most suitable bevel edge etching processes to push the edge exclusion zone further outward towards the edge of substrates. Further the embodiments provide apparatus and methods with tuning gas(es) to change the etching profile at the bevel edge and using a combination of center and edge gas feeds to flow process and tuning gases into the chamber. Both the usage of tuning gas and location of gas feed(s) affect the etching characteristics at bevel edge. Total gas flow, gap distance between the gas delivery plate and substrate surface, pressure, and types of process gas(es) are also found to affect bevel edge etching profiles. 
     It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, or a system. Several inventive embodiments of the present invention are described below. 
     In one embodiment, one example method is for etching a film on a bevel edge of a substrate in a plasma etching chamber. This method includes providing the substrate on a substrate support in the plasma etching chamber. The plasma etching chamber has a top edge electrode and a bottom edge electrode disposed to surround the substrate support. The method positions a gas delivery plate in the plasma processing chamber at a distance of less than about 0.6 mm from the substrate support. The flowing an etching process gas through a plurality of edge gas feeds disposed along a periphery of the gas delivery plate. The periphery of the gas deliver plate is oriented above the substrate support and the bevel edge of the substrate, and the flowing is further directed to a space between the top edge electrode and bottom edge electrode. And, flowing a tuning gas through a center gas feed of the gas delivery plate. The tuning gas is directed over a center region of the substrate so as to flow way from the center region and toward the bevel edge of the substrate and mix with the etching process gas. The method also includes applying RF power to one of the top or bottom edge electrodes, wherein the applied power acts to strike a plasma to etch the film of the bevel edge of the substrate. 
     In another embodiment, a method of etching a thin film on a bevel edge of a substrate in a plasma etching chamber is provided. The method includes placing the substrate on a substrate support in the plasma etching chamber. The method also includes flowing an etching process gas through a center gas feed located or an edge gas feed. The center gas feed and the edge gas feed are disposed above the substrate support. The method further includes flowing a tuning process gas through the center gas feed located or the edge gas feed. The tuning gas is used to change the etching plasma characteristics at the bevel edge. 
     In addition, the method includes generating an etching plasma near the bevel edge of the substrate to etch the thin film on the bevel edge by powering a bottom edge electrode or a top edge electrode with a RF power source and grounding the edge electrode that is not powered by the RF power source. The bottom edge electrode surrounds the substrate support and the top edge electrode surrounds the gas distribution plate, wherein the distance between the top edge electrode and the bottom edge electrode is less than about 1.5 cm to confine the treatment plasma. Additionally, the method includes etching the thin film by the generated etching plasma. 
     Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements. 
         FIG. 1A  shows a cross-sectional view of a thin film near a bevel etch, in accordance with one embodiment of the present invention 
         FIG. 1B  shows a cross-sectional view of a thin film with the film on the bevel edge being removed, in accordance with one embodiment of the present invention. 
         FIG. 1C  shows four different bevel edge etching profiles, in accordance with one embodiment of the present invention. 
         FIG. 2  shows a cross-sectional view of a plasma system configured to generate a bevel edge etching plasma, in accordance with one embodiment of the present invention. 
         FIG. 2A  shows a cross-sectional view of center feeds, in accordance with one embodiment of the present invention. 
         FIG. 2B  shows a cross-sectional view of a center feed with multiple gas sources, in accordance with one embodiment of the present invention. 
         FIG. 2C  shows a cross-sectional view of edge feeds, in accordance with one embodiment of the present invention. 
         FIG. 2D  shows a cross-sectional view of an edge feed with multiple gas sources, in accordance with one embodiment of the present invention. 
         FIG. 2E  shows a cross-sectional view of an enlarged region M with bevel edge of  FIG. 2 , in accordance with one embodiment of the present invention. 
         FIG. 2F  shows a cross-sectional view of a plasma system configured to generate a bevel edge etching plasma, in accordance with another embodiment of the present invention. 
         FIG. 2G  shows a top view of a top chamber assembly of the plasma system of  FIG. 2 , in accordance with an embodiment of the present invention. 
         FIG. 2H  shows an enlarged diagram of a region around a center gas feed, in accordance with an embodiment of the present invention. 
         FIG. 2I  shows an enlarged diagram of a region around an edge gas feed, in accordance with an embodiment of the present invention. 
         FIG. 2J  shows a top view of a top chamber assembly of the plasma system of  FIG. 2 , in accordance with another embodiment of the present invention. 
         FIG. 3A  shows bevel etching profiles of 4 different etching processes, in accordance with one embodiment of the present invention. 
         FIG. 3B  shows bevel etching profiles of 4 different etching processes, in accordance with another embodiment of the present invention. 
         FIG. 3C  shows bevel etching profiles of 3 different etching processes, in accordance with one embodiment of the present invention. 
         FIG. 3D  shows bevel etching profiles of 4 different etching processes, in accordance with another embodiment of the present invention. 
         FIG. 4  shows a process flow of generating a bevel edge etching plasma, in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Several exemplary embodiments for improved mechanisms to remove undesirable deposits on the bevel edges of wafers to improve process yield are provided. It will be apparent to those skilled in the art that the present invention may be practiced without some or all of the specific details set forth herein. 
       FIG. 1A  shows a cross-sectional view of a substrate  105  that has a substrate body  100  with a front side  110 , a backside  120  and an edge  130  between the front and backsides, in accordance with one embodiment of the present invention. Substrate body  100  could be a wafer without other films and features. Substrate body  100  could also have various films and features from prior processing. In  FIG. 1A , there is a thin film layer  101  covering the substrate front side  110  and substrate edge  130 . The thin film layer  101  could be a dielectric layer, such as silicon dioxide (SiO2), or silicon nitride (SiN), a metal layer, such as tantalum (Ta), tantalum nitride (TaN), cupper (Cu), or Aluminum (Al). The thin film layer  101  can be a layer of photoresist or etching byproducts. Further, the thin film layer  101  could also be a dielectric layer or a metal layer mixed with photoresist and/or etching byproducts. The thickness of the thin film  101  can range from a few angstroms to a few microns. 
     The thin film layer  101  extends to a distance Y from the substrate edge  130  of the substrate  105 . In one embodiment, the distance Y extends all the way to the center of backside surface  120  of substrate body  100 . In another embodiment, the distance Y is between about 2 mm to about 15 mm from the edge  130 . The thin film layer  101  on the bevel edge needs to be removed to prevent accumulation of thin film that results in possible flaking during future substrate handling and other substrate processing. As described above, for advanced technologies, the trend is to extend the usable area to the edge of substrate. Distance “X” is the distance from the edge  130  that thin film layer  101  should be removed. For advanced technologies, distance “X” is less than about 2 mm, preferable less than about 1 mm, and more preferably less than about 0.5 mm The surface area beyond distance X (towards the center of substrate) is considered usable area for constructing devices. 
       FIG. 1B  shows that after a bevel edge etching process, the film on the bevel edge is removed. The thin film layer  101  on the front side is removed to distance “X” from the edge  130 . As mentioned above, the substrate surface  110  with thin film layer  101  not removed during substrate etching in  FIG. 1B  is considered usable area. 
       FIG. 1C  shows etch rates (ER) near the bevel edge for bevel edge plasma etching processes. Curves  150 ,  152 ,  154 , and  156  show three different etch rate curves near bevel edge. Curve  150  shows results of a conventional process that produces broader bevel etch profile near substrate edge. The etch rate is non-zero at a distance greater than 2 mm from the edge, such as edge  130  of  FIG. 1A . Curve  152  shows results of a process that produces a narrower bevel etch profile than curve  150 . The etch rate on the substrate surface is zero until about 2 mm from the edge. Curves  154  and  156  are even narrower than curve  152 . Etch rate is non-zero from edge to about 1 mm from substrate edge for curve  154  and to about 0.5 mm for curve  156 . For process technologies that require edge exclusion less than about 2 mm, even to 1 mm or 0.5 mm, processes that can produce etch curves, such as curve  152 , curve  154  and curve  156 , can be used. For the purpose of reducing edge exclusion zone to less than about 2 mm from the edge of substrate, processes that produce curves  152 ,  154 , and  156  are better than process that produces curve  150 . 
       FIG. 2  shows an embodiment of a bevel edge plasma processing chamber  200  for performing plasma etching near the bevel edge of the substrate. Chamber  200  has a substrate support  240  with a substrate  250  on top. In one embodiment, the substrate support  240  is an electrostatic chuck, which is powered by a RF (radio frequency) power source (not shown). In another embodiment, the substrate support  240  is a regular electrode. The substrate support  240  can be DC (direct current) or RF biased. Opposing the substrate support  230  is a gas plate  260  with a center gas feed  261 . The feed point  264  of the center gas feed  261  is near above the center of the substrate. The center gas feed  261  is embedded in the gas plate  260  and located near the center of substrate  250 . In one embodiment, there are a number of center gas feeds, such as gas feeds  261 ′,  261 ″, and  261 ″, which are coupled to different gas sources, such as gas sources  271 ″ (for gas X),  271 ″ (for gas Y), and  271 ″ (for gas Z), as shown in  FIG. 2A . In another embodiment, different gas sources feed into a single center gas feed  261 , as shown in  FIG. 2B . The process chamber is also equipped with edge gas feeds  263 , which are located near the bevel edge of substrate  250 . In one embodiment, there are a number of edge gas feeds, such as gas feeds  263 ′,  263 ″, and  263 ″, at the proximity of a location, which are coupled to different gas sources, such as gas sources  273 ″ (for gas M),  273 ″ (for gas N), and  273 ″ (for gas O), as shown in  FIG. 2C . In another embodiment, different gas sources feed into a single edge gas feed at  263  a particular edge location, as shown in  FIG. 2D . More details of the edge gas feeds  263  will be provided below. 
     The substrate support can also be RF powered, biased, or grounded. During etching of substrate  250 , chamber  200  can be RF powered to generate capacivtively coupled etch plasma or inductively coupled etch plasma. The substrate  250  has a bevel edge  217  that includes a top and a bottom surface of the edge of the substrate, as shown in region F of  FIG. 2  and enlarged region M in  FIG. 2E . In  FIG. 2E , bevel edge  217  is highlighted as a bold solid line and curve. 
       FIG. 2F  shows an embodiment of a bevel edge etching process chamber  250 . The process chamber  250  has a center feed  261   p  for process gas, and a center feed  261   T  for tuning gas. Both center gas feeds  261   P ,  261   T  are coupled to a center gas select  275   C , which is coupled to a center gas manifold  276   C . The center gas manifold  276   C  is coupled to a number of gas tanks that supplied various process gases and tuning gas(es) (not shown). Alternatively, there could be more than one center gas feeds  261 P for process gases and more one center gas feeds  261 T for tuning gases, as described above in  FIGS. 2A and 2C . The process chamber  250  also has a number of edge feeds  263   P  for process gas, and a number of edge feeds  263   T  for tuning gas. All edge gas feeds  261   P ,  261   T  are coupled to an edge gas select  275   P , which is coupled to an edge gas manifold  276   P . The center gas manifold  276   P  is coupled to a number of gas tanks that supplied various process gases and tuning gas(es) (not shown). The center gas select  275   C  receives instructions from a chamber process controller  277  and chooses whether and which gas(es) goes into the center gas feeds,  261   P ,  261   T . Similarly, the edge gas select  275   P  receives instructions from a chamber process controller  277  and chooses whether and which gas(es) goes into the edge gas feeds,  263   P ,  263   T . The chamber process controller  277  is also coupled to other parts of process chamber  250  to controller other process parameters, such as temperature, pressure and movement of the substrate support  240 . In one embodiment, the chamber process controller  277  is coupled to a processor  278 , which is coupled to a key board  280  and a monitor  279 . Operators of the processing system  250  can enter instruction through the keyboard  280  and the instruction and process condition can be displayed in the monitor  279 . 
       FIG. 2G  shows an embodiment of a top view of the chamber top assembly  280  of  FIG. 2 . The top assembly  280  includes the chamber top wall  285  (not shown in  FIG. 2G ) and a gas delivery plate  260 , a top dielectric ring  211 , a top edge electrode, and a top insulating ring  215 . The gas delivery plate  260 , the top dielectric ring  211 , the top edge electrode, and the top insulating ring  215  are coupled to the top chamber wall  285 . The center gas feed  281  is embedded in the gas delivery plate  260 . In the embodiment shown in  FIG. 2G , there are 8 locations of edge gas feeds  263 , which are disposed between the top dielectric ring  211  and the top edge electrode  210 . The 8 locations are evenly distributed around the diameters of the top dielectric ring  211 . The 8 locations are merely used as examples. Other number of locations, such as 4-56 locations, can be used too. 
       FIG. 2H  shows an embodiment of an enlarged diagram of a region  281  around the center gas feed  261  of  FIG. 2G . The embodiment shown in  FIG. 2H  illustrates that there could be more than one center gas feeds. Any reasonable and needed number of center gas feeds is allowed.  FIG. 2I  shows an embodiment of an enlarged diagram of a region  283  around the edge gas feed  263  of  FIG. 2G . The embodiment shown in  FIG. 2I  illustrates that there could be more than one edge gas feeds at each edge location. Any reasonable and needed number of edge gas feeds at each edge location is allowed. 
       FIG. 2  J shows another embodiment of edge gas feed  263  of  FIG. 2 . In this embodiment, edge gas feed  263 ′ is a gas ring between the top dielectric ring  211  and the top edge electrode  210 . Process gas(es) and/or tuning gas(es) can be delivered evenly to the process chamber through the gas ring  263 ′. 
     Surrounding the edge of substrate support  240 , there is a bottom edge electrode  220 , made of conductive materials, such as aluminum (Al). Between the substrate support  240  and the bottom edge electrode  220 , there is a bottom dielectric ring  221  electrically separating the substrate support  240  and the bottom edge electrode  220 . In one embodiment, substrate  250  is not in contact with the bottom edge electrode  220 . Beyond the bottom edge electrode  220 , there is another bottom insulating ring  225 , which extends the surface of the bottom edge electrode  220  facing substrate  250 . 
     Surrounding the gas plate  260 , there is a top edge electrode  210 , made of conductive materials, such as aluminum (Al). The top edge electrode  210  is electrically insulated from the gas plate  260  by a top dielectric ring  211 . As mentioned above, the edge gas feed(s)  263  provides process gas(s) to the bevel edge  217  of substrate  250 . In one embodiment, the edge gas feeds  263  provide process gas(s) to feeding points  262  facing the bevel edge  217  of substrate  260  and are between the top edge electrode  210  and the top dielectric ring  211 . Beyond the top edge electrode  210 , there is top insulating ring  215 , which extends the surface of the top edge electrode  210  facing substrate  250 . 
     In one embodiment, the bottom edge electrode  220  is coupled to an RF power source  223  and the top edge electrode  210  is grounded. During a substrate bevel edge treatment process, the RF power source  223  supplies RF power at a frequency between about 2 MHz to about 60 MHz and a power between about 100 watts to about 2000 watts to generate a treatment plasma. During bevel edge treatment the substrate support  240  and the gas delivery plate  260  are kept electrically floating. In another embodiment, the bottom electrode  240  is coupled to an RF power source  224 . During a substrate bevel edge treatment process, the RF power source  224  supplies RF power at a frequency between about 2 MHz to about 60 MHz and a power between about 100 watts to about 2000 watts to generate a treatment plasma. During bevel edge treatment the gas delivery plate  3 = 260  is kept electrically floating, and both the bottom edge electrode  220  and the top edge electrode  210  are grounded. 
     The two embodiments of hardware configurations described above are merely examples, other configurations of bevel edge reactors can also be used. For details of other types of bevel edge reactors, see U.S. patent application Ser. No. 11/758,576 filed on Jun. 5, 2007, entitled “Edge Electrodes with Variable Power,” U.S. patent application Ser. No. 11/758,584 filed on Jun. 5, 2007, entitled “Edge Electrodes with Dielectric Covers,” U.S. patent application Ser. No. 11/440,561 filed on May 24, 2006, entitled “Apparatus and Methods to Remove Films on Bevel Edge and Backside of Wafer,” U.S. patent application Ser. No. 11/355,458 filed on Feb. 15, 2006, entitled “Plasma Processing Reactor with Multiple Capacitive and Inductive Power Sources,” and U.S. patent application Ser. No. 11/363,703 filed on Feb. 27, 2006, entitled “Integrated Capacitive and Inductive Power Sources for a Plasma Etching Chamber.” The disclosure of each of the above-identified related applications is incorporated herein by reference. 
     In one embodiment, the space between the top edge electrode  210  and the bottom edge electrode  220 , D EE , is less than 1.5 cm to ensure the plasma is confined. A D EE  of less than 1.5 cm allows the ratio between the width (D W ) and gap (D EE ) of the opening near substrate edge to be less than 4:1, which ensures plasma confinement. D W  is the width of the opening near the substrate edge. In one embodiment, D W  is the width of the bottom insulating ring  225  or the width of the top insulating ring  215 . The chamber pressure is kept between about 20 mTorr to about 100 Ton, and preferably between about 100 mTorr to about 2 Torr, during the bevel edge etching process. The spacing between the gas distribution plate  260  and substrate  250 , D S , is less than 0.6 mm to ensure no plasma is formed between the top electrode  260  and the substrate  250  during the bevel edge etching process. 
     The embodiment of plasma chamber  200  shown in  FIG. 2  is merely an example. Other embodiments of plasma chamber for bevel edge etching are also possible. In another embodiment, the RF power supply can be coupled to the top edge electrode  210 , while the bottom edge electrode  220  is grounded to generate the capacitively coupled etching plasma. Alternatively, either the top edge electrode  210  or the bottom edge electrode  220  can be replaced with an inductive coil buried in a dielectric material. In this embodiment, the inductive coil is coupled to a RF power source and the opposing edge electrode is grounded. The RF power source supplies power to generate an inductively coupled etching plasma to treat the bevel edge  217 . For further description of the bevel edge plasma etching chamber see U.S. patent application Ser. No. (11/3440,561) filed on May 24, 2006, entitled “Apparatus and Methods to Remove Films on the Bevel Edge and Backside of Wafer.” The disclosure of the above-identified related applications is incorporated herein by reference. 
     Various experiments have been conducted to study the effects of location of gas feed(s), total gas flow, tuning gas type, tuning gas flow, the gap distance between the gas plate  260  and substrate  250  on the etch rate profiles at the bevel edge. An exemplary reference process for etching dielectric film is used for these studies. The process (etching) gases include NF 3  and CO 2 . The film etched is silicon oxide film (SiO 2 ) deposited from tetra-ethyl-ortho-silicate (TEOS). The tuning gas, which is not a reactive gas, used in the study includes nitrogen (N 2 ), argon (Ar), and helium (He). However, in addition to the above-mentioned tuning gas, other types of non-reactive gas, such as other inert gases, can also be used as tuning gas. 
     The exemplary reference process with 10 sccm NF 3  and 200 CO 2  fed from the center gas feed  261  similar to the center gas feed shown in  FIG. 2 . The pressure is about 1500 mTorr. The gap distance between the gas delivery plate  260  and surface of substrate  250  is about 0.4 mm. 
       FIG. 3A  shows a plot of normalized etch rates on different locations on the substrate surface near bevel edge. The normalized etch rates are plotted with the distance from the center of the substrate. The etch rates are normalized to the etch rate at 149.4 mm from the center of the substrate. The substrate has a diameter of 300 mm and a radius of 150 mm. There are four curves in  FIG. 3A . Curve  301  shows the results of the reference process with 10 sccm NF 3  and 200 sccm CO 2  fed from center gas feed(s). Data for curve  302  are generated using a process similar to the process of curve  301 , but with the CO 2  gas flow increased from 200 sccm to 500 sccm. Comparing curves  301  and  302 , the results show that increasing the CO 2  gas flow pushes the etch rate curve toward the bevel edge. 500 sccm CO 2  gas extends the area with zero etch rate to about 2.5 mm from the edge of substrate. In contrast, when the CO 2  gas is at 200 sccm, the etch rate is not zero even when the distance is at about 2.5 mm from the edge of substrate. 
     Curve  303  shows etching results of a process with 10 sccm NF 3  and 200 sccm CO 2  fed from center process gas feed, and with an additional 300 sccm N 2  tuning gas (non-reactive gas) fed from the center gas feed. Curve  304  shows etching results of a process with 10 sccm NF 3  and 200 sccm CO 2  fed from center process gas feed, and with an additional 500 sccm N2 tuning gas (non-reactive gas) fed from the center gas feed. 
     The results show that both the 300 sccm N 2  tuning gas feed and 500 sccm N2 tuning gas from the center gas feed help to push the bevel edge etching rate profile further out towards the substrate edge, in comparison to the standard process of curve  301 . However, none of the processes of curves  301 ,  302 ,  303 , and  304  generate a bevel edge etching profile that has zero etch rate at about 2 mm (or at 148 mm location in the  FIG. 3A  plot) from the edge of substrate. 
       FIG. 3B  shows a plot of normalized etch rates of 4 different processes on the substrate surface. Curve  305  shows the reference process with 10 sccm NF 3  and 200 CO 2  fed from the center gas feed  261 . Curve  305  is identical to curve  301  of  FIG. 3A . Data for curve  306  are generated using a process similar to the process of curve  305 , with the exception that both the NF 3  gas and CO 2  gas are fed from edge gas feed(s), such as edge gas feed  263 . Comparing curves  305  and  306 , the results show that feeding process gases NF 3  and CO 2  from edge gas feed(s) pushes the etch rate curve toward the bevel edge. Processing gas fed from edge gas feeds extends the area with zero etch rate to about 2 mm from the edge of substrate. In contrast, when the processing gas is fed from the center gas feed, the etch rate is not zero even when the distance is 3 mm from the edge of substrate. 
     Curve  307  uses a process similar with curve  305  (reference process) with process gases fed from center gas feed(s), and with an additional 500 sccm N 2  tuning gas (non-reactive gas) fed from center gas feed. Curve  308  a process similar with curve  306 , with process gases fed from edge gas feed(s), and with a 500 sccm N 2  tuning gas (non-reactive gas) fed from center gas feed. The results show that the 500 sccm N 2  tuning gas feed from the center gas feed help to push the edge of zero etch rate from 2 mm of curve  306  (process gases fed from edge) to 1.8 mm of curve  308  (process gases fed from edge). As shown in  FIG. 3B , the 500 sccm N 2  tuning gas feed from the center gas feed helps to push the edge of zero etch rate from greater than 3 mm for curve  305  (process gases fed from center) to 2.6 mm for curve  307  (process gases fed from center). The results favor feeding process gases from the edge, in comparison to feeding process gases from the center. In addition, the results also show that 500 sccm of N 2  turning gas from center gas feed(s) also can push the boundary of zero etch rate further towards the edge of substrate. Both processes with process gases fed from substrate edge (curves  306  and  308 ), either with 500 N 2  tuning gas (curve  308 ) or without N 2  tuning gas (curve  306 ), generate bevel edge etching profiles that have zero etch rate at about 2 mm or less than 2 mm from the edge of substrate. Feeding process gases near the bevel edge is crucial in pushing the boundary to zero etch rate to 2 mm from the edge of substrate. 
     Experiments with varying amount of N 2  tuning gas, 300 sccm, 500 sccm, and 750 sccm, fed from center gas feed(s) show that etch profile at bevel edge for N 2  tuning gas at 500 sccm is slightly better than results for 300 sccm and 750 sccm N2 tuning gas in terms of pushing the etch profile outward toward the edge. However, the results for 300 sccm and 750 sccm N 2  tuning gas processes are not too different from those of 500 sccm N 2  tuning gas process. 
     Experiments with higher CO 2  flow (300 sccm vs. 200 sccm) fed from center feed shows that increased CO 2  flow helps push the etch rate profile outward towards the edge of substrate. 
     In addition, comparing the results of the reference process to a process with 20 sccm NF 3  and 400 sccm CO 2  (2× total flow) fed from center gas feed shows that increased total flow help to push the etch rate profile outward towards the edge of the substrate. For the 2× total flow process, the edge of zero etch rate is at about 2.2 mm from the edge of substrate. In contrast, the edge of zero etch rate for the reference process is more than 3 mm from the edge of substrate. 
       FIG. 3C  compares the results of 3 different processes. Curve  309  is generated using the process with 10 sccm NF 3  and 200 sccm CO 2  at the substrate edge, and with an additional 750 sccm N 2  tuning gas fed from center. The process is run at normal gap space of 0.4 mm. The results of curve  309  is very close to curve  308  of  FIG. 3B . As mentioned above, the results of using 750 sccm N 2  tuning gas and 500 sccm N 2  gas at center feed(s) are quite close. Curve  310  uses the same process as curve  309 , with the exception of using a gap space of 0.35 mm between gas delivery plate and the substrate. Curve  311  uses the same process as curve  309 , with the exception of using a gap space of 0.45 mm between gas delivery plate and the substrate. The results show that a gap space of 0.4 mm yields the best results. 
       FIG. 3D  compares the results of 4 different processes. Curve  312  is generated using a process with 10 sccm NF 3  and 200 sccm CO 2  fed at the substrate edge. Curve  313  is generated using the same process as curve  309 , but with an additional 500 sccm N 2  tuning gas fed at the center gas feed. The results show similar conclusion, as the previously mentioned, that adding 500 sccm N 2  tuning gas helps push the edge of zero etch rate further outward (comparing curves  306  and  308  of  FIG. 3B ). Curve  314  uses the same process as curve  313 , but with a different tuning gas Ar at the same flow rate of 500 sccm. The effect of adding 500 sccm Ar tuning gas is worse than adding 500 sccm N 2  tuning gas (curve  313 ) and is even worse than not adding any tuning gas at all (curve  312 ). Curve  315  uses a process with 10 sccm NF 3  and 200 sccm CO 2  at the substrate edge (similar to curves  312 ,  313 , and  314 ), but the tuning gas fed at center gas feed is a combination of 200 sccm N 2  with 500 sccm helium (He). The results show that the combination of 200 sccm N 2  with 500 sccm He yields best results. 
     The results above show that there having center and edge gas feeds provide additional process knobs to use for selecting a most suitable bevel edge etching processes. In addition, adding a tuning gas, such as N 2 , Ar, or He, or a mixture of multiple tuning gases can change the etching profile at the bevel edge of substrate. Further total gas flow and gap distance between the gas delivery plate and substrate surface can also affects etching profiles. In addition, as shown in the results and description above, process gas type can have an impact on the etching profiles and interacts with the tuning gas. The various factors mentioned above either change the plasma composition, or changes characteristics at the bevel edge. The changes affect the bevel edge etching profiles. 
       FIG. 4  shows an exemplary process flow  400  of generating a bevel edge etching plasma by feeding process gas from edge gas feed(s) and feeding a tuning gas from center gas feed(s) to a process chamber. At step  401 , a substrate is place on a substrate support in a bevel edge etch plasma chamber. At step  402 , process gas(es) is fed to either an edge gas feed(s) or a center gas feed(s) in the processing chamber. At an optional process step  403 , a tuning gas(es) is fed to either an edge gas feed(s) or a center gas feed(s) in the processing chamber. At step  404 , an etching plasma is generated near the bevel edge of the substrate by powering either a top edge electrode or a bottom edge electrode. If the top edge electrode is powered, the bottom edge electrode is grounded. If the bottom edge electrode is powered, the top edge electrode is grounded. At step  405 , the thin film at the bevel edge is removed by the bevel edge etching plasma. The plasma etching chamber is configured to generate the bevel edge etching plasma that etches thin film at the bevel edge with edge exclusion zone less than about 2 mm from the edge of substrate. In one embodiment, the edge exclusion zone is less than about 1 mm from the edge of substrate. In another embodiment, the edge exclusion zone is less than about 0.5 mm from the edge of substrate. 
     The exemplary processes discussed above are for TEOS SiO 2  etching. However, the concept of the present invention can be for etching any types of films, such as other dielectric films, metal films, semiconductor films, and barrier films, at bevel edges. Tuning gas, location of gas feed(s), gap distance, total gas flow, type of processing gas can all have an impact on the etching profiles at the bevel edge. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.