Patent Publication Number: US-2002000198-A1

Title: The dome: shape and temperature controlled surfaces

Description:
FIELD OF THE INVENTION  
       [0001] The present invention relates to an apparatus and method for processing semiconductor substrates, and more particularly, to a high density plasma (HDP) chemical vapor deposition (CVD) tool for deposition of films, preferably αC, αFC, SiN, SiON, doped and undoped SiO 2  and BiN, onto substrates.  
       BACKGROUND OF THE INVENTION  
       [0002] Plasma tools used for semiconductor processes such as chemical vapor deposition (CVD), etching, reactive ion etching and so forth typically employ either inductive coupling or capacitive coupling to strike and maintain a plasma. One advantage of inductively coupled plasmas over capacitively coupled plasmas is that the inductively coupled plasma is generated with a much smaller bias voltage on the substrate, reducing the likelihood of damage thereto. In addition, inductively coupled plasmas have a higher ion density thereby providing higher deposition rates and mean free paths, while operating at a much lower pressure than capacitively coupled plasmas. These advantages allow in situ sputtering and/or ion directionality during processing.  
       [0003] More recently, high density plasma (HDP) CVD processes have been used to provide a combination of chemical reactions and physical sputtering. HDP-CVD processes promote the disassociation of the reactant gases by the application of radio frequency (RF) energy to the reaction zone proximate the substrate surface thereby creating a plasma of highly reactive ionic species. The relatively non-reactive ionic constituents, i.e., Ar, are given high momentum (e field) used to dislodge deposited film material selectively from specific areas along the profile of the film based on a sputter yield curve. The high reactivity of the released ionic species reduces the energy required for a chemical reaction to take place, thus lowering the required temperature for these processes.  
       [0004] The goal in most HDP-CVD processes is to deposit a film of uniform thickness across the surface of a substrate, while also providing good gap fill between lines and other features formed on the substrate. Deposition uniformity and gap via fill are very sensitive to source configuration, gas flow changes, source radio frequency generator power, bias radio frequency generator power, gas nozzle design, including symmetry in distribution of nozzles, the number of nozzles, the height the nozzles are disposed above the substrate support and the lateral position of the nozzles relative to the substrate support. These variables change as processes performed within the tool change and as process gases change.  
       [0005] One problem encountered in semiconductor fabrication is generation and maintenance of plasma density uniformity above the substrate. Plasma uniformity is dependent upon magnetic and electric fields generated in the tool as well as gas flow into and out of the tool. As substrate sizes increase, i.e., to 300 mm, uniformity over a larger area becomes even more difficult achieve.  
       [0006] Another problem which affects deposition uniformity is uneven gas distribution over the substrate surface. Typically, a gas plenum is provided around the perimeter of a processing region and a plurality of nozzles extend radially inwardly to provide gases to the substrate surface. In some applications, the gases tend to be unevenly distributed across the substrate surface, with more gas provided towards the edge of the substrate and less gas provided towards the center of the substrate. In addition, reactant gases are typically mixed in the gas injection system prior to their introduction into the chamber. In these instances, material tends to deposit within the gas injection system itself, thereby clogging some gas injectors further heightening non-uniform gas distribution.  
       [0007] Still another problem encountered is maintaining a uniform temperature across the substrate surface. As a substrate is processed, there exists a significant heat load due to plasma radiation and ion bombardment exposed to the substrate surface. If a temperature gradient exists across the substrate surface, the deposition of the film can proceed in a non-uniform manner. Therefore, it is important to precisely control the temperature of the substrate.  
       [0008] Another problem is deposition of material on the tool itself. During processing, deposition material deposits throughout the tool, on the substrate support member, and on the gas distribution components. Over time, such material build up can flake off into the chamber resulting in particle contamination on the substrate which can compromise the integrity of the devices being fabricated. Thus, the tool must be periodically cleaned. A favored method of cleaning is to introduce cleaning gases into the chamber to react with the deposited material to form a product which can be exhausted from the chamber. Typically, a cleaning gas, such as a fluorinated gas, is introduced into the chamber and a plasma is struck in the chamber. The resultant excited products react with the deposition material to form gas phase byproducts which are then exhausted from the chamber. One problem with this process is that cleaning is typically localized in regions adjacent to the plasma. In order to enhance cleaning of all exposed chamber surfaces, the time period in which the cleaning process is performed is increased, thereby decreasing throughput, and/or the cleaning process is performed using high temperatures, thereby effectively over cleaning some of the chamber surfaces and increasing the cost of consumables and/or maintenance intervals.  
       [0009] Therefore, there is a need for a process tool which provides more uniform conditions for forming thin CVD films on a substrate, including enhanced cleaning features and high throughput, in a more manufacturing worthy way.  
       SUMMARY OF THE INVENTION  
       [0010] An embodiment of the present invention provides an HDP-CVD tool using deposition and sputtering of doped and undoped silicon dioxide capable of excellent gap fill and blanket film deposition on wafers having sub 0.5 micron feature sizes having aspect ratios higher than 1.2:1. The tool of the present invention includes: a dual RF zone inductively coupled plasma source; a dual zone gas distribution system; temperature controlled chamber components; a symmetrically shaped, turbomolecular pumped chamber body; a dual, cooling zone electrostatic chuck; an all ceramic/aluminum alloy chamber construction; and a remote plasma chamber cleaning system. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011] So that the manner in which the above recited features, advantages and objects of the present invention are attained can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings.  
     [0012] It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are, therefore, not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
     [0013]FIG. 1 is a cross sectional view of a process chamber of the present invention;  
     [0014] FIGS.  2 A- 2 C are electrical schematic views showing three various RF matching configurations which can be used to advance in the present invention;  
     [0015]FIG. 3 is a schematic cross sectional view showing the dual zone RF plasma source of the present invention;  
     [0016]FIG. 4 is an exploded view of the top temperature control assembly and top antenna;  
     [0017]FIG. 5 is a cross sectional view of a substrate support member of the present invention;  
     [0018]FIG. 6 is a top cross sectional view of a substrate support member of the present invention;  
     [0019]FIG. 7 is a top cross sectional view of a chamber having a substrate support member disposed therein;  
     [0020]FIG. 8 is a top view of one embodiment of an electrostatic chuck;  
     [0021]FIG. 8 a  is an alternative embodiment of the electrostatic chuck;  
     [0022]FIG. 9 is a cross sectional view of one embodiment of the electrostatic chuck of FIG. 8;  
     [0023]FIG. 10 is a flow diagram of the temperature control aspects of the electrostatic chuck of FIG. 8 and  9 ;  
     [0024]FIG. 11 is a cross-sectional view of an electrostatic chuck and a cover ring;  
     [0025]FIG. 12 is a cross-sectional view of a cover ring disposed in proximity to a source coil;  
     [0026]FIG. 13 is a side view partially in section showing the gas control system of the present invention;  
     [0027]FIG. 14 is a side view partially in section showing the gas distribution ring and first gas channel;  
     [0028]FIG. 15 is a side view partially in section showing the gas distribution ring and the second gas channel;  
     [0029]FIG. 16 is a side view partially in section showing the center gas feed assembly;  
     [0030]FIG. 17 is an exploded view of the gas distribution ring and the lose plate of the lid assembly;  
     [0031]FIG. 18 is a schematic side view partially in section showing the microwave remote plasma clean and its location on the chamber;  
     [0032]FIG. 19 is a top view of a gas diffuser;  
     [0033]FIG. 20 is a side view of a gas diffuser; and  
     [0034]FIG. 21 is a perspective view of a gas baffler. 
    
    
     DESCRIPTION OF A PREFERRED EMBODIMENT  
     [0035] The tool will be described in detail below with reference to each of the following subassemblies: a chamber body, a chamber lid assembly, a cathode and lift assembly, a process kit, a gas distribution assembly and a remote plasma source.  
     [0036] Chamber Body  
     [0037]FIG. 1 is a cross sectional view of a processing tool  10  of the present invention. The processing tool  10  generally includes a chamber body  12 , a lid assembly  14  and a cantilevered, removable substrate support member  16 . These members in combination form a physically and electrically symmetric, evacuable enclosure and exhaust passage  22  in which substrate processing is carried out.  
     [0038] The chamber body  12  is preferably a unitary, machined structure having a sidewall  18  which defines an inner annular processing region  20  and tapers towards its lower end to define a concentric exhaust passage  22 . The chamber body  12  defines a plurality of ports including at least a substrate entry port  24  sealed by a slit valve  44  and a side port  26  through which the cantilever mounted substrate support member  16  is disposed. The substrate entry port  24  and the support member port  26  are preferably disposed through opposite sides of the chamber body  12 . Two additional side ports are disposed on opposite sides of the chamber wall  18  at about the level of the upper surface of the substrate support member  16  and are connected to a gas channel  28  formed in the chamber wall  18 . Cleaning gases, such as disassociated fluorine containing gases, are introduced into the channel  28  from a remote plasma source  30  and into the chamber through the gas inlet ports provided therefor and shown in FIG. 18. The location of the openings of the ports into the chamber are provided to direct gases towards areas of the reactor where heavy build-up occurs. The remote plasma source and cleaning gas delivery will be described in more detail below.  
     [0039] The upper surface of the chamber wall  18  defines a generally flat landing area on which a base plate  33  of the lid assembly  34  is supported. One or more o-ring grooves  36  are formed in the upper surface of the wall  18  to receive one or more o-rings  38  to form an airtight seal between the chamber body  12  and the base plate  33 . The lid assembly will be described in more detail below.  
     [0040] The substrate support member  16  partially extends through the side access port  26  formed in the chamber wall  18  and is mounted to the chamber wall  18  on a flange  46  to provide a generally annular substrate receiving surface  200  in the center of the chamber. When the support member  16  is positioned in the chamber, an outer wall  50  of the annular support member  16  and an inner wall  52  of the chamber define an annular fluid passage  22  that is substantially uniform about the entire circumference of the support member  16 . It is preferred that the substantially uniform passage  22  and the exhaust port  54  be substantially concentric with the substrate receiving surface of the support member. The exhaust port  54  is centered below the substrate receiving portion of the support member  16  to draw the gases evenly through the uniform passage  22  and out of the chamber. This enables more uniform gas flow over the substrate surface about the entire circumference thereof and radially downwardly and outwardly from the chamber through exhaust port  54  centered in the base of the chamber. The uniform fluid passage  22  promotes uniform deposition of film layers by maintaining pressure and residence time uniformity, lacking in existing processing chambers, such as substrate locations with differing proximity in relation to the pumping port.  
     [0041] A pumping stack comprising a twin blade throttle assembly  56 , a gate valve  58  and a turbomolecular pump  60  is mounted on the tapered lower portion of the chamber body to provide pressure control within the chamber. The twin blade throttle assembly  56  and the gate valve  58  are mounted between the chamber body  12  and the turbomolecular pump  60  to allow isolation via gate valve  58  and/or pressure control at pressures of from about 0 to about 100 milliTorr as determined by settings of the twin blade throttle assembly  56 . A 1600 L/sec turbo pump is a preferred pump, however, any pump which can achieve the desired pressure in the chamber can be used. A foreline  57  is connected to the exhaust port  54  at positions upstream and downstream from the turbo pump. This provides backing pump capability. The foreline is connected to the remote mainframe pump, typically a roughing pump. A port  59  is formed in the pumping stack to mount a flange  61  of the foreline. During chamber cleaning, cleaning gases are flown into the chamber at a high rate, thereby increasing the pressure in the chamber. In one aspect of the invention, therefore, the turbo pump is isolated from the chamber by the gate valve  58  and the mainframe pump is used to maintain the pressure in the chamber during the cleaning process.  
     [0042] During processing of a substrate in the chamber, the vacuum pump evacuates the chamber to a pressure in the range of about 4 to about 6 milliTorr, and a metered flow of a process gas or gases is supplied through the gas distribution assembly and into the chamber. The chamber pressure is controlled by directly measuring the chamber pressure and feeding this information to a controller that opens and closes the valves to adjust pumping speed. Gas flows/concentrations are controlled directly by mass flow controllers through a software set point provided in a process recipe. By measuring the flow rate of gases being pumped out of the chamber through the exhaust port  54 , a mass flow controller (not shown) on the inlet gas supply can also be used to maintain the desired pressure and gas concentration in the chamber.  
     [0043] Chamber Lid Assembly  
     [0044] The chamber lid assembly  34  is generally comprised of an energy transmitting dome  32 , an energy delivery assembly  62  and a temperature control assembly  64  supported on a hinge mounted base plate  33 . The base plate  33  defines an inner annular channel in which a gas distribution ring is disposed. O-ring grooves are formed in the top of the gas distribution ring to receive an o-ring to seal the dome  32  and the top of the gas distribution ring. In combination, the lid assembly provides both the physical enclosure of the plasma processing region as well as the energy delivery system to drive processing. A cover is preferably provided over the entire lid assembly to house the various components.  
     [0045] The dome  32  is generally comprised of a cylindrical sidewall  66  which is closed on one end by a flat top  68 . The cylindrical sidewall is generally perpendicular to the upper surface of the substrate support member  16  and the planar top  68  is generally parallel to the upper surface of the support member  16 . The junction  70  between the sidewall and the top is rounded to provide a curved inner wall of the dome  32 . The dome  32  is made of a dielectric material which is transmissive to RF energy, preferably a ceramic such as aluminum oxide (Al 2 O 3 ), aluminum nitride (AIN) or quartz (SiO 2 ).  
     [0046] Two separately powered RF coils, a top coil  72  and a side coil  74 , are wound external to a dielectric dome  32 . The side coil  74  is preferably covered by a ground shield to reduce electrical crosstalk between the coils  72  and  74 . The RF coils  72  and  74  are powered by two variable frequency RF sources  76  and  78 .  
     [0047] Each power source includes a control circuit which measures reflected power and which adjusts a digitally controlled synthesizer in the RF generator to sweep frequencies, typically starting at 1.8 MHZ, to minimize the reflected power. When the plasma ignites, the circuit conditions change because the plasma acts as a resistor in parallel with the coil. At this stage, the RF generator continues to sweep the frequency until a minimal reflected power point is again reached. The power source circuitry is designed so that each set of windings resonates at or near the frequency at which the minimum reflected power point is reached, so that the voltage of the windings is high enough to drive sufficient current to sustain the plasma. Thus, frequency tuning guarantees that the system remains close to resonance even if the resonance point of the circuit changes during processing. In this way, frequency tuning eliminates the need for circuit tuning and impedance matching by varying the values of impedance matching components (e.g., capacitors or inductors).  
     [0048] Each power source ensures that the desired power is delivered to the load despite any impedance mismatches, even continuously varying impedance mismatches which can arise due to changes in the plasma impedance. To ensure that the correct power is delivered to the load, each RF generator dissipates the reflected power itself and increases the output power so that the delivered power remains at the desired level.  
     [0049] FIGS.  2 ( a ),( b ) and ( c ) show three separate local RF match configurations schematically. FIG. 2( a ) shows a matching configuration for use with a coil L having one end grounded. The two capacitors C 1  and C 2  form an RF voltage divider. In FIG. 2( b ), a balanced coil L having two shunt capacitors C 2  and C 3 , where C 2 ≈C 3 , across it to ground is used to match the load (plasma) frequency. Finally, in FIG. 2( c ), a pi (π) network match is used having two variable capacitors to ground across the coil L. Since the output impedance of most conventional RF generators is designed to be 50 ohms, matching networks  2 ( a ), ( b ) or ( c ) can be used to transfer maximum power to plasmas ranging in impedance from as low as 5 ohms to as high as 900 ohms (in the balanced load case). This dual coil system allows control of the radial ion density profiles in the reaction chamber.  
     [0050]FIG. 3 is a schematic side view of the chamber showing principally the coil geometry and RF feeds for top coil  72  and side coil  74 . The pi network matching system described in FIG. 2( c ) is shown in FIG. 3. A Langmuir probe was introduced into the chamber  13  to measure the plasma ion density at different positions across the chamber  13  using the top coil only, and the side coil only, to generate the plasma. The dual coil arrangement, when properly tuned to a substrate being processed, can generate uniform ion density across its surface.  
     [0051] Uniform ion across the substrate surface contributes to the uniform deposition and gap-fill performance onto the wafer and helps alleviate plasma charging of device gate oxides due to nonuniform plasma densities. When the action of the coils is superimposed, uniform plasma density results and deposition characteristics may be vastly improved.  
     [0052] The dome  32  also includes a temperature control assembly  64  to regulate the temperature of the dome during the various process cycles, i.e., deposition and clean. FIG. 4 is an exploded view of the temperature control assembly  64  and the top coil  72 . The temperature control assembly generally comprises a heating plate  80  and a cooling plate  82  disposed adjacent each other and preferably having a thin layer  84  of a thermally conductive material, such as grafoil, disposed therebetween. Preferably, about a 4 mil to about 8 mil layer of grafoil is disposed therebetween. A thermally conductive plate  86 , such as an AlN plate, is provided with grooves formed in its lower surface to house the coil  72 . A second layer  88  of grafoil, preferably about 1 to about 4 mils thick, is disposed between the thermally conductive plate  86  and the heating plate  80 . A third thermally conductive layer  90  is disposed between the coil  72  and the dome  32 . The third layer is preferably a layer of chromerics having a thickness of about 4 mils to about 8 mils. The thermally conductive layers facilitate heat transfer to and from the dome  32 . During cleaning it is preferred to heat the dome, while during processing it is preferred to cool the dome. As a result, a thermally conductive path is provided to achieve these advantages.  
     [0053] The cooling plate  82  includes one or more fluid passages formed therein through which a cooling fluid such as water is flown. The water channel in the cooling plate is in series with cooling channels  88  formed in the chamber body. A pushlock type rubber hose with quick disconnect fittings supplies water to the chamber body and the cooling channel in the lid. The return line has a visual flowmeter with an interlocked flow switch. The flowmeter is factory calibrated for a 0.8 gpm flow rate at a pressure of about 60 psi. A temperature sensor is mounted on the dome to measure the temperature thereof. The heating plate  80  preferably has one or more resistive heating elements disposed therein to provide heat to the dome during the cleaning phase. Preferably the heating plate is made of cast aluminum, however other materials known in the field may be used. A controller is connected to the temperature control assembly to regulate the temperature of the dome.  
     [0054] Each of the components  80 ,  82 ,  84 ,  86 , and  88  define two channels through which the ends of the top coil  72  extend. Two insulative sleeves  94 ,  96  are disposed in each channel formed in the heating plate  80 , the cooling plate  82  and the grafoil layers to insulate the coil leads extending therethrough. The insulative sleeves may include silicon suction cups disposed on their lower ends to provide a seal at the insulative plate  86 .  
     [0055] By direct conduction, the heating plate  80  and the cooling plate  82  are used to control the dome temperature. Control of the dome temperature to within ≈10° K improves wafer to wafer repeatability, deposition adhesion and has been found to reduce flake or particle counts in the chamber. The dome temperature is generally kept within the range of from about 100° C. to about 200° C. depending on processing requirements. It has been shown that higher chamber clean rates (etch rates) and better film adhesion to the substrate can also be obtained at higher dome temperatures.  
     [0056] Cathode and Lift Assembly  
     [0057] The cathode and lift assembly will now be described with reference to FIGS.  5 - 10 . The support member includes elements which are positionable within the chamber and elements positionable outside of the chamber. The elements of the support member  16  positionable within the chamber extend through access port  26  provided in the sidewall  18  of the chamber and are supported to the sidewall by elements positionable outside of the chamber. FIG. 5 is a cross-sectional view of the substrate support member  16 . The support member  16  generally includes a base  94  having a flange  46  for attachment to the chamber wall, a cantilevered arm portion  96  extending radially inward therefrom, and a substrate receiving portion  98  located at the end of the cantilevered arm  96 . The flange  46  mounts the base  94  of the support member to the chamber wall  18  about the substrate support member access port  26 . The base  94  extends inwardly from the flange  46  to define an inner curvilinear wall portion  51 . The curvilinear wall  51  is preferably an arc or segment of a circle having a radius (r) substantially equal to the overall inner radius (R) of the chamber. The surface of the curvilinear wall  51  in the circumferential direction is received adjacent the inner wall  52  of the chamber. The curvilinear wall  51  along with the inner wall  52  of the chamber form a symmetrical and continuous inner chamber wall when the support member  16  is located in the chamber for processing as shown in FIG. 7.  
     [0058] The cantilevered arm  96  extends inwardly from the lower portion of the base  94  to support the ESC receiving portion  98  having a substrate receiving surface  99  thereon. The ESC receiving portion  98  includes an upwardly extending annular pilot  100 . The annular pilot  100  includes a larger inner diameter portion and a smaller inner diameter portion which form an inner annular step to support an insulative member  102  thereon. An ESC  104  is preferably supported on insulative plate  102  to provide a substrate receiving surface  99 . The outer wall  50  of the ESC receiving portion  98  defines a continuous annular face.  
     [0059] The ESC receiving portion  98  also defines a recess  108  in which a substrate positioning assembly  110  is disposed. A bottom plate  112  is secured to the lower portion of the receiving portion by a threaded screw arrangement to protect the inner components of the support member  16  from the processing environment.  
     [0060]FIG. 7 is a top sectional view showing a support member  16  disposed in a chamber. The cantilevered arm  96  extends across the symmetric fluid passage  22  to support the ESC receiving portion  98  within the chamber. It is preferred that the cantilevered arm minimize interruption, restriction or disturbance of the fluid flow through the fluid passage  22  by including a fluid passage or plurality of passages  114 , such as a radial passage, therethrough. It is also preferred that the support arm  116 , include a passage or plurality of passages  118  therethrough to minimize interruption, restriction or disturbance of fluid flow through the uniform fluid passage.  
     [0061] It is also preferred that the cantilevered arm  96  attach to the ESC receiving portion  98  at a point remote from the substrate receiving surface, such as along the bottom of the ESC receiving portion  98 , in order to further minimize the effect on the gases near the surface of the substrate caused by any interruption, restriction or disturbance of fluid as it passes through and around the cantilevered arm. More generally, it is preferred that any nonuniformity in the fluid passage  22  be minimized and positioned a sufficient distance from the ESC receiving surface  98  to avoid affecting the flow of fluid over a substrate placed thereon.  
     [0062] The substrate lift assembly  120  includes a plurality of radially extending substrate support pins  122  which are aligned with and spaced about the periphery of the ESC receiving member  98  and are received on a winged mounting plate  123 . The mounting plate  123  is disposed within a generally rectangular recess  124  formed in the support member  16 , and is actuated by a vertically moveable elevator assembly  126 . As shown in FIG. 5, the elevator mechanism  126  includes a vertically moveable shaft  128  that mounts a plate  130  at the upper end thereof. The shaft  128  is moved vertically up and down by an actuator, preferably a pneumatic cylinder located outside of the chamber.  
     [0063] The support pins  122  are received in sleeves  132  located in bores  134  disposed vertically through the ESC receiving member  98  and move independently of support member  16  within the enclosure. Support pins  122  extend from the support member  16  to allow the robot blade to remove a substrate from the enclosure, but must sink into the support member  16  to locate a substrate on the upper surface of the ESC  104 . Each pin includes a cylindrical shaft terminating in a lower spherical portion and an upper spherical portion.  
     [0064] In operation, an external blade  138  (with a substrate to be processed supported thereon) is inserted through the slit valve  24  into the chamber to position a substrate over the support member  16 . One example of a suitable blade  138  and an associated robot substrate handling system is described in co-pending, commonly assigned U.S. patent application Ser. No. 944,803, entitled “Multichamber Integrated Process System”, filed in the name of Dan Maydan, Sasson Somekh, David N. K. Wang, David Cheng, Masato Toshima, Isak Harari, and Peter Hoppe, which is hereby incorporated herein by reference. The elevator mechanism  126  raises the substrate support pins  122  above the blade to pick up the substrate. The blade is then withdrawn from the chamber and a pneumatic cylinder closes a door over the blade access slot to seal chamber. The elevator mechanism  126  is actuated to lower support pins  122  until the substrate is received on the upper surface  98  of the support member  16  in position for processing.  
     [0065] After processing, the elevator mechanism raises the support pins  122  to lift the substrate off the substrate support member  16 . The door is then opened and the blade is again inserted into the chamber. Next, elevator mechanism  126  lowers the substrate support pins  122  to deposit the substrate on the blade. After downwardly moving pins  122  clear the blade, the blade is retracted.  
     [0066] During processing, the plasma of the CVD process environment gives off large quantities of heat, the total heat generated by the plasma being at least partially dependent on the power density of the plasma. A portion of this heat is transferred into the substrate, and must be removed from the substrate to maintain the temperature of the substrate, below a pre-defined critical temperature. To remove this heat, a heat transfer system is provided in the substrate support member  16  to control the temperature of the support member and the substrate being processed. FIG. 6 is a top sectional view showing the heat transfer system of the support member  16 . Water inlet  140  and outlet  142  are connected by passages  144  and  146 . A water manifold  148  is located within the support member  16  to facilitate heat transfer from the support member to the coolant fluids. The temperature of the support member  16  is selected to eliminate premature deposition within the gas manifold upstream from the processing region of the chamber. Coolant channels  144 ,  146  received through the mass of the substrate support member  16  are provided for the passage of coolant fluids therethrough. In addition, grooves in the surface of the ESC  104  (which will be described below), wherein gases are flown, transfer heat from the substrate into the support member  16  and subsequently into the coolant fluids.  
     [0067]FIG. 8 is a top view of one embodiment of an electrostatic chuck  104  according to the present invention. FIG. 8 a  is an alternative embodiment which is symmetric and eliminates a wafer flat area. Instead of having a smooth top surface, a number of grooves are provided in the surface to form a large number of protrusions  166 . A central zone  168  of these protrusions is separated from a peripheral zone  170  by a seal  172 . Seal  172  is simply an area which has not had grooves formed in it to provide protrusions, thus forming a solid surface to minimize flow between separate zones. An outer seal  174  provides a barrier to minimize leakage of helium gas into the chamber.  
     [0068] Helium gas is inserted into periphery zone  170  through a ring  176  which is a groove having a series of holes in it which receive higher-pressure helium into this zone from helium line  47  of FIG. 1. An inner ring  178  allows a lower pressure gas to the central zone  168  from pressure helium line  147 . In operation, after establishing an initial low helium pressure in central zone  168 , helium ring  178  typically will be removing helium gas leaking through seal area  172  to maintain the desired low pressure helium. In an optional embodiment, vacuum holes  180 , which may be lift pin holes, can be used to pump out the gas in the central zone using vacuum line  135  of FIG. 1 to further lower the pressure in the central zone. Optionally, additional vacuum holes could be added.  
     [0069] Helium groove  178  is preferably positioned near seal area  172 . By positioning it as close as possible, the desired heat transfer step function can be approached. The high pressure gas is thus contained in a narrow region by the periphery. If the high pressure gas extends too far toward the center of the wafer, the cooler center will become even cooler, partially offsetting the reduction in heat differential provided by the higher pressure gas.  
     [0070] In operation, for heating the wafer, lower pressure helium (1-15 torr) is provided into the central zone  168 , and higher pressure helium (1-20 torr) is provided to peripheral zone  170 . The higher pressure helium in the peripheral zone provides better heat transfer at the periphery of the wafer.  
     [0071] In one embodiment, the seals are made of the same ceramic coating as the remainder of the top of electrostatic chuck  164 . Such a ceramic coating has small interstices, and thus the seal areas do not provide a perfect seal. In addition, the substrate or wafer will have some backside roughness, and may have more roughness than the substrate support. Accordingly, the seal area should have sufficient width to prevent significant leakage of helium from one area to the other.  
     [0072] It has been determined by testing that for a ceramic covered electrostatic chuck with the pressure ranges set forth above, that a seal width of {fraction (1/10)} inch, or 100 mils, is effective. Preferably, the seal width is in the range of 50 to 300 mils. For the outer seal  174 , it is desirable to minimize the width because the area of the wafer above this seal will not have the benefit of the heat conduction from the high-pressure helium. At the same time, the seal must be wide enough to prevent significant leakage of helium into the chamber which could undermine its intended heat transfer capability by reaching the sustained helium pressure due to higher flow levels or affect the reaction in the chamber. The same 100 mil width has been found effective, with an optimum seal width being in the range of 50 to 300 mils. Alternate widths may be appropriate for different materials and smoothness of the substrate support and substrate. For example, if a polymer film, such as Kapton™, available from many well-known suppliers, is used, a small width can be achieved because of its compliancy.  
     [0073] A preferred heat transfer gas is helium because it is inert and relatively inexpensive. Alternately, argon, oxygen, CF 4 , or other gases could be used, or a mixture of gases may be used. A mixture could be used, for instance, to give additional pressure control capabilities. The particular gas could be chosen to be compatible with the chemical process in the chamber so that any leaking gas will have minimal effect on the chemical reactions. For example, in an etching reaction using fluorine as an etching species, it may be desirable to use CF 4  as the backside heat transfer gas.  
     [0074] Because heat conduction occurs primarily through the helium gas, it is desirable to minimize the size and number of the protrusions and seal areas for this purpose. Thus, there should be less contact area than non-contact area over the area of the substrate. On the other hand, the seals are required to prevent gas leakage and the protrusions must be of sufficient size and spacing to mechanically support the wafer. In addition there are other factors to be optimized. The height of the protrusions, which determine the gap between the substrate and the substrate support between the protrusions, must be sufficient to allow the gas to quickly become distributed throughout the zones without affecting a process start up time. Typically, this must be on the order of a few seconds, and preferably the gas is distributed in 10 seconds or less.  
     [0075] For optimum heat transfer, the gap should be small enough so that heat transfer primarily occurs by molecules traveling directly from the substrate to the substrate support without colliding with another gas molecule, giving free molecular heat transfer. Thus, the gap should be less than the mean free path of the gas (or the average free path if a mixture of gases is used).  
     [0076] The mean free path is a function of the pressure of the gas and the molecular collisional cross-section. Where a variety of pressures will be used, the mean free path will vary. In a preferred embodiment, the mean free path of the maximum pressure, to be applied is used to determine the gap dimension.  
     [0077] In addition, the ratio of the gap to the overall dielectric thickness must be kept small to avoid local anomalies on the substrate. If this ratio is significant, the equivalent capacitance will vary significantly between the spaces and the protrusions, applying a significantly different electric field to the substrate. This different field can affect the chemical process, causing non-uniformities in the film that is being deposited, etched, doped, or undergoing other property transformations. Some difference will necessarily be present, but it is desirable to minimize this.  
     [0078] The significance of the ratio also varies depending on the dielectric material, in particular the difference between the dielectric constant of the material and the heat transfer gas (essentially one). The closer the two dielectric constants, the less the concern with a larger gap.  
     [0079] Another concern in setting the gap size is to avoid having a plasma generated with the heat transfer gas between the substrate support and the backside of the wafer. It is believed that this would begin to be a concern if the gap size were several times the mean free path of the heat transfer gas.  
     [0080] For one embodiment of an electrostatic chuck, the thickness of the ceramic coating is on the order of 7-10 mils. If Kapton™ is used, a thickness of 1-2 mils may be used. Ideally, for chucking purposes, the dielectric is as thin as possible within the limits of maintaining manufacturing consistency and avoiding dielectric breakdown. The mean free path of helium at the pressures for the two zones described above is about 1-5 mils (at very high pressures, the mean free path may be less than one). Accordingly, protrusion heights of 0.7-1.2 mils have been chosen, tested, and found effective. This gives a gap less than the mean free path of helium at the desired pressures. Preferably, the gap is less than twice the mean free path of the heat transfer gas at the pertinent pressures, and more preferably less than the mean free path.  
     [0081] The spacing between the protrusions is as large as possible while still supporting the substrate without bowing. In one embodiment, the substrate is kept planar, while in other embodiments it may be desirable to vary the protrusion height, or alternately the top surface of the substrate support (with the protrusions of equal height), to properly support a curved substrate. Another factor is avoiding sharp points that could cause local anomalies in the electric field. Too large a spacing can also affect the movement of charge during dechucking, causing damage.  
     [0082] It has been determined that an optimum center-to-center spacing of the protrusions is in the range of 100-300 mils, more preferably approximately 300 mils. The size of the protrusions themselves is preferably between 10 and 150 mils, more preferably approximately 130 mils in diameter. Square protrusions are shown simply because of their ease in manufacture, and other shapes could be used as well. Annular shapes could be used, for example.  
     [0083] In the embodiment shown, no openings for removing gas are shown in the outer peripheral region, although this can be provided in an alternative embodiment. The control of helium pressure can be done either by providing high or low pressure helium, or by more pumping through a vacuum pump. Similarly, for the central region, the pressure can be controlled in either of these ways or through a combination of both. The placement of the helium source as a ring near the edges in combination with a vacuum near the middle of the support provides an additional pressure gradient within the central region, decreasing towards the center.  
     [0084] An alternate embodiment of the present invention thus provides a coarse adjustment of the heat transfer through the two pressure zones, with a fine tuning occurring through the placement of the helium inlet and vacuum outlets in the central portion. In alternate embodiments, more than one zone could be used for finer adjustments, with the trade off of requiring more hardware.  
     [0085]FIG. 9 is a side view of one embodiment of an ESC  104  showing a varying dielectric thickness of a dielectric  186 . A wafer  182  is shown mounted on the chuck. The chuck includes an electrode portion  184  covered by dielectric  186 . The dielectric extends across the top and along the sides  190  of the electrostatic chuck. As can be seen, the dielectric is thicker at a central portion  192 , and thinner at peripheral portions  194 . The side view shows the multiple protrusions  170  and also shows the inner seal  172  and the outer seal  174 .  
     [0086] The thinner dielectric at peripheral portions  194  provides a stronger electrostatic force at these portions. This is beneficial for a number of reasons. First, it holds the wafer more tightly, ensuring better heat transfer by providing better contact with the top of the electrostatic chuck. Second, a tighter force helps hold in the higher pressure helium between seals  172  and  174  near the periphery. In addition, if the peripheral portion of the wafer has a temperature different from the central portion, this may cause it to bend relative to the central portion, and it may bow up or down, further exacerbating the heat differential problem. This can be overcome by an appropriately higher electrostatic force at the peripheral portion.  
     [0087] In an alternate embodiment, the varying dielectric thickness can be used without the two pressure zones, or without the protrusions. The varying in the dielectric coating can be continuous, or stepwise. A stepwise difference makes the manufacturing simpler and less expensive.  
     [0088] Another advantage of the seal area  174  and the stronger electrostatic force at the edge of the wafer is to prevent arcing of the plasma to exposed metal near the top surface of the electrostatic chuck. Such exposed metal would typically be at the helium inlet ports, which would come up through the aluminum electrode, thus exposing through those holes a path to the electrode. Arcing is prevented by providing a tighter seal, locating the helium inlet holes sufficiently away from the edges of the electrostatic chuck, or putting a groove there to prevent such arcing.  
     [0089] As shown in FIG. 9, a temperature sensor  196  can be placed in the space between the top surface of the electrostatic chuck and the wafer. The temperature of the wafer can thus be inferred from the sensor.  
     [0090]FIG. 10 is a feedback control system signal flow diagram illustrating the temperature control. The FIG. 10 diagram is for a closed loop temperature control system for controlling the helium pressure. Alternately, an open loop system could be used without the temperature sensor. Prior experimentation could dictate the appropriate helium pressure for the desired process parameters, and thus the temperature sensor could be eliminated in an alternate embodiment. FIG. 9 contains both functions performed in a processor, and physical effects.  
     [0091] A temperature set point is provided as a user-programmed input to a controller from a control program in a memory  245 . The temperature set point value is multiplied by a constant  198  by the controller, which adds the result to a feedback signal  213  as indicated by an add function  202 . The result of the add function is used by the controller to control the helium pressure by controlling flow restrictors or valves in the helium supply. This varies the extent of the heat transfer of the helium gas. In a preferred embodiment, the helium pressure is controlled according to a mathematical model; however, empirical results could also be used as the basis of the pressure control. The mathematical model is described below. The helium pressure controls the heat transfer to the ESC as indicated by block  202  (alternately, any type of substrate support may be used). The ESC is either cooled by heat exchanger  233 , or heated by heater  243 , with the amount of heat transfer to the wafer controlled by the helium pressure. This heat transfer can be offset by the heat generated by energy transferred from the plasma (as illustrated by block  204 ), which combines (as illustrated by block  206 ) with the heat transfer to the ESC. The total heat transfer, applied to the wafer thermal mass (as illustrated by block  208 ), produces the temperature  210  of the wafer. Note that alternate substrates may be used rather than a semiconductor wafer. The final temperature  210  of the wafer also impacts the amount of heat transfer to the electrostatic chuck, as indicated by feedback line  211 . The heat transfer function between the ESC and the wafer indicated in block  202  is a function of the temperature of the wafer, as well as the temperature of the ESC. As shown, the heat transfer to the ESC removes heat from the wafer while the heat from the plasma adds heat to the wafer. However, these can be reversed when the electrostatic chuck is used to heat the wafer, and thus provides heat input while heat is removed due to the plasma at a lower temperature, or simply by the chamber in the absence of a plasma.  
     [0092] A block  212  illustrates the transformation of the temperature into an electrical signal by the temperature sensor. Block  214  illustrates the transfer function applied in the processor before combining the temperature signal with the temperature set point as a feedback. Such a transfer function could in its simplest form be a multiplication by a constant, which could be unity, or simply a transformation from an analog signal to a digital signal.  
     [0093] The functions performed by the controller are done under the control of a program in memory  245 . That program will include instructions for performing the various steps, such as instructions for reading the temperature indication from the temperature sensor, an instruction for comparing that temperature to the desired input set temperature, and an instruction for controlling the pressure valve (or flow restrictor) to vary the pressure of the gas in a particular pressure zone. Other instructions are provided to shut off the gas in the event of a fault, etc.  
     [0094] The helium pressure can be controlled by increasing or decreasing the pressure where a simple one pressure electrostatic chuck is used. Alternately, where two pressure zones are used as in the preferred embodiment of the invention, the outer and inner helium pressures can be controlled separately. The temperature of each region can be inferred from a single temperature sensor which may be placed, for instance, near the intersection of the two zones. Alternately, two different temperature sensors could be used. In other alternate embodiments, the temperature sensor could be attached to the top surface of the electrostatic chuck, or alternately be put in direct contact with the wafer itself. The temperature sensor may be used to infer the pressure, such as where there is leakage between zones causing a pressure variance. A pressure regulator may detect only the pressure at its output, which would typically be some distance from the wafer, which could thus have a different pressure under it. A temperature sensor could be used to infer the actual pressure under the wafer. Depending on the wafer surface roughness, the leakage could vary, and the pressure provided may need to be varied.  
     [0095] The control system typically will have certain constraints on it. For instance, the helium pressure is limited so that the wafer is not lifted off the electrostatic chuck, or so much of a pressure differential is provided to cause a thermal gradient that damages the wafer due to thermal stress. In the event that such constraints are exceeded, or some other defined fault occurs, the gas flow is stopped. Process Kit The process kit is comprised of a collar and a cover. Additionally, a skirt may also be used. The ceramic collar is wafer size and type specific and is disposed between the electrostatic chuck and the quartz cover. The primary purpose of the collar is to protect the electrostatic chuck flange from the effects of the plasma. The cover extends from the collar to the outer periphery of the cathode assembly and its primary purpose is to protect the cathode assembly from the effects of the plasma. A skirt may be disposed on the lower chamber to protect the spacer and o-ring which seal the upper and lower chamber from the effects of the plasma.  
     [0096] In one aspect, the present invention provides an improved process kit or shield for an electrostatic chuck in a semiconductor processing chamber that inhibits or resists the deposition of gaseous products thereon. In addition, the shield provides faster removal of oxide deposition which results in enhancing the throughput of the wafer manufacturing process.  
     [0097] In one embodiment, the collar or cover may include a conducting material disposed on one or more surfaces or therein to enhance cleaning of its surface. Generally, the inductive coils disposed about the dielectric dome  32  are used to heat the conducting material in or on the collar or cover which then results in heating the collar or cover surfaces. It has been shown that in situ cleaning processes performed using fluorinated chemistry or other reactive gases is enhanced at elevated temperatures. Using the inductive coil and a conductor disposed in or on the process kit components elevates the temperature of the surfaces of these components to increase cleaning rates.  
     [0098] As one example, a metal can be deposited on one surface of a process kit component, such as a collar or cover, to provide a conductor in which a current can be induced. The operation of the heating process is similar to that which is seen in a transformer with the coil being the external winding and the metal layer being the internal winding.  
     [0099]FIG. 11 is a cross-sectional view of a electrostatic chuck and a processing kit. A substrate support assembly  230  comprises a support body  232  preferably fabricated as an integral block from an electrically conducting material having a high thermal mass and good thermal conductivity to facilitate absorption of heat from a wafer cooled over its upper surface. Aluminum or anodized aluminum is the preferred material for support body  232  because it has a high thermal conductivity of approximately 2.37 watts/cm-° C. and it is generally process compatible with the semiconductor wafer. Support body  232  may comprise other metals, such as stainless steel or nickel, and support body  232  may comprise an additional non-conducting material or the entire support body  232  may comprise a non-conducting or semi-conducting material. In an alternative embodiment, support body  232  comprises a monolithic plate of ceramic. In this configuration, the ceramic plate incorporates a conducting element imbedded therein. The conducting element may comprise a metallic element, green printed metalization, a mesh screen or the like. Support body  232  defines an annular mounting flange  234  extending outwardly from the outer surface of support body  232 . A voltage, preferably about 700 Volts, is applied to the substrate support assembly  230  by a DC voltage source (not shown) to generate the electrostatic attraction force which holds a wafer W in close proximity to the upper surface of support body  232 .  
     [0100] Referring to FIG. 11, substrate support assembly  230  comprises a smooth layer of dielectric material  236  covering an upper surface  238  of support body  232  for supporting the lower surface of wafer W. Dielectric layer  236  covers the entire upper surface  238  of support body  232  except for the region overlying four lift pin holes  240 . Dielectric layer  236  preferably comprises a thin ceramic dielectric layer (preferably on the order of about 0.10 to 0.30 inches) of alumina, aluminum oxide or an alumina/titania composite that is plasma sprayed over upper surface  238  of support body  232 .  
     [0101] In one embodiment, shield  242  comprises a thin annulus of conducting material  244  deposited underneath the collar  246 . The collar  246  is supported by an annular flange  234  and held by a cover  248 . Cover  248  is preferably a ceramic outer jacket for covering and protecting the lateral surfaces of support body  232  to decrease the time required to clean the chamber. The collar  246  is preferably separated from annular flange  234  by a small interstitial gap  250 . Gap  250  is created by the natural surface roughness of the upper surface of the annular flange  234  and the lower surface of the conducting material  244  or the collar  246 . Gap  250  is preferably about 0.5 to about 5 mills thick. In the relatively low-pressure environment of the processing chamber (typically on the order of about 5 milliTorr), gap  250  establishes a thermal barrier that inhibits thermal conduction between the collar  246  and the support body  232 .  
     [0102] As shown in FIGS.  11 , the collar  246  preferably has an inner diameter larger than the diameter of support body  232  to define a second gap  252  therebetween. Gap  252  provides room for expansion of support body  232  when it is heated in the process chamber and also ensures that the shield  242  can be installed and removed without damaging the substrate support  230  or the collar  246 . Collar  246  is comprised of an insulating or dielectric material, preferably ceramic or ceramic, that serves to prevent or inhibit the plasma in the processing chamber above the wafer from contacting, and thereby eroding, part of the electrostatic chuck. However, collar  246  is not necessarily limited to an insulating material and, in fact, applicant has found that a collar  246  made of a semiconducting material may effectively protect the electrostatic chuck from the plasma within the processing chamber.  
     [0103] The collar  246  is a thin ring  254  having a curved upper surface  256  that is exposed to deposition from gases in the process chamber. The ratio of the surface area of exposed upper surface  256  to the thermal mass of collar  246  is preferably high, usually about 0.1 to 5 cm 2 K/J and preferably about 1 to 1.6 cm 2 K/J. The high ratio of exposed surface area to thermal mass of collar  246  causes it to be heated to a substantially high temperature from the RF energy in the chamber. Since the oxide deposition rate is generally inversely proportional to the temperature of a surface in the process chamber, the heat received by the collar  246  inhibits oxide deposition on the exposed upper surface. Thus, the geometry of collar  246  (i.e., the high ratio of exposed surface to thermal mass) minimizes the rate of deposition on upper surface  256 .  
     [0104] During a deposition process, oxide from process gases is deposited onto wafer W and onto a substantial portion of the exposed surfaces of the chamber, such as the inner walls of the enclosure and upper surface  256  of collar  246 . Since the thermal mass of collar  246  is relatively small compared to the surface area of surface  256 , collar  246  will receive a relatively large amount of heat from the RF power supply. Collar  246  is also heated by the thin annulus of conducting material  244  which generates heat through the RF power. This further decreases the rate of oxide deposition onto upper surface  72 .  
     [0105] As shown in FIG. 11, collar  246  is preferably sized so that upper surface of collar  246  is positioned below the upper surface of the wafer when the wafer rests on or is adjacent to the upper surface of dielectric layer  236 . Positioning collar  246  below the upper surface of the wafer further lowers the oxide deposition rate on upper surface  256  and provides an improved line of sight to the wafer edges. Therefore, the edges of the wafer may receive a higher deposition rate than if the shield  242  were to extend above the wafer. In some processes, this may be advantageous to compensate for the higher deposition rate in the center of the wafer that typically occurs during processing.  
     [0106] Referring to FIG. 12, a cross-sectional view of the process kit in a processing chamber, the source RF coil  260  in an inductive HDP source can be used to heat the ceramic process The thin annulus of conducting material  244 , which can be disposed on one or more surfaces or within the ceramic process kit, acts as the secondary coil of a transformer and conducts the current induced by RF currents in the source RF coil  260  which generates heat for the process kit. The resistance of the secondary coil is of primary importance because either too low or too high of a resistance results in inefficient power transfer and thus inefficient heating of the process kit.  
     [0107] For the circular geometry indicated in FIG. 12, the resistance R is approximately 2πrp/w·d, where r is a measure of the radial dimension of the outer radius of the thin annulus of conducting material, w is the width of the conducting material, d is the thickness of the conducting material, and ρ is the resistivity of the conducting material. The resistance R is preferably controlled by varying w·d, the cross-sectional area of the conducting material  244 . To achieve optimal contact with collar  246 , it is preferred that w be as large as possible but smaller than the width of the collar  246 . One preferred method of obtaining the optimal value of d is empirically monitoring the heating rates of various samples with different thickness d of conducting material. In one preferred embodiment, a process kit having graphite as the conducting material with the annulus having an inner radius of 10 cm and outer radius of 12 cm and thickness of 0.13 mm was heated inductively to a temperature of about 288° C.  
     [0108] In another aspect of the invention, the clean rate or deposition removal rate of the process kit is typically a function of its temperature (i.e., the hotter the shield becomes during processing, the faster it can be cleaned). During cleaning, the conducting material  244  acts as the secondary coil of a transformer which conducts the current induced by RF currents in the source RF coil  260  which generates heat for the process kit. Thus, with increased temperature, the clean rate of collar  246  will be increased, which reduces the downtime of apparatus  2 , thereby enhancing the throughput of the process.  
     [0109] Gas Distribution Assembly  
     [0110] The gas distribution assembly  300  will be described below with reference to FIGS.  1320   16 . FIG. 13 is a cross sectional view through a chamber of the present invention showing the gas distribution assembly  300 . Generally, the gas distribution system comprises an annular gas ring  310  disposed between the lower portion of the dome and the upper surface of the chamber body and a centrally located center gas feed  312  positioned through the top of the dome. Gases are introduced into the chamber through both circumferentially mounted gas nozzles  302 ,  304  located near the bottom of the dome  32 , and a centrally located gas nozzle  306  located in the top plate of the dome. One advantage of this configuration is that a plurality of different gases can be introduced into the chamber at select locations within the chamber via the nozzles  302 ,  304 ,  306 . In addition, another gas, such as oxygen or a combination of gases, can be introduced along side nozzle  306  through a gas passage  308  disposed around nozzle  306  and mixed with the other gases introduced into the chamber.  
     [0111] The gas distribution ring and the centrally located gas manifold will be described separately below.  
     [0112] Generally, the gas distribution ring  310  comprises an annular ring made of aluminum or other suitable material  314  having a plurality of ports formed therein for receiving nozzles therein and which are in communication with one or more gas channels  316 ,  318 . Preferably, there are at least two separate channels formed in the gas ring to supply at least two separate gases into the chamber. Each of the ports for receiving the nozzles is connected to at least one of the gas distribution channels  316 ,  318  formed in the ring. In one embodiment of the invention, alternating ports are connected to one of the channels, while the other ports are connected to the other channel. This arrangement allows for the introduction of separate gases, such as SiH 4  and O 2 , separately into the chamber, as one example.  
     [0113]FIG. 14 is a cross sectional view showing a first gas channel  316  connected to one port  314  having a nozzle  302  disposed therein. As shown, the gas channel  316  is formed in the upper surface of the chamber body wall and is preferably annular around the entire circumference the chamber wall. The annular gas ring has a first set of channels  320  longitudinally disposed within the ring which are connected to each of the ports  314  provided for distribution of the gas in that channel. When the gas ring is positioned over the gas channel, the passages are in communication with the channel. The gas distribution ring is sealed in the top surface of the chamber wall via two separately placed o-rings  322 ,  324  disposed outwardly from the channel to prevent gas leaks to the interior of the chamber. A Teflon seal  326 , or the like, is disposed inwardly of the channel in a recess  328  to prevent gas leakage into the chamber.  
     [0114] The nozzles  302 ,  304  disposed in the ports  314  are preferably threaded and mate with threads in the port to provide a seal therebetween and to provide quick and easy replacement. A restricting orifice  330  is located in the end of each nozzle and can be selected to provide the desired distribution of the gas within the chamber.  
     [0115]FIG. 15 is a cross sectional view showing the second gas channel  318 . The second gas channel  318  is formed in the upper portion of the annular gas distribution ring and is similarly disposed in an annular configuration around the circumference of the gas distribution ring. A horizontally disposed passage  332  connects the second gas channel to one or more ports formed in the gas ring and in which additional gas nozzles are disposed. The upper containing surface of the second gas channel is formed by the portion of the lid which supports the dome  32  and is sealed at the top by the base plate  33 . The gas ring  310  is bolted to the base plate  33  which is hingedly mounted to the chamber body.  
     [0116] One advantage of the present invention is that the gas distribution ring can be easily removed and replaced with a ring having ports formed for receiving and positioning the tips of the nozzles at various angles so that the distribution pattern of gases can be adjusted. In other words, in certain applications it may be beneficial to angle some of the gas nozzles upwardly in the chamber, or conversely to angle some of them downwardly in the chamber. The ports formed in the gas distribution ring can be milled so that a desired angle can be selected to provide the desired process results. In addition, having at least two gas channels which can deliver at least two gases separately into the chamber allows greater control of the reaction which occurs between the various gases. Still further, reaction of the gases within the gas distribution assembly can be prevented by delivering the gases separately into the chamber.  
     [0117]FIG. 16 is a cross sectional view showing the center gas feed  312  disposed through the dome  32 . The top gas feed  312  is preferably a tapered structure having a base  334  which is disposed on the top of the dome and a tapered body  336  disposed in a recess formed in the dome. Two separate o-rings  336 ,  338 , one the lower surface of the taper body  336  and one on the side surface of the taper body  338  towards the lower end, provided sealable contact between the gas feed  312  and the dome of the chamber. A port  340  is formed in the lower portion of the body of the top gas feed to receive a nozzle  306  for delivering gases into the chamber. At least one gas passage  342  is disposed through the gas feed  310  connected to the port to deliver gases to the back of the nozzle. In addition, the nozzle  306  is tapered and the port  340  define a second gas  308  passage which delivers a gas along side of the nozzle  306  and into the chamber. A second gas channel  304  is disposed through the gas feed  312  to deliver gas into the passage  308 . A gas, such as oxygen, can be delivered along side a gas such as SiH 4 .  
     [0118]FIG. 17 is an exploded view showing the base plate  33  of the lid assembly and the gas distribution ring  310 . A channel  350  is formed in the lower portion of the base plate  33  to receive the gas distribution ring  310 . The gas ring  310  is bolted, or otherwise mounted, to the base plate  33 . The base plate is hingedly mounted to the chamber body.  
     [0119] A first gas source  352  and a first gas controller  354  control entry of a first gas via line  356  into a first gas channel  316  formed in the chamber wall. Similarly, a second gas source  358  and a second gas controller  360  supply a second desired gas via line  362  into the second gas channel  318  formed in the gas distribution ring.  
     [0120] A third gas source  364  and a third gas controller  366  supply a third gas via line  368  to a gas channel disposed on the top of the chamber. A fourth gas source  370  and a fourth gas controller  372  supply a fourth gas via line  374  to gas passage  308 . The gas introduced through the third gas nozzle and fourth gas nozzle  64  and O 2  are mixed in the-upper portion of chamber as both gases enter the chamber.  
     [0121] Remote Plasma Cleaning System  
     [0122] The remote plasma source generally includes a remote chamber having a gas inlet and a gas outlet, a power source coupled to the chamber by a waveguide, and an applicator tube disposed through the chamber between the gas inlet and gas outlet. FIG. 18 shows a schematic view of a remote plasma source  500  connected to a chamber. A chamber  502  is a cylindrical chamber, preferably made of aluminum, having a gas inlet  504  and a gas outlet  506  disposed on opposite ends thereof. The chamber is preferably cooled using either a fan disposed through a wall of the chamber or by using a fluid cooling system such as a series of coils having a heat transfer fluid such as water flown therethrough. An applicator tube  508 , such as a sapphire tube, or other energy transmissive tube, is disposed between the gas inlet and gas outlet within the chamber  502 . A water cooled delivery conduit  510  connects the gas outlet to a gas channel  28  formed in the lower portion of the processing chamber  10 . A power source is coupled to the chamber by a waveguide  512 . One remote plasma source which can be used to advantage in the present invention is described in U.S. patent application Ser. No. 08/278,605, filed on Jul. 21, 1994, which is incorporated herein by reference.  
     [0123] Preferably, power in the range of from about 2000 W to about 5000 W is delivered into the chamber  502 . The optimum power needed to dissociate the gas should be used. Any additional power is wasted and is typically used in generating additional heat. Lower power than optimum results in an incomplete dissociation of the cleaning gas and a decrease in the clean rate and efficiency. In one embodiment, a single power source is used to drive both the source antenna and the remote plasma chamber.  
     [0124] In the chamber, it is believed that the cleaning reactions which proceed most rapidly are of the type:  
     4F* (Gas) +SiO 3 →SiF 4(Gas) +O 2(Gas)    
     and  
     2F* (Gas) +SiO 2 (Gas) →SiF 2(Gas) +O 2(Gas)    
     [0125] producing gaseous products which are removed from chamber  13  by vacuum pumping the gas phase. The reactant gases which are most effective at producing high concentrations of long lived excited neutral Fluorine species F* are NF 3 , F 2 , SF 6 , ClF 3 , CF 4 , and C 2 F 6 . However, other cleaning gases which are excitable by Microwaves and react with deposition material within the chamber may be used. For the remote microwave cleaning system of FIG. 9 in the present invention, it is preferred to use NF 3  and F 2  diluted to concentrations of from about 10% to about 50% in inert argon gas. The desired cleaning reactions produced by the use of the remote plasma source proceed without any ion bombardment of the chamber or substrate support structures, therefor, the need for cover wafers on the ESC  104 , or periodic replacement of critical chamber assemblies is avoided. Thus, a much more efficient use and throughput of the system is provided.  
     [0126]FIG. 18 also shows the cleaning gas delivery channels formed in the chamber walls. Gas is delivered from the remote source  500  to a first gas channel  28  disposed horizontally in the back wall  520  of the chamber. The first gas channel  28  extends the length of the back wall to deliver gases to opposed sides of the chamber. A central gas  522  connection is formed in the lower portion of the chamber and connects to the first gas channel  28  to the delivery conduit  510 .  
     [0127] A second gas channel  524  is formed in each of the side walls of the chamber and terminate in a slit opening  526  within the chamber. A corner cover is made with a channel formed therein to connect the ends of the first gas channel  28  with each of the side gas channels  524  formed in the sidewalls. The corner cover is preferably welded in position on the chamber body and facilitates gas delivery through the chamber body to the slit openings  526  in the chamber.  
     [0128] A first gas diffusing member  528  is preferably disposed in the slit openings  526  of the second gas channels  524  to guide the cleaning gases into the chamber. FIG. 19 is a top view of the gas diffusing member  528  showing the curved side faces  530 ,  532  which deliver the cleaning gases to opposite sides of the chamber. The curved surfaces  530 ,  532  are disposed across the second gas channels  524  to guide the gases outwardly into the chamber.  
     [0129]FIG. 20 is a side view of the gas diffusing member  528  . The back portion  534  of the gas diffuser is tapered to allow gases to pass beyond the gas diffuser disposed in the channel  524  so that gas is guided into both sides of the chamber. A recess  536  is formed in one end of the gas diffuser to provide wedged engagement of the diffuser in position within the gas channel. A wedge  538  is provided to mate with the recess and a screw forces the wedge into position within the recess and connects the wedge to the diffuser and connects the diffuser to the chamber body.  
     [0130] In an alternative embodiment, a gas baffler can be disposed in the chamber adjacent to each slit opening  526  in the chamber to direct the cleaning gases upwardly and over the process kit and ESC  104 . FIG. 21 shows a perspective view of a baffler  540  which is mounted to the gas diffuser  528  by a flange  542 . The body  544  of the baffler provides a curved face  546  which is angled slightly upwardly when positioned in the chamber to urge the cleaning gases upwardly in the chamber and over the ESC  104  and the process kit.  
     [0131] It has been found that the clean process is most efficient when the cleaning gases enter the chamber from above the ESC and process kit. In addition, it is preferred that the gases flow upwardly in the chamber and away from the ESC and process kit to prevent the cleaning gases from pushing particles or residue loosened during the cleaning process onto the ESC. If particles remain on the ESC, the likelihood that helium leaks will occur during chucking increases. The baffle diverts the gas flow upwards to enhance cleaning and prevents deposition of particles on the ESC.  
     [0132] While the foregoing is directed to the preferred embodiment of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims which follow.