Abstract:
Apparatus and method for delivering processing gas are provided. The apparatus for delivering processing gas from a vaporizer to a processing system comprises: a valve connected between the vaporizer and the processing system, the valve having a valve input connected to a vaporizer output and a first valve output connected to a processing system input and a second valve output connected to a bypass line; and a controller for switching the valve between the first valve output and the second valve output. The apparatus may further comprise: a second valve connected between a carrier gas source, a divert gas source and the vaporizer, the second valve having a first valve input connected to the carrier gas source, a second valve input connected to the divert gas source, and a valve output connected to a vaporizer input.

Description:
[0001]    This application claims benefit of U.S. provisional patent application serial No. 60/195,900, filed on Apr. 10, 2000, which is herein incorporated by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The invention generally relates to a gas delivery system. More particularly, the invention relates to a gas delivery system having one or more vaporizers that provide process gases on demand for substrate processing systems.  
           [0004]    2. Background of the Related Art  
           [0005]    In the production of integrated circuits, many processing methods require one or more reactive chemicals or precursors to be deposited onto a substrate in an atmospherically-controlled heated reactor or chamber. The precursors typically are converted from a solid or liquid state into a gaseous or vapor state to achieve a high degree of uniformity by vapor deposition. The precursor vapor, once generated, is directed into a reaction chamber forms a deposited layer on the substrate. This process is typically called chemical vapor deposition or “CVD”. The deposited precursor chemical may form fine crystalline or amorphous layers which are required for creating microcircuits on the substrate.  
           [0006]    In CVD processing systems, liquid precursors are typically delivered through a liquid flow meter to a vaporizer or bubbler which heats the liquid precursor into a vapor phase. The liquid precursors may be combined with a solvent to enhance the vaporization process. A carrier gas is also introduced into the vaporizer for carrying vaporized precursor molecules in the vapor phase to the processing chamber. The quantity and concentration of precursor introduced into the chamber is dependent on the flow of the carrier gas as well as the amount of precursor introduced into the vaporizer.  
           [0007]    PLIS (precision liquid injection system), EPLIS and Parallel GPLIS have been developed to deliver vaporized liquid precursors to dielectric deposition chambers for deposition processes utilizing multiple liquid precursors, such as BPSG (borophosphosilicate glass), PSG (phosphosilicate glass or phosphorus-doped silicon oxide film), BSG (borosilicate glass or boron-doped silicon oxide film) or USG (undoped silicate glass or undoped silicon oxide film) processes.  
           [0008]    Typically, the flow of the liquid precursor into the vaporizer is controlled by a liquid flow meter (LFM). The response time of the vapor supply into the chamber typically depends on the LFM PID (proportional-integral-differential) control, the liquid vaporizer control valve (injection valve) set up, liquid flow rate, liquid supply pressure, carrier gas flow rate, chamber pressure and etc. For a properly tuned liquid injection system, the response time before stable process gas flow in the chamber is reached typically ranges from about six to ten seconds.  
           [0009]    [0009]FIG. 1 is a graphical illustration showing the standard flow response of vaporized liquid of a typical liquid injection system. The transient state due to the inherent rise time effect of the LFM, as indicated by t r , before liquid stabilizes to set point flow varies from liquid to liquid and from chamber to chamber. The transient film property at the film interface where film starts to grow can not be controlled and results in uncontrolled and inconsistent dopant concentration.  
           [0010]    One example of a problem due to transient film properties is formation of voids at the interface of a BPSG layer and a nitride layer. Another example of a problem due to transient film properties is the consumption of nitride during anneal steps which occurs when a high phosphor content in the initial BPSG film in reaction with water vapors from a steam anneal process causes consumption of nitride by phosphoric acid. Inconsistent dopant concentration, particularly at interfaces with other materials, results in inconsistent processing and defective device formations.  
           [0011]    This transient film property becomes even more significant when the deposition process is short as compared to the time for stabilizing process gas flow. For example, if a process requires a dopant to be introduced for about 12 seconds into the chamber, a majority of the doping process (i.e., about 6-10 seconds) will be required to stabilize the process gas flow, which may vary each time the process is performed, resulting in inconsistent and unrepeatable processing.  
           [0012]    Therefore, there is a need for a process gas delivery system that improves dopant concentration control, particularly at film interfaces. More specifically, there is a need for accurate control of vaporized liquid supply.  
         SUMMARY OF THE INVENTION  
         [0013]    Process gas delivery system and method for improving dopant concentration control, particularly at film interfaces, are provided. More specifically, method and apparatus for providing accurate control of vaporized liquid supply are provided.  
           [0014]    One aspect provides an apparatus for delivering processing gas from a vaporizer to a processing system. The apparatus comprises: a valve connected between the vaporizer and the processing system, the valve having a valve input connected to a vaporizer output and a first valve output connected to a processing system input and a second valve output connected to a bypass line; and a controller for switching the valve between the first valve output and the second valve output. Preferably, the apparatus further comprises: a second valve connected between a carrier gas source, a divert gas source and the vaporizer, the second valve having a first valve input connected to the carrier gas source, a second valve input connected to the divert gas source, and a valve output connected to a vaporizer input.  
           [0015]    Another aspect provides a method for delivering processing gas from a vaporizer to a processing system comprising: connecting a valve between the vaporizer and the processing system, the valve having a valve input connected to a vaporizer output and a first valve output connected to a processing system input and a second valve output connected to a bypass line; and selectively switching the valve between the first valve output and the second valve output.  
           [0016]    Another aspect provides an apparatus for processing a substrate, comprising: a chamber having a gas input; a vaporizer; a valve connected between the vaporizer and the chamber, the valve having a valve input connected to a vaporizer output and a first valve output connected to the chamber gas input and a second valve output connected to a bypass line; and a controller for switching the valve between the first valve output and the second valve output. Preferably, the apparatus further comprises a second valve connected between a carrier gas source, a divert gas source and the vaporizer, the second valve having a first valve input connected to the carrier gas source, a second valve input connected to the divert gas source, and a valve output connected to a vaporizer input.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    So that the manner in which the above recited features, advantages and objects of the present invention are attained and 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.  
         [0018]    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.  
         [0019]    [0019]FIG. 1 is a graphical illustration showing the standard flow response of vaporized liquid of a typical liquid injection system.  
         [0020]    [0020]FIG. 2 is a schematic illustration showing a chemical vapor deposition system having one embodiment of an individual divert gas delivery system.  
         [0021]    [0021]FIG. 3 is a graphical illustration of carrier gas flow and chamber pressure for a deposition process.  
         [0022]    [0022]FIG. 4 is a graphical illustration of an example process for depositing a silicon oxide film having step-wise dopant concentration onto a substrate in the chamber utilizing one embodiment of the individual divert gas delivery system as shown in FIG. 2.  
         [0023]    [0023]FIG. 5 is a graphical illustration of a comparison of SIMS analysis for dopant profile changes for a film formed utilizing a typical standard gas delivery system and a film formed utilizing an individual divert gas delivery system. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0024]    [0024]FIG. 2 is a schematic illustration showing a chemical vapor deposition system having one embodiment of an individual divert gas delivery system. Generally, the chemical vapor deposition (CVD) system  100  includes a chamber  102 , a chamber lid  104  having a gas distributor  106 , a gas delivery system  108  fluidly connected to the gas distributor  106  to deliver one or more processing gases into the chamber  102 , a substrate support member  110  disposed in the chamber, a vacuum exhaust system  112  connected to a gas outlet  114  of the chamber  102 , and a system controller  116  connected to control operation of the CVD system  100 . Examples of CVD systems include the Ultima HDP-CVD™ chamber/system and the DxZ™ chamber/system, which are available from Applied Materials, Inc., located in Santa Clara, Calif.  
         [0025]    The substrate support member  110 , typically made of a ceramic or aluminum nitride (AlN), includes a heater, such as a resistive heating coil disposed inside the substrate support member, and may also include substrate chucking mechanisms for securely holding a substrate, such as a vacuum chuck or an electrostatic chuck. The gas distributor  106  may comprise a showerhead type gas distributor or a plurality of injection nozzles, for providing a uniform process gas distribution over a substrate disposed on the substrate support member  110 . A temperature control system, such as a resistive heating coil and/or thermal fluid channels, may be disposed in thermal connection with the lid and the gas distributor  106 . The temperature control system maintains the temperature of the gas distributor  106  within a desired range throughout processing. The gas distributor  106  is fluidly connected to the gas delivery system  108 . The gas distributor  106  may also be fluidly connected to additional gas sources  120  through additional MFCs  122 .  
         [0026]    The exhaust system  112  includes one or more vacuum pumps  124 , such as a turbomolecular pump, connected to exhaust gases from and maintain vacuum levels in the chamber  102 . The one or more vacuum pumps  124  are connected to the exhaust or gas outlet  114  through a valve such as a gate valve. One or more cold traps  126  are disposed on exhaust lines to remove or condense particular gases exhausted from the chamber.  
         [0027]    The gas delivery system  108  includes one or more vaporizers connected to one or more liquid precursor sources for forming the desired film on the substrate in the chamber. FIG. 2 schematically illustrates one embodiment of a gas delivery system  108  having three vaporizers  202 ,  204 ,  206  for vaporizing three liquid precursors. Although this embodiment is described utilizing three vaporizers, it is understood that the invention contemplates other embodiments of the gas delivery system utilizing any number of vaporizers. Each vaporizer  202 ,  204 ,  206  includes an injection valve  212 ,  214 ,  216  connected to a liquid precursor source  222 ,  224 ,  226  which supplies the liquid precursor to be vaporized. The liquid precursor sources  222 ,  224 ,  226  may include one or more ampules of precursor liquid and solvent liquid. Each ampule is connected to the injection valve of the vaporizer through a liquid flow meter (LFM)  232 ,  234 ,  236 . Optionally, a shut-off valve is disposed between each LFM and each vaporizer.  
         [0028]    Each vaporizer  202 ,  204 ,  206  includes a carrier gas input  242 ,  244 ,  246  and a gas output  252 ,  254 ,  256 . As shown in FIG. 2, each vaporizer includes an input valve  262 ,  264 ,  266  connected the carrier gas input  242 ,  244 ,  246  of the vaporizers and an output valve  272 ,  274 ,  276  connected to the gas output  252 ,  254 ,  256  of the vaporizers. The input and output valve preferably comprises three-way valves to provide substantially instantaneous switching (i.e., less than about 10 milliseconds) between valve inputs and between valve outputs. The input valve  262 ,  264 ,  266  facilitates selection between sources of carrier gas and includes a first input  281 ,  284 ,  287  connected to a process carrier gas source  208  and a second input  282 ,  285 ,  288  connected to a divert carrier gas source  210 . The output  283 ,  286 ,  289  of the input valve  262 ,  264 ,  266  is connected to the carrier gas input  242 ,  244 ,  246  of the vaporizer  202 ,  204 ,  206 . The input valve  262 ,  264 ,  266  is connected to and controlled by the system controller  116  to switch between the input connections  281 / 282 ,  284 / 285 ,  287 / 288  as described below.  
         [0029]    The output valve  272 ,  274 ,  276  includes an input  293 ,  296 ,  299  connected to the vaporized gas output  252 ,  254 ,  256  of the vaporizer  202 ,  204 ,  206  and facilitates selective delivery of process gas to the chamber. The output valve  272 ,  274 ,  276  includes a first output  291 ,  294 ,  297  connected to the gas distributor  106  of the chamber and a second output  292 ,  295 ,  298  connected to a foreline of the exhaust system  112  of the processing system. The output valve  272 ,  274 ,  276  is connected to and controlled by the system controller  116  to switch between the output connections  291 / 292 ,  294 / 295 ,  297 / 298  as described below.  
         [0030]    As shown in FIG. 2, the process carrier gas source  208  includes a helium (He) gas source  208   a  and a nitrogen (N 2 ) gas source  208   b,  each of which is connected through a mass flow controller (MFC)  209   a,    209   b  to the first input  281 ,  284 ,  287  of each input valve  262 ,  264 ,  266 . The MFCs  209   a,    209   b  are connected and controlled by the system controller  116  to provide a desired quantity of process carrier gas flowing through the vaporizers into the process chamber. For example, the MFCs  209   a,    209   b  can be set to provide a total of 6 slm (standard liter per minute) of process carrier gas (e.g., total combined helium gas at 4 slm and nitrogen gas at 2 slm) into the chamber.  
         [0031]    The divert carrier gas source  210  is connected through a fixed flow restrictor  211  which provides a desired amount of divert carrier gas to the second input  282 ,  285 ,  288  of each input valve  262 ,  264 ,  266 . The fixed flow restrictor  211  provides sufficient divert carrier gas to facilitate vaporization of liquid precursors when the vaporizers  262 ,  264 ,  266  are operating in the divert mode as discussed below. Alternatively, the divert carrier gas source can be connected through a MFC to the second input of each input valve to control the amount of divert carrier gas supplied to the vaporizers. As shown in FIG. 2, the divert carrier gas source  210  includes a nitrogen gas source. Although the invention is described utilizing helium and/or nitrogen as carrier gases (process or divert) for the vaporizers, the invention contemplates utilization of a variety carrier gases, including helium, nitrogen, argon, krypton, xenon, and combinations thereof.  
         [0032]    Although the following describes operation of the gas delivery system with respect to one vaporizer, it is understood that other vaporizers of the processing system may also operate similarly. The input valve  262  and output valve  272  connected to the vaporizer  202  operate synchronously to switch input and output of the vaporizer  202  between a process mode and a divert mode. To begin a vaporization process, the LFM  232  is opened to allow flow from the liquid precursor source  222  into the injection valve  212  of the vaporizer  202 . As the liquid precursor is introduced into the injection valve  21  of the vaporizer  202 , the input valve  212  of the vaporizer  202  is switched to receive carrier gas from the second input  282  which is connected to the divert carrier gas source  210 . At the same time, the output valve  272  of the vaporizer  202  is switched to the second output  292  to direct vaporizer output to the foreline of the exhaust system  112 . In this embodiment, when the input valve  262  is set to the second input  282  and the output valve  272  is set to the second output  292 , the vaporizer  202  is defined as operating in a divert mode. Because the LFM  232  has an inherent delay (i.e., rise time) before liquid flow through the LFM is stabilized, the vaporizer  202  operates in the divert mode until the liquid flow through the LFM has stabilized, and the vaporized gas output from the vaporizer is diverted to the foreline of the exhaust system during this initial vaporization period. Thus, the process gas is not introduced into the chamber during this initial period because the process gas has a concentration gradient caused by the rise time of the LFM, and the deposited film formed subsequently on a substrate in the chamber does not exhibit concentration profiles reflecting the rise time of the LFM.  
         [0033]    Once the liquid flow through the LFM has stabilized, the input valve  262  of the vaporizer  202  is switched to receive carrier gas from the first input  281  which is connected to the process carrier gas source  208 , and the output valve  272  of the vaporizer  202  is switched to the first output  291  to direct vaporizer output to the gas distributor  106  of the chamber  102 . In this embodiment, when the input valve  262  is set to the first input  281  and the output valve  272  is set to the first output  291 , the vaporizer  202  is defined as operating in a process mode. In the process mode, the vaporizer  202  provides a stabilized quantity of vaporized precursor, and the resulting deposited film exhibits a consistent concentration profile.  
         [0034]    [0034]FIG. 3 is a graphical illustration of carrier gas flow and chamber pressure for a deposition process. As shown in FIG. 3, the invention provides a constant chamber pressure with constant process carrier gas flow into the chamber. The process carrier gas source is controlled by one or more MFCs to provide a constant 6 slm process carrier gas flow while the divert carrier gas flow is restricted by a fixed flow restrictor to provide 6 slm of divert carrier gas flow.  
         [0035]    During a first period, each input valve of each vaporizer is switched to the first input to receive carrier gas from the process carrier gas source, and each output valve of each vaporizer is switched to the first output to direct vaporizer output into the chamber. The vaporizers are operating at processing mode, and the carrier gas flowing through each vaporizer and into the chamber is equally divided at 2 slm. No divert carrier gas flows through any vaporizer during this first period.  
         [0036]    During a second period, vaporizers A and C remain in processing mode while vaporizer B is switched to divert mode. Vaporizer B is switched to the second input to receive carrier gas from the divert carrier gas source at 6 slm, and the vaporizer output from vaporizer B is diverted to the foreline of the exhaust system. Vaporizers A and C receive carrier gas from the process carrier gas source at 3 slm each because vaporizer B has switched its input to the divert carrier gas source. During the second period, a liquid precursor B, such as a dopant, may be introduced into the vaporizer for liquid precursor B by opening the LFM that controls flow of liquid precursor B. preferably, the duration of the second period is sufficiently long for stabilization of the liquid precursor flow and vaporization. The concentration gradient of the vaporized precursor B due to the rise time of the LFM is thus eliminated from processing in the chamber because the vaporizer output during the rise time of the LFM is diverted to the foreline of the exhaust system.  
         [0037]    During a third period, vaporizer B is switched back to process mode to receive carrier gas from the process carrier gas source through the first input of the input valve and to direct vaporizer output into the chamber through the first output of the output valve. Since vaporization of liquid precursor B is stabilized during the second period, the processing gas in the chamber is changed substantially instantaneously by switching the first and second valves of vaporizer B from divert mode to process mode. During the third period, the carrier gas is equally distributed among the vaporizers at 2 slm each.  
         [0038]    During a fourth period, vaporizer A remains in process mode while vaporizers B and C are switched to divert mode. The process carrier gas source is input solely into vaporizer A at 6 slm and directed into the chamber. Vaporizers B and C receive carrier gas from the divert carrier gas source at 3 slm each, and the output from vaporizers B and C are diverted to the foreline of the exhaust system. During the fourth period, liquid precursor C, such as another dopant, may be introduced into vaporizer C for stabilizing vaporization of liquid precursor C before introducing vaporized precursor C into the chamber. Also during this period, the amount of liquid precursor B may also be changed and stabilized.  
         [0039]    During a fifth period, all vaporizers are again operating at process mode as in the first and third period. The process gas introduced into the chamber includes stabilized concentrations of each liquid precursor. Thus, the invention provides selective switching of processing gas from any combination of vaporizer outputs while maintaining constant chamber pressure and precisely controlled precursor (i.e., dopant) concentration.  
       EXAMPLE  
       [0040]    [0040]FIG. 4 is a graphical illustration of an example process for depositing a silicon oxide film having step-wise dopant concentration onto a substrate in the chamber utilizing one embodiment of the individual divert gas delivery system as shown in FIG. 2. The liquid precursors include TEOS, TEB and TEP, and three vaporizers are utilized, one vaporizer for each liquid precursor. As shown in FIG. 4, at t 1  liquid precursor TEOS is introduced (i.e., LFM opened) into a first vaporizer operating in divert mode until vaporization of liquid precursor TEOS is stabilized at t 3 , typically in about 6-10 seconds. At t 3 , the first vaporizer is switched to process mode to direct vaporized process gas containing vaporized TEOS into the chamber to form a layer of film on a substrate in the chamber. At t 2 , the liquid precursor TEB is introduced into a second vaporizer operating in divert mode until vaporization of liquid precursor TEB is stabilized at t 5 , typically in about 6-10 seconds. At t 5 , the second vaporizer is switched to process mode to direct vaporized process gas containing vaporized TEB into the chamber to dope the silicon oxide film with boron. At t 4  liquid precursor TEPO is introduced into a third vaporizer operating in divert mode until vaporization of liquid precursor TEPO is stabilized at t 6 , typically in about 6-10 seconds. At t 6 , the third vaporizer is switched to process mode to direct vaporized process gas containing vaporized TEPO into the chamber to dope the silicon oxide film with phosphorus in addition to the boron dopant to form BPSG.  
         [0041]    By diverting vaporized output from the vaporizers until liquid flow into the vaporizer is stabilized, the gas delivery system reduces the response time for precursor gases, including dopants, from about 6-10 seconds to substantially instantaneous (i.e., the time required to flip a three-way pneumatic valve). Thus, the invention provides precise control of film content, and particularly for processes having short deposition time as compared to rise time of LFMs, the invention provides consistent and repeatable deposition results that are unaffected by rise time of LFMs.  
         [0042]    [0042]FIG. 5 is a graphical illustration of a comparison of SIMS analysis for dopant profile changes for a film formed utilizing a typical standard gas delivery system and a film formed utilizing an individual divert gas delivery system. The contents of a BPSG film is analyzed with respect to the depth of film. As shown in FIG. 5, a film formed utilizing the individual divert gas delivery system provides a steeper slope for dopant concentration profile as compared to the standard gas delivery system, indicating better dopant profile control provided by the individual divert gas delivery system.  
         [0043]    The individual divert gas delivery system is capable of providing vaporized precursors into a process chamber without the rise time effects or concentration gradient typically associated with LFMs that control flow of liquid precursors into vaporizers. Also, the individual divert gas delivery system is capable to providing precise dopant concentration into a processing chamber for forming films having dopant content, such as BSG, PSG, BPSG, and other doped films. The liquid precursor for the dopant can be introduced into a vaporizer in divert mode a preset time period sufficient for stabilized vaporization of the dopant precursor, typically 6-10 seconds, before the dopant is needed in the process chamber. Thus, when the dopant is needed and introduced into the chamber, the dopant vaporization is stabilized, and the resulting doped film exhibits substantially step-wise dopant concentration profiles.  
         [0044]    Another advantage is that the individual divert gas delivery system can be easily retrofitted (i.e., drop-in retrofit) onto current/existing serial and parallel PLIS systems. The individual divert gas delivery system also enables processing at constant chamber pressure while varying the precursor content in the processing gas.  
         [0045]    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 that follow.