Patent Publication Number: US-2004055636-A1

Title: Method and apparatus for fluid flow control

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The invention relates to a method and apparatus for fluid flow control. More specifically, the invention relates to splitting a fluid flow such as a gas flow into pre-selected proportions.  
       [0003] 2. Background of the Related Art  
       [0004] A chip manufacturing facility is composed of a broad spectrum of technologies. Cassettes containing semiconductor substrates are routed to various stations in the facility where they are either processed or inspected. Semiconductor processing generally involves the deposition of material onto and removal (“etching”) of material from substrates. Typical processes include chemical vapor deposition (CVD), physical vapor deposition (PVD), electroplating, chemical mechanical planarization (CMP), etching and others.  
       [0005] Conventional substrate processing systems often process substrates serially, i.e., one substrate at a time. Unfortunately, processing substrates serially results in throughput limitations corresponding to an individual substrate process time. To overcome the limitations of serial processing, batch (i.e., parallel) processing is often employed. Batch processing allows several substrates to be processed simultaneously using common fluids such as process gasses, chambers, processes, etc. thereby decreasing equipment costs, and increasing throughput. Ideally, batch-processing systems expose each of the substrates to an identical process environment whereby each substrate receives the same process gases and plasma densities for uniform processing of the batch.  
       [0006] One method for batch processing is performed in large single chamber batch-processing systems designed to accommodate more than one substrate. Unfortunately, as the substrates within a single batch-processing chamber share a common area, process gasses and plasma dedicated to one substrate will often intermix with the process gases and plasma dedicated to another substrate causing process variations within each substrate batch. To minimize the intermixing issue, internal chamber divider walls may be used that form sub-chambers within the single batch-processing chamber. However, chamber divider walls increase the cost and complexity of the batch-processing chamber. To eliminate the need for divider walls, multiple single-substrate processing chambers in tandem are often used to provide the benefits of batch processing and uniformity while allowing the careful control and isolation of the process environment for each substrate within a batch.  
       [0007] To control the individual process for each substrate within a batch-processing environment, individual gas, power, and plasma systems are often incorporated within the processing chambers or sub-chambers. In addition, there is usually an individual gas delivery system for each gas or mixture of gases. To reduce the cost of multiple gas supplies and process controls each individual processing region generally has common gas connections and sources. For example, the gas supplies for each sub-chamber or single-substrate processing chamber generally are coupled to a common gas source eliminating the need for multiple gas sources for the same gas or mixture of process gases. Unfortunately, due to variations in gas flow within each individual gas delivery system, each gas delivery system must be individually monitored and calibrated so that each substrate receives the same amount of process gas flow for each process step, according to the process regime. The variations in gas flow rates for each chamber are due to the flow resistance that depends upon the size of pipe used, length of pipe, and pipe joints, valves, etc. of the gas delivery systems.  
       [0008] To alleviate the calibration and control of each individual gas system for the single chamber or multi-chamber types of batch-processing systems, a centralized gas control system is often used to monitor and control the gas flow. Unfortunately, centralized gas control systems generally increase the complexity and cost of the processing systems. Thus, regardless of the batch processing system used, conventional individual gas delivery systems are often complex, require individual or centralized monitoring, require individual calibration, and generally increase the cost of production.  
       [0009] Therefore, there is a need for method and apparatus to provide a uniform fluid flow to each chamber within a batch-processing system in a simple and cost effective manner.  
       SUMMARY OF THE INVENTION  
       [0010] Aspects of the invention generally provide a fluid delivery system for controlling and dividing fluids such as process gases used in substrate processing. In one embodiment, the invention provides an apparatus for dividing a gas flow from a gas source, including a first gas line connected to a gas source, a gas flow meter positioned on the first gas line to output a signal corresponding to a gas flow rate through the first gas line, a second gas line connected to the gas source, and a gas flow controller positioned on the second gas line and responsive to the signal from the gas flow meter to divide the gas flow from the gas source.  
       [0011] In another embodiment, the invention provides an apparatus for dividing a gas flow from a gas source output into a tandem-processing chamber, including a first gas line connecting a gas source output to a first processing region of a tandem processing chamber, a gas flow meter positioned on the first gas line to output a signal corresponding to a first gas flow rate through the first gas line, a second gas line connecting the gas source output to a second processing region of the tandem processing chamber, and a gas flow controller positioned on the second gas line and responsive to the signal from the gas flow meter to divide the gas from the gas source output between the first gas flow rate through the first gas line to the first processing region and a second gas flow rate through the second gas line to the second processing region.  
       [0012] In still another embodiment, the invention provides a method of dividing a fluid flow from a fluid source, including measuring a first fluid flow rate through a first fluid line connected to the fluid source, and controlling a second fluid flow rate through a second fluid line connected to the fluid source using the first fluid flow rate through the first fluid line.  
       [0013] In another embodiment, the invention provides a method of dividing a gas flow in a tandem processing chamber including measuring a first gas flow rate from a gas source through a first gas line coupled to a first processing region of a tandem processing chamber, and using the first gas flow rate, controlling a second gas flow rate from the gas source through a second gas line coupled to a second processing region of the tandem processing chamber.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0014] So that the manner in which the above recited features, advantages and objects of the 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.  
     [0015] 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.  
     [0016]FIG. 1 is a plan-view of a prior art semiconductor batch-processing tool that may be used to advantage.  
     [0017]FIG. 2A is a top perspective view of a semiconductor batch-processing tool of FIG. 1 including a gas delivery system of the invention that may be used to advantage.  
     [0018]FIG. 2B is a bottom perspective view of the semiconductor batch-processing tool of FIG. 1 including a gas delivery system of the invention that may be used to advantage.  
     [0019]FIG. 3 is a cutaway view of the tandem-processing chamber of FIG. 1 including the gas delivery system of FIGS. 2A and 2B.  
     [0020]FIG. 4 is a diagrammatic view illustrating the gas flow control loop of the invention that may be used to advantage.  
     [0021]FIG. 5 is a diagrammatic view illustrating two gas flow control loops of the invention that may be used to advantage.  
     [0022]FIG. 6 is a diagrammatic view of one embodiment of a gas flow measuring apparatus illustrating a flow constriction of the invention that may be used to advantage.  
     [0023]FIG. 7 is a flow diagram of the invention illustrating a method of gas flow control that may be used to advantage.  
     [0024]FIG. 8 is a graphical illustration of the results of an example tandem-chamber substrate deposition process without gas flow control.  
     [0025]FIG. 9 is a graphical illustration of the results of an example tandem-chamber substrate deposition process of the invention that may be used to advantage.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0026] Aspects of the invention generally provide a fluid delivery system for controlling and dividing fluids such as process gases used in substrate processing. In accordance with one aspect of the invention, the system is a staged vacuum system which generally includes a load lock chamber for introducing substrates into the system, a transfer chamber for housing a substrate handler, and one or more processing chambers each having two or more processing regions which are isolatable from each other and preferably share a common fluid supply and a common exhaust pump. Isolatable means that the processing regions have a confined plasma zone separate from the adjacent region that is selectively communicable with the adjacent region via an exhaust system. The processing regions within each chamber also preferably include separate fluid distribution assemblies and RF power sources to provide a uniform plasma density over a substrate surface in each processing region. The processing chambers are configured to allow multiple, isolated processes to be performed concurrently in at least two regions so that at least two substrates can be processed simultaneously in separate processing regions with a high degree of process control provided by shared gas sources, shared exhaust systems, separate gas distribution assemblies, separate RF power sources, and separate temperature control systems. For ease of description, the terms processing region and chamber may be used to designate the zone in which plasma processing is carried out.  
     [0027]FIG. 1 is a plan view of one embodiment of a tandem semiconductor processing system  100  in which embodiments of the invention may be used to advantage. The arrangement and combination of chambers may be altered for purposes of performing specific fabrication process steps.  
     [0028] The tandem-chamber processing system  100  is a self-contained system having the necessary processing utilities supported on a mainframe structure  101  which can be easily installed and which provides a quick start up for operation. The substrate processing system  100  generally includes four different regions, namely, a front end staging area  102  where substrate cassettes  109  are supported and substrates are loaded into and unloaded from a loadlock chamber  112 , a transfer chamber  111  housing a substrate handler  113 , a series of tandem-process chambers  106  mounted on the transfer chamber  111  and a back end  138  which houses the support utilities needed for operation of the system  100 , such as a gas panel  103 , and the power distribution panel  105  for RF power generators  107 . The system can be adapted to accommodate various processes and supporting chamber hardware such as CVD, PVD, etch, and the like.  
     [0029]FIGS. 2A and 2B illustrate a perspective top view and bottom view respectively of one embodiment of a tandem-processing chamber  106  that includes the gas delivery system of the invention. The tandem-processing chamber  106  includes a chamber body  102  mounted or otherwise connected to the transfer chamber  111  and includes two cylindrical annular processing regions in which individual substrates are concurrently processed. The chamber body  102  supports a lid  104  that is hindgedly attached to the chamber body  102  and includes one or more gas distribution systems  108  for delivering reactant and cleaning fluids such as process gases and gas mixtures into the processing regions therein.  
     [0030]FIG. 3 shows a cross-sectional view of the tandem-processing chamber  106  for use with aspects of the invention. The tandem-processing chamber  106  includes a chamber body  102  having a sidewall  112 , an interior wall  114 , and a bottom wall  116 . The sidewall  112  and the interior wall  114  define the two cylindrical annular processing regions  118 ,  120 . The bottom wall  116  of the processing regions  118 ,  120  defines at least two passages  124 ,  122  through which a stem  126  of a pedestal heater  128  and a rod  130  of a substrate lift pin assembly are disposed, respectively. A circumferential pumping channel  125  is formed in the interior chamber walls  114  for exhausting gases and controlling the pressure within each region  118 ,  120 . A chamber liner or insert  127 , preferably made of ceramic, glass, quartz, or the like, is disposed in each processing region  118 ,  120  to define the lateral boundary of each processing region  118 ,  120  and to protect the chamber walls  112 ,  114  from the corrosive processing environment, and to maintain an electrically isolated plasma environment. The liner  127  is supported in the chamber on a ledge  129  formed in the walls  112 ,  114  of each processing region  118 ,  120 . The liner includes a plurality of exhaust ports  131 , or circumferential slots, disposed therethrough and in communication with the pumping channel  125  formed in the chamber walls where the pumping channel  125  is connected to a common vacuum source (not shown). Preferably, there are about forty-eight ports  131  disposed through each liner  127  which are spaced apart by about 7.5° and located about the periphery of the processing regions  118 ,  120 . While forty-eight ports are preferred, any number can be employed to achieve the desired pumping rate and uniformity. In addition to the number of ports  131 , the height of the ports  131  relative to the gas distribution system  108  is adapted to provide an optimal gas flow pattern over the substrate during processing. In addition, the chamber body  102  defines a plurality of vertical gas passages for each reactant gas and cleaning gas suitable for the selected process. The gasses are delivered through the vertical passages in the chamber body  102  into a gas distribution system  108  disposed through the chamber lid  104  to deliver gases into the processing regions  118 ,  120 , from a gas source such as the gas panel  103 .  
     [0031] The gas distribution system  108  of each processing region includes a gas inlet passage  140  that delivers process gases into a showerhead assembly  142  from a gas inlet manifold  117 . The showerhead assembly  142  is comprised of an annular base plate  148  having a blocker plate  144  disposed intermediate a faceplate  146 . A plurality of O-rings  147  are provided on the upper surface of the chamber walls  112 ,  114  around each gas passage to provide sealing connection with the lid  104 . The lid  104  includes matching passages to deliver the gas from the vertical passages within the lower portion of the chamber  102  into the gas distribution system  108 . Gas inlet connections  153  are disposed at the bottom  116  of tandem-processing chamber  106  to connect the gas passages formed in the chamber  102  to a first and a second gas delivery line  139 ,  141 . In one aspect, the base plate  148  defines a gas passage therethrough to deliver process gases to a region just above the blocker plate  144 . The blocker plate  144  disperses the process gases over its upper surface and delivers the gases above the faceplate  146 . In one aspect, holes in the blocker plate  144  can be sized and positioned to enhance mixing of the process gases and distribution over the faceplate  146 . The gases delivered to the faceplate  146  are then delivered into the processing regions  118 ,  120  in a uniform manner over a substrate positioned for processing.  
     [0032] In one aspect, an RF feedthrough (not shown) provides an electrical conduit through the walls  112 ,  114  to provide a bias potential to each showerhead assembly  142 , facilitating the delivery of RF power for the generation of plasma between the faceplate  146  of the showerhead assembly and the heater pedestal  128 . A cooling channel  152  is formed in a base plate  148  of each gas distribution system  108  to cool the base plate  148  during operation. A fluid inlet  155  delivers a coolant fluid, such as water or the like, into the channels  152  that are connected to each other by coolant line  157 . The cooling fluid exits the channel through a coolant outlet  159 . Alternatively, the cooling fluid is circulated through the manifold  117 .  
     [0033]FIG. 4 is a diagrammatic view illustrating a gas flow control loop for the tandem-processing chamber  106  of FIGS.  1 - 3 . As necessary, FIGS.  1 - 3  are referenced in the following discussion of FIG. 4.  
     [0034] Illustratively, one or more fluids such as process gases, or a mixture of process gasses, are supplied to the tandem-process chamber  106  from the gas panel  103  having a gas flow delivery system (GFD)  180  coupled to the gas delivery lines  139 , 141 . In one aspect, the GFD  180  includes a splitter  133  such as a line splitter, t-type, and the like having a gas input coupled to a gas source line  132  from the gas panel  103 . The splitter  133  includes a first splitter output  156  connected to a gas input  183  of a gas flow measuring apparatus (GFM)  182 , such as a gas flow meter, mass flow meter (MFM), and the like, and a second splitter output  158 . The GFM  182  includes a flow output  185  and one or more flow measurement signal outputs  155  adapted to provide flow measurement signals such as digital signals, analog signals, and the like, indicative of the amount of flow through gas delivery line  139 . Further, the GFD  180  includes a gas flow control apparatus (GFC)  184 , such as an adjustable gas flow controller, orifice, venturi, or a valve, such as a gate valve, a ball valve, a pneumatic valve, and the like. The GFC  184  also comprises a gas control input  190  coupled to the second splitter output  158 , a gas control output  191  coupled to the second gas delivery line  141 , and a flow control input  161  coupled to and responsive to the flow measurement signal output  155  from the GFM  182 . In one aspect, the signal level of the flow measurement signal output  155  of the GFM  182  is a function of the gas flow through gas line  139  measured by the GFM  182 . For example, as the gas flow increases through the GFM  182 , the flow measurement signal from the signal output  155  may increase in voltage or current. The gain of the flow control input  161  may be set such that a minimum voltage from the signal output  155  corresponds to a minimum flow and a maximum flow measurement signal output  155  corresponds to a maximum flow through the GFC  184 . In another aspect, the gain of the flow control input  161  and flow measurement signal  155  have about the same flow range so the control signal output  155  indicates that the total flow from the gas line  131  is divided into about a fifty percent flow through the GFM  182  and through the GFC  184  in a steady state condition. Although it is preferred that the values of the minimum flow measurement signal 155 voltage is about zero volts and the maximum voltage is about 5 volts, it is contemplated that the flow measurement signal output  155  may be any value and type of signal such as voltage, current, power, electro-optical, or electromechanical, and the like. Further, it is contemplated that the flow measurement signal  155  may be a digital signal whereby the digital information controls the flow control input  161 . For example, the digital signal may be in a byte format whereby the change in the byte value changes the flow through the GFC  184 . In another aspect, a filter  177 , such as a sintered nickel filter available from PALL or Millipore, is disposed in the gas line  132  upstream and/or downstream from the splitter  133 . In still another aspect, the gas line  132  may be coupled to a mass flow controller within the gas panel  103  to establish a consistent input gas flow to the GFD  180 .  
     [0035]FIG. 4 is merely one hardware configuration for a GFD  180 . Aspects of the invention can apply to any comparable hardware configuration, regardless of whether the GFD  180  is a complicated, multi-gas delivery apparatus or a single gas delivery apparatus. For example, FIG. 5 illustrates combining two GFDs to provide two or more different fluids or mixtures of fluids to the tandem-processing chamber  106  where, for example, a fluid such as a process gas A is delivered by a first GFD  180  and a second fluid such as a process gas B is delivered by a second GFD  181 .  
     [0036]FIG. 6 illustrates a diagrammatic view of one embodiment of a GFM  182 . As necessary, FIGS.  1 - 5  are referenced in the following discussion of FIG. 6.  
     [0037] In one aspect, the GFM  182  includes a gas flow restriction  187  such as an orifice, block, valve, and the like, adapted to provide gas flow resistance. The restriction  187  is sized to set the desired flow rate through the gas delivery line  139  to establish a desired initial gas flow rate through both gas lines  139 ,  141  and provide a gas flow resistance through gas delivery line  139 . The split gas lines  139 ,  141  share a common gas input  131  and are in communication through splitter  133  whereby the flow through each line equals about the total gas flow. Therefore, a flow restriction within either gas delivery line  139 ,  141  affects the gas flow through the other line. For example, if the gas flow were completely restricted through gas delivery line  139  and the gas delivery line  141  was unrestricted, then the gas would flow through gas delivery line  141 . In one aspect, the gas flow restriction  187  includes an orifice  188  having an inner diameter of about 0.03 inches to about 0.06 inches to provide the gas flow resistance. Thus, as a process gas flows through the GFM  182 , the gas flow from gas delivery line  139  is impeded by the gas flow restriction  187  creating backpressure within gas delivery line  139  causing process gas to flow through gas delivery line  141 . In one aspect, the gas restriction  187  may be a fixed value or may be adjustable to further accommodate different process gases and flow requirements. In another aspect, the restriction  187  is a separate device coupled to any portion of gas line  139 .  
     [0038] Fluid Flow Control  
     [0039]FIG. 7 is a flow diagram of one embodiment for a method  700  for fluid flow control for the tandem-processing chamber of FIG. 1 in accordance with aspects of the invention. As necessary, FIGS.  1 - 6  are referenced in the following discussion of FIG. 7.  
     [0040]FIG. 7 is entered at step  705  when for example a fluid such as a process gas is delivered from the gas line  131  to the GFD  180 . At step  710 , the GFC  184  is set to minimum flow and the GFM  184  is set to maximum flow. The process gas flows from the input gas line  131  to the splitter  133  and then to each gas delivery line  139 ,  141 . Initially, due to the setting of the GFC  184  and GFM  182 , the majority of the process gas flow occurs through the GFM  182 . The flow through the GFM  182  is measured at step  715  and the corresponding flow measurement signal  155  is then transmitted to the flow control input  161 . The flow measurement signal  155  then opens the flow of gas through the GFC  184 . As the flow of process gas begins to flow through the GFC  184 , the gas flow through the GFM is proportionally decreased. In one aspect, at step  725 , the value of the flow measurement signal  155  corresponds to the input range of the flow control input  161  such that about fifty percent of the process gas flows through the GFM  182  and GFC  184 . In one aspect, as the gas flows within the gas delivery lines  139 ,  141  are responsive to the gas flows of each other, and the GFM  182  controls the gas flow through the GFC  184  in accordance to the measured gas flow through the GFM  182 , the individual flow through each gas delivery line  139 ,  142  is adjusted until the two flow rates are about equal and in equilibrium. Although, a fifty percent flow through each gas delivery line  139 ,  141  is preferred, other ratios of gas flows are contemplated to allow for variations between processing regions. If the gas flow rate is about identical through GFM  182  and GFC  184 , the gas flow is continued until the process step is finished at step  730 . Subsequently, the method  700  exits at step  735 . Thus, the gas lines  139 ,  141 , and the flow control signal define a closed loop gas control system responsive to the gas flow from the gas input  131  where a change in gas flow results in a proportional change in the gas flow rates through the gas lines  139 ,  141 .  
     [0041] Example Process Parameters  
     [0042] In the described embodiment, the precursor gas may be any gas or gas mixture such as Trimethylsilane (TMS), NF 3 , and the like, adapted to perform substrate processing operations. In one aspect, the flow rate of activated species is about 100 sccm to about 20 slm per minute and the chamber pressure is about 0.5 Torr to about 10.0 Torr. Within the deposition chamber, the RF sources supply about 200 watts to about 2000 watts to the plasma.  
     [0043] Though a RF generator is used in the described embodiment to activate the precursor gas, any power source that is capable of activating the precursor gas can be used. For example, the plasma can employ combinations of DC, radio frequency (RF), and microwave (MW) based discharge techniques. In addition, if an RF power source is used, it can be either capacitively or inductively coupled to the inside of the chamber. The activation can also be performed by a thermally based, gas breakdown technique, a high intensity light source, or an x-ray source, to name just a few.  
     [0044] In general, the reactive gases may be selected from a wide range of options. For example, the reactive gas may be chlorine, fluorine or compounds thereof that include carbon, oxygen, helium, or hydrogen, e.g. CF 4 , SF 6 , C2F 6 , CCl 4 , C2Cl 6 , SiO 2 , etc. Of course, the particular gas that is used depends on the material that is being deposited.  
     [0045]FIGS. 8 and 9 illustrate one example of a tandem process performed with and without using the fluid flow control apparatus and method described above. The following table presents one example of chamber operating conditions for a deposition process performed in one embodiment of a tandem-chamber of the invention for both FIGS. 8 and 9. With reference to FIG. 8, the gas flow apparatus and method are not used. The left chamber and right chamber show a difference in substrate thickness of about 5%. With reference to FIG. 9, the gas flow apparatus and method are used. There is a less than about 1% difference in the substrate thickness variation between the left and right processing regions.  
                                                   Processing Parameter   Parameter Value                          GAS: TMS   About 500 sccm to about 2000 sccm           GAS: O 2     About 400 sccm to about 2000 sccm           Chamber Pressure   About 0.5 Torr to about 10 Torr           RF Power   About 400 W to about 2000 W                      
 
     [0046] Although various embodiments which incorporate the teachings of the invention have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments within the scope of the invention. For example, more than two chambers may be used in tandem where the gas line is split in more than two gas delivery lines. In another embodiment, the process gas may be a mixture of gases where each gas is premixed with other gases and then flowed into the GFD  180 . In still another embodiment, one or more fluids can be divided through both gas delivery lines  139 ,  141  and then brought to a gaseous phase within the tandem-processing chamber  106 .  
     [0047] While 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.