Patent Publication Number: US-2020278084-A1

Title: Gas supply method and gas supply system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2019-035142, filed on Feb. 28, 2019, the entire contents of which are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a gas supply method and a gas supply system. 
     BACKGROUND 
     In a process of manufacturing a semiconductor device, a process using an easy-to-liquefy gas such as an HF gas, a ClF 3  gas or the like may be performed. For example, Patent Documents 1 and 2 disclose technologies for performing a chemical oxide removal process (COR) that chemically removes a silicon oxide film with a hydrogen fluoride (HF) gas and an ammonia (NH 3 ) gas. 
     PRIOR ART DOCUMENT 
     Patent Documents 
     
         
         Patent Document 1: Japanese Laid-Open Patent Publication No. 2005-039185 
         Patent Document 2: Japanese Laid-Open Patent Publication No. 2008-16000 
       
    
     SUMMARY 
     According to one embodiment of the present disclosure, there is provided a gas supply method including: preparing a gas container filled with an easy-to-liquefy gas; and supplying the easy-to-liquefy gas from the gas container to a processing container in which a substrate process is performed using the easy-to-liquefy gas, via a gas supply path, wherein a pressure and a temperature of the easy-to-liquefy gas are controlled such that in the gas supply path, the pressure of the easy-to-liquefy gas decreases in a step-by-step manner and the temperature of the easy-to-liquefy gas increases from the gas container toward the processing container. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the present disclosure, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the present disclosure. 
         FIG. 1  is a schematic configuration diagram showing an example of a gas processing facility using a gas supply method according to an embodiment. 
         FIG. 2  is a schematic configuration diagram showing an example of a gas supply system in the gas processing facility shown in  FIG. 1 . 
         FIG. 3  is a view showing a saturated vapor pressure curve of HF. 
         FIG. 4  is a view showing a detailed configuration of an internal pipe disposed in a cylinder cabinet. 
         FIGS. 5A to 5C  are views for explaining a passivation process for a stainless steel (SUS316L) pipe. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to various embodiments, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. However, it will be apparent to one of ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, systems, and components have not been described in detail so as not to unnecessarily obscure aspects of the various embodiments. 
       FIG. 1  is a schematic configuration diagram showing an example of a gas processing facility using a gas supply method according to an embodiment.  FIG. 2  is a schematic configuration diagram showing an example of a gas supply system  200  in the gas processing facility shown in  FIG. 1 . 
     The gas processing facility  100  is configured to perform a process using an easy-to-liquefy gas, for example, an HF gas or a ClF 3  gas. The easy-to-liquefy gas referred to herein is, for example, a gas having a saturated vapor pressure of 100 kPa or less at room temperature (20 degrees C.). The gas processing facility  100  includes a cylinder cabinet  10  in which a cylinder as a gas container is accommodated, a VMB (Valve Manifold Box)  20  and a gas processing device  50 . The gas processing device  50  includes a gas box  30  and a processing container (chamber)  40 . 
     In a case where the gas processing device  50  is provided in plural numbers, the VMB  20  is provided to distribute a gas to individual devices. The VMB  20  may not be provided when there is one gas processing device  50 . In some embodiments, even when there is a plurality of gas processing devices  50 , a pipe may be merely branched without providing the VMB  20 . 
     A pipe  60  as a gas flow path is provided between the cylinder in the cylinder cabinet  10  and the VMB  20 . The VMB  20  is internally branched into a plurality of parts. A plurality of pipes  70  extends from the VMB  20 . The other end of each pipe  70  is connected to the gas box  30  of the gas processing device  50 . The gas box  30  and the processing container  40  are connected to each other by a pipe  80 . 
     A combination of the cylinder cabinet  10 , the VMB  20 , the gas box  30  and the pipes  60 ,  70  and  80  constitutes the gas supply system  200 . 
     As shown in  FIG. 2 , the cylinder cabinet  10  includes a housing  11 , a cylinder  12  which is a gas container provided in the housing  11 , and an internal pipe  13  for sending out a gas from the cylinder  12 . The internal pipe  13  is provided with a valve  14  for sending out a vaporized gas from the cylinder  12  and a regulator  15  for regulating a pressure. Although not shown in  FIG. 2 , various devices described below are provided in the internal pipe  13  in addition to the regulator  15 . 
     The VMB  20  includes a housing  21  and an internal pipe  22  provided in the housing  21 . The internal pipe  22  includes a main pipe  23  connected to the pipe  60  and a plurality of branch pipes  24  branched from the main pipe  23 . One ends of the pipes  70  are connected to the branch pipes  24 . A regulator  25 , a valve  26  and the like are provided in each of the branch pipes  24 . 
     The gas box  30  includes a housing  31  and an internal pipe  32  provided in the housing  31 . The internal pipe  32  is provided so as to penetrate the housing  31 . One end of the internal pipe  32  is connected to the other end of the pipe  70 . The other end of the internal pipe  32  is connected to one end of the pipe  80 . A regulator  33 , a pressure indicator  34  and a flow rate controller  35  such as a mass flow controller or the like are provided in the internal pipe  32  sequentially from the upstream side. Opening/closing valves  36 ,  37  and  38  are provided on the upstream side of the regulator  33 , between the flow rate indicator  34  and the flow rate controller  35 , and on the downstream side of the flow rate controller  35 , respectively. 
     The processing container  40  is configured to perform a predetermined process, for example, etching of a silicon-based film, such as the above-described COR process or the like, on a substrate as a workpiece, for example, a semiconductor substrate, using an easy-to-liquefy gas, for example, an HF gas. A shower head (not shown) for supplying a gas in the form of a shower to a workpiece mounted on a stage (not shown) inside the processing container  40  is provided in an upper portion of the processing container  40 . The other end of the pipe  80  is connected to the shower head. 
     The pressure of the supplied gas may be adjusted by the regulators  15 ,  25  and  33 . When the gas flow rate is controlled by the flow rate controller  35 , a change in pressure depending on the gas flow rate occurs in the flow rate controller  35 . The pressure of the gas at this time is adjusted into a dynamic pressure by allowing a gas to flow to the processing container  40  at a usable maximum flow rate and operating the regulators. 
     As shown in  FIG. 2 , the gas pressure is controlled so as to decrease in a step-by-step manner from the gas pressure at the time of sending out the gas from the cylinder  12  of the cylinder cabinet  10  to the gas pressure at the time of supplying the gas to the processing container  40 . At this time, a higher pressure on the outlet side of the cylinder  12  is preferable for stable gas supply. However, if there is a large pressure fluctuation at an orifice of the regulator, the gas is likely to be liquefied by adiabatic expansion. Thus, it is preferred that the pressure difference is reduced as far as possible 
     In this example, a gauge pressure from the regulator  15  to the regulator  25  is 0.007 MPaG. A gauge pressure from the regulator  25  to the regulator  33  is 0.00 MPaG (atmospheric pressure). A gauge pressure from the regulator  33  to the flow rate controller  35  is −0.00 to −0.0257 MPaG. Furthermore, parts following the flow rate controller  35  are kept at a vacuum. 
     However, the pressure control shown in  FIG. 2  is merely an example. The pressure may be finely controlled by increasing the number of regulators. When the VMB  20  is not used, the pressures in the regulators  15  to  33  may be the same. In addition, the numerical values of the pressures are also merely an example. 
     A plurality of heater units capable of independently controlling a temperature is provided between the cylinder  12  and the pipe  80 . The heater units control the gas temperature in the gas supply path extending from the cylinder  12  to the processing container  40  so that the gas temperature increases from the cylinder  12  toward the processing container  40 . The temperature control is also performed by a controller  110 . 
     For example, as shown in  FIG. 2 , the heater units include a first heater unit  91 , a second heater unit  92 , a third heater unit  93 , a fourth heater unit  94 , a fifth heater unit  95 , a sixth heater unit  96  and a seventh heater unit  97 . The first heater unit  91  heats the cylinder  12 . The second heater unit  92  heats the internal pipe  13  in the cylinder cabinet  10 . The third heater unit heats the pipe  60 , the VMB  20  and the pipe  70 . The fourth heater unit  94  heats a front stage portion of the internal pipe  32  of the gas box  30  up to just before the flow rate controller  35 . The fifth heater unit  95  heats the flow rate controller  35 . The sixth heater unit  96  heats a rear stage portion of the internal pipe  32  of the gas box  30  beyond the flow rate controller  35 . The seventh heater unit  97  heats the pipe  80 . 
     In this example, the internal temperature of the cylinder cabinet  10  is set to 25 degrees C. the temperature from the cylinder  12  to a portion immediately before the flow rate controller  35  of the gas box  30  is set to 35 to 45 degrees C., the temperature of the flow rate controller  35  is set to 45 degrees C., and the temperature on the downstream side of the flow rate controller  35  is set to 100 degrees C. However, the temperature control shown in  FIG. 2  is merely an example. For example, in the example of  FIG. 2 , there is shown the case where the first to seventh heater units  91  to  97  are provided and the number of heating regions is seven. However, the number of heating regions is not limited thereto, and may be more than or less than seven. In addition, the numerical values of the temperature are also an example. 
     The pressure and the temperature at the time of supplying the gas are set such that the gas filled as a liquid in the cylinder  12  can be vaporized and then supplied to the processing container  40  at a sufficient flow rate without re-liquefaction. The pressure and temperature of the gas are determined based on a saturated vapor pressure curve of the gas. When the gas is re-liquefied, there is a risk of damaging the pipes and various devices. In particular, the HF gas and the ClF 3  gas are corrosive gases, and there is a risk that the liquefaction of the HF gas and the ClF 3  gas may cause corrosion of the pipes and various devices. 
     For example, the saturated vapor pressure curve of the HF gas is as show n in  FIG. 3 , and the temperature and pressure are set to be below the saturated vapor pressure curve. As described above, in the regulator, the pressure of the gas suddenly drops at a throttle portion. Then, the gas adiabatically expands so that the temperature thereof is likely to decrease. Therefore, the gas is likely to be locally liquefied. For this reason, the regulator sets the pressure and the temperature with sufficient margins from the vapor pressure curve. From such a viewpoint, as described above, the pressure and temperature of the gas are controlled so that in the gas supply path extending from the cylinder  12  to the processing container  40 , the gas pressure decreases in a step-by-step manner and the gas temperature increases from the cylinder  12  toward the processing container  40 . 
     In addition, it is preferable that the pipe making contact with an easy-to-liquefy gas such as a HF gas or the like is constructed with a heater and a heat insulating material to further suppress liquefaction of the easy-to-liquefy gas. In particular, it is preferable that the regulator is strictly constructed with a heater and a heat insulating material to prevent the gas from being cooled down by the pressure change. 
     In the present embodiment, in addition to taking the measures to prevent the gas liquefaction as described above, it is preferable not to supply impurities to the processing container as far as possible because the HF gas and the ClF 3  gas are corrosive gases. For this purpose, the following measures may be taken in the present embodiment.
         (1) Stainless steel with fewer impurities is used as the stainless steel used for the pipes.   (2) High-purity gases are used as the gases.   (3) Since the HF gas or the like may react violently with moisture and may cause corrosion of the pipes and various devices, sufficient N 2 -based purging and cycle purging are performed on the gas pipes and various devices before sending out the gases.   (4) An initial gas is discarded when sending out the gases.   (5) Passivation of the pipes is performed to suppress the generation of a contamination gas.       

     In (1) above, stainless steel containing fewer impurities is used for the pipes. It is preferable to use stainless steel in which the contents of Mn and Cu contained as impurities are 0.05 mass % or less and 0.20 mass % or less, respectively. SUS316L is preferred. If the content of Mn exceeds 0.5 mass %, corrosion near a welded portion is recognized. When the content of Cu exceeds 0.20 mass %, the semiconductor device as a workpiece is adversely affected. The content of Cu is preferably kept low, more preferably 0.10 mass % or less. For stainless steel having fewer impurities, it is preferable to use a double melt material obtained by performing vacuum melting twice. The basic composition of the SUS316L double melt material is preferably as follows: Ni: 14.00 to 15.00 mass %, Cr: 17.00 to 18.00 mass %, Mo: 2.50 to 3.00 mass %, C: 0.010 mass % or less, Si: 0.15 mass % or less, P: 0.020 mass % or less. S: 0.002 mass % or less, Al: 0.01 mass % or less, N: 0.0015 mass % or less, O: 0.0020 mass % or less, H: 0.0005 mass % or less, Fe and unavoidable impurities as the balance. For the pipes, it is preferable to use pipes whose gas flow surfaces are electrolytically polished to have a surface roughness Ry of 0.7 μm or less. 
     In (2) above, if impurities are contained in the easy-to-liquefy gas, they may cause corrosion of the pipes, clogging of the shower head, and the like. For example, in the case of the HF gas, it is preferable to use an HF gas having an extremely high purity of 99.999 mass % or more and containing, as impurities, 1 ppm or less of H 2 SiF 6  and 5 ppm or less of H 2 O in terms of mass. If the Si content is high, it may cause clogging of the shower head inside the processing container. If the H 2 O content is high, it may cause corrosion. In the case of the ClF 3  gas, it is preferable to use a ClF 3  gas having a purity of 99.9 mass %. 
       FIG. 4  shows a detailed configuration of the internal pipe of the cylinder cabinet  10  used for performing (3) above. A first pressure indicator  111 , an exhaust line  112  and a purge line  113  are provided in the internal pipe  13  of the cylinder cabinet  10  in addition to the valve  14  and the regulator  15 . A valve  115  is provided on the upstream side of the regulator  15  in the internal pipe  13 . A second pressure indicator  116 , a valve  117 , an adjustment valve  118  and a third pressure indicator  119  are sequentially provided on the downstream side of the regulator  15  in the internal pipe  13 . 
     Since the pipes cannot be sufficiently dried down by merely performing evacuation from the apparatus, the N 2  gas-based purging of the gas supply path is performed by supplying an N 2  gas from the purge line  113  to the gas supply path extending to the processing container  40  including the internal pipe  13 . At the time of cylinder replacement, a cycle purging is performed in which the exhaust is purged using an exhaust line  112  and the N 2 -based purging using the purge line  113  are alternately performed. The transition of the pressure in the internal pipe  13  can be seen on the first pressure indicator  111 , the second pressure indicator  116  and the third pressure indicator  119 . 
     Regarding (4) above, the gas initially discharged from the cylinder  12  contains a large amount of Si component and the like due to the influence of silica polishing of the inner wall of the cylinder  12 , which may cause trouble. Therefore, it is preferable that the initial gas is discarded via the exhaust line  112  or the like, for example, at a flow rate of 1 slm for about 5 hours. 
     When the gas is discharged from the cylinder  12 , it is preferable that the pipe extending to the gas box is not filled with the gas at once. If the volume of the pipe is larger than that of the gas in the cylinder  12 , vaporization may not be caught up and a liquid may be sucked up. For this reason, it is preferable to open the valve  14  gradually instead of opening the valve  14  all at once. 
     Regarding (5) above, a natural oxide film (Cr 2 O 3  or Fe 2 O 3 ) having a thickness of about several nm is formed on the surface of the pipe made of stainless steel (SUS316L) ( FIG. 5A ). When oxygen in the oxide film reacts with the HF gas, a contaminant gas having a high vapor pressure such as CrO 2 F 2  or the like is generated ( FIG. 5B ). Thus, a passivation process of allowing the HF gas to flow through the pipe is performed for 10 hours or more, for example 14 hours, after discharging the gas to form a fluorinated passivation film such as CrFx or FeF 2  on the surface of the pipe ( FIG. 5C ). This makes it possible to suppress generation of contamination gas in the actual process. 
     According to the present embodiment, the easy-to-liquefy gas such as an HF gas or a ClF 3  gas is supplied from the cylinder  12 , which is a gas container, to the processing container  40  via the gas supply path. At this time, the pressure and temperature of the gas are controlled such that in the gas supply path, the pressure of the gas decreases in a step-by-step manner and the temperature of the gas increases from the cylinder  12  toward the processing container  40 . 
     Thus, it is possible to effectively suppress liquefaction of the gas in the middle of the gas supply path. At this time, the pressure and temperature of the gas have a sufficient margin with respect to the saturated vapor pressure curve, which makes it possible to ensure that the gas is hardly liquefied especially at the orifice portion of the regulator where the gas rapidly adiabatically expands. 
     In the related art, the process using an HF gas is disclosed in Patent Documents 1 and 2. However, these Patent Documents 1 and 2 do not teach how to supply an easy-to-liquefy gas such as an HF gas or the like. 
     Thus, in the present embodiment, in order to supply the easy-to-liquefy gas without re-liquefaction, the pressure and temperature of the gas are controlled such that the pressure of the gas decreases in a step-by-step manner and the temperature of the gas increases from the cylinder  12  toward the processing container  40 . 
     The gas supply system of the above-described embodiment is merely an example. The gas supply system may be any gas supply system that supplies an easy-to-liquefy gas by reducing the pressure from an atmospheric pressure to a vacuum state. 
     Furthermore, in the above-described embodiment, the HF gas and the ClF 3  gas are exemplified as the easy-to-liquefy gas. However, the easy-to-liquefy gas is not limited thereto, and may be a TiCl 4  gas, an H 2 O gas (water vapor) or the like. 
     According to the present disclosure in some embodiments, it is possible to provide a gas supply method and a gas supply system capable of supplying an easy-to-liquefy gas from a gas source to a processing container while suppressing liquefaction as far as possible. 
     Although the embodiment has been described above, it should be noted that the embodiment disclosed herein is illustrative and not restrictive in all respects. The above-described embodiment may be omitted, replaced or modified in various forms without departing from the scope and spirit of the appended claims.