Patent Publication Number: US-2013239993-A1

Title: Film-forming apparatus and method for cleaning film-forming apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a film-forming apparatus and a method for cleaning a film-forming apparatus. 
     BACKGROUND ART 
     Chemical vapor deposition (CVD), which is a technique for forming thin films on a substrate using chemical reaction, includes plasma CVD, thermal CVD, hot wire CVD, and catalytic CVD. Hot wire CVD and catalytic CVD use a heated metal wire such as tungsten, which is arranged exposed to a source gas to decompose the gas and generate film formation species. Hot wire CVD and catalytic CVD significantly reduce electric damage and thermal damage on the substrate or on the underlying layers. 
     In continuous film formation performed by CVD, the chemical reaction for forming a film is repeated in the film-forming chamber. The film formation species can partially reside and accumulate in the film-forming chamber. Such film formation residue accumulating in the film-forming chamber may defoliate from the wall surfaces and form particles that contaminate thin films. This may lower the yield or generate process variations. To prevent this, the CVD apparatus undergoes regular cleaning by supplying a cleaning gas containing active species, such as halogen, into the film-forming chamber and chemically removing the film formation residues. This method allows for continuous deposition since the film-forming chamber is not exposed to air after cleaning. 
     However, when the hot wire CVD apparatus or the catalytic CVD apparatus uses this cleaning method, the cleaning gas may corrode and decrease the diameter of the wire functioning as a catalyst. When the corroded catalyst wire is replaced, the film-forming chamber is exposed to air. Whenever the catalyst wire is replaced, exposure of the film-forming chamber to air significantly changes the degree of vacuum as well as the temperature in the film-forming chamber. This lengthens the maintenance time of the apparatus. 
     Patent literature 1 describes heating a heat generator, which corresponds to the catalyst wire, and maintaining the heat generator at 2000° C. or higher to reduce reaction between the cleaning gas and the catalyst wire. 
     Patent literature 2 describes moving the catalyst wire out of the film-forming chamber. 
     PRIOR ART LITERATURES 
     Patent Literatures 
     Patent Literature 1: U.S. Pat. No. 4,459,329 
     Patent Literature 2: Japanese Laid-Open Patent Publication No. 2009-108390 
     SUMMARY OF THE INVENTION 
     Problems that are to be Solved by the Invention 
     However, the method described in patent literature 1, which heats the heat generator corresponding to the catalyst wire at a high temperature of 2000° C. or higher, may diffuse metal atoms or impurities from the catalyst wire into thin films formed in the film formation process. 
     The method described in patent literature 2 complicates the apparatus. Further, when a moving unit is arranged above the substrate to move the catalyst, this may produce particles or cause process variations. 
     To solve the above problems, it is an object of the present invention to provide a film-forming apparatus and a method for cleaning a film-forming apparatus that reduce corrosion of a heat generator without lowering the yield. 
     It is another object of the present invention to provide a film-forming apparatus and a method for cleaning a film-forming apparatus that reduce corrosion of a heat generator without complicating the apparatus. 
     Means for Solving the Problems 
     A first aspect of the present invention is a film-forming apparatus including a heat generator exposed to a film-forming gas drawn into a chamber to generate film formation species. The apparatus includes a film-forming gas supply system that supplies the film-forming gas into the chamber, a control unit that sets the heat generator in a non-heated state during a cleaning process that discharges a film formation residue from the chamber, a cleaning gas supplying system that supplies a cleaning gas including ClF 3  into the chamber, a temperature adjustment unit that adjusts the chamber to a target temperature from 100° C. or higher to 200° C. or less in the cleaning process, and a discharge system that discharges a reaction product produced by a reaction between the film formation residue and the cleaning gas from the chamber. 
     This structure sets the heat generator in a non-heated state during cleaning, and thus reduces corrosion of the heat generator caused by the cleaning gas. In other words, this structure adjusts the chamber to the above temperature range to allow the cleaning gas to thermally decompose in a spontaneous manner without absorbing heat from the heat generator. Thus, there is no need to subject the heat generator to a high temperature that would diffuse atoms from the heat generator. This prevents atoms from being diffused from the heat generator as impurities that contaminate thin films. This structure reduces corrosion of the heat generator in the cleaning process while preventing the yield from decreasing. Although the heat generator is set in a non-heated state in the cleaning process, adjustment of the temperature in the chamber enables cleaning to be performed while reducing corrosion of the heat generator. This eliminates the need for a mechanism that moves the heat generator, and prevents the apparatus from being complicated. 
     Preferably, the temperature adjustment unit includes a temperature adjustment mechanism that uses a heat medium having a boiling point higher than or equal to the target temperature to exchange heat between the heat medium and the chamber. The temperature adjustment mechanism includes a cooling unit, which cools the heat medium in a film formation process, and a heating unit, which heats the heat medium in a cleaning process when the heat medium has a lower temperature than the target temperature. 
     This structure integrates the cooling mechanism for cooling the chamber and the heating mechanism for heating the chamber. Thus, enlargement of the apparatus is avoided. 
     Preferably, the film-forming gas supply system supplies the film-forming gas to form a thin film, which includes at least one of TiN, TaN, WF 6 , HfCl 4 , Ti, Ta, Tr, Pt, Ru, Si, SiN, SiC, and Ge, or to form an organic thin film. 
     This structure efficiently removes film formation residues formed by the film-forming apparatus by using the cleaning gas including ClF 3 and adjusting the temperature in the chamber to the target temperature. 
     Preferably, the film-forming apparatus further includes a seal that hermetically seals the chamber. The seal is formed from a perfluoro rubber or perfluoroelastomer. 
     In this structure uses, the seal for sealing the chamber is resistant to corrosion caused by ClF 3 , which is included in the cleaning gas, and resistant to the heat in the chamber that is adjusted to a temperature from 100° C. or higher to 200° C. or less. This prevents corrosion of the seal in the cleaning process, and provides optimum seal. 
     A second aspect of the present invention is a method for cleaning a film-forming apparatus, wherein the film-forming apparatus performs a film formation process for exposing a heat generator arranged in a chamber to a film-forming gas to generate film formation species and form a thin film on a substrate and then performs a cleaning process to remove a film formation residue from the chamber. The method includes setting the heat generator in a non-heated state, adjusting the chamber to a target temperature from 100° C. or higher to 200° C. or lower, and supplying a cleaning gas including ClF 3  into the chamber so that the cleaning gas reacts with the film formation residue in the chamber and discharging a reaction product produced by a reaction between the cleaning gas and the film formation residue. 
     This method sets the heat generator in a non-heated state during cleaning, and thus reduces corrosion of the heat generator caused by the cleaning gas. In other words, this method adjusts the temperature in the chamber to the above temperature range so that the cleaning gas thermally decomposes in a spontaneous manner without absorbing heat from the heat generator, and there is no need to heat the heat generator to a high temperature that would diffuse atoms from the heat generator. This prevents the heat generator from diffusing atoms as impurities that would contaminate thin films. Accordingly, corrosion of the heat generator in the cleaning process is reduced while preventing a decrease in the yield. Although the heat generator is in a non-heated state in the cleaning process, the temperature in the chamber is adjusted so that cleaning is performed while reducing corrosion of the heat generator. This eliminates the need for a mechanism that moves the heat generator, and prevents the apparatus from being complicated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a catalytic CVD apparatus; 
         FIG. 2  is a schematic view of a temperature adjustment mechanism arranged in the catalytic CVD apparatus; 
         FIG. 3  is a graph showing weight changes of various rubbers when exposed to ClF 3  gas; 
         FIG. 4  is a graph showing the temperature dependency of the rate of etching by ClF 3  gas; 
         FIG. 5  is a graph showing voltage changes of catalyst wires before and after a cleaning process; and 
         FIG. 6  is a table showing the temperature dependency of the rate of etching with ClF 3  gas. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     First Embodiment 
     One embodiment of the present invention will now be described with reference to  FIGS. 1 to 6 . 
     As shown in  FIG. 1 , a film-forming apparatus  1  is a catalytic chemical vapor deposition (CVD) apparatus, and includes a chamber  10 , which forms an internal film-forming chamber  11 . The chamber  10  includes a tubular chamber body  10   a  and a lid  10   b  covering the upper opening of the chamber body  10   a.  The chamber  10  further includes a seal  10   f,  which is arranged between the lid  10   b  and the chamber body  10   a.  The seal  10   f  hermetically seals the film-forming chamber  11 . 
     The chamber body  10   a  further includes a gas intake  10   d,  which draws various gases into the film-forming chamber  11 . A gas supply passage  10   e  extends through the gas intake  10   d.  The chamber body  10   a  includes a side wall incorporating a heater  10   h.  The heater  10   h  increases the temperature of the film-forming chamber  11  through the chamber body  10   a.  The heater  10   h  is connected to a power supply (not shown). When supplied with current, the heater  10   h  heats the inside of the film-forming chamber  11  through the chamber body  10   a.    
     The chamber  10  accommodates a temperature sensor S 1  arranged so as not to receive heat directly from the heater  10   h  (refer to  FIG. 2 ). The temperature sensor S 1  detects the temperature in the film-forming chamber  11 . 
     The chamber  10  is fixed to a support member  12 . An annular seal  10   c  is arranged between the chamber  10  and the support member  12 . The seal  10   c  hermetically seals the inside of the film-forming chamber  11 . 
     The support member  12  includes a gas supply passage  12   a.  The gas supply passage  12   a  is connected to the gas supply passage  10   e  of the chamber  10  when the chamber  10  is fixed to the support member  12 . 
     A film-forming gas supply system  13  is connected to the gas supply passage  12   a  of the support member  12 . The film-forming gas supply system  13  includes gas supply sources  14   a  to  14   c,  a mass flow controller  15 , and a supply valve  16 . The gas supply sources  14   a  to  14   c  are filled with various film-forming gases, such as titanium tetrachloride (TiCl 4 ) gas, ammonia (NH 3 ) gas, and nitrogen (N 2 ) gas. 
     The support member  12  further includes a discharge passage  12   b  that discharges gas out of the film-forming chamber  11 . A pump, such as a turbomolecular pump (not shown), is connected to the discharge passage  12   b.  When the pump is driven, fluids are drawn out of and discharged from the film-forming chamber  11 . The discharge passage  12   b  is an example of a discharge system. 
     The film-forming chamber  11  further accommodates a shower plate  20 , which jets cleaning gas into the film-forming chamber  11 . The shower plate  20  is substantially disc-shaped, and includes a bottom wall  20   a  and a side wall  20   b  surrounding the bottom wall  20   a.  The bottom wall  20   a  and the side wall  20   b  define an inner space that functions as a buffer  20   c  for temporarily storing a cleaning gas. A plurality of nozzles  20   n  extend through the bottom wall  20   a.    
     The shower plate  20  is connected to a cleaning gas supply system  21 , which is arranged outside the chamber  10 . The cleaning gas supply system  21  includes cleaning gas supply sources  22   a  and  22   b,  a mass flow controller  23 , and a supply valve  24 . The cleaning gas supply sources  22   a  and  22   b  are filled with inert gases, such as chlorine trifluoride (ClF 3 ) gas, argon (Ar) gas, and nitrogen (N 2 ) gas. The inert gases are not particularly limited to the above inert gases. 
     The ClF 3  gas is highly corrosive. In the present embodiment, the inside of the film-forming chamber  11  is heated to about 100° C. to 200° C. in a cleaning process and a film formation process. Thus, when the ClF 3  gas is used as a cleaning gas, the seal  10   c  for sealing the film-forming chamber  11  is required to be corrosion resistant and heat resistant.  FIG. 3  shows evaluation results for different seal materials.  FIG. 3  shows the comparison between fluoro rubber, which is a conventional seal material, and a perfluoroelastomer and a perfluoro rubber, which are generally known as being corrosion resistant. Samples formed from different rubbers but having the same shape and the same size were exposed to the ClF 3  gas at a temperature of about 120° C. for two hours. Changes in the weight of each sample were measured. Two perfluoro rubbers with different compositions, or perfluoro rubbers A and B, were used. The samples formed from perfluoroelastomer and perfluoro rubbers A and B showed lower weight changes than the sample formed from fluoro rubber. Although the sample formed from perfluoroelastomer had larger weight changes than the samples formed from perfluoro rubbers A and B, the difference between these materials was subtle. Thus, it was determined that perfluoroelastomer and perfluoro rubbers A and B are both usable. 
     As shown in  FIG. 1 , a catalyst wire  30  is arranged below the shower plate  20 . The catalyst wire  30  is an example of a heat generator. The catalyst wire  30  may be formed from any material and have any shape. In the present embodiment, the catalyst wire  30  is formed from tungsten, and includes two bent portions. The two ends of the catalyst wire  30  are fixed to the lid  10   b  of the chamber  10 . The catalyst wire  30  includes a straight portion between the two bent portions. The straight portion of the catalyst wire  30  extends horizontally in an upper portion of the film-forming chamber  11 . The straight portion of the catalyst wire  30  is arranged near the lower surface of the shower plate  20 . The catalyst wire  30  is connected to a constant current supply  31 , which is activated and deactivated by a control unit  1 C. The catalyst wire  30  generates heat when supplied with current from the constant current supply  31 , and reaches 1700° C. to 2000° C. in a film formation process. The catalyst wire  30  heated to such high temperatures is exposed to ammonia gas. This heats and decomposes ammonia gas and generates radical species. The radical species then react with TiCl 4  to form film formation species. 
     A substrate stage  35  is arranged on the bottom of the film-forming chamber  11 . The substrate stage  35  includes an electrostatic chuck (not shown), which attracts a substrate S with electrostatic force. The substrate stage  35  incorporates a heater  36 , which heats the substrate stage  35  to a predetermined temperature. The heater  36  and the heater  10   h  of the chamber  10  are energized and de-energized under control by the control unit  1 C. 
     A temperature control plate  25  for cooling and heating the chamber  10  and the like is arranged between the shower plate  20  and the lid  10   b  of the chamber  10 . The upper surface of the shower plate  20  is in close contact with the temperature control plate  25 . The temperature control plate  25  is fixed to the lid  10   b  of the chamber  10 . This structure enables efficient heat exchange between the temperature control plate  25  and the chamber  10  and between the temperature control plate  25  and the shower plate  20 . 
       FIG. 2  is a schematic view of a temperature adjustment mechanism  26  including the temperature control plate  25 . In addition to the temperature control plate  25  that is substantially disc-shaped, the temperature adjustment mechanism  26  includes a heat medium reservoir  27 , which stores a heat medium, a pump  28 , which pumps the heat medium, a first heat exchanger  29 A, which cools the heat medium, a second heat exchanger  29 B, which heats the heat medium, and a heat medium pipe  26   a,  which connects the heat medium reservoir  27 , the temperature control plate  25 , and other components to one another. The heat medium pipe  26   a  circulates the heat medium. The first heat exchanger  29 A is an example of a cooling unit. The second heat exchanger  29 B is an example of a heating unit. 
     The heat medium reservoir  27  is a liquid tank that includes an inlet, through which the heat medium flows in, and an outlet, through which the heat medium flows out. The pump  28 , which is arranged in the heat medium pipe  26   a,  pumps the heat medium from the heat medium reservoir  27  to the temperature control plate  25 . A temperature sensor S 2  is arranged between the heat medium reservoir  27  and the temperature control plate  25  in the heat medium pipe  26   a.  The temperature sensor S 2  detects the temperature of the heat medium, which is supplied to the temperature control plate  25 , and outputs a temperature detection signal indicating the detected temperature to the temperature controller  26   c.    
     The temperature control plate  25  is substantially disc-shaped to conform to the shape of the shower plate  20 . The temperature control plate  25  includes a heat medium inlet port  25   a  and a heat medium outlet port  25   b.  The heat medium flows through a flow passage extending through the temperature control plate  25 . The flow passage may be in any shape. In one example, the flow passage may be formed solely by a space storing the heat medium, or may include bent portions (or in a zigzag portions) formed by bending the flow passage at a plurality of positions of the temperature control plate  25 . 
     The first heat exchanger  29 A and the second heat exchanger  29 B, which each exchange heat with the heat medium, are arranged between the temperature control plate  25  and the heat medium reservoir  27 . The first heat exchanger  29 A may have any structure. To enable heat exchange between a coolant and a heat medium, the first heat exchanger  29 A may, for example, include a piping passage that allows circulation of the coolant, a compressor for compressing the gaseous coolant into a liquid, a depressurizing valve that releases the pressure of the high-pressure coolant, and an evaporator that evaporates and cools the liquid coolant. 
     The first heat exchanger  29 A receives a feedback signal from the temperature controller  26   c,  which receives a temperature detection signal from the temperature sensor S 2  and generates the feedback signal in accordance with the temperature detection signal. The first heat exchanger  29 A adjusts the temperature of the heat medium to a target temperature based on the feedback signal. In the film formation process, for example, the temperature of the heat medium is adjusted to a film formation temperature T 1  (about 120° C.). When the temperature of the heat medium on the piping passage is higher than the film formation temperature T 1 , the first heat exchanger  29 A receives a feedback signal that decreases the temperature of the heat medium. The heat medium held at the temperature near the film formation temperature T 1  cools the lid  10   b  and the shower plate  20 , which have been heated to high temperatures by the catalyst wire  30  that has been heated to 1700° C. to 2000° C. in the film formation process. This keeps the temperature in the film-forming chamber  11  substantially constant and reduces the process variations. When the first heat exchanger  29 A for cooling the heat medium is driven, the second heat exchanger  29 B is not driven, and only allows passage of the heat medium. 
     The second heat exchanger  29 B heats the heat medium, whereas the first heat exchanger  29 A cools the heat medium. The second heat exchanger  29 B may have any structure and may, for example, include a conductive plate that is set in contact with the piping passage, through which the heat medium flows, to heat the heat medium with the heat released from the conductive plate through the piping passage. The second heat exchanger  29 B also receives a feedback signal from the temperature controller  26   c,  and controls the temperature of the heat medium based on the feedback signal. In the cleaning process, for example, the heat medium is controlled to a temperature T 2  for cleaning. When the temperature of the heat medium on the piping passage is lower than the cleaning temperature T 2 , the second heat exchanger  29 B receives a feedback signal that increases the temperature of the heat medium. The heat medium adjusted to near the cleaning temperature T 2  increases the temperature in the film-forming chamber  11  to a temperature suitable for cleaning. The first heat exchanger  29 A is not driven when the second heat exchanger  29 B for heating the heat medium is being driven. 
     The temperature controller  26   c  receives a temperature detection signal from the temperature sensor S 1 , which is arranged in the chamber  10 , and determines whether or not the film-forming chamber  11  is maintained at a target temperature set for each process. When the temperature detected by the temperature sensor S 1  differs from the target temperature by a predetermined temperature or more, the temperature controller  26   c  controls the heat exchangers  29 A and  29 B and the heaters  10   h  and  36  to control the temperature in the film-forming chamber  11  accordingly. In the present embodiment, the temperature adjustment mechanism  26  and the heaters  10   h  and  36  each form an example of a temperature adjustment unit. 
     To remove the TiN film formation residue in the cleaning process, it is preferable to adjust the temperature in the film-forming chamber  11  to a temperature that thermally decomposes the cleaning gas, decreases the rate of reaction between at least the decomposed gas and the catalyst wire  30 , and does not deteriorate the catalyst wire  30  even when the cleaning is repeated multiple times.  FIG. 4  shows the correlation between the etching rate and the temperature in the film-forming chamber  11  when a TiN film is etched by ClF 3 . In this example, 200 sccm of ClF 3  and 200 sccm of Ar gas are supplied to the film-forming chamber  11 . The pressure is set to 667 Pa. 
     An increase in the temperature of the heat medium increases the temperature of the film-forming chamber  11 . The TiN film is etched by the ClF 3  gas at 100° C. or greater temperatures in the film-forming chamber  11 . The rate of etching increases as the temperature of the film-forming chamber  11  increases to approximately 100° C. to 160° C. When the temperature of the film-forming chamber  11  exceeds 160° C., the rate of etching converges at approximately 1000 nm/min. Thus, the temperature in the chamber  10 , or specifically the film-forming chamber  11 , is preferably 100° C. or greater. When the temperature exceeds 200° C., the seal  10   c  deteriorates at a faster rate. At temperatures exceeding 200° C., few catalysts can be supplied to the temperature adjustment mechanism  26  while maintained in liquid form. Thus, it is preferable that the cleaning temperature T 2  of the heat medium be from 100° C. or higher to 200° C. or lower. An efficient rate of etching in the process is 100 nm/min or greater. The temperature of the heat medium that achieves this etching rate is about 120° C. It is thus more preferable that the target temperature in the cleaning process be from 120° C. or higher to 160° C. or lower. 
       FIG. 6  shows the correlation between the etching rate and the temperature in the film-forming chamber  11  when a TaN thin film having a thickness of 100 nm is etched by ClF 3 . The etching is performed under the same conditions as for the TiN film. The results show that the TaN thin film was etched only slightly at a temperature of 40° C. in the film-forming chamber  11 , whereas at 100° C. or higher temperatures, the TaN thin film was etched until the underlying Si layer was exposed. It is thus preferable that the temperature be 100° C. or higher to 200° C. or less for the TaN thin film. 
     For stable circulation in the temperature adjustment mechanism  26 , the heat medium is preferably liquid at the cleaning temperature T 2 . Water used as the heat medium would not be circulated in a stable manner. It is preferable that the heat medium is a fluorinated material or a perfluoropolyether having a boiling point by of 150° C. or higher, such as Galden HT (registered trademark). It is also preferable that the heat medium is alkyl diphenyl or silicone oil. The boiling point by is higher than the target temperature of the film-forming chamber  11 . 
     Film Formation Process 
     A process for forming a thin film of TiN, which is an example of the film formation process, will now be described. First, the pump (not shown) connected to the discharge passage  12   b  is driven to evacuate the film-forming chamber  11  to a predetermined vacuum degree. The substrate S is transported from outside through a gate valve (not shown), which is connected to the film-forming apparatus  1 , and set on the substrate stage  35 . The electrostatic chuck (not shown) is driven to attract the substrate S. 
     The gate valve is closed, and the pump is driven again to evacuate the film-forming chamber  11 . Under the control of the control unit  1 C, the constant current supply  31  supplies the catalyst wire  30  with current. When supplied with current, the catalyst wire  30  generates heat. The temperature of the catalyst wire  30  reaches 1700° C. to 2000° C. 
     The heater  10   h  arranged in the chamber  10  is energized so that the heater  10   h  is heated to, for example, approximately 120° C. The heater  36  arranged in the substrate stage  35  is also energized and heated to, for example, approximately 120° C. 
     To maintain the heat medium at the film formation temperature T 1 , the temperature controller  26   c  drives the first heat exchanger  29 A or the second heat exchanger  29 B. In the present embodiment, the film formation temperature T 1  is set at 120° C. When, for example, the temperature of the heat medium is lower than the film formation temperature T 1 , the second heat exchanger  29 B is driven to increase the temperature of the heat medium. When the temperature of the heat medium is higher than the film formation temperature T 1 , the first heat exchanger  29 A is driven to decrease the temperature of the heat medium. The heat medium reaching the film formation temperature T 1  cools the lid  10   b  of the chamber  10 , the shower plate  20 , and other components that have been heated as the catalyst wire  30  generates heat, and maintains the components at an equilibrium temperature of approximately 120° C. 
     When the catalyst wire  30  and the heaters  10   h  and  36  reach the above temperature, the film-forming gas supply system  13  is driven to supply film-forming gas, such as TiCl 4  and NH 3 , into the film-forming chamber  11  through the gas supply passage  10   e.  Among the film-forming gases supplied into the film-forming chamber  11 , the NH 3  gas contacts the catalyst wire  30 , which has been heated to a high temperature. This decomposes the NH 3  gas and generates radical species. The radical species accelerate a radical chain reaction with TiCl 4  and ultimately form film formation species. The film formation species are deposited onto the surface of the substrate S, while diffusing in the film-forming chamber. The deposition forms a thin film of TiN. The intermediate products produced from the radical reaction as well as the film formation species diffused in the film-forming chamber  11  collect on the walls and the like of the chamber  10  and forms film formation residue of TiN. The catalyst wire  30  is heated to high temperatures of 1700° C. or higher. Thus, the film-forming gas decomposes immediately after contacting the catalyst wire  30  and diffuses in the film-forming chamber  11 , without collecting on the surface of the catalyst wire  30 . 
     When the film formation is completed, the film-forming gas supply system  13  stops supplying the film-forming gas, and the electrostatic chuck is deactivated. The substrate S is transported out of the chamber through the gate valve. This completes the film formation process for a single batch. 
     Cleaning Process 
     The film formation process is repeated for a plurality of batches. When the number of batches reaches a predetermined number, the cleaning process is performed. In the present embodiment, ClF 3  gas and Ar gas are used as the cleaning gas. The target temperature of the film-forming chamber  11  is set at 130° C. 
     First, the above pump is driven to discharge the film-forming gas supplied in the film formation process. When the film-forming chamber  11  is evacuated to a predetermined vacuum degree, the control unit  1 C stops energizing the catalyst wire  30  and de-energizes the catalyst wire  30 . When de-energized, the catalyst wire  30  cools rapidly to substantially the same temperature as the temperature in the film-forming chamber  11 . The discharging of gas and the de-energizing of the catalyst wire  30  may be performed in the reversed order. 
     The heater  10   h  arranged in the chamber  10  is energized so that the heater  10   h  is heated to a temperature (e.g., 130° C.) near the target temperature, and the heater  36  in the substrate stage  35  is also maintained at a temperature near the temperature of the heater  10   h.  The temperature of the heaters  10   h  and  35  is set in accordance with the target temperature of the film-forming chamber  11 , and is preferably from 100° C. or higher to 200° C. or lower. 
     The temperature controller  26   c  further controls the heat medium to, for example, 130° C., which is the cleaning temperature T 2  set in the present embodiment. This maintains the temperature in the film-forming chamber  11  at around 130° C. In the present embodiment, the heat medium is near 120° C., which is the film formation temperature T 1 , after the film formation process. Thus, to heat the heat medium to the cleaning temperature T 2 , the temperature controller  26   c  drives the second heat exchanger  29 B and heats the heat medium. 
     The temperature controller  26   c  uses the temperature sensor S 1  arranged in the chamber to determine whether or not the temperature in the film-forming chamber  11  is maintained near the target temperature. When the temperature detected by the temperature sensor S 1  is higher than the target temperature by a predetermined temperature, the temperature controller  26   c  controls the first heat exchanger  29 A to decrease the temperature of the heat medium or outputs a signal for deactivating at least one of the heaters  10   h  and  36  to the control unit  1 C. When the detected temperature is lower than the target temperature by a predetermined temperature, the temperature controller  26   c  controls the second heat exchanger  29 B to increase the temperature of the heat medium. In this manner, the temperature controller  26   c  performs feedback control to maintain the temperature in the film-forming chamber  11  at around 130° C. 
     When the film-forming chamber  11  is held at around 130° C., the control unit  1 C drives the cleaning gas supply system  21  to supply the ClF 3  gas and the Ar gas into the film-forming chamber  11  through the shower plate  20 . It is preferable that the flow amount of ClF 3  gas be from 100 sccm or higher to 500 sccm or lower. When the gas flow amount is lower than 100 sccm, the film formation residues are etched by the ClF 3  gas at a low etching rate. When the gas flow amount is higher than 500 sccm, the etching consumes more gas without increasing the etching rate. The inert gas, which may be the Ar gas, is used to adjust the pressure. Thus, it is preferable that the flow amount of the inert gas be from 0 sccm or higher to 500 sccm or lower. The pressure is preferably 665 Pa or greater. 
     The film-forming chamber  11  is held at approximately 130° C. Thus, the ClF 3  gas decomposes by absorbing thermal energy in the film-forming chamber  11 . The thermally decomposed gas reacts with the film formation residues collected on the walls and the like of the chamber and generates reaction products, such as TiF and TiCl. The reaction products diffuse in the film-forming chamber  11 . When the pump is driven, the reaction products are discharged out of the film-forming chamber  11  through the discharge passage  12   b.    
     The catalyst wire  30  slightly reacts with the cleaning gas. Thus, the catalyst wire  30  is slightly corroded when the cleaning process is performed a number of times.  FIG. 5  shows voltage changes of the catalyst wire  30  before and after the cleaning process. The catalyst wire  30  is supplied with a constant current (e.g., 14.2 A). Thus, when the catalyst wire  30  corrodes, the resistance of the current increases and changes the voltage applied to the catalyst wire  30 . The results show no changes in the voltage of the catalyst wire  30  from the first to 25th batches. The voltage measured after the cleaning process for the 25th batch has no difference from the voltage measured before the cleaning process. In other words, when the ClF 3  gas is supplied at a temperature of 120° C. or higher, the thermally decomposed ClF 3  gas reacts mainly with TiN. Thus, the tungsten catalyst wire  30  is slightly corroded. It is assumed that this is because the thermally decomposed ClF 3  gas reacts mainly with TiN in the above temperature range, and reaction of the ClF 3  gas with tungsten is hindered. Thus, the cleaning process may be performed without diffusing the molecules of the catalyst wire  30  into the film-forming chamber  11  and without corroding the catalyst wire  30 . 
     The above embodiment has the advantages described below. 
     (1) In the above embodiment, the film-forming apparatus  1  includes the film-forming gas supply system  13 , which supplies the film-forming gas for forming a thin film of TiN, and the cleaning gas supply system  21 , which supplies the cleaning gas including ClF 3 , and the control unit  1 C, which sets the catalyst wire  30  in a non-heated state in the cleaning process that discharges film formation residues adhering to inner portions of the chamber  10 . The film-forming apparatus  1  further includes the temperature adjustment mechanism  26 , which maintains the temperature in the chamber  10  at the target temperature (100° C. or higher to 200° C. or less), and the discharge passage  12   b,  which discharges the reaction products resulting from reaction between the film formation residues and the cleaning gas. More specifically, the temperature in the chamber  10  is adjusted to the target temperature to reduce corrosion of the catalyst wire  30  caused by the cleaning gas. Also, the adjustment of the temperature in the chamber  10  to the target temperature allows the cleaning gas to thermally decompose in a spontaneous manner without absorbing heat from the catalyst wire  30 . This obviates the need to heat the catalyst wire  30  to high temperatures that would diffuse metal atoms. Thus, the atoms of the catalyst wire  30  are prevented from being diffused as impurities that would contaminate thin films. This structure reduces corrosion of the catalyst wire  30  in the cleaning process while preventing a decrease in the yield. The cleaning process only sets the catalyst wire  30  in a non-heated state and adjusts the temperature of the chamber  10 . This structure eliminates the need for a mechanism that moves the catalyst wire  30 , and prevents the apparatus from being complicated. 
     (2) In the above embodiment, the temperature adjustment mechanism  26  includes a heat medium that has at least a boiling point that is higher than or equal to the target temperature, and exchanges heat between the heat medium and the chamber  10 . The temperature adjustment mechanism  26  includes the first heat exchanger  29 A, which cools the heat medium in the film formation process, and the second heat exchanger  29 B, which heats the heat medium to heat the chamber  10  in the cleaning process. This structure integrates the cooling mechanism for cooling the chamber and the heating mechanism for heating the chamber  10 . Thus, enlargement of the apparatus is suppressed. 
     (3) In the above embodiment, the seal  10   c  for hermetically sealing the film-forming chamber  11  is formed from perfluoro rubber (or perfluoroelastomer). This allows the ClF 3  gas to be used in the cleaning while reducing the seal corrosion speed. 
     The above embodiment may be modified in the following forms. 
     In the above embodiment, the temperature adjustment mechanism  26  cools and heats the chamber  10  and other components. Alternatively, a cooling unit and a heating unit may be separately arranged. For example, a section of the temperature adjustment mechanism  26  above the shower plate  20  may function solely as the cooling unit, whereas the heater  10   h  arranged in the chamber  10  or the heater  36  may function as the heating unit. The heat medium used in the temperature adjustment mechanism  26  may be a stable gas. 
     In the above embodiment, the film formation temperature T 1  for the heat medium in the film formation process is lower than the cleaning temperature T 2  used in the cleaning process. Alternatively, the film formation temperature T 1  may be higher than the cleaning temperature T 2 . In this case, heat energy stored in the heat medium in the film formation process may be used to radiate the heat stored in the heat medium in the cleaning process performed after the film formation process to maintain the temperature of the film-forming chamber  11  at the cleaning temperature T 2 . 
     In the above embodiment, the cooling unit and the heating unit of the temperature adjustment mechanism  26  are arranged in the heat medium pipe  26   a.  Alternatively, the cooling unit and the heating unit may be arranged in the heat medium reservoir  27 . Although the temperature sensor S 2  is arranged in the piping passage of the heat medium pipe  26   a,  the temperature sensor S 2  may be arranged in the heat medium reservoir  27 . 
     Although the film-forming apparatus  1  forms thin films of TiN in the above embodiment, the film-forming apparatus  1  may form thin films including at least one of TaN, WF 6 , HfCl 4 , Ti, Ta, Tr, Pt, Ru, Si, SiN, SiC, and Ge. The film-forming apparatus may also form organic thin films. In this case as well, a cleaning gas including ClF 3  can be used to remove the film formation residues. 
     Although the film-forming apparatus of the present invention is a catalytic CVD apparatus in the above embodiment, the film-forming apparatus may be a hot-wire apparatus including a hot wire that decomposes a film-forming gas with a hot wire that causes no catalytic actions. The hot-wire apparatus has the same structure as the catalytic CVD apparatus.