Patent Publication Number: US-2013239893-A1

Title: Stabilization method of film forming apparatus and film forming apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Japanese Patent Application No. 2012-057718, filed on Mar. 14, 2012, in the Japan Patent Office, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a stabilization method of a film forming apparatus, which is configured to form a thin film on a target object such as a semiconductor wafer, and a film forming apparatus. 
     BACKGROUND 
     In manufacturing semiconductor integrated circuits, a semiconductor wafer made of a silicon substrate is generally subjected to various processes, e.g., film formation, etching, oxidation, diffusion, modification and native oxide film removal. These processes are carried out by a single wafer processing apparatus which processes wafers one-by-one or by a batch type processing apparatus which processes a plurality of wafers simultaneously. When performing the processes using a vertical batch type processing apparatus, for example, a plurality of wafers are first loaded from a cassette accommodating the wafers therein, e.g., twenty five wafers, into a vertical wafer boat, and then supported by the boat in multi-levels. 
     The number of wafers loaded into the wafer boat may depend on, for example, the size of the wafers, but about thirty to one hundred and fifty wafers may be loaded into the wafer boat. The wafer boat is loaded into a gas-evacuable processing chamber from the bottom side, and then the interior of the processing chamber is kept airtight. Thereafter, a predetermined heat treatment is performed while controlling various process conditions such as flow rates of processing gases, a process pressure and a process temperature. 
     Among several factors affecting characteristics of semiconductor integrated circuits, it is important to improve the characteristics of insulating films in semiconductor integrated circuits. Silicon nitride films tend to be used as the insulating films in semiconductor integrated circuits instead of silicon oxide films due to their good insulation property. In particular, with an increase of demand for higher miniaturization and higher integration, silicon nitride films doped with impurities such as boron (B) are recently being used because they have lower dielectric constants (low-k) to be formed. For example, sealing films for protecting gate electrodes are formed in a semiconductor device such as a dynamic random-access memory (DRAM), and studies are now being made to form the sealing films with impurity-containing silicon nitride films. 
     In practical semiconductor device manufacturing processes, it is required to form various silicon nitride films including pure silicon nitride films and impurity-containing silicon nitride films. In some cases, pure silicon nitride (SiN) films containing no impurities and silicon nitride films containing impurities such as boron or carbon may be formed by using a single semiconductor manufacturing apparatus, for example. 
     In the above-described cases, the pure silicon nitride films containing no impurities and the silicon nitride films containing impurities are selectively formed as needed in the single semiconductor manufacturing apparatus. 
     However, if a silicon nitride film that does not contain boron is formed right after a silicon nitride film containing boron is formed, a problem may occur in that the film thickness of the silicon nitride film that does not contain boron partially increases, which deteriorates in-plane uniformity of the film thickness, or that boron atoms attached to the inner wall of the processing chamber enter into the silicon nitride film that does not contain boron. 
     Hereinafter, deterioration of in-plan uniformity of the film thickness will be described with reference to  FIG. 6 .  FIG. 6  illustrates a graph for explaining an effect of a boron-containing silicon nitride film. Shown in  FIG. 6  are film forming rates and in-plane uniformities of the film thickness when performing film forming processes by using a vertical film forming apparatus capable of simultaneously processing a plurality of semiconductor wafers. In the example of  FIG. 6 , a reference run was firstly performed to form a pure silicon nitride (SiN) film under a state where the inner wall of the film forming apparatus is not contaminated with boron, and then semiconductor wafers were replaced and a SiBN film was formed as a boron-containing silicon nitride film. Thereafter, a first run, a second run and a third run were sequentially performed to form pure silicon nitride (SiN) films. Semiconductor wafers were replaced for each of the runs (film forming processes). 
     In  FIG. 6 , black circles “” denote the film forming rates and white circles “o” denote the in-plane uniformities of the film thickness, while the left-side vertical axis and the right-side vertical axis are scaled by the film forming rates and the in-plane uniformities of the film thickness, respectively. Also, the wafer boat supporting the semiconductor wafers is vertically divided into five regions. In  FIG. 6 , the five regions are denoted by five numbers in such a manner that the top most region, the center region and the bottom most region are denoted by “1”, “3” and “5”, respectively. Further, “T”, “C” and “B” shown in  FIG. 6  denote “top”, “center” and “bottom”, respectively. 
     As clearly shown in  FIG. 6 , the interior of the processing chamber gets unstabilized by the boron-containing SiBN film forming process, and thus the SiN films generated at the first and the second run, which were performed after the SiBN film forming process, have film thicknesses thicker than the film thickness of the SiN film generated at the reference run. In particular, it can be known from  FIG. 6  that the film thicknesses in the top most region  1  increase remarkably at the first and the second run and that the in-plane uniformities at the first and the second run deteriorate. It can be also known from  FIG. 6  that the film forming rate and the in-plane uniformity at the third run are almost the same as those at the reference run and that the processing chamber gets stabilized at the third run to improve the reproducibility. The reason for the above-described remarkable fluctuation in film thickness and deterioration of the in-plane uniformity in film thickness at the first and the second run is thought that boron has a catalytic action for activating silicon. 
     In order to prevent the above-described problems, the inner wall of the processing chamber may be covered with a dielectric insulating film after forming the boron-containing nitride film. However, such countermeasure has a drawback in that an additional film forming process is required. 
     SUMMARY 
     Some embodiments of the present disclosure provide a stabilization method of a film forming apparatus and a film forming apparatus, in which a processing chamber gets stabilized after a boron-containing nitride film forming process to thereby prevent boron from exerting bad influence on a subsequent non-boron-containing nitride film forming process and improve reproducibility of the film forming processes. 
     The present inventors studied an impurity-containing silicon nitride film forming process. Throughout the study, the present inventors have come to know that boron atoms have a catalytic action, which activates silicon and facilitates nitridation of silicon to thereby increase the film thickness of the silicon nitride film, and that this catalytic action can be effectively suppressed by heating the interior of the processing chamber under an oxygen-containing atmosphere. The present disclosure is derived from the above-described knowledge. 
     According to a first aspect of the present disclosure, there is provided a method for stabilizing a film forming apparatus which can selectively perform a boron-containing nitride film forming process or a non-boron-containing nitride film forming process on at least one target object to be processed in a vacuum-evacuable processing chamber, the method includes performing a heat stabilization process to heat the interior of the processing chamber under an oxygen-containing gas atmosphere, between the boron-containing nitride film forming process and the non-boron-containing nitride film forming process when the non-boron-containing nitride film forming process is performed after the boron-containing nitride film forming process. 
     According to a second aspect of the present disclosure, there is provided a film forming apparatus configured to form thin films on one or more target objects to be processed. The apparatus includes a vertical and cylindrical processing chamber configured to be capable of evacuating gas; a holding unit configured to hold the target object in multi-levels and to be inserted into and ejected from the interior of the processing chamber; a heating unit installed around the outer periphery of the processing chamber; a gas supply system configured to supply a plurality of gases into the processing chamber; and a control unit configured to control the film forming apparatus to perform the stabilization method of the first aspect of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE 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 vertical sectional view of a film forming apparatus in accordance with an embodiment of the present disclosure. 
         FIG. 2  is a transverse sectional view of the film forming apparatus in accordance with the embodiment of the present disclosure. 
         FIGS. 3A and 3B  are timing charts illustrating supply timings of various gases. 
         FIG. 4  is a flowchart for explaining a method stabilizing a film forming apparatus in accordance with the embodiment of the present disclosure, in which a series of processes performed in the film forming apparatus is illustrated. 
         FIGS. 5A and 5B  are graphs illustrating evaluation results of the stabilization method of the film forming apparatus in accordance with the embodiment of the present disclosure. 
         FIG. 6  is a graph for explaining an effect of a boron-containing silicon nitride film. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiment(s) of a stabilization method of a film forming apparatus and a film forming apparatus according to the present disclosure will be described in detail with reference to the drawings. In addition, throughout the drawings, like reference numerals are used to designate like elements.  FIG. 1  is a vertical sectional view of a film forming apparatus  2  in accordance with an embodiment of the present disclosure.  FIG. 2  is a transverse sectional view of the film forming apparatus in accordance with the embodiment of the present disclosure. In  FIG. 2 , a heating unit is omitted. The following description will be made with an example using dichlorosilane (DCS) gas as a silane gas, using ammonia (NH 3 ) as a nitride gas, using boron trichloride (BCl 3 ) gas as a boron-containing gas and using oxygen (O 2 ) gas as an oxygen-containing gas to thereby form a SiBN film as a boron-containing nitride film and a SiN (silicon nitride) film as a non-boron-containing nitride film. 
     As shown in  FIGS. 1 and 2 , the film forming apparatus  2  includes a vertical and cylindrical processing chamber  4  having a ceiling and an opening at the bottom end thereof. The entire body of the processing chamber  4  is made of, for example, quartz and a ceiling plate  6  made of quartz is air-tightly provided in the ceiling of the processing chamber  4 . Further, a cylindrical manifold  8  made of, for example, stainless steel is attached to the opening of the processing chamber  4  with a seal member  10  such as an O-ring interposed therebetween. Alternatively, the processing chamber  4  and the manifold  8  may be integratedly formed in such manner that a cylindrical processing chamber made of quartz has a manifold portion also made of quartz. 
     The bottom end of the processing chamber  4  is supported by the manifold  8 . A wafer boat  12 , which is made of quartz, serves as a holding unit mounting thereon a plurality of semiconductor wafers (product wafers) W as target objects in multi-levels, and is vertically-movably inserted into or ejected from the interior of the processing chamber  4  from the underside of the manifold  8 . A support  12 A of the wafer boat  12  supports, for example, 50 to 150 sheets of wafers W having diameters of 300 mm in multi-levels by almost equal pitches. In order to secure thermal stability of the semiconductor wafers W, dummy wafers DW are held as dummy target objects at the upper and the lower portion of the wafer boat  12 , for example. 
     The wafer boat  12  is mounted on a table  16  with a thermal insulation container  14  made of quartz interposed therebetween, and the table  16  is supported by a rotation shaft  20  passing through a lid  18  made of, for example, stainless steel. The lid  18  opens/closes an opening disposed at the lower end of the manifold  8 . The rotation shaft  20  is air-tightly sealed and rotatably supported by, for example, a magnetic fluid seal  22  interposed between the rotation shaft  20  and a through portion of the lid  18 . Further, a seal member  24  such as an O-ring is interposed between the peripheral portion of the lid  18  and the lower end of the manifold  8  so that a sealing property of the interior of the processing chamber  4  is maintained. 
     The rotation shaft  20  is attached to a leading end of an arm  26  supported by an elevation mechanism (not shown) such as a boat elevator, so that the wafer boat  12  and the lid  18  are vertically movable together to be inserted into or ejected from the interior of the processing chamber  4 . Alternatively, the table  16  may be fixedly provided on the lid  18  and the wafers W so that the wafers W are processed while the wafer boar  12  is not rotated. 
     A gas supply system  27  is provided at the manifold  8  to supply various gases into the processing chamber  4 . To be specific, the gas supply system  27  includes a nitride gas supply unit  28  supplying a nitride gas, e.g., ammonia (NH 3 ) gas, a silane gas supply unit  30  supplying a silane gas, e.g., DCS gas, as a film forming gas, a boron-containing gas supply unit  32  supplying a boron-containing gas, e.g., BCl 3  gas, an oxygen-containing gas supply unit  34  supplying an oxygen-containing gas, e.g., O 2  gas, and a purge gas supply unit  36  supplying an inert gas, e.g., N 2  gas. 
     The nitride gas supply unit  28  has a gas distribution nozzle  38  made of quartz. The gas distribution nozzle  38  passes through the sidewall of the manifold  8  and is bent upward to extend along the inner sidewall of the manifold  8 . In the gas distribution nozzle  38 , a plurality of gas injection holes  38 A spaced apart from each other is formed along the lengthwise direction of the gas distribution nozzle  38 , so that the ammonia gas is uniformly injected via the gas injection holes  38 A in the horizontal direction. 
     Similarly, the silane gas supply unit  30  has a gas distribution nozzle  40  made of quartz. The gas distribution nozzle  40  passes through the sidewall of the manifold  8  and is bent upward to extend along the inner sidewall of the manifold  8 . In the gas distribution nozzle  40 , a plurality of gas injection holes  40 A spaced apart from each other is formed along the lengthwise direction of the gas distribution nozzle  40  (see,  FIG. 2 ), so that the DCS gas is uniformly injected via the gas injection holes  40 A in the horizontal direction. 
     Similarly, the boron-containing gas supply unit  32  has a gas distribution nozzle  42  made of quartz. The gas distribution nozzle  40  passes through the sidewall of the manifold  8  and is bent upward to extend along the inner sidewall of the manifold  8 . In the gas distribution nozzle  42 , a plurality of gas injection holes  42 A spaced apart from each other is formed along the lengthwise direction of the gas distribution nozzle  42  (see,  FIG. 2 ), so that the BCl 3  gas is uniformly injected via the gas injection holes  42 A in the horizontal direction. 
     Similarly, the oxygen-containing gas supply unit  34  has a gas distribution nozzle  44  made of quartz. The gas distribution nozzle  44  passes through the sidewall of the manifold  8  and is bent upward to extend along the inner sidewall of the manifold  8 . In the gas distribution nozzle  44 , a plurality of gas injection holes  44 A spaced apart from each other is formed along the lengthwise direction of the gas distribution nozzle  44  (see,  FIG. 2 ), so that the O 2  gas is uniformly injected via the gas injection holes  44 A in the horizontal direction. 
     Similarly, the purge gas supply unit  36  has a gas distribution nozzle  46  passing through the sidewall of the manifold  8 . The gas distribution nozzles  38 ,  40 ,  42 ,  44  and  46  are connected to a gas passages  48 ,  50 ,  52 ,  54  and  56 , respectively, and opening/closing valves  48 A,  50 A,  52 A,  54 A and  56 A and flow rate controllers (mass flow controllers)  48 B,  50 B,  52 B,  54 B and  56 B are provided in the gas passages  48 ,  50 ,  52 ,  54  and  56 , respectively. With this configuration, the gas supply system  27  can supply the NH 3  gas, the DCS gas, the BCl 3  gas, the O 2  gas and the N 2  gas into the processing chamber  4  while controlling the flow rate of the gases. 
     In addition, a nozzle accommodating recess  60  is formed in a portion of the sidewall of the processing chamber  4  in the vertical direction. Further, a thin and long gas exhaust port  62  configured to vacuum-evacuate the inner atmosphere of the processing chamber  4  is formed in an opposite portion to the nozzle accommodating recess  60  in the sidewall of the processing chamber  4  by cutting out the opposite portion of the sidewall of the processing chamber  4  in, for example, a vertical direction. To be specific, the nozzle accommodating recess  60  is formed by cutting out the sidewall of the processing chamber  4  in the vertical direction by a specific width to thereby form a vertically thin and long opening  64  and then by covering the opening  64  with a vertically thin and long partition wall  66 , which is made of, e.g., quartz and has a recess-shaped cross section, from the outside of the processing chamber  4  and air-tightly welding the partition wall  66  to the outer wall of the processing chamber  4 . 
     With the configuration discussed above, a portion of the sidewall of the processing chamber  4  is recessed outwardly and the nozzle accommodating recess  60  having a side open to communicate with the interior of the processing chamber  4  is integrally formed with the processing chamber  4 . That is, the partition wall  66  is integratedly formed with the processing chamber  4  and the inner space of the partition wall  66  communicates with the interior of the processing chamber  4 . The opening  64  is formed to have a height long enough to cover all the wafers W (including the dummy wafers DW) mounted on the wafer boat  12  in the vertical direction. A slit plate having a plurality of slits formed therein may be provided at the opening  64 . Further, as shown in  FIG. 2 , the gas distribution nozzles  38 ,  40 ,  42  and  44  are arranged in parallel in the nozzle accommodating recess  60 . 
     Further, a gas exhaust port cover  68 , which is made of quartz and has a reverse C-shaped cross section to cover the gas exhaust port  62 , is welded to the gas exhaust port  62  facing the opening  64 . The gas exhaust port cover  68  extends upwardly along the sidewall of the processing chamber  4  and forms a gas outlet  70  above the processing chamber  4 . At the gas outlet  70 , a vacuum exhaust system  72  configured to vacuum-evacuate the interior of the processing chamber  4  is provided. To be specific, the vacuum exhaust system  72  includes a gas exhaust passage  74  coupled to the gas outlet  70 , and a pressure control valve  76 , which can be open/closed and has a controllable opening degree, and a vacuum pump  78  are installed in sequence in the gas exhaust passage  74 . In addition, a cylindrical heating unit  80  configured to heat the processing chamber  4  and the wafers W accommodated in the processing chamber  4  is provided to enclose the outer periphery of the processing chamber  4 . 
     Overall operations of the film forming apparatus  2  as described above are controlled by a control unit  82  including, for example, a computer and a computer program controlling the overall operations of the film forming apparatus  2  is stored in a memory  84  such as a flexible disc, a compact disc (CD), a hard disc or a flash memory. To be specific, a start and stop of supply of each of the gases by the opening/closing valves  48 A,  50 A,  52 A,  54 A and  56 A, a flow rate control of the gases, a process temperature control and a process pressure control are carried out by commands issued from the control unit  82 . 
     The control unit  82  includes a user interface (not shown) connected thereto. The user interface includes a keyboard via which an operator inputs commands for managing the film forming apparatus  2  and a display configured to visualize and display the operational status of the film forming apparatus  2 . Further, communications for controlling the film forming apparatus  2  via communication lines may be made with respect to the control unit  82 . 
     Hereinafter, a stabilization method of a film forming apparatus in accordance with an embodiment of the present disclosure carried out by using the film forming apparatus  2  will be described with reference to  FIGS. 3A to 4 . According to the stabilization method of a film forming apparatus in which a boron-containing nitride film forming process of forming a boron-containing nitride film or a non-boron-containing nitride film forming process of forming a non-boron-containing nitride film can be selectively performed on a target object to be processed within a vacuum-evacuable processing chamber, when the non-boron-containing nitride film forming process is performed after the boron-containing nitride film forming process is performed, a heat stabilization process for heating the interior of the processing chamber under an oxygen-containing gas atmosphere is performed between the boron-containing nitride film forming process and the non-boron-containing nitride film forming process. 
     The boron-containing nitride film includes various types of films containing boron, for example, at least one film selected from a group consisting of a SiNB film, a SiBCN film and a BN film. The non-boron-containing nitride film also includes various types of films without containing boron, for example, at least one film selected from a group consisting of a SiN film, a SiCN film and a SiMN film where M denotes a metal. Here, the metal M may include, for example, aluminum (Al), zirconium (Zr), hafnium (Hf), tantalum (Ta), titanium (Ti) and tungsten (W). In the above-described chemical formulas of the nitride films, only types of chemical elements contained in the nitride films are denoted and the number of atoms in the chemical elements are omitted. However, various combinations of the numbers of atoms may be applicable. Further, the oxygen-containing gas may include, for example, at least one gas selected from a group consisting of O 2 , O 3 , H 2 O, N 2 O, NO, NO 2  and CO 2 . 
     First, an example of a general film forming method performed by using the film forming apparatus of the present disclosure will be described. In this example, the boron-containing nitride film and the non-boron-containing nitride film are a silicon boron nitride (SiBN) film and a silicon nitride (SiN) film, respectively.  FIGS. 3A and 3B  are timing charts illustrating supply timings of various gases. 
     The wafer boat  12 , on which a plurality of, for example, 50 to 150 sheets of wafers W having diameters of 300 mm is mounted at a normal temperature, is moved up from the underside of the processing chamber  4  and loaded into the processing chamber  4  of a specific temperature. Then, the opening at the bottom end of the manifold  8  is closed by the lid  18  so that the interior of the processing chamber  4  is sealed. 
     Thereafter, the processing chamber  4  is vacuum-evacuated to maintain the interior of the processing chamber  4  at a specific process pressure, and an electric power supplied to the heating unit  80  is increased to increase the temperature of the wafers W and maintain the wafers W at a process temperature. When forming a SiN film as a non-boron-containing nitride film, a DCS gas is supplied from the silane gas supply unit  30  and a NH 3  gas is supplied from the nitride gas supply unit  28  as shown in  FIG. 3A . 
     To be specific, the DCS gas is injected in the horizontal direction via the gas injection holes  40 A of the gas distribution nozzle  40  and the NH 3  gas is injected in the horizontal direction via the gas injection holes  38 A of the gas distribution nozzle  38 . As shown in  FIG. 3A , a cycle during which the DCS gas and the NH 3  gas are supplied alternately and intermittently is repeated a specific number of times. Between a DCS gas supplying period and a NH 3  gas supplying period (time-adjacent thereto), a purge process for purging residual gases in the processing chamber  4  may be performed. Or, the purge process may be omitted. As shown in  FIG. 3A , the time period between two time-adjacent gas supplying processes of the same gas forms one cycle. 
     By supplying the DCS gas and the NH 3  gas as shown in  FIG. 3A , a SiN film is formed on the surface of each of the wafers W, which are held by the wafer boat  12  being rotated, by an atomic layered deposition (ALD) method. After the SiN film is formed, the wafer boat  12  is unloaded and the processed wafers W are taken out from the interior of the processing chamber  4 . 
     On the contrary, when forming a SiBn film as a boron-containing nitride film, the wafer boat  12  on which the wafers are mounted is loaded into the processing chamber  4  as described above. Then, a DCS gas, a BCl 3  gas and a NH 3  gas are supplied from the silane gas supply unit  30 , the boron-containing gas supply unit  32  and the nitride gas supply unit  28 , respectively, as shown in  FIG. 3B . 
     To be specific, the DCS gas, the BCl 3  gas and the NH 3  gas are injected in the horizontal direction via the gas injection holes  40 A of the gas distribution nozzle  40 , the gas injection holes  42 A of the gas distribution nozzle  42  and the gas injection holes  38 A of the gas distribution nozzle  38 , respectively. As shown in  FIG. 3B , a cycle during which the DCS gas, the BCl 3  gas and the NH 3  gas in this sequence are supplied alternately and intermittently is repeated a specific number of times. 
     Between a DCS gas supplying period and a BCl 3  gas supplying period (time-adjacent thereto) and between a DCS gas supplying period and a NH 3  gas supplying period (time-adjacent thereto), a purge process for purging residual gases in the processing chamber  4  may be performed. Or, the purge process may be omitted. As shown in  FIG. 3B , a time period between two time-adjacent gas supplying processes of the same gas forms one cycle. By supplying the DCS gas, the BCl 3  gas and the NH 3  gas as shown in  FIG. 3B , a SiBN film is formed as a stacked structure on the surface of each of the wafers W, which are held by the wafer boat  12  being rotated, by an atomic layered deposition (ALD) method. 
     The gas supplying timings as shown in  FIGS. 3A to 3B  are merely an example, and gas supplying timings are not limited thereto. Further, though the SiN film and the SiBN film are formed as a non-boron-containing nitride film and a boron-containing nitride film, respectively, in the above-described example, various nitride films as discussed above may be formed as a boron-containing nitride film and a non-boron-containing nitride film. For example, a SiBCN film containing carbon as an impurity may be formed as a boron-containing nitride film. Further, when doping with elements not being used in forming the SiN film and the SiBN film as impurities, a gas supply unit configured to supply a doping gas containing the doping elements may be provided to the film forming apparatus  2  shown in  FIG. 1 . 
     In the above-described manner, both the boron-containing nitride film forming process and the non-boron-containing nitride film forming process are performed using the film forming apparatus  2 . According to need, the boron-containing nitride film forming process and the non-boron-containing nitride film forming process may be performed selectively. As described above, in the stabilization method of the present disclosure, when a non-boron-containing nitride film forming process is performed after a boron-containing nitride film forming process is performed, a heat stabilization process for heating the interior of the processing chamber under an oxygen-containing gas atmosphere is performed between the boron-containing nitride film forming process and the non-boron-containing nitride film forming process. 
     The above-described features will be described with reference to  FIG. 4 .  FIG. 4  is a flowchart for explaining a stabilization method of a film forming apparatus in accordance with an embodiment of the present disclosure, in which a series of processes performed in the film forming apparatus, is illustrated. The processes are performed in sequence shown in  FIG. 4  by using the film forming apparatus  2  shown in  FIG. 1 . As described above, in the method of the present disclosure, when a non-boron-containing nitride film forming process is performed after a boron-containing nitride film forming process is performed, a heat stabilization process is performed between the boron-containing nitride film forming process and the non-boron-containing nitride film forming process. 
     By way of example only, processes S 1  to S 13  are shown in  FIG. 4 , but when necessary, such processes may be also performed after the process S 13 . In  FIG. 4 , non-boron-containing nitride film forming processes are performed in the processes S 1 , S 2 , S 5 , S 9 , S 10  and S 13 , and boron-containing nitride film forming processes are performed in the processes S 3 , S 6 , S 7  and S 11 . Further, heat stabilization processes are performed in the processes S 4 , S 8  and S 12  between the non-boron-containing nitride film forming processes and the boron-containing nitride film forming processes, i.e., right before the non-boron-containing nitride film forming processes when the process type is changed from the boron-containing nitride film forming processes to the non-boron-containing nitride film forming processes. 
     By performing the heat stabilization processes as shown in  FIG. 4 , the interior of the processing chamber  4  gets stabilized after the boron-containing nitride film forming processes, to thereby prevent boron from exerting a bad influence on a subsequent non-boron-containing nitride film forming processes and improve reproducibility of the film forming processes. In order to perform the heat stabilization processes, semiconductor wafers W, on which nitride films are formed during the boron-containing nitride film processes, e.g., the processes S 3 , S 7  and S 11 , performed right before the stabilization processes, are unloaded and taken out from the processing chamber  4 . Then, the stabilization processes are performed under a state where the wafer boat  12  in an empty state of unloading the product wafers W is loaded into the processing chamber  4  again and the processing chamber  4  is sealed. During the heat stabilization processes, the wafer boat  12  is mounted on the thermal insulation container  14  and the dummy wafers DW, for example, which have been permanently held at the upper and the lower portions of the wafer boat  12 , are still kept to be held at the upper and the lower portions of the wafer boat  12 . 
     In the heat stabilization processes, the interior of the processing chamber  4  is heated for a specific time period under an oxygen-containing gas atmosphere, e.g., an O 2  gas atmosphere, while an O 2  gas is injected via the gas injection holes  44 A of the gas distribution nozzle  44 . 
     By performing the heat stabilization processes, boron (B) atoms forming “B—N bonds” in boron-containing nitride films, which are unnecessarily deposited to the inner wall of the processing chamber  4  made of quartz, the surface of the wafer boat  12 , the surface of the thermal insulation container  14  and the dummy wafers DW made of silicon substrates, react with oxygen (O) atoms so that the “B—N bonds” are replaced with stabilized “B—O bonds” without having nitrogen (N) atoms. 
     The boron-containing nitride films unnecessarily deposited on the inner wall of the processing chamber  4  and the like are stabilized, i.e., boron atoms in the boron-containing nitride films are stabilized by forming the “B—O bonds” through the heat stabilization processes as described above. Thus, boron atoms do not have catalytic actions when the non-boron-containing nitride film forming processes, e.g., the processes S 5 , S 9  and S 13 , are performed right after the heat stabilization processes. Namely, since boron atoms do not have catalytic actions, boron atoms do not exert influence on the non-boron-containing nitride films such as SiN films. Thus, the desired film thicknesses of the non-boron-containing nitride films can be obtained and in-plane uniformities of the film thicknesses can be kept to be high, thereby improving the reproducibility of the film forming processes. 
     Regarding process conditions of the heat stabilization process, a process temperature ranges from about 500 degrees C. to about 800 degrees C. and a process pressure ranges from about 1 Torr to about 730 Torr (a normal temperature). In some embodiments, the process temperature may range from about 600 degrees C. to about 700 degrees C. and the process pressure may range from about 100 Torr to about 600 Torr. If the process temperature is below 500 degrees C., it is hard to form the “B—O bonds”. The process temperature may be set to above 800 degrees C. However, considering process temperatures in the processes performed before and after the heat stabilization processes, it is undesirable to set the process temperature of the heat stabilization processes to above 800 degrees C., because it takes a long time to increase the temperature of the processing chamber  4  and the throughput is lowered. 
     If the process pressure is below 1 Torr, it is hard to form the “B—O bonds” because the concentration of the oxygen-containing gas becomes too low. Though there does not exist the upper limit of the process pressure, it is undesirable to set the process pressure to above 760 Torr, because configuration of the film forming apparatus  2  needs to be changed in order to set the process pressure to above 760 Torr. 
     In addition, a process time ranges from about 5 minutes to about 60 minutes. In some embodiments, the process time may range from about 10 minutes to about 30 minutes. If the process time is set to be shorter than 5 minutes, the “B—O bonds” are not formed sufficiently. It is also undesirable to set the process time to be longer than 60 minutes because the throughput is lowered. In addition, a flow rate of the O 2  gas ranges from about 3.0 slm (standard liter per minute) to about 5.0 slm. If the flow rate of the O 2  gas is below 3.0 slm, the “B—O bonds” are not formed sufficiently. It is also undesirable to set the flow rate of the O 2  gas to above 5.0 slm because an unnecessarily large amount of the O 2  gas is consumed. 
     As described above, according the stabilization method of the film forming apparatus  2  in which a boron-containing nitride film forming process or a non-boron-containing nitride film forming process can be selectively performed on the target object W within the vacuum-evacuable processing chamber  4 , when the non-boron-containing nitride film forming process is performed after the boron-containing nitride film forming process is performed, a heat stabilization process for heating the interior of the processing chamber  4  under an oxygen-containing gas atmosphere is performed between the boron-containing nitride film forming process and the non-boron-containing nitride film forming process. Accordingly, the processing chamber  4  gets stabilized after the boron-containing nitride film forming process to thereby prevent boron from exerting a bad influence on the subsequent non-boron-containing nitride film forming process and improve reproducibility of the film forming processes. 
     &lt;Evaluation of the Stabilization Method of the Present Disclosure&gt; 
     Hereinafter, evaluation results of the stabilization method of the present disclosure will be described with reference to  FIGS. 5A and 5B .  FIGS. 5A and 5B  are graphs illustrating evaluation results of the stabilization method of the film forming apparatus in accordance with an embodiment of the present disclosure.  FIG. 5A  is a graph obtained by performing a heat treatment under an oxygen-containing gas free state (no O 2  gas state), and  FIG. 5B  is a graph obtained by performing a heat treatment under an oxygen-containing gas state (O 2  gas atmosphere state), i.e., by performing a heat stabilization process of the present disclosure. 
     In both cases shown in  FIGS. 5A and 5B , film forming processes were performed by using a vertical film forming apparatus capable of simultaneously processing a plurality of semiconductor wafers, e.g., by using the film forming apparatus shown in  FIG. 1 . To be specific, a reference run was first performed to form a pure silicon nitride (SiN) film under a state where the inner wall of the film forming apparatus is not contaminated with boron. Semiconductor wafers were then replaced and a SiBN film was formed as a boron-containing silicon nitride film. Thereafter, the wafer boat was unloaded from the processing chamber and the wafers were taken leaving the wafer boat in an empty state. In the empty state, the dummy wafers DW were still held by the wafer boat. Then, the wafer boat in the empty state was loaded into the processing chamber again and the processing chamber was sealed. 
     Thereafter, in case of  FIG. 5A , a heat treatment without supplying an O 2  gas was performed for 10 minutes at a temperature of 630 degrees C. On the contrary, in  FIG. 5B , a heat treatment (heat stabilization process) was performed for 10 minutes at a temperature of 630 degrees C. while supplying an O 2  gas with a flow rate of 5.0 slm to keep the interior of the processing chamber  4  under an oxygen atmosphere. In both cases, the process pressure was set to 120 Torr. Then, in both cases, a first run and a second run were sequentially performed to form pure silicon nitride (SiN) films. Semiconductor wafers were replaced for each of the runs (film forming processes).  FIGS. 5A and 5B  illustrate film thicknesses and in-plane uniformities of the film thicknesses. 
     In  FIGS. 5A and 5B , black circles “” denote the film thicknesses and white circles “o” denote the in-plane uniformities of the film thicknesses, while the left-side vertical axis and the right-side vertical axis are scaled by the film thicknesses and the in-plane uniformities of the film thicknesses, respectively. Also, the wafer boat supporting the semiconductor wafers is vertically divided into three regions. In  FIGS. 5A and 5B , the three regions are denoted by three numbers in such a manner that the top most region, the center region and the bottom most region are denoted by “1”, “2” and “3”, respectively. Further, “T”, “C” and “B” shown in  5 A and  5 B denote “top”, “center” and “bottom”, respectively. 
     As shown in  FIG. 5A , by simply performing a heat treatment on the processing chamber without supplying O 2  gas after forming the SiBN film as a boron-containing nitride film, the SiN films generated on the first and the second run have film thicknesses thicker than the film thickness of the SiN film generated at the reference run and the in-plane uniformities on the first and the second run deteriorated. That is,  FIG. 5A  shows substantially the same result as that of the conventional film forming process as discussed above with reference to  FIG. 6 . 
     On the contrary, in case of a method of the present disclosure as shown in  FIG. 5B , heat treatment under an O 2  gas atmosphere, i.e., the heat stabilization process, was performed on the processing chamber after forming the SiBN film.  FIG. 5B  shows that film thicknesses and in-plane uniformities at the first and the second run are substantially the same as those at the reference run throughout the entire regions T, C and B and that reproducibility of the film forming process is kept well. 
     By way of example only, the film forming process is performed using an ALD method, in which a plurality of film forming gases are alternately supplied into the processing chamber, in the above-described embodiments. However, the film forming process is not limited thereto. The present disclosure may also be applied to a chemical vapor deposition (CVD) method in which a plurality of film forming gases are simultaneously supplied into the processing chamber. 
     By way of example only, the film forming process is performed using thermal energy in the above-described embodiments. However, the film forming process is not limited thereto. The present disclosure may also be applied to a film forming method and apparatus using plasma energy, in which a plasma generation unit is provided in the processing chamber and film forming gases are activated by plasma. 
     By way of example only, the film forming process is performed on a semiconductor wafer, as a target object to be processed, in the above-described embodiments. The semiconductor wafer includes silicon substrates and compound semiconductor substrates such as GaAs, SiC and GaN substrates. However, the target object is not limited the above-described substrate. The present disclosure may be also applied to glass substrates used in liquid crystal displays or ceramic substrates. 
     According to the present disclosure, in a stabilization method of a film forming apparatus, which is configured to selectively perform a boron-containing nitride film forming process or a non-boron-containing nitride film forming process on at least one target object to be processed in a vacuum-evacuable processing chamber, when the non-boron-containing nitride film forming process is performed after the boron-containing nitride film forming process, a heat stabilization process to heat the interior of the processing chamber under an oxygen-containing gas atmosphere is performed between the boron-containing nitride film forming process and the non-boron-containing nitride film forming process. Accordingly, the interior of the processing chamber gets stabilized after the boron-containing nitride film forming processes, to thereby prevent boron from exerting a bad influence on subsequent non-boron-containing nitride film forming processes and improve reproducibility of the film forming processes. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosures. Indeed, the novel methods and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the disclosures. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosures.