Patent Publication Number: US-7713582-B2

Title: Substrate processing method for film formation

Description:
This application is a Divisional of co-pending application Ser. No. 10/530,527 filed on Dec. 16, 2005 now abandoned, and for which priority is claimed under 35 U.S.C. §120; and this application claims priority of Application No. JP 2002-295323 filed in Japan on Oct. 8, 2002 under 35 U.S.C. 119; the entire contents of all are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a substrate processing apparatus, and more particularly, to a substrate processing apparatus in which a gas supply structure for supplying gas which contributes to film formation is improved. 
     BACKGROUND ART 
     As an example of a process processing of a substrate, a substrate processing apparatus which carries out film form processing using an ALD (Atomic Layer Deposition) method is known. According to this substrate processing apparatus, two (or more) kinds of raw material gases used for forming a film are alternately supplied onto a substrate in a reaction chamber one kind by one kind, the gases adsorb on the substrate one atom layer by one atom layer, and a film is formed utilizing only surface reaction. In this case, the gas supply amount of the raw material gas is controlled in flow rate by a mass flow controller (MFC) provided in a gas supply pipe. 
     When a film is allowed to grow on a substrate by subjecting a substrate to alternative surface reaction of vapor phase reacting materials, the faster the adsorption of the raw material gases to the substrate surface is, the shorter the time required for forming a film becomes, and the productivity is enhanced. Generally, the absorption amount is proportional to pressure×time. When an amount corresponding to the pressure×time is defined as L, if L is constant and the pressure is higher, the same amount of gas can adsorb even if the time is shorter. That is, if the pressure in the reaction chamber is rapidly increased, the raw material gas can adsorb in a short time. 
     Thus, in order to increase the pressure in the reaction chamber, it is necessary to supply the raw material rapidly. Normally, an MFC is used for supplying raw material gas, but since the maximum flow rate of MFC is limited, the supply speed is limited. 
     For this reason, it is proposed that a gas supply pipe located downstream from the MFC is provide with a gas reservoir for storing raw material gas therein. 
       FIG. 6  shows an example in which a gas supply pipe is provided with a gas reservoir. 
     As shown in  FIG. 6 , the gas supply pipe  51  is provided with first and second opening/closing valves  1  and  2  in front of and behind the gas reservoir  10 . When raw material gas is to be supplied, the first valve  1  located between an MFC  27  and the gas reservoir  10  is opened, the raw material gas is once stored in the gas reservoir  10  and then, the second valve  2  located between the gas reservoir  10  and the reaction tube  6  which is a reaction chamber is opened. There exist only the pipe  51  and the opened second valve  2  between the gas reservoir  10  and the reaction tube  6 , and in the conventional supply method using the MFC  27 , there also exist the MFC  27  and the long  51  and thus, conductance of the path becomes great, and the supply speed is increased. This will be explained using an expression. The relational expression between supply speed, conductance and pressure is Q=C×(P 1 −P 2 ). Here, Q represents supply speed (Pa·m 3 /sec), C represents conductance (m 3 /sec), and P 1  and P 2  represent pressures (Pa) in front of and behind the pipe. 
     Thus, if the conductance of the path is increased, the supply speed is also increased, and the raw material gas can adsorb in a short time. That is, if the gas supply pipe is provided with the gas reservoir for storing the raw material gas, the supply speed of the raw material gas to be supplied into the reaction chamber can be increased. Thus, the raw material gas can absorb in a short time, and the film forming time can be shortened. 
     According to the substrate processing apparatus using the ALD method, a plurality of kinds, e.g., two kinds of reaction gases are alternately supplied onto a substrate one kind by one kind, the gases are allowed to adsorb on the substrate one atom layer by one atom layer, and a film is formed utilizing the surface reaction. This step is defined as one cycle. The thickness of the film is controlled by the number of cycles of the supply of the reaction gas. For example, when the film forming speed is defined as 1 Å/cycle, in order to form a film of 500 Å film, the processing is carried out by 500 cycles. That is, an extremely thin film is formed through one cycle, a predetermined cycles is repeated to obtain a desired thickness. 
     The raw material gas is once stored in the gas reservoir, and the raw material gas is supplied onto the substrate from the gas reservoir at higher supply speed. For example, if one kind of raw material gas is supplied onto the substrate from a supply port of that raw material gas along a radial direction of the substrate, a film thickness of the substrate closer to the supply port of the raw material gas becomes thick, the thickness of the film is locally increased, and there is an adverse possibility that only one location of the periphery is convexed. In the next cycle, if the gases are supplied at higher supply speed from the gas reservoir using the gas reservoir, a film is formed on a portion of the substrate other than the locally thick portion (convexed portion). Thus, if the number of cycles is 500, the locally thickened portion is dispersed, and the film thickness is equalized. When a thin film is to be formed, however, if the number of cycles is less than 60, the dispersion of the locally thickened portion is inferior, i.e., the film forming operation is finished before the locally thickened portion is dispersed, and the periphery becomes uneven and the consistency of the film thickness is deteriorated in some cases. 
     Therefore, it is a main object of the present invention is to provide a substrate processing apparatus capable of achieving excellent consistency of film thickness when a thin film is formed. 
     DISCLOSURE OF THE INVENTION 
     According to a preferable aspect of the present invention, there is provided a substrate processing apparatus, comprising: a reaction chamber forming a space in which a substrate is to be processed, a gas supply pipe which is connected to said reaction chamber and which supplies processing gas for said substrate, and a gas exhaust pipe for exhausting an inside of said reaction chamber, wherein a gas reservoir for storing gas to be supplied to said reaction chamber and a bypass line which bypasses said gas reservoir are juxtaposed to each other in a portion of said gas supply pipe, and said substrate processing apparatus further comprises a control unit which allows the processing gas to be supplied to said reaction chamber using one of said gas reservoir and said bypass line when said substrate is processed. 
     With this structure, if the processing gas is supplied to the reaction chamber using the bypass line without using the gas reservoir, the processing gas is not abruptly supplied to the reaction chamber, the gas is sufficiently dispersed and thus, the consistency of film thickness becomes excellent. Therefore, if the bypass line is used when a thin film is formed, a film having equalized or constant thickness can be formed even if its thickness is thin. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES IN THE DRAWINGS 
         FIG. 1  is a schematic traverse sectional view showing one example of a reaction tube of a substrate processing apparatus according to the present invention. 
         FIG. 2  is a schematic vertical sectional view showing the example of the reaction tube of the substrate processing apparatus of the invention. 
         FIGS. 3A and 3B  are perspective view showing one example of a nozzle and gas holes of a second buffer chamber. 
         FIG. 4  show a relation between a substrate and a supply position of gas. 
         FIGS. 5A and 5B  show a state of a substrate, wherein  FIG. 5A  is a plan view and  FIG. 5B  is a side view. 
         FIG. 6  is a schematic transverse sectional view showing one example of a reaction tube of a previously proposed substrate processing apparatus. 
     
    
    
     PREFERABLE MODE FOR CARRYING OUT THE INVENTION 
     Next, a preferable embodiment of the present invention will be explained with reference to the drawings. 
     As an example of a process processing for substrates carried out in a preferred embodiment of the present invention, film forming processing using an ALD (Atomic Layer Deposition) method will be explained. 
       FIGS. 1 and 2  show one example of a vertical substrate processing apparatus according to the embodiment. A basic structure of the vertical substrate processing apparatus will be explained using  FIGS. 1 and 2 . In the explanation, structures of a gas reservoir  10  and a bypass pipe  11  which are added to a basic structure are omitted. 
     As shown in  FIGS. 1 and 2 , a quartz reaction tube  6  is provided inside of a heater  31 . The reaction tube  6  constitutes a reaction chamber which processes wafers (substrates)  7  to be processed. A diameter of the substrate  7  is 200 mm. A lower end opening of the reaction tube  6  is air-tightly closed with a seal cap  35 . A boat  39  is provided in a standing attitude above the seal cap  35  and is inserted into the reaction tube  6 . The boat  39  is connected to a rotation mechanism  20  through a rotation shaft  19  which is rotatably supported by a bearing  18 . To enhance the consistency of the processing, the boat  39  (substrates  7 ) is arranged such that the boat  39  can rotate. The plurality of substrates  7  to be batch-processed are placed in the boat  39  in a multi-stacked manner in their horizontal postures in an axial direction of the reaction tube  6 . The heater  31  heats the substrates  7  in the reaction tube  6  to a predetermined temperature. 
     Two gas supply pipes are provided in the reaction tube  6 . The gas supply pipes function as supply paths for supplying a plurality of kinds of gases (here, two kinds of gases). The first gas supply pipe  51  is connected to one side of the reaction tube  6  without through a remote plasma unit. The second gas supply pipe  52  is connected to the one side of the reaction tube  6  through a remote plasma unit  37 . Thus, there are two kinds of gases are supplied to the substrates  7  in the reaction tube  6 , i.e., gas which is not excited with plasma and is supplied, and gas which is excited with plasma and is supplied as active species. The first supply pipe  51  and the second supply pipe  52  are respectively provided with MFCs  27  and  28  so that flow rates of gases flowing into the first supply pipe  51  and the second supply pipe  52  are controlled. A gas exhaust pipe  40  as an exhaust path for exhausting gas from the reaction tube  6  is connected to the other side of the reaction tube  6 . A vacuum pump as vacuum exhaust means (not shown) is connected to the gas exhaust pipe  40 . 
     A remote plasma unit  37  is connected to a nozzle  43  which stands in a second buffer chamber  41  in the reaction tube  6  along the boat  39 . 
     The second buffer chamber  41  is formed in an arc shape in a space between an inner wall of the reaction tube  6  and the substrate  7  along the inner wall of the reaction tube  6  in the illustrated example. The second buffer chamber  41  extends along the inner wall of the reaction tube  6  and provided along the stacking direction of the substrates  7  from a lower portion to an upper portion of the inner wall of the reaction tube  6 . An end of a wall of the second buffer chamber  41  which is adjacent to the substrate  7  is provided with second buffer chamber holes  46  as gas supply ports. The second buffer chamber holes  46  open toward a center of the reaction tube  6  (substrates  7 ). 
     A nozzle  43  connected to the remote plasma unit  37  is disposed in the second buffer chamber  41  on an end of the second buffer chamber  41  opposite from the end provided with the second buffer chamber holes  46 . The nozzle  43  extends along the stacking direction of the substrate  7  from the lower portion to the upper portion of the reaction tube  6 . The nozzle  43  is provided with a plurality of nozzle holes  47 . 
     The nozzle  43  and the second buffer chamber  41  are respectively provided with the nozzle holes  47  and the second buffer chamber holes  46 . The opening states of the holes will be explained using  FIGS. 3A and 3B . 
       FIG. 3A  is a perspective view of the nozzle shown in  FIG. 1 .  FIG. 3B  is a perspective view of the second buffer chamber  41  shown in  FIG. 1  also. 
     The nozzle  43  shown in  FIG. 3A  is a pipe having a circular cross section. The nozzle holes  47  are straightly formed in a side surface of the nozzle  43  from a substantially uppermost portion of the nozzle  43  to a location corresponding to a bottom of the second buffer chamber  41  such that the nozzle holes  47  are arranged from an upstream side toward a downstream side of gas flow. Opening areas of the nozzle holes  47  are formed such that the opening areas are increased from the upstream side (downward in  FIGS. 3A and 3B ) as viewed from the second supply pipe  52  toward the downstream side (upward in  FIGS. 3A and 3B ), the conductance is varied so that gas can issue equally in any of upstream side and downstream side. 
     The second buffer chamber  41  shown in  FIG. 3B  is a pipe having an arc cross section. The second buffer chamber holes  46  having the same opening areas are formed in an end of an inner curved surface of the second buffer chamber  41  such that the second buffer chamber holes  46  are straightly arranged in the stacking direction of the substrates  7 . 
     As shown in  FIGS. 1 and 2 , the inner wall of the reaction tube  6  is provided with a first buffer chamber  42  which is adjacent to the second buffer chamber  41 . A first supply pipe  51  is connected to a lower portion of the first buffer chamber  42 . Like the second buffer chamber  41 , the first buffer chamber  42  also has first buffer chamber holes  48  formed at the same pitch at locations adjacent to the substrates  7 . The first buffer chamber  42  is provided at its lower portion with a reaction gas introducing port. The first buffer chamber holes  48  are formed such that opening areas thereof are increased from the upstream side toward the downstream side so that gas can issue equally in any of upstream side and downstream side. 
     There is provided a control unit  60  which controls a flowing manner of two kinds of gases and controls film forming temperature of the substrate  7 . The control unit  60  has a gas supply control function for controlling such as to allow the two kinds of gases to flow alternately one kind by one kind. The control unit  60  also has a temperature control function for controlling film forming temperature by heating using a heater. 
     A method for forming a film using the vertical ALD apparatus having the above-described basic structure will be explained. Here, an Si 3 N 4  film is formed. The reaction gas is DCS (SiH 2 Cl 2 : dichlorsilane), and NH 3  active species activated with plasma. 
     First, substrates  7  on which films are to be formed are mounted on the boat  39  and brought into the reaction tube  6  (also simply called furnace, hereinafter). Then, Si 3 N 4  films are formed. The temperature in the reaction tube  6  at that time is set to such a value that a film having excellent adhesion with respect to the ground film and little defect of interface is formed, e.g., 350 to 600° C. For forming the film, the ALD method in which NH 3  and DCS are alternately allowed to flow to form a film one atom layer by one atom layer is used. 
     First, NH 3  is supplied from the second supply pipe  52 . Since the NH 3  has higher reaction temperature than that of the DCS, NH 3  does not react at the temperature in the reaction tube  6 . Thus, the NH 3  is excited with plasma using the remote plasma unit  37  to activate the same and NH 3  is allowed to flow as active species so that the NH 3  reacts even at the temperature in the reaction tube  6 . At that time, the pressure in the reaction tube  6  is maintained at relatively low pressure of 40 to 60 Pa, the NH 3  excited with plasma and brought into the active species is supplied for 5 to 120 seconds. Here, gas flowing into the reaction tube  6  is only NH 3  which was excited with plasma and brought into active species, and no DCS exists. Thus, NH 3  which was excited with plasma and brought into active species does not vapor phase reacts, and adsorbs on the ground film on the substrate  7 . 
     The nozzle holes  47  formed in the nozzle  43  is formed such that their opening areas are gradually increased from the upstream side toward the downstream side of the gas flow so that the flow rate of NH 3  issuing into the second buffer chamber  41  is equalized. 
     Therefore, the flow speed of NH 3  passing through the nozzle holes  47  and issuing into the second buffer chamber  41  is high on the upstream side and low on the downstream side, but the flow rates are all the same between all of the nozzle holes  47 . 
     The NH 3  issuing into the second buffer chamber  41  is once introduced there, and the pressure in the second buffer chamber  41  is equalized. 
     As described above, since all of the opening areas of the second buffer chamber holes  46  are the same, active species of NH 3  supplied to the substrates  7  are supplied with equal flow rate and at equal flow speed. Therefore, uniform film forming processing is carried out for each of the substrates  7 . 
     Further, the second buffer chamber holes  46  are provided such that each of the holes is located at a location corresponding to a middle of a distance between substrates  7  which are placed in the multi-stacked manner. Thus, NH 3  which is processing gas is sufficiently supplied to each of the stacked substrates  7 . 
     Next, DCS is supplied from the first supply pipe  51 . Since the DCS reacts at the temperature in the reaction tube  6 , it is unnecessary to excite with plasma using the remote plasma unit  37 . The pressure in the reaction tube  6  at that time is increased to 266 to 931 Pa which is higher than that when NH 3  is supplied. If DCS is supplied, NH 3  on the ground film and DCS surface reacts with each other and the Si 3 N 4  film is formed. 
     The first buffer chamber  42  is formed with the first buffer chamber holes  48  whose opening areas are gradually increased from the upstream side toward the downstream side of gas flow. The first buffer chamber holes  48  is provided toward the center of the reaction tube  6  (substrates  7 ). As a result, flow rate of DCS supplied from the first buffer chamber holes  48  toward the substrates  7  is the same although the flow speed is different, and the DCS issues into the reaction tube  6 . 
     It is preferable that one more set of the nozzle  43  and the second buffer chamber  41  which are the same as those used for supplying NH 3  is disposed in the reaction tube  6  instead of the first buffer chamber  42 , and DCS is supplied from the second buffer chamber holes  46  because both the flow rate and flow speed can be equalized. 
     In this embodiment, if the flow rate of DCS gas is equalized using the first buffer chamber  42  which is simpler than the combination of the nozzle  43  and the second buffer chamber  41 , sufficiently uniform film forming processing can be carried out for the substrates  7 . 
     The step for alternately flowing NH 3  and DCS is defined as one cycle. An Si 3 N 4  film having predetermined thickness is formed by repeating this cycle. According to the ALD method, since two kinds of gases which contribute to the film formation do not exist in the vapor phase at a time, gas adsorbs the ground surface and reacts with the ground film. Therefore, a film having excellent with respect to the ground film can be obtained, and defect in interface is reduced as compared with the CVD (Chemical Vapor Deposition) method in which two kinds of gases are allowed to flow at a time. Further, of the plurality of kinds of gases, NH 3  which is required to be excited with plasma is excited with plasma and brought into the active species and allowed to flow. Therefore, a film can be formed at the reaction temperature by means of DCS gas which need not be excited with plasma and thus, the film can be formed at temperature as low as 350 to 600° C. 
     In addition to this basic structure, in the substrate processing apparatus of this embodiment, the gas reservoir  10  for storing gas is provided downstream (between the MFC  27  and the reaction tube  6 ) from the MFC  27  of the first supply pipe  51 . The gas reservoir  10  comprises a gas tank or a spiral pipe having greater gas capacity than a normal pipe for example. 
     A bypass pipe  11  is connected to the first supply pipe  51  downstream from the MFC  27 . The bypass pipe  11  bypasses the gas reservoir  10 . 
     The first supply pipe  51  is provided at its upstream side in the vicinity of the gas reservoir  10  with a first valve  1  which opens and closes a pipe path, and at its downstream with a second valve  2  which opens and closes the pipe path. The bypass pipe  11  is provided with a third valve  3  which opens and closes a pipe path. 
     By opening and closing the first, second and third valves  1 ,  2  an  3 , it is possible to store DCS gas as first kind of gas in the gas reservoir  10 , to supply the stored DCS gas to the reaction tube  6 , and to supply DCS gas to the reaction tube  6  through the bypass pipe  11  without using the gas reservoir  10 . 
     The second supply pipe  52  is provided at its upstream side in the vicinity of the remote plasma unit  37  with a fourth valve  4  which opens and closes a pipe path so that if the fourth valve  4  is opened and closed, NH 3  gas as second kind of gas can be supplied to the reaction tube  6  or the supply of the gas can be stopped. The gas exhaust pipe  40  is provided with an exhaust valve (not shown) which adjusts the opening and closing operations and an opening degree of the pipe path. Gas can be exhausted from the reaction tube  6  or the exhausting operation can be stopped by opening and closing the exhaust valve. Gas can be exhausted from the reaction tube  6  while maintaining predetermined pressure in the reaction tube  6  by adjusting the opening degree of the exhaust valve. The exhaust valve may be a single valve having a function for opening and closing and a function for adjusting the opening degree, or may comprise a plurality of valves including a valve having the opening and closing function and a valve having the opening degree-adjusting function. 
     Further, there is provided the control unit  60  which controls the first, second, third and fourth valves  1 ,  2 ,  3  and  4 , as well as the heater  31 . The control unit  60  controls the exhaust valve and the first, second and third valves  1 ,  2  and  3  to allow DCS gas to flow into the first supply pipe  51  and store the gas in the gas reservoir  10 , and DCS gas stored in the gas reservoir  10  is supplied to the reaction tube  6  or DCS gas is supplied to the reaction tube  6  through the bypass pipe  11  without using the gas reservoir  10  in a state in which exhaust operation of the reaction tube  6  is stopped or the exhaust operation is carried out. With this, the pressure in the reaction tube  6  is increased and the substrate  7  is exposed to DCS gas. Further, by supplying NH 3  gas into the reaction tube  6  from the second supply pipe  52  through the remote plasma unit  37  while exhausting gas from the reaction tube  6 , the substrate  7  is exposed to active species obtained by exciting NH 3  gas with plasma. 
     Next, one example of film forming sequence using the gas reservoir  10  will be explained. 
     A case in which DCS and NH 3  are used as the raw material gases will be explained. In this example, a gas supply pipe  52  (line) for NH 3  does not have the gas reservoir  10 , and DCS is supplied using a gas supply pipe  51  (line) having the gas reservoir  10 . Although the raw material gas is first allowed to flow into the reaction tube  6  using a pipe having no gas reservoir  10  in the following example, a method in which raw material gas is first are allowed to flow using a pipe having the gas reservoir  10  can also be employed similarly. 
     First, a substrate  7  on which a film is to be formed is mounted in the boat  39  and transferred into the reaction tube  6 . After the substrate  7  is transferred, the following operations (1) to (4) are defined as one cycle, and this cycle is repeatedly carried out. 
     NH 3  gas which need to be excited with plasma and DCS gas which need not be excited with plasma are allowed to flow together. First, the fourth valve  4  provided in the second supply pipe  52  and the exhaust valve provided in the gas exhaust pipe  40  are both opened, NH 3  is excited with plasma by the remote plasma unit  37  and brought into active species and passes through the second buffer chamber  41  from the second supply pipe  52 , NH 3  is supplied to the substrates  7  from the second buffer chamber holes  46  formed for respective substrates  7  and arrange at the same distances from one another as distances between the substrates  7  provided in the second buffer chamber  41  and in this state, NH 3  is exhausted from the gas exhaust pipe  40 . 
     When NH 3  is excited with plasma and allowed to flow as active species, the exhausting operation from the gas exhaust pipe  40  is appropriately adjusted and the pressure in the reaction tube  6  is set to 10 to 100 Pa. A supply flow rate of NH 3  to be controlled by the MFC  28  is in a range of 100 to 10000 sccm. Time during which the substrate  7  is exposed to the active species obtained by exciting NH 3  with plasma is 2 to 60 seconds. The temperature in the reaction tube  6  is set to 300 to 600° C. Since the reaction temperature of NH 3  is high, NH 3  does not react at the temperature in the reaction tube  6 , but since NH 3  is excited with plasma and brought into active species and then is allowed to flow, NH 3  can react even if the temperature in the reaction tube  6  is maintained in the preset low temperature range. 
     When NH 3  is excited with plasma and brought into active species and supplied, the first valve  1  on the upstream side of the first supply pipe  51  is opened, the second valve  2  on the downstream side is closed, and DCS is also allowed to flow. With this, if DCS is supplied to the gas reservoir  10  provided between the valves  1  and  2  and a predetermined amount of DCS is stored in the gas reservoir  10  under the predetermined pressure, the first valve  1  is also closed to confine DCS in the gas reservoir  10 . DCS is stored in the gas reservoir  10  such that the pressure therein becomes 20000 Pa or higher. A pipe system is constituted such that conductance between the gas reservoir  10  and the reaction tube  6  becomes 1.5×10 −3  m 3 /s or higher. If a ratio of a reaction tube capacity and a capacity of the gas reservoir  10  required for the former capacity is taken into consideration, it is preferable that the gas reservoir capacity is in a range of 100 to 300 cc when the reaction tube capacity is 1001 (100 liters), and the gas reservoir  10  has capacity of 1/1000 to 3/1000 times of the reaction tube capacity as a capacity ratio. 
     Gas flowing into the reaction tube  6  is active species obtained by exciting NH 3  with plasma, and there exists no DCS. Thus, NH 3  does not vapor phase reacts, and NH 3  which was excited with plasma and brought into active species adsorbs to the ground film on the substrate  7 . 
     NH 3  supplied from the nozzle  43  to the second buffer chamber  41  is supplied to the substrates  7  from the second buffer chamber holes  46  which are formed for respective substrates  7  and arrange at the same distances from one another as distances between the substrates  7 . 
     The fourth valve  4  is closed to stop the flow of NH 3  into the reaction tube  6 . 
     Next, remaining NH 3  is removed from the reaction tube  6  and from the second buffer chamber  41 , gas is exhausted from the reaction tube  6  by vacuum exhaust means to 20 Pa or lower, and remaining NH 3  is removed from the reaction tube  6 . At that time, a line of inert gas may be added between the second buffer chamber  41  and the remote plasma unit  37  and combination of purge and evacuation using inert gas is effective for gas replacement. 
     The second valve  2  located downstream from the gas reservoir  10  is opened. With this, DCS stored in the gas reservoir  10  supplied at a dash to the substrates  7  from the first buffer holes  48  which are formed for respective substrates  7  and arrange at the same distances from one another as distances between the substrates  7  through the first buffer chamber  42 . The adjusting means of the pressure in the reaction tube  6  sets such that the pressure is increased so that the partial pressure of DCS is increased to promote the reaction with the NH 3 . 
     For example, the pressure in the reaction tube  6  is abruptly increased by the supply of DCS to about 266 to 931 Pa which is higher that of the case of NH 3 . The supply flow rate of DCS is 100 to 2000 cc. Time during which DCS was supplied is set to 2 to 4 seconds, time during which the substrate was exposed to the increased pressure atmosphere is set to 2 to 4 seconds, and the total time was set to 6 seconds. The temperature in the reaction tube  6  is the same as that when NH 3  is supplied, and is 300 to 600° C. NH 3  on the ground film and DCS are reacted with each other by supplying DCS, and an Si 3 N 4  film is formed on the substrate  7 . 
     The second valve  2  is closed to stop the supply of DCS from the gas reservoir  10 . After the second valve  2  is closed, time elapsed until the next supply starts can be used as DCS storing time (that is, it is unnecessary to spend time wastefully only for storing time action while another operation is being carried out, and the first valve  1  is opened to star the supply of DCS to the gas reservoir  10 ). 
     Next, remaining DCS is removed from the first buffer chamber  42 , gas is exhausted by the vacuum exhaust means, and gas of the remaining DCS after it contributed to film formation is removed from the reaction tube  6 . At that time, a line of inert gas may be added between the first buffer chamber  42  and the second valve  2  and combination of purge and evacuation using inert gas is effective for gas replacement. 
     These operations (1) to (4) are defined as one cycle, and this cycle is repeatedly carried out. With this, an Si 3 N 4  film having predetermined film thickness can be formed on the substrate  7 . 
     In this sequence, the boat  39  on which the substrates  7  are placed is rotated at a constant speed. With this, even if gas is supplied to the substrates  7  from one direction (along the radial direction of the substrates and along the surfaces of the substrates), the entire surfaces of the substrates  7  are subjected to film forming processing more uniformly. That is, the consistency of film thickness within the surface of the substrate is enhanced. In this embodiment, the rotation speed of the substrate  7  is about 14 to 30 seconds in the one cycle, but it is preferable that the rotation speed is set to about 10 seconds in terms of throughput. 
     If the substrate  7  is rotated once during one rotation, the position of the substrate  7  is the same every time when raw material gas, e.g. DCS is supplied. That is, the substrate  7  is rotated but when DCS is supplied from the first buffer chamber holes  48 , gas is supplied from one peripheral edge of the substrate  7  toward the substrate  7 . If gas is supplied in this manner, since the gas reservoir  10  is used, the supply speed of gas is fast. Therefore, as shown in  FIGS. 5A and 5B , there is a tendency that an end  65  of the substrate closer to the first buffer chamber holes  48  (gas supply ports) having narrow width is thickened in film thickness. 
     For this reason, it is preferable that the rotation speed and gas supply timing are finely adjusted so that the same positions of the substrates  7  are not located closer to the first buffer chamber holes  48 . For example, as shown in  FIG. 4 , this fine adjustment is carried out in such a manner that the rotation speed is increased or decreased such that gas is supplied so that the gas supply position P is deviated through 45° each cycle, or the rotation speed is set constant and the gas supply timing is staggered. With this fine adjustment, a state in which only one portion of the substrate  7  is kept opposing to the first buffer chamber hole  48  is avoided, a locally thickened portion can be dispersed, and the consistency can be enhanced. 
     This fine adjustment is effective when a thick film requiring alternative supply of 60 cycles or more is to be formed, but when a thin film of less than 60 cycles is to be formed, although it is possible to avoid the case in which only one portion of the substrate  7  is not opposed to the first buffer chamber hole  48  depending upon the combination of the rotation speed and the gas supply timing, since the rotation number is small, there is an adverse possibility that the degree of dispersion is low and the periphery becomes uneven. As the rotation number is smaller, i.e., as the film thickness formed on the substrate is thinner, the possibility of deterioration of consistency due to unevenness becomes higher. Here, the films are divided into thick films and thin films on the basis of 60 cycles, but this numerical value is only an example and the invention is not limited to this. For example, when a film of about 1 Å thickness is formed in one cycle, the thickness becomes 60 Å in 60 cycles. Generally, a film of 100 Å or less thickness is called a thin film, and a film of 1000 Å or more is called a thick film. 
     When a film of less than 60 cycles is to be formed, raw material gas, in this embodiment DCS is supplied using the bypass pipe  11  without using the gas reservoir  10 . If DCS is supplied using the bypass pipe  11 , the gas supply speed to the substrate  7  is as slow as ⅕ of a case in which gas is supplied using the gas reservoir  10 . Since gas is supplied while taking relatively long time, gas is dispersed, gas is not concentrated on only a narrow portion of the rotating substrate  7 , and gas is dispersed in a wide range. Thus, the adverse possibility of unevenness is eliminated, and even when a thin film is to be formed, the consistency within a surface of the substrate  7  can be enhanced. 
     Therefore, in the substrate processing apparatus of this embodiment, when a thin film is to be formed, gas is not stored in the gas reservoir  10  and supplied, but the bypass pipe  11  capable of supplying gas to the reaction tube  6  through the mass flow controller  27  for desired time is provided. When a thin film of 60 Å or less thickness is to be formed, the bypass pipe  11  is used, and when a film having greater thickness than 60 Å is to be formed, the gas reservoir  10  is used. If the supply paths are properly selected, it is possible to form having excellent consistency of thickness in both thin and thick films. 
     When a thin film is to be formed, since the number of alternative supplies (the number of cycles) is small. Although pressure-rising time of several seconds per one cycle is additionally required, the total time is not increased so much. 
     It is conceived that the first and second valves  1  and  2  are kept opened without using the gas reservoir  10  as a tank, and the gas reservoir  10  is used as a path of gas, i.e., as a pipe. A film was formed using the gas reservoir  10  as a pipe, the consistency of film thickness and film thickness reproducibility were inferior as compared with a case in which the bypass pipe  11  was used. It is believed that this is because gas is accumulated in the gas reservoir  10 , stagnation is generated and this can not be removed even by the subsequent exhausting operation, and the gas vapor phase reacted with subsequent gas. This deterioration was overcome by sufficiently increasing the exhausting operation time after the gas supply. However, this is not preferable because the exhausting operation time is increased in addition to the additional supply time of several seconds per one cycle, and the film forming time is increased. Thus, it is effective to provide the bypass pipe  11 . 
     In this embodiment, while DCS is stored in the gas reservoir  10 , NH 3  is excited with plasma and brought into active species and supplied and gas is exhausted from the reaction tube  6  which are necessary steps for the ALD method. Thus, a special step for storing DCS is not required. Further, since DCS is allowed to flow after gas is exhausted from the reaction tube  6 , NH 3  and DCS do not react on the way to the substrate  7 . The supplied DCS can effectively react with only NH 3  adsorbing to the substrate  7 . 
     In the above-described embodiment, one gas tank or one spiral pipe is provided as the gas reservoir  10 . The present invention is not limited to this, and a plurality of gas reservoirs may be provided juxtaposed to one another. The gas reservoir  10  of this invention is not limited to the gas tank or spiral pipe, and the gas reservoir may be any means only if it can store gas and discharge gas at a dash. For example, the gas supply pipe of DCS may be thicker than a normal pipe and the MFC capacity may be increased correspondingly. The number of the gas supply pipes may be two or more. In this case, the number of cylinders which function as DCS supply sources may be increased in accordance with the number of gas supply pipes. Further, since the vapor pressure of DCS is low, the cylinder may be heated to increase the amount of vaporization of DCS. Further, DCS may forcibly be sent into the reaction tube  6  by a pump. 
     The present invention is applied to the vertical substrate processing apparatus in this embodiment, but the invention can also be applied to a producing method of a semiconductor device. In the producing method of semiconductor device, gas is exhausted from the reaction chamber (reaction tube), processing gas is supplied to the reaction chamber, and a substrate in the reaction chamber is processed. The processing gas is stored in a portion of a supply path through which the processing gas flows, the processing gas stored in the portion of the supply path is supplied to the reaction chamber, or the processing gas is supplied to the reaction chamber without storing the processing gas in the portion of the supply path, and a film is formed on the substrate. According to this method, when a thin film is to be formed, the processing gas is supplied to the reaction chamber at a normal supply speed without storing the processing gas in the portion of the supply path and the processing gas can sufficiently be dispersed over the substrate and thus, the thickness of the formed film is equalized within its surface. Thus, when a thin film is to be formed, since gas is supplied to the reaction chamber without storing the gas, a film having the constant thickness can be formed even if its thickness is thin. 
     Although DCS and NH 3  requiring the remote plasma unit are used as reaction gases in the above embodiment, the present invention is not limited to this, and gas which does not require the remote plasma unit can also be used. For example, when an Si 3 N 4  film is to be formed using HCD (Si 3 Cl 6 ) and NH 3 , gas reservoirs can be used for both the gas supply pipes and thus, a bypass line is also provided for each of them. When an Al 2 O 3  film is to be used using Al(CH 3 ) 3  and ozone O 3 , Al(CH 3 ) 3  is stored in the gas reservoir and O 3  is supplied from an ozone generator. 
     INDUSTRIAL APPLICABILITY 
     According to this invention, as described above, gas is supplied using the bypass line disposed juxtaposed to the gas reservoir, even a thin film has excellent thickness consistency, and a film having excellent consistency can be obtained irrespective of its thickness. 
     As a result, the present invention can preferably be utilized for a substrate film-forming apparatus using the ALD method.