JPH10321557A - Deposition of film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of voids, etc., in a film by maintaining the step coverage of the film in an excellent state even when the deposition speed of the film is high by forming the film on the surface of an object to be treated at a high deposition ratio after the internal surface of a treating container is cooled to a temperature at which the occurrence of a vapor phase reaction can be suppressed at the deposition of the film and the surface of the object is cleaned by reducing the surface with a reducing gas. SOLUTION: The side walls of a treating container 14 are cooled to a temperature of <=5 deg.C at which the occurrence of a vapor-phase reaction between film deposition gases can be suppressed sufficiently by making a coolant, such as the chiller, etc., to flow through coolant passages 60 formed in the side walls of the container 14 and the side walls are maintained at the temperature in the succeeding film deposition process, etc. Then, while the side walls are maintained in the cooled state, H2 reducing gas is supplied to the container 14 from a shower head section 32 and the surface of the a wafer W is reduced and cleaned by the reducing action of the H2 gas. In the succeeding film deposition process, the temperature of the wafer W is raised to about 620 deg.C after the H2 gas is evacuated from the container 14 and a phosphorus- doped polysilicon layer and a tungsten silicide layer are formed at high speeds by supplying SiH4 and PH3 gases together with Ar gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film forming method for forming a gate electrode, a bit line or the like on an object to be processed such as a semiconductor wafer.

[0002]

2. Description of the Related Art Generally, in a process of manufacturing a semiconductor integrated circuit, a desired element is obtained by repeatedly performing film formation and pattern etching on a semiconductor wafer, a glass substrate, or the like, which is an object to be processed. For example, in the case where a MOSFET gate element is formed on the surface using a semiconductor wafer, impurities are diffused into positions to be the source 6 and the drain 3 on the surface of the wafer W as shown in FIG. A gate oxide film 4 made of, for example, SiO ₂ is formed on the surface between them, and a channel between the source and the drain is formed below this. Then, a gate electrode 5 of a conductive film is stacked on the hole on the gate oxide film 4 to form one transistor. The gate electrode 5 is not a single layer, but recently has a two-layer structure in consideration of conductivity and the like. For example, a gate electrode 5 is formed by sequentially laminating a phosphorus-doped polysilicon layer 7 and a metal silicide, for example, a tungsten silicide layer 9 on the gate oxide film 4.

FIG. 4 shows a case where a bit line is formed.
As shown in FIG. 4B, similar to FIG.
Is diffused on the surface to be the source 6 and drain 3 to form a gate oxide film 4 made of, for example, SiO ₂ on the surface between them, and a channel between the source and the drain is formed below this. . Then, a contact 8 of a bit line of a conductive film is buried in a hole on the source 6. The contact 8 is not a single layer,
Recently, it has a two-layer structure in consideration of conductivity and the like. For example, a contact 8 is formed by sequentially laminating a phosphorus-doped polysilicon layer 7 and a metal silicide, for example, a tungsten silicide layer 9 to bury holes.

By the way, with the miniaturization and high integration of semiconductor integrated circuits, the processing line width and the gate width tend to be narrower, and the film thickness tends to become thinner in accordance with the demand for multilayering. Regarding the electrical characteristics between the layers, even if the line width or the like becomes narrow, high performance is required as before or higher. In response to such requirements, for example, as described above, both the gate electrode 5 and the contact 8 have a two-layer structure of polysilicon and tungsten silicide.

Usually, the polysilicon layer 7 has a large number of layers,
For example, while the film deposition is performed by a batch process using 150 sheets as one unit, the tungsten silicide layer 9
Since the film is formed by the single-wafer processing in which the film is formed for each wafer, the time of exposure to the air or the like differs for each wafer, and the thickness of the natural oxide film also changes. Therefore, it has been proposed to continuously form the polysilicon layer 7 and the tungsten silicide layer 9 in one processing vessel or in a cluster tool in which a plurality of processing vessels are assembled in order to eliminate the problem of the natural oxide film. ing.

[0006]

By the way, conventionally, when a film forming process in which a polysilicon layer is formed on a large number of wafers at a time is performed in a single-wafer processing furnace,
In order to obtain a throughput equal to or higher than the conventional one, the film forming speed in the single-wafer processing furnace must be greatly improved. However, in a single-wafer processing furnace, the film forming speed and the step coverage have an opposite relationship. FIG. 5 is a graph showing this state. As shown in FIG. 5, when the film forming rate is increased, the step coverage is considerably deteriorated accordingly, and as shown in FIG. Problems such as generation of voids 10 occur. In particular, the larger the aspect ratio of the hole at the time of filling, the worse the step coverage becomes. The present invention has been made in view of the above problems, and has been devised to effectively solve them. An object of the present invention is to provide a film forming method capable of increasing a film forming speed without reducing step coverage.

[0007]

Means for Solving the Problems As a result of intensive studies on the film forming process, the present inventor has found that the reduction in step coverage during film forming is caused by a large number of product atoms being aggregated into a cluster state by a gas phase reaction. The present invention has been achieved by reaching the idea that this is caused by the deposition at one time and that the product atoms attached to the wafer surface during the deposition hardly move on the surface.

That is, a first method invention is a film forming method for forming a predetermined film on an object to be processed placed in a processing container, wherein the temperature of the inner wall of the processing container is controlled by the gas phase during the film formation. A cooling step of cooling and maintaining the temperature to suppress the reaction, a reduction cleaning step of reducing and cleaning the surface of the object to be treated with a reducing gas, and forming the predetermined film on the cleaned surface. And a film forming step performed at a large deposition ratio. According to this, since the inner wall of the processing container is cooled and maintained at a temperature at which the gas phase reaction is suppressed, the gas phase reaction is suppressed at the time of film formation, and the surface reaction mainly occurs. As a result, even if the film forming speed is increased, the step coverage can be favorably maintained, and the generation of voids and the like can be suppressed.

At the same time, prior to the film forming step, the surface is reduced and cleaned with a reducing gas, so that the products adhering to the surface during the film formation are easily migrated and microscopically formed on the surface. And local concentration of sediment can be avoided. Therefore, the step coverage can be maintained more favorably than this point, and the occurrence of voids and the like can be suppressed. As the reducing gas, H ₂ gas, SiH ₄ gas, SiH ₂ C
l ₂ gas or the like can be used.

According to a second aspect of the present invention, there is provided a film forming method for forming a predetermined film on an object to be processed placed in a processing container, wherein a temperature of an inner wall of the processing container is controlled by a gas phase reaction during the film formation. A cooling step of cooling and maintaining the temperature to a level that suppresses, a thin and clean surface under the conditions of high step coverage using the same gas as the processing gas used in forming the predetermined film on the surface of the object to be processed. It is configured to have a clean film forming step of forming a film and a film forming step of performing the predetermined film formation at a large deposition ratio on the surface of the clean film. According to this, as in the first method invention, since the inner wall of the processing container is cooled, a gas phase reaction can be suppressed during film formation. Furthermore, since a thin and clean film is formed under the condition of high step coverage before the film forming process, the product adhered to this surface during the film forming in the post-process is different from the case of the first method invention. Similarly, migration can be microscopically moved on the surface by migration, so that step coverage can be maintained better.

As such a clean thin film, a polysilicon film can be used. Further, the temperature of the inner wall of the processing vessel is 5 ° C. or less, preferably 0 ° C. in order to suppress a gas phase reaction.
It is better to set the temperature below ° C. Further, in such a film forming process, for example, a film of a phosphorus-doped polysilicon layer and a film of a tungsten silicide layer are continuously formed to form bit lines, gate electrodes, capacitor electrodes, and the like.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a film forming method according to the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a sectional view showing a single-wafer heat treatment apparatus for performing a film forming method according to the present invention. The heat treatment apparatus 12 has a processing container 14 formed into a cylindrical shape or a box shape by, for example, aluminum or the like.
A mounting table 16 made of carbon having a thickness of, for example, several millimeters and coated with iC is detached from a peripheral portion on a cylindrical heat-insulating support column 18 made of, for example, quartz and having a thickness of several tens of millimeters and provided upright from the bottom. It is installed in a way that supports it. A semiconductor wafer W as an object to be processed is mounted on the upper surface of the mounting table 16.

In order to carry the wafer W into and out of the processing chamber 14, it is necessary to raise and lower the wafer above the mounting table or to fix the wafer on the mounting table 16. Therefore, the wafer lift arm 66 is provided on the outer peripheral side of the mounting table 16.
And a wafer clamp 72 having a wafer holding arm 70 are provided so as to be able to move up and down through the bottom of the container. The through portion is provided with a bellows (not shown) that allows the lifter and the clamp to move up and down while maintaining an airtight state in the container.

In this case, since the wafer lifter 68 and the wafer clamp 72 are relatively weak to heat, a ring-shaped protection ring 74 is provided outside the heat-insulating support column 18 to surround the mounting table 16 concentrically. . This protection ring 74
Is cut out integrally with the processing container 14, for example. The upper surface of the mounting table 16 is recessed in a concave shape slightly larger than the diameter of the wafer, and support projections 76 are discretely arranged at regular intervals along the circumferential direction. Are in contact with the peripheral edge of the rear surface of the wafer W to support it.

A relatively large opening is formed in the thick bottom of the processing vessel 14. Outside the opening, a transparent window 20 made of a transparent material, for example, quartz, which is convex downward, is formed. Is mounted airtight. The reason why the transmission window 20 is formed so as to be convex downward is to increase the strength by forming an arc-shaped cross section with respect to an external pressure applied toward the processing chamber in a vacuum atmosphere. Inside the opening, a gas rectifying plate 24 having a large number of gas holes 22 and also made of a transparent material, for example, quartz, is provided.

Further, below the transmission window 20, there are provided a number of heating lamps 28 disposed on a water-cooled rotary table 26, and heat rays from the lamp 28 are transmitted through the transmission window 20 and the gas. The mounting table 1 penetrating the current plate 24
6 is heated from the back surface, thereby indirectly heating the wafer W. In the illustrated example, five heating lamps 28 are described. However, depending on the wafer size, for example, in the case of an 8-inch size wafer, one halogen lamp having a capacity of about 650 W is used. About 23 are provided. The entire heating lamp 28 is
Since the inside of the casing 30 is heated to a high temperature, for example, cooling air is circulated in the casing for the purpose of cooling.

On the other hand, a shower head 32 for supplying a processing gas or the like into the processing chamber is provided on the ceiling of the processing vessel 14 so as to face the mounting table 16 so as to be in parallel with the mounting table 16. The shower head portion 32 is formed of, for example, aluminum as a whole in a circular box shape, and has a gas ejection surface 34, which is a lower surface thereof, formed with a large number of gas ejection holes 36 having a diameter of, for example, about several mm. The gas can be ejected downward. One or a plurality of (two in the illustrated example) rectifying plates 38, 38 are provided in the shower head portion 32, and a large number of diffusion holes 40 are formed in each rectifying plate 38, 38. .
The diffusion holes 40 and the gas ejection holes 36 are arranged, for example, in a staggered manner in the vertical direction so as not to be arranged in a straight line in the vertical direction, so that the flowing gas can be effectively diffused and rectified. .

The shower head section 32 is provided with processing gas sources 46, 48, 50, Ar, which store processing gases such as, for example, SiH ₄ gas, PH ₃ gas, and WF ₆ through a pipe 42 and a plurality of branch pipes 44, respectively. Are connected to a carrier gas source 52 for storing a carrier gas such as H ₂ gas and a reducing gas source 54 for storing a reducing gas such as H ₂ gas, and each gas source is supplied by an on-off valve 56 provided in each branch pipe. The mass flow controller 58 controls the flow rate. Further, a cooling medium passage 60 for flowing cooling is provided on a side wall of the processing container 14, and a chiller, for example, flows as cooling medium through the cooling medium passage 60. As will be described later, in the method of the present invention, the gas phase reaction is suppressed by cooling the side walls to, for example, 5 ° C. or less throughout the film formation period by using the refrigerant. In addition, a gate valve 62 that opens and closes when loading / unloading the wafer W is provided on the side wall of the processing container 14, and an exhaust port 6 connected to a vacuum pump (not shown).
4 are provided.

Next, the method of the present invention performed using the apparatus configured as described above will be described. First, a general flow of a wafer will be described. An unprocessed semiconductor wafer W carried from a load lock chamber (not shown)
Is loaded into the processing chamber 14 via the gate valve 62, and is placed by raising and lowering the wafer lifter 68 at a predetermined position of the loading table 16 which has been heated to the process temperature or lower by the heating lamp 28 in advance. This is fixed by the wafer clamp 72.

Next, a predetermined gas is supplied from the shower head section 32 to maintain a predetermined process pressure and a predetermined process temperature while evacuating the processing chamber. Thus, a film forming process or the like is performed. Next, the first method invention will be described with reference to FIG. In FIG. 2, the same parts as those shown in FIG. 4 are denoted by the same reference numerals.
The feature of the first invention is that the inner wall of the processing vessel 14 is maintained in a state where the inner wall is cooled to a temperature that can sufficiently suppress the gas phase reaction, and the surface is reduced before actually performing the film forming operation. This makes the migration easy to occur. still,
Here, a case where a contact hole for a bit line is buried will be described as an example.

First, an unprocessed wafer W made of, for example, a silicon substrate is introduced into the processing chamber 14 as described above. Here, as shown in FIG. 2A, the unprocessed wafer W has a step portion such as a buried hole 78 for the contact 8 formed in the insulating layer 80 made of, for example, SiO ₂ in the previous step. Say things. Here, a diffusion layer, for example, a source 6 has already been formed. Then, a coolant, for example, a chiller is caused to flow through a coolant passage 60 provided on the side wall of the processing container 14, and the temperature of the side wall is set to a temperature at which the gas phase reaction of the film forming gas can be sufficiently suppressed, for example, 5 ° C. or less. Preferably 0 ° C
The film is cooled to a cold wall state, and this state is maintained during the subsequent film forming step. The cooling of the side wall may be performed before the wafer is loaded.

Next, while the side wall is cooled, the processing vessel 14
H ₂ gas is supplied as a reducing gas from the shower head section 32, and the surface of the wafer W is reduced and cleaned by the reducing action of the H ₂ gas (see FIG. 2B). The process conditions in the reduction cleaning step are as follows: the temperature of the wafer W is set to, for example, about 850 ° C., the process pressure is about 10 Torr, and the flow rate of the H ₂ gas is 1 liter / min.
Such a reduction process is performed for about one minute to clean the wafer surface. In this case, the SiO _{2 on} the wafer surface is
It is reduced and purified as in the following equation. SiO ₂ + H ₂ → SiO {+ H ₂ O} This facilitates migration of the product adhered to the surface during the next film forming process at the atomic level, the molecular level, or the cluster level.

After the completion of the reduction cleaning step, the process proceeds to an actual film forming step. In this film forming step, as shown in FIGS. 2C and 2D, a phosphorus-doped polysilicon layer 7 and a tungsten silicide layer 9 are formed. First, after the H ₂ gas in the processing chamber 14 is evacuated, or while the H ₂ gas is being evacuated, the temperature of the wafer W is maintained at a process temperature, for example, 620 ° C., and at the same time, SiH ₄ gas and PH _{3 are used} as film forming gases. A gas (doping gas) is supplied together with an Ar gas as a carrier gas to form a film at a high speed. The process conditions at this time are as follows: the process pressure is, for example, about ₃₀ Torr; the flow rates of the SiH ₄ gas, PH ₃ gas, and Ar gas are, for example, 300 sccm and 100 s, respectively.
ccm, 500 sccm. This film forming process is performed, for example, for about 2 minutes to form the phosphorus-doped polysilicon layer 7 (see FIG. 2C). The deposition rate at this time is a high rate of, for example, 200 ° / min. However, since the surface of the underlayer is reduced to a clean silicon surface as described above, the product adhered and deposited on this surface is reduced. The particles can easily move or move on the surface due to migration, preventing local deposition. Therefore, the step coverage can be improved.

At the same time, since the side wall of the container is cooled to 5 ° C. or lower as described above, the gas phase reaction in this part is suppressed, and the surface reaction in which products are formed on the wafer surface is mainly performed. Then, the deposition is performed. Therefore, generation of a product having a large particle size caused by the gas phase reaction is suppressed, and the product having the large particle size does not deposit on the periphery of the opening of the contact hole 78. The generation of voids is suppressed more than this point, and the step coverage can be further improved. When the formation of the polysilicon layer 7 is completed, the supply of the PH ₃ gas is stopped, and the WF ₆ gas and the S
iH ₄ gas is supplied into the processing vessel 14 together with Ar gas,
The tungsten silicide layer 9 is formed, and the filling of the gate electrode hole is completed (see FIG. 2D). As a result, the hole 78 is completely buried.

As described above, in the present invention, the gas phase reaction is suppressed by suppressing the temperature of the side wall of the container to 5 ° C. or less, and the film is formed mainly by the surface reaction. The surface of the wafer was cleaned by reduction to facilitate migration, so that a high deposition rate could be maintained while maintaining good step coverage. Can be improved. Further, here, the case where H ₂ gas is used as the reducing gas has been described as an example, but other gases such as SiH ₄ gas and SiH ₂ Cl ₂ gas can be used instead.

Next, the second method invention will be described with reference to FIG. The second method invention is different from the first method invention in that a cleaning film forming step of forming a thin cleaning film on a wafer surface is added instead of the reduction cleaning step of the first method invention. It is in. First, as shown in FIG. 3A, an unprocessed unprocessed wafer W is introduced into the processing chamber 14 up to the buried hole 78 of the contact as in the case of the first method invention, and 14 side walls first
The cooling is maintained at 5 ° C. or lower in the same manner as in the method of the invention.

Next, while the side wall is cooled, a film forming gas for forming a clean thin film, here, a SiH ₄ gas is supplied together with an Ar gas as a carrier gas to form a clean film 82 made of a non-doped polysilicon film. . The process conditions at this time are a wafer temperature of, for example, 620 ° C. and a process pressure of, for example, 0.3 Torr. In addition, SiH ₄ gas, A
The flow rates of the r gas are, for example, 300 sccm and 200 sccm, respectively.
Set to sccm. The conditions for forming the thin film at this time are set so that the film forming speed is, for example, about 100 ° / min or less, so that the step coverage is very good.

At this time, the thickness of the cleaning film 82 is very thin.
For example, the processing time is set to about 1 minute, and the thickness is set to 100 ° or less. The surface of the cleaning film 82 thus formed is a cleaning surface equivalent to the cleaning surface obtained in the reduction cleaning step of the first method invention, and is liable to cause migration. When the clean film forming step is completed as described above, the process proceeds to a normal film forming step.
Here, in this film forming step, the same gas as that used in the previous clean film forming step is partially used, and the film forming temperature is set to the same, for example, 620 ° C., so that the SiH ₄ gas is directly used without performing gas replacement. Is supplied together with Ar gas, and supply of PH ₃ gas as a dopant is started, and a phosphorus-doped polysilicon layer 7 is formed in about 2 minutes as shown in FIG. In this film forming step, the process pressure is increased to, for example, about 30 Torr because high-speed film forming is performed.

At this time, the flow rate of the SiH ₄ gas is, for example, 300 sccm, PH ₃
The gas is set at 100 sccm, and the Ar gas is set at 500 sccm. This is the same film forming condition as in the first method invention. At this time, the side wall of the container is naturally cooled to 5 ° C. or less. This film formation rate is a high rate of, for example, 700 ° / min. However, since the underlying clean film 82 has a clean silicon surface, product particles adhered and deposited on this surface are easily migrated onto the surface by migration. Does not move or move, and is not locally deposited. Therefore, good step coverage can be maintained.

Also, as in the first method invention, since the side wall of the container is also cooled to 5 ° C. or less, the gas phase reaction in this portion is suppressed, and the surface reaction occurring on the wafer surface is mainly performed. A membrane is performed. Therefore, this makes it possible to maintain the step coverage synergistically high. Then, similarly to the first method invention, a tungsten silicide layer 9 is formed as shown in FIG. 3D, and filling of the contact holes is completed.

In this embodiment, the clean film 82 made of a non-doped thin silicon film is formed in the clean film forming step. At this time, however, a PH ₃ gas may also be flown to form a phosphorus-doped polysilicon film. . In addition, since the temperature of the clean film forming step and the film forming step are the same and the gas used is partly the same, the temperature raising / lowering time and the time required for gas replacement are not required, and the throughput can be improved accordingly. . Actually, when the temperature of the side wall of the container was cooled to 5 ° C. and 0 ° C., and experiments similar to those of the above method inventions were performed, a high film forming rate and a good step coverage could be obtained.

In each of the above embodiments, SiH ₂ C was used instead of SiH ₄ when the tungsten silicide layer was formed.
l ₂ may be used, or another inert gas such as N ₂ gas or He gas may be used as a carrier gas. In addition, the flow rate, pressure, temperature, and the like of the gas in each of the above embodiments are merely examples, and are not limited thereto. In addition, here, the case where the polysilicon layer and the tungsten silicide layer are formed in the same processing container is described as an example, but the present invention is not limited to this. The tungsten silicide layer may be formed in another processing container using a so-called cluster tool that can be transported without being exposed to water. Further, here, the case where the phosphorus-doped polysilicon layer and the tungsten silicide layer are formed into two layers is described as an example. However, the present invention is not limited to this, and a single-layer film including only the polysilicon layer may be formed. Needless to say, three or more layers may be formed, and a titanium layer, a titanium nitride layer and the like may also be formed. In the above embodiment, the case of phosphorus doping has been described. However, the present invention is not limited to this. For example, boron as a dopant,
Of course, arsenic, antimony and the like can also be used.

Although a heat treatment apparatus using lamp heating, which has a high temperature rising / falling rate, has been described as an example, it is needless to say that a heat treatment apparatus using resistance heating may be used. In addition, such a film formation method can be used not only for filling a contact hole but also for forming a gate electrode of a transistor, forming a capacitor electrode and other parts. Further, the object to be processed is not limited to a semiconductor wafer, but may be a glass substrate, an LCD substrate, or the like.

[0034]

As described above, according to the film forming method of the present invention, the following excellent functions and effects can be exhibited. According to the first invention, the gas phase reaction is suppressed by cooling the side wall of the container, and the surface is reduced and cleaned before the actual film forming process, so that the film is formed mainly by the surface reaction. Therefore, a cluster-like product having a large particle diameter is hardly generated, and migration is easily generated, so that the product is not locally deposited. Therefore, even in a single-wafer type film forming process, a high step coverage can be achieved while maintaining a high film forming speed. According to the second invention, the gas-phase reaction is suppressed by cooling the side wall of the container, and a thin clean film is formed before the actual film-forming process. As a result, a cluster-like product having a large particle size is hardly generated, and migration is easily generated, so that the product is not locally deposited. Therefore, even in a single-wafer type film forming process, a high step coverage can be achieved while maintaining a high film forming speed. In addition, since the process temperature and the gas used for forming the clean film are substantially the same as those of the subsequent film forming process, the time for raising and lowering the temperature and the time required for gas replacement can be eliminated, and the throughput can be improved accordingly. Can be.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a single-wafer heat treatment apparatus for performing a film forming method according to the present invention.

FIG. 2 is a process chart for explaining the first method invention.

FIG. 3 is a process chart for explaining the second method invention.

FIG. 4 is a diagram schematically showing a general gate electrode and a bit line of a transistor.

FIG. 5 is a graph showing a relationship between a film forming speed and a step coverage.

FIG. 6 is a diagram showing a situation in which a void occurs.

[Explanation of symbols]

 Reference Signs List 3 drain 4 gate oxide film 5 gate electrode 6 source 7 phosphorus-doped polysilicon layer 8 contact 9 tungsten silicide layer 12 heat treatment device 14 processing vessel 16 mounting table 28 heating lamp 32 shower head unit 60 coolant passage W semiconductor wafer (workpiece)

Claims (6)

[Claims] In a film forming method for performing a predetermined film formation on an object to be processed installed in a processing container, a temperature of an inner wall of the processing container is cooled to a temperature that suppresses a gas phase reaction during the film formation. A cooling step of reducing the surface of the object to be treated with a reducing gas to clean the surface of the object to be treated, and a film forming step of performing the predetermined film forming on the cleaned surface at a large deposition ratio. And a film forming method. 2. The film forming method according to claim 1, wherein the reducing gas is one of H ₂ gas, SiH ₄ gas, and SiH ₂ Cl ₂ gas. 3. A film forming method for forming a predetermined film on an object set in a processing container, wherein a temperature of an inner wall of the processing container is cooled to a temperature at which a gas phase reaction during the film formation is suppressed. And a cooling step to maintain the surface of the object,
Under the conditions of high step coverage using the same gas as the processing gas used in forming the predetermined film, a clean film forming step of forming a thin and clean film, and on the surface of the clean film,
A film forming step of performing the predetermined film formation at a large deposition ratio. 4. The film forming method according to claim 3, wherein said clean film forming step forms a thin polysilicon film. 5. The film forming method according to claim 1, wherein said film forming step includes forming a phosphorus-doped polysilicon layer and forming a tungsten silicide layer. 6. The film forming method according to claim 1, wherein the temperature of the inner wall of the processing container is 5 ° C. or less.