Film forming equipment and film forming method

Film forming equipment (20) is provided with a treatment container (22), a gas supplying system for supplying the container with a treatment gas including a film forming gas, and an exhaust system for exhausting the atmosphere in the container. In the treatment container, a placing table (46) having a placing plane for placing a flat board shaped body to be treated (W) is arranged. The body to be treated on the placing table is heated by a heater (80). A clamping apparatus (56) is provided to abut/separate to and from a surface peripheral part of the body to be treated, so as to press/release the body to be treated on and from the placing table. On the placing plane of the placing table, a suction structure (92) having a recessed part (94) is formed for temporarily sucking the body to be treated by pressure difference, by forming a substantially hermetic space between the placing plane and the rear plane of the body to be treated.

FIELD OF THE INVENTION

The present invention relates to a film forming apparatus and method for forming a thin film such as a tungsten film or the like on a target object such as a semiconductor wafer or the like and also relates to a computer program for controlling the film forming apparatus.

BACKGROUND OF THE INVENTION

In general, in the manufacturing process of a semiconductor integrated circuit, forming a thin film of a metal or a metal compound such as W (tungsten), WSi (tungsten silicide), Ti (titanium), TiN (titanium nitride), TiSi (titanium silicide), Cu (copper), Ta2O5(tantalum oxide) or the like has been performed to form a wiring pattern on a semiconductor wafer surface or to fill up a recess formed between wirings or a contact recess. Among these thin films, a tungsten film is widely employed because it has a small resistivity, a low film deposition temperature, and so on. By reducing WF6(tungsten hexafluoride) employed as a source gas by using, e.g., hydrogen, silane, dichlorosilane or the like, tungsten is deposited to thereby form the tungsten film.

In case of forming the tungsten film, the tungsten film is deposited on a barrier layer formed on the wafer surface in advance in order to enhance its adhesivity and to suppress its reaction with a silicon underlayer. A Ti film, a TiN film or a laminated film thereof is thin and uniformly formed on the wafer surface as the barrier layer. In order to form the tungsten film, WF6(tungsten hexafluoride) gas and H2gas are generally used as film forming gases due to their high film forming rate. However, depositing the tungsten film directly on the barrier layer by employing the deposition gases gives rise to problems as follows. First, there may be a long incubation period in which there occurs no film deposition even while the film forming gases are supplied, thereby deteriorating a throughput of processing. Further, fluorine in the WF6gas may be diffused into the barrier layer to react with the Ti (titanium) such that the reacted portion of the barrier layer swells up in a protruded shape, thereby resulting in defects in an integrated circuit device.

To solve the problems, e.g., Japanese Patent Laid-Open Application No. 2003-193233 discloses a film forming method as follows. Namely, before depositing a film by using WF6gas and H2gas, a very thin layer of a seed film made of crystal nuclei of tungsten is formed by using the WF6gas and a gas having a higher reducibility than the H2gas, e.g., a silane-based gas such as monosilane (SiH4) or the like. Thereafter, the WF6gas and the H2gas are supplied to deposit a film on the top of the seed film by CVD (Chemical Vapor Deposition), thereby forming a main tungsten film.

The above film forming method will be briefly described with reference toFIGS. 10A and 10B. A semiconductor wafer W, which is a target object, is mounted on a mounting table2. The mounting table2is installed in an evacuable processing chamber (not shown). By applying a clamp ring4to make a contact with a peripheral portion of the wafer W to press the wafer W against the mounting table2, the wafer W is kept to be prevented from being slid to side for example. In such a state, the WF6gas, the SiH4gas and the H2gas serving as the film forming gases are supplied to deposit a seed film6(first thin film) made of crystal nuclei of tungsten on the wafer W as depicted inFIG. 10A. Then, as shown inFIG. 10B, the WF6and the H2gas are simultaneously supplied as the film forming gases to thereby form a main film8(second thin film) made of metal tungsten starting from the top of the seed film6at a higher film forming rate as shown inFIG. 10B. Further, in the serial film forming processes, an inert gas, e.g., Ar is supplied as a backside gas to a backside of the mounting table2in order to prevent the film forming gases from turning around into the backside of the mounting table2.

As described above, the main film8is formed by depositing the thin film starting from the top of the seed film6, thereby enhancing the overall film forming rate. Furthermore, since the seed film6functions as a barrier, fluorine in the WF6gas can be prevented from being diffused into an underlayer of a TiN film while the main film8is deposited.

However, even though the backside gas is supplied to the backside of a mounting table2when the main film8shown inFIG. 10Bis deposited, the film forming gases infiltrate deeply into innermost region of the gap10between a lower surface of a clamp ring4and a top surface of a peripheral portion of the wafer W. This is because, e.g., a process pressure at this time is set to be higher than that of forming the seed film6shown inFIG. 10A. Accordingly, as shown inFIG. 10B, the main film8is formed such that an outer edge8A of the main film8entirely covers an outer edge6A of the seed film6and is further enlarged to an outer side of the outer edge6A. As a consequence, a peripheral portion12of the wafer at the outer side of the outer edge6A of the seed film6is exposed to and attacked by an excessive amount of fluorine in the WF6gas. Further, since the main film8is directly formed on the peripheral portion12of the wafer not through the seed film6, fluorine is diffused into the barrier underlayer to react with Ti therein, resulting in the reacted portion thereof being swollen up in a protruded shape.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to prevent the second thin film from making a direct contact with the surface of the target object (where the first thin film is not formed) by making the first thin film be formed wider than a forming area of a second thin film, wherein when forming the first thin film such as a seed film or the like on the target object, the target object is held on a mounting table without making a clamp device contact with a peripheral region of the object, thereby allowing the first thin film to be formed wider than the forming area of second thin film.

In accordance with a first aspect of the present invention, there is provided a film forming apparatus including: a processing chamber; a gas exhaust system for exhausting an inner atmosphere of the processing chamber; a mounting table having a mounting surface for mounting thereon a flat target object, the mounting table being provided in the processing chamber; a gas supply system for supplying a processing gas containing a film forming gas into the processing chamber; a heater for heating the target object on the mounting table; a clamp device for pressing and releasing the target object with respect to the mounting table by contacting with and separating from a peripheral portion of a surface of the target object; and an adsorption structure formed on the mounting surface of the mounting table for adsorbing the target object temporarily by means of a pressure difference caused by substantially sealed spaces defined between a backside of the target object and the mounting surface of the mounting table.

In accordance with the film forming apparatus, in case of forming a first and a second thin film sequentially on the surface of the target object, after the clamp device is separated from the target object and the first thin film is formed while the target object is adsorbed on the mounting table with the use of an adsorption structure, the second thin film can be formed while the peripheral portion of the target object being pressed toward the mounting table by the clamp device. As a consequence, it is possible to prevent the second thin film from making a direct contact with the surface of the target object (where the first thin film is not formed) by making the first thin film be formed at outer side extended further than a forming area of the second thin film.

More specifically, the film forming apparatus may further include a controller for controlling the gas exhaust system, the gas supply system, the heater and the clamp device to perform the steps of:

(a) decreasing the pressure in the processing chamber to an initial pressure lower than an atmospheric pressure;

(b) forming a first thin film on the surface of the target object, which includes the sub-steps of (b1) adsorbing the target object on the mounting table with the help of the adsorption structure by adjusting the inner pressure of the processing chamber to a level higher than the initial pressure but lower than the atmospheric pressure while the clamp device is separated from the target object; and (b2) forming the first thin film by supplying a first processing gas into the processing chamber while heating the target object adsorbed on the mounting table; and (c) forming a second thin film on the first thin film, which includes the sub-steps of (c1) pressing the target object against the mounting table by making the clamp device contact with the target object; and (c2) forming the second thin film by supplying a second processing gas into the processing chamber while heating the target object pressed against the mounting table.

Further, in accordance with a second aspect of the present invention, there is provided a film forming method for forming a first and a second thin film sequentially on a surface of a target object by using a film forming apparatus including: a processing chamber; a mounting table having a mounting surface for mounting thereon the flat target object, the mounting table being provided in the processing chamber; a clamp device for pressing and releasing the target object with respect to the mounting table by contacting with and separating from a peripheral portion of a surface of the target object; and an adsorption structure formed on the mounting surface of the mounting table for adsorbing the target object temporarily by means of a pressure difference caused by substantially sealed spaces defined between a backside of the target object and the mounting surface of the mounting table; the film forming method including the steps of: (a) decreasing the inner pressure in the processing chamber to an initial pressure lower than an atmospheric pressure; (b) forming the first thin film on a surface of the target object, which includes the sub-steps of (b1) adsorbing the target object on the mounting table with the help of the adsorption structure by adjusting the pressure in the processing chamber to a level higher than the initial pressure but lower than the atmospheric pressure while a clamp device is separated from the target object; and (b2) forming the first thin film by supplying a first processing gas into the processing chamber while heating the target object adsorbed on the mounting table; and (c) forming the second thin film on the first thin film, which includes the sub-steps of (c1) pressing the target object against the mounting table by making the clamp device contact with the target object; and (c2) forming the second thin film by supplying a second processing gas into the processing chamber while heating the target object pressed against the mounting table.

Furthermore, in accordance with a third aspect of the present invention, there is provided a storage medium storing a program for controlling a gas exhaust system, a gas supply system, a heater and a clamp device to perform a film forming process for forming a first and a second thin film sequentially on a surface of a target object by using a film forming apparatus including: a processing chamber; the gas exhaust system for exhausting an inner atmosphere of the processing chamber; a mounting table having a mounting surface for mounting thereon the flat target object, the mounting table being provided in the processing chamber; the gas supply system for supplying a processing gas containing a film forming gas into the processing chamber, the heater for heating the target object on the mounting table; the clamp device for pressing and releasing the target object with respect to the mounting table by contacting to and separating from a peripheral portion of a surface of the target object; and the adsorption structure formed on the mounting surface of the mounting table for adsorbing the target object temporarily by means of a pressure difference caused by substantially sealed spaces defined between a backside of the target object and the mounting surface of the mounting table; and wherein the first film forming process comprises the steps of: (a) decreasing the pressure in the processing chamber to an initial pressure lower than an atmospheric pressure; (b) forming the first thin film on the surface of the target object, which includes the sub-steps of (b1) adsorbing the target object on the mounting table with the help of an adsorption structure while separating the clamp device from the target object by adjusting the pressure in the processing chamber to a level higher than the initial pressure but lower than the atmospheric pressure; and (b2) forming the first thin film by supplying a first processing gas into the processing chamber while heating the target object adsorbed on the mounting table; and (c) forming the second thin film on the first thin film, which includes the sub-steps of (c1) pressing the target object against the mounting table by making the clamp device contact with the target object; and (c2) forming the second thin film by supplying a second processing gas into the processing chamber while heating the target object pressed against the mounting table.

As described above, the first thin film is formed on the target object while the clamp device is separated from the peripheral region of the target object and the second thin film is formed on the target object while the peripheral portion of the target object is pressed against the mounting table by the clamp device. Accordingly, it is possible to prevent the second thin film from making a direct contact with the surface of the target object by allowing the first thin film to be formed over an area greater than a forming area of the second thin film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the film forming apparatus and film forming method in accordance with the present invention will be described with reference to accompanying drawings.

A film forming apparatus20of an embodiment shown inFIG. 1is a single wafer type film forming apparatus capable of raising a temperature rapidly by using heating lamps80as heaters. The film forming apparatus20includes a cylindrical processing chamber22formed of, e.g., aluminum. A shower head24as a part of a gas supply system for supplying a processing gas containing a film forming gas into the processing chamber is attached to a ceiling portion of the processing chamber22via a sealing member26such as an O-ring or the like. The shower head24has a hollow columnar head body28formed of, e.g., aluminum. A plurality of gas injection openings30, through which gases supplied in the head body28are injected into a processing space S, are uniformly arranged in a gas injection surface, i.e., the bottom surface of the head body28.

The shower head24is not limited to the aforementioned configuration and may have various configurations. For example, in case that the gases are not allowed to be mixed in the head body28, the inside of the head body28is partitioned into a plurality of regions, so that the gases are independently diffused; and the gases will be mixed for the first time when they are supplied into the processing space S through the gas injection openings30. At the ceiling portion of the processing chamber22, a ring-shaped gas flow stabilization member32made of, e.g., quartz is provided at the outside of the shower head24in order to stabilize gas flows.

A gate valve G that is opened and closed when the wafer is loaded or unloaded is disposed at the side wall of the processing chamber22. The processing chamber22is connected via the gate valve G to, e.g., a load-lock chamber or a transfer chamber (not shown) that can be evacuated. Further, a gas exhaust port34is formed at a peripheral portion of the bottom of the processing chamber22. A gas exhaust system for exhausting an inner atmosphere of the processing chamber22while controlling the pressure therein is configured by connecting a gas exhaust path36provided with a vacuum pump (not shown) or the like to the gas exhaust port34.

A cylindrical supporting column38is uprightly provided at the bottom of the processing chamber22. A rectifying plate40for forming a gas flow of downward direction is provided on the upper peripheral portion of the cylindrical supporting column38. A ring-shaped attachment member44made of, e.g., quartz is adhered to an upper inner peripheral portion of the supporting column38via a ring-shaped auxiliary ring42made of, e.g., aluminum.

Further, a mounting table46is supported by an inner peripheral portion of the attachment member44. The mounting table46is formed in a thin circular plate shape having a thickness of about 3.5 mm made of ceramic, e.g., aluminum nitride. The upper surface of the mounting table46serves as a mounting surface for mounting thereon a semiconductor wafer W, i.e., a target object which has substantially the same diameter as the upper surface of the mounting table46. A backside of the mounting table46is colored with black in order to enhance absorption of an irradiated light. As illustrated inFIG. 3, three pin holes48through which respective lift pins are moved are formed at regular interval in a circumferential direction on the outer edge of the mounting table46. Here, each of the pin holes48is formed as a semicircular notch opened outwardly.

Further, a ring-shaped end portion50for supporting the mounting table46is formed at the inner periphery of the attachment member44. Three notches (not shown) through which the respective lift pins are moved in the same manner are formed at the positions corresponding to those of the pin holes48of the mounting table46. Furthermore, three rod holes52through which rod members or the like for supporting a clamp ring, which will be described later, are formed at positions corresponding to the notches on the attachment members44.

Moreover, the three lift pins54are uprightly provided at an outer position under the mounting table46. The lift pins54move through the pin holes48of the mounting table46and the notches of the attachment members44to support the edge of the wafer W; and the wafer can be moved up and down by moving them up and down.

Moreover, a clamp device56for holding the wafer W in place to prevent mislocation of the wafer W is provided in the vicinity of the outer edge of the mounting table46. The clamp device56includes a thin clamp ring58having a lager diameter than that of the wafer W. The clamp ring58is formed of a material that may hardly contaminate the wafer W and is of good heat-resistance and of low expansion-contraction amount, e.g., a ceramic such as aluminum nitride or the like. As shown inFIG. 2, at the inner side of the bottom surface of the clamp ring58, minute protrusions60are circumferentially provided at regular intervals. The clamp devices56clamps/releases the wafer W against the mounting table46by moving the clamp ring58up and down to make the protrusions60of the clamp ring58contact with or separated from the peripheral portion of the wafer W surface.

The clamp ring58is connected to three shaft members62arranged at regular intervals in a circumferential direction. The lower portions of the shaft members62are respectively supported by elastic members (not shown) accommodated in tubes64made of, e.g., quartz so that they can elastically move up and down. An arm member66made of, e.g., quartz and extended outwardly in a horizontal direction with respect to the clamp ring58is connected to an outside of a lower portion of each tube64. Each of the arm members66is connected to a ring-shaped supporting plate68made of, e.g., ceramic such as an aluminum oxide or the like. One side of the supporting plate68is supported by a vertical elevation rod70connected to the bottom surface thereof. A lower end of the elevation rod70is connected to an actuator (not shown) through an expansible/contractible bellows72in order to keep the inside of the processing chamber22in airtight state.

Further, in a bottom portion of the processing chamber provided at a location just below the mounting table46, a transmission window74made of a heat ray transmission material such as quartz or the like is airtightly provided via a seal member76such as an O-ring or the like. A box-shaped lamp vessel78is provided under the transmission window74. In the lamp vessel78, a plurality of heating lamps80as heaters are attached to a rotating table82also serving as a reflection mirror. Irradiation light (heat ray) released from the heating lamps80transmits through the transmission window74to be irradiated to the bottom surface of the mounting table46, thereby heating it.

Moreover, on the bottom of the processing chamber22, a cylindrical reflection member84formed of, e.g., aluminum is provided inside the supporting column38. The reflection member84has a diameter slightly larger than that of the semiconductor wafer W and the inner surface thereof is mirror-finished. The reflection member84is configured to reflect the irradiation light incident thereon obliquely from below and released from the heating lamps80toward the backside of the mounting table46. The top end of the reflection member84is extended to a location just below the attachment member44. Three accommodating spaces86for accommodating the tubes64for the elastic members are defined in the upper portion of the reflection member84, the accommodating spaces86being separated from each other in a circumferential direction.

Provided under the reflection member84is a backside gas supply system88for introducing an inert gas, e.g., Ar gas, as a backside gas into a space below the mounting table46. The backside gas supply system88has a gas introducing path90communicating with the space below the mounting table46and a gas source (not shown), and can supply the Ar gas through the gas introducing path90at a controlled flow rate.

An adsorption structure92for adsorbing the wafer W temporally by a pressure difference is formed in the mounting surface, i.e., the top surface of the mounting table46. As shown inFIGS. 3 and 4, the adsorption structure92includes a plurality of ring-shaped recesses94arranged concentrically with each other (inFIG. 3, each recess is marked with hatching lines). InFIG. 4, each recess94has a rectangular-shaped cross section with, e.g., a width (W1) of about 3 mm and a depth (D1) of about 0.3 mm. Each recess94can form a substantially sealed space of a rectangular shaped cross section together with the backside of the wafer W. The recesses94are separated from each other by a substantially equal distance on the area of the mounting surface that is covered by the wafer W. The distance P1between the recesses94is, e.g., about 5 mm. The distance may be properly determined based on an adsorptive force and an adsorption time, which depend on a pressure difference between before and after process and an airtightness of the space formed between the backside of the wafer and the mounting surface.

Moreover, the film forming apparatus20includes a controller100having, e.g., a micro computer or the like which contains a computer program for controlling the gas exhaust system, the gas supply system, the heating lamps80, the clamp device56and the like to execute a film forming method. The controller100reads the program from, e.g., a storage medium (semiconductor memory, hard disk drive, DVD or the like) that stores the program.

The film forming method will now be described with reference toFIG. 5.

Here, there will be described a case where, after a seed film made of a crystal nucleus of tungsten is formed as a first thin film in a first thin film forming process, a main film made of metal tungsten is formed as a second thin film by employing a CVD method at a higher film forming rate in a second thin film forming process. A feature of the present invention is to form the seed film as the first thin film over a wider area of the peripheral portion of the wafer surface by performing the first thin film forming process that takes relatively a short period of time while the wafer is adsorbed onto the mounting surface with the help of the adsorption structure92.

First, the wafer W is loaded into the processing chamber22via the opened gate valve G to be put on the lift pins54that are lifted up. Next, the wafer W is mounted on the mounting surface of the mounting table46by lowering the lift pins54. The wafer W has an underlying film such as a TiN film formed as a barrier layer in advance in a previous process.FIG. 5Ashows the state at this time and the peripheral portion of the wafer W is not yet clamped by the clamp ring58.

After the gate valve G is closed, a depressurizing process is performed by using the gas exhaust system, the inside of the processing chamber22is depressurized to an initial pressure lower than an atmospheric pressure. The initial pressure is lower than the process pressure of the first thin film forming process, e.g., 1000 Pa or less and preferably about 13.3 Pa.

At this time, since the wafer W on the mounting table46is not clamped by the clamp ring58, the airtightness between the mounting surface and the backside of the wafer W is poor, and thus atmosphere of each recess94of adsorption structure92easily leaks into the processing chamber22. As a consequence, the pressure in each recess94becomes equal to that in the processing chamber22. Though a pressure decreasing time depends on the pressure in the processing chamber22right before the depressurizing process, it is approximately, e.g., about 4 to 10 seconds.

Moreover, the wafer W may be kept lifted up a little bit higher than the mounting surface while the pressure being decreased and then be lowered after the pressure decreasing is completed, thereby reaching the state shown inFIG. 5A.

After the pressure decreasing process is completed in this way, the first thin film forming process is performed next. In the first film forming process, the clamp ring58of the clamp device56is lowered and stopped just before it makes a contact with the peripheral portion of the wafer W so that it remains barely separated therefrom as shown inFIG. 5B. A distance L1between the surface of the wafer W and a bottom surface of the clamp ring58is about 4 mm. Further, a height L2of the protrusion60of the clamp ring58is about 20 to 50 μm and an overlapping width in horizontal direction L3between the clamp ring58and the peripheral portion of the wafer W is about 2 to 4 mm.

First, the inside of the processing chamber22is depressurized to a process pressure that is higher than the initial pressure but lower than the atmospheric pressure. At the same time, heat energy in the form of the irradiation light is radiated while rotating the heating lamps80turned on. The radiated irradiation light transmits through the transmission window74to be irradiated to the backside of the mounting table46, thereby heating it. The mounting table46is very thin, so that it is rapidly heated, which, in turn, can rapidly heat the wafer W mounted thereon to a specific temperature.

When a temperature of the wafer reaches to a process temperature, processing gases including, e.g., as the film forming gas, WF6gas, SiH4gas and H2gas are supplied simultaneously through the shower head24into the processing space S of the processing chamber22. The CVD processing for forming the seed film6made of a crystal nucleus of tungsten as the first thin film is performed. During the film forming process, e.g., Ar gas is supplied as the backside gas through the gas introducing path90of the backside gas supply system88into the space below the mounting table46, while its flow rate being controlled. Accordingly, it is prevented that an unnecessary film is deposited on the backside of the mounting table46or on the top surface of the transmission window74due to the infiltration of the processing gas into the space.

The process conditions in this case are as follow: the process pressure is in a range from about 100 to 12000 Pa, the process temperature is in a range from about 300 to 500° C., and the process time is in a range from about 5 to 60 seconds. Here, as described above, since the Ar gas is supplied into the space below the mounting table46as the backside gas, infiltration of the film forming gas into the space is substantially prevented. Meanwhile, the distance L1between the bottom surface of the clamp ring58and the surface of the wafer W is set to be about 4 mm to form a relatively wide gap96, so that the film forming gas infiltrates quite deeply into the inside of the gap96. Accordingly, the outer edge6A of the seed film6is widely formed to a location near the edge of the wafer W on the peripheral portion thereof. In other words, the outer edge6A of the seed film6becomes extended outwardly much further in a radial direction of the wafer W than in the conventional case shown inFIG. 10A.

In the first thin film forming process, since the wafer W is adsorptively held by the recesses94of the adsorption structure on the mounting table46, it will not be slid to its side on the mounting table46.

That is, since the substantially sealed spaces formed between the backside of the wafer W and the recesses94is made to have a lower inner pressure than the process pressure of the processing space S, the wafer W is adsorptively held on the mounting surface by the pressure difference.

The inner atmosphere of the processing space S of comparatively higher pressure infiltrates from between the backside of the wafer W and the mounting surface into the recesses94little by little, and the pressure difference becomes lowered slowly, thereby deteriorating the adsorptive force. However, since the process time of the first thin film forming process is a short time of length about 30 seconds as described above, a strong enough adsorptive force (pressure difference) to hold the wafer can be maintained during that short time period.

After the first thin film forming process is completed in this way, the second thin film forming process begins to be performed.

In the second thin film forming process, by making the clamp ring58of the clamp device56have a contact with the peripheral portion of the surface of the wafer W as described inFIG. 5C, the wafer W is pressed against the mounting table46to be kept in place. As a consequence, the wafer W is completely kept in place irrespective of the pressure in the recesses94, thereby preventing it from sliding to its side. In this state, the processing gas containing the film forming gas, WF6gas and H2gas, are supplied and the second thin film of tungsten metal film is formed, by employing the CVD film forming process, as the main film8at a higher film forming rate starting from the surface of the seed film6.

At this time, the Ar gas is also supplied as the backside gas into the space below the mounting table46. The process conditions are as follows: the process pressure is in a range from about 1000 to 12000 Pa, e.g., 10666 Pa (80 Torr), the process temperature is in a range from, e.g., about 300 to 500° C., and the process time depending on a film thickness to be formed is, e.g., about 60 sec.

In the second film forming process shown inFIG. 5C, the distance between the bottom surface of the clamp ring58and the surface of the wafer W, i.e., the height of the gap96is much lower than that of the first film forming process shown inFIG. 5B. Therefore, the film forming gas in the processing space S can hardly infiltrate into the inside of the gap96with an additional help of an effect of the backside gas. Accordingly, the outer edge8A of the main film8is formed without being extended too much outwardly in a radial direction of the wafer W. In other words, the outer edge8A of the main film8is terminated at a position located inwardly in a radial direction than the outer edge6A of the seed film6.

As a consequence, unlike the conventional case shown inFIG. 10B, an exposed surface, where the seed film6is not formed, of the peripheral portion of the wafer can be prevented from being attacked and damaged by fluorine of WF6gas. Also, the TiN barrier layer of the exposed surface can be prevented from reacting with the fluorine.

After the second film forming process is completed, temperature of the wafer is decreased by stopping the supply of each gas. However, since the recesses94are substantially uniformly distributed on the mounting surface, the temperature of the wafer W can be decreased while maintaining the in-surface uniformity thereof.

In the first film forming process of this embodiment, the seed film6is formed by employing the CVD film forming method while supplying the WF6, SiH4and H2gases simultaneously, but the present invention is not limited thereto. For example, by supplying the WF6and SiH4gases alternately, an extremely thin seed film with a thickness of atomic level or molecular level may be sequentially deposited. Such a film forming method is referred to as SFD (Sequential Flow Deposition). In case of the SFD film forming, it takes about 2 to 10 seconds, e.g., six seconds to complete a cycle and a series of cycles including from several cycles to less than twenty cycles may be performed successively. Accordingly, since a total film forming process can be completed in a short time of about sixty seconds, it can be performed while the wafer W being adsorptively held by the adsorption structure92.

Here, it was checked how much time was required to decrease the inner pressure of the processing chamber22from 10666 Pa (80 Torr) to 1000 Pa.FIG. 6represents a pressure change during that time. As is clearly shown inFIG. 6, it is confirmed that it takes about 4 seconds to lower the inner pressure of the processing chamber22from 10666 Pa to 1000 Pa or less. Accordingly, it can be confirmed that the time required for the pressure decreasing process performed just before the first film forming process can be very short.

Since it was actually tested whether or not the wafer slid while performing the first film forming process by employing the SFD, the test result will be described. In that test, after the inner pressure of the processing chamber22was set to be 10666 Pa, the pressure decreasing process was then performed and the first film forming process was performed for fifty seconds. Thereafter, whether or not the wafer slid in the first film forming process was investigated. From the result of the test, it was found out that the wafer had slid when a setting time of the pressure decreasing process was about 5 seconds, but that the wafer W did not slide when the setting time was six seconds or greater.

Now, a modification of the adsorption structure92shown inFIG. 8will be described. The adsorption structure92inFIG. 8has a plurality of communication recesses98making the ring-shaped recesses94shown inFIG. 3communicate with each other. Each communication recess98is arranged in a diameter direction of the mounting table46. As a consequence, the ring-shaped recesses94communicate with each other, so that there becomes no pressure difference between ring-shaped recesses94, which can enhance an adsorption uniformity in the wafer W during the first film forming process and can also further enhance an in-surface uniformity of temperature while lowering the temperature of the wafer.

Next, after the second film forming process is completed, results of simulating temporal variations (FIGS. 7A and 7B) in temperature distribution while decreasing the temperature of the wafer in order to unload the wafer will be described.FIG. 7Ashows the temporal temperature variations in a central portion of the wafer andFIG. 7Billustrates the temporal temperature variations in a peripheral portion of the wafer.

In the Figures, curves A1and A2describe the temperature of the wafer processed on the mounting table shown inFIG. 3; and curves B1, B2represent the temperature of the wafer processed on the mounting table shown inFIG. 8.

In case of the mounting table shown inFIG. 3, the temperature is rapidly decreased at the beginning only in the curve A1, but it has been found that the temperature distribution generated in the surface of the wafer is maintained uniform to a certain degree on the whole. Moreover, in case of the mounting table shown inFIG. 8, it has been found that the curves B1and B2represent a similar trends in which the temperature is rapidly decreased at the beginning and that the temperature distribution generated in the surface of the wafer is maintained in a substantially uniform state, which are better than those of the curves A1and A2.

The adsorption structure92of this embodiment is not limited to those formed by the ring-shaped recesses94arranged concentrically as shown inFIGS. 3 and 8. For example, it may have a continuous spiral recess94A shownFIG. 9A, or a plurality of linear recesses94B arranged in a grid pattern as shown inFIG. 9Bor a plurality of linear recesses94C radially arranged as shown inFIG. 9C.

Further, in this embodiment, monosilane (SiH4) is used as a film forming gas for the first thin film, but disilane, dichlorsilane or the like may be used instead of that. Furthermore, although there has been described that the seed film made of a crystal nucleus of tungsten is formed as the first thin film and the main film made of metal tungsten is formed as the second thin film, the present invention is not limited thereto. That is, the present invention may be applied in a case where the first and the second thin film are sequentially formed on a surface of a flat target object.

Furthermore, in this embodiment, the semiconductor wafer has been exemplified as a target object, but the present invention is not limited thereto. For example, the present invention may be applied to a flat target object such as an LCD substrate, a glass substrate or the like.