Film forming method

A film forming method of forming a film containing a metal element on a substrate using a source gas containing the metal element and a reactant gas that reacts with the source gas, which includes: forming a lower layer film containing the metal element on a surface of the substrate through a plasma CVD process by supplying the source gas into a process container and plasmarizing the source gas; and subsequently, laminating an upper layer film containing the metal element on the lower layer film by a plasma ALD process which alternately performs an adsorption step of supplying the source gas into the process container to adsorb the source gas onto the surface of the substrate with the lower layer film formed thereon, and a reaction step of supplying the reactant gas into the process container and plasmarizing the reactant gas.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2016-199162, filed on Oct. 7, 2016, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a technology for forming a film on a surface of a substrate.

BACKGROUND

In a process of manufacturing a semiconductor device, an Atomic Layer Deposition (ALD) method and a Molecular Layer Deposition (MLD) method is used to form a film containing metal on a surface of a semiconductor wafer (hereinafter). The ALD method includes alternately supplying a source gas containing metal and a reactant gas reacting with the source gas to a wafer on which a film is to be formed, and depositing the metal on the surface of the wafer to form a metal film. The MLD method includes forming a film of a compound containing metal. Hereinafter, in the present application, the ALD method and the MLD process will be collectively referred to as an “ALD process”.

For example, a plasma ALD method has been used which facilitates action of a source gas (a first process material) with a plasmarized reactant gas (a second process material).

The ALD method is a film forming method which is capable of forming a film on the surface of a wafer having a stereoscopic structure at a more uniform thickness, thus providing good step coverage. Therefore, the present inventors of the present disclosure have examined, for example, the use of a plasma ALD method as a method for forming a metal film such as a Ti film inside a contact hole formed in an insulation layer.

Further, the present inventors focused on the surface roughness of a film (hereinafter, referred to as “roughness”) as an indicator for determining whether an electrical characteristic of a film obtained using the plasma ALD method is good or bad.

In addition, a resistance element manufacturing technology has been used to form a first resistance layer of tantalum nitride (TaN) by a thermal Atomic Layer Deposition (thermal ALD) method, followed by forming a second resistance layer of TaN by a plasma ALD method. However, this technology does not disclose a method for forming a film while focusing on the improvement of roughness.

SUMMARY

Some embodiments of the present disclosure provide a film method capable of forming a film having low surface roughness.

According to one embodiment of the present disclosure, there is provided a film forming method of forming a film containing a metal element on a substrate using a source gas containing the metal element and a reactant gas that reacts with the source gas, the method including: forming a lower layer film containing the metal element on a surface of the substrate through a chemical vapor deposition process (plasma CVD process) by supplying the source gas into a process container and plasmarizing the source gas, the substrate on which a film is to be formed being disposed inside the process container; and subsequently, laminating an upper layer film containing the metal element on the lower layer film by an atomic layer deposition process (plasma ALD process) which alternately performs an adsorption step of supplying the source gas into the process container to adsorb the source gas onto the surface of the substrate with the lower layer film formed thereon, and a reaction step of supplying the reactant gas into the process container and plasmarizing the reactant gas so that the plasmarized reactant gas reacts with the source gas adsorbed onto the surface of the substrate.

DETAILED DESCRIPTION

Prior to describing a film forming method according to an embodiment of the present disclosure, the tendency of roughness of a film formed by a plasma ALD process, which has been practiced by the present inventors, will be described with reference toFIG. 1andFIGS. 2A to 2C.

FIG. 1shows an example of a general device structure in the course of manufacturing a semiconductor device. The device illustrated inFIG. 1has a structure in which a silicon nitride (SiN) film52as an insulation film is laminated on an upper surface of a Si substrate51as a wafer W, a contact hole50is formed in the SiN film52, a titanium film53as a barrier film is formed on the SiN film52and inside the contact hole50, a tungsten W film54is laminated on the titanium film53, thus filling the interior of the contact hole50with tungsten. The contact hole50serves to connect a wiring of a layer formed above the SiN film52and the Si substrate51.

Further, in a semiconductor device having a multilayer wiring structure, there may be a case in which a via hole through which wirings are connected to each other are formed in an interlayer insulation film laminated on the aforementioned wiring, and a Ti film as a barrier film or the like is formed inside the via hole (the multilayer wiring structure is not illustrated).

In recent years, the contact hole50or a via hole (not shown) tends to have a higher aspect ratio (a ratio of a depth to an opening diameter of the contact hole50or the via hole). Meanwhile, conventionally, a Physical Vapor Deposition (PVD) method, which has been used to form a metal film such as the Ti film53, fails to obtain a film having good step coverage. Thus, the method is not suitable for formation of a film inside a hole having a high aspect ratio.

In this regard, the present inventors have examined a method for forming the Ti film53using a plasma ALD process in which a film having good step coverage is obtained.

In the formation of the Ti film53, a titanium tetrachloride (TiCl4) gas was used as a source gas containing a Ti element which is a source material of the formed Ti film, and a mixed gas of a hydrogen (H2) gas and an argon (Ar) gas was used as a reactant gas that reacts with the source gas. Further, the Ti film53was obtained by a plasma ALD process which alternately repeats an adsorption step of supplying a source gas into a process container having a wafer W accommodated therein, on which a film is to be formed, and adsorbing the source gas onto a surface of the wafer W, and a reaction step of supplying a reactant gas into the process container and turning the reactant gas into plasma so that the reactant gas in a plasma state reacts with the source gas adsorbed onto the surface of the wafer W.

The Ti film53formed by the plasma ALD process was formed on the entire interior of the contact hole50having a high aspect ratio and thus good step coverage was obtained. Meanwhile, the present inventors found that the roughness of the Ti film53is increased as compared with a plasma CVD process in which a mixed gas of a source gas and a reactant gas is turned into plasma inside a process container to deposit a Ti film on the surface of a wafer (see Comparative Example 1-1 described below).

The present inventors understood that the use of the Ti film53having high roughness results in deterioration of electrical characteristics, for example, an increase in contact resistance between the Si substrate51and the wiring via the contact hole50.

In this regard, the present inventors developed a method for improving the roughness of the Ti film53while employing the plasma ALD process which provides good step coverage, and examined a mechanism of increasing the roughness of the Ti film53formed by the plasma ALD process.

FIGS. 2A to 2Cschematically illustrate a mechanism which is estimated to be a reason for why the roughness of the Ti film53formed by the plasma ALD process increases.

FIG. 2Ashows a state in which a TiCl4gas81as a source gas is adsorbed onto the surface of the Si substrate51(the wafer W) by performing a adsorption step.

In general, the ALD process is a method for adsorbing a source gas onto a surface of a wafer W, on which a film is to be formed, to form a uniform molecular layer, followed by making the molecular layer react with a reactant gas, followed by depositing a layer of atoms or molecules obtained by the reaction to obtain a film having a uniform thickness.

However, there is a gap between the TiCl4gases81adsorbed onto the surface of the actual Si substrate51after the adsorption step. Thus, a portion of the surface of the Si substrate51remains exposed.

When a subsequent reaction step is performed in this state, the TiCl4gas81is reduced by active species such as H radicals801generated by turning the reactant gas into plasma, so that titanium metal (Ti)804as a film material is obtained.

Meanwhile, as illustrated inFIG. 2B, when the exposed surface of the Si substrate51is exposed to plasma of a reactant gas and the H radicals801or the like act on the Si substrate51, a portion of the surface of the Si substrate51is scraped, thereby forming a concave portion. Further, a portion of the Ti804obtained by the reduction of the TiCl4gas81is coupled with Si803constituting the Si substrate51to partially generate a compound such as TiSi82that is stable with respect to plasma. Further, reference numeral802is Cl or HCl which is reduced and removed from the TiCl4gas81.

As a result, concave portions formed by scraping the Si substrate51and convex portions formed by a compound (TiSi82in the example shown inFIG. 2B) partially generated on the surface of the Si substrate51are present on the surface of the Si substrate51.

It is estimated that, if the Ti film53is formed by laminating, by a plasma ALD process, the titanium metal on the surface of the Si substrate51having the concave and convex portions formed thereon, the concave and convex portions formed on the Si substrate51as a underlayer are also reflected the surface of the Ti film53, which causes concave and convex portions to be similarly formed on the surface of the Ti film53as illustrated inFIG. 2C, thereby increasing the roughness of the Ti film53.

It is considered that, according to a mechanism related to the increase in the roughness of the Ti film53estimated as above, in an initial step of starting the lamination of the Ti film53on the surface of the Si substrate51, maintaining the surface of the Si substrate51as flat as possible is a critical factor in limiting an increase in the roughness of the Ti film53laminated on the Si substrate51.

Therefore, according to the film forming method of the present embodiment, in the initial step of forming the Ti film53, a plasma CVD process is performed to form a lower layer film53A (to be described later) of titanium metal, and then a plasma ALD process is performed to laminate an upper layer film53B (to be described later) made of the same material as that of the lower layer film53A on the lower layer film53A. In this way, the Ti film53having good coverage is formed while limiting the increase in the roughness of the Ti film53.

Hereinafter, an example of the configuration of a film forming apparatus for implementing the film forming method will be described with reference toFIG. 3.

As illustrated inFIG. 3, the film forming apparatus has a configuration in which a mounting table2on which a wafer W is mounted is installed inside a process container1as a metal vacuum container. A loading/unloading port11through which the wafer W is loaded into or unloaded from the process container1and a gate valve12configured to open/close the loading/unloading port11, are installed in a lateral surface of the process container1.

A metallic exhaust duct13formed by bending a rectangular duct in an annular shape is stacked on a body of the process container1. A slit-shaped opening131through which a gas flowing out of a process space313is exhausted, is formed in an inner peripheral surface of the exhaust duct13. An exhaust part65including a vacuum pump or the like is connected to an exhaust port132formed in an outer wall surface of the exhaust duct13. A combination of the exhaust port132and the exhaust part65constitutes a vacuum exhaust part which evacuates the inside of the process space313.

The mounting table2is disposed inward of the exhaust duct13and is configured by a circular plate made of ceramic or metal. The mounting table2has a heater (not illustrated) embedded therein to heat the wafer W at a film formation temperature having the range of, for example, 350 to 550 degrees C. Further, the mounting table2may include an electrostatic chuck (not illustrated) installed therein to fix the wafer W within a predetermined mounting region. Further, a cover member22configured to cover an outer peripheral portion of the mounting region and a lateral peripheral surface of the mounting table2in the circumferential direction, is installed in the mounting table2.

The mounting table2is connected to an elevating mechanism24via a support member23passing through a bottom surface of the process container1and a plate-shaped support table232. The elevating device24moves the mounting table2up and down between a transfer position of the wafer W (described in dash-dot-dash line inFIG. 3) and a process position at which a film is formed on the wafer W.

The process container1is air-tightly sealed by a bellows231surrounding the support member23and connected to the support table232. Further, a plurality of vertically-movable support pins25is installed under the mounting table2. The plurality of support pins25protrude from the upper surface of the mounting table2via respective through-holes formed in the mounting table2, thereby lifting the wafer W.

A support plate32made of a metal disc member is installed on a top surface of the exhaust duct13. A ring-shaped insulation member134is disposed between the exhaust duct13and the support plate32. The inside of the process container1is air-tightly sealed by an O-ring133received in a groove formed in an upper surface of the insulation member134. Further, the support plate32is insulated from the exhaust duct13by the insulation member134. A ceiling plate member31made of metal is supported by and fixed to a lower surface of the support plate32.

The ceiling plate member31has a concave portion formed in a lower surface thereof. A central region of the concave portion is flat. A metallic shower head42is installed below the ceiling plate member31to cover the entire lower surface of the ceiling plate member31. The shower head42includes a flat circular plate facing the mounting table2and a ring-shaped protrusion43formed in a peripheral portion of the circular plate to protrude downward.

When the mounting table2is lifted up to the process position, a lower end of the ring-shaped protrusion43is positioned to face the upper surface of the cover member22in the mounting table2through a gap. A space, which is surrounded by the lower surface of the shower head42, the ring-shaped protrusion43and the upper surface of the mounting table2, is the process space313in which a film is formed on the wafer W.

Further, a space between the concave portion of the ceiling plate member31and the shower head42is defined as a diffusion space420where a gas diffuses. A plurality of gas discharge holes421is formed in the entire surface of the shower head42. A reactant gas can be supplied toward the wafer W through the gas discharge holes421.

Further, a plurality of gas dispersion parts41is arranged inside the diffusion space420, for example, in a concentric circle shape. As illustrated inFIGS. 3 and 5, and the like, each of the gas dispersion parts41has a configuration in which a plurality of gas discharge holes411is formed along the circumferential direction in a lateral surface of a flat cylindrical member with its upper surface opened and its lower surface closed. The openings formed in the upper surfaces of the gas dispersion parts41are connected to openings of downstream ends of a plurality of gas supply passages312formed in the ceiling plate member31, respectively.

Each of the gas supply passages312is connected to a diffusion space311which is a buffer chamber defined between the upper surface of the ceiling plate member31and the lower surface of the support plate32.

The support plate32includes a reactant gas supply passage321and a source gas supply passage322formed therein. The reactant gas supply passage321is formed to supply a reactant gas containing a hydrogen gas and a plasma-generating argon gas to the diffusion space311. Similarly, the source gas supply passage322is formed to supply a source gas containing a titanium chloride gas and a dilution-purpose argon gas to the diffusion space311.

The reactant gas supply passage321is connected to an argon gas supply part61and a hydrogen gas supply part62through brandied pipes. Further, the source gas supply passage322is connected to an argon gas supply part63and a titanium chloride gas supply part64through branched pipes. An opening/closing valve602configured to perform the supply and cutoff of a gas, and a flow rate regulator601configured to adjust the supply amount of gas are installed in each of the branched pipes. Further, for the sake of convenience in illustration, while inFIG. 3, the argon gas supply parts61and63has been described to be individually installed, a common argon gas supply part may be used.

Further, a high-frequency power supply661for forming plasma is connected to the support plate32via a matcher662. The high-frequency power supply661supplies, for example, a high-frequency power of 13.56 MHz. A combination of the support plate32, the ceiling plate member and shower head42, which are made of a metal member and coupled to one another, constitutes an upper electrode for forming plasma.

Meanwhile, a lower electrode21constituting a parallel plate electrode between the mounting table2and the upper electrode is installed in the mounting table2. For example, in the case where the mounting table2is made of ceramic, a circular plate-shaped lower electrode21is embedded in the mounting table2. In the film forming apparatus of the present embodiment, the lower electrode21is grounded (FIG. 3). Further, in the case where the mounting table2is made of metal, the body of the mounting table2may be grounded and the mounting table2itself may be employed as the lower electrode (this configuration is not illustrated herein).

In the above configuration, by applying the high-frequency power between the lower electrode21of the mounting table2side and the upper electrode, which is composed of the support plate32, the ceiling plate member31and the shower head42, it is possible to turn a gas inside the diffusion space420or the process space313into plasma by capacitive coupling. Further, the high-frequency power is not limited to being applied to the upper electrode but may be applied to the lower electrode21. In this case, the upper electrode is grounded.

The film forming apparatus is connected to a controller7as illustrated inFIG. 3. The controller7is configured by, for example, a computer including a Central Processing Unit (CPU) and a memory part (both not illustrated). The memory part stores a program including a group of commands (instructions) for controlling the film forming method performed by the film forming apparatus, namely a method for supplying a source gas or a reactant gas to the wafer W accommodated in the process container1(the process space313) according to a predetermined sequence or flow rate, and forming plasma of these gases at a predetermined timing to form a Ti film. The program is stored in a memory medium such as a hard disk, a compact disk, magneto-optical disk, a memory card or the like, and is installed in the computer from the memory medium.

Contents of the film forming method performed by the film forming apparatus configured as above will be also described with reference toFIG. 4toFIGS. 8A to 8D.

First, in the process container1which has been previously evacuated by the exhaust part65, the mounting table2is moved down to the transfer position. The gate valve12is opened and a transfer arm of a wafer transfer mechanism installed in an external vacuum transfer chamber enters the process container1. A wafer W on which a film is to be formed is held by the transfer arm. The support pins25are moved up to receive the wafer W from the transfer arm. Thereafter, the support pins25are moved down so as to mount the wafer W on the mounting table2which has been heated by a heater (not illustrated) at a predetermined film formation temperature.

Subsequently, the transfer arm is retracted and the gate valve12is closed. The mounting table2is moved up to the process position and an internal pressure of the process container1is adjusted. Thereafter, the film formation is performed.

Here, according to the film forming method of the present embodiment, the Ti film53is formed in two divided processes, i.e., a plasma CVD process and a plasma ALD process as illustrated inFIG. 4.

First, as illustrated inFIGS. 4 and 5, in the plasma CVD process, the supply of the source gas through the source gas supply passage322and the supply of the reactant gas through the reactant gas supply passage321are performed in parallel. The source gas and the reactant gas supplied at predetermined flow rates join inside the diffusion space311to form a mixture gas of the source gas and the reactant gas. The mixture gas is introduced into the diffusion space420through the gas supply passages312and the gas dispersion parts41.

The mixture gas, which has been introduced into and dispersed in the diffusion space420, flows into the process space313in which the wafer W is disposed, through the gas discharge holes421formed in the shower head42. The mixture gas inside the process space313flows along the upper surface of the wafer W mounted on the mounting table2outward in the diameter direction of the wafer W. Subsequently, the mixture gas flows toward the exhaust duct13through the gap between the cover member22and the end of the ring-shaped protrusion43. The mixture gas flowing into the exhaust duct13is discharged outside through the exhaust port132.

Further, even in an adsorption step or a reaction step of the plasma ALD process described below, various kinds of gases flowing into the diffusion space311flow while manifesting the same behavior as that in an example described with reference toFIG. 5.

As illustrated in the time chart ofFIG. 4andFIG. 5, if a predetermined period of time elapses after starting the supply of the source gas and the reactant gas, the high-frequency power supply661applies the high-frequency power of 300 W, which falls within the range of 100 to 500 W (described as “RF application” inFIG. 4), so as to plasmarize the mixture gas.

By plasmarizing the mixture gas of the source gas and the reactant gas, active species of titanium tetrachloride or hydrogen are generated in the plasma so that titanium metal particles are obtained by reaction between the active species. The titanium metal particles are deposited on the surface of the Si substrate51as the wafer W, thereby forming the lower layer film53A (in the plasma CVD process; seeFIG. 8A).

In the plasma CVD process, energy of plasma is mainly used for a CVD reaction in the respective plasma (a reaction by which titanium metal particles are obtained from active species of titanium tetrachloride or hydrogen). Therefore, in an initial film forming step in which the Si substrate51is exposed, by performing the film formation based on the plasma CVD process, it is possible to suppress the surface of the Si substrate51from being scraped, or suppress a compound which is stable with respect to plasma generated by a reaction between the Si substrate51and the source gas, from being partially produced. This makes it possible to suppress concave and convex portions from being formed on the surface of the Si substrate51.

Further, the power applied from the high-frequency power supply661in the plasma CVD process is less than that in the subsequent plasma ALD process (300 W in the plasma CVD process and 800 W in the plasma ALD process). In a state where the surface of the Si substrate51is exposed, by suppressing the plasma-generating energy at a low level, it is possible to suppress concave and convex portions from being formed on the surface of the Si substrate51.

In the above-described plasma CVD process, the lower layer film53A having a predetermined thickness of 3 nm or less (for example, 1 nm) is formed. Thereafter, the supply of the source gas and the RF application is stopped and the plasma CVD process is terminated.

In the present embodiment, the supply of the reactant gas is continuously performed so that the reactant gas may be also used as a purge gas for purging the source gas remaining in the process space313. Further, instead of the reactant gas, an inert gas such as a nitrogen gas may be supplied as a purge gas (it is desirable to select an inert gas which does not react with the lower layer film53A).

After the source gas inside the process space313is exhausted, the supply of the source gas (the TiCl4gas81) is resumed so that the source gas (the TiCl4gas81) is adsorbed onto the surface of the Si substrate51having the lower layer film53A formed thereon (in an adsorption step illustrated inFIG. 4; seeFIGS. 6 and 8B).FIG. 6shows an example in which the supply of the reactant gas is continuously performed in parallel with the supply of the source gas. However, the supply of the reactant gas may be stopped during the supply of the source gas.

As illustrated inFIG. 8B, the TiCl4gas81in the source gas supplied into the process space313is adsorbed onto the surface of the lower layer film53A formed on the Si substrate51.

After the adsorption step is performed for a predetermined period of time, the supply of the source gas is stopped but the supply of the reactant gas is continuously performed, thereby purging the source gas remaining in the process space313(a first purge period inFIG. 4). After the predetermined period of time elapses and at a timing at which the source gas remaining in the process space313is discharged, the high-frequency power supplied from the high-frequency power supply661is increased to 800 W within the range of 500 to 1500 W, thus plasmarizing the reactant gas (in a reaction step inFIG. 4; seeFIGS. 7 and 8C).

The plasmarization of the reactant gas generates active species such as the H radicals801. The TiCl4gas81adsorbed onto the surface of the lower layer film53A is reduced by the active species so that titanium metal is obtained. As illustrated inFIG. 8C, in this reaction step, the surface of the Si substrate51remains covered with the lower layer film53A formed in the plasma CVD process. It is therefore possible to suppress concave portions from being formed on the surface of the Si substrate51by scraping the surface of the Si substrate51, and suppress convex portions from being formed on the surface of the Si substrate51due to the partial formation of a compound on the surface of the Si substrate51, as compared with the case where the plasma ALD process is performed with the surface of the Si substrate51exposed (FIG. 2B).

After the reaction step is performed for a predetermined period of time, the supply of the high-frequency power from the high-frequency power supply661is stopped and the reaction step is ended. Further, the reactant gas is continuously supplied so as to purge active species of the reactant gas remaining in the process space313(in a second purge period inFIG. 4).

In this way, the cycle of “adsorption step→first purge period→reaction step→second purge period→ . . . ” illustrated inFIG. 4is repeatedly performed a predetermined number of times. Thus, the upper layer film53B having a desired thickness is formed (in the plasma ALD process). Further, the lower layer film53A formed in the plasma CND process and the upper layer film53B formed in the plasma ALD process become the Ti film53formed by the film forming method of the present embodiment.

In the reaction step of the plasma ALD process, by applying the high-frequency power (for example, 800 W) higher than that in the plasma CVD process, it is possible to make the TiCl4gas81adsorbed onto the surface of the lower layer film53A, sufficiently react to each other for a short period of time, thus forming the upper layer film53B at a dense level in a relatively short period of time.

In the plasma CVD process, the lower layer film53A is formed while suppressing the formation of the concave and convex portions on the surface of the Si substrate51, and the upper layer film53B is laminated on the lower layer film53A. It is therefore possible to obtain the Ti film53having low roughness, as compared with the case where the plasma ALD process is performed with the surface of the Si substrate51exposed (see Example 1 described below).

In the plasma ALD process, if the lower layer film53A having a desired thickness is formed by repeating the above-mentioned cycle, for example, several tens of times to several hundreds of times, the supply of the reactant gas as a purge gas is sopped. Thereafter, the mounting table2is moved down to the transfer position and the gate valve12is opened so as to make the transfer arm enter the process container1. Further, in the reverse order of the loading operation of the wafer W, the wafer W after the film formation is transferred from the support pins25to the transfer arm and is unloaded from the process container1. The transfer arm waits for loading of a subsequent wafer W.

The film forming method of the present embodiment provides the following effects. The lower layer film53A including a metal element (the titanium metal in the aforementioned embodiment) is formed on the surface of the Si substrate51(the wafer W) by the plasma CVD process. Thereafter, the upper layer film53B made of the same material as the lower layer film53A is laminated on the lower layer film53A by the plasma ALD process. As a result, when the plasma ALD process is performed, since the surface of the Si substrate51is covered with the lower layer film53A, it is possible to suppress concave and convex portions from being formed on the surface of the Si substrate51due to the performance of the plasma ALD process. Therefore, it is possible to form the Ti film53having low surface roughness.

In the plasma CVD process described above, there has been described an example in which the Ti film53is formed using a source gas containing titanium tetrachloride and a reactant gas containing hydrogen. However, in the plasma CND process, it is not necessarily essential that the lower layer film53A is formed using the reactant gas which generates active species such as the H radicals801or the like. For example, by supplying only a source gas containing a titanium tetrachloride gas and a plasma-generating argon gas and plasmarizing the source gas, it is possible to form the lower layer film53A through the dissolution of the TiCl4gas81.

Further, a film formed by the film forming method of the present embodiment is not limited to the Ti film53either. For example, it may be possible to form a tantalum metal film (Ta film) using a source gas containing tantalum pentachloride (TaCl5) and a reactant gas containing hydrogen.

Further, a film to be formed is not limited to a metal film but an inorganic film may be formed. For example, a SiO2film may be formed by the reaction between a source gas containing tetraethyl orthosilicate (TEOS) and a reactant gas containing an ozone gas. Further, a TiN film may be formed by the reaction between a source gas containing titanium tetrachloride and a reactant gas containing ammonia (NH3). Further, as is the case of forming a composite oxide such as strontium titanate (SrTiO3) or the like, it may be possible to combine three or more source gases reactant gases, such as two kinds of source gases (source gases containing strontium and titanium, respectively) and a reactant gas (containing an ozone gas or the like), and to form a film.

In addition, during the plasma CVD process or the plasma ALD process, a method for forming plasma is not limited to the case in which the parallel plate illustrated inFIG. 3is used. For example, an Inductively Coupled Plasma (ICP) antenna for turning a gas into plasma by inductive coupling or a microwave antenna for turning a gas into plasma by a microwave may be installed at the side of the support plate32to plasmarize a gas inside the diffusion space420or the process space313.

Furthermore, the configuration of the film forming apparatus is not limited to a sheet-type film forming apparatus shown inFIG. 3or the like. For example, it may be possible to use a batch type film forming apparatus, also known as a longitudinal heat treatment apparatus, which performs a plasma CVD process or a plasma ALD process by loading a shelf-shaped wafer boat configured to hold a plurality of wafers that are vertically arranged into a process container made of quartz, and sequentially supplying a source gas, a plasmarized reactant gas or the like into the process container while heating the inside of the process container using an external heater. Further, the film forming method of the present embodiment may be also applied to a semi-hatch type film forming apparatus in which a plurality of wafers W is arranged around a rotation shaft of a rotary table along the circumferential direction of the rotary table, and rotates the rotary table inside a process container having separated process chambers formed therein, wherein a source gas or a plasmarized reactant gas is supplied to each of the separated process chambers, and makes the plurality of wafers W mounted on the rotary table pass through the process chambers, thereby supplying the source gas or the reactant gas to the plurality of wafers W.

EXAMPLES

An experiment was conducted to check the roughness of each of Ti films53by forming the Ti film53on a surface of a Si substrate51under various film formation conditions.

A. Experiment Conditions

The sheet-type film forming apparatus illustrated inFIG. 3was used to form a film by disposing a water W inside an evacuated process container1, and changing process conditions of a plasma CVD process and a plasma ALD process using a source gas containing titanium tetrachloride and argon gas and a reactant gas containing hydrogen and an argon gas. Based on the results of measuring the surface of a Ti film53with an Atomic Force Microscope (AFM), the root mean square (RMS) roughness, the arithmetic mean roughness (Sa), the maximum height roughness (Sz) per unit area in relation to the Ti film53formed by each process were obtained.

The Ti film53was obtained by forming a lower layer film53A having a thickness of 1 nm in the plasma CVD process (the power applied from the high-frequency power supply661was 300 W) and subsequently, forming an upper layer film53B having a thickness of 5 nm in the plasma ALD process (the applied power was 800 W). The internal pressure of the process container1was 1.88 torr (250 Pa) and the film formation temperature was 420 degrees C. Further, the supply flow rate of the source gas was titanium tetrachloride/argon=14.7 sccm/300 sccm, the supply flow rate of the reactant gas was hydrogen/argon=7,000 sccm/300 sccm. The supply time of the source gas in the adsorption step of the plasma ALD process was 0.05 second, and the application time of the high-frequency power in the reaction step was one second.

Comparative Example 1-1

A Ti film53having a thickness of 6 nm was formed only by the plasma ALD process without performing the plasma CVD process. Process conditions of the plasma ALD process were identical to those in Example 1.

Comparative Example 1-2

A Ti film53was obtained by forming a lower layer film53A having a thickness of 1 nm through the plasma ALD process (in which the power applied from the high-frequency power supply661was 300 W) instead of the plasma CVD process and subsequently, forming an upper layer film539having a thickness of 5 nm under the same conditions as Example 1.

Reference Example 1

A Ti film53having a thickness of 6 nm was formed only by the plasma CVD process. Process conditions of the plasma CVD process were identical to those in Example 1 except that the power applied from the high-frequency power supply661is 1,500 W. The roughness of Ti films53, obtained in each Example and each Comparative example, was evaluated with reference to this method in which interaction with the Si substrate51(the formation of concave portions caused by scraping the surface of the Si substrate51or the formation of convex portions resulting from the formation of a compound on the surface of the Si substrate51) is weak.

B. Experiment Results

Table 1 shows the calculation result of the roughness of the Ti films53, obtained in each Example, Comparative example, and Reference example. Further,FIGS. 94 and 9Bshow the results of photographing the Ti films53, which are obtained in Example 1 and Comparative example 1-1, using a Transmission Electron Microscope (TEM).

The Ti film53in Example 1, which was obtained by forming the lower layer film53A in the plasma CVD process and subsequently forming the upper layer film53B in the plasma ALD process, had better roughness than that in the Reference example 1, even when the roughness was calculated in any calculation manner. Further, it can be clearly identified from the TEM image shown inFIG. 9Athat it is possible to form the Ti film53, the surface of which has few concave and convex portions and is smooth.

Meanwhile, the roughness of the Ti film53in Comparative example 1-1, which was formed only by the plasma ALD process, was a high level of at least two times that of Reference example 1, even when the roughness was calculated in any calculation manner. Further, the TEM image inFIG. 9Balso shows the Ti film53having many concave-convex portions and high roughness.

Further, in Comparative Example 1-2 where the lower layer film53A was formed by the plasma ALD process in which the supplied high-frequency power was reduced to 300 W, the roughness of the film was further improved than that in Comparative Example 1-1 using only the plasma ALD process, even when the roughness was calculated in any calculation manner. However, compared with Reference example 1 which is a determination reference of roughness improvement, the roughness became worse, and thus the degree of the improvement thereof was not enough.

According to the results of the above Example and the Comparative examples, it may be evaluated that the film forming method of the present embodiment in which the Ti film53is formed by forming the lower layer film53A in the plasma CVD process and subsequently forming the upper layer film53B in the plasma ALD process, is a desirable film forming method in obtaining a film having good roughness.

An experiment was conducted to check the state of a step coverage of a Ti film53which is formed on the surface of a Si substrate51having a contact hole50formed therein.

A. Experiment Conditions

The Ti film53was formed on the Si substrate51in which the contact hole50having an opening diameter of 12 nm and an aspect ratio of 17 is formed, by the same method as Example 1 and Comparative example 1-1. Thereafter, the thickness of the Ti film53inside the contact hole50was measured.

A Ti film53was formed by the same method as Example 1.

Reference Example 2

A Ti film53was formed by the same method as Comparative example 1-1. As already described, since the plasma ALD process is a film forming method having good step coverage, the step coverage of Example 2 was evaluated on the basis of the Ti film53which is obtained by the present method.

B. Experiment Results

FIG. 10andFIG. 11illustrate TEM images in Example 2 and Reference example 2, respectively, inFIG. 10andFIG. 11, enlarged images of a surface of the Si substrate51(field portion), an upper side surface of the contact hole50(neck portion-top side portion), a middle side surface of the contact hole50(middle side portion), a lower side surface of the contact hole50(bottom side portion), and a bottom surface of the contact hole50(bottom portion) are shown together. Further, numerical values properly written in the enlarged images indicate the thickness of the Ti film53in each portion, and a ratio of the thickness of the Ti film53in each portion to the thickness of the Ti film53in the field portion, in terms of percentage (%).

According to the result of Example 2, even in the middle side portion and the bottom side portion which tend to decrease in the thickness of the Ti film53, the Ti film53can be formed at a thickness of 52 to 62% of that of the field portion. In this regard, it can be evaluated that the formed Ti film53has a thickness sufficient for practical use as compared with the result (61 to 63% of the field part) of Reference example 2 in which a film was formed by only the plasma ALD process. Therefore, it was identified that it is possible to form the Ti film53having good coverage even when the film forming method of the present embodiment of forming the lower layer film53A by the plasma CVD process and subsequently, forming the upper layer film53B by the plasma ALD process, is employed.

According to the present disclosure, a lower layer film containing a metal element is formed on the surface of a substrate in a plasma-based Chemical Vapor Deposition (plasma CVD) process and subsequently, an upper layer film made of the same material as that of the lower layer film is laminated on the lower layer film in a plasma-based Atomic Layer Deposition (plasma ALD) process. As a result, since the surface of the substrate is covered by the lower layer film in the course of performing the plasma ALD process, it is possible to suppress concave and convex portions from being formed on the surface of the substrate due to the performance of the plasma ALD process, it is therefore possible to form a film having a relatively low surface roughness.