JP2005086185A - Deposition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a deposition method that can form a film by using a method to alternately feed different kinds of source gases to cause reaction on a substrate even if a gas kind less clinging to a substrate surface is used as a source gas. <P>SOLUTION: As source gases, TaF<SB>5</SB>and SiH<SB>4</SB>are alternately fed to cause reaction on a substrate, thus generating a thin film of TaSi<SB>x</SB>. Before feeding the source gases, a pretreatment is performed onto the substrate by feeding NH<SB>3</SB>that is a gas having a dipole moment. Otherwise, a TaN film is generated over the substrate surface as a pretreatment. Partial pressure in feeding SiH<SB>4</SB>should be raised over a predetermined threshold. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a film forming method, and more particularly to a film forming method for generating a thin film that functions as a barrier film or the like on a substrate in a semiconductor manufacturing process or the like.

  In a semiconductor manufacturing process such as a transistor, when a copper layer is formed as a conductive layer on an insulating oxide film on a substrate, a barrier film may be provided between the insulating oxide film and the copper layer. The barrier film is provided to separate the copper layer and the insulating oxide film so that copper of the copper layer does not diffuse into the insulating oxide film. As the barrier film, a thin film such as tantalum nitride (TaN) or titanium nitride (TiN) is often used.

  Conventionally, physical vapor deposition (PVD) is generally used as a method for generating the above-described barrier film. However, in order to generate a barrier film more efficiently, chemical vapor deposition (CVD) is used. ) Is also proposed.

For example, a method for producing a tantalum silicide (TaSi) film by vapor phase synthesis of TaF ₅ and SiH ₄ has been proposed (see, for example, Patent Document 1). However, when a thin film is generated by CVD, it is difficult to control the film thickness with high accuracy, and an extremely thin film cannot be generated. In addition, when a thin film is formed by CVD, impurities may be mixed in the thin film even though the amount is small. For example, when a TaSi film is generated by CVD using TaF ₅ and SiH ₄ as described above, fluorine (F) is mixed as an impurity in the TaSi film. The barrier film is required to have a specific resistance as small as possible. However, when impurities are mixed in this way, the specific resistance increases, and good characteristics as a barrier film are impaired.

  Furthermore, in order for the TaSi film to grow on the substrate, nuclei must first be formed on the substrate, but a certain amount of time is required until the nuclei are generated and the TaSi film starts to grow. This time is generally called incubation time. If the incubation time is long, the film forming process takes time, and the throughput decreases.

In view of this, a method has been proposed in which the substrate is pre-processed before the thin film generation process by CVD to promote the generation of nuclei (see, for example, Patent Document 2). In this method, when a thin film is formed by CVD using WF ₆ and SiH ₄ , the substrate is pretreated with ammonia (NH ₃ ). By pretreatment with NH ₃ , WF ₆ and SiH ₄ reacted in the gas phase are easily adsorbed on the substrate, thereby reducing the incubation time.
International Publication No. 02/056348 Pamphlet JP 2000-235962 A International Publication No. 02/48427 Pamphlet

  As described above, a method of generating a barrier film by CVD has been proposed. However, in the present situation where wirings in a semiconductor structure are further miniaturized, a method of generating a higher quality barrier film is desired. .

In order to satisfy such a demand, it has been proposed to produce a barrier film by ALD (Atomic Layer Deposition) in which a thin film is produced by reacting on a substrate while alternately supplying different kinds of source gases. However, for example, when a TaSi film, which has been conventionally generated by CVD using TaF ₅ and SiH ₄ as source gases, is generated by ALD, these source gases have a characteristic that they are not easily adsorbed on the substrate surface. For this reason, there is a problem in that a nucleus growth reaction at the initial stage of film formation hardly occurs and a film cannot be generated by ALD.

  The present invention has been made in view of the above points, and even when a gas species that is difficult to adsorb on the substrate surface is used as a source gas, a method of reacting on the substrate while alternately supplying different types of source gases is used. An object is to provide a film forming method capable of forming a film.

  In order to solve the above problems, according to the present invention, a film forming method for generating a thin film by reacting on a substrate while alternately supplying different types of source gases, wherein the source gases are supplied before being supplied. In addition, there is provided a film forming method characterized in that a pretreatment for promoting the adsorption of the source gas is performed on the surface of the substrate on which the film is formed.

  According to the above-described invention, the pretreatment of the substrate surface promotes the adsorption of the raw material gas, and even when the film formation cannot be performed by the method of alternately supplying the raw material gas, the film having good characteristics as a barrier film Can be generated.

As the pretreatment, a gas having a dipole moment such as NH ₃ may be supplied to the surface of the substrate. Instead, as the pretreatment, a TaN film may be formed on the surface of the substrate. It is preferable that the TaN film is formed by alternately supplying TaF ₅ and plasmatized NH ₃ . Moreover, it is preferable that the pressure of the source gas is set to a predetermined threshold value or more when the source gas is supplied.

In the above invention, the raw material gas is TaF ₅ and SiH _4, the pretreatment is a process for supplying NH ₃ to the substrate surface, when the alternating supply the TaF ₅ and SiH _4, TaF ₅ and SiH _The TaSix film may be formed on the substrate by setting the partial pressure of ₄ to a predetermined threshold value or more. The source gas is TaF ₅ and SiH ₄ , and the pretreatment is a process for generating a TaN film on the substrate surface, and when supplying the TaF ₅ and SiH ₄ alternately, the partial pressure of SiH ₄ is predetermined. A TaSix film may be formed on the substrate by setting the threshold value to be equal to or greater than the threshold value. When TaF ₅ and SiH ₄ are alternately supplied, it is preferable to set the partial pressure of TaF ₅ to a predetermined threshold value or more.

  As described above, according to the present invention, even when a gas species that is difficult to be adsorbed on the substrate surface is used as a source gas, film formation is performed using a film formation method in which different types of source gases are reacted while being alternately supplied on the substrate. Can be performed.

  Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic configuration diagram of a film forming apparatus in which a film forming method according to the present invention is implemented. The film formation apparatus shown in FIG. 1 supplies tantalum fluoride (TaF ₅ ) and silane (SiH ₄ ) alternately as an example of a film formation apparatus that generates a thin film by alternately supplying a plurality of source gases. This is a film forming apparatus for producing a tantalum silicide (TaSi _x ) thin film.

In the processing chamber 2, there is provided a mounting table 4 on which a silicon substrate W is mounted as a base for generating a thin film. Source gases TaF ₅ and SiH ₄ are alternately supplied into the processing chamber 2 together with the carrier gas Ar from the shower head 6 disposed above the mounting table 4. A gas supply pipe 8 is connected to the shower head 6, and SiH ₄ and Ar are supplied from one end of the gas supply pipe 8, flow through the gas supply pipe 8, and are supplied to the shower head. On the other hand, TaF ₅ is supplied to the gas supply pipe 8 through the gas passage 10 connected to the side surface of the gas supply pipe 8 and supplied to the shower head 6 together with Ar.

Here, ammonia gas (NH ₃ ) is also supplied to the processing chamber 2 through the gas supply pipe 8 and the shower head 6, and the supply of NH ₃ is performed for pretreatment as will be described later. Therefore, NH ₃ is not supplied in the process of growing tantalum silicide (TaSi _x ) by alternately supplying TaF ₅ and SiH ₄ .

Of TaF ₅ and SiH ₄ supplied to the processing chamber 2, a portion that did not contribute to the reaction is supplied via a butterfly valve 12 provided at the bottom of the processing chamber 2 through a high vacuum pump (turbo molecular pump: TMP) 14. Is exhausted from the inside of the processing chamber 2 and further exhausted to the outside by a low vacuum pump (dry pump: DP) 16.

The tantalum silicide (TaSi _x ) thin film generated by the film forming apparatus shown in FIG. 1 is used as a barrier film provided between an interlayer insulating film and a copper via, for example, when a copper via is formed in a multilayer thin film structure. Used. FIG. 2 is a diagram showing a process of generating a tantalum silicide thin film used as a barrier film.

  In the example shown in FIG. 2, copper vias for connecting upper and lower wiring layers are formed in a thin film multilayer structure such as a semiconductor device. First, as shown in FIG. 2A, an interlayer insulating film 21 and an etch stopper film 22 are formed on a copper film 20 as a wiring layer. Next, as shown in FIG. 2B, a via hole 23 is formed through the interlayer insulating film 21 and the etch stopper film 22. Subsequently, as shown in FIG. 2C, a trench 24 is formed in the upper portion of the via hole 23.

Usually, a barrier film 25 is formed on the inner surface of the via hole 23 and the inner surface of the trench 24 to prevent copper embedded in the via 23 and the trench from diffusing into the interlayer insulating film 21. In the embodiment of the present invention, a thin film of tantalum silicide (TaSi _x ) is formed as a barrier film as will be described later. Before that, as shown in FIG. 2D, the inner surface of the via hole 23 and the inner surface of the trench 24 are formed. Pre-processing is performed. Thereafter, as shown in FIG. 26E, a TaSi _x barrier film 25 is generated while TaF ₅ and SiH ₄ are alternately supplied. After forming the barrier film 25, as shown in FIG. 2 (f), copper is buried in the trench 24 and the via hole 23 to form the copper via 26. As described above, one feature of the present invention is as follows. This is because the barrier film can be generated by performing the pretreatment even under the condition that the barrier film cannot be generated conventionally. However, pretreatment is not essential, and it is possible to generate a barrier film by alternately supplying source gases by adjusting and controlling other deposition conditions such as increasing the pressure of the source gas to be supplied. it can.

  Here, a method of forming a barrier film according to the first embodiment of the present invention will be described.

Both the source gases TaF ₅ and SiH ₄ are difficult to be adsorbed to the silicon substrate, and a TaSi _x thin film cannot be formed on the substrate by alternating supply under normal conditions. Therefore, in the first embodiment of the present invention, subjected to a pretreatment to the surface of the substrate W prior to alternately supply and TaF ₅ and SiH ₄ into the processing chamber 2, and TaF ₅ and SiH ₄ and the processing chamber 2 By alternately increasing the pressure in the processing chamber 2 when supplying to each other, TaF ₅ and SiH ₄ are easily adsorbed to the substrate, and a TaSi _x thin film can be generated.

As described above, in this embodiment, a pretreatment process for supplying NH ₃ to the surface of the substrate W is performed before the film formation process is performed. That is, since TaF ₅ is hardly adsorbed on the surface of the normal substrate W, pretreatment is performed to adsorb TaF ₅ on the surface of the substrate W.

When NH ₃ is supplied to the surface of the substrate W, a large number of NH ₃ adheres to the surface of the substrate W as shown in FIG. When TaF ₅ is supplied in this state, NH ₃ and TaF ₅ on the substrate are combined, and as shown in FIG. 3B, a large number of NH _x -TaF _x is attached on the substrate. This state can be considered as a state in which TaF _x N _y adheres to the surface of the substrate. TaF _x N _y has a property of easily adsorbing SiH ₄ . Therefore, when SiH ₄ is supplied to the substrate in the state shown in FIG. 3B, SiH _x reacts with TaF _x to generate HF and TaSi as shown in FIG. 3C. HF diffuses away from the substrate and into the surrounding gas, while TaSi remains deposited on the substrate. Thereby, TaSi nuclei are generated on the substrate.

Thereafter, by alternately supplying TaF ₅ and SiH ₄ , TaSi nuclei grow and a TaSi _x film can be generated. However, at the stage where SiH ₄ reacts with TaF _{5 as} shown in FIG.

Therefore, in this embodiment, increasing the pressure when supplying the SiH ₄ source gas, i.e., by increasing the partial pressure of SiH _4, to increase the rate of reaction between SiH ₄ and TaF _5, the TaSi _x film The generation time has been shortened. In order to increase the partial pressure of SiH _4, a method of increasing the supply amount of SiH _4, a method to narrow the exhaust from the process chamber 2 during the supply of the SiH ₄ is considered. In this embodiment, the pressure in the processing chamber 2 is controlled to increase by decreasing or closing the opening of the butterfly valve 12 provided at the exhaust port of the processing chamber 2.

FIG. 4 is a time chart showing the source gas supply sequence after the pretreatment. The time chart of FIG. 4 shows a sequence for supplying TaF ₅ , SiH ₄ as source gases and Ar as a carrier gas to the processing chamber, and in addition, a butterfly valve 12 provided at the exhaust port of the processing chamber. The degree of opening is shown. By adjusting the opening of the butterfly valve 12, the exhaust speed can be adjusted, and therefore the pressure in the processing chamber 2 can be adjusted.

In this embodiment, after NH ₃ is supplied and pretreatment is performed, TaF ₅ , SiH ₄ and Ar are supplied to the processing chamber 2 in the sequence shown in FIG. The pretreatment is performed, for example, by supplying NH ₃ and Ar to the processing chamber 2 at a flow rate of 400/100 sccm for 2 seconds, and performing evacuation in the next 2 seconds. After such pretreatment, TaF ₅ and SiH ₄ are alternately supplied in the sequence shown in FIG.

First, TaF ₅ and Ar are supplied to the processing chamber 2 at a flow rate of 0.5 / 100 sccm for 1 second (FIGS. 4A and 4C). At this time, the butterfly valve 12 is fully closed (0 degree) (FIG. 4D). Next, the butterfly valve 12 is fully opened (90 degrees), and TaF ₅ and Ar in the processing chamber 2 are exhausted for 5 seconds (FIG. 4D). When the evacuation is completed, SiH ₄ and Ar are supplied to the processing chamber 2 at a flow rate of 165/100 sccm for 6 seconds (FIGS. 4B and 4C). At this time, the butterfly valve 12 is fully closed (0 degree) (FIG. 4D). After supplying SiH ₄ and Ar for 6 seconds, the butterfly valve 12 is fully opened (90 degrees), and the SiH ₄ , Ar, and reaction products in the processing chamber 2 are evacuated for 5 seconds (FIG. 4D). The above sequence is repeated 100 times, for example, until the TaSi film has a predetermined thickness.

As described above, a result of the alternating supply and TaF5 and SiH4 in the sequence shown in Figure 4 after the pre-treatment by NH3, TaSi _x film begins to be generated at the time of repeated 50 times a sequence shown in FIG. 4, 100 At that time, a TaSi _x film having a thickness of about 200 mm was obtained. Thereafter, a TaSi _x film having a thickness of about 300 mm at the 200th time and about 400 mm at the 300th time was obtained (see FIG. 6 described later).

In this embodiment, NH ₃ is supplied to the substrate surface as a pretreatment. However, as will be described later, an extremely thin TaN film may be formed on the substrate surface. Even in this case, a TaSi film can be formed on the TaN film by the above-described sequence.

As described above, since the source gases TaF ₅ and SiH ₄ are both gases having no polarity and are difficult to be adsorbed on the surface of the substrate, in this embodiment, before the NH ₃ having a dipole moment, By performing the treatment to promote the adsorption of TaF ₅ , a TaSi _x film can be generated. Although NH ₃ is preferably used as the pretreatment gas, the present invention is not limited to this, and another gas having a dipole moment may be used.

In this embodiment, the TaSi _x film can be generated by setting the partial pressure of SiH ₄ during film formation to a certain threshold value or higher, for example, 130 Pa (1 Torr) or higher. The butterfly valve 12 is closed in order to increase the partial pressure of SiH ₄ , but it is not always necessary to close it completely, and the opening degree may be adjusted so that the partial pressure is equal to or higher than the threshold value.

  Next, a film forming method according to the second embodiment of the present invention will be described.

In the second embodiment of the present invention, an ultrathin TaN film is formed on the surface of the substrate W as a pretreatment. Since the TaN film adsorbs the source gas TaF ₅ , if there is a TaN film on the substrate surface, a TaSi _x film can be efficiently generated. A TaN film is preferable as a film generated by such pretreatment. However, the present invention is not limited to this, and any other type of film may be used as long as it has a property of adsorbing a source gas.

  In this embodiment, a TaN film is generated as a pretreatment. The TaN film can be formed by alternately supplying a source gas while heating the substrate (hereinafter referred to as thermal ALD), or by supplying the source gas outside the processing chamber. There is a method (hereinafter referred to as remote plasma enhanced ALD: REALD) in which plasma is supplied alternately.

Hereinafter, in this embodiment, a TaN film is generated by REALD and pre-processed, and then TaF ₅ and SiH ₄ are alternately supplied based on the sequence shown in FIG. 4 to generate a TaSi _x film.

As a pretreatment, the TaN film is formed by REALD as follows. First, the substrate is heated to 400 ° C., and TaF ₅ and Ar are supplied at a flow rate of 0.5 / 100 sccm for 1 second. Thereafter, vacuum exhaust is performed for 3 seconds to exhaust TaF ₅ in the processing chamber 2. Next, plasmaized NH ₃ , H ₂ , and Ar are supplied at a flow rate of 220/220/100 sccm for 6 seconds. Thereafter, evacuation is performed for 1 second. By repeating the above sequence 10 to 20 times, an extremely thin TaN film is generated on the substrate.

In this embodiment, for example, a high-frequency plasma generator is connected to the gas supply pipe 8 in FIG. 1 in order to supply plasmad NH ₃ , H ₂ , Ar.

  After performing the above pretreatment, the sequence shown in FIG. 4 was repeated 100 times at a substrate temperature of 400 ° C. to produce a TaSi film.

  FIG. 5 is a graph showing a pressure profile in the processing chamber 2 when a film is formed by the above-described sequence.

In the above-described sequence, the butterfly valve 12 is closed when TaF ₅ is supplied. However, the butterfly valve 12 is not necessarily closed, and may be opened depending on pretreatment conditions. In the pressure profile shown in FIG. 5, since the time for supplying TaF ₅ is as short as 1 second, the pressure in the processing chamber 2 hardly increases even when the butterfly valve 12 is closed. Subsequently, the butterfly valve 12 is opened, the supply of TaF ₅ and Ar is stopped, and the exhaust is performed for 5 seconds. Thereby, TaF ₅ in the processing chamber that has not been adsorbed to the substrate is almost completely exhausted.

Next, the butterfly valve 12 is closed and the supply of SiH ₄ and Ar is started. Since the source gas is supplied with the butterfly valve 12 closed, that is, without exhausting, the pressure in the processing chamber 2 rises, and in the pressure profile shown in FIG. 5, 156 Pa (1.2 Torr) around the 12th second. ).

Here, in FIG. 5, the pressure when the raw material gas is supplied while the butterfly valve 12 is not closed is shown by a dotted line. In this case, the pressure in the processing chamber 2 hardly increased, and therefore the partial pressure of SiH ₄ was low, so that no TaSi film was generated. According to experiments by the present inventors, a pressure at the time of supplying SiH ₄ of 130 Pa (1 Torr) or more was necessary to produce a TaSi film. The pressure threshold is considered to change depending on the film forming conditions. However, when TaF ₅ and SiH ₄ are alternately supplied to form a TaSix film, at least the partial pressure of SiH ₄ is greater than a certain threshold. It was found that it was necessary.

In the above processing, when the pressure was set to about 1.56 Pa (0.012 Torr) when the TaF ₅ was supplied, a TaSi film having a film thickness of 373 mm and a specific resistance of 225 μΩcm was obtained. Further, when the butterfly valve was closed when TaF ₅ was supplied and the pressure was about 2.73 Pa (0.021 Torr), a TaSi film having a film thickness of 639 mm and a specific resistance of 224 μΩcm was obtained. Therefore, when supplying TaF ₅ , the butterfly valve may be opened or closed, but it has been found that the film forming rate increases when the pressure is increased by closing the butterfly valve.

FIG. 6 is a graph showing the film thickness of a TaSi _x film generated using a method of supplying NH ₃ as a pretreatment and a method of generating a TaN film.

When a TaN film is generated as a pretreatment, the film formation starts immediately after the TaSi _x film generation process is started, and the film thickness is about 700 mm when the sequence is repeated 100 times. Thus, when a TaN film is generated as a pretreatment, it is considered that there is almost no incubation time.

On the other hand, when NH ₃ is supplied as a pretreatment, the generation of the TaSi _x film starts when the sequence is repeated about 50 times after the TaSi _x film generation process is started. Thereafter, the film thickness is about 200 mm at 100 times. Thus, when NH3 is supplied as a pretreatment, a certain amount of incubation time occurs.

As described above, the deposition conditions for the TaSi _x film differ depending on the pretreatment. FIG. 7 is a diagram showing the presence / absence of film formation and the film formation speed when the pretreatment and pressure conditions are changed.

  In FIG. 7, “Close” means closing the butterfly valve 12 to increase the pressure, and “Open” means opening the butterfly valve 12 to perform exhaust. Further, x means that no film is formed, and ○ means that a film is formed. GR is the film growth rate per cycle, and the unit is Å / cycle (cy.).

As can be seen from FIG. 7, no film was formed when no pretreatment was performed. Further, when NH ₃ is supplied as a pretreatment, film formation is possible only when the butterfly valve 12 is closed both when TaF ₅ is supplied and when SiH ₄ is supplied, and the film formation rate is 2.8 liters / cycle. Met.

When a TaN film is formed by REALD as a pretreatment, film formation is possible when the butterfly valve 12 is closed both when TaF ₅ is supplied and when SiH ₄ is supplied, and the film formation rate is 6.8 cm / cycle. Met. Further, even when the butterfly valve 12 was opened at the time of supplying TaF ₅ and the butterfly valve 12 was closed at the time of supplying SiH ₄ , film formation was possible, and the film formation rate was 3.7 mm / cycle.

It is a schematic block diagram of the film-forming apparatus with which the film-forming method by this invention is implemented. It is a figure which shows the process of producing | generating the tantalum silicide thin film used as a barrier film. It is a diagram for explaining the mechanism of the reaction at the time of supplying NH ₃ as pre-treatment. It is a time chart which shows the sequence of the source gas supply after a pretreatment. It is a graph which shows the pressure profile in the processing chamber at the time of forming into a film by the sequence shown in FIG. A method for supplying NH ₃ as pre-treatment is a graph showing the film thickness of TaSi _x film formed by using the method for generating the TaN film. It is a figure which shows the presence or absence of the film-forming at the time of changing pre-processing and pressure conditions, and the film-forming speed | rate.

Explanation of symbols

2 processing chamber 4 mounting table 6 shower head 8 gas supply pipe 10 gas passage 12 butterfly valve 14 turbo molecular pump 16 dry pump 20 copper film 21 interlayer insulating film 22 etch stop film 23 via hole 24 trench 25 barrier film 26 copper via

Claims (9)

A film forming method for generating a thin film by reacting on a substrate while alternately supplying different kinds of source gases,
Before supplying the source gas, a film forming method is characterized in that a pretreatment for promoting the adsorption of the source gas is performed on the surface of the substrate on which the film is formed. The film forming method according to claim 1,
A film forming method comprising supplying a gas having a dipole moment to the surface of the substrate as the pretreatment. The film forming method according to claim 2,
The film forming method, wherein the gas having a dipole moment is NH ₃ . The film forming method according to claim 1,
As the pretreatment, a TaN film is formed on the surface of the substrate. The film forming method according to claim 4,
The TaN film is formed by alternately supplying TaF ₅ and plasmatized NH ₃ . The film forming method according to claim 1,
A film forming method, wherein a pressure of the source gas is set to a predetermined threshold value or more when the source gas is supplied. The film forming method according to claim 1,
The source gas is TaF ₅ and SiH ₄ ,
The pretreatment is a treatment for supplying NH ₃ to the substrate surface,
A film forming method, wherein, when TaF ₅ and SiH ₄ are alternately supplied, a TaSix film is formed on the substrate by setting a partial pressure of TaF ₅ and SiH ₄ to a predetermined threshold value or more. The film forming method according to claim 1,
The source gas is TaF ₅ and SiH ₄ ,
The pretreatment is a treatment for generating a TaN film on the substrate surface,
A film forming method, wherein, when TaF ₅ and SiH ₄ are alternately supplied, a TaSix film is formed on the substrate by setting a partial pressure of SiH ₄ to a predetermined threshold value or more. The film forming method according to claim 8,
A film forming method, wherein when TaF ₅ and SiH ₄ are alternately supplied, a partial pressure of TaF ₅ is set to a predetermined threshold value or more.

Images