JP2000077357A - Formation of wiring layer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a method for forming a wiring layer, which can suppress formation of an abnormal film caused by tungsten (W). SOLUTION: Since abnormal W film formation results from the fact that a growth rate of a W film based on W nuclei initially formed is faster than a W nucleus formation rate on a TiN film, the W nucleus formation rate is set to be faster than the growth rate of the W film. More concretely, at a nucleus formation stage, the W film formation is carried out by a CVD process using WF6-SiH4-based gas, at which time it is controlled that the film formation based on reduction of H2 gas is not carried. As a result, before abnormal film formation takes place in W nuclei, W nuclei 16 can be uniformly formed on the entire surface of the TiN film 13 as an underlying adhesion layer. Thereafter, film formation is carried out by a CVD process using an WF6-H2-based gas to form a W film 15 having a uniform thickness all over the entire film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wiring layer forming method for forming a wiring layer of a semiconductor device, and more particularly to a blanket CVD for forming a film using tungsten (W).
The present invention relates to a method for forming a wiring layer using a (Chemical Vapor Deposition) method.

[0002]

2. Description of the Related Art In recent years, with the progress of high integration and high performance of semiconductor devices, the ratio of wiring portions on a device chip is increasing. In order to prevent a significant increase in chip area due to this, a technique of multilayer wiring is now indispensable. As a method of forming a wiring, various techniques have been proposed in which a high melting point metal is buried in a contact hole (contact hole) by a CVD method instead of the conventional technique of forming a metal thin film such as aluminum (Al) by a sputtering method. ing. Examples of the high melting point metal include tungsten (W), molybdenum (Mo), and tantalum (Ta).

[0003] Of these, the tungsten (W) film formed by the CVD method is excellent in step coverage,
It is widely used as a material for filling connection holes between wirings. As a method of forming the W film, a method of forming the W film only in the connection hole (selective WCVD method) and a method of forming the W film on the entire
It is roughly classified into a method of forming a film and leaving a W film only in the connection hole by etch-back (blanket WCVD method). The former is simple in process, but the latter is generally used because it is difficult to secure selectivity and difficult to apply to connection holes having different depths.

[0004] In the blanket WCVD method,
Since the adhesion between the W film and the insulating film is poor, the formation of an adhesion layer is indispensable. However, a TiN (titanium nitride) film is generally formed of a titanium nitride (TiN) film because of its performance as a barrier metal and ease of etching back. It is used as And this Ti
When an N film is used as an adhesion layer, a method of forming a film using a WF ₆ (tungsten hexafluoride) -H ₂ (hydrogen) system (hereinafter, referred to as a “film”)
Called with H ₂ reduction method) it is said to exhibit good step coverage.

[0005]

However, the above-described H ₂ reduction method has a problem that the thickness of the W film cannot be uniform. As an improvement measure, an initial film (hereinafter, referred to as a nucleus) is formed using a WF ₆ (tungsten hexafluoride) -SiH ₄ (silane) system, and then W is grown from the W nucleus by the H ₂ reduction method to form W. A method of filling a connection hole with a film has been proposed and widely used. Note that WF ₆ -Si
Hereinafter, a method using an H ₄ -based gas is referred to as a SiH ₄ reduction method.

As nucleation conditions in the SiH ₄ reduction method, H ₂ is added in addition to the above-mentioned WF ₆ and SiH ₄ because of good step coverage. However, in this case, depending on the conditions when the adhesion layer (TiN film) is formed, so-called W abnormal film formation in which W excessively grows locally may occur. Therefore, in the conventional SiH ₄ reduction method, if such W abnormal film formation is not removed in an etch-back step in a later step, there is a problem that a short circuit between wirings is caused and a production yield is reduced.

The present invention has been made in view of the above problems, and has as its object to suppress the occurrence of abnormal film formation, prevent the occurrence of short circuit between wirings, and improve the manufacturing yield of devices. An object of the present invention is to provide a method for forming a wiring layer.

[0008]

The wiring layer forming method according to the present invention comprises a first step of forming a large number of nuclei of a refractory metal material on the surface of an underlayer, and a step of forming a high nucleus from the nuclei formed in the first step. The method includes a second step of forming a wiring layer by growing a film of a melting point metal material, and in the first step, the rate at which a nucleus of the high melting point metal material is formed on the surface of the underlayer is determined by the high melting point metal in the nucleus. The film is formed under conditions that are faster than the growth rate of the material. Specifically, a gas (H ₂₎ that causes the formation of nuclei such as W on the surface of the underlayer to be slower than the growth rate of W in the nuclei.
, Etc.), or the surface treatment of the underlayer is performed before starting the film formation.
As a specific method of the surface treatment, the wafer on which the adhesion layer is formed is placed in an atmosphere of WF ₆ and an inert gas in the range of 1 to 1.
There is a method of exposing for 0 second or performing a plasma treatment with H _{2 on} the underlying layer.

[0009] a method for forming a wiring layer according to the invention, in particular, a high melting point metal material is W (tungsten), as a deposition method of the W (tungsten), WF ₆ (tungsten hexafluoride) -SiH ₄ (silane ) CV using system gas
This is effective when the method D is used.

In the wiring layer forming method according to the present invention, in the first step of forming a nucleus, the speed at which the nucleus of the refractory metal material is formed on the surface of the underlayer is higher than the growth rate of the refractory metal material at the nucleus. The nuclei are uniformly formed on the entire surface of the underlayer while suppressing the occurrence of abnormal film formation, and thereafter, a stable film is formed based on these nuclei.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Before describing the embodiments of the present invention, the basic principle of the present invention will be described. FIG. 4 shows the mechanism by which the above-mentioned W abnormal film formation occurs. In this figure, a Ti film 103 as a barrier metal and a T film as an adhesion layer are formed on an interlayer insulating film 102 such as silicon oxide (SiO ₂ ) on a silicon substrate 101.
After each of the stacked films of the iN film 104 is formed by the CVD method, Ti is formed by the SiH ₄ reduction method to which H ₂ gas is added.
The state when the W film is formed on the N film 104 is shown. In this case, it is desirable that a W nucleus is originally formed by a WF ₆ -SiH ₄ -based gas, and then a film is grown from the W nucleus by an H ₂ reduction method to form a W film.

On the TiN film 14 serving as an adhesion layer, WF ₆
The reaction between WF ₆ / SiH ₄ proceeds faster than the reaction between / H ₂ and W nuclei 105 are formed locally. However, as is clear from FIG. 5 showing the relationship between the film formation time and the film thickness in the W nucleus in the case of the H ₂ reduction method,
In the W nucleus 105, the reaction between WF ₆ / H ₂ proceeds relatively easily. That is, in the W nucleus 105 formed earlier by the reaction between WF ₆ / SiH ₄ , a reaction between WF ₆ / H ₂ occurs. Then, the growth rate is faster than the rate at which the W nuclei 105 are formed on the TiN film 14, and the growth of the W nuclei 105 formed initially is promoted, resulting in the W abnormal film formation 106.

The present invention has been made by examining the mechanism of such an abnormal film formation. That is, in the present invention, the W abnormal film formation as described above is performed by using the initially formed W
Taking into account that the growth rate of the W film at the nucleus is higher than that of the W nucleus on the adhesion layer,
An attempt is made to suppress the occurrence of abnormal film formation by performing nucleation under the condition that the nucleation rate is higher than the growth rate of the W film at the W nucleus.

As a countermeasure, first, a film is formed on the TiN film by the H ₂ reduction method, in which the growth rate of the W nucleus (film) is high despite the extremely low rate of W nucleation, Is not applied. FIG. 2 shows the transition (the relationship between time and film thickness) of W film formation on the TiN film depending on the presence or absence of H ₂ gas at the stage of forming W nuclei. As is clear from this figure, in the nucleus formation stage, regardless of the presence or absence of the H ₂ gas, the time T until the film formation is started (hereinafter, the incubation time (incu
After the incubation time T has passed and the film formation has started, the growth rate of the W film at the W nucleus is lower than the W nucleation rate due to the presence of H ₂ gas. Be faster. This causes abnormal film formation. Therefore, in the nucleation stage, it is important to eliminate such an H ₂ reduction reaction in order to suppress occurrence of abnormal film formation. That is, in the nucleation stage, the H ₂ reduction reaction is inhibited to suppress the film growth on the W nuclei formed initially, and the W nuclei are formed uniformly over the entire surface of the underlayer, thereby forming an abnormal film. The occurrence of the phenomenon can be prevented.

As another measure, increasing the nucleation speed higher than in the past is effective in suppressing the occurrence of abnormal film formation. By increasing the nucleation rate, the W nucleus is formed before the film growth on the W nucleus proceeds, and as a result,
Uniform nuclei are formed on the entire surface of the TiN film, and thereafter, stable film formation can be performed.

Hereinafter, specific embodiments will be described.

[First Embodiment] FIG. 1 shows a first embodiment of the present invention.
1 illustrates an example of a wiring layer to which the embodiment is applied. This figure shows that the blanket WCVD method
This shows a step in the process of embedding a W film in a contact hole (contact hole) 12 a formed in an interlayer insulating film 12 such as SiO ₂ on a silicon substrate 11. In this step, the Ti film 13 as a barrier metal and the TiN film 1 as an adhesion layer including the inside of the connection hole 12a on the silicon substrate 11 are formed.
4 are formed by the CVD method. Then, the W film 1 is formed on the TiN film 14 by the SiH ₄ reduction method.
5 is formed, and this W film 15 is formed of TiN film 14 and T
Via i-film 13, it is electrically connected to impurity layer 11 a formed in silicon substrate 11 in advance.

FIGS. 2A and 2B show W of the wiring structure of FIG.
The state at the time of film formation is shown by enlarging a partial region. FIG. 2A shows a first step for forming a large number of W nuclei on the surface of the underlayer (TiN film 14), and FIG.
Shows a second step of forming a wiring layer by growing a W film from a nucleus formed in the first step.

In this embodiment mode, in the first stage of FIG. 2A, W is formed by a CVD method using a WF ₆ (tungsten hexafluoride) -SiH ₄ (silane) -based gas. A gas that, for said reasons, slows the formation of W nuclei relative to the growth rate of W in the nuclei;
That is, the process is performed under the condition not using H ₂ gas. Therefore, at this stage, as shown in FIG. 2A, the surface of the TiN film 13 has
Before the abnormal film formation occurs in Step 6, the W nuclei 16 are formed uniformly over the entire surface. After that, a film is formed by a CVD method using a WF ₆ -H ₂ based gas, thereby forming a W film 15 having a uniform film thickness over the whole as shown in FIG. . Therefore, in the device manufactured according to the present embodiment, the problem of short circuit between wirings caused by abnormal film formation unlike the related art does not occur, and the manufacturing yield is improved.

The specific conditions of this embodiment include, for example, the following conditions.

WF ₆ flow rate 20 sccm SiH ₄ flow rate 10 sccm N ₂ flow rate 1000 sccm Ar flow rate 1000 sccm Pressure 4.5 Torr Temperature 450 ° C.

[Second Embodiment] Next, a second embodiment will be described. In the first embodiment, the H ₂ gas is not used in the nucleation stage, so that the film growth on the initially formed W nucleus is suppressed. However, in the present embodiment, before the film formation, By performing the surface treatment of the underlayer, the nucleus formation speed is made higher than before.
Thereby, occurrence of abnormal film formation can be suppressed.
By increasing the nucleation rate, the W nuclei are formed before the film growth on the W nuclei progresses. As a result, uniform nuclei are formed on the entire surface of the TiN film, and stable film formation is achieved. It can be performed.

In the present embodiment, Ti is used as the surface treatment.
The wafer on which the adhesion layer made of N (titanium nitride) is formed is exposed to an atmosphere of WF ₆ and an inert gas for 1 to 10 seconds. Specifically, for example, the following conditions may be satisfied.

Time 1 to 10 seconds WF ₆ flow rate 20 sccm Ar flow rate 1000 sccm Pressure 4.5 Torr Temperature 450 ° C.

By performing the surface treatment under such conditions, W
Does not occur, but the incubation time T (see FIG. 3) for the W film formation is reduced. That is, it is presumed that the surface modification treatment of the TiN film is performed by flowing only WF ₆ prior to the nucleation, thereby increasing the W nucleation rate. If the time for flowing only WF ₆ is long, there is a concern that the TiN film is peeled off or the substrate is eroded by WF ₆ in the contact hole. Therefore, it is considered that 10 seconds is the limit as the time under the above conditions.

[Third Embodiment] In the present embodiment, similar to the second embodiment, the nucleus formation speed is made higher than in the past by performing the surface treatment of the underlayer before film formation. Things. Specifically, as a surface treatment, for example, a plasma treatment with H ₂ is performed on the adhesion layer made of TiN (titanium nitride) under the following conditions. According to such a method, as in the second embodiment, the nucleation speed is increased, and occurrence of abnormal film formation can be suppressed.

Time 20 seconds H ₂ flow rate 1000 sccm Pressure 4.5 Torr RF power 400 W Temperature 450 ° C.

Next, specific examples corresponding to the above embodiments will be described.

(First Embodiment) In the nucleation stage, H
₂ Film formation was performed under the following conditions without using the reduction reaction. At the same time, a film was formed under conventional conditions as a comparative example.

WF ₆ flow 20 sccm SiH ₄ flow 10 sccm N ₂ flow 1000 sccm Ar flow 1000 sccm Pressure 4.5 Torr Temperature 450 ° C.

[Conventional conditions] WF ₆ flow rate 20 sccm SiH ₄ flow rate 10 sccm H ₂ flow rate 1000 sccm Ar flow rate 1000 sccm Pressure 4.5 Torr Temperature 450 ° C.

As a result, no abnormal film formation was observed under the conditions of the first embodiment, although an abnormal film formation phenomenon was confirmed under the conventional conditions. Therefore, it was confirmed that it was effective to suppress the film growth at the W nucleus due to the H ₂ reduction reaction under the condition where the W nucleus formation rate was low.

(Second Embodiment) Prior to the film formation under the conventional conditions described as a comparative example in the first embodiment, the following processing was performed, and as a result, abnormal film formation was able to be suppressed.

Time 3 seconds WF ₆ flow rate 20 sccm Ar flow rate 1000 sccm pressure 4.5 Torr temperature 450 ° C.

(Third Embodiment) As a method of improving the W nucleus formation speed, the following process (H ₂ plasma process) is performed prior to the film formation under the above-mentioned conventional conditions, thereby forming an abnormal film formation. Could be deterred.

Time 20 seconds H ₂ flow 1000 sccm Pressure 4.5 Torr RF power 400 W Temperature 450 ° C.

Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above-described embodiment and can be variously modified. For example, although the description has been made using W as the wiring material, the present invention is also applicable to other high melting point metal materials such as Co. Further, in the nucleation step it has been described using H ₂ gas as the gas conditions to promote film growth in the nucleus, as H ₂ gas, W is in contact layer such as TiN
As long as the reaction with F ₆ hardly occurs and the W nucleus reacts with WF ₆ , any other gas can be used.

[0039]

As described above, according to the wiring layer forming method of the present invention, in the nucleus forming step, the speed at which the nucleus of the high melting point metal material is formed on the surface of the underlayer is increased. The film formation is performed under conditions that are faster than the growth rate of GaN, so abnormal film formation is suppressed, and nuclei can be formed uniformly over the entire surface of the underlayer, thereby reducing short-circuits between wirings. This has the effect of improving the manufacturing yield.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a state during a manufacturing process of a buried wiring layer to which a wiring layer forming method of the present invention is applied.

FIG. 2 is a cross-sectional view for explaining a nucleus forming step of the wiring structure of FIG. 1;

FIG. 3 is a characteristic diagram showing a relationship between a film formation time and a film thickness of a W film in order to explain a transition of a W film depending on the presence or absence of H ₂ in a nucleation stage.

FIG. 4 is a cross-sectional view for explaining a process of occurrence of W abnormal film formation by a conventional method.

FIG. 5 is a characteristic diagram showing the relationship between the film formation time and the thickness of the W film in order to explain the progress of the reduction reaction of H ₂ on the W film.

[Explanation of symbols]

11 silicon substrate, 12 interlayer insulating film, 13 Ti
Film, 14 ... TiN film, 15 ... W nucleus, 16 ... W film

Claims (10)

[Claims] A first step of forming a number of nuclei of a high melting point metal material on the surface of an underlayer; and forming a wiring layer by growing a film of the high melting point metal material from the nuclei formed in the first step. In the method for forming a wiring layer including a second step, the rate at which the nucleus of the high melting point metal material is formed on the surface of the underlayer in the first step is higher than the growth rate of the high melting point metal material at the nucleus. A method for forming a wiring layer, wherein film formation is performed under conditions that speed up the process. 2. The method according to claim 1, wherein the refractory metal material is W (tungsten). 3. In the first step, the W (tungsten) film is formed by WF ₆ (tungsten hexafluoride).
-SiH ₄ (silane) based wiring layer forming method according to claim 2, characterized in that the chemical vapor deposition method using gas. 4. The film formation is performed under conditions that do not use a gas that causes the formation of W (tungsten) nuclei on the surface of the underlayer to be slower than the growth rate of W (tungsten) in the nuclei. Item 4. The wiring layer forming method according to Item 3. 5. The method according to claim 4, wherein the gas is a hydrogen (H ₂ ) gas. 6. The method according to claim 2, wherein a surface treatment of the underlayer is performed before the film formation is started. 7. The method according to claim 6, wherein the underlayer is an adhesion layer made of TiN (titanium nitride). 8. As the surface treatment, a wafer on which an adhesion layer made of TiN (titanium nitride) is formed is placed in an atmosphere of WF ₆ (tungsten hexafluoride) and an inert gas.
The method according to claim 7, wherein the exposure is performed for 10 to 10 seconds. As claimed in claim 9, wherein said surface treatment, the wafer adhesion layer is formed consisting of TiN (titanium nitride), H ₂
8. The method for forming a wiring layer according to claim 7, wherein a plasma treatment with (hydrogen) is performed. 10. In the second step, the tungsten (W) is formed by a chemical vapor deposition method using a WF ₆ (tungsten hexafluoride) -H ₂ (hydrogen) -based gas. 3. The method for forming a wiring layer according to claim 2, wherein: