JPH09246212A - Formation of barrier layer and semiconductor device with barrier layer formed thereby - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfy various demands such as step coverage, a low chrome content and a low film-forming temperature by a method wherein mixed has containing metal halogen and hydrogen is used and a metal film is formed by a plasma CVD method followed by performing a nitriding treatment on the metal film for being converted into a metal nitriding film. SOLUTION: After forming a metal film 4 on the substrates 1, 2 by using a mixed gas containing a metal halogenide and hydrogen and by a plasma CVD method, the metal film 4 is provided with a nitriding treatment for being converted into a metal nitride film 5. For instance, an interlayer insulating film 2 is formed on a lower layer conductive material layer 1 consisting of a semiconductor substrate and a connecting hole 3 is opened followed by performing plasma cleaning and forming a metal film 4 made of Ti. Next, plasma nitriding of the metal film 4 is performance by using mixed gas of N2 /H2 /Ar so as form a metal nitride film 5 consisting of TiN. Later, when necessary, a forming process of the metal film 4 and a nitriding process are repeated so as to form metal nitride film 5 with a desired thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a barrier layer used in a manufacturing process of a semiconductor device, and a semiconductor device having a barrier layer formed by the method. More specifically, the barrier layer formed is good. The present invention relates to a method for forming a barrier layer having excellent step coverage and a small content of residual halogen element in the barrier layer, and a semiconductor device having the barrier layer formed thereby.

[0002]

2. Description of the Related Art As the design rules of semiconductor devices such as LSI have been miniaturized from half micron to quarter micron or lower, and a multi-layer wiring structure has been frequently used, connection holes for connecting wiring layers have been formed. The aspect ratio also tends to increase. For example, in a semiconductor device of 0.18 μm rule, the opening diameter of the connection hole is 0.2 μm.
On the other hand, since the thickness of the interlayer insulating film is about 1.0 μm, the aspect ratio reaches 5. In order to achieve a highly reliable multilayer wiring structure with such fine and high aspect ratio contact holes, Ti for ohmic contact is provided in the contact holes.
Layer, etc., and Ti that is a barrier layer that prevents the diffusion of wiring materials.
A method of forming an upper layer wiring and a contact plug by high-temperature sputtering of an Al-based metal or W CVD after forming a thin and conformal N layer and the like is being adopted.

Usually, in order to form a Ti layer or a TiN layer, sputtering using a bulk Ti metal as a target material or reactive sputtering is adopted. Above all, attention has been focused on, for example, collimated sputtering in which the perpendicular incidence component of sputtered particles is increased and long-distance sputtering in which the distance between the target and the substrate is increased, which is disclosed in, for example, JP-A-6-140359. According to these sputtering methods, advantages such as reduction of contact resistance and improvement of barrier properties have been confirmed as compared with conventional sputtering methods. However, since these sputtering methods are methods in which the vertically incident component of the sputtered particles on the substrate to be processed is increased, the thickness of the film may be formed on the shoulder portion of a fine connection hole with a large aspect ratio and the periphery of the bottom portion of the connection hole. However, an extremely thin portion is inevitably formed. In this case, when blanket CVD of W or the like is performed in the next step, WF _{6 as a} raw material gas invades from a portion having a small film thickness, erosion of a base material layer, abnormal growth of W, Ti layer or Ti layer.
Inconvenience such as peeling of the N layer occurs.

In order to solve the problem of step coverage of the barrier layer, which cannot be solved by these sputtering methods including the collimation method, etc., a conformal Ti film formed by the CVD method utilizing a chemical reaction on the surface of the substrate to be processed is used.
A method for forming a Ti-based material layer such as a layer or a TiN layer is expected.

[0005] Currently proposed CVD of Ti-based material layer
The method is roughly classified into a method using an inorganic metal halide such as TiCl ₄ reported in the 44th Symposium on Semiconductor / Integrated Circuit Technology, p. 31 (1993), Proc. 11th. Int. IEEE V
TD reported in MIC, p440 (1994), etc.
MAT (Tetrakis (dimethylamino) titanium) and TDEA
There are two types: a method using an organometallic compound such as T (Tetrakis (diethylamino) titanium). Either method has the advantage that the Ti layer formation by H ₂ reduction and the TiN layer formation by addition of a nitriding agent such as NH ₃ can be continuously performed in the same CVD apparatus. However, the method using an organometallic compound tends to increase the sheet resistance due to carbon remaining in the Ti layer or the TiN layer, and requires a special source gas, so an inorganic metal halogen such as TiCl ₄ is required. The CVD method using a compound is more common.

By the way, TiC which is a metal halide
In the CVD method using an inorganic reaction system of l ₄ and NH ₃ , it is possible to form a conformal TiN layer by utilizing surface reaction, but in order to realize this surface reaction, TiCl ₄ It is necessary to supply TiCl ₄ in a sufficient amount so that the CVD reaction is not rate-controlled in the supply.

[0007]

[Problems to be Solved by the Invention] However, TiC
When the supply amount of l ₄ , that is, the partial pressure of TiCl ₄ gas in the source gas is increased, the amount of residual chlorine in the deposited TiN layer also increases. When the residual chlorine in the TiN layer exceeds 1 mol%,
It is known that corrosion of the Al-based metal wiring in contact with the TiN layer may occur.

Therefore, Ti in contact with the Al-based metal wiring
It is necessary to control the residual chlorine content in the TiN layer and the TiN layer to 1% or less. For this purpose, a film formation temperature of 650 ° C or higher is required, and the lower layer wiring becomes a via contact on the Al-based metal wiring. Not applicable.

Several proposals have been made so far as methods for reducing the amount of residual chlorine in the TiN layer and the film forming temperature. As one of them, there is a method of using a reducing organic nitriding agent such as methylhydrazine. According to this method of adding a large amount of methylhydrazine, it is possible to achieve both purposes, but since the reaction takes a feed-rate-determining form, the step coverage in the connection hole having a high aspect ratio is significantly deteriorated. .

As another method, ECR (Select
There is a trend to adopt a plasma CVD apparatus having a high-density plasma generation source such as ron cyclotron resonance plasma, helicon wave plasma, or inductively coupled plasma. CVD using high density plasma
Also in the method, it is necessary to supply TiCl ₄ sufficiently, that is, to set the hydrogen flow rate relatively low in order to give priority to the surface reaction and obtain good step coverage. Plasma CV under such a low hydrogen flow ratio condition
Problems associated with D will be described with reference to FIGS.

FIGS. 4A to 4D show Ti as a source gas.
ECR using Cl ₄ / H ₂ / N ₂ / Ar mixed gas
By the plasma CVD method, a metal nitride film 5 made of a TiN film is formed on a substrate to be processed having a connection hole (via hole) 3 opened in an interlayer insulating film 2 on a lower conductive material layer 1 made of an Al-based metal wiring. It is a schematic sectional drawing of the connection hole 3 part at the time of forming. The plasma CVD conditions at this time are as follows. TiCl ₄ 20 sccm H ₂ 26 to 75 sccm N ₂ 8 sccm Ar 170 sccm Gas pressure 0.4 Pa Microwave power 2.8 kW (2.45 GHz) Substrate stage temperature 460 ° C. FIGS. 4 (a) to 4 (d) are The H ₂ flow rates correspond to 26, 40, 50 and 75 sccm, respectively. In each figure, the bottom coverage, that is, the ratio of the film thickness of the metal nitride film 5 at the bottom of the contact hole 3 to the film thickness of the metal nitride film 5 above the interlayer insulating film 2 is also shown. In this case, bottom coverage is a concept equivalent to step coverage. As is clear from the figure, when the hydrogen flow rate is high, the bottom coverage deteriorates, and in particular, it is understood that the metal nitride film 5 having a rough morphology like an eaves grows at the opening of the connection hole 3.

The reason for this is considered as follows. That is, TiCl _x (x is a natural number of 1 to 3) -based reactive species having a low chlorine component generated by reducing TiCl ₄ by a large amount of hydrogen plasma has extremely high activity and high reactivity. Therefore, this reactive species is immediately nitrided by the nitrogen plasma when the nitriding gas is introduced, and the deposition proceeds mainly on the opening of the connection hole 3 and on the interlayer insulating film 2, and the depletion at the bottom of the connection hole 3 occurs. Position rate decreases. Therefore, in order to prevent the deterioration of the step coverage, the reduction reaction by hydrogen plasma is suppressed, a large amount of TiCl _x- based reactive species having a high chlorine component and a low reaction activity is generated, and these reactive species reach the bottom of the connection hole. It is necessary to let However, such a method cannot take advantage of the advantage of promoting the reduction of TiCl ₄ by high-density plasma,
The effect of reducing the chlorine content is small.

The present invention is proposed in view of the above-mentioned problems of the prior art. That is, an object of the present invention is to provide a barrier layer forming method capable of satisfying various requirements of step coverage, low chlorine content and low film forming temperature, and a highly reliable and highly integrated semiconductor device having the barrier layer formed thereby. Is to provide.

[0014]

A method for forming a barrier layer of the present invention is proposed to solve the above-mentioned problems, and a mixed gas containing a metal halide and hydrogen is used to perform treatment by a plasma CVD method. The method is characterized by including a step of forming a metal film on a substrate and a step of subjecting the metal film to a nitriding treatment to convert it into a metal nitride film.

In a preferred embodiment of the method for forming a barrier layer of the present invention, the step of forming a metal film and the step of converting the metal film into a metal nitride film are repeated a plurality of times. Further, in the step of forming the metal film, it is desirable that the surface of the substrate to be processed is formed while being uniformly terminated by the hydrogen active species. The nitriding treatment in the present invention is performed by using N ₂ ,
Plasma nitriding or thermal nitriding using at least one nitriding agent selected from the group consisting of NH ₃ , N ₂ H ₄ and its derivatives, alkylamine compounds and the like is preferable. In the present invention, it is desirable that both the step of forming the metal film and the step of converting the metal film into the metal nitride film are performed at a temperature of 500 ° C. or lower.

The semiconductor device of the present invention is characterized by having a barrier layer formed by the method for forming a barrier layer described above.

Next, the operation will be described. The gist of the method for forming a barrier layer of the present invention is, on a substrate on which a via hole, a contact hole or the like is formed, having a smooth morphology and good step coverage, and a metal film having a low chlorine content, for example, A Ti film is formed in advance and is converted into a metal nitride film, for example, a TiN film by nitriding the Ti film, and a TiN film having a desired thickness is formed by repeating this method a plurality of times. .

Therefore, since the nitriding gas is not introduced in the plasma CVD process, TiCl containing a large amount of chlorine is used.
_It is not necessary to improve the step coverage by using _x- based reactive species, and TiCl is highly active with sufficient elimination of chlorine components.
_{Since the x-} type reactive species reach the bottom of the contact hole to form a metal film, and then the metal film is converted to a metal nitride film by nitriding treatment, both step coverage and low chlorine content can be achieved. At this time, since the formed metal nitride film of TiN or the like has a high gas barrier property, there is a limit to the layer thickness that can be nitrided especially at a nitriding temperature of 500 ° C. or less, and the nitriding time, the type of the nitriding agent, and the plasma density are also limited. However, the upper limit is, for example, a thickness of about 10 nm. Therefore, for example, in order to form a barrier layer having a thickness of 10 nm or more, the metal film forming step and the nitriding step may be repeated a plurality of times.

As a plasma CVD method for forming a metal film by allowing TiCl _x -based reactive species from which chlorine components have been sufficiently desorbed to reach the bottom of the contact hole, the present inventor has previously filed Japanese Patent Application No. 8-1.
The technique disclosed in the 1272 specification can be used. In this method, when a metal film is formed by a plasma CVD method using a mixed gas of a metal halide and hydrogen, the mixing ratio of hydrogen is set to a mixing ratio at which the deposition rate of the metal film is saturated, The surface of the substrate to be processed is uniformly terminated by the active hydrogen species.

By setting the plasma CVD step and the nitriding step of the metal film to 500 ° C. or less, it is possible to apply to a device structure using Al-based metal wiring as the lower structure of the barrier layer.

By adopting the barrier layer forming method as described above, it is possible to provide a highly reliable semiconductor device having a high degree of integration.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below with reference to the accompanying drawings. The following examples are for plasma CVD
ECR plasma CVD equipment was adopted as the equipment, and TiC
In this example, a Ti metal film is formed using a mixed gas of l ₄ / H ₂ / Ar and then nitriding is performed. In the drawings used for the description of the following embodiments, the same components as those in FIG. 4 referred to in the description of the conventional example are designated by the same reference numerals.

Embodiment 1 This embodiment is an example in which a metal film forming step and a plasma nitriding step are repeated a plurality of times to form a metal nitride film having a predetermined thickness. It will be described with reference to FIG.

An interlayer insulating film 2 made of SiO ₂ is formed to a thickness of, for example, 1.0 μm on a lower conductive material layer 1 made of a semiconductor substrate made of silicon or the like on which an impurity diffusion layer (not shown) or the like is formed, A contact hole (contact hole) 3 facing the impurity diffusion layer is opened. In this embodiment, the connection hole 3 has an opening diameter of, for example, 0.25 μm and an aspect ratio of 4.0. After removing the natural oxide film at the bottom of the contact hole 3 with a dilute hydrofluoric acid solution, the substrate to be processed is subjected to ECR plasma CVD.
It is set on the substrate stage of the apparatus and plasma cleaning is performed with a reducing mixed gas such as H ₂ / Ar or H ₂ / Ar / N ₂ .

Next, in the same ECR plasma CVD apparatus, a metal film 4 made of Ti is formed to a thickness of 5 nm as an example under the following plasma CVD conditions. FIG. 1A shows a schematic cross-sectional view of the substrate to be processed in the vicinity of the connection hole 3 after the metal film 4 is formed. TiCl ₄ 3 sccm H ₂ 100 to 300 sccm Ar 170 sccm Gas pressure 0.4 to 2.0 Pa Microwave power 2.0 to 2.8 kW (2.45 GHz) Substrate stage temperature 300 to 460 ° C. The film formation conditions are such that smooth morphology, low chlorine content of 1% or less and good bottom coverage are obtained so that the surface of the substrate to be processed is uniformly terminated by hydrogen active species, that is, TiCl ₄ flow rate is sufficient. Excessive H
_{2 Use} flow rate conditions. This plasma CVD condition can be monitored by monitoring changes in the emission spectrum intensity of hydrogen atom beams and chlorine from plasma. This method is disclosed in Japanese Patent Application No. 7-33.
It was proposed as the specification of No. 6309. In this example, the bottom coverage of the metal film 4 was 50% and the chlorine content was 0.2 mol%.

Subsequently, the same ECR plasma CVD apparatus is used to plasma-nitrid the metal film 4 under the following conditions. N ₂ 100 to 300 sccm H ₂ 0 to 300 sccm Ar 10 to 100 sccm Gas pressure 0.4 to 2.0 Pa Microwave power 2.0 to 2.8 kW (2.45 GHz) Substrate stage temperature 300 to 460 ° C. The standard heat of formation of the nitriding reaction between the nitrogen active species (N ^* and N ⁺ ) generated by the dissociation of N ₂ in plasma and Ti metal is -1.
The system is an exothermic reaction with 84.4 kcal / mol, which is a system in which the reaction easily proceeds. In addition, in this example, ECR
High-density plasma treatment with plasma is possible.
As shown in (b), high throughput nitriding with a large amount of nitrogen active species (N ^* and N ⁺ ) is possible.

As a result, as shown in FIG. 1 (c), TiN
A metal nitride film 5 made of is formed. The thickness of the metal nitride film 5 was also about 5 nm, the bottom coverage was 50%, and the chlorine content was 0.2 mol% or less. Figure 2 below
As shown in (d) to (f), the metal film 4 forming step and the nitriding step are repeated as necessary to form the metal film nitride film 5 having a desired thickness. In this example, the metal nitride film 5 having a thickness of 20 nm was formed by repeating each four times. Since this repetition is performed in the same ECR plasma CVD apparatus, there is little risk of a decrease in throughput. According to the present embodiment, the step of coverage, morphology, low chlorine content and high throughput of barrier layer can be formed by continuously performing the plasma CVD of the metal film by the ECR plasma CVD apparatus and the subsequent plasma nitriding. .

Embodiment 2 This embodiment is an example in which a metal film forming step and a thermal nitriding step are repeated a plurality of times to form a metal nitride film having a predetermined thickness. Will be described with reference to.

In this embodiment, the steps up to the step of forming the metal film 4 shown in FIG. 1 (a) are the same as those in the first embodiment, and a duplicate description will be omitted. In this example, an ECR plasma CVD apparatus and a thermal nitriding apparatus connected by a gate valve were used as a film forming apparatus. As a heat source of the thermal nitriding device, any heating means such as heater heating, lamp heating or high frequency induction heating can be adopted.

After forming the metal film 4, ECR plasma CVD
The substrate to be processed is transferred to a thermal nitriding apparatus connected to the apparatus without being exposed to the air, and the metal film 4 is nitrided under the following thermal nitriding conditions as an example. NH ₃ 10 to 1000 sccm H ₂ 0 to 100 sccm Ar 0 to 100 sccm Gas pressure 0.4 to 100 Pa Substrate stage temperature 300 to 460 ° C. In the thermal nitriding step shown in FIG. 1B, Ti + NH ₃ → Ti
Nitriding proceeds according to the reaction formula of N + 3 / 2H ₂ . Therefore, most of the nitrogen active species (N ^* and N ⁺ ) in this case correspond to NH ₃ molecules whose kinetic energy such as translation, rotation and vibration is increased by heating. Note that excitation light irradiation such as a low pressure mercury lamp may be performed simultaneously with heating.

When N ₂ is used as the nitriding agent, the standard heat of formation of TiN by thermal nitriding is -80.4 kcal / mol.
The reaction is an exothermic reaction, and the reaction is relatively easy to proceed. However, when NH ₃ or N ₂ H ₄ is adopted as in this embodiment, thermal nitriding is further facilitated. This state is represented by the Gibbs free energy ΔG of Ti and various nitriding agents shown in FIG.
It is clear from the data.

As a result, as shown in FIG. 1 (c), TiN
A metal nitride film 5 made of is formed. The thickness of the metal nitride film 5 was also about 5 nm, the bottom coverage was 50%, and the chlorine content was 0.2 mol% or less. Figure 2 below
As shown in (d) to (f), the metal film 4 forming step and the thermal nitriding step are repeated as necessary to form the metal film nitride film 5 having a desired thickness. In this example, the metal nitride film 5 having a thickness of 20 nm was formed by repeating each four times. Since this repetition is performed in the continuous processing apparatus, there is relatively little risk of a decrease in throughput. According to this embodiment, the ECR
Plasma CVD of a metal film by a plasma CVD apparatus,
Successive thermal nitridation can be performed continuously to form a barrier layer with step coverage, morphology, low chlorine content and high throughput.

Although the method of forming the barrier layer of the present invention and the semiconductor device having the barrier layer formed by the method of the present invention have been described above with reference to two examples, the present invention is not limited to these examples. Various implementations are possible. For example, TiCl ₄ (mp
= −25 ° C., bp = 136 ° C.), but TiBr
₄ (mp = 39 ° C, bp = 230 ° C) and TiI ₄ (mp
= 150 ° C., bp = 377.1 ° C.) and other Zr,
Halides of various metals such as Hf, Nb, Mo and W can be used.

Although N ₂ and NH ₃ are exemplified as the nitriding agent,
N ₂ H ₄ , CH ₃ NHNH ₂ (mp = −52.4 ° C., b
p = 87.5 ° C.) or (CH ₃ ) ₂ NNH ₂ (mp = −5)
8 ° C., bp = 63.9 ° C.) and the like, hydrazine derivatives such as alkylhydrazines, CH ₃ NH ₂ (mp = −93.5)
℃, bp = -6.3 ℃) and _{(CH 3) 3 CNH 2 (} mp
= −72.6 ° C., bp = 44 to 46 ° C.) and the like, and the like may optionally be used.

As the target for forming the barrier layer, the substrate to be processed having the contact hole facing the diffusion layer is exemplified, but the semiconductor substrate having the via hole facing the wiring layer such as Al-based metal wiring or polycrystalline silicon, or the like. You may employ | adopt the to-be-processed object suitably. The thickness of the first metal film formed was 5 nm because of the ease of nitriding. However, the metal film is formed to have a thickness of, for example, 30 nm, and only 5 nm on the surface is nitrided to form the remaining 25 nm lower metal film. Can also be used as the contact metal.

Although the ECR plasma CVD apparatus was used as the plasma CVD apparatus, a parallel plate type plasma CVD apparatus, a helicon wave plasma CVD apparatus, an ICP (Indu)
ctively Coupled Plasma) CV
D device, TCP (Transformer Couple)
ed Plasma) CVD equipment, surface wave plasma CV
It may be a D device or the like. At the same time as plasma, low pressure H
If a photoplasma CVD method that irradiates an excitation light beam, such as a g-lamp or an excimer laser, is adopted, it is possible to utilize a reaction with higher reduction efficiency.

[0037]

As is apparent from the above description, according to the method for forming the barrier layer, the surface morphology and the step coverage of the metal nitride film to be formed are good, and the low chlorine content and the low film formation temperature etc. It becomes possible to satisfy the various requirements of the above at the same time. Further, by adopting such a barrier layer as a part of the electrode / wiring material of a highly integrated semiconductor device, it is possible to provide a highly reliable semiconductor device having excellent barrier properties without wiring corrosion. Becomes

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating the first half of the method of forming a barrier layer according to the present invention.

FIG. 2 is a schematic cross-sectional view explaining the latter half of the method of forming a barrier layer according to the present invention.

FIG. 3 is a graph showing Gibbs free energy in thermal nitriding.

FIG. 4 is a schematic cross-sectional view showing a problem of the conventional technique.

[Explanation of symbols]

1 ... Lower conductive material layer, 2 ... Interlayer insulating film, 3 ... Connection hole, 4
... metal film, 4a ... eaves part, 5 ... metal nitride film

Claims (7)

[Claims] 1. A step of forming a metal film on a substrate to be processed by a plasma CVD method using a mixed gas containing a metal halide and hydrogen, and a step of nitriding the metal film to convert it into a metal nitride film. A method for forming a barrier layer, comprising: 2. The method for forming a barrier layer according to claim 1, wherein the step of forming a metal film and the step of converting the metal film into a metal nitride film are repeated a plurality of times. 3. The method for forming a barrier layer according to claim 1, wherein in the step of forming the metal film, the surface of the substrate to be processed is uniformly terminated with hydrogen active species. 4. The nitriding treatment is plasma nitriding using at least one nitriding agent selected from the group consisting of N ₂ , NH ₃ , N ₂ H ₄ and its derivatives, and alkylamine compounds. Item 2. The method for forming a barrier layer according to Item 1. 5. The nitriding treatment is thermal nitriding using at least one nitriding agent selected from the group consisting of N ₂ , NH ₃ , N ₂ H ₄ and its derivatives, and alkylamine compounds. Item 2. The method for forming a barrier layer according to Item 1. 6. The barrier layer formation according to claim 1, wherein both the step of forming the metal film and the step of converting the metal film into the metal nitride film are performed at a temperature of 500 ° C. or lower. Method. 7. A semiconductor device having a barrier layer formed by the method for forming a barrier layer according to claim 1. Description: