JPH06283465A - Formation of diffusion-proof layer of lsi - Google Patents

Abstract

PURPOSE:To deposit titanium silicide thinly and uniformly in an ohmic contact section and to form a titanium nitride layer which is thick enough. CONSTITUTION:Sputtering is conducted using a target whose atomic weight ratio of nitrogen to titanium 1 to deposit on silicon a thin film whose atomic weight ratio of nitrogen to titanium is less than 1. Nextly, by heat treatment, titanium silicide is deposited at the silicon side of the thin film and a layer for preventing diffusion of an ohmic contact section, not titanium nitride layer, at the wiring layer side of the thin film. After the wiring layer is formed, reactive sputtering is conducted using a target whose atomic weight ratio of nitrogen to titanium is less than 1 to form a layer for preventing diffusion of the wiring layer which is composed of titanium nitride.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a diffusion barrier layer for an LSI, which uses a titanium nitride layer as a diffusion barrier layer.

[0002]

2. Description of the Related Art With the recent high integration of LSIs, a P-type or N-type doped layer formed under a contact hole in an ohmic contact portion has been formed in a shallower and narrower region. When the above-mentioned LSI dope layer is shallow, when aluminum or the like used as wiring is directly formed on the silicon substrate, they cause an interdiffusion reaction, and aluminum or the like easily breaks through the dope layer and destroys the semiconductor junction structure. The problem occurs. In order to prevent the mutual diffusion reaction in the ohmic contact part, a diffusion prevention layer (also called a barrier metal layer) made of a high melting point material such as a titanium-tungsten alloy layer or a titanium nitride compound layer is formed between the wiring and the silicon substrate. Is being done.

Of the diffusion prevention layers, the titanium nitride compound layer is said to be particularly excellent in diffusion prevention. In addition, since this titanium nitride layer has an extremely small difference in lattice constant from the aluminum layer that will be the wiring layer, when the aluminum layer is formed on the highly-oriented titanium nitride layer, the orientation of the aluminum layer also becomes high, so stress It is known to be effective in preventing wiring breakage due to migration, electromigration and the like. Since the contact resistance with the silicon substrate is high just by directly forming the titanium nitride layer on the silicon substrate, research for lowering the contact resistance is currently underway. Monthly Semiconductor World 1989.12, p189-p19 as one means to reduce contact resistance between silicon substrate and titanium nitride compound layer
As shown in Fig. 2, it has been found effective to form a titanium silicide layer having a low contact resistance between the titanium nitride compound layer and the silicon substrate.

The formation of the titanium silicide layer is carried out by (1) forming a pure titanium thin film on a silicon substrate by sputtering as shown in the above-mentioned literature, and then heat-treating it in a nitrogen or ammonia gas atmosphere to form pure titanium. The surface layer of the thin film is nitrided to form a titanium nitride compound layer, and a pure titanium thin film is reacted with a silicon substrate to form titanium silicide, or (2) an ultrathin pure titanium thin film is formed by sputtering, followed by heat treatment. As a titanium silicide film, a method in which a titanium nitride thin film having a stoichiometric composition is formed on the titanium silicide film by reactive sputtering in which nitrogen in a sputtering gas is reacted with a titanium target is usually used. All of them agree with each other in that a pure titanium thin film reacts with a silicon substrate.

Also (3) Applied Surface Science 41/4
2 (1989) 272-276, a pure titanium is used as a target, a TiNx film is formed by an ion plating method in which it reacts with nitrogen in a gas phase, and then heat treatment is performed to form a silicide. It has also been attempted to cause nitrogen in the film to move to the surface of the film at the same time as causing a chemical reaction to form titanium nitride having a stoichiometric composition close to the surface.

Incidentally, the diffusion prevention layer of an LSI is often formed not only on the ohmic contact portion described above but also on the wiring. This is formed by providing a diffusion prevention layer on the upper part of the wiring for the purpose of preventing disconnection or short circuit of the wiring due to stress migration or the like and for preventing reflection of light from the aluminum wiring layer during exposure. The diffusion preventing layer on the wiring is usually formed by using pure titanium as a target and forming a titanium nitride thin film having a stoichiometric composition by reactive sputtering in which nitrogen in the sputtering gas is reacted with the titanium target. . This is because if the thermal nitriding treatment heated to 400 ° C. or higher is performed, the diffusion prevention layer of the ohmic contact portion formed earlier may be destroyed.

[0007]

As described above, the diffusion prevention layer of the ohmic contact is formed by various methods. With the recent higher integration of LSIs, the contact hole for forming the ohmic contact is formed. It is required to make the diameter of the GaN smaller and the depth of the underlying doped layer shallower. When a shallower doped layer is formed, the titanium silicide layer formed at the interface between the diffusion prevention layer and the doped layer needs to be uniformly formed as thin as possible. This is because titanium silicide consumes and produces silicon of the silicon substrate, and therefore it is necessary to be as thin as possible so as not to erode the thin doped layer on the silicon substrate too much.

In the method (2) of previously forming a pure titanium film to form titanium silicide, the side wall of the contact hole has a large influence of shadowing and it is difficult to make the film thickness uniform. In order to cover the titanium film sufficiently, the titanium film thickness must be increased. When the titanium film thickness is increased, a large amount of silicon of the substrate that reacts with titanium is consumed, and there is a problem that a thin titanium silicide layer cannot be formed.
Further, in the above method (1) of forming a titanium nitride layer and a silicide layer by a nitriding reaction and a silicide reaction by heating a pure titanium thin film in a nitriding atmosphere, the surface layer portion of the titanium film is consumed by the nitriding reaction. Therefore, the titanium silicide layer can be made thinner than the method (2). However, since the formation speed of the titanium nitride layer by supplying nitrogen from the vapor phase is slow, it is difficult to form a thick titanium nitride layer that requires a sufficient thickness as a diffusion preventing layer.

In contrast to the above methods (1) and (2), the present inventors have proposed a method (3) in which a TiNx film, which is titanium nitride in which titanium is in excess of the stoichiometric composition, is subjected to a silicidation reaction. As a result of the study, it is sufficient to form the thin film only once, and since nitrogen is initially present in the thin film, the titanium nitride layer that is sufficiently thick as the diffusion preventing layer is not restricted by the nitrogen supply rate from the gas phase. It was predicted that it could be formed. However, the Applied Surface Science 41 disclosing the above (3).
/ 42 (1989) 272-276, the method (3) says that titanium silicide film cannot be formed to a uniform thickness because it is partially or island-shaped at the interface between titanium nitride and silicon. Have challenges. It is considered that this is because pure titanium is used as the target and all the nitrogen in the TiNx film needs to be taken in by a chemical reaction, so that unreacted titanium is likely to remain and titanium in the film is omnipresent.

Further, as described above, it is necessary to form the diffusion prevention layer not only on the ohmic contact portion but also on the wiring layer in the LSI. When the ohmic contact portion is heated after the wiring is formed, the diffusion prevention layer in the ohmic contact portion is destroyed, so that the diffusion prevention layer cannot be formed by the thermal nitriding method. Therefore, the formation of the diffusion prevention layer on the wiring is limited to the reactive sputtering method in which pure titanium is used as a target and reacted with nitrogen. An object of the present invention is to form titanium silicide thinly and uniformly in an ohmic contact portion, to form a sufficiently thick titanium nitride layer, and to form a titanium nitride layer on a wiring layer in a short time. It is to provide a layer forming method.

[0011]

As a sputtering target, the present inventors have replaced the conventional pure titanium with a target containing less nitrogen than the stoichiometric composition (hereinafter referred to as TiN).
_X target) is used to form the ohmic contact portion by a normal sputtering method to form a thin film (hereinafter referred to as TiN _X film) containing less nitrogen than the stoichiometric composition on a silicon substrate, and then heating this TiN _X film. When a silicidation reaction was performed by the treatment to form a titanium nitride layer and a titanium silicide layer, it was found that the titanium silicide layer can be thin and have a uniform thickness, and a thick titanium nitride layer can be obtained. Further, they have found that when a TiN _x target is used as a target for reactive sputtering in which reaction is performed with nitrogen gas, a necessary diffusion prevention layer can be formed on a wiring layer in a short time.

That is, according to the present invention, sputtering is carried out using a target consisting essentially of titanium and nitrogen and having an atomic weight ratio of nitrogen to titanium of less than 1, and a thin film having a composition having an atomic weight ratio of nitrogen to titanium of less than 1 is silicon. A film is formed on top of it, and then heat treatment is performed to cause the thin film to react with silicon to generate titanium silicide on the silicon side of the thin film, and at the same time, to prevent diffusion of ohmic contact parts made of a titanium nitride layer on the wiring layer side of the thin film. After forming a layer, and then forming a wiring layer, reactive sputtering is carried out by reacting with a sputtering gas containing nitrogen using a target consisting essentially of titanium and nitrogen and having an atomic weight ratio of nitrogen to titanium of less than 1. LSI characterized by forming a diffusion barrier layer for wiring made of titanium nitride
This is the method for forming the diffusion prevention layer.

The atomic weight ratio of nitrogen to titanium in the TiN _x target used in the present invention (nitrogen / titanium) is preferably 0.85 or less. This is because a target having a nitrogen / titanium atomic ratio of more than 0.85 and having a stoichiometric composition and poor sinterability causes a large number of large particles, so-called particles, to be generated in the film formed by sputtering. Further, the heat treatment in the present invention is carried out from the vapor phase to Ti
It may or may not be accompanied by a thermal nitriding reaction for supplying nitrogen to the N _x film.

[0014]

The technique forming the basis of the present invention is that the TiN _x film for the silicidation treatment was obtained by sputtering a TiN _x target as described above. Siliding a TiN _x film obtained by sputtering a TiN _x target, rather than silicifying a TiN _x film obtained by an ion plating method in which conventional pure titanium is vaporized and reacted with gas-phase nitrogen, A uniform titanium silicide layer is obtained. The reason is unknown, but it is considered as follows.

In the present invention for sputtering a TiN _x target, the sputtered particles are approximately film composition,
There are almost no uneven distribution factors of titanium atoms in the film forming process. Further, the sputtered particles collide with the silicon substrate to form a film, which is rapidly cooled at this time, so that the film becomes amorphous or extremely fine crystalline. Therefore, in the TiN _x film obtained by the present invention, titanium atoms are uniformly distributed in the plane, and the crystal growth points are innumerable at the interface with the silicon substrate. It is considered that the titanium silicide formed has a uniform thickness. On the other hand, in the conventional ion plating method, since pure titanium is used as the target, it is necessary to react pure titanium vapor with nitrogen in the gas phase, unreacted titanium tends to remain, and titanium in the film is inevitable. It is considered that titanium silicide is formed in an island shape due to uneven distribution.

As described above, the present invention produces titanium silicide from the TiN _x film sputtered from the target. In the silicidation reaction in the present invention, titanium in excess of the stoichiometric composition in the TiN _x film participates in the silicidation reaction. Therefore, in the present invention, as in the conventional method of heat-treating pure titanium in a nitrogen atmosphere to form a titanium nitride layer and a titanium silicide layer, the thickness of each layer can be determined only by the reaction rate of the nitriding reaction and the silicidation reaction. The thickness of the titanium silicide layer is limited because the amount of titanium that can participate in the silicidation reaction is limited, and the titanium nitride layer having the minimum thickness can be secured. This is a very convenient method for forming an ohmic contact portion because it can overcome the drawbacks of the conventional method using a pure titanium film that the titanium nitride generation rate is slow and the titanium silicide layer is generated more than necessary. is there.

Another important feature of the present invention is that the diffusion barrier layer on the wiring layer is obtained by reactive sputtering of a TiN _x target. Since the TiN _x target is used for the titanium nitride layer as the diffusion prevention layer on the wiring layer, the nitrogen required for the reaction in the reactive sputtering can be small and the sputtering rate can be substantially increased. Further, the present invention has a very advantageous feature in manufacturing that the diffusion preventing layer on the ohmic contact portion and the wiring layer can be formed by the same operation of sputtering. Therefore, in the present invention,
It is also possible to form both the ohmic contact portion and the diffusion prevention layer on the wiring layer with the same device and the same target by simply changing the gas composition in the sputtering device.

[0018]

Example 1 A titanium nitride powder having a stoichiometric composition in which the atomic ratio of nitrogen to titanium is 1 and having a purity of 99.99% or more and an average crystal grain size of 40 μm, and a purity of 99.99.
% Or more, and pure titanium powder having an average crystal grain size of 40 μm was mixed at a mixing ratio such that the atomic ratio of nitrogen to titanium was 0.00 to 0.92 and mixed with a V blender. The nitrogen / titanium atomic ratio of 0.00 is the case where only titanium hydride is used as the raw material.

The obtained mixed powder was filled in a capsule for hot isostatic pressing having an inner diameter of 133 mm, dehydrogenated at 700 ° C., and then hot isostatic pressed at 120 MPa for 5 hours at 120 ° C. to obtain 75 mm in diameter. The TiN _x target was obtained by machining to a size of 6 mm. Table 1 shows the relationship between the atomic weight ratio of nitrogen to titanium (N / Ti) and the relative density of the obtained target. Using the targets shown in Table 1, φ
Normal sputtering was performed on a 6-inch silicon wafer under the sputtering conditions shown in Table 2 to obtain a 1000 Å TiN _x film. No significant difference was observed between the TiN _x film composition and the target composition. Obtained T
Table 1 shows the result of counting the number of particles of 0.3 μm or more generated on the iN _x film.

[0020]

[Table 1]

[0021]

[Table 2]

As shown in Table 1, it is understood that the target having an atomic ratio of nitrogen to titanium exceeding 0.85 has a low sintering density and many particles are generated. The obtained silicon wafer having the TiNx film formed was divided and subjected to the following two heat treatments. (1) 700 ° C. under a vacuum of 10 −3 Pa or less,
Heat treatment for 1 minute. Hereinafter referred to as simple heat treatment. (2) Heat treatment accompanied by thermal nitriding reaction at 735 ° C. for 30 seconds in an atmospheric ammonia atmosphere. Hereinafter referred to as thermal nitriding treatment.

The film thickness ratio of the titanium nitride layer and the titanium silicide layer obtained by these heat treatments (dTiN /
Simple heat treatment the relationship DTiSi ₂ and hereinafter) and the atomic weight ratio of nitrogen to titanium thin film formed with (denoted as N / Ti atomic ratio) in FIG. 1, the thermal nitridation process are shown in FIG. Here, the thicknesses of the titanium nitride layer and the titanium silicide layer were obtained by ESCA analysis. The surfaces of all the obtained samples had a golden color showing a stoichiometric amount of titanium nitride.

As shown in FIG. 1, if the content of nitrogen in the target is increased, the film thickness ratio between the titanium nitride layer and the titanium silicide layer can be significantly increased. That is, Ti obtained by sputtering using a titanium nitride target containing more titanium than the stoichiometric composition as in the example of the present invention.
It can be seen that the N _x film can provide the diffusion prevention layer in the ohmic contact portion having a high film thickness ratio between the titanium nitride layer and the titanium silicide layer. Further, from FIG. 1 and FIG. 2, the film thickness ratio (dTiN / dTiSi ₂ ) can be obtained by performing the thermal nitriding reaction.
It can be seen that can be further increased.

Next, assuming formation of a diffusion prevention layer on the wiring, aluminum was sputtered on the obtained φ6 inch wafer under the conditions shown in Table 3. On the obtained aluminum layer, TiN _{x having} a composition of N / Ti = 0.40.
Using a target and a pure titanium target as a comparative example, reactive sputtering was performed under the conditions shown in Table 4,
A 1000 Å substantially stoichiometric titanium nitride layer was formed. At this time, the sputtering power was adjusted so that the stoichiometric composition was obtained. 100
The time required for film formation up to 0 angstrom was 2/3 that of a pure titanium target.

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

INDUSTRIAL APPLICABILITY According to the present invention, a thin film obtained by sputtering a TiN _x target can be heat-treated to form titanium silicide in a thin and uniform thickness, and a thick titanium nitride layer can be formed. Also the same TiN
By reactively sputtering the _x target, the titanium nitride layer, which is the diffusion prevention layer on the wiring layer, can be formed more quickly than the method using pure titanium. Therefore, the present invention can cope with the trend toward higher integration of LSIs for forming a shallower doped layer, and can also improve the production efficiency, which is an extremely effective means for LSI manufacturing.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a composition of a formed thin film and a film thickness ratio between a titanium nitride layer and a titanium silicide layer in a thin film subjected to simple heat treatment.

FIG. 2 is a diagram showing a relationship between a composition of a formed thin film and a film thickness ratio of a titanium nitride layer and a titanium silicide layer in the thin film subjected to thermal nitriding treatment.

Claims (3)

[Claims] 1. A thin film having a composition in which the atomic ratio of nitrogen to titanium is less than 1 and which is substantially composed of titanium and nitrogen and the atomic ratio of nitrogen to titanium is less than 1 is formed on silicon. A film is formed, and then heat treatment is performed to react the thin film with silicon,
Titanium silicide is generated on the silicon side of the thin film, an ohmic contact diffusion preventing layer made of a titanium nitride layer is formed on the wiring layer side of the thin film, and then a wiring layer is formed. And diffusion of an LSI characterized in that a wiring diffusion preventing layer made of titanium nitride is formed by performing reactive sputtering in which a sputtering gas containing nitrogen is used to react with a target having an atomic weight ratio of nitrogen to titanium of less than 1. Method for forming prevention layer. 2. The method for forming a wiring of an LSI according to claim 1, wherein the heat treatment does not involve a thermal nitriding reaction. 3. The method of claim 1, wherein the heat treatment is accompanied by a thermal nitriding reaction.