JPH065604A - Wiring forming method and wiring structure of integrated circuit - Google Patents

Abstract

PURPOSE:To provide a wiring forming method and a wiring structure for an integrated circuit with which the disconnection of integrated wirings generating due to stressmigration and the like can be prevented. CONSTITUTION:A sputtering process is conducted using the sputtering gas substantially composed of titanium and nitride in the N/Ti atomic ratio target of 0.2 to 0.9, a barrier metal layer, consisting of a nitride-titanium thin film substantially having NaCl type crystal structure and also having the nitride more than the above-mentioned nitride-titanium atom ratio, is formed and an integrated circuit wiring, with which a wiring layer mainly composed of aluminum will be formed, is formed on the barrier metal layer. It is desirable that the barrier medal layer is formed in such a manner that the ratio of X-ray diffraction intensity on the (200) crystal face and the (111) crystal face is set at 0.15 or smaller, and that the half power width of the peak of the (111) crystal face of aluminum of X-ray diffraction analysis of the wiring layer is set at 2.5 degree or smaller.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated circuit wiring forming method using a titanium nitride film as a barrier metal layer and an integrated circuit wiring structure.

[0002]

2. Description of the Related Art In recent years, there have been remarkable improvements in the degree of integration of LSIs, and for this reason, the wiring widths that make up circuits are being further miniaturized. In addition, a diffusion prevention layer called a barrier metal layer is formed in the LSI in order to prevent reaction diffusion of both elements between aluminum which is an electrode portion and silicon which is an element portion. This barrier metal layer is also required to be thinner as the wiring width becomes finer, and a barrier metal layer having a high melting point and a high diffusion preventing effect is also required.

Further, since the barrier metal layer becomes a part of the electrode, it is desirable to use a material having a specific resistance value as low as possible.
At present, a titanium nitride film is attracting attention as a material having a characteristic of having a high melting point and a low specific resistance value and having an extremely excellent diffusion preventing effect. This titanium nitride film has an extremely small difference in the lattice constant from the aluminum used as the wiring layer, as typified by the paper by H. Kageyama et al., Proc. Of the 1991, IRPS P.677. It is known that when an aluminum film is formed on a high titanium nitride film, the orientation of the aluminum film also becomes high, and therefore it is effective in preventing disconnection breakage due to stress migration, electromigration and the like.

When the orientation of the aluminum film is enhanced, the aluminum film has a so-called bamboo-like crystal structure. Therefore, the grain boundaries along the stress and the gradient of the electric field are reduced, and as a result, wire breakage due to migration can be prevented. This titanium nitride layer is usually formed by a reactive sputtering method targeting pure titanium. In this reactive sputtering method, a target of pure titanium is bombarded with charged particles such as nitrogen ions and argon ions formed by glow discharge to nitride the target surface and release the titanium nitride particles by the impact force. Then, a titanium nitride film is formed on the silicon wafer placed facing the target.

The advantages of the reactive sputtering method are that the composition ratio of nitrogen and titanium in the thin film to be formed can be easily controlled by controlling the concentration of nitrogen contained in the sputtering gas, and that the target is pure titanium, which is a simple metal. Therefore, a high-density and high-purity target can be obtained. The reason for forming the titanium nitride layer by the reactive sputtering method is that if a target is made of titanium nitride having an atomic ratio of stoichiometric nitrogen and titanium of 1, the target is a compound, so it is very difficult to sinter, and sputtering is performed. This is because a dense target cannot be obtained. When the target density is low, abnormal discharge easily occurs during sputtering,
It causes defects such as generation of particles.

[0006]

However, in the above-mentioned reactive sputtering method using pure titanium as a target, titanium nitride is produced by nitrogen introduced into the sputtering apparatus, but nitrogen contained in the sputtering gas is deposited on the thin film. Therefore, there is a problem in that the surface diffusion of titanium nitride on the thin film is hindered and the orientation of the thin film is lowered, resulting in a reduction in the orientation of aluminum and the wiring layer. As described above, the low orientation of aluminum forming the wiring layer causes stress migration and electromigration. Since the occurrence of such migration leads to disconnection of the integrated circuit wiring, a solution for increasing the orientation of the wiring layer is required. An object of the present invention is to provide a wiring forming method of an integrated circuit and a wiring structure of an integrated circuit capable of preventing disconnection of the integrated wiring due to stress migration and electromigration.

[0007]

The present inventor has examined the orientation of a titanium nitride thin film formed by reactive sputtering, and the target used for reactive sputtering is not pure titanium but an atomic ratio of nitrogen and titanium ( Below N / Ti
It was found that the orientation of titanium nitride can be enhanced, and as a result, the orientation of aluminum or aluminum alloy can be enhanced by using a target having a ratio of 0.2 to 0.9).

That is, according to the present invention, a target consisting essentially of titanium and nitrogen and having N / Ti of 0.2 to 0.9 is sputtered using a sputtering gas containing nitrogen. In addition, a barrier metal layer formed of a titanium nitride thin film having a large nitrogen ratio and a substantially NaCl type crystal structure is formed, and a wiring layer containing aluminum as a main component is formed on the barrier metal layer. It is a method for forming a characteristic integrated circuit wiring.

By this method, a wiring structure having a high orientation was obtained, and a wiring structure capable of preventing migration was obtained. That is, the wiring structure of the integrated circuit of the present invention is (20
The ratio of the X-ray diffraction intensities of the (0) crystal face and the (111) crystal face (2
(00) / (111) is substantially less than 0.15
On the barrier metal layer made of a titanium nitride film having a crystal structure of
1) It is characterized in that a wiring layer containing aluminum as a main component and having a half-value width of a peak of a crystal plane of 2.5 degrees or less is formed.

[0010]

The feature of the present invention is that the target is not pure titanium but the atomic ratio N / Ti of nitrogen and titanium is 0.2.
By carrying out reactive sputtering with a target of 0.9 to 0.9, it is possible to make the orientation of the titanium nitride thin film extremely high, which could not be achieved with a pure titanium target. According to the method of the invention, (2
The ratio (200) / (111) of the X-ray diffraction intensities of the (00) crystal face and the (111) crystal face is substantially Na of 0.15 or less.
A titanium nitride film having a Cl-type crystal structure is obtained, and if a film containing aluminum as a main component is formed on this titanium nitride film, the half-width of the peak by X-ray diffraction analysis is mainly 2.5% or less. A wiring layer as a component can be formed.
The method of the present invention has an extremely excellent feature in the technical field of forming a titanium nitride film by performing reactive sputtering in that a film having a high orientation which cannot be achieved by a pure titanium target can be formed.

In the present invention, the atomic ratio of nitrogen and titanium
N / Ti is specified to be 0.2 to 0.9. When N / Ti is less than 0.2, the amount of nitrogen in the sputtering gas introduced to bring the composition closer to the stoichiometric titanium nitride composition is increased due to the reactive sputtering. This is because the reduction of the orientation cannot be avoided due to the adsorption of nitrogen to the thin film and the reduction of the average incident energy of the film-forming atoms, and a large improvement in the orientation cannot be expected as compared with the case where pure titanium is used as the target. On the other hand, if N / Ti exceeds 0.9, it is close to the stoichiometric composition of titanium nitride, so the sinterability during target production becomes extremely poor, and a relative density of 95% or more cannot be obtained. A low-density target is not preferable because it causes the generation of particles.

The NaCl type is defined in the present invention because it is a crystal type of a titanium nitride film having a low resistance. Further, the present invention is not limited to aluminum alone,
It is also applicable to wiring alloys made of aluminum alloys such as Al-Si, Al-Cu, and Al-Si-Cu. However, in order to maintain the FCC phase single phase similar to pure aluminum in these wiring alloys, the addition amount of Si, Cu, etc. must be 10 atm% or less. Since the atomic radius difference between Si and Cu with respect to aluminum is small, the lattice constant change is 1% or less with respect to pure aluminum even if 10 atm% is added.

Further, a sputtering method or a chemical vapor deposition method (CVD) can be applied to the film formation of aluminum.
Particularly, the sputtering method has an advantage that the apparatus is simple and easy to use. In addition, Jpn.JA of T. Kobayashi et al.
Further high reliability thin film formation can be expected by applying an epitaxial CVD method as described in the paper of ppl. Phys., 27 (1988) P.L1775 to form a film of aluminum. The target used in the present invention can be obtained by mixing titanium nitride powder and pure titanium powder in a specific ratio and sintering. Further, a method of using titanium hydride powder instead of pure titanium, mixing, dehydrogenating, and sintering can prevent oxidation of titanium, and is therefore preferable for use in integrated circuits requiring high purity. For sintering, a pressure sintering method such as hot isostatic pressing or hot pressing is preferable for obtaining a high-density target.

[0014]

(Example 1) 22.6% by weight nitrogen having N / Ti of 1, balance titanium, purity 99.99% or more, titanium nitride powder having an average particle size of 40 μm, and purity 99.99% or more, pure particle having an average particle size of 40 μm Titanium powder was mixed in a mixing ratio such that N / Ti was 0 to 1.0, and mixed with a V-type blender. An atomic ratio of nitrogen to titanium of 0 means that only titanium powder was used as a raw material, and an atomic ratio of nitrogen to titanium of 1 means that only titanium nitride powder was used as a raw material. After filling the obtained mixed powder into a capsule for hot isostatic pressing with an inner diameter of φ400 mm, 1250 ° C × 5
Hot isostatic press under conditions of 100 MPa for 75 mm
A target of × 6 mmt was obtained. N of the obtained target
The relationship between / Ti and relative density is shown in FIG.

From FIG. 1, it can be seen that if N / Ti exceeds 0.9, a rapid decrease in density occurs, which is not preferable. Films of these targets were formed on a φ6 inch wafer by using a sputtering gas composed of a mixed gas of argon and nitrogen. Sputtering was performed on the targets of the respective compositions under the conditions shown in Table 1 to obtain a titanium nitride thin film of 10,000 Å. Table 2 shows common conditions that do not depend on the target composition. Table 3 also shows N / Ti of the obtained titanium nitride thin film and the number of particles of 0.5 μm or more generated on the φ6 inch wafer.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

The obtained titanium nitride thin films shown in Table 3 all showed a golden color obtained by the composition in the vicinity of N / Ti = 1. From FIG. 1 and Table 3, it can be seen that the generation of particles increases as the target density decreases. In particular, it was found that when a target having a composition ratio of N / Ti exceeding 0.9 and out of the composition range of the present invention was used, the number of particles generated remarkably increased, which is not preferable as a titanium nitride thin film. It was also confirmed that the number of particles generated increased even when a target having N / Ti of less than 0.2 was used.

The surfaces of the thin films shown in Table 3 were analyzed by an X-ray diffractometer with an acceleration voltage of 40 KV using Kα1 of cobalt as the radiation source. All the titanium nitride thin films thus obtained were essentially only NaCl-type titanium nitride. Further, the diffraction intensity of the (200) crystal face and the (220) crystal face, which were confirmed when the diffraction angle 2θ by this X-ray diffraction was between 40 and 100 degrees, was calculated from the diffraction intensity with respect to the (111) face diffraction intensity which is the closest packed face. The ratio is shown in FIG. From FIG. 2, if N / Ti of the composition of the target used is 0.2 or more,
The diffraction intensity ratios of the non-closest (200) crystal face and the (220) crystal face to the closest (111) crystal face are each 0.15% or less, and N / Ti is 0. It was found that the crystal orientation was remarkably higher than that when the titanium target was used. Further, from Table 3 and FIG. 2, in order to suppress the generation of particles and obtain a titanium nitride thin film having a high crystal orientation, a target defined by the present invention with N / Ti of 0.2 to 0.9 is used as a reactive sputtering target. It turns out that you should use it.

Next, aluminum was sputtered on the titanium nitride thin film formed on the φ6 inch wafer shown in Table 3 under the conditions shown in Table 4.

[0022]

[Table 4]

The surface of the obtained aluminum thin film was analyzed by an X-ray diffractometer with an acceleration voltage of 40 KV using Kα1 of cobalt as the radiation source. The orientation of aluminum was evaluated from the half width of the peak of the (111) crystal plane, which is the closest packed plane. The full width at half maximum includes information on the frequency and the inclination angle of a so-called slightly inclined surface inclined by several degrees from the closest surface, and the smaller the full width at half maximum, the higher the crystal orientation. The results are shown in Fig. 3. From FIG. 3, the full width at half maximum of the obtained aluminum thin film formed on the titanium nitride thin film formed by the target having N / Ti of 0.2 or more is 2.5 degrees or less, and N
It was found that the crystal orientation was significantly higher than that of the aluminum thin film formed on the titanium nitride thin film obtained by the pure titanium target having / Ti of 0. As described above, the aluminum nitride thin film formed on the titanium nitride thin film obtained by the method of the present invention has a high orientation and can provide a preferable wiring structure in order to prevent migration which is a problem in an integrated circuit. all right.

[0024]

According to the method of the present invention, since the target used for the reactive sputtering is a target having a specific atomic ratio of N / Ti of 0.2 to 0.9, the generation of particles is reduced and the nitriding with high crystal orientation is achieved. A barrier metal layer made of titanium can be formed. As a result, it is possible to suppress the occurrence of defects such as disconnection of the integrated circuit due to the generation of particles. Furthermore, if a film containing aluminum as a main component is formed as a wiring layer on the barrier metal layer, the orientation of the wiring layer can be made high because the close-packed surfaces of aluminum and titanium nitride are the same. It is possible to provide a highly reliable wiring structure in which disconnection or the like due to occurrence of electromigration and stress migration, which are problems in circuit wiring, does not easily occur.

[Brief description of drawings]

FIG. 1 is a diagram showing the relationship between the target composition and the relative density of the obtained target.

FIG. 2 is a diagram showing a relationship between a target composition and an X-ray diffraction intensity of a formed titanium nitride film.

FIG. 3 is a diagram showing a half-value width of a close-packed surface of a target composition and an aluminum film formed on a formed titanium nitride film by X-ray diffraction analysis.

Claims (4)

[Claims] 1. A target consisting essentially of titanium and nitrogen and having an atomic ratio N / Ti of nitrogen to titanium of 0.2 to 0.9 is sputtered using a sputtering gas containing nitrogen, and the target of nitrogen and titanium is A barrier metal layer formed of a titanium nitride thin film having a ratio of nitrogen to atomic ratio and having a substantially NaCl type crystal structure is formed, and a wiring layer containing aluminum as a main component is formed on the barrier metal layer. A method for forming an integrated circuit wiring, comprising: 2. The barrier metal layer has a ratio (200) / (1 of X-ray diffraction intensities of a (200) crystal face and a (111) crystal face.
11. The titanium nitride film 11) is a titanium nitride film having a substantially NaCl type crystal structure of 0.15 or less.
A method for forming an integrated circuit wiring according to claim 1. 3. The wiring layer is a layer containing aluminum as a main component, wherein a half value width of a peak of a (111) crystal plane of aluminum by X-ray diffraction analysis is 2.5 degrees or less. 3. The method for forming an integrated circuit wiring according to any one of items 1 to 2. 4. A sputtering method having a substantially NaCl-type crystal structure in which the ratio (200) / (111) of the X-ray diffraction intensities of the (200) crystal face and the (111) crystal face is 0.15 or less. On the barrier metal layer made of titanium nitride film
1) A wiring structure of an integrated circuit, wherein a wiring layer containing aluminum as a main component and having a peak half-width of a crystal plane of 2.5 degrees or less is formed.