JP3528980B2 - Tungsten silicide target material and method of manufacturing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tungsten silicide target material used for forming electrodes or wiring for semiconductor devices and a method for manufacturing the same.

[0002]

2. Description of the Related Art With the recent high integration of LSI, LSI
A tungsten silicide film is used as the electrode and the wiring. As a method for forming this tungsten silicide film, a sputtering method, a chemical vapor deposition method or the like is used, and the sputtering method is predominant in view of productivity, reproducibility of the film and work safety. This sputtering method is a method in which an inert gas ion such as argon is made to collide with the target surface using a target composed of tungsten and silicon to form fine particles emitted as a thin film.

As the above-mentioned target, in order to prevent the occurrence of cracks during use, to ensure the uniformity and low resistance of the thin film, or to generate projections on the target surface due to local discharge during sputtering, particles are generated. In order to prevent the generation, a method for manufacturing a target having high density and few impurities is being studied. For example, JP-A-6
In Japanese Patent Laid-Open No. 1-145828, there is disclosed a method in which a high-purity high-melting point metal powder and a high-purity silicon powder are mixed, pressed and sintered to obtain a sintered body, and then electron beam melting is performed to obtain a silicide-melted product. It is disclosed. Also, JP-A-61-141
No. 673 or JP-A-61-1141674 discloses a high density target by a method of mixing a molybdenum powder or a tungsten powder and a silicon powder, molding and silicidizing the pellets, and then crushing the pellets to obtain a sintered body by hot pressing. Is getting

Further, as described in JP-A-63-219580, a refractory metal (M) powder and a silicon powder are subjected to a silicidation reaction in a vacuum to obtain a finer structure, which is obtained. A method of hot isostatic pressing a calcined body has also been proposed. Furthermore, recently, the Japanese Examined Patent Publication 6-4162
As described in Japanese Patent Publication No. 9, paying attention to the fact that the amount of carbon is related to the reduction of particles, after producing a mixed powder of metal powder and silicon powder, in a high vacuum to reduce carbon and oxygen. A method of adding a step of heating to reduce carbon and oxygen is also disclosed.

[0005]

The above-mentioned densification, reduction of impurities and refinement of the structure are effective methods for the tungsten silicide target. However, the high integration of LSIs in recent years has been remarkable, and the width of the thin film required for wiring and the like has become submicron, and the generation of particles in fine devices can be further reduced only by the above-mentioned conventional method. Is not enough for. The present invention is to provide a novel target material capable of further reducing the generation of particles and a method for producing the same in order to meet the above-mentioned demand.

[0006]

SUMMARY OF THE INVENTION The present inventor has hypothesized that a variety of techniques may be used to produce tungsten silicide target materials, which are composed of stoichiometric tungsten silicide WSi ₂ and pure silicon Si. The relative density, which is the ratio of the true density of the target material to the theoretical density when calculated, exceeds 101%, and it was found that it is possible to manufacture a target material that has never been produced, and the relative density exceeds 101%. It was found that the above target material is extremely effective in reducing particles, and has reached the present invention.

That is, according to the present invention, the relative density, which is the ratio of the true density of the target material to the theoretical density calculated assuming that the target material is composed of stoichiometric tungsten silicide WSi ₂ and pure silicon Si, is 101
% Or more, and the atomic ratio of silicon and tungsten is Si /
W is a tungsten silicide target material characterized by exceeding 2.

The manufacturing method for obtaining the target material of the present invention is the atomic ratio Si of silicon to tungsten Si.
/ W is mixed so that tungsten powder and silicon powder are mixed in a reducing atmosphere to cause a silicidation reaction to form a calcined body, and then the pulverized powder obtained by crushing the calcined body is 1200 ° C to 1400 ° C. The relative density, which is the ratio of the true density to the theoretical density calculated by assuming that it is composed of stoichiometric tungsten silicide WSi ₂ and pure silicon Si, is 101% or more after sintering at 110 MPa or more. A method for manufacturing a tungsten silicide target material, which comprises obtaining a target material.

[0009]

As described above, one of the greatest features of the present invention is that the relative density of the tungsten silicide target material is 101% or more. It is considered that the conventional tungsten silicide target material is composed of stoichiometric tungsten silicide WSi ₂ and free silicon as its structure. By making the relative density close to 100%, the cause of abnormal discharge during sputtering Higher density has been studied for the purpose of reducing the number of voids. On the other hand, when the present inventor further studied the above-mentioned conventional method, 1200 ° C. to 1400 ° C.
1414, which is the melting point of silicon of 10 MPa or more
By selecting an extremely high pressure condition just below ℃, relative density of 101%, which is not considered to be composed only of stoichiometric tungsten silicide and free silicon
They have found that the above new target materials can be actually manufactured.

The reason why the target material having a relative density of 101% or more can reduce the particles is unknown, but due to the condition of high temperature and high pressure, some diffusion occurs at the interface between the tungsten silicide phase and the silicon phase in the structure, and the compound It is considered that the difference in the sputter rate between the tungsten silicide phase and the silicon phase is alleviated. The relative density in the present invention is preferably 102% or more. Alternatively, it is considered that the mechanical bond strength between the tungsten silicide phase and the silicon phase is strengthened and the generation of particles is suppressed.

In the present invention, it is defined that the atomic ratio Si / W of silicon and tungsten exceeds 2 is S.
This is because if i / W is 2 or less, a large tensile stress is generated in the thin film to be produced, and there is a risk of impairing the adhesion of the thin film. When used as an LSI electrode or wiring, there is a problem that the sheet resistance increases when Si / W exceeds 4, so Si / W is preferably 4 or less.

The most characteristic of the manufacturing method for obtaining the target material of the present invention is 1200 ° C. to 1400.
℃, 110MPa or more, melting point 141 of pure silicon
That is, an extremely high pressure was applied just below 4 ° C. This makes it possible to obtain the above-described target material of the present invention. For sintering under such high temperature and high pressure conditions, for example, a hot isostatic pressing method can be applied. Conventionally, when the hot isostatic pressing method is applied to manufacture a tungsten silicide target material, the temperature is usually not 1200 ° C. or higher, and the high pressure condition of 110 MPa or higher at such a high temperature is not applied. . This means that the relative density is about 10 even without applying such high temperature and high pressure conditions.
This is because it was 0%, and no further attempt was made to increase the density. In the present invention, the upper limit of the sintering temperature is 140
The reason for setting the temperature to 0 ° C. is that if the temperature exceeds 1400 ° C., the silicon melts and the texture of the sintered body becomes non-uniform. A preferable sintering temperature range is 1250 to 1350 ° C., and a preferable sintering pressure is 120 MPa or more.

In the manufacturing method of the present invention, first, the tungsten powder and the silicon powder mixed so that the atomic ratio Si / W of silicon and tungsten exceeds 2 are subjected to a silicidation reaction in a reducing atmosphere to form tungsten silicide and free silicon. And a calcinated body is crushed to obtain a sintering raw material. The reason why the calcined body is manufactured in advance is that tungsten is silicidized to be tungsten silicide, and silicon that is not involved in the reaction is fine free silicon. In addition, it is necessary to perform W in a reducing atmosphere due to the silicide reaction.
This is because the oxygen adsorbed on Si is dissociated, and the impurity oxygen can be effectively reduced. A hydrogen-containing atmosphere or a reduced pressure atmosphere can be used as the reducing atmosphere. Further, the reason why the calcined body is further crushed is to obtain a uniform and high-density sintered body.

In the present invention, the theoretical density can be calculated, for example, as follows. Atomic ratio of silicon and tungsten Si
/W=2.75 target material. The density and molecular weight of the stoichiometric tungsten silicide WSi ₂ are as follows. Density 9.83 [g / cm ³ ] Molecular weight 240.022 [g / g-mol] The density and molecular weight of pure silicon are as follows. Density 2.33 [g / cm ³ ] Atomic weight 28.086 [g / g-mol] Target material is essentially WSi ₂ 1 [g-mol] and Si 0.75 [g-mo]
Assuming that it is composed of only l], the target material weight is (1 [g-mol] × 240.022 [g / g-mol]) + (0.75 [g-mol] × 28.086
[g / g-mol]) = 261.085 [g] Target material volume is (1 [g-mol] × 240.022 [g / g-mol] /9.83 [g / cm ³ ]) + (0.75 [g-
mol] × 28.086 [g / g-mol] /2.33 [g / cm ³ ]) = 33.458 [cm ³ ] The density at this time is target material weight / target material volume = 7.803 [g / cm ³ ]. This is the theoretical density. On the other hand, the true density can be obtained by determining the volume of the target material by the Archimedes method, and by weighing the target material. If the true density thus obtained is, for example, 7.90 / [g / cm ³ ], the relative density is (true density × 100) / theoretical density = (7.90 [g / cm ³ ] × 100) /7.803 [ g /
cm ³ ] = 101.2%.

[0015]

[Example] High-purity tungsten powder (purity of 99.999% or more,
An average particle size of 4.2 μm) and high-purity silicon powder (purity 99.999% or more, average particle size of 16 μm) were weighed in a compounding ratio of Si / W = 2.75 and mixed with a blender. 13 of the mixed powder obtained by mixing
The calcined body was obtained by silicidation reaction under the high vacuum of 5 × 10 -4 Torr or less under the condition of 50 ℃ × 2hr. This calcined body was crushed to 100 mesh (150 μm) or less in an argon atmosphere, the crushed powder was pressure-sintered under the conditions shown in Table 1, and a target material of 300 mmφ was obtained by machining. HIP shown in Table 1 means hot isostatic pressing, and HP means hot pressing. The results of measuring the density of the obtained target material are shown in Table 1. Further, the obtained target material was sputtered under the conditions shown in Table 2 and the number of particles of 0.3 μm or more generated on a 6-inch wafer was measured. The results are shown in Table 1.

[0016]

[Table 1]

[0017]

[Table 2]

Further, in order to show the basic structure of the target material of the present invention, Sample No. The structure photograph of 600 times that of No. 2 is shown in FIG. As shown in FIG. 1, the target material of the present invention is
It can be seen that the tungsten silicide phase represented by white and the free silicon phase appearing black are uniformly dispersed. Among the samples shown in Table 1, Samples 1 to 3 are target materials of the present invention, and Samples 4 to 6 are comparative samples. As shown in Samples 4 and 5, when either the pressure or the temperature is lower than that of the present invention, 101
It was not possible to achieve a density of more than%. Also, sample 6
Was applied with the limit conditions of ordinary hot pressing, but a target material having a relative density of 101% or more could not be obtained.

When the sintering conditions of the present invention of 1200 ° C. or higher and 110 MPa or higher are applied to the target material of such a comparative example as shown in Table 1, the relative density of the target material is much higher than the theoretical density. It can be seen that a target material having a relative density of 101% or more, which exceeds the above, could be obtained. The number of particles generated in the target material of the comparative example having a relative density of less than 101% is almost twice as large as that of the target material of the present invention, and the target material having a relative density of 101% or more generates particles. It turns out that it is effective in suppressing.

[0020]

According to the present invention, it is possible to obtain a target material having a relative density of 101% or more, which has not been heretofore considered, and it is possible to effectively suppress the generation of particles by this target material. Became. Therefore, by using the target material of the present invention, the manufacturing yield of semiconductor devices is improved or the reliability of semiconductor devices is improved, which is extremely effective in industry.

[Brief description of drawings]

FIG. 1 is a metal microstructure photograph showing an example of the structure of a target material of the present invention.

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-2-247379 (JP, A) JP-A-4-191366 (JP, A) JP-A-5-140739 (JP, A) JP-A-6- 10123 (JP, A) JP-A-6-10124 (JP, A) JP-A-6-16412 (JP, A) JP-A-6-322529 (JP, A) JP-A-62-230676 (JP, A) JP 62-70270 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C23C 14/34

Claims (2)

(57) [Claims] 1. The relative density, which is the ratio of the true density of the target material to the theoretical density calculated assuming that the target material is composed of stoichiometric tungsten silicide WSi ₂ and pure silicon Si, is 101% or more. And the atomic ratio Si / W of silicon and tungsten is more than 2, a tungsten silicide target material. 2. An atomic ratio Si / tungsten Si /
Tungsten powder and silicon powder mixed so that W exceeds 2 undergoes a silicidation reaction in a reducing atmosphere to form a calcined body, and then the calcined body is pulverized to obtain 1 pulverized powder.
Sintering at 200 ° C to 1400 ° C and 110 MPa or more,
A target material having a relative density of 101% or more, which is a ratio of true density to theoretical density calculated on the assumption that it is composed of stoichiometric tungsten silicide WSi ₂ and pure silicon Si. Method of manufacturing tungsten silicide target material.