JP2590091B2 - Refractory metal silicide target and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION OBJECTS OF THE INVENTION (FIELD OF THE INVENTION) silicide alloy of the present invention is a refractory metal (M) and silicon (Si): the sputtering target made of (MSi _n n ≧ 2) Regarding the production method, more specifically, high purity, especially MS with very few oxygen impurities and few alkali metals
i _n target and a method for manufacturing the same.

(Prior Art) On a surface of various semiconductor elements, a wiring network having a complicated pattern is formed using a conductive metal material in accordance with the purpose of use. In order to form this wiring network, first, for example, a sputtering
A thin film of a conductive metal such as Si or Al is formed, and then a predetermined etching process is performed on the thin film to remove a portion other than a desired wiring circuit and leave a wiring network.

By the way, recently, the elements have been reduced in size and thickness, and as one of the efforts, efforts have been made to form a dense wiring network, that is, to reduce the circuit width and the circuit thickness.

As the degree of integration in a semiconductor device increases in this way, a signal delay problem may occur due to the wiring resistance of the used wiring material, or when the material is a low melting point material, the device may be in operation. The problem that the breaking of the wiring occurs due to the diffusion of the movement of the crystal defect due to the resistance heat generation in the wiring network, which starts to occur.

For this reason, as a wiring material, a material that has a high melting point and at the same time a low resistance and that does not require a significant change in LSI, VLSI, and ULSI processes is strongly demanded. Such materials include Mo, W, Ti, Ta, Zr
These silicides of M are attracting attention along with high melting point metals (M).

In particular, in the case of silicide, the molar ratio of M: Si is 1: 2 to
3 (i.e., when expressed in MSi _{n, n} = 2~3) when the composition, a thin film of a semiconductor device surface are known to exhibit excellent low resistance and process consistency.

On the other hand, a sputtering method is mainly applied to a step of forming a conductive metal thin film, which is a preceding step of forming a wiring network on a surface of a semiconductor element.

This method is a method in which a predetermined ion species is incident on a target made of a constituent material of a thin film to be formed on the surface of a semiconductor element, the target constituent material is beaten out, and the target constituent material is adhered to the surface of the semiconductor element.

In applying this sputtering method, it is necessary to manufacture a sputtering target with the above-described metal material.

That is, for example, when the above-described wiring network of MSi ₂ to ₃ is formed, the material of MSi ₂ to ₃ is used as the target.

In this case, the MSi ₂ to ₃ materials need to have high purity.

For example, when the MSi ₂ to ₃ materials contain oxygen as an impurity, the formed thin film has an increased electric resistance and fragility, and many accidents such as breakage of a wiring network have started, and Fe Heavy metals such as, Ni and Cr constitute the cause of the leak phenomenon at the interface junction between the VLSI and the formed thin film, and alkali metals such as Na and K easily move on the VLSI etc. This is because the characteristics are deteriorated. Also, U, Th
Causes malfunction of the device due to the emitted α-rays,
Eventually, the operation reliability of the device is significantly reduced.

By the way, the targets of MSi ₂ to ₃ currently have the following modes. That is, first, a high-purity powder such as Ti, Ta, W, and Mo and a high-purity Si powder are mixed at a predetermined ratio (molar ratio 1: 2 to
The mixed powder is mixed in 3), the mixed powder is sintered by a conventional method, and the obtained sintered body is used. Second, each of the refractory metal (M) and the high-purity Si or the respective metal lump is separately arranged in a mosaic form to be a target.

However, in the case of the former target, since it is manufactured by a so-called powder metallurgy method, the specific surface area of each powder is increased, so that, for example, about 200 ppm or more of oxygen is adsorbed during the manufacturing, and the purity tends to decrease. As a result, the resistance of the thin film formed on the surface of the semiconductor element by the sputtering method tends to be high and brittle.

In the latter case, there is a problem that the processing of the mosaic pieces is required, so that the overall cost is increased and the resistance of the formed thin film is slightly higher.

Vulnerable this reason, it has been attempted to alloying with the melting method and the M and Si, but also occurs and general reaction vigorously contamination of the MSi ₂ ~ ₃ crucible produced in this way In the process of solidification from the molten state, cracks occur everywhere, and it is practically impossible to dispose them in a sputtering apparatus.

For this reason, the applicant has developed a MSi _n target and its manufacturing method which solves the problems of the melting method, it has already filed a patent application No. Sho 61-221912.

How the applicant disclosed herein, for example electron a Si-rich MSi _n alloy prepared by applying a beam (EB) melting method, then After grinding the alloy ingot, the stoichiometry in the resulting powder Excessive free Si or eutectic components of MSi ₂ and Si by-produced during alloy preparation are eluted and removed with, for example, hydrofluoric nitric acid to obtain a powder having a composition of MSi ₂ , and then the MSi ₂ powder In this method, a fixed amount of Si powder is further added to form a mixed powder, and this mixed powder is filled in a bottomed container made of M and melted and solidified under predetermined conditions.

(Problems to be solved by the invention) However, in the subsequent research, it was found that the above-mentioned method had the following problems to be further improved.

The first improvement to be a problem, when eluting remove excess free Si and eutectic component, for example, using nitric-hydrofluoric acid from MSi _n powder, not only free Si and eutectic component, MSi ₂ also erode M
Is eluted in large quantities. This is MSi ₂
This is extremely inconvenient industrially because the yield of powder is reduced.

The second problem to be solved is that free Si was eluted and removed.
In the process of adding Si powder to MSi ₂ powder and re-adjusting the molar ratio of M and Si again, the surface activity of Si powder is relatively large,
The point is that oxygen that adversely affects the film properties is incorporated into the obtained reconditioned powder. That is, in the obtained target, the amount of oxygen impurities increases.

It is true that the Si block is pulverized into Si powder immediately before mixing of both powders, and it is true that the amount of oxygen taken in is reduced by using this powder. Therefore, it cannot be used in actual production lines.

Third problem to be improved (dissolution / coagulation)
When the target block is manufactured by dissolving and coagulating the silicide powder whose molar ratio has been readjusted, segregation occurs due to the difference in the cooling state at the surface portion and the center portion in the coagulation process, and the eutectic component is generated again That is the point. When sputtering is performed using such a target, the eutectic component scatters into the chamber and adheres to the thin film of the refractory metal silicide being formed, thereby deteriorating its properties.

A fourth problem to be improved is that the target is contaminated by the alkali metal in the normal elution treatment of Si with an alkaline solution, and cannot be put to practical use.

An object of the present invention is to provide a refractory metal silicide target having an extremely small amount of oxygen impurities and containing no eutectic component, and a method for industrially producing the same, which solves the above-mentioned improvements.

[Structure of the Invention] (Means and Actions for Solving the Problems) The present inventors have developed the present invention by addressing the above-mentioned improvements as follows. That is, for the first improvement, explore the treatment solution selectively eluting only free Si from MSi _n powder, as a result, found a fact that highly effective organic alkaline solution, which will be described later . Regarding the second improvement, be coupled with a solution basically Si powder that the may be used MSi _n which has been previously adjusted to a predetermined molar ratio without adding first improvement It was solved by. That, MSi _{n (n} ≧ 2) the molar ratio of Si in the starting point is greater than the stoichiometric amount in advance prepared alloy, the powder was predetermined time processing by the following organic alkali solution free Si Is eluted, and when the amount of residual free Si becomes the same as the target molar ratio n 'at the time of readjustment, the elution treatment is stopped to control the composition of the treated powder. Thus, oxygen uptake does not occur.

Regarding the third point of improvement, liquid phase sintering is applied to the above-mentioned treated powder by applying a sintering method instead of a melting method, and thus the MSi ₂
This is a solution that does not generate a eutectic component of Si and Si.

Further, the fourth improvement point could be solved by using an organic alkali solution described later.

Therefore, the refractory metal silicide target of the present invention has an oxygen content of 200 ppm or less, preferably 150 ppm or less, more preferably 100 ppm or less, and an alkali metal of 1 ppm or less, preferably 50 ppb or less. and characterized in that it is free, and its method of manufacture, MSi _n in (a) and the refractory metal, the molar ratio with respect to the refractory metal
(Where M represents a high melting point metal, and n represents the number of moles of silicon); and (B) melting, coagulating or react-sintering the obtained mixture under vacuum. step alloying Te; (C) and grinding the resulting alloy powder, a predetermined molar ratio by processing the powder with an organic alkaline solution MSi _n '(although, M
Represents a refractory metal, n represents the number of moles of silicon,
n> n ′ ≧ 2); and (D) a step of subjecting the obtained silicide powder to a decontamination treatment, followed by molding and sintering.

First, the process of A, the MSi ₂ from M and Si in order to obtain a silicide as a skeleton component, both in the mixing ratio such composition is an alloy containing excess free Si in MSi _{n (n} ≧ 2) Is a step of mixing

Here, M is preferably any one of Ti, Zr, Ta, Mo, and W.

In the step A, M and Si are both high-purity granular materials, for example. For example, if M is Ti,
In addition to the conventional Kroll method, preferably, Ti purified by a molten salt electrolysis method or an iodide method is used. In any case, it is preferable that M is as small as possible in the above-mentioned impurities, that is, as low as possible in oxygen, a polymer group such as Fe, Ni, and Cr, an alkali metal such as Na and K, and U and Th.

M and Si may each be mixed in the form of granules,
It may be mixed in small lumps.

But even in either case, the mixing ratio of M and Si, and since the desired product is a composition of _{MSi n (n ≧ 2),} M in a molar ratio: Si = 1: to 2 or less .

Step B is a step of, for example, melting and alloying the mixture prepared in Step A.

Melting is performed in a vacuum, and the degree of vacuum at that time is 5 × 10
It is preferably at most ^-5 Torr. The temperature is not particularly limited as long as the mixture can completely melt and alloy.

This B step is usually preferably performed using an EB melting furnace.

C steps, obtained in step B the composition of MSi _n (n ≧
After pulverizing the silicide alloy ingot of 2) to a predetermined particle size, a predetermined amount of free Si is eluted and removed from the obtained powder, that is, a predetermined mole number of free Si is left.

In the grinding, in order to prevent contamination of the alloy, for example, a tool of the same material as that of the selected M is used, or grinding is performed with a low carbon steel tool. However, since the same tool as M is expensive, a low carbon steel tool is usually used industrially. At this time, MSi _n powder obtained but is contaminated by Fe, however, can easily be decontaminated by the process described below.

The organic alkali solution used for the elution treatment is a quaternary ammonium hydroxide compound, which is represented by the following general formula.

(However, in the above, R ₁ , R ₂ , R ₃ , and R ₄ represent an alkyl group, an aralkyl group, and a hydroxyalkyl group, and particularly, R ₁ ,
The number of carbon atoms of R _2, R ₃ is 1 to 4, carbon atoms of R ₄ is from 1 to 12). For example, commercially available products include trimethylethanol ammonium hydroxide, tetramethylammonium hydroxide, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, tetrabutylammonium hydroxide, and dimethyldiethanolammonium hydroxide (all manufactured by Tama Chemical Co., Ltd.). ) Can be given.

If the concentration of the organic alkali solution is too dilute, the selective elution of free Si does not proceed smoothly, and if the concentration is too high, the Si is rapidly dissolved and the amount of dissolved Si can be adjusted. Since a problem that becomes difficult starts to occur, it is preferable that the solution concentration is set in the range of 5 to 50%.

Processing operations, the MSi _n powder of predetermined particle size and charged to the organic alkali solution may be stirred at room temperature. The input amount of the powder is not particularly limited. For example, about 5 to 500 g of powder is contained in one solution.

This process free Si which were present in the MSi _n is gradually eluted into a processing solution over time. Namely, the abundance of free Si in MSi _n is decreasing with time. Therefore, if the composition of the silicide powder obtained after a certain time has elapsed is _denoted as MSIn ″, a relationship of n> n ″ ≧ 2 is established between n and n ″.

Therefore, if the desired composition in step a molar ratio of readjustment in the conventional method is assumed MSi _n ', the n "
If the elution treatment is stopped at the time when n becomes n ′, the composition of the powder after the treatment can be adjusted to a state that approximates the target composition.

In this treatment liquid, not only free Si but also the eutectic component of MSi ₂ and Si can be selectively eluted, so the eutectic component generated during melting and solidification in the B step is also removed in the C step. The resulting treated powder will have only the desired composition.

The step D is a step of decontaminating the Fe component of the treated powder obtained in the step C, and then molding and sintering the target to produce a target.

The decontamination is usually carried out by pickling, and aqua regia is preferably used as the acid solution.

After decontamination, the treated powder is molded into a predetermined shape by, for example, a rubber press, and then the obtained molded body is subjected to vacuum hot pressing to temporarily sinter and remove occluded gas. For example, a vacuum degree of 10 ⁻⁵ Torr or less, about 1000 ° C., and a time of about 30 minutes are suitable. As the conditions for the subsequent vacuum hot pressing, for example, vacuum hot pressing or HP processing is performed at a temperature of 1380 to 1400 ° C. The partial liquid phase sintering reaction proceeds to produce a target material. Finally, by subjecting this material to a grinding process, an intended target can be obtained.

(Examples of the invention) High-purity Ti powder (oxygen content 20 to
150 ppm, Fe 4 ppm or less, Cr 8 ppm or less, Ni 2 ppm or less, Na 0.1 pp
1.37kg, polycrystalline Si block 2.63kg
kg. This mixture ratio is silicide composition: TiSi
Equivalent to _3.3 . This mixed powder is charged into an EB melting furnace and 10 ^-5 T
The alloy was melted under a vacuum of orr to prepare an alloy ingot having a diameter of 150 mm and a thickness of 50 mm.

The obtained ingot was pulverized with a low carbon steel jaw crusher to obtain a powder passing about 150 mesh (Tyler sieve).

3.7 kg of this powder was put into 30 l of a 25% aqueous solution of tetramethylammonium hydroxide, and the mixture was stirred for about 48 hours. The composition of the obtained powder was TiSi _2.6 . This TiSi
_{2.6 The} powder was washed with aqua regia and decontaminated. As a result, the Fe content is 1
It decreased from 30 ppm to 6 ppm.

Next, this powder was press-molded, and
After degassing by applying a vacuum hot press at 1000 ° C. for 20 minutes, a HIP treatment at a pressure of 400 ton / cm ² was performed at 1280 ° C. for 2 hours and sintered. The sintered body was machined to 250φ × 15 ^t to obtain a target.

The oxygen content in this target was 180 ppm. In addition, this target is built into the actual machine and
When a thin film for VSLI was formed and its resistance was measured,
An original low resistance value of 1 Ω / port was actually measured.

For comparison, the composition performed elution removal of free Si with hydrofluoric nitric acid and powder only TiSi _2, then the alloy composition T
After setting a target so as to obtain iSi _2.5 and mixing the Si powder, a target was manufactured by applying the EB melting method to the mixed powder. The oxygen content in this target was 610 ppm.

Electron micrographs showing the composition of these two types of targets are shown in FIG. 1 (magnification: 50) and FIG. 2 (magnification: 400). FIG. 1 relates to the target of the present invention,
FIG. 2 shows a comparative example.

As is clear from the figure, the Ti shown in the conventional example of FIG.
The eutectic component of Si ₂ and Si (white streaks scattered in black portions in the figure) does not exist in the structure of the present invention in FIG. This is a target manufactured by a melting method in the conventional example. After the target of the present invention also removes this eutectic component in the elution treatment of the step C, the MSi _2.6 containing no eutectic component is used.
This is because the target is manufactured by sintering the powder.

[Effects of the Invention] As is clear from the above description, the high-melting-point silicide target of the present invention uses the silicide powder itself from which free Si is selectively and eluted and removed by an arbitrary amount as a raw material powder. Since the oxygen content is low and the amount of the eutectic component is suppressed, a silicide thin film having excellent characteristics can be formed at the time of sputtering, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph showing the metal structure of a target manufactured by the method of the present invention, and FIG. 2 is a scanning electron micrograph of the metal structure of a conventional target.

Continuation of front page (56) References JP-A-61-58866 (JP, A) JP-A-61-108132 (JP, A) JP-A-61-179534 (JP, A) JP-A-49-22081 (JP, A) , A)

Claims (4)

(57) [Claims] 1. A refractory metal silicide target having an oxygen content of 200 ppm or less and containing no eutectic component. 2. The content of an alkali metal is 1 ppm or less.
The refractory metal silicide target according to claim 1. 3. The high melting point metal is any one of titanium, zirconium, tantalum, molybdenum, and tungsten.
3. The high melting point silicide target according to claim 1 or 2. 4. A (A) a refractory metal, MSi _n (however, M represents a refractory metal, n represents represents the number of moles of silicon) in a molar ratio with respect to the refractory metal and silicon so that (B) melting and solidifying or reacting and sintering the obtained mixture under vacuum to form an alloy; (C) pulverizing the obtained alloy into a powder; in process to predetermined molar ratio MSi _n '(although, M
Represents a high melting point metal, n ′ represents the number of moles of silicon, and n> n ′ ≧ 2); and (D) decontaminating the obtained silicide powder, Forming and sintering; a method for producing a high melting point silicide target.