JPS60221538A - Molybdenum purification method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for fabricating molybdenum for use in gate-to-electrode formation of low-alkali molybdenum in large-scale integrated circuits, particularly very large-scale circuits.

Conventionally, polycrystalline silicon films to aluminum films have been used for gate electrodes of large-scale integrated circuits (LSIs).
As the degree of integration increases, materials with lower electrical resistance and resistance to high temperatures are being sought. #1LS as the M department
Molybdenum silicide is preferred because it has good bonding properties with the I-element j and temporary single-crystal silicon wafer, and has a thermal expansion coefficient φ that is not small.

Is the fine metal molybdenum used in the production of silico-1-hypomolybdenum usually locust molybdenum ore? Cultivate to form molybdenum trioxide, elute and remove inclusions with ferric acid, dissolve in aqueous ammonia, crystallize evaporated rock w4 as ammonium molybdate in one ridge, and decompose this by YKA. Molybdenum trioxide is despised as a raw material for molybdenum trioxide, and there is also a product obtained by reducing molybdenum trioxide with hydrogen, which is relatively ambivalent and is coated with molybdenum trioxide by high-temperature volatilization. All of them are unsatisfactory in terms of purity for LSI applications. In other words,
These conventional molybdenum materials have Na' and K, which have poor properties such as drowsiness and corrosion resistance of semiconductor devices, ranging from tens of ppm to hundreds of ppm (1) pm, %, which can cause malfunctions in VLSI electronics of 64 kilobits or more. U and Th, which generate alpha a that causes soft errors), are included from several ppb to several tens of ppb. , Th is required to be 1 ppb or less, but in addition, the direction of integration,
Along with the above-mentioned requirements for element reliability, the tolerance level for Na and In is becoming increasingly strict, and materials with both Na and In of 0.1 pI) or less are now required. Of course, it is also necessary to minimize the amount of impurities such as Fe that affect the semiconductor properties.

The present inventors have previously proposed a method for removing U*Tb by recrystallizing molybdenum ammonium, but although this recrystallization method can sufficiently reduce U and Thi, Na and K The problem with 4X was that it had a low removal effect and had to repeat the re-debt operation many times in order to achieve the required high loading.

, 4: Therefore, the present inventors have proposed a more effective method for producing molybdenum using molybdenum trioxide in an atmosphere containing water vapor. We proposed a method in which refined molybdenum is precipitated as acicular crystals in a low-temperature region. According to this method, Na.

It has become possible to obtain products with a K content level of 0.5 pJ) that is just below In, but in order to further increase the purity, J
It is necessary to smoke the four-shot decomposition repeatedly, especially Na, as the content level is 0.1 pI) InJ! )'(+-Achieving Rutame K HNa, with the decrease in the content level, '4II
It has been found that the production efficiency tends to decrease, and thus the practicality decreases as the number of required volatilization purification increases.

Therefore, the present inventors investigated a more efficient method for removing Na from molybdenum, and found that the chemical forms of Na present in molybdenum range from the precursor ammonium molybdate to molybdenum halide. I came to think that it was a molybdate that was present in the metal and did not undergo reduction to the above metal. Therefore, after repeated experiments, we thought that if the metallic molybdenum powder obtained by reduction with hydrogen etc. is washed with water, sodium molybdate and potassium molybdate, which are originally OT-soluble in water, will be eluted and removed. As long as the molybdenum powder is obtained at a reduction temperature of 1.0000 C or lower, any commonly obtained raw material can be used, such as ammonium molybdate obtained through a recrystallization operation or molybdenum trioxide obtained through a volatilization operation. It was discovered that the alkali content was removed more efficiently than molybdenum, even if the molybdenum was removed, due to the clear cleaning effect of water.
We have arrived at the present invention.

That is, the gist of the present invention is a method for purifying metal molybdenum, which comprises washing a metal molybdenum powder containing sodium and potassium with water to elute metal molybdenum and potassium.

Note that the temperature commonly used for reducing molybdenum (1,000
temperatures exceeding 1,500°
When reduction with C is effective, or when metal molybdenum powder is heated to such high temperatures, the powder particles tend to aggregate and become coarser, and the alkali content tends to be encapsulated within the coarse particles. Although this is thought to be due to this, it is necessary to keep in mind that this often results in a decrease in the removal efficiency of alkalinity.

The conditions for washing with water in the present invention include water amount and water temperature.

Various combinations such as stirring conditions can be used, and the required processing time is determined by these combinations, which can be determined with reference to the examples described below.

As described above, the present invention provides a method for efficiently purifying molybdenum for forming gate electrodes of large-scale integrated circuits, especially ultra-large-scale integrated circuits, and its industrial value is extremely high.゛Next, the present invention will be explained in more detail with reference to examples, but the scope of the present invention is not limited by these actual cases.

Actual case 1 Molybdenum oxide containing Na2.91)I)m, K14 ppm per molybdenum obtained by thermally decomposing purified ammonium molybdate was heated at a temperature of 400°C2 in a hydrogen gas stream.
Next, it was reduced at 750°C to obtain molybdenum metal powder.

Na and Ki in this molybdenum metal powder matched the above values within the analytical error range.

Place 1 kg of the molybdenum metal powder in a Teflon container,
Distilled water 3 at a temperature of 45°C was stirred for 1.5 hours, left to stand, the upper liquid was removed, and then newly added to distilled water Xt at a temperature of 45°C.
was added, stirred for 10 minutes, filtered, and dried in a nitrogen gas stream at a temperature of 100°C to obtain 980 g of molybdenum metal powder. The content of Na in this product is 0.1 p.
pm or less, and it was found that Na and K were sufficiently removed by water washing.

Practical fee 2 J, [II H-produced Na O per molybdenum, 4 pI
)m, KO, 3 ppm in a hydrogen gas stream at a temperature of s o o'c and then at 800°C.
It is heated and reduced to molybdenum metal powder. 10 kg of this molybdenum metal powder was placed in a polypropylene container (501) together with 40 t of deionized water, stirred at a temperature of 70° C. for 1 hour while blowing nitrogen gas, and then allowed to stand still.

After cooling, the supernatant was removed, and then washed with methanol and ethanol in that order, and dried at a temperature of 80°C in a vacuum dryer. The Na content in the obtained molybdenum metal powder is 0.1 pl)In or less, and Na.

It was found that K was sufficiently removed by washing with water.

Applicant Mitsubishi Metals Co., Ltd. Substitute Yoshinao Shirakawa

Claims (1)

[Claims] (1) Mix molybdenum powder containing sodium and potassium with water & re L, the sodium and potassium wH
To let it out? Characteristic method of making molybdenum treetops.