JPH09165692A - Low alpha ray lead for semiconductor material and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a low α ray lead having the α ray dose extremely lower than the α ray dose of the conventional products and to provide a process for smelting such lead. SOLUTION: The low α ray lead for semiconductor materials having a grade of 4i4 nines and a count number of radioactive αparticles of <=0.05CHP/cm<2> is produced by executing electrolyte refining using the crude lead obtd. by heating and melting lead sulfide together with an alkaline metal salt having the α ray dose of <=1CHP/cm<2> and a reducing agent in a nonoxidizing atmosphere, thereby subjecting the alkaline metal salt to reduction decomposition and subjecting the lead sulfide to desulfurization reduction as anode and sulfamic acid contg. substantially no radioactive isotope as an electrolyte.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to lead for semiconductor materials, which has a significantly lower count number (α dose) of radioactive α particles than conventional products and maintains a low α dose over time, and a method for producing the same.

[0002]

2. Description of the Related Art Lead is used not only as a solder material for assembling circuits of electronic devices, but also as an alloy thereof as a brazing material for die bonding of various LSIs and joining of device members. It is also used as a glass component for a package sealing material and the like. By the way, in these electronic devices, with the high integration of semiconductor elements, soft errors have become a problem, and this is mainly due to α rays emitted from the packaging material of the elements, There is a need for low α-lead that has as low an α-dose as possible.

As a method of obtaining lead having a small α dose, a method of electrolyzing a sulfamic acid solution as an electrolytic solution (Japanese Patent Publication No. 62-47955) or a source of α rays by weight-separating lead ore is used. There is conventionally known a method (Japanese Patent Laid-Open No. 1-132725) for removing the host rock and gangue and reducing the alkali in an oxygen atmosphere.

[0004]

According to the former electrolytic refining method, it is possible to obtain metallic lead having a much smaller α dose than the usual electrolytic method using hydrofluoric acid as an electrolytic bath, but it is subjected to electrolysis. It is greatly affected by the alpha dose of lead metal. If the α dose of lead metal used for electrolysis is high, there is a limit to the reduction of α by this electrolysis method. Conventionally, lead bullion is obtained by roasting lead ore mainly composed of galena and converting it to lead oxide for smelting reduction, or by air reduction simultaneously with oxidation. Therefore, the yield of crude lead is low, and it is difficult to obtain lead with a small α dose at low cost.

In the latter alkali reduction method, the host rock or gangue, which is a source of α-rays, is removed by weight separation treatment, and the lead ore is used as coarsely dispersed as possible. It is difficult to maintain stable quality because the α-ray dose varies greatly depending on the production site and the influence of the production site is large. Further, the smelting method after beneficiation follows the general reduction method described above, and therefore there is a problem that the yield of crude lead is low and the manufacturing cost is high. Furthermore, there is a limit to lowering α, and the α dose of crude lead obtained is about 0.01 to 0.05 immediately after electrolysis.
Although it is about CPH / cm ² , there is a problem that after 1 to 2 years, the α dose becomes about 10 times the above value.

The present invention solves the above problems in the conventional low α-lead, and provides a lead for semiconductor material which has a significantly lower α-ray dose than the conventional product and which maintains a low α-ray dose over time. It is an object of the present invention to provide a production method having a high yield.

[0007]

According to the present invention, the following low α-ray lead for semiconductor material is provided. (1) A low α-ray lead for a semiconductor material, which has a quality of 4 nines or more and a radioactive α particle count of 0.05 CHP / cm ² or less.

Further, according to the present invention, a low α for the above semiconductor material is used.
As a method for obtaining the lead wire, the following manufacturing method described in claims 2 to 3 is provided. (2) Lead sulfide is obtained by desulfurizing and reducing lead sulfide by heat-melting it with an alkali metal salt having an α dose of 1 CHP / cm ² or less and a reducing agent in a non-oxidizing atmosphere, and reductively decomposing the alkali metal salt. The crude lead is used as an anode, and sulfamic acid containing substantially no radioactive isotope is used as an electrolytic solution for electrolytic refining to have a quality of 4 nines or more and a radioactive α particle count of 0.05 CHP / cm ² A method for producing a low α-ray lead for a semiconductor material described below. (3) α dose of 1 as alkali metal salt and reducing agent
Using sodium hydroxide and carbon of CHP / cm ² or less, the lead concentration in the electrolytic solution is 30 to 150 g / l, the sulfamic acid concentration is 30 to 150 g / l, and the cathode current density is 0.5 to 2.0 Am.
The production method according to (2) above, in which p / dm ^{2 is used} for electrolytic refining.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. (I) Smelting step In the manufacturing method of the present invention, in the smelting step of obtaining lead bullion from a raw material ore (sulfide ore), a conventional roasting reduction in which lead sulfide is roasted to convert into lead oxide and then reduced Method, or unlike the above alkaline reducing agent that uses sodium carbonate alone as a reducing agent, lead sulfide is heated and melted together with an alkali metal salt and a reducing agent, and directly reduced and desulfurized without oxidizing and roasting to obtain lead metal. . According to this method, the decomposition of the alkali metal salt is promoted, the desulfurization of lead sulfide is promoted, and the recovery rate of metallic lead is significantly improved. The raw material lead sulfide (lead sulfide) may contain a small amount of copper or zinc.

The alkali metal salt is one in which an alkali metal produced by its decomposition reduces lead sulfide and combines with sulfur to desulfurize lead sulfide, and hydroxides and carbonates such as sodium and potassium are used. The use of an alkaline earth metal salt is not preferable because the recovery rate of metallic lead is lower than that of an alkali metal salt. In order to obtain low α-lead, it is necessary to use an alkali metal salt having a small α-ray source. Specifically, an α-ray dose of 1 CPH / cm ² or less is suitable. Sodium hydroxide, potassium hydroxide, sodium carbonate and the like are available as low α products of alkali metal salts, and sodium hydroxide is most suitable in terms of temperature conditions and economy.

The reducing agent reductively decomposes the above alkali metal salt, and carbon such as graphite, coal and coke is preferable from the viewpoint of reducing power and reaction products. The carbon used reacts with an alkali metal salt such as sodium hydroxide, and reductively decomposes this to become carbon monoxide, carbon dioxide gas, etc., and goes out of the system. In order to obtain low α-lead, it is necessary to use a reducing agent with a small α-ray source, but carbon is also easy to obtain low-α products with an α dose of 0.5 CPH / cm ² or less. preferable.

When sodium hydroxide as an alkali metal salt is added to lead sulfide and heated and melted with carbon as a reducing agent in a non-oxidizing atmosphere, sodium hydroxide is decomposed by carbon according to the following formula, and sodium reacts with lead sulfide. And lead to sulfur, so lead sulfide is reduced and desulfurized to obtain lead metal. Carbon becomes carbon monoxide and escapes to the outside of the system. The generated sodium sulfide becomes slag together with excess caustic soda. PbS + 2NaOH + C → Pb + Na ₂ S + H ₂ O + CO ↑ --- (1)

The amount of each raw material generally follows the equivalence ratio in the above reaction formula, but it is preferable to use the amounts of sodium hydroxide and carbon in a slightly excess amount than the equivalence ratio. Specifically, lead sulfide 10
It is suitable to use 30 to 80 parts by weight of sodium hydroxide and 4 to 12 parts by weight of carbon to 0 parts by weight. These raw materials are charged into a melting furnace or crucible and heated and melted in a temperature range of 700 to 1300 ° C. in a non-oxidizing atmosphere.
By this reaction, lead metal is accumulated at the bottom of the melting furnace or crucible, and slag of sodium sulfide is deposited on it. The sodium sulfide slag also absorbs other impurity elements in the raw lead sulfide and silica in the ore, and is removed from the lead metal.

The recovery rate of metallic lead in the above smelting method is
As shown in Examples described later, it is 90% or more, and a recovery rate significantly higher than that of the conventional smelting method is achieved. Further, in the above smelting method, the use of a low α product alkali metal salt and a reducing agent results in an α dose of 0.
Lead with an extremely low α dose of 02 CPH / cm ² or less can be obtained.

(II) Electrolytic refining step By electrolytically refining the low α-dose lead metal obtained in the above smelting step, a high-quality ultra-low α-dose purified metallic lead is obtained. Electrolytic refining uses the lead metal obtained in the above smelting process as the anode,
Sulfamic acid containing substantially no radioisotope is used as an electrolytic solution. The following ranges are suitable for the liquid composition and the electrolysis conditions. Electrolyte composition: Lead concentration 30 to 150 g / l, sulfamic acid concentration 30 to 150 g / l, liquid temperature: 15 to 50 ° C. Cathode current density: 0.5 to 2.0 Amp / dm ²

As the electrolytic solution, sulfamic acid containing substantially no radioisotope is used, which may be commercially available sulfamic acid. It is not preferable to use silicofluoric acid, which is commonly used in general lead electrolytic refining, in the electrolytic solution instead of sulfamic acid. Due to the high content of thorium in commercial silica hydrofluoric acid, the α dose of purified lead is higher than that of crude lead.

A suitable lead concentration in the electrolytic solution is 30 to 150 g / l. If the lead concentration is lower than this range, elements other than lead also precipitate, and this becomes an impurity and the quality deteriorates. On the other hand, when the lead concentration exceeds the above range, the electrolysis efficiency decreases.
Similarly, the concentration of sulfamic acid in the electrolyte is 30 to 150 g /
l is appropriate. If the concentration of sulfamic acid is lower than this, dissolution of lead will not proceed smoothly, and if the concentration exceeds this range, precipitation of sulfamine will occur, which is not preferable.

The liquid temperature of the electrolytic solution is suitably 15 to 50 ° C. When it is less than 15, the electric resistance of the electrolytic solution becomes large, so that the electrolytic efficiency is lowered, and when it exceeds 50 ° C., the loss due to evaporation of the electrolytic solution becomes large. The current density of the cathode is 0.5-2.
0 Amp / dm ² is suitable. If the current density is lower than this, the electrolysis time will be prolonged, and if the current density is higher than the above range, elements other than lead will precipitate and cause contamination of impurities.

(III) α-Dose and Quality of Purified Lead Purified lead obtained by the above production method has a quality of 4 nines or more and a radioactive α particle count of 0.03 CH
P / cm ² or less. The α dose of purified lead obtained by the conventional manufacturing method is limited to about 0.1 CHP / cm ² , and therefore, according to the above manufacturing method, the α dose is 1/3 or less of the conventional product, which is low for a long time. An extremely low α dose of purified lead that maintains an α dose is obtained.

[0020]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the present invention are shown below together with comparative examples. Example 1 To 2000 g of raw material lead ore (galena) of the grade shown in Table 1, sodium hydroxide (purity 98%, α dose 0.2 CPH / cm ² ) 90
0g and graphite powder (purity 99%, α dose 0.4CPH / c
m ² ) 160 g was mixed in a graphite crucible, charged together with the crucible into a heating furnace under a nitrogen atmosphere, heated to 400 ° C. to remove water and oxygen, and further heated at 950 ° C. for 3
The raw material was melted by heating for a time. After gradual cooling, the slag and metal were separated to obtain lead metal. Table 2 shows the α dose, quality and recovery rate of crude lead along with the type and amount of alkali metal salt added.
It was shown to. Using this lead metal as an anode, lead was purified according to the electrolytic solution composition and electrolysis conditions shown in Table 2 to obtain purified metallic lead. Table 2 also shows the quality, α dose and yield of this purified lead.

Example 2 Instead of sodium hydroxide, sodium carbonate (purity 98.5
%) 1200 g of lead metal was obtained in the same manner as in Example 1. Using this lead metal as an anode, lead was purified according to the electrolytic solution composition and electrolysis conditions shown in Table 2 to obtain purified metallic lead. The results are summarized in Table 2.

Comparative Example 1 (oxidative desulfurization) Instead of the sodium hydroxide and the graphite powder of Example 1, 800 g of sodium carbonate and 400 g of sodium chloride were used, and the mixture was heated to a temperature of 800 to 1000 ° C. for 6 hours while blowing air into lead. I got a bullion. With this lead metal as an anode,
Purified lead was obtained by purifying lead according to the electrolytic solution composition and electrolysis conditions shown in Table 2. The results are summarized in Table 2.

Comparative Example 2 (Iron Nail Method) Iron powder was used as a reducing agent in place of the sodium hydroxide and graphite powder of Example 1, and the raw material was heated and melted under the same conditions as in Example 1 to obtain crude lead. It was Using this lead metal as an anode, lead was purified according to the electrolytic solution composition and electrolysis conditions shown in Table 2 to obtain purified metallic lead. The results are summarized in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

As shown in the results of Table 2, the α dose of purified lead in this example was 0.002 to 0.01 CHP / cm ² immediately after electrolysis, which was slightly higher after 2 years, but was less than 0.2. 01-
It is about 0.03. On the other hand, the α dose of purified lead in the comparative example is 0.03 to 0.05 CHP / cm ² immediately after electrolysis,
After 2 years, it is 0.1 to 0.15 CHP / cm ^2, which is about 5 times or more that of the present invention.

[0027]

According to the present invention, there is provided a purified lead having an α dose of 0.05 CHP / cm ² or less, which has been conventionally difficult to produce, and a method for producing the same. The purified lead obtained by the present invention has a high quality, an extremely low α dose, and since it maintains this low α dose for a long period of time, it is most suitable for semiconductor materials and is advantageous in preventing a soft error of a memory in a semiconductor device. is there. Further, according to the production method of the present invention, the extremely low α-ray dose can be obtained in a high yield, which is suitable for industrial implementation and excellent in practicality.

Claims (3)

[Claims] 1. A low α-ray lead for a semiconductor material, having a quality of 4 nines or more and having a radioactive α particle count of 0.05 CHP / cm ² or less. 2. Lead sulfide is desulfurized and reduced by heat-melting lead sulfide together with an alkali metal salt having an α dose of 1 CHP / cm ² or less and a reducing agent in a non-oxidizing atmosphere, and reductively decomposing the alkali metal salt. The crude lead thus obtained was used as an anode, and sulfamic acid containing substantially no radioisotope was used as an electrolytic solution for electrolytic refining to have a quality of 4 nines or more and a radioactive α particle count of 0.05 CHP / A method for producing low-alpha lead for a semiconductor material of cm ² or less. 3. An alkali metal salt and sodium hydroxide and carbon having an α dose of 1 CHP / cm ² or less as an reducing agent are used, and the lead concentration in the electrolytic solution is 30 to 150 g / l and the sulfamic acid concentration is 30 to 150 g / l. l, cathode current density 0.5〜
The method according to claim ² , wherein the electrolytic refining is carried out at 2.0 Amp / dm ² .