JPH0433739B2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention is a method for producing lead titanate, which can be used as a filler for low-melting glass, which is a sealant for semiconductor devices, in order to reduce malfunctions of semiconductor devices. It is related to.

BACKGROUND OF THE INVENTION Lead titanate (PbTiO ₃ ) powder is already widely used as a component of low-melting glass for sealing semiconductor devices, piezoelectric materials, pyroelectric materials, and the like.

Among these uses, for example, Japanese Patent Application Laid-Open No. 54-36314 is used as a low-melting glass for hermetically sealing semiconductor devices.
As described in JP-A No. 54-36316, JP-A No. 55-100239, etc., the main components are PbO and B ₂ O ₃ , and a small amount of A ₂ O ₃ ,
Boric acid made by adding about 50-60% by weight of non-devitrification, low-melting glass powder made of SiO ₂ , ZnO, PbF ₂ etc. and about 50-40% by weight of low-expansion lead titanate powder, which is a filler. Lead-based low melting point glass is the mainstream.

By the way, semiconductor devices that use such glass as a sealant have a phenomenon in which semiconductor memory temporarily malfunctions, which is caused by radioactive alpha particles generated by the semiconductor device. Therefore, various studies have been made to prevent α particles from entering semiconductor devices and to remove sources of α particles.

For example, in the specification of JP-A-59-169955, in order to reduce the occurrence of memory errors, the content of radioactive isotopes is set to less than 20 ppb as a non-devitrification low melting point glass powder, and the number of counts of radioactive α particles is reduced.
It is taught that it should be less than O.1 CPH/cm ² .

On the other hand, conventional methods for producing lead titanate powder can be roughly divided into two methods: PbO and TiO ₂
The so-called "dry method" involves mechanically pulverizing a bulk PbTiO ₃ compound synthesized by heating a mixed powder of PbTiO 3 after cooling.
The so-called "co-wetting method" has been known, which consists of adding a mixed solution of a lead compound and a titanium compound to a precipitate forming solution to cause coprecipitation, and drying and calcining the coprecipitate.

Problems to be Solved by the Invention As mentioned above, in lead borate-based low melting point glass made of non-devitrification low melting point glass powder and low expansion lead titanate powder as a sealing agent for semiconductors, conventional It was proposed that the count number of radioactive α particles should be kept below 0.1 CPH/cm ² for non-devitrified, low-melting glass powder in order to prevent the adverse effects of radioactive isotopes. No attention was paid to the powder, and as a result, it was not possible to completely prevent memory errors in semiconductor devices.

In addition, regarding the manufacturing method of lead titanate powder with low expansion property, the conventionally known dry method has a relatively high Curie point of lead titanate powder of approximately 500°C, and furthermore, the crystal lattice has a very large distortion. However, the sinterability was not sufficient due to the presence of carbon dioxide, and it also had the disadvantage that it was difficult to obtain a product with a uniform composition.

On the other hand, according to the known co-precipitation method, although a powder with excellent uniformity can be obtained, it has the disadvantage that secondary particles are likely to be formed and, therefore, it is difficult to easily sinter. Furthermore, as a titanium compound, it is desirable to use titanium tetrachloride, which is inexpensive, but when this is used, there is a problem that the chlorine ions in titanium tetrachloride react with lead ions to form a white precipitate. There was a problem in that expensive compounds such as titanium oxynitrate had to be used.

In view of the current situation, the present invention aims to improve or eliminate the drawbacks of the prior art as described above, and to provide a lead titanate for low melting point glass that satisfies the requirements of easy sinterability, uniformity, and low cost. The present invention provides a method for producing lead titanate, particularly lead titanate, which is used to reduce semiconductor malfunctions and can be suitably used as a filler for low-melting glass, which is a sealing agent for semiconductor devices.

Means for Solving the Problems That is, the present invention consists of (i) dissolving metallic lead or lead oxide with a grade of 4 nines or higher in nitric acid so that the concentration of free nitric acid becomes 5 to 10 mo, and then cleaning with an anion exchange resin. A precipitate is produced by mixing an aqueous solution of a liquid-treated lead compound and a precipitate forming solution, and the precipitate is dried and calcined to produce a lead compound; () a thermal decomposition product of titanium tetrachloride purified by distillation;
or the sealing of a semiconductor device, characterized in that the precipitate produced by mixing the aqueous solution or alcohol solution of titanium tetrachloride and the precipitate liquid is mixed with a fired product obtained by drying and firing, and calcining the mixture. The present invention relates to a method for producing lead titanate with a radioactive α particle count of 0.1 CPH/cm ² or less, which is used as a low-melting glass agent.

In the present invention, the number of counts of radioactive α particles generated from radioactive isotopes such as U and Th is
Lead titanate is produced in the following manner in order to reduce the concentration to 0.1 CPH/cm ² or less and to prevent memory errors in semiconductor devices.

As the lead compound that is a component of lead titanate, a lead compound () manufactured by the following method is used.

That is, metal lead of grade 4 nines or higher or lead oxide such as lead zinc oxide, lead monoxide, trilead tetroxide, lead dioxide, etc. is dissolved in nitric acid so that the concentration of free nitric acid is 5 to 10 mo, and U, Th (In addition, the adsorption efficiency of U, Th, etc. is good in the above free nitric acid concentration range,
It has been found that when it is lower than the above range, the adsorption efficiency deteriorates, while when it is too high, it has an adverse effect on the ion exchange resin. ) Thereafter, a liquid purification treatment is performed using an anion exchange resin to obtain an aqueous solution in which radioactive isotopes are adsorbed and removed. Next, the aqueous solution is added to a precipitate-forming liquid such as ammonia, ammonium oxalate, caustic alkali, etc. while stirring, or vice versa, to form a precipitate. Or after cleaning with alcohol etc.
Dry, bake and crush at 120-800℃.

On the other hand, as a titanium compound which is a constituent of lead titanate, a titanium compound () manufactured by the following method is used.

That is, titanium dioxide obtained by thermal decomposition of purified and distilled titanium tetrachloride, or an aqueous or alcoholic solution of titanium tetrachloride, is added to the precipitate-forming liquid, or vice versa, to form a precipitate. The precipitate is washed with pure water, alcohol, etc. as necessary, then dried at 120 to 900°C, calcined, and pulverized before use.

The aqueous or alcoholic solution of titanium tetrachloride may be purified using an anion exchange resin in the same manner as in the production of the lead compound (2).

The lead titanate powder of the present invention is produced by thoroughly mixing the lead compound () and the titanium compound (), and then
Obtained by calcining at approximately 400-1200°C.

If the above calcination temperature is lower than 400℃, the solid phase reaction of the mixed powder will be insufficient;
If the temperature exceeds 1,200°C, the powder becomes coarse, resulting in poor sinterability.

Effects of the Invention According to the method of the present invention, easily sinterable and uniform lead titanate powder can be obtained. Furthermore, since titanium dioxide obtained from inexpensive titanium tetrachloride can be used, the manufacturing cost is also low. Furthermore, the obtained lead titanate powder has a high count of radioactive α particles.
Since it is 0.1 CPH/cm ² or less, it can be suitably used as a filler for low-melting glass, which is a sealant for semiconductor devices.

Examples Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 Reagent grade (PbO 99.9% or more) lead monoxide 22.31g
In addition to 150 m of reagent grade nitric acid [free nitric acid concentration 6.3 mo] diluted with pure water (1:1),
The mixture was heated and dissolved to form an aqueous solution. This aqueous solution was passed through a tower filled with an anion exchange resin to adsorb and remove U, Th, etc., and then added dropwise to 4N ammonia 1 with stirring to form a precipitate of lead hydroxide.

This precipitate was washed with pure water, dried at 120°C for 1 hour, calcined at 750°C for 1 hour, and ground in a ball mill.

Next, 7.68 g of chlorine-method titanium dioxide powder prepared by thermal decomposition of first-class reagent titanium tetrachloride (purity 99.95% or more, specific gravity 1.72 to 1.76) was added to the pulverized material, and the mixture was milled in a ball mill. After mixing, the mixture was calcined at 850° C. for 2 hours and further ground in a ball mill to obtain lead titanate (PbTiO ₃ ) powder.

The count number of radioactive α particles in this powder was measured using an α-ray measuring device and found to be 0.074 CPH/cm ² .

When this powder was observed using a scanning electron microscope, it was found that it had a uniform particle size of approximately 0.3μ, and β cos θ ~ sin θ (where β is the half width of the diffraction line,
θ represents the black angle. ), it was confirmed that the composition was almost parallel to the horizontal axis (sinθ axis) and had a uniform composition with almost no compositional fluctuations.

Example 2 100 ml of an aqueous solution prepared by dissolving 18.97 g of the distilled and purified titanium tetrachloride in pure water was dropped into one portion of 4N ammonia water with stirring to form a precipitate of titanium hydroxide. Wash this precipitate with pure water and
After drying at ℃ for 1 hour, baking at 750℃ for 1 hour,
Then, it was ground in a ball mill.

Then, in the same manner as in Example 1, U,
Using metallic lead with a count number of radioactive α particles of 0.05 CPH/cm ² that adsorbed and removed Th, etc., 22.31 g of lead monoxide produced by a conventional method was added, mixed in a ball mill, and then baked at 850°C for 2 hours. , Further, it was ground in a ball mill to obtain lead titanate powder. Results of measuring the number of counts of radioactive α particles in this powder
It was 0.066CPH/ ^cm2 . The powder has a uniform particle size of approximately 0.3μ, and βcosθ~
As a result of plotting the relationship of sinθ, it was confirmed that the composition was uniform.

Comparative Example 1 Commercially available reagent grade PbO and TiO ₂ powders were blended to have a composition of PbTiO ₃ and mixed in a ball mill.
Calcined at 950℃ for 2 hours, powdered again using a ball mill,
I made a powder.

The count number of radioactive α particles in this powder was measured and found to be 3.85 CPH/cm ² . Also, this powder
As a result of plotting the relationship between β cos θ and sin θ using X-ray diffraction, compositional fluctuations were observed.

Comparative Example 2 Lead titanate powder was obtained in the same manner as in Example 1 except that 150 m of pure reagent grade nitric acid (free nitric acid concentration 3.0 mo) diluted (1:3) was used as the nitric acid aqueous solution.

The count number of radioactive α particles in this powder is
It was 0.62CPH/ ^cm2 .

Comparative Example 3 20% HCl aqueous solution of titanium trichloride (1.5 mol)
Acicular titanium dioxide was produced by keeping 500 ml at 95° C. and supplying air at a rate of 5 N/min for 40 hours, and the white precipitate produced was thoroughly washed with water, filtered, and dried. Lead titanate powder was produced in exactly the same manner as in Example 1, except that 7.68 g of this titanium dioxide powder was used in place of 7.68 g of titanium dioxide powder produced from distilled and purified titanium tetrachloride.

The count number of radioactive α particles in this powder is
It was 1.58CPH/ ^cm2 .

Claims (1)

[Claims] 1(i) A lead compound obtained by dissolving metallic lead or lead oxide with a grade of 4 nines or higher in nitric acid so that the concentration of free nitric acid becomes 5 to 10 mol, and then treating the solution with an anion exchange resin. A precipitate is produced by mixing an aqueous solution of and a precipitate-forming liquid, and the precipitate is dried and calcined to produce a lead compound; () a thermal decomposition product of titanium tetrachloride purified by distillation;
or a fired product obtained by drying and firing a precipitate produced by mixing the aqueous solution or alcohol solution of titanium tetrachloride and a precipitate forming liquid, and then calcining the mixture, for bonding a semiconductor device. A method for producing lead titanate with a count number of radioactive α particles of 0.1 CPH/cm ² or less for use in low-melting glass as an agent.