JPH0367970B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention can be used as a sealing agent for airtight sealing in the assembly of semiconductor devices such as not only ordinary ICs but also large-capacity memory devices such as 64K RAM and 256K RAM, and various types of VLSI. The present invention relates to a method for producing lead oxide, which is a raw material for suitable low-melting glass, particularly low-melting glass that reduces the occurrence of memory errors. 2. Description of the Related Art Generally, as one type of semiconductor device, a dipping type package shown in a schematic vertical cross-sectional view in FIG. 2 is known. This ceramic type package mainly consists of alumina ceramic containers 2 and 2' each having a recess for forming a predetermined cavity 3, and a semiconductor element 5 soldered to the recess of one of the alumina ceramic containers. It consists of leads 4, 4' and a glass seal 1 that airtightly seals a pair of alumina ceramic containers 2, 2' with the lead wires in between. For example, a glass powder slurry 1' is applied to the surfaces of a ceramic container 2, 2' to be joined to each other, as shown in FIG. It can be obtained by heating and melting. Low melting point glasses for hermetically sealing semiconductor devices include a small amount of Al ₂ O ₃ , SiO ₂ , ZnO,
Lead borate glass containing PbF ₂ etc. as its main components, usually PbO: 70-85% by weight and B ₂ O ₃ : 10-13% by weight, is conventionally used. The semiconductor device used as the agent had a phenomenon in which the semiconductor memory temporarily malfunctioned, and this memory error caused problems in the reliability of the device. As a result of repeated research to prevent the occurrence of memory errors in the above-mentioned semiconductor devices, the inventor of the present application has found that the occurrence of memory errors is caused by the main component of low melting point glass.
We discovered that this is caused by radioactive isotopes contained as unavoidable impurities in PbO, and if the content is less than 20 ppb, we can suppress the number of radioactive α particle counts to 0.1 CPH (counts/hour)/cm ² or less. We have obtained the knowledge that it is now possible to obtain an extremely reliable semiconductor device without the occurrence of memory errors. That is,
Lead oxide produced by normal methods contains more than 100 ppb of radioactive isotopes such as U and Th, which is measured by the number of radioactive α particles.
Equivalent to CPH/cm ² to several 100 CHP/cm ² . In this way, when low-melting glass whose main component is lead oxide, which has a high content of radioactive isotopes, is used to seal semiconductor devices, radioactive α particles emitted from this glass can cause memory errors and reduce reliability. It becomes something that does not exist. Therefore, in order to prevent the negative effects of these radioisotopes from appearing, the content of radioisotopes contained in lead oxide should be kept below 20 ppb, and the count number of radioactive α particles should be kept at 0.1 CPH/ ^cm2. It is necessary to do the following. The present invention has been made based on the above findings, and consists of dissolving lead having a grade of 4 nines or higher in high-purity concentrated nitric acid, and converting radioactive isotopes such as U and Th into complex anions. , adjust the free nitric acid concentration to 5-10 molar concentration with pure water. The reason why the concentration is 5 to 10 molar is because the adsorption efficiency of U and Th is good within this range. Thereafter, the radioactive isotopes U and Th can be adsorbed and removed by performing anion exchange resin purification treatment. The solution with a low content of U and Th thus obtained is neutralized using aqueous ammonia or an alkaline agent such as caustic soda to precipitate lead hydroxide, which is then filtered and roasted to obtain lead oxide. . The lead oxide obtained as above has a content of radioisotopes such as U and Th of less than 20 ppb,
It was also confirmed that the count number of radioactive α particles was 0.1 CPH/cm ² or less. Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to the following examples unless the gist thereof is exceeded. Example 4 After dissolving lead having a grade of nine or higher in concentrated nitric acid, the free nitric acid concentration was adjusted to 5 mol, 7.5 mol,
Each was adjusted to 10 mol. Next, U and Th are adsorbed and removed by passing through a column filled with a commercially available anion exchange resin such as Diamond Ion, neutralized with caustic soda to precipitate lead hydroxide, and this is roasted to form lead oxide. I got it. When we measured the content of radioactive isotopes in these lead oxides, they were all less than 20 ppb, and the alpha particle count was 0.1 CPH/cm ²
It was confirmed that: Furthermore, it was confirmed that no memory errors occurred due to the low melting point glasses manufactured using these lead oxides. The test conditions and results were changed to Test 1, corresponding to the above free nitric acid concentrations of 5 mol, 7.5 mol, and 10 mol.
2 and 3 are shown in Table 1.

[Table] As shown above, lead oxide produced by the method of the present invention contains less than 20 ppb of radioactive isotopes such as U and Th, so the number of alpha particles counted is
It was 0.1 CPH/cm ² or less, and when these were used as raw materials for glass for semiconductor devices, no memory errors caused by the α particles were observed.

[Brief explanation of drawings]

Figure 1 shows the sealant slurry applied to an alumina ceramic container for IC, and Figure 2 shows the state where the sealant slurry is applied.
FIG. 2 is a schematic vertical cross-sectional view of a deep-type IC package. 1...Sealing agent, 1'...Sealing agent slurry, 2,
2'... Alumina ceramic container, 3... Cavity, 4, 4'... Lead wire, 5... Semiconductor element.

Claims (1)

[Claims] 1 Lead with a grade of 4 nines or higher with a free nitric acid concentration of 5 to 5
The content of radioactive isotopes is less than 20 ppb, which is obtained by dissolving in nitric acid to a concentration of 10 molar, followed by anion exchange resin purification treatment, and then neutralization and precipitation with an alkaline agent. A method for producing lead oxide for low melting point glass for sealing semiconductor devices, which is large in size and has a count number of radioactive α particles of 0.1 CPH/cm ² or less.