JP3090174B2 - Low radiation glass - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cover glass used as a window glass of a ceramic package such as alumina for accommodating a solid-state imaging device such as a CCD, and more particularly, to a solid-state imaging device which hardly causes soft errors and damages the device. The present invention relates to a cover glass for an element.

[0002]

2. Description of the Related Art Conventionally, as a solid-state imaging device, a solid-state imaging device such as a CCD is mounted in a ceramic package such as alumina, and a cover glass having a function as a window glass is sealed in a ceramic package. Those having a structure in which elements are housed are widely used.

A solid-state image sensor is a device in which a number of fine light-receiving elements are integrated on a silicon substrate like a semiconductor IC. Radiation generated due to a package or glass around the solid-state image sensor is used. Is incident on these light-receiving elements, a hole-electron pair is induced by the energy of radiation, and this causes a problem called a so-called soft error that instantaneously causes a bright spot or a white spot on an image. Is Nikkei Electronics (1979.8.6
No. 58-72). In addition to the problem of the soft error, there is a case where the incident of the radiation causes a permanent damage to the element and a problem such that a white spot occurs at the time of a dark signal.

In a solid-state image pickup device, since it is necessary to take an optical signal into an element, a cover glass as a window glass is always sealed in a package, and the material of this kind of cover glass is excellent in weather resistance and fogging. Borosilicate glass or alkali-free barium silicate glass, which is less likely to cause odor, is used.

However, these borosilicate glass and alkali-free barium silicate glass have a large radiation dose, and the cover glass is mounted so as to face the element, so that radiation radiated therefrom is large for the element. Affect.

Particularly, in recent years, as the precision has been improved by increasing the number of pixels per unit area, the elements have become finer and finer, so that the influence of radiation has become more noticeable.

[0007] Under such circumstances, various countermeasures against radiation generated from the cover glass have been attempted. For example, Japanese Patent Application Laid-Open No. 1-173639 discloses that high-purity quartz glass is used for the cover glass, 3-74874
Japanese Patent Application Laid-Open Publication No. H11-163873 proposes that a silicate glass thin film containing lead is formed on an element to shield radiation.

[0008]

SUMMARY OF THE INVENTION However, Japanese Patent Laid-Open No.
In Japanese Patent No. 173636, high-purity quartz glass is used for the cover glass, and the thermal expansion coefficient of the ceramic package is set to an intermediate value between the thermal expansion coefficient of the high-purity silica glass and the thermal expansion coefficient of the solid-state imaging device. However, high-purity quartz glass is very expensive and requires the use of a special package other than alumina, which makes it difficult to reduce the cost of the solid-state imaging device.

Japanese Patent Application Laid-Open No. 3-74874 discloses that a silicate glass thin film containing lead is formed in a sensor portion to shield radiation, but the number of process steps for film formation is increased, In order to shield radiation, a film having a considerable thickness is required, so that a long time is required for the film forming process.

The present invention has been made in view of such conventional problems, and has as its object to reduce the radiation dose even when a film is not formed when used as a cover glass of a solid-state imaging device. Accordingly, an object of the present invention is to provide a low radiation glass that does not cause a soft error or permanent damage to a solid-state imaging device.

Still another object of the present invention is to make the thermal expansion coefficient close to that of alumina ceramic and use the same ceramic package as before, so that it is inexpensive and easy to manufacture. Is to provide glass.

[0012]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, the radiation emitted from a cover glass made of a multi-component silicate glass such as borosilicate glass or alkali-free barium silicate glass. The main cause of the generation of α-rays, which is a kind of, is due to U and Th contained in glass as impurities,
It has been found that the main cause of Th lies in the zirconia raw material and the barium raw material.

It has been well known that a zirconia-based material is a source of alpha rays from a detailed investigation of glass materials. However, in addition to the zirconia-based material, a barium material has a high α-dose. There was found. For example, for barium carbonate generally used as a barium raw material,
The α-ray measurement values of the normal-grade product and the high-purity product were as follows.

Conventional barium carbonate 0.5 to 15 C / cm ² · hr. High purity barium carbonate 0.1 C / cm ² · hr.

The present inventor has also reported that the main cause of β-ray generation, which is a kind of radiation emitted from a cover glass, is that K included in the glass.
Is of by ⁴⁰ K is a radioactive isotope, by suppressing the content of K ₂ O in the glass below a predetermined value, and also found that it is possible to lower the β-ray radiation amount.

That is, the low-radiation glass of the present invention is composed of 62.0 to 75.0% of SiO ₂ and Al ₂ O by weight percentage.
_{3 4.0~10.0%, B 2 O 3} 8.0~15.0
_{%, Na 2 O 10.5~12.5%,} Li 2 O + Na
_{2 O 10.5 ~20.0%, K 2} O 0~2.0%,
MgO + CaO + SrO + ZnO 0.3-21.0
%, BaO 0~ 1.0%, and having a composition of ZrO ₂ 0 to 1.0%.

The low-radiation glass of the present invention preferably has a SiO ₂ content of 62.0 to 75.0% by weight,
Al ₂ O ₃ 4.0 to 10.0%, B ₂ O ₃ 8.0 to
_{15.0%, Li 2 O 0~3.0%} , Na 2 O 1
0.5-12.5% , K ₂ O 0-0.5%, MgO 0
１10.0%, CaO 0 to 10.0%, SrO 0
5.0%, ZnO 0.3-5.0%, BaO 0
0.4%, and having a composition of ZrO ₂ 0 to 0.5%.

Further, the low-radiation glass of the present invention is used as a cover glass of a ceramic package for a solid-state imaging device.
It is preferable that the thermal expansion coefficient in the temperature range of 50 ° C. be 50 to 75 × 10 ⁻⁷ / ° C., which is close to that of alumina (70 × 10 ⁻⁷ / ° C.), because it can be easily sealed with the alumina ceramic package.

[0019]

Next, the reason why the preferred composition of the low radiation glass in the present invention is limited as described above will be described.

First, SiO ₂ is a component having an effect of improving the weather resistance of glass, and its content is 62.0%.
%, The effect is small. On the other hand, if it exceeds 75.0%, melting of the glass becomes difficult.

Al ₂ O ₃ also has an effect of improving the weather resistance of the glass. However, if its content is less than 4.0%, the effect is small, while if it exceeds 10.0%, melting of the glass becomes difficult. Become.

B ₂ O ₃ has the effect of lowering the viscosity of the glass to increase the homogeneity and improving the devitrification resistance of the glass. However, if the content is less than 8.0%, the effect is small. On the other hand, if it exceeds 15.0%, the weather resistance of the glass deteriorates, and the amount of volatilization during melting increases, making it difficult to obtain a homogeneous glass.

[0023] Li ₂ O ₃ and Na ₂ O, as well as to increase the homogeneity decreasing the viscosity of the glass and has an effect of adjusting the thermal expansion coefficient of the glass, Na ₂ O is less 10.5%
, The viscosity of the glass increases and the homogeneity decreases
And solid-state imaging using an alumina ceramic package.
As a cover glass for imaging devices, the thermal expansion coefficient is low.
Too much. Na ₂ O is 12.5% or more, or Li
_{When the} total amount of ₂ O and Na ₂ O is 20.0% or more, the weather resistance of the glass deteriorates and the coefficient of thermal expansion becomes too high.

K ₂ O has the same action as Li ₂ O and Na ₂ O, but its content must be suppressed to 2.0% or less in order to reduce the generation of β-rays.

MgO, CaO, SrO and ZnO have the effect of improving the weather resistance of the glass, lowering the viscosity of the glass, and suppressing volatilization during melting to increase the homogeneity. If it is less than 0.3%, the effect cannot be sufficiently obtained, while if it exceeds 21.0%, the glass tends to be devitrified.

BaO is also MgO, CaO, SrO, Zn
O has the same effect as O, but since the raw material contains a large amount of U and Th that emit α rays, its content needs to be suppressed to 1.0% or less.

Further, as described above, ZrO ₂ also contains a large amount of U and Th that emit α rays in its raw material, so that its content must be suppressed to less than 1.0%.

In the present invention, As ₂ O ₃ , Sb ₂ O ₃ , chloride and fluoride are contained as fining agents in addition to the above-mentioned components as long as the properties of the glass are not deteriorated. It is also possible.

[0029]

EXAMPLES Hereinafter, the low radiation glass of the present invention will be described in detail based on examples.

Tables 1 and 2 show Examples (Sample Nos. 1 to 4 ).
And Comparative Examples (Sample Nos. 5 to 8 ).

[0031]

[Table 1]

[0032]

[Table 2]

No. in the table. Each of the samples 1 to 8 was prepared as follows.

First, a glass raw material prepared so as to obtain a glass having the composition shown in the table is placed in a platinum crucible and placed in an electric furnace.
After melting at 00 ° C. for 5 hours, the molten glass was poured out on graphite, and then strained in a slow cooling furnace.

Using the samples thus prepared, the amount of α-ray radiation and the coefficient of thermal expansion in the temperature range of 30 to 380 ° C. were measured.

As is apparent from the table, the N
o. Each sample of Nos. 1 to 4 has an α-ray emission of 0.007 C / c.
m ² · hr. And the coefficient of thermal expansion is 66 to
It was 74 × 10 ⁻⁷ / ° C., which was similar to that of alumina ceramic.

On the other hand, in Comparative Example No. Each of the samples 5 and 6 has a coefficient of thermal expansion of 60 × 10 ⁻⁷ / ° C., 52
× 10 ⁻⁷ / ° C., but the α-ray emission was 0.6 C / c
m ² · hr. , 0.7 C / cm ² · hr. And both were high.

No. The sample of No. 7 had an α-ray emission of 0.
1 C / cm ² · hr. Therefore, since the thermal expansion coefficient is as low as 47 × 10 ⁻⁷ / ° C., it is considered that it is difficult to seal the alumina ceramic package as compared with the samples of the examples.

However, no. 8 has an α-ray emission of 0.008 C / cm ² · hr. Low and the coefficient of thermal expansion is 6
It was 5 × 10 ⁻⁷ / ° C., and all the characteristics were good.

Next, a cover made of the composition of each sample of the example was used.
Glass was produced and sealed in an alumina ceramic package to which a solid-state imaging device was attached, and this solid-state imaging device was used for a long time. However, no soft error or permanent damage of the solid-state imaging device occurred.

For comparison, no. When a cover glass having the composition of Sample No. 8 was prepared, and a solid-state imaging device was prepared and used for a long time in the same manner as described above, a soft error of the solid-state imaging device occurred. The reason is as follows. It is considered that Sample No. 8 contained 3.0% of K ₂ O, so that the glass contained a large amount of ⁴⁰ K, and a large amount of β rays were generated from the cover glass.

In the table, the amount of α-ray radiation is measured by using a gas flow proportional counter measuring device, and the coefficient of thermal expansion is measured by using a quartz tube dilatometer.

[0043]

As described above, the low-radiation glass of the present invention, even when used as a cover glass for a solid-state imaging device, generates a soft error or permanent damage to the device because of a small radiation dose. By making the thermal expansion coefficient close to that of alumina ceramic, the same ceramic package as that of the related art can be used, so that it is inexpensive and easy to manufacture.

──────────────────────────────────────────────────続 き Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C03C 1/00-14/00 H01L 27/14 H01L 21/339 H01L 29/762 H01L 23 / 02,23 / 04,23 / 10 H01L 33/10

Claims (4)

(57) [Claims] 1. The composition according to claim 1, wherein the weight percentage of SiO _{2 is} 62.0-7.
_{5.0%, Al 2 O 3 4.0~10.0} %, B 2 O 3
8.0~15.0%, Na ₂ O 10.5~12.5
_{%, Li 2 O + Na 2} O 10.5 ~20.0%, K 2
O 0-2.0%, MgO + CaO + SrO + ZnO
0.3-21.0%, BaO 0-1.0%, ZrO ₂
A low radiation glass having a composition of 0 to 1.0%. 2. The composition according to claim 1, wherein the SiO ₂ content is 62.0-7% by weight.
_{5.0%, Al 2 O 3 4.0~10.0} %, B 2 O 3
_{8.0~15.0%, Li 2 O 0~3.0%} , Na 2
O 10.5-12.5% , K ₂ O 0-0.5% , M
gO 0-10.0%, CaO 0-10.0%, Sr
O 0-5.0%, ZnO 0.3-5.0%, BaO
0 to 0.4%, low radiation glass according to claim 1, characterized in that it has a composition of ZrO ₂ 0 to 0.5%. 3. The low radiation glass according to claim 1, which is used as a cover glass of a ceramic package for a solid-state imaging device. 4. The low radiation glass according to claim 3, wherein a coefficient of thermal expansion in a temperature range of 30 to 380 ° C. is 50 to 75 × 10 ⁻⁷ / ° C.