JPH07215733A - Cover glass for solid-state image pickup element - Google Patents

Abstract

PURPOSE:To provide an inexpensive cover glass for solid-state image pickup device small in radiant quantity of alpha-ray beta-ray, having excellent weather resistance and capable of sealing in an alumina package since the average coefficient of linear expansion is 60-75X10<-7>/ deg.C. CONSTITUTION:This cover glass has the composition of, by wt.%, 65.0-75.0% SiO2, 7.0-11.0% Al2O3, 8.0-12.0% B2O3, 3.1-6.9% Li2O does not practically contain K2O and each quantity of uranium (U) and thorium (Th) is <=50ppb.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cover glass for a solid-state image pickup element used as a window glass of a ceramic package such as alumina for accommodating a solid-state image pickup element called CCD, and particularly to suppressing the deterioration of the function of the solid-state image pickup element. The present invention relates to a cover glass that can be used.

[0002]

2. Description of the Related Art Conventionally, as a kind of solid-state image pickup device, a solid-state image pickup device such as CCD is mounted in a ceramic package such as alumina, and a cover glass functioning as a window glass is sealed on the outer surface of the ceramic package. As a result, electronic components housing a solid-state image sensor are widely used.

Similar to a semiconductor IC, a solid-state image pickup element is an integration of a large number of fine light-receiving elements on a silicon substrate, and since it is necessary to take an optical signal into the element, the solid-state image pickup device has a cover glass. It is required that the solid-state image sensor has high light transmission characteristics and does not impair the function of the solid-state image sensor.

Borosilicate glass and non-alkali glass are generally used as the material for this type of cover glass. However, these borosilicate glass and non-alkali glass have a large amount of α-ray radiation, and the cover glass is Since the device is mounted so as to face the device, the α rays emitted from the device have a great adverse effect on the device.

That is, when α rays are emitted from the cover glass and enter the solid-state image sensor, the energy of α rays induces a hole-electron pair, which causes a bright spot or a white spot in the image instantaneously. A phenomenon called a soft error occurs that causes

In particular, in recent years, as the precision has been improved by increasing the number of pixels per unit area, the element has become finer and finer, and the influence of α rays has become more prominent.

Under the circumstances described above, various attempts have been made to prevent α rays generated from the cover glass, for example, Japanese Patent Laid-Open No. 1-1.
In Japanese Patent No. 73639, it is proposed to use high-purity quartz glass having a small amount of α-ray radiation as a cover glass, and in Japanese Patent Laid-Open No. 3-74887, a silicate glass thin film containing lead is formed on an element. By doing α
It has been proposed to shield the lines.

Further, Japanese Unexamined Patent Publication (Kokai) No. 5-279074 proposes a cover glass for a solid-state image pickup device, which is made of borosilicate glass which emits a small amount of α rays.

[0009]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
No. 9, it is proposed that high-purity quartz glass is used as the cover glass, and the coefficient of thermal expansion of the ceramic package is set to an intermediate value between the coefficient of thermal expansion of the high-purity quartz glass and the coefficient of thermal expansion of the solid-state image sensor. However, high-purity quartz glass is very expensive, and its coefficient of linear expansion is considerably larger than that of alumina ceramics (about 70 × 10 ⁻⁷ / ° C.). Therefore, it is difficult to reduce the cost of the solid-state image sensor.

Further, in Japanese Patent Laid-Open No. 3-74874, a film-forming process is required, and a film having a considerable thickness is required to shield α rays, so that the film-forming process is long. It takes time.

The cover glass disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-279074 has a small amount of α-ray radiation because it is made of an inexpensive material and contains few radioactive isotopes such as uranium (U) and thorium (Th). However, since this glass contains Al ₂ O _{3 in an amount} of 5.0% or less, it has a drawback that the weather resistance of the glass is poor. That is, when the weather resistance of glass is poor, crystals of alkali metal or alkaline earth metal are precipitated from the glass surface during long-term use, and the transparency is impaired.

Further, this cover glass contains K ₂ O for the purpose of accelerating melting, and therefore the amount of β-ray radiation increases. β-rays have higher transparency than α-rays, so the influence on the image sensor is weak, but this may also impair the function of the element. It is also desirable that the radiation dose be low. In order to reduce the amount of β-ray radiation, it is necessary to avoid a component having a β-decaying isotope as a constituent of glass, but potassium falls under this component.

The present invention is inexpensive, has a small amount of α-ray and β-ray radiation, has excellent weather resistance, and has an average linear expansion coefficient of 60 to 75 × 10 ^-7 / ° C. It is an object of the present invention to provide a cover glass for a solid-state image sensor that can be sealed.

[0014]

The cover glass for a solid-state image pickup device according to the present invention has a weight percentage of SiO _{2 of} 65.0-.
75.0%, Al ₂ O ₃ 7.0-11.0%, B ₂ O
_{3 8.0~12.0%,} Li ₂ O _3.1~6.9
%, Na ₂ O 4.5 to 7.5%, essentially no K ₂ O, and the amounts of uranium (U) and thorium (Th) contained in the glass are respectively It is characterized by being 50 ppb or less.

The cover glass for a solid-state image pickup device of the present invention preferably has a weight percentage of SiO _{2 of} 67.0.
73.0%, Al ₂ O ₃ 8.0 to 10.0%, B ₂ O
₃ 9.0 to 11.0%, Li ₂ O 3.1 to 6.9%,
Na ₂ O having a composition of 4.9-6.9% and having essentially K
It is characterized by not containing ₂ O.

[0016]

The main cause of α-ray generation of glass is U and Th contained as impurities in the glass, and if the amount of these is kept below a certain value, the amount of α-ray radiation can be reduced. Specifically, if each amount is 50 ppb or less, α
It is possible to prevent a soft error of the solid-state image sensor due to the lines.

It has been widely known that U and Th are contained in the zirconia raw material in a large amount, but the barium raw material also contains a large amount of U and Th. Therefore, in order to reduce the amounts of U and Th to 50 ppb or less, it is necessary to minimize the content of BaO and use a high-purity material as a raw material even when it is contained.

Further, in the present invention, it is required to select raw materials for all other components besides barium, and it is also necessary to avoid mixing U and Th during melting and processing as much as possible.

Further, the raw material of potassium has a radioactive isotope of ⁴⁰ K, which causes β-ray emission, and therefore it is necessary to avoid the inclusion of K ₂ O.

The cover glass for a solid-state image sensor of the present invention comprises
In addition to the radiation dose of α-rays and β-rays, the weather resistance, the coefficient of linear expansion, and the ease of manufacturing are taken into account when determining the composition. The reason for limiting the composition as described above is as follows. It is as follows.

First, SiO ₂ has a function of improving the weather resistance of glass. If the content of SiO ₂ is 65.0% or less, it becomes difficult to obtain such a function, and if it is 75.0% or more, Melting and shaping of glass becomes difficult.

Al ₂ O ₃ also has an effect of improving the weather resistance of glass, but when the content thereof is 7.0% or less,
If the weather resistance is poor and the practicality is poor and the content is 11.0% or more, it becomes difficult to melt the glass.

B ₂ O ₃ has the function of improving the melting property and devitrification resistance of the glass, but if its content is less than 8.0%, the workability becomes worse as the molding temperature rises. ,
If it is 12.0% or more, the chemical durability of glass deteriorates.

Li ₂ O has the effect of adjusting the linear expansion coefficient and improving the meltability of the glass, but if the content thereof is 3.1% or less, the meltability of the glass deteriorates and the average If the coefficient of linear expansion is less than 60 × 10 ⁻⁷ / ° C., on the other hand, if it is more than 6.9%, the weather resistance deteriorates and vapor deposition from the glass surface during melting of the glass becomes remarkable, resulting in poor striae. It is not preferable because it causes the problem.

Na ₂ O also has the effects of adjusting the linear expansion coefficient and improving the meltability of the glass, but if its content is less than 4.5%, the meltability of the glass deteriorates and the average When the linear expansion coefficient is 60 × 10 ⁻⁷ / ° C. or less, on the other hand, when it is 7.5% or more, the water resistance is significantly deteriorated and the average linear expansion coefficient is easily 75 × 10 ⁻⁷ / ° C. or more.

In the present invention, in addition to the above components, As ₂ O ₃ , Sb ₂ O ₃ , chloride,
It is possible to contain corn starch, carbon, sucrose, metal powder, and fluoride. Further, it is possible to add F or Cl to the glass by adding a fluoride or a chloride. Further, in order to finely adjust the expansion coefficient and the viscosity, the alkaline earth element Mg,
It is also possible to add Ca, Sr, and Ba by a carbonate raw material. It is also possible to add a trace amount of ions of a transition metal element as a salt such as a carbonate as an additive for coloring the glass, if necessary.

[0027]

EXAMPLES The cover glass for a solid-state image pickup device of the present invention will be described in detail below based on examples.

Tables 1 and 2 show examples of the present invention (Sample No.
1 to 8) and comparative examples (sample Nos. 9 to 13).

[0029]

[Table 1]

[0030]

[Table 2]

No. in the table. Each sample of 1 to 13 was prepared as follows.

First, glass raw materials prepared to give a glass having the composition shown in the table are put in a platinum crucible and placed in an electric furnace for 15 minutes.
After melting under the conditions of 00 ° C. for 5 hours, the molten glass was poured onto graphite and then strained in a slow cooling furnace.

The amount of impurities, the amount of α-ray and β-ray radiation, the average coefficient of linear expansion and the amount of alkali elution were measured for each of the samples thus prepared, and the results are shown in the table. Further, after determining the amount of alkali elution of each sample, the sample was subjected to a high temperature and high humidity test, and the results are also shown in the table.

As is apparent from the table, No.
In each of the samples 1 to 8, since the amounts of U and Th that are impurities are 50 ppb or less, the α-ray emission amount is 0.009.
C / cm ² · hr. Below, the β-ray radiation dose is 4 × 10 ^-6 μ
It was as low as Ci / cm ² or less. Moreover, the average linear expansion coefficient is 60.0 to 70.0 × 10 ⁻⁷ / ° C., which is close to that of alumina ceramics, and the amount of alkali elution is
As little as 0.06 mg or less, even when subjected to a high temperature and high humidity test,
No abnormalities were observed on the surface and it had excellent weather resistance.

On the other hand, No. The sample No. 9 had a large amount of U as an impurity of 200 ppb and a large amount of Th of 150 ppb.
/ Cm ² · hr. There were many. In addition, No. Sample No. 10 contained 0.5% of K ₂ O, and therefore had a large β-ray radiation amount of 6 × 10 ⁻⁶ μCi / cm ² . Furthermore N
o. Sample No. 11 had a low Li ₂ O content of 3.0% and thus had a low average linear expansion coefficient of 58 × 10 ⁻⁷ / ° C. In addition, No. The sample of No. 12 had a small Al ₂ O ₃ content of 5.0%, so the alkali elution amount was 0.12 mg.
Precipitation of crystals was observed on the surface by the high temperature and high humidity test. Furthermore, No. Sample No. 13 contained Na ₂ O at 7.6
%, The average linear expansion coefficient is 77 × 10 ^-7 / ° C.
And the amount of alkali elution is as high as 0.15 mg,
Precipitation of crystals was recognized on the surface by the high temperature and high humidity test.

The amounts of U and Th that are impurities in the table are
It is obtained by ICP (inductively coupled high frequency plasma) analysis. The α-ray radiation amount and β-ray radiation amount were measured using a gas flow proportional counter measuring device, and the average linear expansion coefficient was obtained by using a quartz tube type dilatometer at 30 to 380 ° C. It is a thing. Furthermore, the alkaline elution amount is
It is obtained based on the regulation of JIS R3502.

In the high temperature and high humidity test, each sample was subjected to an alkali elution test, and then mirror-polished with cerium oxide to form a plate having a size of 20 × 20 × 1 mm, which was then heated at 85 ° C.-85 ° C. %, The state of the surface after being left under the condition of 500 hours was observed by an electron microscope. When no change was observed on the surface, it was regarded as normal and the precipitation of alkali metal or alkaline earth metal crystals was confirmed. What was recognized was defined as crystal precipitation.

[0038]

As described above, the cover glass for a solid-state image pickup device of the present invention has a small amount of α-ray and β-ray radiation, and therefore does not cause a soft error in the device and has excellent weather resistance. Moreover, since the coefficient of linear expansion is similar to that of alumina ceramic, it can be sealed in an alumina package.

Claims (2)

[Claims] 1. A weight percentage of SiO ₂ 65.0-7.
5.0%, Al ₂ O ₃ 7.0-11.0%, B ₂ O ₃
8.0 to 12.0%, Li ₂ O 3.1 to 6.9%,
Na ₂ O 4.5-7.5% composition, essentially K
Uranium (U), which does not contain ₂ O and is contained in glass,
A cover glass for a solid-state image pickup device, wherein the amount of thorium (Th) is 50 ppb or less, respectively. 2. SiO ₂ 67.0 to 7 by weight percentage.
3.0%, Al ₂ O ₃ 8.0 to 10.0%, B ₂ O ₃
9.0 to 11.0%, Li ₂ O 3.1 to 6.9%,
Na ₂ O having a composition of 4.9-6.9% and having essentially K
_The cover glass for a solid-state image pickup device according to claim 1, which does not contain ₂ O.