JP7655461B2 - Glass for covering semiconductor elements and semiconductor covering material using the same - Google Patents

Description

The present invention relates to glass for coating semiconductor elements and semiconductor coating materials using the same.

Semiconductor elements such as silicon diodes and transistors generally have their surfaces, including the P-N junctions, covered with glass. This stabilizes the surface of the semiconductor element and prevents deterioration of characteristics over time.

The properties required for glass for covering semiconductor elements include (1) a thermal expansion coefficient that matches that of the semiconductor element to prevent cracks due to differences in thermal expansion coefficients with the semiconductor element, (2) the ability to cover the semiconductor element at low temperatures (e.g., 900°C or less, particularly 860°C or less) to prevent deterioration of the characteristics of the semiconductor element, and (3) the absence of impurities such as alkaline components that adversely affect the surface of the semiconductor element.

Conventionally, zinc-based glasses such as ZnO-B ₂ O ₃ -SiO _2- based glasses and lead-based glasses such as PbO-SiO ₂ -Al ₂ O ₃ -based glasses and PbO-SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -based glasses have been known as glasses for covering semiconductor elements. However, at present, from the viewpoint of workability, lead-based glasses such as PbO-SiO ₂ -Al ₂ O _3- based glasses and PbO-SiO ₂ -Al ₂ O ₃ -B ₂ O ₃ -based glasses are becoming mainstream (for example, see Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 58-64424 Special Publication No. 11-236239

In recent years, in addition to the characteristics (1) to (3), glass for semiconductor coating is required to have the following characteristics: (4) after coating, the amount of charge in the glass becomes an appropriate amount of negative charge (initial NFB) that matches the design of the semiconductor device, and (5) during bias testing involving heating and voltage application, the change in the amount of negative charge in the glass is small. In particular, characteristic (5) is considered important in order to increase the reliability of semiconductor elements.

An example of glass that shows little change in negative charge due to bias testing is glass that is primarily composed of zinc. However, because zinc-based glass has low acid resistance, it may be corroded by acid during the manufacturing process of semiconductor devices, and may not be able to perform to its full potential.

The present invention has been made in consideration of the above circumstances, and its technical objective is to provide a glass for covering semiconductor elements that exhibits small changes in the amount of negative charge in the glass during bias testing and has high acid resistance.

As a result of intensive research, the present inventors have found that the above technical problems can be solved by adding at least one of GeO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ and Bi ₂ O ₃ to PbO-SiO _{2 -Al 2} O 3 based glass, and propose this invention. That is, the glass for covering semiconductor elements of the present invention is characterized by having a glass composition containing, in mole percent, 55-85% SiO ₂ , 12-40% PbO, 0.1-10% Al ₂ O ₃ and 0.1-6% GeO ₂ +Ta ₂ O ₅ +Nb ₂ O ₅ +Bi ₂ O ₃ . Here, "GeO ₂ + Ta ₂ O ₅ + Nb ₂ O ₅ + Bi ₂ O ₃ " refers to the total amount of GeO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ and Bi ₂ O _3. In addition, the glass for covering semiconductor elements of the present invention preferably has a GeO ₂ content of 0.1 to 6%.

As described above, the glass for covering semiconductor elements of the present invention has a regulated content range for each component. This allows the glass to have a small change in the amount of negative charge in a bias test and a high acid resistance. As a result, the semiconductor elements can be covered appropriately.

The semiconductor element coating material of the present invention preferably contains 75 to 100% by mass of glass powder made of the above-mentioned semiconductor element coating glass and 0 to 25% by mass of ceramic powder.

The semiconductor element covering material of the present invention preferably has a thermal expansion coefficient of 20×10 ⁻⁷ /° C. to 55×10 ⁻⁷ /° C. in the temperature range of 30 to 300° C. Here, the "thermal expansion coefficient in the temperature range of 30 to 300° C." refers to a value measured using a push rod type thermal expansion coefficient measuring device.

The present invention provides a glass for covering semiconductor elements that exhibits small changes in the amount of negative charge in the glass during bias testing and has high acid resistance.

The glass for covering semiconductor elements of the present invention is characterized by containing, in mole percent, 55-85% SiO ₂ , 12-40% PbO , 0.1-10% Al ₂ O ₃ , and 0.1-6% GeO ₂ +Ta ₂ O ₅ +Nb ₂ O ₅ +Bi ₂ O ₃ as a glass composition. The reasons for limiting the content of each component as described above are explained below. In the following explanation of the content of each component, the percentage indicates mole percent unless otherwise specified.

_SiO2 is a component that enhances acid resistance. The _SiO2 content is preferably 55-85%, 60-80%, and particularly 65-75%. If the _SiO2 content is too low, the acid resistance is easily reduced and vitrification is difficult. On the other hand, if the _SiO2 content is too high, the firing temperature becomes high, which easily deteriorates the characteristics of the semiconductor element in the coating process. In addition, the melting temperature becomes too high, making vitrification difficult.

PbO is a component that lowers the firing temperature. The PbO content is preferably 12-40%, 14-36%, 16-32%, and especially 18-28%. If the PbO content is too low, the firing temperature becomes high, which can easily degrade the characteristics of the semiconductor elements during the coating process. In addition, the melting temperature becomes too high, making vitrification difficult. On the other hand, if the PbO content is too high, the thermal expansion coefficient becomes too high, resulting in significant warping of the wafer.

Al ₂ O ₃ is a component that stabilizes glass. The content of _{Al 2} O ₃ is preferably 0.1 to 10%, 2 to 8%, 2 to 7%, and particularly preferably 3 to 6%. If the content of _{Al 2} O ₃ is too low, vitrification becomes difficult. On the other hand, if the content of Al ₂ O ₃ is too high, there is a risk that the firing temperature will be too high.

GeO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ and Bi ₂ O ₃ are all components that stabilize the glass skeleton and suppress the change in the amount of negative charge due to bias testing. The total amount of these components is preferably 0.1 to 6%, 0.3 to 5%, 0.5 to 4%, and particularly preferably 0.5 to 3.5%. The individual contents of these components are also preferably 0.1 to 6%, 0.3 to 5%, 0.5 to 4%, and particularly preferably 0.5 to 3.5%. In particular, it is preferable that GeO ₂ is 0.1 to 6%. If the contents of these components are too small, the change in the amount of negative charge due to bias testing will be large. On the other hand, if the contents of these components are too large, it will be difficult to obtain electrical properties suitable for semiconductor coating.

In addition to the above components, other components may be incorporated. For example, _B2O3 , CaO _, SrO, BaO, _MnO2 , _CeO2 , _{Sb2O3 , etc.} may be contained in an amount of up to 7% (preferably up to 3%). The total amount of other components is preferably 7% or less, particularly 3% or less.

From the viewpoint of the influence on the semiconductor element, it is preferable that the glass is substantially free of alkali metal oxides (Li ₂ O, Na ₂ O, and K ₂ O) that adversely affect the surface of the semiconductor element. Here, "substantially free of alkali metal oxides" means that the content of alkali metal oxides in the glass composition is less than 0.1 mol%.

The glass for covering semiconductor elements of the present invention is preferably in powder form, that is, glass powder. If it is processed into glass powder, it can be easily used to cover the surface of a semiconductor element, for example, by using a paste method, electrophoretic coating method, etc.

The average particle diameter _D50 of the glass powder is preferably 25 μm or less, particularly 15 μm or less. If the average particle diameter _D50 of the glass powder is too large, it becomes difficult to make a paste. In addition, it becomes difficult to apply the paste by electrophoresis. The lower limit of the average particle diameter _D50 of the glass powder is not particularly limited, but in reality, it is 0.1 μm or more. The "average particle diameter _D50 " is a value measured on a volume basis, and refers to a value measured by a laser diffraction method.

The glass for covering semiconductor elements of the present invention can be obtained, for example, by mixing raw powders of each oxide component into a batch, melting it at about 1500°C for about 1 hour to vitrify it, and then molding it (and then crushing and classifying it as necessary).

The semiconductor element coating material of the present invention preferably contains 75 to 100 mass% glass powder and 0 to 25 mass% ceramic powder, more preferably contains 85 to 100 mass% glass powder and 0 to 15 mass% ceramic powder, even more preferably contains 95 to 100 mass% glass powder and 0 to 5 mass% ceramic powder, and particularly preferably contains more than 99 to 100 mass% glass powder and 0 to less than 1 mass% ceramic powder. The addition of ceramic powder makes it easier to adjust the thermal expansion coefficient. On the other hand, if the content of ceramic powder is too high, the softening flowability is impaired, making it difficult to coat the surface of the semiconductor element.

The average particle diameter _D50 of the ceramic powder is preferably 30 μm or less, particularly 20 μm or less. If the average particle diameter _D50 of the ceramic powder is too large, the surface smoothness of the coating layer is likely to decrease. The lower limit of the average particle diameter _D50 of the ceramic powder is not particularly limited, but is practically 0.1 μm or more.

In the semiconductor element covering material of the present invention, the thermal expansion coefficient in the temperature range of 30 to 300° C. is preferably 20×10 ⁻⁷ /° C. to 55×10 ⁻⁷ /° C., particularly 30×10 ⁻⁷ /° C. to 50×10 ⁻⁷ /° C. If the thermal expansion coefficient is outside the above range, cracks, warping, etc. are likely to occur due to the difference in thermal expansion coefficient with the semiconductor element.

In the semiconductor element coating material of the present invention, the softening point is preferably 880°C or less, 860°C or less, and particularly 840°C or less. If the softening point is too high, the firing temperature becomes high, and there is a risk of impairing the characteristics of the semiconductor element in the coating process. Here, the "softening point" is the temperature of the fourth inflection point obtained by macro-type differential thermal analysis.

The present invention will be described in detail below based on examples. Note that the following examples are merely illustrative. The present invention is not limited to the following examples in any way.

Table 1 shows examples of the present invention (samples No. 1 to 7) and comparative examples (samples No. 8 to 11).

Each sample was prepared as follows. First, raw material powders were mixed to obtain the glass composition shown in the table, and then the raw material powders were melted at 1500°C for 1 hour to be vitrified. The molten glass was then formed into a film, pulverized in a ball mill, and classified using a 350 mesh sieve to obtain glass powder with an average particle size _D50 of 12 μm. In addition, in sample No. 4, 10 mass% of cordierite powder (average particle size _D50 : 12 μm) was added to the obtained glass powder to obtain a composite powder.

The softening point, firing temperature, thermal expansion coefficient, electrical properties, acid resistance, and change in negative charge were evaluated for each sample. The results are shown in Table 1.

The softening point is the temperature of the fourth inflection point obtained by macro-type differential thermal analysis. The firing temperature is 20°C higher than the softening point.

The thermal expansion coefficient was measured using a push rod type thermal expansion coefficient measuring device in the temperature range of 30 to 300°C.

The electrical properties were measured as follows. First, glass powder was attached onto a silicon wafer by electrophoresis, and then the wafer was baked for 15 minutes at the baking temperature shown in the table. Aluminum was evaporated onto the glass surface of the silicon wafer thus obtained as an electrode, and the amount of negative charge was measured. Cases in which the amount of negative charge was 1×9 ¹¹ /cm ² to 10×9 ¹¹ /cm ² were marked as "○", and other cases were marked as "×".

The acid resistance was evaluated as follows: Each sample was press-molded to a size of about 20 mm in diameter and 4 mm in thickness, and then fired at the firing temperature in the table to prepare a pellet-shaped sample. The sample was immersed in 30% nitric acid at 25°C for 1 minute, and the mass change per unit area was calculated from the mass loss. A mass change per unit area of less than 1.0 mg/ ^cm2 was marked as "○", and a mass change of 1.0 mg/cm2 or ^more was marked as "×".

The change in the amount of negative charge was evaluated as follows. First, glass powder was attached onto a silicon wafer by electrophoresis, and then baked for 15 minutes at the baking temperature in the table. Aluminum was evaporated onto the glass surface of the silicon wafer thus obtained as an electrode. Next, the silicon wafer was placed in a thermostatic chamber at 150° C., and held for 24 hours with a voltage of 400 V applied between the back surface of the silicon wafer and the electrode, after which the electrical characteristics were evaluated. When the change in the amount of negative charge measured was less than 5×10 ¹¹ /cm ² , it was marked as “○”, and otherwise marked as “×”.

As is clear from Table 1, Samples No. 1 to No. 7 have a thermal expansion coefficient of 44×10 ⁻⁷ /°C to 49×10 ⁻⁷ /°C, a firing temperature of 860°C or less, and are good in the evaluation of electrical properties, acid resistance, and negative charge amount change. Therefore, Samples No. 1 to No. 7 are considered to be suitable as semiconductor element coating materials.

On the other hand, sample No. 8 did not vitrify because the melting temperature was too high. Sample No. 9 did not have good electrical properties. Sample No. 10 had too large a change in the amount of negative charge. Sample No. 11 had poor acid resistance.

Claims (3)

A glass for covering semiconductor elements, characterized in that the glass composition contains, in mole percent _, 55-85% _SiO2 , 12-40 % _PbO , _{0.1-10 % Al2O3 ,} 0.1-6% GeO2 , 0-7 % _B2O3 , and 0.1-6% _{GeO2 +} Ta2O5 + _Nb2O5 + _{Bi2O3 .} A material for covering a semiconductor element, comprising 75 to 100 mass % of a glass powder made of the glass for covering a semiconductor element according to claim 1 , and 0 to 25 mass % of a ceramic powder. 3. The semiconductor element coating material according to claim 2 , characterized in that the thermal expansion coefficient in the temperature range of 30 to 300° C. is 20×10 ⁻⁷ /° C. to 55×10 ⁻⁷ /° C.