JP7185181B2 - Semiconductor device coating glass and semiconductor coating material using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a glass for covering semiconductor elements and a material for covering semiconductors using the same.

Semiconductor devices such as silicon diodes and transistors are generally covered with glass on the surface including the PN junction of the semiconductor device. As a result, the surface of the semiconductor element can be stabilized, and deterioration of characteristics over time can be suppressed.

The properties required of the glass for covering semiconductor devices are (1) that the coefficient of thermal expansion matches the coefficient of thermal expansion of the semiconductor device so that cracks or the like do not occur due to the difference in thermal expansion coefficient from that of the semiconductor device, and (2) In order to prevent deterioration of the characteristics of the semiconductor element, it should be able to be coated at a low temperature (for example, 900° C. or less), and (3) should not contain impurities such as alkaline components that adversely affect the surface of the semiconductor element.

Zinc-based glasses such as ZnO--B ₂ O ₃ --SiO _2- based glasses, PbO--SiO ₂ --Al ₂ O ₃ -based glasses, and PbO--SiO ₂ --Al ₂ O ₃ --B ₂ have been conventionally used as glasses for covering semiconductor devices. Lead-based glasses such as O ₃ -based glasses are known, but currently, from the viewpoint of workability, PbO--SiO ₂ -Al ₂ O ₃ -based glasses and PbO--SiO ₂ -Al ₂ O ₃ -B ₂ O are used. Lead-based glass such as ₃ -based glass has become mainstream (for example, see Patent Documents 1 to 4).

JP-A-48-43275 JP-A-50-129181 Japanese Patent Publication No. 1-49653 JP 2008-162881 A

However, the lead component of lead-based glass is harmful to the environment. Since the above zinc-based glass contains a small amount of lead and bismuth components, it cannot be said that it is completely harmless to the environment.

In addition, zinc-based glass is inferior to lead-based glass in chemical durability, and there is a problem that it is easily eroded in an acid treatment process after forming a coating layer. Therefore, it was necessary to form a protective film on the surface of the coating layer and perform acid treatment.

On the other hand, when the content of SiO ₂ in the glass composition is increased, the acid resistance is improved and the reverse voltage of the semiconductor element is improved, but there arises a problem that the reverse leakage current of the semiconductor element is increased. In particular, in a semiconductor device for low breakdown voltage, since suppression of reverse leakage current and reduction of surface electrification density are prioritized over improvement of reverse voltage, the above problem becomes more serious.

Accordingly, the present invention has been made in view of the above circumstances, and a technical object thereof is to provide a glass for covering semiconductor elements that has a low environmental load, excellent acid resistance, and a low surface charge density.

As a result of intensive studies, the present inventors found that the above technical problems can be solved by using SiO ₂ —B ₂ O ₃ —Al ₂ O ₃ —ZnO glass having a specific glass composition. This is proposed as an invention. That is, the glass for covering a semiconductor element of the present invention has a glass composition of 18 to 43% SiO _{2 ,} 5 to 21% B ₂ O ₃ , 8 to 21% Al ₂ O ₃ , and 10 to 25% ZnO in terms of mol %. , MgO+CaO 10 to 25%, and substantially free of lead. Here, "MgO+CaO" refers to the total amount of MgO and CaO. In addition, "substantially free from" means that the corresponding component is not intentionally added as a glass component, and does not mean that even impurities that are unavoidably mixed are completely eliminated. Specifically, it means that the content of the corresponding component including impurities is less than 0.1% by mass.

As described above, the glass for covering a semiconductor element of the present invention regulates the content range of each component, thereby reducing the environmental load, improving the acid resistance, and lowering the surface charge density. As a result, it can be suitably used for covering semiconductor elements for low breakdown voltage.

Further, the material for coating a semiconductor device of the present invention preferably contains 75 to 100% by mass of glass powder and 0 to 25% by mass of ceramic powder composed of the glass for coating a semiconductor device.

Further, the semiconductor element coating material of the present invention preferably has a thermal expansion coefficient of 20× ^{10 -7} /°C. Here, the “thermal expansion coefficient in the temperature range of 30 to 300° C.” refers to the value measured by a push rod type thermal expansion coefficient measuring device.

The glass for covering a semiconductor element of the present invention has a glass composition of 18 to 43% SiO ₂ , 5 to 21% B ₂ O _{3 ,} 8 to 21% Al ₂ O ₃ , 10 to 21% ZnO, and MgO+CaO in terms of mol %. It is characterized by containing 10 to 25% and being substantially free of lead components. The reason for limiting the content of each component will be explained below. In addition, in the following description of the content of each component, % display means mol % unless otherwise specified.

SiO ₂ is a network-forming component of glass and a component that enhances acid resistance. The content of SiO ₂ is 18-43%, preferably 20-40%, in particular 22-36%. If the content of _SiO2 is too low, the acid resistance tends to decrease. On the other hand, if the content of _SiO2 is too high, devitrification during melting becomes strong, making it difficult to obtain a homogeneous glass.

B ₂ O ₃ is a network-forming component of glass and a component that enhances softening fluidity. The content of B ₂ O ₃ is 5-21%, preferably 5-18%, especially 7-15%. If the content of B ₂ O ₃ is too small, the crystallinity will be strong, which will impair softening fluidity during coating, making it difficult to uniformly coat the surface of the semiconductor element. On the other hand, if the content of B ₂ O ₃ is too high, the coefficient of thermal expansion tends to be unduly high and the acid resistance tends to decrease.

Al ₂ O ₃ is a component that stabilizes the glass and adjusts the surface charge density. The content of Al ₂ O ₃ is 8-21%, preferably 5-20%, especially 8-18%. If the content of Al ₂ O ₃ is too small, the glass tends to devitrify. On the other hand, if the content of Al ₂ O ₃ is too high, the surface charge density may become too high.

ZnO is a component that stabilizes glass. The content of ZnO is 10-25%, preferably 12-22%. If the ZnO content is too low, the devitrification property during melting becomes strong, making it difficult to obtain a homogeneous glass. On the other hand, if the ZnO content is too high, the acid resistance tends to decrease.

MgO and CaO are components that reduce the viscosity of glass. The total amount of MgO and CaO is 10-25%, preferably 12-20%. If the total amount of MgO and CaO is too small, the firing temperature of the glass tends to rise. On the other hand, if the total amount of MgO and CaO is too large, the coefficient of thermal expansion may become too high, the acid resistance may deteriorate, and the insulating properties may deteriorate. The content of MgO is preferably 0-20%, particularly 0-5%. The content of CaO is preferably 1-25%, especially 10-20%.

In addition to the above components, other components (e.g., SrO, BaO, MnO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , CeO ₂ , Sb ₂ O ₃ etc.) are contained up to 7% (preferably up to 3%) You may

From an environmental point of view, it is preferable that substantially no lead component (for example, PbO, etc.) is contained, and substantially no Bi ₂ O ₃ , F, or Cl is contained. Further, it is preferable that substantially no alkaline components (Li ₂ O, Na ₂ O, and K ₂ O) that adversely affect the surface of the semiconductor element are contained.

The glass for covering a semiconductor element of the present invention is preferably in the form of powder, ie, glass powder. If processed into glass powder, the surface of the semiconductor element can be easily coated using, for example, a paste method, an electrophoretic coating method, or the like.

The average particle size _D50 of the glass powder is preferably 25 μm or less, in particular 15 μm or less. If the average particle diameter _D50 of the glass powder is too large, it becomes difficult to form a paste. In addition, powder adhesion by electrophoresis also becomes difficult. Although the lower limit of the average particle diameter _D50 of the glass powder is not particularly limited, it is practically 0.1 μm or more. In addition, "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 coating a semiconductor device of the present invention is prepared by, for example, preparing a batch of raw material powders of each oxide component, melting at about 1500° C. for about 1 hour to vitrify the glass, and then molding (and then pulverizing if necessary). , classification).

The material for covering a semiconductor element of the present invention contains a glass powder composed of the glass for covering a semiconductor element, and if necessary, it may be mixed with a ceramic powder to form a composite powder. Addition of ceramic powder facilitates adjustment of the coefficient of thermal expansion.

Ceramic powder is preferably less than 25%, particularly less than 20%, relative to 100 parts by mass of glass powder. If the content of the ceramic powder is too high, the softening fluidity of the glass is impaired, making it difficult to coat the surface of the semiconductor element.

The average particle size _D50 of the ceramic powder is preferably 30 μm or less, in particular 20 μm or less. If the average particle diameter _D50 of the ceramic powder is too large, the surface smoothness of the coating layer tends to deteriorate. Although the lower limit of the average particle diameter _D50 of the ceramic powder is not particularly limited, it is practically 0.1 μm or more.

In the semiconductor device coating material of the present invention, the thermal expansion coefficient in the temperature range of 30 to 300° C. is preferably 20×10 ⁻⁷ /° C. or more and 55×10 ⁻⁷ /° C. or less, particularly 30×10 ⁻⁷ /° C. ° C. or more and 50×10 ⁻⁷ /° C. or less. If the coefficient of thermal expansion is out of the above range, cracks, warping, etc. are likely to occur due to the difference in coefficient of thermal expansion from the semiconductor element.

In the semiconductor device coating material of the present invention, the surface charge density is preferably 6×10 ¹¹ /cm ² or less, particularly 5×10 ¹¹ /cm ² or less when coating a semiconductor device surface of 1000 V or less, for example. If the surface charge density is too high, the breakdown voltage will be high, but at the same time the leakage current will tend to be large. "Surface charge density" refers to a value measured by the method described in the Examples section below.

The present invention will be described in detail below based on examples. It should be noted that the following examples are merely illustrative. The present invention is by no means limited to the following examples.

Table 1 shows examples of the present invention (samples Nos. 1 to 4) and comparative examples (samples Nos. 5 and 6).

Each sample was produced as follows. First, raw material powders were mixed so as to have the glass composition shown in the table to form a batch, which was then melted at 1500° C. for 1 hour to be vitrified. Subsequently, the molten glass was formed into a film, pulverized with a ball mill, and classified using a 350-mesh sieve to obtain a glass powder having an average particle diameter _D50 of 12 μm. In addition, sample no. In 4, 15% by mass of cordierite powder (average particle diameter D ₅₀ : 12 μm) was added to the obtained glass powder to obtain a composite powder.

Each sample was evaluated for thermal expansion coefficient, surface charge density and acid resistance. Table 1 shows the results.

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

The surface charge density was measured as follows. First, each sample was dispersed in an organic solvent, adhered to the surface of a silicon substrate by electrophoresis so as to have a certain thickness, and then baked to form a coating layer. Next, after forming an aluminum electrode on the surface of the coating layer, the change in capacitance in the coating layer was measured using a CV meter to calculate the surface charge density.

Acid resistance was evaluated as follows. After pressing each sample to a size of about 20 mm in diameter and 4 mm in thickness, it was fired to prepare a pellet-shaped sample. The change in mass per unit was calculated and used as an index of acid resistance. A change in mass per unit area of less than 1.0 mg/cm ² was evaluated as “◯”, and a change of 1.0 mg/cm ² or more was evaluated as “X”.

As is clear from Table 1, sample no. Nos. 1 to 4 had a surface charge density of 6×10 ¹¹ /cm ² or less and were also evaluated as good in acid resistance. Therefore, sample no. Nos. 1 to 4 are considered to be suitable as semiconductor element covering materials used for covering low voltage semiconductor elements.

On the other hand, sample no. 5 and 6 were unsatisfactory in the acid resistance test. Furthermore, sample no. 6 had a high coefficient of thermal expansion and a high surface charge density.

Claims (3)

The glass composition contains 18 to 43% SiO ₂ , 13 to 21% B ₂ O ₃ , 8 to 21% Al ₂ O ₃ , 10 to 25% ZnO, and 10 to 25% MgO+CaO in terms of mol %, and substantially A glass for covering a semiconductor element, characterized in that it does not contain a lead component. A material for coating a semiconductor device, comprising: 75 to 100% by mass of a glass powder made of the glass for coating a semiconductor device according to claim 1; and 0 to 25% by mass of a ceramic powder. 3. The semiconductor element coating material according to claim 2, wherein the thermal expansion coefficient in a temperature range of 30 to 300° C. is 20×10 ⁻⁷ /° C. or more and 55×10 ⁻⁷ /° C. or less.