JPS6238302B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION This invention relates to a method of making improved glass compositions for use in semiconductor coatings. [Technical background of the invention and its problems] In general, semiconductor devices such as diodes, thyristors, and transistors made of single crystal silicon are manufactured using PN technology for the purpose of improving reliability and increasing withstand voltage.
A so-called glass cladding is being carried out in which the surface of the joint is covered and protected with a glass layer.
The glass used for this glass packaging is required to have the following various properties. (1) High withstand voltage is achieved through glass coating, and leakage current when reverse voltage is applied is below the limit. (2) Characteristics should not deteriorate when subjected to so-called blocking treatment, in which the coated element is heat-treated with reverse bias. (3) It has excellent acid resistance and water resistance, and is stable during the etching process using photoresist. (4) The coefficient of thermal expansion is close to that of silicon, making it difficult for the glass to crack or the wafer to warp after coating. Incidentally, zinc borate-based and lead silicate-based glasses have conventionally been used as semiconductor coating glasses, but none of these fully satisfies the above-mentioned four characteristics. In particular, zinc borate glass has poor chemical resistance, while lead silicate glass has poor electrical properties (particularly BT properties). For these reasons, the applicant has already developed SiO ₂ −PbO−ZnO−, which has high chemical resistance and electrical properties (reliability).
We proposed an RO (R is an alkaline earth metal) glass composition for semiconductor coating. On the other hand, it is known that when a semiconductor element is covered with glass, charges are generated at the interface between silicon and glass of the element, and this interfacial charge density has a large effect on the electrical characteristics of the element. The interfacial charge density can be controlled to some extent by the firing temperature and firing atmosphere, for example, in a method in which glass powder is attached to a semiconductor element, then fired and fluidized to form a glass coating.
It essentially depends on the properties of the glass itself. Therefore, when manufacturing glass for semiconductor coating, care must be taken to ensure that the interfacial charge density is appropriate. Conventionally, in order to control the interfacial charge density by the glass itself, changing the component ratio of the glass or adding a small amount of transition metal oxide has been carried out. However, changing the composition may cause the glass to fall out of the vitrification range, or even if the glass is stable, other required properties such as reliability, chemical resistance, and coefficient of thermal expansion may deteriorate. It was not possible to freely control the interfacial charge density. In particular, the SiO ₂ -PbO-ZnO-RO glass composition mentioned above satisfies both high reliability and chemical resistance, so it is possible to control the interfacial charge density by changing the composition ratio without impairing these properties. It was difficult to do so. [Object of the Invention] The present invention aims to improve chemical resistance, initial electrical properties (reliability), thermal expansion properties close to those of silicon, etc. in the SiO ₂ -Pbo-ZnO-RO glass composition without changing the composition ratio. The object of the present invention is to provide a method for producing a glass composition for semiconductor coating, which can control the interfacial charge density without impairing the surface charge density. [Summary of the Invention] The present invention comprises Al ₂ O ₃ 3-8% by weight, SiO ₂ 35-45% by weight, ZnO 10-30% by weight, PbO 5-30% by weight, B ₂ O ₃ 1
When melting a glass raw material having a composition of ~10% by weight and RO (where R is an alkaline earth metal), add 1 to 10% by weight of nitrate in terms of nitrate ions to the glass raw material and melt it. This is a characteristic feature. Although the glass raw material of the present invention has extremely high chemical resistance, it has good electrical properties, especially stability against temperature. For example, even when immersed in a diluted nitric acid solution for 5 minutes at 80°C, no deterioration was observed, and a thin layer of glass was formed on a silicon substrate, and electrodes such as Al were formed on top of it. , a so-called MIS element was fabricated, and 1.7×
The amount of variation in interfacial charge when treated with an applied voltage of 10 ⁵ V/cm at 175° C. for 10 hours is 2×10 ¹¹ /cm ² or less. Although the conventionally known lead silicate glass satisfies the above acid resistance test, the interfacial charge becomes more than 10 ¹² /cm when treated at 120°C at most. Further, boric acid glass satisfies the above interface charge test, but in the acid resistance test, it is etched by 1 μm or more after immersion for 1 second. The reason why the glass raw material of the present invention exhibits such high properties is that a stable glass composition was found in which the SiO ₂ concentration in the glass is high and the PbO concentration is low. In order to improve acid resistance, it is necessary to increase the SiO ₂ concentration in the glass, for example to around 50 mol% or more. However, ZnO−
In B ₂ O ₃ -SiO ₂ -based glasses, SiO ₂ is out of the vitrification range at a maximum of 20% by weight, or about 25% in molar concentration. Therefore, in order to form a glass that is stable up to around 50 mol% or more of SiO ₂ , it was necessary to replace most of the ZnO with PbO. but,
In this way, the basic composition becomes SiO ₂ −PbO−B ₂ O ₃
system, which impairs the temperature stability of electrical characteristics. Therefore, the present invention solves the above-mentioned contradictory phenomena by incorporating an alkaline earth metal oxide such as BaO, SrO, CaO, etc. as another glass component. High-quality materials containing alkaline earth metal oxides as one component
Glasses with SiO ₂ concentration are known. However, this type of glass composition has an extremely large coefficient of thermal expansion, making it virtually impossible to coat silicon and making it difficult to obtain good device characteristics. It was not used as such. In contrast, the present invention optimizes the blending amount and blending ratio of alkaline earth metal oxides, blends PbO within a range that does not adversely affect the electrical characteristics, and uses other materials such as B ₂ O ₃ and Al ₂ O ₃ . By adding ZnO and regulating its amount, ZnO can be reduced to 10
Despite ~30 wt% higher _SiO2 concentration of 35
It can be stably blended up to a high concentration of ~45% by weight, has a thermal expansion coefficient of 5 x 10 ^-7 /°C or less, and has the excellent properties mentioned above that allow sufficient adhesion with silicone. It is. Therefore, the present invention has the advantage of adding a predetermined amount of nitrate in terms of nitrate ions to the glass raw material having the above-mentioned composition and melting the mixture. We have found a method for producing a glass composition for semiconductor coating that can reduce the interfacial charge density when coated on semiconductor devices without inhibiting the process. Although the glass having the above-mentioned composition can sufficiently withstand electrical properties, it is also possible to use Bi ₂ O ₃ , CeO ₂ , In ₂ O ₃ , MnO ₂ ,
_P2O5 , _{Sb2O3 , Ta2O5 , V2O3 , Y2O3 , WO3 ,}
By blending at least 2% by weight of at least one of MoO ₃ , ZrO ₂ and Nb ₂ O ₅ , electrical properties, especially thermal stability, can be improved. Next, the reasons for limiting the proportions of each component of the glass raw material used in the method of the present invention will be described below. (i) Al ₂ O ₃ Al ₂ O ₃ contributes to improving chemical resistance and suppressing phase separation, and if its amount is less than 3% by weight, it will cause phase separation and devitrification of the glass composition. On the other hand, if the amount exceeds 8% by weight, the melting temperature of the glass composition becomes extremely high, making it difficult to form a film, and the negative charge at the interface with silicon becomes too large, causing problems when applying a reverse voltage. Leakage current exceeds permissible limits. (ii) SiO ₂ SiO ₂ is a necessary component for improving chemical resistance,
If the amount is less than 35% by weight, a sufficient improvement in chemical resistance cannot be expected;
If it exceeds this, the melting temperature becomes extremely high, making it difficult to form a film and further inducing phase separation and devitrification of the glass composition. (iii) ZnO ZnO contributes to improving electrical properties and lowering melting temperature. If the amount of ZnO is less than 10% by weight, it will not be possible to sufficiently improve the electrical properties and reduce the melting temperature;
If it exceeds this, devitrification of the glass composition will increase and it will become unstable. (vii) PbO PbO is a component that contributes to improving electrical properties and lowering and stabilizing glass. If the amount of PbO is less than 5% by weight, the effects of PbO cannot be expected to be sufficient, while if the amount exceeds 30% by weight, the electrical properties of the glass composition will deteriorate, especially the stability against temperature. be damaged. (v) B ₂ O ₃ B ₂ O ₃ is a component that contributes to lower melting and stabilization of the glass composition. If the amount of B ₂ O ₃ is less than 1% by weight, the desired effects of lowering the melting temperature and stabilizing it cannot be achieved sufficiently, while if it exceeds 10% by weight, phase separation and crystallization of the glass composition may occur. invite. (vi) RO (BaO, MgO, SrO, CaO) Alkaline earth metal oxides contribute to stabilizing the glass composition and improving electrical properties. If the amount of RO is less than 3% by weight, the reverse leakage current will increase, while if it exceeds 15% by weight, the coefficient of thermal expansion in the glass composition will increase.
The melting temperature becomes significantly high, making it difficult to manufacture glass and coat silicon. In particular, if BaO is added as an essential component as RO, the electrical properties can be improved more effectively. (vii) Bi ₂ O ₃ , CeO ₂ , In ₂ O ₃ , MnO ₂ , P ₂ O ₅ ,
_Sb2O3 , _Ta2O5 , _{V2O5 , Y2O3 , WO3 , MoO3 ,}
ZrO ₂ , Nb ₂ O ₃ These components contribute to further improving the electrical properties. In addition, by combining these components, the reverse leakage current is reduced and the BT characteristics are improved, but if the amount (or the amount of two or more) exceeds 2% by weight, the reverse leakage current decreases. This leads to an increase in the amount of water and devitrification of the glass composition. Next, the method of the present invention will be explained in detail. First, glass raw materials are prepared by weighing and mixing high-purity silica, alumina, boric acid, barium zinc oxide carbonate, strontium carbonate, red lead, and other metal oxides to a target composition. Subsequently, 1 to 10% by weight of nitrate in terms of nitrate ions is added to this glass raw material. Examples of the nitrate used here include magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, zinc nitrate, aluminum nitrate, lead nitrate, and the like. However, if the addition of nitrate disrupts the balance of the oxide component in the raw material due to the metals (magnesium, etc.) that make up the nitrate, the amount of other raw materials containing the oxide component may be reduced in accordance with the addition of the nitrate. It is desirable to Among nitrates, barium nitrate is particularly effective because it is non-deliquescent and easy to handle. The reason why the amount of nitrate added is limited to the above range is that if the amount added is less than 1% by weight in terms of nitrate ions, it will not be possible to reduce the interfacial charge density during coating.
This is because if it exceeds 10% by weight, the homogeneity of the glass will be impaired. Next, the glass raw material to which nitrate has been added is placed in, for example, a platinum crucible and heated in an electric furnace.
A glass composition for semiconductor coating is produced by melting and stirring at a temperature of 1400°C or higher. In order to coat a semiconductor with the glass composition obtained by the above-mentioned method, the glass composition is crushed into coarse powder using an ice crusher, a water-cooled roller, etc., and further crushed using a ball mill, etc., and then sieved to an appropriate particle size. The powder is applied onto a semiconductor element by an electrodeposition method, a precipitation method, a doctor blade method, etc., and is subsequently baked to make it dense. [Embodiments of the Invention] Next, embodiments of the present invention will be described. Examples 1 to 12 First, 12 types of glasses having different composition ratios shown in Table 1 below were prepared. In these glasses, 3% by weight of barium nitrate (calculated as BaO) was added to the raw material. Each raw material was placed in a platinum crucible in an electric furnace and melted at 1420°C for 3 hours. For each glass obtained, the thermal expansion coefficient, chemical resistance, withstand voltage of the element when coated on the element, leakage current,
The interfacial charge density was also investigated. The results are shown in Tables 2 to 4 below. In addition, each table also lists, as a comparative example, the characteristics of a glass manufactured in the same manner as in Table 1 with the same composition but without the addition of nitrate. The coefficient of thermal expansion, chemical resistance, withstand voltage, leakage current, and interfacial charge density were determined by the following tests. (1) Coefficient of thermal expansion The average coefficient of thermal expansion was measured at a temperature of 100 to 300°C using an interference dilatometer. (2) Chemical resistance After mirror-polishing one side of the glass composition block and covering the other side with epoxy resin or Apiezon wax, the bare surface is etched in the chemicals shown in Table 2 to form a coating. The etching depth of the glass composition was determined from the level difference with the surface and evaluated as chemical resistance. (3) Initial electrical characteristics Each glass powder that has been crushed in a ball mill and passed through a 325 mesh sieve is applied to the pn junction of silicon diode element 1 as shown in the figure, and
After baking at .degree. C. to form a glass coating 2, and further forming an Al electrode 3 on the upper surface of the element 1, a solder electrode 4 was formed on the lower surface thereof to produce a mesa diode. Then, the withstand voltage (voltage value at which breakdown occurs) of these diodes and the leakage current when a voltage of 600 V was applied in the reverse direction were determined and are shown in Table 3. (4) Interfacial charge density Each glass was ground in a ball mill, passed through a 325-mesh sieve, and after further grinding, it was deposited on an n-type silicon wafer with a specific resistance of 3.5 to 5.5 Ωcm by the precipitation method, and oxygen In airflow, 810
C. for 15 minutes to form a glass coating, and then an aluminum electrode with a diameter of 0.5 mm was deposited using a mask on the glass coating to fabricate a MIS baraque diode having an aluminum/glass/silicon structure. The interfacial charge density between glass and silicon was determined from the CV characteristics of these MIS devices and is shown in Table 4.

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〔Effect of the invention〕

As detailed above, according to the present invention, SiO ₂ −PbO
-With ZnO-RO glass composition, when coating semiconductor elements without changing the composition ratio and without impairing its own chemical resistance, initial electrical properties (reliability), thermal expansion similar to silicon, etc. Therefore, it is possible to provide a method for producing a glass composition that can reduce the interfacial charge density of the glass composition, and can stably exhibit long-term protection and high durability of semiconductors.

[Brief explanation of the drawing]

The figure is a schematic diagram of a mesa diode used to evaluate the electrical characteristics of a glass film. 1... Silicon diode element, 2... Glass film,
3...Aluminum electrode, 4...Solder electrode.

Claims (1)

[Claims] 1 Al ₂ O ₃ 3-8% by weight, SiO ₂ 35-45% by weight,
ZnO10~30wt%, PbO5~30wt%, _{B2O3 1} ~10
Weight% and RO (R is alkaline earth metal)3
Production of a glass composition for semiconductor coating, characterized in that when melting a glass raw material having a composition of ~15% by weight, 1 to 10% by weight of nitrate in terms of nitrate ions is added to the glass raw material and melted. Method. 2 Glass raw materials include Bi ₂ O ₃ , CeO ₂ , In ₂ O ₃ , MnO ₂ ,
_P2O5 , _{Sb2O5 , Ta2O5 , Y2O3 , WO3} , _{MoO3 ,}
The method for producing a glass composition for semiconductor coating according to claim 1, characterized in that at least one of ZrO ₂ and Nb ₂ O ₅ is blended in an amount of 2% by weight or less.