Glass for covering semiconductor devices, materials for covering semiconductor devices, and sintered bodies for covering semiconductor devices

Abstract

This invention provides a semiconductor device cover glass with low environmental impact, low coefficient of thermal expansion, and low surface charge density. The semiconductor device cover glass is characterized in that, as a glass composition, it contains, in molar percentages, 30% to less than 53% SiO2, 15% to 30% ZnO, 2% to 14% Al2O3, 0% to 10% B2O3, and more than 11% MgO+CaO but equal to or less than 30%, and substantially contains no lead.

Description

Technical Field

[0001] The present invention relates to a glass for covering semiconductor devices, a material for covering semiconductor devices, and a sintered body for covering semiconductor devices. Prior Technology

[0002] Semiconductor devices such as silicon diodes and transistors generally have their surfaces, including the PN junction, covered with glass. This helps stabilize the surface of the semiconductor device and suppresses the degradation of its characteristics over time.

[0003] The characteristics required for glass used to cover semiconductor elements include: (1) the coefficient of thermal expansion is suitable for the coefficient of thermal expansion of the semiconductor element in order to avoid cracks caused by the difference in the coefficient of thermal expansion of the semiconductor element; (2) in order to prevent the degradation of the semiconductor element's characteristics, it can be covered at low temperatures (e.g., below 900°C); and (3) it does not contain impurities such as alkaline components that have an adverse effect on the surface of the semiconductor element.

[0004] Previously, zinc-based glasses such as ZnO-B₂O₃-SiO₂, lead-based glasses such as PbO-SiO₂-Al₂O₃, and PbO-SiO₂-Al₂O₃-B₂O₃ were known as covers for semiconductor devices. However, from a workability point of view, lead-based glasses such as PbO-SiO₂-Al₂O₃ and PbO-SiO₂-Al₂O₃-B₂O₃ have become the mainstream (for example, see Patent Documents 1 to 4). [Existing Technical Documents] [Patent Literature]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 48-43275 [Patent Document 2] Japanese Patent Application Publication No. 50-129181 [Patent Document 3] Japanese Patent Publication No. 1-49653 [Patent Document 4] Japanese Patent Application Publication No. 2008-162881 Summary of the Invention

[0006] [Problem to be Solved by the Invention] However, lead in lead-based glass is an environmentally harmful component. Furthermore, since zinc-based glass contains small amounts of lead or bismuth, it cannot be asserted that it is completely harmless to the environment.

[0007] Furthermore, zinc-based glasses tend to have a higher coefficient of thermal expansion, which may cause cracks or warping in semiconductor devices when used to cover the surface of semiconductor devices such as Si.

[0008] On the other hand, increasing the SiO2 content in the glass composition reduces the coefficient of thermal expansion and increases the reverse voltage of the semiconductor device, making it less prone to failure. However, this increased reverse voltage leads to a larger reverse leakage current in the semiconductor device. Reverse leakage current is particularly problematic in low-voltage semiconductor devices, thus requiring a reduction in the surface charge density of the glass to suppress it.

[0009] Therefore, the present invention was made in view of the above circumstances, and its technical objective is to provide a semiconductor device cover glass with low environmental impact, low coefficient of thermal expansion and low surface charge density. [Methods for solving problems]

[0010] The inventors conducted intensive research and discovered that the aforementioned technical problem can be solved by using a SiO₂-ZnO-Al₂O₃ series glass with a specific glass composition, thus proposing this invention. Specifically, the semiconductor device cover glass of this invention is characterized by containing, in molar percentage, 30% to less than 53% SiO₂, 15% to 30% ZnO, 32% to 14% Al₂O, 30% to 10% B₂O, and more than 11% MgO + CaO but equal to or less than 30%, and substantially free of lead. Here, "MgO + CaO" refers to the combined amount of MgO and CaO. Furthermore, "substantially free of" means that the corresponding components are not intentionally added as glass components, and does not mean that unavoidably mixed impurities are completely eliminated. Specifically, it means that the content of the corresponding components containing impurities is less than 0.1% by mass.

[0011] As described above, the glass for covering semiconductor devices of the present invention limits the content range of each component. This results in a low environmental impact, a low coefficient of thermal expansion, and a reduced surface charge density. Consequently, it can be preferably used for covering semiconductor devices used in low-voltage applications.

[0012] The semiconductor element cover glass of the present invention preferably contains Zn₂SiO₄ as the main crystal after heat treatment. Here, "heat treatment" refers to heat treatment at 800°C to 1000°C for more than 10 minutes.

[0013] The semiconductor element covering material of the present invention is preferably a glass powder containing the aforementioned semiconductor element covering glass.

[0014] The semiconductor element covering material of the present invention preferably has a coefficient of thermal expansion of 20 × 10⁻⁷ / ℃ or higher and 48 × 10⁻⁷ / ℃ or lower in the temperature range of 30℃ to 300℃ after heat treatment. This easily avoids cracking or warping of the semiconductor element. Here, "coefficient of thermal expansion in the temperature range of 30℃ to 300℃" refers to a value obtained by measuring using a push-rod type coefficient of thermal expansion measuring device.

[0015] The sintered body for semiconductor device covering of the present invention is characterized in that it contains Zn₂SiO₄ as the main crystal, and the volume ratio of Zn₂SiO₄ is 10% to 40%. Furthermore, the so-called sintered body for semiconductor device covering is formed by heat treatment of semiconductor device covering material.

[0016] The sintered body for covering semiconductor devices of the present invention is characterized in that it contains Zn2SiO4 as the main crystal and has a porosity of less than 10%.

[0017] The sintered body for covering semiconductor devices of the present invention is preferably composed of glass and contains, in molar percentage, 30% to less than 53% SiO2, 15% to 30% ZnO, 32% to 14% Al2O, 30% to 10% B2O, and more than 11% MgO+CaO and equal to or less than 30%, and substantially does not contain lead. [The effects of the invention]

[0018] The present invention provides a semiconductor device cover glass with low environmental impact, low coefficient of thermal expansion and low surface charge density. Simple Explanation of the Diagram

[0019] none Implementation

[0020] The semiconductor element cover glass of the present invention is characterized in that, as a glass composition, it contains, in molar percentages, 30% to less than 53% SiO2, 15% to 30% ZnO, 32% to 14% Al2O3, 30% to 10% B2O, and more than 11% MgO+CaO and equal to or less than 30%, and substantially contains no lead. The reasons for limiting the crystalline phase and the content of each component are explained below. Furthermore, in the following descriptions of the content of each component, unless otherwise specified, % refers to molar percentages. Additionally, unless otherwise specified, the numerical range indicated by "~" in this specification refers to the range of values ​​before and after "~" as the minimum and maximum values, respectively.

[0021] SiO2 is a component that forms the glass mesh and improves acid resistance. It is also a constituent of Zn2SiO4. The SiO2 content is 30% to less than 53%, preferably 30% to 52%, 30% to 51%, 30% to 50%, 30% to less than 50%, 32% to 48%, and particularly preferably 35% to 45%. If the SiO2 content is too low, the coefficient of thermal expansion tends to increase, and acid resistance tends to decrease. Furthermore, Zn2SiO4 is difficult to precipitate, resulting in an excessively high coefficient of thermal expansion for the coating material, leading to greater warpage during firing. On the other hand, if the SiO2 content is too high, the firing temperature becomes too high, making it impossible to form the coating layer at an appropriate temperature.

[0022] ZnO is a component that stabilizes the glass. It is also a constituent of Zn₂SiO₄. The ZnO content is 15%~30%, preferably 17%~28%, 19%~26%, 19.5%~less than 25%, and particularly preferably 20%~24%. If the ZnO content is too low, the devitrification during melting becomes stronger, making it difficult to obtain homogeneous glass. Furthermore, Zn₂SiO₄ is difficult to precipitate, resulting in an excessively high coefficient of thermal expansion of the coating material and increased warping during firing. On the other hand, if the ZnO content is too high, acid resistance tends to decrease. Additionally, excessive crystallinity leads to a sharp increase in viscosity during firing, making it easier to trap defects such as air bubbles within the coating material.

[0023] The preferred content of SiO₂ + ZnO (total amount of SiO₂ and ZnO) is 45% to less than 80%, 50% to 70%, and ideally 55% to less than 65%. If the total amount of SiO₂ and ZnO is too low, Zn₂SiO₄ will be difficult to precipitate, resulting in an excessively high coefficient of thermal expansion of the covering material and increased warpage during firing. On the other hand, if the total amount of SiO₂ and ZnO is too high, the crystallinity will be too strong, leading to a sharp increase in viscosity during firing and making it easier to trap defects such as air bubbles in the covering material.

[0024] Al₂O₃ is a component that stabilizes the glass and adjusts its surface charge density. The content of Al₂O₃ is 2% to 14%, preferably 4% to 12%, and even more preferably 5% to 10%. If the content of Al₂O₃ is too low, the glass is prone to devitrification during forming. On the other hand, if the content of Al₂O₃ is too high, there is a risk that the surface charge density will become too high.

[0025] B₂O₃ is a component that forms the glass mesh and improves its softening and fluidity. The content of B₂O₃ is 0%~10%, preferably 0%~7% or 0%~5%, and ideally 0%~3%. If the content of B₂O₃ is too high, it will be difficult for the glass to crystallize, and it will also tend to reduce its acid resistance.

[0026] MgO and CaO are components that reduce the viscosity of glass. The combined amount of MgO and CaO is greater than 11% and equal to or less than 30%, preferably 12%~28%, 15%~25%, and even more preferably 16%~24%. If the combined amount of MgO and CaO is too low, the firing temperature of the glass is prone to rise. On the other hand, if the combined amount of MgO and CaO is too high, there is a risk of excessively high coefficient of thermal expansion, reduced chemical resistance, and reduced insulation.

[0027] From an environmental perspective, it is preferable that the device is substantially free of lead (e.g., PbO) and also substantially free of Bi₂O₃, F, and Cl. Furthermore, it is preferable that it is also substantially free of alkaline components (Li₂O, Na₂O, and K₂O) that could adversely affect the surface of semiconductor devices.

[0028] In addition to the aforementioned components, it may also contain up to 7% (preferably up to 3%) of other components (e.g., SrO, BaO, MnO 2, Nb 2O 5, Ta 2O 5, CeO 2, Sb 2O 3, etc.).

[0029] The semiconductor element cover glass of the present invention preferably contains Zn₂SiO₄ as the main crystal after heat treatment. Zn₂SiO₄ has a coefficient of thermal expansion very close to that of silicon, the object to be covered by the glass of the present invention, and has the effect of significantly suppressing warping during firing after covering. Furthermore, in addition to containing Zn₂SiO₄, it may also contain crystals such as ZnAl₂O₄.

[0030] Furthermore, the preferred volume fraction of Zn₂SiO₄ is 10%~40%, 12%~35%, and particularly preferably 15%~30%. If the volume fraction of Zn₂SiO₄ is too small, the coefficient of thermal expansion of the covering material becomes too high, resulting in greater warping during firing after covering. On the other hand, if the volume fraction of Zn₂SiO₄ is too large, the viscosity of the glass increases sharply above the softening point, making it prone to defects such as internal bubbles. The "volume fraction of Zn₂SiO₄" refers to the value obtained by removing the background from the peaks of Zn₂SiO₄ obtained by X-ray diffraction, dividing the integrated intensity of the sharp peaks of the crystalline phase by the integrated intensity of the broad peaks of the amorphous layer (glass), and then multiplying by a factor of 100.

[0031] The semiconductor device covering material of the present invention is preferably a glass powder obtained by processing the semiconductor device covering glass into powder form. If processed into glass powder, the surface of the semiconductor device can be easily covered using, for example, a paste method or an electrophoretic coating method. Subsequently, the semiconductor device covering material is heat-treated, thereby enabling the semiconductor device surface to be covered by a sintered body for semiconductor device covering.

[0032] The average particle size D50 of the glass powder is preferably 25 μm or less, and preferably 15 μm or less. If the average particle size D50 of the glass powder is too large, it is difficult to form a paste. In addition, powder adhesion by electrophoresis becomes difficult. Furthermore, there is no particular lower limit for the average particle size D50 of the glass powder, but in practice it is 0.1 μm or more. Moreover, "average particle size D50" is a value obtained by measuring according to volume, specifically using laser diffraction.

[0033] Glass powder can be obtained by mixing raw material powders of various oxide components to form a compound, melting it at about 1500°C for about 1 hour to vitrify it, and then shaping it (after which it is crushed and graded as needed).

[0034] In the semiconductor element covering material of the present invention, it is preferable that, after heat treatment, the coefficient of thermal expansion in the temperature range of 30°C to 300°C is 20×10⁻⁷ / °C or higher and 48×10⁻⁷ / °C or lower, and particularly preferably 30×10⁻⁷ / °C or higher and 45×10⁻⁷ / °C or lower. If the coefficient of thermal expansion is outside the aforementioned range, cracks, warping, etc., caused by the difference in thermal expansion coefficient with that of the semiconductor element are likely to occur.

[0035] In the semiconductor element covering material of the present invention, it is preferable that the surface charge density is 10 × 10¹¹ / cm² or less after heat treatment, and more preferably 8 × 10¹¹ / cm² or less. If the surface charge density is too high, the withstand voltage is improved, but at the same time, there is a tendency for the leakage current to increase. Furthermore, "surface charge density" refers to the value obtained by measurement using the method described in the embodiments section below.

[0036] The sintered body for semiconductor device cover of the present invention contains Zn₂SiO₄ as the main crystal. Furthermore, it is preferably composed of a glass with the following composition (in molar percentage): SiO₂ 30% to less than 53%, ZnO 15% to 30%, Al₂O 32% to 14%, B₂O 30% to 10%, and MgO+CaO more than 11% and equal to or less than 30%, and substantially free of lead. Moreover, the preferred ranges for the content of each component in the sintered body for semiconductor device cover, and the preferred range for the amount of Zn₂SiO₄ precipitated, are the same as those for the glass for semiconductor device cover.

[0037] The sintered body for covering semiconductor devices of the present invention preferably has a porosity of 10% or less, 8% or less, and particularly preferably 5% or less. If the porosity is too high, the coverage becomes insufficient, which may adversely affect the withstand voltage. Furthermore, the actual lower limit of the porosity is 0.1% or more.

[0038] Furthermore, nucleating agents such as ZnO powder can be mixed into amorphous glass powder, and the mixed powder can be heat-treated to produce a sintered body for covering semiconductor devices containing Zn2SiO4 as the main crystal. [Example]

[0039] The present invention will now be described in detail based on embodiments. Furthermore, the following embodiments are merely examples. The present invention is not limited to any of the following embodiments.

[0040] Table 1 shows the embodiments (samples No. 1 to No. 5) and comparative examples (samples No. 6 to No. 9) of the present invention.

[0041] [Table 1] (mol%) No.1 No.2 No. 3 No. 4 No. 5 No. 6 No.7 No.8 No.9 SiO 2 41 44 36 48 51 28 38 33 30 ZnO 23 20 28 29 17 20 45 50 35 Al 2O 3 9 7 5 8 8 18 7 8 10 B 2O 3 4 8 8 0 2 18 0 0 8 MgO 13 15 13 8 14 10 7 7 10 CaO 10 6 10 7 8 6 3 2 7 MgO+CaO twenty three twenty one twenty three 15 twenty two 16 10 9 17 Volume ratio (%) of Zn₂SiO₄ 28 twenty two 32 39 17 0 45 47 Opacity Coefficient of thermal expansion (×10⁻⁷ / ℃) 40 42 39 37 41 53 34 34 Unable to determine Surface charge density (×10¹¹ / cm²) 9 7 4 6 7 9 4 7 Unable to determine Defective inclusion status ○ ○ ○ ○ ○ ○ × × Unable to determine Warpage (μm) 230 290 210 170 250 510 150 150 Unable to determine Porosity (%) 3 3 2 3 2 2 25 27 Unable to determine

[0042] Each sample was prepared as follows. First, the raw material powder was mixed to form a batch according to the glass composition shown in the table, and vitrified by melting at 1500°C for 1 hour. Then, the molten glass was formed into a film, pulverized using a ball mill, and classified using a 350-mesh sieve to obtain glass powder with an average particle size D50 of 12 μm.

[0043] The volume ratio, coefficient of thermal expansion, surface charge density, defect inclusion, warpage, and porosity of Zn₂SiO₄ were evaluated for each sample. The results are shown in Table 1.

[0044] The volume ratio of Zn₂SiO₄ was determined as follows: Glass powder was shaped into a button and pulverized by heat treatment at 800°C to 950°C for 10 minutes using a mortar. The resulting powder was then subjected to X-ray diffraction to obtain diffraction peaks. After background removal, the integral intensity of the peaks attributable to Zn₂SiO₄, originating from crystallization, was divided by the integral intensity of the peaks originating from glass and multiplied by 100.

[0045] The coefficient of thermal expansion is the value obtained by heat-treating the sample at 800℃~950℃ for 10 minutes, using a pusher-type coefficient of thermal expansion measuring device, and measuring the value within a temperature range of 30℃~300℃.

[0046] The surface charge density was measured as follows. First, each sample was dispersed in an organic solvent and attached to the surface of a silicon substrate to a certain film thickness by electrophoresis. Then, it was calcined at the temperature required for crystallization to form a capping layer. Next, an aluminum electrode was formed on the surface of the capping layer, and the change in capacitance in the capping layer was measured using a CV meter to calculate the surface charge density.

[0047] The defect inclusion condition is measured as follows. The glass on the calcined silicon substrate is observed using a stereomicroscope. If no bubbles with a diameter of 10 μm or more are found, it is marked as "○"; if bubbles with a diameter of 10 μm or more are found, it is marked as "×".

[0048] The warpage is measured as follows. First, the silicon substrate is placed on a pressure plate with its surface convex downwards, and double-sided tape is used to secure any point on the circumference of the silicon substrate to the pressure plate. Next, a laser displacement meter is used to measure the height displacement along a straight line from the fixed point of the silicon substrate to the center of the circle. The difference between the heights of the highest and lowest points of the obtained displacement is calculated, and this difference is evaluated as the warpage. Furthermore, if the warpage is less than 300 μm, the warpage is considered small.

[0049] Porosity was measured as follows. First, glass powder was mixed with a photoresist solution and uniformly coated onto a smooth silicon substrate of known weight. Next, the mixture was calcined at 500°C for 1 hour and then at 950°C for 20 minutes. The thickness of the sintered glass film was measured using a micrometer, and its weight was also measured to determine the bulk density of the sintered glass film. Finally, the porosity was calculated as "(density of glass - bulk density of sintered film) / density of glass".

[0050] Table 1 clearly shows that the coefficient of thermal expansion, surface charge density, and warpage of samples No. 1 to No. 5 exhibit the desired values. Furthermore, the defect inclusion condition is also good. Therefore, samples No. 1 to No. 5 are considered preferable as semiconductor element cover materials for use in covering low-voltage semiconductor devices.

[0051] On the other hand, sample No. 6 did not crystallize, had a high coefficient of thermal expansion, and resulted in a poor evaluation of warpage. Samples No. 7 and No. 8 were highly crystalline, and their viscosity increased sharply during firing, thus resulting in internal defects. Sample No. 9 had excessive devitrification and could not be formed into glass.

[0052] none

Claims

1. A glass for covering semiconductor devices, characterized in that, as a glass composition, it contains, in molar percentage, 30% to less than 53% SiO2, 15% to 30% ZnO, 2% to 14% Al2O3, 0% to 10% B2O3, 16% to 24% MgO+CaO, and less than 10% CaO, and substantially contains no lead.

2. The semiconductor element cover glass as claimed in claim 1, wherein after heat treatment, it contains Zn2SiO4 as the main crystal.

3. A material for covering semiconductor devices, characterized in that it contains glass powder comprising the glass for covering semiconductor devices as described in claim 1 or 2.

4. The semiconductor element covering material as claimed in claim 3, wherein, after heat treatment, the coefficient of thermal expansion in the temperature range of 30°C to 300°C is 20×10⁻⁷ / °C or higher and 48×10⁻⁷ / °C or lower.

5. A sintered body for covering semiconductor devices, characterized in that it contains Zn2SiO4 as the main crystal, wherein the volume ratio of Zn2SiO4 is 10% to 40%.

6. A sintered body for covering semiconductor devices, characterized in that it contains Zn2SiO4 as the main crystal and has a porosity of less than 10%.

7. The sintered body for covering semiconductor devices as claimed in claim 5, wherein the glass composition contains, in molar percentages, 30% to less than 53% SiO2, 15% to 30% ZnO, 2% to 14% Al2O3, 0% to 10% B2O3, 16% to 24% MgO+CaO, and less than 10% CaO, and substantially contains no lead.