JPH0559071B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for forming a high-density zirconia substrate with as little glass content as possible.

IC as a way to process huge amounts of information at high speed.
The unit elements of semiconductor devices such as LSIs are becoming smaller and larger in capacity, and VLSIs and other devices are being put into practical use, but at the same time improvements are being made in semiconductor materials.

In other words, in most cases silicon (Si) is used as the material for conventional semiconductor devices due to its wide operating temperature range and the ease with which it can be planarized due to its oxide film. Gallium arsenide (GaAs) compound semiconductors, which have high mobility, are attracting attention, and demand for them is increasing as high electron mobility transistors and other devices are put into practical use.

Semiconductor devices are manufactured by using thin film formation technology and photolithography to create a large number of semiconductor devices on a semiconductor substrate (wafer) made of a single semiconductor or a compound semiconductor, and then each device is separated into individual devices. The chips were cut into chips, mounted on a ceramic substrate, and packaged.

Taking Si as an example, Si after pattern formation has been completed.
The chip is made of alumina (α-
After adhering to a wiring board made of Al ₂ O ₃ ) or glass ceramic using an adhesive or eutectic bonding method, and connecting the circuit between the terminals of the chip and the wiring of the wiring board using a method such as wire bonding, the resin exterior or A semiconductor device is formed by applying a hermetic seal.

As mentioned above, the chip is used mounted on a wiring board, but in this case it is necessary that the thermal expansion coefficients of both are similar, and if this is not met, the chip may be damaged or peeled off from the board. This results in a significant decrease in the reliability of the device.

The present invention relates to a method of manufacturing a zirconia substrate suitable for mounting a GaAs chip.

[Conventional technology]

The thermal expansion coefficient of GaAs is 9~10×10 ^-6 /℃ and α-Al ₂
This is about twice as large as the thermal expansion coefficient of O ₃ , which is 5 to 6×10 ^-6 /°C, and therefore conventional alumina substrates cannot be used.

Here, it is necessary to use a substrate made of a heat-resistant material with a coefficient of thermal expansion close to that of GaAs, and examples of such materials include zirconia (ZrO ₂ ) and magnesia (MgO).

In other words, the coefficient of thermal expansion of ZrO ₂ is 9 to 10 × 10 ^-6 /℃
Furthermore, the coefficient of thermal expansion of MgO is 10 to 11×10 ^-6 /°C, which is close to that of GaAs.

However, the melting point of ZrO ₂ is 2700℃, and the melting point of MgO is
The temperature of 2800℃ is much higher than that of α-Al ₂ O ₃ at 2015℃, so sintering is not easy.

Additionally, multi-layered substrates are required as substrates for mounting chips such as ICs and LSIs, which are becoming increasingly dense.
It is desirable to use metals with high specific conductivity such as gold (Au) and copper (Cu) as the conductor pattern used for this, but since the melting point of these metals is around 1000℃, they cannot be used as conductors for multilayer boards. It is impossible to form a pattern.

In order to overcome this problem, methods have been taken such as making the grain size of ceramic finer to increase its surface energy and lowering the sintering temperature, but these efforts have had little effect.

This problem is the same in conventional alumina ceramics, and as a solution to this problem, glass ceramics in which alumina powder is mixed with glass powder and the mixture is sintered have been put into practical use.

In other words, when a uniform mixture of alumina powder and borosilicate glass is molded and heat treated, the melting point of the borosilicate glass is as low as 500 to 800°C, depending on the composition ratio, and this acts as a binder for the alumina powder to form a composite dielectric. Because of its structure, glass-ceramic substrates with low dielectric constants and low coefficients of thermal expansion can be produced with a relatively low firing process of around 900°C.

In other words, borosilicate glass has a coefficient of thermal expansion of 1 to 2×
The dielectric constant is as low as 10 ^-6 /°C, and the dielectric constant is as low as 4 to 5, compared to a relatively high 9 to 10 for alumina magnetic substrates.

For these reasons, a glass-ceramic multilayer substrate using alumina is suitable as a mounting substrate for Si chips.

However, this method cannot be directly applied to glass ceramics whose main components are ZrO ₂ or MgO.

The reason for this is that the zirconia or magnesia substrate must have a high coefficient of thermal expansion commensurate with the GaAs chip, but ZrO ₂ reacts with silicic acid (SiO ₂ ), the main component of borosilicate glass. Zircon (ZrO ₂ .SiO ₂ ) is formed, and the coefficient of thermal expansion becomes as small as 5 to 6× ^{10 -6} /°C, which is not suitable for the purpose.

Furthermore, in the case of MgO, there are problems in that it has extremely poor wettability with borosilicate glass and is not uniformly dispersed, and that gaps are formed at the interface with the glass after firing, making it impossible to form a dense glass-ceramic substrate.

Furthermore, if a large amount of borosilicate glass is added as in the conventional method, a composite dielectric is formed, which inevitably changes various properties including the coefficient of thermal expansion.

For these reasons, ceramic substrates suitable for mounting GaAs chips have not yet been put into practical use.

[Problem that the invention seeks to solve]

As mentioned above, GaAs chips have a large coefficient of thermal expansion, and although ZrO ₂ is a suitable substrate material, its melting point is high, making it difficult to form multilayer substrates. When the substrate is formed, it reacts with SiO ₂
There is a problem that as ZrO ₂ ·SiO ₂ is formed, the coefficient of thermal expansion decreases as a whole.

[Means for solving problems]

The above problem can be solved by applying α− to the surface by chemical vapor deposition.
Borosilicate glass having a particle size at least one order of magnitude smaller than the ZrO ₂ powder is added to the ZrO ₂ powder coated with a thin film of Al ₂ O ₃ , a solvent is added and kneaded, and the substrate is molded and dried. This problem can be solved by a method for manufacturing a zirconia substrate, which is characterized in that the substrate is subjected to a firing treatment.

[Effect]

The present invention is based on the reaction between ZrO ₂ and borosilicate glass.
In order to prevent the formation of ZrO ₂ and SiO ₂ , the surface of ZrO ₂ is coated with a thin film of α-Al ₂ O ₃ using chemical vapor deposition, and borosilicate glass powder used as a binder is coated with ZrO ₂ powder. By using particles that are one order of magnitude smaller than the particle size, a high-density zirconia substrate can be formed by adding a minimum amount of borosilicate glass.

FIG. 1 explains the outline of the present invention. The ZrO ₂ powder 1 used is coated with α-Al ₂ O ₃ on the surface by chemical vapor deposition (CVD) in order to prevent the formation of ZrO ₂ and SiO ₂ . The borosilicate glass 3 used to bond the membrane 2 to each other has a particle size of
Using ZrO ₂ powder, which is more than an order of magnitude smaller,
As shown in FIG. 1A, by firing the mixed state, the α-Al ₂ O ₃ film 2 is formed as shown in FIG. 1B.
A fired body is obtained in which the gap between the ZrO ₂ powder 1 coated with borosilicate glass 3 is filled with borosilicate glass 3.

In this way, the α-Al ₂ O ₃ film 2 and the borosilicate glass 3 are compatible, so no gaps such as pores are formed, and since the borosilicate glass 3 is only used as a binder, the thermal expansion of ZrO ₂ The effect on the rate is small.

〔Example〕

Figure 2 shows the configuration of a CVD apparatus for coating ZrO ₂ with α-Al ₂ O ₃ . Partially stabilized particles with a particle size of 3 to 5 μm are contained in a quartz reaction chamber 5 equipped with a heater 4 .
ZrO ₂ powder 6 is placed therein, and the structure is such that the powder can flow through sieve-like pores provided at the bottom.

Further, there is an aluminum chloride (Al Cl ₃ ) vaporizer 7 on the lower side of the reaction chamber, which is connected to a carbon dioxide gas (CO ₂ ) cylinder 9 and a hydrogen gas (H ₂ ) cylinder 10 through a tank 8 .

Further, the upper part of the reaction chamber 5 is connected to a vacuum pump 12 and a trap 13 through a tank 11.

Using such a CVD device, α is deposited on the surface of _ZrO2 .
- To coat the Al ₂ O ₃ film, partially stabilized ZrO ₂ powder 6 with a particle size of 3 to 5 μm is placed in the reaction chamber 5, and after being evacuated using the vacuum pump 12, CO ₂ and
While flowing a mixed gas of _H2 at a flow rate of approximately ^50cm3 .
Heat to 1200℃ to form a fluidized bed.

In this state, Al vaporized from the Al Cl ₃ vaporizer 7
α− on top of ZrO ₂ powder 6 by flowing Cl ₃
Al ₂ O ₃ coating is applied.

This reaction can be expressed by the following reaction formula.
2Al Cl ₃ +3CO ₂ +3H ₂ →Al ₂ O ₃ +3CO + 6HCl After mixing 80% by weight of the ZrO ₂ powder thus obtained and 20% by weight of borosilicate glass powder with a particle size of 0.1 to 0.5 μm, alumina balls were formed. Dry milling was carried out in a pot using the following method to form aggregates of ZrO ₂ powder and borosilicate glass powder.

Next, a solvent such as acetone and a small amount of acrylic resin were added to the aggregates, and the mixture was thoroughly kneaded to form a thriller shape, which was then used to form a substrate and dried at a temperature of approximately 150°C.

The substrate was placed in an electric furnace and heated at a temperature of 900°C for 2
By firing for several hours, a zirconia substrate with a relative density of 99% could be obtained.

Next, the thermal expansion coefficient of this substrate was measured and showed a value of 9×10 ^-6 /°C.

Note that for a substrate prototype produced under similar conditions with the amount of borosilicate glass added at 5% by weight, the coefficient of thermal expansion remained the same at 9 x 10 ^-6 /°C, but the relative density was 95.
%.

〔Effect of the invention〕

As described above, by carrying out the present invention, a glass ceramic substrate with a high density and a coefficient of thermal expansion close to that of a GaAs chip can be formed, and since it can be fired at a temperature of 1000° C. or less, it becomes possible to manufacture a multilayer wiring board.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing the structure of the present invention. FIG. 1A is before firing, FIG. B is after firing, and FIG. 2 is a configuration diagram of a CVD apparatus necessary for the present invention. In the figure, 1 is ZrO ₂ powder, 2 is α-Al ₂ O ₃
Membrane, 3 is borosilicate glass, 5 is reaction chamber, 6 is ZrO ₂
It is a powder.

Claims (1)

[Claims] 1 Add borosilicate glass having a particle size at least one order of magnitude smaller than the zirconia powder to the zirconia powder whose surface is coated with a thin film of alumina, add a solvent and knead, then mold the substrate and dry it. 1. A method for manufacturing a zirconia substrate, the method comprising: then subjecting the substrate to a firing treatment.