JPH0793394B2 - Ceramic package for mounting semiconductor substrate - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a ceramic package for mounting a semiconductor substrate, and more particularly to a high thermal conductivity package suitable for accommodating a semiconductor integrated circuit substrate in which heat generating elements are integrated at high density.

[Background of the Invention]

In the past, since electronic computers are required to have high calculation speed, in recent years, a large number of semiconductor elements that generate heat are integrated in a limited semiconductor substrate, which makes it possible to increase the length of electrical communication wiring between each element. Semiconductor device shortened as much as possible
Large Scale Integrated Circuit (hereinafter referred to as LSI) chips have been developed. Also, it is mounted with the LSI chip,
The board or package that electrically connects the chip and an external circuit and doubles as a storage container for the chip is also electrically wired in multiple layers and at high density, and thus the relay connection wire length has been substantially shortened. A mounting structure that efficiently releases the heat generated by the chip to the outside has also been developed. As an example of this, (1) El. M. Bipolar Device Packaging-Electrical Thermal and Mechanical in Solid State Technology 163-173, May (1984) by LM Mahalingam et al.
Stress Concurrency (Bipolar Device Packa
ging-Electrical, Thermal and Mechanical Stress Con
in a paper entitled "siderations", the Pin Grid Array Package (PGA).
In order to improve the heat dissipation of the chip, it is disclosed that the recess for die-bonding the chip is composed of beryllia and alumina in a composite manner. That is, a beryllia with a high thermal conductivity (400 W / m · k) is used for the part where the chip is mounted, and the wire bonding pad and the external terminal are arranged on the alumina having the hollow part and the pad is connected to the external terminal. Electrical wiring is provided to finally provide a role as a substrate for relay electrical wiring from the chip to an external circuit. A heat radiation fin is thermally engaged with the surface of the belly rear surface opposite to the chip mounting surface.

In the above structure, the thermal resistance from the junction of the heat generating part to the outer surface of the beryllia plate as a case is about 1 ° C / w, and about 3.5 when the beryllia plate is replaced by an alumina plate.
Has excellent heat dissipation compared to ° C / W. Further, in the above structure, from the viewpoint of ensuring high airtightness and proof stress for the subsequent thermal process, the beryllia plate and the alumina substrate are generally integrated by silver brazing. The thermal expansion coefficient of this structure is similar (Berrillia: 8 × 10 ^-6 / ℃, alumina:
7 × 10 ^-6 / ℃, all room temperature to 400 ℃) and is based on the joined body of ceramic members with established metallization technology that can withstand silver brazing (about 800 ℃). Therefore,
The structure can be a highly reliable package that can follow thermal changes.

However, the biggest drawback of the above prior art example (1) is that
It has a toxicity problem.

On the other hand, the aluminum nitride sintered body has been provided with preferable physical properties notable as a substrate material for electronic parts with the recent improvement of sintering technology and refining technology.

For example, (2) Proceeding of
The Just A Good Symposium (Proceeding
of the 1st IEEE Symposium) pages 23-28, Oct., (1984
Development of High Thermal Conductive Aluminum Nitride Substrate Material Bi-Precisionless Sintering (Development of High Thermal Conductiv
e Aluminum Nitride Substrate Material by Pressure
less Sintering In) article entitled, Y ₂ O ₅ added thermal conductivity 40~100W / m · aluminum nitride body by pressureless sintering
k, volume resistivity 10 ¹⁴ Ωcm or more (room temperature), dielectric constant 8.8 (1MH
z), dielectric strength 140-170KV / cm (room temperature), thermal expansion coefficient 4.5
It is disclosed that it has a property of × 10 ⁻⁶ / ° C. (room temperature to 400 ° C.) and bending strength of 40 to 50 kg / mm ² .

Also, (3) Proceeding of the symposium by Kurokawa
e 1st IEEE Symposium) Page 15-22, Oct., (1984), NL Substrates with High Thermal Conductivity (AIN Substrates with High)
In the paper entitled Thermal Conductivity),
High-density refined aluminum nitride powder is pressure-sintered to have a thermal conductivity of 160 W / m · k (room temperature) and an electrical resistivity of 5 × 10 ^13.
Ωcm (room temperature), dielectric constant 8.9 (1MHz), bending strength 5000kg / mm
^2. Disclosed is an aluminum nitride body having a property of a thermal expansion coefficient of 4.3 × 10 ⁻⁶ / ° C. (room temperature to 400 ° C.).

[Object of the Invention]

SUMMARY OF THE INVENTION It is an object of the present invention to remedy the drawbacks of conventional ceramic packages and to provide a semiconductor package for mounting a semiconductor substrate on which high heat dissipation and airtightness are stably maintained.

[Outline of Invention]

The present invention relates to a first ceramic substrate as a circuit wiring substrate that forms an electrical relay circuit between a semiconductor substrate and an external circuit,
In a semiconductor-base-mounting ceramic package, which is joined to a second ceramic substrate having a portion for mounting the semiconductor base, the first ceramic substrate is made of alumina, mullite, or glass ceramic as a base material. The second ceramic substrate is made of a ceramic material, and the second ceramic substrate is made of sintered aluminum nitride.

If sintered aluminum nitride is used as the second ceramic substrate having a portion on which the semiconductor substrate is mounted, the thermal conductivity is high, so that even if the heating element is directly mounted, high heat dissipation can be realized. Further, the coefficient of thermal expansion of the sintered aluminum nitride is similar to that of the heating element, so that the residual stress generated in the bonded portion of the element is reduced.

On the other hand, if the first ceramic substrate as a circuit wiring substrate is a ceramic material having alumina, mullite, or glass ceramic as a base material, these are formed into green sheets of ceramics or through sheets due to the nature of the material. Since holes can be formed easily and deformation and foaming that occur during firing of the laminated body are small, it is particularly easy to form a multilayer wiring. Further, since the above-mentioned ceramic material has a relatively low dielectric constant, the wiring formed on the first ceramic substrate has a small signal propagation delay.

When the above-mentioned ceramic materials of the first ceramic substrate and the second ceramic substrate are adopted, bonding between the substrates is a problem. In the present invention, by bonding the first ceramic substrate and the second ceramic substrate through at least one metal selected from the group of aluminum, copper and nickel and a metal layer made of a silicon alloy of the above metal, High airtightness and high strength bonding are realized.

Specifically, at least the second ceramic substrate and the metal layer have a joining force maintained by interposing an alloy layer composed of the metal for forming the metal layer and silicon.

In the present invention, the first ceramic substrate and the second ceramic substrate have a metal layer made of at least one metal selected from the group consisting of aluminum, copper and nickel interposed therebetween, and a thermocompression bonding method. That is, they are joined together by heat treatment under the application of pressure. In this case, an important issue is that it is difficult to apply the solid-phase diffusion bonding method, which has been conventionally adopted for the integral bonding of the alumina ceramic and the metal, to the bonding of the aluminum nitride and the metal. This is because an excessive residual stress is generated in the vicinity of the aluminum nitride bonding interface. In order to overcome this technical problem, the most novel point introduced into the package of the present invention is a transition mainly composed of a eutectic alloy having a grain size of 1 μm or less and fine crystal grains at the bonding interface between aluminum nitride and metal. This is because a region is provided to prevent excessive stress from remaining due to the excellent plastic deformation performance of the transition layer.

The reason for paying attention to the eutectic alloy is that the grain boundary plastic deformation performance increases as the alloy becomes finer.

Therefore, according to the method of manufacturing the ceramic package for mounting a semiconductor substrate of the present invention, at least one metal layer selected from the group consisting of aluminum, copper and nickel is interposed in a required portion of the first ceramic substrate and the second ceramic substrate. At this time, silicon is adjusted to have a high concentration between the second ceramic substrate and the metal layer, and a eutectic alloy having the minimum melting point of the metal and the silicon-based alloy is applied under pressure. It is characterized in that it is heat-treated at a temperature at which it is generated.

The above heat treatment temperature is (1) when the metal is mainly aluminum or aluminum, the melting point of aluminum is 660.
Below ℃ and a melting point of Al-11.3 wt% eutectic alloy of 577 ℃ or more, (2) when the metal is mainly copper or copper, the melting point of copper is below 1083 ℃ and Cu-16 wt% Si eutectic Alloy melting point 80
In the range of 2 ° C or higher, and (3) when the metal is mainly nickel or nickel, the melting point of nickel is less than 1453 ° C and the melting point of the Ni-38 wt% Si eutectic alloy is 966 ° C or more.

The more detailed bonding mechanism between the aluminum nitride and the metal layer by the heat treatment is awaiting further elucidation, but the present inventors presume that the following process steps will be taken. That is, the first process in which the metal layer and the aluminum nitride are subjected to pressure and heat energy to increase the contact interface, and the region where the silicon concentration is adjusted to high is melted, and the melting of aluminum and nitrogen into the same region is promoted. And a second step in which the bond between silicon and nitrogen is promoted, and a transition region composed of the eutectic alloy of aluminum and silicon in which the molten region is solidified and fine crystal grains mainly composed of silicon nitride, This is the third step of forming an interface between the metal and aluminum nitride.

Example of Invention

Embodiments of the present invention will now be described in more detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a PGA according to a first embodiment of the present invention and an enlarged schematic cross-sectional view of a main part constituting the PGA.

Referring to FIG. 1, reference numeral 11 denotes a hollow hole (opening approximately 11 mm × 11 mm) provided through the center of the flat plate 111, and a metal pad for wire bonding (longitudinal direction 0) at the upper edge of the hollow hole 111. .
(8 mm) provided with a step 112 and a two-layer electric wiring (not shown) from the pad of the step 112 to the metal pins (144) 14 the first ceramic substrate using an alumina sintered body as a base material ( 39.4 mm × 39.4 mm × 1.77 mm), and 10 is a second ceramic substrate (16 mm × 16 mm × 0.6 mm) made of an aluminum nitride sintered body provided with a metallization layer 101 for die-bonding the semiconductor substrate. . The first and second ceramic bases are joined by interposing a metal layer 12 made of a closed loop aluminum piece, and in particular, a transition region 121 exists between the second ceramic base 10 and the metal layer 12, and the joining force is increased. Contribute to the maintenance of.

The second ceramic 10 is a high-purity synthetic material obtained by heat-treating a mixture of high-purity alumina powder and carbon powder in a nitrogen atmosphere at 1600 ° C. for 5 hours, and then removing excess carbon by heating in the presence of oxygen. It is a plate obtained by pressure sintering (200 kg / cm ² , 2000 ° C., 3 hours) of aluminum nitride powder (particle size: 1 μm or less) in a nitrogen atmosphere. The second ceramic 10 is, for example, Y ₂ O ₅ or
It is possible to substitute sintered aluminum nitride with additives that do not impair the thermal conductivity, as represented by materials such as CaO. Further, although aluminum nitride is well known as a substance that easily imparts translucency, it is desirable that the second ceramic be a non-translucent treatment from the standpoint of avoiding malfunction of the LSI chip due to light irradiation. .

Although not shown in FIG. 1, the metal pin 14 is joined to the wiring of the first ceramic 11 by silver brazing, for example, and a hollow hole 111 is formed on the mounting surface side of the metal pin 14 of the first ceramic 11. A metallization layer, for example for gold-tin brazing, is provided for sealing, and these metal pins and metallization layers are stepped.
Together with the pad of 112 and the metallization layer 101 for die bonding, a metal layer having gold as the outermost layer is provided to facilitate subsequent wire bonding and brazing.

In order to obtain the above PGA, in the manufacturing method of the present invention, the inner dimension is 12 mm between the first ceramic 11 and the second ceramic 10, and the external attachment method is used.
16mm, 0.1mm thick closed loop Al-Si alloy clad aluminum 12 is inserted, heated to 600 ℃ in vacuum (7.5 × 10 ^-8 Pa) and under pressure (5 kg / mm ² ) for 30 minutes. Hold, then cool to about 100 ° C. and release vacuum and pressure. In this heat treatment, aluminum 12 is clad Al
-Si alloy is placed in contact with the second ceramic 10,
At the contact interface, a series of changes in the interface state from the first process to the third process described above occur, and a transition region 121 containing fine particles mainly composed of aluminum and silicon is formed to complete the bonding. The pressing force, temperature, time and the like in the bonding heat treatment are important factors for accelerating the reaction particularly in the second process described above, and various values can be selected.

FIG. 2 is an enlarged schematic view showing a joined state of main parts. Also in the second ceramic, aluminum nitride has crystal grains 102 sintered in a polycrystalline form through grain boundaries 103. At the interface between aluminum 12 and aluminum nitride 10 as the metal layer, the average grain size generated by the above interface reaction is about 0.3 μm.
m of aluminum lit particles (silicon is a solid solution in aluminum) and silicon particles
There is a transition region 121a and a transition region 121 composed of the above-mentioned mixture and the second transition region 121b in which silicon nitride is interposed in the crystal grain 103, and contributes to maintaining the bonding force. The first transition region 121a was analyzed by an electron probe X-ray microanalyzer (EPMA), and it was found that Al-11
It was confirmed to have a composition of wt% Si.

In this embodiment, the alumina 12 as the first ceramic 11 and the aluminum 12 are joined by diffusion of aluminum through the contact interface during the pressure heat treatment. In this joining process, the liquid phase generation process as in the case of forming the transition region 121 described above is not performed. However, even on the first ceramic 11 side, it is not special that the silicon source is positively introduced to undergo the liquid phase generation process, that is, the Al-Si alloy is arranged so as to be in contact with the first ceramic 11. Is not hindered.

The PGA having the structure shown in FIG. 1 was subjected to a temperature cycle test of −55 to + 150 ° C. The He leak rate was tracked during this test process,
In the cycle, a value equal to or less than the initial value was obtained at 5 × 10 ^-11 atm cc / sec or less. Such excellent airtightness was maintained because the aluminum 12 and the aluminum nitride 10 were densely and metallurgically bonded together, and were an aggregate of fine particles, which was excellent in the grain boundary plastic deformability. This is due to the fact that excessive stress remains due to 121a.

In the temperature cycle test, the continuity of the wiring provided on the first ceramic substrate was also examined. As a result, no conduction failure due to disconnection was observed after 3000 cycles. This is largely due to the stress relaxation of the first transition region 121a described above, but it is also due to the fact that the combination is selected so that the thermal expansion coefficient of the first ceramic substrate is larger than that of the second ceramic substrate. That is, in the case of the first ceramic substrate, the residual stress due to the thermal contraction after the integration becomes a compressive stress, and the mechanical fracture accompanied by the disconnection is suppressed. Although 300 samples were put in the temperature cycle test, the defect occurrence rate from the viewpoint of maintaining airtightness and disconnection was 3000 temperature cycles.
Cycle is less than 0.003%.

As described above, the selection of heat treatment conditions such as pressure, temperature, and time is important for forming the transition region 121, and the higher the pressure, the higher the temperature, and the longer the time, the easier the formation of the region 121. become. However, even if the above method is not used, the transition region 121 can be positively introduced.

Next, an LSI chip was die-bonded to the above PGA and predetermined wire bonding was performed, and then a Kovar plate was Au-Su brazed to form a sealing body. The encapsulant was finally energized and stopped so that the chip temperature was substantially varied from 20 ° C to 125 ° C. In the process of applying and releasing the electric energy, the thermal resistance from the chip to the outer surface of the second ceramic plate 10 as a case and the bubble leak test of the sealing body were performed. This result 25
After 000 cycles, the thermal resistance was 1 ° C / W, which was equivalent to the initial value, and no bubble leak was observed. The thermal resistance is low and does not change until a high number of cycles because the second ceramic plate 10 equipped with a chip has a thermal expansion coefficient substantially equal to that of silicon and is an aluminum nitride sintered body having a large thermal conductivity. Due to being. Although the heat transferred from the chip to the second ceramic substrate 10 is finally released into the air, it is not possible to engage the second ceramic substrate 10 with a heat sink member such as an aluminum fin to assist heat dissipation. It is preferable.

In the present invention, the aluminum as the metal layer 12 disclosed in the first embodiment can be replaced with another metal. The case where copper is applied in the second embodiment will be described above.

First ceramic 11 and second ceramic similar to those of the first embodiment
Between 10 and 10, a closed loop copper 12 'of the same size made by cladding a copper-silicon alloy with a second ceramic
It is placed in contact with 10 and heated to 950 ° C in vacuum (7.5 × 10 ^-8 Pa) and under pressure (5 kg / mm ² ) and held for 30 minutes, then cooled to about 100 ° C and vacuum and PGA was obtained through the process of releasing pressure.

At the interface between the second ceramic 10 and the copper 12 ', a first transition region 121a' composed of eutectic particles having an average particle size of about 0.25 μm generated by an interfacial reaction, and the eutectic particles are grain boundaries 103.
Transition region constituted by the second transition region 121b 'interposed in the
121 'exists and contributes to the maintenance of the bonding force, and serves to relax the residual stress based on the plastic deformation performance of the first transition region 121a'. Therefore, the various effects received in the first embodiment can be similarly received in this embodiment. Incidentally, the copper 12 'can be changed to the nickel 12 ". Even in such a case, silicon can be positively introduced into the bonding interface as in the case of aluminum.

In the present invention, the first ceramic substrate should be selected with an emphasis on the point that the dielectric constant is low, and alternative materials selected from this viewpoint include mullite ceramics and glass ceramics. The same effect can be obtained whether the wiring of the first ceramic substrate is a single-phase wiring or a multi-layer wiring having two or more layers. Therefore, the number of pins also increases or decreases depending on the wiring density, but this does not change the effect of the present invention.

The aluminum nitride plate as the second ceramic substrate is preferably a large plate with a large area from the viewpoint of enhancing heat dissipation, but it is preferably as thick as possible from the viewpoint of reducing warpage of an integrated product with the first ceramic substrate. desirable. Therefore, the formation and size of the second ceramic substrate that is actually selected should be an appropriate shape according to the specifications required for the PGA,
The dimensions should be chosen. In particular, a disc-shaped second ceramic substrate is used to disperse residual stress and a metal layer is used.
It is more preferable to select 12 as a ring.

The semiconductor substrate to be mounted is most preferably silicon whose coefficient of thermal expansion is substantially the same as that of the second ceramic substrate. However, even with a compound semiconductor represented by a material such as gallium arsenide or gallium phosphide, there is no change in the effects and advantages of the package of the present invention.

〔The invention's effect〕

As described in the above embodiments, according to the present invention, for mounting a semiconductor substrate on which high heat dissipation and airtightness are stably maintained, which has been difficult to solve by the conventional prior art and its stress technology. It is effective in realizing a ceramic package.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a PGA showing an application example of the present invention, and FIG. 2 is a schematic view of a metal layer at a joint. 10 …… Second ceramic substrate, 11 …… First ceramic substrate, 12 …… Metal layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaaki Takahashi 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Laboratory Ltd., Hitachi Research Institute, Inc. (72) Komei Hachino 4026 Kuji Town, Hitachi City, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory (72) Inventor Mamoru Sawahata 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-50-139674 (JP, A) JP-A-60-178647 (JP, A)

Claims (2)

[Claims] 1. A semiconductor formed by joining a first ceramic substrate as a circuit wiring substrate forming an electrical relay circuit between a semiconductor substrate and an external circuit and a second ceramic substrate having a portion for mounting the semiconductor substrate. In the ceramic package for mounting on a base body, the first ceramic substrate is made of a ceramic material having alumina, mullite, or glass ceramic as a base material, and the second ceramic substrate is made of sintered aluminum nitride. The first ceramic substrate and the second ceramic substrate are bonded to each other through a metal layer made of at least one kind of metal selected from the group of aluminum, copper and nickel and a silicon alloy of the metal, and the second ceramic substrate. At the interface between the substrate and the metal layer, at least one selected from the group of aluminum, copper and nickel is selected. Also has a transition region mainly composed of a eutectic alloy composed of crystal grains having a grain size of 1 μm or less containing one kind of metal-silicon alloy, and the transition region is composed of a eutectic grain of the metal and silicon. A ceramic package for mounting on a semiconductor substrate, comprising a transition region and a second transition region in which the eutectic grains are present in a grain boundary of the second ceramic substrate and aluminum nitride. 2. The ceramic package for mounting on a semiconductor substrate according to claim 1, wherein the second ceramic substrate has a coefficient of thermal expansion smaller than that of the first ceramic substrate.