JPH0714014B2 - Substrate material for semiconductor device and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat dissipation structure for a semiconductor device and a manufacturing method thereof. The structure of the present invention can be used as a heat dissipation structure particularly useful in the thermal design of a package such as a semiconductor device for various integrated circuits in which a substrate of a surrounding member for a semiconductor device and a heat sink are combined.

Here, the semiconductor device is a chip of GaAs or Si. Sometimes it is an integrated circuit, transistor, LE
It may be an individual component such as D, CD, or diode. These chips are obtained by forming a desired circuit on a GaAs or Si single crystal as a substrate by a wafer process. Although the substrate portion of the chip is sometimes called a substrate, the chip is not called a substrate because the present invention relates to the substrate for mounting the chip. Therefore, it will be referred to as a semiconductor device or a semiconductor chip.

The present invention relates to a substrate to which a semiconductor chip is to be fixed, and here it is a semiconductor device substrate or a semiconductor device heat dissipation substrate including the meaning of heat dissipation. Not to be confused with single crystal substrates (of chips).

(B) Prior Art Since the semiconductor chip is fixed, the semiconductor device substrate is required to have a high thermal conductivity and a coefficient of thermal expansion similar to that of the semiconductor chip. It is also required to have mechanical strength, but this is a condition that is satisfied in many materials and is not a serious problem.

The structure of a conventional semiconductor device substrate will be described with reference to FIGS.

The substrate shown in FIG. 3 is obtained by applying an alumite treatment 31 to the surface of an aluminum plate 30 and then coating a resin 32 thereon. The semiconductor chip 33 is fixed on this. Since this is mainly aluminum, it has a large coefficient of thermal expansion. At room temperature, the coefficient of thermal expansion of aluminum is 23 × 10 ^-6 deg ^-1 .

On the other hand, GaAs is 5.7 × 10 ^-6 deg ^{-1 at} room temperature and Si is 2.5 × 10 ^-6 deg at room temperature.
^-1 .

If the semiconductor chip is small, it does not matter much,
If the semiconductor chip is large, the difference in expansion coefficient becomes a problem.

Further, a resin 32 is used as an insulating layer between the semiconductor chip 33 and the Al plate 30. Alumite 31 is also an insulating layer. Two insulating layers are used because they cannot provide sufficient insulating properties by themselves. However, since there is resin 32,
The effective thermal conductivity is reduced. Therefore, it becomes an obstacle to heat dissipation. Further, since the resin is weak against heat, the heat resistance of the substrate also deteriorates.

The most fatal drawback is the difference in the coefficient of thermal expansion between the Al plate and the chip described above.

In particular, as the scale of ICs has been increasing in recent years, the size of semiconductor chips tends to increase. Therefore, the difference in thermal expansion coefficient between the semiconductor chip and the Al substrate is becoming a serious problem that cannot be overlooked.

FIG. 4 shows the same aluminum plate 30 coated with AlN. AlN35 is interposed for insulation. It replaces the alumite 31 and the resin 32 shown in FIG. However, there is no change in that Al is the main subject. The difference in the coefficient of thermal expansion still poses a problem.

The substrate of FIG. 4 not only has thermal expansion between Al and the chip,
There is also the problem of a difference in the coefficient of thermal expansion between Al and AlN. AlN at room temperature
Has a linear expansion coefficient of 2.5 × 10 ^-6 deg ^-1 . Therefore, the expansion coefficients of the chip and AlN are similar, but the difference in expansion coefficient between Al and AlN is large. Therefore, there is a drawback that the AlN film is easily separated from the Al plate.

The main choice for Al is high thermal conductivity, good heat dissipation,
This is because it has mechanical strength and is chemically stable. However, Al has a problem of a difference in coefficient of thermal expansion from a semiconductor chip, and thus has a problem as a substrate for a semiconductor device which is becoming larger in scale.

(C) Purpose It is an object of the present invention to provide a substrate for a semiconductor device having a low coefficient of thermal expansion and excellent heat dissipation and a method for manufacturing the substrate.

(D) Constitution Al ₂ O ₃ , AlN, etc. are known as compounds mainly composed of aluminum, and their production has been established. These are similar to semiconductor chips in terms of coefficient of thermal expansion (Al ₂ O ₃ 5.4
× 10 ^-6 deg ^-1 ), but Al ₂ O ₃ has poor heat conduction. The same applies to AlN. Therefore, it cannot be used as a substrate.

At room temperature, the thermal conductivity of Al ₂ O ₃ is 0.11 (cal / cm sec ℃), AlN
Is 0.072, Al is 0.56 and Si is 0.35.

Other than this, Al ₄ C ₃ , AlB ₂ , AlAs, and the like are available as Al compounds. Both have problems as substrates.

The compounds of Si include SiO ₂ , Si ₃ N ₄ , SiC, SiS, TiSi ₂ ,
Examples include VSi ₂ , V ₃ Si, and WSi ₂ .

There is no compound of Al and Si. At least unknown until now. Both do not make stable compounds.

However, Si is the material of the semiconductor chip itself (in the case of Si chip), and the expansion coefficient is similar even when GaAs is the chip.

The disadvantage of Al lies in its high expansion coefficient. It is a material with satisfactory thermal conductivity and mechanical properties.

Therefore, the present inventor has obtained a new idea of using a substrate that is a mixture of Al and Si as a substrate for a semiconductor device.

The material itself, Si / Al, is new. More specifically, the substrate is mainly made of Al and contains 30 to 60% of Si. The manufacture of the plate will be described later.

FIG. 5 is a sectional view of a semiconductor device substrate according to the present invention.

Al containing 30-60% Si will be simply written as Al-30-60% Si. The al-30 to 60% Si6 mainly to form a nitride layer 7 mainly composed AlN, the Si ₃ N ₄ thereon.
This is the substrate of the present invention.

Since the Si / Al plate is nitrided to form a film, the film is mainly a mixed film of AlN and Si ₃ N ₄ . This is a film for obtaining insulation.

FIG. 8 shows a schematic view of the structure after the surface of Al-30 to 60% Si was subjected to the ion nitriding treatment. When the nitriding treatment is performed in this manner, the Al portion of the matrix mainly becomes AlN and other Al nitrides, and the primary Si portion mainly becomes Si ₃ N ₄
And the like, and a mixed nitride layer mainly composed of AlN and Si ₃ N ₄ is formed.

The coefficient of thermal expansion is Si ₃ N ₄ 0.8 (× 10 ^-6 dg ^-1 ) AlN 2.5 Si 2.5 GaAs 5.7 Al 23.0 at room temperature, so the thermal expansion of the mixed film mainly composed of AlN and Si ₃ N ₄ is not The same as the thermal expansion of.

Furthermore, the coefficient of thermal expansion of Si / Al decreases almost linearly with the concentration of Si. Therefore, for example, the coefficient of linear expansion is 18 × 10 ^-6
Those below deg ^-1 can be easily obtained.

It was confirmed that the Si / Al plate has sufficient mechanical strength.
Further, the Si / Al plate has a high thermal conductivity, unlike Al ₂ O ₃ and AlN.

Further, the semiconductor chip adheres well to the insulating film of AlN or Si ₃ N ₄ . Good adhesion between Si / Al plate and AlN, Si ₃ N ₄ .

(E) Manufacturing method of Al-30 to 60% Si alloy Fig. 7 shows an example of the manufacturing process chart.

Here, 30 to 60% of Si is the weight% of Si to the whole. It is not the weight% with respect to Al.

Simply melting the Si / Al material containing 30-60 wt% of Si
Does not disperse uniformly in Al.

Therefore, in order to uniformly disperse Si, the solution is rapidly solidified into a powder at a cooling rate of 10 ³ ° C / sec or more using a gas atomizing method, a rotating disk atomizing method or the like.

If the cooling rate is slow, coarse primary crystal silicon is generated in Al, so that an alloy in which Si is evenly distributed cannot be obtained.

If the cooling rate is on the order of 10 ℃ / sec-100 ℃ / sec,
Not only does the primary crystal of silicon grow and it does not disperse uniformly, but processing becomes difficult. Therefore, the cooling rate must be 10 ³ ° C / sec or more. Under this condition, the size of the primary crystal silicon is at most 50 μm or less.

The alloy powder is collected and CIP-treated to solidify the powder. Cold Isostatic Press refers to the process of applying hydrostatic pressure to powder at room temperature to solidify it.

It has a suitable internal shape. Fill a rubber mold with powder, put in water and apply hydrostatic pressure.

Since the three-dimensional force is applied isotropically, the powder solidifies in the shape of the mold.

This is a mass of Al-30-60% Si alloy.

This alloy is hot extruded and rolled to obtain a thin plate. This is the lowermost Al-30-60% Si6 substrate in FIG. The width and thickness of the plate can be set arbitrarily. The temperature of hot extrusion is A
l and melting point of Si are lower than that of Si.

Next, the surface of the thin plate is ion-nitrided. Ion nitriding is performed by flowing a mixed gas of nitrogen and hydrogen onto the surface of a heated thin plate. By this treatment, nitrogen reacts with Al and nitrogen reacts with Si, and the surface changes mainly to AlN and Si ₃ N ₄ .

Ion nitriding is performed for the purpose of forming these insulating films. The film thickness can be controlled by the time of ion nitriding.

If the nitride film is too thin, sufficient insulation cannot be obtained. In terms of insulation, the thickness of the nitride film should be 2.0 μm or more.

On the contrary, if the nitride film is too thick, the thermal conductivity deteriorates, which is not preferable. Here, the thermal conductivity means the thermal conductivity in the direction perpendicular to the plate surface. Since the heat of the chip flows in the direction perpendicular to the plate surface and radiates the heat, it is natural to consider the heat conduction in the perpendicular direction.

It can be seen that the nitride film must be 20 μm or less from the viewpoint of heat conduction. After all, the thickness of the nitride film AlN and Si ₃ N ₄ is 2 to 20 μm.

(F) Weight% of Si When Si is 30% by weight or less, Al becomes predominant and the expansion coefficient does not sufficiently decrease. When Si is 30% by weight, the coefficient of thermal expansion is 18 × 10 ^-6
It becomes deg ^-1 . Must be lower than this value, so S
The ratio of i is 30% by weight or more. When the ratio of Si increases,
The coefficient of expansion decreases almost linearly.

On the other hand, when the ratio of Si exceeds 60% by weight, Si segregates,
Primary crystal silicon appears largely. If this happens, a difference in thermal expansion between the Si grain boundary and the Si / Al alloy occurs, which weakens the temperature change and reduces the mechanical strength.

Therefore, Si is 30 to 60% by weight.

(G) Effect (1) The difference in the coefficient of thermal expansion between the semiconductor chip and the substrate is reduced. Therefore, it is possible to reduce the occurrence of strain due to thermal stress. For this reason, the life of the element is extended.

(2) Since it is an alloy of Al and Si and has a high thermal conductivity coefficient,
Excellent heat dissipation.

In particular, the heat conductivity of the insulating layer is better than that of the resin layer shown in FIG. 3, so that the heat dissipation as a whole is excellent.

Further, in the structure shown in FIG. 4, AlN serves as an insulating film. It does not have sufficient insulation without a considerable thickness.

In the present invention, the nitride layer mainly consisting of AlN and Si ₃ N ₄ serves as an insulating film, and even if it is thinner, good insulating properties can be obtained. Since the insulating film (nitride film) can be thinned, the thermal conductivity can be increased.

(3) Since the difference in thermal expansion coefficient between the insulating film and the substrate is small,
Good film adhesion. Does not easily peel from the substrate.

(4) Most suitable as a substrate for IC chips with large dimensions.

(5) Since the density is relatively low, the weight can be reduced.

(6) Since the substrate has excellent machinability, the cost can be dramatically reduced.

(H) Example Powders of Al-40 wt% Si alloy and Al-50 wt% Si alloy were produced by a rotary atomizing method, and powder of 42 mesh or less was powdered in a container made of aluminum. Filled and hot extruded at 450 ℃, thickness 20mm, width 4
An extruded material having a length of 0 mm and a length of 1000 mm was obtained.

This extruded material is rolled to a thickness of 4 mm x width 40 mm x length 60 mm.
The plate-shaped material of was cut out.

Ion nitriding is performed for various times in an atmosphere gas (N ₂ : H ₂ = 4: 1) at 400 ° C and 2 Torr to form ion nitride films of various thicknesses on the surface of the plate material. It was

After performing the ion nitriding treatment, cut out the test piece,
The heat conduction plate and the insulating property were measured.

Further, a heat cycle test (-60 to 125 ° C, 50 cycles) was performed.

Table 1 shows the results for Al-40 wt% Si.

As a comparative example, the same test is performed on an aluminum nitride sheet on which an ion nitride film AlN is formed (Fig. 4) and on an aluminum sheet that is anodized and then coated with epoxy resin. The results are also shown in Table 1.

As can be seen from this table, if the film thickness of the nitride film is less than 2.0 μm, good insulation cannot be obtained. Therefore, the film thickness is 2.0
It must be at least μm.

The substrate of the present invention has a film thickness of 2.0 μm or more, and each has a leak current of 10 ⁻⁶ A or less. The leak current after the heat cycle test is also 10 ⁻⁶ A or less. This means that the nitride film is stable and does not peel off.

If the film thickness is 20 μm or less, the thermal conductivity is 0.24 ca.
l / sec ℃ cm or more. Therefore, the desired film thickness is 2.0-20
μm.

The substrate obtained by ion-nitriding AlN on an Al plate, which is given as a comparative example, has a leakage current of 10 ⁻⁶ A or more after a heat cycle test. During the heat cycle test,
-Peeling occurs between AlN and the insulation is impaired.

Moreover, it was revealed that the substrate composed of Al / alumite / resin has poor thermal conductivity because it is a resin.

(X) Application Example An application example of an IC package using the semiconductor device substrate material of the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1, a substrate 2 made of the substrate material for a semiconductor device of the present invention is mounted on the upper surface of an enclosure 1 made of ceramic such as alumina. A semiconductor chip 3 is bonded to the lower surface of the semiconductor device substrate material 2 with solder 4 interposed therebetween. The lead terminal 5 protruding to the lower surface is a Kovar wire.

In FIG. 2, the semiconductor chip 13 is connected via the solder 14,
It is bonded to a substrate material 16 made of a copper-tungsten alloy material. The semiconductor device substrate material 17 of the present invention has a shape in which a large number of cooling fins are formed.

The copper-tungsten alloy substrate material 16 is bonded to the lower surface of the semiconductor device substrate material 17.

The envelope 11 is a ceramic such as alumina. The fact that the Kovar wire lead-out terminal 15 is provided on the lower surface is not different from that shown in FIG.

[Brief description of drawings]

FIG. 1 is a sectional view showing an application example of an IC package using the substrate for a semiconductor device of the present invention. FIG. 2 is another cross-sectional view showing an application example of an IC package using the semiconductor device substrate of the present invention. FIG. 3 is a cross-sectional view of a semiconductor device substrate according to a conventional example. FIG. 4 is a sectional view of a semiconductor device substrate according to another conventional example. FIG. 5 is a cross-sectional view of the semiconductor device substrate of the present invention. FIG. 6 is an enlarged sectional view of the semiconductor device substrate of the present invention. FIG. 7 is a manufacturing process diagram of the Al-30-60 wt% Si alloy of the present invention. FIG. 8 is a cross-sectional view of the substrate surface before and after ion nitriding. 1 ... Enclosure 2 ... Substrate material of the present invention 3 ... Semiconductor chip 4 ... Solder 5 ... Leading terminal 6 ... Al-30-60% Si substrate 7 ... Nitride film 13 ... Semiconductor chip 14 …… Solder 16 …… Copper-tungsten alloy substrate material 17 …… Invention substrate material 30 …… Al substrate 31 …… Almite 32 …… Resin 33 …… Semiconductor chip 35 …… AlN

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-103156 (JP, A) JP-A-60-32343 (JP, A) JP-A-61-168941 (JP, A) JP-A-61- 189789 (JP, A)

Claims (6)

[Claims] 1. An Al alloy plate comprising 30 to 60% by weight of Si and the balance substantially consisting of Al.
A substrate material for a semiconductor device, characterized in that a nitride layer of AlN and Si ₃ N ₄ is formed. 2. The size of the primary crystal silicon in the Al alloy is
The substrate material for a semiconductor device according to claim (1), which has a thickness of 50 μm or less. 3. The coefficient of thermal expansion of the Al alloy is 18 × 10 ^-6 deg ^-1
Claims (1), characterized in that
Alternatively, the substrate material for a semiconductor device according to the item (2). 4. The nitride layer formed on the surface of the Al alloy is 2
The substrate material for a semiconductor device according to any one of claims (1) to (3), wherein the substrate material has a thickness of not less than μm and not more than 20 μm. 5. The nitride layer formed on the surface of the Al alloy is formed by an ion nitriding method, according to any one of claims (1) to (4). A substrate material for a semiconductor device as described above. 6. Si is contained in an amount of 30 to 60% by weight, and the balance is substantially Al.
The material is heated and melted to form a mixed melt.
^The alloy powder is rapidly solidified at a cooling rate of ³ ° C / sec or more to form an alloy powder, which is hydrostatically pressed at room temperature to form a solid, which is then hot extruded.
A method for producing a substrate material for a semiconductor device, which is characterized in that the substrate material is further processed to form a thin plate, and the surface is ion-nitrided to form a nitride layer mainly composed of AlN and Si ₃ N ₄ .