JPH0955453A - Carbon substrate for semiconductor integrated circuit chip mounting use and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the fault of glassy carbon layers of a low heat conductivity and to obtain a carbon substrate for chip mounting use by a method wherein the glassy carbon layers with the mirror-polished surface are respectively provided on both sides of an intermediate layer containing fibers made of graphitizable carbon and whose fiber axes are parallel to the carbon layers. SOLUTION: Glassy carbon layers 1 with the mirror-polished surface are respectively provided on both sides of an intermediate layer 3 containing fibers made of graphitizable carbon. Layers constituting the layer 3 are provided in such a way that the fiber axes of the fibers are parallel (the X- and Y- directions) to the layers 1. In the case where such a carbon substrate is manufactured, both surfaces of a layer containing fibers made of graphitizable carbon, are held between thermosetting resins to turn the sheet into a composite sheet, the composite sheet is heat-treated at 1200 deg.C or higher in an inert atmosphere to turn the thermosetting resin into glassy carbon layers and thereafter, the surfaces of these glassy carbon layers have only to be mirror-polished. As the thermosetting resin to be used here, a phenolic resin is preferable.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a carbon substrate suitable for mounting a plurality of semiconductor integrated circuit chips, and a useful method for manufacturing such a substrate.

[0002]

2. Description of the Related Art As the integration density in semiconductor integrated circuit chips has increased, there has been a demand for higher density mounting of these chips. In recent years, in particular, not only high densification within a semiconductor integrated circuit chip, but also development of a technique for mounting a highly integrated chip at a high density has been advanced. In order to cope with such high-density mounting, a plurality of semiconductor integrated circuit chips (bare chips) are directly mounted on a substrate, and the bare chips are electrically connected via a multilayer wiring layer formed on the substrate. A multi-chip module connected to is being developed.

The characteristics required for the substrate of the above multi-chip module are: (a) the surface is flat and smooth, (b) it has a thermal expansion coefficient close to that of a semiconductor integrated circuit chip, and (c) ) High thermal conductivity,
(D) High purity without impurities, (e) High chemical stability, (f) Light weight (small specific gravity)
And so on.

As a material for the substrate as described above, ceramic materials such as alumina, aluminum nitride and silicon carbide, and metal materials such as copper-tungsten alloy, copper-molybdenum alloy and Kovar are conventionally used. However, the materials used so far cannot be said to satisfy all the properties required for the substrate, and each has the following drawbacks.

[0005]

Since the ceramic material is basically manufactured by sintering raw materials, grain boundaries remain, and since it is essentially a polycrystalline material, it has high surface smoothness. Is difficult to achieve. In particular, with the miniaturization of multilayer wiring connecting chips, a high level of smoothness required of a substrate is required to be close to that of a Si wafer, and in a non-homogeneous ceramic material, such a high level of smoothness is required. Achieving smoothness is difficult. Further, in a ceramic material, it is necessary to add a small amount of a binding aid at the time of sintering, and there is a possibility that impurities resulting from this may be mixed. Of the ceramic materials, alumina materials are often used, but in addition to the above-mentioned drawbacks, this material also has the drawback that the thermal conductivity is lower than that required for the substrate.

On the other hand, in a metal-based material, the coefficient of thermal expansion is generally too large, and the stress due to the mismatch of the coefficient of thermal expansion with the bare chip may adversely affect the reliability of the module. . It is possible to use a metal-based material whose coefficient of thermal expansion is close to that of the substrate, but such metal-based material is generally high in density, and lightweight is also a substrate material that is required as one of its characteristics. Is inappropriate as Further, molybdenum, tungsten, or alloys thereof can be said to be less problematic in terms of the coefficient of thermal expansion, but have another drawback of poor workability.

By the way, the carbonaceous material has been attracting attention as a strong candidate as a material for the substrate of the multi-chip module because of its light weight, thermal conductivity, electrical conductivity, thermal expansion characteristics, high purity and mechanical properties. However, among the known carbonaceous materials, the high-density graphite material has a drawback that it is not practical because it has poor surface smoothness and generates a lot of dust.

On the other hand, glassy carbon obtained by heat-treating a thermosetting resin such as phenol resin or furan resin in an inert atmosphere has almost no drawbacks of the above-mentioned high-density graphite material and is particularly expected as a substrate material. It is a carbon-based material. This glassy carbon is a very homogeneous glassy substance (amorphous), and has the characteristic that it can achieve high surface smoothness comparable to that of Si wafers, and is superior to other carbon-based materials. It is said that However, glassy carbon has a low thermal conductivity due to its amorphous nature, and thus has a problem in terms of heat dissipation as a material for a substrate of a multichip module.

The present invention has been made by paying attention to the above circumstances, and the glassy carbon is effectively utilized while eliminating the drawbacks of the glassy carbon. The most suitable carbon substrate for mounting,
And a method for manufacturing such a substrate.

[0010]

Means for Solving the Problems According to the present invention capable of solving the above problems, a glassy carbon layer whose surface is mirror-polished is provided on both sides of an intermediate layer containing fibers made of graphitizable carbon. The carbon substrate for mounting a semiconductor integrated circuit chip is characterized in that the layer constituting the intermediate layer is provided such that its fiber axis is parallel to the glassy carbon layer. Here, "graphitizable carbon" means, as is well known, carbon that is easily graphitized when treated at a high temperature such as 3000 ° C., and is a typical fiber of graphitizable carbon. Examples include carbon fibers obtained by melt-spinning mesophase pitch and then infusibilized and carbonized. The "mirror surface" is Ra (center line surface roughness) of 10 nm or less and Rmax (maximum surface roughness) of 1
It means a surface state such that it is not more than 00 nm.

In producing the carbon substrate as described above, a thermosetting resin is sandwiched between both surfaces of a layer containing fibers made of graphitizable carbon to form a composite, and the composite is placed in an inert atmosphere. After heat-treating at 1200 ° C. or above for forming the thermosetting resin into glassy carbon, the surface of the glassy carbon may be mirror-polished.

In the above manufacturing method, the thermosetting resin used is preferably a phenol resin. Further, as the fiber made of easily graphitizable carbon, mesophase pitch is melt-spun and then infusibilized, and then 400 to 800
It is preferable that the material is primarily fired at ℃. Furthermore,
After heat treatment at 1200 ° C. or higher in an inert atmosphere, it is preferable to further perform hot isostatic pressing.

[0013]

It is well known that glassy carbon can be obtained by heat-treating a phenolic resin, a furan resin or other thermosetting resin in an inert atmosphere. This glassy carbon is a homogeneous amorphous material, and a very smooth surface, a so-called mirror surface, can be obtained by polishing. Therefore, by utilizing these characteristics, application to the field of electronic components such as magnetic disk substrates and head sliders is being promoted.

The inventors of the present invention have found that the glass-like carbon material has a high degree of specularity as a substrate for mounting a semiconductor integrated circuit chip, that is, a so-called multi-chip module substrate.
I thought it was the best one. In the high-density mounting as described above, the electrical connection between the chips is made through the multilayer wiring layer formed on the substrate, and the multilayer wiring layer also tends to be highly densified. As a result, the surface smoothness of the mounting substrate is required to be as high as that of a Si wafer. The above-mentioned glassy carbon is considered to be a material very suitable for such a purpose because of its homogeneity. Further, the properties such as thermal expansion characteristics, mechanical strength, small amount of impurities, and chemical stability (no corrosion or deterioration) are suitable for high-density mounting.

However, as described above, since glassy carbon is an amorphous material, its thermal conductivity is 3 to 8 Wm ^-1 K.
It is about ^-1, which is a drawback compared to graphite materials. For example, hot isostatic pressing at high temperature and high pressure (HIP
The heat conductivity does not greatly exceed 10 Wm ⁻¹ K ⁻¹ even if the bulk density is increased to 1.8 g / cm ³ by the treatment. This poor thermal conductivity has been the only drawback that prevents the application of glassy carbon as a substrate for high-density mounting.

On the other hand, although the graphite-based carbon material has a large anisotropy due to the crystal structure, the thermal conductivity in the direction along the hexagonal network, that is, in the ab plane direction of the crystal is 20.
It is as high as 00 Wm ^-1 K ^-1 , and is superior to metal materials such as aluminum and copper. Graphitizable carbon fibers represented by mesophase pitch carbon fibers have a structure in which hexagonal meshes of graphite are arranged in the fiber axis direction, and as a result, extremely high thermal conductivity is exhibited in the fiber axis direction. . The final heat treatment temperature determines the crystallinity, that is, the degree of graphitization, and the thermal conductivity can be changed accordingly.

According to the present invention, by combining glassy carbon and easily graphitizable carbon fiber, the characteristics of both materials can be exhibited at the same time, and a carbon substrate most suitable as a substrate for mounting a semiconductor integrated circuit chip is realized. I was able to do it.
That is, the substrate surface part is composed of glassy carbon, its homogeneity is utilized to secure a high degree of smoothness, and a layer (intermediate layer) containing fibers made of graphitizable carbon is formed inside. This ensures high thermal conductivity of the substrate as a whole.

FIG. 1 is a schematic explanatory view showing the constitution of the substrate of the present invention, in which 1 is a glassy carbon layer, 2 is an intermediate layer containing fibers made of graphitizable carbon, and 3 is a glassy carbon layer. 1 shows a mirror-polished surface of No. 1 respectively. Also the middle layer 3
The layers constituting the are provided so that their fiber axes are parallel to the glassy carbon layer 1 (X and Y directions in FIG. 1).

As the fiber made of easily graphitizable carbon, mesophase pitch which is a kind of liquid crystal is melt-spun and
Typical examples are so-called mesophase pitch-based carbon fibers that have been infusibilized and then heat-treated in an inert atmosphere. Fibers made from such mesophase pitch desorb aromatic hydrogen in the pitch by heat treatment,
At the treatment temperature of 1200 ° C., the hydrogen content becomes extremely small, and the conversion to carbon is substantially completed. Along with this, various characteristics also become unique to carbon. At this time, the heat treatment at a temperature exceeding 1200 ° C. is responsible for the physical formation of the graphite crystal structure mainly due to the chemical change. With the formation of the graphite crystal structure by such heat treatment, the thermal conductivity in the fiber axis direction also increases. At about 2800 ° C., which is close to the upper limit of the heat treatment temperature under normal pressure, the thermal conductivity is about 330 Wm ⁻¹ K ^−1, which is similar to that of metal.

The glass-like carbon can be generally produced by heat-treating a thermosetting resin in an inert atmosphere. As the glass-like carbon layer 1 used in the substrate of the present invention, phenol resin is used as the heat-resistant resin. It is preferable to use glassy carbon as a curable resin material. That is, the phenol resin is preferable because it has a carbonization yield of more than 60% and belongs to the highest category among various thermosetting resins.

In producing the carbon substrate as described above, both surfaces of a layer containing fibers made of graphitizable carbon are sandwiched by thermosetting resins to form a composite, and the composite is placed in an inert atmosphere. After heat-treating at 1200 ° C. or above for forming the thermosetting resin into glassy carbon, the surface of the glassy carbon may be mirror-polished. At this time, the heat treatment temperature needs to be 1200 ° C. or higher, for the following reason. That is, when the heat treatment temperature is less than 1200 ° C., the carbonization of the phenol resin becomes insufficient, and the microscopic open pores particularly generated in the process of forming the glassy carbon are not sufficiently closed pores. Even if it is applied, miniaturization does not proceed efficiently. Further, as described above, from the viewpoint of being responsible for the physical formation of the graphite crystal structure of the mesophase pitch-based carbon fiber, 1200 ° C.
It is necessary to do above.

On the other hand, the upper limit of the heat treatment temperature is not particularly limited. However, when the HIP treatment is performed, the heat treatment temperature is preferably 2000 ° C. or lower. That is, when the heat treatment temperature exceeds 2000 ° C., the physical structural change proceeds too much, and even if the HIP treatment described later is performed, the fineness cannot be obtained.

In the above manufacturing process, at the time of "sandwiching between thermosetting resins to form a composite", the thermosetting resin is preliminarily heated and pressed to form a plate, as shown in Examples below. Alternatively, the intermediate layer may be sandwiched with the intermediate layer, or the intermediate layer may be sandwiched with a thermosetting resin so as to be integrally heated and pressed.

By the way, the intermediate layer 2 of the substrate of the present invention achieves its function by containing at least a fiber made of graphitizable carbon. The intermediate layer 2 is made of, for example, glassy carbon other than the fiber. Composed by.
Like the glassy carbon layer 1, the glassy carbon constituting the intermediate layer 2 is preferably glassy carbon made of a phenol resin as a thermosetting resin material. That is, in the case of glassy carbon using phenolic resin as a thermosetting resin raw material, the weight loss due to carbonization occurs gently over a wide temperature range of 150 to 800 ° C. In addition, since the shrinkage in the carbonization process is smaller and gentler than that of other resins, it is possible to suppress the occurrence of stress between the carbon fibers and the glassy carbon as the matrix as much as possible.

Therefore, it is most preferable that the glassy carbon constituting the intermediate layer 2 and the glassy carbon constituting the glassy carbon layer 1 are glassy carbons using a phenol resin as a thermosetting resin material. It is a form. However, in the substrate of the present invention, the glassy carbon forming the intermediate layer 2 and the glassy carbon forming the glassy carbon layer 1 do not necessarily have to be formed from the same thermosetting resin raw material. Is.

As the carbon fiber used in the present invention, among the fibers obtained by melt-spinning mesophase pitch, infusibilized, and then heat treated in an inert atmosphere, the heat treatment temperature (primary firing temperature) is 400 to 800 ° C. It is preferably one. Heat treatment of the infusibilized pitch fiber at 400 to 800 ° C. corresponds to an intermediate state between the pitch which is an organic substance and the carbon which is an inorganic substance. Therefore, the fiber itself has sufficient strength to be composited, and the fiber itself can be shrunk in accordance with the thermosetting resin by the heat treatment after the composition. As a result, the contraction between the fibers and the matrix can be further reduced, and the generation of minute defects inside can be suppressed. By suppressing the generation of such fine defects, the thermal conductivity of the substrate can be kept high.

The heat treatment temperature of the pitch fiber after infusibilization is 4
When the temperature is lower than 00 ° C., the carbonization reaction is insufficient and the fiber strength sufficient to withstand complexing is not expressed. Further, when the heat treatment temperature exceeds 800 ° C., the carbonization reaction proceeds too much, so that the shrinkage margin in the heat treatment after compounding becomes small and it becomes difficult to suppress the occurrence of stress between the matrix and the matrix. The preferable range of the primary firing temperature is 500 to 6
It is about 50 ° C.

In the production method of the present invention, it is preferable that after heat treatment under an atmospheric pressure in an inert atmosphere, further HIP treatment is carried out. By performing this treatment, the fine closed pores of the glassy carbon itself, which is the matrix, are reduced, and the adhesion between the matrix and the fibers is also improved by miniaturizing the whole substrate. The thermal conductivity of can be further increased.

The present invention will be described in more detail with reference to the following examples. The following examples are not intended to limit the present invention, and the present invention can be carried out with appropriate modifications within a range compatible with the gist of the preceding and the following. It goes without saying that all of them are within the technical scope of the present invention.

[0030]

Example 1 A plain woven cloth of mesophase pitch carbon fibers was dissolved in ethanol and then impregnated with granular phenolic resin to prepare a prepreg. Both surfaces of this prepreg were sandwiched between plates formed by molding granular phenol resin under heat and pressure, and further integrated under heat and pressure. Such a composite was sandwiched between artificial graphite plates and carbonized and fired at 1500 ° C. in an inert atmosphere.

The surface of the glassy carbon composite material thus prepared was subjected to GC (glassy carbon) having a particle size of # 2000.
After lapping both sides with a grindstone, γ of particle size: 50 nm
Finished polishing was performed with an alumina grindstone. The surface roughness of the obtained substrate was measured with a non-contact optical surface roughness meter,
Ra was 1.2 nm and Rmax was 11 nm. The thermal conductivity of the substrate in the in-plane direction (the X and Y directions) is 35.
It was Wm ^-1 K ^-1 .

Example 2 A granular prepreg resin was dissolved in ethanol and immersed in a felt of mesophase pitch carbon fiber having a primary firing temperature of 550 ° C. to prepare a prepreg. Both surfaces of this prepreg were sandwiched between plates formed by molding granular phenol resin under heat and pressure, and further integrated under heat and pressure. Such a composite was sandwiched between artificial graphite plates and carbonized and baked at 1600 ° C. in an inert atmosphere.

The surface of the glassy carbon composite material thus produced was lapped on both sides with a GC grindstone having a particle size of # 2000, and then subjected to final polishing with a γ-alumina grindstone having a particle size of 50 nm. When the surface roughness of the obtained substrate was measured by a non-contact optical surface roughness meter, Ra was 1.2 nm, Rm
It was 11 nm in ax. The thermal conductivity of the substrate in the in-plane direction was 40 Wm ^-1 K ^-1 .

Example 3 A granular prepreg resin was dissolved in ethanol and then immersed in a felt of mesophase pitch carbon fiber having a primary firing temperature of 550 ° C. to prepare a prepreg. Both surfaces of this prepreg were sandwiched between plates formed by molding granular phenol resin under heat and pressure, and further integrated under heat and pressure. Such a composite was sandwiched between artificial graphite plates and carbonized and baked at 1600 ° C. in an inert atmosphere. This substrate was further subjected to heat treatment (HIP treatment) at 2600 ° C. under an isotropic pressure of 1900 kgf / cm ² using argon as a heating medium.

The surface of the glassy carbon composite material thus produced was lapped on both sides with a GC grindstone with a particle size of # 2000, and then subjected to finish polishing with a γ-alumina grindstone with a particle size of 50 nm. When the surface roughness of the obtained substrate was measured by a non-contact optical surface roughness meter, Ra was 1.0 nm, Rm
It was 10 nm in ax. The thermal conductivity of the substrate in the in-plane direction was 120 Wm ^-1 K ^-1 .

Example 4 A plain woven cloth of mesophase pitch carbon fibers was dissolved in ethanol with granular phenol resin and then impregnated to prepare a prepreg. Both surfaces of this prepreg were sandwiched between plates formed by molding granular phenol resin under heat and pressure, and further integrated under heat and pressure. Such a composite was sandwiched between artificial graphite plates and carbonized and fired at 1200 ° C. in an inert atmosphere. This substrate was further heat-treated at 2600 ° C.

The surface of the glassy carbon composite material thus prepared was lapped on both sides with a GC grindstone having a particle size of # 2000, and then subjected to final polishing with a γ-alumina grindstone having a particle size of 50 nm. When the surface roughness of the obtained substrate was measured by a non-contact optical surface roughness meter, Ra was 1.2 nm, Rm
It was 11 nm in ax. The thermal conductivity of the substrate in the in-plane direction was 75 Wm ^-1 K ^-1 .

Comparative Example 1 A plate obtained by molding a granular phenol resin under heat and pressure was sandwiched between artificial graphite plates and heat-treated at 1600 ° C. in an inert atmosphere. The substrate manufactured in this manner was used as a GC with a grain size of # 2000.
After lapping both sides with a grindstone, γ of particle size: 50 nm
Finished polishing was performed with an alumina grindstone. When the surface roughness of the obtained substrate was measured with a non-contact optical surface roughness meter, R
a was 1.0 nm and Rmax was 10 nm. The thermal conductivity of the substrate in the in-plane direction was 5 Wm ^-1 K ^-1 .

Comparative Example 2 A plate obtained by molding a granular phenol resin under heat and pressure was sandwiched between artificial graphite plates and heat-treated at 1600 ° C. in an inert atmosphere. This substrate is further heated with argon as a heating medium.
Heat treatment (HIP treatment) was performed at 2600 ° C. under an isotropic pressure of 900 kgf / cm ² .

This substrate thus prepared was treated with a grain size of # 20.
After lapping both sides with 00 GC grindstone, particle size: 5
Final polishing was performed with a 0 nm γ-alumina grindstone. When the surface roughness of the obtained substrate was measured by a non-contact optical surface roughness meter, Ra was 1.0 nm and Rmax was 10 nm. The thermal conductivity of the substrate in the in-plane direction was 9 Wm ^-1 K ^-1 .

[0041]

EFFECT OF THE INVENTION The present invention is constituted as described above, and by interposing the intermediate layer containing the fiber made of graphitizable carbon between the glassy carbon layers, the drawbacks of the glassy carbon are While eliminating these problems, we were able to realize an optimal carbon substrate for mounting semiconductor integrated circuit chips.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram showing a configuration of a substrate of the present invention.

[Explanation of symbols]

 1 glassy carbon layer 2 intermediate layer 3 mirror-polished surface

Claims (6)

[Claims] 1. A glassy carbon layer having a mirror-polished surface is provided on both sides of an intermediate layer containing a fiber made of graphitizable carbon, and the fiber axis of the layer constituting the intermediate layer is glassy. A carbon substrate for mounting a semiconductor integrated circuit chip, which is provided so as to be parallel to the carbon layer. 2. The carbon substrate for mounting a semiconductor integrated circuit chip according to claim 1, wherein the fiber made of graphitizable carbon is a carbon fiber obtained by melt-spinning mesophase pitch, and then infusibilized and carbonized. 3. In manufacturing the carbon substrate according to claim 1 or 2, both surfaces of a layer containing fibers made of graphitizable carbon are sandwiched by thermosetting resins to form a composite. Of a carbon substrate for mounting a semiconductor integrated circuit chip, comprising: heat-treating a glassy carbon at 1200 ° C. or higher in an inert atmosphere to form glassy carbon, and then mirror-polishing the surface of the glassy carbon. Production method. 4. The method according to claim 3, wherein the thermosetting resin is a phenol resin. 5. Fibers made of easily graphitizable carbon are melt-spun mesophase pitch and then infusibilized after 4
The production method according to claim 3 or 4, which is a product that is primarily fired at 00 to 800 ° C. 6. The production method according to claim 3, wherein after the heat treatment at 1200 ° C. or higher in an inert atmosphere, a hot isostatic pressing treatment is further performed.