JP2001332544A - Method of manufacturing insulating material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the manufacturing method of an insulating material which exhibits a remarkably low dielectric constant and satisfactory insulating property and which is superior in heat resistance. SOLUTION: In the manufacturing method of the insulating material, a process for dissolving gas in a gaseous state at an ordinary temperature and ordinary pressure into the insulating material at a high temperature and high pressure, for exposing it to an atmosphere lower than pressure in the dissolution at the reducing speed of 1 to 100 MPa/Hr, and for generating a micro gap is installed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an insulating material, and more particularly to a method for producing an insulating material having excellent characteristics for use in electric / electronic devices and semiconductor devices.

[0002]

2. Description of the Related Art Among the characteristics required for materials for electric / electronic devices and semiconductor devices, electric characteristics and heat resistance are the most important characteristics. In particular, in recent years, with miniaturization of circuits and speeding up of signals, an insulating material having a low dielectric constant has been required.
An insulating material using a heat-resistant resin is expected as a material for satisfying these two characteristics. For example, conventionally used inorganic insulating materials such as silicon dioxide have high heat resistance, but have a high dielectric constant and the required characteristics are becoming increasingly sophisticated. Yes, heat-resistant resin represented by polyimide resin has excellent electrical properties and heat resistance, and can achieve both properties.It is actually used for insulation layer of printed circuit, coverlay, passivation film of semiconductor device, etc. Have been.

[0003] However, with recent advances in the functions and performance of semiconductor devices, remarkable improvements in electrical characteristics and heat resistance have been required, so that even higher performance resins have been required. ing. In particular, a low dielectric constant material having a dielectric constant of less than 2.5 is expected, and the properties required by conventional insulating materials have not been achieved. In contrast, heretofore, for example, to a resin composition comprising polyimide and a solvent, a heat-decomposable resin other than polyimide is added, and a heating step is performed to decompose the heat-decomposable resin to form voids. Thus, attempts have been made to reduce the dielectric constant of the insulating material. However, when the heat-resistant resin such as polyimide and the heat-decomposable resin are compatible with each other, the glass transition point is lowered, so that when the heat-decomposable resin is decomposed, the voids are crushed and the effect of reducing the dielectric constant is reduced. Less is. In addition, even if a heat-resistant resin such as polyimide and a thermally decomposable resin are successfully formed into a phase-separated structure without being compatible with each other, a great deal of labor is required for a heating method for decomposing the thermally decomposable resin. It was necessary.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an insulating material which exhibits an extremely low dielectric constant and good insulating properties, and also has excellent heat resistance.

[0005]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned conventional problems, and as a result, have completed the present invention by the following means. That is, according to the present invention, a gas in a gaseous state at normal temperature and normal pressure is dissolved in an insulating material under high temperature and high pressure, and then exposed to an atmosphere lower than the pressure at the time of melting at a decompression rate of 1 to 100 MPa / Hr to form fine voids. It is a method for manufacturing an insulating material including a step of generating.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As a specific example of the method for producing an insulating material according to the present invention, a resin for an insulating material is dissolved in a solvent to form a varnish, and then a suitable support, for example, glass, metal, silicone wafer or the like is used. Apply to ceramic base etc. As a specific coating method, spin coating using a spinner,
Spray coating using a spray coater, dipping, printing, roll coating and the like can be mentioned. After forming the coating film in this way, heat drying is performed at a high temperature to remove the solvent and cure the resin. At this time, a gaseous gas at normal temperature and normal pressure is dissolved in the insulating material at a high pressure. After letting
By exposing to an atmosphere lower than the pressure at the time of melting at a reduced pressure of MPa / Hr, minute voids are generated inside the insulating material. Since the inside of the gap is kept at a high pressure, it is possible to overcome the problems of the prior art that the gap is crushed, and also to form a phase-separated structure, a method for heating and decomposing the thermally decomposable resin, and to remove the residual components by thermal decomposition. Many problems due to the addition of the conductive resin do not occur. Only by performing conventional heating and drying under high pressure, an insulating material having a low dielectric constant can be easily formed.

[0007] The pressure reduction rate at the time of exposure to the low-pressure atmosphere is preferably 1 to 100 MPa / Hr, more preferably 3 to 80 MPa / Hr, since it is necessary not to make the inside of the system suddenly unstable. Preferably 5 to 50
MPa / Hr. If it is less than 1 MPa / Hr, there is no change in the state of generation of voids, and only the time required for depressurization becomes longer, which is not preferable in terms of productivity. Conversely 10
If the pressure exceeds 0 MPa / Hr, the inside of the system becomes rapidly unstable, so that individual voids grow and become large, and the mechanical strength of the insulating material is remarkably reduced.

Since the dielectric constant inside the void is lower than that of the resin or its precursor contained in the insulating material, the dielectric constant is 10 to 80% by volume.
By generating the voids inside the insulating material, the dielectric constant can be reduced. If the porosity is less than 10% by volume, the effect of reducing the dielectric constant is small, and it is difficult to reach the target level of a dielectric constant of 2.5 or less. Conversely, if it exceeds 80% by volume, the mechanical strength of the insulating material is significantly reduced because the proportion of the voids in the insulating material is too high, which is not preferable.

The gas constituting the void used in the present invention is not particularly limited as long as it has a lower dielectric constant than the resin or its precursor contained in the insulating material and is inert to the resin. An organic gas such as a hydrocarbon having a molecular weight can be used, but an inorganic gas is preferable because the gas does not need to be recovered. The inorganic gas is not particularly limited as long as it is an inorganic substance that is a gas at normal temperature and normal pressure and is soluble in an insulating material, and is preferably, for example, carbon dioxide, nitrogen, argon, neon, helium, oxygen, or the like. Carbon dioxide and nitrogen are more preferred because they have high solubility in insulating materials and are easy to handle. These may be used alone or in combination of two or more.

When the gas is dissolved in the insulating material, it is preferable that the gas be dissolved in a supercritical state. The supercritical state means a state in which the temperature is equal to or higher than the critical temperature and the critical pressure. For example, in the case of carbon dioxide, the temperature is 30 ° C or higher and 7.3 MPa or higher. In the supercritical state, it has the property of being less viscous and more diffusive than the liquid state, and has a higher density than the gas state, so that a large amount of gas can be rapidly dissolved in the insulating material. It is preferred.

The resin contained in the insulating material of the present invention includes a precursor thereof, and examples thereof include polyimide, polyamic acid, polyamic ester, polyisoimide, polyamideimide, polyamide, bismaleimide, and poly (maleimide). Examples thereof include benzoxazole, polyhydroxyamide, polybenzothiazole, and epoxy, but are not limited thereto. Among these, a polyimide resin, a polyimide precursor such as polyamic acid, polyamic acid ester and polyisoimide, a polybenzoxazole resin, and a polybenzoxazole precursor such as polyhydroxyamide are preferable because of their high heat resistance and adhesion. If required, epoxy resins are preferred. These may be used alone, or may be mixed or copolymerized.

Solvents used for the resin varnish contained in the insulating material include N, N-dimethylacetamide, N-methyl-2-pyrrolidone, tetrahydrofuran, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, γ-butyrolactone, 1,1,2,
Examples include, but are not limited to, 2-tetrachloroethane. Further, two or more of these may be used simultaneously. Further, a surfactant may be added in order to improve applicability and impregnation.

[0013]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which by no means limit the present invention. In a separable flask equipped with a "resin varnish A" stirrer, nitrogen inlet tube and raw material inlet, 2,2-bis (4-
5.18 g (0.01 mol) of (4,4′-aminophenoxy) phenyl) hexafluoropropane and 2,2 ′
9.60 g (0.03 mol) of -bis (trifluoromethyl) -4,4'-diaminobiphenyl was dried in N
-Methyl-2-pyrrolidone (hereinafter abbreviated as NMP) 200
Dissolve in g. Cool the solution to 10 ° C under dry nitrogen,
2.94 g of biphenyltetracarboxylic dianhydride (0.
01 mol) and hexafluoroisopropylidene-2,
13.32 g of 2'-bis (phthalic anhydride) (0.03
mol) was added. Five hours after the addition, the temperature was returned to room temperature, and the mixture was stirred at room temperature for 2 hours to obtain a solution of polyamic acid as a polyimide precursor.

[0014] 50 g of pyridine is added to this polyamic acid solution.
After the addition of, 5.1 g (0.05 mol) of acetic anhydride was added dropwise, and the imidation reaction was carried out for 7 hours while maintaining the temperature of the system at 70 ° C. This solution was dropped into 20 times the volume of water to collect a precipitate, which was then vacuum-dried at 60 ° C. for 72 hours to obtain a solid polyimide resin as a heat-resistant resin. The molecular weight of the polyimide resin was a number average molecular weight of 26,000 and a weight average molecular weight of 54,000. 10.0 g of the polyimide resin synthesized as described above was mixed with γ-butyrolactone / 1,1,2,2-
Tetrachloroethane (70/30, vol / vol) 5
It was dissolved in 0.0 g to obtain a resin varnish for an insulating material (resin varnish A).

"Resin Varnish B" 5.18 g of 2,2-bis (4- (4,4'-aminophenoxy) phenyl) hexafluoropropane used for the synthesis of the polyimide precursor in the resin synthesis of resin varnish A .01 mol) and 9.60 g (0.03 mol) of 2,2′-bis (trifluoromethyl) -4,4′-diaminobiphenyl 8.01 g of 4,4′-diaminodiphenyl ether.
(0.04 mol), 2.94 g (0.01 mol) of biphenyltetracarboxylic dianhydride and hexafluoroisopropylidene-2,2'-bis (phthalic anhydride)
13.32 g (0.03 mol) was replaced with 8.72 g (0.04 mol) of pyromellitic dianhydride,
In the same manner as in Example 1, a solution of a polyamic acid as a polyimide precursor was obtained.

This solution was dropped into 20 times the volume of water to collect a precipitate, which was then vacuum-dried at 25 ° C. for 72 hours to obtain a solid of polyamic acid, which is a precursor of polyimide as a heat-resistant resin. The number average molecular weight of the obtained polyamic acid is 270.
The weight average molecular weight was 55,000. 10.0 g of the polyamic acid synthesized as described above was mixed with γ-butyrolactone / 1,1,2,2-tetrachloroethane (70/3).
(0, vol / vol) to obtain a resin varnish for an insulator (resin varnish B).

Example 1 A silicon wafer on which a 200 nm-thick tantalum film was formed and spin-coated with a resin varnish A was placed in a high-pressure container, and heated and cured in a carbon dioxide atmosphere. In the case of heat curing, the container is kept at 120 ° C. for 4 minutes and at 150 ° C. for 30 minutes.
It was kept at 00 ° C. and 50 MPa for 60 minutes. Thereafter, the heating was stopped and the pressure was reduced to normal pressure at an average pressure reduction rate of 8 MPa / Hr. Thus, a 0.8 μm thick coating of an insulating material was obtained. On this insulating material film, an area of 0.1 cm
The electrodes ² of aluminum is formed by vapor deposition, the capacitance between the tantalum substrate was measured by an LCR meter. The dielectric constant of the insulating material calculated from the film thickness, the electrode area, and the capacitance was 2.3. The density of the insulating material was determined to be 1.07 by a density gradient tube. The density when no carbon dioxide was injected and no voids were found to be 1.41.
It was calculated to be 1%. The results are summarized in Table 1. Further TE
When the cross section of the insulating material film was observed at M, the diameter was found to be 0.
It was found that voids having a length of 7 nm and a length of 5 nm were uniformly dispersed.

Example 2 A silicon wafer on which a 200 nm-thick tantalum film was formed and spin-coated with a resin varnish B was accommodated in a high-pressure container and heated and cured in a carbon dioxide atmosphere. In the case of heat curing, at 120 ° C for 4 minutes,
After maintaining at 150 ° C. for 30 minutes, the inside of the container was kept at 400 ° C. while supplying carbon dioxide under pressure using a plunger pump.
The temperature was maintained at 50 MPa for 60 minutes. Thereafter, the heating was stopped and the pressure was reduced to normal pressure at an average pressure reduction rate of 8 MPa / Hr. Thus, a coating of an insulating material having a thickness of 0.7 μm was obtained. Table 1 shows the results of measuring the dielectric constant and density of this insulating material and calculating the porosity in the same manner as in Example 1. Further, when the cross section of the insulating material film was observed with a TEM, it was found that voids having a diameter of 0.7 nm and a length of 6 nm were uniformly dispersed.

Comparative Example 1 A resin varnish A was spin-coated on a silicon wafer on which a 200 nm-thick tantalum film was formed, and then heated and cured in an oven in a nitrogen atmosphere.
In the case of heat curing, after holding at 120 ° C. for 4 minutes and at 150 ° C. for 30 minutes, holding at 400 ° C. for 60 minutes, heating was stopped. Thus, a 0.8 μm thick coating of an insulating material was obtained. Table 1 shows the results of measuring the dielectric constant and density of this insulating material and calculating the porosity in the same manner as in Example 1. No void was observed in the cross section of the insulating material film by TEM.

Comparative Example 2 A resin varnish B was spin-coated on a silicon wafer on which a 200 nm-thick tantalum film was formed, and then cured by heating in an oven in a nitrogen atmosphere.
In the case of heat curing, after holding at 120 ° C. for 4 minutes and at 150 ° C. for 30 minutes, holding at 400 ° C. for 60 minutes, heating was stopped. Thus, a 0.8 μm thick coating of an insulating material was obtained. Table 1 shows the results of measuring the dielectric constant and density of this insulating material and calculating the porosity in the same manner as in Example 1. No void was observed in the cross section of the insulating material film by TEM.

[0021]

[Table 1]

[0022]

According to the method of the present invention for producing an insulating material having the step of generating minute voids, it is possible to obtain an insulating material having excellent electrical characteristics and heat resistance. It is useful as various fields required, for example, as an interlayer insulating film for a semiconductor, an interlayer insulating film of a multilayer circuit, and the like.

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Claims (5)

[Claims] 1. A gas in a gaseous state at normal temperature and normal pressure is dissolved in an insulating material under high temperature and high pressure, and then 1 to 100 MPa / Hr
A method for producing an insulating material, comprising the step of exposing to an atmosphere lower than the pressure at the time of melting at a reduced pressure rate to generate minute voids. 2. The method for producing an insulating material according to claim 1, wherein the high temperature and high pressure are in a supercritical state of the gas. 3. The method according to claim 1, wherein the porosity of the insulating material is 10 to 80% by volume. 4. The method for producing an insulating material according to claim 1, wherein the insulating material includes at least one of a polyimide resin or a polyimide precursor, a polybenzoxazole resin, a polybenzoxazole precursor, and an epoxy resin. . 5. The method according to claim 1, wherein the gas is carbon dioxide, nitrogen, or a mixed gas thereof.