JPH0477584A - Low-viscosity varnish and production of electronic device using the same - Google Patents

Abstract

PURPOSE:To obtain the subject low-viscosity varnish capable of providing polyimide films, excellent in flatness and exhibiting low dielectric properties at a high concentration by using a specific electron attractive group-containing tetracarboxylic acid dianhydride and a specified electron attractive group- containing diamine. CONSTITUTION:The objective varnish is obtained by blending equimolar amounts of a tetracarboxylic acid dianhydride expressed by formula I [Ar is formula II or III (R, R' and R'' are fluorinated alkyl, fluorinated alkoxy, etc.; (l) is 1-2; (m) is 1-3), etc.] and a diamine (e.g. diaminodiphenyl sulfone) expressed by formula IV (X is formula V or SO2; (n) is 1-4) in a solvent (e.g. THF) capable of dissolving both. The above-mentioned varnish has <=0.1 P viscosity of the solution. For example, phenyltetracarboxylic acid dianhydride having a fluorinated alkyl group in the benzene skeleton is cited as the compound expressed by formula I.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a low viscosity varnish that provides a low dielectric constant polyimide film with extremely high flatness, and to an electronic device in which a cured film of the varnish is used as a glabellar insulating film.

[Background Art] In recent years, as electronic devices such as semiconductor devices are increasingly required to have higher performance and smaller size, their structures have become finer and more complex. Taking LSI as an example, multilayer wiring is essential, and the interlayer insulating film of multilayer wiring elements has insulation properties that can sufficiently insulate both upper and lower wirings even if it is thin, and at the same time, during manufacturing,
There is a need for a highly reliable device that does not cause steps or disconnections when forming the next layer of wiring.

In response to these demands, the insulating layer materials include organic,
Although both inorganic and inorganic materials have been studied, organic materials are more advantageous in terms of flattening performance (hereinafter referred to as flatness).

Until now, PIQ manufactured by Hitachi Chemical has been cited as a typical example of such organic materials.6PIQ is a varnish that provides a polyimide resin by heat curing or chemical imidization, and the resulting insulating film is heat resistant. , has excellent mechanical properties.

When used as an insulating layer of an LSI, the desired glabellar insulating film can be obtained by applying it onto a wafer using a suitable method such as a spin cord, and performing heat treatment or the like.

Furthermore, such varnishes are currently used in electronic devices other than LSIs. For example, in addition to devices in which flatness is particularly important, such as II-film magnetic heads and magnetic bubble elements, examples include α-ray shielding films and passivation films for semiconductor devices, substrates for flexible printed boards, and the like. The concentration of the varnish used to form these insulating films and the like is relatively low, typically around ten percent.

[Problems to be Solved by the Invention] The insulating film exhibits superior flatness compared to inorganic films obtained by CVD of inorganic materials, etc., but even higher flatness is required.

Improving the flatness of the insulating film is also achieved by increasing the solids content in the varnish. However, an increase in solids content leads to a significant increase in viscosity, which reduces workability.

For the above, a method for reducing the molecular weight of polyamic acid to form oligoamic acid (Japanese Patent Application Laid-Open No. 62-280257
(Japanese Patent Application Laid-Open No. 63-207867) has been proposed. This has made considerable progress in achieving high concentration and low viscosity. These methods include:
Although it is an oligomer during work such as a spin cord, the reactive end groups react with treatments such as heating, and the aim is to eventually increase the molecular weight and obtain an excellent insulating film.

As mentioned above, the concentration of these varnishes is generally low;
Its concentration is more than ten percent. This is because a coating film with sufficient characteristics could not be obtained at a concentration higher than this.

Multi-chip module systems are being actively developed in large-scale computers in order to speed up signal transmission. This uses an organic thin film such as polyimide as the insulating layer,
The goal is to use microfabrication technology to lower the dielectric constant and speed up signal transmission.

Fluorine-containing polyimide is considered effective for lowering the dielectric constant. Research on fluorine-containing polyimides had been conducted since before the advent of the United Kingdom, but the aim was not to lower the dielectric constant, but to provide transparency, solubility, meltability, etc. (British Patent No. 1,077).
No. 243, U.S. Pat. No. 3,356,648, No. 3,9
No. 59,350).

As a low dielectric polyimide, ■Anne K, St.

C1air, T, L, St, C] air and W,
P, Winfree, Proc, AC5Div, Po
lym, Mat, : Sci, Eng, , 59.
p, 28, 1988 Fall Meeting L, A
, , @David L, Goff and Edw
ard L.

Yuan, Proc, AC3Div, Polym, M
at, : Sci, Eng, , 59°p, 18
6.1988 Fall Meeting L, A,
, ■G., Houghham, J.

Shaw and G, Te5oro, Intern
ational Conference Poly
imides, Proc, /Abstracts of
There are reports such as Th1rd, (1988). These are intended to lower the dielectric constant by introducing (CF2)n or hexafluoroisopropylidene groups.

However, these have the problem of lowering the glass transition temperature of polyimide.

An object of the present invention is to provide a low-viscosity varnish that provides a polyimide with excellent flatness and a low dielectric constant, and to provide an electronic device using the varnish.

[Means for Solving the Problems] The flatness of a varnish applied on an uneven surface depends on the concentration of the varnish and the melt flow characteristics when the varnish is cured. This is because the higher the concentration of the varnish, the less the shrinkage of volume during curing, and the better the melt flow, the better the level difference can be eliminated.

It is known that the following equation [4] exists between the concentration and viscosity of a concentrated polymer solution.

ηoc n"φ6 ... [4] (where n is the degree of polymerization and φ is the polymer volume fraction) In other words, when the concentration of the varnish is increased, its viscosity increases rapidly,
It cannot be used as a varnish. As shown in formula [4], the present invention provides a high polymerization solution that suppresses the degree of polymerization of the polymer in the varnish.
Moreover, it is a low viscosity varnish, and the gist thereof is: a tetracarboxylic dianhydride represented by the formula [1] and 1]11 CC (wherein, Ar is R, R', R'' is a fluorinated alkyl group , a fluorinated alkoxy group, and a fluorine group, e is an integer of 1 to 2, m is an integer of 1 to 3, and n is an integer of 1 to 4.) Diamine CF3 represented by formula [2] (However, , X is -C--SO.

C.F.

R and R' are selected from a fluorinated alkyl group, a fluorinated alkoxy group, and a fluorine group, and n is an integer of 1 to 4. ) are blended in substantially equimolar amounts in a solvent that dissolves both, and the viscosity of the solution is 0.1 poise or less, and an electronic varnish using the varnish as an insulating layer. It's in the manufacturing method of the device.

The above-mentioned tetracarboxylic dianhydride has an electron-withdrawing group such as a fluorine group, a fluorinated alkyl group, or a fluorinated alkoxyl group in the benzene skeleton, and is a phenyltetracarboxylic dianhydride with a strongly acidic carbonyl group. dianhydride, biphenyltetracarboxylic dianhydride, and terphenyltetracarboxylic dianhydride.

The diamine is a low-reactivity diamine, that is, an aromatic diamine having an electron-withdrawing group such as a fluorine group, a fluorinated alkyl group, or a fluorinated alkoxy group in the benzene skeleton, and includes diaminodiphenylsulfone, diaminodiphenylhexafluoro, etc. There are propane, etc.

Examples of the solvent for the tetracarboxylic dianhydride and the diamine include polar solvents such as N-methylpyrrolidone, dimethylformamide, dimethylsulfoxide, dimethylacetamide, and tetrahydrofuran, or mixed solvents of these and nonpolar solvents. The amount of the solvent is adjusted so that the viscosity of the varnish is 0.1 voice or less. Than this,
If the viscosity becomes high, flatness decreases, which is not preferable.

In addition, regarding the flatness, it is preferable that the flatness ratio shown by the predetermined formula [3] is 0.7 or more.

The reaction of the tetracarboxylic dianhydride and the diamine with the tetracarboxylic dianhydride is controlled because the reactivity of the diamine is low at room temperature, and even if the reaction occurs, the resulting oligomer is at most a dimer or trimer, and its viscosity is low. low,
It becomes possible to increase the concentration of varnish.

When the varnish is heated, the diamine and the tetracarboxylic dianhydride react to form a high molecular weight polyimide.

By using the varnish of the present invention, a polyimide film having excellent flatness can be formed. At this time, since fluorine is present in the molecule, it attracts and strongly fixes the polarized electrons of the molecule, thereby decreasing the polarizability of the molecule and lowering the dielectric constant of the polymer.

As mentioned above, by the introduction of electron-withdrawing groups.

The reaction between diamine and tetracarboxylic dianhydride can be controlled, and a polyimide having both flatness and low dielectric constant properties can be obtained.

[By using tetracarboxylic dianhydride having an electron-withdrawing group, diaminodiphenylsulfone, and diaminodiphenylhexafluoropropane, the reaction between the two can be controlled and the viscosity of the varnish can be kept low. The concentration of the varnish can be increased.

[Example Tables 1 to 3 show the tetracarboxylic dianhydrides and diamines of the varnishes used in the examples of the present invention. In addition, the results of evaluating the flattening rate, dielectric constant, heat resistance, and tensile strength of the polyimide insulating film obtained using the varnish are shown in Section 4.
It is shown in Table 5.

In this example, N-methylpyrrolidone was used as the solvent for the varnish.

The planarization performance in Table 1 was evaluated using a test substrate in which the pattern shown in FIG. 4 was formed on a silicon substrate using aluminum. The varnish is applied onto a test substrate by a spin code method, and cured under the same conditions as the sample preparation for measuring the coefficient of thermal expansion to prepare a sample with a predetermined film thickness. In addition, the rotation speed of the 6-svinner is 1000 to 80 depending on the required film thickness.
Adjusted to 00 rpm. The flatness of the sample was measured using a stylus-type surface roughness meter (α-step 200: tencar In
(manufactured by STURUMENTS). In addition,
The degree of flattening P in Table 4.5 is defined by the following formula [3], and the values listed are the results when a 2 μm film is formed on the batten.

ΔHP=1−
[3] The definitions of ΔH and H in the formula are shown in FIG.

Heat resistance was expressed as the temperature at which a weight loss of 3% by weight was observed after 100 minutes of heating.

The tensile strength was measured at room temperature using a thermomechanical testing machine using a sample prepared in the same manner as the sample for measuring the coefficient of thermal expansion.

The beer strength was measured by cutting a rectangular sample with a width of 10 mm and a length of 20 mm, making a scribe groove from the back side of the substrate corresponding to the center position in the length direction, and cutting the silicon substrate so as not to break the polyimide film in the width direction. . This was performed using the pressure Kutzker test (PCT: 120'C, 2a
tm water vapor) for a predetermined period of time, one side was fixed to a steel cylindrical base and the other to a phosphor bronze plate (thickness 0.1 mm) with adhesive, and the tensile speed was measured using a universal tensile tester. Measurement was made at 0.5 mm/min.

According to the embodiments of the present invention, it is possible to obtain a planarization characteristic that is more than twice that of the conventional method, and at the same time, a polyimide film having a dielectric constant of 2.8 or less can be obtained.

Next, the case where the varnish of the present invention is used in an electronic device will be described using a specific example.

FIG. 1 shows a cross section of a multilayer wiring section of an LSI.

On the thermally oxidized silicon wafer 11112, an aluminum wiring 3 is formed, and as an interlayer insulating layer 4 of the wiring 3, an insulating thin film of flat and low corrosion rate polyimide is formed. If the insulating thin film is formed using the varnish of the present invention by a spin code method, the steps of the AA wiring can be reduced and flattened, so that a highly reliable wiring structure can be obtained.

FIG. 2 shows a cross section of the thin film magnetic head.

A lower magnetic body 6 and a gap alumina 7 are formed on the lower alumina 5 . The first conductor coil 8 and the second conductor coil 10 are insulated by a polyimide interlayer insulating film 9. An upper magnetic body 11 is provided in the outermost layer. By forming the interlayer insulating film 9 by the spin code method, the step difference in the interlayer insulating film 9 formed by the conductor coils 8 and 10 is alleviated.

Conventionally, after coating thickly, an etch bag was performed to process the film to the required thickness and flatten it, but by using the varnish of the present invention, the film thickness accuracy has been improved and the amount of etchback has been reduced compared to the conventional varnish. The manufacturing process can be reduced by approximately half.

FIG. 3 shows a cross section of the multichip module. A copper interconnect 14 is formed on the thermal oxide film 2 of the silicon wafer 1, and an interlayer insulating film 9 of polyimide is formed thereon. The copper wiring 14 has a Pb/Sn electrode 16 and a BLM 17.
is provided.

By forming the interlayer insulating film 9 using the varnish of the present invention, the step difference in the copper wiring 14 can be greatly reduced and flattened, so that a highly reliable wiring structure can be obtained.

[Effects of the Invention] According to the present invention, a heat-resistant insulating film that achieves both flatness and low dielectricity can be provided, and by using the insulating film, a highly reliable electronic device can be provided. I can do it.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of an LSI multilayer wiring, Figure 2 is a cross-sectional view of a thin film magnetic head, Figure 3 is a cross-sectional view of a multi-chip module, Figure 4 is a schematic diagram of an evaluation pattern, and Figure 5 is a diagram of a prepared sample. FIG. 2. Thermal oxide film, 3. Aluminum wiring, 4. Insulating thin film, 5. Lower alumina, 6.
...Lower magnetic material, 7.Gap alumina, 8..Conductor coil, 9..Interlayer insulating film, 10..Second conductor coil, 11..Upper magnetic material, 14..Copper wiring. , 16
=・P b / S n electrode, 17'-B L M (B
all LimitingMetall 1zatio
n).

Claims (1)

[Claims] 1. Tetracarboxylic dianhydride represented by the formula [1] and ▲ has a mathematical formula, chemical formula, table, etc. ▼... [1] (However, Ar has ▲ a mathematical formula, a chemical formula, a table, etc.) There are ▼, ▲mathematical formulas, chemical formulas,
There are tables, etc. ▼, ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼
, R, R', R'' are selected from fluorinated alkyl groups, fluorinated alkoxy groups, and fluorine groups, l is an integer of 1 to 2, m is an integer of 1 to 3, and n is an integer of 1 to 4. ) Diamine represented by formula [2] ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ ... [2] (However, X is ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼, -S
O_2-, R, and R' are selected from a fluorinated alkyl group, a fluorinated alkoxy group, and a fluorine group, and n is an integer of 1 to 4. ) are blended in substantially equimolar amounts in a solvent that dissolves both, and the viscosity of the solution is 0.1 poise or less. 2. Low viscosity, characterized in that the viscosity of a solution obtained by dissolving equimolar oligomers of the tetracarboxylic dianhydride represented by the above formula [1] and the diamine represented by the above formula [2] is 0.1 poise or less varnish. 3. The equimolar cured product of the tetracarboxylic dianhydride represented by the above formula [1] and the diamine represented by the above formula [2] has a flatness ratio P shown by the formula [3] of 0.7 or more. The low-viscosity varnish according to claim 1 or 2, which is a solution capable of forming a coating film. ΔH P=1−ΔH/H… [3] [However, H indicates the degree of unevenness of the surface of the coated film forming body, and ΔH indicates the degree of unevenness of the surface of the coating film. ] 4. The tetracarboxylic dianhydride represented by the above formula [1] and the diamine represented by the above formula [2] are blended in substantially equimolar amounts in a solvent that dissolves both, and the viscosity of the solution is 1. A method for manufacturing an electronic device, comprising applying a low viscosity varnish having a varnish of 0.1 poise or less to an insulating layer forming part of the electronic device, and drying and curing by heating. 5. The insulating layer is formed between the silicon wafer and the wiring and/or between the wirings, and after drying, the insulation layer is heated at 250°C.
5. The method for manufacturing an electronic device according to claim 4, wherein the electronic device is cured at a temperature higher than 100%.