JPH07105594B2 - Method for forming multilayer insulating film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a multilayer ceramic printed circuit board, wherein a multilayer insulating film for insulating between multilayer thin film patterns formed on the ceramic printed circuit board is obtained with a uniform thickness. After applying the insulating film forming material, the substrate is allowed to stand in an atmosphere of a predetermined temperature and a predetermined humidity for a predetermined time to uniformly diffuse the insulating layer forming material applied and formed on the substrate. A first baking treatment step of heat treatment at a prescribed temperature for a prescribed time; an exposure step and a development step of exposing and developing the insulating film into a prescribed pattern to form a via hole of a prescribed size; and the substrate in an inert gas atmosphere. The insulating film is applied in multiple layers on the substrate by using the plurality of processing steps including the second baking processing step of heating at a predetermined temperature for a predetermined time as one cycle processing step. A third baking treatment step in which the insulating film formed into a multi-layered structure by repeating the above-mentioned plurality of treatment steps is heated stepwise at a predetermined temperature in an inert gas atmosphere in a stepwise manner. It is configured by performing.

[Industrial application field]

The present invention relates to a method for forming a multilayer insulating film for insulating and separating a multilayer thin film pattern formed on a multilayer ceramic substrate.

When a multilayer thin film pattern is formed on a multilayer ceramic printed board on which an inner conductor layer is formed, a polyimide resin is used as an interlayer insulating film of the thin film pattern. This polyimide resin has a high viscosity, can be applied in a thin layer using a spin coater, and can be cured by heating to exhibit insulating properties. It is also exposed and developed to be exposed to light such as ultraviolet rays. As a result, there are many advantages such as easy formation of via holes for connecting conductor layers, and therefore, it is attracting attention as an interlayer insulating film of a multilayer thin film conductor layer pattern formed on a multilayer printed circuit board.

[Conventional technology]

Conventionally, when a multilayer insulating film is formed using such a polyimide resin, it has a via-hole conductor (not shown) as shown in FIG. 8 and a silicon dioxide (SiO ₂ ) film 1 on its surface. A first layer insulating film 4 made of polyimide having a viscosity of 4000 to 5000 poise is formed on a ceramic substrate 3 having a thin conductor layer pattern 2 formed thereon by using a spin coater 5 such as a spinner shown in FIG. It is applied and formed.

Next, as shown in FIG. 2, the first insulating layer 4 is baked at a temperature of 80 ° C. for 30 minutes, exposed and developed to open the first via hole 6, and then, as shown in FIG. Then, a second insulating film 7 made of polyimide is spin-coated to a thickness of 10 μm by using the above spinner, then baked at a temperature profile as shown in FIG. Two via holes 8 are opened.

The first via hole 6 thus formed in the first-layer insulating film 4
Second via hole 8 formed in the second insulating film 7 from the diameter of
By increasing the diameter of the conductive layer, the inner wall of the via hole is surely covered with the conductive layer of the metal film by the sputtering method.

[Problems to be Solved by the Invention]

However, when the above-mentioned polyimide resin is spin-coated, the viscosity of this polyimide resin is as high as 4000 to 5000 poise, so that the cross-sectional view taken along the line VII-VII ′ in FIGS. 7 (a) and 7 (a) is shown. In addition, there is a problem that the stripe-shaped concave region 9 is formed radially from the center O of the ceramic substrate 3 and the surface of the applied polyimide film is not flat.

Further, when the first layer polyimide film is formed in a predetermined pattern and the second layer polyimide film is applied thereon, the first layer polyimide film must be in a semi-cured state that is not completely cured. Therefore, N-methylpyrrolidone, which is contained in the second layer polyimide film and serves as a solvent for the polyimide resin,
The polyimide film of the first layer absorbs and deforms.

Therefore, as shown in FIG. 9A, the second-layer insulating film 7 made of the second-layer polyimide film is concavely formed toward the center of the ceramic substrate 3, so that the second-layer insulating film is formed. 7 is different in thickness between the central part and the peripheral part of the substrate.
There is a problem that the polyimide film of the second-layer insulating film having a thin central portion shown in FIG. 6B is overdeveloped and a via hole having a predetermined size is not formed.

The present invention solves the above-mentioned problems, prevents the above-mentioned spin-coated polyimide film from being formed with irregularities extending radially around the substrate, and further ensures that the first-layer polyimide film is securely baked. An object of the present invention is to provide a method for forming a multi-layered insulating film, which is cured so as to prevent the solvent of the second layer polyimide film from permeating when the second layer polyimide film is formed by coating.

[Means for Solving the Problems]

The method for forming a multilayer insulating film of the present invention to achieve the above object,
A diffusion coating step of applying an insulating film forming material on a substrate and then leaving the substrate in an atmosphere of a predetermined temperature and a predetermined humidity for a predetermined time to uniformly diffuse the insulating film forming material applied and formed on the substrate, A first baking treatment step of heat-treating the substrate at a prescribed temperature for a prescribed time; an exposure step and a developing step of forming a via hole of a prescribed size by exposing and developing the insulating film to a prescribed pattern; The plurality of processing steps including the second baking processing step of performing a heat treatment at a predetermined temperature for a predetermined time in a gas atmosphere are repeatedly performed as one cycle of the processing steps each time an insulating film is applied in multiple layers on the substrate. A third baking treatment step of heating the insulating film formed into a multi-layered structure after finishing the plurality of treatment steps by raising the temperature stepwise at a predetermined time in an inert gas atmosphere To.

[Action]

The method of the present invention includes a step of leaving a substrate at a predetermined temperature and a predetermined humidity after applying a polyimide film, and the polyimide resin formed by spin coating is uniformly diffused in the peripheral portion of the substrate. Establish a process. In this way, the spin-coated polyimide film is uniformly diffused and spread on the substrate.

The polyimide film of the first layer, which is exposed and developed to form via holes, is cured by baking at a high temperature of 200 ° C. in an inert gas atmosphere. In this way, even if the second layer polyimide film is applied, the solvent contained in the second polyimide film cannot be absorbed because the first layer polyimide film is cured.

Further, after forming a via hole in the second layer polyimide film by developing and exposing, a heat treatment for raising the temperature stepwise at a predetermined time in an inert gas atmosphere is performed, whereby an interlayer formed in a multilayer structure is formed. The insulating film can be reliably cured without cracks or cracks, and a highly reliable multilayer insulating film can be obtained.

〔Example〕

An embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory view showing the steps of the method for forming a multilayer insulating film according to the present invention, FIG. 2 is a temperature profile diagram of the first baking step according to the present invention, and FIG. 3 is a second baking step according to the present invention. FIG. 4 is a temperature profile diagram of the process, FIG. 4 is a temperature profile diagram of the third baking process in the present invention, and FIG. 5 is a sectional view of an essential part of a printed circuit board for explaining the method of the present invention.

Although FIG. 5 shows a state in which an insulating film is formed on the upper portion of the substrate for the sake of simplicity, it is assumed that a similar insulating film is formed on the lower portion of the substrate.

As shown in FIGS. 1 and 5, a conductor layer is provided inside.
A coating step 101 for coating and forming a first layer polyimide film 16 with a thickness of 10 μm on a conductor layer pattern 14 provided on a ceramic substrate 13 having a via hole 12 formed with a SiO ₂ film 15 with a spinner. carry out.

Then, as shown in FIG. 1, a diffusion coating step 102 is carried out in which the substrate having the polyimide film formed thereon is allowed to stand at a temperature of 22 ± 3 ° C. and a humidity of 45 ± 5% for 5 minutes.

When the substrate is left to stand in such an environment of temperature and humidity, the polyimide film loosely diffuses in all directions of the substrate without cracks and the like, and the thickness becomes uniform.

Next, as shown in FIGS. 1 and 2, a first baking step 103 is performed in which the polyimide film of the first layer is baked at a temperature of 80 ° C. for 30 minutes in the atmosphere.

Next, as shown in FIG. 1, an exposure step 104 of exposing the first layer polyimide film in a predetermined pattern is performed.

Next, as shown in FIG. 1 and FIG. 5, a developing step of developing the exposed first layer polyimide film with a developing solution.
Step 105 is performed to form a first via hole 17 having a predetermined size.

Then, as shown in FIG. 1 and FIG. 3, the first layer polyimide film 16 having the first via holes 17 opened by the above-mentioned development treatment is heated to 200 ° C. in a nitrogen gas atmosphere having an oxygen gas content of 5 ppm or less. A second baking step 106, in which the polyimide film 16 is baked at the temperature of 60 minutes, is performed to surely cure the polyimide film 16.

Next, as shown in FIG. 1 and FIG. 4, a coating step 101 is carried out in which the second layer polyimide film 18 is spin coated to a thickness of 10 μm using a spinner.

Then, the diffusion coating step 102 shown in FIG. 1 is performed again.

Then, the first baking step 103 shown in FIGS. 1 and 2 is performed again.

Then, as shown in FIG. 1 and FIG.
The exposure process 104 and the development process 105 are performed again on the layer polyimide film 18 to form a second via hole 19 having a diameter larger than that of the first via hole.

Then, as shown in FIG. 1 and FIG.
The baking step 106 is performed again.

Next, as shown in FIGS. 1 and 4, the substrate is subjected to a third baking step 107 in which the temperature rises stepwise to a predetermined value every 30 minutes.

By raising the temperature stepwise and baking, the insulating film can be cured without cracks or the like.

By doing so, the via holes shown in FIGS. 1 and 2 having different opening sizes can be accurately formed in the insulating film formed in the multilayer structure, and the conductor layer may be cracked in such via holes by the sputtering method. Since the inner wall of the via hole is sufficiently covered in the state where it does not occur, a highly reliable multilayer printed circuit board can be obtained.

Further, when the above is performed, the interlayer insulating film can be accurately formed to a predetermined thickness without any unevenness or waviness, and the conductor layer pattern formed on the interlayer insulating film can be obtained in a state where the thickness does not change. The inconvenience that the resistance value of the conductor layer pattern partially changes is eliminated, and a highly reliable multilayer ceramic printed board can be obtained.

Although nitrogen gas is used in the second and third baking processing steps in this embodiment, an inert gas such as helium or argon may be used.

Also, the oxygen concentration is 5 ppm in the second and third baking steps.
By controlling the concentration to the following, the conductor layer pattern 14 will not be oxidized.

In the present embodiment, the case of forming an insulating film having a two-layer structure has been described. However, every time a new insulating film is applied, the steps from the diffusion coating step 102 to the second baking step 106 in FIG. 1 are repeated. The third baking step 107 may be finally performed.

〔The invention's effect〕

As is clear from the above description, according to the method for forming a multilayer insulating layer of the present invention, the insulating layer can be obtained in a flat state, and the via hole to be formed can also be formed with a predetermined size and with high precision. There is.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing the steps of the method for forming a multilayer insulating film according to the present invention, FIG. 2 is a temperature profile diagram of the first baking process, FIG. 3 is a temperature profile diagram of the second baking process, and FIG. FIG. 5 is a temperature profile diagram of the second baking step, FIG. 5 is a sectional view of a main part of a printed circuit board for explaining the method of the present invention, FIG. 6 is an explanatory view of a conventional method, and FIG. 7 (a) is a conventional method. FIG. 7 (b) is a sectional view taken along line VII-VII ′ of FIG. 7 (a), FIG. 8 is a sectional view showing a method for forming a multilayer insulating film, and FIG. 9 is a conventional method. FIG. 6 is a cross-sectional view showing an inconvenient state in FIG. In the figure, 11 is a conductor layer, 12 is a via hole, 13 is a ceramic substrate, 14 is a conductor layer pattern, 15 is a SiO ₂ film, 16 is a first layer polyimide film, 17 is a first via hole, 18 is a second layer polyimide film, and 19 is a second layer polyimide film. Is a second via hole, 101 is a coating process, 102 is a diffusion coating process,
103 is a first baking step, 104 is an exposure step, 105 is a developing step, 106 is a second baking step, and 107 is a third baking step.

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Claims (3)

[Claims] 1. After applying an insulating film forming material on a substrate (13),
A diffusion coating step (102) for uniformly diffusing an insulating film forming material applied and formed on the substrate by leaving the substrate in an atmosphere of a predetermined temperature and a predetermined humidity for a predetermined time; A first baking step (103) of performing heat treatment at a temperature for a predetermined time, an exposure step (104) of exposing and developing the insulating film in a predetermined pattern to form a via hole of a predetermined size, and a developing step (105); The plurality of treatment steps including the second baking step (106) in which the heat treatment is performed at a predetermined temperature for a predetermined time in an inert gas atmosphere are repeated as one cycle of the treatment step each time the insulating film is applied onto the substrate. And performing a third baking step (107) of heating the insulating film formed in the multi-layered structure after finishing the plurality of processing steps in a stepwise manner at predetermined time intervals in an inert gas atmosphere. Characterized by Method for forming the insulating film. 2. The multilayer according to claim 1, wherein in the diffusion coating step (102), the temperature of the atmosphere for installing the substrate is 22 ± 3 ° C. and the humidity is 45 ± 5%. Method of forming insulating film. 3. The second and third baking steps (106,10)
The method for forming a multilayer insulating film according to claim 1, wherein the inert gas used in 7) is an inert gas having an oxygen content of 5 ppm or less.