JPH09321428A - Photo-via formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo-via formation method which does not cause poor continuity at corner parts. SOLUTION: An insulating film comprises two layers of an insulating layer 13 (a lower layer) which is hard to be roughened and an adhesive layer 14 (an upper layer) which is easy to be roughened, and a hole is formed with one exposure and development, and roughened, so that a via diameter is enlarged at the part of adhesive layer 14, thus a stepped photo-via whose opening is enlarged larger than its bottom is formed. Thanks to the step form, a plating liquid is circulated at plating, and current density is dispersed, and a required plating thickness is obtained even at the corner parts. So that poor continuity is hard to occur and high reliability is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the formation of photo vias in the manufacture of printed wiring boards, and more particularly, a method of forming photo vias that improves the contact reliability by improving the distribution of plating within the vias. It is about.

[0002]

2. Description of the Related Art Conventionally, a photo via for making contact between an inner conductor layer and an outer conductor layer in a printed wiring board has been
It is formed as follows. That is, as shown in FIG. 5, the substrate 12 having the conductor portion 11 is covered with the insulating layer 24, the via shape is formed by photolithography, and then roughened. Metal plating is applied to cover the insulating layer 24 with the plating layer 26. The plated layer 26 makes contact between the conductor portion 11 which is the inner conductor layer and the outer conductor layer.

[0003]

However, the formation of the photovia according to the above-mentioned conventional technique has a problem that the reliability of the contact is insufficient. That is, as shown in FIG. 6, the plating layer 26 tends to be thin at the corner portion of the boundary between the bottom surface and the side wall of the photo via, and the conductor portion 11
There may be insufficient contact with. For this reason,
The reliability of contacts is insufficient. In particular, when the aspect ratio of the shape of the photo via is high, as in the case of a highly integrated substrate, this contact problem is remarkable. There are two causes for this: the wraparound of the plating solution and the current distribution.

First, the wraparound of the plating solution will be described. That is, since the plating solution tends to form a vortex inside the photo via and the liquid exchange with the outside of the via becomes insufficient, the concentration of copper ions becomes less than that outside the via when the copper ions are consumed by plating. Therefore, the thickness of the plating layer 26 becomes thinner inside the photo via due to the lack of ions than at the outside. This phenomenon is remarkable at the corners because the plating solution is especially hard to get around compared to near the center of the bottom surface.
It is a major cause of contact failure.

Next, the current distribution will be described. The current distribution during plating is directly connected to the coating amount distribution, but depends on the electric field distribution (interval between equipotential surfaces) in the vicinity of the substrate-side surface that is the cathode. And because of the shape of the photo via,
Since the distance between the equipotential surfaces is small near the edge portion between the upper surface and the side wall and the electric field is strong (edge effect), the current density at that portion also becomes high. On the other hand, in the vicinity of the bottom surface of the photo via, since the equipotential surface is large and the electric field is weak, the current density at that portion is low. This problem of current density is also more prominent in the corner portion than in the vicinity of the center of the bottom surface, which is a major cause of contact failure due to insufficient plating adhesion amount at that portion.

As measures against this, for example, Japanese Patent Publication No. 7-10
As described in Japanese Patent No. 5593, a step in which the diameter of the top opening is made larger than the diameter of the bottom portion by performing the photolithography for forming the photo via in two steps (may be three times or more). It is conceivable that the photo via is shaped. In this way, both the problem of the wraparound of the plating solution and the problem of the current distribution are significantly alleviated, and the lack of the plating thickness at the corners can be eliminated to ensure the reliability of the contacts. However, with this method,
Since photolithography is performed twice or more to form photo vias and different pattern masks are used,
There is another problem that the cost of the mask is high and the number of steps is large.

The present invention has been made in order to solve the above-mentioned conventional problems, and provides a highly reliable photo via which eliminates the insufficient plating thickness at the corner portion of the photo via and ensures contact with the inner conductor layer. It is an object of the present invention to provide a method of forming a photo via that can be formed by one-time photolithography.

[0008]

To achieve the above object, the invention of claim 1 is a method of forming a photo via for electrically contacting an inner layer conductor portion with the outside through an opening provided in an insulating layer. A first coating step of coating a substrate having an inner-layer conductor portion on its surface with a first insulating layer; and a step of coating a substrate coated with the first insulating layer with a material that is more easily roughened than the first insulating layer. A second coating step of coating with a second insulating layer, a developing step of forming an opening penetrating the first insulating layer and the second insulating layer to expose the inner layer conductor portion, and at least the second And a step forming step of forming a step by roughening the insulating layer to make the opening diameter of the second insulating layer larger than the opening diameter of the first insulating layer.

In this forming method, a substrate having an inner layer conductor portion provided on the surface is used as the substrate. This is usually patterned by etching a copper clad laminate as a starting material by a subtractive method. In the first coating step, the substrate including the inner layer conductor portion is coated with the first insulating layer. Then, in the second coating step, the second insulating layer is covered on the first insulating layer, so that the substrate is doubly covered with the insulating layer. The materials of the two insulating layers are selected so that the second insulating layer is roughened more strongly than the first insulating layer, though the two insulating layers will be roughened later.

After the substrate is covered with the double insulating layer, a developing step of the insulating layer is performed before roughening to form the shape of the photo via. That is, a hole penetrating the first and second insulating layers is formed, and the inner layer conductor portion is exposed at the hole. This is usually because the first and second insulating layers are made of a photosensitive material, and the portions other than the portions that will become holes in photolithography are cured by exposure to light, and the first and second insulating layers in the unexposed portions are Remove and do. Alternatively, instead of making the first and second insulating layers themselves photosensitive, a photoresist is separately applied to form a photosensitive layer, and the first and second insulating layers are processed by etching after development of the photosensitive layer. You may. The via shape formed by penetrating the first and second insulating layers by such a developing process has sidewalls that are substantially vertical, and a step is especially formed at the boundary between the first insulating layer and the second insulating layer. There is no.

Then, a step forming step is performed next. That is, it is roughening. When the roughening is performed, the second insulating layer that is the upper layer is roughened more strongly than the first insulating layer that is the lower layer as described above, and as a result, the via diameter in the first insulating layer is larger than that of the first insulating layer. The via diameter in the second insulating layer is larger. As a result, a step-shaped photo via is formed in which the diameter of the top opening is larger than the diameter of the bottom portion.

When the photo via thus formed is plated, the diameter of the top opening is larger than the diameter of the bottom, so that the plating solution inside and outside the via is sufficiently exchanged during plating, and ions are deficient in the via. And the non-uniformity of the current density due to the edge effect is also light,
It has good plating coverage and a sufficient plating layer is formed even at the corners of the boundary between the bottom surface and the side wall, resulting in good contact and high reliability. Even when sputtering or the like is performed instead of plating, the shadowing effect is light, and therefore the coverage is good and the contact is good. Note that only one photomask is required to form such photo vias.

A second aspect of the present invention is the method for forming a photo via according to the first aspect, wherein the first insulating layer contains silica powder and the second insulating layer contains epoxy powder. It is characterized by containing.

In this case, the silica powder contained in the first insulating layer does not dissolve in the roughening agent during the step forming step, whereas the epoxy powder contained in the second insulating layer does not dissolve in the roughening agent. Since the powder dissolves in the roughening agent, the second insulating layer undergoes roughening more strongly than the first insulating layer, and a step-shaped photo via in which the diameter of the top opening is larger than that of the bottom is formed. .

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below in detail with reference to the drawings. First, the copper clad laminate is etched by a known subtractive method to process the surface copper plate into a predetermined pattern. By this pattern processing, the inner conductor layer (thickness: 15 to 20 μm) is formed on the integrating plate.
Degree) is formed. Then, an insulating layer and an adhesive layer are applied to this copper clad laminate using a roll coater. Both the insulating layer and the adhesive layer have a thickness of about 40 μm. Therefore, as shown in the cross-sectional view of FIG.
3 is present, the conductor portion 11 (inner conductor layer) is also covered with this, and the insulating layer 13 is further covered with the adhesive layer 14.

Here, the materials of the insulating layer 13 and the adhesive layer 14 will be described. Both of these materials have an epoxy resin varnish as a matrix and are mixed with a powdery filler.

The matrix used for the insulating layer 13 is
Cresol novolac type epoxy resin (manufactured by Kyoeisha) 60
Parts by weight, bisphenol A type epoxy resin (made by Yuka Shell) 40 parts by weight, imidazole type curing agent (made by Shikoku Chemicals)
It is a mixture containing 5 parts by weight, 5 parts by weight of a photosensitive monomer (manufactured by Kyoeisha), 5 parts by weight of a photoinitiator (manufactured by Kanto Kagaku), and 0.5 parts by weight of a photosensitizer. The filler is silica fine powder (Tatsumori, average particle size about 3 μm). Knead the matrix and the filler (40 parts by weight) to obtain 500
Adjust the viscosity to about ps before use.

On the other hand, the adhesive layer 14 uses substantially the same matrix as the insulating layer 13 as a matrix, and the filler is epoxy fine powder (manufactured by Toray, average particle size: about 5 μm).
m 20 parts by weight + average particle size of about 0.5 μm 10 parts by weight). Then, the matrix and the filler are kneaded to adjust the viscosity to about 800 ps and applied. Both the insulating layer 13 and the adhesive layer 14 are dried at 80 ° C. for 15 minutes after application, and the solvent component is volatilized to such an extent that the varnish does not adhere to the finger even if the application surface is touched with the finger.

Next, the insulating layer 13 and the adhesive layer 14 are exposed. That is, parallel light is irradiated through the mask 17 on which the pattern is printed to expose the portions of the insulating layer 13 and the adhesive layer 14 other than the pattern of the mask 17 to light. An opaque pattern is printed on a portion of the mask 17 that will be a photo via, and that portion blocks light.
As a result, the portions of the insulating layer 13 and the adhesive layer 14 exposed to light are cured by exposure to light. Then, development is performed. That is, when the insulating layer 13 and the adhesive layer 14 in the unexposed portion are removed with a solvent, as shown by reference numeral 15 in FIG.
3 and a hole penetrating the adhesive layer 14 are formed, and the conductor portion 11 is exposed at that portion. In this state, the side wall of the hole 15 is vertical, and the diameter of the hole 15 is substantially the same in both the insulating layer 13 portion and the adhesive layer 14 portion.

Then, roughening is performed. When the state shown in FIG. 2 is immersed in a corrosive liquid such as chromic acid or permanganate, the insulating layer 13 and the adhesive layer 14 are etched to form fine irregularities on the surface. At this time, since fine silica powder having high corrosion resistance is added as a filler to the insulating layer 13, the insulating layer 13 is not roughened so much. On the other hand, since the filler of the adhesive layer 14 is an epoxy fine powder that is easily dissolved in the corrosive liquid, the adhesive layer 14 is much roughened and is much etched than the insulating layer 13. Therefore, in the insulating layer 13, the via diameter is not much different from that before the roughening, whereas in the adhesive layer 14 thereabove, the via diameter is slightly wider than that before the roughening due to etching. This state is shown in FIG. In FIG. 3, the via diameter in the insulating layer 13 portion is indicated by d ₁ , and the via diameter in the adhesive layer 14 portion is indicated by d ₂ . Although d ₁ is almost the same as the via diameter in the state of FIG. 2, d ₂ is larger than that. As a result, there is a step between the insulating layer 13 and the adhesive layer 14, and a step-shaped photo via is formed in which the opening is wider than the bottom.

Then, plating is performed. First, the insulating layer 13 and the adhesive layer 14 in the state shown in FIG.
0.5 to 0.5% by electroless copper plating.
After forming a plating layer having a thickness of 1 μm, a plating layer 16 having a thickness of 10 to 20 μm is formed thereon by electrolytic copper plating.
Then, as shown in FIG. 4, the conductor portion 1 on the bottom surface of the photo via is formed.
The copper plating layer 16 is formed from 1 to the sidewall of the photo via and the upper surface of the adhesive layer 14. The copper plating layer 16 secures electrical contact between the conductor portion 11 and an external conductor layer.

The above-described photo via has the following characteristics because it has a step shape in which the opening is wider than the bottom. That is, at the time of plating after the formation of the photo via, a plating layer having a required thickness is formed at the corner portion of the boundary between the bottom surface and the side wall, and therefore contact failure does not occur and reliability is high. The reason why the plating layer does not become thin at the corners is the supply of copper ions into the via and the distribution of the current density. That is, since the opening has a step shape and the opening is wider than the bottom, the plating solution circulates well inside and outside the via during plating, and copper ions are replenished and supplied into the via without any shortage. Further, since the step shape reduces the current concentration on the edge portions of the side wall and the upper surface, the current density at the corner portion, which tends to decrease the current density, increases. Therefore, the copper plating layer 16 is surely continuous at the bottom surface portion, the side wall, and the upper surface portion, and the contact reliability is high.

Further, in forming such a step-shaped photo via, the difference in the roughening resistance between the insulating layer 13 and the adhesive layer 14 is utilized, so that the exposure only needs to be performed once. Only need one. Therefore, the number of steps is not excessive and the mask cost is not increased.

As described in detail above, according to the present embodiment, a step-shaped photo via having an opening larger than the bottom can be formed with one photomask, so that copper can be formed in the via during plating. Ions are well replenished,
Therefore, it is possible to form a photo via having a high contact reliability without concentration of current density at low cost.

Of course, the above embodiment does not limit the present invention. Therefore, it goes without saying that the present invention can be improved and modified in various ways without departing from the scope of the invention. For example, in the above-described embodiment, the insulating layer 13 and the adhesive layer 14 are directly patterned by the mask 17 by using a photosensitive material, but instead, they are non-photosensitive themselves and are patterned by using a separate photoresist. You may do it.
Further, although the copper plating layer 16 is formed by a wet method such as electroplating after forming the photo via, it may be formed by a vapor phase method such as vapor deposition or sputtering. In this case, too, the step shape reduces shadowing. , Contact reliability is high.

[0026]

As described above, according to the method for forming a photo via of the present invention, a photo via can be formed once by making it possible to reliably make contact between the inner conductor layer and the outside by eliminating the insufficient plating thickness at the corner portion. It can be formed by lithography, and has a great effect on improvement of reliability and cost reduction.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which exposure is performed after forming an insulating layer and an adhesive layer in the present embodiment.

FIG. 2 is a cross-sectional view showing a state of development after exposure in the present embodiment.

FIG. 3 is a cross-sectional view showing a state where roughening is performed after development in the present embodiment.

FIG. 4 is a cross-sectional view showing a state where plating is performed after roughening in the present embodiment.

FIG. 5 is a cross-sectional view showing a state where roughening is performed after development in the conventional technique.

FIG. 6 is a cross-sectional view showing a state where plating is performed after roughening in a conventional technique.

[Explanation of symbols]

11 Inner Layer Conductor 13 Insulating Layer (First Insulating Layer) 14 Adhesive Layer (Second Insulating Layer) d ₁ Via Diameter in Insulating Layer d ₂ Via Diameter in Adhesive Layer

Claims (2)

[Claims] 1. A method of forming a photo via for electrically contacting an inner conductor section with the outside through an opening provided in an insulating layer, comprising: coating a substrate having an inner conductor section on its surface with a first insulating layer. 1 coating step, and 2nd coating the substrate coated with the first insulating layer with a second insulating layer of a material that is more easily roughened than the first insulating layer
A coating step, a developing step of forming an opening penetrating the first insulating layer and the second insulating layer to expose the lower conductor section, and at least roughening the second insulating layer. And a step forming step of forming a step by making an opening diameter of the second insulating layer larger than an opening diameter of the first insulating layer. 2. The photovia forming method according to claim 1, wherein the first insulating layer contains silica powder, and the second insulating layer contains epoxy powder. Method.