JPH06268378A - Formation method for via hole of multilayer interconnection board - Google Patents

Abstract

PURPOSE:To remove the overhangs of a nonphotosensitive polyimide produced at he time of the formation of via holes in the polyimide by the use of wet etching. CONSTITUTION:Concerning to an method of forming via holes in a multilayer interconnection, a nonphotosensitive polyimide precursor 13 is applied to a board 11, and the solvent is dried. And a via pattern 16 is formed by developing positive photoresist 14. Next, a process of wet-etching the nonphotosensitive polyimide 13 using an alkaline aqueous solution and forming via holes 17 is performed, and the positive photoresist 14 as exfoliated from the nonphotosensitive polyimide 13, and the overhangs 18 of the nonphotosensitive polyimide 13 are removed by performing wet etching again. And the tapering processing of the via holes 17 is performed, and heating and hardening is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming via holes in a multilayer wiring board using polyimide as an insulating film, which is used in switch modules of ATM exchanges, CPU modules of computers and the like.

[0002]

2. Description of the Related Art Conventionally, as a technique of this kind of field,
J. Summers, D.M. Murray, M .; Moce
lla, M .; Springman, J .; Howe an
d W. Lautenberger E. I. du P
ont De Nemours & Company I
nc. "WET ETCHING POLYIMIDE
S FOR MULTICHIP MODULE AP
PLICATIONS "ICMCM Proceedi
ng '92, P.N. 247-P. 250 were disclosed.

Along with the speeding up, high integration, and high density of LSIs, it has become necessary to establish a technology capable of realizing high-density wiring and high-speed signal transmission on a substrate on which these LSIs are mounted. Therefore, as a method of satisfying these problems, attention has been paid to making a multilayer wiring of a substrate. Among the multi-layer wiring technology, a method of forming a fine through hole by photolithography using an organic polymer film as an insulating layer and forming a wiring by using a metal thin film process has been studied. Polyimide has come to be widely used for this organic polymer film for a multilayer wiring board because of its low dielectric constant and thermal stability.

Polyimides used for multi-layer wiring are roughly classified into photosensitive and non-photosensitive ones. The photosensitive polyimide contains a photosensitive group in the skeleton of the polymer and is exposed to light to be polymerized by using g rays (a kind of ultraviolet ray) or the like.
Further, the photosensitive polyimide has a photosensitive group introduced into the skeleton of the original polymer, and a sensitizer is added to further increase the sensitivity. This increases the sensitivity of polyimide to the same level as photoresist and enables the processing of fine via hole patterns.

However, the photosensitive polyimide is very expensive because the contents such as introduction of a photosensitive group and addition of a sensitizer are added to the original polymer. Furthermore, not all of these photosensitive groups / sensitizers are involved in the polymerization. Therefore, after forming the polyimide film, the photosensitive group / sensitizer not used in the reaction is left behind between the polymers. As a result, when left for a long period of time, the polyimide film absorbs moisture and loses the original characteristics of the polyimide, such as excellent insulation and low dielectric constant.

On the other hand, since the non-photosensitive polyimide is polymerized only by heat treatment, a very stable film can be obtained in the finished polyimide with less impurities. However, it is necessary to process the fine via hole pattern by using a dry etching method such as RIE. Therefore, the material itself can be purchased at a low price, but the number of steps required for processing increases the cost of the finished substrate.

Therefore, there is a method disclosed in the above-mentioned document as a method of forming a via hole pattern in a non-photosensitive polyimide which is cheap in material by using a wet etching method which requires less man-hours as compared with dry etching and can be processed at low cost. The non-photosensitive polyimide via hole forming process will be sequentially described with reference to FIG.

First, as shown in FIG. 3 (a), the substrate 1 on which the lower layer wiring 2 is formed is brought into a normal state by a cleaning method such as degreasing cleaning and pure water cleaning. 3B, the polyimide precursor (polyamic acid) 3 was dropped and spin-coated as shown in FIG. 3 (b), and then NMP (N-, which is a solvent of the polyimide precursor at 100 ° C.). Methyl-2-pyrrolidone).

As shown in FIG. 3C, the dried substrate is coated with a positive photoresist 4 using a spin coater and prebaked at 90.degree. Next, FIG.
As shown in (d), the prebaked substrate is exposed to light hν using a photomask 5 having a via pattern 6, and an alkaline aqueous solution [KOH (potassium hydroxide), TMA-H (tetramethylammonium) is used. = Hydroxide)] is used for development.

Next, as shown in FIG. 3E, the via hole 7 is formed by etching the polyimide with the same alkaline aqueous solution as the resist developing solution. Next, FIG.
As shown in (f), the substrate on which the polyimide etching has been completed is stripped of the resist with butyl acetate and subjected to final cure at 350 ° C. in an oxygen-free atmosphere.

After these steps, as shown in FIG. 3G, after forming the via hole 7, the upper wiring 8 is formed by using the sputtering method or the like.

[0012]

However, as described above, in order to form a via hole in the non-photosensitive polyimide by wet etching, patterning is performed using a photoresist. As shown in FIG. 4A, the polyimide in contact with the resist has an eaves-like shape due to poor circulation of the developing solution, and an overhang 9 remains. Therefore, as shown in FIG. 4B, when the upper layer wiring 8 is formed by the sputtering method after the via hole 7 is formed, the overhang 9 makes the sputtered film on the sidewall of the via hole extremely thin, so that the lower layer wiring 2 is formed. Sufficient interlayer connection of the upper layer wiring 8 cannot be achieved, and it is difficult to secure reliability of interlayer connection of via holes.

As described above, when the via hole of the non-photosensitive polyimide is formed by using the wet etching method, the polyimide which is in contact with the resist causes an overhang and a highly reliable interlayer connection is achieved. It was difficult to do. The present invention removes the polyimide overhang that occurs when forming a via hole of a non-photosensitive polyimide using the wet etching method described above, and uses an existing conductor film forming method such as a sputtering method to improve reliability. It is an object of the present invention to provide a method for forming a via hole of a multilayer wiring board that can obtain high interlayer connection.

[0014]

In order to achieve the above object, the present invention provides a via hole forming method for forming a via hole in a multilayer wiring using an organic polymer film as an insulating layer between wiring layers. A step of applying a precursor of a molecular film to a substrate and drying a solvent, a step of developing a photoresist to form a via pattern, and a wet etching of the organic polymer film using an alkaline aqueous solution,
A step of forming a via hole, a step of peeling the resist from the organic polymer film, and an overhang of the organic polymer film generated by the formation of the via hole dilutes the concentration of the alkaline aqueous solution used for forming the via hole. Then, the entire surface is again wet-etched to remove the overhang, and the via hole is subjected to a taper process and a heat curing process.

The organic polymer film is a non-photosensitive polyimide film. Further, the resist developing solution and the non-photosensitive polyimide film etching solution are alkaline aqueous solutions. The alkaline aqueous solution is KOH or TMA.
-H (tetramethylammonium-hydroxide) aqueous solution.

[0016]

According to the present invention, the via hole is once formed in the non-photosensitive polyimide which is the organic polymer film by wet etching. Then, an overhang is formed in the via hole. Therefore, the overhang is removed by using an alkaline developing solution.

That is, after a non-photosensitive polyimide precursor is applied to a substrate and the solvent is dried, a via pattern is formed using a positive photoresist, an aqueous solution of TMA-H (tetramethylammonium hydroxide), etc. Wet etching of the polyimide is performed using the alkaline aqueous solution to form a via hole. After that, the positive photoresist is peeled off from the polyimide, and the polyimide overhang generated in the step of forming the via hole is diluted with the concentration of the alkaline aqueous solution used to form the via hole, and the entire surface is wet-etched again. After the overhang is removed and the via hole is tapered, it is heat-cured.

Therefore, it becomes possible to form a uniform thin film as an upper layer wiring on the side surface in the via hole, and highly reliable interlayer connection can be obtained.

[0019]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing a process of forming a via hole of a multilayer wiring board showing an embodiment of the present invention. First,
As shown in FIG. 1A, the lower layer wiring 12 is formed on the substrate 11.

Next, as shown in FIG. 1 (b), a non-photosensitive polyimide (for example, Piraline PI-produced by du Pont, which is an organic polymer film as an interlayer insulating film is formed thereon.
2611D) 13 is applied to a thickness of 15 μm. Then, as shown in FIG. 1C, a positive photoresist (for example, positive resist OFPR-860 manufactured by Tokyo Ohka Co., Ltd.) is used.
0) 14 is applied.

Then, as shown in FIG. 1 (d), a photomask 15 having a via pattern 16 is used for exposure to light hν, and an alkaline aqueous solution [KOH (potassium hydroxide), TMA-H (tetramethylammonium) is used. = Hydroxide)] is used for development. Next, as shown in FIG. 1E, an alkaline aqueous solution (for example, 0.26N TMA-H: NMD- manufactured by Tokyo Ohka Co., Ltd.) is used as an etching solution.
39) is used to etch the polyimide to form via holes 17.

Next, as shown in FIG. 1F, the positive photoresist 14 is removed with an alkaline aqueous solution. A polyimide overhang 18 is formed in the via hole thus obtained. Therefore, the polyimide overhang 18 of the via hole, which is the main feature of the present invention, is removed.

That is, as the etching solution, the alkaline aqueous solution (0.26
Etching was carried out by dipping the solution (TMH-H of N) and pure water in a ratio of 1: 7 and dipping it for 10 seconds to 15 seconds at room temperature. At this time, the etching amount of the polyimide is about 1 μm, and the film thickness of the polyimide is about 13 μm. Immediately after the etching is completed, the surface of the polyimide melted with alkali is cleaned by cleaning with pure water. Then, 135 ℃, 200 ℃, 350
It is heat-cured in three stages of ° C.

Thus, as shown in FIG. 1G, the via hole 19 having the taper 20 is finally formed in the non-photosensitive polyimide 13 having a film thickness of about 9 μm. Next, copper is deposited to a thickness of about 0.3 μm using a sputtering method, and copper is further deposited to 5 μm using an electrolytic plating method, as shown in FIG.
As shown in, the upper wiring 21 is formed. FIG. 2 is a cross-sectional view showing the process, which is the main feature of the present invention, in a further enlarged manner.

As shown in FIG. 2A, the via hole 17
A polyimide overhang 18 is formed on the surface. Therefore, as described above, etching is performed by immersing the etching solution in which the concentration of the alkaline aqueous solution used previously in the step of forming the via hole is diluted and immersing it for about 10 to 15 seconds at room temperature. Immediately after the etching is completed, the surface of the polyimide melted with alkali is cleaned by cleaning with pure water. Then, it is heat-cured.

Thus, as shown in FIG. 2B, the via hole 19 having the taper 20 is formed in the non-photosensitive polyimide 13. Next, copper is applied to a thickness of about 0.3 μm by using a sputtering method, and copper is applied to 5 μm by using an electrolytic plating method to form an upper layer wiring 21 as shown in FIG. 2C. FIG. 5 shows an example of drilling by the via hole forming method of the present invention.

For comparison, FIG. 6 shows an example processed by a conventional via hole forming method. Both figures are micrographs by Hitachi, Ltd. S-570LB scanning electron microscope. As shown in FIG. 6, after the via hole is formed, wet etching is performed using an alkaline aqueous solution as described above to perform taper processing. As a result, as shown in FIG. The hang is eliminated.

Therefore, a uniform film is formed in the subsequent formation of the upper wiring. It should be noted that the present invention is not limited to the above-described embodiments, and various modifications can be made based on the spirit of the present invention, and they are not excluded from the scope of the present invention.

[0029]

As described above in detail, according to the present invention, the overhang of the polyimide at the upper portion of the via hole opening is removed by performing wet etching on the via hole once formed. It is possible to form a uniform thin film as an upper layer wiring on the side surface in the via hole, and highly reliable interlayer connection can be obtained.

Further, since the polyimide etching treatment liquids have only different concentrations, the waste liquid treatment can be performed in the same treatment pipe. That is, it can be carried out by using the same alkaline aqueous solution for the resist developing solution, the polyimide etching solution, and the overhang removing etching solution.

[Brief description of drawings]

FIG. 1 is a sectional view of a process of forming a via hole of a multilayer wiring board showing an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the process, which is the main feature of the present invention, in a further enlarged manner.

FIG. 3 is a cross-sectional view of a conventional non-photosensitive polyimide via-hole forming process.

FIG. 4 is a diagram showing a problem of forming a via hole of a conventional non-photosensitive polyimide.

FIG. 5 is a photograph of a fine pattern formed on a substrate, which shows a state where a hole is formed by the method for forming a via hole according to the present invention.

FIG. 6 is a photograph of a fine pattern formed on a substrate, which shows a state in which holes have been drilled by a conventional via hole forming method.

[Explanation of symbols]

 11 substrate 12 lower layer wiring 13 non-photosensitive polyimide 14 positive photoresist 15 photomask 16 via pattern 17 via hole 18 polyimide overhang 19 via hole 20 taper 21 upper layer wiring

Claims (4)

[Claims] 1. A method of forming a via hole in a multi-layered wiring using an organic polymer film as an insulating layer between wiring layers, comprising: (a) applying a precursor of the organic polymer film to a substrate and drying the solvent. And (b) developing a photoresist to form a via pattern, (c) wet etching the organic polymer film with an alkaline aqueous solution to form a via hole, and (d) Using a step of peeling the resist from the organic polymer film, and (e) diluting the concentration of the alkaline aqueous solution used to form the via hole, the overhang of the organic polymer film generated by the formation of the via hole. , Wet-etch the entire surface again to remove the overhang,
A method of forming a via hole in a multilayer wiring board, comprising: performing a step of tapering the via hole; and (f) performing a heat curing step. 2. The method for forming a via hole of a multilayer wiring board according to claim 1, wherein the organic polymer film is a non-photosensitive polyimide film. 3. The method for forming a via hole of a multilayer wiring board according to claim 2, wherein the resist developing solution and the non-photosensitive polyimide film etching solution are alkaline aqueous solutions. 4. The alkaline aqueous solution is KOH or TM.
The method for forming via holes in a multilayer wiring board according to claim 3, wherein the solution is an AH (tetramethylammonium-hydroxide) aqueous solution.