JPS6125210B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a resin insulating film used, for example, as a surface protection film of a semiconductor substrate.

There are many types and combinations of insulating films in semiconductor structures in terms of their uses, forming methods, etc., and they are used depending on the purpose, and new developments are also active.

The present invention relates to a method for forming an insulating film made of a polyimide resin that can withstand relatively high temperatures and can be photo-etched. It is something.

The present invention is intended to simplify the process and thereby improve the yield and reduce defects such as pinholes.The following examples of the conventional forming method and the method according to the present invention are described below. It is obvious that the effect is great.

FIG. 1 illustrates the process of forming a polyimide insulating film by a conventional general method. A polyimide film 11 is coated to a thickness of 1.2 μm on a silicon substrate 10, and after heat treatment at 200° C. for 30 minutes, a way coat photoresist 12 is coated to a thickness of 6000 Å.
Ultraviolet rays 13 are selectively irradiated using ordinary photolithography (Figure A), the photoresist 12 is developed (Figure B), and the exposed polyimide film 11 is selectively etched using a hydrazine-based etchant. (Figure C), and finally the photoresist 12 is removed (Figure D).

The disadvantage of the conventional method shown in FIG. 1 is that it requires a large number of steps, and the adhesion between the photoresist 12 and the polyimide film 11 is poor, so the hydrazine-based etchant may cause the resist film to peel off and the film boundary In order to prevent this, the polyimide must be thoroughly washed and dried before coating the photoresist. or,
Since the resistance of the photoresist 12 is weak, defects such as pinholes in the photoresist 12 are greatly exaggerated and transferred to the polyimide film 11, which inevitably lowers the yield.

The present invention has been made in view of the above points, and instead of using a photoresist, a mixed solution of polyamic acid, which is a prepolymer of polyimide, and potassium dichromate as a photocrosslinking accelerator is used on semiconductor substrates. A resin layer is formed by coating on the surface, a desired area of the resin layer is irradiated with ultraviolet rays to form a partially polymerized layer, and the difference in degree of polymerization between the polymerized layer and the non-polymerized resin layer is utilized. It is developed to dissolve and remove the non-polymerized resin layer, and finally light ash is performed using oxygen plasma.

Next, specific examples of the present invention will be described.

The substrate 20 is a silicon wafer with a thickness of 350 μm and a diameter of 2.5 inches that has been mirror-polished on one side and has an oxide film of 4000 Å thick formed thereon by a thermal oxidation method. Polyamic acid having the following molecular formula is used as the resin material for the photosensitive polyimide film.

Polyamic acid has a concentration of 14% using N-methyl-2-pyrrolidone as a solvent, then the viscosity is
It is 150 centipoise.

A solution of 0.023 g of potassium dichromate per 1 c.c. of dimethyl sulfoxide as a photosensitizer is prepared, and a mixed solution is obtained in which 4 parts of the polyamic acid are mixed with 1 part of potassium dichromate solution. Immediately after mixing, the mixture is dropped onto the substrate 20 and spin coated for 60 seconds using a spinner at 5000 rpm to obtain the resin layer 21. At this time, the thickness of the resin layer 21 is approximately 1.5 μm. Light irradiation in this state provides the best sensitivity, but since the photomask and the resin layer 21 stick together, a heat treatment is performed at 80° C. for 2 minutes under reduced pressure of 1 Torr or less to dry the surface. Next, selectively use UV 2 using a mask aligner that uses normal UV rays.
2 exposures (Figure 2, A). The exposure time is about 40 times longer than that of typical photoresists.
For example, if the time is 4 seconds in the case of a way coat, 160 seconds is appropriate for the resin layer 21. As a result of this exposure to ultraviolet rays 22, the resin layer 2 at the exposed location
1 undergoes cross-linking polymerization to form a polymer layer 23 (Fig. 2,
B). The exposed resin layers 21 and 23 are developed using ultraviolet light by immersing them in a solution of 5 parts of hexa-natyl phosphoamide and 1 part of dimethyl sulfoxide.
Hold for 15 minutes, then rinse by immersing in hexamethyl phosphoamide and xylene for 1 minute each. As a result of this development process, the polymer layer 23 remains, and the resin layer 21 remains unirradiated with ultraviolet light.
is removed (Fig. 2, C). After development, the polymer layer 23 is heated in air at 300° C. for 15 minutes to imidize polyamic acid, which is the main component, to form polyimide. Finally, the resin layer 21 was exposed to oxygen plasma with an oxygen partial pressure of 1.5 Torr and an excitation power of 200 W for 2 minutes in a cylindrical plasma etching device to remove the residual high-temperature particles that remained partially on the surface of the area where the resin layer 21 had been removed even after the development process. A light ash process is performed to completely remove the molecular film.

In the above description of the present invention, a case was described in which a silicon wafer provided with an oxide film was used as the substrate, but a case in which a resin layer was directly provided on the surface of the silicon wafer to obtain a surface protective film made of polyimide was described. Needless to say, it can also be used.

As is clear from the above description, the present invention provides a resin layer made of a mixed solution of polyamic acid, dichromic acid, and potassium on a substrate, and partially irradiates this resin layer with ultraviolet rays. Since the resin insulating film of the desired shape is obtained by polymerizing and depending on the difference in the degree of polymerization between this polymerized layer and the non-UV irradiated resin layer, the process is greatly simplified and it is easy to avoid using photolithography. It is possible to obtain an insulating film with high yield and reliability without the occurrence of pinholes.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the conventional method in the order of steps;
The figure is a sectional view showing the method of the present invention in the order of steps, 20 is a substrate, 21 is a resin layer, 23 is a polymer layer,
are shown respectively.

Claims (1)

[Claims] 1 Step of applying a mixed solution of polyamic acid and potassium dichromate to the substrate surface to form a resin layer, irradiating only desired areas of the resin layer with ultraviolet rays to form a polymerized layer, and leaving the polymerized layer A method for forming a resin insulating film, which comprises: a step of removing a resin layer that is not irradiated with ultraviolet rays; a step of thermally curing the remaining polymerized layer; and a light ashing step using oxygen plasma.