JPS6026294B2 - Photo etching method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a photoetching method.

2. Description of the Related Art In manufacturing semiconductor devices, microfabrication using photoetching is strongly required as the performance of the devices improves. 2. Description of the Related Art Conventionally, a positive photoresist film has been used as an etching mask to form fine patterns in semiconductor devices by photoetching.

However, positive photoresist films have poorer adhesion to the substrate to be etched, such as the underlying aluminum film, than negative photoresist films, so they have the disadvantage that side etching is worse than negative photoresist films. be. In addition, positive photoresists have a low softening point, so they must be subjected to post-baking at a temperature of around 110°C (heat treatment above 140°C is not possible), and they have the disadvantage that subsequent high-temperature heat treatment cannot be performed. . In this way, positive photoresists are etched with weak adhesion to the base film, so the undesired areas of the base film to be etched are attacked by the etching solution, resulting in large side etching. Therefore, there is a problem that a desired pattern cannot be etched with good resolution. Therefore, the purpose of the present invention is to solve the above-mentioned problems, improve the heat resistance of positive photoresists, and strengthen the adhesion to the substrate, thereby causing adverse effects on microfabrication such as side etching. It is an object of the present invention to provide a new photoetching method capable of photoetching fine patterns without the need for photoetching.

In order to achieve such an object, the present invention covers a positive photoresist in the form of a condensate of a noporak resin and diazoquinone naphthalene sulfonyl chloride to which a coupling agent consisting of a silane-based primer is added. After coating the aluminum film as an etching body, exposing and developing the film, and performing a first post-bake at a low temperature, a second post-bake is performed at a higher heat treatment temperature of 190 to 240°C. and a step of selectively etching the object to be etched, which is the underlying film, using the photoresist as a mask.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a photo-etching method for an aluminum wiring film in a semiconductor device, which is an embodiment of the present invention, will be described in detail in the order of steps with reference to the drawings.

As a starting material, a material is prepared in which two aluminum wiring films 3 to be etched are formed on the entire surface of a field insulating film 2 on the surface of a semiconductor wafer 1 on which elements are formed (FIG. 1).

This aluminum wiring film 3 is formed by electron beam evaporation.
It is provided at a temperature of about 0.00 qo and is used as a wiring film in ordinary semiconductor devices.
Kawa: Next, a positive photoresist film 4, which will serve as a photoetching mask, is applied to the entire surface of the aluminum wiring film 3, which is the object to be etched, to a film thickness of about 1.8 cm (FIG. 2).

This positive photoresist film 4 is one to which a coupling agent, which is an adhesive strengthening agent, is added.

For example, OFPR as the positive photoresist film 4
-2 (product name) is silane-based pliers ×12-41
Use one containing 8% of 2 (trade name). 'Uh
After pre-baking at 9pi○ for about 30 minutes, exposure,
Developing is performed to remove unnecessary photoresist film 4 (Fig. 3).

This step is performed using a well-known process.

〇) As a post-bake, heat treatment is performed at 150°C for about 30 minutes to harden the photoresist film 4.

Next, a second postbare is heated at a temperature of 190 to 240 qo.
A process is performed to strengthen the adhesion of the photoresist film 4 to the aluminum wiring film 3, which is the underlying film. This only needs to be done for about 30 minutes, which is a feature of the present invention.If the photoresist film 4 is baked at 190 to 230 CO all at once as a post-bake, the photoresist film 4 will be softened, but once it is baked at a low temperature of about 150°C, the photoresist film 4 will be softened. By performing the first post-bake and further performing the second post-bake at a higher temperature of 190 to 240 qo, the adhesive strength with the substrate can be increased. Example Using the above positive photoresist film 4 as an etching mask, the aluminum wiring film 3 whose surface is exposed is etched with an etchant such as a phosphoric acid etchant to form a fine pattern of the aluminum wiring film 4 (FIG. 4). .

Then, the photoresist film 4 is peeled off. FIG. 5 shows the side etch amount (half the value obtained by subtracting the wiring dimension L' after peeling off the photoresist film 4 from the dimension L before post-baking from the dimension L before post-baking) according to the above-mentioned post-baking temperature according to the present invention. It shows.

In the same figure, parameter A is 8% coupling agent x 12 - 412 to positive photoresist film OFPR-2.
Parameter B shows the normal positive photoresist film OFPR-2 to which no coupling agent ×12-412 was added. As shown in the figure, the latter has poor heat resistance and cannot be used because it becomes soft when baked for more than 180 hours, and therefore has weak adhesive strength with the base. Such a positive photoresist film (containing a coupling agent) has improved heat resistance and stronger adhesion to the substrate, and the amount of side etching is extremely small, especially at post-baking temperatures of 190 to 24,000 °C. This makes it possible to etch fine patterns. Furthermore, the reason for achieving the object of the present invention will be explained based on the infrared absorption spectrum diagrams of the positive photoresist film shown in FIGS. 6 and 7.

In the figure, parameters C and D indicate those before and after the second post-bake process according to the present invention. The positive photoresist according to the present invention is in the form of a condensate of novolac resin and diazoquinone naphthalene sulfonyl chloride, and decomposes as follows when irradiated with light. {a- Absorption of infrared wavelength 1 total ratio -1 is decreasing.

This is the The absorption of the photoresist shows changes in the photoresist.

This is considered to have a certain shape, and strengthens the adhesion between the photoresist film and the underlying aluminum wiring film.

'b - Absorption of infrared wavelengths 400-1000 skin-1 increases significantly after the second post-bake.

This is proof that the post-baking temperature can be increased because the thermoplastic resin Nopolac is changed to the thermosetting resin Resol. {c- Absorption of infrared wavelength 600-1 is eliminated. This is evidence that C-CI and C-S of sulfonyl chloride are eliminated, which leads to strengthening of adhesive strength. {d}
Absorption of infrared wavelengths 2,700 to 2,900 ka-1 is significantly reduced.

This is evidence that the plasticity -OH is reduced by the absorption of 1-OH, and the photoresist film becomes hydrophobic and has increased acid resistance, making it suitable as an etching mask for microfabrication. 'e} Since a coupling agent is added to the photoresist film, it is well known that the adhesive force is strengthened by this.

As described above in detail, the photoetching method according to the present invention uses a positive photoresist to which a coupling agent that strengthens the adhesive force to the object to be etched is added, and performs a second post-bake. , photoetching is performed using a positive photoresist film with enhanced heat resistance and strong adhesion to the underlying layer as an etching mask.

Therefore, it is possible to perform photo-etching with as much microfabrication as possible with side etching. The present invention is a photo-etching method that can be applied to various types of objects to be etched and that can produce fine patterns.

[Brief explanation of the drawing]

FIGS. 1 to 4 are cross-sectional views showing the photo-etching method according to an embodiment of the present invention in the order of steps, and FIGS. 5 to 7 are
FIG. 2 is a diagram for explaining the present invention. 1... Semiconductor wafer, 2... Field insulating film, 3... Aluminum wiring film, 4
...Positive photoresist film. chrysanthemum! Illustrations, illustrations, 3 illustrations, 4 illustrations, 5 illustrations, 7 illustrations.

Claims (1)

[Claims] 1. A step of applying a positive photoresist in the form of a condensate of novolak resin and diazoquinone naphthalene sulfonyl chloride to which a coupling agent made of silane-based pliers is added to an aluminum film to be etched, exposing it to light, and developing it. , a step of performing a first post-bake at a low temperature and then a second post-bake at a higher heat treatment temperature of 190 to 240°C, and using the photoresist as a mask to remove the underlying film to be etched. A photo etching method comprising the step of selectively etching the body.