JPH0463535B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to photolithography. More specifically, the present invention relates to a method of forming a resist pattern useful as a mask, particularly in photolithography of semiconductor integrated circuits. Background of the Technology In recent years, various excellent photoresists have been developed and put into practical use as semiconductor integrated circuits such as ICs and LSIs have become more precise, miniaturized, and highly integrated. In addition to such improvements in materials, research has also been conducted into improving photolithography processes, that is, methods for forming resist patterns useful as masks in photolithography. Prior Art and Problems In conventional resist pattern forming methods, positive photoresists are used more often than negative photoresists, especially because of their superior resolution. This pattern forming method usually involves applying a solution of a selected photoresist onto a semiconductor substrate to obtain a resist-coated substrate, and if necessary, pre-baking this to remove the solvent in the resist coating, and then preparing the resist for use. Patterning exposure is performed using an appropriate exposure light source, the resist film in the exposed area is dissolved and removed by development, and finally, post-baking is performed to improve the adhesion between the substrate and the remaining resist film. By the way, although the final post-bake step is effective for improving the adhesion between the substrate and the resist film as described above, it also strengthens the resist itself, that is, improves the heat resistance and etching resistance of the resist at the same time. Although it has some effect, it is not sufficient. Therefore, for example, when this conventional method is used for etching aluminum wiring, the performance of the formed resist mask is insufficient, and as a result, satisfactory processing accuracy cannot be expected. . OBJECTS OF THE INVENTION It is an object of the present invention to provide a method for forming a resist pattern in which the resulting patterned resist exhibits both excellent heat resistance and etching resistance. Structure of the Invention The present inventor has conducted extensive research to find a new processing process that can replace the post-bake process after patterning exposure and development of a resist-coated semiconductor substrate. However, even if ultraviolet curing is applied instead of post-bake, post-bake and ultraviolet curing, or ultraviolet curing and post-bake are performed sequentially, the three treatments of post-bake, ultraviolet curing and post-bake are combined. Even though
It was not possible to achieve satisfactory heat resistance and etching resistance. However, surprisingly, when post-baking is performed by heating at 140°C or lower under irradiation with far ultraviolet light, that is, when both are performed simultaneously, the heat resistance and etching resistance are improved. It has been found that this can be significantly improved. As used herein, "deep ultraviolet light" refers to light whose main spectral energy peak is within the wavelength range of about 200 to 360 nm. That is, advantageous results can be obtained when post-baking is performed under irradiation with light having such a wavelength, particularly light having a wavelength of approximately 253.7 nm. If the wavelength of the light is below the lower limit of the above range, it is undesirable as ozone may be generated and affect the resist.On the other hand, if the wavelength of the light is above the upper limit of the above range, the surface of the resist film may be damaged. This is not preferable because it may have an adverse effect on the resist pattern, such as the formation of wrinkles. The light source for this far ultraviolet light irradiation includes light sources commonly used in this technical field,
For example, a high pressure mercury lamp, a low pressure mercury lamp, a xenon-mercury lamp, etc. can be used. In the method of the present invention, at a temperature of about 80 to 140°C, about 20 to
Post-bake can be advantageously performed for 100 seconds. Of course, you can arbitrarily select the baking temperature and time within the above range.
Furthermore, it is also possible to select a temperature and time outside the above range as necessary. A heating means such as an oven or a hot plate can be used for post-baking. Although the formation of a resist pattern according to the present invention was briefly explained above, it can be carried out, for example, by the following procedure. Although we will discuss the use of positive-tone resists here, it should be understood that negative-tone resists may also be used if desired: First, the selected positive-tone photoresist is dissolved in a suitable solvent. A solution is obtained, for example an MCA (methyl cellosolve acetate) solution. Next, this resist solution is applied to the substrate to be etched by dipping or spin coating. After coating is completed, the resist is prebaked in an oven or the like to completely remove the solvent in the resist film. After prebaking, the resist is patterned and exposed using an appropriate exposure method using exposure radiant energy beams such as X-rays and electron beams. After exposure, development is performed using the previously used developer such as MCA, and the resist film in the exposed area is dissolved and removed. Following development, a post-bake step of the present invention is performed to strengthen the resist. For example, 253.7n from a low pressure mercury lamp
The resist is post-baked on a hot plate at about 120° C. for about 60 seconds under irradiation with deep ultraviolet light having a wavelength of m. The resist pattern obtained through this series of processes is positive and has excellent resolution as well as heat resistance and etching resistance. Examples of the Invention In order to confirm the effect of post-baking under deep ultraviolet light irradiation according to the present invention, comparative experiments were conducted under various conditions as listed below: (i) Control (post-development treatment) None) (ii) Post-bake 120℃, 60 seconds) (iii) Ultraviolet curing (UV cure) (200-360nm, mainly 253.7nm, 60 seconds) (iv) Post-bake (120℃, 60 seconds) +UV cure ( 200-360nm, mainly 253.7nm,
(v) UV cure (200-360nm, 60 seconds) + post-bake (120℃, 60 seconds) (vi) Post-bake (120℃, 60 seconds) + UV cure (200-360nm, 60 seconds) + post Bake (120℃, 60 seconds) (vii) Invention (200-360nm, mainly 253.7nm, 120
℃, 60 seconds) The series of steps from resist coating to development that were carried out prior to these treatments will be explained as follows.
It is as follows: Positive resist: OFPR-800 manufactured by Tokyo Ohka Co., Ltd. (Mw
A 27.4% solution of 1.0 μm in thickness was prepared and spin-coated to a thickness of 1.1 μm on a silicon substrate having an aluminum wiring layer (1.0 μm in thickness). After prebaking this resist-coated substrate at 110° C. for 7 minutes in a nitrogen atmosphere, patterning exposure was performed using a high-pressure mercury lamp with a peak wavelength of 360 nm as an exposure light source. Thereafter, development was carried out using TMK-12 as a developer to dissolve and remove the resist film in the unexposed area. A positive resist pattern having a cross-sectional shape as shown in the attached FIG. 5a was obtained (in the figure, 1 is a silicon substrate, 2 is an aluminum layer, and 3 is a resist film). Each resist pattern obtained after the six types of experiments described above was evaluated for heat resistance and etching resistance. The following results were obtained (we were able to summarize the evaluation of heat resistance and etching resistance using one standard as described below, so we will list them here in 6 stages in the "Effect" column): Treatment Condition effects (i) Control (no treatment) 0 (ii) Post-bake 0 (iii) UV cure 1 (iv) Post-bake + UV cure 2 (v) UV cure + post-bake 2 (vi) Post-bake + UV cure + post Bake 4 (vii) The present invention (Deep UV cure/post bake)
5 Evaluation of effects: 5...Excellent, 4...Good, 3...Fair, 2...Difficult, 1...Unsatisfactory, 0...Not eligible for evaluation (significant sagging) As is clear from the above results, according to the present invention, special Excellent heat resistance/etching resistance can be obtained without any complicated treatment. In the method of the comparative example, an acceptable effect of 4 can only be achieved by repeating post-bake, UV cure and post-bake. Additionally, the method of the invention described above was repeated using various bake temperatures and times. The following results were obtained.

[Table] When a high baking temperature was applied, the resist film sagged and no good results were obtained. Furthermore, for comparison, at room temperature (20℃)
DeepUV cure was performed. As shown below,
Effect equivalent to the present invention: 5 was obtained only after a long period of time (120 seconds) had passed:

[Table] Evaluation Criteria for Effects In evaluating the effects as described above, the following evaluation criteria were established: As described above, the series of steps from resist coating to development is completed. As described above, the profile of the resist film immediately after development is approximately as shown in FIG. 5a. This resist film is 170
When heated at ℃, the profile changes in various ways depending on the length of heating time. For example, Figure 4a
As shown in FIG. 1A, the edges of the resist film 3 are slightly rounded, and as shown in FIG. Various profiles can be obtained, including ones that cannot be evaluated. Furthermore, when reactive ion etching is performed using these resist films as masks, profiles as shown in FIGS. 1b to 5b are obtained, respectively. Combining these results, a rating of 1 (unsatisfactory) is given to those that produce profiles such as those shown in Figure 1 a and b, a rating of 2 (difficult) is given to those that produce profiles such as those shown in Figure 2 a and b, and a rating of 2 (difficult) is given to those that produce profiles such as those shown in Figure 2 a and b. 3 for those that produce profiles such as a and b
(Acceptable), 4 (Good) for the profile shown in Figure 4 a, b, 5 (Excellent) for the profile shown in Figure 5 a, b, and 5 (Excellent) for the profile shown in Figure 5 a, b. Those for which the isle could not be determined were given a rating of 0 (not subject to evaluation). Effects of the Invention According to the present invention, a resist pattern with excellent heat resistance and etching resistance can be obtained without any complicated steps and without taking a long time.

[Brief explanation of the drawing]

Figure 1 a, b; Figure 2 a, b; Figure 3 a, b;
Figure 4 a, b; and Figure 5 a, b are, respectively,
This figure shows evaluation criteria for heat resistance and etching resistance, which are the issues of the present invention. In the figure, 1 is the substrate, 2 is the aluminum layer, 2' is the aluminum layer after etching, and 3 is the resist film.

Claims (1)

[Claims] 1. A resist-coated semiconductor substrate after patterning exposure and development is irradiated with deep ultraviolet light,
A method for forming a resist pattern, characterized by post-baking by heating at 140°C or lower. 2. The method according to claim 1, wherein the deep ultraviolet light has its main spectral energy peak within a wavelength range of 200 to 360 nm. 3. The method of claim 2, wherein the deep ultraviolet light has its main spectral energy peak at a wavelength of 253.7 nm. 4. Post-bake at a temperature of about 80 to 140°C.
A method according to claim 1, which is carried out for a period of 20 to 100 seconds.