JPH1097975A - Formation of pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a resist pattern used for forming an element having a worked part which is smaller in size than the minimum beam diameter of an aligner on a substrate. SOLUTION: A positive resist is applied to the surface of a silicon wafer 21 and baked in a resist applying process. A pattern 22 (namely, the area other than the part corresponding to an element) is plotted with an exposure of 50μC/cm<2> by using an electron beam lithography system in a first exposing process and a first developing process. Then a first resist pattern 21R is formed by developing the resist with xylene for 120 seconds and removing the resist from the pattern 22. In a second exposing process and a second developing process, two linear patterns 23 are plotted with the same exposure as that in the first exposing process. After the patterns 23, a second resist pattern 21RA having a minimum worked part 21a which is smaller in size than the diameter of the electron beam is obtained by developing the patterns 23 for 20 seconds which is shorter than the first developing process and removing the resist from the patterns 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for manufacturing a semiconductor device such as an LSI (Large Scale Integrated Circuit), for forming an element having a processed portion smaller than a minimum beam diameter of an exposure apparatus on a substrate. The present invention relates to a pattern forming method for forming a resist pattern.

[0002]

2. Description of the Related Art Conventionally, techniques in such a field include:
For example, there is one described in the following literature. Literature; Electron, Ion and Photon Beam Technology and
Nanofabrication (1995), Effendi Leobandung, Lingjie
Guo, Yun Wang and Stephen Y. Chou, “77 K Silicon
Quantum-Dot Transistors ”, pp. 333-334.
Prototyping of devices with the following gate lengths is also in progress. Also, devices with a gate length of about 0.01 μm have been studied for the purpose of lower power consumption and higher speed. Further, research on a single-electron transistor (Single Electron Transistor, hereinafter referred to as SET) utilizing the movement of one electron is being advanced as its ultimate form. Electron beam drawing is mainly used as a means for patterning these on a substrate.

FIG. 2 is a structural view of the SET described in the above-mentioned document. In FIG. 2, SIOMX (Separation by Impl
anted Oxygen) The structure of the SET using the substrate 1 is shown. FIG. 3 is a view showing a resist pattern used for forming the SET of FIG. In FIG. 3, a constriction 11 is formed in order to form the island pattern 2 at the center of the SET of FIG. Using the resist pattern as a mask, the Si layer 3 on the SIMOX substrate 1 is etched and then oxidized to electrically separate the island pattern 2 from the substrate 1b with a Si oxide film 1a. By properly forming the Si oxide film 1a, a tunnel oxide film can be obtained.
Such a resist pattern can be formed relatively favorably by electron beam lithography by using a positive resist.

[0004]

However, the electron beam drawing used for forming the resist pattern shown in FIG.
There were the following issues. That is, even if electron beam lithography is used, the contrast of the island pattern 2 is small because the size of the island pattern 2 to be manufactured is close to the electron beam diameter (expansion of the electron beam). Therefore, the shape of the constriction 11 cannot be controlled well, and there is a problem that a tunnel junction having a small capacity (that is, short) cannot be formed.

[0005]

According to a first aspect of the present invention, a resist pattern for forming an element on a substrate by using an exposure apparatus is formed on the substrate. In the pattern forming method, the following steps are performed. That is, a resist coating step of coating a positive resist on the substrate, a first exposure step of exposing a region of the positive resist other than a portion corresponding to the element, and exposure in the first exposure step A first developing step of developing and removing the portion to form a first resist pattern; a second exposing step of exposing a minimum processed portion of the first resist pattern;
Developing and removing the exposed portion in the exposing step, leaving a second resist pattern on the substrate for forming an element having a processed portion smaller than the minimum beam diameter of the exposure apparatus on the substrate. And the developing process of (1).

In the second invention, the first and second exposure steps of the first invention are performed with the same amount of exposure, and the second development step is performed in a shorter time than the first development step. I have to. According to the first and second inventions, since the pattern forming method is configured as described above, the minimum processing portion is exposed in the second exposure step, and thereafter, the second exposure step is performed in the second development step. Is developed in a shorter time than in the first developing step. Therefore, the minimum processing portion is smaller than the beam diameter of the exposure apparatus. In the third invention, the second exposure step of the first invention is performed with an exposure amount equal to or more than the exposure amount in the first exposure step, and the second development step is performed by using a developer used in the first development step. Also, development is performed using a developing solution having a low developing speed. According to the first and third aspects, the minimum processing portion is exposed in the second exposure step, and then, in the second development step, the first exposed portion is exposed to the portion exposed in the second exposure step. Development is performed using a developing solution having a lower dissolution rate than the process. Therefore, the minimum processing portion is smaller than the beam diameter of the exposure apparatus. Therefore, the above problem can be solved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment FIGS. 1A to 1C are process diagrams of a pattern forming method showing an embodiment of the present invention. Hereinafter, the pattern forming steps (1) to (3) of the first embodiment will be described with reference to FIGS. 1 (a) to 1 (c). (1) Resist Coating Step A positive resist (for example, ZEP520 (Zeon)) is applied to a thickness of 70 nm on the silicon wafer 21 on which the alignment mark for electron beam drawing is formed, and baked on a hot plate at 200 ° C. for 2 minutes. . (2) First exposure step and first development step (FIG. 1)
Step (a)) Using an electron beam lithography machine (for example, HL-700F2 manufactured by Hitachi, Ltd.), align an alignment mark (not shown) in FIG.
A pattern 22 (that is, a region other than the portion corresponding to the element) as shown in FIG.
Draw with ² . Thereafter, the resist of the pattern 22 is removed by developing with xylene for 120 seconds, thereby forming a first resist pattern 21R.

(3) Second Exposure Step and Second Development Step (Step in FIG. 1B) Alignment is again performed so as to overlap the pattern 22.
The two line patterns 23 are exposed at the same exposure amount as in the first exposure step.
Drawing is performed at 50 μC / cm ² . Thereafter, the same xylene as used in the first development step is used to reduce the length of the first development step.
s for development to remove the resist of the pattern 23, and FIG.
A second resist pattern 21RA having a minimum processed portion 21a having an electron beam diameter or less as shown in FIG. FIG. 4 is a diagram showing the dependence of the dissolution rate of the ZEP resist on the exposure dose. The vertical axis represents the dissolution rate, and the horizontal axis represents the exposure dose. The reason why a pattern smaller than the electron beam diameter shown in FIG. 1C is obtained will be described with reference to FIG.

FIG. 4 shows that in the region where the exposure amount is 35 μC / cm ² or less, the change in the dissolution rate with respect to the change in the exposure amount is large in the region where the exposure amount is 35 μC / cm ² or less. The intensity of the electron beam is spread in a normal distribution, with the intensity being strong at the center and becoming weaker toward the periphery. When the development dissolution characteristics shown in FIG. 4 are used, even if the dissolution rate is increased at the center of the electron beam, it can be suppressed at the periphery of the electron beam, so that high-contrast development can be performed. When forming a constricted pattern, the constricted part is only slightly dissolved, so when exposing and developing simultaneously with other patterns, all must be exposed at a low dissolution rate exposure, The development contrast decreases. On the other hand, in the present embodiment, since development is performed in a short time so as to form only a constricted pattern, exposure can be performed with a high exposure amount, and development with high contrast is performed. Therefore, a stable pattern can be formed. In the second development, since the surface at the start of the development of the constricted portion becomes the side wall of the thin line portion, the reduction in the thickness of the resist in the constricted portion can be reduced, thereby stabilizing the pattern formation. Since this method can be performed with the same developing solution, there is no need to add a new developing line. As described above, in the first embodiment, the constricted portion is drawn by the second exposure, and then the development is performed in a shorter time than the first development. A pattern smaller than the electron beam diameter which cannot be obtained by development can be stably obtained.

[0010] The pattern forming method of the second embodiment the second embodiment (1) to (3),
Description will be made with reference to FIGS. 1A to 1C as in the first embodiment. The pattern forming method of the present embodiment differs from the first embodiment in the following points. That is, in the second exposure step (the step of FIG. 1B), the two line patterns 23 are exposed at an exposure amount equal to or more than the first exposure (for example, 80 μm).
C / cm ² ) for 20 s using a developer (eg, n-hexyl acetate) having a lower dissolution rate than the first development.
The second resist pattern 2 which has been developed and has a minimum processed portion 21a having an electron beam diameter or less as shown in FIG.
Get 1 RA. FIG. 5 is a diagram showing the dependence of the dissolution rate of xylene and n-hexyl acetate in the ZEP resist on the exposure dose. The vertical axis represents the dissolution rate, and the horizontal axis represents the exposure dose.

In FIG. 5, the exposure amount is 40 μC / cm ^2.
Comparing the dissolution rates of the two types of developers, it is shown that xylene is at least 10 times greater than n-hexyl acetate. When the first exposure is performed at about 50 μC / cm ² , the thin line portion is exposed to about 35 μC / cm ² due to the influence of the first exposure, but the development is slow in the second development. Since it hardly dissolves in the second pattern, the effect of the first exposure is ignored, and the second pattern formation can be performed. In this case, although the number of types of the developer increases as compared with the first embodiment, the pattern becomes complicated, but a pattern with higher contrast can be formed. As described above, in the second embodiment,
Draw the constricted part with the second exposure, and then
By performing development using a developing solution having a lower dissolution rate than the first development, a pattern smaller than the electron beam diameter, which cannot be obtained by one exposure and development, can be stably obtained. In the embodiment, the pattern formation using an electron beam has been described. However, this method uses another exposure light source, for example, an electromagnetic wave such as visible light, ultraviolet light, deep ultraviolet light, X-ray, or an ion beam. May be.

[0012]

As described above in detail, according to the first and second aspects, the minimum processing portion is exposed in the second exposure step, and thereafter, the second exposure step is performed in the second development step. Since the exposed portion in the process is developed for a shorter time than the first developing process, it is possible to stably obtain a pattern smaller than the beam diameter of the exposure apparatus, which cannot be obtained by a single exposure and development. Can be. According to the first and third aspects, the minimum processed portion is exposed in the second exposure step, and then, in the second development step, the first exposure step is performed on the portion exposed in the second exposure step. Since the development is performed using a developing solution having a lower dissolution rate, a pattern smaller than the beam diameter of the exposure apparatus, which cannot be obtained by a single exposure and development, can be stably obtained. According to the fourth aspect, when an electron beam is used as the exposure source of the exposure apparatus, the required processing dimension may be equal to or smaller than the electron beam diameter. The formation method is particularly effective. According to the fifth invention, the exposure source of the exposure apparatus is provided with a deep ultraviolet light, an X-ray, an ion beam, or a wavelength of 150 nm to 450 nm.
required when the minimum beam diameter of the exposure apparatus is 0.61 * λ / NA when the numerical aperture of the exposure apparatus is NA and the exposure wavelength is λ, using light in the ultraviolet and visible regions of m 2. The processing dimension may be equal to or smaller than the minimum beam diameter. In such a case, the pattern forming method of the present invention is effective similarly to the fourth invention.

[Brief description of the drawings]

FIG. 1 is a process chart of a pattern forming method showing an embodiment of the present invention.

FIG. 2 is a structural diagram of a SET.

FIG. 3 is a view showing a resist pattern for forming the SET of FIG. 2;

FIG. 4 is a diagram showing the dependence of the dissolution rate of a ZEP resist on the exposure dose.

FIG. 5 is a graph showing the exposure dose dependence of the dissolution rates of xylene and n-hexyl acetate.

[Explanation of symbols]

Reference Signs List 21 silicon wafer (substrate) 21R first resist pattern 21a minimum processing part 21RA second resist pattern 22 pattern (area other than part corresponding to element)

Claims (5)

[Claims] 1. A pattern forming method for forming a resist pattern for forming an element on a substrate using an exposure apparatus, the resist applying step of applying a positive resist on the substrate; A first exposing step of exposing a region other than the part corresponding to the element, and developing and removing the exposed part in the first exposing step;
A first developing step of forming a first resist pattern; a second exposing step of exposing a minimum processed portion of the first resist pattern; and a developing step of exposing the portion exposed in the second exposing step. Remove
A second developing step of leaving, on the substrate, a second resist pattern for forming, on the substrate, an element having a processed portion smaller than the minimum beam diameter of the exposure apparatus. Method. 2. The method according to claim 1, wherein the first and second exposure steps are performed with the same exposure amount, and the second development step is performed in a shorter time than the first development step. 2. The pattern forming method according to 1. 3. The second exposure step is performed with an exposure amount that is equal to or greater than the exposure amount in the first exposure step, and the second development step is performed with a developer that is more developed than the developer used in the first development step. 2. The pattern forming method according to claim 1, wherein the development is performed using a developing solution having a low speed. 4. The pattern forming method according to claim 1, wherein the exposure source of the exposure apparatus is an electron beam. 5. An exposure apparatus according to claim 1, wherein the exposure source is a deep ultraviolet light,
Ray, ion beam, or light in the ultraviolet and visible regions having a wavelength of 150 nm to 450 nm. In this case, when the numerical aperture of the exposure apparatus is NA and the exposure wavelength is λ, the minimum beam diameter of the exposure apparatus is 0. 4. The pattern forming method according to claim 1, wherein the ratio is 61 * λ / NA.