JPH0789532B2 - Electronic beam exposure method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raster scan type electron beam exposure method, and more particularly to an electron beam exposure method for reducing the XY dimension difference of a resist pattern.

[Technical background of the invention and its problems]

In recent years, various electron beam exposure apparatuses have been proposed as a method for forming a fine resist pattern on a sample such as a semiconductor wafer or a mask substrate. The beam scanning method of these devices can be roughly classified into a raft scanning method and a vector scanning method. Generally, the raster scan method is widely used, but in this method, X
Since there is a difference in the total energy received by the resist in the Y direction and the Y direction, there is a problem in forming a precise pattern.

The above problem will be described with reference to FIGS. 7 and 8. 7th
The figure is a schematic diagram showing a beam shape 71 and a beam intensity distribution 72. FIG. 8 is a schematic diagram showing resist pattern profiles in the X and Y directions when a rectangular pattern is exposed by the beam. Reference numeral 81 in the drawing denotes a circular beam, and the rectangular pattern is exposed by scanning the beam in the Y direction while continuously moving the sample in the X direction. That is, the exposure is performed by a so-called raster scan method in which the beam is scanned from end to end within the beam scanning range and the beam is irradiated at the pattern portion. Reference numeral 82 denotes a beam distribution in the X direction (sub scanning direction) when the beam 81 is scanned. Since the total energy received by the resist is large, a steep beam distribution can be obtained. Reference numeral 83 indicates a beam distribution in the Y direction (main scanning direction). Since the total energy received by the resist is smaller in the Y direction than in the X direction, the beam distribution becomes gentle. 84 indicates the development level. 85 is a resist cross-sectional profile in the X direction,
86 is a resist cross-sectional profile in the Y direction.

As described above, when exposure is performed with a raster scan method using a Gaussian beam, the beam distribution in the X direction is steep, while the beam distribution in the Y direction has a gentle slope, so that the Y direction has a gentler slope. Develops slowly, this is X
-Y dimensions how difference had appeared as (x ₀ -y _0). Furthermore, the cross-sectional shape of the resist pattern was also formed to be more inclined in the Y direction than in the X direction.

For these reasons, comparing the line widths of the X-direction pattern orthogonal to the beam scanning direction and the Y-direction pattern parallel to the beam scanning direction, the X-direction pattern is the Y-direction pattern. There is a problem that the line width becomes narrower than that of.

[Object of the Invention]

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to make it possible to make an XY dimensional difference of a line width of a resist pattern extremely small, which can contribute to improvement of pattern processing accuracy. An object is to provide an electron beam exposure method.

[Outline of Invention]

The essence of the present invention is to make the energy distribution steep and make X, Y
The purpose is to eliminate the anisotropic difference in the dose distribution in the direction and reduce the dimensional difference in the line width due to the directionality of the pattern.

That is, the present invention is an electron beam exposure method for exposing a desired pattern on a sample by scanning an electron beam in a raster scan system, exposing the pattern by exposing the pattern by scanning the beam in one direction, After or at the same time, the beam is scanned so that the beam scanning direction with respect to the sample becomes a direction orthogonal to that in the first exposure step, and the same pattern as the above pattern is exposed.

〔The invention's effect〕

According to the present invention, by performing two exposures in which the beam traveling directions with respect to the sample are orthogonal to each other, X, Y
It is possible to make the beam dose distribution in the directions close to the same profile. Therefore, the dimensional difference of the line width due to the directionality of the pattern can be made extremely small, and the pattern processing accuracy can be improved. Further, there is an advantage that the beam irradiation amount can be doubled and the developing time can be shortened.

Example of Invention

First, before describing the embodiments, the basic principle of the present invention will be described.

As shown in FIG. 1A, a pattern 12 parallel to the Y direction and a pattern 13 parallel to the X direction are exposed on a sample 11 by raster scanning (first exposure). At this time, the scanning direction of the beam 14 is the Y direction. Then, as shown in FIG. 1B, the scanning direction of the beam 14 is set to a direction orthogonal to the case of FIG. 1A, and the patterns 12 and 13 are exposed again by raster scanning (second exposure). ).

Here, in the case where the second exposure is not performed, that is, the same method as the conventional method, the resist pattern profile (cross section in the line width direction of the line-shaped pattern) in the patterns 12 and 13 is shown in FIGS. This is the same as described with reference to FIG. In FIG. 2, 21 is a circular beam, 22 is the beam distribution in the X direction (sub scanning direction) of the Y direction pattern 12 (total beam intensity distribution), and 23 is the Y direction of the X direction pattern 13 (main scanning direction). ) Beam distribution, 24 is the development level, 25 is the X-direction resist cross-sectional profile of the Y-direction pattern 12, and 26 is the Y-direction of the X-direction pattern 13.
The resist cross-sectional profile in the direction is shown. As can be seen from this figure, the line width y ₀ of the X-direction pattern 13 is smaller than the line width x ₀ of the Y-direction pattern 12.

On the other hand, when the second exposure is performed in addition to the first exposure, the resist pattern profile becomes as shown in FIGS. 3 (a) and 3 (b). That is, the beam scanning direction is made orthogonal to the second
By performing the above exposure, the beam distribution 35 in the X direction of the Y direction pattern 12 becomes the beam distribution 22 plus the beam distribution 33. Therefore, the resist cross-sectional profile of the Y-direction pattern 12 in the X-direction becomes steep, and the line width x ₁ becomes 2Δx longer than that of the conventional x ₀ . Furthermore, the beam distribution 36 in the Y direction of the X direction pattern 13 is the beam distribution 23 plus the beam distribution 34, and the Y direction resist cross-sectional profile of the X direction pattern 13 is also steep,
The line width y ₁ becomes 2Δy (Δy> Δx) longer than the conventional line width y ₀ . Therefore, the XY dimension difference is improved, and the pattern processing accuracy can be improved.

The beam distributions 22 and 34 are characteristics when the beam scanning directions with respect to the sample are the same, and these are substantially the same. Further, the beam distributions 23 and 33 are also characteristics when the beam scanning directions with respect to the sample are the same, and these are substantially the same. Therefore, the beam distribution 35 including the beam distributions 22 and 23 and the beam distribution 3 including the beam distributions 23 and 34
6 is almost equal.

Hereinafter, an example method of the present invention will be described.

FIGS. 4 (a) to 4 (d) are schematic views for explaining the method of the embodiment. First, as shown in the sectional view of FIG.
A resist 42 made of PMMA (polymethylmethacrylate) was applied on a Si substrate 41 to a thickness of 1 [μm].

Then, the acceleration voltage of the electron beam was set to 50 [KV], and a line and space of 0.5 [μm] was exposed by the raster scan method as shown in the plan view of FIG. 4B (first exposure step). As for the line and space patterns 43 and 44, the beam is moved to the Y direction while continuously moving the sample in the X direction.
By scanning in the direction, the one 43 parallel to the X direction and the one 44 parallel to the Y direction were exposed.

Then, the sample was rotated 90 ° as shown in the plan view of FIG. 4 (c), and then the patterns 43 and 44 were exposed by raster scan under the same conditions as in the first exposure step (second exposure step). . At this time, the scanning direction of the beam is the same as the Y direction, but the pattern 43 parallel to the X direction is parallel to the Y direction, and the pattern 44 parallel to the Y direction is parallel to the X direction. . That is, in the second exposure step, the beam scanning direction for the sample is orthogonal to that in the first exposure step.

After that, IAA (isoamyl acetate) was used as a developing solution to form a resist pattern as shown in the sectional view of FIG. 4 (d). Here, S indicates the size of the resist 42 to be removed.

FIG. 5 shows the difference in line width between the resist patterns in the X and Y directions formed by the above method. Here, the X-direction pattern is a resist pattern corresponding to the pattern 43, and the Y-direction pattern is a resist pattern corresponding to the pattern 44. FIG. 6 shows the irradiation dose of the exposed portion where the residual film ratio becomes zero when the resist is developed until the residual film ratio in the unexposed portion becomes 80%. When the beam irradiation amount in the first exposure step is 25 [μc / cm ² ] and the beam irradiation amount in the second exposure orthogonal to it is 25 [μc / cm ² ], the total irradiation amount is 50 [ μc / cm ² ]. In that case, the line width of the X-direction pattern is -0.02 [μm] compared to the line width of the Y-direction pattern, that is, -4 for the design pattern.
[%]Met.

The total irradiation dose is 100 when the beam irradiation doses in the first and second exposure steps are 50 [μc / cm ² ].
[Μc / cm ² ]. In that case, the X-direction pattern was +0.02 [μm] compared to the Y-direction pattern, that is, +4 [%] with respect to the design pattern. Further, the total irradiation dose is 150 [μc / cm ² ] when the beam irradiation doses in the first and second exposure steps are 75 [μc / cm ² ] respectively. In that case, the difference between the line width of the Y-direction pattern and the line width of the X-direction pattern was zero, that is, it was formed according to the design pattern size.

When the resist pattern is exposed by the raster scan method as described above, the conventional exposure step (first exposure step) and the second exposure step in which the beam scanning direction of the sample is orthogonal to the exposure step X by combining
The beam distributions in the line width direction of the patterns in the Y direction and the Y direction can be made substantially equal. Therefore, the dimension difference of the line width of the resist pattern finally formed, that is, the XY dimension difference can be made extremely small, and the pattern processing accuracy can be greatly improved.

The present invention is not limited to the above embodiment. For example, the resist is not limited to the positive type, but may be the negative type. Further, the resist material, the type of the developing solution, and the like can be appropriately changed according to the specifications. Further, the present invention is not limited to the Gaussian beam, but can be applied to a shaped beam. Further, the sample is not limited to the so-called hybrid raster scan method in which the electron beam is scanned in a direction orthogonal to this while moving in one direction, and the beam scanning range is scanned from end to end to irradiate the beam at a point with a pattern. Any raster scan method can be applied.

Further, instead of rotating the sample in the first and second exposure steps, the beam scanning direction itself may be changed to the orthogonal direction. Further, the order of the first and second exposure steps may be first. It is also possible to perform the first and second exposure steps simultaneously by using two electron beam exposure apparatuses. In addition, various modifications can be made without departing from the scope of the present invention.

[Brief description of drawings]

1 to 3 are each for explaining the basic principle of the present invention. FIG. 1 is a schematic diagram showing a pattern to be exposed and a beam scanning direction, and FIG. 2 is only the first exposure step. FIG. 4 is a schematic diagram showing resist pattern profiles in the X and Y directions in the case of exposure, and FIG. 3 is a schematic diagram showing resist pattern profiles in the X and Y directions when the first and second exposure steps are performed. 6 to 6 are for explaining a resist pattern forming method according to an embodiment of the present invention. FIG. 4 is a process chart, and FIG. 5 is a characteristic showing an XY dimensional difference with respect to a beam irradiation amount. Figure, 6th
FIG. 7 is a characteristic diagram showing the residual film ratio with respect to the beam irradiation amount. FIGS. 7 and 8 are for explaining the conventional problems, respectively. FIG. 7 is a schematic diagram showing the shape and beam intensity distribution of the Gaussian beam. FIG. 8 is a schematic diagram showing a resist pattern profile in the X direction and the Y direction when a rectangular pattern is exposed with an optimum irradiation amount. 11 …… Sample, 12,44 …… Y direction pattern, 13,43 …… X direction pattern, 14,21 …… Electron beam, 22 …… X direction beam distribution by first exposure, 23 …… First pattern Y direction beam distribution by exposure, 24 ... Development level, 33 ... X direction beam distribution by second exposure, 34 ... Y direction beam distribution by second exposure, 35 ... First and second exposure X-direction beam distribution, 36 ... Y-direction beam distribution by the first and second exposures, 41 ... Si substrate, 42 ... resist.

Claims (3)

[Claims] 1. An electron beam exposure method of exposing a desired pattern on a sample by scanning an electron beam in a raster scan system, comprising a first exposure step of scanning the beam in one direction to expose the pattern. A second exposure step of exposing the same pattern as the pattern by scanning the beam so that a beam scanning direction of the sample is a direction orthogonal to the first exposure step. Beam exposure method. 2. The electron beam exposure method according to claim 1, wherein the sample is rotated by 90 ° between the first exposure step and the second exposure step. 3. The beam scanning direction in the first exposure step and the beam scanning direction in the second exposure step are in a relationship orthogonal to each other. Electron beam exposure method.