JP3050178B2 - Exposure method and exposure mask - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for exposing a mask pattern on a semiconductor substrate and an exposure mask, and more particularly, to a first exposure using a first mask and a second exposure using a first mask to form a desired pattern. An exposure method including a step of performing a second exposure using the mask and the mask.

[0002]

2. Description of the Related Art In recent years, the miniaturization of semiconductor integrated circuits is remarkable, and the minimum pattern size is 0.30 μm in mass production level.
At the research and development level, it has reached about 0.18 μm. These patterns are formed mainly by ultraviolet light (g-line; 436n
m and i rays; 365 nm) and far ultraviolet light (KrF excimer laser; 248 nm; ArF excimer laser; 193)
nm) as a light source.

[0003] In light exposure, it is generally well known that the depth of focus (DOF) at the time of pattern transfer decreases with miniaturization. The DOF strongly depends on the pattern shape. Even if the line patterns have the same line width, the dimensions of the line portion and the space portion are equal, so-called 1: 1L.
& S (L ine and S pace ; hereinafter L & called S) there is no pattern in the adjacent regions with the value of the DOF so-called isolated lines are significantly different. As an example, FIG. 6 shows a change in the pattern dimension with respect to the L & S of 0.25 μm and the defocus of the isolated line. For exposure, Kr
An F excimer stepper and a positive chemically amplified resist are used, and the optical conditions are a numerical aperture (NA) = 0.50 and a coherence factor (σ) = 0.7. If DOF is defined as a focal range in which a dimensional variation is within ± 10% with respect to a design dimension, it is 1.30 μm for L & S and 0.80 μm for an isolated line.

[0004] The isolated line pattern is a pattern frequently used in a gate process of a logic device such as a gate array, and requires strict processing accuracy. In recent years, resolution and D
The development of super-resolution techniques for improving OF has been active, and some super-resolution techniques such as annular illumination and a halftone phase shift mask have begun to be applied to production. For the isolated line pattern, an auxiliary pattern method and a double exposure method have been devised, which will be described below.

In the auxiliary pattern method, a fine line pattern is arranged (on a reticle) so as not to be resolved on both sides or one side of an isolated line, and the DOF is provided by giving a periodicity.
(Matsuo et al., "K using super-resolution"
rF Excimer Laser Lithography ", Spring Federation of Applied Physics, 1993, P567). DOF is improved, but narrower and less than that of L & S.

In the double exposure method, as shown in FIG. 2, L & S is exposed in the first exposure, and unnecessary lines are exposed and removed in the second exposure, and a DOF equivalent to L & S is obtained in principle. Can be The idea of dividing the exposure into two parts and removing unnecessary patterns in the second exposure is described in, for example, Japanese Patent Application Laid-Open No. 5-72717.
Issue.

[0007]

However, even with the above-mentioned auxiliary pattern method and double exposure method, 0.25 μm is required.
There is a problem that the DOF is insufficient for a fine isolated line pattern of m or less.

The reason for this is that the DOF itself has become narrower due to miniaturization, and a super-resolution technique for providing a DOF equal to or greater than L & S has not been developed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an exposure method and an exposure mask for enlarging the DOF of a line pattern, especially a so-called isolated line pattern having no pattern adjacent to the pattern.

[0010]

To achieve the above object, an exposure method according to the present invention is an exposure method having a first mask pattern exposure step and a second mask pattern exposure step, The first mask pattern exposure step is a step of exposing a first mask pattern including a pattern having periodicity to the photosensitive organic film formed on the semiconductor substrate, and the second mask pattern exposure step is performed. The step is a step performed subsequent to the first mask pattern exposure step, and is a step of exposing a second mask pattern including a periodic pattern having a period different from the periodic pattern. The ratio between the line portion and the space portion of the periodic pattern included in the first mask pattern is set in a range from 1: 1.1 to 1: 1.4.

An exposure mask according to the present invention is an exposure mask including a periodic pattern used in an exposure method performed in two stages, wherein the exposure method includes a step of exposing a first mask pattern. And a step of exposing the second mask pattern subsequent to the exposure using the first mask pattern, wherein the ratio of the line portion to the space portion of the periodic pattern is from 1: 1.1. 1: Include patterns that are in the range of 1.4.

The ratio between the line and space dimensions of the periodic pattern is preferably set to 1: 1.2.

The periodic pattern is included in a first mask pattern.

Assuming that the size of the line portion of the exposure mask is L and the size of the space portion is S, the pitch P of the repetitive pattern is
Becomes P = L + S. FIG. 7 shows the DOF when L is fixed and S is gradually increased from L = S (the same applies to P). L is 0.25 μm. A positive type chemically amplified resist was used as a resist, and NA = 0.5 as an optical condition.
0, σ = 0.7, NA = 0.50, σout =
The case of 0.7 / σin = 0.42 (zonal illumination) is shown. The definition of DOF is that the dimension is designed value ± 10%
Focus area.

As shown in FIG. 7, as the space width increases, the DOF increases and then decreases. DOF
Showed the maximum value when the space width was between 0.30 and 0.325 μm. This corresponds to S between 1.2L and 1.3L.

The reason is considered as follows. The DOF of the isolated pattern is smaller than that of the periodic pattern. This is because the periodic pattern is formed by interference of three light beams (normal illumination) and two light beams (ring zone illumination), as described in, for example, “Ultra-fine processing technology, edited by the Japan Society of Applied Physics, Ohmsha, p. On the other hand, in the case of an isolated pattern, a continuous pattern appears on the pupil plane, and interference is unlikely to occur. In FIG. 7, the space width is 0.35 μm.
This is why the DOF is reduced in the region of m or more. This is generally true in optical lithography.

On the other hand, the DOF increased in the region where the space width was slightly wider than the line width, because the pitch increased,
That is, the pattern size has increased. When the pattern size increases, the diffraction angle of the ± 1st-order light decreases, and the DOF increases as a result of the reduction in the pupil plane.
Therefore, it is considered that the DOF peak was obtained when the space width was approximately 1.2 times the line width due to the competition between the increase in the DOF due to the increase in the pitch and the decrease in the DOF due to the isolation of the pattern. This relationship does not always hold, but generally holds in a region near the resolution limit of a certain optical system.

Therefore, in the first exposure, the ratio of the line and space dimensions of the periodic pattern is changed from 1: 1.1 to 1: 1.1.
By setting an appropriate value between 1.4, preferably 1: 1.2, a wide DOF can be obtained.

[0019]

Next, an embodiment of the present invention will be described in detail.

(Embodiment 1) FIG. 1 is a plan view showing an exposure mask used for the first and second exposures according to Embodiment 1 of the present invention.

The exposure mask shown in FIG. 1A is a mask used for the first exposure. This exposure mask has a periodic pattern formed on a quartz substrate 101 by a light shielding film 102 made of chromium. The line width L1 of the line pattern composed of the light-shielding film 102 is set to 0.25 μm, and the space width (S1) between the line patterns is set to 0.3 μm (all on the semiconductor substrate).

The exposure mask shown in FIG. 1 (b) is used for the second exposure. In FIG. 1 (a), corresponding masks are used to leave only the second, fourth and seventh line patterns counted from the left. The pattern of the light-shielding film 2 made of chromium is disposed at a position where the light-shielding film 2 is formed. The size of the light-shielding film 2 in the exposure mask shown in FIG. 1B is slightly larger than the pattern of the light-shielding film 2 in the first exposure in order to shield the unexposed part in the first exposure. Is set to 0.35 μm.

FIG. 2 is a process chart showing an exposure method according to the first embodiment of the present invention in the order of steps. First, as shown in FIG. 2A, a positive chemically amplified resist film 1 is formed on a semiconductor substrate.
04 is applied with a film thickness of 1.0 μm. Next, FIG.
As shown in FIG. 1, using the exposure mask shown in FIG.
Exposure is performed using a first exposure mask with a KrF excimer laser stepper. 105 is an exposed resist film,
Reference numeral 104 denotes an unexposed resist film.

Next, as shown in FIG. 2C, before development, exposure is performed using a second exposure mask shown in FIG. 1B. At this time, the second exposure is
Must be precisely aligned. For this purpose, it is effective to perform superposition using the same alignment mark formed in the previous step. However, if the first exposure is the first exposure for the semiconductor substrate, this method is used. Not applicable. In this case, it is possible to detect the position from the latent image of the first exposure and perform the position adjustment.

The unnecessary pattern is erased by the second exposure,
After PEB (P ost E xposure B ake ), to perform development. For development, an aqueous solution of tetramethylammonium hydroxide (TMAH) was used.
After performing paddle development for 0 second, rinsing with pure water is performed to obtain a desired resist pattern on the semiconductor substrate 103 as shown in FIG.

FIG. 3 is a plan view showing a resist pattern formed according to the process shown in FIG. In FIG. 3, the design line width of each of the resist patterns 107, 108 and 109 is 0.25 μm. The design space widths S2 and S3 are 0.75 μm and 1.25 μm.

Resist patterns 107, 108, 109
FIG. 4 shows the relationship between the defocus amount and the pattern size. For exposure, a KrF excimer laser stepper with NA = 0.50 was used at σ = 0.7.

Resist patterns 107, 108 and 10
9 is a DO defined with a dimensional error within ± 10%.
F is not less than 1.4 μm and not less than 1: 1 L & S. Compared to the isolated line shown in FIG.
Has improved significantly.

As described above, according to the first embodiment of the present invention, in the first exposure, the ratio of the line width of the periodic pattern to the line width of the space pattern is 1: 1.1 to 1: 1.4. Since the DOF is set within the range, the DOF of the isolated line pattern can be set to be equal to or larger than that of the one-to-one line and space pattern.

(Embodiment 2) Next, Embodiment 2 of the present invention
Will be described with reference to the drawings. FIG. 5 is a plan view showing a resist pattern in a case where a periodic pattern and an isolated line pattern coexist. This is a case where an isolated line pattern is formed at a considerable distance from the end of the periodic pattern. The dashed line shows the pattern 110 erased by the second exposure.

Two line patterns are formed on both sides of the isolated line in the first exposure. Pattern D
In order to maximize OF, the line width L1 and the space width S1 of these line patterns are set to 0.25 μm and 0.30 μm, respectively, as in the first embodiment.

In the first exposure, the number of patterns arranged on both sides of the isolated line pattern is preferably two or more on each side. Although one DOF has the effect of enlarging the DOF, it is not enough compared with the case of two or more DOFs. In FIG. 5, S4
May be set arbitrarily, and of course, S
4 = S1.

In the present embodiment, there is an advantage that the periodic pattern and the isolated line pattern can be simultaneously formed with a wide DOF.

(Embodiment 3) Next, Embodiment 3 of the present invention.
Will be described.

In the first embodiment, the illumination condition at the time of exposure is σ = σ
Although the normal illumination is set to 0.7, the DOF can be further improved in Embodiment 3 of the present invention by using the annular illumination. Using the exposure mask used in Embodiment 1 shown in FIG. 1, the illumination condition of the excimer laser stepper with NA = 0.50 was set as σout = 0.70 / σin =
As a result of exposure as annular illumination of 0.42, the DOF of the isolated line was 2.3 μm.

[0036]

As described above, according to the present invention, the DOF of an isolated line pattern can be made wider than that of a one-to-one line and space pattern. The reason is that the ratio of the line width of the periodic pattern to the line width of the space pattern is set in the range of 1: 1.1 to 1: 1.4 in the first exposure of the second exposure method. .

[Brief description of the drawings]

FIG. 1 is a plan view showing an exposure mask used in Embodiment 1 of the present invention.

FIG. 2 is a process chart showing Embodiment 1 of the present invention in the order of steps.

FIG. 3 is a plan view showing a resist pattern according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a relationship between a pattern dimension and a focus shift according to the first embodiment of the present invention.

FIG. 5 is a plan view showing a resist pattern according to a second embodiment of the present invention.

FIG. 6 is a diagram showing the relationship between L & S, pattern size and focus shift for isolated lines.

FIG. 7 is a diagram illustrating a relationship between a space line and a DOF.

[Explanation of symbols]

 Reference Signs List 101 quartz substrate 102 light shielding film 103 semiconductor substrate 104 resist coating (unexposed) 105 resist coating (exposed) 106, 107, 108, 109 resist pattern 110 resist pattern erased by second exposure

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 1/00-1/16

Claims (4)

(57) [Claims] A first mask pattern exposing step;
A mask pattern exposing step, wherein the first mask pattern exposing step comprises exposing a first mask pattern including a pattern having periodicity to a photosensitive organic film formed on a semiconductor substrate. The second mask pattern exposure step is a step performed subsequent to the first mask pattern exposure step, and includes the step of forming a periodic pattern having a different cycle from the periodic pattern. And performing a process of exposing a second mask pattern including the first mask pattern. The ratio of the line portion to the space portion of the periodic pattern included in the first mask pattern is 1: 1.1 to 1: 1.4.
An exposure method characterized in that the exposure method is set within the range. 2. An exposure mask including a periodic pattern used in an exposure method performed in two stages, the exposure method comprising: exposing a first mask pattern; And a step of exposing the second mask pattern following the exposure by the step (b), wherein the ratio of the line portion to the space portion is in the range of 1: 1.1 to 1: 1.4. An exposure mask comprising the pattern described in (1). 3. The exposure mask according to claim 2, wherein the ratio of the line and space dimensions of the periodic pattern is preferably set to 1: 1.2. 4. The method according to claim 2, wherein the periodic pattern is included in a first mask pattern.
Exposure mask according to 1.