JP3212117B2 - 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 an exposure mask,
In particular, it relates to a lithography mask.

[0002]

2. Description of the Related Art Semiconductor integrated circuits are becoming ever more highly integrated and finer. When manufacturing the semiconductor integrated circuit,
Lithography technology is particularly important as a key to processing.

In the current lithography technology, a method of projecting and exposing a mask pattern onto an LSI substrate via a reduction optical system is mainly used. If a high-pressure mercury lamp is used as a light source, the minimum line width is about 0.5 μm. Is the limit. 0.5
Development of direct writing technology using KrF excimer laser or electron beam and X-ray equal-size exposure technology for pattern dimensions of μm or less are being promoted. However, due to the reasons of mass productivity and process versatility, optical lithography Expectations have become very high.

In such a situation, for the light source, g
Various light sources such as X-rays, i-rays, excimer lasers, and X-rays have been studied, and development of new resists and new resist treatments such as REL have been studied for resists. Research is also being conducted on the CEL image reverse method and the like.

[0005] On the other hand, for the mask manufacturing technology,
Though not fully reviewed, the 1982 IBM
A phase shift method has been proposed and attracted attention by Levenson et al.

The phase shift method is a technique for improving the resolution and contrast of a projected image by controlling the phase of light transmitted through a mask.

In this method, as shown in FIG. 8A, chromium (C) formed on a quartz substrate 11 by sputtering or the like is used.
r) or one of a pair of adjacent transparent portions of a mask pattern 12 made of chromium oxide (Cr ₂ O ₃ ).
As shown in FIG. 8 (b), the phase of this portion is inverted so that the amplitude of the light cancels out at the boundary between the two transmission portions, using the mask on which the mask 3 is formed (FIG. 8 (c)). ). As a result, the light intensity at the boundary between the two transmitting portions becomes 0, and the pattern formed on the wafer can be separated from the two transmitting portions as shown in FIG. Thus, a 0.7 μm pattern was resolved by a g-line stepper with NA = 0.28, and the resolution was improved by about 40%. At this time, in order to invert the phase, the film thickness d of the phase shifter is d = λ / 2, where n is the refractive index of the shifter material and λ is the exposure wavelength.
The relationship of (n-1) is required.

In addition, Nitayama et al. Of Toshiba have proposed a phase shift mask structure in which a phase shifter is provided around a transmission part or a light shielding part.

FIG. 9 illustrates this principle. As shown in FIG. 9A, this mask extends around a mask pattern 12 formed of a laminated film of chromium (Cr) and chromium oxide (Cr ₂ O ₃ ) formed on a quartz substrate 11. As shown in FIG. 9B, using a mask having a transparent film as the formed phase shifter 13, the phase of this portion is inverted, and the light having a phase of 0 ° and a phase of 180 ° at both ends of the transmission portion is formed. The light intensity is reduced so that the contrast is improved (FIG. 9 (c)). As a result, the light intensity at both ends of the transmission portion becomes substantially zero, and the pattern formed on the wafer can be separated from the two transmission portions as shown in FIG. 9D.

In this mask, PMMA is used as a phase shifter.
Although PMMA has high transmittance,
Since the resist profile is sharp, a good phase shifter is obtained. Further, in this method, since the phase shifter pattern can be formed in a self-aligned manner, the mask alignment and the selective processing step are not required, and the formation can be performed easily.

When exposure is performed using such a mask,
Since the light passing through each opening has a phase inverted with respect to each other as shown by a broken line, the light intensity at a portion below the mask layer is greatly reduced, and the light as a whole is represented by a solid line. In view of the intensity distribution, it is possible to achieve resolution up to almost half the size as compared with the case where a conventional mask is used.

Further, the shifter edge type mask has a phase shifter disposed on a translucent substrate as shown in FIG. The mask forming process is simple, the effect of improving the resolving power is large, and a large focus margin can be expected.

FIG. 11 shows a comparison of the effect of improving the resolving power by simulation of each of these phase shift methods, and FIG. 12 shows a comparison of the focus margin. According to these comparisons, it can be said that the Levenson type and the shifter edge utilizing type have a larger resolution improving effect and a larger focus margin than the self-alignment type.

Here, the Levenson-type phase shift mask can be applied to an isolated pattern by using an auxiliary pattern. However, the mask formation process needs to form a shifter after patterning a light shielding material on a transparent substrate. It contains complex elements such as

On the other hand, the shifter edge type mask has a problem that the resist pattern size after exposure is determined uniformly, though the mask forming process is simple and the resolution improving effect is large, and a large focus margin can be expected. That is, as shown in FIG. 13, the light transmitted through the mask shown in FIG. 13A exposes the resist with an intensity distribution as shown in FIG. As shown in c), the size becomes constant. That is, the pattern size F of the resist formed using this mask is determined only by the exposure amount.

Therefore, when a pattern other than a fine pattern is formed by using the edge-based phase shift method, the edge-based phase shift method as shown in FIG. 14 is used. In this case, when the pattern width d is large, dark portions of transmitted light formed at the respective edges are combined. Here, the light transmitted through the mask shown in (a) exposes the resist with an intensity distribution as shown in (b), so the resist pattern when using a negative resist is as shown in (c). This is slightly larger than the pattern width d. This method is called a double-edge utilization type. With this method, a small pattern other than the fine pattern can be formed.

In order to form such a phase shifter using both edges, it is necessary that the phase shifter has such a size that dark portions of the transmitted light formed at the respective edges can be satisfactorily combined. A method of forming a large pattern by combining patterns of a predetermined size has been proposed, but if one shifter size is too large as shown in FIG.
As shown in (1), there is a problem that unevenness is formed at the end of the resist pattern.

Therefore, it is good to make the size sufficiently small, but if one shifter size is small as shown in FIG. 16A, the resist pattern ends are formed smoothly as shown in FIG. When the number of data is increased and computer processing is attempted, the CAD data becomes enormous, which is not practical.

[0019]

As described above, when a large-area pattern is formed on the same plane as a fine pattern by using a conventional shifter edge-based phase shift method, it is necessary to arrange a small-sized phase shifter. There is a problem that the number of shifters increases and the CAD data becomes enormous, which makes practical use difficult.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to easily provide an exposure mask having sharp edges and capable of performing high-precision pattern transfer.

[0021]

Therefore, in the exposure mask of the present invention, at least a part of the mask pattern is constituted by a phase shifter. For a large-area pattern of the phase shifter, the internal region of the pattern has a relatively large size. And a small size shifter pattern in the area near the pattern edge.

This small pattern is desirably a grid pattern or a stripe pattern.

[0023]

According to the above-mentioned structure, for a large-area pattern, the inner region of the pattern is constituted by a small pattern having a relatively large size, and the region near the pattern edge is constituted by a shifter pattern of a small size. In addition to reducing the number of
An exposure image with a smooth edge can be formed.

[0024]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1 FIG. 1 is a view showing a cross section of an exposure mask according to a first embodiment of the present invention.

This exposure mask is shown in FIGS. 1 (a) and 1 (b).
As shown in a plan view and a cross-sectional view, a quintuple mask is formed, and a film thickness of 0.25 μm
An internal region R1 composed of a 0.35 μm × 0.35 μm square (on a wafer) cross-shaped first small pattern 2 s composed of a semi-transparent film 2 (having substantially the same transmittance as that of a quartz substrate);
0.25 μm made of the same translucent film as the small pattern 2s
A phase shifter pattern composed of a × 0.25 μm square (on the wafer) cross-shaped second minute pattern 2b and an edge region R2. In other regions, a fine pattern portion (not shown) composed of only a fine pattern is also formed.

As the translucent film, a silicon oxide film having an optical constant almost equal to that of the quartz substrate 1 is selected.

The film thickness is configured to have a thickness of λ / 2 (n-1). The phase of the light transmitted through the translucent film and the normal phase transmitted through the transmission region adjacent to that portion are determined. Differs from the phase of the light by 180 degrees. The allowable range of the phase shift due to the variation of the film thickness is about ± 10%. Here, λ is the wavelength of the exposure light, and n is the refractive index of the shifter material (semi-transparent film) at the exposure wavelength.

The exposure mask thus formed is mounted on a KrF excimer laser stepper having a projection lens of NA = 0.42, and the pattern is transferred (λ) to a wafer having a silicon substrate coated with a negative resist. = 248
nm, coherence factor σ = 0.5) and developed with a dedicated developer.

This pattern is exposed and transferred onto the resist pattern to form a large resist pattern having a smooth edge as shown in FIG.

According to this exposure mask, even when a minute pattern and a large area pattern coexist, they can be formed simultaneously, and can be drawn with a smaller amount of data. Can be obtained.

As the phase shifter, a translucent film such as a resist or a silicon oxide film may be formed on a transparent substrate. However, as shown in a modified example in FIG. A part of the conductive substrate 1 may be removed by the thickness λ / 2 (n−1) by etching. Here, n is the refractive index of the substrate at the exposure wavelength. The phase of the light transmitted through the removed portion and the phase of the normal non-removed light adjacent to the portion are 18
0 degrees different. The allowable range of the phase shift due to the variation in the etching amount is about ± 10%.

FIG. 3 shows the dependence of the shifter size on the exposure amount. The shifter size on the vertical axis also changes depending on the stepper and the resist. The lower limit of the exposure amount is determined by the residual film characteristics (D curve) of the resist as shown in the figure. Here, the lower limit of the exposure amount is shown by a curve of the remaining film ratio of 80% as an example. The size of the shifter used at the center of the pattern is made as large as possible in order to reduce data in a portion below the shift amount dependence of the exposure amount (A curve or B curve) and on the right side of the D curve. For example, when the shape of the shifter is a grid, the size is increased as much as possible in the hatched portion in the figure. What is necessary is just to select the shifter size as large as possible in the right part of the D curve below the C curve in the figure so as to smooth the end of the pattern.

In the above embodiment, the internal area is formed in a grid pattern, but may be formed in a stripe pattern as shown in FIGS. At this time, a fine pattern may be formed on the longitudinal side of the stripe as shown in FIG. 4, or a fine pattern may not be formed on the longitudinal side as shown in FIG. A pattern may be formed. 4B and 5B, (b) is a pattern formed on the resist pattern.

The structure of the phase shifter is shown in FIG.
2, a structure in which a translucent film is formed on a light-transmitting substrate may be used, or a structure in which the light-transmitting substrate is etched by a predetermined thickness as shown in FIG.

FIG. 6A shows the corners of the pattern.
It is desirable to form such that a fine pattern comes as shown in FIG. The exposure pattern image on the resist at this time is shown in FIG.
It is shown in (b). When the blank is formed at the corner as shown in FIG. 6 (c), the exposed pattern image on the resist at this time has a pattern lack at the corner as shown in FIG. 6 (d). The desired pattern cannot be obtained.

Another example will be described.

When it is desired to obtain a resist pattern having a complicated edge as shown in FIG. 7A, the internal region R1 is composed of a large stripe phase shifter and the edge region R2 is minute as shown in FIG. 7B. A phase shifter composed of a pattern may be used.

Further, as shown in FIG. 7 (c), the internal region R1 may be constituted by a phase shifter having a large grid pattern, and the edge may be constituted by a phase shifter having a minute pattern.

[0040]

As described above, according to the present invention, it is possible to reduce the number of small shifter patterns and reduce CAD data, and at the same time, it is possible to perform pattern transfer with sharp edges and high precision. A mask can be provided.

[0041]

[Description of the drawings]

[0042]

FIG. 1 is a view showing an exposure mask according to a first embodiment of the present invention;

[0043]

FIG. 2 is a view showing a modified example of the exposure mask.

[0044]

FIG. 3 is a view showing the exposure amount dependency of a shifter size.

[0045]

FIG. 4 is a diagram showing another embodiment of the present invention.

[0046]

FIG. 5 is a diagram showing another embodiment of the present invention.

[0047]

FIG. 6 is a view showing another embodiment of the present invention.

[0048]

FIG. 7 is a diagram showing another embodiment of the present invention.

[0049]

FIG. 8 is a diagram showing a Levenson-type phase shift method;

[0050]

FIG. 9 is a diagram showing a self-alignment type phase shift method.

[0051]

FIG. 10 is a diagram illustrating an edge-based phase shifter;

[0052]

FIG. 11 is a comparison diagram of a resolution improving effect by simulation of each phase shift method of the conventional example.

[0053]

FIG. 12 is a diagram showing comparison of focus margins by simulation of each phase shift method of the conventional example.

[0054]

FIG. 13 is a diagram showing a phase shift method using one edge.

[0055]

FIG. 14 is a diagram showing a phase shift method using both edges.

[0056]

FIG. 15 is a diagram showing an example of a conventional phase shift pattern.

[0057]

FIG. 16 is a diagram showing an example of a conventional phase shift pattern.

[0058]

[Explanation of symbols]

 11 quartz substrate 12 light shielding film 13 phase shifter (semi-transparent film)

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

Claims (4)

(57) [Claims] 1. A light-transmitting substrate comprising a large-area pattern serving as a light-shielding region for exposure light formed by combining a plurality of phase shifters for changing the phase of exposure light, wherein the large-area pattern is a phase of an internal region. An exposure mask, wherein a phase shifter size in a region near an edge is smaller than a shifter size. 2. The exposure mask according to claim 1, wherein the phase shifter is made of a translucent film. 3. The exposure mask according to claim 1, wherein the phase shifter is formed by etching the translucent substrate. 4. The exposure mask according to claim 1, wherein the phase shifter in the internal region is formed in a grid pattern or a stripe pattern.