JPH04120538A - Pattern forming method - Google Patents

Abstract

PURPOSE:To obtain a fine pattern of a desired line width by transferring the pattern by using a photomask formed with the phase shift pattern below the resolution threshold of an exposing device at the edge or near the edge of a phase shift layer. CONSTITUTION:Exposing is executed by using a reticule formed with the phase shifter on a glass substrate 1. The edge of the phase shifter is formed partly to a straight shape and partly to a pleat shape. A stepper is used as the exposing device and since the resolution threshold of this exposing device is below the resolution threshold, the pleats are not resolved. A wafer coated with a negative resist is subjected to exposing by using this reticule and is then subjected to development to obtain the resist pattern 5 having a space in the part corresponding to the edge of the phase shift pattern. The patterns of desired sizes are freely formed from extremely fine patterns to the large patterns by a phase shift method.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to semiconductor devices, magnetic bubble devices, superconducting devices, surface acoustic wave devices, etc., and particularly to a method for forming fine patterns suitable for optical lithography.

[Conventional technology]

A mask with an original pattern drawn on it (hereinafter referred to as a reticle)
In the projection exposure method, in which the pattern on the reticle is transferred onto the wafer by illuminating the reticle with an illumination system, there is a demand for miniaturization of the pattern that can be transferred. The resolution, which indicates how fine a pattern a projection exposure apparatus can transfer, is evaluated by whether two adjacent bright areas can be separated when a pattern on a reticle is transferred onto a wafer. It is known that one method for improving this resolution is to provide a phase difference to the exposure light beams at two adjacent transparent parts on the reticle. A reticle pattern that provides a phase difference to exposure light is described in, for example, Japanese Patent Laid-Open No. 2-078216. In this method, a transparent thin film that changes the phase of transmitted light by 180 degrees is used as a phase shifter, and this shifter is placed in a part of the light-transmitting part. 180° depending on whether or not there is a shifter
Because of this phase difference, a complete dark area appears along the edge of the shifter, and the line width of this dark area is extremely narrow. Therefore, when a positive resist is used, an extremely fine line pattern can be obtained, and when a negative resist is used, an extremely fine space pattern can be obtained.

[Problem to be solved by the invention]

Although the above conventional techniques can form extremely fine patterns, there is a problem in that patterns with various line widths cannot be obtained simultaneously. For example, although it is possible to form a space pattern with a width of 0.2 μm using the above conventional technology, the pattern that can be formed is only a 0.2 μm space pattern, and it is not possible to simultaneously form a 0.3 μm or 0.35 μm space pattern. There wasn't. By combining the above phase shift method and conventional exposure technology using a light-shielding film, it is possible to form, for example, a 0.2 μm space pattern using the phase shift method, and a pattern of 0.5 μm or more using an exposure method using Cr. However, a pattern between 0.2 and 0.5 μm cannot be obtained. Further, the patterns that can be formed using the above-mentioned conventional techniques are space patterns and line patterns, and there is a problem in that they are not effective for hole patterns.

[Means to solve the problem]

The above problem is solved by the following means.

To solve the problem of simultaneously obtaining patterns with various line widths, a fine phase shifter pattern below the resolution limit is formed at the edge of the phase shift.

The edge of the phase shifter may have a pleated pattern,
It may also be a dot-like pattern placed around the phase shifter of the main body. By controlling the length of the pleats and the area of the dots, a pattern with a desired line width is obtained.

At least two or more reticles are used to form the hole pattern, and each reticle is provided with a phase shifter.

Here, the edges of the phase shifter are crossed at the location where the hole pattern is to be formed. When exposed using these reticles,
When a negative resist is used, a fine hole can be obtained, and when a positive resist is used, a fine dot pattern can be obtained.

The size of the hole is controlled by notching the edge of the phase shifter.

[Effect]

If the edges of the shifter are made with creases that are below the resolution limit to form pleats, the exposure light that passes through them will be greatly diffracted, diverged out of the lens, and will not form an image on the wafer.

Therefore, the size of the dark area depends on the size (length) of the folds. Therefore, the size of the area containing this notch (
By controlling the line width (length), it is possible to control the line width. In this method, the purpose can be achieved only by processing the phase shifter film, so problems such as misalignment between the shifter film and the light shielding film, which occur in exposure methods using both the phase shifter film and the Cr light shielding film, do not occur. The reason why holes can be formed is as follows.

Since the phase changes by 180 degrees at the edge of the shifter, the light intensity at the location corresponding to the edge becomes 0. Therefore, a complete dark area appears on the line along the edge. Other parts are illuminated.

In this method, exposure is performed using two phase shift reticles. At this time, a first exposure is performed using the first reticle, and then a second exposure is performed using the second reticle. Here, the edges of the shifter on each reticle are crossed at the location where the hole is to be made. If this is done, the light intensity at the intersection will be completely O, but the light from at least one of the reticles will hit the area other than the intersection. A fine hole pattern can be formed by using a negative resist and performing exposure at an exposure amount such that at least a sufficient resist film remains after one exposure.

In the phase shift method, the light intensity along the edge of the shifter is completely O, so it remains zero no matter how many times the exposure is repeated, and resolution does not deteriorate. On the other hand, in a normal reticle (a reticle using a glass substrate and a Cr light-shielding film), some of the light goes around to the light-shielding part, so when one exposure is repeated, the light intensity at the light-shielding part gradually increases.

degrade resolution. Overexposure using the phase shift method differs from overexposure using the normal exposure method in this respect.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 As shown in FIG. 1(a), exposure was performed using a reticle in which a phase shifter layer 2 was formed on a glass substrate 1. Here, the phase shifter material is SiC formed by sputtering.
2 was used. However, this material is not limited to SOG (Sp
in on Glass), IT.

(Indium Tin Oxide), a nitride film, a polyimide film, or any other material that can sufficiently transmit exposure light may be used. As the film thickness of the shifter deviates from 6180 degrees, which is set so that the phase of the exposure light that passes through the shifter changes by 180 degrees with respect to the exposure light that passes through the glass surface, the resolution deteriorates, but the amount of deviation is ±10" If it is within 10, the dimensional deterioration is 10
% or less. The edge of the phase shifter was partially straight as shown in 2a of FIG. 1, and partially folded as shown in 2b. Fold length 3 is 2 μm on the reticle, width 4
was 1 μm. As an exposure device, the numerical aperture N of the lens
A (Numerical Aperture) 0,
A 42 i-line (wavelength: 365 nm) stepper was used. The reduction rate is 1/10. Therefore, the length of the pleats on the wafer 1 corresponds to 0.2 μm and the width corresponds to 0.1 μm. Since the resolution limit of this exposure apparatus is 0.35 μm-0.4 μm, the width of 0.1 μm is below the resolution limit. For this reason, the folds are not resolved.

As a result of exposing a wafer coated with a negative resist using this reticle and then developing it, a resist pattern 5 as shown in FIG. 1(b) with spaces corresponding to the edges of the phase shifter pattern was obtained. It was done. Here, the space width 6 of the portion corresponding to the straight portion 2a of the edge of the shifter is approximately 0.
．． Space width 7 of the part corresponding to the pleated part 2b at 2 μm
was approximately 0.3 μm. Here, the space width 7 changes depending on the pleat length 3. For example, if the length 3 on the reticle is 3 μm, the space width 7 is about 0.4 μm. Note that the fold radius 4 is not limited to this value as long as it is sufficiently smaller than the resolution limit of the lens. For example, similar results were obtained even if the thickness was 0.5 μm on the reticle.

In this example, the NA of the lens is 0.42, and i
Although a case is shown in which a line is used as the exposure light, the present invention is not limited to this. However, the line width depends on the NA of the lens and the wavelength of the exposure light, and becomes thinner as the NA increases and the wavelength decreases. The line width also depends on the coherence range value σ of the illumination system. The smaller the σ value, the thinner the line width becomes.

Example 2 Here, as shown in FIG.
A reticle on which a phase shifter layer 12 was formed was used. The phase shifter layer 12 includes a square auxiliary shifter pattern row 12a having a size of 1 μm on the reticle and a shifter body 12.
b and a square auxiliary shifter pattern row 12c.

Here, 12a has one row of shifters, and 12c has two shifters.

The dimension between the auxiliary shifter pattern rows was 1 μm on the reticle. Note that the minimum resolution dimension of this lens is the same as in Example 1, and the dimension of 1 μm on the reticle is sufficiently smaller than the minimum resolution dimension.

A wafer coated with a negative resist was exposed to light using this reticle, and then developed. As a result, Figure 2 (b
) was obtained. Here, the space width of this resist pattern varied depending on the presence or absence of the auxiliary shifter, and was approximately 0.2 μm at the 14th location, approximately 0.3 μm at the 15th location, and approximately 0.5 μm at the 16th location.

In this embodiment, the size of the square auxiliary shifter pattern on the reticle is set to 1 μm, but the size is not limited to this as long as it is sufficiently smaller than the minimum resolution dimension; for example, it may be 0.5 μm. Moreover, it is not necessarily limited to a square, but may be a square, a circle, or a triangle.

With this method, the line width can be controlled by the size of the area occupied by the square auxiliary shifter. Therefore, the smaller the square auxiliary shifter, the more finely the line width can be controlled. On the other hand, the smaller the square auxiliary shifter, the more this shifter is arranged.

This means that the time required to draw this shifter pattern with an electron beam drawing device is extended. It is preferable to decide the size of the square auxiliary shifter by considering both of these factors. With this method, the line width can be controlled using an auxiliary shifter pattern of a fixed size, so it is easy to design the reticle pattern.

Example 3 As shown in FIG. 3(a), a first exposure was performed on a wafer coated with a negative resist using a reticle in which a phase shifter 32 was provided on a glass substrate 31. Next, a second exposure was performed using a second reticle in which a phase shifter 33 was provided on a glass substrate 31. Both the first and second exposures were carried out at an exposure dose that would leave a sufficient amount of resist after development. The remaining film rate in this experiment was approximately 95%.

It is not limited to this. By developing this wafer, the intersections 34 and 35 of phase shifters 32 and 33 are
As shown in FIG. 3(b), hole patterns 34' and 35' were formed at locations on the wafer corresponding to the above. The size of the hole pattern was approximately 0.2 μm. Since an i-line stepper with NAo of 42 was used as the exposure device, the minimum diameter of a hole in a normal exposure method using a Cr light-shielding film is about 0.4 μm. A hole pattern with a maximum/JS diameter of about half that of a normal case could be formed. Note that the diameter of the hole pattern depends on the exposure amount. Therefore, the hole diameter can be finely adjusted by adjusting the exposure amount. It goes without saying that the shape of the hole can be adjusted to a rectangular or elliptical shape by changing the first and second exposure amounts.

Although two reticles were used here, the hole position accuracy was the same as when one reticle was used. Focusing on the hole 34', its positional accuracy in the X direction is determined by the positional accuracy of the shifter 32, and its positional accuracy in the Y direction is determined by the positional accuracy of the shifter 33. This is because the positional accuracy of the hole does not depend on the mutual position of the two reticles, but each direction is determined by the positional accuracy of each reticle.

Example 4 As shown in FIG. 4(a), a first exposure was performed using a reticle in which a phase shifter 42 was provided on a glass substrate 41. The exposure apparatus, wafer, exposure conditions, etc. are the same as in Example 3. The reduction ratio of the exposure device is 1/10. here,
As shown at 42', one side edge of the phase shifter was pleated. The length of the folds was 2 μm on the reticle, and the width was 1 μm. Next, a second exposure was performed using a second reticle in which a phase shifter 43 was provided on a glass substrate 41. Also in the phase shifter 43, as shown at 43', the edge of the - side is formed into a pleated shape. The length of the folds was 2 μm on the reticle, and the width was 1 μm. Phase shifters 42 and 4 are developed by developing the exposed wafer.
Hole patterns 44' and 45' were formed on the wafer at locations corresponding to the intersections 44 and 45 of No. 3. The diameter of hole pattern 44' is approximately 0.3 μm, and the diameter of hole pattern 45' is approximately 0.3 μm.
It was 2 μm. In this manner, by making the edges of the phase shifter in a pleat shape, it was possible to form extremely fine hole patterns (0.2 μm), and also hole patterns with different dimensions.

It goes without saying that the diameter of the hole can be controlled by changing the length of the folds on the edge of the shifter. It goes without saying that by changing the length of the pleats using shifters 42 and 43, a rectangular or elliptical hole can be obtained. In addition to making the edge of the shifter pleated,
A dot-shaped auxiliary phase shifter as shown in Example 2 can also be used.

Example 5 In Example 3, instead of the two reticles used in Example 3, a reticle was used in which a phase shifter 52 and a light shielding film 53 made of Cr were provided on a glass substrate 51 as shown in FIG. 5(a). 1
The first exposure was performed using the reticle. Next, a second exposure was performed using a second reticle in which a phase shifter 54 was provided on a glass substrate 51. Here, the phase shifter 52 and the phase shifter 54 are arranged so as to intersect at 5S and 56, and as shown at 57, the Cr light shielding film 53 is connected to the phase shifter 5.
It was placed so as to surround a part of the edge of the shifter No. 4. Next, development is performed to form hole patterns 55' and 56' at locations corresponding to 55 and 56, as shown in FIG. 5(b).
A space pattern 57' was formed at a location corresponding to 57. The diameter of the hole pattern 55' is approximately 0.2 μm,
The line width of the space pattern 57' was also about 0.2 μm.

Example 6 In Example 3, instead of the two reticles used in Example 3, three reticles were used to form a resist pattern. As shown in FIG. 6(a), the first reticle was provided with a phase shifter 62 on a glass substrate 61, and the second reticle was provided with a phase shifter 63 on a glass substrate 61. Third
A Cr film having a portion 64 placed on a glass substrate 61 was formed on the reticle. Therefore, in the third reticle, the portion 64 is a transparent portion, that is, a window;
The remaining part is a light shielding part.

Phase shifters 62 and 63 were positioned such that the edges of the shifters intersected at locations 65 and 66, and window 64 was positioned to include intersection point 66 therein. Exposure is performed three times in sequence using these three reticles, and then development is performed to form a hole pattern 6 on the wafer corresponding to the intersection 65.
5' was formed. The diameter of the pattern was approximately 0.2 μm.

With this method, extremely small 1
It was possible to form several hole patterns.

Example 7 As shown in FIG. 7(, ), a first reticle in which a phase shifter 72 and a Cr light-shielding film 73 were formed on a glass substrate 71, and a second reticle in which a phase shifter 74 was formed were used. The resist pattern 75 in the shape of a hole as shown in FIG. 7(b) was formed in the same manner as in Example 3 by sequentially performing two exposures. Here phase shifters 72 and 73
The shifters were placed so that their edges intersected at the position where the hole pattern was desired. Further, the Cr light-shielding film 73 was placed in a place where no phase shifter was placed in either the first or second reticle, and the glass substrate was exposed. Here, the Cr light-shielding film 73 occupied about 273 of the reticle area. Then, the influence of stray light was investigated using a stepper equipped with a lens in which about 10% of the light becomes stray light. As a result, when using a reticle with an exposed glass part without a Cr light-shielding film, the minimum resolution was 0.3 μm, but by using a single reticle, the minimum resolution was improved to 0.25 μm. I was able to do it.

Example 8 Using the pattern forming techniques shown in Examples 1 to 6, L S
I (Large 5cale Integrate
dC1rcuit), the chip area was reduced to 1
The size can be reduced by about 30% per aI, and the operating speed can also be improved by about 10% due to the ability to reduce the wiring length.

Reducing the chip area increases the number of chips that can be obtained per wafer, making it possible to reduce the manufacturing cost of the chips.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to freely form patterns of desired dimensions from extremely fine patterns to large patterns using the phase shift method.

Furthermore, a fine hole pattern can be formed. This makes it possible to manufacture LSIs with ultra-fine patterns,
This is effective for improving LSI characteristics or reducing chip area.

[Brief explanation of drawings]

Figures 1.2, 3, 4, 5, 6 and 7 are schematic diagrams showing one embodiment of the present invention. 2.12, 32, 33, 42, 43, 52, 54°62
,63,72.74...phase shifter, 1,11°31
．． 41,51,61.71...Glass substrate, 5°13
．． 34', 35', 44', 45',
55'56', 57', 65', 75...Resist pattern (b)

Claims (1)

[Claims] 1. In a pattern forming method in which a resist pattern is formed using a photomask provided with a phase shift layer that changes the phase of exposure light on an optically transparent substrate, the edge or edge of the phase shift layer A pattern forming method characterized in that the pattern is transferred using a photomask in which a phase shift pattern below the resolution limit of an exposure device is formed in the vicinity of the exposure device. 2. The pattern forming method as set forth in claim 1, wherein the phase shift pattern below the resolution limit as set forth in claim 1 is a dot pattern. 3. In a pattern forming method in which a resist pattern is formed using a photomask provided with a phase shift layer that changes the phase of exposure light on an optically transparent substrate, the resolution of the exposure device is applied to a desired edge of the phase shift layer. A pattern forming method characterized by the creation of fine scratches that are below the limit. 4. In a photomask comprising an optically transparent substrate and at least a phase shift layer provided on the substrate that changes the phase of exposure light, an exposure device is provided at or near the edge of the phase shift layer. A photomask characterized by forming a phase shift pattern below the resolution limit. 5. A pattern forming method comprising forming a pattern using at least two phase shift masks whose phase shift edges intersect with each other at one or more locations. 6. Claim 5, characterized in that a phase shift pattern smaller than the resolution limit of the exposure device is formed at the edge of the phase shift or at least a part of the vicinity of the edge. The pattern formation method described.