JP2000077303A - Method for forming pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for forming a pattern for highly precisely forming an isolated pattern in photoresist. SOLUTION: This method forms an isolated pattern 206 by exposing an isolated pattern 204 of a reticule R, whose short side is 0.3 μm or less to a photoresist formed on the surface of a wafer W by a multiplex focal exposure method. A negative photoresist NPR is used for the photoresist. Even when the isolated pattern is operated by the multiplex focal exposure method, the negative photoresist is used as the photoresist so that the isolated pattern 204 of the reticule R can be made light transmissive, and the surrounding region can be made light non-transmissive. Thus, the surrounding area of the photoresist NPR corresponding to the isolated pattern 204 can be prevented from being exposed by lights from the surrounding of the isolated pattern 204, and the isolated pattern 206 of the photoresist can be formed highly precisely, even at adopting the multiplex focal exposure method for obtaining high intensity of light.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern forming method for exposing a photoresist to a required pattern and developing the same to form a pattern corresponding to the required pattern on the photoresist. The present invention relates to a method for forming a pattern with high precision.

[0002]

2. Description of the Related Art In a photolithography process frequently used in a semiconductor device manufacturing process, a region other than a process target is selectively covered in order to selectively introduce impurities into a semiconductor substrate or perform various processes such as etching. It is necessary to form a photoresist pattern for the purpose. For that purpose, a photoresist film is formed on a semiconductor substrate, and after prebaking, the photoresist is exposed to light using a reticle having a light transmitting or light opaque pattern corresponding to a pattern to be formed, and By developing the exposed photoresist, the photoresist in the light-transmitting region or the light-impermeable region is selectively left. Thereafter, by performing post-baking, pattern formation of a photoresist having a shape corresponding to the pattern is completed.
There are two types of photoresist, a bodied type and a negative type. In a positive type photoresist, an area exposed by a light-impermeable pattern formed on a reticle is removed by development, and an unexposed area is left as a pattern. . Also,
On the other hand, in the negative type, the unexposed area is removed by development, and the exposed area is left as a pattern. For example, as shown in FIG. 6A, a reticle R1 is provided with a light-transmitting substrate 301.
A pattern 302 is formed in which a region corresponding to the pattern to be formed is light-impermeable, and pattern exposure is performed on the positive photoresist PPR shown by a dashed line formed on the surface of the semiconductor wafer W using the reticle R. After the development and the development, the region corresponding to the pattern 302 is not exposed, and this region is formed as a photoresist pattern P1. On the other hand, as shown in FIG. 6B, in the case of a negative photoresist, the reticle R
Reference numeral 2 denotes a light-transmitting pattern 30 on a light-transmitting substrate 301 in which a region excluding a pattern region to be formed is light-opaque.
When pattern exposure is performed on the negative photoresist NPR shown by the dashed line in the figure and development is performed using the reticle R2, exposure is performed on a region other than the pattern, and this region is It is formed as a pattern P2.

In recent years, with the increase in the degree of integration of semiconductor integrated circuits, the pattern size of this type of photoresist pattern has been reduced, and attempts have been made to improve the resolution of the pattern in the photoresist. As a technique for increasing the resolution of this pattern, there is a technique for increasing the numerical aperture of a projection optical system for projecting and exposing a reticle pattern onto a photoresist. In this technique,
Although an improvement in resolution is effective, the depth of focus of the reticle pattern image on the photoresist is reduced with an increase in the numerical aperture, and it becomes difficult to accurately focus the pattern image on the photoresist. Therefore, the focus shift when the pattern image deviates from the in-focus position affects the photosensitive effect of the photoresist, and as a result, affects the accuracy of the pattern dimension of the pattern to be exposed. As a technique for preventing the influence of the defocus on the pattern dimensional accuracy, there is a multi-focus exposure method.
The multifocal exposure method is a method of performing exposure each time while changing a reticle pattern image on a photoresist to a plurality of positions along the optical axis direction of a projection optical system. This is because, as described later with reference to FIG. 3, the pattern image of the reticle R to be formed is formed at two different positions S1 and S2 in the optical axis direction across the original focus position S0 of the photoresist PR.
In the above, exposure is performed in a state where a reticle pattern image is formed, and effective exposure is performed on the photoresist by superposing the light intensities resulting from the exposure at these two locations.

In this multifocal exposure method, the light intensity contributing to exposure when each exposure position is shifted in the optical axis direction with respect to the focus position S0 of the photoresist PR shown in FIG.
As shown in FIG. 7, it is hardly affected by defocus. That is, (a1) of FIG. 7 shows a state where the image forming position of the projection optical system coincides with the focus position (defocus = 0), and the light intensity Iu by the above-described two exposures sandwiching the focus position ,
Id is equal, and the total light intensity It obtained by superimposing these light intensities Iu and Id is (a2). On the other hand, (b1)-
In (e1), the imaging position of the projection optical system is shifted from the in-focus position, and the defocus amounts are 0.25 μm and 0.5 μm, respectively.
The figure shows a case where it is shifted in the plus direction (downward in FIG. 2) by m, 0.75 μm, and 1 μm. In this case, the effective light intensity of the light intensity Iu on the side away from the focus position gradually decreases, but the other light intensity Id increases because the light intensity Iu approaches the focus position, and as a result, the light intensity Iu As shown in (b2) to (e5), the light intensity It obtained by superimposing the light intensity Id is substantially equal to the light intensity (a2) at the in-focus position. Therefore, according to the multifocal exposure method, even when a defocus occurs, the same light intensity as that at the time of focusing can be secured, and a highly accurate pattern can be formed.

In the case of a pattern in which line patterns having the same line width are densely arranged, such as a pattern for forming a logic device, the line pattern and the pattern size are adjacent to each other along with the high integration of the semiconductor device. The spacing between the patterns also needs to be miniaturized. The above-described multifocal exposure method is also effective when such a high-density pattern is formed. However, when this exposure method is compared between a positive photoresist and a negative photoresist, as shown in FIG. 6B, the exposed area is hardened and the negative photoresist remains as a pattern after development. Photoresist N
In the PR, as the light intensity for exposing the pattern P2 is increased as described above, a part of the exposure light goes around to the adjacent non-exposure region by diffracting or diffusing in the photoresist, The non-exposed area is exposed. For this reason, the exposed area is enlarged, the dimension of the pattern to be exposed increases, and when the photoresist is developed to form a pattern, adjacent patterns are short-circuited to each other, and as a result, a fine pattern cannot be resolved. In this regard, in the case of a positive photoresist in which the exposed photoresist is removed after development and the non-exposed area remains as a pattern after development, a sufficient exposure amount is obtained by the multifocal exposure method as shown in FIG. Is obtained, even if the exposure light goes around to the adjacent non-exposure area, even if the width dimension of the finally formed pattern is reduced, such as a negative photoresist Adjacent patterns are not short-circuited to each other, and the required resolution can be satisfied.

[0006]

However, the distance between adjacent patterns is significantly larger than the pattern size, and the situation is different when a so-called isolated pattern is formed. According to the simulation by the inventor, as described above, the isolated pattern is exposed by the multi-focus exposure method using a positive photoresist,
Compared to normal single focus exposure pattern formation,
It was confirmed that the dimensional accuracy of the pattern had decreased. FIG. 8 is a diagram showing the simulation result.
(A1) to (e1) respectively show the light intensity in the pattern exposure area when the amount of defocus increases gradually as in the case of FIG. 7 in the single focus exposure method. It should be noted that the reference light intensity in the figure indicates the limit at which the light intensity becomes higher than that, the positive photoresist becomes photosensitive and cannot be left as a highly accurate pattern after development. According to the characteristics of the single focus exposure method, when the defocus amount becomes 0.5 μm, both sides of the pattern start to be exposed, and when the defocus amount becomes 0.75 μm or more, even at the center of the pattern, the light intensity becomes larger than the reference light intensity I0. , The entire area of the pattern is exposed. Therefore, it can be seen that a defocus amount of up to 0.5 μm is permissible and a highly accurate pattern can be formed.

On the other hand, FIGS. 8 (a2) to 8 (e2) show the characteristics of the light intensity in the pattern with respect to the amount of defocus when the multifocal exposure method is applied to the positive photoresist. When the isolated pattern is exposed by the multiple bookstore exposure method, the state becomes close to the reference light intensity I0 even when the defocus amount in FIG. 9A is 0, and both sides of the pattern are exposed. Therefore, it can be seen that, when the defocus amount in FIGS. 9B to 9E gradually increases, the light intensity further becomes higher than the reference light intensity, and appropriate exposure is not performed on the entire pattern. This is because, when exposing an isolated pattern in a positive photoresist, the isolated pattern of the reticle is formed as a light-impermeable area, and the exposed area on both sides of the isolated pattern is large. This is considered to be due to an increase in the amount of light that reaches the pattern area.

Therefore, when a pattern is formed on a positive photoresist using a reticle in which a high-density pattern and an isolated pattern are mixed, when a multifocal exposure method is employed with priority given to exposure of a high-density pattern. In addition, the isolated pattern is excessively exposed, and the pattern width dimension of the isolated pattern formed on the photoresist is reduced. If the isolated pattern is remarkable, the isolated pattern may not be formed at all. In particular, M
If the dimension of the gate electrode in the direction of the channel length, which is the dimension in the channel length direction, becomes 0.3 μm or less with the increase in the density and integration of the OS transistor, when the pattern is formed as an isolated pattern, It has been confirmed that the above phenomenon becomes remarkable, and a state occurs in which an isolated pattern cannot be formed at all.

In the case of an isolated pattern, such as a contact hole pattern, in which the photoresist in the isolated pattern region is removed, even in the case of a positive photoresist, exposure is performed only on the isolated pattern. And there is no exposure around it,
The wraparound of the exposure light from the surroundings as described above does not occur, and the above-described problem does not occur. That is, the above problem occurs when the photoresist in the region corresponding to the isolated pattern is to be removed.

As a technique for increasing the resolution,
Conventionally, there is a phase shift exposure method, but this phase shift exposure method is effective when applied to a specific pattern, especially a repetitive pattern, and an irregular pattern or one or several patterns are different from other patterns. It is difficult to apply the method to isolated patterns arranged at a distance. .

An object of the present invention is to provide a pattern forming method capable of forming an isolated pattern in a photoresist with high precision. Another object of the present invention is to provide a pattern forming method capable of forming each pattern with high precision in a reticle pattern in which a high-density pattern and an isolated pattern are mixed.

[0012]

According to the present invention, the short side has a length of 0.3.
A method of exposing an isolated pattern on a reticle having a size of μm or less to a photoresist formed on a wafer surface by a multifocal exposure method to form a pattern corresponding to the isolated pattern on the photoresist. It is characterized by using a resist. In particular, in the present invention, a remarkable effect can be expected when applied to the case where the isolated pattern on the reticle is a light transmission pattern.

Here, the multi-focus exposure method is a method of multiplexing the isolated pattern at two or more different positions sandwiching the focus position in the exposure optical axis direction with respect to the focus position of the photoresist. Focus exposure can be used. For example, when the center position in the thickness direction of the photoresist is set as the focus position of the photoresist, the two or more different imaging positions are the focus positions within the range of the thickness of the photoresist. Is a position to sandwich.

In the present invention, the reticle includes the isolated pattern and a high-density pattern in which a plurality of patterns are densely arranged in a region apart from the isolated pattern, and the photoresist includes the isolated pattern. It is possible to simultaneously form a pattern and a pattern corresponding to a high-density pattern. In particular, the isolated pattern is a gate electrode of a MOS transistor, and the short side is the MOS transistor.
It is suitable to be applied to the case where the length is in the channel length direction of the transistor.

According to the present invention, even when an isolated pattern is formed by the multi-focus exposure method, the isolated pattern is light-transmissive and the surrounding area is a light-impermeable region by using a negative photoresist for the photoresist. With this configuration, light from the periphery of the isolated pattern hardly affects the isolated pattern, and a highly accurate pattern can be formed even when the multi-focus exposure method that can obtain high light intensity is adopted.

[0016]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of a projection reduction exposure apparatus to which the present invention is applied. A light source 101 for emitting light for exposing the photoresist to expose the photoresist, and a condenser lens 102 and a reflection mirror 103 for converting the light emitted from the light source 101 into a parallel light beam or a converged light beam , Condenser lens 104
And the like, and a projection optical system 106 for projecting and reducing exposure of the reticle R illuminated by the illumination optical system 102 onto the semiconductor wafer W. The reticle R is held on a reticle stage 107, and is configured as a negative reticle in which a pattern region formed on the semiconductor wafer is formed as a light transmitting region as described in detail later. On the other hand, the semiconductor wafer W
Is mounted on a wafer stage, and its surface is coated with a negative photoresist to be patterned as described later. Further, the wafer stage 108 on which the semiconductor wafer W is mounted can adjust the wafer position in the plane xy direction and the θ direction by the stage driving mechanism 109, and the thickness direction of the semiconductor wafer W, that is, the projection optical system 106 The position can be adjusted in the optical axis direction. The position adjustment in the optical axis direction is performed so that the position is set continuously in the optical axis direction or at a plurality of positions in the optical axis direction set in advance. In this embodiment, two positions in the optical axis direction are set. The position can be adjusted at the location.

FIG. 2 is an enlarged cross-sectional view of the reticle R and the semiconductor wafer W. In the reticle R, a light-impermeable light-shielding film 202 such as chrome is formed on the surface of a light-transmissive substrate 201 such as glass. Is formed, and the light-shielding film 202 is selectively removed to form a pattern. Here, as the pattern shape of the reticle R, a high-density pattern 203 in which many line-shaped patterns are arranged at high density, and an isolated pattern 2 in which similar line patterns do not exist in the periphery.
04 are mixed.
The surface of the semiconductor wafer W is coated with a negative photoresist NPR and prebaked. The high-density pattern 203 provided on the reticle R
The light from the illumination optical system 102 is transmitted through each light transmission region of the isolated pattern 204 and the transmitted light is used by the projection optical system 106 to transfer the patterns 203 and 204 to the photoresist NPR on the surface of the semiconductor wafer W. Exposure is performed to expose an area corresponding to the pattern shape.

At this time, FIG. 3 is an enlarged cross-sectional view of the exposed region of the negative photoresist NPR.
In the initial stage of exposure, the wafer stage 108 shown in FIG. 1 is set to a position displaced by a small distance toward the projection optical system 106 along the optical axis direction of the projection optical system 106 by the stage driving mechanism 109, and 106, the pattern image Z of each pattern 203, 204 of the reticle R
Is the original focus position of the photoresist NPR,
Here, a substantially central position S0 in the thickness direction of the photoresist is used.
Exposure is performed while focusing on a position S1 displaced closer to the surface of the wafer W than the surface S1. Next, in the later stage of exposure, the wafer stage 108 is adjusted to a position displaced to the side opposite to the projection optical system side 106, and the image formation position of each pattern by the projection optical system 106 is adjusted to the photoresist NPR.
Exposure is performed while focusing on a position S2 displaced to the opposite side of the wafer W from the in-focus position S0. This allows
With respect to the negative photoresist NPR, two side positions S1 and S2 in the optical axis direction with respect to the focus position S0.
2, a multi-focus exposure is performed in which the respective patterns 203 and 204 of the reticle R are imaged.

As a result, the high-density pattern 2 of the reticle R
In 03, pattern exposure is performed using the advantages of the conventional multifocal exposure method as they are. In this pattern exposure, the resolution is slightly reduced as compared with the multifocal exposure using a positive photoresist, but it is possible to form a pattern with desired accuracy. On the other hand, in the isolated pattern 204 of the reticle R, by performing multifocal exposure, extremely high pattern dimensional accuracy can be obtained unlike the case of a positive photoresist. FIG. 4 is a view showing the state, and shows the reference light intensity and the light intensity corresponding to the defocus amount in the negative photoresist. Here, it is shown that it is difficult to form a pattern with high accuracy if the light intensity is lower than the reference light intensity I0 because the photoresist is a negative photoresist. 4 (a1) to 4 (e1) show that the defocus amounts are 0 μm, 0.25 μm, 0.5 μm and 0.75 μm.
The light intensity characteristics by the single focus exposure method in each case of m and 1 μm are shown. Here, the defocus is 0.75 μm.
Above, the light intensity is equal to or lower than the reference light intensity I0, and the degree is the same as that of the positive photoresist shown in FIG. However, FIGS. 4 (a2) to (e)
2) In the case of the multifocal exposure method shown in FIG.
In this case, a light intensity almost equal to the reference light intensity I0 can be secured. Therefore, by performing the multifocal exposure method using the negative photoresist, the width dimension of the isolated pattern is not reduced or increased, and a highly accurate pattern can be formed.

Actually, the reticle R in which the high-density pattern 203 and the isolated pattern 204 coexist is used, and in particular, the reticle R in which the high-density pattern having the short side dimension of 0.3 μm or less and the isolated pattern coexist is used. When a pattern was formed on a negative photoresist and a negative photoresist by a multifocal exposure method, pattern formation of a high-density pattern was effective with a positive photoresist, but pattern defects occurred in an isolated pattern. On the other hand, with the negative photoresist NPR as shown in FIG. 2, the formation of the high-density pattern 205 and the isolated pattern 206 of the photoresist could be realized corresponding to the high-density pattern 203 and the isolated pattern 204, respectively. In addition, not only the reticle in which the high-density pattern and the isolated pattern are mixed as described above, but also the reticle in which the isolated pattern is formed can realize the formation of the high-precision pattern.

In support of the above-described embodiment, FIG. 5 shows the results of experiments performed by the present inventor on a positive photoresist and a negative photoresist for the above-described isolated pattern. Here, the pattern width (shortest pattern dimension) in the short side direction of the isolated pattern is set to 180 μm, and a bodied photoresist and a negative photoresist are each formed to a thickness of 500 nm.
Exposure was performed with a projection reduction exposure apparatus using KrF light of = 0.6 as a light source. FIGS. 5A and 5B respectively show the line width-focus curve of the bodied photoresist and the negative photoresist. The depth of focus of each of the hoji type and negative type photoresists in the single focus exposure method is 0.1 mm.
35 μm and 0.45 μm. Therefore, the depth of focus when multifocal exposure with a focal width of 1.5 μm is performed on a negative photoresist is 0.75 μm, which is more than twice as large as in the case of the single-focus exposure method using a positive photoresist.
As described above, it is needless to say that the dimensional error of the isolated pattern due to the defocus is reduced by increasing the depth of focus in the negative photoresist.

Further, the present invention is not limited to the case of forming a pattern of a gate electrode of a MOS transistor constituting a logic device or the like. The present invention can be applied to a case where a photoresist pattern is formed by using a reticle including the above.

[0023]

As described above, the present invention forms an isolated pattern by exposing an isolated pattern on a reticle having a short side of 0.3 μm or less to a photoresist formed on a wafer surface by a multifocal exposure method. The method is characterized in that a negative photoresist is used as the photoresist. In particular, in the present invention, by applying when the isolated pattern on the reticle is a light transmission pattern,
The isolated pattern is light-transmissive and has a configuration in which the surrounding area is a light-impermeable area. Light from the periphery of the isolated pattern is less likely to affect the isolated pattern, and multiplexing that provides high light intensity is obtained. Even when the focus exposure method is adopted, highly accurate pattern formation can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a projection exposure apparatus for carrying out a method of the present invention.

FIG. 2 is an enlarged sectional view of a part of a reticle and a semiconductor wafer.

FIG. 3 is a diagram for explaining an image formation position by a multiple (double) focus exposure method.

FIG. 4 is a diagram showing light intensity characteristics of a negative photoresist by a single focus exposure method and a multiple focus exposure method.

FIG. 5 is a diagram showing a simulation result supporting the operation and effect of the present invention.

FIG. 6 is a schematic diagram for explaining pattern exposure on a bodied photoresist and a negative photoresist.

FIG. 7 is a diagram showing light intensity characteristics for explaining an advantage of the multifocal exposure method.

FIG. 8 is a diagram showing light intensity characteristics of a single focus exposure method and a multiple focus exposure method on a bodi type photoresist.

[Explanation of symbols]

 Reference Signs List 101 light source 102 illumination optical system 106 projection optical system 107 reticle stage 108 wafer stage 109 stage driving mechanism 201 glass substrate 202 light-shielding film 203 high-density pattern (reticle) 204 isolated pattern (reticle) 205 high-density pattern (photoresist) 206 isolated pattern (Photoresist) R Reticle W Semiconductor wafer NPR Negative photoresist PPR Positive photoresist

Claims (6)

[Claims] An isolated pattern on a reticle having a short side of 0.3 μm or less is exposed on a photoresist formed on a wafer surface by a multifocal exposure method to form a pattern corresponding to the isolated pattern on the photoresist. A method of forming a pattern, wherein a negative photoresist is used as the photoresist. 2. The pattern forming method according to claim 1, wherein the isolated pattern on the reticle is a light transmitting pattern. 3. The multi-focus exposure method according to claim 1, wherein the focus is formed on the photoresist at two or more different positions sandwiching the focus in the exposure optical axis direction. 3. The pattern forming method according to claim 2, which is an exposure method. 4. When the center position of the photoresist in the film thickness direction is a focus position of the photoresist, the two or more different imaging positions are within the range of the photoresist film thickness. The pattern forming method according to claim 3, wherein the pattern is a position sandwiching the focus position. 5. The reticle includes the isolated pattern,
5. A high-density pattern in which a plurality of patterns are densely arranged in a region apart from the isolated pattern, and a pattern corresponding to the isolated pattern and the high-density pattern is simultaneously formed on the photoresist. The pattern forming method according to any one of the above. 6. The pattern forming method according to claim 1, wherein said isolated pattern is a gate electrode of a MOS transistor, and said short side is a length dimension in a channel length direction of said MOS transistor.