JPH0955350A - Exposure method and aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exposure method and an aligner in which an arbitrary light-source shape can be obtained by using a comparatively simple filter and without using a special filter. SOLUTION: An exposure method and an aligner comprise at least a process in which a mask is irradiated with exposure light through a first filter 52 within one exposure time and a process in which the mask is irradiated with the exposure light through a second filter 54 whose optical transmittance distribution is different from that of the first filter 52.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method and an exposure apparatus for forming a fine pattern on the surface of a semiconductor substrate, for example.

[0002]

2. Description of the Related Art Currently, in the research and development of semiconductor integrated circuits, devices having a design rule in the sub-half micron region are being researched and developed. Photolithography technology is essential in the development of these devices. It is no exaggeration to say that the resolution performance of the exposure apparatus used in this photolithography technique, that is, the so-called reduction projection exposure apparatus, determines the success or failure of R & D and mass production of semiconductor devices.

[0003]

In such an exposure apparatus, a filter for controlling the light transmittance is provided between the light source of the semiconductor exposure apparatus and the mask, and the light intensity distribution is normally a Gaussian distribution. The so-called modified illumination method, in which the resolution and the depth of focus are improved by various changes, is drawing attention.

For example, as shown in FIG. 1, a simple filter in which four circular openings 4 are formed on a disk 2 having a transmittance of 0 is used to realize modified illumination. However, the conventional modified illumination method using a filter has an effect only on a specific pattern and rather has a bad influence on a certain pattern, so various light sources have been proposed from the viewpoint of practical use. .

For example, a light source having a flat intensity distribution with no difference in intensity or a light source provided with a filter for giving a phase difference to light has been proposed. In order to create such a light source, conventionally, a filter having a complicated shape, a so-called halftone type filter having partially different transmissivity, etc. have been used. However, such a filter is difficult to make, and the intensity uniformity of the light source is deteriorated, and as a result, a good pattern may not be formed.

The present invention has been made in view of the above circumstances, and provides an exposure method and an exposure apparatus capable of obtaining an arbitrary light source shape by using a relatively simple filter without using a special filter. With the goal.

[0007]

In order to achieve the above object, a first exposure method according to the present invention irradiates a mask with exposure light through a first filter within one exposure time. The method further includes at least a step and a step of irradiating the mask through the exposure light through the second filter having a light transmittance distribution different from that of the first filter.

The second exposure method of the present invention comprises the step of irradiating the mask with the exposure light through the first filter within one exposure time, and the exposure light without passing through the first filter. And a step of irradiating the mask. An exposure apparatus according to the present invention includes a first filter that is movably arranged in an optical path between a light source and a mask and that changes a light intensity distribution of exposure light, and the first filter within one exposure time. Has a high-speed switching means for switching between a position crossing the optical path and a position not crossing the optical path.

The exposure apparatus according to the present invention further has a second filter having a transmittance distribution different from that of the first filter and changing the light intensity distribution of the exposure light, and the high-speed switching means allows one exposure to be performed once. It is preferable to switch the filter inserted into the optical path to the first filter and the second filter within a time period. Furthermore, in the exposure apparatus according to the present invention, the plurality of filters that can be switched within one exposure time may be a total of three or more filters in addition to the first filter and the second filter.

The high-speed switching means is not particularly limited, but includes a rotary disk having a plurality of filters formed along the circumferential direction, a slide disk having two or more filters formed along the slide movement direction, and the like. It can be illustrated. In the exposure method using the exposure apparatus according to the present invention, each filter has a relatively simple shape. In the present invention, the filters having different transmittance distributions are switched at high speed within one exposure time. Or when performing exposure through a filter of a certain type within one exposure time,
It switches at high speed when performing exposure without passing through the filter. For example, assuming that the total exposure time of one time is T, the exposure through the first filter is performed in the first 0.2T time, and the exposure through the second filter is performed in the remaining 0.8T time. To do. The transmittance distribution of the first filter and the transmittance distribution of the second filter are different from each other. That is, the light intensity distribution of the light source obtained in the first 0.2T time is different from the light intensity distribution of the light source obtained in the next 0.8T time.

According to Hopkins' partially coherent theory, the lights coming from the respective points of these light sources do not interfere with each other, but by adding them together, an actual light intensity distribution can be obtained. Therefore, in the present invention, without using a filter having a complicated shape or a halftone filter,
It is possible to easily obtain a light intensity distribution equivalent to the case where these are used.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An exposure method and an exposure apparatus according to the present invention will be described below in detail with reference to the embodiments shown in the drawings. First Embodiment First, the overall configuration of the exposure apparatus will be described with reference to FIG.

As shown in FIG. 2, this exposure apparatus comprises a laser device and a stepper device. The laser device
An excimer laser 30, a dose control unit 31,
It is composed of a shifting unit 33 and a firing optical system 34. The stepper device includes a beam splitter 35,
The prism unit 36, a fly-eye lens 37, a masking blade 38, a reticle 39, and a projection lens 40. The exposure light emitted from the excimer laser 30 passes through the various optical systems described above,
The light enters the fly-eye lens 37, and the fly-eye lens 37 serves as a secondary light source (effective light source). The exposure light passes through the reticle 39 on which the mask pattern is formed, and the wafer 41 is exposed.
Then, the pattern of the reticle 39 is transferred onto the wafer surface. The reticle 39 is not particularly limited,
A conventional chrome mask or phase shift mask is used.

A plurality of fly-eye lenses 37 (for example, 1
The total outer diameter is 5 cm to 20 cm. In this embodiment, in order to improve the secondary source light intensity distribution of the exposure light from the fly-eye lens 37 as an effective light source to the reticle 39, the light-incident side or the light-exit side of the fly-eye lens 37 is A slide movement type filter switching device 50 shown in FIG. 3 is arranged. The filter switching device 50 has a filter body 51 formed with a first filter portion 52 and a second filter portion 54. The first filter section 52 and the second filter section 54 have different light transmittance distributions. The intensity distribution of the light after passing through the first filter unit 52 is as shown by a curve 52a in FIG.
The intensity distribution of light after passing through the filter unit 54 is shown in FIG.
It becomes like a curve 54a in (B). That is, the first filter portion 52 has a high transmittance in the central portion, and the second filter portion 54, on the contrary, has a low transmittance in the central portion.

In this embodiment, the two filter units 5
The filter main body 51 formed with 2, 54 is slid by a switching device. For example, when the total exposure time is 1 second, the exposure light is passed through the first filter unit 52 for 0.5 second. , For the remaining 0.5 seconds,
Exposure light is passed through the second filter unit 54 to perform exposure.
From the viewpoint of improving throughput, this slide movement is
It is preferable to do it instantly.

As described above, by switching the filter section through which the exposure light is transmitted within one exposure time, the light intensity distribution curve 52a shown in FIG. 3B and the light intensity distribution curve 52a shown in FIG. 3B can be obtained from Hopkins' partially coherent theory. Intensity distribution curve 54
The light intensity distribution shown in FIG. 3 (C) is obtained by adding a and a. This light intensity distribution is, for example, as shown in FIG.
The transmittance of the central part is several tens of percent, and the transmittance around it is 0%.
And is equivalent to the case where exposure is performed using a single filter 56 having a transmittance of 100% around it.

In this embodiment, in the light intensity distribution shown in FIG. 3 (C), the exposure light is passed through the first filter portion 52 with respect to the height ratio between the central peak and the peripheral peak. It can be freely adjusted by changing the ratio between the time and the time during which the exposure light is passed through the second filter unit 54. That is, in the present embodiment, two or more filter portions having a relatively simple shape are created, and by switching these, it is possible to obtain the same effect as when a filter having a complicated shape is used. Moreover, the resulting figure 3
In the light intensity distribution shown in (C), the height of each peak of the light intensity distribution can be freely changed.

As shown in FIG. 3C, by emphasizing the light in the peripheral portion and leaving the light in the central portion to some extent, compared with normal exposure using Gaussian distribution or modified illumination, It is expected to have a light intensity distribution close to a flat shape, have no weak points in a specific pattern, and realize good pattern resolution.

Embodiment 2 In this embodiment, the filter body 51 shown in FIG. 5A is replaced with a filter body 58 and a switching device 59 instead of the filter body 51 shown in FIG. 3 used in the first embodiment. Exposure is performed in the same manner as in the first embodiment. Switching device 59
Is a slide type switching device as in the first embodiment. The filter body 58 includes a first filter portion 60.
The second filter portion 62 and the third filter portion 64 are formed. The light transmittance distribution of the first filter unit 60 is similar to the distribution curve 52a shown in FIG.
The light transmittance distribution of the second filter portion 62 is a distribution in which a region having a high light transmittance exists in a relatively small ring shape.
Further, the light transmittance distribution of the third filter portion 64 is a distribution in which a relatively large ring-shaped region having a high light transmittance exists.

The light intensity distribution of the light source obtained as a result of the exposure light being switched by the slide device and transmitted through these three filter portions within one exposure time is as follows.
The distribution is as shown in FIG. In the present embodiment, three or more filter parts having a relatively simple shape are created, and by switching these, it is possible to obtain the same effect as when a filter having a complicated shape is used. Moreover,
In the resulting light intensity distribution shown in FIG. 5B, the height of each peak in the light intensity distribution can be freely changed.

Further, in this embodiment, as in the first embodiment, as shown in FIG. 5B, the light in the peripheral portion is emphasized while leaving the light in the central portion to some extent. Compared with normal exposure using Gaussian distribution and modified illumination, it has a light intensity distribution that is closer to a flat shape, and it is expected to realize good pattern resolution without weak points in the specific pattern.

Example 3 This example is the same as Example 1 except that the device shown in FIG. 6A was used as a means for changing the light intensity distribution from the resulting light source. Then, exposure was performed. Other configurations are the same as those in the first embodiment.

In this embodiment, a rotary disc type filter switching device 90 shown in FIG. 6A is arranged on the light incident side or the light emitting side of the fly-eye lens 37 shown in FIG. The filter switching device 90 has a rotary disk 92 and a rotary drive shaft 94 that drives the rotary disk 92.
On the rotating disk 92, a light transmitting opening 95, a filter 96, and other filters are formed along the circumferential direction. For example, as shown in FIG. 7A, the filter 96 is designed to block light in the range of 0.5 at the center when the outer diameter is 1.0.

When the total exposure time of one time is set to 1 second, the opening 9 shown in FIG.
5, light for exposure (light having the distribution shown in FIG. 8) is passed through, and then,
The rotary disk 92 is instantaneously rotated, and exposure light is passed through the filter 96 for exposure in the remaining 0.8 seconds. As a result, as shown in FIG. 9, the light intensity distribution from the effective light source per exposure time is the product of the light intensity distribution and time shown in FIG. 8 and the filter shown in FIG. The light intensity distribution is equal to the sum of the product of the light intensity distribution and the time.

In the present embodiment, by adjusting the balance between the time for passing through the opening portion 95 shown in FIG. 6A and the time for passing through the filter 96, the light quantity distribution of the resulting irradiation light ( (Equivalent to light intensity distribution) can be changed. In this embodiment, by combining the case of exposing through a filter having a relatively simple shape and the case of exposing without a filter, a light intensity distribution of a light source equivalent to that obtained by a filter having a relatively complicated shape is obtained. Obtainable.

Therefore, also in the present embodiment, as in the first embodiment, by emphasizing the light in the peripheral portion and leaving the light in the central portion to some extent, the specific pattern does not have a weak point. It is expected to realize good pattern resolution. Example 4 This example is the same as Example 1 except that the device shown in FIG. 6B was used as a means for changing the light intensity distribution from the resulting light source. The optimum light source shape was searched. Other configurations are the same as those in the first embodiment.

In this embodiment, it is assumed that the intensity distribution of light incident on the fly-eye lens 37 as an effective light source is a flat light intensity distribution as shown in FIG. In this embodiment, for example, the slide type filter switching device 97 shown in FIG.
Are arranged on the light incident side or the light emitting side of the fly-eye lens 37 shown in FIG. The filter switching device 97 has a filter holder 98 that accommodates a plurality of types of filters 96a to 96d and can slide these filters at high speed. The filter 96a is, for example, as shown in FIG.
As shown in (A), when the outer diameter is 1.0, the central range of 0.5 blocks light. Further, as shown in FIG. 7B, the filter 96b is designed to block light in a cross-shaped range having a width of 0.35 when the outer diameter is 1.0.

When the total exposure time of one time is set to 1 second, the holder 9 shown in FIG.
All of the filters 96a to 96d are moved backward in 8 and the exposure light is not passed through the filters. afterwards,
The filter 96a is instantly slid and moved, and the exposure light is passed through the filter 96a for exposure at 0.3 seconds. Next, the filter 96a shown in FIG. 6 (B) is instantaneously slid into the holder 98 to move backward, and at the same time,
The filter 96b is slid and moved forward, and in the remaining 0.5 seconds, exposure light is passed through the filter 96b to perform exposure. As a result, as shown in FIG. 10, the light intensity distribution from the effective light source per exposure time is the product of the light intensity distribution and time shown in FIG. 8 and the filter shown in FIG. The product of the above-mentioned light intensity distribution and time is equal to the sum of the product of the light intensity distribution through the filter and the time shown in FIG.

In the present embodiment, the light quantity distribution of the light emitted as a result (equivalent to the light intensity distribution) is adjusted by adjusting the time when the filters 96a to 96d shown in FIG. The shape of can be changed. In the present embodiment, by combining the case of exposing through two kinds of filters having a relatively simple shape and the case of exposing without a filter, a light source equivalent to that obtained by a filter of a relatively complicated shape is obtained. The light intensity distribution can be obtained.

Therefore, also in the present embodiment, as in the first embodiment, by emphasizing the light in the peripheral portion and leaving the light in the central portion to some extent, the specific pattern has no weak point, It is expected to realize good pattern resolution. Example 5 In this example, the same procedure as in Example 1 was carried out except that the device shown in FIG. 6C was used as a means for changing the light intensity distribution from the resulting light source. The optimum light source shape was searched. Other configurations are the same as in the first embodiment.

In this embodiment, it is assumed that the intensity distribution of light incident on the fly-eye lens 37 as an effective light source is a flat light intensity distribution as shown in FIG. In this embodiment, for example, the optical shutter type optical material 100 shown in FIG. 6C is arranged on the light incident side or the light emitting side of the fly-eye lens 37 shown in FIG. This optical shutter type optical material is, for example, PLZT.
(La-added lead zirconate titanate), which is a material whose light transmittance changes by providing a plurality of thin electrodes on at least one surface of a substrate and applying a voltage. By devising the shape of the electrode provided on the surface of the optical material 100,
The central region 102 and the peripheral region 104 can be separately controlled, and a voltage is applied to the central region 102 in an instant.
Only the light can be shielded.

When the total exposure time of one time is set to 1 second, the central portion 1 shown in FIG.
02 and the peripheral portion 104 are set in a light transmitting state, and exposure light is passed through these regions. After that, a voltage is instantaneously applied only to the electrode of the central portion 102 to bring the central portion 102 into a light-shielded state, and the exposure light is passed in that state. As a result, the same result as in the third embodiment can be obtained.

In the present embodiment, various light intensity distribution shapes can be obtained as a result by devising the shape of the electrodes formed on the surface of the optical material 100, the arrangement interval, the voltage application conditions, and the like. In this embodiment, by using the optical shutter, it is possible to obtain the light intensity distribution of the light source that is equivalent to that obtained by using the filter having a relatively complicated shape.

Therefore, also in the present embodiment, as in the first embodiment, by emphasizing the light in the peripheral portion and leaving the light in the central portion to some extent, the specific pattern has no weak point, It is expected to realize good pattern resolution. Sixth Embodiment In this embodiment, the secondary light source having the light intensity distribution shown in FIG. 11 is realized by adopting the means of any of the above-mentioned respective embodiments.

FIG. 11 (A) shows the light intensity distribution by numbers, where * indicates the peak portion of the light intensity, and the numbers 0-9 indicate the peak portion of 10. The ratio of the light intensity is shown, and the light intensity distribution is low in the central part and high in the peripheral part. In addition, FIG. 11B is the same as FIG.
3 is a three-dimensional view of the light intensity distribution shown in FIG.

By combining and using an effective light source having this light intensity distribution and a phase shift mask,
As shown in FIG. 3, it was confirmed that the DOF (depth of focus) can be increased without causing the problem of resolution due to the secondary peak in the dense pattern.

In FIG. 12, (B) shows an effective light source having a low light intensity at the central portion and a halftone phase shift mask, and a KrF excimer laser stepper with an NA of 0.45, and an inner diameter of 0.30 μm. An example in which a contact hole pattern is formed on a substrate is shown. In this experiment, the chemically amplified positive resist (WKR-P) was used as the resist.
T2) was used. The ratio (duty ratio) of the inner diameter of the contact hole and the distance between them is 1: 3, 1: 1.5,
A contact hole pattern was formed for each pattern changed to 1: 1. The result of the SEM photograph is shown in FIG.

For comparison, contact hole patterns were formed under three different conditions in the same manner except that the light intensity distribution applied to the fly-eye lens was changed to the Gaussian distribution shown in FIG. 12 (A). . Further, for comparison, contact hole patterns were formed under three different conditions in the same manner except that the light intensity distribution for illuminating the effective light source was an annular illumination distribution (light intensity at the central portion was 0). . The result observed with the SEM photograph is shown in FIG. From these experimental results, exposure having a light source with a weak light intensity distribution in the central portion even when the distance between the contact holes is narrowed (FIG. 12 (B),
In (C), it was confirmed that the secondary peak was hardly resolved.

A curve B in FIG. 13 shows the relationship between the hole size and the focus when the isolated pattern is formed by using the light source shape shown in FIG. 12B. The wider the curve is, the higher the DOF becomes. wide. In addition, the curve A in FIG.
2A shows the relationship between the hole size and the focus when an isolated pattern is formed using the light source shape shown in FIG. Furthermore, a curve C in FIG. 13 shows the relationship between the hole size and the focus when the isolated pattern is formed using the light source shape shown in FIG.

In this example (curve B), it was confirmed that the DOF was wider than that in the case of conventional annular illumination (curve C), although it was less than that of conventional ordinary illumination (curve A). . Note that the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the present invention.

[0041]

As described above, according to the present invention,
By using a filter having a relatively simple shape in combination, it is possible to obtain the same effect as when a filter having a complicated shape is used.

Further, according to the present invention, it is possible to realize a light source having a free light intensity distribution in which light in the central part is left to some extent while emphasizing light in the peripheral part, and there is a weak point in a specific pattern. Therefore, good pattern resolution can be realized.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a modified light source according to a conventional example.

FIG. 2 is a diagram showing an overall configuration of an exposure apparatus.

3A to 3C are diagrams showing a relationship between a filter and a light intensity distribution according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a filter for realizing the distribution shown in FIG. 3C with a single filter.

5A and 5B are diagrams showing a relationship between a filter and a light intensity distribution according to another embodiment of the present invention.

6A to 6C are views showing another example for changing the shape of the light source.

7A and 7B are diagrams showing examples of filters used in the examples.

FIG. 8 is a diagram showing a light intensity distribution used in an example.

FIG. 9 is a conceptual diagram showing addition of light intensity distributions.

FIG. 10 is a conceptual diagram showing addition of light intensity distributions.

FIG. 11A is a diagram showing numerical values of the light amount distribution in the embodiment, and FIG. 11B is a diagram showing the light amount distribution in three dimensions.

12A to 12C are SEM photographs of hole patterns showing the influence of the secondary pattern due to the light intensity distribution of the light source.

FIG. 13 is a graph showing that DOF is also improved in the case of the light source shape obtained by the method according to the embodiment of the present invention.

[Explanation of symbols]

 35 ... Beam splitter 36 ... Prism unit 37 ... Fly's eye lens 39 ... Reticle 41 ... Wafer 50 ... Switching device 51, 59 ... Filter main body 52, 60 ... 1st filter part 54, 62 ... 2nd filter part 64 ... 3rd Filter section

Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display location H01L 21/30 515D

Claims (4)

[Claims] 1. An exposure method in which exposure light from a light source is passed through a mask and the pattern formed on the mask is transferred to a substrate, wherein the exposure light is passed through a first filter within one exposure time. An exposure method comprising at least a step of irradiating a mask, and a step of irradiating a mask with exposure light through a second filter having a light transmittance distribution different from that of the first filter. 2. An exposure method in which exposure light from a light source is passed through a mask and the pattern formed on the mask is transferred onto a substrate, wherein the exposure light is passed through a first filter within one exposure time. An exposure method comprising at least a step of irradiating a mask and a step of irradiating the mask with exposure light without passing through the first filter. 3. An exposure apparatus which passes exposure light from a light source through a mask and transfers a pattern formed on the mask onto a substrate, wherein the exposure light is movably arranged in an optical path between the light source and the mask. An exposure apparatus having a first filter for changing the light intensity distribution of 1., and a high-speed switching unit for switching between a position where the first filter crosses the optical path and a position where the first filter does not cross within one exposure time. 4. A second filter having a transmittance distribution different from that of the first filter and changing the light intensity distribution of the exposure light, further comprising: 4. The exposure apparatus according to claim 3, wherein the filter inserted into the optical path is switched between the first filter and the second filter.