JP2001007020A - Exposure method and aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a pattern, having a complicated shape on a wafer by using two exposure methods which are the two-beam interference exposure method and a normal exposure method. SOLUTION: When a photosensitive substrate is subjected to normal exposure after the substrate is subjected to two-beam interference exposure, a multilevel exposure distribution is given to the substrate. Here by 'multileverl' is meant that the exposure given to the substrate is not a binary value (two kinds, including the case where the exposure is zero), but a ternary or higher value (three or more kinds, including the case where the exposure is zero). Here 'normal exposure' means an exposure where it can be made in various patterns, which are different from those of the two beam interference exposure even through the resolution is lower than the that of two-beam interference exposure.

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, and more particularly to an exposure method and an exposure apparatus for exposing fine circuit patterns on a photosensitive substrate. It is used for manufacturing various devices such as semiconductor chips such as ICs and LSIs, display elements such as liquid crystal panels, detection elements such as magnetic heads, and image pickup elements such as CCDs.

[0002]

2. Description of the Related Art Conventionally, when manufacturing devices such as ICs, LSIs, and liquid crystal panels using photolithography technology, a photomask or a reticle (hereinafter, referred to as a “mask”) is used.
It is written. The circuit pattern is projected onto a photosensitive substrate such as a silicon wafer or a glass plate (hereinafter, referred to as a "wafer") coated with a photoresist or the like by a projection optical system and transferred (exposed) there. 2.) A projection exposure method and a projection exposure apparatus are used.

In response to the high integration of the above-mentioned devices, there is a demand for a fine pattern, ie, a high resolution, to be transferred to a wafer and a large area of one chip on the wafer. In the above-mentioned projection exposure method and projection exposure apparatus, which are the center of the above, improvement in resolution and exposure area is being attempted to form an image having a dimension (line width) of 0.5 μm or less over a wide range.

FIG. 19 shows a schematic view of a conventional projection exposure apparatus. In FIG. 19, reference numeral 191 denotes an excimer laser which is a light source for exposure to far ultraviolet rays, 192 denotes an illumination optical system, 193 denotes illumination light, 194 denotes a mask, and 195 denotes an object side exposure which exits from the mask 1944 and enters the optical system 196. Light, 196 is reduction projection optical system, 197 is optical system 196
198 denotes a wafer which is a photosensitive substrate, and 199 denotes a substrate stage for holding the photosensitive substrate.

The laser light emitted from the excimer laser 191 is guided to an illumination optical system 192 by a drawing optical system, and a predetermined light intensity distribution, a light distribution, and an opening angle (numerical aperture NA) are projected by a projection optical system 192. ) Is adjusted so as to become the illumination light 193, and illuminates the mask 194. On the mask 194, a pattern having a size obtained by reversing a fine pattern to be formed on the wafer 198 by a reciprocal number (for example, 2, 4, or 5 times) of the projection magnification of the projection optical system 192 is formed on a quartz substrate by chrome or the like. The illumination light 193 is transmitted and diffracted by the fine pattern of the mask 194, and becomes the object side exposure light 195. The projection optical system 196 is
The object-side exposure light 195 is converted into image-side exposure light 197 that forms a fine pattern on the mask 194 on the wafer 198 at the above-described projection magnification and with sufficiently small aberration. As shown in the enlarged view at the bottom of FIG. 19, the image-side exposure light 197 has a predetermined numerical aperture NA (= sin θ).
) Converges on the wafer 198 to form an image of a fine pattern on the wafer 198. The substrate stage 199 is formed along the image plane of the projection optical system when a fine pattern is sequentially formed in a plurality of different areas (shot areas: areas forming one or more chips) of the wafer 198. The position of the wafer 198 with respect to the projection optical system 196 is changed by the step movement.

However, it is difficult for a projection exposure apparatus using the above-described excimer laser as a light source to form a pattern of 0.15 μm or less.

The projection optical system 196 has a resolution limit due to a trade-off between the optical resolution due to the exposure (used) wavelength and the depth of focus. The resolution R of the resolution pattern and the depth of focus DOF by the projection exposure apparatus are expressed by the following relay equations such as equations (1) and (2).

R = k ₁ (λ / NA) (1) DOF = k ₂ (λ / NA ² ) (2) where λ is the exposure wavelength, and NA is the brightness of the projection optical system 196. The numerical aperture on the image side, k ₁ , and k _{2, which} are represented, are constants determined by the development process characteristics of the wafer 198 and the like, and are usually about 0.5 to 0.7. From Equations (1) and (2), it can be seen from the equations (1) and (2) that the numerical aperture NA should be increased by increasing the numerical aperture NA to increase the resolution R to a small value.
However, in actual exposure, the depth of focus DOF of the projection optical system 196 needs to be set to a certain value or more, so a high NA
It is not possible to advance the process beyond a certain level, and to increase the resolution, the exposure wavelength λ is eventually reduced.
Is required.

However, as the wavelength becomes shorter, a serious problem arises. This problem is that the glass material of the lens of the projection optical system 196 runs out. The transmittance of most glass materials is close to 0 in the deep ultraviolet region, and fused quartz currently exists as a glass material manufactured for exposure equipment (exposure wavelength: about 248 nm) using a special manufacturing method. Also decreases sharply for exposure wavelengths below 193 nm,
Exposure wavelength 150nm corresponding to fine pattern of 0.15μm or less
In the following areas, it is very difficult to develop a practical glass material. In addition, the glass material used in the deep ultraviolet region must satisfy various conditions such as durability, uniformity of refractive index, optical distortion, workability, etc., in addition to transmittance. Existence is at stake.

As described above, in the conventional projection exposure method and projection exposure apparatus, in order to form a pattern of 0.15 μm or less on the wafer 198, it is necessary to shorten the exposure wavelength to about 150 nm or less. Since there is no practical glass material in this wavelength region, a pattern of 0.15 μm or less cannot be formed on the wafer 198.

US Pat. No. 5,415,835 discloses a technique for forming a fine pattern by two-beam interference exposure.
According to the light beam interference exposure, a pattern of 0.15 μm or less can be formed on the wafer.

The principle of two-beam interference exposure will be described with reference to FIG. The two-beam interference exposure is performed by dividing a laser beam having coherence from the laser 151 and being a parallel beam into two beams by a half mirror 152 and reflecting the two beams by a plane mirror 153, respectively. The laser beam (coherent parallel light beam) crosses at an angle greater than 0 and less than 90 degrees to form an interference fringe at the intersection, and the wafer 154 is formed by the interference fringe (light intensity distribution). By exposing and exposing, a fine periodic pattern according to the light intensity distribution of the interference fringes is formed on the wafer.

When the two light beams intersect on the wafer surface in the opposite direction to the vertical line of the wafer surface at the same angle in the opposite direction, the resolution R in the two light beam interference exposure is expressed by the following equation (3). Is done.

[0014] Here, R represents the width of each of L & S (line and space), that is, the width of each of the bright and dark portions of the interference fringes, and θ represents the incident angle (absolute value) of each of the two light beams with respect to each image plane, NA = sinθ
It is.

Expression for resolution in normal projection exposure
Equation (1) and equation for resolution in two-beam interference exposure (3)
Comparing with the equation, the resolution R of the two-beam interference exposure is (1)
Since this corresponds to the case where k ₁ = 0.25 in the equation, it is possible to obtain a resolution twice or more as high as that of a normal projection exposure in which k ₁ = 0.5 to 0.7 in two-beam interference exposure.
Although not disclosed in the above U.S. patent, for example, λ = 0.24
When NA = 0.6 at 8 nm (KrF excimer), R = 0.10μ
m is obtained.

[0016]

However, the two-beam interference exposure basically obtains only a simple fringe pattern corresponding to the light intensity distribution (exposure amount distribution) of the interference fringes.
A circuit pattern having a desired shape cannot be formed on a wafer.

The above-mentioned US Pat. No. 5,415,835 discloses that
After giving a simple fringe pattern, that is, a binary exposure amount distribution to the wafer (resist) by light beam interference exposure, a normal lithography (exposure) is performed using a mask having a certain opening, and then another binary is performed. It is proposed to obtain an isolated line (pattern) by giving a typical exposure distribution to a wafer.

However, the exposure method disclosed in the above-mentioned US Pat. No. 5,415,835 is more complicated because only the ordinary binary exposure amount distribution is formed in each of the two exposure methods of the two-beam interference exposure and the normal exposure. A circuit pattern having a shape could not be obtained.

Although the above-mentioned US Pat. No. 5,415,835 discloses that two exposure methods, two-beam interference exposure and normal exposure, are combined, an exposure apparatus which achieves such a combination is specifically shown. Not.

An object of the present invention is to provide an exposure method and an exposure apparatus capable of forming a pattern having a more complicated shape on a wafer by using two exposure methods, two-beam interference exposure and normal exposure. It is in.

Another object of the present invention is to provide an exposure method and an exposure apparatus capable of obtaining a circuit pattern having a portion having a line width of 0.15 μm or less.

Another object of the present invention is to provide an exposure apparatus capable of performing two exposure methods, two-beam interference exposure and normal exposure.

[0023]

An exposure method and an exposure apparatus according to the present invention perform two-beam interference exposure and normal exposure on a substrate to be exposed (photosensitive substrate), and perform at least one of the two exposures. Wherein a multilevel exposure amount distribution is given to the photosensitive substrate. "Multi-valued" means that the exposure given to the photosensitive substrate is not binary (two types including zero exposure), but the exposure given is three or more (three types including zero exposure). Above). In addition, `` normal exposure '' is exposure in which the resolution is lower than that of the two-beam interference exposure, but exposure can be performed in a pattern different from that of the two-beam interference exposure, and is typically masked by the projection optical system shown in FIG. Projection exposure for projecting the above pattern.

Each of the two-beam interference exposure and the normal exposure in the exposure method and the exposure apparatus of the present invention comprises one or more exposure steps. Different exposure distributions are given to the photosensitive substrate.

Further, the exposure method and the exposure apparatus of the present invention
Either the two-beam interference exposure or the normal exposure may be performed first.

When the second exposure is a projection exposure, the exposure wavelength of the first exposure and the second exposure of the exposure method and the exposure apparatus of the present invention are both 400 nm or less, preferably 25 nm or less.
0 nm or less. A KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 nm) is used to obtain light having an exposure wavelength of 250 nm or less.

In the present application, "projection exposure" means that three or more parallel light beams from an arbitrary pattern formed on a mask are incident on an image plane at various angles different from each other to perform exposure. It is what is done.

The exposure apparatus of the present invention has a projection optical system for projecting a mask pattern onto a wafer, and a mask illumination optical system capable of performing both partial coherent illumination and coherent illumination. It is characterized by performing normal exposure and performing two-beam interference exposure by coherent illumination. “Partial coherent illumination” is illumination in which the value of σ (= numerical aperture of the illumination optical system / numerical aperture of the projection optical system) is greater than zero and less than 1.
The term “coherent illumination” means that the value of σ is zero or a value close thereto, and is considerably smaller than σ of partially coherent illumination.

The exposure wavelength of this exposure apparatus is 400 nm or less, preferably 250 nm or less. To obtain light with an exposure wavelength of 250 nm or less, use a KrF excimer laser (about 248 nm).
m) or an ArF excimer laser (about 193 nm).

In an embodiment of the invention described later, an optical system capable of switching between partially coherent illumination and coherent illumination is disclosed as a mask illumination optical system.

Another exposure apparatus of the present invention is characterized by having a two-beam interference exposure apparatus, a normal (projection) exposure apparatus, and a moving stage for holding a substrate to be exposed (photosensitive substrate) shared by both apparatuses. . The exposure wavelength of this exposure apparatus is also 400 nm or less, preferably 250 nm or less. In order to obtain light having an exposure wavelength of 250 nm or less, a KrF excimer laser (about 24
8 nm) or an ArF excimer laser (about 193 nm).

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of an exposure method according to the present invention will be described with reference to FIGS.

FIG. 1 is a flowchart showing the exposure method of the present invention. FIG. 1 shows the two-beam interference exposure step, the projection exposure step (normal exposure step), and the development step, which constitute the exposure method of the present invention, and the flow thereof. The two-beam interference exposure step and the projection exposure step May be reversed from that shown in FIG. 1, or if either one of the steps includes a plurality of exposure steps, the steps may be performed alternately. Although there is a step of performing precise alignment between each exposure step, it is not shown here.

When performing exposure according to the flow of FIG.
First, a wafer (photosensitive substrate) is exposed by a two-beam interference exposure with a periodic pattern (interference fringes) as shown in FIG. The numbers in FIG. 2 represent the exposure amount, and the hatched portions in FIG. 2A indicate the exposure amount 1 (actually arbitrary) and the white portions indicate the exposure amount 0.

When developing only such a periodic pattern after exposure, usually, the exposure threshold value E of the resist on the photosensitive substrate is used.
th is the exposure amount 0 and 1 as shown in the lower graph of FIG.
Set between. The upper part of FIG. 2B shows a finally obtained lithography pattern (concavo-convex pattern).

FIG. 3 shows the dependence of the film thickness after development on the amount of exposure and the exposure threshold value of the resist on the photosensitive substrate in this case, with the positive resist (hereinafter referred to as "positive") and the negative resist. Each of the resists (hereinafter referred to as “negative type”) is shown, and the film after development is indicated when the positive type is equal to or more than the exposure threshold, and when the negative type is equal to or less than the exposure threshold. The thickness becomes 0.

FIG. 4 is a schematic diagram showing a state in which a lithography pattern is formed through the development and etching processes in the case of performing such exposure, for a negative type and a positive type.

In this embodiment, unlike the normal exposure sensitivity setting, as shown in FIGS. 5 (same as FIG. 2A) and FIG. 6, the maximum exposure amount in the two-beam interference exposure is set to 1. Then, the exposure threshold value Eth of the resist on the photosensitive substrate is set to be larger than 1. When the exposure pattern (exposure amount distribution) obtained by performing only the two-beam interference exposure shown in FIG. 2 is developed, the exposure amount becomes insufficient. Does not occur, and no lithography pattern is formed by etching. This can be considered as the disappearance of the two-beam interference exposure pattern (the present invention will be described using an example in which a negative type is used. But you can do it.) In FIG. 6, the upper part shows the lithography pattern (nothing can be done), and the lower part shows the relationship between the exposure amount distribution and the exposure threshold. Incidentally, E ₁ according to bottom the exposure amount in the two-beam interference exposure, E ₂ represents an exposure amount in the conventional projection exposure.

The feature of this embodiment is that a high-resolution exposure pattern, which is apparently lost only by two-beam interference exposure, is fused with an exposure pattern by ordinary projection exposure to selectively expose a desired region only in a resist. Exposure is performed at a threshold value or more to finally form a desired lithography pattern.

FIG. 7A shows an exposure pattern by ordinary projection exposure. In this embodiment, the resolution of ordinary projection exposure is about half that of two-beam interference exposure. The line width of the pattern is shown as approximately twice as large as the line width of the exposure pattern obtained by the two-beam interference exposure.

Assuming that the projection exposure for forming the exposure pattern shown in FIG. 7A is performed over the same region of the same resist without the development step after the two-beam interference exposure shown in FIG. Is shown in the lower graph of FIG. 7B. Here, the ratio of the exposure amount E ₂ of the exposure amount E ₁ and the projection exposure of two-beam interference exposure is 1: 1, the resist exposure threshold E _th exposure amount E ₁ (= 1) and the exposure amount E ₁ 7 is set to the sum (= 2) of the exposure amount E ₂ of the projection exposure and FIG.
The lithography pattern shown in the upper part of (B) is formed. The isolated line pattern shown in the upper part of FIG. 7B has a resolution of two-beam interference exposure, and has no simple periodic pattern. Therefore, a pattern having a resolution higher than that which can be realized by ordinary projection exposure is obtained.

Here, suppose that the projection exposure for forming the exposure pattern shown in FIG. 8 (the line width twice as large as that of the exposure pattern shown in FIG. 5 and the exposure threshold or more (here, the exposure amount twice as large as the threshold)). )
Is performed over the same region of the same resist without the development step after the two-beam interference exposure in FIG. 5, the total exposure distribution of the resist is as shown in FIG.
The exposure pattern of the light beam interference exposure disappears, and finally only the lithography pattern by the projection exposure is formed.

As shown in FIG. 9, the same principle applies to the case where the exposure is performed with a line width three times as large as the exposure pattern of FIG. The line width of the finally obtained lithography pattern is obvious from the combination of the exposure pattern having the width and the exposure pattern having the triple line width, and all the lithography patterns that can be realized by the projection exposure are formed in the present embodiment. It is possible.

By adjusting the exposure amount distribution (absolute value and distribution) and the threshold value of the resist on the photosensitive substrate by the two-beam interference exposure and the projection exposure briefly described above,
6, consisting of a combination of various patterns as shown in FIGS. 7 (B), 8 (B) and 9 (B), and having a minimum line width of 2
A circuit pattern having the resolution of the light beam interference exposure (the pattern of FIG. 7B) can be formed.

The principles of the above exposure method can be summarized as follows: The pattern area where projection exposure is not performed, that is, the two-beam interference exposure pattern which is equal to or less than the exposure threshold value of the resist disappears by development. 2. Regarding the pattern area of the projection exposure performed with the exposure amount equal to or less than the exposure threshold value of the resist, the exposure pattern having the resolution of the two beam interference exposure determined by the combination of the pattern of the projection exposure and the two beam interference exposure is used. It is formed. 3. The pattern area of the projection exposure performed with the exposure amount equal to or larger than the exposure threshold value forms an arbitrary pattern (corresponding to the mask) as in the case of the projection exposure alone. It turns out that. Further, an advantage of the exposure method is that a much larger depth of focus can be obtained in the two-beam interference exposure portion having the highest resolution than in the normal exposure.

In the above description, the two-beam interference exposure and the projection exposure are performed in the order of the two-beam interference exposure, but are not limited to this order.

Next, another embodiment will be described.

The present embodiment is directed to a so-called gate type pattern shown in FIG. 10 as a circuit pattern (lithographic pattern) obtained by exposure.

In the gate pattern of FIG. 10, the minimum line width in the horizontal direction, that is, in the AA 'direction in the figure is 0.1 μm, whereas in the vertical direction, it is 0.2 μm or more. According to the present invention, such a two-dimensional pattern that requires high resolution only in the one-dimensional direction is used.
Need high resolution which requires two beam interference exposure
It only has to be done in the dimension direction.

In this embodiment, an example of a combination of two-beam interference exposure only in one-dimensional direction and normal projection exposure will be described with reference to FIG.

FIG. 11A shows a periodic exposure pattern by two-beam interference exposure only in one-dimensional direction. The period of this exposure pattern is 0.2 μm, and this exposure pattern corresponds to a line width of 0.1 μmL & S pattern. Numerical values in the lower part of FIG. 11 represent exposure amounts.

As an exposure apparatus for realizing such two-beam interference exposure, an interferometer-type demultiplexing / multiplexing optics using a laser 151, a half mirror 152, and a plane mirror 1534 as shown in FIG. There is an apparatus having a system and an apparatus in which a mask and an illumination method are configured as shown in FIG. 17 or FIG. 18 in a projection exposure apparatus as shown in FIG.

The exposure apparatus shown in FIG. 15 will be described.

In the exposure apparatus shown in FIG. 15, multiplexing is performed as described above.
Each of the two light beams obliquely enters the wafer 154 at an angle θ and forms an interference fringe pattern (of an exposure pattern) that can be formed on the wafer 154.
The line width is represented by the above equation (3). The relationship between the angle θ and the NA on the image plane side of the demultiplexing / multiplexing optical system is NA = sin θ. The angle θ can be arbitrarily adjusted and set by changing the angle of each of the pair of plane mirrors 153. If the value of the pair of plane mirrors θ is set to a large value, the line width of each fringe of the interference fringe pattern is set. Becomes smaller. For example, when the wavelength of the two light beams is 248 nm (KrF excimer), an interference fringe pattern having a line width of about 0.1 μm can be formed even at θ = 38 degrees. In this case, NA = sin θ = 0.62. If the angle θ is set to be larger than 38 degrees, it goes without saying that higher resolution can be obtained.

Next, the exposure apparatus shown in FIGS. 16 to 18 will be described.

The exposure apparatus shown in FIG. 16 is a projection exposure apparatus using, for example, a normal reduction projection optical system (consisting of a large number of lenses). .

In FIG. 16, reference numeral 161 denotes a mask, and 162 denotes a mask 161.
163 is a projection optical system, 164 is an aperture stop, 165 is an image side exposure light coming out of the projection optical system 163 and incident on the wafer 166, and 166 is a photosensitive substrate. 167 is an explanatory diagram showing the position of the light beam on the pupil plane corresponding to the circular opening of the stop 164 by a pair of black dots. FIG. 16 is a schematic diagram showing a state in which two-beam interference exposure is being performed. Both the object-side exposure light 162 and the image-side exposure light 165 are shown in FIG.
Unlike normal projection exposure, it consists of only two parallel light beams.

In order to perform two-beam interference exposure in a normal projection exposure apparatus as shown in FIG. 16, a mask and its illumination method may be set as shown in FIG. 17 or FIG.
Three examples will be described.

FIG. 17 shows a Levenson-type phase shift mask. The pitch PO of the light-shielding portion 171 made of chromium is 0 in the equation (4), and the pitch POS of the phase shifter 172 is (5).
This is a mask represented by an equation.

P _O = MP = 2 MR = Mλ / (2NA) (4) P _OS = 2P _O = Mλ / (NA) (5) where M is the projection magnification of the projection optical system 163 and λ Is the exposure wavelength,
NA indicates the numerical aperture on the image side of the projection optical system 163.

On the other hand, the mask shown in FIG. 17 (B) is a shifter edge type phase shift mask made of chrome without a light-shielding portion, and the pitch POS of the phase shifter 181 satisfies the above equation (5) as in the Levenson type. It is configured as follows.

In order to perform two-beam interference exposure using the phase shift masks shown in FIGS. 17A and 17B, these masks are subjected to so-called coherent illumination with σ = 0 (or a value close to 0). Specifically, the mask is irradiated with a parallel light beam from a direction perpendicular to the mask surface (a direction parallel to the optical axis).

When such illumination is performed, with respect to the 0th-order transmitted diffracted light emitted from the mask in the above-described vertical direction, the phase difference between the adjacent transmitted lights becomes π by the phase shifter, and they cancel each other out. The next two parallel ray bundles of the transmitted diffracted light are generated symmetrically from the mask with respect to the optical axis of the projection optical system 163, and the two object-side exposure lights in FIG.
In addition, second-order or higher-order diffracted light is used for the aperture stop of the projection optical system 163.
Since it does not enter the aperture 164, it does not contribute to imaging.

In the mask shown in FIG. 18, the pitch PO of the light-shielding portion of the light-shielding portion made of chrome is the same as that of the expression (4) (6).
This is a mask represented by an equation.

P _O = MP = 2MR = Mλ / (2NA) (6) where M is the projection magnification of the projection optical system 163, λ is the exposure wavelength,
NA indicates the numerical aperture on the image side of the projection optical system 163.

The mask having no phase shifter shown in FIG. 18 is subjected to oblique incidence illumination using one or two parallel light beams.
In this case, the incident angle θ ₀ of the parallel light beam to the mask is
It is set so as to satisfy the expression (7). In the case where two parallel light beams are used, θ0 is opposite to each other with respect to the optical axis.
The mask is illuminated by the oblique parallel light beam.

Sin θ ₀ = M / NA (7) Here, M is the projection magnification of the projection optical system 163, and NA is the image-side numerical aperture of the projection optical system 163.

When a mask having no phase shifter shown in FIG. 18 is subjected to oblique incidence illumination with a parallel light beam satisfying the above equation (7), the mask travels straight at an angle θ ₀ with respect to the optical axis. 2 light fluxes of the first-order transmitted diffracted light and the 0th-order transmitted diffracted light traveling along an optical path symmetrical with respect to the optical axis of the projection optical system (advancing at an angle −θ ₀ with respect to the optical axis) Is a figure
The two light beams are generated as 16 object-side exposure light beams 162, and these two light beams enter the aperture of the aperture stop 164 of the projection optical system 163 to form an image.

In the present invention, such one or two
Oblique incidence illumination by a bundle of parallel rays is also treated as "coherent illumination".

The technique for performing two-beam interference exposure using a normal projection exposure apparatus has been described above. The illumination optical system of the normal projection exposure apparatus as shown in FIG. 19 is configured to perform partial coherent illumination. 19, the aperture stop (not shown) corresponding to 0 <σ <1 of the illumination optical system in FIG. 19 can be replaced with a special aperture stop corresponding to σ ≒ 0, etc. It can be configured to provide coherent illumination.

Returning to the description of the embodiment shown in FIGS.

In the present embodiment, a normal projection exposure (for example, a device in which partial coherent illumination is performed on a mask with the apparatus shown in FIG. 19) performed after the above-described two-beam interference exposure is performed by using the process shown in FIG. Is exposed. The upper part of FIG. 11B shows the relative positional relationship with the exposure pattern by two-beam interference exposure and the exposure amount in five areas of the exposure pattern of the normal projection exposure, and the lower part of the figure shows the normal projection exposure. Is a map of the exposure amount of the wafer on the resist with a resolution of 0.1 μm vertically and horizontally.

The line width of the exposure pattern by this projection exposure is
It is 0.2 μm, which is twice that in the case of two-beam interference exposure. A method of performing projection exposure for generating a multi-level exposure amount distribution in which the exposure amount differs for each region (multi-value because the exposure amount has three values of 0, 1, and 2) is shown in FIG. Using a special mask with multiple stages of transmittance, where the transmittance of the mask opening corresponding to the region indicated by T% is T%, and the transmittance of the mask corresponding to the region indicated by 2 in the figure is 2T% In this method, the projection exposure can be completed in one exposure, and when using this special mask, the exposure amount ratio in each exposure is two-beam interference exposure: transmittance on the wafer (photosensitive substrate). Projection exposure at an opening of T: projection exposure at a transmittance of 2T = 1: 1: 2.

As another method for performing projection exposure in which the exposure amount differs for each region, a method of sequentially exposing using two types of masks that produce an exposure pattern shown in the upper part and the lower part of FIG. In this case, since the exposure amount of each mask may be one step, the transmittance of the opening of the mask may be one step. In this case, the exposure ratio is 2 on the wafer (photosensitive substrate).
Light beam interference exposure: first projection exposure: second projection exposure = 1: 1: 1.

The manner in which the fine circuit pattern shown in FIG. 10 is formed by a combination of the two-beam interference exposure described above and ordinary projection exposure will be described. In this embodiment,
There is no development process between two-beam interference exposure and normal projection exposure. Therefore, the exposure amounts in the areas where the exposure patterns of each exposure overlap each other are added, and a new exposure pattern is generated depending on the added exposure amount (distribution).

The upper part of FIG. 11C is the same as FIG.
FIG. 11A shows an exposure amount distribution (exposure pattern) obtained by adding the exposure amounts of the exposure pattern of FIG. 11B and the exposure pattern of FIG. 11B, and the lower part of FIG. The pattern obtained as a result of performing the development is shown in gray. In this embodiment, the resist of the wafer has an exposure threshold greater than 1 and less than 2,
Therefore, only the portion where the exposure amount is greater than 1 appears as a pattern due to development. The shape and size of the pattern shown in gray in the lower part of FIG. 11C match the shape and size of the gate pattern shown in FIG. 10, and are as fine as 0.1 μm by the exposure method of the present invention. For example, a circuit pattern having a wide line width can be formed using a projection exposure apparatus having an illumination optical system capable of switching between partially coherent illumination and coherent illumination.

FIG. 12 shows still another embodiment of the present invention.
This will be described with reference to FIGS. This alternative embodiment is based on 2
A multi-value (exposure amounts of 0, 1, and 2) obtained by superimposing vertical fringe interference fringe patterns and horizontal fringe interference fringe patterns by two-beam interference exposure
This is characterized in that an exposure pattern having an exposure amount distribution of (4 values of 3 and 3) is formed.

FIG. 12 shows an exposure pattern obtained by mapping the exposure pattern when the vertical fringe interference fringe pattern and the horizontal fringe interference fringe pattern are overlapped by two two-beam interference exposures.
Here, in order to increase the variation of the exposure pattern (lithography pattern) finally obtained by the superposition of the two-beam interference exposure and the normal exposure, the exposure amount of the bright portion of the vertical stripe interference fringe pattern (2) To the horizontal fringe pattern
The exposure amount (1) in the bright part of the image is twice as large. The exposure amounts of the two types of bright portions are not limited to those of the present embodiment.

FIG. 12 shows that the exposure pattern has four exposure levels of 0 to 3 as a result of two double-beam interference exposures in the exposure pattern. The number of exposure steps in projection exposure that is sufficiently effective for such two-beam interference exposure is five or more. In this case, the exposure threshold value of the resist on the wafer (photosensitive substrate) is larger than 3 which is the maximum value of the exposure amount of the two-beam interference exposure, and the maximum value of the exposure amount (0, 1, 2, 3 and 4) of the projection exposure. Set to a value less than 4.

FIG. 13 shows the respective exposure amounts of the exposure pattern obtained as a result of performing the projection exposure with such five stages (0, 1, 2, 3, 4). The hatched portion in FIG. 13 indicates a location above the exposure threshold, which is the final exposure pattern. Note that FIG. 13 shows the resolution of the projection exposure as half of that of the two-beam interference exposure in units of blocks having sides twice as long as those in FIG.

FIG. 14 shows an example in which an exposure pattern (lithography pattern) is formed over a wider area by changing the exposure amount of the projection exposure in such a block unit.
From FIG. 14, it can be seen that according to the present embodiment, it is possible to form a circuit pattern having a resolution of two-beam interference exposure and containing a variety of patterns other than the periodic pattern.

In the present embodiment, the normal exposure is performed in units of a block twice as large as the line width of the two-beam interference exposure. However, the present invention is not limited to this. Exposure can be performed.

In this embodiment, the line width of the exposure pattern by the two-beam interference exposure is described as being the same for the vertical stripes and the horizontal stripes. However, the respective line widths may be different from each other. Also, the angles of the two types of stripes can be arbitrarily selected.

FIG. 20 is a schematic view showing an example of an exposure apparatus for two-beam interference exposure. In FIG. 20, reference numeral 201 denotes a two-beam interference exposure optical system, and its basic configuration is the same as the optical system of FIG. 202 is a KrF or ArF excimer laser, 203 is a half mirror, 204 is a plane mirror, 20
Reference numeral 5 denotes an off-axis type alignment optical system whose positional relationship with the optical system 201 is fixed or can be appropriately detected as a base line (amount). The off-axis type alignment optical system 5 observes a two-beam interference alignment mark on the wafer 206 and detects its position. I do. Reference numeral 206 denotes a wafer serving as a photosensitive substrate, and 207, a plane orthogonal to the optical axis of the optical system 201 and an XYZ stage movable in the optical axis direction. The position of the XYZ stage is accurately controlled using a laser interferometer or the like. Since the configurations and functions of the devices 205 and 207 are well known, a detailed description is omitted.

FIG. 21 is a schematic view showing a high-resolution exposure apparatus comprising a two-beam interference exposure apparatus and a normal projection exposure apparatus.

In FIG. 21, reference numeral 212 denotes a two-beam interference exposure apparatus having the optical systems 201 and 205 shown in FIG.
Reference numeral 13 denotes an illumination optical system (not shown), a reticle positioning optical system 214, a wafer positioning optical system (off-axis positioning optical system) 217, and a projection optical system 216 for reducing and projecting the circuit pattern of the mask 215 onto the wafer 218. This is a normal projection exposure apparatus including:

The reticle positioning optical system 214 observes the positioning mark on the mask 215 and detects the position. The wafer alignment optical system 217 observes an alignment mark for projection exposure or dual light beam interference on the wafer 206 and detects its position. Optical systems 214 and 21
Since the configurations and functions of the modules 6 and 217 are well known, a specific description is omitted.

Reference numeral 219 in FIG. 21 denotes a two-beam interference exposure apparatus 2
12 is one XYZ stage shared by the projection exposure apparatus 213, and this stage 219
A plane orthogonal to each optical axis 13 and the optical axis can be moved in the optical axis direction, and its position in the XY directions is accurately controlled using a laser interferometer or the like.

Stage 219 Holding Wafer 218
Is an apparatus 2 which is fed to a position (1) in FIG. 21 and whose position is accurately measured, and which is indicated by a position (2) based on the measurement result.
12, the two-beam interference exposure is performed on the wafer 218, and then the wafer 218 is sent to the position (3) where the position is accurately measured and the device 213 indicated by the position (4) is detected.
And the wafer 218 is subjected to projection exposure.

In the apparatus 213, instead of the off-axis positioning optical system 217, a positioning mark on the wafer 218 is observed via the projection optical system 216, and a TTL positioning (not shown) for detecting the position is detected. An optical system or a TTR alignment optical system (not shown) for observing the alignment mark on the wafer 218 via the projection optical system 216 and the mask (reticle) 215 and detecting the position can also be used.

FIG. 22 is a schematic view showing a high-resolution exposure apparatus capable of performing both two-beam interference exposure and normal projection exposure.

In FIG. 22, reference numeral 221 denotes KrF or Ar
F excimer laser, 222 is an illumination optical system, 223 is a mask (reticle), 224 is a mask stage, 227 is a projection optical system for reducing and projecting the circuit pattern of the mask 223 onto the wafer 228, and 225 is a mask (reticle) changer. In order to selectively supply the stage 224 with a normal reticle and one of the aforementioned Levenson type phase shift mask (reticle), edge shifter type mask (reticle), or periodic pattern mask (reticle) having no phase shifter. It is provided in.

Reference numeral 229 in FIG. 22 denotes one XYZ stage shared by the two-beam interference exposure and the projection exposure. This stage 229 is movable in a plane orthogonal to the optical axis of the optical system 227 and in the optical axis direction. The position in the XY directions is accurately controlled using a laser interferometer or the like.

The apparatus shown in FIG. 22 includes a reticle positioning optical system (not shown) and a wafer positioning optical system (the off-axis positioning optical system, the TTL positioning optical system, and the TTR positioning optical system described with reference to FIG. 21). And

The illumination optical system 222 of the apparatus shown in FIG. 22 is configured to be able to switch between partially coherent illumination and coherent illumination. In the case of coherent illumination, the above-mentioned (1a) or (1) shown in the block 230 is used. The illumination light of 1b) is supplied to one of the aforementioned Levenson-type phase shift reticles or edge shifter-type reticles or one of the periodic pattern reticles having no phase shifter, and is illustrated in a block 230 in the case of partial coherent illumination. The illumination light of (2) is supplied to a desired reticle. Switching from partial coherent illumination to coherent illumination can be achieved by replacing the aperture stop, which is usually placed immediately after the fly-eye lens of the optical system 222, with a coherent illumination stop having an aperture diameter sufficiently smaller than this aperture stop. .

Various devices such as semiconductor chips such as ICs and LSIs, display elements such as liquid crystal panels, detection elements such as magnetic heads, and image pickup elements such as CCDs can be manufactured using the above-described exposure method and exposure apparatus. .

The present invention is not limited to the above-described embodiments, but can be variously modified without departing from the gist of the present invention. In particular, the number of exposures and the number of exposure steps in each step of the two-beam interference exposure and the normal exposure can be appropriately selected, and the exposure can be adjusted as appropriate, for example, by shifting the overlap. A circuit pattern that can be formed by performing such adjustments
Variations increase.

[0098]

As described above, according to the present invention, it is possible to obtain a complicated pattern having a fine line width of, for example, 0.15 μm or less by fusing two-beam interference exposure with ordinary exposure.

[Brief description of the drawings]

FIG. 1 is a flowchart of the exposure method of the present invention.

FIG. 2 is an explanatory diagram showing an exposure pattern by two-beam interference exposure.

FIG. 3 is an explanatory diagram showing exposure sensitivity characteristics of a resist.

FIG. 4 is an explanatory diagram showing pattern formation by development.

FIG. 5 is an explanatory diagram showing an exposure pattern by ordinary two-beam interference exposure.

FIG. 6 is an explanatory diagram showing an exposure pattern by two-beam interference exposure in the present invention.

FIG. 7 is an exposure pattern that can be formed in the first embodiment.
FIG. 4 is an explanatory diagram showing an example of a pattern (lithography pattern).

FIG. 8 is an exposure pattern that can be formed in the first embodiment.
FIG. 4 is an explanatory diagram showing another example of the pattern (lithography pattern).

FIG. 9 is an exposure pattern that can be formed in the first embodiment.
FIG. 4 is an explanatory diagram showing another example of the pattern (lithography pattern).

FIG. 10 is an explanatory diagram showing a gate pattern.

FIG. 11 is an explanatory diagram showing a second embodiment.

FIG. 12 is an explanatory diagram showing a two-beam interference exposure pattern according to a third embodiment.

FIG. 13 is an explanatory diagram showing a pattern formed by a two-dimensional block in the third embodiment.

FIG. 14 is an explanatory diagram showing an example of an exposure pattern that can be formed in the third embodiment.

FIG. 15 is a schematic view showing an example of a two-beam interference exposure apparatus.

FIG. 16 is a schematic diagram illustrating an example of a projection exposure apparatus that performs two-beam interference exposure.

FIG. 17 is an explanatory diagram showing an example of a mask and an illumination method used in the apparatus of FIG.

FIG. 18 is an explanatory view showing another example of a mask and an illumination method used in the apparatus of FIG. 16;

FIG. 19 is a schematic view showing a conventional projection exposure apparatus.

FIG. 20 is a schematic view showing an example of a two-beam interference exposure apparatus of the present invention.

FIG. 21 is a schematic view showing an example of a high-resolution exposure apparatus of the present invention.

FIG. 22 is a schematic view showing another example of the high-resolution exposure apparatus of the present invention.

[Explanation of symbols]

 221 Excimer laser 222 Illumination optical system 223 Mask (reticle) 224 Mask (reticle) stage 225 2 Light flux interference mask and mask for normal projection exposure 226 Mask (reticle) changer 227 Projection optical system 228 Wafer 229 XYZ stage

Claims (7)

[Claims] 1. When performing two-beam interference exposure and normal exposure on a substrate to be exposed, a multilevel exposure amount distribution is given to the substrate in at least one of the two exposures. Exposure method. 2. The method according to claim 1, wherein when performing two-beam interference exposure and normal exposure on the substrate to be exposed, a multilevel exposure amount distribution is given to the substrate in at least one of the two exposures. Exposure equipment. 3. The exposure method according to claim 1, wherein each of the two-beam interference exposure and the normal exposure includes one or more exposure steps. 4. A projection optical system for projecting a pattern of a mask onto a wafer, and a mask illumination optical system capable of performing both partial coherent illumination and coherent illumination, and performing normal exposure by partial coherent illumination. An exposure apparatus for performing two-beam interference exposure using coherent illumination. 5. An exposure apparatus comprising: a two-beam interference exposure apparatus; a normal exposure apparatus; and a moving stage for holding a substrate to be exposed, which is shared by both apparatuses. 6. An exposure wavelength of each of the two-beam interference exposure and the normal exposure is equal to or less than 250 nm.
The exposure method according to any one of claims 1 to 4, or the exposure apparatus according to any one of claims 2, 3, 4, and 5. 7. A device manufacturing method, wherein a device is manufactured using one of the exposure method according to claim 1, the exposure apparatus according to claim 2 to claim 5, the exposure method according to claim 6, and the exposure apparatus. .