JP2000021753A - Exposure method and apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce high resolution by matching the direction in which the resolution of a projecting optical system is best with the direction of diffraction light emitted by a fine pattern on the surface of a first body. SOLUTION: A resolution determined by measurements is best in a direction Xa at an angle θ in the counterclockwise direction with respect to a standard direction SD. The direction Xa is a direction in which RMS(root mean square) of resolutions (aberrations) calculated in all directions from the standard direction SD is minimum. Next, a mask is turned counterclockwise an angle of θ' from the standard direction SD in such a way that the direction of diffraction light emitted by a fine pattern on the mask (first body) agrees with the Xa direction and a wafer is then turned counterclockwise an angle of (θ-θ') from the standard direction SD to match the Xa direction of the mask with the baking direction Xb of the wafer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposing method and an exposing apparatus, and more particularly, to exposing a photosensitive substrate with a fine circuit pattern, for example, a semiconductor chip such as an IC or LSI, a display element such as a liquid crystal panel, a magnetic head, and the like. It is suitable for use in the manufacture of various devices such as a detection device and an imaging device such as a CCD.

[0002]

2. Description of the Related Art Conventionally, when devices such as ICs, LSIs, and liquid crystal panels are manufactured using photolithography technology, circuits formed on the surface of a photomask or reticle (hereinafter, referred to as "mask"). A projection exposure method and projection in which a 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. An exposure apparatus is used.

In recent years, in response to the higher integration of the above devices, there has been a demand for miniaturization of a pattern to be transferred to a wafer, that is, higher resolution and larger area of one chip on the wafer. Therefore, even in the above-described projection exposure method and projection exposure apparatus that form the center of microfabrication technology for wafers,
Image (circuit pattern image) with dimensions (line width) of 0.5 μm or less
In order to form an image over a wide range, the resolution is increased and the exposure area is increased.

FIG. 28 is a schematic diagram of a conventional projection exposure apparatus. In FIG. 28, reference numeral 191 denotes an excimer laser as a light source for exposure to far ultraviolet rays, 192 denotes an illumination optical system, 193 denotes illumination light emitted from the illumination optical system 192, 194 denotes a mask,
Reference numeral 95 denotes an optical system (projection optical system) 19 which exits from the mask 194.
Reference numeral 196 denotes an object-side exposure light, reference numeral 196 denotes a reduction type projection optical system, reference numeral 197 denotes an image-side exposure light which exits from the projection optical system 196 and enters a substrate 198, reference numeral 198 denotes a wafer which is a photosensitive substrate,
Reference numeral 99 denotes a substrate stage for holding a photosensitive substrate.

[0005] The laser light emitted from the excimer laser 191 is guided to the illumination optical system 192 by the routing optical systems (190a, 190b), and the illumination optical system 192 provides a predetermined light intensity distribution, light distribution, and opening angle (Sekiguchi). Number NA),
It is adjusted to become the illumination light 193 having the projection magnification and the like,
The mask 194 is illuminated. The mask 194 has a wafer 19
8 is formed on the quartz substrate by chrome or the like, the pattern having a size obtained by reciprocally multiplying (for example, 2 times, 4 times, or 5 times) the projection magnification of the projection optical system 196 with respect to the fine pattern to be formed on the quartz substrate. Are transmitted and diffracted by the fine pattern of the mask 194 to become the object side exposure light 195. The projection optical system 196 converts the object-side exposure light 195 into image-side exposure light 197 that forms a fine pattern of the mask 194 on the wafer 198 with the above-described projection magnification and sufficiently small aberration. As shown in the enlarged view at the bottom of FIG. 28, the image-side exposure light 197 has a predetermined numerical aperture NA (= Sin (θ)).
8 and forms an image of a fine pattern on the wafer 198. The substrate stage 199 moves stepwise 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. This changes the position of the wafer 198 with respect to the projection optical system 196.

A projection exposure apparatus using the above-described excimer laser as a light source has a high projection resolution, but it is technically difficult to form a pattern image of, for example, 0.15 μm or less.

[0007] The projection optical system 196 has a resolution limit due to a trade-off between the optical resolution due to (exposure) 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 Rayleigh formulas (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 apertures on the image side, k ₁ and k ₂ , which represent the image quality, are constants determined by the development process characteristics of the wafer 198 and the like.
The value is about 5 to 0.7. From the equations (1) and (2), it is apparent that the numerical aperture N
There is "higher NA" to increase A. 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 that it is difficult to increase the NA to a certain value or more. It is understood that "short wavelength" for reducing the wavelength λ is required.

However, as the exposure wavelength becomes shorter, a serious problem arises. It is the projection optical system 196
Is that the glass material of the lens that constitutes is lost. The transmittance of most glass materials is close to 0 in the deep ultraviolet region,
Using a special manufacturing method for exposure equipment (exposure wavelength about 248
nm), fused quartz exists as a glass material.
The transmittance of this fused quartz also sharply decreases with respect to the exposure wavelength of 193 nm or less, and practical glass material development is extremely difficult in the region of 150 nm or less corresponding to fine patterns with a line width of 0.15 μm or less. Difficult. 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, it is necessary to reduce the exposure wavelength to about 150 nm or less in order to form a pattern having a line width of 0.15 μm or less on a wafer. On the other hand, at present, there is no practical glass material in this wavelength region, so that a pattern having a line width of 0.15 μm or less cannot be formed on the wafer.

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

The principle of two-beam interference exposure will be described with reference to FIG. In the two-beam interference exposure, a laser beam L151 having coherence from a laser 151 and being a parallel beam is converted into laser beams L151a and L151 by a half mirror 152.
The two laser light beams (coherent parallel light beams) are divided from larger than 0 to 9 by being split into two light beams of ab and reflecting the split two light beams by the plane mirrors 153a and 153b, respectively.
An interference fringe is formed at the intersection by intersecting at an angle of less than 0 degree on the surface of the wafer 154. By exposing and exposing the wafer 154 with (the light intensity distribution of) the interference fringes, a fine periodic pattern corresponding to the light intensity distribution of the interference fringes is formed on the wafer 154.

The two light beams L151a and L151b are
In the case where the wafer intersects with the perpendiculars formed on the 54 surfaces in a state inclined at the same angle in the opposite directions to each other on the wafer surface, the resolution R in the two-beam interference exposure is expressed by the following equation (3).

R = λ / (4 sin θ) = λ / 4NA = 0.25 (λ / NA) (3) where R is the width of each L & S (line and space), ie, interference fringes. The width of each of the light and dark portions is shown. Β represents the incident angle (absolute value) of the two light beams with respect to each image plane, and NA = Sin θ.

Comparing equation (1), which is the equation for resolution in normal projection exposure, and equation (3), which is the equation for resolution in two-beam interference exposure, the resolution R of two-beam interference exposure is expressed by equation (1). Since this corresponds to the case where k ₁ = 0.25, 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 US patent, for example, when λ = 0.248 nm (KrF excimer) and NA =
At 0.6, R = 0.10 μm is obtained.

[0017]

A recent projection lens used in an exposure apparatus has advanced design techniques, and although the aberrations are almost zero in design values, random aberrations caused by errors in manufacturing remain. As for the aberration at the time of this production, the wavefront aberration is measured from the aerial image, and the detailed amount of the aberration at each point of the wavefront is known.

Regarding the influence of aberration, for example, if there is a spherical aberration, the image is blurred and the line width is widened, or the line width is different between plus and minus of defocus. Also, the presence of coma has adverse effects such as a difference in line width between the left and right sides of the pattern.

In particular, in the projection optical system, due to a production error, a rotationally asymmetric aberration with respect to the optical axis occurs, and the projection resolution varies depending on the direction in a plane perpendicular to the optical axis.

Further, the wavefront aberration of the projection lens is larger at the peripheral portion than at the central portion. Therefore, as the pattern becomes finer, the influence of the aberration becomes greater. Therefore, the line width of the fine pattern does not conform to the design value of the mask, and the line width reproducibility is very poor.

In the above-described two-beam interference exposure, basically, only a simple fringe pattern corresponding to the light intensity of the interference fringes (exposure amount distribution) can be obtained. Therefore, a circuit pattern having a desired shape is formed on the wafer. It is difficult.

In the above-mentioned US Pat. No. 5,415,835, a simple fringe pattern (periodic pattern), that is, a binary exposure amount distribution is given to a wafer (resist) by two-beam interference exposure, and then the resolution of the exposure apparatus is increased. Obtaining an isolated line (pattern) by performing normal lithography (exposure) using a mask in which an opening having a size within the range is formed and giving another binary exposure distribution to the wafer Has been proposed.

However, US Pat. No. 5,415,583 mentioned above.
The exposure method disclosed in Japanese Patent Application Laid-Open No. 5-205
In each of the two exposure methods, only a normal binary exposure amount distribution is formed, so that it is difficult to obtain a circuit pattern having a more complicated shape.

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.

For this reason, when the pattern on the mask surface is projected and exposed on the wafer surface by the projection optical system, it is preferable that the direction of the highest resolution (resolution direction) of the projection optical system does not match the direction of forming the fine pattern. I can't get the resolution.

In particular, in an exposure method in which multiple exposure is performed by two-beam interference exposure and normal exposure, a good pattern image cannot be obtained unless the direction of forming a fine pattern does not coincide with the direction of good resolution.

An object of the present invention is to provide an exposure method and an exposure apparatus capable of easily obtaining a high resolution by appropriately setting the direction of the resolution of the projection optical system and the direction of the fine pattern of the mask.

In addition, the present invention employs two exposure methods, a periodic pattern exposure typified by two-beam interference exposure and a normal pattern exposure (normal exposure) not including a periodic pattern, thereby forming a circuit pattern having a complicated shape. It is an object of the present invention to provide an exposure method and an exposure apparatus which can be formed on a wafer.

Another object of the present invention is to provide a line width of 0.15 μm.
An exposure method and an exposure apparatus capable of easily obtaining a circuit pattern including the following parts are provided.

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

[0031]

According to the present invention, there is provided an exposure method comprising the steps of: (1-1) patterning a pattern on a first object plane by a projection optical system;
In a projection method of projecting and exposing on an object plane, a direction in which the resolving power of the projection optical system is the best and an emission direction of the diffracted light of the fine pattern on the first object plane coincide with each other. And

In particular, (1-1-1) the direction in which the resolving power is the best at a plurality of image heights of the projection optical system is measured, and the pattern image height at which the fine pattern is located on the first object plane is determined. It is characterized in that the resolving power at the image height of the projection optical system at the same height coincides with the direction in which the resolution is the best.

(1-2) In an exposure method, a plurality of first objects having mutually different patterns are used to perform multiple exposures of the same area on a second object with different patterns using a projection optical system. It is characterized in that the direction in which the resolving power is the best coincides with the emission direction of the diffracted light of the fine pattern on the first object plane.

In particular, (1-2-1) the direction in which the resolving power of the projection optical system is the best is measured at a plurality of image heights, and the pattern image height at which the fine pattern is located on the first object plane is determined. It is characterized in that the resolving power at the image height of the projection optical system at the same height coincides with the direction in which the resolution is the best.

In the other configurations (1-1) and (1-2), (1-2-2) the direction in which the resolution of the projection lens is the best is the rms (root mean square) of the measured wavefront aberration.
e) is the direction in which it becomes the smallest.

(1-2-3) The direction of emission of the diffracted light of the finest pattern of the pattern on the first object plane is perpendicular to the longitudinal direction of the finest pattern.

(1-2-4) The image height and the aberration amount at this measured image height or the coefficient expanded by Zernike are stored in the control unit of the exposure apparatus, and the rms of the aberration amount in each direction is stored. To calculate.

(1-2-5) The direction in which the previously calculated rms is minimized is stored in the control unit of the exposure apparatus, and is read from this storage.

(1-2-6) Input the direction in which the aberration is minimized at the time of exposure.

(1-2-7) Writing the image height of a portion of the first object having the fine pattern and the emission direction of the diffracted light of the fine pattern in a bar code of the first object.

(1-2-8) First alignment at the time of alignment of the first object
To read a bar code on an object.

(1-2-9) The direction of emission of the diffracted light of the finest pattern of the pattern of the first object is input at the time of exposure.

(1-2-10) The projection lens is manufactured such that aberration is reduced in only one direction, and that direction is set as a reference direction.

(1-2-11) To correct the aberration of the emission direction of the diffracted light of the fine pattern by rotating the aberration correction system capable of correcting the aberration in one direction.

(1-2-12) Rms of aberration amount of the projection lens
Scanning at a right angle in the direction that minimizes the exposure. And so on.

The exposure apparatus of the present invention is characterized in that (2-1) the pattern on the mask is transferred to a photosensitive substrate using the exposure method of the constitution (1-1) or (1-2). And

The method for manufacturing a device according to the present invention comprises the steps of: (3-1) exposing a pattern on a mask surface to a wafer surface using the exposure method of the constitution (1-1) or (1-2); It is characterized in that devices are manufactured through a wafer development process.

(3-2) After the pattern on the mask surface is exposed on the wafer surface using the exposure apparatus of the configuration (2-1), the wafer is subjected to a developing process to manufacture a device. It is characterized by.

In the present invention, "multiple exposure" refers to "exposing the same area on a photosensitive substrate with different light patterns without passing through a developing process".

[0050]

FIG. 1 is a schematic view showing a high-resolution exposure apparatus according to the present invention which can perform both two-beam interference exposure and ordinary projection exposure.

In this embodiment, in order to improve the line width reproducibility of a fine pattern near the resolution limit, the direction perpendicular to the finest pattern of the mask pattern is adjusted to the direction in which the aberration of the projection lens is minimized. The mask and the wafer can be rotated in the same direction by the same amount and relative to the projection lens for exposure.

Another feature is that the aberration correction system capable of correcting the aberration in one direction can be rotated so that the aberration is corrected in parallel to a direction perpendicular to the finest pattern of the mask pattern.

In FIG. 1, 221 denotes KrF or ArF
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 a wafer 228, and includes a correction optical system 231. 23
Reference numeral 1 denotes an aberration correction system in only one direction, which can rotate arbitrarily. Reference numeral 225 denotes a mask (reticle) changer. The stage 224 includes a normal reticle and the above-mentioned Levenson phase shift mask (reticle), an edge shifter type mask (reticle), or a periodic pattern mask (reticle) having no phase shifter. It is provided for selectively supplying one.

The mask stage is provided with a function of rotating the mask based on information previously drawn on a bar code or the like in order to make the direction of the fine pattern parallel to the direction of the periodic pattern. .

Reference numeral 229 in FIG. 1 denotes one XYZ stage shared by the two-beam interference exposure and the projection exposure. This stage 229 is movable in a plane perpendicular 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. 224,229
Is relatively rotated based on the stored or input information on the direction in which the aberration of the projection lens is minimized and the information on the emission direction of the diffracted light of the fine pattern of the mask.

The apparatus shown in FIG. 1 includes a reticle positioning optical system (not shown) and a wafer positioning optical system (off-axis positioning optical system, TTL positioning optical system, and TTR).
Positioning optical system).

The illumination optical system 222 of the exposure apparatus shown in FIG. 1 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 (1a) shown in the block 230 is used. The illumination light of (1b) is supplied to one of the above-described 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. (2
The illumination light of a) is supplied to a desired reticle. Switching from partial coherent illumination to coherent illumination can be achieved by replacing the aperture stop 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. .

Next, the features of this embodiment will be described.
In the present embodiment, first, the entire exposure apparatus is assembled, and the state at this time is set as a reference state. Then, the pattern on the mask (first object) plane is projected onto the wafer (second object) plane at this reference state position with the projection optical system (projection lens) 227 set in a stepwise manner with the optical axis as the rotation center from the reference state position. Is sequentially exposed while rotating several times.

Alternatively, a mask on which a resolution chart (pattern) is arranged over the entire screen is projected and exposed on the wafer surface. Then, the pattern image projected on the wafer surface is measured, and the direction having the highest resolution (the direction in which the aberration is most corrected) is detected on the screen of the projection optical system.

At this time, the direction of the highest resolving power at each image height of the projection optical system is simultaneously detected, or the wavefront aberration is directly measured from the aerial image by a wavefront aberration measuring device in advance. Hereinafter, this direction is also referred to as “resolution direction”.

FIG. 2 shows that the direction rotated by an angle θ in the counterclockwise direction with respect to the reference direction SD of the projection lens is the direction (xa direction) with the best resolution determined by measurement.

This Xa direction is the reference direction SD of the projection lens.
Rms (root) of the resolving power (amount of aberration) in each direction from
(mean square) is calculated to determine the direction in which rms is the smallest.

Next, as shown in FIG. 3, a mask (first object)
Fine pattern on M surface (pattern with the smallest line width) M
The mask M is rotated counterclockwise by an angle θ ′ from the reference direction SD so that the emission direction DP of the diffracted light generated from P coincides with the Xa direction.

FIG. 4 shows the Xa direction of the projection lens and the D of the mask.
This shows a state in which the direction P is matched.

Next, as shown in FIG. 5, the wafer (second object)
W is rotated counterclockwise by an angle θ-θ ′ from the reference position SD. This makes the Xa direction of the mask coincide with the baking direction Xb of the wafer.

As described above, the mask is rotated by the angle θ ′ in the direction of the resolving power of the projection lens so that the directions of the diffracted light from the fine pattern on the mask surface coincide with each other.
By turning, the projection exposure preparation is completed.

Next, projection exposure in a step-and-repeat method and a step-and-scan method (scanner)
, And multiple exposure, which will be described later.

In particular, it is preferable to scan the scanner at right angles to the direction in which the rms amount of aberration of the projection lens is minimized.

In the present embodiment, by performing such operations, the pattern on the mask surface can be projected and exposed on the wafer surface with a high resolution.

In this embodiment, the direction of the resolving power of the projection optical system is determined for each image height, and a mask (first object) is obtained.
Corresponding to the image height where the fine pattern on the surface is located,
The direction of the resolving power of the projection optical system and the direction of the DP of the mask are preferably matched.

In addition, the aberration amount at each point of the wavefront at the image height measured at this image height or the Zernike-expanded coefficient is stored in the control unit of the exposure apparatus, and the rms of the aberration amount is calculated. Alternatively, the image height and the direction in which the rms at this image height is minimized may be calculated in advance, stored in the control unit of the exposure apparatus, and read from this storage. Alternatively, it may be input at the time of exposure. According to this, a higher-resolution pattern image can be easily obtained.

In the present embodiment, an aberration correction system is provided rotatably in the optical path of the projection optical system, and the aberration correction system is rotated to correct the aberration known in advance, and in this direction, the DP direction of the mask is changed. 1 and the baking direction of the wafer may be matched.

As for the emission direction in the diffraction direction of the fine pattern of the mask, the image height of a portion where the fine pattern is present and the emission direction of the diffracted light of the fine pattern are written in the bar code of the mask
At the time of mask alignment, the bar code of the mask is read, and the mask and the wafer are rotated by the same amount in the same direction. Alternatively, it may be input at the time of exposure.

The projection lens may be manufactured by adjusting the aberration in only one direction so that the aberration is reduced, and the mask and the wafer may be rotated by the same amount in the same direction with the direction as a reference direction.

The present embodiment can be applied not only to an exposure apparatus for exposing a pattern on a mask surface once onto a wafer surface but also to multiple exposure.

Next, the multiple exposure for projecting and exposing a plurality of different patterns to the same area on the wafer surface by adjusting the projection optical system, the mask, and the wafer as described above will be described.

The exposure method and exposure apparatus of the present invention
When the second exposure is a projection exposure, the exposure wavelength of the first exposure and the second exposure in the double exposure is 400 nm or less, and preferably 250 nm or less. 250n
In order to obtain light having an exposure wavelength of less than m, a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 n) is used.
m).

In the present invention, the term "projection exposure" refers to exposure in which 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. Things.

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. By performing normal exposure and performing two-beam interference exposure by coherent illumination, it is characterized by periodic pattern exposure.
“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, and “coherent illumination” means that the value of σ is zero. Or a value close thereto, which is considerably smaller than σ of the partially coherent illumination.

In coherent illumination in periodic pattern exposure, σ is set to 0.3 or less. Partial coherent illumination during normal exposure makes σ 0.6 or more. σ = 0.8 is desirable. Furthermore, it is still more effective to use annular illumination in which the illuminance distribution is lower on the inside than on the outside.

The exposure wavelength of this exposure apparatus is 400 nm or less, preferably 250 nm or less. 250n
In order to obtain light having an exposure wavelength of less than m, a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 n) is used.
m).

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

The exposure apparatus of the present invention has a two-beam interference exposure apparatus and a moving stage for holding a substrate to be exposed (photosensitive substrate) which is shared by both apparatuses.

The exposure wavelength of this exposure apparatus is also 400 nm or less, preferably 250 nm or less. 250n
In order to obtain light having an exposure wavelength of less than m, a KrF excimer laser (about 248 nm) or an ArF excimer laser (about 193 n) is used.
m).

Using the above-described exposure method and exposure apparatus, 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. .

The present invention is not limited to the embodiment described above, 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 appropriately adjusted such that the exposure is superimposed and shifted. By performing such an adjustment, variations in circuit patterns that can be formed increase.

FIGS. 6 to 14 are explanatory diagrams of Embodiment 1 of the multiple exposure method (hereinafter, also simply referred to as "exposure method") of the present invention. FIG. 6 is a flowchart showing the exposure method of the present invention. FIG. 6 shows each block of the periodic pattern exposure step, the projection exposure step (normal pattern exposure step), and the development step, which constitute the exposure method of the present invention, and the flow thereof. In the figure, the order of the periodic pattern exposure step and the projection exposure step may be reversed, and when one of the steps includes a plurality of exposure steps, each step may be performed alternately. Also, between each exposure step. Although there is a step of performing precise alignment, the illustration is omitted here.

The exposure method and the exposure apparatus according to the present invention are characterized in that double exposure of periodic pattern exposure and normal exposure is performed on a substrate to be exposed (photosensitive substrate).

Here, the normal pattern exposure is an exposure which has a lower resolution than that of the periodic pattern exposure but can perform exposure in an arbitrary pattern, and a typical example is a projection exposure in which a mask pattern is projected by a projection optical system.

The pattern (normal pattern) exposed by the normal pattern exposure includes a fine pattern having a resolution equal to or less than the resolution, and the periodic pattern exposure forms a periodic pattern having substantially the same line width as the fine pattern. A large pattern having a resolution equal to or larger than the resolution of the normal pattern exposure is not limited to the line width of the periodic pattern exposure, but an integer multiple is effective.

Normally, the pattern exposure has an arbitrary shape and may be directed in various directions. Generally, an IC pattern has two directions, one direction and the direction perpendicular to the other.
In many cases, it is oriented in a direction, and the finest pattern is often limited to only one specific direction.

When performing periodic pattern exposure by double exposure, it is important that the direction of the periodic pattern matches the direction of the finest pattern of the normal pattern.

The exposure is performed so that the center of the peak of the periodic pattern coincides with the center of a fine pattern having a resolution lower than that of the normal pattern.

The double exposure in the present invention means a double exposure of a periodic pattern exposure and a normal pattern exposure. The periodic pattern exposure is repeated several times in parallel with the direction of the finest pattern of the normal pattern exposure. Exposure.

Each of the periodic pattern exposure and the normal pattern exposure of the exposure method and the exposure apparatus of the present invention comprises one or a plurality of exposure steps. Different exposure dose distributions are given to the photosensitive substrate.

When exposure is performed according to the flow of FIG.
First, the wafer (photosensitive substrate) is exposed in a periodic pattern as shown in FIG. The numbers in FIG. 7 represent the exposure amount, and the hatched portions in FIG. 7A 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 set between the exposure amounts 0 and 1 as shown in the lower graph of FIG. The upper part of FIG. 7B shows a finally obtained lithography pattern (concavo-convex pattern).

FIG. 8 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, as a positive resist (hereinafter referred to as "positive") and a negative resist. Each of the resists (hereinafter referred to as “negative type”) is shown. In the case of the positive type, when the exposure threshold value Eth or more, and in the case of the negative type, the exposure threshold value Eth or less,
The film thickness after development becomes zero.

FIG. 9 is a schematic diagram showing a state in which a lithography pattern is formed through the development and etching processes when such exposure is performed, for a negative type and a positive type.

In this embodiment, unlike the normal exposure sensitivity setting, as shown in FIGS. 10 (same as FIG. 7A) and FIG. 11, the central exposure amount in the periodic pattern exposure is set to 1
, The exposure threshold Eth of the resist on the exposed substrate
Is set to be larger than 1. When the exposure pattern (exposure amount distribution) obtained by performing only the base pattern exposure shown in FIG. 7 is developed, the exposure amount is insufficient. Does not occur, and no lithography pattern is formed by etching. This can be regarded as the disappearance of the periodic pattern (note that the present invention will be described using an example using a negative type, but the present invention can also be applied to a positive type). .

In FIG. 11, the upper part shows the lithography pattern (nothing can be done), and the lower part shows the relationship between the exposure distribution and the exposure threshold. Incidentally, E ₁ according to bottom the exposure amount in the periodic pattern 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 the periodic pattern exposure, is fused with an exposure pattern of an arbitrary shape including a pattern having a size equal to or smaller than the resolution of an exposure apparatus by ordinary projection exposure. And selectively exposing only the desired area to the exposure threshold or more of the resist,
Finally, a desired lithography pattern can be formed.

FIG. 12A shows an exposure pattern by normal projection exposure (normal pattern exposure), which is a fine pattern and cannot be resolved, and the intensity distribution on the object to be exposed is blurred and wide. . In the present embodiment, a fine pattern having a paper width of about half the resolution of normal projection exposure is used.

Assuming that the projection exposure for forming the exposure pattern of FIG. 12A is performed over the same region of the same resist without the development step after the periodic pattern exposure of FIG.
FIG. 12B shows the total exposure distribution on the resist surface.
It looks like the graph below. Here, the ratio of the exposure amount E ₂ of the exposure amount E ₁ and the projection exposure of the periodic pattern exposure is 1:
1. The exposure threshold value Eth of the resist is equal to the exposure amount E ₁ (=
1) The sum of the exposure amount E ₁ and the exposure amount E ₂ of the projection exposure (= 2)
Therefore, the lithography pattern shown in the upper part of FIG. 12B is formed.

At this time, the center of the normal pattern is made to coincide with the peak of the periodic pattern. Also, the direction of the normal pattern and the direction of the periodic pattern are matched.

The isolated line pattern shown in the upper part of FIG. 12 (B) has a resolution of periodic pattern exposure and has no simple periodic pattern. Therefore, a high-resolution pattern higher than the resolution that can be realized by ordinary projection exposure is obtained.

Here, it is assumed that the projection exposure for forming the exposure pattern shown in FIG. 13 (the line width twice as large as the exposure pattern shown in FIG. 10 and the exposure threshold or more (here, the exposure amount twice as large as the threshold)). ) Is overlaid on the same region of the same resist without the development step after the periodic pattern exposure of FIG. At this time, the symmetry of the superposed pattern is good by making the center of the normal pattern coincide with the peak position of the periodic pattern exposure,
A good pattern image is obtained.

The total exposure distribution of this resist is shown in FIG.
As shown in (B), the exposure pattern of the two-beam interference exposure (periodic pattern exposure) disappears, and finally only the lithography pattern by the projection exposure is formed.

As shown in FIG. 14, the principle is the same when the exposure is performed with a line width three times the exposure pattern of FIG.
With an exposure pattern having a line width of four times or more, the line width of a finally obtained lithography pattern is obvious from a combination of an exposure pattern having a double line width and an exposure pattern having a triple line width. All the lithography patterns that can be realized by projection exposure can also be formed in the present embodiment.

By adjusting the exposure amount distribution (absolute value and distribution) and the threshold value of the resist on the photosensitive substrate by each of the periodic pattern exposure and the projection exposure briefly described above,
11, 12 (B), 13 (B), and 14
The minimum line width is formed by a combination of various patterns as shown in FIG.
A circuit pattern serving as the pattern (B) can be formed.

The principles of the above exposure methods can be summarized as follows: (A-1) A pattern area not subjected to projection exposure (normal pattern exposure), that is, a periodic exposure pattern equal to or less than the exposure threshold of a resist disappears by development.

(A-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 periodic pattern exposure determined by the combination of the projection exposure and the periodic pattern exposure is It is formed.

(A-3) In the pattern area of the projection exposure performed with the exposure amount not less than the exposure threshold value, a fine pattern (corresponding to a mask) which is not resolved only by the projection exposure is formed. It turns out that. Further, as an advantage of the exposure method, if the periodic pattern exposure having the highest resolution is performed by two-beam interference exposure, a much larger depth of focus can be obtained as compared with normal exposure.

In the above description, the order of the periodic pattern exposure and the projection exposure is the order of the periodic pattern exposure, but is not limited to this order.

Next, a second embodiment of the present invention will be described.

This embodiment is directed to a so-called gate type pattern shown in FIG. 15 as a circuit pattern (lithography pattern) obtained by exposure.

In the gate pattern of FIG. 15, 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, it is possible to obtain a high resolution only in such a one-dimensional direction.
For two-dimensional patterns, two-beam interference exposure (periodic pattern exposure) may be performed only in one-dimensional directions that require such high resolution.

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. 16A 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. 16 represent exposure amounts.

As an exposure apparatus for realizing such two-beam interference exposure, an exposure apparatus having an interferometer-type demultiplexing / multiplexing optical system using a laser 151, a half mirror 152, and a plane mirror 153 as shown in FIG. , As shown in FIG.
There is a projection exposure apparatus in which a mask and an illumination method are configured as shown in FIG. 22 or FIG.

The exposure apparatus shown in FIG. 20 will be described.

In the exposure apparatus shown in FIG. 20, as described above, each of the two multiplexed light beams obliquely enters the wafer 154 at an angle θ, and the line width of the interference fringe pattern (exposure pattern) that can be formed on the wafer 154 is as described in (3) above. It is expressed by an equation. 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 is a pair of flat mirrors 153 (153a, 15a).
3b) can be arbitrarily adjusted and set by changing each angle. If the value of the angle θ is set to be large with a pair of plane mirrors, the line width of each interference fringe pattern becomes small.
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. 21 to 23 will be described.

The exposure apparatus shown in FIG. 21 is, for example, a projection exposure apparatus using an ordinary step-and-repeat or step-and-scan type reduction projection optical system (comprising a large number of lenses), and currently has an exposure wavelength of 248 nm. On the other hand, there are those having NA of 0.6 or more.

In FIG. 21, reference numeral 161 denotes a mask; 162, an object-side exposure light which emerges from the mask 161 and enters the optical system 163; 163, a projection optical system; 164, an aperture stop; 165, a wafer which emerges from the projection optical system 163; Image-side exposure light 166 incident on the wafer 166 indicates a wafer serving as a photosensitive substrate.
FIG. 9 is an explanatory diagram showing the position of a light beam on the pupil plane corresponding to the circular opening of the stop 164 by a pair of black dots.

FIG. 21 is a schematic diagram showing a state in which the two-beam interference exposure is being performed, and shows the object-side exposure light 162 and the image-side exposure light 16.
Both 5 are different from normal projection exposures and consist of only two parallel light beams.

In order to perform two-beam interference exposure (periodic pattern exposure) in a normal projection exposure apparatus as shown in FIG. 21, the mask 161 and its illumination method may be set as shown in FIG. 22 or FIG. Hereinafter, these three examples will be described.

FIG. 22A shows a Levenson-type phase shift mask 173, in which a light-shielding portion 17 made of chrome is used.
The pitch PO of 1 is 0 in the equation (4), and the pitch POS of the phase shifter 172 is the mask of the equation (5).

P ₀ = MP = 2MR = Mλ / (2NA) ‥‥‥ (4) P _OS = 2P ₀ = Mλ / (NA) ‥‥‥ (5) where M is the projection magnification of the projection optical system 163. , Λ indicates the exposure wavelength, and NA indicates the numerical aperture of the projection optical system 163 on the image side.

On the other hand, the mask 174 shown in FIG. 22B is a shifter edge type phase shift mask made of chrome without a light-shielding portion, and is similar to the Levenson type.
The pitch POS of No. 5 is configured to satisfy the above equation (5).

In order to perform two-beam interference exposure using the phase shift masks shown in FIGS. 22A and 22B, these masks are subjected to so-called coherent illumination with σ = 0 (or a value close to 0). Specifically, as shown in FIG.
The mask 170 is irradiated with a parallel light beam from a direction perpendicular to the mask (a direction parallel to the optical axis).

Here, σ = numerical aperture of the illumination optical system / numerical aperture of the projection optical system.

When such illumination is performed, the phase difference between adjacent transmitted lights becomes π by the phase shifter 172 (175), and the 0th-order transmitted diffracted light emitted from the mask 170 in the vertical direction cancels out. The two parallel ray bundles of ± 1st-order transmitted diffraction light are generated symmetrically from the mask 170 with respect to the optical axis of the projection optical system 163, and the two object-side exposures 165 in FIG. I do. Also 2
The higher-order diffracted light of higher order is transmitted through the aperture stop 1 of the projection optical system 163.
Since it does not enter the aperture 64, it does not contribute to imaging.

The mask 180 shown in FIG. 23 is a mask in which the pitch PO of the light shielding portion 181 made of chrome is expressed by the same expression (6) as the expression (4).

P ₀ = MP = 2MR = Mλ / (2NA) ‥‥‥ (6) where M is the projection magnification of the projection optical system 163, λ is the exposure wavelength, and NA is the image-side aperture of the projection optical system 163. Indicates a number.

The mask without the phase shifter shown in FIG. 23 is subjected to oblique incidence illumination using one or two parallel light beams. In this case, the incident angle θ of the parallel light beam to the mask 180
₀ is set to satisfy Expression (7). When two parallel light fluxes are used, the mask is illuminated with parallel light fluxes inclined by θ _{0 in} opposite directions with respect to the optical axis.

Sin θ ₀ = M / NAＮＡ (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 obliquely illuminating a mask having no phase shifter shown in FIG. 23 with a parallel light beam satisfying the above equation (7), the mask 180 outputs an angle θ with respect to the optical axis.
₀ proceeds along symmetrical optical paths with respect to the optical axes of the rectilinear to 0-order transmitted diffracted light and the optical path of the 0-order transmitted diffracted light projection optical system (traveling at an angle - [theta] ₀ with respect to the optical axis) -1 order transmission Two light beams of the diffracted light are generated as two object-side exposure light beams 162 in FIG. 16, and these two light beams enter the opening of the aperture stop 164 of the projection optical system 163 to form an image.

In the present invention, such oblique incidence illumination using one or two parallel light beams 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 is configured to perform partial coherent illumination. By exchanging an aperture stop (not shown) corresponding to 0 <σ <1 with a special aperture stop corresponding to σ ≒ 0, the projection exposure apparatus can be configured to perform substantially coherent illumination. .

Returning to the description of the second embodiment shown in FIGS. In the present embodiment, FIG. 16B shows a normal projection exposure (normal pattern exposure) (for example, one in which partial coherent illumination is performed on a mask) subsequent to the two-beam interference exposure (periodic pattern exposure) described above. The gate pattern is exposed.

The upper part of FIG. 16C shows the relative positional relationship with the exposure pattern by the two-beam interference exposure and the exposure amount in the area of the exposure pattern of the normal projection exposure, and the lower part of FIG. The exposure amount of the resist on the wafer by projection exposure is mapped in the vertical and horizontal directions with the resolution of the pitch of the minimum line width.

The exposure amount distribution shown in the lower part of FIG. 16 shows the intensity distribution for exposing the wafer with the light intensity incident from the mask as 1.

Although the exposure amount distribution by the exposure of the periodic pattern in FIG. 16A should ideally be a rectangular wave of 1 and 0, a line width near the resolution limit of the two-beam interference exposure is used. Therefore, it is a sine wave formed by only the zero-order light and the first-order light. Io the maximum value of the sin wave, a minimum value represented as I _1. At this time, the values of I ₀ and I ₁ are determined by σ of the illumination condition.

FIG. 16B shows a typical exposure value of each portion in the exposure amount distribution by the normal projection exposure. The portion of the minimum line width of the exposure pattern by this projection exposure is blurred and widened without resolution, and the value of the light intensity at each store decreases. The exposure is
Generally, the center of the pattern is denoted by b, both sides are denoted by d, and the center of the blurred image from both sides is denoted by c. The line width twice as large as the minimum line width is larger than the values of b, c, and d. However, since the line width is near the resolution limit of the projection exposure, the value of a is slightly blurred. These values of a, b, c, d change depending on the lighting conditions.

The exposure amount distribution shown in FIG. 16C is obtained as a result of adding the exposure amounts of the exposure pattern shown in FIG. 16A and the exposure pattern shown in FIG. 16B.

The light amount ratio in each of the two-beam interference exposure and the projection exposure differs depending on the illumination conditions of each exposure. The light amount ratio in each exposure in the addition is set as two-beam interference exposure: projection exposure = 1: k as the illuminance ratio of the illumination system, and the value of k is obtained as follows.

The exposure distribution shown in FIG. 16C can be expressed by the following equation using the above exposure distribution and light amount ratio.

A ′ = k × a + I ₀ a ″ = k × a + I ₁ b ′ = k × b + I ₀ c ′ = k × c + I ₁ d ′ = k × d + I ₁ desired gate In order to obtain the pattern, a relational expression with the threshold value Ic of exposure of the resist is obtained, for example, when the resist is a negative type,

[0150] _{a '> I C a ">} I C b'> I C c '<I C d'<I C a ', a", b' is it is desirable difference is less, c 'and particularly b' It is desirable to have a difference with

By solving these equations, the optimum light amount ratio under each illumination condition can be obtained. Particularly, the following two equations related to the fine pattern are important. When the resist is negative type, k × b + I ₀ > I _C k × c + I ₁ <I _C resist is positive type, k × b + I ₁ <I _C k × c + I ₀ > I _C resist is positive type. Although the magnitude relationship of the amount distribution is inverted and the inequality sign is inverted with respect to the resist threshold value Ic, the optimum light amount ratio is similarly obtained.

The manner in which the fine circuit pattern shown in FIG. 17 is formed by combining two different illumination methods of the two-beam interference exposure and the ordinary projection exposure described above will be described. In this embodiment, there is no developing process between the two-beam interference exposure and the normal projection exposure. Therefore, the exposure amount in the region where the exposure pattern of each exposure overlaps is added, and a new exposure pattern is generated by the added exposure amount (distribution).

FIG. 17, FIG. 18, and FIG.
This is a specific example using an rF excimer stepper.

As shown in FIG. 17, a gate pattern having a minimum line width of 0.12 μm is normally exposed, and a periodic pattern is superposed and exposed with a Levenson-type phase shift mask so as to overlap the minimum line width.

The NA of the projection lens was 0.6, and the σ of the illumination system was 0.3 in exposure using a Levenson mask. At the time of normal mask exposure, σ = 0.3, 0.6, 0.8 and annular illumination.

When exposing a periodic pattern by two-beam interference such as a phase shift mask, coherent illumination is σ
Is zero or a value close to it, but if it is too small, the amount of exposure per unit time will be small and the time required for exposure will be long, which is not practical.

In the case of periodic pattern exposure, σ is desirably 0.3 or less, and in exposure using a Levenson mask, the maximum σ is set to 0.3. In general exposure, partial coherent illumination is generally used. However, when σ is increased, reproducibility of a complicated shape is improved and depth is increased.
In so-called annular illumination in which the illuminance distribution is lower on the inside than on the outside, this tendency is remarkable, but there is a disadvantage that the contrast is reduced.

In the normal exposure, if the aberration around the lens is large, the influence is likely to be exerted on the resolution of the fine pattern, and the influence of the aberration is hard to occur in the periodic pattern exposure having the same fine line width.
Because, in the periodic pattern, many fine lines are arranged at the same width interval as the fine lines, and since the pitch is a repetitive pattern, the pitch is fixed. This is because, in the multiple exposure performed here, a part near the center of the periodic pattern is used. In addition, since the depth is much wider than that of the normal exposure, the defocus is less likely to be asymmetric.

The lens used in the exposure apparatus is well adjusted and sufficiently corrected for aberrations. In a normal resolution range, there is almost no influence of aberration, and there is no problem. Exert. FIG. 19A shows this example, and FIG. 19B shows the result of exposure using the method of the present invention.

FIG. 19 (A) shows the result of exposure in which the direction in which the aberration rms of the lens in which the aberration before adjustment is large remains largely for comparison and the emission direction of the fine pattern diffracted light coincide with each other. .

In particular, the fine portion has a left-right asymmetric shape due to the effect of asymmetric aberration, and the result is asymmetric with respect to defocus due to the influence of spherical aberration.

FIG. 19B shows a case where the direction in which the aberration rms is minimized and the emission direction of the fine pattern diffracted light are matched to minimize the asymmetric aberration, and the spherical aberration is corrected using a one-way aberration correction system. The result of exposing by the exposure device in which aberration was corrected is shown.

In this figure, the pattern has a symmetrical shape, and the result is also symmetric with respect to defocus. A good image was obtained at a defocus of ± 0.1 μm or less.

Therefore, in the exposure apparatus that realizes the method of the present invention, the reproducibility of the shape is improved and the depth is increased.

As described above, a fine circuit pattern is formed by double exposure with periodic pattern exposure. Normally, the fine pattern of the exposure pattern has low light intensity and low contrast, so it is not usually resolved.However, by overlapping double exposure and periodic pattern exposure with high contrast, the fine pattern has enhanced contrast, It will be resolved.

At this time, since the influence of aberration is likely to occur in the normal exposure, the influence of the aberration is minimized by aligning the direction in which the aberration is minimized with the emission direction of the fine pattern diffraction light. Furthermore, it is more effective if the aberration in the emission direction of the fine pattern diffracted light is corrected.

On the other hand, since the influence of aberration is relatively small in a large pattern having a resolution higher than that of the normal exposure, even if the pattern has an arbitrary shape and the emission direction of the diffracted light has an arbitrary direction, as described above. However, the deterioration of the shape is not a problem in a normal resolution range. Moreover, when the line width is an integral multiple of the line width of the periodic pattern exposure, it is superimposed on the periodic pattern exposure, which is hardly affected by aberration, thereby enhancing the contrast, forming a sharp edge image, and correcting the shape.

According to the exposure method of the present invention, a circuit pattern having a fine line width of 0.12 μm can be formed, for example, by means of matching the direction in which aberration is minimized with the emission direction of the fine pattern diffracted light, or by emitting the fine pattern diffracted light. It can be formed using a projection exposure apparatus having an aberration correction system for correcting directional aberration, and an illumination optical system capable of changing illumination conditions for changing the light amount ratio of σ and illuminance.

The light amount ratio between the periodic pattern and the normal exposure pattern was determined by the above-mentioned formula using the optimum value based on the combination of the illumination conditions and the optimum value based on the above-described combination.

As shown in FIG. 18A, the σ of the normal exposure
Is set to 0.3 which is the same as σ of the periodic pattern exposure, and the double exposure is performed under the same illumination condition, the gate pattern is defocused to 0.
Although the resolution is within the range of ± 0.2 μm, the line pattern portion is undulating, and the narrow portion causes disconnection, which is not preferable.

In the case of normal pattern exposure, σ = 0.6
It is better to do above. As shown in FIG. 18B, when σ of the normal exposure is set to 0.6, the gate pattern is resolved within the range of defocus 0 ± 0.4 μm, and the undulation of the line pattern is eliminated. Set the exposure amount ratio between normal exposure and periodic pattern exposure to normal exposure: periodic pattern exposure =
1.5: 1.

As shown in FIG.
When is increased to 0.8, the reproducibility of a complicated shape is slightly improved. The exposure amount ratio between normal exposure and periodic pattern exposure was set to normal pattern exposure: periodic pattern exposure = 2: 1. In the case of normal pattern exposure, the exposure amount is preferably twice or more as compared with the periodical pattern exposure.

In FIG. 19 (B), the normal exposure is annular illumination, and the illuminance from 0.6 inside the ring to 0.8 outside the ring is 1, and
This is a two-dimensional intensity distribution in the case where the illuminance is set to 0 or less inside 0.6 of the ring. The exposure amount ratio between normal exposure and periodic pattern exposure was set to normal exposure: periodic pattern exposure = 2.5: 1.

In the annular illumination, the reproducibility of a complicated shape is improved and the depth is increased as compared with when σ is 0.8. A good image was obtained with a defocus of ± 0.4 μm or less.

The fine circuit pattern is formed by double exposure with periodic pattern exposure. Normally, the fine pattern of the exposure pattern is not normally resolved because the light intensity is low and the contrast is low. Become imaged.

On the other hand, even a large pattern having a resolution equal to or larger than the resolution of the normal exposure pattern is superimposed on the intensity of the periodic pattern exposure, and the contrast is enhanced. According to the exposure method of the present invention, a circuit pattern having a fine line width of 0.12 μm can be formed by using a projection exposure apparatus having an illumination optical system capable of switching illumination conditions such as changing σ or a light amount ratio of illuminance. And

The optimum value of the light quantity ratio between the periodic pattern exposure and the normal pattern exposure was determined by the above-mentioned formula using the combination of the illumination conditions.

Lighting condition 1 The exposure of the periodic pattern is σ = 0.
3. Normal pattern exposure: σ = 0.3 Exposure amount distribution by periodic pattern exposure shown in the lower part of FIG. 16A and exposure amount distribution by normal projection exposure shown in the lower part of FIG. ) Are shown below.

I ₀ = 0.80 I ₁ = 0.23 a = 1.31 b = 0.34 c = 0.61 d = 0.09 k = 1.0 is optimal, a '= 2.11 a "= 1.54 b' = 1.21 c '= 0.89 d' = 0.32. For the later comparison, the maximum value a 'is normalized by 1 as follows.

A '= 1.0 a "= 0.73 b' = 0.57 c '= 0.42
d '= 0.15 I ₀ = 0.38 Illumination condition 2 σ = 0.3 for periodic pattern exposure, σ = 0.6 I ₀ = 0.80 I ₁ = 0.23 a = 1.25 b = 0.44 c = 0.53 d = 0.13 k = 1.5 for normal pattern exposure Is optimal, and a '= 2.68 a "= 2.11 b' = 1.46 c '= 1.03 d' = 0.43. For later comparison, when the maximum value a 'is normalized by 1, the following is obtained. .

A '= 1.0 a "= 0.79 b' = 0.55 c '= 0.38
d '= 0.16 I ₀ = 0.30 Illumination condition 3 σ = 0.3 for periodic pattern exposure, σ = 0.8 for normal pattern exposure I ₀ = 0.80 I ₁ = 0.23 a = 1.20 b = 0.48 c = 0.47 d = 0.16 k = 2.0 is optimal, and a '= 3.20 a "= 2.63 b' = 1.76 c '= 1.17 d' = 0.55. Normalizing the maximum value a 'to 1 gives the following.

A '= 1.0 a "= 0.82 b' = 0.55 c '= 0.37
d '= 0.17 I ₀ = 0.25 Illumination condition 4 Periodic pattern exposure is σ = 0.3, normal pattern exposure is σ = 0.8, annular illumination, inner (inner zone) σ
Illuminance distribution of 0.6 or less was set to zero.

I ₀ = 0.80 I ₁ = 0.23 a = 1.10 b = 0.47 c = 0.36 d = 0.19 k = 2.5 is optimal, and a '= 3.55 a "= 2.98 b' = 1.98 c '= 1.13 d' = 0.71 and the maximum value a ′ is normalized by 1 as follows.

A '= 1.0 a "= 0.84 b' = 0.56 c '= 0.32
d '= 0.20 I ₀ = 0.23 In the discussion so far, the resist threshold value was 1.5 when the maximum exposure amount was 3, so if normalized with the maximum exposure amount, the resist threshold value would be 0.5. Looking at this normalized exposure distribution, a ', a ", b' are normalized resist threshold values of 0.
It is larger than 5 and c ', d', I ₀ is smaller than the threshold.

Since a portion where the exposure amount is larger than the resist threshold value by development is left, only the exposure amount a ′, a ″, and b ′ remains after development as a pattern.
The part shown in gray below is the shape after development.

In general, when exposing a normal exposure pattern, an exposure amount approximately twice as large as that for exposing a periodic pattern is appropriate.
There is an optimum exposure amount ratio depending on a combination of illumination conditions when exposing the periodic pattern, and it can be obtained by the above-described formula.

As a result of calculating various combinations of illumination conditions from the above-described formula, the following was shown. When σ = 0.3 at the time of periodic pattern exposure and the illumination condition σ of the normal pattern exposure is smaller than 0.8, the exposure amount at the time of exposing the normal pattern is set to be twice or less than the exposure amount at the time of exposing the periodic pattern. Good.

In the case of a periodic pattern, when σ = 0.3 and the illumination condition for exposing the normal pattern is annular illumination, when the width of the annular pattern is small, the exposure amount for exposing the normal pattern is equal to the periodic pattern. It is preferable that the exposure amount is twice or more than the exposure amount at the time of exposure.

Illumination condition σ when exposing periodic pattern
Is smaller than 0.3, the exposure amount for exposing the normal pattern should be at least twice the exposure amount for exposing the periodic pattern.

FIG. 24 is a schematic view showing an example of an exposure apparatus for two-beam interference exposure according to the present invention.
Reference numeral 201 denotes an optical system for two-beam interference exposure.
0 is the same as the optical system. 202 is a KrF or ArF excimer laser, 203 is a half mirror, 204 (20
4a, 204b) are plane mirrors, 205 is an optical system 201
Observing the two-beam interference alignment mark on the wafer 206 with an off-axis type alignment optical system in which the positional relationship with the position can be fixed or appropriately detected as a baseline (amount).
The position is detected. 206 is a wafer which is a photosensitive substrate,
Reference numeral 207 denotes 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 device 205 and the XYZ stage 207 are well known, a detailed description is omitted.

FIG. 25 is a schematic view showing a high-resolution exposure apparatus comprising the two-beam interference exposure apparatus of the present invention and the projection exposure apparatus in which the resolution direction is set as described above.

In FIG. 25, reference numeral 212 denotes a two-beam interference exposure apparatus including the optical system 201 and the apparatus 205 shown in FIG. 24. Reference numeral 213 denotes an illumination optical system (not shown), a reticle positioning optical system 214, and a wafer positioning optical system. (Off-Axis Positioning Optical System) A projection optical system 216 for reducing and projecting the circuit pattern of the mask 215 and 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
6, 217, the configuration and function of which are well-known, and thus a detailed description is omitted.

In FIG. 25, reference numeral 219 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 of the optical axes 13 and in the optical axis direction can be moved, and its position in the XY directions can be accurately controlled using a laser interferometer or the like.

Stage 219 holding wafer 218
25 is sent to the position (1) in FIG. 25, the position is accurately measured, and based on the measurement result, the light is sent to the exposure position of the device 212 indicated by the position (2), and the two-beam interference exposure is performed on the wafer 218. The device 213 is then fed into position (3) and its position is accurately measured and indicated by position (4).
And the wafer 218 is subjected to projection exposure.

In the apparatus 213, instead of the off-axis positioning optical system 217, a TTL positioning optical system (not shown) for observing the positioning mark of the wafer 218 via the projection optical system 216 and detecting the position is detected. System and
A TTR alignment optical system (not shown) for observing an 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.

In the present invention, (a) as the illumination method of the illumination optical system, it is applicable to illuminate the mask pattern with light from a KrF excimer laser, an ArF excimer laser or an F2 excimer laser.

(B) In an exposure apparatus, a refracting system and a reflecting system
It is applicable to project the mask pattern by a projection optical system composed of either a refraction system or a reflection system.

(C) As the exposure apparatus, a step-and-repeat type reduction projection exposure apparatus having the exposure method of the present invention as an exposure mode, a step-and-scan type reduction projection exposure apparatus having the exposure method of the present invention as an exposure mode, and the like are applied. It is possible.

In the present invention, the method proposed by the applicant of the present invention in Japanese Patent Application No. 8-357746 can be applied to the correction of the optical performance due to the manufacturing error of the projection optical system.

For example, a correction lens 2 as shown in FIG.
31 may be provided in the projection optical system.

This figure shows a one-way aberration correction system.
It is composed of two parallel plane plates, and the facing surfaces have an aspherical shape expressed as a function of x as follows.

[0203] z = f (x) This function depends aberrations to be corrected, for example, if the low order spherical aberration correction, z = ax is ^5, a is a constant determined by the aberration correction amount and the relative eccentricity is there.

Next, an embodiment of a method of manufacturing a semiconductor device using the above-described projection exposure apparatus will be described.

FIG. 26 shows a flow of manufacturing a semiconductor device (a semiconductor chip such as an IC or an LSI, or a liquid crystal panel or a CCD).

In step 1 (circuit design), the circuit of the semiconductor device is designed. Step 2 is a process for making a mask on the basis of the circuit pattern design.

In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4
The (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the prepared mask and wafer.

The next step 5 (assembly) is called a post-process, and is a process of forming a semiconductor chip using the wafer produced in step 4, and includes an assembly process (dicing and bonding) and a packaging process (chip encapsulation). And the like.

In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device manufactured in step 5 are performed. Through these steps, a semiconductor device is completed and shipped (step 7).

FIG. 27 shows a detailed flow of the wafer process. Step 11 (oxidation) oxidizes the wafer's surface. Step 12 (CVD) forms an insulating film on the wafer surface.

In step 13 (electrode formation), electrodes are formed on the wafer by vapor deposition. In step 14 (ion implantation), ions are implanted into the wafer. Step 15
In (resist processing), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the above-described exposure apparatus to print and expose the circuit pattern of the mask onto the wafer.

In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeating these steps, multiple circuit patterns are formed on the wafer.

By using the manufacturing method of this embodiment, it is possible to easily manufacture a highly integrated semiconductor device which has conventionally been difficult to manufacture.

[0214]

As described above, the present invention provides (a-1) periodic pattern exposure represented by two-beam interference exposure and normal pattern exposure not including the periodic pattern (normal exposure)
An exposure method and an exposure apparatus capable of forming a circuit pattern having a complicated shape on a wafer by using the two exposure methods.

(A-2) An exposure method and an exposure apparatus capable of easily obtaining a circuit pattern having a portion having a line width of 0.15 μm or less.

(A-3) An exposure apparatus capable of performing two exposure methods, periodic pattern exposure and normal exposure. Can be achieved.

In particular, according to the present invention, (a-4) 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.

According to the present invention, (a-5) an exposure method and an exposure apparatus which can easily obtain a high resolution by appropriately setting the direction of the resolution of the projection optical system and the direction of the fine pattern of the mask. Can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an embodiment of an exposure apparatus of the present invention.

FIG. 2 is a diagram illustrating a part of the exposure apparatus according to the first embodiment of the present invention.

FIG. 3 is an explanatory view of a part of the exposure apparatus according to the first embodiment of the present invention;

FIG. 4 is an explanatory view of a part of the exposure apparatus according to the first embodiment of the present invention.

FIG. 5 is an explanatory view of a part of the first embodiment of the exposure apparatus of the present invention.

FIG. 6 is a flowchart of an exposure method according to the present invention.

FIG. 7 is an explanatory view showing an exposure pattern by two-beam interference exposure.

FIG. 8 is an explanatory diagram showing exposure sensitivity characteristics of a resist.

FIG. 9 is an explanatory view showing pattern formation by development.

FIG. 10 is an explanatory view showing an exposure pattern by ordinary two-beam interference exposure.

FIG. 11 is an explanatory view showing an exposure pattern by two-beam interference exposure in the present invention.

FIG. 12 is an explanatory view showing an example of an exposure pattern (lithography pattern) that can be formed in the first embodiment of the present invention.

FIG. 13 is an explanatory view showing another example of an exposure pattern (lithography pattern) that can be formed in the first embodiment of the present invention.

FIG. 14 is an explanatory view showing another example of an exposure pattern (lithography pattern) that can be formed in the first embodiment of the present invention.

FIG. 15 is an explanatory diagram showing a gate pattern according to the second embodiment of the present invention.

FIG. 16 is an explanatory view showing Embodiment 2 of the present invention.

FIG. 17 illustrates a gate pattern.

FIG. 18 is an explanatory diagram of a formed gate pattern.

FIG. 19 is an explanatory diagram of a formed gate pattern.

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

FIG. 21 is a schematic diagram illustrating an example of a projection exposure apparatus that performs two-beam interference exposure.

FIG. 22 is an explanatory view showing an example of a mask and an illumination method used in the apparatus shown in FIG.

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

FIG. 24 is a schematic view showing an example of a two-beam interference exposure apparatus of the present invention.

FIG. 25 is a schematic view showing an example of a high-resolution exposure apparatus of the present invention.

FIG. 26 is a flowchart of a device manufacturing method of the present invention.

FIG. 27 is a flowchart of a device manufacturing method of the present invention.

FIG. 28 is a schematic view showing a conventional projection exposure apparatus.

[Explanation of symbols]

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

Claims (18)

[Claims] 1. A projection method for projecting and exposing a pattern on a first object plane onto a second object plane by a projection optical system, wherein: a direction in which the resolving power of the projection optical system is the best; An exposure method, wherein an emission direction of a diffracted light of a fine pattern is made to coincide. 2. A direction in which the resolving power is the best at a plurality of image heights of the projection optical system is measured, and the projection optics at the same height as the pattern image height at which the fine pattern on the first object plane is located. 2. The exposure method according to claim 1, wherein the direction in which the resolving power at the image height of the system is the best is matched. 3. An exposure method in which a plurality of first objects having mutually different patterns are used to perform multiple exposures of the same area on a second object with different patterns using a projection optical system. An exposure method, wherein the direction in which the light beam is improved and the direction in which the diffracted light of the fine pattern on the first object surface is emitted coincide with each other. 4. A direction in which the resolving power of the projection optical system is best measured at a plurality of image heights, and the projection optical system at the same height as the pattern image height at which the fine pattern on the first object plane is located. 4. The exposure method according to claim 3, wherein the direction in which the resolving power at the image height of the system is the best is matched. 5. The direction in which the resolution of the projection lens is the best is the rms (root mean sq) of the measured wavefront aberration.
5. The exposure method according to claim 1, wherein ure) is the direction in which the ure is smallest. 6. The output direction of the diffracted light of the finest pattern of the pattern on the first object plane is perpendicular to the longitudinal direction of the finest pattern. Or the exposure method of 4. 7. The image height and the aberration amount at this measured image height or the Zernike-expanded coefficient are stored in a control unit of the exposure apparatus, and the r of the aberration amount in each direction is stored.
5. The exposure method according to claim 2, wherein ms is calculated. 8. The exposure apparatus according to claim 1, wherein a direction in which the previously calculated rms is minimized is stored in a control unit of the exposure apparatus, and is read from the storage.
2, 3 or 4 exposure methods. 9. The exposure method according to claim 1, wherein a direction in which aberration is minimized is input at the time of exposure. 10. The exposure method according to claim 2, wherein an image height of a portion of the first object having the fine pattern and an emission direction of the diffracted light of the fine pattern are written in a barcode of the first object. . 11. The barcode of the first object is read at the time of alignment of the first object.
2, 3 or 4 exposure methods. 12. The exposure method according to claim 1, wherein the direction of emission of the diffracted light of the finest pattern of the pattern of the first object is inputted at the time of exposure. 13. The exposure method according to claim 1, wherein said projection lens is manufactured by adjusting such that aberration is reduced in only one direction, and said direction is set as a reference direction. . 14. An aberration correcting system for correcting an aberration in a direction in which diffracted light of a fine pattern is emitted by rotating an aberration correcting system capable of correcting an aberration in one direction.
Or the exposure method of 4. 15. The exposure method according to claim 1, wherein the exposure is performed by scanning at right angles to a direction in which the rms amount of aberration of the projection lens is minimized. 16. An exposure apparatus, wherein a pattern on a mask is transferred onto a photosensitive substrate using the exposure method according to claim 1. Description: 17. A device is manufactured by exposing a pattern on a mask surface to a wafer surface by using the exposure method according to claim 1, and then subjecting the wafer to a development process. A method for manufacturing a device, comprising: 18. A device according to claim 16, wherein after the pattern on the mask surface is exposed on the wafer surface using the exposure apparatus according to claim 16, the wafer is subjected to a developing process to produce a device. Production method.