JPH08330223A - Exposure method - Google Patents

Abstract

PURPOSE: To obtain an exposure method for fully exposing and transferring even a further fine mask pattern while maintaining the wavelength of exposure light. CONSTITUTION: Illumination light l and illumination light 2 which are eccentric from and are separated from the light axis of a lighting optical system are applied to a mask so that they can be inclined on a pattern surface symmetrically in reference to a vertical direction, and a zero-order diffraction light from a pattern due to the illumination of the illumination light 1 and first-order diffraction light from a pattern due to the illumination of the illumination light 2 are allowed to reach the substrate through an optical path l of a projection optical system. Zero-order diffraction light from the pattern due to the application of the illumination light 2 and first-order diffraction light from the pattern due to the application of the illumination light l are allowed to reach the substrate via an optical path 2 of the projection optical system. The optical path l and the optical path 2 are allowed to be eccentric by nearly an equal distance from the light axis of the projection optical system on the Fourier transformation surface of the projection optical system for the pattern or near it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure method for transferring a pattern of a mask onto a sample substrate by using an exposure apparatus used for manufacturing a semiconductor memory device or a liquid crystal device, and more specifically, a fine pattern formed on the mask. The present invention relates to a technique of improving the resolution (fineness of a resist image) of a transfer pattern formed on a sample substrate by positively utilizing the diffracted light generated in the fine pattern by utilizing the regularity of.

[0002]

2. Description of the Related Art Generally, a method of transferring a mask pattern onto a sample substrate, which is called a photolithography technique, is adopted for forming a circuit pattern of a semiconductor memory or a liquid crystal element. In this case, the mask pattern is photographically transferred onto the sample substrate by irradiating the sample substrate on which the photosensitive resist layer is formed with exposure light such as ultraviolet rays through a mask on which the mask pattern is formed. .

In recent years, with the miniaturization of semiconductor memory and liquid crystal element circuit configurations, projection type exposure apparatuses such as steppers, which can reduce the mask pattern and project and transfer it onto a sample substrate, have been widely used. Specialized ultraviolet light having a narrow wavelength distribution having a shorter wavelength has been used.

Here, the reason for narrowing the wavelength distribution width is to eliminate the blurring of the projected image due to the chromatic aberration of the projection optical system of the projection type exposure apparatus, and the reason for selecting a shorter wavelength is the contrast of the projected image. This is to improve. But,
At present, the shortening of the wavelength of the exposure light has reached the limit due to the restriction of the lens material and the resist material as there is no suitable light source for further miniaturization of the required mask pattern.

In such a miniaturized mask pattern, since the resolution line width of the pattern approaches the wavelength of the exposure light, the influence of the diffracted light generated when transmitting the pattern cannot be ignored and the mask on the sample substrate It becomes difficult to secure a sufficient light / dark light amount difference in the pattern projection image, and the contrast at the light / dark boundary also decreases.

[0006]

That is, exposure light incident on the mask from above at various incident angles is generated at each point on the mask pattern, and the 0th order, ± 1st order, ± 2nd order,
Each diffracted light of .. passes through the projection optical system, and is reassembled at each point on the sample substrate conjugate with each point to form an image. However, ± 1st order, ± 2 for finer mask patterns
Next, because the diffracted light of ... becomes larger in diffraction angle, it becomes incident on the sample substrate at a shallower angle.
The depth of focus of the projected image is remarkably reduced, causing a problem that the entire thickness of the resist layer cannot be exposed.

From this point of view, the applicant of the present application previously disclosed that, in Japanese Patent Application Laid-Open No. 2-50417, a diaphragm is provided in the illumination optical system and the projection optical system to restrict the incident angle of the exposure light with respect to the mask. An invention has been proposed in which the aperture amount of the diaphragm is adjusted according to the mask pattern to maintain the depth of focus while maintaining the light amount difference between the light and dark of the projected image on the sample substrate.

However, also in the present invention, ± 0th order and ± 2th order are applied to the 0th order diffracted light which reaches the sample substrate almost vertically.
Next, because the diffraction angle of the diffracted light is large, it does not reach the sample substrate beyond the lens. As a result, the mask pattern projection image on the sample substrate is flat with poor contrast in which only the 0th order light component is emphasized. It became a thing.

Further, the ± first-order diffracted light in the portion which reaches the sample substrate after being housed in the lens is incident on the sample substrate at a shallow angle, whereas the 0th-order light is incident almost vertically, so that it is also sufficient. It was pointed out that a sufficient depth of focus cannot be secured.

By the way, a general type of such a fine mask pattern can be regarded as a lattice pattern arranged at equal intervals vertically or horizontally. In other words, a grid pattern in which transparent and opaque lines are alternately arranged at equal intervals, which realizes the minimum line width that can be formed on the sample substrate, is adopted in the most dense place in the mask pattern. Elsewhere, the pattern is relatively loose and fine, with diagonal patterns being exceptional.

The properties of general resist layer materials are as follows.
It has a non-linear photosensitivity, and when the amount of light received exceeds a certain level, the chemical change proceeds rapidly, but when the amount of received light is less than that, the chemical change hardly progresses. Therefore, for the projected image of the mask pattern on the sample substrate, as long as the light amount difference between the bright portion and the dark portion is ensured, even if the contrast at the boundary between the bright portion and the dark portion is slightly low, the required resist pattern according to the mask pattern is obtained. The image is obtained.

The present invention positively utilizes the fact that the exposure light has a narrow wavelength distribution, the mask pattern can be regarded as a diffraction grating, and the resist material has a comparator property of the amount of received light. , Which makes it possible to form a finer resist image while maintaining the wavelength of the exposure light.
It is an object of the present invention to provide an exposure method capable of sufficiently exposing and transferring even a fine mask pattern for which a sufficient light amount difference has not been conventionally obtained on a sample substrate.

[0013]

In order to achieve the above object, an exposure method according to the invention of claim 1 is an illumination optical system for illuminating a mask with illumination light, and an image of a pattern of the mask. In an exposure method of transferring the pattern of the mask onto the substrate using an exposure apparatus having a projection optical system for projecting onto the substrate, the illumination light is decentered from the optical axis of the illumination optical system, and The first illumination light and the second illumination light are converted into separate first illumination light and the first illumination light so that the first illumination light and the second illumination light are inclined symmetrically with respect to a direction substantially perpendicular to the pattern surface. The mask is irradiated with second illumination light, and the 0th-order diffracted light generated from the pattern by the irradiation of the first illumination light and the 1st-order diffracted light generated from the pattern by the irradiation of the second illumination light are described above. First light of projection optical system The 0th-order diffracted light generated from the pattern by irradiation of the second illumination light and the 1st-order diffracted light generated from the pattern by irradiation of the first illumination light are made to reach the substrate through a path. It is made to reach the substrate through a second optical path of a projection optical system, and the first optical path and the second optical path are projected onto the Fourier transform plane of the projection optical system with respect to the pattern of the mask or in the vicinity thereof. It is characterized in that they are decentered from each other by an approximately equal distance from the optical axis of the optical system.

The exposure method according to claim 2 of the present application is the same as the exposure method according to claim 1, wherein the first optical path and the second
Light other than the respective light that has passed through the optical path is characterized in that it does not reach the substrate.

According to a third aspect of the present invention, in the exposure method of projecting an image of a mask pattern onto a substrate using a projection optical system, the mask is irradiated with at least two illumination lights, and the one set Illumination light is tilted symmetrically by a predetermined angle with respect to a direction perpendicular to the surface of the pattern, and the predetermined angle is the 0th order diffracted light generated from the pattern for each of the two illumination lights. One 1st-order diffracted light is defined to be substantially symmetrical with respect to a direction perpendicular to the surface of the pattern, and the 0th-order diffracted light and the 1st-order diffracted light form an image of the pattern on the substrate via the projection optical system. It is characterized by being formed into.

An exposure method according to a fourth aspect of the present invention is an exposure method of exposing a pattern of a mask onto a substrate via a projection optical system, wherein the pattern is illuminated with at least first illumination light and second illumination light. That is, the second illumination light is generated from the pattern through the same optical path of the projection optical system as the diffracted light other than the 0th-order diffracted light generated from the pattern by the irradiation of the first illumination light. 0
The second diffracted light is made to reach the substrate.

According to a fifth aspect of the present invention, in the exposure method according to the fourth aspect, a semiconductor element is manufactured by utilizing the exposure method.

An exposure method according to claim 6 of the present application is an exposure method of exposing a substrate with a pattern having at least a linear portion extending in a predetermined direction, wherein the exposure surface is inclined with respect to an incident surface including the predetermined direction. The pattern is illuminated with light along a pair of optical paths, and an image of the pattern is projected onto the substrate.

An exposure method according to a seventh aspect of the present invention is the exposure method according to the sixth aspect, characterized in that a semiconductor element is manufactured using the exposure method.

[Action]

In the conventional projection type exposure apparatus, the exposure light incident on the mask at various incident angles from above is used indiscriminately, and 0th order, ± 1st order and ± 2th order generated in the mask pattern.
Next, each of the diffracted lights of ... Passed through the projection optical system almost indefinitely and was imaged on the sample substrate.

On the other hand, in the exposure method of the present invention, the exposure light obliquely incident on the mask pattern at a specific direction and angle is selectively used, and the selected exposure light is used as the mask pattern. The 0th-order diffracted light and the 1st-order diffracted light generated in 1 are preferentially made to reach the sample substrate, interfere with each other, and form an image.

That is, by selecting the optimum 0th-order diffracted light and 1st-order diffracted light by using a light-shielding plate according to the fineness of the mask pattern, an image-forming pattern having a larger light-dark difference in light quantity and a larger depth of focus than in the past. Can be obtained.

Here, to select the exposure light incident on the mask, "exposure light incident on the mask pattern at a specific direction and angle to the pupil plane of the illumination optical system and its vicinity or a conjugate surface thereof is selected. A light-shielding plate having a light-transmitting portion arranged so as to block other unnecessary exposure light.

However, the "0th-order diffracted light and the 1st-order diffracted light generated in the mask pattern are safely transmitted to the pupil plane of the projection optical system and the vicinity thereof. Even if a light-shielding plate in which a light-transmitting part is arranged so as to block the diffracted light due to the exposure light is provided, the diffracted light that reaches the sample substrate and participates in image formation becomes almost equal, and similar effects can be expected. .

Further, in the light shielding plate provided in the pupil plane of the projection optical system and in the vicinity thereof, the exposure light selected by the light shielding plate arranged in the pupil plane of the illumination optical system and in the vicinity thereof or in the conjugate plane is used as a mask pattern. It also has a function of removing the diffracted light other than the 0th-order diffracted light and the 1st-order diffracted light generated in.

When a light shielding plate is arranged on the pupil plane of the illumination optical system and its vicinity or its conjugate plane, exposure light having a predetermined wavelength is incident on the diffraction grating-shaped mask pattern in a specific incident direction and incident angle. Then, on the pupil plane of the projection optical system, a spot array is formed by the Fourier expanded 0th, 1st, 2nd, 3rd, ... However, usually, the spots of the 2nd-order, 3rd-order, and higher-order diffracted lights are projected (vignetting) outside the projection optical system.

The light-shielding plate disposed on the pupil plane of the illumination optical system and its vicinity or a conjugate plane thereof blocks the exposure light that is incident almost perpendicularly to the mask, and the exposure light having a specific incident direction and incident angle. Only the mask is selectively incident on the mask. here,
When high-order diffracted light is an obstacle, a light-shielding plate is further provided on the pupil plane of the projection optical system and its vicinity to block it. As a result, a projection pattern image is formed on the sample substrate by using the 0th-order diffracted light and the 1st-order diffracted light generated by the mask pattern as the exposure light having the preferable incident angle.

Here, the portion of the mask pattern that requires high resolution, that is, the lattice pattern in which transparent and opaque lines are alternately arranged at equal intervals, can be regarded as a rectangular wave shape with a duty of 0.5, and is used in the illumination optical system. When a light-shielding plate is provided on the pupil plane and its vicinity, or on its conjugate plane, the diffracted light generated by this lattice pattern is distributed in the direction crossing the lattice on the pupil plane of the projection optical system. , ± 2
Form spots of diffracted light of the respective orders of ...

At this time, as is known as the Fourier expansion of a rectangular wave, the 0th-order diffracted light is a bias component in the projection image on the sample substrate, and the ± 1st-order diffracted light is a sine wave component having the same period as the grating. Due to the interference of the components, an image formation pattern having a sufficient light-dark difference in light quantity necessary for exposing the resist layer can be obtained on the sample substrate.

Further, since a general mask pattern can be regarded as a combination of a plurality of vertical or horizontal gratings arranged on the mask, the exposure light having the optimum incident direction and incident angle with respect to each grating. , The Fourier patterns formed on the pupil plane of the projection optical system are aligned in the angular direction corresponding to the direction of each grating, and the Fourier patterns are arranged in accordance with the wavelength of the exposure light and the pitch of the grating. A group of spots at intervals is formed, and the intensity of each spot depends on the number of pitches of the grating and the order of diffracted light.

Therefore, it is also possible to provide a light-shielding plate provided with a light-transmitting portion at a required spot position in the projection optical system to select similar diffracted light. When a light-shielding plate is provided on the pupil plane of the projection optical system, a light-shielding plate provided with a light-transmitting portion at the spot position of useful diffracted light is adopted to selectively transmit useful diffracted light.
Blocks diffracted light that gets in the way.

As described above, since the number and arrangement of the light-transmitting portions on the light shielding plate are unique and different according to the mask pattern, the light shielding plate is naturally exchanged together with the mask, and the mask is replaced with the mask. Should be strictly aligned.

Next, exposure light having a specific incident direction and incident angle is incident on the mask pattern, and an image formation pattern is formed on the sample substrate using the 0th-order diffracted light and the 1st-order diffracted light. The reason why the depth of focus becomes large will be described.

When the sample substrate is coincident with the focal point of the projection optical system, each diffracted light which exits one point on the mask and reaches one point on the sample substrate is not affected by which part of the projection optical system. Even if they pass through, they all have the same optical path length. Therefore, even when the 0th-order diffracted light penetrates almost the center of the projection optical system pupil as in the conventional case, the optical path lengths of the 0th-order diffracted light and other diffracted lights are equal to each other, and the mutual wavefront aberration is also zero.

However, when the sample substrate does not coincide with the focus position of the projection optical system, the optical path length of obliquely incident high-order diffracted light is short in front of the focus with respect to the 0th-order diffracted light passing through the shortest distance. , And becomes longer behind the focal point, and the difference depends on the difference in the incident angle. Therefore, the 0th-order, 1st-order, ... Diffracted light forms wavefront aberrations mutually, and blurs the imaging pattern before and after the focus position. This wavefront aberration △
W is represented by the following equation (1).

ΔW = (1/2) × (NA) ² × Δf (1) Δf: Defocus amount NA: Distance from the center on the pupil plane expressed by numerical aperture

Therefore, with respect to the 0th-order diffracted light (ΔW = 0) that passes through almost the center of the pupil plane, the 1st-order diffracted light that passes the radius r ₁ around the pupil plane is expressed by the following equation (2). Therefore, the resolution before and after the focus position, that is, the depth of focus is reduced.

ΔW = (1/2) × (r ₁ ) ² × Δf ... (2)

On the other hand, a light-shielding plate is provided on the pupil plane of the illumination optical system or in the vicinity thereof, or on the conjugate plane thereof, so that the 0th-order diffracted light and the 1st-order diffracted light from the mask pattern are substantially centrally symmetric on the pupil plane (both. In the case of the exposure method of the present invention in which the light passes through a radius r ₂ ), the wavefront aberrations of the 0th-order diffracted light and the 1st-order diffracted light before and after the focus are equal to
There is no blur due to wavefront aberration associated with defocus. That is,
The depth of focus is increased by this amount.

ΔW = (1/2) × (r ₂ ) ² × Δf ... (3)

The pair of exposure lights that have passed through the light-transmitting portion of the light-shielding plate are parallel lights that are obliquely and symmetrically incident on the grating of the mask pattern, but one of the ± 1st-order diffracted lights is a projection light. About the optical axis of the system, it goes through a path symmetrical with the 0th order light,
It is incident on the sample substrate at an angle as deep as the zero-order light. As a result, the substantial numerical aperture of the projection optical system involved in image formation is reduced, and a deeper depth of focus can be obtained.

Further, in the exposure method of the present invention, the exposure light having a symmetrical incident angle from two directions is incident on the grating of the mask pattern by using the light shielding plate arranged in the illumination optical system. Here, the incident angle is adjusted by the mutual spacing of the light-transmitting portions of the light-shielding plate, and after passing through the mask, the 0th-order light of one exposure light travels in substantially the same direction as the 1st-order light of the other exposure light. On the pupil plane of the system, spots are formed at almost the same position.

For selecting such diffracted light, exposure light incident on the mask at various incident angles from above is used, and a light-shielding plate having a light-transmitting portion formed at the spot position is formed on the pupil plane of the projection optical system. The same operation is performed in the case of disposing and blocking the diffracted light due to the exposure light other than the pair of incident angles.

Further, for a general mask pattern in which a plurality of gratings are combined, a pair of light-transmitting portions having angular positions and mutual intervals defined for the respective gratings are arranged on the light shielding plate. .

The pair of light-transmitting portions of the light-shielding plate provided in the illumination optical system are formed by the first-order diffracted light generated by one grating of the exposure light from one light-transmitting portion and the exposure light from the other light-transmitting portion. The mutual spacing is determined so that the 0th-order diffracted light generated by the same grating transmits almost the same position on the pupil plane of the projection optical system.

The pair of light-transmitting portions of the light-shielding plate provided in the projection optical system transmits the 0th-order diffracted light and the 1st-order diffracted light generated by the pair of exposure lights having the above-mentioned incident angle with respect to one grating. The mutual interval is defined in.

Further, in the exposure method of the present invention, if the light shielding plate is rotated or moved in parallel by using the adjusting mechanism,
It is possible to correct the positional deviation of the light shielding plate with respect to the grid. Also, the mutual spacing of the light-transmitting portions can be appropriately adjusted to better suit the pitch of the grating.

Furthermore, in the exposure method of the present invention,
A light-shielding plate incorporating an electro-optical element such as a liquid crystal element is adopted, and the position of the light-transmitting portion can be adjusted by an electric signal.

[0049]

BEST MODE FOR CARRYING OUT THE INVENTION One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of a projection type exposure apparatus used to realize the exposure method of this embodiment. In FIG. 1, a one-dimensional grid pattern 12 having a duty ratio of 0.5 is formed on the mask 11 as an example of a typical fine pattern. The illumination optical system for illuminating the mask 11 is a mercury lamp 1, an ellipsoidal mirror 2, a cold mirror 3, a condensing optical element 4, an optical integrator element 5, a relay lens 8 (pupil relay system), a mirror 9, a condenser lens. It consists of 10.

The Fourier transform plane of the illumination optical system, that is, in the vicinity of the exit end surface of the integrator element 5 where the secondary light source image of the mercury lamp 1 is formed (in other words, the pupil plane of the illumination optical system or its conjugate plane). , And their neighboring positions)
A light-shielding plate (spatial filter) 6 is arranged in the. The light shielding plate 6 is provided with a pair of light transmitting portions 6a and 6b whose positions and sizes are determined based on the two-dimensional Fourier transform of the mask pattern 12.

Further, on the pupil plane 14 of the projection optical system 13 for projecting the image of the pattern 12 onto the wafer 17, a light shielding plate (spatial filter) 15 similarly provided with light transmitting portions 15a and 15b is arranged. .

Here, in the present embodiment, since the one-dimensional diffraction grating pattern is used as the mask pattern 12, both the light shielding plates 6 and 15 have a pair of transparent portions 6.
a, 6b or 15a, 15b are formed, and a pair of translucent portions are substantially symmetrical in the pupil plane with respect to the optical axis of the optical system, and the arrangement direction thereof is the pitch direction of the grating pattern 12. They are arranged so that they almost match.

Further, the shading plates 6 and 15 are provided with a driving mechanism 7 or 16 composed of a motor, a cam, etc., respectively, and the shading plates 6 and 15 can be replaced with other ones according to the mask pattern. And the translucent part 6 in the pupil plane
Fine adjustment of the positions of a, 6b or 15a, 15b is possible. The light transmitting portions 6a of the light shielding plates 6 and 15,
The opening shapes of 6b and 15a, 15b may be arbitrary, and both are shown as circular openings in FIG.

In the exposure apparatus thus constructed,
The exposure light generated from the mercury lamp 1 arranged at the first focus of the ellipsoidal mirror 2 is reflected by the ellipsoidal mirror 2 and the cold mirror 3 and is condensed at the second focus of the ellipsoidal mirror 2. After passing through the condensing optical element 4 including a collimator lens and a cone-shaped prism for correcting the luminous flux distribution, an integrator element 5 including a fly-eye lens group provides a substantial surface light source on the arrangement surface of the light shielding plate 6. Form.

In this embodiment, the secondary light source image of the integrator element 5 is formed on the pupil plane 14 of the projection optical system 13, which is so-called Koehler illumination. This surface light source itself should provide the exposure light that enters the mask from above at various incident angles, as in the conventional case. However, since the light shielding plate 6 is provided in front of the condenser lens 10 here, the two light transmitting portions 6 of the light shielding plate 6 are provided.
Only parallel light fluxes passing through a and 6b are passed through the relay lens 8, the mirror 9, and the condenser lens 10 to the mask 11 at a predetermined incident angle which is symmetric with respect to the optical axis in a plane which crosses the line of the grating pattern 12 almost vertically. Incident.

The parallel luminous flux is the pattern 12 of the mask 11.
Incident on the pattern 12, 0th order, ± 1st order, ± 2th order from the pattern 12
Next, each diffracted light of ... Here, the parallel luminous flux is a light shielding plate 6 arranged on the Fourier transform surface of the illumination optical system.
Since the distance from the optical axis and the position around the optical axis are determined by the translucent portions 6a and 6b of the mask, and the incident angle to the pattern 12 of the mask 11 is determined by the condenser lens 10, the projection optical system 13 Of the diffracted lights of the respective orders, most of the ± 1st-order diffracted lights and the 0th-order diffracted lights are incident, and the other diffracted lights are extremely small.

As a result, on the pupil plane 14 of the projection optical system 13, a main diffracted light spot of one of the ± 1st-order diffracted light and the 0th-order diffracted light and other unnecessary diffracted light spots of the order are formed. It is formed for each order according to the Fourier expansion pattern. Another light shielding plate 15 arranged on the pupil plane 14 of the projection optical system 13 selectively passes only the main diffracted light to the wafer 17 side and blocks other diffracted light of other orders.

In this case, one of the ± 1st-order diffracted lights and the main diffracted light with the 0th-order diffracted light can pass with maximum intensity, and the unnecessary diffracted light can be completely blocked. The positions of the light shielding plates 6 and 15 with respect to the pattern 12 of the mask 11 are adjusted using the drive mechanisms 7 and 16.

FIG. 2 is a diagram schematically showing a basic optical path configuration of exposure light in the projection type exposure apparatus used in the exposure method of this embodiment. Here, for the sake of illustration, the light shield plate 6 is arranged directly above the condenser lens 10, but this position is different from the relay lens 8 in FIG.
It is a surface conjugate with and is substantially the same as the case of FIG. 1 in terms of function and effect.

In FIG. 2, the numerical aperture of the projection optical system 13 is NA, the wavelength of the exposure light is λ, the pitch of the pattern 12 is 0.75 times λ / NA, and the line-and-space ratio of the pattern 12 is 1: 1 (grating duty ratio of 0.
5). At this time, the Fourier transform q (u, v) in consideration of the wavelength λ of the pattern 12 is expressed by the following equation (4) when the pattern 12 is p (x, y).

Q (u, v) = [p (x, y) .exp {-2.pi.i (ux + vy) /. Lamda.}] Dxdy .. (4)

Here, when the pattern 12 is uniform in the vertical direction, that is, in the y direction and has a regular change in the x direction, as shown in FIG. Space ratio is 1: 1 and pitch is 0.75λ / NA
Then, the Fourier transform q (u, v) can be expressed by the following equation (5).

Q (u, v) = q ₁ (u) × q ₂ (v) ··· (5)

Therefore, each of q ₁ (u) and q ₂ (v) can be expressed as follows. q ₁ (u) = 1, u = 0 q ₁ (u) = 0.637, u = ± NA / 0.75 q ₁ (u) = − 0.212, u = ± 3 NA / 0.75: q ₁ (u) = 0.637 / ( 2n-1) ・ (-1) ^{(n + 1)} , u = ± (2n-1) ・ NA / 0.75 q ₁ (u) = 0, u is other than the above, and q ₂ (v) = 1, v = 0 q ₂ (v) = 0, v ≠ 0

FIG. 3 and FIG. 5 are plan views of the light-shielding plate 6 for the illumination optical system and the light-shielding plate 15 for the projection optical system used in this embodiment, respectively. Here, the energy distribution of the Fourier transform, that is, the position that gives the peak value of | q (u, v) | ² is (u, v) = (0,0), (± NA / 0.75,0), ( ± 3NA / 0.75, 0) ...

Therefore, the light-shielding plates 6 and 15 are (u, v) = (0, 0), (± NA / 1.5, 0), (± 2NA, 0), which is 1/2 of the peak position. Of the positions (u, v) within the numerical aperture of the projection optical system 13
= (± NA / 1.5, 0) and the position in the vicinity of the translucent part 6
a, 6b and 15a, 15b, and the position of (u, v) = (0, 0) is the light shielding portion.

The positions (u, v) = (0, 0) of the light shielding plates 6 and 15 are the illumination optical system (1-10) and the projection optical system 1 respectively.
3 so as to match the optical axis of the drive mechanism 7 or 1 of FIG.
The position is adjusted by 6.

Here, the light-shielding plates 6 and 15 may be formed by removing a part of a metal plate to form a transparent part, or by patterning a metal thin film on a transparent holder such as glass to form a transparent part. It may be formed. Further, in the example shown in FIG. 1, the mercury lamp 1 is assumed as the illumination light source,
This may be another light source such as a laser light source. Furthermore,
In this example, the pattern 12 of the mask 11 is a line-and-space pattern that changes with a duty of 1: 1 only in the x direction, but the present invention is applicable to any pattern.

In FIG. 2, the pattern 1 in the illumination optical system is different from the pattern 12 having the pitch of 0.75λ / NA.
By providing the light shielding plate 6 as shown on the Fourier transform surface of No. 2, the illumination light Li that illuminates the pattern 12 is limited to parallel light fluxes Lil and Lir. When the illumination light Lil, Lir is applied to the pattern 12, the diffracted light is generated from the pattern 12.

The 0th order diffracted light of the illumination light Lil is L10, +1
Let the first-order diffracted light be L11, and let the 0th-order diffracted light of the illumination light Lir be Ll.
Let r0 be the r0 and −1st order diffracted light. At this time, the separation angles of the diffracted light L10 and the diffracted light L11 and the diffracted light Lr0 and the diffracted light Lr1 can be expressed by the following equation (6).

Sin θ = λ / (pitch of pattern 12) = λ / (0.75λ / NA) = NA / 0.75 (6)

Originally, the incident light Lil and the incident light Lir
Are separated by 2NA / 1.5, the diffracted light L10
And diffracted light Lr1 both pass the same first optical path, and diffracted light Lr0 and diffracted light Ll1 both pass the same second optical path. Here, the first optical path and the second optical path are symmetrically apart from the optical axis of the projection optical system 13 by the same distance.

FIG. 6 schematically shows the intensity distribution of the diffracted light on the pupil plane 14 of the projection optical system 13. In FIG. 6, the spot 22l formed on the pupil plane 14 is the diffracted light Lr.
0 and the diffracted light Ll1 are condensed, and the spot 22r is the diffracted light Ll0 and the diffracted light Lr1 condensed.

As is clear from FIG. 6, in the exposure method of the present embodiment, the pitch of 0.
The 0th-order diffracted light and the + 1st-order or -1st-order diffracted light from the 75λ / NA pattern 12 are transmitted through the projection optical system 13 to almost 1
The light can be condensed on the 00% wafer 17. Therefore, even in the case of a pattern finer than the pitch (λ / NA), which is the resolution limit in the conventional exposure method, the exposure transfer can be performed by using the light shielding plate having the transmissive portion according to the pitch of the mask pattern. .

Next, the pattern resolution on the sample substrate 17 in the exposure method of the present embodiment will be described below in comparison with that in the exposure method using the projection type exposure apparatus of various reference examples.

= Case of Reference Example = FIGS. 7 and 8 are cited as reference examples.
FIG. 9 is a diagram schematically showing an optical path configuration of exposure light (FIG. 7) in the projection exposure apparatus shown in No. 7 and a light amount distribution (FIG. 8) on a pupil plane of the projection optical system. In these figures, members having the same functions and functions as those of the device according to the above-described embodiment of the present invention are designated by the same reference numerals as those in FIG.

In FIG. 7, an aperture stop (a light shielding plate having a circular light transmitting portion concentric with the optical axis, a so-called spatial filter) 6 A is provided on the pupil plane of the illumination optical system, and the exposure light is incident on the mask 11. The corner is restricted. The 0th-order diffracted light (solid line) and the ± 1st-order diffracted light (broken line) generated from the pattern 12 of the mask 11 both enter the projection optical system 13 and travel on different optical paths. Here, as shown in FIG. In, the spot 20l of the + 1st-order diffracted light, the spot 20c of the 0th-order diffracted light, and the spot 22r of the -1st-order diffracted light are formed at different positions.

FIGS. 9 and 10 show the optical path structure of the exposure light in the projection type exposure apparatus (FIG. 9) as another reference example, and the light amount distribution on the pupil plane of the projection optical system (FIG. 10).
It is the figure which each showed typically. In this other reference example, instead of the aperture stop 6A of FIG. 7, a light shielding plate 6B provided with an annular light transmitting portion concentric with the optical axis is employed.

In FIG. 9, the pupil plane of the illumination optical system is provided with a light-shielding plate 6B in which an annular light-transmitting portion is formed concentrically with the optical axis, and the exposure light is obliquely directed to the mask 11, that is, reverse. It is incident in the shape of a cone. As a result, at least in the plane that crosses the grating of the pattern 12 almost vertically, as in the case of the present embodiment shown in FIG. 2, the 0th-order diffracted light (solid line)
Is incident on the projection optical system as obliquely as the first-order diffracted light (broken line), partially overlaps with another first-order diffracted light coming from the opposite side, passes through the projection optical system, and reaches the wafer 17 to form a projected image. To do.

At this time, on the pupil plane 14 of the projection optical system 13, as shown in FIG. 10, a donut-shaped spot 21c of 0th-order diffracted light which is concentric with the optical axis and a + 1st-order adjacent to which a part of the spot 21c overlaps. A spot 21l of broken light and a spot 21r of -1st-order diffracted light are formed. Here, most of the spots 21l and 21r are projected to the outside of the projection optical system 13, and the light of these projected portions is vignetted by the lens barrel of the projection optical system.

= In the case of the embodiment of the present invention = FIGS. 11 to 14 show the intensity distribution of the lattice pattern of the projected image on the wafer 17 in the present embodiment shown in FIG. It is the diagram compared with the case. This intensity distribution has an NA of the projection optical system of 0.5 and an exposure light wavelength λ of 0.
This is a result obtained by calculation for a plane crossing the optical axis in the pitch direction of the pattern 12 on the substrate, assuming that the pattern pitch is 365 μm and the pattern pitch on the wafer 17 is 0.5 μm (approximately 0.685λ / NA).

FIG. 11 is a diagram showing the intensity distribution of the grid pattern of the projected image formed on the substrate by the projection type exposure apparatus according to the present embodiment (FIG. 2). This distribution has a sufficient light amount difference between the bright portion and the dark portion at the edge of the pattern.

In FIG. 12, in the reference example of FIG. 7, the diameter of the aperture stop 6A is relatively small, and the ratio between the numerical aperture of the illumination optical system and the numerical aperture of the projection optical system, that is, the so-called σ value is 0.5. It is a diagram of the intensity distribution of the lattice pattern of the projected image on the substrate in the case. Since the ratio (σ value) between the numerical aperture of the illumination optical system and the numerical aperture of the projection optical system is set to 0.5 here, a flat distribution with almost no difference in light amount between the bright and dark portions of the pattern of the projected image is obtained. is there.

In FIG. 13, in the reference example of FIG. 7, the aperture of the aperture stop 6A is relatively large, and the ratio between the numerical aperture of the illumination optical system and the numerical aperture of the projection optical system, so-called σ value, is 0.9. It is a diagram of the intensity distribution of the lattice pattern of the projected image on the substrate in the case. Here, since the ratio (σ value) of the numerical aperture of the illumination optical system and the numerical aperture of the projection optical system is 0.9, FIG.
Although there is a light amount difference between the bright part and the dark part of the pattern of the projected image, the distribution is still flat with a relatively large 0th-order diffracted light component, which is insufficient in view of the photosensitive characteristics of the resist. Recognize.

FIG. 14 is a diagram showing the intensity distribution of the lattice pattern of the projected image on the substrate in the case of another reference example of FIG. Here, the inner edge of the annular light-transmitting portion of the light shielding plate 6B is σ
The value corresponds to 0.7 and the outer edge corresponds to a σ value of 0.9. This projected image has a light amount difference between the bright portion and the dark portion of the pattern as compared with the case of FIG. 12, but also has a relatively large 0th-order diffracted light component and is still a flat distribution, which is insufficient in view of the photosensitive characteristics of the resist. It can be seen that it is.

As apparent from FIGS. 11 to 14, FIG.
In the present embodiment shown in FIG. 2, the substantial resolution of the projected image on the substrate is significantly improved as compared with the case of the reference example of FIG.

By the way, in the case of FIG. 9, if a shading plate similar to the shading plate used in the above-described embodiment of FIG. 2 is arranged on the pupil plane 14 of the projection optical system 13, the result of FIG.
It is also possible to selectively transmit the 0th order light and the ± 1st order diffracted light of the portion indicated by the cross hatch to improve the resolution of the projected image on the wafer 17 slightly more than in the case of FIG.

Conventionally, as a technique for improving the resolution of the projection optical system by positively utilizing the diffracted light in the mask pattern, a so-called dielectric for inverting the phase of the exposure light at every other transmissive part of the pattern, so-called. A technique for providing a phase shifter has been reported. However, it is practically difficult to provide a phase shifter on a complicated semiconductor circuit pattern, and a method for inspecting a photomask with a phase shifter has not been established yet.

The effect of improving the resolution of the projected image in the present embodiment of FIG. 2 according to the present invention is comparable to that of the phase shifter, but the conventional photomask without the phase shifter is used as it is. Therefore, the conventional photomask inspection technology can be used as it is.

Further, if the phase shifter is adopted, the effect of increasing the depth of focus can be obtained, but in the present embodiment of FIG. 2 as well, as shown in FIG. 6, the spots 22l, 22r on the pupil plane 14 are Since it is located equidistant from the center of the pupil, it is less susceptible to the wavefront aberration due to defocus as described above, and therefore a deep depth of focus can be obtained.

In the present embodiment, the line and space showing a regular change in the x direction is taken up as the circuit pattern, but the above effects can be applied to general patterns other than the line and space. , Can be sufficiently achieved by combining appropriate light-shielding plates with each. Here, when the circuit pattern is a one-dimensional line-and-space, the number of light-transmitting portions on the light-shielding plate is two, but in the case of any other pattern, the number of light-transmissive portions is 2n according to the spatial frequency of the pattern. It will have a translucent part. For example,
In the case of a two-dimensional diffracted photon pattern, it is sufficient to form two light transmissive portions, which are arranged in a cross shape, for a total of four light transmissive portions.

Further, in the present embodiment, in order to simplify the description, the light-shielding portion of the light-shielding plate has been treated as not transmitting the exposure light at all, but by making it semi-transmissive,
It is also possible to increase the contrast of the projected image of only a specific fine pattern while performing the same exposure as in the past.

Further, in the present embodiment, the description has been centered on the light-shielding plate in the illumination optical system, but it is considered that the light-shielding plate in the projection optical system basically has the same operation and effect. You can That is, if a spatial filter satisfying the above conditions is arranged on at least one of the pupil plane of the illumination optical system or its conjugate plane and the pupil plane of the projection optical system, the same effect as that of the present embodiment can be obtained. You can

Further, for example, a spatial filter as shown in FIG. 3 is provided on the pupil plane of the illumination optical system, and a spatial filter having an annular light transmitting portion is arranged on the pupil plane of the projection optical system. I do not care. In this case, in the latter spatial filter provided with an annular transmission part, an annular transmission is provided so that both the 0th-order diffracted light and the + 1st (or -1st) -order diffracted light from the mask pattern are transmitted. It goes without saying that it is necessary to arrange the light section. Further, by using both spatial filters in combination, there is also an effect of cutting diffused light reflected by the projection optical system or the wafer and preventing stray light.

Furthermore, in the present embodiment, the case where the spatial filters (light-shielding plates 6 and 15) are mechanically replaced according to the mask pattern has been mainly described. However, for example, a liquid crystal display device or an EC (electrochromic) device is used. A filter that uses elements may be used. In this case, the filter replacement mechanism becomes compact, and the size, shape, and position of the translucent part can be adjusted easily and at high speed. There is an advantage of becoming.

[0096]

In the exposure method of the present invention, the light-shielding plate selectively allows the exposure light having a preferable incident angle to selectively reach the sample substrate among the diffracted light generated in the fine pattern of the mask. Since the image is formed, even with a fine pattern that cannot be resolved conventionally, it is possible to obtain a sufficient light-dark difference and sufficient light difference for exposure of the resist layer in the image formation pattern on the sample substrate without changing the exposure light or the projection optical system. A deep depth of focus can be secured.

Further, in the exposure method of the present invention, by selecting the light shielding plate corresponding to the fine pattern of the mask and appropriately adjusting the angle and the center position thereof, the image forming pattern on the sample substrate can be adjusted. A large light / dark difference in light quantity and a deeper depth of focus are achieved.

Further, in the exposure method of the present invention, it is possible to obtain the optimum positional relationship between the mask and the light shielding plate by changing the position or the interval of the light transmitting portion of the light shielding plate by the adjusting mechanism. The same light-shielding plate can be used together for masks having different patterns.

Furthermore, in the exposure method of the present invention,
The electro-optical element allows any position of the shading plate to be freely adjusted to be transparent or opaque, so it is possible to obtain the optimum positional relationship between the mask and the shading plate, and it is the same for a mask having another pattern. The light shield plate of can be used together.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a projection type exposure apparatus used to realize an exposure method according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an optical path of a projection type exposure apparatus used to realize an exposure method according to an embodiment of the present invention.

FIG. 3 is a plan view of a light shielding plate arranged in an illumination optical system of a projection type exposure apparatus used to realize an exposure method according to an embodiment of the present invention.

FIG. 4 is a pattern plan view of a mask of a projection exposure apparatus used to realize an exposure method according to an embodiment of the present invention.

FIG. 5 is a plan view of a light shielding plate arranged in a projection optical system of a projection type exposure apparatus used to realize an exposure method according to an embodiment of the present invention.

FIG. 6 is a diagram showing an intensity distribution of diffracted light on a pupil plane of a projection optical system of a projection exposure apparatus used to realize an exposure method according to an embodiment of the present invention.

FIG. 7 is a schematic view showing an optical path of a projection type exposure apparatus according to a reference example of the present invention.

FIG. 8 is a diagram showing an intensity distribution of diffracted light on a pupil plane of a projection optical system of a projection exposure apparatus according to a reference example of the present invention.

FIG. 9 is a schematic view showing an optical path of a projection type exposure apparatus according to another reference example of the present invention.

FIG. 10 is a diagram showing an intensity distribution of diffracted light on a pupil plane of a projection optical system of a projection exposure apparatus according to another reference example of the present invention.

FIG. 11 is a diagram showing a light amount distribution of a lattice pattern of a projected image in the embodiment of the present invention.

FIG. 12 is a diagram showing a light quantity distribution of a lattice pattern of a projected image in a reference example of the present invention (where σ = 0.5).

FIG. 13 is a diagram showing a light amount distribution of a grid pattern of a projected image in a reference example (assuming σ = 0.9) of the present invention.

FIG. 14 is a diagram showing a light quantity distribution of a lattice pattern of a projected image in another reference example of the present invention.

[Explanation of symbols]

1: Mercury lamp, 2: Ellipsoidal mirror, 3: Cold mirror,
4: Condensing optical element 5: Integrator element, 6: Light-shielding plate, 7: Drive mechanism,
8: relay lens 9: mirror, 10: condenser lens, 11: mask, 12: pattern 13: projection optical system, 14: pupil plane, 15: light-shielding plate, 16:
Drive mechanism, 17: Wafer

Claims (7)

[Claims] 1. An exposure apparatus having an illumination optical system for irradiating an illumination light on the mask and a projection optical system for projecting an image of the pattern of the mask on the substrate, and the mask on the substrate. In the exposure method of transferring the pattern, the illumination light is converted into first illumination light and second illumination light that are decentered and separated from the optical axis of the illumination optical system, and the first illumination light and the second illumination light are separated. The first portion is arranged so that the illumination light is inclined symmetrically with respect to a direction substantially perpendicular to the pattern surface.
The mask is irradiated with illumination light and second illumination light, and the 0th-order diffracted light generated from the pattern by the irradiation of the first illumination light and the 1st-order diffracted light generated from the pattern by the irradiation of the second illumination light. Through the first optical path of the projection optical system onto the substrate, and the 0th-order diffracted light generated from the pattern by the irradiation of the second illumination light, and the pattern by the irradiation of the first illumination light. First-order diffracted light generated from the projection optical system to reach the substrate through the second optical path of the projection optical system, and the first optical path and the second optical path are the projection optical system for the pattern of the mask. 2. The exposure method, wherein each of them is decentered by an approximately equal distance from the optical axis of the projection optical system on or near the Fourier transform surface of the. 2. The exposure method according to claim 1, wherein the light other than the light that has passed through the first optical path and the second optical path does not reach the substrate. 3. An exposure method for projecting an image of a pattern of a mask onto a substrate by using a projection optical system, wherein the mask is irradiated with at least two illumination lights, and the one set of illumination lights is a surface of the pattern. Is symmetrically inclined by a predetermined angle with respect to a direction perpendicular to, and the predetermined angle is such that the 0th-order diffracted light and the 1st-order diffracted light generated from the pattern for each of the two illumination lights are It is defined to be substantially symmetrical with respect to a direction perpendicular to the surface of the pattern, and the 0th-order diffracted light and the 1st-order diffracted light form an image of the pattern on the substrate via the projection optical system. Exposure method. 4. An exposure method for exposing a pattern of a mask onto a substrate via a projection optical system, illuminating the pattern with at least first illumination light and second illumination light, and irradiating with the second illumination light. The 0th-order diffracted light generated from the pattern by the irradiation of the first illumination light reaches the substrate through the same optical path of the projection optical system as the diffracted light other than the 0th-order diffracted light generated from the pattern. An exposure method characterized by the above. 5. The exposure method according to claim 4, wherein a semiconductor element is manufactured using the exposure method. 6. An exposure method for exposing a substrate with a pattern having at least a straight line portion extending in a predetermined direction, wherein the light is emitted along a pair of optical paths inclined with respect to an incident surface including the predetermined direction. An exposure method comprising illuminating a pattern and projecting an image of the pattern onto the substrate. 7. The exposure method according to claim 6, wherein a semiconductor element is manufactured using the exposure method.