JPH07201697A - Aligner - Google Patents

Abstract

PURPOSE:To enhance utilization efficiency of illumination beams generated by a light source in an aligner for exposing by changed illumination. CONSTITUTION:A collimator lens 70 and a condensing optical element are arranged between a light source 12 and an integrator lens 13, and a desired light strength distribution is obtained on a front surface of the integrator lens. Further, condensing optical element selecting means capable of selecting an optimum condensing optical element according to transfer patterns is provided. Thus, as compared with a conventional system using a screening plate, it is possible to reduce an exposing period, remove influences on an oscillation during the exposing period accompanying an increase in the exposing period, and enhance precision in transfer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus, and more particularly, it relates to a semiconductor exposure apparatus for forming an image with high resolution without reducing the light utilization efficiency.

[0002]

2. Description of the Related Art Conventionally, in the manufacture of semiconductor devices, a circuit pattern on a mask is projected and exposed onto a wafer coated with a photoresist through a reduction lens, and after development, etching is performed to form a circuit. Photolithographic methods of forming patterns have been used. It is generally known that the minimum line width that can be resolved by projection exposure is proportional to the exposure wavelength and inversely proportional to the NA (Numerical Aperuture) of the reduction lens. However, since the depth of focus is inversely proportional to the square of the NA of the reduction lens, increasing the NA reduces the depth of focus.

Therefore, in order to cope with the miniaturization of semiconductor devices, the exposure wavelength is being shortened, and the exposure light source is changed from a conventional mercury lamp (wavelength 365 nm) to a KrF excimer laser (wavelength 248 nm) and further to X. Wire (wavelength 5-10n
It is under consideration to change to m). However, these short-wavelength light sources are very expensive, have high maintenance costs, and increase the manufacturing cost of semiconductors.

Therefore, so-called modified illumination for shaping the light intensity distribution of the secondary light source image of the illumination optical system from the conventional circular shape to a distribution having peaks in annular zones or four places changes the wavelength and NA of the reduction lens. It is attracting attention as a method of improving the resolution without doing so. For example, regarding the former, Japanese Patent Application Laid-Open No. 5-2131
2, the latter is disclosed in JP-A-4-267515 and JP-A-4-329623.

The principle of resolution improvement by modified illumination will be described below with reference to FIGS. 6 and 7.

FIG. 6 shows line and line on the mask.
In the optical system in which the space pattern 21 is projected onto the wafer 4 by the reduction lens 3, the illumination light 901 is incident on the line-and-space pattern 21 perpendicularly. At this time, + 1st order diffracted light 903 or -1
The angle θ formed by the 0th-order light 902 and the diffracted light 904 is given by the following equation.

[0007]

[Equation 1]

Where λ is the wavelength of the illumination light and P is the line
The pitch of the and space pattern 21. Here, NA on the wafer side of the reduction lens is NA, and reduction ratio is 1 /
5, and the component 90 of the illumination light that is vertically incident on the mask
Focusing on 1,

[0009]

[Equation 2]

At this time, the ± first-order diffracted lights 903 and 904 cannot pass through the reduction lens pupil 31 and are not imaged on the wafer. Because the image on the wafer 4 is the 0th order light 902 and the ± 1st order diffracted light 9
This is because 03 and 904 are formed by being incident on the wafer 4 at a predetermined angle.

On the other hand, considering a component 911 incident at an angle of θ / 2 with respect to the optical axis 900 as shown in FIG. 7,
Although the first-order diffracted light 914 does not pass through the reduction lens pupil 31,
The 0th-order light 912 and the + 1st-order diffracted light 913 can be transmitted and imaged. Therefore, if only the component of the illumination light 911 is selected and illuminated, an imaging pattern with good contrast can be obtained without changing the wavelength or NA.

Next, a conventional device configuration using this principle will be described with reference to FIG.

The light emitted from the mercury lamp 11 is condensed on the front surface of the integrator lens 13 after passing only the exposure light wavelength by the wavelength selection filter 16, and the light emitted from the rear surface of the integrator lens 13 is the condenser lens 1.
4, an image is formed on the reduction lens pupil 31 via the mirror 15. At this time, the shielding plate 801 is arranged behind the integrator lens 13 in order to select the component incident on the mask 2 at the angle θ / 2. The shield plate 801 has, for example, an opening of a ring zone, and at this time, the light intensity distribution 311 on the pupil 31.
Has an annular shape corresponding to the shielding plate 801.

Since the angle θ is a function of the pitch P of the pattern on the mask as shown in "Equation 1", the opening shape of the shield plate 801 depends on the pattern to be transferred, for example, the inner diameter forming the opening. And it is necessary to change the outside diameter.
Therefore, a plurality of shading plates are inserted into the shading plate holding plate 51, and the shading plate holding plate 51 is rotated by the drive unit 52 to select a desired shading plate.

The pattern on the mask 2 is the pattern 221.
In the case where only the patterns that are orthogonal to each other like the pattern 222 and the pattern 222 are provided, the resolution of the transfer is further improved if the light blocking plate 802 has four openings. At this time, the light intensity distribution 312 on the pupil 31 is obtained. However, like pattern 223, 45
When the pattern in the degree direction is included, the light shielding plate 801 is used so that the transfer resolution does not depend on the pattern direction.

[0016]

The light shielding plate 80 of FIG. 8 is to be solved.
1. The light shielding plate 802 transmits only a part of the light flux incident on the integrator lens 13, and the utilization efficiency of the light emitted from the mercury lamp is poor at 1/5 to 1/3. As a result, the exposure time is increased and the throughput of the exposure apparatus is reduced. Further, the wafer 4 needs to be stationary during the exposure time, but as the exposure time increases, the wafer 4 is more likely to be affected by the vibration of the apparatus during the exposure, and the transfer accuracy deteriorates.

[0017]

By providing a condensing optical element, the illumination light is condensed at a desired position without blocking the light emitted from the mercury lamp. Annulus and 4
An example of a condensing optical system that condenses light at a location will be described with reference to "FIG. 2", "FIG. 3", "FIG. 4", and "FIG. 5". The kinoform 811 in FIG. 2 shows a diffractive lens in which the pitch becomes coarser toward the periphery. Surface shape d1 of kinoform 811
(R1) can be represented by "Equation 3".

[0018]

[Equation 3]

Here, r1 is the distance from the center, λ is the wavelength of the illumination light, f1 is the distance from the kinoform 811 to the focusing position, R1 is the distance from the optical axis to the focusing position, and m is 1 or more. Is an integer, dmax is the maximum thickness of the kinoform 811, and the refractive index of the kinoform 811 is n1,

[0020]

[Equation 4]

Can be expressed as

The range of the integer m is kinoform 81.
If the diameter of the parallel light flux 911 entering 1 is D1, it can be expressed by the following equation.

[0023]

[Equation 5]

By this kinoform 811, the parallel light flux 911 is condensed into an annular shape 912 having a radius R1.

When R1 / f1 is small, if the surface shape determined by "Equation 3" can be realized, theoretically an efficiency of almost 100% can be achieved. A condensing optical element for condensing light in an annular shape may be a refraction element 812 whose thickness increases toward the periphery as shown in FIG.

The radius of curvature r2 of the cross-sectional profile of the surface can be expressed by "Equation 6".

[0027]

[Equation 6]

Here, f2 is the distance from the refractive element 812 to the condensing position, n2 is the refractive index of the refractive lens 812,
Is. When the light is focused on the annular shape 913 having a radius R2 with the optical axis as the center, the center of the radius of curvature r2 is set at a position R2 from the optical axis.

Next, referring to FIGS. 4 and 5, a method for converging parallel light beams at four points will be described.

The phase hologram 821 shown in FIG. 4 is composed of four concentric phase holograms. "Figure 5"
The phase hologram element 831 is a constituent element of the phase hologram 821 and is a kind of diffractive lens. If the distance from the center is r3, the area of the phase pattern portion 832 (white portion in the plan view, shaded portion in the cross-sectional view) can be expressed by the following equation.

[0031]

[Equation 7]

Here, k is an integer of 0 or more.

Further, the thickness d3 of the phase pattern portion 832 is defined by the refractive index n3 of the material of the phase pattern portion 832.

[0034]

[Equation 8]

Is given by However, λ is the wavelength of the illumination light.

For example, the coordinates (a,
a), (-a, a), (-a, -a), (a, -a), the phase hologram element 831 is arranged so that the center thereof corresponds to each coordinate, and The hologram 821 may be configured. In the plan view of the phase hologram 821, the black portion shows a portion without a phase pattern, and the white portion shows a portion with a phase pattern. This phase hologram 82
The efficiency of 1 is about 40%. In addition, although efficiency decreases,
The phase hologram 821 may be configured by a zone plate having a black portion as a light shielding portion and a white portion as a transmitting portion in the plan view.

The phase hologram element 831 may be a sawtooth-shaped kinoform similar to that shown in FIG.

[0038]

If the condensing optical element as described above is used, the illuminating light can be condensed at a desired position, and the utilization efficiency of the illuminating light can be significantly improved. It is possible to prevent an increase in exposure time.

[0039]

EXAMPLE One example of the present invention will be described with reference to FIG.

The illumination light emitted from the mercury lamp is collimated by the collimator lens 70, is transmitted through the wavelength selection filter 16 only the wavelength required for exposure, and is incident on the condensing optical element 80. When the kinoform 811 of FIG. 2 is used as the condensing optical element, the illumination luminous flux is condensed on the front surface of the integrator lens 13 in a ring shape. At this time, the central ray 921 of the illumination light flux after passing through the kinoform 811 is made incident vertically on the front surface 131 of the integrator lens by the input lens 71. This is necessary to obtain a uniform illuminance distribution on the mask 2.

The illumination light emitted from the rear surface of the integrator lens 13 is condensed by the condenser lens 14 on the reduction lens pupil 31 via the folding mirror 15, and the mask 2
The above circuit pattern can be transferred onto the wafer 4 by annular illumination. When the phase hologram 821 of FIG. 4 is used as the condensing optical element, it is condensed at four points on the front surface of the integrator lens 13. At this time, the input lens 71 is not necessary.

As shown in "Equation 1", the optimum illumination light incident angle θ / 2 required for good image formation needs to be changed according to the pattern pitch P. Therefore, the integrator lens 1
The shape of the light intensity distribution focused on the front surface of 3 must also be changed according to the pattern. Therefore, a plurality of focusing optical elements are attached to the holder 53, and the driving unit 52 is rotated to select the optimal focusing optical element according to the pattern on the mask 2. Since the central ray 921 also changes depending on the condensing position of the kinoform 811, if the kinoform 811 is changed, the input lens 71 also needs to be changed. Therefore, the input lens 71 is attached to the holding part 53 together with the kinoform 811, and the driving part 52 is driven to select the optimum kinoform 811 and the input lens 71.

Next, the manufacturing method of the kinoform 811 shown in FIG. 2 will be described with reference to FIG.

In this manufacturing method, the kinoform 8 shown in FIG. 2 is used.
The surface shape of 11 is approximated by a four-step staircase shape. In steps 1 and 2, "SP I E Vol. 1211 19"
1990 tributes 125 to 136 (SPIE, Vol. 121
1, 1990, 125-136)]. First, similar to the lithography process used in the semiconductor manufacturing process in step 1,
Silicon substrate 62 coated with an etching resistant photosensitive material
After the pattern of the first mask 611 is transferred onto the No. 1 and developed,
Etching.

Next, in step 2, the second mask pattern 612 is used and the same process as in step 1 is carried out to 4
A silicon master 622 having a stepped surface shape is manufactured.

According to step 3, the silicon substrate 622 is formed by a chemical reaction or a physical method such as sputtering.
A conductive thin film 630 such as gold or silver is formed on the surface of the.

Next, in step 4, nickel is deposited on the conductive thin film 630 by electroplating to form a mold 640. The mold 640 is released from the conductive thin film 630 and the silicon master 622.

In step 5, an ultraviolet curable resin 660 is inserted between the mold 640 and the glass substrate 650, and ultraviolet rays are irradiated from the glass substrate side for a certain period of time, so that the ultraviolet curable resin 66 is irradiated.
Cure 0.

In step 6, the UV curable resin 660 is released from the mold 640 to obtain the kinoform 811. When the surface shape of the kinoform 811 is approximated by 4 steps, the light utilization efficiency is 81%. However, if the number of masks used is increased to 3 and 4, the shapes of 8 steps and 16 steps are approximated. The light utilization efficiency at this time was 95% and 9 respectively.
It can be increased to 9%.

In general, it is known that the light use efficiency η can be expressed by “Equation 9” when approximating “Equation 6” by M = 2k steps using k masks.

[0051]

[Equation 9]

In addition, in manufacturing the silicon master 622, "O Plus E March 1989, p. 104-111.
As described in "Page", the shape of "Equation 3" may be formed directly on the silicon substrate by drawing while controlling the exposure amount of the electron beam drawing apparatus. But in this case, compared to the above method using multiple masks,
The time required for exposure is significantly increased.

The phase hologram 821 of "FIG. 4" can also be manufactured by using a single mask in the same manner as in "FIG. 8". The refraction element 812 of FIG. 3 can be manufactured by cutting a glass material with a diamond lathe or by injection molding.

[0054]

According to the present invention, the illumination light can be focused at a desired position, the efficiency of utilization of the illumination light can be greatly improved, and the exposure time when the modified illumination is used is increased. Can be prevented. Further, it is less likely to be affected by vibration as the exposure time increases.

[Brief description of drawings]

FIG. 1 shows an embodiment of an exposure apparatus of the present invention

FIG. 2 is an explanatory diagram of kinoform.

FIG. 3 is an explanatory view of a refraction type element.

FIG. 4 is an explanatory diagram of a phase hologram.

FIG. 5 is an explanatory diagram of a phase hologram element.

FIG. 6 Contribution of vertically incident illumination light to image formation

FIG. 7: Contribution of illumination light incident at half the first-order diffraction angle to image formation

FIG. 8: Conventional exposure apparatus compatible with modified illumination

FIG. 9: Method for manufacturing kinoform and phase hologram

[Explanation of symbols]

2 ... Mask, 3 ... Reduction lens, 4 ... Wafer, 11
... mercury lamp, 12 ... parabolic mirror, 13 ... integrator lens, 14 ... condenser lens, 15 ... folding mirror, 16 ... wavelength selection filter, 31 ... reduction lens pupil, 52 ... drive unit, 53 ... holder, 70 ... Collimating lens, 71 ... Input lens, 811
... Kinoform, 921 ... Central ray of illumination luminous flux

Claims (16)

[Claims] 1. An exposure apparatus comprising: a projection optical system for projecting a circuit pattern formed on a mask onto a photosensitive substrate; and an illumination optical system for illuminating the mask substantially uniformly with illumination light from a light source. An exposure apparatus comprising a condensing optical element for condensing illumination light in a desired area. 2. The exposure apparatus according to claim 1, wherein the desired area is a plurality of points or a ring-shaped area apart from the optical axis of the illumination optical system. 3. The exposure apparatus according to claim 2, wherein the condensing optical element is composed of a diffractive lens. 4. The exposure apparatus according to claim 3, wherein the pitch of the diffractive lens becomes coarser as the distance from the optical axis of the illumination optical system increases. 5. The exposure apparatus according to claim 3, wherein the diffractive lens is a sawtooth type kinoform. 6. The exposure apparatus according to claim 5, wherein the kinoform has a stepped surface shape of 2k steps (k is an integer of 1 or more). 7. The exposure apparatus according to claim 3, wherein the diffractive lens is composed of a plurality of phase holograms. 8. The exposure apparatus according to claim 3, wherein the diffractive lens is composed of a plurality of zone plates having a transmissive portion and a light shielding portion. 9. The condensing optical element is a refraction type lens whose surface shape is formed by rotating an arc whose center is not on the rotation axis around the rotation axis. The exposure apparatus described. 10. The illumination optical system comprises an illumination light source, a collimator lens for collimating an illumination light beam, an integrator lens, an input lens for causing the focusing optical element and the center of the light beam to enter the integrator lens vertically. 3. An exposure apparatus according to claim 2, further comprising a condenser lens for forming an image of the rear surface of the integrator lens on a reduction lens pupil and a selection unit for selecting the condensing optical element. 11. The exposure apparatus according to claim 10, wherein the condensing optical element is installed between the collimator lens and the integrator lens. 12. In the method of manufacturing a diffraction type lens, a silicon master manufacturing process for manufacturing a silicon master having a stepped shape or a single stepped surface shape by using a plurality of or one mask, and conductive on the silicon master. A conductive thin film forming step of forming a conductive thin film, a mold forming step of forming a mold on the conductive thin film, and a diffractive lens forming step of molding the diffractive lens on a glass substrate using the mold. A method of manufacturing a characteristic diffractive lens. 13. The method of manufacturing a diffractive lens according to claim 12, wherein the mold forming step is electroplating of nickel. 14. The diffractive lens forming step comprises: inserting an ultraviolet curable resin between the mold and the glass substrate and irradiating ultraviolet rays to cure the diffractive lens. A method for manufacturing a diffractive lens according to the item. 15. The optimum condensing optical element is selected from the plurality of condensing optical elements by the selecting means according to the circuit pattern formed on the mask, and the illumination light is directed to the desired area. An exposure method of exposing a substrate coated with a photosensitive material by focusing light. 16. A semiconductor device manufactured by using the exposure method according to claim 15. Description: