JP3173100B2 - Projection exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus used for photolithography in the field of manufacturing semiconductor devices and the like, and in particular, it is possible to improve resolution by increasing the relative intensity of harmonic components of exposure light. The present invention relates to a projection exposure apparatus.

[0002]

2. Description of the Related Art In the field of semiconductor integrated circuits, processing at the submicron level has already been realized in mass production factories, and processing at the quarter micron level, which will be indispensable in the future at the half micron level and also in the 64 Mbit DRAM class. Research is ongoing.

The technology that has been the key to the progress of such fine processing is photolithography. Conventional advances have been made to shorten the exposure wavelength and to increase the numerical aperture of a reduction optical lens of a stepper (reduction projection exposure apparatus). NA). Of these, regarding the shortening of the wavelength, KrF excimer
Although deep ultraviolet lithography using laser light (248 nm) is promising, development of a resist material having sufficient performance has been delayed, and it is difficult to immediately introduce it into a mass production site.

[0004] On the other hand, many attempts have been made to extend the life of i-line lithography using a conventional high-pressure mercury lamp as a light source by a so-called super-resolution technique for increasing the resolution by using a harmonic component of exposure light. . One of the technologies that have been spotlighted as super-resolution technology is a phase shift method. This is a method of improving the resolution by giving a phase difference to the exposure light transmitted through the reticle and utilizing the mutual interference of the transmitted light. In the phase shift method, in order to generate a phase difference, it is necessary to form a transparent film (phase shifter) having a different refractive index from a glass substrate constituting a reticle in a specific pattern on the glass substrate. However, there are many issues that need to be overcome before practical use, such as the fact that the manufacture, inspection, and defect correction of a reticle are extremely complicated, and a special CAD technique is required.

Therefore, in recent years, attempts have been made to improve the resolution within the current technical range by improving the optical system of the stepper. This uses a method that has long been known in the field of optics, in which the darkness of the light source or the center of the pupil enhances the image contrast near the resolution limit due to the super-resolution phenomenon. It is effective in such a partially coherent imaging system.

FIG. 1 shows an optical system of a general stepper. In this optical system, ultraviolet light emitted from a light source 1 such as a high-pressure mercury lamp is condensed by an elliptical mirror 2, then its optical path is bent by a mirror 3, and a specific wavelength (for example, i-line ), The light is incident on the fly-eye lens 4 (14), and the in-plane illuminance is made uniform. The light is then reflected by a mirror 5 to form a condenser lens 6, a reticle 7, and reduction projection lenses 8,9.
, And finally the Cr film on the reticle 7 is applied to the photoresist coating on the wafer 10 placed on the stage 11.
The pattern is adapted to be projected.

In this optical system, when the pupils of the reduction projection lenses 8 and 9 are located, for example, at positions indicated by lines BB in the figure, a filter for shielding the center of the pupil plane is a super-resolution filter. is called. On the other hand, a technique of changing the shape of the light source surface by inserting various light-blocking filters behind the fly-eye lens 4 (14), for example, at the position of the aperture stop indicated by line AA in the figure, is called a modified illumination method. Have been.
Among the modified illumination methods, annular illumination is provided by providing a circular light shielding portion at the center to enable donut-shaped illumination. For example, the 52nd Annual Meeting of the Japan Society of Applied Physics (Autumn Meeting of 1991) Shu, p. 601, lecture number 12a-ZF-
6 reports the results of the study. According to the annular illumination, it is possible to remove a part of the 0th-order diffracted light that causes a decrease in contrast, to relatively increase harmonic components, and to improve the resolution.

However, in the annular illumination, there occurs a region where the contrast is reduced due to the incidence of only the 0th-order diffracted light without the incidence of the ± 1st-order diffracted light. In order to solve this problem, there is a method in which the shape of the light shielding portion is changed to improve the depth of focus of the fine pattern. For example, the proceedings of the lecture, p. 600, Lecture No. 12a-ZF-2, reports a filter having a band-shaped light shielding portion in the center. Further, in order to eliminate the dependence of the strip-shaped light-shielding portions on the pattern in the vertical and horizontal directions, a filter in which the strip-shaped light-shielding portions are orthogonal to each other in a cross shape has been proposed. 601, lecture number 12a-
Reported in ZF-4.

In addition, the proceedings of the lecture, p. 602, lecture number 12a-ZF-8, oblique incidence illumination for obliquely entering exposure light is being studied. This is intended to increase the apparent NA of the reduction projection lens and increase the resolution by blocking the -1st order diffracted light and allowing only the 0th order diffracted light and the + 1st order diffracted light to enter.

[0010]

As described above, each of the above-mentioned various modified illumination methods has been successful. However, since all of them use a light-blocking filter, if the temperature of the light-blocking filter rises and is deformed by light irradiation, the stability of resolution may be impaired. Further, if such a temperature change occurs inside the stepper whose temperature, pressure, etc. are precisely controlled, there is a possibility that disturbance may adversely affect other optical systems.

Therefore, the present invention realizes a stable resolution,
An object of the present invention is to provide a projection exposure apparatus that does not have a possibility of causing a bad influence on an optical system.

[0012]

SUMMARY OF THE INVENTION A projection exposure apparatus according to the present invention has been proposed to achieve the above object, and is an apparatus for projecting a reticle pattern onto a substrate by a projection optical system. The fly-eye lens in the projection optical system is characterized in that the light-shielding portion is integrally incorporated.

[0013]

According to the present invention, a light-shielding portion is provided in the fly-eye lens instead of using a light-shielding filter as in the conventional modified illumination method. A fly's eye (fly's eye) lens is formed by optically bonding a large number of minute lenses vertically and horizontally, so that light from a single light source such as a high-pressure mercury lamp can be transmitted from multiple virtual point light sources. It is an optical component that resolves uneven illuminance in the reticle plane by converting it into light. Therefore, replacing a part of the minute lens with the light shielding portion is nothing but changing the shape of the light source surface. In addition, since the light-shielding portion is integrated with the fly-eye lens, the light-shielding portion is less likely to be deformed by heating, and does not adversely affect other optical components.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

First, the structure of a fly-eye lens used in the projection exposure apparatus of the present invention will be described with reference to FIG. FIG. 2 is an enlarged perspective view showing the fly-eye lens 4 in FIG. 1 described above. The fly-eye lens 4 is an aggregate of minute lenses L having a rectangular cross section. The microlenses L are arranged such that the longitudinal direction is along the optical axis direction of the optical system of the stepper, and the contact surfaces of the microlenses L adjacent to each other are optically bonded.

Here, FIG. 2A shows a part of the minute lens L near the center, which is extracted symmetrically with respect to the optical axis.
a, and FIG. 2B shows a configuration in which the minute lens L in the central vertical direction is replaced with a band-shaped light shielding portion 4b.
(C) shows a configuration in which the minute lens L in the vertical and horizontal directions at the center is replaced with an orthogonal band-shaped light shielding portion 4c.

FIG. 2 shows only a small number of microlenses L for convenience of explanation, and an actual fly-eye lens is composed of more microlenses L. That is, in FIG. 2A, the light-shielding portion 4a, which is drawn so as to have a cross-sectional shape in a cross shape, also approaches a circular shape with an increase in the number of the microlenses L. FIG.
3 shows a fly-eye lens 14 including a large number of microlenses L and a light-shielding portion 14a having a substantially circular cross-sectional shape provided at the center. The fly-eye lens 14 has the same effect as the annular illumination in the related art.

Here, assuming that the virtual radii when both the fly-eye lens 14 and the light-shielding portion 14a are approximately circular are R ₁ and R ₂ , respectively, in order to achieve a good resolution, 0.5R ₁ ≦ R Satisfying the relationship of ₂ ≦ 0.9R ₁ may be used as a rough guide. Similarly, FIG.
The fly-eye lens 4 shown in (b) has the same effect as the modified illumination using a filter having a band-shaped light-shielding portion in the related art, and is particularly effective for a unidirectional pattern. In this figure, the light shielding portion 4b is provided in the vertical direction, but may be provided in the horizontal direction.

Further, the fly-eye lens 4 shown in FIG. 2 (c) exhibits the same effect as the modified illumination using a filter having a rectangular band-shaped light shielding portion. That is, resolution with less pattern dependence can be achieved than the fly-eye lens 4 shown in FIG. 2B.

The material constituting the light shielding portions 4a, 4b, 4c is not particularly limited as long as it has a high light absorption coefficient for exposure light and a small thermal expansion coefficient. It is most convenient to make it common with the constituent materials. In particular, the light shielding portions 4b and 4c can be integrally formed with the outer frame of the fly-eye lens 4. In order to enhance the heat radiation effect, a temperature control mechanism may be incorporated in the light shielding units 4a, 4b, 4c. Furthermore, it is possible to configure light-shielding portions of various shapes other than those shown in the figure, and thereby oblique incident illumination and the like are also possible.

Next, the resolution was actually evaluated using a modified i-line stepper equipped with the fly-eye lens 14 described above. Fly-eye lens 14 used in the test, the virtual radius R ₂ of the light-shielding portion 14a which was set as R ₂ = 0.8 R _1, which i-line stepper (manufactured by Canon Inc .; trade name FPA-2000il, NA = 0.52, reduction ratio = 1 /
5 times).

The sample wafer is preliminarily prepared at 200 ° C. and 90 ° C.
A positive photoresist material for i-line (manufactured by Tokyo Ohka Kogyo Co., Ltd .; product name: THMR-iP1800) is formed on a 5-inch diameter silicon wafer after dehydration baking for 2 seconds.
This was prepared by spin coating to 2 μm and removing the solvent by baking at 90 ° C. for 90 seconds. This sample wafer is set on the i-line stepper, and
After performing exposure at a light exposure of 250 mJ / cm ² through a reticle having an and space pattern,
Post-exposure baking (PEB) was performed at 90 ° C. for 90 seconds, and paddle development was performed for 60 seconds using an alkaline developer (manufactured by Tokyo Ohka Kogyo Co., Ltd .; product name: NMD-W).

When the developed sample wafer was observed with a scanning electron microscope, it was found that the line and space up to 0.28 μm was well resolved, which was better than the resolution 0.4 μm before the modification of the fly-eye lens. Had improved significantly. Further, in order to evaluate the reproducibility when the number of processed wafers was increased, the same continuous exposure test was performed on 2,000 sample wafers. Inspection of the uniformity of the line width of the 0.3 μm line and space in the wafer surface revealed that the first processed wafer was 3.5% and the 2,000 th wafer was 3.20%.
It was 8%, indicating that there was almost no deterioration even after a large amount of processing.

COMPARATIVE EXAMPLE In this comparative example, a filter provided with a circular light-shielding portion having a radius equal to R ₂ = 0.8R ₁ at the rear stage of the fly-eye lens before remodeling, that is, at the position of line AA in FIG. It was inserted and the same exposure test as in the example was performed. In this comparative example, conventional annular illumination was performed.
Line and space up to 28 μm could be resolved. However, when a continuous exposure test was performed on 2,000 sheets, the in-plane uniformity of the 0.3 μm line and space was 3.6% for the first sheet, whereas the uniformity was 20%.
In the 00th sheet, it was halved to 7.2%. This is considered to be due to the thermal deformation of the filter and the resulting disturbance.

[0025]

As is clear from the above description, when the projection exposure apparatus of the present invention is used, the same effect as that of the conventional modified illumination using a light-shielding filter can be obtained, while the resolution stability is improved. Can be done. Therefore, the present invention
It is very promising as a life extension measure of line lithography.

[Brief description of the drawings]

FIG. 1 is an explanatory view schematically showing an optical system of a general stepper.

FIG. 2 is a schematic perspective view schematically showing a configuration example of a fly-eye lens mounted on the projection exposure apparatus of the present invention;
(A) is a configuration in which a part of the micro lens near the center is extracted symmetrically with respect to the optical axis and is replaced with a light shielding part, (b) is a configuration in which the central vertical micro lens is replaced with a band-shaped light shielding part, (C) shows a configuration in which the minute lenses in the vertical and horizontal directions in the center are replaced by orthogonal strip-shaped light shielding portions.

FIG. 3 is a schematic plan view showing a configuration example of a fly-eye lens mounted on the projection exposure apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Elliptical mirror 3, 5 ... Mirror 4, 14 ... Fly-eye lens 4a, 4b, 4c, 14a ... Light shielding part L ... Micro lens 6 ... Condenser・ Lens 7 ・ ・ ・ Reticles 8, 9 ・ ・ ・ Reduction projection lens 10 ・ ・ ・ Wafer 11 ・ ・ ・ Stage

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 521

Claims (1)

(57) [Claims] 1. A projection exposure apparatus for projecting a reticle pattern onto a substrate by a projection optical system, wherein a fly-eye lens in the projection optical system has an integrated light-shielding portion.
A projection exposure apparatus characterized in that the projection exposure apparatus is incorporated into a projection exposure apparatus.