JPH081490B2 - Projection lens and exposure apparatus using the same - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus using a projection lens, and more particularly to an exposure apparatus using a photolithography technique used for manufacturing semiconductor elements.

Furthermore, it was devised to realize ultra-fine processing in the photolithography process in semiconductor device manufacturing,
The present invention relates to an exposure apparatus using discontinuous, for example, pulsed energy rays, more specifically, for example, excimer laser light.

2. Description of the Related Art Conventionally, reduction projection exposure apparatuses (steppers) using an ultra-high pressure mercury lamp as a light source have already been put on the market for fine processing of semiconductor elements, particularly LSI, VLSI and the like. However,
The conventional stepper uses g-line (436 nm) and i-line (365 nm) of the ultra-high pressure mercury lamp, so the resolution is 0.8μ for g-line.
The limit was 0.6 μm for m and i lines. At these wavelengths, it is almost impossible to obtain the 0.5 μm resolution required for 4M or 16M bit dynamic memory manufacturing in the future.

Therefore, in recent years, XeCl has a shorter wavelength than g-line and i-line.
(308 nm), KrF (249 nm), ArF (193 nm) and other development of exposure equipment using a light source that emits excimer laser light has come into consideration.

Problems to be Solved by the Invention However, the projection lens for a reduction projection exposure apparatus using an excimer laser has the following problems.

That is, since the exposure wavelength is short, the material selection of the optical material glass (glass material) used for the reduction projection lens is controlled by the transmittance. By the way, KrF (249nm), ArF
The laser wavelength of (193 nm) is limited to about two types, quartz (SiO ₂ ) and fluorite (CaF ₂ ). Therefore, conventionally, in a reduction projection lens design, various aberrations such as chromatic aberration must be corrected in units of a fraction of the wavelength by utilizing a slight difference in refractive index and dispersion of the glass material forming the lens. It was However, as far ultraviolet rays such as excimer laser light are limited in the materials that can be used as described above, only the method of gradually changing the radius of curvature of the spherical surface of the material having the same refractive index is necessarily used when designing the reduction projection lens. It was not possible, and there was the problem that the lens would be very long, about 1 m, using only the reduction projection lens.

It should be noted that CaF is softer than SiO ₂ and has a drawback that it is difficult to process, and since a glass material having a small variation in refractive index cannot be obtained, it is practically useless.

Therefore, the present invention provides a method of easily designing a lens by using quartz having different refractive indexes in the case of producing a single quartz lens, and also improves the performance of the projection lens. is there.

Means for Solving the Problems The projection lens of the present invention is a combination of two or more kinds of glass materials whose refractive index is controlled by anomalous dispersion at a specific wavelength. Two or more types are used in which the anomalous dispersion wavelength is moved by controlling and mixing to change the refractive index at a specific wavelength.

Therefore, a projection lens for use in a semiconductor exposure apparatus that can specify the wavelength used, such as KrF excimer light (248 nm), X
eCl excimer light (308nm), ArF excimer light (193nm)
In designing a projection lens for use with synthetic quartz and multiple types of glass materials with controlled refractive index by mixing impurities into synthetic quartz, it is possible to improve lens design freedom and chromatic aberration correction performance. Becomes

Practical Example First, the method for making quartz having different refractive indexes available uses the principle described below.

Generally, an optical material (glass material) undergoes anomalous dispersion near the absorption spectrum, and as shown in FIG. 1, the refractive index increases, decreases, and increases as it moves toward the shorter wavelength side. Returns to the original value. On the other hand, it is extremely easy to mix arbitrary impurities (for example, metals such as Fe, Al ...) into glass materials with very few impurities such as synthetic quartz. It is possible to shift the absorption edge of the spectrum. Therefore, by specifying the wavelength used for the projection lens (for example, 248 nm of KrF excimer laser light),
Even with the same silica glass material, it is possible to use a plurality of glass materials whose refractive index is controlled by the mixing amount of impurities, that is, silica glass materials having different refractive indexes.

For example, the wavelength dependence of the refractive index of synthetic quartz showing the light transmittance curve (c) in FIG. 2 becomes the refractive index curve (a), and now the wavelength used for the projection lens is set to KrF excimer light, that is, 248 nm. Once determined, the refractive index will be 1.508. On the other hand, in the case of a glass material (quartz mixed with impurities) in which impurities are mixed in several PPM and showing a light transmittance curve (d), the refractive index is 1.53 at 248 nm. That is, even with the same quartz glass material, 248n
If it is used with m light, two types of refractive index 1.508 and 1.53 can be used. Similarly, by controlling the amount of impurities mixed in, the glass lens material having a different refractive index may be used as needed to design the lens, whereby the desired lens can be manufactured.

Theoretically, if the amount of impurities is increased,
Quartz glass material with an extremely large refractive index can be obtained, but if it has too large absorption at the wavelength used (for example, if impurities are mixed in at a high concentration so that the transmittance becomes 80% or less), it is practical as a lens. It will be clear that it will disappear.

Furthermore, the lens of the present invention utilizes the change in refractive index due to anomalous dispersion of the glass material, and the light source having a very wide wavelength range to be used, for example, i-line and j-line emitted from an ultra-high pressure mercury lamp (with a dispersion of about ± 10 nm). ), It cannot be used because the refractive index changes in the used wavelength range, and general coherent laser light and excimer laser light sources (eg KrF, XeC
It is also clear that it can be used only for light sources with small wavelength dispersion (± 0.3 nm) such as (1, ArF).

By the way, FIG. 3 shows a design example of a 12-element reduction lens for far-ultraviolet rays using glass materials having five types of refractive indexes.

In the figure, 11 indicates an individual lens using a glass material produced by the method of the present invention, 12 indicates a light beam, and 13 indicates a wafer surface.

Next, an embodiment of the exposure apparatus using the projection lens of the present invention will be described with reference to FIG.

That is, for example, as a light source unit, a KrF (248 nm) excimer laser light source 21, an integrator 22 that shapes and homogenizes light emitted by oscillation excitation from the laser light source, and a large total reflection mirror 23 that makes an optical path vertical, a reticle 25, and Quartz condenser lens for illuminating reduction lens 27
The optical system includes a reticle 24, a reticle 25, a main beam splitter 26 for alignment, an opposed mirror 26A, and a reduction projection lens 27 made of quartz. XYZ at the image formation point
A main optical system of a reduction projection exposure apparatus for transferring onto a wafer 29 installed on a stage 28, and the main beam splitter 26.
And on the optical axis which is substantially perpendicular to the exposure optical path, an alignment lens 30, an alignment beam splitter 31, an image processing / wavelength conversion IIT 32, an image processing CCD camera 33, and an alignment beam splitter 31 are arranged in the order of the light. An alignment optical system including an alignment light source 34 for vertically illuminating an alignment mark (for example, light of an ultra-high pressure mercury lamp dispersed by a cut filter or a monochromator, or a laser) is used for illuminating an arbitrary place on a wafer. It is held in the XY drive system 35. Then, the XYZ stage 28 on which the alignment optical system and the wafer 29 are installed is designed to be controllable by the control computer 36 for image processing and alignment signal processing.

The alignment optical system will be described in more detail. Alignment illumination system 34 For example, Xe-Hg ultra high pressure lamp using a cut filter for i-line (365 nm) or j-line (313 nm) (when reducing projection lens 7 and excimer laser light source 21 are KrF excimer light (248 nm)) Illuminate light and use alignment beam splitter 31 for alignment lens
The main beam splitter 26 of the main optical system is illuminated via 30. At this time, the alignment system XY drive system 35 can arbitrarily illuminate according to the alignment mark positions of the reticle and the wafer. Alignment illumination light passes through the main beam splitter 26, and simultaneously illuminates the alignment mark 25A on the reticle 5 and the alignment mark on the wafer 29 via the main beam splitter 26 and the facing mirror 26A with ultraviolet light of 313 or 365 nm. The reflected light is further transmitted through the main beam splitter 26 and the opposing mirror 26A, the alignment mark on the wafer 29 and the image of the alignment mark 25A on the reticle 25 to the alignment lens 30 via the main beam splitter 26 at the same time. Will be returned. At this time, the exposure wavelength (248 nm) and the alignment wavelength (for example, 313 nm, 3
(65 nm) light causes chromatic aberration, and in a reduction lens used in the present invention, normal chromatic aberration cannot be completely eliminated, so that the exposure focus and the alignment focus deviate from each other. So the opposite mirror
By properly adjusting the position L of 26A, it is possible to change the optical path length of the alignment light so that the alignment key on the reticle and the alignment key on the wafer have the same focal point as the light of the exposure wavelength.

Further, the images of the alignment marks on the wafer 29 and the reticle 25 are enlarged images by the reduction projection lens 7 and the alignment lens 30, respectively, so that a very large resolution can be obtained. Furthermore, it is equipped with a wavelength conversion to make the image of ultraviolet rays (visual or video processing not observable in the ultraviolet region visible) visible, and a micro channel plate (MCP) to amplify the image signal to improve the S / N ratio. The image will be processed using the image intensifier (IIT) 32. At this time, the wavelength of the image is usually set to 500 nm or more to enable observation in the visible range, and finally, the CCD camera 13 performs the pattern recognition processing of picture elements. It is natural that the higher the resolution of the CCD camera, the better, but there is no problem with the effects of magnifying the image and visible light.

Also, as an image intensifier, V1506 (Hamamatsu Photonics Co., Ltd. model name), which has Cs-Te on the photocathode and has a sensitivity of 150 to 320 nm, and as a microchannel plate, F1217 (Hamamatsu Photonics Co., Ltd. ))
Etc. can be used.

In the above-mentioned embodiment, the exposure wavelength is 248 nm of KrF and the alignment light is 313 nm (j-line) or 365 nm (i-line). It is also possible to use lines for alignment light. Note that e
When I or D line is used as alignment light, IIT is not necessary because it is visible light, but since the chromatic aberration is larger than that of i line or j line, the distance (L) between the opposing mirror and the main beam splitter is It needs to be significantly larger.

EFFECTS OF THE INVENTION By using the present invention, a single-quartz high-precision projection lens that can be used in the far ultraviolet region can be manufactured. Further, when a lens is designed using the present invention, the degree of freedom in selecting a glass material is greatly increased, so that it is easy to improve lens design accuracy such as chromatic aberration correction, and the design time can be significantly shortened. is there.

Furthermore, the lens of the present invention can exhibit a high resolution in an exposure apparatus for manufacturing ultra-ultra-LSI, which requires a resolution of about 0.5 μm, and particularly in an exposure apparatus that uses far-ultraviolet light such as KrF excimer light. There are some great improvements. The excimer light source is not limited to KrF. It is also clear that the same effect can be obtained with a reflection reduction projection exposure apparatus.

[Brief description of drawings]

FIG. 1 is a diagram for explaining anomalous dispersion development used in the present invention, FIG. 2 is a diagram showing changes in refractive index with wavelength of synthetic quartz and quartz glass material containing impurities, and FIG. FIG. 4 is a view showing an example of the formed optical lens, and FIG. 4 is a conceptual view of the example for explaining the excimer exposure apparatus of the present invention. 21 ... Excimer light source, 22 ... Integrator, 23 ...
… Mirror, 24 …… Condenser lens, 25 …… Reticle,
26 …… Main beam splitter, 26A …… Face mirror, 27
...... Reduction projection lens, 28 …… XYZ stage, 29 …… Wafer, 30 …… Alignment lens, 31 …… Alignment beam splitter.

Front page continuation (72) Inventor Masataka Endo 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Inventor Ken Ishihara 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd. (56) Reference Reference JP-A-61-129828 (JP, A) JP-A-57-53701 (JP, A)

Claims (5)

[Claims] 1. A projection lens comprising a combination of two or more kinds of glass materials in which a change in refractive index caused by anomalous dispersion at a specific wavelength is controlled and used for light of the specific wavelength. 2. The projection lens according to claim 1, wherein the specific wavelength is in the region of far-ultraviolet light. 3. A glass material comprising two or more kinds of glass or quartz having a refractive index changed at a specific wavelength by shifting anomalous dispersion wavelength by controlling and mixing impurities into quartz. The projection lens according to item 1 or 2. 4. The far-ultraviolet light is KrF, ArF, or XeCl.
The projection lens according to claim 2, wherein the projection lens is excimer light. 5. An excimer light source, a reticle stage,
An exposure apparatus including a reduction projection lens constructed by combining two or more kinds of glass materials whose refractive index is controlled by anomalous dispersion at a specific wavelength, an XY wafer stage, and an alignment optical system.