JPH0533371B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is applicable to, for example, a projection type scanning exposure apparatus, particularly
The present invention relates to a reflective optical system suitable for application to an optical system for aligners used in the manufacture of LSIs and the like. Conventional reflective optical systems of this type include, for example, reflective optical systems that use concentric or non-concentric concave mirrors and convex mirrors, and nearly concentric reflective systems that use concave mirrors and convex mirrors, as well as negative meniscus lenses and chromatic aberration correction mechanisms. Various types of optical systems are known. These reflective optical systems have a good image area formed in an off-axis semi-arc-shaped area, and a partial image of the mask corresponding to this good image area is formed on the wafer, and the mask and wafer are integrated into the reflective optical system. Aligners are known that form an entire image of a mask on a wafer by scanning relative to the system. however,
All conventional reflective optical systems have large astigmatism and field curvature, and therefore the width of the good image area is extremely narrow, for example, about 1 mm, and when adapted to an aligner, it takes a long scanning time, that is, exposure time. requires
The drawback was that the amount of wafers printed per hour was relatively small. The purpose of the present invention is to improve the drawbacks of the conventional example, sufficiently correct astigmatism and field curvature using an aspherical concave mirror, and expand the good image area of the corrected image height. The object of the present invention is to provide a reflective optical system that increases the amount of wafer printing per hour, and the gist thereof is as follows. That is, in a reflective optical system, a concave mirror and a convex mirror are arranged so that their reflective surfaces face each other, and light from an object off the optical axis is reflected in the order of the concave mirror, the convex mirror, and the concave mirror to form an image on the image plane. , the reflective surface of the concave mirror has a negative polarity as it moves away from the optical axis, so that the light rays emitted parallel to the optical axis from each point of the subject are reflected by the concave mirror and then incident on the intersection of the convex mirror with the optical axis. A reflective optical system characterized by having an aspheric surface that has an increased refractive power component and satisfies the following conditions. 8.5/10 ⁴ ≦ | (ΔRH2 − ΔRH1) / ΔH | ≦7.5/10 Here, ΔH is the width of the area surrounded by the height H1 and the height H2 from the optical axis where the subject exists,
ΔRH2 and ΔRH1 are the amounts of deviation of the reflecting surface from the reference spherical surface at the heights H1 and H2, with the direction in which the negative refractive power increases relative to the reference spherical surface as positive. The present invention will be explained in detail based on illustrated embodiments. In the embodiment shown in FIG. 1, a concave mirror M1 and a convex mirror M2 having a smaller radius are placed so that their optical axes O coincide and their centers of curvature are in the same direction. Mirror surfaces are placed facing each other. The concave mirror M1 and the convex mirror M2 are aspherical. The light beam emitted from the object S1 passes through the concave mirror M1,
Since it advances in the order of convex mirror M2 and concave mirror M1, object height P1 is reflected three times in total between these two mirror surfaces M1 and M2, and then is imaged at the same magnification at point P2 on image plane S2. The convex mirror M2 serves as a diaphragm for this reflective optical system. Since this reflective optical system is arranged symmetrically with respect to the center O2 of the effective diameter of the convex mirror M2, asymmetric aberrations such as coma aberration and distortion aberration do not occur, but in a normal optical system, astigmatism and image Occurrence of surface curvature is inevitable. Therefore, in this reflective optical system, astigmatism and field curvature are corrected by an aspherical concave mirror M1. For this purpose, the aspheric surface of the concave mirror M1 is arranged so that the principal ray parallel to the optical axis O at each image height within the correction area h shown in the astigmatism diagram of FIG. 2 always enters the center O2 of the convex mirror M2. The shape is determined. In this case, since the concave mirror M1 has the same effect as a convex lens, negative spherical aberration occurs depending on the value of positive spherical aberration occurring at each incident height of the concave mirror M1 corresponding to each image height of the correction area h. I try to do that. Therefore, if the shape of the aspherical concave mirror M1 is selected so that the positive and negative spherical aberrations cancel each other out at each image height in the correction area h, the principal ray parallel to the optical axis O at each image height will be It enters the center O2. In other words,
When the infinity chief ray of each image height within the correction area h is corrected so that it is always focused on the center O2 of the optical system, the astigmatism of the entire reflective optical system is corrected due to the symmetry at the center O2. It means that it was done. Since the correction area h is determined by the relationship between the inclination of the sagittal image surface s and the meridional image surface m and the permissible depth, correction of astigmatism, that is, eliminating the astigmatic difference between the sagittal image surface s and the meridional image surface m, Correction area h
By reducing the field curvature of each image plane in
The aspherical concave mirror M1 was adopted in order to expand the correction area h and increase the slit width. This corrects astigmatism, and as mentioned above, due to the symmetry of the optical system, no comatic aberration or distortion occurs, but if even higher performance is required, , the lateral aberration caused by making the concave mirror M1 aspherical cannot be ignored.
Therefore, in this embodiment, by making the convex mirror M2 aspherical, it is possible to correct the lateral aberration caused by the introduction of the aspherical concave mirror M1. In Fig. 1, due to the action of the aspherical concave mirror M1, the principal ray parallel to the optical axis O at each image height within the correction area h always enters the center O2 of the convex mirror M2. without affecting related aberrations, namely astigmatism and field curvature,
Aberrations in the upper ray UR and lower ray LR can be corrected. In the first embodiment shown in FIG. 1, the concave mirror M1 and the convex mirror M2 are concentric, and FIGS. 2a, b, and e are astigmatism diagrams, and FIGS. 3a to 3g are lateral aberration diagrams. It is. Numerical examples of the optical configuration in this first embodiment are listed in Table 1. In addition, Ri is the radius of curvature of the i-th optical member surface according to the order of light progression, Di is the i-th air interval, and the positive and negative signs are positive when the light travels from left to right. .

【table】

【table】

[Table] Figures 4, 5 a, b, e, and 6 a to g are
A configuration diagram, an astigmatism diagram, and a lateral aberration diagram of the second embodiment are shown, respectively, and the concave mirror M1 and the convex mirror M2 are non-concentric. Table 2 shows numerical examples of this second embodiment.

【table】

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[Table] Figure 7, Figure 8 a, b, e, Figure 9 a to g are
These are a configuration diagram, an astigmatism diagram, and a lateral aberration diagram, respectively, of the third embodiment, and the concave mirror M1 and the convex mirror M2 have even greater non-concentricity. Table 3 shows numerical examples of this third embodiment.

【table】

【table】

[Table] In each of the above-described embodiments, both the concave mirror M1 and the convex mirror M2 are made aspheric, but astigmatism and field curvature can be sufficiently corrected by making only the concave mirror M1 aspheric. In addition, in these tables, the aspherical concave mirror M1
The aspherical amount ΔS is defined as ΔS = (ΔRH2 − ΔRH1)/ΔH. Here, ΔH indicates the semi-arc shaped good image area given by H2-H1 with the aspherical concave mirror M2 as shown in Fig. 10a, and ΔRH1 and ΔRH2 are the 10th
As shown in FIG. b, the aspheric amount from the reference spherical surface at heights H1 and H2 is shown. Note that the solid line A in b indicates a reference plane centered on point O3, and the dotted line B indicates an aspherical surface. As can be seen from these tables, the aspherical amount ΔS is between 8.5/ ¹⁰⁴ and 7.5/10, and ΔS is 8.5/104 and 7.5/10.
If it is smaller than 10 ⁴ , the amount of change in the aspherical surface will be small, the effect of the aspherical surface will be weakened, and a wide slit width will not be obtained. Also, when ΔS becomes larger than 7.5/10, the amount of change in the aspheric surface increases, and the sagittal image surface s
As a result, the meridional image plane m becomes farther apart, making it impossible to obtain a wide slit width. Also, the aspherical amount Δx of the convex mirror M2 is
When the effective diameter of convex mirror M2 is D and the aspherical amount obtained from the reference spherical surface of convex mirror M2 at a height of 70% of the effective radius of convex mirror M2 from the optical axis as in Fig. 10b is ΔR, then ΔR/D Defined. Roller aspherical amount Δx
is between 1.2/10 ⁶ and 8/10 ⁶ and Δx is 1.2/10 ⁶
If it is smaller than , the effect of the aspheric surface will be reduced,
When Δx becomes larger than 8/10 ⁶ , the amount of change in the aspherical surface increases, making it impossible to obtain a wide slit width. Next, an example in which the reflective optical system according to the present invention is applied to a semiconductor printing apparatus will be described with reference to FIGS. 11 and 12. FIG. 11 shows the optical arrangement of the printing apparatus, in which 1 is an optical system for mask illumination, and along the horizontal optical axis are a spherical mirror 2, a light source 3 consisting of an arcuate mercury lamp, a lens 4, a filter 5, 45 A degree mirror 6 and a lens 7 are arranged. Note that the filter 5 removes light that is photosensitive to the wafer, and is inserted into the illumination optical path during mask-wafer alignment. This mask illumination optical system 1 limits the imaging area of the reflective optical system to a circular arc or a semi-arc by illuminating the mask in an arc or a semi-arc. Reference numeral 8 denotes a mask placed on the upper horizontal plane, and this mask 8 is held by a known mask holder (not shown). A reflective optical system 10 according to the present invention is arranged below the mask 8 to form an image of the mask 8 on a wafer 9. Note that, unlike the previous embodiment, the object side S1 and the image plane S2 side are separated, and are used by deflecting the light flux by mirrors 11 and 12, respectively.
The wafer 9 is held by a known wafer holder, and the wafer holder can be finely adjusted in the X, Y, and θ directions like a normal holder. A microscope optical system 13 is inserted as an illumination optical system between the mask 8 and the mask 8 during alignment, and it is determined whether the mask 8 and the wafer 9 are in a predetermined positional relationship. If the mask 8 and wafer 9 are not in a predetermined positional relationship, the wafer 9 is adjusted and moved relative to the mask 8 using the X, Y, and θ adjustment members of the wafer holder described above to bring them into a predetermined relationship. Next, the twelfth photo shows the external appearance of this printing device.
Explain the diagram. In FIG. 12, 20 is a lamp house, inside which is the illumination optical system 1 shown in FIG.
is built-in. Reference numeral 21 denotes a unit in which the alignment microscope optical system 13 is disposed, and this unit 21 is supported so as to be movable back and forth. 22 is a mask supporter, 23 is a wafer supporter, and these supports 22 and 23 are connected to the coupling member 2.
4 so as to move integrally. Here, the supports 22 and 23 move together, but the wafer 9 can be moved minutely with respect to the support 23. 25 is an arm fixed to the coupling member 24, and this arm 25 is supported by a guide 26. The supports 22 and 23 are integrally moved horizontally and linearly by the horizontal movement mechanism included in the guide 26. 27 is a tube that houses the reflective imaging optical system; 28 is a base; 29
is a turntable, and 30 is an auto feeder. By this auto feeder 30, the wafer 9
is the wafer support 2 via the turntable 29.
3 automatically supplied. Next, the operation of this apparatus will be explained. First, the mutual positional relationship between the mask 8 and the wafer 9 is aligned. During this alignment, the aforementioned filter is inserted into the illumination optical system 1, and a semi-arc shaped light source image is formed on the mask 8 by the lenses 4 and 7 using non-photosensitive light. At this time, the microscope optical system 13 is also inserted between the lens 7 and the mask 8. Using this microscope optical system 13, the alignment marks on the mask 8 and wafer 9 are observed,
Adjust both alignment marks using wafer support 2.
This is done by operating 3. After the alignment of the mask 8 and wafer 9 is completed, the aforementioned filter and microscope optical system 13 are retracted from the optical path. At the same time, the light source 3 is turned off or shielded from light by a shutter means (not shown), and then a photosensitive semi-arc shaped light source image is formed on the mask 8 by turning on the light source 3 or opening the shutter. At the same time, the arm 25 starts moving the guide 26 in the horizontal direction. This horizontal movement causes the entire image of the mask 8 to be printed onto the wafer 9. As explained above, the reflective optical system according to the present invention can correct the sagittal image surface s and the meridional image surface m at each image height of the correction area so that they coincide over a wide range by making the concave mirror aspheric. Furthermore, by expanding the good image area, that is, by increasing the slit width, it is possible to shorten the exposure time in the exposure device. In particular, since there is no restriction on the concentricity of the concave mirror and the convex mirror, there is an advantage that a high-performance reflective optical system can be obtained without having to worry too much about their arrangement positions. Further, by making the convex mirror also aspherical if necessary, it becomes possible to correct the lateral aberrations generated in the aspherical concave mirror and further expand the good image area of the corrected image height. According to the example,
The good image area is expanded when the image height h is 100 to 90 mm, that is, the slit width is about 10 mm.

[Brief explanation of the drawing]

The drawings show an embodiment of the reflective optical system according to the present invention, and FIG. 1, FIG. 2 a, b, e, and FIG. Aberration diagrams, lateral aberration diagrams, FIGS. 4, 5 a, b, e, and 6 a to g are the configuration diagrams of the second embodiment, astigmatism diagrams, lateral aberration diagrams, and FIG. 7, respectively. Figure 8 a, b,
e, FIGS. 9a to 9g are the configuration diagram, astigmatism diagram, and lateral aberration diagram of the third embodiment, respectively. FIGS. 10a and b are explanatory diagrams of the aspherical amount ΔS, and FIGS. 11 and 12. 1 is a configuration diagram of a printing apparatus using a reflective optical system according to the present invention. Symbol M1 is a concave mirror, M2 is a convex mirror, h is a correction area, O2 is the center of the convex mirror, ΔH is a good image area, s is a sagittal image surface, m is a meridional image surface, 1 is an illumination optical system, 8 is a mask, 9 1 is a wafer, 10 is a reflective optical system, and 13 is a microscope optical system.

Claims (1)

[Scope of Claims] 1. A concave mirror and a convex mirror are arranged so that their respective reflecting surfaces face each other, and light from an object off the optical axis is reflected in the order of the concave mirror, the convex mirror, and the concave mirror to form an image on the image plane. In the reflective optical system, the reflective surface of the concave mirror is aligned with the optical axis so that the light rays emitted from each point of the object parallel to the optical axis are reflected by the concave mirror and then incident on the intersection of the convex mirror with the optical axis. A reflective optical system characterized by having an aspherical surface whose negative refractive power component increases as the distance from the surface increases and which satisfies the following conditions. 8.5/10 ⁴ ≦ | (ΔRH2 − ΔRH1) / ΔH | ≦7.5/10 Here, ΔH is the width of the area surrounded by the height H1 and the height H2 from the optical axis where the subject exists,
ΔRH2 and ΔRH1 are the amounts of deviation of the reflecting surface from the reference spherical surface at the heights H1 and H2, with the direction in which the negative refractive power increases relative to the reference spherical surface as positive. 2. The reflective optical system according to claim 1, wherein the convex mirror has an aspherical reflecting surface that satisfies the following conditions in order to correct lateral aberration caused by the aspherical reflecting surface. 1.2/10 ⁶ <ΔR/D<8/10 ⁶ Here, D is the effective diameter of the convex mirror, and ΔR is the amount of deviation of the reflecting surface from the reference spherical surface at a height of 70% of the radius of the convex mirror with effective diameter D. It is.