JPH0533370B2 - - 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, to sufficiently correct astigmatism and field curvature by introducing an aspherical lens, and to 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 in which 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,
A first optical member is provided between the concave mirror and the subject, a second optical member is provided between the concave mirror and the image plane, and the light rays emitted from each point of the subject parallel to the optical axis are 1, reflected by the concave mirror through the first optical member, and then reflected at the intersection of the convex mirror with the optical axis, and reflected at the intersection of the convex mirror with the optical axis, then reflected by the concave mirror, and
The passing surface of at least the first optical member is made an aspherical surface so that the light beam is incident on the image plane parallel to the optical axis through the optical member, and the light beam passes through the first and second optical members.
In order to correct chromatic aberration occurring in the optical member, the convex mirror is provided with a refractive surface on its surface, and is a back reflecting mirror that satisfies the following conditions. |R5|<|R4|<|R5|+d/2 0.005≦d/D≦0.03 Here, R4 is the radius of curvature of the refractive surface of the convex mirror, R5 is the radius of curvature of the reflective surface of the convex mirror, and d is the refractive surface. and the axial wall thickness between the reflecting surface and D is the effective diameter of the convex mirror. 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 with a smaller radius are arranged so that their optical axes O coincide and their centers of curvature are in the same direction. Mirror surfaces are placed facing each other. Then, a point O1 between the object S1 and the convex mirror M2, and between the object S1 and the optical axis O.
An aspherical lens L1 is arranged symmetrically about the optical axis O between the image plane S2 and the convex mirror M2, which are symmetrically located about It is considered to be spherical. 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 plays the role of a diaphragm in 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, the light flux is
When the light is incident on the lens, coma aberration and distortion aberration, which are asymmetrical aberrations, do not occur, but astigmatism and field curvature cannot be avoided. Therefore, in this reflective optical system, astigmatism and field curvature are corrected by the aspheric lens L1. For this reason, the shape of the aspherical lens L1 is such that all principal rays parallel to the optical axis O at each image height within the correction area h shown in the astigmatism diagram in FIG. 2 enter the center O2 of the convex mirror M2. , and the shape of the aspherical lens L1 is determined so that each principal ray reflected from the center O2 of the convex mirror M2 is all incident parallel to the image plane. In addition, as long as the aberration can be well corrected,
Even if all of the principal rays are slightly off-center, some of the principal rays may be incident off-center.
Further, the shape of the aspherical lens L1 may be determined so that all the principal rays are incident on the image plane somewhat non-parallelly, or some principal rays are incident somewhat non-parallelly on the image plane. In such a case, for example, it is possible to provide an aspherical surface on the object S1 side of the lens L1 and use a meniscus lens member on the linear surface S2 side. However, it is easier to manufacture when both surfaces are formed with an aspheric surface than when only one side is formed with an aspheric surface. In this case, since the concave mirror M1 functions as a convex lens, the non-concave mirror M1 is adjusted according to the value of the positive spherical aberration generated in the concave mirror M1 at each incident height of the concave mirror M1 corresponding to each half-arc image height of the correction area h. Negative spherical aberration is generated in the corresponding incident light of the spherical lens L1. Therefore,
If the shape of the aspherical lens L1 is selected so that the positive and negative spherical aberrations cancel each other out at each image height in the correction area h, the chief ray parallel to the optical axis O at each image height will be directed to the center O2 of this optical system. It will be incident. In other words, when the infinity chief ray at each image height within the correction area h is corrected so that it is always focused on the center O2 of the optical system,
Due to the symmetry at the center O2, the astigmatism of the entire reflective optical system is corrected. Since the correction area h in FIG. 2 is determined by the relationship between the inclination of the sagittal image surface s and the meridional image surface m and the permissible depth, it is necessary to correct astigmatism, that is, the astigmatism of the sagittal image surface s and the meridional image surface m. Eliminate the gap,
An aspherical lens L1 is employed to reduce the field curvature of each image plane within the correction area h, thereby making it possible to enlarge the correction area h and increase the slit width. Note that the number of this aspherical lens L1 is 1.
There is no particular problem in using a plurality of these instead of one. 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, , chromatic aberration and other aberrations caused by the glass thickness of the aspherical lens L1 cannot be ignored. Therefore, by making the convex mirror M2 a back mirror and further making it aspherical, the aspherical lens L
This made it possible to correct chromatic aberration and lateral aberration caused by the introduction of 1. That is, the aspherical lens L
1, the chromatic aberration is corrected by using the convex mirror M2 as a back mirror, and the lateral aberration is corrected by the aspheric surface formed on the reflective surface of the convex mirror M2. In Fig. 1, the principal ray parallel to the optical axis O at each image height within the correction area h is always incident on the center O2 of the convex mirror M2 due to the action of the aspherical lens L1, so even if the convex mirror M2 is aspherical, the principal ray 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 almost concentric, and the aspherical lens L
1 is a slightly convex lens whose surface on the concave mirror M1 side is an aspherical surface, and the portion through which each chief ray in the correction area h passes forms a negative component. The correction of chromatic aberration caused by the introduction of the aspherical lens L1 is as follows:
This can be done using the positive component of the back mirror. As mentioned above, Fig. 2 is the astigmatism diagram, and Fig. 3 is the astigmatism diagram.
Figures a and b are lateral aberration diagrams when the amount of asphericity of the convex mirror M2 is changed for wavelengths of 365 nm, 290 nm, and 632.8 nm. 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 axial thickness or air gap of the i-th optical member, and the positive and negative signs indicate that the light travels from the left. The part that progresses to the right is considered positive, and the material names on the right side of the table indicate the lens constituent materials.

【table】

[Table] Tables 2 and 3 are modified examples of the first embodiment in which the numerical values regarding the convex mirror M2 are slightly changed, respectively, and lateral aberration diagrams are shown in FIGS. 4 and 5, respectively. .

【table】

【table】

[Table] Figures 6, 7, and 8 a and b show the configuration diagram, astigmatism diagram, and lateral aberration diagram of the second embodiment, and the concave mirror M1 and the aspherical convex mirror M2 are almost concentric. and
The refractive surface of the convex mirror M2 is an aspherical surface. The aspherical surface portion through which the principal ray of each image height passes within the correction region h is formed to have a more negative component than the reference spherical surface as the image height becomes higher, that is, as the refractive power of the concave mirror M1 becomes larger. has been done. Table 4 shows numerical examples of this second embodiment.

【table】

[Table] Also, Tables 5 and 6 are modified examples of the second embodiment in which the numerical values regarding the convex mirror M2 are slightly changed, and Figs. 9 and 10 show lateral aberration diagrams, respectively. .

【table】

【table】

[Table] In addition, in these tables, aspherical lens L
1, the aspherical amount ΔS of L2 is ΔS=(ΔRH2−
Defined as ΔRH1)/ΔH. Here, ΔH is the first
As shown in Figure 1a, H2-H1 with aspherical lens L
It shows the semi-arc shaped good image area given by ΔRH1,
ΔRH2 is the height H1, H as shown in Figure 11b.
2 represents the aspherical amount from the reference spherical surface. Note that the solid line A in b indicates a reference spherical surface centered at point O3, and the dotted line B indicates an aspherical surface. As can be seen from these tables, the aspherical amount ΔS of an aspherical lens is between 1/10 ⁴ and 1/10, and when ΔS is smaller than 1/10 ⁴ , the amount of change in the aspherical surface is small. As a result, the effect of the aspherical surface is weakened and a wide slit width cannot be obtained. Also, ΔS is 1/10
If it becomes larger, the amount of change in the aspherical surface increases, the sagittal image surface s and the meridional image surface m become separated, and a wide slit width cannot be obtained. Also, the aspherical amount Δx of the convex mirror M2 is
When the effective diameter of M2 is D and the aspherical amount obtained from the reference spherical surface of the convex mirror M2 at a height of 70% of the effective radius of the convex mirror M2 from the optical axis as shown in Fig. 11b is ΔR, then ΔR/D and Defined. The aspheric amount Δx is between 9/10 ⁶ and 8.6/10 ⁵ , and when Δx becomes smaller than 9/10 ⁶ , the effect of the aspheric surface decreases, and Δx
If it is larger than 8.6/ ¹⁰⁵ , the amount of change in the aspherical surface will increase, making it impossible to obtain a wide slit width. Furthermore, from these tables, it can be seen that the allowable value of the aspherical amount ΔS of the aspherical lens changes depending on the size of the reference spherical surface. That is, the reference sphere |R| is 1000
When it is larger than mm, the aspherical amount ΔS is between ^1/103 and 1/10, and if ΔS exceeds these lower and upper limits, the same disadvantages as in the case described above will occur. . Furthermore, if the reference sphere |R| is less than 200mm,
ΔS is between 1/10 ₄ and 1/10 ³ , and similar disadvantages occur when these lower and upper limits are exceeded. Assuming that the Atsube numbers of the glasses constituting the two optical parts of the aspheric lenses L1 and L2 are ν ₁ and ν ₂ , it is desirable to satisfy the following conditions: 60<ν ₁ <100 60<ν ₂ <100. When the Abbe numbers ν ₁ and ν ₂ are smaller than the lower limit value 60, the occurrence of chromatic aberration increases and the usable wavelength range is extremely narrowly limited. Note that optical glasses with Atsube numbers ν ₁ and ν ₂ larger than 100 do not currently exist. Then, to correct chromatic aberration, the radius of curvature of the refractive surface of convex mirror M2 is R4, that of its reflecting surface is R5, the effective diameter of convex mirror M2 is D, and the thickness on optical axis O is d, |R5|<|R4 It is preferable to satisfy |<|R5|+d/2. Further, it is desirable that 0.005≦d/D≦0.03 be satisfied, and if these conditions are exceeded, chromatic aberration will increase. 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. 12 and 13. FIG. 12 shows the optical arrangement of the printing apparatus, in which 1 is an optical system for illuminating the mask, and along the horizontal optical axis are arranged 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 this mask 8 to form an image of the mask 8 on a wafer 9. Note that the object side S1 and the image plane S2 side, which are symmetrical with respect to the optical axis O of the aspherical lens L, are separated from each other, unlike the previous embodiment, and mirrors 11 and 1, respectively, are separated.
2, the light beam is deflected and used. wafer 9
is held by a known wafer holder, and the wafer holder has X,
Fine adjustment is possible in the Y and θ directions. 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 thirteenth section shows the appearance of this printing device.
Explain the diagram. In FIG. 13, 20 is a lamp house, in which the illumination optical system 1 of FIG. 12 is built. 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 integrally, but the wafer 9 can move minutely relative 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 blocked 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, arm 2
5 starts moving the guide 26 in the horizontal direction. Due to this horizontal movement, the entire image of the mask 8 is transferred to the wafer 9.
It will be baked on top. In this way, according to the reflective optical system according to the present invention, the sagittal image plane s and the meridional image plane m at each image height of the correction area are corrected so as to coincide with each other over a wide range by introducing the aspherical lens, and the corrected image It becomes possible to expand the good image area at high altitudes. Further, by expanding the good image area, that is, by increasing the slit width, the exposure time can be shortened. In particular, concave mirror M
1 and the convex mirror M2, and unlike a lens configuration with only a spherical system, there is no restriction on the placement position, and it is only necessary to focus on the correction of the aspherical surface, making it possible to create a high-performance reflective optical system. is obtained. According to the embodiment, the good image area is expanded to an image height h of 100 to 90 mm, that is, a slit width of about 10 mm.

[Brief explanation of the drawing]

The drawings show an embodiment of the reflective optical system according to the present invention. FIG. 1 is a configuration diagram of the first embodiment, FIG. 2 is an astigmatism diagram thereof, FIGS. 3a and b are lateral aberration diagrams, and FIG. 4
5 and 5 are lateral aberration diagrams in a modification of the first embodiment, respectively, and FIG. 6 is a configuration diagram of the second embodiment,
Figure 7 is an astigmatism diagram, Figures 8a and b are lateral aberration diagrams, Figures 9 and 10 are lateral aberration diagrams of a modified example of the second embodiment, and Figures 11a and b are lateral aberration diagrams. FIGS. 12 and 13, which are explanatory diagrams of the aspherical amount ΔS, are configuration diagrams 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, L1, L
2, L is the aspherical lens, h is the correction area, O2 is the center of the convex mirror, ΔH is the good image area, s is the sagittal image surface,
m is the meridional image plane, 1 is the illumination optical system, 8
is a mask, 9 is a wafer, 10 is a reflective optical system, 1
3 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, a first optical member is provided between the concave mirror and the subject, a second optical member is provided between the concave mirror and the image plane, and light is emitted from each point of the subject parallel to the optical axis. The light ray is reflected by the concave mirror via the first optical member, and then reflected at the intersection of the convex mirror with the optical axis, and after being reflected at the intersection of the convex mirror and the optical axis, it is reflected by the concave mirror. At least the passing surface of the first optical member is made an aspherical surface so that the light beam is incident on the image plane parallel to the optical axis via the second optical member, and the first and second optical members A reflective optical system characterized in that the convex mirror is provided with a refractive surface on its surface in order to correct chromatic aberration occurring in the member, and is a back reflecting mirror that satisfies the following conditions. |R5|<|R4|<|R5|+d/2 0.005≦d/D≦0.03 Here, R4 is the radius of curvature of the refractive surface of the convex mirror, R5 is the radius of curvature of the reflective surface of the convex mirror, and d is the refractive surface. and the axial wall thickness between the reflecting surface and D is the effective diameter of the convex mirror. 2. Claim 1: At least one of the reflecting surface and the refractive surface of the convex mirror is made an aspherical surface in order to correct lateral aberrations occurring in the first and second optical members.
Reflective optical system as described in Section. 3. The reflective optical system according to claim 2, wherein an aspherical surface is formed on the reflective surface of the convex mirror, and the aspherical surface of the first optical member and the aspherical surface of the convex mirror satisfy the following conditions. . 1/10 ⁴ ≦ | (ΔRH2 − ΔRH1) / ΔH | ≦ 1/10 9/10 ⁶ < ΔR/D < 8.6/10 ⁵ Here, ΔH is the height H1 from the optical axis where the subject is located and the height The width of the area surrounded by H2,
ΔRH2 and ΔRH1 are the deviations in the radial direction of the aspherical surface from the reference spherical surface at heights H1 and H2, with the direction in which the negative refractive power increases with respect to the reference spherical surface as positive, and D is the deviation of the reference spherical surface in the radial direction from the reference spherical surface at heights H1 and H2. effective diameter of,
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. 4 When the radius of curvature of the reference spherical surface is R, claim 3 satisfies the following conditions.
Reflective optical system as described in Section. If ^{| R} | /10 ³ 5 After the light rays emitted parallel to the optical axis from each point of the object together with the first optical member are reflected by the concave mirror via the first optical member, the intersection of the convex mirror with the optical axis the second optical member so as to be reflected by the concave mirror and incident on the image plane parallel to the optical axis via the second optical member. A reflective optical system according to claim 3 or 4, wherein the optical member is a meniscus lens. 6. Reflecting the light rays emitted parallel to the optical axis from each point of the subject together with the first optical member by the concave mirror via the first optical member, and then reflecting at the intersection of the convex mirror with the optical axis. , and the second optical member is configured to be reflected at an intersection of the convex mirror with the optical axis, then reflected by the concave mirror, and incident on the image plane parallel to the optical axis via the second optical member. 5. The reflective optical system according to claim 3, wherein said light beam passing surface has an aspherical surface that satisfies said conditions.