JPS61203419A - Optical system for reflecting and reducing projection - Google Patents

Abstract

PURPOSE:To realize reflected projection with a high reduction ratio by using an aplanatic surface, a concentric reflecting surface, and a concentric refracting surface in combination. CONSTITUTION:A reflected and reduced projection optical system has the 1st partial optical system K1 and 2nd partial optical system K2; and an enlarged image of a body on a body surface O is formed on an image surface I through the optical system I and an enlarged image is further formed on an image surface I' through the optical system K2. The optical system K1 has the 1st aplanatic lens LA1, the 1st reflecting surface M1, and the 2nd aplanatic lens LA2, and the optical system K2 has a concentric lens Lc, the 2nd, the 3rd, and the 4th reflecting surfaces M2, M3, and M4, and the 3rd aplanatic lens LA3. Centers of curvature of those reflecting surfaces nearly coincide with on-axis object point positions of the respective reflecting surfaces and centers of curvature of respective refracting surface except the aplanatic surfaces are nearly coincident on at on-axis object point positions of the respective refracting surfaces; and the property that the image magnification based upon the aplanatic surfaces is the square of the ratio of refractive indexes is utilized to realize projection of high magnification.

Description

[Detailed Description of the Invention] The present invention provides a method for manufacturing integrated circuits such as ICs and LSIs.
The present invention relates to a reflective optical system for projecting and exposing a pattern of a mask (original plate) onto a wafer coated with photoresist.

(Background of the Invention) Conventionally, various configurations have been proposed as this type of reflective optical system, but since all of them have unit magnification, when used as an optical system of a projection exposure apparatus, a mask ( The original board) must be made to the same size as the actual integrated circuit,
This was accompanied by difficulties in manufacturing masks. In addition, there are optical systems that perform reduction projection using only a refractive system without using a reflective surface, but these are generally constructed from ten pieces of glass members, so the problem is that the absorption of light by the glass members increases. have.

A catoptric reduction projection optical system that can solve these problems is
Patent application No. 59-152502 by the same inventor as the present application
The application was previously filed by the same applicant. The catoptric reduction projection optical system disclosed in this prior application has a concentric reflecting surface and a refractive surface, and a curvature arranged at an object point position on the optical axis or an image point position on the optical axis of the entire optical system, or a position conjugate thereto. It was composed of a refracting surface with an infinite radius. Assuming that the materials used as refractive members have the same refractive index N, each time an aerial image is formed in the optical system, it is reduced (or enlarged) by ±1/N times (or ±N times). ) Magnification can be obtained, and by combining a partial optical system with three reflections with a concentric reflecting surface and a partial optical system with one reflection, the Petzval sum can be well corrected and excellent imaging performance can be maintained. It was something to do.

However, in the configuration disclosed in this prior application, in order to obtain a higher reduction ratio (enlargement ratio), it is necessary to use several stages of partial optical systems, which makes the configuration complicated and large. There was a drawback.

(Object of the Invention) An object of the present invention is to solve the above-mentioned problems, and to create a catoptric reduction projection optical system that has a relatively simple and compact configuration and is capable of reducing projection at a higher magnification. Our goal is to provide the following.

(Summary of the Invention) The catoptric reduction projection optical system according to the present invention uses an aplanatic surface in addition to a concentric reflecting surface to enable projection with a higher reduction ratio (higher magnification ratio).

That is, the catoptric reduction projection optical system according to the present invention is basically a coaxial optical system in which a plurality of reflecting surfaces and refractive surfaces are arranged with their centers of curvature located on the same optical axis. The refractive surfaces include aplanatic refractive surfaces,
The object point position on the optical axis of each of the plurality of reflective surfaces substantially coincides with the center of curvature of each of the reflective surfaces, and the center of curvature of each refractive surface other than the aplanatic refractive surface coincides with the center of curvature of each of the reflective surfaces. A plane refractive surface that is configured to coincide with the object point position on the optical axis of the optical system, or configured to be located at the object point position or image point position of the optical system, or at a position conjugate thereto. It is something that exists.

The specific requirements for the configuration of the present invention are summarized as follows.

(Requirement 1) The magnification of all reflective surfaces is 11 times, that is, the position of the object point on the optical axis and the position of the image point on the optical axis for each reflective surface are the same.

(Requirement 2) Regarding the refractive surface, it must be one of the following three types.

(1) Refracting surface No. 1: The position of the object point on the optical axis of the refractive surface coincides with the center of curvature of the refractive surface. That is, they form concentric refractive surfaces.

■Refraction surface 2: The object point distance of the refraction surface is S, the image point distance is S', the refraction surface of the space in front of the refraction surface is N, and the refraction index of the space behind is set as S'. When N is the radius of curvature R of the refracting surface, the relationship Ns N's'N+N'N+N' is satisfied. In other words, it forms an abrasive refractive surface.

■Refracting surface 3: It is placed at the object point position on the optical axis or the image point position on the optical axis of the entire optical system, or at a position conjugate thereto, and its radius of curvature is infinite.

The terms used in the above requirements shall be interpreted in a broad sense. That is, when we say aplanatic, we also include a more aplanatic state, and when we say concentric, we also include a more concentric state. Furthermore, in the present invention, reduction and enlargement are only differences when the positions of the image plane and object plane are reversed, and it goes without saying that they are substantially equivalent based on the principle of ray reversal. do not have.

The magnifications of the refractive surface and the reflective surface, which are the basis of the present invention, will be explained below.

As can be easily seen from Gaussian optics, a concentric reflecting surface has a magnification of -1, and a refractive surface with an infinite radius of curvature has a magnification of +
It is 1. Also, the magnification β on the concentric refractive surface. is β,=N/N', where N is the refractive index of the medium in the front space and N' is the refractive index of the medium in the rear space along the traveling direction of the light rays incident on the surface. In other words, when light enters a concentric refracting surface formed of a medium with a refractive index n from air, the magnification on this surface is 1/
On the other hand, when a concentric refractive surface formed of a medium with a refractive index of n is ejected from this medium into the air, the magnification on this surface is n.

On the other hand, the magnification β on the aplanatic refractive surface is β, = (N/N’)” It is.

That is, as shown in FIG. 2, a medium with a refractive index N and a refractive index N'
Suppose that the radius of curvature of the interface with the medium is R, and that an image Q' of an on-axis object Q at an object distance S is formed at an image distance so', then this boundary for this object Q When the surface is aplanatic, N'5o-(1+)Rso'=(1+)RN' holds true, and the magnification β for this aplanatic surface is the ratio of the object distance to the image distance. Since it is defined as s, /N, by substituting the above value, β, = (N
/N')" is obtained.

In other words, the image magnification due to the aplanatic surface is equal to the square of the ratio of the refractive index of the medium in the space in front of the surface to the refractive index of the medium in the space behind the surface.

Therefore, when light enters an aplanatic surface formed of a medium with a refractive index n from air, the magnification on this surface is (1
/n)'', and conversely, when an aplanatic surface formed of a medium with a refractive index n is ejected from this medium into the air, the magnification on this surface is nt.

The present invention focuses on the properties of such aplanatic surface,
The combination of the aplanatic surface, the concentric reflecting surface, and the concentric refracting surface enables a catoptric projection optical system with a higher reduction ratio or higher magnification.

By the way, in reflective optical systems, the advantage of arranging the optical surfaces concentrically and arranging the object point and image point in a plane that includes the center and is perpendicular to the optical axis has been pointed out for a long time. , we will give an overview of its properties in the configuration of the present invention. In particular, third-order aberration coefficients will be used to represent aberrational properties. The symbol for the third-order aberration coefficient is based on the one described in "Lens Design Method" (written by Yoshiya Matsui, published by Kyoritsu Publishing). That is, where l: spherical aberration, ■: comatic aberration, ■: astigmatism, ■ two-sphere truncated field curvature, ■=distortion aberration, and P: Peppard sum, there is the following relationship: rV=II[+P.

If the on-axis object point position of the reflective or refractive surface of interest coincides with the center of curvature of that surface, ■=■=0.

Furthermore, since the angle of incidence of the light beam in the spherical direction is always 90'' on the surface, it simply passes through without receiving regular reflection or refraction, so it is V-0.

Next, for a refractive surface with an infinite radius of curvature located at the axial object point position or axial image point position of the entire optical system, or a position conjugate thereto, the incident height of the paraxial marginal ray is h = o
By being I-II 薗■! 0 Also, since the radius of curvature is infinite, P; 0 and -m+p, rV-0.

Therefore, in an optical system consisting of a concentric reflecting surface and a refractive surface, and a refractive surface with an infinite radius of curvature located at the object point position or image point position of the entire optical system, or at a position conjugate thereto, the concentric reflecting surface and the refractive surface are By appropriately selecting the radius of curvature with the refractive surface, P=
If we make it 0, then t-n=m=p-■-.

An optical system can be realized.

The above is the content disclosed in the earlier application (Japanese Patent Application No. 59-152502).

Next, aberrations in the aplanatic refractive surface, which is a feature of the present invention, will be explained. In the aplanatic refractive surface, I=II=I[I=0. Therefore, the radius of curvature of the aplanatic refractive surface should be selected so that the Petzval sum due only to the aplanatic refractive surface cancels out and becomes almost zero. Therefore, if P-0, the curvature of the spherical field surface due only to the aplanatic refractive surface is -m+p, so it becomes V-0.

Further, it is necessary that a plurality of aplanatic refractive surfaces be provided in the optical system of the present invention, and that the Petzval sum regarding only these aplanatic surfaces be independently corrected.

That is, if the radius of curvature of the aplanatic refractive surface is RL, the refractive index of the space in front along the direction of propagation of the light ray is N1, and the refractive index of the space behind it is N8', there are no aplanatic refractive surfaces in the entire optical system. It is also a requirement of the present invention that the condition ``' Ri N!N+ ' is approximately satisfied when there is a surface.

It is also necessary that the Petzval sum for only refractive surfaces and reflective surfaces excluding aplanatic refractive surfaces be corrected. That is, when the radius of curvature of the reflective surface and refractive surface other than the aplanatic refracting surface is ri, and when the entire optical system includes the L plane of the reflective surface and refractive surface other than the aplanatic refracting surface, the refractive index is as shown above. Similarly, it is also a requirement of the present invention that the following conditions are substantially satisfied.

(Example) Hereinafter, the present invention will be described in detail based on the configuration of the illustrated example.

In the following, a case will be described in which the object plane is placed on the reduction side for convenience in design, and an image of this object is projected in an enlarged manner. As mentioned above, whether it is a reduction or an enlargement, the direction in which the light ray travels is simply reversed, and they are substantially equivalent.

The configuration of the first embodiment shown in FIG. 1A is the basic configuration of a catoptric reduction projection optical system according to the present invention, and FIG. 1B is a partially enlarged view. This first embodiment is a catoptric reduction projection optical system with a reduction ratio of about 1/3.4, and includes a first partial optical system and a second partial optical system Kg. Here, in the first partial optical system, an enlarged image of the object on the object plane 0 is formed on the image plane I, and from this enlarged object image, the second partial optical system 2 forms an enlarged image of the object on the image plane I′. The following explanation assumes that an object image further enlarged is formed. In this case, the configuration is such that the image plane (2) of the first partial optical system coincides with the object plane 0' of the second partial optical system.

This first embodiment is composed of a total of 12 refractive surfaces and reflective surfaces, and the first partial optical system includes: i) a first concentric refractor whose center of curvature coincides with the on-axis object point C0; Aplanatic first for the plane PCI and the on-axis object point C0
a first aplanatic lens L1 having an aplanatic surface RAI; ii) an axial image point C by the first aplanatic surface RAI;
1ii) a second concentric refractive surface Rez having the same center as the first reflective surface M1;
And the second concentric refractive surface Rc! A second aplanatic lens LA! having a second aplanatic surface Rat that is aplanatic with respect to the axial image point C3. It consists of

Further, the second partial optical system includes a third concentric refractive surface RCff and a fourth concentric refractive surface centered on the axial image point C8 formed by the second aplanatic surface Rkt in the first partial optical system. RC4, a concentric lens Les V) a concave second reflecting surface h whose center of curvature is the axial image point C2 of the concentric lens L; vi) a convex second reflecting surface h whose center of curvature coincides with the second reflecting surface H2; 3 reflective surface 1, vi) a fourth concave surface whose center of curvature coincides with the third reflective surface;
Reflection surface L% The third reflection surface is arranged to face the second reflection surface M2 and the fourth reflection surface.

vii) A fifth concentric refracting surface RC5 whose center of curvature is the same as the fourth reflecting surface M4, and an on-axis image point C by the fifth concentric refracting surface.
3rd aplanatic surface RA that is aplanatic to 2
It consists of a third rapeseed cleansing L having 3.

Therefore, in the above configuration, considering the conjugate relationship regarding the three aplanatic surfaces Ra1n Rag+RA3, it can be said that it is an optical system consisting of a reflective surface and a refractive surface that are substantially concentric with each other. In this embodiment, the object 0 side has a telesend link configuration.

In the configuration of the first embodiment shown in FIG. 1, the second reflective surface and the fourth reflective surface coincide on the same curved surface, resulting in a simple configuration, but the configuration is not limited to this. Moreover, although the third reflecting surface H1 and the exit surface RC4 of the concentric lens L have the same radius of curvature, there is no need to make them particularly inferior.

Specific numerical examples of the first embodiment are shown in Table 1 below. The following tables, including Table 1, show the radius of curvature, surface spacing, and refractive index of each curved surface in the order from the object surface 0 side to the final image surface 1'. In the table, the radius of curvature and refractive index of each surface are defined as positive in the direction in which the ray travels from left to right in the figure, and their positive and negative values are determined based on this. It is assumed that the light is positive in a certain medium, and negative in a medium where the traveling direction of the ray is negative. Therefore, in the configuration of the first embodiment illustrated, for example, since the light ray from the object plane 0 first travels from left to right, the object plane 0 and the first concentric refractive surface R
The distance from el and the refractive index therebetween are given as positive values. In addition, the image magnification on each surface is also listed in the table.

11 Magnification of the entire system = (1,5ν=3,375 Here, the rays are displayed in the order in which they were traced in the opposite direction, so the magnification is magnified, but it is 1 / 3.375 times This is an optical system that can perform reduced projection.

The focal length of the entire system in the first embodiment is f=243.789, which is normalized to f·1.0 to calculate the third-order aberration coefficient. Table 2 below shows the results. α is the inclination angle on the object plane of the paraxial marginal ray required for aberration calculation. , the height from the optical axis, and the inclination angle of the paraxial principal ray on the object plane. , the height from the optical axis is five. When considering the object plane as the 0th plane, h0=0. Also, since it is used in a telesend link state on the object side, α. , π. Regarding the value of α, it only has the function of multiplying the aberration coefficient by a certain constant, so here, α
・=R-1, h, =0, Sae. −〇、5. In the table, Σ represents the total of the entire system.

Table 2 (Third-order aberration coefficients of the first embodiment) From the values of the third-order aberration coefficients above, it can be seen that the optical system of the first embodiment has 4
It is clear that aberrations are well corrected.

FIG. 3A is a diagram showing the basic configuration of a second embodiment of the present invention, and FIG. 3B is a partially enlarged view. In addition to the configuration of the first embodiment described above, this embodiment has a planar refractive surface that coincides with or is close to the object surface.

The catoptric/reducing projection optical system having a plane refractive surface near the object plane or image plane has the configuration disclosed in the previous Japanese Patent Application No. 152502/1983, but this second embodiment is similar to the structure disclosed in the above-mentioned order. By adding an aplanatic refractive surface to the structure, a higher reduction ratio is possible.

In FIGS. 3A and 3B, the same symbols are given to members having the same basic functions as those shown in FIGS. 1A and 1B. In this second embodiment, the reduction rate is approximately 1/7.6.
This is a catoptric reduction projection optical system.

This second embodiment also has 1 in the first partial optical system and 2 in the second partial optical system. Each partial optical system is basically similar to the configuration of the first embodiment, but instead of having concentric refractive surfaces, each system has an infinite radius of curvature near the object plane and its conjugate surface. This is a reflective optical system having a refractive member having a flat refractive surface. The position of this plane refractive surface is placed near the object plane or image plane on the reduction side of each partial optical system, so that the image plane of the first partial optical system coincides with the object plane of the second partial optical system. The structure is as follows. Here again, the enlarged image of the object on the object plane O is converted to the image plane I by the first partial optical system.
The following description assumes that the first partial optical system Km forms an enlarged object image on the image plane I' from this enlarged object image.

The second embodiment is composed of a total of 12 refractive surfaces and reflective surfaces, and the second partial optical system Kl includes: i) a first plane refractive surface R that coincides with the object plane and an on-axis object point; C
・First aplanatic surface RA that is aplanatic to
a first refractive member P8 having I, Ii) a first reflective surface M1 of a concave surface having a center of curvature at an axial image point C1 by the aplanatic surface R1 of the first refractive member P; , a first concentric refractive surface R6 having the same center as , and a second aplanatic surface R that is aplanatic with respect to the axial image point CI by the first concentric refractive surface RCI.
It consists of a first aplanatic lens AI having a radial shape.

Also, the second partial optical system! iv) The first partial optical system has a second planar refractive surface R0 formed by the second aplanatic surface R1 in 1 that coincides with the axial image point C8 and is perpendicular to the optical axis, and a center of curvature at the axial image point Ct. V) The second refractive member P2 has a second concentric refractive surface R0 that matches the second refractive surface R0.V) The second refractive member P! vi) a concave second reflecting surface h whose center of curvature is the on-axis image point C2;
reflective surface 6, vi) a concave fourth reflective surface Me whose center of curvature is the same as the third reflective surface H2, and a third reflective surface with respect to the second reflective surface M2 and the fourth reflective surface M4; The two are placed opposite each other.

vIiii) A third reflective surface whose center of curvature coincides with the fourth reflective surface M4.
A third aplanatic surface R that is aplanatic with respect to the axial image point C1 by the concentric refractive surface RCJ and the third concentric refractive surface
2nd rapeseed cleanse LA with 0! It consists of

Therefore, in the above configuration, except for the plane refractive surface arranged almost coincident with the object plane or the image plane, if we consider including the conjugate relationship regarding the three aplanatic surfaces Ra1n Rat+Ras, they are substantially different from each other. It can be said that it is an optical system consisting of a reflective surface and a refractive surface that are configured concentrically. Note that this embodiment also has a telecentric configuration on the object 0 side.

In the configuration of the second embodiment shown in FIG. 3, the object plane 0.0' of each partial optical system is configured to match the incidence plane of each refractive member P+Pz, but there is a slight separation. is also possible.

Particularly at the final image plane of the optical system, a working distance is required to place the wafer, so it is effective to provide an air gap of several millimeters.

Specific numerical examples of the second embodiment are shown in Table 3 below. Table 3 also shows it as an enlarged projection system for convenience of design.
The radius of curvature, surface spacing, and refractive index of each curved surface are shown in the order from the object plane 0 side to the final image plane side.

Magnification of the entire system - (1,5)' -7,5938 Again, the light rays were traced in the opposite direction and displayed in the same order, resulting in an enlarged magnification, but the reduced projection of 1/7.5938 times is This is a possible optical system.

In this embodiment as well, the aplanatic refractive surface, i.e. the second,
The Petzval sum pza due to the 5th and 12th surfaces (RAI, R□, Ro) is zero as shown below.

120 1.5 1 10 The focal length of the entire system in the first embodiment is f = -184,051, which is changed to f・-1,
Normalize to 0 and 1. As in the case of the first embodiment, α
. =-1, h, -0, Sae. -〇15. The results of calculating the third-order aberration coefficient with an initial value of -1, are shown in Table 4 below.
In the table shown in 0, Σ represents the total of the entire system.

Table 4 (Third-order aberration coefficients of the second embodiment) From the values of the third-order aberration coefficients above, it can be seen that the optical system of the second embodiment also excludes distortion among the Seidel 5 aberrations, and 4
It can be seen that aberrations are well corrected.

In addition, from the table of third-order aberration coefficients above, the first example, the second example
In both examples, aplanatic refractive surfaces, that is, the second, fifth,
It is also confirmed that the Petzval sum due to the 12th surface and the Petzval sum due to the other surfaces are each independently zero.

(Effects of the Invention) As described above, according to the present invention, it is possible to achieve a reduction projection type reflective optical system with a higher reduction ratio, which is advantageous for manufacturing integrated circuits. Then, by correcting the Petzval sum independently for the aplanatic refractive surfaces, and by correcting the Petzval sum independently for other refractive surfaces and reflective surfaces, the entire optical system eliminates distortion among Seidel's 5 aberrations. It is possible to satisfactorily correct the other four aberrations related to image sharpness.

In addition, by using a reflective optical system that can perform projection at such a high reduction ratio, it is possible to create a mask (original plate) for an integrated circuit pattern larger than the actual size of the circuit, making mask manufacturing extremely difficult. In addition to being easy to manufacture, it is also very effective in manufacturing integrated circuits with finer patterns. Furthermore, even when using light in the far ultraviolet region as the exposure wavelength, there is a small number of refractive members such as glass, so there is an advantage that the transmittance is not deteriorated due to absorption by these members. Furthermore, most of the refractive power of the entire optical system depends on convex and concave reflective surfaces, so when designing with chromatic aberration in mind, it is difficult to remove chromatic aberration in the case of an optical system consisting only of a refractive system. It also has the advantage of being relatively easy.

Furthermore, the aplanatic lens of the present invention has the advantage that the centering process in the manufacturing stage thereof is easier than the concentric meniscus lens as in the embodiment described in the previous application.

[Brief explanation of drawings]

FIG. 1A is an optical configuration diagram of a first embodiment consisting of the basic configuration of a catoptric reduction type projection optical system according to the present invention, and FIG. 1B is a diagram of the first embodiment.
FIG. 2 is an explanatory diagram of magnification on an aplanatic refractive surface, FIG. 3A is a configuration diagram of a second embodiment according to the present invention, and FIG. 3B is a partially enlarged diagram of the second embodiment. . [Explanation of symbols of main parts] Rag, R□+RA! ...Aplanatic refractive surface Rcl+ RC! , RC3+ Rc4+ Rc%+
"・Concentric refractive surface 0.0'...Object surface I, I"
... Image surface L ... concave first reflecting surface K1 ... first
Partial optical system M... concave second reflective surface K...
First partial optical system h... Convex third reflecting surface h... Concave fourth reflecting surface

Claims (1)

[Claims] 1. In a coaxial optical system in which a plurality of reflective surfaces and a refractive surface are arranged with their centers of curvature located on the same optical axis, the plurality of refractive surfaces are aplanatic refractive surfaces. including, the center of curvature of the plurality of reflective surfaces substantially coincides with the on-axis object point position of each of the reflective surfaces, and the center of curvature of each of the refractive surfaces other than the aplanatic refractive surface corresponds to each of the refractive surfaces. A catoptric reduction projection optical system characterized in that it is configured to match the position of an on-axis object point. 2. In the catoptric projection optical system according to claim 1, the Petzval sum at the aplanatic refractive surface is approximately corrected independently by a plurality of aplanatic refractive surfaces, and A catoptric reduction projection optical system characterized in that the Petzval sum on a refractive surface and a reflective surface is almost independently corrected by each of these surfaces. 3. A coaxial optical system in which a plurality of reflective surfaces and refractive surfaces are arranged with their centers of curvature located on the same optical axis, and has an object surface and an image surface on a plane perpendicular to the optical axis, The plurality of refractive surfaces include an aplanatic refractive surface and a planar refractive surface provided near the image plane or the object surface or a conjugate position thereof and substantially parallel to the surface, and the center of curvature of the plurality of reflective surfaces is The center of curvature of each refractive surface other than the planar refractive surface coincides with the on-axis object point position related to each of the reflective surfaces, and the center of curvature of each refractive surface other than the planar refractive surface is the on-axis object point position related to each of the refractive surfaces. What is claimed is: 1. A catoptric reduction projection optical system, characterized in that it is configured in accordance with the above. 4. In the catoptric reduction projection optical system according to claim 3, the Petzval sum at the aplanatic refractive surface is approximately corrected independently by a plurality of aplanatic refractive surfaces, and A catoptric reduction projection optical system characterized in that the Petzval sum on a refractive surface and a reflective surface is almost independently corrected by each of these surfaces.