JPH06331942A - Projection lens system - Google Patents

Abstract

PURPOSE:To extend the effective depth of field of a projection lens system. CONSTITUTION:In a projection lens system including at least one diffractive optical element, one element 7 among the diffractive optical elements is composed of plural zones, the plural zones have mutually different image forming actions so that light beams transmitted through the plural zones form the images on at least two points 3, 4 slightly separated in the direction of an optical axis. By such constitution, plural image forming surfaces are formed by exposure at a time, consequently, the contrast of an optical image is maintained longitudinally in the direction of the optical axis and the effective depth of field is extended. By using an optical system of high resolution, the improvement of the revolving power and the extension of the depth of field are simultaneously realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection lens system used in a projection exposure apparatus (hereinafter referred to as a stepper) for exposing a fine integrated circuit pattern such as IC and LSI onto a semiconductor substrate, and more particularly to an excimer system. The present invention relates to a projection lens system effective for exposing an integrated circuit pattern onto a semiconductor substrate using a light source such as a laser having a wavelength range from ultraviolet of about 300 nm to 150 nm to vacuum ultraviolet.

[0002]

2. Description of the Related Art Conventionally, steppers have been used to expose patterns of ICs, LSIs, liquid crystal displays, thin film magnetic heads onto substrates such as semiconductors. With the recent increase in the degree of integration of integrated circuits. The projection lens system of the stepper is also required to have a higher resolution and a wider exposure area. Further, the structure of the integrated circuit has been relatively simple and flat in the past, but has become complicated with a large surface step due to high integration.

Generally, the following equation is established between the resolving power / depth of focus of a lens system, wavelength, and numerical aperture. Resolution = k ₁ · λ / NA (Equation 1) Depth of focus = k ₂ · λ / NA ² (Equation 2) where λ is the wavelength, NA is the numerical aperture, and k ₁ and k ₂ are proportional to the process. It is a constant.

Therefore, in order to improve the resolving power of the projection lens, the exposure wavelength may be shortened or the NA may be increased, but both of them cause a decrease in the depth of focus. As described above, compatibility between high resolution and large depth of focus is essentially conflicting.

In order to solve this problem, attempts have been made to achieve a high resolution and a large depth of focus by devising the exposure method and process.

One of them is the phase shift method. For the phase shift method, for example, “Monthly Semiconductor World,
June 1992 ”, the case of using a typical phase shift mask (Levenson type phase shift mask) will be described with reference to FIG. When a thin film called a shifter is provided on the mask as shown in FIG. 14 (b) and the phase of light from the adjacent openings is inverted, the diffraction angle becomes half as compared with the conventional mask of FIG. 14 (a). And the 0th order light disappears. As a result, the cut-off frequency is doubled as compared with the conventional case, and the depth of focus can be expanded.

A second technique is Japanese Patent Laid-Open No. 58-58
There is a so-called FLEX method disclosed in Japanese Patent No. 17446. In this method, the intensity distribution as shown in FIG. 15A is obtained by the first exposure, and the intensity distribution of FIG. 15B is obtained by the second exposure in which the mask image plane is imaged at different positions in the optical axis direction. obtain. These composite images are such that the optical image contrast is long in the optical axis direction as shown in FIG. 15C, and the effective depth of focus is expanded.

A third technique is Japanese Patent Laid-Open No. 2-1.
There is a method of using a phase type super resolution filter shown in Japanese Patent Laid-Open No. 109. The structure of the phase-type super-resolution filter 30 in the plane perpendicular to the optical axis is shown in FIG.
FIG. 16B shows a sectional view of the phase-type super-resolution filter 30 taken along the straight line L in FIG. For example, as shown in FIG. 16 (b), if a phase shift of half a pinch is applied at the boundary between zone A and zone B, wavefront A of zone A and zone B
A phase difference of π is generated on the wavefront B of. Therefore, if this filter 30 is installed on the pupil plane of the optical system, it functions as a phase-type super-resolution filter, so that the depth of focus can be increased.

[0009]

The above-mentioned prior art has some problems. First, the phase shift method has problems that the applicable patterns are limited and that it is difficult to manufacture, inspect, and correct defects in a highly accurate phase shift mask. On the other hand, the FLEX method is effective for an isolated pattern such as a contact hole, but is not effective for an L / S pattern. Further, since the stage is directly moved to perform the exposure a plurality of times, the throughput is deteriorated. Further, the phase-type super-resolution filter has a limit in expanding the depth of focus.
As described above, the conventional technique has some problems.

The present invention has been made to solve the above problems, and an object thereof is to increase the effective depth of focus of a projection lens system.

[0011]

In order to achieve the above object, the projection lens system of the present invention comprises a diffractive optical element (hereinafter, D).
OE: Diffractive Optical Element) at least 1
One of the diffractive optical elements in a projection lens system including one
Each of the plurality of zones has a plurality of zones, and the plurality of zones have mutually different image forming actions so that a light beam passing through the plurality of zones forms an image at at least two slightly different positions in the optical axis direction. It is characterized by.

[0012]

The operation of the projection lens system according to the present invention will be described below with reference to the drawings. As shown in the optical path in FIG. 1, the optical element 1 that simultaneously images the object 2 on different image planes 3 and 4 that are Δ apart from each other has a multifocal effect similar to the FLEX method.

Now, as shown in FIGS. 2A and 2B, there are an optical element 5 for forming an image of the object 2 on the image plane 3 and an optical element 6 for forming an image of the object 2 on the image plane 4. To do. In order to realize the multifocal effect as shown in FIG. 1, in the present invention, for example, as shown in FIG. 3, the DOE 7 including a plurality of zones is used.
The light beam incident on is split into a light beam which forms an image on the image plane 3 and a light beam which forms an image on the image plane 4. As described above, when the multifocal DOE 7 formed by a plurality of zones having different image forming effects is used, a plurality of image forming planes are formed by one exposure.
As a result, the contrast of the optical image can be maintained long in the optical axis direction, and the effective depth of focus can be increased.

Therefore, if such a multifocal DOE is used in a high resolution optical system, it is possible to simultaneously improve the resolution and increase the depth of focus.

The advantages of using a DOE as the optical element 1 having the multifocal effect of FIG. 1 will be described below. In particular, when a light source having a wavelength range from ultraviolet of about 300 nm to 150 nm to vacuum ultraviolet such as an excimer laser is used, many advantages occur.

First, it is easy to manufacture. If a refraction lens is used as an element having a multifocal effect as in the present invention, the structure of the refraction lens becomes very complicated and it is extremely difficult to manufacture. On the other hand, in the case of the DOE, the manufacturing method is the same for manufacturing the DOE having a normal imaging action and the multifocal DOE of the present invention, and there is no difference in difficulty in manufacturing.

Second, the achromatization of the projection lens system becomes easy. As can be seen from (Equation 1) above, in order to increase the resolution of the lens system, the wavelength can be shortened or the NA can be increased. However, increasing the NA is accompanied by a drastic decrease in the depth of focus and difficulty in optical design.

Therefore, in order to increase the resolution without deteriorating the depth of focus, an attempt has been made to shorten the exposure wavelength. Specifically, g-line (436 nm) and i-line (3 nm) of the ultra-high pressure mercury lamp used in the conventional stepper are used.
At 65 nm), the resolution was insufficient, so the KrF excimer laser (248 nm) and A
The rF excimer laser (193 nm) shows promise. The half width of the excimer laser light is 0.
Since it is as large as about 3 to 0.4 nm, it is necessary to achromatize the projection lens system.

However, in the wavelength region of the excimer laser light, the transmittance of ordinary glass is insufficient, so that usable glass materials are limited to quartz, fluorite, MgF _{2 and the} like.
However, since fluorite has low hardness, is easily scratched, and optical polishing is not easy, and since MgF ₂ has a problem of workability such as deliquescent, the glass material practically usable for the projection lens system is limited to quartz. Has been done.

Therefore, it is a general method to prevent the occurrence of chromatic aberration in the optical system by making the projection lens system a monochromatic design lens made of only quartz and narrowing the band of the light source. However, the optical system having such a structure has the following problems. The laser output decreases due to the narrow band. The laser becomes complicated in order to maintain the center wavelength, the half width, etc. with high accuracy.

By the way, in an ordinary optical element based on a refraction phenomenon, a light beam is Snell's law n.sin.theta. = N'.sin.theta. '(Equation 3) where n: refractive index of the medium on the incident side n': Refractive index of exit side medium θ: Incident angle of light ray θ ′: Bent based on exit angle of light ray.

On the other hand, in the case of the DOE, as shown in FIG. 4, the light beam 9 is bent by the diffraction surface 8 by the diffraction phenomenon expressed by (Equation 4).

N · sin θ−n ′ · sin θ ′ = mλ / d (Equation 4) where n: refractive index of the incident side medium n ′: refractive index of the exit side medium θ: incident angle θ ′ of the light beam : Emission angle of light ray m: Diffraction order λ: Wavelength d: Pitch of DOE As is clear from (Equation 4), in DOE, the bending angle of long wavelength light is large and the bending angle of short wavelength light is small. , Has a dispersion opposite to that of an ordinary refractive optical element. By the way, when we find the Abbe number ν _{d of} DOE, ν _d = −
It becomes 3.45, and it can be seen that it has a very large inverse dispersion. Since the difference in dispersion with quartz (Abbé number ν _d = 68) is large, use of the DOE 11 in which the diffractive surface 8 is processed on the surface of the quartz substrate 10 as shown in FIG.
Achromatization can be effectively performed with a small number of lenses. Therefore, it is possible to solve the problem of chromatic aberration that accompanies the use of the excimer laser for high resolution. The DOE 11 whose cross section is shown in FIG. 5 is blazed in order to increase the diffraction efficiency.

Thirdly, when the DOE is used, the aberration correction capability of the projection lens system is improved, and it is relatively easy to increase the NA and wide the field. In the case of DOE, in order to obtain the desired bending angle of the light beam at each part of the lens, d may be set so that the desired θ ′ is obtained in (Equation 4). The method of manufacturing a DOE equivalent to such an aspherical lens is the same as the method of manufacturing a DOE equivalent to a spherical lens, and there is no difference in the difficulty of manufacturing. That is, DOE
Can positively give an aspherical function without any problem of manufacturability, and thus has a large aberration correction capability.

[0025]

EXAMPLES Examples of the projection lens system according to the present invention will be described below. First, a method of designing an optical system including a DOE used in the present invention will be described first.

The Sweat model is known as a method for designing an optical system including a DOE. For this,
"WCSweatt," NEW METHODS OF DESIGNING HOLOGRAPHI
C OPTCALELEMENTS ", SPIE, Vol.126, pp.46-53 (1977)
], But will be briefly described below with reference to FIG.

In FIG. 6, 12 is a refraction lens (ultra-high index lens) with n >> 1, 13 is a normal line, z is a coordinate in the optical axis direction, and h is a coordinate along the substrate. According to the above paper, (Equation 5) holds.

(N _u −1) dz / dh = n · sin θ−n ′ · sin θ ′ (Equation 5) where the refractive index of n _u : ultra-high index lens (in the design described below, n _u = 10001.) z: Coordinate in the direction of the optical axis of the ultra-high index lens h: Distance from the optical axis n: Refractive index of the incident side medium n ': Refractive index of the exit side medium θ: Incident of light ray Angle θ ′: Exit angle of light ray Therefore, from (Equation 4) and (Equation 5), the following (Equation 6) is established.

(N _u −1) dz / dh = mλ / d (Equation 6) That is, “n >> 1 surface shape of refraction lens” and “D
Since the equivalence relation expressed by (Equation 6) is established between the “OE pitch”, the ultr designed by the Sweatt model
The DOE pitch distribution can be obtained from the surface shape of the a-high index lens.

Specifically, assuming that the ultra-high index lens is designed as an aspherical lens defined by (Equation 7), z = ch ² / {1+ [1-c ² (k + 1) h ² ] ^{1 / 2} } + Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰ (Equation 7) where, z: deviation from the tangent plane contacting the lens on the optical axis (sag value) c: curvature h: distance from optical axis k: conical constant A : 4th-order aspherical coefficient B: 6th-order aspherical surface coefficient C: 8th-order aspherical surface coefficient D: 10th-order aspherical surface coefficient From (Equation 6) and (Equation 7), d = mλ / [(n-1) dz / dh] = [mλ / (n-1 )] × [ch 2 / {1+ ^{[1-c 2 (k + 1} ) h 2 ] ^{1/2} + Ah 4 + Bh 6} + ch 8 + Dh 10] -1 ... ( equation 8) Is obtained. The DOE pitch d distribution may be determined according to this (Equation 8). In the embodiments described below, only the 10th-order aspherical terms are used, but of course 12th-order, 14th-order aspherical-terms may be used.

(First Example) Numerical data of the projection lens system 14 using the DOE in this example will be described later.
The sectional view is shown in FIG. In FIG. 7, reference numeral 15 is a multifocal DOE of the present invention, and the structure of the DOE 15 is shown in FIG.
Shown in.

As shown in FIG. 8, the DOE 15 of the present embodiment.
Is divided into a plurality of annular zones 19 and 20 having a predetermined width such that the areas of each zone are equal, each zone having a slightly different imaging effect. Here, the ring zone 19 has an image forming action corresponding to 5 in FIG. 2A, and the ring zone 20 has an image forming action corresponding to 6 in FIG. 2B. As described above, the multi-focus DOE 15 in which the annular zones having different image forming actions are alternately arranged in the radial direction has the image forming action corresponding to 7 in FIG. That is, among the light fluxes emitted from the object point, the light flux that has passed through the ring zone 19 is at the image point a, and the light flux that has passed through the ring zone 20 is away from the image point a by Δ in the optical axis direction. Focus on the image point b. Therefore, when a mask image is formed by the projection lens system 14 including the multifocal DOE 15, the light intensity distribution with respect to defocus is greatly improved, and the effective depth of focus is expanded.

When the DOE 19 corresponding to 5 in FIG. 2 (a) is used (when the DOE 15 is composed only of the annular zone 19) and when the DOE 20 corresponding to 6 in FIG. 2 (b) is used (DOE 15 is (When configured with only the ring zone 20)
The relationship between the defocus and the on-axis MTF is shown in (a) and (b) of FIG. 9, respectively. The spatial frequency of the MTF is 1900 lines / mm, which is about half the cutoff frequency, and the separation amount Δ of each best image plane is Δ = 1 μm. The curves (a) and (b) corresponding to the two focal points exhibit good characteristics of co-diffraction limit, and can be sufficiently used as a high resolution stepper lens. this is,
It reflects the high aberration correction capability of DOE.

At this time, the amount of separation Δ of the image plane and the width and number of each zone may be optimized according to the actual use condition, for example, the resolution of the projection lens system used and the fineness of the pattern to be exposed. . In the case of double focus, if Δ is too large, 2
The image light intensity between two image planes deteriorates. Therefore, it is preferable that 0 <Δ <3λ / NA ² .

In this embodiment, the areas of the zones are made equal in order to make the light amounts of the image planes of the double focus equal.
The area of each zone may be unequal.

Further, in the present embodiment, the DOE 15 is given the double focus action, but it is of course possible to give the DOE 15 a multiple focus action such as a triple focus and a quadruple focus.

The multi-focus DOE 15 is blazed in each region so that the image-forming light can efficiently pass through each of the ring zones 19 and 20. Alternatively, for example, as shown in Japanese Patent Application Laid-Open No. 2-1109, "Exposure →
By repeating the process of “etching (or deposition)” n times, the cross-sectional shape of each ring of the DOE 15 is 2 ^n.
It is also possible to make it in a stepped shape and approximate it to a blaze.

Details of the projection lens system 14 shown in FIG. 7 will be described below. When the DOE 19 corresponding to 5 in FIG. 2A is used (when the DOE 15 is composed of only the ring zone 19), the DOE corresponding to 6 in FIG. 2B.
FIGS. 10 and 11 are aberration diagrams showing spherical aberration, astigmatism, distortion, and coma, respectively, when 20 is used (when the DOE 15 is composed of only the annular zone 20). The reason why such good aberration correction is performed will be described.

Correction of Petzval sum is important for designing a wide field lens as in this embodiment. Figure 7
The projection lens system 14 includes a lens group 16 composed of the lens L7 and the lens L8, and a lens group 17 composed of the lens L12 and the lens L13, two lens groups having concave surfaces facing each other. , 17, a convex lens group 18 is arranged. With this configuration, the height of the light beam on the concave surface is made relatively small, and the concave power of this concave surface is strengthened to correct the Petzval sum. Further, since the DOE 15 is equivalent to a refractive lens having an infinite refractive index, the Petzval sum does not deteriorate at all.

Generally, in the case of a stepper lens, correction of spherical aberration is particularly important. As chromatic aberration, it is important to correct the movement of the Gaussian image plane (axial chromatic aberration) due to wavelength fluctuation. Therefore, the DOE is effective near the pupil or where the marginal ray height is large, which is effective for correcting spherical aberration and axial chromatic aberration.
Is effective, so in this embodiment, the DOE 15 is arranged at a location where the height of the marginal ray is large.
Further, the DOE 15 in the present embodiment produces a large aberration having a sign opposite to that of the aberration occurring in the refracting system due to the aspherical surface action, and satisfactorily corrects the aberration of the lens system. For the reasons described above, the projection lens system 14 achieves good performance.

Further, the projection lens system 14 of the present embodiment is image-side (wafer-side) telecentric in order to prevent a change in image shape due to defocus.

The exit pupil position is naturally different between the case where the DOE 19 corresponding to 5 in FIG. 2A is used and the case where the DOE 20 corresponding to 6 in FIG. 2B is used.
In this embodiment, the difference between the exit pupil positions is about 0.2 μm, which is a level that poses no practical problem. Further, there is little pupil aberration, and there is no practical problem.

In this embodiment, in order to increase the DOE aberration correction effect, the DOE 1 is set at a portion having a relatively large light beam diameter.
5 is used, but if one does not want to use a DOE having a large outer diameter, the DO having the multifocal effect of the present invention is used.
E15 may be arranged in the vicinity of the pupil where the light beam diameter is relatively small.

The numerical data of this embodiment are shown below. The surface number is a serial number counted from the object side of the lens surface,
Ultr, which is equivalent to DOE15 in the surface number, as described above
The number of the lens surface of the a-high index lens is included. R
Is the radius of curvature, d is the surface spacing, VM is the glass material, and the glass material name DO
E indicates a virtual glass material forming the above ultra-high index lens. Here, the refractive index of the virtual glass material forming the ultra-high index lens is 10001, and the refractive index of quartz is 1.5.
08379. Further, λ is the wavelength, NA is the numerical aperture, φ is the diameter of the exposure area, □ is the length of one side of the exposure area,
β is a magnification, and OID is a distance between object images. The 33rd surface of this embodiment is an aspherical surface, and the aspherical surface shape is defined by (Equation 7). The DOE is defined by the 31st and 32nd surfaces.
In the 15th substrate, the ultra-high index lens that represents the diffractive surface is defined by the 33rd surface and the 34th surface. In the present embodiment, in order to achieve high resolution as described above, KrF
The excimer laser is used as the exposure light source. In the case of this embodiment, the minimum pitch of the DOE 15 is about 4.2 μm (+1
In the case of next light) and the value that can be manufactured.

First Embodiment λ = 248 nm, NA = 0.48, φ = 36 mm (□ 25 mm),
β = 1/5, OID = 800 mm Surface number R d VM Object point ∞ 120.000 1 -167.091 10.000 Quartz 2 -220.301 0.100 3 391.804 10.000 Quartz 4 143.316 10.955 5 392.338 10.000 Quartz 6 173.912 11.404 7 1141.448 17.336 Quartz 8 -263.656 0.100 9 178.092 22.471 Quartz 10 -842.798 0.100 11 221.371 23.979 Quartz 12 -242.910 0.359 13 1269.457 10.000 Quartz 14 74.859 22.064 15 -176.106 10.000 Quartz 16 122.286 42.427 17 17 394.138 10.324 Quartz 18 175.766 30.559 20 370 20.559 20470. 22 3770.502 0.100 23 236.098 10.042 Quartz 24 141.985 27.902 25 -106.885 10.000 Quartz 26 430.396 54.720 27 10132.811 17.921 Quartz 28 -311.818 5.238 29 552.716 31.806 Quartz 30 -222.709 0.100 31 ∞ 10.000 Quartz (DOE 0.000 33) 32 32 ) (19) 2.80941 × 10 ⁷ 0.000 DOE (20) 2.80968 × 10 ⁷ 34 ∞ 0.100 35 462.221 30.751 Quartz 36 -255.706 0.100 37 120.114 50.000 Quartz 38 526.404 4.447 39 177.603 27.882 Quartz 40 58.574 13.389 41 135.821 10.000 Quartz 42 72.347 0.100 43 57.087 13.499 Quartz 44 74.847 31.119 45 82.137 10.000 20.00 47 179 47. -99.190 10.000 Quartz 50 -317.487 12.000 Image plane ∞ Aspheric coefficient 33rd surface (DOE19) 33rd surface (DOE20) R = 2.80941 × 10 ⁷ R = 2.80968 × 10 ⁷ k = -1 (parabolic surface) k =- 1 (parabola) A = -3.22280 × 10 ^-12 A = -3.22278 × 10 ^-12 B = -1.06989 × 10 ^-17 B = -1.07041 × 10 ^-17 C = -2.48146 × 10 ^-22 C = -2.47291 × 10 ^-22 D = -1.88973 × 10 ^-26 D = -1.89479 × 10 ^-26
.

(Second Embodiment) Multifocal DOE of this embodiment
21 is shown in FIG. In the multi-focus DOE 21, the zone groups 22 having the first image forming effect and the zone groups 22 having the second image forming effect are alternately arranged in the radial direction. Then, as shown in FIG. 16B, at the boundary between the area A and the area B,
The connection deviation of half a pitch is given. As a result, area A
There is a phase difference of π between the wave front passing through the region B and the wave front passing through the region B. Therefore, by arranging the DOE 21 of the present embodiment on the pupil plane of the optical system, it is possible to further increase the effective depth of focus and improve the resolving power by the phase-type super-resolution filter effect and the multifocal effect. it can.

In this embodiment, there are only two regions where the phase difference is generated, that is, the regions A and B, but the number of regions may be increased to three or more, and the phase difference is π. Any value other than can be used. Unlike the refraction-type optical element, the DOE can easily have such a complicated image forming action without a problem of manufacturability.

(Third Embodiment) In this embodiment, in order to prevent a light beam having a specific aperture ratio from forming an image only on a specific image plane, as shown in FIG. Dividing is performed so that each divided area on one ring zone contributes to the formation of each of the plurality of image planes formed. The other structure is the same as that of the first embodiment.

[0049]

As described above, since the projection lens system of the present invention is a multifocal lens in which the DOE is formed of a plurality of zones having different focal lengths, a plurality of imaging planes can be formed by one exposure. Is formed. As a result, the contrast of the optical image can be maintained long in the optical axis direction, and the effective depth of focus can be increased. Therefore, by using a high-resolution optical system, it is possible to simultaneously improve the resolution and increase the depth of focus.

[Brief description of drawings]

FIG. 1 is a diagram showing an optical path of an optical element having a multifocal effect used in the present invention.

FIG. 2 is a diagram showing each imaging action of the optical element of FIG.

FIG. 3 is a conceptual diagram of a diffractive optical element having a multifocal effect used in the present invention.

FIG. 4 is a diagram for explaining the principle of the diffractive optical element.

FIG. 5 is a sectional view showing one form of a diffractive optical element.

FIG. 6 is an ultra-high index lens corresponding to a diffractive optical element.
It is explanatory drawing of s.

FIG. 7 is a sectional view of a first embodiment of the projection lens system of the present invention.

FIG. 8 is a front view of the diffractive optical element in the first example.

FIG. 9: Defocus and MT by each ring zone of the first embodiment
It is a figure which shows the relationship of F.

FIG. 10 is an aberration diagram showing spherical aberration, astigmatism, distortion, and coma aberration of an image formed by passing through one ring zone in the first example.

FIG. 11 is an aberration diagram similar to FIG. 10 for image formation passing through the other annular zone in the first example.

FIG. 12 is a front view of a diffractive optical element having a multifocal effect according to a second example.

FIG. 13 is a front view of a diffractive optical element having a multifocal effect according to a third example.

FIG. 14 is an explanatory diagram of a conventional phase shift method.

FIG. 15 is an explanatory diagram of a conventional FLEX method.

FIG. 16 is an explanatory diagram of a conventional phase-type super-resolution filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Optical element which has a multifocal effect 2 ... Object 3 ... 1st image surface 4 ... 2nd image surface 5 ... Optical element which forms a 1st image surface 6 ... Optical element which forms a 2nd image surface 7 ... DOE having a multifocal effect 8 ... Diffractive surface 9 ... Rays 10 ... DOE substrate 11 ... Blazed DOE 12 ... Ultra-high index lens 13 ... Normal line 14 ... Projection lens 15 in the first embodiment 15 ... First implementation Multifocal DOE 16 in the example ... First lens group 17 with concave surfaces facing each other 17 ... Second lens group 18 with concave surfaces facing each other ... Convex lens group 19 between both lens groups 19 ... First imaging action The annular zone having 20 ... The annular zone having the second image forming action 21 ... The multi-focus DOE 22 in the second embodiment ... The annular zone having the first image forming action 23 ... The annular zone having the second image forming action 24 ... Multifocal DOE L7, L8 in the third embodiment ... Lens L12 constituting the first group of lenses, L13 ... lenses constituting the second lens group

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[Procedure amendment]

[Submission date] June 11, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] 0030

[Correction method] Change

[Correction content]

Specifically, assuming that the ultra-high index lens is designed as an aspherical lens defined by (Equation 7), z = ch ² / {1+ [1-c ² (k + 1) h ² ] ^{1 / 2} } + Ah ⁴ + Bh ⁶ + Ch ⁸ + Dh ¹⁰ (Equation 7) where, z: deviation from the tangent plane contacting the lens on the optical axis (sag value) c: curvature h: distance from optical axis k: conical constant A : 4th-order aspherical coefficient B: 6th-order aspherical surface coefficient C: 8th-order aspherical surface coefficient D: 10th-order aspherical surface coefficient From (Equation 6) and (Equation 7), d = mλ / [(n-1) dz / dh] = [mλ / (n−1)] × [ch / [1-c ² (k + 1) h ² ] ^1/2 + 4Ah ³ + 6Bh ⁵ + 8Ch ⁷ + 10Dh ⁹ ] ^-1 (Equation 8) is obtained. The DOE pitch d distribution may be determined according to this (Equation 8). In the embodiments described below, only the 10th-order aspherical terms are used, but of course 12th-order, 14th-order aspherical-terms may be used.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0046

[Correction method] Change

[Correction content]

(Second Embodiment) Multifocal DOE of this embodiment
21 is shown in FIG. In the multifocal DOE 21, zone groups 22 having a first image forming effect and zone groups 23 having a second image forming effect are alternately arranged in the radial direction. Then, as shown in FIG. 16B, at the boundary between the area A and the area B,
The connection deviation of half a pitch is given. As a result, area A
There is a phase difference of π between the wave front passing through the region B and the wave front passing through the region B. Therefore, by arranging the DOE 21 of the present embodiment on the pupil plane of the optical system, it is possible to further increase the effective depth of focus and improve the resolving power by the phase-type super-resolution filter effect and the multifocal effect. it can.

Claims (1)

[Claims] 1. In a projection lens system including at least one diffractive optical element, one of the diffractive optical elements is composed of a plurality of zones, and light beams passing through the plurality of zones are slightly different in the optical axis direction. A projection lens system characterized in that the plurality of zones have mutually different image forming actions so as to form images at positions of at least two points.