RU2305857C1 - Objective with telecentric ray path - Google Patents

Abstract

FIELD: optics.

SUBSTANCE: objective has five lens groups. Objective is provided with additional lens group, which has front focus brought into coincidence with plane of images of objective. Φv₁=φv, where Φv₁ is focal power of additional lens group, v is magnification of five lens groups and φ is focal power of whole objective. First four lens groups form first projection component (PC). Fifth lens group forms second projection component (PC₂). Magnifications VPC and VPC2 of the components meet condition of V_PC=V_PC2=(0,9+2,1). First lens group is made of two lenses; first lens is aplanatic meniscus: 0,6≤φ₁/φ≤0,7. Second and fourth lens groups have same focal powers φ_II/φ=φ_IV/φ=-0,45+-0,55. Second lens group is made in form of biconcave single lens; fourth lens group is made in form of biconcave glued lens. Third lens group is made of four positive lenses; second and third lenses of group are biconvex, and first and second lenses are menisci mounted to have their convex sides oriented in direction of biconvex lenses. Focal power of third lens group meets condition of 0,75≤φ_II/φ≤0,8. Fifth lens group is made of three lenses; first two lenses of the group have to be negative menisci mounted to have their concave sides to meet each other and third lens has to be positive meniscus. Exit pupil is removed for distance being equal at least two focal lengths of objective; front section is increased up to focal length value and "tube-infinity" condition is provided.

EFFECT: widened functional abilities.

1 dwg, 1 att

Description

The alleged invention relates to optical instrumentation and can be used in the photolithographic microelectronic industry, and, in particular, for monitoring photolithographic objects, silicon wafers, etc.

Control of the studied objects is carried out using a photoelectric microscope, the main node of which is a projection lens located in the head of the microscope.

The main requirements for the lens are:

- high aperture in the space of the object A≥0.6 ÷ 0.9;

- focal length over 20-30 mm;

- “tube-infinity”, i.e. the image of the object is at infinity;

- the front working segment S≥f ′, where f ′ is the focal length of the lens;

- telecentric ray path in the space of the object;

- remote aperture diaphragm (exit pupil), the distance to which is 1.5 ÷ 2f ′, necessary for the installation of amplitude and phase plates;

- linear field of the lens 2Y≥0.2 ÷ 0.3f ′;

- distortion - less than 0.3 ÷ 0.4%;

- diffraction-limited image quality over the entire field, i.e. the mean-square deformation of the wavefront for all points of the field should be less than 0.07λ, where λ is the working wavelength.

Classical microscopes with visual and photoelectric recording channels are known, which use lenses [1] with A≥0.6, with a telecentric ray path, a tube-infinity.

A feature of all microscope lenses is their small focal lengths. So, for example, - objects 40 × 0.65 [2] with A = 0.65 has a focal length f ′ = 4 mm. Image quality corresponds to diffraction only for the center of the field, and for the edges of the field it deteriorates significantly even for lenses with plan-correction of aberrations. Moreover: the front segment is S ′ <0.4 ÷ 0.5f ′, and the size of the object is 2Y≤0.1 ÷ 0.2f ′.

In addition, if the lens is proportionally converted to f = 30 ÷ 40 mm, i.e. increase by 8-10 times, the lens aberrations proportional to the focal length also increase by 8-10 times. The image quality of such a lens becomes unsatisfactory.

Therefore, despite the external similarity, the lenses of classical microscopes or lenses proportionally converted from them to large values of f ′ cannot be used for photoelectric microscopes to control photolithographic objects.

Known optical imaging system and a lens for ultraviolet (UV) radiation [3], containing a collimating lens that collimates the light emanating from a UV radiation source, and a lens that forms an image

In this case, the back focal point of the collimating lens is extended and located in its image space, the front focal point of the forming lens is inside the lens itself.

The rear focal point of the collimating lens coincides with the front focal point of the forming lens, and aperture is set in this plane.

The system includes a forming lens containing three groups of lenses, the first of which consists of negative lenses, the second group of positive lenses, and the third group of positive lenses in which there is at least one negative lens, and they are installed in the specified order from the side of the light source.

A known projection optical system, a projection exposure device and a projection exposure method [4], which are designed to project an image of an object located in the space of objects in the space of images.

The system comprises at least one first refractive optical element containing a first fluorine compound, at least a second refractive optical element containing a second fluorine compound.

A known projection exposure device for microlithography [5], containing a refractive projection lens made of one lens material for a wavelength of less than 200 nm and a bandwidth of less than 0.3 pm

The projection lens forms an image with a maximum size of 12 to 25 mm, and the numerical aperture on the image side is in the range from 0.75 to 0.95 and provides monochromatic correction of the wavefront to rms <15% of the wavelength of the light source (λ≈157 nm).

In addition, the projection lens consists of five lens groups, while the second and fourth lens groups have negative refractive power, and the first group has at least one lens with an aspherical surface.

The lenses of the projection lens are made of fluoride.

Known projection lens [6], consisting of five groups of lenses, and at least two adjacent lenses have aspherical surfaces, forming a double aspherical lens.

A dual aspherical lens is mounted at a distance from the image plane corresponding to the maximum diameter of the lens.

A common drawback of these lenses is:

- the aperture diaphragm is located inside the lens,

- not satisfied the condition "tube-infinity",

- the front segments S are significantly smaller than the focal lengths f ′.

Known lenses close to those proposed for their intended use, used in photolithographic projection systems.

They have:

- high aperture A≥0.6 ÷ 0.9:

- telecentric ray path in the lens space;

- the front segment S, close to f ′, with f ′ = 20-30 mm;

- - 2y≥0.2 ÷ 0.3f ′.

- distortion <0.2-0.3%;

- diffraction image quality throughout the field.

In most cases, such lenses are monochromatic and operate at the same wavelength.

Closest to the claimed technical solution is the projection lens of the projection exposure system [7], which consists of five lens groups (LG), of which the second and fourth have negative optical power.

The first lens group I includes five lenses and has a positive optical power, the second lens group II includes six lenses and has a negative optical power, the third lens group III consists of six lenses and has a positive optical power, the fourth lens group IY consists of two lenses and has a negative optical power and the fifth lens group Y is a complex component with a large number of lenses and has a positive optical power.

The disadvantage is:

- image of the object at a finite distance, and not at infinity, which limits the use of the lens in photoelectric microscopes;

- a small value of the front segment S <0.2f ′, which does not allow direct illumination of the object in front of the lens;

- the aperture diaphragm (AD) is placed inside the lens, which limits the operational capabilities of the lens: the ability to install amplitude and phase plates in the AD plane.

The main task to which the invention is directed is to expand the functionality of the lens by ensuring that the exit pupil is taken out by a distance of at least two focal lengths of the lens, increasing the front segment to a value of the order of the focal length, and ensuring the “tube-infinity” condition.

To solve this problem, a lens with a telecentric ray path is proposed, which, like the prototype, contains five lens groups, the second and fourth of which have negative optical powers.

In contrast to the prototype, the lens is equipped with an additional two-lens group, the front focus of which is combined with the image plane of the lens, while:

Ф _VI = φv,

where f _VI - the optical power of the additional lens group;

v - an increase in five lens groups;

φ is the optical power of the entire lens,

in addition, the first four lens groups form the first projection component (1PC), and the fifth lens group forms the second projection component (2PC), the magnifications of which satisfy the condition:

V _1PC = -V _2PC = (1.9 ÷ 2.1), where

V _1PC - an increase in the first projection component;

V _2PC - an increase in the second projection component,

moreover, the first lens group is made of two lenses, the first of which is an aplanatic meniscus, with 0.6≤φ ₁ / φ≤0.7, the second and fourth lens groups have the same negative optical power φ _II / φ = φ _IV / φ = -0.45 ÷ -0.55, while the second lens group is made in the form of a biconcave single lens, and the fourth lens group is made in the form of a biconcave glued lens, the third lens group is made in the form of four lenses with positive optical forces, while the second and the third lens is biconvex, and the first and four Single - a meniscus established convex sides to the lenticular lens, the optical power of the third lens group satisfies condition 0,75≤φ _1II / φ≤0,8, the fifth lens group is formed of three lenses, the first two of which - with menisci negative optical forces set by the concave sides towards each other, and the third lens is made in the form of a positive meniscus, with 0.35≤φ _V / φ≤0.4.

The essence of the invention lies in the fact that, thanks to the proposed scheme of the lens, consisting of five lens groups and an additional sixth lens group, and five lens groups project an object with a negative magnification V _{I, II, III, IY, Y} in the plane of the intermediate image, combined with the front focus of the additional group, which provides:

что позволяет построить объектив с большим передним отрезком (S), величина которого S≥f′ при любом значении f′;- getting the focal length of the entire lens

that allows you to build a lens with a large front segment (S), the value of which S≥f ′ for any value of f ′;

- the removal of the exit pupil at a distance of more than 2f ′ from the last surface of the system.

Thus, the combination of the above features allows us to solve the problem.

The essence of the invention is illustrated by the drawing, which shows the optical diagram of the lens with a telecentric path of rays, and the Appendix, which shows the design parameters and optical characteristics of the lens.

A lens with a telecentric ray path contains six lens groups (LG I, LG II, LG III, LG IY, LG Y and LG YI), the second and fourth of which have negative optical powers.

The front focus of the additional LG YI is aligned with the image plane of the lens, while the condition:

Ф _VI = φv,

where Ф _VI - optical power of additional LG YI;

v - an increase in five lens groups;

φ is the optical power of the entire lens.

The first four lens groups (LG I, LG II, LG III and LG IY) form the first projection component (1PC), and the fifth lens group (LG Y) forms the second projection component (2PC), the increases of which satisfy the condition:

V _1PC = -V _2PC = (1.9 ÷ 2.1),

where V _1PC - an increase in the first projection component;

V _2PC - an increase in the second projection component.

The first lens group (LG I) is made of two lenses 1 and 2, the first of which is the aplanatic meniscus 1, with 0.6≤φ ₁ / φ≤0.7.

The second lens group (LH II) is made in the form of a biconcave single lens 3.

The third lens group (LG III) is made in the form of four lenses 4, 5, 6 and 7 with positive optical forces, while the second lens 5 and the third lens 6 are biconvex, and the first lens 4 and the fourth lens 7 are in the form of menisci installed convex sides to biconvex lenses, while the optical power of the third lens group satisfies the condition:

0.75≤φ _1II / φ≤0.8.

The fourth lens group (LG IY) is made in the form of a biconcave glued lens 8-9.

The second and fourth lens groups have the same negative optical power φ _II / φ = φ _IV / φ = -0.45 ÷ -0.55.

The fifth lens group (LG Y), the second projection component, is made of three lenses, the first two are 10 and 11, of which menisci with negative optical forces are installed with concave sides facing each other, and the third lens 12 is made in the form of a positive meniscus, this 0.35≤φ _V / φ≤0.4.

The sixth lens group (LG VI), an additional component, is a two-lens non-glued lens, the first lens 13 of which is made in the form of a negative meniscus of glass with a refractive index n _d ≥1.8, and the second 14 is in the form of a biconvex lens made of fluorite.

The operation of the lens with a telecentric ray path is as follows.

1PC designs an object with a negative increase in V _1PC , and 2PCs with a positive V _2PCs , so 1PC and 2PC aberrations have opposite signs, and if V _1PC = -V _2PC, = 1.9 ÷ 2.1, then the best mutual compensation of 1PC aberrations and 2pcs.

1PC consisting of four lens groups (LG) is constructed according to the following principle: for LG I, the object is located near its front focus and when the condition 0.6≤φ ₁ / φ≤0.7 is fulfilled, the requirement S≥f ′ is satisfied, since the focal length of LG I corresponds to the front segment of the lens. The implementation of the first lens 1 in the form of an aplanatic meniscus reduces spherical aberration on the axis, and for field points of the object reduces the values of spherical aberration, coma and astigmatism with a large positive image curvature.

The use of LG II and LG IV with the same negative values of the optical forces φ _II / φ = φ _IV / φ = - (0.45 ÷ 0.55), made in the form of biconcave lenses - LG II - single, and LG IV - glued, allows you to minimize the curvature of the image LGI.

The third lens group (LG III) projects the image produced by LG I and LG II with a negative magnification V _III <1, and its optical power corresponds to the condition 0.75≤φ _1II / φ≤0.8. The implementation of LG III in a symmetrical design consisting of two biconvex lenses 5 and 6, on both sides of which are positive menisci 4 and 7, facing the convex sides to biconvex lenses 5 and 6, allows you to get a large positive spherical aberration, opposite in sign and close in magnitude to spherical aberration given by LH I, LH II and LH IV.

LH V forms 2PCs. The implementation of LG V from three lenses, of which the first two 10 and 11 are negative menisci, set with concave sides facing each other, and the third lens 12 is made in the form of a positive meniscus, with 0.35≤φ _V / φ≤0.4, receive:

- a positive increase in V _2PC = -V _1PC

- negative in sign and close in absolute value value of spherical aberration and image curvature to that which gives 1 PC (LG I ÷ LG IV).

In addition, LG V compensates for higher order aberrations introduced by 1PC. The design of LG V ensures the position of the exit pupil in the rear focal plane of the lens and, accordingly, the telecentric path of the rays in the space of the object.

An object located at a finite distance from LG I near its front focus is projected by LG I at a large distance. LH II gives an imaginary image near its back focus. LH III projects it into a real plane, and LH IV lengthens the posterior segment given by LH III. Thus, LG I ÷ LG IV, forming 1PC, design an object from a finite to a finite distance with a negative increase in V _1PC .

LG V, forming 2PCs, projects an intermediate image given by 1PCs to a finite distance with a positive increase in V _2PCs .

Thus, 1PC and 2PC give a real image that is aligned with the front focal plane of LG VI, which provides an image of the object at infinity.

The exit pupil (aperture diaphragm) is located 2f ′ from LG VI, and its intermediate image is located inside LG III, providing a telecentric move in the space of the object.

а заднюю апертуру 2ПК (А′_2ПК) в

раз

The design of the lens, which consists of two projection components (1PC and 2PC) with magnifications V _1PC and V _2PC , the same in magnitude equal to 1.9 ÷ 2.1, and different in sign and additional lens group VI, allows you to reduce the rear aperture of 1PC (A ′ _1PC ) V _1PC times

and the rear aperture is 2PC (A ′ _2PC ) in

time

Since the design of the lens and their constituent lens groups (LH) is largely determined by the aperture, the 2PC optical circuit is much simpler than the 1PC circuit, and the LG VI is simpler than 2PC.

Information sources

1. Russian Federation, copyright certificate No. 1509800, IPC: G02B 21/02, 1989

2. Russian Federation, utility model patent No. 37239, IPC: G02B 21/02, 2004

3. United States Patent No. 5930032, IPC: G02B 13/14, 1999.

4. USA, patent No. 6714280, IPC: G02B 13/14, 2002

5. USA, patent No. 6788471, IPC: G03F 7/20, 2003

6. United States Patent No. 6646718, IPC: G02B 3/14, G02B 13/14, 2003.

7. Germany, patent No. 10143385, IPC: G03F 7/20, G02B 13/14, 2003 - prototype.

Claims (1)

A lens with a telecentric ray path containing five lens groups, the second and fourth of which have negative optical powers, characterized in that the lens is equipped with an additional two-lens group, the front focus of which is aligned with the image plane of the lens, with: Ф _VI = φ · v, where φ _VI is the optical power of the additional lens group; v - an increase in five lens groups; φ is the optical power of the entire lens; in addition, the first four lens groups form the first projection component (PC), and the fifth lens group forms the second projection component (2PC), the magnifications of which satisfy the condition: V _1PC = -V _2PC = (1.9 ÷ 2.1), where V _1PC - an increase in the first projection component; V _2PC - an increase in the second projection component; moreover, the first lens group is made of two lenses, the first of which is an aplanatic meniscus, with 0.6≤φ ₁ / φ≤0.7, the second and fourth lens groups have the same negative optical power φ _II / φ = φ _IV / φ = -0.45 ÷ 0.55, while the second lens group is made in the form of a biconcave single lens, and the fourth lens group is made in the form of a biconcave glued lens, the third lens group is made in the form of four lenses with positive optical powers, while the second and third the lenses are biconvex, and the first and fourth the fifth — in the form of menisci installed by the convex sides to biconvex lenses, while the optical power of the third lens group satisfies the condition 0.75≤φ _1II / φ≤0.8, the fifth lens group is made of three lenses, the first two of which are menisci with negative optical forces set by the concave sides towards each other, and the third lens is made in the form of a positive meniscus, with 0.35≤φ _V / φ≤0.4.