CN105652606A - Method for designing catadioptric deep-ultraviolet lithography objective lens - Google Patents

Abstract

The invention provides a method for designing a catadioptric deep-ultraviolet lithography objective lens. The method comprises the following specific process: step one, initial structures of three lens sets of the deep-ultraviolet lithography objective lens between a mask and a silicon chip are determined; step two, the initial structure of an object-space lens set G1 is set, and is enabled to meet design requirements, including that (1) the object space is telecentric, and (2) the image-space main light ray incident angle and the magnification M1 cannot cause blockage to the light path; step three, the initial structure of an image-space lens set G3 is optimized, and enabled to meet design requirements, including that (1) the image space is telecentric, (2) the object-space main light ray incident angle cannot cause blockage to the light path, and (3) the magnification M3 is equal to M/M1; step four, a middle lens set G2 is of a structure with two concave reflecting mirrors, the Petzval's sum of the object-space lens set and the image-space lens set is calculated, and radii of the two concave reflecting mirrors in the middle lens set are calculated based on the Petzval's sum; step five, structure parameters of the image-space lens set G3 are optimized, so that the entrance pupil of G3 is matched with the exit pupil of G2. The method has the advantages of high design efficiency and high implementation speed.

Description

A kind of refraction-reflection type deep-UV lithography objective designing method

Technical field

The present invention relates to a kind of refraction-reflection type deep-UV lithography objective designing method, belong to optical design techniques field.

Background technology

Deep-UV lithography is the photoetching technique of current industry. Deep-UV lithography object lens are the keys realizing high resolution lithography as the core component of deep-UV lithography machine. Deep ultraviolet wave band can optical material only remaining fused quartz and calcium fluoride, the refractive index of above two material is relatively low, and therefore the focal power of deep-UV lithography objective system needs to be assigned to and could realize aberration correction on more element. Initial deep-UV lithography adopts full folding objective lens design, and whole objective system only has refracting element without reflecting mirror. Full folding deep-UV lithography object lens are in order to correct the curvature of field, it is necessary to adopt the bigger minus lens of focal power to balance hereby ten thousand He of plus lens. This bore resulting in the plus lens near negative lens group increases sharply with the increase of numerical aperture of objective and imaging viewing field. When numerical aperture is more than 1, the element bore of full folding objective lens design is very big, and it is unfavorable for the processing of objective system, manufacture and integrated. Concave mirror has a positive light coke, and it is just the opposite with plus lens to the contribution of hereby ten thousand curvature of field simultaneously. It is introduced into full refractive power to carve in objective system, it is possible to share the curvature of field calibrating (base measuring) pressure of negative lens group, reduce the focal power that negative lens group undertakes, thus effectively controlling objective system element bore. Lithographic objective system as litho machine important component part is most important to improving whole litho machine performance, therefore designs the important step that refraction-reflection type deep-UV lithography objective system has been whole projection exposure system therefor. Considerably less about the report of refraction-reflection type deep-UV lithography objective designing method both at home and abroad, in order to obtain refraction-reflection type deep-UV lithography object lens initiating structure, it is proposed to a kind of effective method for designing is necessary.

Pertinent literature (Proc.ofSPIE2006.6342:63420L.) is for the optimization of deep-UV lithography object lens, it is proposed that saddle point structured approach. The similar optical designers of operating process of the method by virtue of experience adds new element to improve the way of image quality further in optical system. Saddle point structured approach is fundamentally based on the optimization method of initiating structure, it is impossible to effectively obtain object lens initiating structure. Pertinent literature (US20070013882) proposes the manufacture method overlapping deep-UV lithography object lens more.Objective system is divided into some mirror groups by the method, and different objective systems shares same mirror group, and other mirror group carries out respective change thus realizing the requirement of different optical property. The method does not illustrate how each mirror group structure and whole objective lens arrangement design.

Summary of the invention

In view of this, the present invention provides a kind of deep-UV lithography objective designing method, and the method can require design refraction-reflection type deep-UV lithography object lens according to different parameters, which reduces lens design difficulty, design efficiency is high, it is fast to realize speed.

Realize technical scheme as follows:

A kind of deep-UV lithography objective designing method, detailed process is:

Step one, determine the initiating structure of three the mirror groups of deep-UV lithography object lens being placed between mask and silicon chip, the position relationship of three mirror groups is: respectively thing Fang Jing group G1, intermediate mirror group G2 and image space mirror group G3 from mask to silicon chip, and the enlargement ratio of intermediate mirror group G2 is M₂=1;

Step 2, optimize thing Fang Jing group G1 initiating structure so that it is meet design requirement: (1) thing side telecentricity, the enlargement ratio M of (2) image space chief ray incidence angles and thing Fang Jing group₁Light path will not be caused to block;

Step 3, optimize image space mirror group G3 initiating structure so that it is meeting design requirement: (1) image space telecentricity, (2) thing side chief ray incidence angles will not cause light path to block, (3) enlargement ratio M₃=M/ (M₂��M₁), the enlargement ratio of M lithographic objective;

Step 4, intermediate mirror group G2 are the structure of two panels concave mirror, calculate hereby ten thousand He of thing Fang Jing group and image space mirror group, and according to hereby ten thousand with calculate the radius of two panels concave mirror in intermediate mirror group, make the entrance pupil of G2 mate (being placed on the emergent pupil face of G1 by the aperture diaphragm of G2) with the emergent pupil of G1 simultaneously;

Step 5, optimize image space mirror group G3 structural parameters, make the entrance pupil of G3 mate with the emergent pupil of G2; So far, the structure of junctional complex Fang Jing group, intermediate mirror group, the image space mirror group whole objective system of acquisition.

Further, the optimization process of step 2 of the present invention and step 3 is:

First, for each surface in mirror group to be optimized, normalization light focal power and/or the symmetry factor of its correspondence are calculated;

Secondly, selecting the F place, surface of maximum normalization light focal power and/or the symmetry factor, insert thin meniscus lens, the radius of curvature of the surface F that the radius of curvature of described thin meniscus lens is corresponding is identical;

Again, be respectively smaller than with morphological parameters S and W and set threshold value and meet described designing requirement as the constraints optimized, mirror group is optimized, in optimization process, be stepped up thin meniscus lens thickness and with the distance of corresponding surface F;

$W={\left(\frac{1}{N}\underset{j=1}{\overset{N}{\Σ}}{w}_j^2\right)}^{1/2}S={\left(\frac{1}{N}\underset{j=1}{\overset{N}{\Σ}}{s}_j^2\right)}^{1/2}$

Wherein, N is the number of optical surface, w in system_jFor the normalization light focal power of surface j, s_jThe symmetry factor for surface j.

Further, basis of the present invention hereby ten thousand and calculate the radius r of two panels concave mirror in intermediate mirror group₁And r₂;

If r₁With-r₂Value equal,

$\frac{2}{r_2}-\frac{2}{r_1}={\mathrm{pet}}_{G1}+{\mathrm{pet}}_{G3}$

Wherein, pet_G1And pet_G3Respectively G1 and G3 is to hereby ten thousand curvature of field.

Further, the employing damped least square method that is optimized for of the present invention realizes.

Beneficial effect

The present invention is directed to refraction-reflection type deep-UV lithography object lens and propose a set of method for designing, can quickly obtain refraction-reflection type deep-UV lithography object lens initiating structure according to the method. The method significantly reduces the design complexities of whole objective system, has higher design efficiency.

Accompanying drawing explanation

Fig. 1 is the flow chart of deep-UV lithography objective designing method;

Fig. 2 is the packet mode of refraction-reflection type deep-UV lithography object lens;

The initial double gauss structure that Fig. 3 (a) is thing Fang Jing group G1;

Fig. 3 (b) inserts the structure of thing Fang Jing group G1 after plus lens near object plane;

Fig. 3 (c) is the structure of thing Fang Jing group G1 after division cemented doublet;

Fig. 3 (d) is for having designed the structure of rear thing Fang Jing group G1;

Fig. 4 (a) is the initiating structure of image space mirror group G3;

Fig. 4 (b) is for having designed the structure of rear image space mirror group G3;

Fig. 5 is the index path of intermediate mirror group G2.

Detailed description of the invention

Below in conjunction with accompanying drawing, the present invention is described in detail further.

The present invention provides a kind of deep-UV lithography objective designing method, and detailed process is:

Determine objective system Optic structure parameter to be designed: the image-side numerical aperture NA of object lens should determine according to resolution requirement; Enlargement ratio M is generally-1/4 times; The chief ray incidence angles of thing side and image space should be parallel to optical axis to realize doubly telecentric requirement; Thing height H_oShould ensure that whole system does not occur light path to block, as shown in Figure 2. After above-mentioned parameter is determined, the object-side numerical aperture NAO of objective system can be determined by formula NAO=NA �� | M |, image height H_ICan by formula H_I=H_o�� | M | determines.

After above-mentioned objective system Optic structure parameter to be designed is determined, start to perform following optimization process, as shown in Figure 1:

Step one, determining the initiating structure of the sub-mirror group of three, deep-UV lithography object lens being placed between mask and silicon chip, wherein the position relationship of three mirror groups is: respectively thing Fang Jing group G1, intermediate mirror group G2 and image space mirror group G3 from mask to silicon chip. Formed between G1 and G2 and form intermediary image IM2 between intermediary image IM1, G2 and G3, as shown in Figure 2. G2 introduces concave mirror, and it is positioned in the middle of G1 and G3. G1 and G3 defines intermediary image IM1 and the IM2 introduced needed for G2. G2 is concave mirror group, and it undertakes hereby the ten thousand and correction of G1 and G3 mirror group.

Step 2, thing Fang Jing group G1 are relay lens groups, and object point is become intermediary image. Therefore the initiating structure of thing Fang Jing group G1 is optimized, it is made to meet design requirement: (1) G1 should thing side's telecentricity and thing side's chief ray incidence angles be 0 ��, (2) its image space chief ray incidence angles will not cause light path to block, and namely should ensure that the light path of G2 is not blocked; Determine the enlargement ratio M of G1₁, M₁Should be taken into account the generation avoiding light path to block.

The detailed process of this step is: before it has been determined that the relatively simple typical optical structure of structure is as the initiating structure of thing Fang Jing group. In order to meet optical characteristics requirement described in step 2, it is necessary to increase more design freedom. Therefore, in G1 optimization process, it is necessary to introduce new element on the basis of initiating structure and it is adjusted and Optimum Operation. The Optimizing Flow of G1 is:

First, on the basis of initiating structure, with camera lens morphological parameters for according to " optimum position " of determining insertion element. The structure of camera lens morphological parameters is based on paraxial rays trace, and it does not rely on the aperture of optical system, size, conjugate condition and the angle of visual field. Wherein morphological parameters W reflects the distribution situation of each optical surface focal power in optical system, and it is defined as:

$W={\left(\frac{1}{N}\underset{j=1}{\overset{N}{\Σ}}{w}_j^2\right)}^{1/2}---\left(1\right)$

Wherein, N is the number of optical surface, w in system_jNormalization light focal power for surface j:

$w_j=-\frac{1}{1-m}\frac{y_j}{n^{\′}{u}_N^{\′}}\frac{n^{\′}-n}{R_j}---\left(2\right)$

Wherein, m is the enlargement ratio of system, the refractive index of medium, R before and after n and n ' respectively surface j_jFor the radius of curvature of surface j, y_jFor the paraxial marginal light delivery altitude on the j of surface, n ' u^��NProduct for image space refractive index Yu paraxial marginalray line angular aperture.

Another one morphological parameters S reflects " symmetry " (" symmetry " embodies the concentric degree at optical surface and diaphragm center or meet the degree of aplanatic condition) of each optical surface in optical system, and it is defined as:

$S={\left(\frac{1}{N}\underset{j=1}{\overset{N}{\Σ}}{s}_j^2\right)}^{1/2}---\left(3\right)$

Wherein, s_jIt is expressed as:

$s_j=\frac{1}{1-m}\frac{1}{{\stackrel{\‾}{A}}_{stop}\left(n^{\′}{u}_N^{\′}\right)}\stackrel{\‾}{A_j}{(\frac{u^{\′}}{n^{\′}}-\frac{u}{n})}_j---\left(4\right)$

Wherein,For the refractive index n of medium before the j of surface_jWith paraxial principal ray angle of incidence i on the j of surface_jProduct, the paraxial marginalray line angular aperture before and after u and u ' respectively surface j,ForNumerical value on aperture diaphragm face. The optical system of less W and S value, is generally of good aberration balancing character and provides the potentiality of good image quality. Therefore, when the needs of thing Fang Jing group increase new optical element, the form number that the introducing of this optical element should make system current obtains maximally effective reduction.

According to w_jDefinition, it meets:

$\underset{j=1}{\overset{N}{\Σ}}{w}_j=1---\left(5\right)$

Ideally, as the w of all optical surfaces_jTime equal, W obtains minima, and namely system focal power is uniformly distributed on each surface. And practical situation is the requirement in order to meet optical characteristics and image quality, the w of each optical surface_jNumerical value varies, also have just have negative. w_jAbsolute value is more big then should be more big in the face of the contribution of total focal power, and the higher order aberratons of its introducing is also more big under normal circumstances. Therefore, in order to reduce each optical surface optical power profile uniformity in W value, improvement system, it should at w_jIt is worth maximum F place, surface and inserts new element, to sharing the contribution to total focal power of this surface. Similarly, when the principal element of influential system image quality is the aberration relevant to visual field, in order to reduce " symmetry " of each optical surface in S value, improvement system, it should at s_jMaximum F place, surface inserts new element. The more than determination foundation of newly-increased element " optimum position ".

Secondly, after " optimum position " of newly-increased element is determined, at the surface location place (w specified_jOr s_jThe surface that value is maximum) insert thin meniscus lens. The radius of curvature of thin meniscus lens is identical with the radius of curvature of corresponding surface F.

Finally, utilize damped least square method that the G1 mirror group after increasing element is optimized. In optimization process, be stepped up thin bent moon thickness and with the distance of corresponding surface F, the designing requirement of thing Fang Jing group and morphological parameters S and/or W are respectively smaller than the threshold value of setting simultaneously and meet design requirement as the constraints optimized, to ensure that the G1 system after optimizing has both good aberration correction potentiality while meeting design requirement.

In conjunction with the embodiments, select NAO0.25 finite conjugate from double Gauss objective as the initiating structure of G1, as shown in Fig. 3 (a). In order to realize thing side's telecentricity, near object plane, insert a piece of plus lens, as shown in Fig. 3 (b). Owing to not allowing there is glued part at deep ultraviolet wave band, two panels cemented doublet is divided, as shown in Fig. 3 (c). In order to meet the requirement of enlargement ratio, image space angle of incidence of light and numerical aperture further, successively at surface 7 and surface 9 place (w_jTwo maximum surfaces) insert " thin bent moon ", and G1 is optimized. The G1 structure that final design obtains is such as shown in Fig. 3 (d), and its NAO has reached require 0.3. In the design process morphological parameters is controlled as constraints so that the structure of G1 more aberration correction potentiality.

Step 3, image space mirror group G3 are that finite conjugate is from system, for realizing big image-side numerical aperture, G3 adopts reversal design, initial picture point is the object point of inverse system, therefore the initiating structure of image space mirror group G3 is optimized, it is made to meet design requirement: (1) G3 should thing side's telecentricity and thing side's chief ray incidence angles be 0 ��, (2) its image space chief ray incidence angles will not cause light path to block, (namely should ensure that the light path of G2 is not blocked), the enlargement ratio M of (3) G3₃=M/ (M₁��M₂), its value also should ensure that G2 is capable of explicit light path.

The adjustment of G3 is identical with thing Fang Jing group G1 with optimization method, is not repeating here.

In conjunction with the embodiments, selecting the full folding deep-UV lithography object lens in patent US20080043345, the latter half it separated from " girdle the waist " is as the initiating structure of G3, as shown in Fig. 4 (a). First, adjust the structural parameters of G31, increase its focal power and reduce the center thickness of thick lens. The element bore and the material usage that are adjusted rear G31 ' mirror group are effectively reduced. Increase due to G31 ' focal power so that the convergence arriving G32 light beam increases accordingly. So when not changing G32 structural parameters, its beam size also also can reduce accordingly with component size. Then, G33 (introducing of G2 mirror group alleviates the curvature of field calibrating (base measuring) pressure of G33, and therefore its focal power can reduce accordingly) is replaced by G33 ' the mirror group that focal power is less. Further, in order to form intermediary image and meet the requirement of enlargement ratio, add positive light coke mirror group G34^��. G3 after above-mentioned complication is optimized, and its final structure is such as shown in Fig. 4 (b).

Step 4, optimization intermediate mirror group G2 are the version of two panels concave mirror. Calculate hereby ten thousand He of thing Fang Jing group and image space mirror group. According to hereby ten thousand and condition, it is determined that the radius of intermediate mirror group concave mirror. Emergent pupil according to thing Fang Jing group, it is determined that the position of intermediate mirror group aperture diaphragm.

In conjunction with the embodiments, G2 adopts-1 times of system of two reflecting mirrors, as shown in Figure 5. Wherein, two panels concave mirror needs balance G1 and the G3 contribution amount pet to hereby ten thousand curvature of field_G1And pet_G3. According to hereby ten thousand and condition:

$\frac{2}{r_2}-\frac{2}{r_1}={\mathrm{pet}}_{G1}+{\mathrm{pet}}_{G3}---\left(6\right)$

Due to r₁With-r₂Value equal, two concave mirrors constitute the symmetrical structure that enlargement ratio is-1 times. After the structural parameters of G1 and G3 are determined, r₁And r₂Numerical value formula (6) can be utilized to calculate. In order to realize the connection of light path, the entrance pupil parameter of G2 must be mated with the emergent pupil parameter of G1, to be therefore arranged on the emergent pupil face of G1 by the aperture diaphragm of G2; Meanwhile, the emergent pupil according to thing Fang Jing group, it is determined that the aperture diaphragm position of intermediate mirror group.

Step 5, utilize damped least square method that the structural parameters of image space mirror group G3 are carried out fine optimization so that it is entrance pupil mates with the emergent pupil of intermediate mirror group G2. Junctional complex Fang Jing group G1, intermediate mirror group G2, image space mirror group G3 obtain the initiating structure of whole objective system, as shown in Figure 2.

The embodiment of the present invention:

Design obtains thing Fang Jing group G1, and its structural parameters are as shown in table 1.

Table 1

Design obtains image space mirror group G3, and its structural parameters are as shown in table 2.

Table 2

According to hereby ten thousand and condition, it is determined that intermediate mirror group G2, its structural parameters are as shown in table 3.

Table 3

Face sequence number	Face type	Radius	Interval	Mode of operation
					Object plane	Sphere	Infinity	83.5728	Refraction
1	Sphere	-176.4591	-202.000	Reflection
					2	Sphere	176.4591	83.5728	Reflection
3	Sphere	Infinity	-	Refraction

In sum, these are only presently preferred embodiments of the present invention, be not intended to limit protection scope of the present invention. All within the spirit and principles in the present invention, any amendment of making, equivalent replacement, improvement etc., should be included within protection scope of the present invention.

Claims (4)

1. a deep-UV lithography objective designing method, it is characterised in that detailed process is:

Step one, determine the initiating structure of three the mirror groups of deep-UV lithography object lens being placed between mask and silicon chip, the position relationship of three mirror groups is: respectively thing Fang Jing group G1, intermediate mirror group G2 and image space mirror group G3 from mask to silicon chip, and the enlargement ratio of intermediate mirror group G2 is M₂=1;

Step 2, optimize thing Fang Jing group G1 initiating structure so that it is meet design requirement: (1) thing side telecentricity, the enlargement ratio M of (2) image space chief ray incidence angles and thing Fang Jing group₁Light path will not be caused to block;

Step 3, optimize image space mirror group G3 initiating structure so that it is meeting design requirement: (1) image space telecentricity, (2) thing side chief ray incidence angles will not cause light path to block, (3) enlargement ratio M₃=M/ (M₂��M₁), the enlargement ratio of M lithographic objective;

Step 4, intermediate mirror group G2 are the structure of two panels concave mirror, calculate hereby ten thousand He of thing Fang Jing group and image space mirror group, and according to hereby ten thousand with the radius of two panels concave mirror in calculating intermediate mirror group, make the entrance pupil of G2 mate with the emergent pupil of G1 simultaneously;

Step 5, optimize image space mirror group G3 structural parameters, make the entrance pupil of G3 mate with the emergent pupil of G2;

So far, the design of deep-UV lithography object lens is completed.

2. deep-UV lithography objective designing method according to claim 1, it is characterised in that the optimization process of described step 2 and step 3 is:

First, for each surface in mirror group to be optimized, normalization light focal power and/or the symmetry factor of its correspondence are calculated;

Secondly, selecting the F place, surface of maximum normalization light focal power and/or the symmetry factor, insert thin meniscus lens, the radius of curvature of the surface F that the radius of curvature of described thin meniscus lens is corresponding is identical;

Again, be respectively smaller than with morphological parameters S and W and set threshold value and meet described designing requirement as the constraints optimized, mirror group is optimized, in optimization process, be stepped up thin meniscus lens thickness and with the distance of corresponding surface F;

$\begin{array}{cc}W={\left(\frac{1}{N}\underset{j=1}{\overset{N}{\Σ}}{w}_j^2\right)}^{1/2}& S={\left(\frac{1}{N}\underset{j=1}{\overset{N}{\Σ}}{s}_j^2\right)}^{1/2}\end{array}$

Wherein, N is the number of optical surface, w in system_jFor the normalization light focal power of surface j, s_jThe symmetry factor for surface j.

3. deep-UV lithography objective designing method according to claim 1, it is characterised in that described basis hereby ten thousand and calculate the radius r of two panels concave mirror in intermediate mirror group₁And r₂;

If r₁With-r₂Value equal,

$\frac{2}{r_2}-\frac{2}{r_1}={\mathrm{pet}}_{G1}+{\mathrm{pet}}_{G3}$

Wherein, pet_G1And pet_G3Respectively G1 and G3 is to hereby ten thousand curvature of field.

4. deep-UV lithography objective designing method according to claim 1 or claim 2, it is characterised in that described in be optimized for employing damped least square method realize.