WO2016155426A1 - Optical system for measurement of illumination pupil polarization state of mask aligner - Google Patents

Abstract

An optical system for measurement of an illumination pupil polarization state of a mask aligner, wherein an aperture diaphragm, Fourier transform objectives (L1-L5), a quarter wave plate, a polarization analyzer, relay objectives (L6-L11) and an image sensor are sequentially included in the optical axis direction of the optical system, and the optical system is used for transforming a pinhole in a pinhole mask picture surface into a target face (i.e. a photosensitive face) of the image sensor. The requirements for the size of the image sensor, and the positions and sizes of the quarter wave plate and the polarization analyzer can be satisfied, an imaging angle is relatively large, a back working distance is relatively long, and the whole structure is compact; and the requirements for a sine condition are satisfied, and a spherical aberration, a comatic aberration, astigmatism, the curvature of the field, and a wave aberration etc. are well corrected.

Description

Photoelectric machine illumination diaphragm optical system for measuring polarization state Technical field

The present invention relates to an optical system for measuring the polarization state of a pupil, and more particularly to an optical system for measuring the polarization state of an illumination pupil of a lithography machine.

Background technique

A lithography machine is a device that transfers a desired pattern to a target location of a substrate coated with a photosensitive material. The lithography machine can be applied to integrated circuit (IC) manufacturing, printed circuit board (PCB) manufacturing, liquid crystal panel (LCD) manufacturing, and the like. In general, the desired pattern is on a mask or reticle (mask) that can transfer the desired pattern to a target location on the substrate (eg, a silicon wafer) (eg, including one or more chips) On the exposure field, the substrate is coated with a photosensitive material (eg, a photoresist, also referred to as a photoresist). Known lithography machines include:

In a contact lithography machine, the reticle is in direct contact with the substrate, and the light source emits light through the reticle to expose the substrate to complete the pattern transfer;

In a proximity lithography machine, there is a micron-order gap between the reticle and the substrate, and the light emitted by the light source is exposed on the substrate through the reticle to complete the pattern transfer;

The projection lithography machine has a projection objective lens for imaging between the reticle and the substrate, and the light emitted by the light source is exposed on the substrate through the illumination system, the reticle and the projection objective lens to complete the pattern transfer. The projection objective of the projection lithography machine images the pattern on the reticle on the substrate, and the magnification is generally reduced by 10 times, 5 times, 4 times, 1 time, and the like. A known projection lithography machine includes: a stepper that exposes a desired pattern to a target position of the substrate at a time by exposing the desired pattern to a target position of the substrate, and by stepping motion; and scanning Machine, the illumination beam scans the desired pattern along a given direction (scanning direction), and scans the substrate target position in parallel or anti-parallel direction in the direction to complete the pattern transfer, forming a scanning exposure field, and stepping motion, under A scan exposure field completes the next graphics transfer. Known next-generation lithography techniques include: imprint technology that transfers a desired pattern from a reticle to a substrate target by imprinting the desired pattern onto the substrate; Maskless Lithography , ML2), transferring the desired graphics to the substrate target location through a virtual mask.

A known projection lithography machine includes an illumination system and a projection objective. In operation, the reticle is located between the illumination system and the projection objective. Typically, there is a desired exposure circuit formed of metallic chromium on the lower surface of the reticle. Graphics. The wafer is precisely positioned during exposure so that the circuit pattern on the reticle is imaged by the projection objective on the surface of the photoresist on the wafer.

Semiconductor lithography continues to advance, and critical dimensions continue to advance toward higher-node technologies, resulting in an ever-increasing numerical aperture (NA) of the projection objective. When the angle of the light in the lithography machine with respect to the optical axis increases with the increase of NA, the vector characteristic of the light wave becomes more important for lithographic imaging, because only the polarization component of the light wave with the same vibration direction can perform interference imaging. Therefore, it contributes to the transfer of the pattern, and the polarization component of the light wave whose orthogonal direction is vibrating cannot participate in the interference imaging, thereby contributing to the pattern transfer. Therefore, the contrast of the lithographic pattern is determined not only by the wavefront quality of the projection objective, but also when the numerical aperture NA is increased to a certain extent, the polarization state of the illumination pupil has a very large influence on the contrast of the lithographic pattern.

The current semiconductor front lithography machine adopts argon fluoride excimer laser and immersion lithography (ArFi), polarization illumination technology, and multiple resolution enhancement technologies such as multiple exposure technology, and has realized 2X nm to 1X nm. Mass production of technology nodes. Among them, the typical equipment supporting the 2X nm technology node is the lithography machine TWINSCAN NXT: 1960Bi from ASML of the Netherlands and the lithography machine NSR-S622D from Nikon Corporation of Japan; the typical equipment supporting the 1X nm technology node is the lithography machine TWINSCAN of ASML company. NXT: 1970Ci and Nikon's lithography machine NSR-S630D, where NSR-S630D is a lithography machine that supports mass production of 10nm nodes. All four types of lithography machines use a liquid-immersed projection objective with a numerical aperture NA of 1.35 and a magnification of -1/4 times. The polarized illumination system is an essential device for implementing these node technologies. In the early ASML company's projection lens with a numerical aperture NA of 1.20 and a 1750i, the polarized illumination system is an optional device for the lithography machine. Both generations of lithography machines need to measure the polarization state of the illumination pupil projected on the reticle by the polarized illumination system. The polarization direction, polarization degree, polarization purity and other parameters of the illumination pupil are essential for achieving accurate exposure of various patterns. Without the measurement and control of the illumination pupil polarization state, there is no qualified exposure pattern.

Existing photosensors established in lithography machines, such as pinhole cameras for illuminating pupil measurements, typically cannot measure polarization states. If it is desired to measure the polarization state of the illumination pupil, it is necessary to introduce modulation and conversion elements for the polarization state of the optical wave, such as wave plates, analyzers, and the like. Therefore, the optical system used for measuring the polarization state of the illumination pupil of the lithography machine generally needs to include: a pinhole reticle, a Fourier transform objective lens, a wave plate, an analyzer, a relay objective lens, an image sensor, etc., as shown in FIG. As shown, the pinhole mask is located at the mask surface position of the lithography machine, which is also the object plane position of the projection objective, and the pupil field is used to perform pupil sampling measurement on different illumination field positions. The function of the Fourier transform objective is to convert the pupil angle distribution of the illumination beam through the pinhole into a spatial position distribution on the back focal plane of the Fourier transform objective, ie obtained at the back focal plane position of the Fourier transform objective The pupil of the illumination beam. The function of the waveplate and analyzer is to modulate and convert the pupil polarization state of the illumination beam, where the modulation is by rotation Wave plate to achieve. The relay objective is a key component that functions to select the modulated beam required for the illumination pupil polarization state measurement and continue imaging it onto the target surface of the image sensor. The target surface of the image sensor is located at the image plane position of the relay objective lens. Typically, a CMOS camera or a CCD camera is generally used as the image sensor.

Summary of the invention

An object of the present invention is to disclose an optical system for measuring the polarization state of an illumination pupil of a lithography machine, the function of which is to convert a pinhole in a pinhole mask pattern plane to a target surface of the image sensor (ie, a photosensitive surface) The optical system not only can effectively correct various required correction aberrations, but also meet the pinhole mask size, wave plate and analyzer size, structure requirements like sensor size, and meet the illumination of the lithography machine. Practical application requirements for polarization measurement.

The object of the invention is achieved in this way:

An optical system for measuring a pupil polarization state of a lithography machine for transforming a pinhole in a pinhole mask pattern into a target surface (ie, a photosensitive surface) of a sensor, along the optical system The optical axis direction includes, in order, an aperture stop plane, a Fourier transform objective lens, a quarter wave plate, an analyzer, a relay objective lens, and an image sensor, wherein the aperture stop plane is located in the Fourier transform objective lens. a front focal plane, a quarter wave plate is located at a back focal plane of the Fourier transform objective lens, and a sensor photosurface is located at an image plane position of the relay objective lens, the Fourier transform objective lens including a first lens and a second lens a third lens, a fourth lens and a fifth lens, wherein the first lens, the fourth lens and the fifth lens are meniscus lenses having a concave surface facing the aperture stop surface, and the third lens is a meniscus having a concave surface facing the image plane a lens, the second lens is a lenticular lens, and the relay objective lens comprises a sixth lens, a seventh lens, an eighth lens, a ninth lens, a tenth lens and an eleventh lens, the sixth lens and the tenth a lens is concave toward the aperture light Surface of the meniscus lens, a ninth lens and a tenth lens is a meniscus lens having a concave surface facing the image plane, a seventh lens is a biconcave lens, the eighth lens is a biconvex lens.

The Fourier transform objective lens has a focal length of 10.771 mm, wherein the first lens, the second lens, and the fifth lens have positive power, and the third lens and the fourth lens have negative power.

The sixth lens, the eighth lens, and the ninth lens in the relay objective lens have positive power, and the seventh lens, the tenth lens, and the eleventh lens have negative power, in the relay objective lens The combined focal length of the sixth lens, the seventh lens, and the eighth lens is 75 mm, and the combined focal length of the ninth lens, the tenth lens, and the eleventh lens is 75 mm, and the relay objective lens constitutes a 1-fold transfer system.

Said first lens is made to eleventh lenses all with high transmittance fused silica material, optionally Corning 7980 fused silica grades of material may be selected from the SCHOTT company Lithosil ^TM Q0 / 1-E193 melting Quartz material. The quarter wave plate is made of quartz crystal material. The analyzer is made of magnesium fluoride (MgF ₂ ) crystal material.

Compared with the prior art, the invention has the following advantages and positive effects:

1. The optical system for measuring the polarization state of the illuminating device of the lithography machine of the present invention can effectively satisfy the size requirement of the image sensor, has a large field of view angle, and has a long working distance, and satisfies the quarter wave plate and the analyzer. Position and size requirements, and compact structure;

2. The optical system for measuring the polarization state of the illuminating device of the lithography machine of the present invention adopts a reasonable matching of positive and negative optical powers, satisfies the sinusoidal condition requirement required for the pupil measurement, and has spherical aberration, coma, and Astigmatism, field curvature, and wave aberrations are well corrected;

3. The optical system for measuring the polarization state of the illumination of the lithography machine of the present invention uses only a lens having a spherical surface type, and does not introduce an aspherical lens, thereby reducing the difficulty of processing, detecting and mounting the lens.

DRAWINGS

1 is a schematic view showing the application of an optical system for measuring the polarization state of an illumination pupil of a lithography apparatus according to the present invention;

2 is a view showing the structure and optical path diagram of an optical system for measuring the polarization state of an illumination pupil of a lithography apparatus according to the present invention;

3 is a diagram showing a diffraction modulation transfer function MTF of an optical system for measuring a polarization state of an illumination pupil of a lithography apparatus according to the present invention;

4 is a RMS wave aberration distribution diagram of an optical system for measuring a polarization state of an illumination pupil of a lithography apparatus according to the present invention;

5 is a spherical aberration, astigmatism, field curvature, and distortion distribution diagram of an optical system for measuring a polarization state of an illumination pupil of a lithography apparatus according to the present invention;

6 is a sine condition deviation DSC distribution diagram of an optical system for measuring a polarization state of an illumination pupil of a lithography apparatus according to the present invention;

Figure 7 is an incident angle of the optical system for measuring the polarization state of the pupil of the illuminating device of the present invention on the incident surface of the wave plate;

Fig. 8 is a view showing the distribution of the image square telecentric angle error of the optical system for measuring the pupil polarization state of the lithography apparatus of the present invention.

detailed description

The optical system for measuring the pupil polarization state of the lithography machine of the present invention will be further described in detail below.

The optical system for measuring the pupil polarization state of the lithography machine of the present invention is a lithography illumination pupil whose projection objective lens has a numerical aperture NA of 1.35 and a magnification of -0.25. Due to the use of argon fluoride (ArF) excimer laser with a wavelength of 193.368nm, all lenses are made of high-transmittance fused silica. Corning's 7980 grade fused silica material can also be selected from SCHOTT. Lithosil ^TM Q0/1-E193 fused silica material, quarter-wave plate is made of quartz crystal material, and analyzer is made of magnesium fluoride (MgF ₂ ) crystal material.

At a wavelength of 193.368 nm, the refractive index of the fused silica material is 1.560259, the refractive index of the magnesium fluoride crystal material is 1.427670, and the refractive index of the quartz crystal material is 1.66091.

The image size requirement of the optical system for measuring the polarization state of the pupil of the lithography apparatus of the present invention is:

The pixel size of the image sensor is 16 μm × 16 μm, and the number of pixels is 512 × 512. The design considers that the edge is left unused for 12 pixels, so that the image size of the sensor is 8 mm × 8 mm and the half height is 4 mm. The angle of view of the object field of the optical system for measuring the polarization state of the illumination pupil should be matched with the image numerical aperture of the illumination system. The system design requires a design margin of 10%, so that the object angle of view is:

U=arcsin(1.35/4*1.1)=21.80°

The illumination pupil polarization state measurement requires obtaining the pupil of the illumination system on the image sensor surface, and the pixels at different positions correspond to different pupil positions, so that the focal length of the optical system is required to be:

The system design requires that the pinhole reticle has a pinhole diameter of 0.2 mm, a distance from the pinhole face to the image face of less than 310 mm, and an image working distance of more than 17.53 mm.

The optical system for measuring the polarization state of the illuminating device requires perfect imaging. Generally, the RMS value of the wave aberration is less than 1/14 wavelength, that is, less than 13.67 nm.

The pupil polarization state measurement requires obtaining the illumination system aperture on the image sensor target surface, and needs to meet the sine condition requirements. Therefore, it is necessary to retain a certain negative distortion. The system design requires the sine condition to deviate from DSC<1 μm.

The constraint parameters of the optical system for measuring the pupil polarization state of the lithography machine of the present invention are shown in Table 1.

Table 1 Optical system constraint parameters for lithography illumination pupil polarization measurement

Constrained project	Constraint parameter
Working wavelength	193.368nm
Half angle of object field of view	21.80°
Image sensor surface radius	4.0mm

Constrained project	Constraint parameter
Total focal length	10.771mm
Pinhole diameter	0.2mm
CCD target surface pixel size	16μm × 16μm
Wave aberration RMS value	<13.67nm
Sine condition deviates from DSC	<1μm
Image telecentric angle error	<5mrad
Angle of incidence at the surface of the waveplate	<1°
Image working distance	>17.53mm
Distance from pinhole face to image face	<310mm
Fused silica material refractive index	1.560259@193.368nm
Magnesium fluoride o light refractive index	1.427670@193.368nm
Quartz crystal o light refractive index	1.660910@193.368nm

The lithography machine of the present invention illuminates the optical system for measuring the polarization state of the pupil, as shown in FIG. 2, the lithography machine illuminates the optical system for measuring the polarization state of the pupil, and the optical system is used for the pattern of the pinhole mask The pinholes therein are transformed into the target surface of the image sensor (ie, the photosensitive surface), and include, along the optical axis direction of the optical system, an aperture stop plane, a Fourier transform objective lens, a quarter wave plate, and an analyzer. , the relay objective lens, the image sensor, the aperture stop plane is located at the front focal plane of the Fourier transform objective lens, the quarter wave plate is located at the back focal plane position of the Fourier transform objective lens, and the image sensor photo surface is located at the relay objective lens Image position.

The Fourier transform objective lens includes a first lens L1, a second lens L2, a third lens L3, a fourth lens L4, and a fifth lens L5, the first lens L1, the fourth lens L4, and the fifth lens L5 is a meniscus lens whose concave surface faces the aperture stop surface, the third lens L3 is a meniscus lens whose concave surface faces the image plane, and the second lens L2 is a lenticular lens.

The relay objective lens includes a sixth lens L6, a seventh lens L7, an eighth lens L8, a ninth lens L9, a tenth lens L10, and an eleventh lens L11, the sixth lens L6 and the eleventh lens L11 is a meniscus lens having a concave surface facing the aperture stop surface, the ninth lens L9 and the tenth lens L10 are meniscus lenses having a concave surface facing the image plane, the seventh lens L7 is a biconcave lens, and the eighth lens L8 is a lenticular lens.

The focal length of the Fourier transform objective lens is 10.771 mm, wherein the first lens L1, the second lens L2, and the fifth lens L5 have positive power, and the third lens L3 and the fourth lens L4 have negative power.

The sixth lens L6, the eighth lens L8, and the ninth lens L9 in the relay objective lens have positive refractive power, The seventh lens L7, the tenth lens L10, and the eleventh lens L11 have a negative refractive power, and the combined focal length of the sixth lens L6, the seventh lens L7, and the eighth lens L8 in the relay objective lens is 75 mm, The combined focal length of the nine lens L9, the tenth lens L10, and the eleventh lens L11 is 75 mm, and the relay objective lens constitutes a -1 times the image transfer system.

Said first lens is made to eleventh lenses L1 ~ L11 all high transmittance fused silica material, optionally Corning 7980 fused silica grades of material may be selected from the SCHOTT company Lithosil ^TM Q0 / 1 -E193 fused silica material. The quarter wave plate is made of quartz crystal material. The analyzer is made of magnesium fluoride (MgF ₂ ) crystal material.

According to the constraint parameters of the optical system for measuring the pupil polarization state of the lithography machine in Table 1 above, the present invention discloses that the design data of the optical system is as shown in Table 2. For optical processing, ease of optical inspection, and cost reduction, the optical surfaces of all of the elements of the present invention are spherical without any aspherical elements.

Table 2 shows the specific design parameter values of each lens, quarter-wave plate, and analyzer of the optical system for measuring the pupil polarization state of the lithography machine of the embodiment, wherein the "surface" column indicates The number of each optical surface from the object to the image, where STOP represents the aperture stop. The Radius column gives the spherical radius for each surface. The "Thickness/Interval" column gives the axial distance between two adjacent surfaces. If the two surfaces belong to the same lens, the value of "Thickness/Interval" indicates the thickness of the lens, otherwise it indicates the object/image surface to The distance of the lens or the spacing of adjacent lenses. The column "Optical Materials" indicates the material of the corresponding lens. The "Half Aperture" column indicates the 1/2 aperture value of the corresponding surface, ie the half height. The "Affiliated Objects" column indicates the respective lenses corresponding to each surface from the object plane to the image plane.

Table 2 Design data of the optical system for measuring the polarization state of the illumination pupil of the lithography machine of the present invention

Taking the lenses L1 and L2 as an example, the spherical surface radius of the front surface 2 of L1 is -5.577 mm (the sign indicates the bending direction of the surface), and the distance from the front surface 2 of the L1 to the aperture stop is 4.000 mm, and its optical The material is corning7980, the half hole diameter of the front surface 2 of L1 is 1.6055mm; the spherical surface radius of the rear surface 3 of L1 is -5.078mm, the front surface 2 of L1 is the rear surface 3 of L1, that is, the center thickness of the lens L1 is 2.345mm, The half surface diameter of the rear surface 3 of L1 is 2.3366 mm, that is, L1 is a meniscus lens having a concave surface facing the aperture stop.

The spherical radius and the half aperture of the front surface 4 of L2 are 13.838 mm and 2.6249 mm, respectively, the pitch of the front surface 4 of L2 to the rear surface 3 of L1 is 0.200 mm, the optical material of the lens L2 is corning 7980, and the rear surface 5 of L2 The spherical radius and the half aperture are - 9.644 mm and 2.8309 mm, respectively, and the thickness of the lens L2 is 2.702 mm. Except that the half aperture of the image plane (surface image) represents the image field half height, the meaning of the parameter values of the other surfaces can be analogized according to the description of the lenses L1, L2. The representation of the waveplate and analyzer parameters is consistent with the lens, with 1.0E+18 representing the plane.

In addition to the 11 lenses L1 to L11, the quarter wave plate, and the analyzer, the lens L1 is also provided with an aperture stop STOP in front of it, and the change in the aperture size affects the imaging effect of the optical system.

Under the conditions of working wavelength, field of view angle, aperture stop diameter and other parameters in Table 1, according to the analysis and calculation of professional optical design software CODE_V, the degree of aberration correction is as follows:

Figure 3 shows the diffraction modulation transfer function MTF of the optical system. Since the pixel size is 16 μm (corresponding to a spatial frequency of 31.25 line pairs/mm), it can be seen from Fig. 3 that the MTF is greater than 0.58 at 32 line pairs/mm (better than the resolution). The required MTF is >0.4).

4 is a distribution of RMS wave aberration of the optical system with a maximum value of 0.19 nm, which reflects that the imaging quality of the optical system of the present invention is close to perfect imaging.

Figure 5 is a spherical aberration, astigmatism, field curvature, and distortion diagram of the optical system, wherein the spherical aberration maximum value is -0.3 μm, the field curvature maximum value is -29 μm, and the astigmatism maximum value is -19 μm, all of which are in the aberration tolerance Within the limits. The maximum distortion is -7.2%, which is the negative distortion reserved to meet the sine condition requirements.

According to the data disclosed in the preferred embodiment of the present invention, the actual image height of different angles of view is obtained by using CODE_V software for actual ray tracing, and compared with the image height required to satisfy the sine condition, as shown in Table 3 below, The maximum absolute deviation is 0.661 μm. The actual image height of each field of view and the deviation of the image height required by the sine condition satisfy the requirement that the sine condition deviates from DSC<1 μm (as shown in Fig. 6).

Table 3 compares the actual image height and sine conditions to the image height

Figure 7 is the incident angle of the optical system on the incident surface of the quarter-wave plate, wherein the maximum incident angle of the chief ray is 0.25 degrees, and the maximum incident angle of the mergon rays is 0.75 degrees, which satisfies the incident on the incident surface of the wave plate. Angle <1° requirement.

Figure 8 is the incident angle of the chief ray of the optical system on the image plane (i.e., the image telecentric angle), wherein the maximum incident angle of the chief ray is 2.79 mrad, which satisfies the requirement of an image square telecentric angle error <5 mrad.

From the data in Table 2, the distance from the pinhole surface to the image surface is 309.998 mm, which satisfies the requirement of <310 mm. The data on the 28th side of Table 2 is 60.199, which also satisfies the requirement of the image working distance > 17.53 mm.

The optical system for measuring the polarization state of the pupil by using the lithography machine of the invention fully satisfies the technical requirements for measuring the polarization state distribution of the illumination pupil, has excellent imaging quality, and meets the application requirements of the actual illumination pupil polarization state measurement.

Claims (4)

1. An optical system for measuring the pupil polarization state of a lithography machine, comprising: an aperture stop, a Fourier transform objective lens, a quarter wave plate, an analyzer, and a relay in the optical axis direction of the optical system An objective lens, an image sensor, wherein an aperture stop plane is located at a front focal plane of the Fourier transform objective lens, and the quarter wave plate is located at a back focal plane of the Fourier transform objective lens, The photosensitive surface of the image sensor is located at an image plane position of the relay objective lens, and the Fourier transform objective lens comprises a first lens, a second lens, a third lens, a fourth lens and a fifth lens, the first lens, The fourth lens and the fifth lens are meniscus lenses having a concave surface facing the aperture stop surface, the third lens is a meniscus lens having a concave surface facing the image plane, the second lens is a lenticular lens, and the relay objective lens includes a sixth lens, a seventh lens, an eighth lens, a ninth lens, a tenth lens and an eleventh lens, wherein the sixth lens and the eleventh lens are meniscus lenses having a concave surface facing the aperture stop surface, a ninth lens and a tenth The lens is a meniscus with a concave surface facing the image plane a mirror, the seventh lens is a biconcave lens, the eighth lens is a lenticular lens, the focal length of the Fourier transform objective lens is 10.771 mm, and the first lens, the second lens and the fifth lens have positive power, the first lens The third lens and the fourth lens have negative power, the sixth lens, the eighth lens, and the ninth lens of the relay objective lens have positive power, and the seventh lens, the tenth lens, and the eleventh lens have negative light The combined focal length of the sixth lens, the seventh lens and the eighth lens of the relay objective lens is 75 mm, and the combined focal length of the ninth lens, the tenth lens and the eleventh lens is 75 mm, the first The lens to the eleventh lens are all made of high-permeability fused silica material, selected from Corning's 7980 grade fused silica material, or selected by SCHOTT's Lithosil ^TM Q0/1-E193 fused silica material, one quarter The wave plate is made of quartz crystal material, and the analyzer is made of magnesium fluoride (MgF ₂ ) crystal material.
2. The optical system according to claim 1, wherein the specific design parameter values of each of the optical components are as follows:

   

   
3. The optical system according to claim 1, wherein the optical system has an operating wavelength of 193.368 nm, an entrance pupil diameter of 0.2 mm, and an object-side field of view angle of 21.80 degrees.
4. The optical system according to claim 1, wherein said relay objective lens constitutes a -1x image transfer system.

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