Lithography Smash Sensor Objective Product Requirements Document

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1 Lithography Smash Sensor Objective Product Requirements Document Zhaoyu Nie (Project Manager) Zichan Wang (Customer Liaison) Yunqi Li (Document) Customer: Hong Ye (ASML) Faculty Advisor: Julie Bentley Graduate Advisor: Yang Zhao Document Number 005 Revisions Level Date E This is a computer-generated document. The electronic master is the official revision. Paper copies are for reference only. Paper copies may be authenticated for specifically stated purposes in the authentication block. Authentication Block 005 Rev E Litho Team 1

2 Revision History Rev Descriptions Date Authorization A Initial PRD 24-Oct WHK B Updated housing constrains 5-Nov WHK C Updated coating design specifications 28-Nov WHK D Updated more startpoints information 5-Dec WHK E Format editing 16-Dec WHK 005 Rev E Litho Team 2

3 Table of Contents 1. INTRODUCTION GROUP RESPONSIBILITIES ENVIRONMENT MANUFACTURABILITY SPECIFICATIONS... 6 DESIGN SPECIFICATIONS... 6 TOLERANCE SPECIFICATIONS... 6 SIZE REQUIREMENTS LENS DESIGN FORM... 8 PETZVAL CORECTION... 8 LONG WORKING DISTANCE... 9 COLOR CORRECTION PRELIMINARY DESIGN COATING DESIGN TIMELINE APPENDIX A & B REFERENCE Rev E Litho Team 3

4 1. Introduction This microscope objective lens is an essential part of the Smash Sensor that is used for high precision lithography wafer alignment. Various lasers with different wavelengths can be directed through this objective to illuminate alignment marks; the diffracted higher-order beams will then be collected by the same objective to provide alignment signals. The goal of this project is to design an objective with excellent color correction. Smash Sensor objective is a customer driven product. As such, its design inputs were derived from interactions with ASML and our faculty adviser Julie Bentley. Vision: During the semiconductor manufacturing process, the wafer is rapidly moving beneath the lithography primary lens. The precision of the wafer movement directly determines the quality of semiconductor products. This requires our objective to have negligible chromatic aberrations and odd-order aberrations. Figure 1: This is a simplified diagram of illumination and imaging parts before the interferometer. Our task is to design the objective lens at the lower right corner of this figure. The objective is a critical component of this setup because it is part of both the illumination and imaging parts. The objective needs to provide uniform illumination onto the mark and collect the reflected higher-orders. 005 Rev E Litho Team 4

5 2. Group Responsibilities We are responsible for Lens design Tolerance Monte Carlo analysis, including chromatic focal shift Odd order fringe Zernike analysis Coating design Things are good to have Housing design Cost estimation Prototyping 3. Environment As an instrument working in a lithography system, it needs to operate in the following environment: Temperature: 22 ± 0.5 C Negligible vibrations 4. Manufacturability Our customer generously suggested us to be not so concerned with the budget. In design phase, we can use any types of surfaces and materials that best suit the purpose of our design. However, we will still try to start with accessible and eco-friendly choices. The lens tolerances will be discussed in the following section. 005 Rev E Litho Team 5

6 5. Specifications Lens Specifications Aperture (NA) 0.6 Field of View (mm) ±0.05 Wavelength (nm) , , , Design Wavelength (nm) 532, 633, 775, 852 Focal Length (mm) 15 ± 775 nm Working Distance (mm) >7.7 Overall Length (mm) <62.3 Vignetting Transmission 95% Anti-reflection Coating No vignetting All surfaces including cemented surfaces Reflectivity <0.3% for all wavelengths Max ray AOI & AOR on surfaces starting from <40 RMS Wavefront (wv) <0.05 Chromatic Focal Shift (µm) <0.5 Odd Order Aberrations fringe Zernike coefficients P-V: <0.15 wv S-FPL51, S-TIH6, CaF2, S-NBM51, N-KZFS8, N-FK51A, N-LASF44, N-SF57HT, N-SK2, Preferred Glass FUSE SILICA Tolerance Specifications Decenter 5 µm Lens thickness 50 µm Lens radius 10 µm Glass V# 0.80% Glass index Roll/tilt/wedge remains unknown, we need to provide a reasonable value. Surface Irregularity remains unknown, we need to provide a reasonable value. 005 Rev E Litho Team 6

7 Size requirements Figure 2: This graph briefly illustrates the total volume constraint, including lens and housing volume. The lenses need to be designed as small as possible so we can leave more room for the housing. 005 Rev E Litho Team 7

6. Lens Design Form 1. Petzval Correction The correction uniformity over the field size is one of the major criteria for the quality of microscope lenses.

8 6. Lens Design Form 1. Petzval Correction The correction uniformity over the field size is one of the major criteria for the quality of microscope lenses. If no special effort is made to flatten the field of a positive lens, the overall performance will be affected greatly. There are several design principles, which help to reduce the Petzval sum and to flatten the field of view. According to the Petzval formula, in a microscope objective lens, the main positive refractive power is located on the front element or group, it is desirable to reduce the generation of curvature in this part of the system. This can be achieved by using lenses with high refractive indices, which enlarge the radii of the surfaces and which also reduce the Petzval contribution. Other methods used to flatten the field curvature are layouts of the Double Gauss or retrofocus type. The usual correction of the Petzval curvature is mainly done in the rear group of a highperformance microscope lens. Possible layouts are shown below [19]: Our design requires excellent color correction, so design form d) and e) are desirable. 005 Rev E Litho Team 8

2. Long Working Distance If the working distance is large, the marginal ray bundle will have a large diameter because of the high aperture angle. Therefore, the diameter of the system increases.

9 2. Long Working Distance If the working distance is large, the marginal ray bundle will have a large diameter because of the high aperture angle. Therefore, the diameter of the system increases. The front part of the system needs to consist several shell-shaped thin meniscus lenses. This front building block is typical and necessary to deal with spherical aberration in the front part for large diameters. However, the meniscus lenses in the front part usually introduce a lot of axial colors. Therefore, a great effort must be made in the middle part to correct the system for color. The fish shape (retrofocus) lens is an excellent solution for that; however due to our mechanical constraint, the fish shape is a little hard to use. Therefore, Double Gauss is a good candidate, shown below [19]. More design forms are shown in Appendix B. 3. Color Correction As discussed above, the middle part of the lens needs to play a key role in color correction. Apochromate and Plan-apochromate have the best correction for field curvature and color aberration. However, these types of lens are mainly used in high NA imaging system. But we can use the middle part of these lenses for our color correction purpose. More design forms are shown in Appendix B. 005 Rev E Litho Team 9

7. Preliminary Design RMS Wavefront (Y 0) 0.0243 (Y 0.5) 0.0265 (Y 0.71) 0.03 (Y 0.86) 0.0342 (Y 1) 0.0394 EFL=15 mm; OAL =55 mm; IMC =8 mm; Figure 3: Picture of lens and chromatic focal shift.

10 7. Preliminary Design RMS Wavefront (Y 0) (Y 0.5) (Y 0.71) 0.03 (Y 0.86) (Y 1) EFL=15 mm; OAL =55 mm; IMC =8 mm; Figure 3: Picture of lens and chromatic focal shift. The lens meets specifications (odd order fringe Zernike analysis hasn t been performed). The peak to valley value of the green curve indicates the chromatic focal shift. 005 Rev E Litho Team 10

4 ARC MIN; Tilt: 1 ARC MIN; Decenter: 0.005mm;

11 Lens Tolerance Tolerance values used: Radius: 0.01 mm; Test Plate fit: 0.5 Fringes; IRR: 0.05 (increase to 0.1 next time); Thickness: 0.05 mm; Index: ; V_No: 0.8%; Wedge: 0.9~1.4 ARC MIN; Tilt: 1 ARC MIN; Decenter: 0.005mm; Roll: 0.005mm. Compensators: The ideal situation is to have one image compensator, one decenter compensator, and one thickness compensator. This design uses two thickness compensators. 005 Rev E Litho Team 11

12 8. Coating Design Requirements: At least 99.7% transmission for required wavelengths, all polarization across all field. Try to reach 40 angle of incidence. (We may lower designed AOI according to the design) No more than 8 layers. No more than 4 materials for each surface. We may need to design AR coating not only for glass/air interface but also between cemented lens elements if the refractive index difference is large. The light source is left-handed circular polarized. Phase-preserving is not required. Coating between cemented doublets If two elements of cemented doublet have a large difference of refractive indices, the Fresnel reflection can cause the transmission between the doublets lower than 99.7%. For example, in the case of CaF2 and SF11, which has approximately 1.43 and 1.75 refractive indices, respectively, has the transmission shown in the following plot: Figure 4: this figure shows the transmission of interface between CaF2 and SF11 at different angles. The transmission is significantly lower than requirements due to Fresnel reflection 005 Rev E Litho Team 12

13 One simple method to solve this problem is to coat a single layer anti-reflection coating before cementing. The thickness of the coating should be quarter wave optical thickness (QWOT) and the refractive index of the coating material should be the geometrical mean of indices of elements: n " = n $ n % (1) In equation (1), n l is the index of refraction of the AR coating and n 1 and n 2 denote indices of two glass materials, respectively. In this case, I used refractive index for the coating material and the improved transmission is shown: Figure 5: This figure shows the reflection of CaF2-SF11 interface with one layer of QWOT coating. The reflection is more than 99.7% at all required bands. Importance of reducing angle of incidence The effective indices of refraction are not only dependent on wavelength but also polarization for oblique angle incidence [18]. The effective indices of s and p polarized light are given by the following equations: n & = ncosθ (2) n + = n/cosθ (3) In these equations, n & and n + denote effective indices of refraction of s and p polarized light, respectively. If I use SF11 as an example, the effective refractive indices at different incident angles are shown in the following table: 005 Rev E Litho Team 13

14 angles, wavelengths polarizations 532 nm 633 nm 775 nm 852 nm , s , p , s , p , s , p As shown in the table above, the change of refractive indices with incident angle is much more significant in compare with dispersion. Also the difference of s and p polarization in high angle makes the designing of coating very challenging. Starting point design The design of polarization coating is similar to an ultra-broad band, anti-reflection coating [18]. I can start with LHHM design, which is a common broadband AR coating. Figure 6: This figure illustrates basic form of LHHM coating design. In the figure shown above, n 1, n 2, n denote coating materials with low, medium, high indices of refraction, respectively. n s is the substrate, which is lens materials in our case and n 0 is the incident medium, which is air. The optical thickness of low index material and medium index material is quarter wavelength, while the optical thickness of high index material is half wavelength. This design provides a high transmission with only 4 layers. However, it is not high enough to meet the requirements. Needle optimization is needed when the index of substrate and incident angle are known. 005 Rev E Litho Team 14

15 9. Timeline January Design multiple lenses with different starting points and pick the one with the best tolerance. Write Monte Carlo macro for RMS wavefront and chromatic focal shift. Write macro for odd order fringe Zernike P-V. Preliminary coating design and tolerance. Housing design study and consult with ME department. February Finalize coating design while adjusting incident angles accordingly in lens design. Finalize lens design. Preliminary housing design. Communicate with our customer for housing specifications on tolerance. March Finish housing design. Cost estimation (possible) Prototyping (possible). April Testing (possible). 005 Rev E Litho Team 15

16 Appendix Appendix A: An example of a real product: 005 Rev E Litho Team 16

17 Appendix B: start points and existing patent that can be useful for future reference. Long working distance lens 1) U.S. Patent # 4,563,060; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 17

18 2) U.S. Patent # 4,591,243; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 18

19 3) U.S. Patent # 4,232,941; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 19

20 4) U.S. Patent # 4,521,083; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 20

21 5) U.S. Patent # 4,231,637; assignee: American Optical Corp; objective description: long working distance 005 Rev E Litho Team 21

22 6) U.S. Patent # 3,806,231; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 22

23 7) U.S. Patent # 4,721,372; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 23

24 8) U.S. Patent # 5,739,958; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 24

25 9) U.S. Patent # 3,925,910; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 25

26 10) U.S. Patent # 4,540,248; assignee: Olympus; objective description: long working distance 005 Rev E Litho Team 26

27 Plan-apochromate type 1) U.S. Patent # 5,517,360; assignee: Olympus; objective description: 60x, 1.4 NA Plan Apo. 2) U.S. Patent # 5,659,425; assignee: Olympus; objective description: 100x, 1.65 NA Apo. 005 Rev E Litho Team 27

28 3) U.S. Patent # 6,519,092; assignee: Nikon; objective description: 60x, 1.4 NA Plan Apo. 4) U.S. Patent # 7,046,451; assignee: Nikon; objective description: 60x, 1.5 NA TIRF (modeled as 1.49 NA to match possible commercial realization). 005 Rev E Litho Team 28

29 5) U.S. Patent # 7,889,433; assignee: Nikon; objective description: 60x, 1.25 water immersion. More Plan-Apo design form can be found in Comparative analysis of imaging configurations and objectives for Fourier microscopy Rev E Litho Team 29

30 Apochromate type 1) U.S. Patent # 5,502,596; assignee: Olympus; objective description: 40x, 1.0 NA Apo. 005 Rev E Litho Team 30

31 Reference 1. Yamagishi, M. (1986). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 2. Yamagishi, M. (1986). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 3. Tojo, T. (1980). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 4. Togino, T. (1985). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 5. Sussman, M. (1980). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 6. Taira, A. (1974). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office 7. Yokota, A. (1988). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 8. Abe, K. (1998). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 9. Matsubara, M. (1975). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 10. Togino, T. (1985). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 11. Suzuki, T. (1996). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 12. Suziki, T. (1997). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 13. Yamaguchi, K. (2003). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 14. Abe, K. (1998). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 15. Mandai, M., Yamaguchi, K. (1996). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 16. Yoshida, M. (2011). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 17. Suzuki, T. (1996). U.S. Patent No Washington, DC: U.S. Patent and Trademark Office. 18. Oliver, J. (n.d.). Lecture 8 - Anti-Reflection Coatings. Lecture presented at OPT 246, Thin Film Coating Technology, Rochester, NY. 19. Gross, H., Zugge, H., Peschka, M., & Blechinger, F. (2013). Handbook of optical systems, Aberration Theory and Correction of Optical Systems (Volume 3). Weinheim: Wiley-VCH. 005 Rev E Litho Team 31

Lithography SMASH Sensor Objective Design Description Document

Lithography SMASH Sensor Objective Design Description Document Zhaoyu Nie (Project Manager) Zichan Wang (Customer Liaison) Yunqi Li (Document) Customer: Hong Ye (ASML) Faculty Advisor: Julie Bentley Graduate