lithography smash sensor objective product requirements

Lithography Smash Sensor Objective Product Requirements Document

005 Rev E Litho Team 1


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 12-16-2016

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.

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Wayne H Knox

Sticky Note

OK Litho Team - thanks for lots of effort that you put into this project so far you have made great progress in understanding exactly what your customer wants i believe that you have a realistic chance to deliver a great design to the customer ; of course the prototyping part will be difficult to get done, also you haven't specified your testing procedure anyway as to this document, I am giving you a team grade of 91 on this document, for several reasons 1. certain items are not clear in the spec table 2. numerous typos and grammatical corrections - you should have gone to the Writing Center for extra help with that *** as i said - this is not just a design course, it is also a writing course ! 3. i made a lot of comments throughout - please take these into consideration - we will want to discuss these when we start design reviews in january 4. you will start making up a DDD Design Description Document for Spring...



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



Table of Contents

1. INTRODUCTION .............................................................................................................. 4

2. GROUP RESPONSIBILITIES ........................................................................................... 5

3. ENVIRONMENT ............................................................................................................... 5

4. MANUFACTURABILITY................................................................................................. 5

5. SPECIFICATIONS ............................................................................................................ 6

• DESIGN SPECIFICATIONS ................................................................................. 6

• TOLERANCE SPECIFICATIONS ........................................................................ 6

• SIZE REQUIREMENTS ........................................................................................ 7

6. LENS DESIGN FORM ...................................................................................................... 8

• PETZVAL CORECTION ....................................................................................... 8

• LONG WORKING DISTANCE ............................................................................ 9

• COLOR CORRECTION ........................................................................................ 9

7. PRELIMINARY DESIGN................................................................................................ 10

8. COATING DESIGN ......................................................................................................... 12

9. TIMELINE ........................................................................................................................ 15

APPENDIX A & B ................................................................................................................. 16

REFERENCE .......................................................................................................................... 31



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.

Wayne H Knox

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this word 'excellent' does not mean very much here - the point is that you will design it with specifed color correction - i guess that you are suggesting that it is a **tight** spec here...

Wayne H Knox

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illuminated

Wayne H Knox

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uniformity specified ? how can you do that without designing the whole system ?



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.

Wayne H Knox

Sticky Note

you mean they would like for you to have it made ? i thought that they wanted to do that -



5. Specifications Lens Specifications

Aperture (NA) 0.6 Field of View (mm) ±0.05 Wavelength (nm) 527-537, 628-638, 770-780, 845-855 Design Wavelength (nm) 532, 633, 775, 852 Focal Length (mm) 15 ± 0.04 @ 775 nm Working Distance (mm) >7.7 Overall Length (mm) <62.3 Vignetting No vignetting

Transmission 95%

Anti-reflection Coating 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

Preferred Glass

S-FPL51, S-TIH6, CaF2, S-NBM51, N-KZFS8, N-FK51A, N-LASF44, N-SF57HT, N-SK2, FUSE SILICA

Tolerance Specifications Decenter 5 µm Lens thickness 50 µm Lens radius 10 µm Glass V# 0.80% Glass index 0.0005 Roll/tilt/wedge remains unknown, we need to provide a

reasonable value. Surface Irregularity remains unknown, we need to provide a

reasonable value.

Wayne H Knox

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what does this mean ? don't you really mean "not less than 7.7 mm"?? or do they want "not less than 7.7mm and not too much longer than that" ??

Wayne H Knox

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what does this mean ? don't they want transmission of 95% or greater ? i don't think they want exactly 95% transmission

Wayne H Knox

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what does this mean ? less than 40 degrees incidence angle on any surface ?

Wayne H Knox

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measured at which wavelength ? at all wavelengths ?



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.

Wayne H Knox

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this looks funny - do you mean that they did not specify the thickness of the housing ?



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 high-performance microscope lens. Possible layouts are shown below [19]:

Our design requires excellent color correction, so design form d) and e) are desirable.

Wayne H Knox

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no figure caption on this one ?



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.

Wayne H Knox

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Wayne H Knox

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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;

7. Preliminary Design

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.

Wayne H Knox

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what was your starting point for this ? did you start with a design included in Code V ?



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: 0.0005; 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.

Wayne H Knox

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what is this parameter ? a thickness ?



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

Wayne H Knox

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Wayne H Knox

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Wayne H Knox

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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), nl is the index of refraction of the AR coating and n1 and n2 denote indices of two glass materials, respectively. In this case, I used 1.585 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:

Wayne H Knox

Sticky Note

this would require the two elements to be optically contacted with the coating applied to one element will this work with the air film in there, or perhaps you would need some index matching fluid ?



angles, wavelengths polarizations

532 nm 633 nm 775 nm 852 nm

0° 1.7948 1.7786 1.7662 1.7618 15°, s 1.7336 1.7180 1.7060 1.7018 15°, p 1.8581 1.8413 1.8285 1.8239 30°, s 1.5543 1.5403 1.5296 1.5258 30°, p 2.0724 2.0538 2.0394 2.0344 45°, s 1.2691 1.2577 1.2489 1.2458 45°, p 2.5382 2.5153 2.4978 2.4916

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, n1, n2, n denote coating materials with low, medium, high indices of refraction, respectively. ns is the substrate, which is lens materials in our case and n0 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.

Wayne H Knox

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Wayne H Knox

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Wayne H Knox

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hey this is a team document !! WE

Wayne H Knox

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please explain that optimization procedure you should include the reference to Optilayer, since not everybody knows that



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).

Wayne H Knox

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do you have your MechE contact ?



Appendix Appendix A:

An example of a real product:

Wayne H Knox

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complicated mechnics here - threaded skinny little rings etc... yikes !! :0



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



5) U.S. Patent # 4,231,637; assignee: American Optical Corp; objective description: long working distance



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.



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).



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” https://arxiv.org/pdf/1507.04037.pdf



Apochromate type

1) U.S. Patent # 5,502,596; assignee: Olympus; objective description: 40x, 1.0 NA Apo.

Wayne H Knox

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Reference

1. Yamagishi, M. (1986). U.S. Patent No. 4563060. Washington, DC: U.S. Patent and Trademark Office.

2. Yamagishi, M. (1986). U.S. Patent No. 4591243. Washington, DC: U.S. Patent and Trademark Office.

3. Tojo, T. (1980). U.S. Patent No. 4232941. Washington, DC: U.S. Patent and Trademark Office.

4. Togino, T. (1985). U.S. Patent No. 4521083. Washington, DC: U.S. Patent and Trademark Office.

5. Sussman, M. (1980). U.S. Patent No. 4231637. Washington, DC: U.S. Patent and Trademark Office.

6. Taira, A. (1974). U.S. Patent No. 3806231. Washington, DC: U.S. Patent and Trademark Office

7. Yokota, A. (1988). U.S. Patent No. 4721372. Washington, DC: U.S. Patent and Trademark Office.

8. Abe, K. (1998). U.S. Patent No. 5739958. Washington, DC: U.S. Patent and Trademark Office.

9. Matsubara, M. (1975). U.S. Patent No. 3925910. Washington, DC: U.S. Patent and Trademark Office.

10. Togino, T. (1985). U.S. Patent No. 4540248. Washington, DC: U.S. Patent and Trademark Office.

11. Suzuki, T. (1996). U.S. Patent No. 5517360. Washington, DC: U.S. Patent and Trademark Office.

12. Suziki, T. (1997). U.S. Patent No. 5659425. Washington, DC: U.S. Patent and Trademark Office.

13. Yamaguchi, K. (2003). U.S. Patent No. 6519092. Washington, DC: U.S. Patent and Trademark Office.

14. Abe, K. (1998). U.S. Patent No. 5739958. Washington, DC: U.S. Patent and Trademark Office.

15. Mandai, M., Yamaguchi, K. (1996). U.S. Patent No. 7046451. Washington, DC: U.S. Patent and Trademark Office.

16. Yoshida, M. (2011). U.S. Patent No. 7889433. Washington, DC: U.S. Patent and Trademark Office.

17. Suzuki, T. (1996). U.S. Patent No. 5502596. 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.

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