Ideas for Metrology of Silicon Diffractive Optics

This talk was given around November of 2013 to members of the Si Diffractive Optics Group at UT Austin. The talk highlights summarizes the 27 tasks or ideas our group was working on at that moment in time, and details one specific idea for enhanced metrology of Si immersion gratings.

Transcript

1. ideas for Si diffractive optics UT Austin Silicon Diffractive Optics Group
2. michael gully-santiago astronomer, engineer, graduate student, bicycle rider
3. I made a list of 27 ideas. There were so many that I gave them all id #’s.
4. The goal of this presentation is to inform you about the ideas.
5. Rank ID Idea # # - 1 Si01 Measure the ICP etch time – phase relation 2 Si02 Predict and characterize the effect of poor lithographic contacting 3 Si03 Measure the UV exposure dose – phase relation 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics All 27 ideas
6. 1 Si01 Measure the ICP etch time – phase relation 2 Si02 Predict and characterize the effect of poor lithographic contacting 3 Si03 Measure the UV exposure dose – phase relation The ones we’ve done 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics The ones we haven’t
7. 1 Si01 Measure the ICP etch time – phase relation 2 Si02 Predict and characterize the effect of poor lithographic contacting 3 Si03 Measure the UV exposure dose – phase relation The ones we’ve done Let’s recap
8. 1 Si01 Measure the ICP etch time – phase relation 2 Si02 Predict and characterize the effect of poor lithographic contacting 3 Si03 Measure the UV exposure dose – phase relation Si03 Measure the UV exposure dose – phase relation We measured the UV exposure dose-phase relation: dL/dE ~ 1000 ± 250 nm/E0 It is important to distinguish between phase and line- edge position. -1000 -500 0 500 1000 1500 2000 0 2 4 dL / dE E/E 0 wafer 081213_01 Zygo Results UTexas 30 micron S1800 0.6 micron Linear(UTexas 30 micron) Linear(S1800 0.6 micron) There are clearly horizontal discontinuities in the Zygo interferometry. The regions pictured received discrete UV exposure doses of 60 – 80 s.
9. 1 Si01 Measure the ICP etch time – phase relation 2 Si02 Predict and characterize the effect of poor lithographic contacting 3 Si03 Measure the UV exposure dose – phase relation Si01 Measure the ICP etch time – phase relation dn !3" w h Silicon nitride Silicon Photoresist xs xn Sidewall etching can arise from a sloped photoresist or isotropic chemical etching. Zygo interferometry constrains the ICP sidewall etch rate from t = 55-125 s dL/dt < 5 nm/s Image: cbrooks We predicted 4 horizontal discontinuities in the below image. We see only 1 discontinuity, so the ICP etch has negligible effect on phase.
10. 1 Si01 Measure the ICP etch time – phase relation 2 Si02 Predict and characterize the effect of poor lithographic contacting 3 Si03 Measure the UV exposure dose – phase relation Si02 Predict and characterize the effect of poor lithographic contacting 25 nm undulations measured w/ Zygo are consistent with fringe amplitude = 2.5 ± 1.6% Directly measured resist reflectivity integrated against the UV lamp spectrum are consistent with 1% fringe amplitude. Not shown: grayscale lithography with Dektak measured film thickness is consistent with 2% fringe amplitude.
11. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics The ones we haven’t Now let’s look at
12. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Some ideas are innovative metrology techniques metrology
13. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Some ideas are for improving our process metrology process
14. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Some ideas are not ideas at all- they are commitments we have to make devices metrology process make devices
15. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Two ideas are about investing in organization metrology process make devices organization
16. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Two ideas are about the design of gratings metrology process make devices organization design
17. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics The rest are ongoing experimental R&D efforts metrology process make devices organization design R&D
18. 4 Si04 High spatial resolution measurements of bonded Si pucks 5 Si05 Characterization of heritage grating surfaces 6 Si23 Improve UV illumination uniformity 7 Si22 Reduce the dose-phase curve 8 Si21 Reduce the UV fringe amplitude 9 Si07 e-beam silicon immersion grating production 10 Si06 A contacted grism for Mimir 11 Si08 Does thermal anneal eliminate IR bubbles in bonded Si? 12 Si09 L- and M- band immersion grating for iSHELL 13 Si10 J-, H-, and K- band immersion grating for iSHELL 14 Si11 ACT immersion grating prototype 15 Si12 Internal transfer of skills and knowledge I-VI 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 18 Si15 The geometrical efficiency loss from dispersion at high λ and m 19 Si16 SPIE paper idea: applications and specifications for immersion gratings 20 Si17 A higher performance immersion grating for IGRINS 21 Si18 Robust inventory and travelers for silicon and optical parts 22 Si19 Quantify vendor provided defect density, compare to specifications 23 Si20 Improve Si wafer mounting strategy to better simulate optical surfaces 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 26 Si26 Characterize the effect of high temperature annealing on precision optics 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Let’s talk about the metrology ones metrology
19. 5 Si05 Characterization of heritage grating surfaces 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Let’s talk about the metrology ones
20. 5 Si05 Characterization of heritage grating surfaces 16 Si13 Directly measured moderate order HeNe spectral purity of photo masks 17 Si14 Characterization of stock lab optics with Cary 5000 24 Si24 Directly measure blaze angle in reflection 25 Si25 Directly measure on-blaze efficiency in reflection 27 Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics Let’s talk about the metrology ones specifically these two
21. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope.
22. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. 0 degree (groove tops)
23. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The illuminated width of the facet depends on viewing orientation Shallow facet (e.g. 38° for complement of R3) Front surface illumination in air
24. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The illuminated width of the facet depends on viewing orientation Steep facet (e.g. 71.6° for R3) Front surface illumination in air
25. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. By the way: The illuminated width of the facet depends on viewing orientation Steep facet (e.g. 71.6° for R3) Front surface illumination in air Immersed in Si
26. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope.
27. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. 1 2 3 1.  Groove tops (always 0°) 2.  Shallow facet (e.g. 38° for complement of R3) 3.  Steep facet (e.g. 71.6° for R3)
28. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. 1 2 3 1.  Groove tops (always 0°) 2.  Shallow facet (e.g. 38° for complement of R3) 3.  Steep facet (e.g. 71.6° for R3) What Astronomers want: -know the realized* R3 blaze angle and its uncertainty -a small** uncertainty -no avoidable*** efficiency loss *the realized blaze angle may differ from the design blaze angle since it depends intimately on the Si cutting angle (well known) and the anisotropic KOH wet etch rates (poorly known, variable) **small means negligible contribution to the overall uncertainty in the alignment of the spectrograph during integration and testing. Ask Dan Jaffe what X is. ***geometrical efficiency loss comes from groove shadowing, which can be anticipated in the design. δ= 71.6 ± ε° ε << X
29. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. Depending on the illumination angle, some facets are shadowed. shadowed ✔ ✔ ✗ What Astronomers want: -know the realized* R3 blaze angle and its uncertainty -a small** uncertainty -no avoidable*** efficiency loss *the realized blaze angle may differ from the design blaze angle since it depends intimately on the Si cutting angle (well known) and the anisotropic KOH wet etch rates (poorly known, variable) **small means negligible contribution to the overall uncertainty in the alignment of the spectrograph during integration and testing. Ask Dan Jaffe what X is. ***geometrical efficiency loss comes from groove shadowing, which can be anticipated in the design.
30. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. Depending on the illumination angle, some facets are shadowed. shadowed ✔ ✗ What Astronomers want: -know the realized* R3 blaze angle and its uncertainty -a small** uncertainty -no avoidable*** efficiency loss *the realized blaze angle may differ from the design blaze angle since it depends intimately on the Si cutting angle (well known) and the anisotropic KOH wet etch rates (poorly known, variable) **small means negligible contribution to the overall uncertainty in the alignment of the spectrograph during integration and testing. Ask Dan Jaffe what X is. ***geometrical efficiency loss comes from groove shadowing, which can be anticipated in the design. ✗ Immersed in Si
31. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. Depending on the illumination angle, some facets are shadowed. shadowed ✔ ✗ What Astronomers want: -know the realized* R3 blaze angle and its uncertainty -a small** uncertainty -no avoidable*** efficiency loss *the realized blaze angle may differ from the design blaze angle since it depends intimately on the Si cutting angle (well known) and the anisotropic KOH wet etch rates (poorly known, variable) **small means negligible contribution to the overall uncertainty in the alignment of the spectrograph during integration and testing. Ask Dan Jaffe what X is. ***geometrical efficiency loss comes from groove shadowing, which can be anticipated in the design. ✗ Immersed in Si GROOVE TOP SHADOWING MEMO MICHAEL GULLY-SANTIAGO 1. Introduction This document describes the geometry of micromachined silicon immersion gratings being developed at the University of Texas Department of Astronomy Silicon Diffractive Optics Group and the MIT Nanoruler Group. Specifically, we calculate the acceptable groove top to pitch length ratio above which the efficiency of the devices is degraded. This information is useful for the design of gratings using direct writing systems, where the groove width is a free parameter. Maintaining a large groove top to pitch length ratio is important to avoid failures during processing, such as undercutting or over etching. 2. Geometry Figure 1 shows an overview of a silicon immersion grating. Figure 2 shows a detail of a single groove, chronicling the relevant geometry; the parameters are listed below. t is the groove top width p is the groove spacing (also called the groove pitch) δ is the blaze angle a is the silicon etch angle; for this document we adopt a = 70.53 ◦ , the maximum allowable ratio of t p is given by: t p = 1 1 + tan(a) tan(δ) , So, for the adopted value of a, and tan(δ) = 2 (i.e. an R2 echelle), we have t p ∼ = 0.41. For an R3 echelle, we have t p ∼ = 0.51. References [Marsh et al.(2007)] Marsh, J. P., Mar, D. J., & Jaffe, D. T. 2007, Applied Optics, 46, 3400 MICHAEL GULLY-SANTIAGO 1. Introduction This document describes the geometry of micromachined silicon immersion gratings being developed at the University of Texas Department of Astronomy Silicon Diffractive Optics Group and the MIT Nanoruler Group. Specifically, we calculate the acceptable groove top to pitch length ratio above which the efficiency of the devices is degraded. This information is useful for the design of gratings using direct writing systems, where the groove width is a free parameter. Maintaining a large groove top to pitch length ratio is important to avoid failures during processing, such as undercutting or over etching. 2. Geometry Figure 1 shows an overview of a silicon immersion grating. Figure 2 shows a detail of a single groove, chronicling the relevant geometry; the parameters are listed below. t is the groove top width p is the groove spacing (also called the groove pitch) δ is the blaze angle a is the silicon etch angle; for this document we adopt a = 70.53 ◦ , the maximum allowable ratio of t p is given by: t p = 1 1 + tan(a) tan(δ) , So, for the adopted value of a, and tan(δ) = 2 (i.e. an R2 echelle), we have t p ∼ = 0.41. For an R3 echelle, we have t p ∼ = 0.51. References [Marsh et al.(2007)] Marsh, J. P., Mar, D. J., & Jaffe, D. T. 2007, Applied Optics, 46, 3400 Date: May 27, 2009. 1 δ is the blaze angle a is the silicon etch angle; for this document we adopt a = 70.53 ◦ , the maximum allowable ratio of t p is given by: t p = 1 1 + tan(a) tan(δ) , So, for the adopted value of a, and tan(δ) = 2 (i.e. an R2 echelle), we have t p ∼ = 0.41. For an R3 echelle, we have t p ∼ = 0.51. References [Marsh et al.(2007)] Marsh, J. P., Mar, D. J., & Jaffe, D. T. 2007, Applied Optics, 46, 3400 Date: May 27, 2009. 1 GROOVE TOP SHADOWING MEMO MICHAEL GULLY-SANTIAGO 1. Introduction This document describes the geometry of micromachined silicon immersion being developed at the University of Texas Department of Astronomy Silicon Di Optics Group and the MIT Nanoruler Group. Specifically, we calculate the ac groove top to pitch length ratio above which the efficiency of the devices is degrad information is useful for the design of gratings using direct writing systems, w groove width is a free parameter. Maintaining a large groove top to pitch length important to avoid failures during processing, such as undercutting or over etchin 2. Geometry Figure 1 shows an overview of a silicon immersion grating. Figure 2 shows a de single groove, chronicling the relevant geometry; the parameters are listed below. t is the groove top width p is the groove spacing (also called the groove pitch) δ is the blaze angle a is the silicon etch angle; for this document we adopt a = 70.53 ◦ , the maximum allowable ratio of t p is given by: t p = 1 1 + tan(a) tan(δ) , So, for the adopted value of a, and tan(δ) = 2 (i.e. an R2 echelle), we have t p For an R3 echelle, we have t p ∼ = 0.51. References [Marsh et al.(2007)] Marsh, J. P., Mar, D. J., & Jaffe, D. T. 2007, Applied Optics, 46, 3400 Date: May 27, 2009. 1
32. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The width of the facet is inversely related to the breadth of the blaze envelope. 1 2 3 1.  Groove tops (always 0) 2.  Shallow facet (e.g. 38° for complement of R3) 3.  Steep facet (e.g. 71.6° for R3) What Astronomers want: -know the realized* R3 blaze angle and its uncertainty -a small** uncertainty -no avoidable*** efficiency loss *the realized blaze angle may differ from the design blaze angle since it depends intimately on the Si cutting angle (well known) and the anisotropic KOH wet etch rates (poorly known, variable) **small means negligible contribution to the overall uncertainty in the alignment of the spectrograph during integration and testing. Ask Dan Jaffe what X is. ***geometrical efficiency loss comes from groove shadowing, which can be anticipated in the design. δ= 71.6 ± ε° ε << X ✔
33. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The blaze angle is encoded in the measured brightness of diffraction orders 3
34. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The blaze angle is encoded in the measured brightness of diffraction orders 3 Figure 9 from Marsh, Mar, and Jaffe 2007. Jasmina Marsh (a former grad student) did this all the time. This technique fell out of favor because the measurement was time-consuming and subject to a major systematic uncertainty.
35. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The illuminated width of the facet is inversely related to the breadth of the blaze envelope. Figure 9 from Marsh, Mar, and Jaffe 2007. Jasmina Marsh (a former grad student) did this all the time. This technique fell out of favor because the measurement was time-consuming and subject to a major systematic uncertainty. 3
36. Si24 Directly measure blaze angle in reflection A typical grating has 3 blaze angles. The blaze angle of the facet is at the peak of the blaze envelope. Figure 9 from Marsh, Mar, and Jaffe 2007. Jasmina Marsh (a former grad student) did this all the time. This technique fell out of favor because the measurement was time-consuming and subject to a major systematic uncertainty. 3
37. Si24 Directly measure blaze angle in reflection Figure 9 from Marsh, Mar, and Jaffe 2007. Jasmina Marsh (a former grad student) did this all the time. This technique fell out of favor because the measurement was time-consuming and subject to a major systematic uncertainty. How do you know which order you are in? How confident are you that you are not off-by-one? (or two or three…) For example, how do you know you are measuring order #426 and not #427? For 426th order, off-by-one means uncertainty in blaze angle is ± ε = 1/426 =0.002 radians =0.13°
38. Si24 Directly measure blaze angle in reflection Figure 9 from Marsh, Mar, and Jaffe 2007. Jasmina Marsh (a former grad student) did this all the time. This technique fell out of favor because the measurement was time-consuming and subject to a major systematic uncertainty. How do you know which order you are in? How confident are you that you are not off-by-one? (or two or three…) For example, how do you know you are measuring order #426 and not #427? For 426th order, off-by-one means uncertainty in blaze angle is ± ε = 1/426 =0.002 radians =0.13° The solution to this problem is that you have to find zero order and start counting from zero to 426.
39. Si24 Directly measure blaze angle in reflection We need a rotation stage to rotate the many (~80) diffraction orders onto a detector. The detector will detect and measure the brightness of every order. detector Figure 9 from Marsh, Mar, and Jaffe 2007. Jasmina Marsh (a former grad student) did this all the time. This technique fell out of favor because the measurement was time-consuming and subject to a major systematic uncertainty.
40. Si24 Directly measure blaze angle in reflection We need a rotation stage to rotate the many (~80) diffraction orders onto a detector. The detector will detect and measure the brightness of every order. This is definitely zero order. No doubt there. 0° 71.6° We can centroid wicked good dude! -38°
41. Si24 Directly measure blaze angle in reflection We need a rotation stage to rotate the many (~80) diffraction orders onto a detector. The detector will detect and measure the brightness of every order. BOOM shakalaka! This is definitely zero order. No doubt there. 0° 71.6° We can centroid wicked good dude! -38°
42. Si24 Directly measure blaze angle in reflection We need a rotation stage to rotate the many (~80) diffraction orders onto a detector. The detector will detect and measure the brightness of every order. 0° 71.6° -38° Actually there are a few challenges: Measurements must be done in Littrow, which means the non-constant illuminated groove width is a nuisance parameter. So results are model-dependent. You need huge dynamic range. Like ~ 80 dB? You need very-high-precision clocking with a goniometer. I don’t actually know how well you can centroid… probably depends on the groove spacing and blaze angle. Is a bare laser beam OK or do you need to collimate and focus? Collimating gives spurious secondary images.
43. Si24 Directly measure blaze angle in reflection We need a rotation stage to rotate the many (~80) diffraction orders onto a detector. The detector will detect and measure the brightness of every order. 0° 71.6° -38° Actually there are a few challenges: Measurements must be done in Littrow, which means the non-constant illuminated groove width is a nuisance parameter. So results are model-dependent. You need huge dynamic range. Like ~ 80 dB? You need very-high-precision clocking with a goniometer. Is a bare laser beam OK or do you need to collimate and focus? Collimating gives spurious secondary images. I don’t actually know how well you can centroid… probably depends on the groove spacing and blaze angle. Lock-in amplifier + ND filter + HDR repeats Just buy a goniometer! Might not be better than Џ= 0.2° which isn’t good enough Extra alignment/dithering work. See memo.
44. Si24 Directly measure blaze angle in reflection So I actually already did this for CA1. Sorta.
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47. Si24 Directly measure blaze angle in reflection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° uncertainty isn’t good enough as it stands. We need: 1)  more better data (i.e. more orders, lower uncertainty) 2)  Better model
48. Si24 Directly measure blaze angle in reflection The main reason the uncertainty is so large is that my scalar diffraction model is bad. But of course it is. I am most excited about this idea because it is an easy experimental way to constrain non-scalar diffraction effects that we only ever speculate about. Rank gratings in ascending blaze angle much better than 0.2°. We will then have a data-driven model. Intermediate phases of wet etching- anisotropic etch rate. We could pin this relation to CA1, and bootstrap. Monitor before and after thermal cycling / aluminization, etc. Evidence for groove bottom completion. $$ $
49. An advert for the other metrology ideas
50. Si25 Directly measure on-blaze efficiency in reflection Above: Cary 5000 breadboard accessory with custom optical layout. A reference mirror is shown on the left. We can put an immersion grating here to rapidly measure the near-blaze efficiency. Right: Plots from CROWBAR. The top scan was taken near Littrow only. 1.0 1.5 2.0 2.5 3.0 h (!m) 0.0 0.2 0.4 0.6 0.8 1.0 Raw efficiency 70 75 80 85 90 95 100 110 120 130 140 150
51. Si13 Directly measured moderate order HeNe spectral purity of photo masks Amanda Turbyfill demonstrating the HeNe laser beam position at the photo mask. The photomask is challenging to measure because it is an unblazed grating. Figure 13 from Marsh, Mar, and Jaffe 2007. Monochromatic spectral purity can reveal ghosts in photomasks down to the 5 nm level, if moderate orders at steep enough incidence angles can be reliably measured. “Steep enough” is ~10-30°
52. Si05 Characterization of heritage grating surfaces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manda and I are working on this, and I’m giving a separate presentation on it.
53. Si27 Quantify the Fabry-Pèrot effect of finite thickness Si optics This is too complicated to get into right now. Ask Dan Jaffe.
54. Si14 Characterization of stock lab optics with Cary5000 FEL1450 0 10 20 30 40 50 60 70 80 90 1400 1450 1500 1550 1600 1650 Wavelength (nm) Transmission% Very simple. Our stock lab filters and mirrors will be much more useful if we know and verify their properties.
55. gully@astro.as.utexas.edu | astronomer and engineer attribution to: les vieux garçons, from The Noun Project Pierre TORET, from The Noun Project Sá Ferreira - Purple Matter, from The Noun Project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driano Emerick, from The Noun Project Renee Ramsey-Passmore, from The Noun Project Nherwin Ardoña, from The Noun Project Thank you. Please ask me about the ideas.