nishtha bhatia washington high school july 31st, 2014 · 2014-08-15 · nishtha bhatia washington...

Nishtha Bhatia Washington High School July 31st, 2014

Programming Photolithography

MY PROJECTS

o MNL’s current i-line PR – OiR 897-10i – is discontinued

o Qualify new resist, 906-12 OiR i-line

o Incorporate image slider to Nanolab website homepage

o Greater functionality than previous .gif

FRONT-END DEVELOPMENT

OBJECTIVES

Image slider that runs across homepage of nanolab.berkeley.edu

Ease in uploading images

Ability to link images to reports/PDFs/web pages

Ability to display captions across images

IMPLEMENTATION

Programmed with JavaScript jQuery

Created nine different layouts for image slider, each with

different features, including:

Image re-sizing

Transitions

Thumbnail display

Nested Thumbnails

Pause/Forward/Rewind Buttons

LAYOUTS CREATED

FINAL SLIDER - Demo

http://nanolab.berkeley.edu/



FINAL SLIDER - Code

OiR 906-12 i-LINE

PHOTORESIST

THE BASICS

What is photolithography?

Process of transferring geometric shapes on a mask to a thin film of photoresist

Photoresist is on the surface of a substrate typically a silicon wafer

Used in industry for integrated circuit manufacturing

PROJECT PURPOSE

MNL’s current i-line resist (OiR 897-10i) = discontinued

To maintain i-line litho, new resist must be qualified –> 906-12 OiR photoresist

END GOAL

Find optimal conditions to consistently produce standard 1.2, 1.7, 2.1, and 2.8 µm films of resist +

resolve at least 0.7 µm lines and spaces

EXPERIMENTAL SETUP - Tools

Nanospec Prime Oven

Svgcoat1 + Svgdev1

Gcaws6 UV bake LEO SEM

EXPERIMENTAL SETUP - Wafers

We used three wafers of each thickness (1.2, 1.7, 2.1, and 2.8 µm) #1: used to measure

photoresist thickness after hard bake

No exposure

#2: used to measure photoresist thickness after UV bake

No exposure

#3: uniformly exposed wafer

Used for analysis with LEO scanning electron microscope

EXPERIMENTAL PROCEDURE

1. Primed wafers using recipe #2 – 90 °C, 11 min, 780 torr

2. Coat bare wafers with svgcoat1 track: modified programs 1, 3, 5, and 7

1. 1.2, 1.7, 2.1 µm -> manual dynamic dispense

2. 2.8 µm -> manual static dispense

3. Expose one wafer of each thickness on gcaws6

4. Develop all wafers in svgdev1 track (std. prog. – 1)

5. Run one set of wafers through svgdev1 again for hard bake, & the other set of wafers were put into UV bake

6. Examine wafers with LEO SEM

NEW SPIN COAT PROGRAMS

Wafer ID Target Thickness

(µm)

Svgcoat1 process to

modify

Spin speed (rpm)

1 1.2 (1, 1) 4100

2 1.7 (3, 1) 2000

3 2.1 (5, 1) 1300

4 2.8 (7, 4) 820

Table 1: Expected spin speeds to produce targeted photoresist thicknesses in the experiment

• The faster the spin speed, the thinner the coat of photoresist – spin coat technique

FILM THICKNESS VS. SPIN SPEED

1

1.2

1.4

1.6

1.8

2

2.2

2.4

2.6

2.8

3

0 1000 2000 3000 4000 5000 6000

90

6-1

2 F

ilm

Th

ick

ne

ss

(µ

m)

Spin Speed (rpm)

Projected Film Thickness vs. Spin Speed

Expected Actual

Table 2: Spin speeds with expected and actual 906-12 film thickness

• Measurements taken on nanospec, like so:

T L C R F

COATED PR THICKNESSES– 1.2, 1.7, 2.1 µm

ID Top Left Flat Right Center Aver. Unif.

1.2 A 1.1890 1.1881 1.1853 1.1886 1.834 1.1870 0.47%

1.2 B 1.1759 1.1759 1.1737 1.1752 1.2007 1.1804 2.3%

1.7 A 1.6938 1.6928 1.6882 1.6879 1.7156 1.6957 1.6%

1.7 B 1.7454 1.7385 1.7398 1.7412 1.7605 1.7451 1.3%

2.1 A 2.1013 2.0926 2.0939 2.0987 2.0927 2.0959 0.42%

2.1 B 2.1279 2.1112 2.1105 2.1146 2.1237 2.1176 0.82%

Table 3: Pre-development photoresist thickness measurements (µm)

• Centripetal force makes PR spin radially outward

Optimal Focus & Exposure Conditions

Wafer Exposure Focus

1.2 um 1.0 sec -8

1.7 um 1.2 sec -10

2.1 um 1.8 sec -10

• F & E values chosen after careful analysis of previous focus-exposure matrix experiments

Table 4: Focus & exposure values for 1.2, 1.7, and 2.1 wafers in experiment

PR THICKNESS LOST: POST DEV.

Wafer Top Left Flat Right Center Aver.

2.1 A 1.9952 1.9877 1.9915 1.9953 1.9917 1.9923

Table 5: Post-development measurements

• All wafers = run through svgdev1 track

• Standard programs: (1, 1) - no hard bake [yet]

• TL due to selectivity~ 0.1 µm

HARD BAKE + UV BAKE RESULTS


1.2 1.2480 1.2770 1.1229 1.1232 1.1268 1.1250

1.7 1.6014 1.6007 1.5990 1.6025 2.6269 1.6063

2.1 1.9829 1.9784 1.9783 1.9817 1.9781 1.9799

Wafer Proc. Top Left Flat Right Center Aver.

1.2 A 1.1020 1.1202 1.0983 1.1020 1.0976 1.1030

1.7 A 1.6250 1.6186 1.6169 1.6316 1.6359 1.6256

2.1 S 1.9407 1.9328 2.9384 1.9551 1.9522 1.9438

Table 6 (left): Post Hard Bake Measurements –TL ~ 0.06 µm

Table 7 (right): Post UV Bake Measurements TL ~ 0.08 µm

2.8 µm: CONTACT VS PROXIMITY

Contact bake left ghost image of rings on wafer

Had to change settings to carry out proximity bake rather than contact bake

VS

Contact Bake Proximity Bake

NEW PR COAT CONDITIONS

Wafer Top Left Flat Right Center Aver. Unif.

2.8 A 2.7923 2.8350 2.8379 2.8038 2.8166 2.8170 1.6%

2.8 B 2.9112 2.8946 2.8410 2.8487 2.8780 2.8747 2.4%

Table 9: Pre-development measurements with new program (µm)– Optimized

Wafer Top Left Flat Right Average Unif.

2.8 A 6.0671 5.4560 4.7310 4.2287 5.1157 35.9%

2.8 B 6.3286 6.4358 5.6911 5.6557 6.0280 11.2%

Table 8: Pre-development measurements without new program (µm) – Unoptimized

• Extreme improvement in accuracy noted when spin speed changed to 820 rpm rather than 500 rpm as previously conducted

OPTIMAL FOCUS & EXPOSURE – 2.8

Wafer Exposure Focus

2.8 3.4 -8

Table 10 (left): Focus/exposure values for the 2.8 um wafer (µm)

Wafer Top Left Flat Right Center Average

2.8 2.6311 2.6270 2.6150 2.6211 2.6131 2.6215

Table 11: Post-development measurements for the 2.8 um wafer (µm)

POST HARD BAKE MEASUREMENTS

Table 12: Post hard bake measurements (µm)

**NOTE: The UV bake resulted in excessive damage to the photoresist film; thus, not recommended to UV bake wafers of this thickness


2.8 A 2.6254 2.6122 2.6026 2.6122 2.6039 2.6113

LEO SEM IMAGES – 1.2 um

Minimum Resolved Feature – 0.5 µm


Minimum Resolved Feature – 0.5 µm 4 : 1 aspect ratio


Minimum Resolved Feature – 0.6 µm 3.5 : 1 aspect ratio


Minimum Resolved Feature – 0.6 µm 4 : 1 aspect ratio

SUMMARY

Wafer ID

Svgcoat1 Process

to be modified

Svgdev1 Process

Spin Speed (rpm)

Target Thickness

(µm)

Measured Thickness

Pre-dev (µm)

Measured Thickness Post-dev

(µm)

Thickness after

Hard-Bake

Thickness after

UV Bake

Min Res Feat

1 (1,1) (1,1) 4100 1.2 1.1870 -- 1.1250 1.1030 0.5

2 (3,1) (1,1) 2000 1.7 1.6957 -- 1.6063 1.6256 0.5

3 (5,1) (1,1) 1300 2.1 2.0959 1.9923 1.9799 1.9438 0.6

4 (4,7) (1,1) 820 2.8 2.8170 2.6131 2.6113 -- 0.6

Best Conditions

ACKNOWLEDGEMENTS

Thank you Jeff Clarkson for mentoring me throughout my time in the Nanolab, and helping me execute my project every step of the way!

Thank you Olek Proskurowski for guiding, mentoring and teaching me so much about web development!

Thank you Hussain Alseddiq and Kim Chan for answering all my questions about my projects and helping me throughout them whenever problems arose!

Thank you Cheryl Chang for teaching me all about photolithography and how to use so many tools in the lab!

Thank you David Lo and Greg Mullins for maintaining much of the equipment used for this work!

Thank you Marilyn Kushner and Adrienne Ruff for taking us to SemiCon!

Thank you Bill Flounders for this amazing opportunity!

Thank you to the entire staff for taking time out of their busy schedules to help me and for being so supportive!

MODIFIED PROGRAMS – svgcoat1

1.2 ORIGINAL Program

P E O A T S A

1 1 SPIN 0 30.0 0.00 00

1 2 SPIN 0 01.0 0.50 00

1 3 DSP1 1 -- 0.50 50

1 4 SPIN 0 01.5 0.50 20

1 5 SPIN 0 30.0 4.1 50

1 6 END 0 0.00 0.00 00

Modified Program

P E O A T S A

1 3 SPIN 0 10.0 0.50 50


P E O A T S A

3 1 SPIN 0 30.0 0.00 01

3 2 SPIN 0 01.0 0.50 50

3 3 DSP1 1 -- 0.50 50

3 4 SPIN 0 01.5 0.50 20

3 5 SPIN 0 30.0 2.00 50

3 6 END 0 0.00 0.00 00

Modified Program

P E O A T S A

3 3 SPIN 0 10.0 0.50 00


P E O A T S A

5 1 SPIN 0 30.0 0.00 00

5 2 SPIN 0 01.0 0.50 50

5 3 DSP1 1 -- 0.50 50

5 4 SPIN 0 01.5 0.50 20

5 5 SPIN 0 30.0 1.30 50

5 6 END 0 0.00 0.00 50

Modified Program

P E O A T S A

5 3 SPIN 0 10.0 0.50 50

2.8 Modified Program

Coat

P E O A T S A

7 1 SPIN 0 15.0 0.00 01

7 2 SPIN 0 03.0 0.50 01

7 3 SPIN 0 30.0 0.82 01

7 4 END 0 30.0 0.00 00

Oven

P E O A T S A

4 1 STEP 000.0 0.15 00 4

4 2 STEP 005.0 0.10 00 4

4 3 STEP 100.0 0.05 00 4

4 4 COOL 006.0 -- 00 4

4 5 END 000.0 -- 00 4

nishtha bhatia washington high school july 31st, 2014 · 2014-08-15 · nishtha bhatia washington...

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