1 - Frontier



Photoresist and Photomask Knowledge (2.5 points each) 25 points total

1. If acid from a previous step is left on the wafer (trapped in a small crack), what type of defect would you expect after exposure/PEB/development with:

a) DUV CAR positive resist:

b) DUV CAR negative resist:

c) DNQ positive resist:

d) DNQ AHR resist:

2. What does the “Q” factor in DNQ photoresist formulations mean?

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3. What process technique has the greatest effect and why on:

a) Swing curve:

(b) Standing waves:

4. What is the simplest and least expensive way to improve the DOF for 130nm gate linewidths on a 4 gegabit DRAM memory cell and how does this work?

5. Explain the CARL and CEL multi-layer techniques and when would you implement them ?

6. What is the MEEF?

7. What re the physical limitations of CaF2 ?

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8. What coating material and thickness would one use to reduce the reflection on an under-water camera lens front surface? Assume green light for wavelength (550nm) Lens is borosilicate glass. Show all work!

9. As storm moves in from the west and the barometric pressure rapidly changes from 1023 to 1006 m barr. The barometric compensator on the scanner is not working. What is the focal plane shift and will it put the 0.40um contact CDs outside the +/-10% CD window (0.36 to 0.44um)? The stepper is an ASML 5500/100 with NA set to 0.54 and sigma = 0.70 Source image diameter = 79.18 mm and use refractive index lens = 1.53.

What pellicle thickness and refractive index would cancel this focus shift?

Barometric pressure has a significant effect on optics, including focal length and magnification: Problem: Find focal plane shift ΔV?

10. 3 letter>> Definitions:

• LER

• LES.

• RET:

• PEC

• EUV:

• LAER.

• HAER

• COG:

• MLR

• NGL:.

• MTF.

• DMI:

• PSF.

• OPE

• EAPSM.

• MMP.

Process Control Problems Develop innovative solution to each. CHOOSE ONLY 2 ! : (10 points each) 20 points total

Explain all work. Use any source to find a solution ( notes and or web) Explain how and why your solution will correct the problem. USE KNOWN PROPERITIES OF PHOTOLITHOGRAPHY! DO NOT SPECULATE OR GUESS AT A SOLUTION!

1. Photoresist CDs on one side of the wafer (1/8 wafer) are too large and the die/wafer yield in that area is very low causing the 4 GHz microprocessor speeds to be 50 Mhz slower!

a. Redefine problem and define what photoresist layer this is ( gate, diffusion, implant, metal, via, etc)

b. Propose an effective solution and explain the physics behind it!

2. The isolated to dense linewidth bias has changed on multiple steppers in your fab.

a. Redefine problem and define what photoresist layer this is ( gate, diffusion, implant, metal, via, etc)

b. Propose an effective solution and explain the physics behind it!

3. In a lot of 25 wafers the first and last wafer have good yields, while all the wafers in between (2-24) yield poorly.

a. Redefine problem and define what photoresist layer this is ( gate, diffusion, implant, metal, via, etc)

b. Propose an effective solution and explain the physics behind it!

4. You just installed a new I-line photoresist ( A = 0.596, B = 0.169, and C = 0.016) and the die/wafer yields have gone down due to the 0.30 um contacts ( on oxide) being closed.

a. Redefine problem

b. Propose an effective solution and explain the physics behind it!

5. Your DUV photo module just when down hard due to the 100 nm NMOS gate linewidths on the polysilicon layer are falling over at specific locations in each field. Production manger Mrs Kepler is yelling at you!

a. Redefine problem and why is Mrs K. yelling agin?

b. Propose an effective solution and explain the physics behind it!

General Photolithography Knowledge (2 Points each) 20 POINTS TOTAL

1. Which phase shift mask design is design is for dense 120nm DRAM linewidths? Discuss why.

2. Describe 3 OPC techniques (shapes) and how they improve specific features.

3. Form 3 sets of the 3 terms that would be used together

|CaF2 |g-line |Acrylate |

|PHS |Borosilicate |193 nm |

|KrF |Novolak |Fused Silica |

4. Describe 2 OAI techniques and how they increase process latitude for specific features.

5. A very thick DNQ photoresist film coating (20-60um) may suffer from two problems. What are they and why would they occur?

6. How would you know if your mask vendor used a sodalime glass substrate instead of quartz on your KrF process? Explain effects and reasons.

7. What does sub-wavelength lithography mean? What process “tricks” does one use with this sub-wavelength lithography ?

8. List 3 technical advantages and disadvantages of X-ray lithography.

9. Explain the NGL proposed SCALPEL lithography

10. When would one use a TARC film instead of a BARC film?

Optical Knowledge (2.5 points each) 25 POINTS TOTAL

1. If the birefringence of the quartz reticle changes from 5 to 10 nm/cm phase error, what might occur on a:

a. 1X Ultratach stepper

b. 5X ASML 2500 stepper

c. SVGL MSIII+ DUV scanner

2. What is the significance of the “Strehl ratio”?

3. What is Kohler illumination?.

4. Why does a swing curve for DUV illumination have a larger amplitude than I-line illumination? What do you do to correct this?

5. How does an ASM stepper adjust field magnification?

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6. Light having a wavelength of 500nm passes from a vacuum into a diamond ( n = 2.40). Assume that the frequency is unaltered as the light traverses different substances. What is the speed of this radiation and wavelength in the diamond? Do you think this concept could be used to enhance resolution in optical lithography? Explain why or why not?

7. If you look at an oil film on water (n=1.33), it has a rainbow type appearance. Estimate with an equation the thickness of the oil film for the “orange” colored band. Assume you are viewing at normal incidence

8. If the interference filter to filter the Hg ARC lamp down to 248nm wavelength in a lamp based DUV scanner were tilted by +5 degrees what would occur? Explain why and give equation.

9. What is the Maximum spatial frequency that can enter a lens and the resulting resolution for:

a. Coherent illumination

b. Incoherent illumination

10. What is FLEX? How does it work and what are the benefits?

Identification Knowledge (5 Points each) 10 POINTS TOTAL

Define what the photo is. Define what caused the problem if any and how to correct it.

PHOTO I:_____________________________

PHOTO II:_____________________________

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