Selective Etching Using Argon Plasma

By: C. Joseph LustAdvisor: Prof. Kvam

Overview Objectives Approach Equipment Used Problems Findings

Introduction To selectively etch silicon nitride

and aluminum deposited on a silicon substrate.

Silicon

Silicon Nitide

Aluminum

Approach Cut samples to a size of about

0.75cm by 0.75 cm. Clean samples using acetone and

methanol Use spinner at 4000 rpm to apply

AZ 1518 photoresist Bake at 900 C for 10 minutes

Approach Place mask on sample and expose

to UV light for one minute at a height of four inches

Place in AZ developer for approximately 10 to 15 seconds then rinse in DI water

Bake at 900 C for 10 minutes Use Carbon tape to attach samples

to blank sputter ring

Approach Etch in sputterer using Argon

Plasma for desired time Take off Photoresist using Acetone Used profilometer to measure

height difference

Sputtering Used times of 10 minutes, 20

minutes, 30 minutes, 40 minutes, and 50, minutes, and 60 minutes

Kept pressure at around 80 millitorrs

Kept current at around 15 milliamps

Photoresist The photoresist used was AZ 1518

which is made by Clariant. AZ 1518 is a positive photoresist. When it is exposed to UV light that

part can be removed by using AZ developer.

Positive Resist

Sample to be etched

Resist

Equipment Used Headway Reasearch, Inc Spinner Blak-Ray Longwave ultraviolet

lamp Anatech LTD Hummer 6.2

sputtering system Tencor instruments Alpha-step 200

profilometer

Problems Getting Photoresist on samples

took a couple of attempts to get righto First batch resist just washed away

o Mask wasn’t close enough or no prebakeo Second batch resist wouldn’t come off

o Developer was too diluted

Mask

Before Etching

After Etching for 60 minutes

Findings When using the profilometer, the

sections that were covered by resist were left unharmed. The results were comparable to a sample that had not been used at all.

Findings On the sections of Silicon Nitride

and Aluminum that were exposed, the results were not as expected. While it was being etched the plasma caused the material to rise up. This caused a peaks to form when the profilometer was used.

Findings These peaks were usually between

1 to 3 microns higher then the unetched section. When comparing the different runs there was no pattern between height of the peaks and run time.

Profilometer graph for SiN

-0.5

0

0.5

1

1.5

2

2.5

0 500 1000 1500 2000 2500

microns

microns

Series1

Profilometer graph for Al

-0.5

0

0.5

1

1.5

2

2.5

0 500 1000 1500 2000 2500

microns

microns

Series1

Future Work Try using different pressure and

current for the plasma. Try using a wet etch to selectively

etch the materials.

Acknowledgements Prof. Kvam Mark McCormick Patty Metcalf Purdue University