Selective Etching Using Argon Plasma By: C. Joseph Lust Advisor: 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 90 0 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 90 0 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 right o First batch resist just washed away o Mask wasn’t close enough or no prebake o 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

Profilometer graph for Al

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