Corey Lust

Ohio Northern University

Chemistry

Selective Etching Using Argon Plasma

Introduction

Selective etching can be used in the fabricating of microelectric devices. It can be used to etch silicon and other materials used in computer chips. There are to main types of etching. One type is wet or chemical etching. This involves using a type of acid like hydrofluoric acid to etch away selective parts of the surface. There are two drawbacks to using this approach. The first is that it when it etches is does not etch anisotropically. Also, when using this method care must be taken when handling the chemicals involved. The second method is dry or plasma etching. This involves using an easily excitable gas like argon to selectively etch away material. This also has some drawbacks. One of these is that the machinery used to generate plasma can be quite expensive. Plasmas are not as selective as the chemicals when they etch. Lastly, some of the gases that were used were chlorofluorocarbons that damage the ozone layer.

Objectives

  • Use Argon plasma to selectively etch Silicon Nitride and Aluminum on a Silicon Substrate.
  • Determine the rate of etching on each substance when etched with Argon plasma

Experimental Approach

  • Cut samples to a size of about 0.75cm by 0.75 cm.
  • Clean samples using acetone then methanol
  • Use spinner to apply photoresist AZ 1518
  • Bake samples in oven at 90oC for 10 minutes
  • Place mask on sample and expose to UV light for one minute from a height of about 4 inches
  • Place in AZ developer for about 10 to 15 seconds then rinse in water
  • Bake at 90oC for another 10 minutes
  • Use Carbon tape to attach samples to blank sputter ring
  • Etch using argon place at 80 millitorr and 15 milliamps for desired time
  • Take off photoresist with acetone
  • Use profilometer to measure height difference

Research Findings

When the sample was ran through the profilometer, the data that we received showed that the unetched sections were relatively flat. On the other hand the sections that were etched were many different peaks about 2 to 3 microns higher then the unetched surface. This is believed to be caused by the etching process where the area where the etching takes place causes the surface to flake and rise up. In conclusion, this is not a practical way to etch silicon nitride and aluminum. While parts were etched away, the underlying areas flaked up and were taller then the unetched sections.

Before etching.
After 1 hr. etching.
Final Research Presentation