Question

Photolithography

1. List some of the advantages of plasma cleaning. 2. Photoresist thickness and quality depends on spin-speed, temperature, humidity and photore- sist viscosity. Discuss how these parameters affected you experiment. 3. Present a comparison of negative and positive photoresists. Describe what happens chemically to both positive and negative resists when ex- posed to UV radiation. 4. Why is it easier to obtain a lift-off profile with a negative resist than with a positive resist? 5. Compare UV, X-ray, ion-beam, and electron- beam lithography. Summarize in a comparison table. Which techniques are used mostly in the IC industry today? How are the photons or charged particles created in each case?

Answer 1

1. The removal of impurities and contaminants from surfaces by using an energetic plasma or dielectric barrier discharge(DBD) plasma (created from gases) is known as "plasma cleaning". Plasma cleaning has many advantages such as:

• An unlimited number of chemical modifications is possible as different choices of gases and chemicals are available.
• In most of the cases, it can be a dry process. This effectively results in a cutback of the water consumption and energy to dry the treated materials.
• The cutback in the water usage results in reducing the amount of waste water and the cost of its disposal.
• It is quite ecofriendly as the plasma byproducts can be trapped rather than being released to the environment.