Date of Award

Spring 2006

Document Type


Degree Name

Doctor of Philosophy (PhD)


Electrical/Computer Engineering

Committee Director

Amin Dharamsi

Committee Member

Ravindra Joshi

Committee Member

Linda Vahala

Committee Member

James Yuan


Plasma processing is widely used in the microelectronics industry for deposition of thin films. It is also used in etching of semiconductors, metals and organic materials such as photoresists. In addition, plasmas are widely used to modify material surfaces. Plasma surface modification can improve the surface adhesion of polymeric materials, which can be used as insulating layers in multilayer semiconductor structures. In deposition and etching, relatively a large amount of material is added to or removed from the surface. In plasma surface modification, only the surface layer is changed in composition or structure, and no significant amount of material is added or removed. In this research, two atmospheric-pressure plasmas were generated and characterized, and were used to modify polyethyleneterephthalate (PET) surfaces.

An atmospheric-pressure helium plasma source was generated without any need of vacuum. The plasma was first characterized with a Langmuir Probe for electron density estimation. The emission spectrum was measured and the spectroscopic identification allowed main components of the plasma to be identified. In addition, absorption spectroscopy was used to measure the ozone density from the plasma. A PET surface was modified with this plasma. Contact angles were measured on the modified PET surface. Hydrophilic and Hydrophobic PET surfaces were obtained with different minority gas or chemicals added to the feeding helium gas. The changes of the contact angles of the modified surfaces were monitored as a function of time. The surface modification was determined to be mainly a chemical and photochemical process through analysis and experiments on ions, ultraviolet photons, oxygen atoms and ozone molecules.

An atmospheric-pressure air plasma source was developed without the need of vacuum and the need of expensive helium gas. The peak electron density was determined by measuring and analyzing current-voltage characteristics of the plasma. The emission spectrum was measured and the main peaks were identified. Absorption spectroscopy was used to estimate ozone density. This plasma was used to modify PET surfaces with very high throughput.