Doctoral Dissertations

Date of Award

12-1994

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Metallurgical Engineering

Major Professor

Anthony J. Pedraza

Committee Members

Londes, Liaw, Joy

Abstract

The purpose of this thesis is to develop new techniques to produce very fine, strongly adhering metallic paths on ceramic substrates for electronic packaging using excimer laser irradiation. The thesis has been divided into three parts. In the first part, the effects of laser irradiation on surface smoothing, melting and ablation depths, surface chemistry and subsurface structure of alumina and aluminum nitride substrates has been characterized as a function of laser energy density and laser pulses. This characterization has been used extensively to explain results which are obtained in latter stages of this work.

The second part of this thesis deals with the discovery that excimer laser irradiation of polycrystalline alumina leads to a remarkable surface smoothing and simultaneously modifies the surface properties, which leads to an adhesion enhancement for subsequent thin film copper deposition. This adhesion enhancement has been correlated to the near surface structure, studied using cross-sectional transmission electron microscopy (TEM). Additionally, this adhesion enhancement has been correlated to high resolution transmission electron microscopy (HRTEM) results obtained by Dr. Siqi Cao, and to X-ray photoelectron spectroscopy data acquired by Mr. Jaewon Park on laser irradiated single crystal alumina.

The third part of this thesis involves research on a new two step process to generate metallic patterns on dielectric materials. This method involves excimer laser involves excimer laser induced surface activation for electroless deposition. Deposition takes place on the laser irradiated (activated) region only. It is thus possible to generate metallic patterns as well as plated vias directly on the substrate by laser irradiating the substrate through a laser projection mask followed by electroless deposition. Nucleation, growth kinetics, and adhesion studies have been performed for patterns generated on alumina and aluminum nitride. Scanning electron microscopy studies of the initial stages of growth show that nucleating sites are separated by 2-5 µm, indicating that minimum line widths of 10-20 µm can be obtained by this technique. Low temperature annealing of electroless copper films deposited on substrates activated at low laser energies gives adhesion strengths of 40-50 MPa. This technique has also been developed for industrial applications with respect to pattern generation. In this work, 20 µm narrow lines have been produced by using this technique in conjunction with photolithography. Additionally 40 µm patterns were obtained without using any masking photoresists on the surface through the use of a laser mask projector system.

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