An Overview of Laser Chemical Processing
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AN OVERVIEW OF LASER CHEMICAL PROCESSING
RICHARD M. OSGOOD, JR. Microelectronics Sciences Laboratory, Columbia University,
Laboratories and New York, NY 10027
Columbia
Radiation
ABSTRACT A overview of the recent developments in laser chemical processing is provided. The review covers advances in understanding fundamental process physics, the development of new techniques, and the implementation of applications.
INTRODUCTION Since the first MRS Symposium in this field in 1982, laser chemical modification of surfaces has evolved from an exciting but untested technique to one that has well established, commercial applications. During this same time, new laser-based fabrication techniques have been developed, suggesting, in turn, new types of applications. In addition to these practical interests, a series of studies has been performed on the fundamental surface physics involved in processing. Basic insight has been gained, for example, into the the physics of UV decomposition of molecules on surfaces, photon-assisted etching of semiconductors, and photooxidation of semiconductors. The purpose of this paper is to present a brief personal overview of the more recent developments in the field of laser chemical processing. The review will proceed from the fundamental to the applied. In particular, it will start with a discussion of new insights into the photochemistry occurring on the surfaces of semiconductors, both in liquids and in a gas ambient. Next, new microfabrication techniques, which are based on the unusual physical phenomena in laser surface interactions, will be reviewed. The use of photochemical techniques to 0 grow crystal layers at low temperatures, i.e. -200 C, will then be described. The review will conclude with the application of laser chemistry to in situ processing and to making custom interconnections on integrated circuits. Finally, we point out as a very important note of caution, this overview is not in any sense a complete review. It does not include many important areas of research in the field of laser chemical processing. Instead, I have chosen to present a number of selected topics which give a sense of the dynamic research in this area.
Fundamental Mechanisms Laser chemical reactions at surfaces can be initiated either as a result of thermal or direct electronic excitation of the substrate or the reactant [1,2]. Within the last few years, the most fundamental work on mechanisms has been in the area of direct electronic chemistry. In general, this research has been divided into two categories: I) the surface electromagnetic effects that control the spatial distribution of the laser light at the interface; and 2) the detailed photophysics of the dissociation process. In this section, we will review recent advances in understanding the process of photodissociation on surfaces. Surface photodissociation is an essential step in ultraviolet direct
Mat. Res. Soc. Symp. Proc. Vol. 75.
1987 Materials Research Society
4
laser writing, from gas, adsorbed, and spun-on precursor molecules, a
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