Semiconductor Processing with Excimer Lasers: An Overview
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SEMICONDUCTOR PROCESSING WITH EXCIMER LASERS:
AN OVERVIEW
R. T. YOUNG Helionetics, Inc., San Diego, California 92123 and Solid State Division, Oak Ridge National Laboratory Oak Ridge, Tennessee 37831 ABSTRACT
The present level of development of excimer lasers, as it relates to semiconductor processing, and the advantages of these lasers for such processing, are reviewed. Extensive comparisons of the quality of annealing of ion-implanted Si obtained with XeCl and ruby lasers are presented. Major applications in the area of solar cell fabrication, siliconon-sapphire technology, laser photochemical processing, and submicron optical lithography are outlined and discussed. INTRODUCTION Rare gas halide (RGH) excimer lasers form a class of newly developed lasers which are capable of efficiently generating high powered pulses of radiation at ultraviolet wavelengths. The rapid advancement of excimer laser technology and the many unique characteristics associated with these lasers have made them very attractive for many aspects of semiconductor device fabrication. Major applications include the modification of nearsurface properties by ultrarapid nonequilibrium melting and recrystallization, UV photon-induced photochemical film deposition, etching, and doping, and the utilization of the short wavelength and incoherent nature of the laser radiation for submicron optical lithography. This paper will give a general overview in each of these areas. Since excimer lasers are relatively new on the market, a brief discussion of the present state of their development, as it relates to semiconductor processing, will be given and a comparison of the characteristics of excimer lasers with those of the solid state lasers most commonly used in semiconductor processing will be discussed. EXCIMER LASERS The term excimer was originally introduced in 1960 [1] to refer to an "excited dimer" which are certain molecular species, such as Xe , Ar*, and 2 Hg2 , that exist only in the upper or excited state and have a repulsive and, therefore, dissociative lower state. It was subsequently found [2,3] that certain molecular complexes such as KrF*, XeOH*, etc., also exhibited the same characteristics and these were referred to as exciplexes. These two classes of molecules provide a nearly ideal situation for creating the nonequilibrium population inversion required for laser action. In practice, the distinction between excited dimers and exciplexes is frequently ignored and they are commonly referred to as excimers. From the mechanism and kinetics of excimer formation, it is predicted that among all the excimers the RGH excimer lasers offer the advantages of high average power and high efficiency; they are the most commonly discussed excimer lasers. Since the demonstration of the first e-beam-pumped RGH excimer laser in 1975 [4,5], the present technology has advanced to the point that e-beampumped lasers with kilojoule output energies have been constructed. Although e-beam-pumped lasers can be scaled to high pulse energies, they
Mat. Res.Soc.Symp.
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