Real Time Optical Diagnostics in Laser Etching and Deposition
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REAL TIME OPTICAL DIAGNOSTICS IN LASER ETCHING AND DEPOSITION IRVING P. HERMAN, HUA TANG, and PATRICK P. LEONG Department of Applied Physics and the Microelectronics Sciences Laboratories, Columbia University, New York, NY 10027. ABSTRACT Optical probing of laser-assisted chemical reactions on surfaces in real time can help explain and control these processes. Raman microprobe spectroscopy and micro laser induced fluorescence are the two optical probes employed here to investigate several examples of localized laser surface reactions. Raman microprobe analysis is used to monitor in real time the CuCI and CuCI2 products on the surface during local laser etching of copper films by C12 and the concomitant loss of the Cu20 passivation layer. It is also used to follow the production of Cu20 during the laser oxidation of Cu. Polarization Raman analysis is utilized to identify and analyze partially molten silicon during laser heating in vacuum and during the etching of silicon by chlorine. Laser induced fluorescence is used as a real time microprobe of desorbed products during local laserassisted etching of Si and Al surfaces. INTRODUCTION Optical spectroscopic methods have long been used as nondestructive, in stu probes of the gas phase and of the film itself during thin film processing. Film properties, such as composition, crystallinity, and stress, and the film temperature can be measured with optical probes, which can also be utilized to determine the identity, concentration, and energy level distribution of reactants and products in the gas medium above the films. The focus of this work is on the use of optical diagnostics to probe laser microchemical reactions on surfaces in real time. Optical probes with very high spatial resolution are needed in such studies because the lateral spatial extent of the surface modification is typically - I pm. The most common and the simplest optical probes of films in laser-assisted processing are transmission and reflection spectroscopy.[ 1,2] By examining film absorption and interference effects, the film thickness can be probed in real time. The emphasis of this work is on the use of another technique, Raman microprobe spectroscopy, to probe films during and in sidu after laser processing. Raman spectroscopy has several strengths, particularly the unique information it can provide about semiconductor and insulator films and its insensitivity to surface roughness, that often outweigh its principal
Mat. Res. Soc. Symp. Proc. Vol. 201. • 1991 Materials Research Society
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Roman Shift (1/cm) Figure 1. The Raman spectrum (a) before, (b) during, and (c) after laser etching of a 1.4 pam-thick copper film on glass (4880 A, 60 mW, 10 Torr Cl 2 during etching). (Adapted from Ref. 3.)
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x (u m) Figure 2. Raman scattering intensity of CuC1 (- 125 cm-1 feature, open circles) and CuCI2 (282 cm-n peak, filled circles) in a transverse scan across a laser-etched
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