Laser-Chemical Deposition and Etching on the Metallization Level of Integrated Circuits
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LASER-CHEMICAL DEPOSITION AND ETCHING ON THE METALLIZATION LEVEL OF INTEGRATED CIRCUITS A. WAYNE JOHNSON AND K. E. GREENBERG Sandia National Laboratories, Laser and Atomic Physics Division, P. 0. Box 5800, Albuquerque, NM 87185 ABSTRACT Laser-controlled chemical deposition and etching techniques were used to modify integrated circuits. This work used a pulsed laser to initiate and control the etching, by chlorine gas, of aluminum conductors. New conducting paths were then formed by laser-chemical vapor deposition of highly-doped silicon from silane and diborane. Improved conductivity of laser-deposited connectors was achieved by the selective deposition of tungsten on the silicon. These techniques were used to "rewire" an integrated circuit allowing the full evaluation of the corrected circuit design. INTRODUCTION Laser-initiated etching and deposition processes can be used for a number of different microelectronic applications including design-fault analysis, circuit customization, and redundant memory circuit processing. These applications require techniques for locally etching and depositing conducting materials in an integrated circuit (see articles in two recent reviews) [1,2]. Using laser-initiated deposition and etching, we have demonstrated that integrated circuits can be modified on the metallization level by redirecting the interconnects. The circuits were "rewired" by locally etching a section of an aluminum interconnect and, subsequently, depositing a new conducting link. The laser-initiated dry-chemical etching and deposition were implemented in a single vacuum system and required only a simple exchange of gases to go from an etching to a deposition environment.
EXPERIMENTAL APPARATUS These studies used a laser-microscope system to focus laser light onto the surface of a VLSI circuit with a spot size of approximately one The circuit was placed in a vacuum cell that was mounted on a micrometer. The laser beam was positioned computer-controlled x-y translation stage. A onto the desired part of the circuit by moving the entire vacuum cell. video display permitted in-situ observation of the etching or deposition process. 7 The vacuum cell was evacuated to a base pressure of approximately 5 x Torr before it was filled with the appropriate etching or deposition 10 Aluminum was etched by irradiating samples, maintained in a chlorine gases. ambient, with a KrF laser or with one of the harmonics of a Nd:YAG laser. For very small features applications, the pulsed lasers were spatially The deposition of silicon and tungsten were obtained by the filtered. pyrolytic decomposition of silane and tungsten hexafluoride, respectively, using the UV lines of an argon ion laser to heat the surface. LASER-INITIATED ETCHING OF ALUMINUM Laser-initiated etching of aluminum with a KrF laser has been described This technique takes advantage of the fact that aluminum previously. reacts spontaneously with chlorine, but, aluminum oxide does not.
Mat. Res. Soc. Symp. Proc. Vol. 75. ' 1987 Materials Research Society
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