Excimer Laser Direct Write Aluminum on Aluminum Nitride
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ABSTRACT Fabrication of metal lines on aluminum nitride (AIN) ceramic is important for application of AIN as a microcircuit board. An Al line can be made directly from AIN by excimer laser exposure. All lines in this paper were written by pulsed KrF excimer laser (248 nm) in air and vacuum at different scan speeds with a constant laser energy. The morphology of the Al lines was observed by optical and scanning electron microscopies. The lines become more metallic when the scan speed decreases. Consequently the resistance, measured by the four-point probe technique, decreased to a minimum value in the scan speed range of 400 jtm/s to 900 jim/s for the samples made in air. The resistance of Al lines written in air is greater than that in vacuum because of oxidation. The samples made in air with scan speed lower than 400 jim/s were heavily oxidized. SAXPS spectra showed a strong oxidation state and that the excimer laser exposure depletes nitrogen from AMN. The Al lines produced by laser-induced decomposition of AMN board are being evaluated as catalysts for laser assisted CVD and conventional electroless plating. The oxidation layer on the surface of Al lines may effect the adhesion between the Al lines and the deposited or plated metal.
INTRODUCTION Materials with high thermal conductivity can quickly dissipate a great amount of heat as is becoming necessary in high speed electronics. In microelectronics, aluminum nitride ceramic is being considered as a substrate material because of its high thermal conductivity (-165 W/mK which is 10 times greater than that of alumina) and better thermal expansion match to silicon 1 Thin film metallization of ceramic substrates can be accomplished by a number of techniques. Sputtering 2 is very efficient, but in most cases, there needs to be an intermediate layer to enhance the adhesion between the substrate and the conductive layer. Photolithography patterning ' is a traditional approach, but this technique requires a time-consuming process for generating the masks and a waste producing etching process. Argon ion laser direct-writing techniques have been demonstrated in a variety of applications such as fabrication of MOSFETs 4 and multilevel interconnection s. A similar technique is being developed for laser direct write metallization of aluminum nitride using an excimer laser. Excimer laser pulses are highly absorbed by aluminum nitride because the energy gap of aluminum nitride is 6.2 eV (200 nm) 6. In this paper, the aluminum nitride substrates were decomposed by a pulsed excimer KrF laser with a wavelength of 248 nm either in air and in vacuum. Our current efforts are focused on characteristic of the irradiated regions.
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Mat. Res. Soc. Symp. Proc. Vol. 390 * 1995 Materials Research Society
EXPERIMENT
Energy Monitor
Lase Vacuum Chamber
4" travel
8" travel w
Figure 1. Experimental setup. The commercially available aluminum nitride substrates from Carborundum are 1 x 1 inch in size. They were cleaned ultrasonically in acetone for 20 minutes and then dried in air. I
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