UV Laser-Induced Metal Deposition on Semiconductors From Electroplating Solutions
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UVLASER-INDUCED METAL DEPOSITION ON SEMICONDUCTORS FROM ELECTROPLATING SOLUTIONS JOSEPH ZAHAVI* AND PEHR E. PEHRSSON*" * Israel Institute of Metals, Technion City, Haifa 32000, Israel. ** Electronics Technology Division, Naval Research Lab., Washington, D.C. 20375-5000, U.S.A. NRL-NRC Postdoctoral Fellow. ABSTRACT We have demonstrated metal deposition on semiconductors immersed in electroplating solution by exposure to UVlaser radiation. N-type G-SiC and Si in gold or Pd/Ni electroplating solutions were exposed to 20 ns pulses of 193 nm or 248 nm excimer laser radiation. The energy per pulse was 20-100 mJ. Au and Pd/Ni metallizations deposited in lines and circles on SiC showed leaky Schottky barrier I-V characteristics. The thickness increased with increasing pulse energy or number. Both masked and maskless deposition were demonstrated without apparent damage to the substrate. Details of the process, potential mechanisms, and sample characterization are discussed. INTRODUCTION Ohmic and Schottky barrier metallizations are needed for many semiconductors, e.g., 6-SiC for high power microwave devices, HgCdTe for IR detectors, etc. Localized metal deposition on semiconductors by pulsed Nd:YAG laser irradiation of electroplating solutions at 1060 and 530 nm has been reported [1,13].Pulsed UVexcimer lasers have recently been shown to In drive chemical reactions at metal and semiconductor surfaces [2,3]. this paper we describe metal deposition on semiconductor surfaces, principally n-type 6-SiC and Si, immersed in electroplating solutions and exposed to If, as UV laser radiation, without application of an external bias.
expected, the deposition process is driven by photoelectron emission, it may be applicable for metallization of other semiconductors which cannot withstand high temperatures or sputtering damage, e.g., HgCdTe. EXPERIMENTAL Lambda Physik Model 103 ArF and Lumonics Hyper EX-400 KrF lasers,
operating at 193 and 248 nm. respectively, were used with associated optics, with a pyrex electroplating cell partially filled with solution and containing the semiconductor samples. The cell moved on an XYZ table under the fixed laser beam. No external potential was applied. The electroplating solutions were Aurospeed CVD for Au and Pallamet 75 for Pd/Ni depositions (Lea-Ronal Co., N.Y.). N-type 6-SiC and Si were used. The SiC samples, provided by Dr.R. Davis of N.C. State University, and by Dr. Ph. Klein of NRL, were 20 1pm7 thick layers grown on Si(100). Both were unintentionally doped to 10 /cm 3 . Samples were cleaned with trichloroethylene, acetone, methanol, and deionized water. Some of the SiC samples were then etched 1 hour prior to metallization with HF, K2 CO The Si(100) samples were 14-16 3 , HCI, and HF again. mils thick, p-doped to 5 ohm-cm. Some of the SiC samples were Si 3 N4 masked to make either positive or negative annuli.
Mat. Res. Soc. Symp. Proc. Vol, 75. 1987 Materials Research Society
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The laser radiation was focussed through a cylindrical lens onto sample surfaces covered with plating sol
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