JOURNAL OF MATERIALS SCIENCE 35 (2 0 0 0 ) 5951 – 5956 Laser induced diffusion of indium in silicon W. K. HAMOUDI, R. O. DALA ALI Department of Applied Sciences, University of Technology, P.O. Box 35010, Baghdad, Iraq E-mail: waleed-hamoudi@mail.com In this work, a 300 µs pulsed Nd:YAG laser was employed to induce indium diffusion in silicon wafer. Electrical properties were studied for a range of laser pulse energies (0.225–0.369 J) and substrate temperature (300–398 ◦ k). The four point probe measurements showed that a minimum sheet resistance (54 /) was resulted at the melting threshold energy and room temperature. The sheet resistance was a decreasing function of the temperature rise of the substrate. The (I -V ) and (C -V ) measurements expressed improvement in the characteristics of the fabricated diodes when substrate temperature rises and irradiating pulse energy increases up to melting threshold value after which these characteristics starts to deteriorate. C  2000 Kluwer Academic Publishers 1. Introduction Laser beam is widely used nowadays to develop elec- tronic devices. It is employed in etching, drilling and annealing [1]. Laser induced diffusion of impurities in semiconductor has been adopted to manufacture diodes, solar cells [2, 3] and thin film transistor [4]. This technique relies on changing electrical properties of semiconductors was first reported by Narayan et al. [5] when large p-n junction of good characteristic where fabricated by boron deposition on silicon, followed by Q. switched ruby laser irradiation. One group irradi- ated a semiconductor material (immersed in the impu- rity solvent) with a laser beam [6] while others made use of the gas [7] and solid phase [8] of impurity with a laser beam to obtain diffusion. In the present work an indium thin film was coated on a silicon wafer then irradiated with a Nd:YAG laser pulses. The characteristics of the manufactured diodes were studied as a function of laser energy and substrate temperature. 2. Experimental work N-type single-crystal (111) Silicon wafers were doped with indium. The 500 µm thick wafers of (5 /) were first washed with warm water and immersed in ethanol container then in an ultrasonic bath for (10) minutes and then dried by hot air. Chemical etching was em- ployed using a mixture comprising CH 3 COOH, HNO 3 and HF at ratios (2 : 3 : 2) at concentrations 99%, 70% and 49% respectively for (10) minutes to remove the oxide layer from the silicon surface. This was followed by thorough cleaning by ethanol and finally dried. A thin (300 ˚ A) indium layer was deposited on the surface of the silicon wafer using Balzer (BAE 370) thermal coating unit at vacuum (10 −7 torr.). Each wafer was cut into (1X1 cm 2 ) samples that were irradiated by a 300 µs pulsed Nd:YAG laser. The laser pulsed energy (0.225–0.369 J) and substrate temperature (300–398 ◦ k) were variable parameters. The small laser spots size (0.028 cm 2 ) necessitated the use of overlapped laser spots, as shown in Fig. 1, to obtain relevant area re- quired to accomplish electrical measurements. Fig. 2 shows the experimental sketch of induced diffusion. The substrate of the sample was heated using a (650 W) Figure 1 Shows overlapped laser spots. Figure 2 Shows the experimental sketch of induced diffusion. 0022–2461 C  2000 Kluwer Academic Publishers 5951