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Mat. Res. Soc. Symp. Proc. Vol. 388 0 1995 Materials Research Society

(99.99%) Si 3N 4 powder into a one-inch diameter disk and subsequently sintered at 900'C for 24 hours in a He gas environment. Three different substrates, Si(100), NaCI (100) and electrically-conducting indium-tin-oxide (ITO) coated glass, were used for the purpose of film characterizations for different physical properties. The substrate was mounted on a rotating substrate holder facing the target. The separation between the target and the substrate was about 5.5 cm. The substrate temperature was measured using a thermocouple and controlled by a temperature controller (EUROTHERM, 818p). Irradiation at a wavelength of 193 nm (ArF) was provided by a pulsed (duration width = 23 ns) excimer laser (LAMBDA PHYSIK, LPX210i) at a repetition rate of 5 to 15 Hz, with a laser fluence at the target was about 1- 2 J/cm 2 . After loading the substrate and target, the chamber was evacuated to about 2x10-6 torr, prior to heating the substrate to 300 'C for 30 minutes to reduce outgassing and to clean the substrate. The substrate was then gradually cooled to the deposition temperature. Different pressure levels of oxygen gas were introduced into the chamber by a mass flow controller to alter the oxygen/nitrogen (0/N) ratio in the film. With the above growth conditions, the typical deposition rate was about 0.05 - 0.1 A per laser pulse depending on the oxygen gas pressure. Deposition was stopped after 20,000 pulses for the Si and NaCl substrates and after 60,000 pulses for the ITO substrates. FOCUSING

MIRROR EXCIMER LASER (X=193 nm)

COMPUTER/

MOTOOTOR MOTO

MFCHEAT

VIEW WINDOW 02

/5%F2

/

A He N2 /He

EXCHANGER N2

Figure 1. Schematic diagram of pulsed laser deposition system Results and discussion The surface morphology of the as-grown SiOxNy thin films on Si (100) substrates at different deposition temperatures was examined using an atomic force microscope (TopoMetrix, TMX 2000). Pictures in Figure 2 clearly show that the morphology is a sensitive function of substrate temperature. Islands larger than 500 nm in size are present in the films deposited at 25 'C and 100 'C. The dimensions of the islands become smaller as substrate temperature is increased to 200 'C [Figure 2(c)] and can hardly be seen within an area of 2 Itm x 2 gtm at T = 300 'C [Figure 2(d)]. This temperature dependence of surface morphology can be understood from a kinetic thin film growth argument. At a low substrate temperature, although the impinged particles (atoms, ions) ablated by the excimer laser carry a certain amount of kinetic energy, they are still not energetic enough to undergo sufficient surface diffusion. Particles hardly have time to find a low energy site to stay before being buried by the incoming particles from the target. Under such circumstances surface becomes kinetically roughened [9]. As the temperature increases, particles gain more kinetic energy once they impinge onto the substrate. They can move farther and have a better chance to find a low energy site, the