Pulsed Laser Deposition of Thin Silicon Nitride Films
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PULSED LASER DEPOSITION OF THIN SILICON NITRIDE FILMS
XIANGQUN XU, KANEKAZU SEKI, NAIQUN CHEN, HIDEO OKABE, JOAN M. FRYE AND JOSHUA B. HALPERN Materials Science Research Center of Excellence and Department of Chemistry, Howard University, Washington, DC 20059
Pulsed laser deposition of compressed Si 3N4 powder has been used to grow thin SiNX films on a variety of substrates at substrate temperatures ranging from room temperature to 350 *C. Film composition was analyzed by Auger electron spectroscopy. The SiN 0 . 33 films have a band gap of 5.60 eV as measured by UV absorption. The FT-IR spectrum shows an absorption characteristic of Si-N. The Si/N ratio in the deposited films corresponding to various substrate temperatures has also been determined.
INTRODUCTION Thin films of high quality silicon nitride are important as dielectric materials and functional memory layers in microelectronic and optoelectronic device." Conventional deposition techniques of silicon nitride films include chemical vapor deposition(CVD),1 plasma enhanced CVD(PECVD),2 and direct thermal nitridation.3 Each of these techniques has disadvantages. For example, CVD is a high temperature technique (>600 °C) which may cause atom migration and/or dopant diffusion in some semiconductors. PECVD uses low deposition temperature (-300 °C) but often incorporate too much hydrogen in the dielectric and may cause damage due to the high energy ions (hundreds to thousands of eV) 5. Pulsed laser deposition (PLD) has emerged as a powerful means for the deposition of superconducting thin films as well as semiconducting, insulating, ferroelectric and other thin films. This work reports growth of SiNL films from room temperature to 350 0 C using pulsed laser deposition. Auger analysis, fourier transform infrared (FT-IR) analysis and UV absorption were used to analyze the composition and properties of the deposited films.
EXPERIMENTAL Target pellets were prepared by compressing Si 3N4 powder (electronic grade, Johnson Matthey Co.) in a die similar to that used for IR sample preparation. The die was placed in a hydraulic press (2.5 ton/cm2) and a small tablet, 13mm in diameter and 3mm in thickness, was formed. Fig. 1 is a diagram of the stainless steel vacuum chamber used for growth. The Mat. Res. Soc. Symp. Proc. Vol. 285. (01993 Materials Research Society
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target pellet was placed parallel to the substrate and oriented at 450 to the laser beam. This produced a plume of ablated material perpendicular to the target surface and the substrate which was placed at a distance of 3cm from the target. Films were grown on Si (100) wafers, KBr plates and Suprasil quartz plates. Si (100) wafers were cleaned with pure methanol, then dipped in 6% hydrofluoric acid for 30s, rinsed with deionized water and dried in flowing air. Suprasil quartz plates were cleaned with pure acetone. Irradiation at 248 nm (KrF) or 193 nm (ArF) was provided by a pulsed (20 ns width) excimer laser using a repetition rate of 1-10 Hz. The laser was focused by a 160-mm-focal-length lens. The l
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