Effect of excimer laser annealing on the structural properties of silicon germanium films
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Jeremy Schroeder and Timothy Sands School of Materials Engineering & School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907
Tsu-Jae King Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California 94720
Roger T. Howe Department of Electrical Engineering and Computer Sciences, and Berkeley Sensor & Actuator Center, University of California, Berkeley, California 94720 (Received 23 March 2004; accepted 30 July 2004)
We investigated the use of a pulsed excimer laser having a wavelength of 248 nm, a pulse duration of 38 ns, and an average fluence between 120 and 780 mJ/cm2 to locally tailor the physical properties of Si1−xGex (18% < x < 90%) films deposited by low-pressure chemical vapor deposition at temperatures between 400 and 450 °C. Amorphous as-deposited films showed, after laser annealing, strong {111} texture, a columnar grain microstructure, and an average resistivity of 0.7 m⍀ cm. Atomic force microscopy indicated that the first few laser pulses resulted in a noticeable reduction in surface roughness, proportional to the pulse energy. However, a large number of successive pulses dramatically increased the surface roughness. The maximum thermal penetration depth of the laser pulse is demonstrated to depend on the fluence and the film structure being either polycrystalline or amorphous. Finally, a comparison between excimer laser annealing and metal-induced crystallization and rapid thermal annealing is presented.
I. INTRODUCTION
The monolithic integration of microelectromechanical systems (MEMS) with electronics is desirable for improved microsystem performance and reliability.1 Ideally, the MEMS would be fabricated in a modular fashion on wafers with completed electronics. However, this approach limits the thermal process budget for MEMS cofabrication. Over the last two decades, several techniques have been developed to reduce the thermal budget for crystallization of silicon films, such as metal-induced crystallization,2–4 laser-induced crystallization,5–7 and metal-induced crystallization with laser annealing.8,9 Also, alloying silicon with germanium10 and using in situ boron doping11 can reduce the crystallization temperature to 450 °C or lower. Many studies have been performed to understand the effect of laser annealing on the average grain size and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0450 J. Mater. Res., Vol. 19, No. 12, Dec 2004
stress of silicon films deposited by low-pressure chemical vapor deposition (LPCVD)12 or radio-frequency (rf) sputtering.13 The effects of pulsed laser annealing in locally tuning the electrical and structural properties of silicon14–16 and SiGe17–20 have also been widely investigated. Recently, the possibility of using pulsed laser annealing to control the physical properties of SiGe for surface micromachining applications monolithically integrated on top of pre-fabricated electronics was explored.21 In this work, we study the
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