Pulsed Laser Deposition of Boron Doped Si 70 Ge 30
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0910-A12-02
Pulsed Laser Deposition of Boron Doped Si70Ge30 Sherif Sedky1, Ibrahim ElDeftar2, and Omar Mortagy3 1 Physics, The AMerican Univeristy in Cairo, 113 Kars EL Eini Street, Cairo, 11511, Egypt 2 The Sceince and Technology Research Center, The American University in Cairo, Cairo, 11511, Egypt 3 The Sceince and Technology Research Center, The American University in Cairo, Cairo, Egypt ABSTRACT The main objective of this work is to investigate the possibility of combining pulsed laser deposition (PLD) and pulsed laser annealing to realize p-type Si1-xGex thin films suitable for post-processing MEMS on top of standard pre-fabricated driving electronics. The main advantage of this approach is that the substrate is kept at a CMOS backend compatible temperature throughout the deposition and thus the MEMS integration process will have no thermal impact on the underlying electronics. In addition, it is demonstrated that PLD Si1-xGex has good adhesion to SiO2. Therefore, there is no need for a silicon nucleation in contrast to LPCVD and PECVD. Furthermore, this technique is much more economical than CVD as it does not use expensive gas precursors such as germane and silane. INTRODUCTION Silicon germanium (Si1-xGex) is considered an attractive material for a wide variety of applications [1]. The incorporation of Ge into heavily doped p-type poly Si causes the gate work function to be noticeably reduced, allowing both PMOS and NMOS surface channels to be realized. Its low thermal conductivity as compared to silicon makes it suitable for the realization of high performance uncooled thermal detectors [2]. The capability of Si1-xGex to absorb solar radiation falling in the near infrared improves the efficiency of solar cells [3]. In addition, the low transition temperature from amorphous to polycrystalline is attractive for low-thermal budget applications such as the fabrication of high-performance thin-film transistors on glass substrates, for flat-panel display applications, where the processing temperature should be limited below 550°C [4]. Recently, LPCVD and PECVD Si1-xGex films have been used as structural and sacrificial layers for MEMS that can be monolithically integrated with the driving electronics [5, 6]. For these studies, the deposition temperature was reduced down to 370°C to achieve compatibility with standard CMOS backend and at the same time minimize the mean stress and stress gradient to realize flat suspended structures at such low temperature. This paper reports on depositing Si1-xGex by ablating Boron doped Si70Ge30 target using KrF excimer laser operated at 50 Hz and at a pulse fluence varying from 0.38 J/cm2 to 3 J/cm2. The effect of the type of background gas, being either Ar, N2 or vacuum, on the quality of the deposited films is investigated using field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), four point measurements and bow measurements. It is demonstrated that the optimal deposition conditions that yield a smooth film having low cluster density are a pulse
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