Synthesis of Thin Membranes in Si Technology by Carbon Ion Implantation
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ABSTRACT The use of high dose carbon ion implantation in Si for the production of ultrathin membranes is investigated. Carbon implantations with doses up to 1018 cm 2 and energies up to 300 keV, at room temperature and 500'C were used, followed by 10 hours annealing at 1150'C. Structural and chemical analysis has been performed (including TEM, XPS, Raman and IR spectroscopies), and the etch properties have been investigated for KOH and TMAH etchants. It is found that doses higher than 101? cm-2 are needed to obtain efficient etch-stop layers in TMAH, independently of the annealing conditions, while in contrast with previous work, it was not possible to obtain satisfactory results using KOH. According to this, ultrathin crystalline membranes (below 500 nm thick) with average surface roughness as low as 4.8 nm, measured by AFM, were obtained, and the structural analysis revealed the formation of a highly stable buried layer of crystalline /3-SiC precipitates aligned with the Si matrix. These results corroborate the ability of high dose C ion implantation to obtain buried layers usable for micomachining applications. INTRODUCTION
Different authors have reported the use of epitaxially grown f3-SiC films as a mechanical material [1-3] in a micromachining context. Its mechanical strength, high thermal conductivity and extreme chemical inertness in all kinds of liquid electrolytes make 3-SiC particularly attractive for these purposes. However, SiC layers grown by standard deposition techniques on Si substrates present rough interfaces, due to the large thermal and lattice mismatch (about 20%) between the substrate and the deposited layer. SiC layers have also been synthesised by ion implantation and anneal processes [4-7]. Implanting at room temperature leads to the formation of amorphous SiC and annealing is needed to crystallize the SiC. Implanting at higher temperatures allows the direct synthesis of crystalline f3-SiC, and high crystalline quality f3-SiC has been obtained for implantation temperatures as low as 500'C, with SiC grains well aligned with the Si matrix [8]. On the other hand, the implantation of species with low electrical activity in Si, as C or N, is a process with potential interest to obtain of etch-stop layers [9,10]. Such layers are required for the fabrication of integrated sensors in Si and need to be stable under the CMOS processes required for the integration of control electronics. In general, the development of all these applications needs a deep understanding of the structural changes which take place during the implantation and annealing processes, as well as their dependence on the different processing parameters, mainly implantation dose and temperature. In this work, the use of high dose 727
Mat. Res. Soc. Symp. Proc. Vol. 396 0 1996 Materials Research Society
carbon ion implantation to obtain buried layers usable for micomachining applications is investigated, as a function of the technological parameters, showing the dependence of the etch stop properties on the distribution of the
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