The aim of this experiment is to grow a thin silicon layer (<50μm) by Liquid Phase Epitaxy (LPE) onto porous silicon. This one acts as a sacrificial layer in order to transfer the 50 μm epitaxial layer onto foreign substrates like ceramics. After transfer, the silicon wafer is then re‐usable. In this work, we used the following procedure : the porous silicon formation by HF anodisation on (100) or (111) Si wafers is realised in first step, followed by an eventual annealing in H2 atmosphere, and finally LPE silicon growth with different temperature profiles in order to obtain a silicon layer on the sacrificial porous silicon (p‐Si). We observed a pyramidal growth on the surface of the (100) porous silicon but the coalescence was difficult to obtain. However, on a p‐Si (111) oriented wafer, homogeneous layers were obtained.
Experiments on the intrinsic gettering of Cr in p-type Czochralski-grown Si including lamp pulse annealings have been carried out. Transmission Electron Microscopy observations of both oxide and metallic precipitates on cross-sectional specimens, as well as quantitative results about the electrically active metal depth-profiles, using Deep Level Transient Spectroscopy measurements, are presented. We have observed that a lamp pulse (1200 °C/5 s) applied prior to a three-step gettering cycle produced a strong retardation of the oxygen precipitation, and consequently an inhibition of the Cr bulk precipitation during the nucleation step. Besides, it was observed that the Cr-precipitates formed in the bulk during the oxygen nucleation step were highly unstable upon a post-gettering 2–4 s lamp pulse at 1000 °C, whereas the same lamp pulse did not produce a significant re-dissolution of Cr-precipitates formed during the oxide precipitate growth step. The reversibility of the intrinsic gettering of Cr upon a post-gettering lamp pulse thus critically depends on the oxide precipitate growth rate during the gettering process.
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The interaction of lamp pulses with the internal gettering of chromium (Cr) in Czochralski-grown silicon (St) has been studied by deep level transient spectroscopy profiling of the electrically active Cr concentration on beveled samples. B-doped Si wafers were submitted to various sequences of thermal treatments consisting in different combinations of Cr diffusion, gettering treatments (high-low-high or high-low), and lamp pulse annealings. An inhibition of the internal gettering mechanism was observed whenever Cr was diffused in a lamp furnace before gettering, or when a lamp pulse was applied before Cr diffusion in a quartz tube furnace. In addition,the stability of the Cr precipitates, formed inside the wafer after internal gettering, was found to depend significantly on the gettering temperature. These results were consistently explained in the framework of the "oxygen precipitation" gettering model, taking into account the two basic requirements of efficient denuded zone formation by oxygen nucleation, and further oxygen precipitate growth rate enhancement of the metal precipitation.
The specific effects of lamp pulse annealings on the oxygen precipitates morphology and on the chromium precipitate formation during intrinsic gettering in Czochralski-grown silicon were investigated by transmission electron microscopy. High-low-high gettering treatments were carried out after deposition of a chromium film onto the silicon substrates and a subsequent in-diffusion anneal. In order to test the effect of a lamp pulse on the gettering effects, the chromium diffusion (980~ for 30 nm) has been performed either in a cold wall lamp furnace or in a classical quartz tube furnace. The effect of a shorter lamp pulse at a higher temperature (1200~ for 5 s) applied prior to the chromium diffusion was also tested. When no lamp pulse was used, the oxygen has precipitated into two forms, i.e. platelets and polyhedra, depending on the gettering cycle. However, chromium precipitates were observable only in the presence of the polyhedra and in that case the CrSi2 phase was unambiguously identified. Moreover, it was observed that the lamp pulse annealings used in this work, applied prior to the gettering sequence, produced a significant retardation of the oxygen precipitation together with the impediment of chromium precipitate growth.
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