Structuring of Silicon Wafer Surfaces on the Sub-100 nm Scale by Hydrogen Plasma Treatments
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L3.34.1
Structuring of Silicon Wafer Surfaces on the Sub-100 nm Scale by Hydrogen Plasma Treatments R. Job1), Y. Ma1), A. G. Ulyashin1), 2) 1) University of Hagen (LGBE), P.O. Box 940, D-58084 Hagen, Germany 2) IMEC, Kapeldreef 75, B-3001 Leuven, Belgium
ABSTRACT Hydrogen plasma treatments applied on standard Czochralski silicon (Cz Si) wafers cause a structuring of the surface regions on the sub-100 nm scale, i.e. a thin ‘nano-structured’ Si layer is created up to a depth of ∼ 150 nm. The formation of the ‘nano-structures’ and their evolution in dependence on the process conditions was studied. The impact of post-hydrogenation annealing on the morphology of the structural defects was studied up to 1200 °C. The H-plasma treated and annealed samples were analyzed at surface and sub-surface regions by scanning electron microscopy (SEM), atomic force microscopy (AFM), and µ-Raman spectroscopy.
INTRODUCTION The impact of hydrogen on the properties of Si wafers plays a vital role for the development of semiconductor devices. E.g. a lot of studies were carried out to clarify the role of hydrogen for the passivation of defects, impurities, and deep or shallow levels in the Si bandgap [1, 2]. Recently, research focused also on hydrogen related catalytic effects. With this regard hydrogen enhanced oxygen diffusion [3] or the support of thermal donor (TD) formation by hydrogen [49] are typical examples. We recently exploited catalytic properties of hydrogen to develop low thermal budget processes, which are compatible to the standard silicon technology, for the production of semiconductor structures/devices [7-11]. Hydrogen is incorporated into Si wafers by H-plasma treatments at moderate temperatures (≤ 500 °C). Since hydrogen is highly reactive, the plasma exposure causes a strong impact on the treated Si wafers, which can be separated either into surface, subsurface or bulk effects depending on the local regions, where the hydrogen caused actions occur. E.g. in the Si bulk defect passivation [1, 2] or hydrogen enhanced TD formation occur under appropriate conditions [4-9]. In the subsurface regions of H-plasma treated wafers (up to 1 - 2 µm depth) the formation of platelets, i.e. quasi twodimensional (111)- and (100)-oriented defects, can be observed, which are very thin (in the order of 10 nm) but large in diameter (∼ 500 nm) [12-15]. The surface regions of Si wafers, which have been immersed in H-plasma, are modified due to the strong reactivity of the H atoms; i.e. at the wafer surface a thin ‘nano-structured’ layer is created. By cross-sectional transmission electron microscopy (XTEM) it can be seen that the ‘nano-structures’ at the wafer surface have dimensions in the sub-100 nm scale and can be found up to a depth of ∼ 150 nm [14, 15]. Oxidization of such ‘nano-structured’ surfaces layers can even cause a broad light emission in the visible spectral range originating from Si-O-H complexes [16]. In this article the formation of ‘nano-structured’ Si surface layers after H-plasma treatments and their evolution upon a
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