No abstract

We investigate the structural changes in porous silicon multilayers during annealing. Porous silicon multilayers play an important role in layer transfer technologies, where a thin crystalline silicon layer is separated from a wafer and transferred to a foreign substrate. High processing temperatures during epitaxial growth on top of the porous silicon layer lead to a restructuring of the porous layer. With transmission electron microscopy, we evaluate porous silicon monolayers and double-layers. The pore shape changes from open channel-like pores to closed facetted pores during anneal. In double-layers we observe a strong interaction between the two layers leading to an enhanced porosity in the high porosity layer. The observed microstructural evolution is discussed by means of the classical theory of sintering.

We have passivated boron‐doped, low‐resistivity crystalline silicon wafers on both sides by a layer of intrinsic, amorphous silicon (a‐Si:H). Local aluminum contacts were subsequently evaporated through a shadow mask. Annealing at 210°C in air dissolved the a‐Si:H underneath the Al layer and reduces the contact resistivity from above 1 Ω cm2 to 14·9 m Ω cm2. The average surface recombination velocity is 124 cm/s for the annealed samples with 6% metallization fraction. In contrast to the metallized regions, no structural change is observed in the non‐metallized regions of the annealed a‐Si:H film, which has a recombination velocity of 48 cm/s before and after annealing. Copyright © 2004 John Wiley & Sons, Ltd.

In this paper we study the dynamics of pore coarsening in porous silicon during annealing. We model the sintering of pores with two-dimensional and three-dimensional simulations. We compare our simulations with transmission and scanning electron micrographs of experimentally annealed porous silicon samples.Simulations and experiments yield lognormally distributed pore sizes. The quantitative agreement between simulation and experiment shows that minimization of the inner surface energy is the driving force for morphological changes in PS during annealing. Surface diffusion is the dominant mechanism in the reorganization of Si-atoms in PS.

Porous silicon can be used as separation layers in layer transfer technology where a thin layer of crystalline silicon is separated from a large wafer and transferred onto a cheap foreign substrate. The porous layers are part of the fabrication process and undergo the processing treatment, especially the thermal treatments. We have analyzed by transmission electron microscopy the structural development of porous silicon layers in dependency of annealing and layer preparation conditions. The fabrication of solar cells by layer transfer technology is based on double layers and we used in addition single layers for evaluating the details of structural changes. We can explain the structural development during annealing by means of the classical sintering theory.