Abstract
This paper presents the development of a new technique to prevent occurrence of compressive stress in epipoly. The use of an epitaxial reactor to grow polysilicon enables the growth of monocrystalline silicon (for bipolar electronics) and polysilicon on top of oxide (for MEMS) in a single deposition step. However, after bipolar processing the early structures show compressive strain in the epipoly layer, which required careful MEMS design. We have found the cause of this compressive strain to be the oxidation steps in the bipolar process. The occurrence of this strain can be explained by the presence of oxygen in the epipoly. An alternative processing technique, where the epipoly is doped using implantation and shielded from oxygen by a nitride layer during further bipolar processing, yields epipoly layers without compressive strain. The full thermal budget of the bipolar process is used to diffuse and activate the implanted epipoly dopant.
Published Version
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