Epitaxial regrowth of n + polycrystalline silicon at 850 °C, induced by fluorine implantation

A study is made of fluorine implantation into n+ polycrystalline silicon (polysilicon), with the aim of producing completely epitaxially regrown polysilicon emitters at lower temperatures. Polysilicon-on-silicon sheet resistance measurements are made to obtain an indication of the amount of polysilicon regrowth, and cross-section transmission electron microscope examinations to directly observe the regrowth. Samples given a fluorine implant, followed by a 1000 °C/10 min preanneal, show 50% epitaxial regrowth of the polysilicon after an emitter drive-in of only 850 °C/30 min. In contrast, in the absence of fluorine, negligible regrowth occurs even after an emitter drive-in of 850 °C/480 min.