The rnicrostructures of in situ boron-doped silicon films deposited by low-pressure chemical vapor deposition using SiH4 and BCl3 source gases on SiO2 substrates have been characterized. As-deposited films have a decreasing sheet resistance with increasing boron concentration up to 3.1 +/- 0.6 x 10(21)/cm(3), and are polycrystalline. As the boron concentration exceeds 3.1 +/- 0.6 x 10(21)/cm(3), the sheet resistance increases dramatically. It is shown that as the boron concentration in the silicon film exceeds 3.1 +/- 0.6 x 10(21)/cm(3), the films transition from a completely polycrystalline phase to a combination of polycrystalline and amorphous phases as deposited. The amorphous phase has a higher boron concentration than the polycrystalline phase, as shown by selective Auger electron spectroscopy and secondary ion mass spectrometry. The relative fraction of amorphous phase can be controlled by boron concentration. (C) 2004 American Vacuum Society.