Work function of boron-doped polycrystalline Si/sub x/Ge/sub 1-x/ films

Abstract

The work function of p-type polycrystalline Si/sub x/Ge/sub 1-x/ films deposited by LPCVD using SiH/sub 4/ and GeH/sub 4/ was determined by CV measurements on MOS structures. Boron was introduced in the Si/sub x/Ge/sub 1-x/ films either exsitu by ion implantation or insitu by adding B/sub 2/H/sub 6/ in the reactants during film deposition. The work function of the Si/sub x/Ge/sub 1-x/ films is found to decrease as the Ge content increases; it is 5.16 eV for Si, 4.76 eV for Si/sub 0.49/Ge/sub 0.51/, and 4.67 eV for Ge. The work function of the Si and Ge films coincides well with that of single crystalline Si and Ge, respectively. It is also found that a thin Si adhesion layer of about 3 nm (nominal thickness), deposited prior to the Si/sub x/Ge/sub 1-x/, has a negligible effect on the work function determination.