J. Phys. IV France 05 (1995) C5-887-C5-893
Influence of the Doping Gas on the Axial Uniformity of the Growth Rate and the Electrical Properties of LPCVD In-Situ Doped Polysilicon LayersD. Briand1, M. Sarret1, P. Duverneuil2, T. Mohammed-Brahim1 and K. Kis-Sion1
1 Groupe de Microélectronique et Visualisation, URA 1648 du CNRS, Université de Rennes 1, Campus de Beaulieu, Bât. 11B, 35042 Rennes cedex, France
2 Laboratoire de Génie Chimique, URA 192 du CNRS, ENSIG/INPT, 18 Chemin de la Loge, 31078 Toulouse cedex, France
We report in-situ doping of polysilicon grown on glass substrates by a LPCVD process. The growth rate, the resistivity and the dopant concentration of boron in-situ doped polysilicon layers are studied as a function of the deposition pressure and the dopant gas to silane mole ratio. A dependence of the axial uniformity on pressure and B2H6/SiH4 mole ratio is put forward, and this effect appears to be very strong especially at high pressure. It is explained by a lowering of the diborane concentration in the gas mixture along the load, because of a different threshold for the thermal decomposition of diborane and silane. It is also put forward that a critical concentration of boron exists above which the growth rate is increasing. Improvements of the horizontal homogeneity are obtained by varying the total gas flow rate.
© EDP Sciences 1995