EFFECTS OF MICROSTRUCTURE AND AS DOPING CONCENTRATION ON THE ELECTRICAL-PROPERTIES OF LPCVD POLYSILICON

Abstract

The microstructure and electrical properties of polysilicon films deposited by low-pressure chemical vapor deposition on silicon dioxide have been investigated as a function of deposition condition and As doping concentration. The deposition temperature was varied from 560-degrees-C to 625-degrees-C, and the As doping concentration from 1 x 10(17) to 5 x 10(20)/cm3. The polysilicon films deposited at 625-degrees-C and annealed at 900-degrees-C have an average grain size of 200-300 angstrom and a rough surface with columnar grain structure, while the films deposited at 560-degrees-C followed by the 900-degrees-C anneal have 1000 angstrom grains and smooth surfaces. For the same As doping concentration, the conductivity and Hall mobility of the polysilicon deposited at 560-degrees-C are larger than those of the polysilicon deposited at 625-degrees-C, due mainly to less grain boundary trapping. The grain boundary potential barrier decreases from 0.063 eV in films with As doping concentration of 5 x 10(18)/cm3 to 0.001 eV in films doped to 2.5 x 10(20)/cm3. The trap density of the grain boundary, however, is almost independent of the deposition conditions and the values are determined to be 3.6-5 x 10(12)/cm2.