Contribution to electron beam annealing of high-dose ion-implanted polysilicon

Abstract

Polysilicon layers of a thickness of 500nm with grains of GS 100nm diameter grown on a 50 nm thick SiO, layer are implanted with As+ doses of 2 X 1016 cm-a a t 110 keV and P+ doses of 2 x 1016 cm-8 a t 50 keVand annealed by a scanned and to a line focused electron beam of 1.1 mA/cma current density and 18 keV electron energy. A first annealing stage is due to the recrystallization of the amorphous zone governed by an activation energy of 2.35 eV and a reverse one by activation energies of GS 2.7 eV attributed to the migration of E-centers to grain boundaries and other extended lattice defects.Polysiliziumschichten werden mit einer Dicke von 500 nm und einem Korndurchmesser von ungefihr 100 nm auf 50 nm dicke Si0,-Schichten abgeschieden, mit As+-Dosen von 2 x 1016 cm-2 bei 110 keV und P+-Dosen von 2 x los bei 50 keV implantiert und mit einem zu einer Linie fokussierten Elektronenstrahl der Stromdichte 1,l mA/cm8 und der Energie 18 keV unter Abrastern ausgeheilt. Eine erste Ausheilstufe gehort mit der Aktivierungsenergie von 2,35 eV zur Rekristallisation der amorphen Zone, eine zweite reverse kann mit der Aktivierungsenergie von etwa 2,7 eV der Diffusion von E-Zentren zu Korngrenzen und anderen ausgedehnten Gitterdefekten zugeschrieben werden.

Modelling of dopant profiles modified by diffusing defects in polycrystalline silicon

“…Simultaneously with the diffusion of these defects the dopant concentration decreases, in coilsequence of which ! he carrier mobility increases evidenced by Hall measurements [9], proving that the diffusing point defects react with dopants. The migrating defects can be attributed t o divacancies in different charge states 1141 also discussed extensively for laserannealed samples [ 121.…”

“…Relevant work in this field like electron and laser beam processing of semiconductors concerns recrystallizing thin polycrystalline silicon layers grown on the top of amorphous silicon dioxide substrates [l to 51 and iricorporating active devices like MOS transistors and integrated circuits in such layers [S to 81. These films are doped by ion implantation. Resulting deleterious redistribution of dopants due to long distance diffusion during furnace annealing, however, forced to introduce short-time annealing for instance by laser or electron beam irradiation which make it also possible to analyse the reordering reactions of dopants and defects simiiltarieously with the annealing procedure with an appropriate time resolution [9].…”

“…In order to avoid such complications, polycrystalline silicon layers were deposited without doping [9], i.e. thegrain boundaries were initially completely empty of dopants.…”