Zn. Fan et al., Surface hydrogen incorporation and profile broadening caused by sheath expansion in hydrogen plasma immersion ion implantation, IEEE PLAS S, 28(2), 2000, pp. 371-375
Hydrogen plasma immersion ion implantation (PIII) in conjunction with ion-c
ut is an efficient and economical technique to synthesize silicon-on-insula
tor (SOI) substrates. Unlike beam-line ion implantation, the PIII hydrogen
profile usually exhibits multiple peaks because of different implanted spec
ies, such as H+, H-2(+), and H-3(+). In addition, a certain amount of adsor
bed hydrogen exists near the surface and the hydrogen in-depth distribution
is broader than that of a beam-line implant also as a result of a low-ener
gy component. For the ion-cut process, the broadened hydrogen profile and s
urface hydrogen can decrease the efficiency of the blistering process, Indu
ce uneven exfoliation, and degrade the interfacial quality of the bonded wa
fer. Hydrogen can adsorb on the wafer surface during the "off-cycle" of the
sample voltage pulse and consequently be driven in by ion mixing or diffus
ion. In order to reduce surface hydrogen incorporation, the implantation ti
me must be short, and this requires an efficient cooling mechanism on the s
ample stage because a high ion current is needed to implant a high dose in
a short time (less than 5 min). Another mechanism of profile broadening is
that the expanding sheath creates low-energy ions during PIII, Our experime
ntal and simulation data disclose that profile broadening is less severe fo
r a shorter sample voltage pulsewidth and that good blistering characterist
ics can he achieved using a long pulse, in spite of a relatively long impla
ntation time of 1 h.