Electron Microscope Characterization of Pulse Annealed Semiconductors
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and Tan, eds.
393
Defects in Semiconductors
ELECTRON MICROSCOPE CHARACTERIZATION OF PULSE ANNEALED SEMICONDUCTORS
A. G. CULLIS Royal Signals and Radar Establishment,
St. Andrews Road,
Malvern,
England
ABSTRACT The pulse processing techniques that have assumed prominence over the past few years offer various important advantHowever, the useages for device fabrication technology. fulness of each individual method depends substantially upon This article the specific annealing mechanism involved. demonstrates the role of electron microscopy in elucidating such mechanisms and in analysing annealed semiconductor structures of importance to both research workers and semiconductor technologists. The range of laser and electron beam pulse annealing methods is covered and defect structure transitions observed are related to the solid and liquid phase processes occurring. Characteristic impurity trapping and segregation phenomena are described.
INTRODUCTION The tremendous increase in world-wide interest in the pulse annealing of semiconductors reflects, in part, the very great potential that exists for novel However, the various pulse applications in the field of device processing. annealing techniques also permit the solid-state physicist to probe new regimes Therefore, their importance in the area of basic materials of crystal growth. Due to these considerations, a wide range of research is also most substantial. physical analytical techniques has been used to study the properties of pulse In particular, work based on electron microscopy annealed semiconductor layers. has provided a very large amount of structural information and it is the purpose Some of the present article to outline many of the general results obtained. emphasis will be placed on studies of Q-switched laser annealed material since Nevertheit is here that most detailed analytical work has been carried out. less, the effects of scanning CW laser annealing and rapid pulsed and scanning electron beam annealing also will be described. Q-SWITCHED LASER ANNEALING The use [1-4] of Q-switched laser radiation to anneal semiconductor layers Short pulses ('lO-lOOnsec) of radiation at has received in-depth study. typically 694nm or 1060nm from, respectively, ruby and Nd-YAG lasers are often employed. The laser spots may be small and overlapped by a scanning process [3) In the latter case, to obtain or single, large area pulses can be utilized. maximum uniformity in the annealed region, it is desirable to use a laser beam diffuser which can give a uniform energy density of irradiation [5]. Most studies have concerned the annealing behaviour of ion implanted Si specimens. The general structural changes that take place in initial ioninduced amorphous layers have been elucidated by transmission electron microFor a single laser pulse scope (TEM) investigations of plan-view specimens [6]. anneal, as is clear from Fig. 1, increasing the radiation energy density leads to the production of a range of residual layer defects from polycrystals to dislocated single cryst
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