Radiation Damage and its Annealing in Semiconductors
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RADIATION DAMAGE AND ITS ANNEALING IN SEMICONDUCTORS
J. NARAYAN and J. FLETCHER Solid State Division, Oak Ridge National Laboratory, Oak Ridge,
TN 37830
ABSTRACT Residual damage in the form of point defect clusters and amorphous regions has been investigated in ion and neutron irradiated silicon specimens. Annealing of this damage during conventional heating, flame annealing, and pulsed laser irradiation has been studied by plan-view and cross-section electron microscopy techniques. These results provide detailed information on annealing mechanisms, and emphasize the characterization of damage in the as-irradiated state.
INTRODUCTION Ion implantation and neutron irradiation (via transmutation) have proved to be very useful techniques of doping semiconductors [1,2]. However, the displacement damage created by energetic ions must be removed in order to achieve electrical recovery of dopants. Conventional techniques of removing displacement damage involved thermal heating in a furnace. Recently other methods such as laser- and electron-beam annealing, although limited to near-surface ( 1.0 MeV): specimens; (b) after annealing at 250'C for 20 min.; (c) and Cd) further annealing at (e) and (f) further annealing 400'C, 20 min.; 0 at 600 C, 20 min.; (g) further annealing at 700'C, 20 min.
193 Fig. 2 shows size distributions of dislocation loops and 700'C for 20 minutes. The differences in size distributions after annealing at 400%C and 600CC. between as-irradiated specimens and those annealed at 400'C, were very small. The results in Fig. 2 indicate that the agreement between size distributions determined by TEM and X-ray [5] is fairly good for larger sizes (Ž 20 X), however, for loop sizes below 20 A X-ray measurements consistently indicated The average size increases only higher number densities of dislocation loops. slightly (from 28 to 32 A) after annealing at 600'C, however, the total number of point defects contained in the dislocation loops remains largely unaffected Since infrared measurements up to 600'C, and then decrease rather rapidly. indicate the presence of high concentrations of divancies [6], an inescapable conclusion in view of these results, is that interstitials and divacancies, which were undetected by TEM and X-ray techniques, annihilate each other below The main result from the neutron-damage annealing studies is that most 600'C. of the intrinsic damage anneals out by 750'C, and during this annealing glide and climb of the dislocations, leading to coarsening of the loops, is not significant. ORNL-DWG 80-20627
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(550°cT Fig. 2. Size distribution of dislocation loops in neutron-irradiated silicon after annealing at 400'C and 0 600 C (as determined by TEM), and at 550°C (as determined by X-ray).
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194 One of the interesting observations in the neutron irradiated specimens was the presence of short interstitial dipoles (encircled in Fig. 3) in The directio
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