ANALYSIS OF LATTICE-DEFECTS INDUCED BY ION-IMPLANTATION WITH PHOTOACOUSTIC DISPLACEMENT MEASUREMENTS

Subsurface lattice defects in silicon induced by ion implantation were studied by the use of the photo-acoustic displacement (PAD) method ba sed on the sensitive measurements of the surface displacement due to t he absorption of laser-light energy. A definite correlation between PA D and displaced atoms density (DAD) was found because PAD reflects the change in thermal conductivity associated with the net amount of disp laced atoms in the crystal lattice beneath the surface. According to t he linear dependence of 1/PAD on DAD, defects below a DAD of 10(14)/cm (2) (corresponding to implant doses of 2X10(11), 8X10(10), and 6X10(10 ) ions/cm(2) for 100 keV B+, P+, and As+, respectively) were concluded to be point defects. After the DAD reached 10(14)/cm(2), the PAD show ed a gentle increase, and this can be attributed to the growth of poin t-defect clusters. A marked dependence of the PAD on the DAD was not o bserved beyond a DAD of 10(16)/cm(2). In this region, the presence of an amorphous layer was observed by cross-sectional transmission electr on microscopy. Annealing behavior due to low-temperature heating was s tudied by the change in temperature dependence curves of the PAD, and the results reflected the characteristics of the defects described abo ve.