Electron Beam Annealing of Shallow BF 2 Implantations
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ELECTRON BEAM ANNEALING OF SHALLOW BF
2
IMPLANTATIONS
C. JAUSSAUD, A.M. CARTIER, J. ESCARON L.E.T.I. - COMMISSARIAT A L'ENERGIE ATOMIQUE 85 X, 38041 GRENOBLE CEDEX, FRANCE
ABSTRACT A multiple scan electron beam system has been used to anneal silicon implanted with BF2 (25 Kev, 1, 2 and 5 x 1015 ions x cm-2 ). The annealing temperatures range from 1000 to 12000 C and the annealing times from 3 to 18 seconds. The curves of sheet resistance as a function of annealing time show a minimum. The increase in sheet resistance at longer annealing times is due to boron outdiffusion. Junction depths have been measured by spreading resistance and are presented. For implanted doses below 2 x 10 ions x cm- boron outdiffusion limits the sheet resistance value at about 100 R and this minimum value corresponds to an increase in junction depths of about 500 A. For implanted doses of 5 x 1015 ions Scm-0, 60 Q sheet resistance can be obtained, but with about 1000 A increase in junction depth.
INTRODUCTION Transient thermal processing systems using lamps, graphite heaters and electron beams have been used to anneal Arsenic and Boron implanted silicon (1-5). For Arsenic good electrical activities can be obtained with negligible diffusion of the dopant. For Boron most studies (6-9) show that activation of the implanted atoms is accompanied with a diffusion of the dopant of a few hundred to 1000 K. We have used a multiple scan electron beam systems to anneal silicon implanted with 25 Kev BF2+ ions, at doses ranging from 1 to 5 x10 15 ions x cm- 2 . After annealing, sheet resistance and junction depth were measured. For some samples the amount of Boron lost by out diffusion during the annealing was measured by nuclear reaction
EXPERIMENT The electron beam annealing system used in this study has been described elsewhere (10), and we rapidly give its main characteristics : the beam (15 KV, 20 mA for this study) is focused on the sample and scanned in two perpendicular directions at different frequences (200 Hz and 20 KHz). The samples (1,2 x 2 cm 2) are thermally isolated. The beam is directed onto the non polished side of the sample, and the surface scanned by the the beam is larger than that of the sample. The anneal times (a few seconds) are sufficient to heat uniformly all the sample. The temperature of the sample is monitored by a two wavelength pyrometer and the measurement is independent of the sample emissivity. The power densities used are 18, 24 and 30 W x cm- , corresponding to 1000, 1100 and 12000 C equilibrium temperatures. For the annealing done at 18 W x cm- 2 , the times used are sufficient for the sample to reach thermal equilibrium. But for higher power densities, the sample does not reach thermal equilibrium. All annealed samples were implanted with BF 2 + at 25 Kev, with doses ranging from I to 510 15 ions x cm- 2 . After annealing the values of junction depths were measured by spreading resistance on bevels.
Mat. Res. Soc. Symp. Proc. Vol. 23 (1984) @Elsevier Science Publishing Co., Inc.
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RESULTS All the resu
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