Annealing of High Dose Implanted GaAs with Halogen Lamps
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Laboratoire
de Bagneux,
ABSTRACT Halogen lamps are used to anneal implanted GaAs. Surface protection is obtained by mouting the substrate in a sandwiched configuration between a silicon and a quartz plate. Raman scattering measurements are carried out to follow simultaneously lattice reconstruction and surface degradation due to Arsenic loss. The evolution of the Raman spectra is compared to a T.E.M. analysis carried out on the same samples. INTRODUCTION The annealing of ion implanted GaAs is the object of a constant effort to achieve a good control in GaAs devices. The strong research effort on beam processing of materials has merged recently in the use of a rapid thermal heating to produce annealing. Halogen lamps have been used to achieve good electrical activation in ion implanted GaAs layers [1,21. Similar results were obtained with a graphite strip heater [3]. The novelty of the technique is a more distributed thermal gradient at the surface of the semiconductor and a longer annealing time (few seconds) as compared to laser irradiation. Furthermore the irradiation time is still short enough to perform a capless heat treatment in GaAs. In this presentation, the annealing of high dose implanted GaAs with a system of two 150 watts halogen lamps is studied. The optimisation of irradiation time has been made for a given induced temperature on the basis of best lattice recovery and minimum surface degradation. The confinement of the sample mounted in a sandwiched configuration during irradiation allows long exposure time at high temperature (30sec.at 1000 0 C) before surface decomposition. EXPERIMENTAL SET UP A first generation annealing system made of two 150W halogen lamps was used in these experiments [4]. The two lamps are facing each other and a silicon sample holder is placed in between them. The lower lamp is strongly defocussed with respect to the sample holder and is utilised to prepare it at a constant initial temperature (300 0 C). This procedure is necessary to reduce the thermal stress in the semiconductor when the thermal pulse is suddenly induced by the upper lamp. The temperature induced on the irradiated sample was carefully measured with a thermocouple in mechanical contact with the sample holder. The spatial profile (fig.1) indicates that the temperature is relatively uniform across the studied samples (4x4mm). The temporal temperature profile is shown in fig.2. It indicates that the final temperature induced by the lamps due to the experimental choice of the upper lamp position is 10000C and that 8 sec of transient regime are necessary to reach thermal equilibrium. The GaAs substrate needs to be protected from sudden surface decomDosition at this temperature. A close contact configuration was chosen for protection with the sample sandwiched between the silicon sample holder and a quartz plate. The GaAs sample is placed on a floating silicon wafer so
Mat. Res.
Soc.Symp. Proc. Vol. 23 (1984) Published by Elsevier Science Publishing Co.,
Inc.
676
100C
L
UPPER LAMP 7mmOFF THE FOCALPOINT
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