Si 1-x-y . Ge x C y Film Formation by Pulsed Excimer Laser Crystallization of Heavily Ge and C Implanted Silicon
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Mat. Res. Soc. Symp. Proc. Vol. 354 ©1995 Materials Research Society
The SiGeC film crystallinity as well as the Ge fraction located in substitutional lattice sites after PLA were investigated by Rutherford Backscattering (RBS) ion channeling experiments carried out with a 2 MeV He+ beam and also by Raman spectroscopy performed using source lines from an Ar+ ion laser. The redistribution of Ge and C atoms into the laser-molten layer was monitored by RBS and Secondary Ion Mass Spectrometry (SIMS) measurements. Finally, infrared transmission measurements were used to detect eventual SiC formation into the SiGeC system through the presence of the strong SiC absorption band located at around 12.6 gm (790 cm- 1) [12]. Table I : Influence of the C dose on the minimum yield after pulsed laser processing System Impl. C dose (at.cm-2 )
SiGe 0
1 x 1015
SiGeC 1 x 1016 5 x 1015
Max C concentration (%)
0
0.29
1.45
2.9
14.5
Xroin (%) laser, 1.2 J/cm 2 , 3 shots
9.5
10.3
13.5
15.5
36
Zmin (%)
4.7
6.8
8.3
15
36
5 x 1016
2
laser, 1.2 J/cm , 10 shots RESULTS AND DISCUSSION The values of the minimum yield (Xmin), extracted from the RBS channeling spectra, characterize the crystalline quality of the laser regrown layers. Table I summarizes the different values of Xmin measured in pulsed laser treated (1.2 J/cm2 , 3 and 10 shots) SiGeC samples containing various concentrations of carbon (up to 15 %) according to the implantation conditions. The laser regrown carbon-free SiGe layer presents a high crystalline quality with a Xmin of 9.5 % (after 3 shots) and 4.7 % (after 10 shots), the latter value being very close to that of virgin silicon (- 4 %). In presence of a low dose of C (1 x 1015 at.cm-2 ), we observe (Fig. 1) only a very small increase of the Xroi value which depends as in the previous study [11] on the number of laser shots. The minimum yield value which is about 10.3 % after 3 shots (Fig. la) decreases to 6.8 % following 10 shots (Fig. lb). By contrast, for the highest implanted C dose (5 x 1016 at.cm-2 ), as shown in Fig. 2, the minimum yield value measured after 10 shots (- 36 %) stays very high. This points out the influence of an heavy concentration (- 15 %) of carbon which strongly disturbs the crystallization process. It is interesting to notice that, whatever the carbon implantation conditions are, the measured fraction of Ge incorporated into substitutional Si lattice sites is close to 95 %. As mentionned above, the minimum yield decreases by repeating the laser treatment (from 3 to 10 shots). This result is mainly related to some Ge redistribution due to the iterative meltingresolidification process. In fact, as previously observed in the SiGe system [11], a multipulse laser treatment has been shown to turn the initial (gaussian) implantation profile into a box-like distribution characterized by a deeper extent but with an average lower concentration. The SIMS experiments confirm this behaviour in the SiGeC layers. As shown in Fig. 3a, the implanted Ge atoms are redistributed very uniformly
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