Effects of Arsenic Deactivation on Arsenic-Implant Induced Enhanced Diffusion in Silicon
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diffusion, the type-V loops may decrease the amount of enhanced diffusion by absorbing the interstitials. In this work, arsenic was implanted into silicon at various doses with the same energy. Buried boron layers were used as markers of interstitial supersaturation. Most of the chosen doses give rise to peak arsenic concentrations above the electrical solid solubility. It has been previously reported that the density of the type-V loops is a very strong function of the arsenic concentration [2] and the interstitial supersaturation during arsenic deactivation increases abruptly above a certain arsenic concentration [1]. Hence, an abrupt change in the diffusivity of the buried boron layer can be expected if arsenic deactivation has an appreciable effect on damage enhanced diffusion. EXPERIMENT After depositing 20 nm of oxide on silicon to reduce ion channelling, boron was implanted at 10 keV with a dose of 3x10 12 cm- 2 . The oxide was then etched with a HF solution and an approximately 0.6 gm thick epi layer was Srown. Arsenic was implanted at 50 keV at 7' tilt with doses ranging from 4x 1014 to 4x1015 cm- . The peak arsenic concentrations determined from SIMS are shown in Table I along with the implanted doses. The arsenic concentrations were normalized to the implanted dose. The samples were annealed at different times and temperatures:
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Mat. Res. Soc. Symp. Proc. Vol. 396 ©1996 Materials Research Society
TABLE I: DOSES AND PEAK CONCENTRATIONS OF ARSENIC IMPLANTS Dose (cm- 2 )
4x10 14
8x10
3 Peak Concentration (cm- )
1.1 x 1020
2x 1020
14
1.6x1015
2.4x10 15
4x10 15
4x 1020
6.4x 1020
1x 1021
750 0 C 2 hr., 900'C 1 min., and 1050'C 15s. It has been previously reported that the damage enhanced diffusion due to interstitial cluster dissolution is complete for boron implants within the anneal times selected for each temperature [3,4]. Arsenic and boron profiles were obtained by secondary ion mass spectrometry (SIMS) using an oxygen beam. The defects were studied by transmission electron microscopy with a JEOL 200 CX electron microscope operating at 200 keV. Plan-view and cross-section samples
were analyzed in g220 and g 11 conditions. RESULTS AND DISCUSSION The annealed profiles of the boron buried layer are shown in Figure 1 for different arsenic doses at 750 0 C. The doses of the original SIMS profiles were normalized to that of the unannealed sample. The damage enhanced diffusion of the boron buried layer is reduced as the arsenic dose is increased. This trend is also observed after the 900 0 C and 1050'C anneals. The reduction in the diffusivity is also supported by the arsenic SIMS profiles. After the 750'C anneal, the highest dose arsenic profile moves 200 A less than the 8x 1014 cm-2 profile. The amount of the diffusion of the boron profiles and the corresponding enhancements in the diffusivity can be seen in Figure 2. At both 750 0 C and 900 0 C, the boron diffusivity drops nearly by a factor of 2 from the lowest to the highest arsenic dose. 1o18
E0 0
1o17
Ca 00 0 .m
1o16 0 CI
1015 LL
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