Oxide and Nitride Formation and Segregation of Metals During Oxygen and Nitrogen Bombardment of Silicon
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addition, nitride formation and possible segregation of metal species during nitrogen bombardment is important for sputter profiling using secondary ion mass spectrometry (SIMS). In this paper we compare oxide and nitride formation during irradiation of Si with oxygen and nitrogen beams and examine segregation of metals. EXPERIMENTAL Cz-Si wafers of (100) orientation and with a resistivity of 1-10 02 cm, n-type, were used. The Si was irradiated either in a keV ion implanter or a SIMS apparatus. In the case of SIMS, an 8-10 keV O2+ beam or a 10-12 keV N 2 + beam was used in a Riber MIQ 256 instrument. For implantation, 15 or 25 keV Obombardment was carried out at ANU over a substrate temperature range from liquid nitrogen to 250°C. Also 30 keV N2+ bombardment was undertaken on a Lintott mk-4 implanter at Harwell with substrate temperatures varying from about 150-450°C. Oxygen and nitrogen doses covered the range from 1017 to 5 x 1018cm- 2 . Prior to oxygen or nitrogen bombardment, some Si samples were implanted with either Cu or Au in an energy range 70-100 keV (projected range around 300-500A) to study possible segregation effects during oxide and nitride formation. Samples were analysed by high depth resolution Rutherford 153
Mat. Res. Soc. Symp. Proc. Vol. 504 ©1998 Materials Research Society
backscattering and channeling (RBS-C) using 2 MeV He+ ions or in SIMS using both Cs+ and 02+ beams. RESULTS AND DISCUSSION Fig.1 illustrates stoichiometric Si0 2 formation for 15 keV O" bombardment of Si to a dose of 1 x 1018 cm"2 at room temperature. The solid curve is a RUMP simulated RBS-C spectrum for the structure indicated in the inset. SiO 2 forms even at liquid nitrogen temperature [1] indicating the strong chemical driving force for Si0 2 formation and the mobility of 0 in Si0 2 under ion irradiation.
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temperature into Si (100).
The random spectrum (0)
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and the channeled spectrum ( 0 ) confirm the structure in the inset. The solid curve is a RUMP simulation of the
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0 -crystalline, 250 200 150
RBS-C spectra illustrating Si0 2
inset structure: the c-Si, part of 300 Channel
350
400
450
the spectrum is fitted with a straight line.
Fig.2 shows RBS-C spectra illustrating typical behaviour for 10 keV N 2 + irradiation of Si in the SIMS apparatus at room temperature. At a beam incidence of 550 to the normal, sputtering does not allow the nitrogen concentration to reach Si 3N4 even at very high doses. At normal incidence, however, a slightly N-rich Si3N 4 layer is formed. With increasing dose the Ncontent remains unchanged. The solid curve is a RUMP simulation for 170A of Si 3N 4 on an amorphous Si layer of - 150A [2]. Fig.3 illustrates the angular dependence of oxygen and nitrogen content for irradiation in the SIMS. For angles less than about 300, stoichiometric Si0 2 and slightly N-rich Si 3N4 layers are fo
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