Effects on Selective CVD of Titanium Disilicide by Substrate Doping and Selective Silicon Deposition
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implanted doses of both As, and B. EXPERIMENTAL Two sets of samples were prepared one with B and another with As implanted ion species. Si wafers with oxide patterns were implanted to a dose of 3e+ 14, 1e+ 14 and 5e+ 15 ions/cm 2 each with B at 10keV and As at 35keV through a 5nm screen oxide. The samples were each given a rapid thermal anneal (RTA) in N2 at 1050C for 30s. The screen oxide was wet chemically removed from the wafers before loading into a rapid thermal CVD (RTCVD) system where the samples received a 980'C in situ H2 bake. On some samples SEG Si was deposited at 950'C using a gas mixture of dichlorosilane and hydrogen after the in situ H2 bake. Titanium disilicide was deposited at 780'C using a gas mixture of titanium tetrachloride, silane, dichlorosilane, and hydrogen. Line resistance was measured from 100rnim wide line resistors formed in the patterned oxide. Oxide thickness was measured using an ellipsometer. TiSi2 thickness was calculated using knowledge of the oxide thickness and from two step height measurements made using a step profilometer. Step height measurements were made (1) after selective CVD TiSi 2 deposition, measuring the step height difference between the oxide pattern and the TiSi 2 surface,
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Mat. Res. Soc. Symp. Proc. Vol. 564 @1999 Materials Research Society
and (2) after wet chemical removal of the oxide and selective CVD TiSi 2, measuring the step height difference between the surfaces beneath the oxide and beneath the TiSi 2 films. RESULTS Selective Evitaxial Growth of Si Films The thickness of SEG Si (-25nm) was weakly a function of the initial the highest B and As ion dose used in this study the resulting SEG Si for the same SEG Si process. Though no analysis has been done at this it is assumed that the -25nm SEG Si layer was autodoped during the SEG Si deposition step.
implanted ion dose. For film was slightly thinner time (e.g. SIMS or SRP) high temperature 950'C
130 A
-A
E 110
c.J C,
no SEG Si
A-As, with SEG Si
-- B, withSEGSi
UC
As, no SEG Si
S~--W1--B,
120
100 90 80 70 60
30=s --
..-- ---------
30s CVD TiSi 2 process
50 1.E+14
1.E+15
1.E+16
initial implanted dose (ions/cm2) Figure 1: A plot of selective CVD TiSi 2 thickness deposited in 30s as a function of initial implanted ion dose processed with and without SEG Si.
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Substrate Dependence of Selective CVD TiSi, Films: Substrates with and without SEG Si
L. TiSi 2 Thickness A plot of selective CVD TiSi 2 thickness deposited in 30s as a function of initial implanted ion dose is shown in Figure 1. The solid curves trace the process with no SEG Si and dashed curves trace the process which used -25nm SEG Si. For the case of As implanted Si (triangle symbols in Figure 1), it is clear that the addition of SEG Si has two effects on subsequent selective CVD TiSi 2 deposition (i) the rate of selective CVD TiSi 2 deposition is decreased as seen in the smaller selective CVD TiSi 2 thickness vs. selective CVD TiSi 2 thickness with no SEG Si, and (ii) the variation in selective CVD TiSi 2 thickness as
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