The diffusion of B and Sb in samples with, or without, a 20nm-thick molecular beam allotaxial CoSi2 top-layer was investigated during annealing and oxidation by using doping superlattices. The latter were grown by means of molecular beam epitaxy, and consisted of 6 spikes with peak concentrations of 1018/cm3 (B) or about 1019/cm3 (Sb); with peak centres that were spaced 100nm apart. The shallowest spike was capped with 100nm of Si, followed by 20nm of CoSi2. Annealing in pure N2 and oxidation in pure O2 were carried out at 800 to 1200C. The concentration depth-profiles were measured by means of secondary ion mass spectrometry. The results showed that dopant diffusion was markedly different with, as compared to without, the CoSi2 layer. In the latter specimens, oxidation-enhanced diffusion of B and oxidation-retarded diffusion of Sb were observed. However, the effect of CoSi2 layers was to retard B diffusion strongly and enhance Sb diffusion (tables 4 and 5). The B diffusivity was retarded by a factor of between 2 and 10, as compared to the thermal diffusivity, and by a factor of 20 to 100 when compared with the corresponding diffusivity for oxidized Si without a CoSi2 layer. The Sb diffusivity was enhanced by a factor of 2 with respect to thermal diffusivity, and by about a factor of 5 when compared with the CoSi2-free case.

Effect of an Epitaxial CoSi2 Layer on Diffusion of B and Sb in Si during Annealing and Oxidation A.K.Tyagi, L.Kappius, U.Breuer, H.L.Bay, J.S.Becker, S.Mantl, H.J.Dietze: Journal of Applied Physics, 1999, 85[11], 7639-45. See also: Fresenius’ Journal of Analytical Chemistry, 1999, 365[1-3], 282-5

 

 

Table 4

Effect of CoSi2 Coating on B Diffusion in Si

 

CoSi2 Layer

Pre-Treatment

Diffusion Treatment

Diffusivity Enhancement

yes

1050C, 20s, N2+O2

900C, 840s, O2

0.21

yes

1050C, 20s, N2+O2

950C, 360s, O2

0.28

yes

1050C, 20s, N2+O2

1000C, 60s, O2

0.53

yes

1050C, 20s, N2+O2

1050C, 20s, O2

0.56

yes

-

1050C, 20s, N2+O2

0.75

yes

-

1050C, 40s, N2+O2

0.52

yes

-

1100C, 20s, N2+O2

0.80

no

-

800C, 900s, O2

1.43

no

-

850C, 600s, O2

7.63

no

-

900C, 300s, O2

1.60

no

-

950C, 30s, O2

3.12

no

-

950C, 90s, O2

4.24

no

-

1000C, 40s, O2

4.20

no

-

1050C, 10s, O2

1.38

no

-

1050C, 20s, O2

4.65

 

 

Table 5

Effect of CoSi2 Coating on Sb Diffusion in Si

 

CoSi2 Layer

Pre-Treatment

Diffusion Treatment

Diffusivity Enhancement

yes

1050C, 30s, N2+O2

1050C, 180s, O2

2.11

yes

1050C, 30s, N2+O2

1050C, 360s, O2

1.87

yes

1050C, 30s, N2+O2

1050C, 540s, O2

2.17

yes

1050C, 30s, N2+O2

1100C, 60s, O2

2.07

yes

1050C, 30s, N2+O2

1100C, 120s, O2

1.49

yes

1050C, 30s, N2+O2

1150C, 20s, O2

1.52

yes

1050C, 30s, N2+O2

1200C, 5s, O2

1.05

yes

1050C, 30s, N2+O2

1200C, 10s, O2

1.53

yes

-

1050C, 30s, N2+O2

3.90

yes

-

1150C, 20s, N2+O2

1.83

no

-

1050C, 960s, O2

0.33

no

-

1100C, 240s, O2

0.26

no

-

1100C, 540s, O2

0.24

no

-

1150C, 180s, O2

0.13

no

-

1200C, 20s, O2

0.42