
168 Nanosensors: Physical, Chemical, and Biological
giving
D = −
×
= −
×
−
= ×
−
−
−
−
2.78 2.78
cm
2
10
10
10
6 907755
4 0245 10
12
3
12
13
ln( ) .
. s
−1
(3.25)
Substituting for D from Equation 3.25 in Equation 3.19
Q D= × × = × × × ×
=
−
1 10 11 304 1 10 11 304 4 0245 10
6 745 10
18 18 13
13
, , .
. × atomms cm
2−
(3.26)
For phosphorus diffusion, compounds such as PH
3
(phosphine) and
POCl
3
(phosphorus oxychloride) are used. In the case of P-diffusion
using POCI
3
, Figure 3.8, the reactions occurring at the silicon wafer sur-
face are
Si O SiO (silica glass) 4POCl 3O 2P O 6Cl
2 2 3 2 2 5 2
+ = + = +;
(3.27)
This results in the production of a glassy layer on the silicon ...