Diffusion #1. ECE/ChE 4752: Microelectronics Processing Laboratory. Gary S. May January 29, 2004. Outline. Introduction Apparatus & Chemistry Fick’s Law Profiles Characterization. Definition.
ECE/ChE 4752: Microelectronics Processing Laboratory
Gary S. May
January 29, 2004
Example reaction: 2As2O3 + 3Si → 4As + 3SiO2
(forms an oxide layer on the surface)
C(0, t) = Cs
C(∞, t) = 0
For a boron diffusion in silicon at 1000 °C, the surface concentration is maintained at 1019 cm–3 and the diffusion time is 1 hour. Find Q(t) and the gradient at x = 0 and at a location where the dopant concentration reaches 1015 cm–3.
The diffusion coefficient of boron at 1000 °C is about 2 × 1014 cm2/s, so that the diffusion length is
When C = 1015 cm–3, xj is given by
C(∞, t) = 0
Arsenic was pre-deposited by arsine gas, and the resulting dopant per unit area was 1014 cm2. How long would it take to drive the arsenic in to xj = 1 µm? Assume a background doping of Csub = 1015 cm-3, and a drive-in temperature of 1200 °C. For As, D0 = 24 cm2/s and Ea = 4.08 eV.
t • log t – 10.09t + 8350 = 0
y = t • log t and y = 10.09t – 8350.
xj = junction depth (where C(x)=Csub)
where: (for n heat cycles)
1) Known current (I) passed through outer probes
2) Potential (V) developed across inner probes
r = (V/I)tF
where: t = wafer thickness
F = correction factor (accounts for probe geometry)
OR: Rs = (V/I)F
where: Rs = sheet resistance (W/)
=> r = Rst
where: s = conductivity (W-1-cm-1)