EE143 Fall 1992
Midterm #2
A. R. Neureuther, Mansun Chen, Sang Yup Kim, David Newmark
Problem #1 (45 points) Diffusion
An emitter-base doping process is carried out on an arsenic doped substrate with 5x10^15 cm^-3 according to
a four step process flow of:
1 Implant Boron 3x10^13 cm^-2
2 Drive 1075 C 60 min
3 Implant Phosphorus 1x10^15 cm^-2
4 Drive 1025 C 120 min
a) Find the depth of the junction formed by boron and arsenic.
b) Find the depth of the junction formed by phosphorus and boron.
c) Suppose an additional phenomena of field enhanced diffusion occurs with the following characteristics. It
is only present at depths where one of the dopant concentrations exceeds n_i = 5x10^18 cm^-3. Here it
produces an electric field which increases by 2 or more the diffusion coefficient of all species of the same
type. This electric field also reduces the diffusion coefficient of all species of the opposite electrical type.
Indicate on the sketch how the distributions of boron, phosphorus and arsenic change with this effect.
Problem #2 (30 points) Vacuum, Deposition and Etching
a) To what pressure should the chamber be pumped down to prevent the residual partial pressure of air from
depositing 0.1% or less oxygen when aluminum is deposited at a rate of 0.2 um/min? Assume 21% of the
partial pressure of air is due to O2.
b) On a single sketch show the difference in profile shape resulting from vertical and isotropic deposition of
1.0 um of material over the initial profile shown below. Give dimensions and descriptions of profile
segments.
EE143, Midterm #2, Fall 1992
EE143 Fall 1992 Midterm #2 A. R. Neureuther, Mansun Chen, Sang Yup Kim, David Newmark 1
