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Homework #8 Solutions EE 528, Fall 2010
9.7. (a) Plot the deposition rate (on a log scale) versus 1/T
(K), for 600-1200C for a
CVD system with the following parameter values:
hG = 0.5 cm sec-1
, kS = 4x106
exp(-1.45 eV/kT) cm sec-1
Partial pressure of incorporating species = 1 torr, Total
pressure = 1 atm
CT/n=1/10,000
Identify the reaction and mass transfer limited regimes.
(b) Redo the problem when the total pressure is decreased to 1
torr, so that hG
increases by 100 times. Assume that the partial pressure of the
incorporatingspecies remains the same, and CT decreases by the same
factor as the total
pressure.
Answer:
By Equation 9.10: v kShG
kS hG
CT
N
Y 1
1hG
1kS
CT
N
Y ,
hG = 0.5 cm sec-1
kS = 4x106
exp(-1.45 eV/kT) cm sec-1
where T = T C + 273CT/N= 1/10,000
Y = Pg/Ptotal = 1 torr / 760 torr
For low pressure case, only hg changes (increased by 100 times).
CT/N times
Pg/Ptotal remains constant since n and Pg each remains constant,
and the CT/Ptotal ratiostays constant as stated above.
For the 1 atm total pressure case, the transition between
surface reaction controlledand diffusion controlled is at about 800
C, while for the low pressure case (low
P), the transition occurs above 1200 C.
10-5
10-4
10-3
10-2
10-1
0.60 0.75 0.90 1.05 1.2
VV(low P)
V (microns/sec)
1000/T(K)
600C1200C 800C
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Homework #8 Solutions EE 528, Fall 2010
10.7. (a) In a particular etch process, if selectivity is the
biggest concern, which
type(s) of etch equipment should be used?(b) If the biggest
concern is ion bombardment damage, which type(s) of etch
equipment should be used?
(c) If the biggest concern is obtaining vertical sidewalls,
which type(s) of etchequipment should be used?
(d) If the biggest concerns are selectivityandvertical
sidewalls, which type(s)of etch equipment should be used?
(e) What about selectivity andvertical sidewalls anddamage,
while maintain-
ing reasonable etch rate?
Answer:
a. If biggest concern is selectivity? barrel or remote plasma or
wet etching
b. If biggest concern is damage? barrel or remote or wet
c. If biggest concern is vertical sidewalls? sputtering or
RIE/HDP
d. What about selectivity AND vertical sidewalls? RIE/HDP
e. What about selectivity AND vertical sidewalls AND damage,
while maintaining
reasonable etch rate? HDP
