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Solution Felder 9.16

This document describes a chemical vapor deposition (CVD) process used to deposit silicon dioxide films on silicon wafers. The process involves the reaction of silane and oxygen gases at low pressure. Given information about the feed gas composition and operating conditions, the document asks the reader to: 1) Calculate the moles of each component in the feed and product mixtures and the extent of reaction. 2) Determine the standard heat of reaction and construct an enthalpy table to calculate component amounts and specific enthalpies. 3) Calculate the heat transferred to or from the reactor and the required heat transfer rate.

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Alya Sholikhatul
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391 views3 pages

Solution Felder 9.16

This document describes a chemical vapor deposition (CVD) process used to deposit silicon dioxide films on silicon wafers. The process involves the reaction of silane and oxygen gases at low pressure. Given information about the feed gas composition and operating conditions, the document asks the reader to: 1) Calculate the moles of each component in the feed and product mixtures and the extent of reaction. 2) Determine the standard heat of reaction and construct an enthalpy table to calculate component amounts and specific enthalpies. 3) Calculate the heat transferred to or from the reactor and the required heat transfer rate.

Uploaded by

Alya Sholikhatul
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Problem 9.6.

1
In the production of many microelectronic devices, continuous chemical vapor
deposition (CVD) processes are usedto deposit thin and exceptionally uniform silicon
dioxide films onsilicon wafers. One CVD process involves the reaction between
silane and oxygen at a very low pressure.
SiH4(g) + O2 SiO2(g) + 2H2 (g)

The feed gas, which contains oxygen andsilane in a ratio 8.00 mol O-/mol SiH,,
enters the reactor at 298 K and 3.00 torr absolute. The reaction products emerge at
1375 K and 3.00 torr absolute. Essentially all of the silane in the feed is consumed.
(a)Taking a basis of 1m3 of feed gas, calculate the moles of each component of the
feed and product mixtures and the extent of reaction, £(mol).
(b)Calculate the standard heat ofthe silane oxidation reaction (kJ/mol). Then, taking
the feed and
product species at 298 K (25"C) as references, prepare an inlet-outlet enthalpy table
and calculate and fill in the component amounts (mol) and specific enthalpies
(kJ/mol). (See Example 9.5-1)
Data

The temperatures in the formulas for C, are in kelvin.


(c) Calculate the heat (kJ) that must be transferred to or from thereactor (state which
it is). Then determine the reguired heat transfer rate (kW) reguired for a reactor feed
of 27.5 m3/h.

Solution
9.12 a.
1 m3 at 298K, 3.00 torr Products at 1375K, 3.00 torr
n0 (mol) n1 (mol O2)
0.111 mol SiH4/mol n2 (mol SiO2)
0.8889 mol O2/mol n3 (mol H2)
SiH 4 ( g) + O 2 ( g) → SiO 2 (s) + 2H 2 (g)
3
Ideal Gas Equation of state : n = 1 m 273 K 3.00 torr 1 mol = 0.1614 mol
o 298 K 760 torr 22.4 ×10-3 m3
ni = nio +ν i ξ
SiH4 : 0=0.1111(0.1614 mol) − ξ ⇒ ξ = 0.0179 mol

O2 : n1 = 0.8889(0.1614 mol) − ξ = 0.1256 mol O2

SiO2 : n2 = ξ = 0.0179 mol SiO2

H2 : n3 =2ξ =0.0358 mol H2


o o o
H ) −(
)
b. Hr = ( f SiO 2 ( s) Hf SiH 4 (g)

= [−851 − ( −61.9)] kJ mol = −7891. kJ / mol

References : SiH4 (g),O2 (g),SiO2 (g),H2 (g) at 298 K


n ˆ n ˆH
Substance in H
in
out out

(mol h) (kJ mol) (mol h) (kJ mol)


SiH4 0.0179 0 − −
ˆ
O2 0.1435 0 0.1256 H1
ˆ
SiO2 − − 0.0179 H
2

H H
ˆ
2 − − 0.0358 3
Table B.8
B
o
=H
O2 (g,1375K): H 1 O2 (1102 C) = 3614. kJ / mol
1375

SiO2 (s,1375K): H 2 = z (C p )SiO 2 (s) dT = 79.18 kJ / mol


298
Table B.8
B
o
=H
H 2 (g,1375K): H 3 H2 (1102 C) = 32.35 kJ / mol
c. ˆo ˆ ˆ 3
Q= H =ξ H + ∑ n H − ∑n H = −7.01 kJ/m feed
r i i i i

out in
−7.01 kJ 27.5 m3 1h 1 kW
Q= =−0.0536 kW (transferred from reactor)
m3 h 3600 s 1 kJ/s

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