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Name:____________________
CHEMICAL ENGINEERING 179
Exam 2
Wednesday, April 11 2012
Closed Book with 3x5 Card
kB = 1.381 x 10-23 J K-1; R = 8.314 J (mole K)-1 = 1.987 cal (mole K)-1 ; NA = 6.022 x 1023 (mole)-1; e = 1.602
x 10-19 C; mp = 1.673 x 10-27 kg = 1.007 amu ; 1 liter = 1000 cm3 ; STP = 273 K, 760 torr (1 atm); 1 atm = 1.013
x 105 Pa; 1 Pa = 1 J/m3; 1 eV = 1.602 x 10-19 J
Short Answer. 5 pts. each.
1.What is the chief advantage of plasma etching over wet liquid etching in semiconductor
manufacturing?
Anisotropy is possible in the etch profile.
2. A measurement of Si etch rate is made with F atoms only hitting the surface, then F atoms
plus Ar+ (500 eV), then only Ar+ (500eV). Sketch the expected etch rate vs. time for this
experiment, labeling the different regions.
Low etch rate, followed by a high etch rate, followed by a low rate again.
3. Chemical vapor deposition (CVD) reactor design calculations usually require chemical
kinetics rather than chemical thermodynamics. Why is this?
The chemical processes are not at equilibrium, which is required to use chemical
thermodynamics.
4. In semiconductor manufacturing, CVD processes are usually conducted at reduced pressure.
List 2 reasons why low pressure is preferred to atmospheric pressure for CVD.
- higher diffusivity leads to better film deposition uniformity; lower pressure reduces particle
formation;
