A silicon wafer is etched in a Cl2 plasma. A mass flow controller (used to meter

Question

A silicon wafer is etched in a Cl2 plasma. A mass flow controller (used to meter the gas flow fed to the reactor) shows a reading of 100 sccm (sccm=standard cm3 per min; standard conditions are 273 K and 1 atm). The etching reactor operates at 100 mTorr pressure, and the reactor gas temperature is 500 K. (note: 1 atm =760 Torr.)

(a) What is the chlorine flow rate at the reactor pressure and temperature?

(b) If the etching rate of silicon is 0.50 ?/min, and the wafer is 300 mm in diameter, how many moles of silicon are etched per hour?

(please show work)

Explanation / Answer

problem 1 Find volume of Si wafer (in cm^3): V = A*t = p(5 cm)^2*(0.01 cm) = 0.7854 cm^3 Weight of Si wafer (in g): weight = density*volume = 0.7854*2.3 3 = 1.8300 gmoles of Si: moles = weight/MW = 1.8300/28 = 0.06536 mol So 0.06536 mol SiO2 were produced in the complete oxidation. Now work backwards: weight of SiO2 produced: 0.06536 mol x 60 g/mol = 3.921 g volume of SiO2: 3.921 g / 2.27 g/cm^3 = 1.7273 cm^3 Given the same 100 mm diameter, the thickness is: 1.7273/(p(5 cm)^2) = 0.02199 cm or 219.9 µm n

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