As a general rule of thumb, the ratio of the rate of etch-product formation to the flow rate of etch gas should be greater than 0.1 for uniform etching. Suppose a 7.5-cm diameter silicon wafer is etched at a rate of 50 nm/min in a CF4 plasma.
(a) How many atoms of Si are removed per minute?
(b) What evolution rate of SiF4 does this correspond to in standard cubic centimeters per minute (sccm)?
(c) What minimum CF4 flow rate should be maintained?

Afoot bridge is made as a simple deck, 4 m long, with a cross section 2 m (wide) and 20 cm thick, and made of wood. the deck is supported at the two ends. the maximum load allowable on the bridge is 10 tons, provided it is uniformly distributed on the deck. to sense this load, a strain gauge is placed at the center of the bridge and its resistance is monitored. if the sensor has a nominal resistance of 350 s2 and a gauge factor of 3.6, what is the reading of the strain gauge at maximum load? the modulus of elasticity for the wood used in the construction is 10 gpa.