(Problem solving) The concept of mean free path can help you to understand semic

Question

(Problem solving) The concept of mean free path can help you to understand semiconductor process theory better. For example in ion implant, ions are accelerated to high energy to shoot at wafers. The ions impinged into the wafer surface become dopants in silicon. A) can you imagine what will happen to the ions if they collide with gas molecules not pumped out in the implant chamber before they get to the wafer? Is it desirable for ion implant? (Part A not graded) B) if you do not want this collision to happen, you need to pump down the chamber until on average, an ion will not collide with a single gas molecule in the entire length of its travel until it hits the wafer. The entire length of its travel is say 10m. Can you estimate the level of pressure the chamber has to be under before on average the collision will not occur? (Part B graded)

Explanation / Answer

a) yes, they will collide which will decreae the kinetic energy plus change the trajectory/path of the particle

b) no, you want a direct path to the wafer

b)

L = 10 m

You gotta use vacuum

that is

Pg = Patm

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