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TimeDomain CVD, Inc. |
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"Zero-dimensional" analysis (simplest non-trivial transport analysis):
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Notation: pre = precursor chemical for deposition F = volume flow (e.g. m3/second) Ks = surface reaction rate constant (units of velocity, e.g. cm/second or m/second) ch = concentration in chamber |
Limits:
| The concentration of precursor in the reactor
is essentially equal to the inlet concentration when the residence time
is short compared to the time required to consume the species (i.e.
conditions of high flow); this is the "differential" condition
in which uniformity is likely to be good but efficiency of utilization
is low. Since the consumption time is set by the surface reaction rate,
differential conditions are likely for activated reactions at low
temperatures, where the reaction rate is slow: this condition is often
referred to as "surface limited".
The concentration of precursor is much less than the inlet concentration when the consumption time is fast (i.e. conditions of low flow or fast reaction rate). Here the uniformity of deposition is likely to be poor since large gradients in concentration have been created. This is the "starved" reactor condition; it is likely to occur for activated reactions at high temperatures, where the surface reaction rate is large, and is often known as "mass transport limited" deposition. |
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