TimeDomain CVD, Inc.

Kinetic Theory Example

T = 300 °K [room temperature]

Nitrogen (N2 molecule), M = 28 gm/mole a = 3.7 Å

Pressure
density
mean free path
mean velocity
flux to surface
"growth rate"

(Torr)
(molecules/cm3)
(microns)
(cm/sec)
(molecules/cm2 sec)
(microns/minute)

0.1
3.2E15
500
47,000
3.8E19
10

10
3.2E17
50
47,000
3.8E21
1000

760
2.5E19
0.07 (70 nm)
47,000
2.9E23
77,000

[the "growth rate" is the approximate amount of solid material that would be formed if each nitrogen molecule were incorporated into a solid on the surface -- shown here to demonstrate the very high growth rates that would be possible if every molecule was incorporated at high partial pressures of a precursor material]

Things to note:

47,000 cm/second: a molecule will cross a 1-meter chamber in 2 msec @ 1,000 miles/hour!
the impingement-limited growth rate greatly exceeds actual growth rates:
- the actual deposition precursor is rare (partial pressure at surface << total pressure) OR
- the probability of incorporation into the surface is small

Introduction: Table of Contents

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Pressure	density	mean free path	mean velocity	flux to surface	"growth rate"
(Torr)	(molecules/cm3)	(microns)	(cm/sec)	(molecules/cm2 sec)	(microns/minute)
0.1	3.2E15	500	47,000	3.8E19	10
10	3.2E17	50	47,000	3.8E21	1000
760	2.5E19	0.07 (70 nm)	47,000	2.9E23	77,000