TimeDomain CVD, Inc.

Kinetic Theory Example

T = 300 K [room temperature]

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

 

 

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

 

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