Simulation of Low Energy Electron-Enhanced Etching of GaN
 
 
 
 
 
 

Weiqiao Deng Richard Muller Lu Sun William A. Goddard III

Materials and Process Simulations Center, Beckman Institute, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA
 
 

Pat H. Gillis

Department of Chemistry and Biochemistry, University of California, Los Angeles
 
 

Abstract


 






The simulation of Low Energy Electron-Enhanced Etching (LE4) of GaN will be studied for the first time. The processing is assumed to be simulated in three steps:

First is to simulate the distribution of electron beam. Second is to simulate the collision between electron and surface of GaN. Third is to simulate the reaction between vibrational or electronic excited GaN and the plasma molecule on the surface. This simulation is expected to explain the mechanism of LE4, which is unclear currently.

The surface of GaN

Present LE4 etching experimental results:

  1. Etch rates will increase dramatically depending on temperature.
  2. Surface stoichiometry is maintained in Cl2 plasma and H2 plasma at temperatures below 1000C.
  3. Surface roughness is not increased over the as-grown values.
  4. Anisotropy of etch profiles is limited by as-grown surface roughness.

 
 
 
 
 
 
 
 
 
 

Advantages of LE4 etching

  1. Good anisotropy, high selectivity relative to the masking materials.
  2. Very smooth surfaces. (Root mean square [RMS] surface roughness 3-5 Å)
  3. Etch rate can reach as high as 2,500 Å /min with no ion bombardment.
Methods Used in Simulation:

Castep: the total-energy pseudopotential ab initio quantum-mechanical method.

To study the potential surface and interaction about the surface of GaN.

Molecular dynamics: the classical mechanics method based on solving classical Hermition Netwon equation.

To study the physical processing occurred in the etching such as energy transfer, collision event, etc.

Statistics theory:

To study the rate constant of reactions occurred on the surface of GaN.
 
 

Simulation models of LE4
 
 

1. Charging Dynamics:
 
 

To study the angular Distribution of Electron beam.
 
 
 
 

2. Assumed Physical LE4 Etching Model
Kinetic Energy Transfer: Through the collision, the kinetic energy of electrons is transfer to the vibration energy of surface.

Electron Energy Transfer: The electrons will locate at the surface of GaN, then ionize the Ga.


 
 


 
 

Reference:
 
 

"The Dry Etching of Group III-Nitride Wide-Bandgap Semiconductors" Journal of Materials 48, 50-55, (1996)

H. P. Gillis D.A. Choutov, and K.P. Martin
 
 

"The surface-radical-surface-olefin recombination step for CVD growth of diamond. Calculation of the rate constant from first principles" Chemical Physics Letters 247, 359-365 (1995)

Charles B. Musgrave Stephen J. Harris and William A. Goddard
 
 

"Charging Effects during High-Density Plasma Etching"

Gyeong Soon Hwang