PE1-1.4 Etching, Ion Implantation & Diffusion

Work through these

• Chemical etching

  Removing material with liquid chemistry, which etches equally in all directions. That isotropy is the limitation the plasma methods below were developed to escape.

• Electrochemical etching

  The variant where a current drives the reaction, giving more control over rate and selectivity. A specialised tool rather than a mainstream one.

• Plasma (dry) etching and reactive plasma etching

  Etching with a plasma, which can be made to attack downwards far faster than sideways. Vertical sidewalls are what let features be packed closely, so this is the enabling step for small geometries.

• Ion implantation: range and penetration depth

  Firing dopant atoms in at speed, and how deep they end up. The distribution is statistical, which is a different way of thinking from the diffusion topic below.

• Implantation damage and annealing

  The atoms arrive by breaking the crystal, so the crystal has to be repaired afterwards. Annealing does that and moves the dopant slightly, which has to be accounted for.

• The ion implantation machine

  The equipment, in outline, because it explains where the control and the cost come from. Beam current and scanning uniformity are the parameters that matter.

• Constant source and infinite source diffusion

  The older method, driven by heat rather than momentum, in two limiting cases. Which case applies depends on whether the surface concentration is held constant.

• Diffusion profiles and diffusion systems

  The shapes the dopant distribution takes and the furnaces that produce them. Comparing these profiles with the implanted ones above is the real content of this topic.