What is Reactive Ion Etching?

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In Reactive Ion Etching (RIE), gas plasma is generated between two
parallel electrodes, the RF powered electrode holds the sample, and the
top electrode is ground.

The directional etching is assisted by the migration of ionic species
to the powered electrode.

These ions, together with the free radicals, generated by the plasma
react faster than either one of the individual species alone.

The free radicals etch in every direction, but because the ions are
accelerated and move in one direction, perpendicular to the sample,
etching takes place primarily in that downward direction and provides
the good “straight” wall or anisotropic etching.

The basic design of the vacuum chamber effects the uniformity of the
etch. The lower the pressure the better the directional etch.

However, the etch rate decreases with lower pressure.

The voltage potential across the electrode is a function of the
relative sizes or surface area of the ground and powered electrodes.

The greater the ratio of the ground to powered electrode size, the
greater the voltage, and the better the anisotropic etching.

When the size ratio increases over 1.5 to 1, then anisotropic etching
can be performed at pressures from 100 to 300 mTorr.

At these pressures, high etch rates can be achieved with good
uniformity.