Method for Gate Charging Reduction Using
Plasma With Wavelengths Greater Than 1.07 um
Disclosed is a method for significantly reducing charging
damage in the gate oxide during the metal etch process.
Background
Current
metal etch process uses plasma that has a wide range of light spectrum. A
significant portion of this spectrum falls into the range of wavelengths which
are less than
1.07
. This range of plasma light has photons carrying energy
greater than 1.12 eV, capable of exciting electrons from the silicon valence
band into the conduction band. As a result, a significant amount of
electron-hole current is generated. These photon induced junction leakages
represent more than 90% of the total junction leakages, and are the major
source of charging damage current in the gate oxide.
General Description
The disclosed method’s equivalent circuit model (see Figure
1) is used to illustrate the mechanism in the S/D junction region. The
relationship between various current components in this model is given below:
(1)
: gate oxide
current
: current
absorbed at gate antenna
: dark source
junction leakage
: plasma
illumination induced current in source
junction
: dark drain
junction leakage
: plasma
illumination induced current in drain
:
depletion-region current under gate channel
Equation (1) shows that is supplied by current coming into the gate antenna, but it
is “limited” by the sum of dark source and drain junction leakage, plasma
illumination induced current in the S/D junctions, and depletion-region current.
Experimental data suggest that the plasma illumination induced current is much
larger than the dark junction leakage (more than 90% of total junction leakage
comes from plasma illumination induced junction leakage). The depletion-region
current is insignificant due to high impedance in the depleted region and the
small width defined by the distance between the source and drain. As a result,
the plasma illumination induced S/D junction leakage is capable of inflicting
large charging damage when a large antenna is at the gate (see Figure 1). In
other words, if this mechanism of photon induced current in the S/D junction
can be largely suppressed or comple...