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...