~ Deprocessing ~
Nitride Etch followed by Pyrhana Etch

Example #2
Isolation of Circuit Elements

 

The SEM photo on the right is an IC shown after 12 minutes in nitride etch at 120-130°C.  The passivation removed was about 0.9 microns of plasma nitride over about 0.1 micron of deposited SiO2.  The goal of this step was to expose metal 2 while leaving metal 1 protected by interlayer dielectric.   SEM photo of IC after BOLIDE nitride etch (365 KB)
 

 
The SEM image on the right shows the same area after metal 2 was removed by a 5 second etch in freshly mixed 1:1 combination of 98% sulfuric acid and 30% H2O2.  This etch, sometimes called pyrhana etch, self heats upon mixing and is very aggressive.  It attacks organics and most metals.  Pyrhana etch may not be suitable for deprocessing a packaged die because the package material will be attacked.

Note that ridges in the dielectric define the path of removed metal lines.

This information should be documented before removing dielectric with an HF containing etch.

  SEM image of IC after BOLIDE nitride etch and metal 2 removed by pyrhana etch (493 KB)
 

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