Satish,

    this happen due to PR reticulation during plasma etching. in that case
normally plasma ashing and chemicals that you have used will not work. In
this case you can use Piranha Solution (H2SO4+H2O2) heated at 110 degree
celcius for about 30 minutes, you can get rid from this problem, but you
can use piranha only if you are not having metal on your sample.

If you have metal than you can use EKC Polymer remover heated at 65 degree
celcius for 15 minutes.

I hope by using this you can be out of trouble.

Good Luck!

Manish Hooda