Masking material for TMAH etching

Hi all,

does anyone know of any material besides silicon oxide and nitride that can withstand 6-7 hours of TMAH etching?

I need to protect the front side during etching silicon from the back side.

And front side has LTO patterns, so covering with oxide and nitride would ruin my pattern.

Please let me know if you have any idea.

Thanks,

Donguk