I would like to achieve complete aluminium passivation with 25% TMAH. I
could acheive aluminium passivation at 5% TMAH by adding 35 gm/ltr silicic
acid. In 25% TMAH, i added upto 200 gms/ltr silicic acid (for 5% TMAH,
35gms'ltr and hence i tried upto 200 ms/ltr for 25% TMAH) but could not
achieve aluminium passivation. 1 micron aluminium could withstand only upto
30 minutes, but for my device fabrication i need to do micromachining for
5-6 hours. Whether amount of silicic acid has further to be increased to
achieve complete aluminium passivation. Any comments?

Thanks in advance,
Best Regards,
A. Ravi Shankar,
Senior Research Scholar,
Microelectronics Lab,
Electronics &ECE Department,
IIT Kharagpur, India.