Try the following;

  1. More stable solution: 3 HCl:1 HNO3:1 H2O
  2. About 2um thick positive photoresist AZ 1512

  Good luck.

  jjiah  wrote:
  Dear All,

I am currently trying to process Broad Area Lasers on 1cm2 AlGaAs sample. On
the Epi side i am depositing Ti/Au by e-beam evaporation. Then using
photolithography to create openings on the sample to isolate the devices from
each other by etching all the way to the substrate using wet etching. The
photoresist i am using is a positive photoresist (S1813).

My problem is this:

I know that (3 HCl:1 HNO3) will etch Au and AlGaAs and HF will etch Ti, but my
photoresist will not hold against either etchants. As a result, my photoresist
will not cover and protect the areas i don't want to be etched.

Can someone please suggest a solution for my problem?