I believe there is a reaction at the interface. Si is covered by native oxide (SiO2). Group III elements like Al and In have a stronger bonding to oxygen than Si (more negative reaction enthalpy). Many years ago it was shown that Al can reduce SiO2, when some energy is placed to the interface. The result is Al2O3 plus Si. I think In, when it is coming as hot vapour, has the same potential. It forms In2O3 plus Si. If this reduction occurs an alloying between Si and and In (not including the In2O3!) should be taken place. The covering native oxide SiO2 which would help you in your lift off process is partially destroyed. The alloy has strong adhesion directly to the elemental Si. Is an evaporation of pure Au possible? Au should not form an alloy.

Rahul,

I don't have experience depositing indium, or using double layers of PMMA, but this does sound odd...

Were there any problems with edge bead when you spun the resists on your Si substrate? Any chance the metal was deposited all around the edges of the chip on the substrate and now you can't lift the PMMA off because it's capped all around by the metal to the substrate?

It should be removed after heating in acetone, However, put for long in acetone and see if it can work. May be PMMA layers was crack, it can be one of the possible reason. I had this kind of experience once during training when acetone caught onto my substrate and no lift-off after deposition.

Hi Inayat Uddin ,

You can try aqua regia (HCl mixed with HNO3) to remove Au and In. The duration could be carefully set to the minimal necessary one.

Regards,

Sidi