Hi,

If you use PAN solution for Al etching or cesium ammonium nitrate based
solution for Cr etching at room temperature, there shouldn't be serious
attack, if any, on SiO2. So you don't need this intermediate resist layer?
The fact that your metal layer crack after baking your second resist layer
is probably because the thermal stress between your metal and first resist
layer is too great. I assume your first resist layer has been well baked
otherwise it will outgas in your evaporator chamber.

Regards,
Isaac Chan, Ph.D.

On Thu, 5 Oct 2006, Xiaojing Zou wrote:

> Hi:
>
>   Currently I am doing dry etch SiO2 with Al or Cr as hard mask, which will be
removed by wet etch later. But I always found the surface of the SiO2 will be
damaged a little after the wet etch. So I plan to insert a thin layer of "soft
materials" (like PMMA) between SiO2 and the metal layer. But a problem occurs
when I bake the second resist: the metal layer will crack. The following is what
I did:
>
> 1. spin and bake the first PMMA (very thin) 2. evaporate the metal layer
> 3. spin and bake the second resist. During the bake I can see the metal
> crack.
>
> Does it mean I did not bake the first PMMA "hard"enough??  Do you have better
ideas??