Hi Lee,

You can expose the first layer SU-8 first. Then
deposite a layer Cr/Au, and coat the second layer
SU-8. Pattern the second layer SU-8, the UV light will
not go through the metal layer. Develop the second
layer SU-8, etch metal layer, then develop the second
layer SU-8 to get what you want.

There is a paper. It may be helpful: ~{!0~}Fabrication
of microscale two-level surface-engineered mold
inserts for MEMS applications by UV-LiGA and conformal
coating deposition~{!1~}, Photonics West, Jan 2005 San
Jose, CA, Proceedings of SPIE Vol.5717,  [5717-24],
p175-184

Ren Yang


--- Chen-Han Lee  wrote:

> Hi mems-talk members,
>
> I need some advice.
> I am trying to fabricate a two-layer SU-8
> structures.
> the bottom layer has 15um holes and the top layer
> has 5um holes.
> the problem is that becuase SU-8 is a negative
> resist, if the structure is
> done from normal two layer process, the bottom will
> have 5um holes as the
> top layer.
> when exposing the top layer, UV light will penetrate
> through the top and
> exposing the bottom one too.
>
> could anyone help me with these obstacles?