You should try Dry-laminated photoresist based lithography.

It is working fine for wafers having etched cavities, as resist does not go
inside the cavities. Some of my wafers have 1-2 mm wide cavities. still i
can get satisfactory lith results.


Thanks,
Pradeep

On Tue, Nov 2, 2010 at 10:43 AM, Dibyadeep Paul  wrote:

> Hi,
>
> I have a wafer, which contains some deep trenches. I fabricated these 250
> micron deep trenches using DRIE, with AZ9260 as the mask layer. Now I have
> to do a DRIE, to etch away 150 micron more, in the trenches already
> fabricated as well as in some other regions.
>
> In order to do this 2 level DRIE, I had grown an oxide layer 2 microns
> thick
> to act as the masking layer for the second DRIE. I had planned to use 9260
> as the masking layer for the first DRIE and the oxide as the masking layer
> for the second DRIE. However after growing the oxide layer, and etching
> away
> the unwanted regions, I found that some of the masking oxide layer has also
> been removed.
>
> As I said for the first DRIE, I used 9260, and the DRIE went fine. I had
> initially thought that I would use the 9260 layer which would remain after
> the DRIE and do a contact exposure-development, to expose the areas where I
> wanted the next DRIE to happen. This would help me do the DRIE on regions I
> wanted to expose, to circumvent the problem created by the presence of the
> holes in oxide layer.
>
> However after the first DRIE I found that the 9260 layer has become
> complete
> inert to the the developer AZ 400K, even after multiple and long expsures.
>
> Next, I removed the 9260 on one of the test wafers, and tried doing a
> contact exposure-development with various photoresists in AZ and SC series.
> In all of them I found that even after long exposures, some of the
> photoresist always remains within the trenches, and I cannot remove that. I
> am not sure why this happens.
>
> So I wonder if somebody could help me with these questions:
>
> a) how do I do a fabricate a photoresist based masking layer for a wafer,
> which already contains deep trenches of ~ 250 microns?
>
> b) Is it possible to activate the photoresist top surface after a DRIE, so
> that I can do a contact exposure-development on the photoresist already
> present?
>
> --
> Thanks
>
> Dibyadeep Paul