[labnetwork] Resist coating of tiny pieces

[Demis D. John]

In our lab, users will often do the following (I’ve just seen them do this, and asked about it):
• dice shim pieces that are of similar thickness (eg. Within 50-100\microns) of the main sample piece. These will be re-used throughout the ‘fab process. 
• shim pieces are same width as the real piece. Eg. If the real piece is 3x3mm 500µm thick, the shim pieces (of any material) would also be 3mmx3mm and 450-550µm thick or so. 
• on Nitto Denko Blue tape, low adhesion, sticky side up: place the real piece in the middle, and a number of the shim pieces around the real piece, placed as close as possible to the real piece.  I don’t remember if they do only 4 shims (edges only), or all 8 shims (fully surrounding). Probably cut off some excess tape around the edges to match the vacuum chuck in next step, although I’ve seen them spin with excess tape hanging off. 
• place this assembly onto the vacuum chuck, where the vacuum chuck is large enough to support all the pieces - eg. 2.5cm wide. 
• after spinning, un mount and bake the small piece by itself. The blue tape assembly can be reused to spin other pieces, although I imagine this can be tricky. 

Mostly our GaN users have done this, those who really needed to recover the edge bead regions.
It obviously takes a good amount of extra effort (additional 5-10min per spin), but it appears the point is to reduce the thicker edge bead and produce a larger area of good die, improving contact uniformity as well.
 If they were ok with the the thicker/wider edge bead, they’d just use the chuck that has a small vacuum pedestal (eg. 2mm wide). 

I hope that helps!
-- Demis


> On Nov 16, 2020, at 14:39, Lino Eugene <lino.eugene at uwaterloo.ca> wrote:
> 
> 
> Dear Orad, Michael, Nathanael and Carsen,
>  
> Thanks for your reply. It is good to know that mounting a tiny piece on a carrier wafer is sufficient for EBL.
>  
> Sorry for not providing the context . We have currently an user who wants to plasma etch several microns of dielectric on a diced chip of ~3 mmx 3 mm. A thick photoresist is needed and I think that just mounting the chip on a carrier wafer would not work well. I was suggested to use dummy pieces placed all around the chip, which should work well for this process. Also, I believe that this would avoid also to break the chip or the carrier wafer (or the photomask?) because of the pressure applied during the wedge compensation on the mask aligner but maybe there is nothing to be worried about.
>  
> Best,
>  
> Lino Eugene, P.Eng., Ph.D.,
> Micro/nanofabrication process engineer
> Quantum Nano-Fabrication and Characterization Facility
> QNC 1611
> University of Waterloo
> 200 University Avenue West
> Waterloo, ON, Canada  
> N2L 3G1
>  
> Ph: +1 519-888-4567 #37788
> Cell: +1 226-929-1685
> Website: https://qnfcf.uwaterloo.ca/
>  
>  
>  
> From: Orad Reshef [mailto:orad at reshef.ca] 
> Sent: November 16, 2020 16:19
> To: Lino Eugene <lino.eugene at uwaterloo.ca>
> Cc: labnetwork at mtl.mit.edu
> Subject: Re: [labnetwork] Resist coating of tiny pieces
>  
> Dear Lino,
>  
> We need a little more context for what you consider a "tiny piece". I routinely work with 1x1 cm pieces, and for those we use chucks that have an o-ring about 0.5 cm in diameter.
>  
> I have colleagues who have worked with 1mm x 1mm square diced samples. They mounted those on a large si handle wafer using double-sided carbon tape, like you would use to mount a sample on an SEM stub.
>  
> Hope this helps,
> Orad
> 
> Orad Reshef, PhD
> 
> Département de physique | Department of Physics
> Université d’Ottawa | University of Ottawa
> boydnlo.ca | reshef.ca
>  
>  
> On Mon, Nov 16, 2020 at 11:44 AM Lino Eugene <lino.eugene at uwaterloo.ca> wrote:
> Dear colleagues,
>  
> We are having more users who work on tiny pieces to be coated with photo and e-beam resist.
>  
> I am thinking of different ways to coat these pieces:
> ·       custom chucks with a recess of the size of the chip
> 
> ·       Si carrier wafer with recess etched by SF6 plasma
> 
> ·       MicroSpray photoresist
> 
>  
> I am wondering if you could share the techniques you use to get uniform coating on very small pieces.
>  
> Best,
>  
> Lino Eugene, P.Eng., Ph.D.,
> Micro/nanofabrication process engineer
> Quantum-Nano Fabrication and Characterization Facility
> QNC 1611
> University of Waterloo
> 200 University Avenue West
> Waterloo, ON, Canada  
> N2L 3G1
>  
> Ph: +1 519-888-4567 #37788
> Cell: +1 226-929-1685
> Website: https://fab.qnc.uwaterloo.ca/
>  
>  
> 
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