In my project I need to fabricate small features on an insulating substrate (specifically borofloat glass). I am using a lift off technique, and depositing a thin layer of gold overtop of my bilayer PMMA resist. to control the charging problem associated with using an insulating substrate. The problem with the features I have to fabricate is that I have 2 long, relativily wide eletrodes and I want a narrow gap between them. Anyways, just wondering if anyone here has any experience with EBL on an insulating substrate that might have any tips. I have yet to achieve any acceptable results.

Can you etch the metal electrodes instead? I don't know your material options.

Not chemically. I have tired this, but because of isotropic etching the resolution I want is impossible to achieve, and using glass I can not really use ion milling. At the facility I am at they do not allow glass into the ion mill. I might be able to use the ion mill if I deposited a thin layer of SiO2 on the glass, but I am not sure what sort of problems that would cause later on when I needed to bond two pieces of glass together....does SiO2 bond well to glass?

Maybe you can evaporate metal through a stencil mask onto the glass? The stencil can be conducting.

That sounds interesting....do you know where I could find out more information about how to go about doing this? Any papers that you could suggest for me to read?

It is sometimes called "shadow mask deposition".

This is one of the article found through google.

Still not easy, you would have a narrow feature that is thin as well.

Steveo,

Maybe you can use a thick metal underlayer for the resist. After liftoff, this layer can be etched using the electrodes as an etch mask.

For example, maybe you can use a ruthenium underlayer. Oxygen etches ruthenium but will not etch the metals (it will oxidize them).

Or maybe a chromium underlayer would be safer. That would require more careful chemical etching, so you don't attack the electrodes.

I have actually been getting some decent results as of late. 60nm gap so far, and thats without a fine proximity correction. Thankfully I don't have to try to etch chromium chemically as my annealling process is already harsh enough on the chromium. Have already lost plenty of larger electrodes with my annealling process due to oxidation. Sometimes even 3 nights in overpressured nitrogen and an hour long 'bake' at 100 degrees C to promote diffusion isn't even to evacuate all of the oxygen from the microfluidic channel. It works most of the time...........depends how much trapped air there is after glass bonding. I think something serious can go wrong at every step in my process. Hahaa

Oops I guess my suggestions wouldn't help I didn't know the specifics. Well, one final suggestion for direct etching of chromium or polysilicon, use ZEP instead of PMMA. Much better dry etch resistance.

Maybe it's too later. But FYI, people use conducting polymer (some kind of monolayer) as a conducting agent to solve the charging problem for insulator EBL. One of these kind of agents is called ESPACER which has no effect on the EBL resolution and is water soluable. The ploblem of those polymer is, they are all expensive.

Arent we all forgetting something? The electrons go way past the top thin films and deep into the substrate. that's where the negative charge is stuck. They won't make it back up to the conducting layer.