Successfully patterned and Ti/Au lift-off of dose arrays for large gratings on glass using copolymer resist process (not bilayer resist). Doses required for this process are low for PMMA based resist, 150-200 uC/cm2 at 50kV. We were able to produce gratings using a bilayer process, but the gratings actually looked nicer with just the copolymer.
Recently, liftoff using optimized dose from dose array of Ti/Au on glass is showing issues. It appears much of the gold is removed during the liftoff. This was not the case in the dose array studies. Some pattern remains, but it is too thin to be diffractive. AFM studies will be performed in early June to determine the thickness of remaining metal. If possible, EDX will also be performed to determine if the remaining pattern is composed of Ti or Ti/Au. I plan on repeating the process with Ti/Au as the control, thick Ti, thick Cr, and Cr/Au to determine if the adhesion of Au to Ti is the issue.
Gratings were also created using the copolymer process and by depositing MgF2 onto glass. The deposition and liftoff process were determined (Physics lab equipment). The user needs to transfer this process to their specific thin film. Currently, we are working to optimize the draw size and dose on the required thin film. We'll be running another dose array in early June to determine the dose shift required by their film.
More recent dot patterns (4 different patterns) are hanging the tool. These are dose arrays only, so only part of the pattern is being exposed. Leica (Vistec) is working on the problem. Suggestions from other Leica tool owners are to use a single dot exposure (make the beam the size of the required dot size). This would be a good solution if we can guarantee no stigmation in the beam throughout the exposure. For many patterns, this approach is sufficient. For others, however, we need to reproducibly create the same pattern over a large area. I believe that we need to use a smaller beam and draw the dots using an address grid that is smaller than the dot itself. I hope to hear some information from Leica at the Users' group meeting on Friday/Saturday June2/3rd.