Nanosphere litho quick update
I will keep this post short and start by saying that the process of establishing a reliable set-up for nanosphere deposition, by evaluating the repeatability of the deposition parameters, has been longer than anticipated.
The nanospheres self-assemble at the hexane-water interface and stabilize laterally through electrostatic forces. The main deposition steps are:
- Add water to a beaker, place substrate below the water surface and add hexane
- Inject the nanospheres near the interface (hexane side)
- Wait for 10 min
- Withdraw the water phase for the interface to drop as a way to retrieve the sample
A snapshot of the timeline is described below:
- Saw very good results in terms of symmetry but not uniformity
- Tried to optimize deposition parameters to increase uniformity of the film
- Uniformity improved, symmetry was lost
We also evaluated the effect of reducing the tilt angle and varying the withdrawal speed and found that 45o tilt and 45 um/s yields the best results. We decided to keep these conditions constant and evaluate the effect of other parameters such as temperature, concentration of ions, hexane volume, and injecting speed.
Additionally, below are some micrographs of a similar sample taken with an SEM and an optical microscope. These SEM micrographs were taken to evaluate image quality and were taken from a sample that at the time was the “best” one in terms of symmetry and uniformity.
We will continue to optimize this deposition to move into integrating the rest of the fabrication process.