Nanoimprint can easily produce cavities in resist, but it is very challenging to produce protrusions. One way to achieve protruding patterns in the resist is to transform the cavity pattern into a protrusion pattern via a process called tone reversal. Developing a tone reversal process will enable nanoimprint technology to produce the full range of patterns that can be produced using the more established techniques such as photolithography and ebeam lithography.
Develop a tone reversal process for nanoimprint.
We have explored a couple of approaches to achieve tone reversal without much success. Below is a brief description of our failed ideas:
The experiment is described below:
Figure 1 is a graph of the etch rates for SiO2 and HSQ at various ICP power. After realizing that the etch rates for both SiO2 and HSQ is the same at an ICP power of 200 W, we decided to run the experiment again to confirm our results. From the second set, we confirmed that the data results at an ICP power of 200 watts is repeatable and therefore real. It will be interesting to perform another experiment in the future to determine what the etch rates at ICP power between 0 and 350 watts.
Figure 1: The etch rate increases monotonically with ICP power and the two sets of measurements are in agreement.
Figure 2 is a graph of the etch selectivity of SiO2 and HSQ. At 350W and above the selectivity of SiO2 to HSQ is approximately 0.6 to 1. An anomaly occurs at an ICP power of 200 W, where the selectivity is almost 1 to 1.
Figure 2: The etch selectivity of SiO2 and HSQ is approximately 0.6 for all ICP power values except 200 W.
Figure 3 is a graph of the DC bias that is observed at each etch process. Normally, the DC bias is deliberately decreased to increase selectivity. In this case, we have the highest selectivity at the highest DC bias. What is going on?
Figure 3: The DC bias decreases monotonically as ICP power increases.