NanoFab Trainer Update

1. NanoFab Trainer Update Nick Reeder, April 11, 2014

2. Update to Exposure Code • New code creates UV intensity profile based on incident intensity, width of mask opening, distance of mask from surface, and thickness of resist layer. • Intensity profile is a Gaussian function whose width is based on a 2-dimensional look-up table, with opening width and distance-plus-one-half-resist-thickness as the look-up parameters. How to populate this look-up table with realistic numbers?

3. Sample Runs with Varying Mask Height • Next two slides compare two 10-second exposures with same mask and same resist layer, but with mask at different heights above the surface.

5. Note that exposed area is wider but degree of exposure is less.

6. Sample Runs with Varying Distance between Mask Openings • Next three slides compare three 10-second exposures with same resist layer and same mask height, but with two mask openings separated by different distances.

8. Is it reasonable that exposed areas merge at the top but not at the bottom?

10. Update to Materials Database • To model the effect of layers between the resist and the substrate, materials database now contains a value for the complex refractive index (at 365 nm) of each material. • Values are from http://refractiveindex.info/ (except for photoresists). • See next slide for values used.

11. Refractive Index Values

12. Update to Exposure Code • Code now handles layers of material between the resist and the substrate. • Current assumptions: • All layers have uniform thickness across the width of the structure. • Resist is the top layer.

13. Sample Runs with Multiple Layers • Next three slides compare 10-second exposure with layers of: • Photoresist above glass substrate • Photoresist above SiO2 above glass substrate • Photoresist above Al above glass substrate • Should users have the option of using non-Si substrate (such as glass)?

14. Ten-second exposure, photoresist above glass substrate.

15. Ten-second exposure, photoresist above SiO2 layer above glass substrate.

16. Ten-second exposure, photoresist above Al layer above glass substrate. • Note emergence of standing-wave pattern. • Is it reasonable that exposed area is also wider with Al than in previous samples?

17. Next Steps: Varying Layer Thicknesses • Code needs to handle cases such as: • Layer thicknesses constant for each mask opening, but different for different openings. • Layer thicknesses vary within a mask opening.How to handle this?

18. Next Steps: Resist Under Other Layers • What should happen if there is a layer of some other material on top of the resist? • Is this a realistic scenario that we should address, or should we somehow prevent the user from doing it in the first place?

19. MNT Conference • June 4-6 in Albuquerque. • I plan to distribute software on CDs so that people can start using it and provide feedback.