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NanoFab Trainer Update. Nick Reeder, February 28, 2014. Updates to User Interface. Added progress bars to show progress during time-consuming operations. Performance Improvement.
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NanoFabTrainer Update Nick Reeder, February 28, 2014
Updates to User Interface • Added progress bars to show progress during time-consuming operations.
Performance Improvement • Added code that removes points from displayed polygons if the points are spaced more closely than a pixel’s width; in some cases this greatly reduces the number of polygon vertices, improving performance of subsequent operations. • See next slide for comparison of original code to revised code.
Performance Improvement Original Code SiO2 polygons contain 2112 vertices. Revised Code SiO2 polygons contain 29 vertices.
Change to Etch Code • Etch code now has a time resolution of one second instead of one-half minute. New code requires considerably more time for etch operations but gives the user greater control and sometimes results in smoother edge profiles after an etch. (See next slide.) • Question: Should dialog box for etch let user specify time in seconds only or in combined minutes:seconds?
Change to Etch Code Original Resolution (One half-minute ) SiO2 polygons contain 29 vertices. New Resolution (One second) SiO2 polygons contain 32 vertices.
Change to Materials Database • Added Cl2 plasma as an etchant. • Williams’ 1996 paper has little data for Cl2 plasma, and 2003 paper has none. See next slide for etch rates.
Etch Rates (nm/min) per Williams 1996 Proposed Simulated Etch Rates (nm/min)
Updates to Expose Code • Making progress on passing results from Andrew’s Dill exposure code to the trainer. Image below is from 15 second exposure.
Questions about Exposing Photoresist • How to generate the incident beam profile at resist surface (as in the figure at right from p. 5 of Andrew’s photoresist chapter), given intensity, wavelength, distance of mask from surface, and width of mask opening? • What if surface of resist being exposed is uneven? Can Andrew’s code handle this?
Another Question about Exposing Photoresist • Page 1 of Andrew’s photoresist chapter states that solubility of exposed resist is about four orders of magnitude greater (i.e., about 10,000 times greater) than solubility of unexposed resist. Why on page 5 do we use S0 = 2 µm/min and S1= 0.05 µm/min, an increase of less than two orders of magnitude?
Question about Developing Photoresist • Page 5 of Andrew’s photoresist chapter states that example uses S0 = 2 µm/min. How can image on p. 6 show about 1.0 µm removed in a 15-second develop, which equates to a rate of 4 µm/min?
Performance of Expose Code • Wondering how far can we reduce the following parameters in Andrew’s code without sacrificing accuracy? • Number of columns in 2D grid (xp) = 1001 • Number of rows in 2D grid (zp) = 500 • Number of time points (tp) = 1000 • See next slide for test using 501 for xp and 500 for tp.
Performance Comparison 10-second exposure, resist thickness 1.5 µm. xp = 1001zp= 500tp = 1000 Time to run = 221 seconds xp = 501zp= 500tp = 500 Time to run = 42 seconds
More Questions about Exposing Photoresist • In Andrew’s code, what is the point of including a two-wavelength-thick layer of air above the resist surface? Is it just to leave some blank space in the final images, or does the air layer play a role in the computations? • Can Andrew’s model based on Dill parameters handle negative resist as well as positive? • Do we want to let user choose UV wavelengths other than 365 nm? If so, where to find Dill values for other wavelengths? • Do we want to wash out the interference ripples, as discussed on last page of Andrew’s photoresist chapter?
