Submicron Maskless Photolithography

Recent progress into 1um feature sizes and beyond with a LCoS projector and a metallurgical microscope. Given a numerical aperture of 0.98 on the microscope objective and with an exposure wavelength of 365nm the simple calculated resolution is 0.227um however the actual resolution is probably around 0.5um due to diffraction limitations inherent in this projection system. The depth of focus @ NA = 0.98 is calculated to be approximately 1.8um but is likely worse.

Laser illumination of the projector is avoided due to interference patterns. A SMD 395nm LED is used in some tests and a standard high pressure mercury arc vapor lamp in others.

Screen Shot 2017-09-02 at 8.03.03 PM

Exposure times calculated by integration of total UV dosage measured at different wavelengths with the radiometer. To calculate exposure time for AZ4210 resist, for example, the datasheet is consulted to see a recommended dose of around 135 mJ/cm^2 for a 3.5um film thickness. If exposed with a 5x objective on my system, the exposure time @ 410nm is (135 mJ/cm^2)/(4.05mW/cm^2) = approx. 33 seconds. This is a bit longer than I would like but given that it is a positive resist that is to be expected.

Basic mask set for a MOSFET. Fiducials should be added to the corners for subsequent layer alignment. Active area is etched into field oxide, active area is doped, gate oxide is etched and regrown as thin a possible without pinholes, contact area is etched into oxide, then aluminum or copper is sputtered or evaporated and patterned.

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