Characterization of processes used in nanofabrication of Digital Electrostatic e-beam Array Lithography (DEAL) devices

by 1982 - Rucker, Ryan Benjamine

The ultimate goal of this research was to nanofabricate an advanced field emission electron beam lithography platform using an electron beam induced deposition process (EBID) to deposit tungsten (W) nanofibers cathodes. In order to fabricate the devices, it was necessary to characterize the reactive ion etching (RIE) processes for the fabrication of the Digital Electrostatic e-beam Array Lithography (DEAL) device. To optimize the reactive ion etch processes of the silicon and silicon dioxide layers, a JMP desktop statistical discovery software from SAS iv ® was employed to design a set of experiments. The design of experiments (DOE) employed variable conditions of R.F. power, gas pressure, and gas ratios. Specifically for the silicon etch DOE the R.F. power ranged from 100 to 400 (W), the gas pressure ranged from 75 To 400 (mTorr) and a SF6/O2 gas flow ratio varied from 2 to 10. Single crystal silicon wafers were used due to the thickness of the n+ polycrystalline silicon film and the effectiveness of characterizing such a thin film. The responses that were measured included the silicon etch rate, the silicon to silicon dioxide etch selectivity, the silicon to photoresist etch selectivity, and the silicon etch profile. For the silicon oxide etch DOE, the R.F. power ranged from 200 to 300, the gas pressure ranged from 30 to 70 and a CF4/CHF3 gas flow ratio varied from 0.34 to 1.34. The responses that were measured included the silicon oxide etch rate, the silicon oxide to silicon etch selectivity, and the silicon oxide to photoresist etch selectivity. The results from both experimental designs adequately optimized the etch processes for the n+ polycrystalline silicon and silicon oxide and will be used for subsequent nanofabrication of DEAL devices. A DOE for the growth of tungsten nanopillars via electron beam induced deposition (EBID) was also performed as a method to deposit nanoscale field emission cathodes. The goal was to correlate the growth parameters to the nanopillar structure and ultimately the structure to the field emission properties. The DOE varied the precursor pressure, beam energy, and specimen current, and the responses were growth rate, nanopillar width, and the sharpness of the nanopillar tip. An optimum high growth rate, sharp pillar process was determined, however field emission the field emission measurements could not be made. v