Direct-write electron beam lithography in silicon dioxide at low energy
(Color online) Schematic of the variables involved in the calculation of oxide etch ratios after development in HF-based solutions.
(Color online) Etch ratio measured by profilometry for several EBL energies ranging from 0.5 to 6 kV as a function of the area dose. Measurements were performed on structures developed in a (1:6:93) solution (HF concentration of 1% in volume) for 180 s.
(Color online) Electrons range simulated with the software CASINO 2.42 as a function of the acceleration voltage in an 80 nm thick layer over a Si substrate. The inset illustrates how the stopping range is defined: the areas represented under the electron beam with shades ranging from light to dark represent the increasing ratio of energy transferred from incident nonbackscattered electrons to the target material.
(Color online) Mean etch ratio extracted from the plateaus of Fig. 2 plotted versus the acceleration voltage and compared to values calculated by Eq. (1).
(Color online) (a) Plot of the total absorbed energy simulated with an acceleration voltage of 1.5 kV versus depth. (b) Thickness removed in the patterns plotted versus the thickness etched out of the patterns.
(Color online) Etch ratio plotted versus the dose/energy ratio. Shapes of data points correspond to the acceleration voltage used for lithography: 0.5 kV (squares), 1 kV (triangles), and superior to 1.5–6 kV (circles).
(Color online) (a) Density of energy absorbed in as a function of the depth and (b) plot of the averaged density of energy versus the inverse of the incident energy.
(Color online) Etch ratio versus the HF percentage in volume of the developer. Electron beam lithography was performed with an acceleration voltage of 1.5 kV and a dose of .
(Color online) Schematic illustrating the process used for the fabrication of stair-shaped structures. After patterning and metal deposition (a), metal-filled trenches are revealed by CMP (b).
(Color online) (a) Optical micrograph of four single electron transistors surrounding a three-stair damascene end point. (b) Cross-sectional sketch along the dotted line in the optical micrograph illustrating the depth of the patterns.
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