By exposing periodic test patterns in nitrocellulose at the writing field boundaries and viewing them at high magnification, the magnitude of the stitching error can be measured precisely, which can be used to derive the optimal zoom and rotation value in the Raith 150TWO system. We have reproducibly obtained nearly perfect (<50-nm stitching error) alignment with a large writing field of 1 mm × 1 mm, as compared to an average stitching error of approximately 500 nm obtained without using nitrocellulose as in situ feedback. Figure 4 Cr pattern created by electron beam lithography with
PMMA resist followed by a liftoff process. Wheel array at writing BTK activity field center (a) and learn more corner (b) exposed without beam optimization by defocus. Wheel array at writing field center (c) and corner (d) exposed with beam optimization using self-developing nitrocellulose resist. The exposure dose increases from the top left to the lower right wheel structure. Table 1 The resulting Cr line width as a function of exposure dose with or without beam optimization Line dose (nC/cm) Well focused at the center (nm) Well focused
at the corner (nm) Defocused at the center (nm) Defocused at the corner (nm) 0.4 42 Resist not developed click here to the bottom due to beam broadening at the writing field corner, thus no Cr pattern after liftoff Resist developed to the bottom Resist not developed to the bottom
0.56 43 0.79 47 1.10 51 78 84 1.15 62 89 91 2.15 70 120 128 3.01 91 210 127 138 4.21 108 251 146 152 5.90 117 272 167 172 Conclusions Here, we studied the exposure properties of nitrocellulose resist and its application as in situ feedback for electron beam optimization in electron beam lithography. It was found that, as a self-developing resist, nitrocellulose showed low sensitivity and low contrast, making it unsuitable for patterning high-resolution dense features. Nevertheless, it achieved 15-nm resolution for sparse pattern where proximity effect is insignificant. In addition to self-development, nitrocellulose resist can also Carnitine palmitoyltransferase II be developed using a solvent that displayed a mixed tone behavior – negative tone for low doses and positive for high doses. Using nitrocellulose as in situ feedback to optimize the electron beam (notably working distance) across a large writing field of 1 mm × 1 mm, we achieved approximately 80-nm resolution across the entire writing field, as compared to 210 nm (occurred at the writing field corners) without the beam optimization process. This approach is most efficient in reducing the writing time for large writing field size such as 1 mm × 1 mm as needed for large area exposure of moderate resolution pattern. References 1.