(a) Configuration and (b) photographic views of the laser lithographic system.
Optical components to generate the autofocusing error signal. The three different kinds of spot shape are formed on the QD according to the distance between the objective and the material surface. Position 2 indicates the exact focal point.
Designed spot diagram at the focal positions. Commercial software for optics design was used for this simulation.
Photographic view of the autofocusing controller and schematic of its circuitry.
Bode diagram about current to voltage conversion. (a) and (b) are the capacitance of 100 and 10 nF. (c) is in the case of optimal capacitance of 1 nF for fast response of the PZT actuator. (d) shows no condenser case.
Alignment of QD to find out center at the exact focal point. (a) The exact QD center, (b) a case of off center.
Experimental setup to check the performance of the autofocusing system.
Residual error after the autofocusing. The higher frequency (larger than 75 Hz) test is meaningless because it is over the Nyquist (Ref. 5) sampling limitation (the maximum speed of our PZT actuator is 150 Hz).
CCD snapshots of a focal point variation on the rotating substrate (a) before and (b) after the autofocusing control.
Fabrication results: comparison of (a) before with (b) after the autofocusing control. The arrowed circles in (a) is a result with the autofocusing control to show the significance of it.
Fabrication results obtained by a commercial white-light scanning interferometer (field of view: , magnification: 50×). Regions (a)–(c) show uniform linewidth of , respectively.
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