Scanner Focus window of the lithographic process becomes much smaller due to the shrink of the device node and multipatterning approach. Consequently, the required performance of scanner focus becomes tighter and more complicated. Focus control/monitoring methods such as “field-by-field focus control” or “intra-field focus control” is a necessity. Moreover, tight scanner focus performance requirement starts to raise another fundamental question: accuracy of the reported scanner focus.
The insufficient accuracy of the reported scanner focus using the existing methods originates from:
a) Focus measurement quality, which is due to low sensitivity of measured targets, especially around the nominal production focus.
b) The scanner focus is estimated using special targets, e.g. large pitch target and not using the device-like structures (irremovable aberration impact).
Both of these factors are eliminated using KLA-Tencor proprietary “Focus Offset” technology.
We experimentally demonstrate optical clock recovery from quantum dot mode-locked semiconductor lasers by
interband optical pulse injection locking. The passively mode-locked slave laser oscillating on the ground state is locked
through the injection of optical pulses generated via the first excited state transition from the hybridly mode-locked
master laser. When an optical pulse train generated via the first excited state from the master laser is injected to the slave
laser oscillating via ground state, the slave laser shows an asymmetric locking bandwidth around the nominal repetition
rate of the slave laser.
Quantum-dot lasers have shown remarkable properties, such as temperature-insensitive operation, low loss, efficient
carrier recombination, ultrafast gain recovery time, suppression of beam filamentation, reduced sensitivity to optical
feedback, etc. These excellent performances will contribute to open new cost effective and improved lightwave
communication systems. We exploit the performance of mode-locking of quantum-dot lasers for ultrashort, high power,
and low noise optical pulse generation using two-section mode-locked laser diodes and a semiconductor optical
amplifier (SOA)-based ring laser cavity.
We study the characteristics of wavelength tunable quantum-dot mode-locked lasers using a curved two-section device, external grating, and optical bandpass filter. Wide wavelength tunability is demonstrated due to the fact that the center wavelength of mode-locking is extended to excited state transitions as well as ground state transitions of the quantum-dot gain media.