The Study Of Nanoimprint Lithography And Its Application In The Optoelectronic Chip Fabrication

With the development of semiconductor industry, the size of chip becomes smaller and smaller, the feature size also becomes smaller and smaller, the pattern complexity also increases gradually. Nanoimprint Lithography (NIL), with the advantages of low cost, high resolution, high throughput and high flexibility, has become one of the most promising research interests in micro and nano fabrication. In this thesis, the deformation and filling of polymer in the Nanoimprint process and its application in optoelectronic chip fabrication are discussed. It mainly includes:Firstly, the deformation and filling of polymer in hot embossing is discussed using the finite element method (FEM). In a periodic pattern, the filling degree of the cavity variation with the thickness of polymer, pressure and duty cycle are discussed. In a cross-scale pattern, the filling degree variation with the feature size of the small cavity, the distance between the large cavity and the small cavity and the height of the cavities are also discussed.Secondly, the high resolution diffraction grating is fabricated in the InP substrate using soft mold UV-NIL (Ultraviolet Nanoimprint Lithography, UV-NIL), and key processes are described, including the production of high resolution grating mask, transferring grating structure from mask to substrate and the removing of the etched residual resist. In response to these key processes, improved process is proposed for each step. Due to the easy deformation characteristics for soft mold, imprinted grating structure will be distorted when a high pressure was used. High pressure difference (HPD) method is used to obtain good filling degree and thin residual resist layer. A new grating mask is designed to improving the uniformity of wet-etched grating. Multi-mask layer is used to imprint grating, which is easy to remove etched residual resist.Thirdly, the complex diffraction grating used in Distributed Feedback laser (DFB laser) is fabricated by nanoimprint, the DFB laser is fabricated and tested also. The tested results show that threshold current of the laser is less than20mA, side-mode suppression ratio(SMSR) is more than40dB and the life meets the needs of the commercial life of the semiconductor laser. The peak wavelength corresponds to the Bragg wavelength at the center of the stop-band, indicating that the phase-shifted gratings function properly. Fourthly, the monolithic integration of1.5-μm four channels phase shift distributed feedback lasers array (DFB-LD array) with4×1multi-mode interference (MMI) optical combiner is fabricated. The key methods of photonics integration are demonstrated, including NIL for grating fabrication, butt-joint regrowth (BJR) for active/passive region integration, multi-layer masks for passive/active region deep/shallow waveguide etching. The threshold currents of the lasers are less than10mA and the side mode suppression ratios (SMSR) are better than40dB for all channels. Quasi continuous tuning is realized over7.5nm wavelength region with the30℃temperature variation. The results indicate that the integration device we proposed can be used in wavelength division multiplexing passive optical networks (WDM-PON).