Study On The Fabrication Of Nano-periodic Au Free-standing Gratings And The Micro-Nano Hybrid Mold

The fabrication of free-standing gratings with sub-micron and nano-periods has been improved greatly with the development of high energy physics, X-ray astronomy, and so on. But most of the scientific research institutions fabricate free-standing gold gratings by interference lithography at the moment. Equipments of the interference lithography are expensive, and the exposure system is complex. Furthermore, it is difficult to fabricate the gratings with period under200nm because of the diffraction effect. In this thesis, we fabricated200nm free-standing grating using nanoimprint lithography combining with other fabrication techniques including physical vapor deposition (PVD), inductively coupled plasma etching(ICP), micro electroplating, photo-lithography, wet etching, etc. Nanoimprint lithography is a low cost and high efficiently nanofabrication technique without diffraction effect, so we use it to fabricate grating patterns. The work in this thesis mainly includes three parts.In the first part, we have studied the fabrication of200nm period free-standing Au gratings. First, we deposited5nm thick chrome and20nm thick gold on a silicon wafer as the electrode layer for the electroplating process, and then we used nanoimprint lithography to replicate the grating patterns from the mold into resist film. After imprint, the ICP was introduced to remove the residual layer, and expose the gold layer. The gold was deposited into the concave trenches of the imprinted resist gratings via non-cyanide electroplating. The fabrication of200nm periodic gold grating was finished after removing the imprint resist by ICP. The support structure was fabricated through photo lithography and electroplating of gold. Finally, silicon substrate was removed by the mixture of HF and HNO3and We got the200nm periodic free-standing gold grating with the height100nm. We have also studied the deep etching process and got520nm high polymer gratings with the aspect ratio of5:1.In the second part, we have studied the fabrication of the nano-micro hybrid mold. The nano-micro hybrid mold was a nanoimprint mold combined with nano-structures and micro-structures at the same area. First, we fabricated500nm period polymer gratings by interference lithography or nanoimprint lithography, and then deposited20nm thick Cr layer on the polymer grating. Then the polymer grating was lifted off in acetone whith ultrasonic cleaning. After that, micro-structures were fabricated by photo lithography, and we transferred the designed structure into silicon wafer by ICP etching process. The fabrication of nano-micro hybrid mold with the gratings of500nm and10μm periods was finished. The fabrication process of the free-standing gold gratings could be simplified by directly using nano-micro hybrid mold since the nano-gratings and the supporting micro-structures could be patterned in only one imprint step..In the third part, we have studied the fabrication technology of the nanoimprint molds with the reversed pyramid structures. We first deposited500nm thick silicon nitride layer on a<100> silicon wafer, and got square structures with the period of100μm by photo lithography. Then we got100μm period Cr check structures by the PVD and lifting off process,respectively. The ICP was employed to etch silicon nitride with the Cr layer as the etching mask. In the following step, the reversed pyramid structures were obtained by KOH wet etching. Finally, we studied and discussed the imprint results by the reversed pyramid structure mold and the related processes.