Fabrication Of Microdisk Optical Resonators

Re-circulation of light within optical microresonators' volumes enables the storage of optical power near specific resonant frequencies, The interaction of active or reactive material with the modal fields of optical microresonators provides key physical models for basic research such as cavity quantum electrodynamics (QED) experiments, spontaneous emission control, nonlinear optics, bio chemical sensing and quantum information processing. Optical high quality optical microresonators which work in the form of whispering gallery mode (WGM), such as microcylinders, microdisks, and microspheres have been achieved. The combination of their ultrahigh quality factor, very small mode volume, and relatively easy fabrication process, makes them potential means for cavity QED experiments. The proposal based on cavity quantum electrodynamics (QED) is one of the most potential ones to realize quantum gates, which are the most pivotal devices in the experimental schemes to realize quantum computation and quantum computer. In this paper, we research the technics to fabricate microdisk optical resonators with photolithography and etching, and the high Q(about 1×10⁵) microdisk optical resonators have been achieved with standard UV photolithography, reactive ion beam etching(RIBE), and silicon etching with XeF₂. The most significant advance of the work described in this thesis is as follow.1) The silica microdisk optical resonator which exhibit whispering-gallery-type modes with quality factors (Q) 1×10⁵ have been fabricated firstly with standard photolithographic techniques and dry etching in China. The following fabrication steps have been adopted: silicon wafers coated with certain thickness silicon dioxide (SiO₂) are painted with photoresistant (PR); mask graphics is transferred to PR over silica with standard photolithograph; PR graphics is transferred to silica layer with ion beam etching (IBE); silicon under the silica disk is etched with isotropic silicon etching to form mushroom like microresonators. The microdisk optical resonators are free form negative character of microsphere cavity, fabrication process with standard photolithography and dry etching can achieve geometry control and the repeatable fabrication of high Q microdisk cavity; the repeatable and controllable microresonators fabrication process can provide the favorable prophase technical fundament of development of quantum gates.2) The research of photolithography technics in this fabrication process. The wafer cleaning, photoresist painting, pre-bake and latter-bake of PR, exposal, developing all can affect the PR figures, which are the masks of latter etching and define the microresonators' capability. These technics parameters have been optimized with experiments.3) Research of fabrication of the SiO₂ microresonators. The reactive ion beam etching with Ar/CHF₃ mixed work gas has been used to form the SiO₂ microdisks,, the PR to SiO₂ etching selectivity has been improved with the addition of CHF₃, and the controllable sidewall angle can been achieved with suitable ion energy, gas composition and incident angle. In the fabrication process of microdisk resonators, the SiO₂ microdisk cavity has been achieved with RIBE with 2:1 CHF₃/Ar mixture with smooth edge and vertical sidewall. This etching method has favorable transfer precision and controllability, which is important to keep microcavity's geometrical and physical character. The SiO₂ microdisk resonators with vertical sidewall have been achieved with RIBE in the world. 4) Research of the silicon etching. This silicon etching is used to fabricate the silicon pillar under the SiO₂ microdisk, which support the microresonators. XeF₂ can react with silicon in room temperature and be used as silicon dry etching gas, it is a kind of isotropic dry etching. A XeF₂ pulse etching system with simple structure and easy operating has been constructed to perform SiO₂/Si etching. With this system, the mushroom-like SiO₂/Si structure has been fabricated, and the etching selectivity between silicon and silica mask exceed 1000. SiO₂ microdisk resonators have been fabricated by this etching, which are the fundament of the future quantum computation research.