Fabricating And Transferring Of GaAs Microtips

Scanningnear-field optical microscopy (SNOM) is a novel tool for the research down tonanometer scale. It utilizes the evanescent field confined at the tiny aperture for providingimages of object surfaces with a resolution beyond the classical optical diffraction limit, andwill have great influences not only in the fields of physics, chemistry, biology and materialscience, but also in medicine and information technology. One of the most important potentialapplications may be found in ultrahigh density optical data storage. For this application, apromising architecture of monolithic integrated SNOM sensor has been proposed. This sensoris composed by a GaAs microtip, a vertical-cavity surface-emitting laser (VCSEL) cavity anda pin monitor. Up to now, the techniques for manufacturing VCSEL cavity with a PINdetector are quite mature and many techniques have also been developed to fabricate GaAsmicrotips on independent GaAs substrates. So fabricating the GaAs micrtip with better qualityand integrating the tip onto the VCSEL wafer with a pin monitor becomes the key to realizethe integrated SNOM sensor.In this paper, a simple and reproducible fabricating and transferring of GaAs microtipstechnique is presented for hybrid integrated SNOM sensor. GaAs microtips are grown usingselective liquid phase epitaxy and the tips are improved by changing the method of fabricatingSiO₂ layer. For the tips transfer technique, a GaAs/Al_0.7Ga_0.3As/GaAs sandwich structure isfirstly formed on GaAs (001) substrate by metalorganic chemical vapor deposition, and thenGaAs pyramidal microtips are grown on the sandwich structure using selective liquid-phaseepitaxy. The GaAs microtips are removed from the sandwich structure by selective wetetching Al_0.7Ga_0.3As layer using concentrated HCl solution. Finally, the tips are glued onto thetarget wafer by a negative photoresist. During this transfer process the tips are completelyencapsulated in a positive photoresist to protect against attack. Scanning electron microscopyimages show that GaAs tips can be successfully transferred without any damage by thistechnique. The achievement reported here represents a significant step towards the applicationof scanning near-field optical microscopy sensor.