In-chip microstructures and photonic devices fabricated by nonlinear laser lithography deep inside silicon

Silicon is an excellent material for microelectronics and integrated photonics 1-3, with untapped potential for mid-infrared optics 4 . Despite broad recognition of the importance of the third dimension 5,6, current lithography methods do not allow the fabrication of photonic devices and functional microelements directly inside silicon chips. Even relatively simple curved geometries cannot be realized with techniques like reactive ion etching. Embedded optical elements 7, electronic devices and better electronic-photonic integration are lacking 8 . Here, we demonstrate laser-based fabrication of complex 3D structures deep inside silicon using 1-μm-sized dots and rod-like structures of adjustable length as basic building blocks. The laser-modified Si has an optical index different to that in unmodified parts, enabling the creation of numerous photonic devices. Optionally, these parts can be chemically etched to produce desired 3D shapes. We exemplify a plethora of subsurface - that is, 'in-chip' - microstructures for microfluidic cooling of chips, vias, micro-electro-mechanical systems, photovoltaic applications and photonic devices that match or surpass corresponding state-of-the-art device performances. © 2017 The Author(s)

Subsurface Silicon Processing by Microsphere Focusing of Ultrafast Infrared Laser

Attention on applications of femtosecond lasers in semiconductor materials processing is ever growing. There has been an increasing research momentum especially towards multi-photon absorption based silicon (Si) processing with infrared lasers in the last decade. Since Si is transparent at wavelengths >1.1 mu m, the processing inside Si is triggered by the nonlinear optical phenomenon of two or more photon absorption which requires laser amplitude to reach and pass beyond threshold conditions. A method that utilizes back-reflection at the Si-air interface was developed and demonstrated to be useful for subsurface processing of Si at the micro-scale. In previous studies, pixels of such processed regions were limited to 5-10 mu m size despite use of high numerical aperture lenses due to strong refraction of light in Si. In order to deem the laser processing of Si useful for photonic applications, pixel size needed to be reduced down to a micron or below. In this work, we demonstrate subsurface modification of Si using microsphere based focusing of a 1.5 mu m wavelength ultrafast laser pulses in Si