![]() The diagram in Figure 1 summarizes the classifications of silicon micro-machining technologies and commonly used etchants.Īcidic solutions containing oxidizing agents are used in an isotropic silicon wet etch. Reaction between reactive species and silicon, on the other hand, yields chemical etching behavior to dry etch. ![]() Positively charged ion bombardment and polymer deposition from reactive and neutral species are responsible for providing directionality and physical etchings in dry etch. As in the wet etch, dry etch can also be divided into isotropic and anisotropic. Although there are also other forms of dry etch that involve ion creation other than plasma, our focus will be on plasma based dry etch. They are responsible for physical and chemical etching effects in dry etch. Positively charged ions and reactive species are created in the plasma. For example, 25% TMAH water solution etches (100) crystal planes at 300 times faster than (111) crystal planes.ĭry etch in silicon is often accomplished by generating RF driven plasma. Isotropic etch displays the same etch rate in all directions while anisotropic etch has directional etch rate dependency, which arises from differences in the etching rates of various crystallographic orientations in silicon by certain chemical solutions. The wet etch can be further classified into isotropic and anisotropic silicon etch. These technologies can be broadly categorized as wet and dry etch. It can be achieved through various technologies. Silicon micro-machining refers to the physical and chemical mechanisms of removing silicon material in a precisely controlled fashion, with the precision going down to a nano-scale. Special emphasis will be given to those which are particularly useful for optical MEMS applications. ![]() In this section, the various silicon micro-machining technologies available and the fundamental principles behind the technologies will be described. Silicon micro-machining is the technology that is instrumental for realizing such alignment structures and mechanical components on the chip for optical coupling purposes. Such precise alignment is enabled by the formation of structures and mechanical components on the chip that positions the core of the fibre at the desired location with sub-micron precision. Precise alignment is necessary to increase the optical coupling. ![]() These optical components include planar optical waveguides, micro-mirrors, photo-detectors, optical-switches, and micro-lenses among others. Whenever optical interface to a silicon chip is required, optical signals must be coupled to optical components on the chip via optical fibres. Currently, silicon-photonics have become a promising technology to increase processing speed and reduce power consumption in multi-core micro-processor architecture. Integrated optics and planar light wave circuits have also extensively employed silicon as a substrate. Silicon has excellent mechanical properties, which make it suitable for realizing sensors and actuators on chip, which are often classified as Micro-Electro-Mechanical Systems. It is a common platform for integrated circuits due to its well understood and established technological processes such as ionic implantation, diffusion, oxidation and others. Silicon is a typical substrate on which most devices on chip are made. ![]()
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