Glass Microfabrication by Wet Etching

This lecture covers the process of glass microfabrication using wet etching with hydrofluoric acid. It explains the etching mechanism, effect of etchant and glass composition, and the etching process sequence. Historical background on hydrofluoric acid etching is discussed, along with the overall reaction and etching constants. The lecture also delves into the detailed mechanisms of HF-SiO₂ etching, surface morphology, and the impact of additives like NH4F. Various factors affecting the etching rate, such as agitation and HCI addition, are explored. The lecture concludes with insights into the surface roughness effects, thermal annealing, and the application of photosensitive glass in microfabrication.

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MICRO-431: Materials and technology of microfabrication

The student will learn procedures and applications of modern microfabrication technologies, as practiced in a clean room environment, in particular modern techniques that go beyond the classical steps

Etching (microfabrication)

Etching is used in microfabrication to chemically remove layers from the surface of a wafer during manufacturing. Etching is a critically important process module, and every wafer undergoes many etching steps before it is complete. For many etch steps, part of the wafer is protected from the etchant by a "masking" material which resists etching. In some cases, the masking material is a photoresist which has been patterned using photolithography. Other situations require a more durable mask, such as silicon nitride.

Reactive-ion etching

Reactive-ion etching (RIE) is an etching technology used in microfabrication. RIE is a type of dry etching which has different characteristics than wet etching. RIE uses chemically reactive plasma to remove material deposited on wafers. The plasma is generated under low pressure (vacuum) by an electromagnetic field. High-energy ions from the plasma attack the wafer surface and react with it. A typical (parallel plate) RIE system consists of a cylindrical vacuum chamber, with a wafer platter situated in the bottom portion of the chamber.

Plasma etching

Plasma etching is a form of plasma processing used to fabricate integrated circuits. It involves a high-speed stream of glow discharge (plasma) of an appropriate gas mixture being shot (in pulses) at a sample. The plasma source, known as etch species, can be either charged (ions) or neutral (atoms and radicals). During the process, the plasma generates volatile etch products at room temperature from the chemical reactions between the elements of the material etched and the reactive species generated by the plasma.

MEMS

MEMS (Microelectromechanical systems) is the technology of microscopic devices incorporating both electronic and moving parts. MEMS are made up of components between 1 and 100 micrometres in size (i.e., 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres to a millimetre (i.e., 0.02 to 1.0 mm), although components arranged in arrays (e.g., digital micromirror devices) can be more than 1000 mm2.

Mineral acid

A mineral acid (or inorganic acid) is an acid derived from one or more inorganic compounds, as opposed to organic acids which are acidic, organic compounds. All mineral acids form hydrogen ions and the conjugate base when dissolved in water. Commonly used mineral acids are sulfuric acid (H2SO4), hydrochloric acid (HCl) and nitric acid (HNO3, they are also known as bench acids). Mineral acids range from superacids (perchloric acid) to very weak ones (boric acid). Mineral acids tend to be very soluble in water and insoluble in organic solvents.

Fabrication extended: Etching ME-426: Micro/Nanomechanical devices

Covers the process of etching using wet and dry techniques, explaining definitions, steps, examples, challenges, and solutions.