Microfabrication

In the last two decades, microelectromechanical systems (MEMS), microsystems (European usage), micromachines (Japanese terminology) and their subfields have re-used, adapted or extended microfabrication methods.

[1] The major concepts and principles of microfabrication are microlithography, doping, thin films, etching, bonding, and polishing.

Microfabrication resembles multiple exposure photography, with many patterns aligned to each other to create the final structure.

For optical devices or flat panel displays, transparent substrates such as glass or quartz are common.

Examples of deposition techniques include: It is often desirable to pattern a film into distinct features or to form openings (or vias) in some of the layers.

The substrate is exposed to an etching (such as an acid or plasma) which chemically or physically attacks the film until it is removed.

Etching techniques include: Microforming is a microfabrication process of microsystem or microelectromechanical system (MEMS) "parts or structures with at least two dimensions in the submillimeter range.

However, as Fu and Chan pointed out in a 2013 state-of-the-art technology review, several issues must still be resolved before the technology can be implemented more widely, including deformation load and defects, forming system stability, mechanical properties, and other size-related effects on the crystallite (grain) structure and boundaries:[4][5][8] In microforming, the ratio of the total surface area of grain boundaries to the material volume decreases with the decrease of specimen size and the increase of grain size.

There is a critical need to establish the systematic knowledge of microforming to support the design of part, process, and tooling with the consideration of size effects.

[8]a wide variety of other processes for cleaning, planarizing, or modifying the chemical properties of microfabricated devices can also be performed.

Some examples include: Microfabrication is carried out in cleanrooms, where air has been filtered of particle contamination and temperature, humidity, vibrations and electrical disturbances are under stringent control.

Smoke, dust, bacteria and cells are micrometers in size, and their presence will destroy the functionality of a microfabricated device.

Wafer cleaning and surface preparation work similarly to the machines in a bowling alley: first they remove all unwanted bits and pieces, and then they reconstruct the desired pattern so that the game can go on.

Synthetic detail of a micromanufactured integrated circuit through four layers of planarized copper interconnect, down to the polysilicon (pink), wells (greyish) and substrate (green)
Simplified illustration of the process of fabrication of a CMOS inverter on p-type substrate in semiconductor microfabrication. Each etch step is detailed in the following image. The diagrams are not to scale, as in real devices, the gate, source, and drain contacts are not normally located in the same plane.
Detail of an etch step.