selfaligned

Selfaligned is a term used in manufacturing and nanofabrication to describe a process or feature whose alignment is achieved by the design or physics of the process rather than by direct lithographic alignment of masks. In semiconductor contexts, it often means critical elements are positioned relative to another feature automatically by diffusion, oxidation, or spacer structures.

In device fabrication, selfaligned techniques rely on an intermediate structure such as a diffusion layer, oxide spacer, or sidewall to place subsequent features with high precision relative to a reference feature like a gate or trench. This reduces overlay errors and enables tighter geometries, often lowering parasitic capacitances and improving yield.

A common application is the self-aligned gate in MOSFET technology, where the source and drain regions form in relation to the gate edge through spacers or diffusion barriers, minimizing overlap with the gate. The approach has also been used to create self-aligned sources/drains and self-aligned contacts in various CMOS processes.

Historically, selfaligned processes emerged in the late 1960s and became a standard aspect of modern CMOS fabrication, contributing to higher device density and better electrical performance. The concept has since extended to other nanofabrication domains that employ spacer and diffusion-based methods to achieve alignment without lithography on every layer.

See also: self-aligned gate, spacer technique, self-aligned contact, diffusion-based alignment.