**What is Radius
Of Curvature?**

In the case of differential
geometry, the radius of curvature or R is the reciprocal of the curvature. For
a given curve, it is equal to the radius of circular arc that perfectly
approximates the curve at a particular point.

For surfaces, the radius of
curvature is given as radius of circle that best fits the normal section or
combination thereof. The major applications of the concept can be seen in
differential geometry, to measure the radius of curvature of earth or bending of
beams in a three-part equation. It is also used in optics as well.

The concept can be understood
better by studying stress in semiconductor structures that usually involves the
evaporation of thin films results from thermal expansion. This stress happens
because film depositions are usually made up of the room temperature. When
temperature is cool down to the room temperature then the difference in thermal
expansion coefficients of substances will cause the stress.

**Radius Of
Curvature Formula**

The intrinsic stress results due to microstructure created in films as atoms and deposited on substrate. The same stress in thin films semiconductor is the reason of buckling in wafers. Here, the radius of curvature of stressed structure can be described by modified Stoney formula.

Also, the radii of curvature can be measured through the optical scanner methods. There are modern scanner tools as well that are used to measure the full topography of substrate and to measure the principal radii of curvature too. It can give accuracy of the order of 0.1% for radii of curvature of 90 meters and more.