Hello Sudhanshu,

As James pointed out, Stoney's formula is generally used to convert a
cantilever deflection to a measure of surface stress.  Although there are
several enhancements to this formula, it is correct to first order.  John
Sader published several papers on the topic with much more detail and
validation through finite element analysis.  From an experimental point of
view, one problem with these approaches is that the cantilever's Young's
Modulus must be known in order to use Stoney's formula.  Young's modulus for
single crystal silicon cantilevers should be well-known, but it can be more
difficult in the case of commonly-used SiN levers or ones coated with metal
films.  The following paper gets around this issue by allowing one to
calculate surface stress from the cantilever's deflection and its
experimentally determined spring constant.
Appl. Phys. Lett. 79, 551 (2001)

Mike