Liquid crystal hot spot detection with infinitesimal temperature control

Claim 1

In a method of detecting a hot spot on a die or a wafer, said method comprises: applying a liquid crystal to form a liquid crystal film on the top surface of said die or said wafer, adjusting the thickness of said liquid crystal film with a thickness adjustment process; placing said die or said wafer on the stage of a microscope that has a polarized illuminating light and an analyser, said analyser is placed on the viewing path of said microscope, said polarizer and said polarized illuminating light are cross polarized; said polarized illuminating light illuminates said die or said wafer that are placed on said stage; delivering a current to the site of said hot spot of said die or said wafer by a current injecting means; controlling the temperature of said liquid crystal film with a temperature control means; locating a change in optical property on said liquid crystal film by a means of viewing said liquid crystal film through said analyser, using a differentiation means to confirm said change is induced by a localized phase transition in said liquid crystal film, thus said hot spot is located at location where said localized phase transition takes place; wherein the improvement comprises: an infinitesimal temperature control method for controlling the temperature of said liquid crystal film; said infinitesimal temperature control method comprises an operation on a heating system; said heating system comprises: a power supply means; a heat generating means; and an adjustment means; said power supply means delivers power to said heat generating means, said heat generating means generates heat for heating up said liquid crystal film, said adjustment means controls the heating output magnitude of said heat generating means, said adjustment means also controls the turning on and turning off of said heat generating means, the action of said turning on and turning off of said heat generating means brings said temperature of said liquid crystal film to an infinitesimally close below the phase transition temperature of said liquid crystal for a limited length of time, whereby enabling said hot spot of an arbitrary small power level on said die or said wafer to produce said localized phase transition in said liquid crystal film, for said limited length of time; a reduction in said heating output magnitude prolongs said limited length of time, whereby increasing the chances of detecting said localized phase transition; said operation comprises: step (a): adjusting said adjusting means to an output level such that the combined heating from said heat generating means and said current is sufficient to heat up said liquid crystal film that at said site to beyond said phase transition temperature; step (b): turning off said heating means to allow said liquid crystal film to be cooled below said phase transition temperature; step (c): turning on said heat generating means to heat up said liquid crystal, till said liquid crystal film at said site is heated to beyond said phase transition temperature; step (d): if said hot spot cannot be detected because said limited length of time is too short, then reducing said output level to a low output level such that the combined heating from said heat generating means and said current is still sufficient to heat up said liquid crystal film that at immediate adjacent area of said site to beyond said phase transition temperature; then repeating said step (b) and said step (c); step (e): repeating said step (d) till said limited length of time is long enough such that said hot spot can be detected by said method.