In 1998, as semiconductor device technology pushed the 180 nm node boundary (huge by today’s standards), the influence of low levels of strain birefringence on optical path integrity ushered in an era requiring radically improved sensitivity in birefringence measurement metrology. Hinds scientists responded with Exicor® technology, which a decade and a half later continues to provide leading edge measurement sensitivity as the industry approaches the 14 nm node.
Strain birefringence can affect the polarization of transmitted light as it passes through any optic. In semiconductor lithography applications, critical areas are the lens and the photomask. Exicor systems are widely used for evaluation in both areas and a broad range of specialized models have been developed for specific measurement samples, wavelengths, cycle time and other requirements. Two models of particular relevance include the OIA for lenses and the 300AT for photomasks.
More recently, stress levels in the bulk silicon have become an area of concern as semiconductor equipment manufacturers push for ever smaller feature sizes.
In addition, semiconductor lithography equipment manufacturers have ingeniously employed the ultra-sensitive modulation characteristics of the photoelastic modulator, upon which Exicor technology is based, for level sense and alignment within scanners and steppers.