Fused silica used in photomask substrates is susceptible to residual stress birefringence. The residual birefringence can be a result of the boule growing process, processing and machining damage as well as handling damage. In polarization-based lithographic processes, the magnitude and orientation of this birefringence will have a critical impact on the overall performance of the photomask.
Light passes through these lithography systems at a particular polarization state orientation. Any birefringence in any optic in the beam path could change the polarization state of the light, reducing or even increasing intensity in an area where resists expect a certain amount of light. The change in intensity could mean that portions of the chip are not imaged correctly, which adversely affects yield and the end chip performance.
As current and next generation photolithography has continued to push the boundaries of 193nm light technology and aims for smaller and smaller critical dimension performance, the polarization characteristics and residual stress of the photomasks are even more important.
Understanding the stress at the wavelength of use (e.g. at 193nm) is even more critical to understanding how an optic will perform and how the process engineer can account for it. The photomask birefringence characteristics over the life of the photomask can also help identify individual photomask problems early and allow proactive steps to improve and prolong a photomask set production life.
How Exicor has assisted optical lithography customers:
→Measurements at the wavelength of use give the clearest picture of the material's performance characteristic.
→Exicor's unsurpassed sensitivity ensures repeatable low-level measurements.
→Customers requiring multiple instruments in different facilities can count on measurement accuracy and repeatability from instrument to instrument.
→Exicor provides the most precise measurement available at a faster speed than any competitor.
Contact us for more information about using Exicor systems to measure residual stress in DUV materials.