Reticle Haze Characterization and Management in a DRAM fab

Reticle, the graphical medium, is of vital importance in the lithography process. With the introduction of 193nm lithography, reticle surface contamination has been a major contributor to reticle costs and semiconductor yield loss. The most common contaminant identified is ammonium sulfate, usually called haze. In this paper, haze management in CXMT will be introduced, including the high-resolution inspection, automated defect disposition, in-house haze characterization, and a unique prevention method by mask alteration. CXMT implemented a systematic reticle inspection scheme with KLA advanced reticle inspection tool Teron™ SL670, and automated defect disposition and long-term monitor with KLA Reticle Analyzer. Other than the most discussed ammonium sulfate haze, which has been well controlled with the optimization of reticle manufacture and management process, CXMT characterized two types of new haze - Molybdenum Oxide and organic haze - regarding their distribution, size, and chemical composition. To investigate possible sources of such haze composition and to prevent its growth, CXMT modified the thickness of silicon oxide on MoSi material. Long-term production monitor shows that the lifetime of modified reticles was doubled and the development of on-MoSi haze was mitigated, indirectly revealing the formation mechanism of this type of haze. Haze management has not only been greatly improved by the inspection process and accurate disposition, but also benefited from the study of haze characterization and optimization of reticle materials.