SPC based in-line reticle monitoring on product wafers

In the area of advanced IC manufacturing, reticle contamination, especially through crystal growth (progressive defects), is increasingly becoming an issue. These small contaminants on the reticle which grow over time can cause both yield-sort and catastrophic defects in the printed pattern, and so will be a constant threat for the lithography process as 193 nm wavelength and 300 mm wafer proliferation continues. Bright-field inspection on KLA-Tencor 2351 patterned wafer inspection tools is the industry standard for detecting catastrophic yield events on wafers, and STARlight inspection is the industry standard for detecting all types of contaminants found on reticles. The STARlight reticle requalification determines whether the reticle can be used at all, and the 2351 bright-field wafer inspections can be performed as insurance to ensure no progressive defects have become catastrophic before the reticle ´s next scheduled STARlight requalification. If found, the affected wafers can be reworked (not scrapped later in line), and the STARlight requalification interval can be shortened. 2351 complements the STARlight inspection. This paper describes a method developed at Infineon Technologies in Dresden based on a sensitive defect inspection of patterned resist on DRAM/NROM product wafers. Advanced repeater filtering on the KLA-Tencor 2351 brightfield patterned wafer inspection tool based on the reticle layout can effectively separate the relevant repeaters. These parameters are not globally defined, but can be adjusted recipe-fine, i.e. they can be adjusted to the overall defect density and thus the average distance between adjacent defects. Thus specific layer noise and sensitivity levels can be respected