Predictive chrome-film haze mask management for mass production

Abstract

In general, it is defined "Chrome-Film Haze", as an invisible film reside on the chrome surface. This type of Haze defect can poise as a "silent killer" because it cannot be seen by naked eyes, nor can be easily detected by our inline Inspection tool. We hypothesize that this kind of haze will block its transmission at chromeside, thus causing its dosage trending on one direction & intrafield corners/centre CD drifting. This type of "haze", if not properly managed, especially on a "Dark-field Low-Transmission" Mask (i.e..Contact)... can cause "Contact Bridging" as a matter of time, resulting catastrophe yield loss on thousands of wafers, in a mass production FAB environment.So far, "Chrome-Film Haze" phenomenon is evident only on our Binary 193nm Reticles, with increased ArF exposures. Somehow, it does not occur on our 193nm PSM Mask yet. This could be attributed to the differences in the PSM & Binary Mask Cleaning material;-193nm PSM Reticle utilise 100% sulphate-free cleaning while 193nm Binary Mask is not. Thus, we can presumely expect that the sulphate "seeds" left on Chrome side, could have grown over increased ArF exposition, in a matter of time.Current FAB plant managed this kind of "Chrome-Film" Haze, by inserting a "APC Dosage control limit" & "Intrafield Corners/Centre CD" control so that it's dosage will not be allowed to trend unknowingly, causing corners-CD to drift away from its target. From our historical dosage trends, it became so apparent that we can almost predict when it'll hit its next APC dosage limit. Thus, we can draw a conservative wafer exposure count limit before it trigger its APC Dosage limit. In this way, we can be better prepared to plan and manage our production wafer input, in order to minimise the impact of reticle being sent for cleaning.