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.