|
The present practice of managing reticle haze defectivity involves reticle inspection at regular intervals, coupled with
inspection of print-down wafers in between reticle inspections. The sensitivity of the reticle inspection tool allows it to
detect haze defects before they are large enough to print on the wafer. Cleaning the reticle as soon as the reticle inspector
detects haze defects could result in a shorter reticle lifetime. Thus there is strong motivation to develop a methodology to
determine what size defect on the reticle results in a printable defect on the wafer. Printability depends upon several
variables in the litho process as well as whether the defect resides in a high-MEEF (Mask Error Enhancement Factor) or
low-MEEF area of the die.1 Trying to use wafer inspection to identify the first appearance of haze defects may require
inspector recipe settings that are not suited to a practical wafer scan.
A novel method of managing such defects is to map the coordinates of the defects from the reticle onto the wafer, and
apply a separate, hyper-sensitive threshold to a small area surrounding the given coordinates. With this method, one can
start to correlate the size of the defects printed on the wafer to the light transmission rate from the corresponding site on
the reticle scan, and thus can predict the starting point at which the haze defects on the reticle are likely to print on the
wafer. The experiment described in this paper is a first step in exploring the feasibility of this method to help track the
growth of nascent haze defects and optimize the timing to rework the reticles. The methodology may have extendibility
to other applications in which hyper-sensitive wafer inspection at localized areas within the die would be beneficial, such
as monitoring weak spots found by Optical Rule Check, Process Window Qualification, electrical test or failure analysis.
|
