Accurate and reproducible microlithography processing is critical for developing smaller
and more dimensionally accurate semiconductor structures. As modern microprocessors
and memory devices scale down to deep submicron dimensions, defects originating in the
microlithography processes become increasingly effective in reducing yield. Careful and
efficient methods of measuring the variability of these defect levels by utilizing a shortloop
monitoring process is essential in controlling the quality of lithography process for
these semiconductor devices. During the conventional photo process, a defect can result
from either an external process variable (e.g. manual wafer handling), or an internal one
from environmental sources (unclean equipment sets). Others may be related to the
process parameters themselves; such as a pattern anomaly, marginal processing by the
equipment, or a previous defect on the wafer creating a nucleation site for more defects.
Since microlithography defects can arise from a variety of sources, adopting flexible and
efficient methods of measuring their effects are essential in maximizing the yield.
This study will discuss the methodologies used to characterize and monitor complete
microlithography processing for two distinct cases: one in which the resist is mostly
unexposed with the exception of a pattern of contact holes, and one in which most of the
resist is exposed, leaving behind a developed pattern of resist lines. These two strategies,
when used in conjunction and properly sampled in a defect metrology tool can lead to
timely in-line feedback about the nature of possible processing defects present.
Furthermore, the results of such a short loop may suggest continued short loop processing
involving fewer processing steps to narrow the source.