After critical lithography steps, overlay and CD are measured to determine if the wafers need to be re-worked. Traditionally, overlay metrics are applied per X/Y-direction and, a CD metric is computed independently. From design standpoint, electrical failure is based on a complex interaction between CD deviations and overlay errors. We propose a method including design constraints, where results of different measurement steps are not judged individually, but in a combined way. We illustrate this with a critical design feature consisting of a contact requiring minimum distance to a neighboring metal line, resulting in much better correlation to yield than traditional methods.
Scatterometry critical dimension (SCD) technology in state of the art semiconductor manufacturing is a well-accepted
and powerful technique to determine profile properties such as critical dimensions, sidewall angles, trench depths as well
as layer thicknesses of microelectronic structures. The amount and combination of information receivable via SCD
measurements makes it, as long as interpreted correctly and incoming process variations especially incoming material
variations are well understood, superior to other measurement techniques such as critical dimension scanning electron
microscopy (CDSEM), transmission electron microscopy (TEM) or atomic force microscopy (AFM). For high
throughput inline process monitoring and feedback SCD models are usually generated for uniform gratings having fixed
pitches representing dense areas of the microelectronic chip design. However, for purposes such as improvement in
process tool matching, wafer uniformity or optical proximity correction (OPC) it is of great value if the measured test
patterns do have different layout properties being representative for other design elements and styles as well.
In this paper a through pitch SCD measurement within the shallow trench isolation (STI) layer on the 28nm node is
presented. This approach allows to interpret, to tune and to monitor process tool behavior for different pattern densities
using only one single specially designed lithography mask. Two different use cases are shown: for varying pitch sizes
either the designed line CD or the designed space CD is kept constant.
General SCD modelling approaches and examples to illustrate the key idea and practical use will be provided.