In this paper, we present a study on the overlay (OVL) shift issue in contact (CT) layer aligned to poly-silicon (short as poly) layer (prior layer) in an advanced technology node [1, 2]. We have showed the wafer level OVL AEI-ADI shift (AEI: After Etch Inspection; ADI: After Developing Inspection; AEI-ADI: AEI minus ADI). Within the shot level map, there exists a center-edge difference. The OVL focus subtraction map can well match the OVL AEI-ADI shift map. Investigation into this interesting correlation finally leads to the conclusion of PR tilt. The film stress of the thick hard mask is responsible for the PR tilt. The method of OVL focus subtraction can therefore be a powerful and convenient tool to represent the OVL mark profile. It is also important to take into account the film deposition when investigating OVL AEI-ADI shift.
Proc. SPIE. 9424, Metrology, Inspection, and Process Control for Microlithography XXIX
KEYWORDS: Semiconductors, Electron beams, Metals, Inspection, Electron microscopes, Control systems, Scanning electron microscopy, Process control, Optical proximity correction, Critical dimension metrology
As the technology node of semiconductor industry is being driven into
more advanced 28 nm and beyond, the critical dimension (CD) error
budget at after-development inspection (ADI) stage and its control are
more and more important and difficult (1-4). 1 nm or even 0.5 nm CD
difference is critical for process control. 0.5~1 nm drift of poly linewidth
will result in a detectable off-target drift of device performance. The
0.5~1 nm CD drift of hole or metal linewidth on the backend interconnecting
layers can potentially contribute to the bridging of metal
patterns to vias, and thereby impact yield. In this paper, we studied one
function in the scanning electron microscope (SEM) measurement, i.e.
the adjustment of brightness and contrast (ABC). We revealed how the
step of addressing focus and even the choice of addressing pattern may
bring in a systematic error into the CD measurement. This provides a
unique insight in the CD measurement and the measurement consistency
of through-pitch (TP) patterns and functional patterns.