In recent years, 193nm immersion lithography has been extended instead of adopting EUV lithography. And multi-patterning technology is now widely applied, which requires tighter specification as the pattern size gets smaller on advanced semiconductor devices. Regarding the mask registration metrology, it is necessary to consider some difficult challenges like tight repeatability and complex In-Die pattern measurement. In this study, the registration measurement capability was investigated on new registration metrology tool IPRO5+, and new measurement method called Model-Based measurement was evaluated. And the performance and the prospect for advanced technology masks of the IPRO5+ were discussed based on the evaluation results.
The control of critical dimension uniformity (CDU), especially intra-field CDU, is an important aspect for
advanced lithography, and this property must be controlled very tightly since it affects all of the exposure fields. It is
well known that the influence of the mask CDU on the wafer intra-field CDU is becoming dominant because the mask
error enhancement factor (MEEF) is quite high for low-k1 lithography. Additionally, the abovementioned factors impact
the CDU through global (field-level) and local (grating-level) variations. In this paper, we analyze in detail CDU budgets
by clarifying the impact of local CD variation.
The 50-nm staggered hole features using Att-PSM showed a mask global CDU of 1.64 nm (3sigma at the mask
level) and a wafer intra-field CDU of 2.30 nm, indicating that the mask global CDU was a major part of the intra-field
CDU. By compensating for the contribution of the mask CD, the wafer intra-field CDU can be reduced to 0.986 nm.
We analyzed the budgets of wafer intra-field CDU, which is caused by local CD variation (mask and process) and
measurement noise. We determined that a primary cause of the wafer intra-field CDU after applying a mask CD
correction was these local CD variations, which might disturb the proper use of dose correction for the mask CD. We
demonstrated that the impact of mask local CD variation on the correction flow can be greatly reduced by averaging
multiple point measurements within a small area, and therefore discuss the optimum conditions allowing for an accurate
intra-field CDU determination. We also consider optimization of the CD sampling scheme in order to apply a dose
correction on an exposure system to compensate for the mask CDU.
A requirement for CD control on wafer is increasing with shrinking design rule. This is especially true for dense
contacts because of higher MEEF. It is considered that contact mask LER impact on lithographic performance is
comparatively large. Nevertheless, a relationship between contact mask LER and wafer performance has not been
evaluated in recent years.
Therefore we studied contact mask roughness impact on wafer in order to determine specs for improvement of
mask quality. We assumed the thin MoSi binary mask which was called Opaque MoSi On Glass (OMOG). The
programmed roughness patterns data for 28 nm nodes was made. The frequency and depth of roughness was
changed. In addition, we also drew bump patterns. A lithography simulator was used to investigate which kind of
mask roughness impacted significantly on wafer. We compared the difference between wafer experiment and
simulation. Finally a relationship between contact mask roughness and lithographic performance was obtained.