https://cyberleninka.org/article/n/1380904.pdf

ASAP7: A 7-nm finFET predictive process design kit

Double patterning (DP) is today the main solution to extend immersion lithography to the 32 nm node and beyond. Pitch
splitting process with hardmask transfer and spacer process have been developed at CEA-LETI-Minatec. This paper
focuses on experimental data using dry ArF lithography with a k1 factor of 0.20 ; the relative impact of each DP step on
overlay and CD uniformity budgets is analyzed. In addition, topography issues related to the presence of the patterned
hard mask layer during the second imaging step is also investigated. Tool-to-itself overlay, image placement on the
reticle and wafer deformation induced by this DP process are evaluated experimentally and resulting errors on CD
budget have been determined. CD uniformity error model developed by Nikon describing the relationship between CD
and overlay in different DP processes is validated experimentally.

Impact of CD and overlay errors on double-patterning processes

As mask dimensions continue to shrink to meet the ITRS roadmap and with the extension of 193 nm immersion
lithography, the masks are affected by electromagnetic field at high NA. Absorber degradation is regularly reported
under long term 193 nm exposures in the subwavelength diffraction regime. The damage mechanism known as Electric
Field induced Migration of chrome (EFM) partly contributes to the lifetime reduction of advanced masks. The EFM
results in a progressive alteration of the Critical Dimension (CD), CD uniformity (CDU) degradation and assist features.
This study evaluates the impact and the rate of absorber degradation due to an intensive ArF irradiation on assist features
and its influence on the through pitch process window for sub-45 nm technology nodes. Lithographic performance is
characterized after cumulative reticle aging stages. The aging test exposures are carried out directly on 193 nm scanner
to duplicate the production environment. The analysis of printed wafers is correlated to advanced mask inspection
(AIMSTM). This paper reports results on irradiation damage sensitivity on two types of reticles: conventional 6%
attenuated PSM and new binary material OMOG (Opaque MoSi On Glass) reticle. Test patterns have been generated
with and without a set of Optical Proximity Corrections (OPC) model calibration structures based on 45nm down to
28nm half-pitch design. The combination of metrology measurements used in this work between printed wafers and
reticles enables to define accurately the impact of mask damage caused by EFM effects on various test patterns and CD
evolution and highlight some trends about advances masks aging phenomenon.

Aging study in advanced photomasks: impact of EFM effects on lithographic performance with MoSi binary and 6% attenuated PSM masks

Systems and methods to detect, quantify, and control process-induced asymmetric signatures using patterned wafer geometry measurements are disclosed. The system may include a geometry measurement tool configured to obtain a first set of wafer geometry measurements of the wafer prior to the wafer undergoing a fabrication process and to obtain a second set of wafer geometry measurements of the wafer after the fabrication process. The system may also include a processor in communication with the geometry measurement tool. The processor may be configured to: calculate a geometry-change map based on the first set of wafer geometry measurements and the second set of wafer geometry measurements; analyze the geometry-change map to detect an asymmetric component induced to wafer geometry by the fabrication process; and estimate an asymmetric overlay error induced by the fabrication process based on the asymmetric component detected in wafer geometry.

Process-Induced Asymmetry Detection, Quantification, and Control Using Patterned Wafer Geometry Measurements

For advanced lithography metrology, SCD (Scatterometry Critical Dimension) is a common metrology
technique applied to control processes. SCD has the capability to report accurate data information such as
CD (Critical Dimensions), photoresist SWA (Side Wall Angle) and photoresist HT (Height). The shape of
photoresist correlates with inline process controllers, namely scanner focus and dose. However, SCD is a
model-based metrology method. In order to decode the process controllers, it requires computation from a
geometric model. Once the model extracts the resist shape information from the spectra, one needs further
correlation of those geometric parameters with the process controllers for monitoring. Thus, information
loss through multiple modeling is a major concern. Indeed, during data transformation, noise and model
approximation can distort the signals, in other words, the critical parameters, focus and dose, may not be
measured accurately.
This study therefore seeks a methodology to monitor focus and dose with the least amount of information
transformation. Signal Response Metrology is a new measurement technique that obviates the need for
geometric modeling by directly correlating focus, dose or CD to the spectral response of a SCD-based
metrology tool.

Lithography process controllers and photoresist monitoring by signal response metrology (SRM)

Double Patterning Technology (DPT) is now considered as the mainstream technology for 32 nm node lithography The main DPT processes have been developed according targeted applications: spacer and pitch splitting either by dual line or dual trench approaches However, the successful implementation of DPT requires overcoming certain technical challenges in terms of exposure tool capability, process integration, mask performance and finally metrology (1, 2) For pitch splitting process, the mask performance becomes critical as the technique requires a set of two masks (3) 
This paper will focus on the mask impact to the global critical dimension (CD) and overlay (OVL) errors for DPT The mask long-distance and local off target CD variation and image placement were determined on DP features at 180 nm and 128 nm pitches, dedicated to 45 nm and 32 nm nodes respectively The mask data were then compared to the wafer CD and OVL results achieved on same DP patterns
Edge placement errors have been programmed on DP like-structures on reticle in order to investigate the offsets impact on CD and image placement The CD lines increases with asymmetric spaces adjacent to the drawn lines for offsets higher than 12 nm, and then have been compared to the corresponding density induced by individual dense and sparse symmetric edges and have been correlated to the simulated prediction The single reticle trans-X offsets were then compared to the impact on CD by OVL errors in the double patterning strategy 
Finally, the pellicle-induced reticle distortions impact on image placement errors was investigated (4) The mechanical performance of pellicle was achieved by mask registration measurements before and after pellicle removal
The reticle contribution to the overall wafer CD and OVL errors budgets were addressed to meet the ITRS requirements

B. Connolly

Papers

Mask contribution on CD and OVL errors budgets for double patterning lithography