In-Line Critical Dimension and Sidewall Roughness Metrology Study for Compound Nanostructure Process Control by in-Line 3D Atomic Force Microscope
Authors: Kim Tae-Gon , Ryu Heon-Yul , Jo Ah-jin , Cho Sang-Joon , Park Sang-il , Vandeweyer Tom 
Published: February 2020

Critical dimension control is a key quality factor for better semiconductor device performance and yield and it is even more critical in 5 nm technology node beyond Si and SiGe device, where very high-mobility channel or new devices based on III-V and Ge, like directed self-assembled vertical nanowires, and tunnel FETs. Several in-line metrology techniques such as CD-SEM and scatterometry (or OCD) show a strong value in CD, LER, LWR, pitch and height monitoring in terms of throughput. The optical metrology technique especially OCD is sensitive to the refractive index, n and extinction coefficient, k of film on the structure. Thus it is hard to develop robust OCD library for III-V compound nanostructure due to change of n and k values as composition variation. Thus, it requires an unique in-line metrology technique that is less sensitive to material properties for robust process monitoring and yield control. In addition, as the drive current in a FinFET device flows along the vertical sidewalls, the surface quality of the sidewall strongly influences carrier mobility and device lifetime, leakage current so on and rough sidewall makes them worse. Sidewall roughness characterization, thus, become a critical issue and it needs to be controlled and monitored during process. However, in-line metrology technique could not been introduced for monitoring the quality of sidewall roughness yet. In this study, in-line 3 dimension atomic force microscopy (3D-AFM) was investigated to measure critical dimension parameters as complementary solution to the current in-line metrology tool sets and to develop fab compatible and high throughput in-line sidewall roughness monitoring solution. 3D-AFM (or CD-AFM) is used to consider as a reference tool for CD calibration in the ITRS roadmap because of high accuracy and atomic resolution without sample damage during measurement, but it is very slow. Therefore, we focus on not only measurement technique itself for compound nanostructure, but also how to implement the technique into the operation from process control perspective.

Si, SiGe and InGaAs/InP fins with various pitch were used and their CD, height and sidewall roughness were measured by in-line 3D-AFM (NX-3DM, Park Systems). The system consists of XY and Z scanners independently, which allows the Z scanner head to tilt by 0, 19˚ and 38˚ depending on pattern dimension. Measurement In order to measure fin with the pitch of 45 nm, e-beam deposited amorphous carbon fiber with the diameter of 10 nm and the height of 150 nm (M-CNT-150, Nanotools) was used. In order to evaluate fab operation capabilities such as mapping capabilities, probe to probe reliability and long term reliability of tool, recipes with 27 die map were developed. In order to verify the measurement accuracy TEM verification was performed.

Critical dimension of Si, SiGe and InGaAs/InP fins were successfully measured and especially CD and height of Si and SiGe fin with 45 nm pitch were measured successfully with CNT probe and all measured parameters were verified by TEM and it showed all good agreement. It means that CD and height information with material insensitive could be done by in-line 3D-AFM. Long term reliability was also evaluated and it showed that its 3σ value was 0.6 nm and peak to valley of the value was less than 1 nm. We think that non-contact measurement technique allows to reach this good repeatability.

In-line 3D-AFM could successfully measure and differentiate between sidewall roughness of Si and InGaAs/InP nanostructures, which were treated at different process. Tilt angle influence was evaluated and different tilt angle did not influence roughness value and its resolution. Roughness value at different space was measured and it shows similar sidewall roughness. Probe to probe repeatability was checked and it shows good long term reliability and repeatability of the in-line 3D AFM system.

In-line 3D AFM successfully measured critical dimension and sidewall roughness of Si, SiGe and InGaAs/InP nanostructure in atomic scale with good reliability. AFM with tilt head allows AFM probe to access pattern sidewall. As a result in-line 3D AFM could be used as a process monitoring for next generation device fabrication process such as III-V FinFET and GAA FET. In-line 3D-AFM could be used as complementary solution to other in-line metrology tools. Hybridization of in-line 3D-AFM with CD-SEM and OCD could make metrology system more accurate and learning cycle and recipe development faster.