Research Overview 
ultralow-noise fs lasers 
and comb sources 
timing and synch for 
ultrafast science 
ultrafast, ultra-precise 
TOF sensing and imaging 
photonic on-chip 
clock distributions 
optical metrology for 
semiconductor manufacturing

Optical metrology for 3D semiconductor manufacturing

With the recent explosive demand for data storage, ranging from data centers to various smart and connected devices, the need for higher-capacity and more compact devices is constantly increasing. As a result, semiconductor devices are now moving from 2D to 3D. We are currently working on various problems in the metrology of such 3D semiconductor devices.

We recently worked on multilayer thickness metrology for 3D-NAND flash memories. By combining optical spectral measurements and machine learning algorithms, we demonstrated a non-destructive method for thickness characterization of each layer in >200-layer semiconductor multilayer stacks used in 3D-NAND flash semiconductor devices. We could predict the thickness of each layer with an average root-mean-square error (RMSE) of only ~1.6 A over >200-layer structure [1].

We are also working on rapid, large-area imaging and height/depth profiling of various 3D semiconductor devices. For this, we are extending the idea of our recently demonstrated ultrafast, ultraprecise TOF detection method [2] optimized for this purpose.

Related Publications
[1] H. Kwak, S. Ryu, S. Cho, J. Kim, Y. Yang, and J. Kim, "Non-destructive thickness characterisation of 3D multilayer semiconductor devices using optical spectral measurements and machine learning," Light: Advanced Manufacturing 2, 1 (2021)
[2] Y. Na, C. Jeon, C. Ahn, M. Hyun, D. Kwon, J. Shin, and J. Kim, "Ultrafast, sub-nanometre-precision and multifunctional time-of-flight detection," Nature Photon. 14, 355-360 (2020)