This kind of configuration is designed for wafer shape measurements at various process steps such as film deposition, etch, CMP, Epi, grind and plating. The Metrology System is equipped with various measuring instruments to monitor all parameters required to calculate the process induced stress.
The SemDex Metrology System is using Spectral Coherence Interferometry instruments with different numerical apertures to cover the full range of typical materials and wafer shapes. Single point, trace lines and full wafer maps are configurable in the SW and the evaluation is according to SEMI standards. The stress calculation is following to the Stoney equation. Bow monitoring with a repeatability (1σ) of below 0.5 µm can be achieved. For high topo wafers the flat backside can be measured with the bottom sensor for improved repeatability. Chuck design is usually 3 resting pins near the wafer edge.
As a unique feature, the SemDex Metrology System can be equipped with an additional StraDex t instrument to also measure the thin film thickness to give the most accurate stress value. Automatic pre and post process comparison is also included. Correlation to legacy laser and profilometer stress monitor tools has been shown for various wafer and process types.