Ulvac has introduced two new high speed spectroscopic ellipsometers for thickness and optical parameter measurement of thin films on 200mm or 300mm diameter wafers.
While many spectroscopic ellipsometers claim to be fast, they may still rely on rotating compensators and electro optic modulators for signal measurement. ULVAC’s UNECS series instruments, however, employ a novel new approach to deriving the physical constants necessary to determine thin film thicknesses.
Using a white light source and a series of multi high order wave-plates in the optical path, the full spectrum carrying the information about the wavelength-dependant parameters of the reflected polarized light is generated and captured in a single snapshot measurement.
No mechanical or active components for polarization control such as a rotating compensator or electro optic modulator is required. The signal is captured at the receiver end of the instrument by a CCD-based spectrophotometer, in the form of a single snapshot of the full spectrum from 530nm to 750nm.
In as little as 20ms, a high resolution measurement of film thickness (0.1nm) can be made from the 4,000 data points that are generated and analyzed in each snapshot.
The 300mm diameter wafer moves automatically under the optical path via an R-0- stage. In addition, the Z-height range (0-30mm) is adjusted automatically.
Thanks to the high speed measurement of the instrument, and the high speed motion and compact design of this rotating sample stage, a high resolution film thickness distribution map of a 300mm wafer can be performed (106 points) in as little as 120s.