Ellipsometer
Ultra-precise dual-compensator rotation for Mueller-matrix metrology
An ellipsometer measures sub-nanometer film thickness and optical constants from the interaction of polarized light with thin films — an indispensable metrology tool in wafer manufacturing. The dual rotating compensator (DRC) at the heart of a generalized ellipsometer demands direct-drive motors, a professional motion controller and advanced synchronization to meet strict precision, sync and low-vibration requirements. The AGD200 two-axis controller with an ultra-precise electronic-gearing algorithm, paired with Akribis ACD hollow direct-drive rotary motors, delivers a reliable high-precision solution already in volume use at leading semiconductor manufacturers.
Why Agito
Microsecond synchronization
16 kHz servo loop plus electronic gearing keep both axes in strict sync; measured angular deviation about 0.0006° (82 ns difference at 1200 rpm).
Zero-cogging smoothness
ACD57 ironless direct-drive motors with FOC sine-wave drive give extremely low speed ripple (±0.0417%), stabilizing optical measurement data.
One controller, two axes
A single AGD200 drives both rotary axes, saving hardware versus separate drives; maintenance-free direct drive lowers lifetime cost.
Low vibration by design
Full-chain vibration suppression from the ironless motor structure to the control algorithm keeps vibration below 0.1 g RMS for sub-nanometer measurement.
Performance
| Angular sync deviation | about 0.0006° (0.0005904° measured) |
|---|---|
| Following error | ≤ 0.00375° at 1:5 ratio (240 / 1200 rpm) |
| Speed fluctuation | ±0.0417% |
| Gear ratio | Software-configurable, multiple encoder protocols |
Solution & system configuration
AGD200 two-axis drive-control unit paired with Akribis ACD57 ironless hollow direct-drive rotary motors: zero cogging torque, high dynamic response, a hollow bore for the optical path, backlash-free and maintenance-free operation, and sub-arcsecond positioning.