Highly-Dynamic 4-Axis Piezo Wafer Stage for Inspection & Metrology
Hybrid Piezo Motor Principle for Increased Range and Dynamics, with Integrated Wafer Lift
Dynamic positioning, scanning, and alignment with precision down to the subnanometer realm is critical to success in wafer inspection and metrology.
As feature sizes in semiconductor manufacturing shrink and design complexity increases, the demands on the motion systems continue to grow. Metrology processes are therefore highly dependent on precise wafer positioning solutions to enable the fast and reliable analysis of defects or particles at each step of the manufacturing process to prevent yield loss. PI offers proven wafer scanning subsystems that take advantage of piezo technology to meet demanding process requirements where conventional electromagnetic solutions reach their limits.
With the development of a multi-axis piezo wafer nanopositioning stage in an innovative hybrid kinematics configuration, PI expands the system options for wafer platforms with four independent degrees of freedom: Tip, Tilt, Z and rotation around Z. Loading and unloading is performed by an integrated wafer lift. The hybrid kinematics configuration features unique piezo actuators for high-precision Z-axis motion. These provide fast step-and-settle over long travel ranges as well as real-time dynamic motion over small areas. Adopters of the new technology are streamlining their design processes and achieving greater precision and reliability. At the same time, they are able to minimize equipment complexity and integration efforts, thereby reducing costs and risks.
Next-Generation Standards
Z Axis – Dynamic Tracking
- Piezo motor technology
- Power off holding ability
- High resonant frequency enables highly dynamic tracking and correction mode for fine motion
- Travel range: up to 4 mm coarse and 50 µm fine
- Move and settling time <10 ms (0.01 µm - 50 µm)
- Bidirectional repeatability: 10 nm (1 sigma)
- Position stability <5 nm
Z-Rotation Axis – High-Accuracy Motion up to 360°
- Piezo motor technology
- High resonance frequency for highest stability
- Travel range: up to +/-6 mrad for highest accuracy, can be extended to up to 360°
- Move and settling time <20 ms (0.1 µrad - 100 µrad)
- Bidirectional repeatability: 0.5 µrad (1 sigma)
- Position stability <0.05 µrad
Advantages
Our hybrid piezo wafer stage concept offers several advantages. Piezo motors are inherently stiff, self-clamping and can hold a position without power. They do not introduce additional servo jitter, and the high stiffness and bandwidth can be used for dynamic tracking or compensation of external disturbances and instabilities. With move and settle times down to <10 ms and position stability of <5 nm and <0.05 µrad, respectively, this new piezo wafer stage combines ultra-high performance with excellent value.
Dynamic Operation
The newly developed piezo wafer stage from PI offers significant advantages over electromagnetic concepts. With native support for wafer fiducial alignment, before positioning/moving the wafer, the module first corrects the rotational misalignment of the wafer and holds the wafer in the correct position under the tool. Wafer thickness and machine static characteristics are taken into account.
Once the process is complete, the actuators can be turned off and held in position so that no more energy is needed, and therefore, no heat is generated in the wafer area that could affect precision. This eliminates the need for additional cooling or balancing.
The secondary mode of the piezo actuators is used to locate and track the focus. The analog element mode allows for highly dynamic operation, compensating for flatness and angular errors and ensuring that the focus is maintained.
