Wafer inspection stages for improved performance

The wafer inspection stage with XY2Z-Theta motion is designed for next-generation wafer inspection and metrology machines. The inspection stage is designed for 200 and 300 mm wafers which can be loaded/unloaded with the course Z-axis. The design of this wafer inspection stage is very flat, with all axes integrated, and offers great advantages against stacked stages.

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What is a wafer inspection stage?

A wafer inspection stages provide travel in X,Y, Z, and Theta axes to support 200, 300, and 450mm diameter wafers. The stage positioning of the wafer with high positioning accuracy and stability under the microscope for non-contact inspection. Inspection is done either by optical or e-beam depending on the application.

The 5-axis wafer inspection stage on the image is an XY2Z-Theta motion platform. it is designed for next-generation optical wafer inspection and metrology applications. It can be used for Critical Dimension, Overlay, and Thin Film Metrology. However, its modularity and scalability allow customization of this positioning stage to suit other applications.

At PM we understand the industry's challenges. We can either modify our existing motion platforms or design entirely new ones, depending on your requirements.

The design of the inspection stage is inspired by the results of in-house developed topology optimization software. Hence, the stage is well-balanced in terms of mass and stiffness. The integrated design has inherent advantages over conventionally stacked systems: dynamic performance is increased and Abbe errors are reduced.

This design raises the bar in terms of throughput and precision for our customers.

The first linear gantry axis is built on a granite structure, to provide a solid and accurate base. The second linear axis that moves perpendicularly to the first one is not stacked but integrated into the gantry axis. This makes sure that the stage adheres to the philosophy in which all bearings, centers of gravity, and motors are aligned in a single plane. 

Finally, the 2Z-Theta Module for the inspection stage is placed inside the gantry, making the design incredibly compact and bringing all drive dynamics into one plane. Reducing the arm of the moving masses increase the observable stiffness and hence system performance benefits. This meets customer demands for high acceleration and short settling times which are crucial for high wafer throughput.

Lightweight Design

The specifications of the XY stage are a result of a clear design philosophy as well as thorough analyses of the stage structure and smart selection of components.


Acceleration: 20 m/s2
Accuracy: <1.5 μm
Jitter: on request

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Video of the wafer inspection stage

Thermal Management

The challenge for dynamically moving systems is to keep the stage centre at the location where it is expected despite the significant amount of heat that is put into the moving parts. Thermal stability of the system is guaranteed by a number of innovative solutions. Special alloy materials are used to reduce movement of the wafer centre, heat sinks are used to extract heat from the motors and isolating materials are used to prevent heat from being transferred to critical components.

2Z-Theta Module

The compact 2Z-Theta module of the wafer inspection stage combines two Z-axes and a rotating axis in one compact package. There is a fine Z axis with a 5 mm stroke that allows for the focus of the wafer. The coarse-Z axis with 15 mm travel allows for wafer loading and unloading. Both Z axes are gravity compensated. Bearings for these axes are PM's RSDE type such as shown on the left. Smoothness, precision, and stiffness are key characteristics of these bearings. 

The theta axis includes a specially designed variant of the precision flat-mounted table bearing FMB. These bearings are famous for their low runout and wobble. At the same time, they provide high rigidity and smooth running characteristics.

Special features that are included in this module are three separate vacuum lines at waferchuck level for fast chucking and de-chucking.

2Z-Theta module specifications

Coarse Z-axis
Stroke: 15 mm

Fine Z-axis
Stroke: 5 mm
Jitter: on request

Stroke: 360o (continuous)
Speed: 5 rev/s
Acceleration: 30 rev/s
Accuracy: <15 μrad
Jitter: on request

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