Displacement Measuring Interferometer (DMI) - Laser Interferometer Systems and Components

Motion X Corporation is an industry leader in homodyne displacement measuring interferometers (DMIs). DMI’s have grown to become one of the most powerful tools for advanced position feedback. Our DMI product development is driven by the aggressive technology roadmap of the semiconductor industry and our newest generation of DMI’s will provide our customers with significant advantages to obtain their metrology and non-contact measurement requirements.

Displacement Measuring Interferometer (DMI) - Laser Interferometer Systems and Components
Displacement Measuring Interferometer (DMI) - Laser Interferometer Systems and Components
Laser Inferometer System
Laser Inferometer System
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MX Laser Interferometer ManualMX Laser Interferometer Manual (PDF, 1360KB)

DMI System

A DMI uses the physical phenomenon of the interference of light to measure relative displacements. Precise knowledge of the wavelength of the laser light provides the fundamental accuracy of a DMI system.

A homodyne interferometer utilizes a single-frequency laser source and tracks the deviation in amplitude that occurs as a result of a change in optical-path difference (OPD) in the interferometer. Displacement of the measurement leg of the interferometer, with respect to a fixed reference, will results in an increase or decrease in the signal amplitude depending on the direction of movement. , depending on the direction of the movement. The displacement signal is monitored by a photo detector placed in the path of the interfering beams at the output of the interferometer (see Fig. 1).

DMI System

FIGURE 1. A homodyne interferometer is based on a single-frequency laser source and tracks the deviation in amplitude that occurs as a result of a change in optical-path difference in the interferometer.

A typical DMI system consists of a laser, interferometer and beam-steering optics, measurement electronics, and a reflective target. The target, which is usually an optical-quality reflector, is located on the component that will be translated or rotated. The capability to integrate the DMI target at the plane of interest eliminates Abbe error-which results from a combination of a beam offset from the center of the translation stage and an angular error-highlighting one of the key advantages of a DMI over mechanical measurement techniques (see Fig. 2). In addition, the alignment steps for a DMI provide a square beam path (perpendicular axes) that minimizes the potential for geometrical inaccuracies such as cosine error and opposite-axis error. Cosine error results when the measurement axis is not parallel to the axis of travel; opposite-axis error is caused by a non-perpendicularity between opposing axes.

DMI System

FIGURE 2. Abbe error results when the axis of measurement is offset from the axis of interest (axis of travel). Integrating the DMI target at the plane of interest eliminates Abbe error.

Applications

DMIs are the primary measurement device for high-precision stage metrology in semiconductor metrology tools and lithography processes for the production of integrated circuits (ICs) and flat panel displays (FPDs). Additional applications include; characterization and calibration of machine tools, stages, piezoelectric transducers, encoders and grid plates.

Technical Information

Motion X Corporation’s line of homodyne DMI systems and components is extremely flexible and can be offered in many configurations that will suit your application's requirements. Our price versus performance is unmatched in the DMI market and we invite you to contact our sales department for more information regarding our line of DMI systems and DMI system components.

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