Ultra

Positioning

Today, the diverse applications of nanotechnology research and the ongoing trend of shrinking feature sizes in the semiconductor industry demand precise positioning at the nanometer level more than ever before.

Introduction

Most nanofabrication or nanoanalytic applications need to be able to blindly center the points of interest within one write field / field of view. And due to the typically high zoom values it is necessary to address nanopositioning with a few nm accuracy even over large distances. Different measures, always based on the RAITH laser interferometer stage technology, ensure this on our systems.

Meeting nanofabrication’s
toughest demands

Key features

Benefits for applications

Mastering nanopositioning with accuracy and flexibility

Exact placement to the point of interest

The precision and resolution of the interferometric measurement, coupled with the hybrid positioning system’s capabilities, guarantee precise positioning from increments as small as a few nanometers to the scale of wafers.

Precise stitching and overlay for large-area applications

Accurate high-resolution displacement correction capabilities and exact alignments ensure seamless stitching of individual write or scan fields and overlay precision in the nanometer range.

Stacked 3D SEM
imaging

The recombining of chip layers through the stacking of several high-resolution large-area image mosaics in Reverse Engineering applications is enabled, even for state-of-the-art technology nodes, due to the high absolute accuracy over the entire travel range.

High position stability

As position deviations are permanently tracked and corrected, mechanical drift and other disturbances are significantly reduced for higher stability during the application.

Quick and easy
calibration

The highly precise laser interferometer stage can be used as an intrinsic alignment and calibration reference, enabling quick and easy calibration with (semi)automatic routines.

Technical details

UltraPositioning is based on our laser interferometer stages

Measurement system and setup

We utilize a double-pass displacement measuring interferometer for each horizontal stage axis, employing a high-precision L-shaped plan mirror setup positioned atop the stage at sample level. This setup serves as a reliable reference for straightness and squareness.

Laser interferometry capitalizes on the interference of laser light. A monochromatic laser beam is split by a semi-transparent mirror into a measurement arm and a reference arm. While the reference beam reflects off a fixed mirror, the measurement beam reflects twice off a moving mirror on the stage. Interference occurs when the beams recombine, detected by optical sensors. Signal analysis determines the measurement mirror’s displacement.

This measurement is traceable to the laser wavelength, offering an optical resolution of lambda fourths (approximately 158 nm) before further interpolation. This intrinsic resolution is 12-120 times finer than the typical grating pitch of optical linear encoder scales.

Frequency stabilization of the laser ensures long-term stability and measurement accuracy. Conducting measurements within the vacuum chamber eliminates typical errors introduced by air refractive index changes in interferometric measurements.

Unlike setups with linear encoder scales, our interferometer-based configuration is designed to measure both lateral displacement axes in the sample plane, minimizing or eliminating Abbe offsets. This setup detects and corrects runout on one axis and position cross-talk between both axes, while reducing typical Abbe errors.

Positioning unit

The interferometer signals are directly processed and interpolated in the motion controller, providing high update rates and serving as feedback for the position control loop.

The majority of RAITH laser interferometer stages, integrated into our nanofabrication systems, feature a unique drive chain capable of completely correcting position errors through ultra-precise mechanical displacements. This capability is achieved through a combination of DC motors for long-stroke positioning and piezo actuators for ultra-fine positioning.

In some RAITH systems, fine positioning is achieved via beam deflection through a direct interface between the motion controller and scan generator. While this method offers faster settling, the purely mechanical correction is more versatile and does not require adjustment, particularly when significant changes are made to column operation parameters. Some RAITH systems offer a combination of both methods for enhanced flexibility.