Nanometrics Inc.

John D Heaton

Roger R Lowe-Webb

Weidong Yang

Blaine R Spady

Richard A Yarussi

Robert Buchanan

Guoguang Li

Pablo I Rovira

Silvio J Rabello

Duane C Holmes

Dan M Colban

Christopher W Blaufus

Guonguang Li

Guorong Vera Zhuang

A metrology/inspection system moves the imaging and/or measuring equipment of the system relative to a wafer. Accordingly, measurement or inspection of the wafer does not require that the wafer be mounted on a precision stage. This allows the wafer to be at rest on any structure native in a processing apparatus when the system measures or inspects the wafer. Accordingly, measurement does not require removing the wafer from the processing apparatus and does not delay processing since the wafer can be measured, for example, during a required cool down period of device fabrication process. Alignment of an optical system includes pre-alignment base on edge detection using the optical system and more precise alignment using image recognition. An R-&#x3b8; stage can position the optical system at inspection areas on the wafer. Image rotation can provide a fixed orientation for all images at the various inspection areas and can maintain the fixed orientation when moving from one inspection area to the next.

Metrology/inspection positioning system

A metrology system includes a positioning system that produces linear and rotational motion between an imaging system and the wafer. The imaging system produces signals representing the image of the wafer in the field of view of the imaging system. A control system receives and processes the image signals, and generates corrected signals that compensate for rotational movement between the imaging system and the wafer. In response to the corrected signals, a monitor displays an image with the orientation of features on the wafer within the field of view unaffected by the rotational movement.

Image control in a metrology/inspection positioning system

An alignment target includes periodic patterns on two elements. The alignment target includes two locations, at least one of which has a designed in offset. In one embodiment, both measurement locations have a designed in offset of the same magnitude but opposite directions. For example, two separate overlay patterns that are mirror images of each other may be used. Alternatively, the magnitudes and/or directions may vary between the measurement locations. The radiation that interacts with the measurement locations is compared. The calculated difference is extremely sensitive to any alignment error. If the difference between the patterns is approximately zero, the elements are properly aligned. When an alignment error is introduced, however, calculated difference can be used to determine the error. In one embodiment, the alignment target is modeled to determine the alignment error. In another embodiment, additional overlay patterns with additional reference offsets are used to determine the alignment error.

Alignment target with designed in offset

An alignment system for aligning two elements includes an alignment target with periodic patterns on each element. The alignment target includes two locations, at least one of which has a designed in offset. If desired, both locations may have designed in offsets of the same magnitude but in opposite directions. The diffraction patterns produced at the two locations are compared. If the difference between the patterns is at a minimum, the elements are properly aligned. When an alignment error is introduced, however, the calculated difference can be used to determine the error. In another embodiment, bands in the moir&#xe9; fringes from the different locations may be compared to determine the alignment error. The two elements may then be moved relative to each other to minimize the alignment error. Thus, the alignment target may advantageously be used in any alignment system, such as an exposure tool.

Positioning two elements using an alignment target with a designed offset

An alignment target includes periodic patterns on two elements. The periodic patterns are aligned when the two elements are properly aligned. By measuring the two periodic patterns with an incident beam having a single polarization state and detecting the intensity of the resulting polarized light, it can be determined if the two elements are aligned. The same polarization state may be detected as is incident or different polarization states may be used. A reference measurement location may be used that includes a third periodic pattern on the first element and a fourth periodic pattern on the second element, which have a designed in offset, i.e., an offset when there is an offset of a known magnitude when the first and second element are properly aligned. The reference measurement location is similarly measured with a single polarization state.

Measuring an alignment target with a single polarization state

Method and apparatus for using an alignment target with designed in offset

An encoder includes a layer on the scale that has a thickness that varies as a function of position along the length of the scale. The position of the sensor head with respect to the scale may be determined by measuring the thickness of the layer or index of refraction, e.g., using a reflectometer, and converting the thickness to the lateral position. In one embodiment, the thickness of the layer is used to provide a rough position of the sensor head with respect to the scale and an alignment target that includes periodic patterns on both the sensor head and scale is used to provide a refined position.

Encoder measurement based on layer thickness

An encoder uses an alignment target that includes periodic patterns on the movable element and the stationary element. The alignment target may include at least two measurement locations, each location having a different offset between the periodic pattern on the movable element with respect to the periodic pattern on the stationary element. Alternatively, two measurements using different polarization states may be made at one location. When the periodic patterns on the movable element and the stationary element are aligned, the difference between the two measurements will produce a minimum, i.e., approximately a zero value plus noise. By counting the minima, the precise position of the movable element with respect to the stationary element can be determined. The resolution of the encoder may be further increased using reference measurements.

Encoder with an alignment target

A polar coordinate stage that may be used in a chamber includes a rotating chuck that moves in a linear direction and has the motors that drive the motion of the chuck outside the chamber. The stage can include a linkage of arms to support and drive the linear motion of the chuck. The chuck is coupled to a horizontal rail such that rotational motion of a first arm is translated into precise linear motion of the chuck along the horizontal rail through a second arm. In addition, a system of pulleys within the arms translates rotational (or linear) motion through the arms and rotates the chuck. Vertical motion may be provided by an actuator between the second arm and the chuck or by a motor under the stage. Because of the compact nature of the stage, it can be easily placed within a chamber.

Precision polar coordinate stage

A normal incidence spectroscopic polarimeter is combined with an oblique incidence spectroscopic polarimeter to provide an accurate characterization of complex grating structures, e.g., structures with sloping sidewalls, with notches and with multiple underlying layers. The normal incidence spectroscopic polarimeter includes a polarizing element that is in the path of the normal incidence light beam such that the light beam is transmitted through the polarizing element before reaching the sample and after being reflected off the sample. The two systems may advantageously share a single light source and/or the spectrophotometer.

Combination of normal and oblique incidence polarimetry for the characterization of gratings

An optical measurement instrument that detects and analyzes reflected light includes a sample support, such as a wafer supporting chuck, with a sample bearing surface that is configured so as to not reflect light back to the optical measurement instrument. In one embodiment, the sample bearing surface of the sample support is a layer of material that absorbs light in the wavelength or wavelengths being used by the optical measurement instrument. For example, a hard plastic, such as poly-ether-ether-ketone (PEEK), may be used to absorb light in the infrared wavelengths. In another embodiment, the entire sample support may be manufactured from the light absorbing material. In yet another embodiment, the top surface of the sample support is configured with light scattering depressions, which prevent light that is incident on the sample bearing surface from being reflected back to the optical measurement instrument.

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Fremont, CA, United States of America

John D Heaton