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Laser-Based Thermal Particle Detector

IP.com Disclosure Number: IPCOM000040127D
Original Publication Date: 1987-Sep-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 3 page(s) / 37K

Publishing Venue

IBM

Related People

Utterback, SG: AUTHOR

Abstract

A laser-based thermal detector device can be used to provide fast detection of contamination on a variety of surfaces in standard atmospheres. The device uses the characteristic thermal signature of contaminants to identify them by their rapid thermal rise during the short time they are heated. It is able to distinguish a contaminant from the background by using a short wavelength infrared (IR) detector which is not sensitive to ambient temperature blackbody thermal emissions. The infrared detector operates to restrict the detector field of view with a cooled aperture, using collection optics with an effective f-number of 16 or greater. A diagram of the device is shown in the figure. The operating principle is to detect the contaminant's infrared thermal emission upon heating.

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Laser-Based Thermal Particle Detector

A laser-based thermal detector device can be used to provide fast detection of contamination on a variety of surfaces in standard atmospheres. The device uses the characteristic thermal signature of contaminants to identify them by their rapid thermal rise during the short time they are heated. It is able to distinguish a contaminant from the background by using a short wavelength infrared (IR) detector which is not sensitive to ambient temperature blackbody thermal emissions. The infrared detector operates to restrict the detector field of view with a cooled aperture, using collection optics with an effective f-number of 16 or greater. A diagram of the device is shown in the figure. The operating principle is to detect the contaminant's infrared thermal emission upon heating. In this device, the thermal pump is the beam from an ultraviolet laser 1. The beam is directed with mirrors through a beam expander 2 and a square aperture 3. The beam is spatially filtered such that only the center of the beam profile is used for the pump. This assures uniform illumination over the width of the beam. The beam is then directed off of a rotating mirror beam scanner 4 through a lens 5 into a reflecting microscope objective 6. The objective lens is positioned such that the beam is defocused to a square-micron-sized spot with a power of about 100 milliwatts at the surface to be inspected. The surface is vacuum mounted to an XY set of translation stages 7 which are driven by stage drivers 9 at a preset velocity in the X and Y directions. The infrared emission from the surface is collected with a parabolic mirror lens assembly 8 which directs the beam away from the surface and focuses it onto an infrared detector 9. The detector is a cooled InSb detector array with a restricted field of view, mounted on a Joule- Thompson cold-finger. The scan is accomplished using a combination of the laser line scan and the XY scan of the translation stages. The laser beam is continually swept across the wafer surface in the positive X direction at a preset velocity and frequency while the stages are simultaneously translationally scanned at the same velocities. The operation of the scanning mirror and the translation stages is controlled via a computer 11, as is the data collection and storage via preamp 12 and signal p...