Patent ID: 6813026
Filing Date: 2004-11-02
Classification: G01N

Abstract:
An arrangement for use in an optical metrology instrument where light is detected and analyzed after reflecting from a measurement position on a sample comprising:an optical system connected to a support, the support including a faceplate having an exterior surface that is substantially planar and faces the sample, said faceplate further including at least one aperture for transmitting the incident and reflected light between the optical system and the measurement position; a stage arranged such that the sample surface is substantially parallel to the faceplate and configured such that multiple locations on the sample surface can be sequentially located at the measurement position, the separation between the faceplate and the sample being arranged such that during measurement the volume bounded by the faceplate and the sample surface approximates a thin plate; and an apparatus for maintaining a purge-gas flow within said bounded volume, comprising: a source of purge-gas; and means for introducing said purge-gas at an injection point within the bounded volume and arranged so that a purge gas flow directed toward the measurement position travels substantially radially away from the measurement position and is exhausted at a periphery of the sample in order to purge a measurement region including the measurement position where the light is reflected.