US 5,666,197 AGranted

Apparatus and methods employing phase control and analysis of evanescent illumination for imaging and metrology of subwavelength lateral surface topography

AssigneePolaroid Corporation

InventorJohn M. Guerra

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Abstract

Imaging and metrology devices employ controlled phase shifting and analysis of evanescent light to provide enhanced ability to image and/or resolve substantially subwavelength lateral features on a surface illuminated by the evanescent light. The light waves comprising the evanescent electromagnetic field are inhomogeneous in that their planes of equal phase are substantially perpendicular to the direction of propagation and to their planes of constant amplitude. The planes of equal phase are therefore normal to the surface to which the evanescent field is adjacent and to a sample surface illuminated by this field as well. By controlling the phase of the source of illumination and analyzing the output from the surface, either by phase analysis or phase to amplitude decoding, subwavelength lateral surface topography resolution is enhanced without sacrificing vertical resolution. Methods and means for dynamic or static phase shifting of inhomogeneous waves comprising the evanescent field are disclosed, as well as other non-imaging applications.

Claims37

Dependent claims

A phase controlled evanescent field imaging system for visualizing and measuring subwavelength topographic features of a sample, said system comprising:

lighting means for providing at least one beam of radiation having at least one predetermined wavelength and phase angle;
optical means for receiving said beam of radiation from said lighting means and creating at a surface a wavelength evanescent field having planes of equal intensity parallel to said surface and planes of equal phase substantially perpendicular to said surface so that light initially bound within said wavelength evanescent field may be converted into propagating light when the sample is brought proximate to said surface and such that, in the absence of a sample near said surface, or if a sample surface is distant from said surface, no evanescent light energy is converted into propagating light, the phase and intensity of said propagating light varying in correspondence with the topographic features of said surface and their local proximity to said evanescent field;
phase control means for selectively controlling said predetermined wavelength and phase angle of said beam of radiation such that the intensity of said evanescent light varies as a function of the phase of said beam of radiation and the lateral position of the local topographic features of the sample;
imaging means having at least one optical axis positioned to collect said propagating light and form images with it in which the topographic features of the surface are encoded as imagewise variations in image intensity in correspondence with the phase of said beam of radiation;
photodetector means for generating image signals having an amplitude that varies in accordance with the imagewise variation in intensity in said images;
and
image processing means for receiving said image signals and generating a composite image signal from which the topographic features of the sample can be visually displayed or measured.

4 more elements

A method for visualizing and measuring subwavelength topographic features of a sample utilizing phase controlled evanescent field illumination, said method comprising the steps of:

providing at least one beam of radiation having at least one predetermined wavelength and phase angle;
receiving said beam of radiation and creating at a surface a wavelength evanescent field having planes of equal intensity parallel to said surface and planes of equal phase substantially perpendicular to said surface so that light initially bound within said wavelength evanescent field may be converted into propagating light when the sample is brought proximate to said surface and such that, in the absence of a sample near said surface, or if a sample surface is distant from said surface, no evanescent light energy is converted into propagating light, the phase and intensity of said propagating light varying in correspondence with the topographic features of said surface and their local proximity to said evanescent field;
selectively controlling said predetermined wavelength and phase angle of said beam of radiation such that the intensity of said evanescent light varies as a function of the phase of said beam of radiation and the lateral position of the local topographic features of the sample;
collecting said propagating light and forming images with it in which the microtopographic features of the surface are encoded as imagewise variations in image intensity in correspondence with the phase of said beam of radiation;
generating image signals having an amplitude that varies in accordance with the imagewise variation in intensity in said images;
and
receiving said image signals and generating a composite image signal from which the topographic features of the sample can be visually displayed or measured.

4 more elements

Dependencies are inferred from the claim text.