Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J4/00—Measuring polarisation of light
  • G01J4/04—Polarimeters using electric detection means
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/21—Polarisation-affecting properties
  • G01N21/211—Ellipsometry

Definitions

• the present invention relates to spectroscopic ellipsometry.
• Ellipsometry is a non-destructive optical measurement technique which consists in comparing the state of polarization of an incident ray illuminating a sample with the state of polarization of the ray reflected by said sample, with a view to deducing information therefrom. the properties of the layers and materials constituting said sample.
• a spectroscopic ellipsometer in US-A-5608526, includes a source emitting a broadband light beam which is polarized by a polarizer to produce an incident polarized beam intended to illuminate the sample.
• An analyzer receives the ray reflected by the sample thus illuminated and produces an exit ray in response to this reflected ray.
• a detector converts the output ray into a signal capable of being processed by processing means in order to determine the phase and amplitude changes of the polarization state of the output ray caused by the reflection of the incident ray polarized on the sample.
• all the optical elements which are placed between the polarizer and the analyzer are optical elements of the reflector type, with a small angle of incidence relative to normal.
• the present invention provides a solution to this problem.
• - a source capable of emitting a broadband light ray;
• an analyzer for receiving the ray reflected by the thus illuminated sample and producing an exit ray in response to this reflected ray
• - processing means for processing the detector output signal and determining the phase and amplitude changes of the polarization state of the output ray caused by the reflection of the incident ray polarized on the sample;
• At least one reflective optical element disposed between the source and the sample and / or between the sample and the detector, to focus the incident ray and / or the reflected ray according to a chosen spot.
• the ellipsometer further comprises at least a first refracting optical element disposed between the sample and the detector and / or between the source and the sample to collect and focus said reflected ray and / or said incident ray.
• the ellipsometer according to the invention makes it possible to improve the transmission of the incident and / or reflected ray, d '' avoid any phase change effect on the polarization state of the incident and / or reflected ray, and improve the compactness and stability of the ellipsometer.
• a first optical fiber connects the analyzer to an optical device of the type belonging to the group formed by a detector, a spectrograph, a spectrometer, and the like:
• the ellipsometer according to the invention further comprises a second refracting optical element disposed between the analyzer and the input of the first optical fiber, the second refracting optical element being able to focus the exit ray from the analyzer into the entry of the first optical fiber.
• Such a second refracting optical element has the advantage of allowing the adaptation of the exit ray coming from the analyzer to the entry of the optical fiber, and if necessary to make up for a difference in depth (that is to say say in Z, in the case of an orthonormal reference frame XYZ) on the sample.
• a second optical fiber connects the source to the polarizer.
• the first and / or the second refracting optical element is a simple or compound transmission lens, preferably comprising a minimum of polarization effect and capable of forming with the associated optics an achromatic assembly.
• the refractive optics can have an anti-reflective coating in order to improve the optical transmission of the system.
• the first refractive optical element comprises an opening capable of letting the incident ray polarized towards the sample pass, and of collecting the reflected ray in order to focus it on the analyzer.
• the ellipsometer further comprises an optical compensating element disposed between the polarizer and the analyzer, upstream or downstream of the sample according to the direction of the propagation of the light.
• a compensating optical element can be achromatic, rotary, and / or removable.
• the ellipsometer according to the invention further comprises an optical blocking element disposed downstream of the polarizer in the direction of propagation of the light in order to eliminate parasitic radiation from the source and the polarizer, and keep the source image fixed, without the deflection, deflection, and chromatism of the polarizer.
• the polarizer and the optical elements associated with said polarizer as well as the analyzer and the optical elements associated with said analyzer are placed in a single optical head, which further improves the co paticity of the ellipsometer according to the invention.
• the optical head is movable in translation along the X and / or Y axis in order to move the incident ray longitudinally and / or laterally on the sample.
• the optical head is movable along the Z axis in order to move the incident ray on the sample in height.
• the ellipsometer comprises a fixed and / or mobile sample holder in X, Y and / or Z and / or in rotation around a Z axis.
• the ellipsometer comprises a window arranged in a plane substantially parallel to the surface of the sample and through which the incident ray and the reflected ray pass under oblique incidence.
• FIG. 1 schematically shows an ellipsometer having a reflective element disposed between the polarizer and the sample and a refractor element disposed between the sample and the analyzer according to the invention
• FIG. 2 schematically shows the ellipsometer of Figure 1 with an optical fiber routing the illumination ray from the source to the sample;
• FIG. 3 schematically shows the ellipsometer of Figure 1 with an ellipsometry measurement performed through a window 1 according to the invention
• FIG. 4 schematically shows a spectroscopic ellipsometer having a refractor element disposed between the polarizer and the sample and a reflector element disposed between the sample and the analyzer according to the invention
• FIG. 5 shows schematically the ellipsometer of Figure 1, to which is added another refractor element disposed between the analyzer and the input of the optical fiber according to the invention;
• FIG. 6 schematically represents the ellipsometer of FIG. 4, to which is added another refractor element disposed between the analyzer and the input of the optical fiber according to the invention:
• Figure 7 shows an ellipsometry arrangement according to the invention in which the polarizer is arranged between the reflective element and the sample;
• FIG. 8 shows an ellipsometry arrangement according to the invention in which the analyzer is placed upstream of the refractor element;
• FIG. 9 is a diagram showing an alternative embodiment in which a blocking element is placed upstream of the refractor element placed between the sample and the analyzer according to the invention.
• FIG. 10 is a diagram showing an alternative embodiment in which a blocking element is placed downstream of the polarizer according to the invention.
• FIG. 11 is a diagram showing an alternative embodiment in which a compensating element is placed upstream of the analyzer according to the invention.
• FIG. 12 is a diagram showing an alternative embodiment in which a compensating element is placed downstream of the polarizer according to the invention.
• FIG. 13 schematically shows an alternative embodiment in which a network provides a spectral dispersion crossed according to the angle of incidence according to one invention
• FIG. 14 is an ellipsometry assembly operating in infrared according to the invention.
• FIG. 15A to 15D schematically represent an optical head containing the analyzer, the polarizer and the associated optics, the means for fixing the various elements not being shown; and - Figures 16A to 16D illustrate the movement of the optical head according to the invention.
• an ellipsometer 1 comprises a source 2 emitting a broadband light beam 4.
• the source 2 is for example a xenon arc lamp which emits radiation having broadband frequency components in the 'ultraviolet, visible, and / or near infrared.
• the source may be a tungsten lamp combined with a deuterium lamp to cover a spectral range substantially similar to that of the xenon lamp.
• the broadband light ray 4 propagates in a polarizer 10 after having been focused by focusing means 6 and delimited by an entry slit 8.
• the light ray 12 which leaves the polarizer 10 is a polarized incident ray, constituting the measurement beam with a known state of polarization.
• the polarizer 10 has a circular opening to limit the size of the incident polarized ray in order to prevent the two polarization states from overlapping.
• the diameter of the circular opening of the polarizer is of the order of 1 mm and the distance between the slot 8 and the polarizer 10 is of the order of 50 mm.
• the ray 4 from the source 2 can be routed through the polarizer 10 via an optical fiber 3. Under these conditions, the source 2 can advantageously be offset, as will be described in more detail below.
• the polarized incident ray 12 strikes a mirror 14 with an angle ⁇ 1 of low incidence (that is to say close to the normal NI at the reflecting surface of the mirror 14).
• the mirror 14 is for example an elliptical mirror.
• the mirror 14 projects the image of the entry slit 8 according to a small spot (for example 25 ⁇ X 25 ⁇ , (of square shape) on the sample 16.
• the polarized incident ray 12 is projected on the sample 16 at a high angle of incidence AI with respect to the normal N2 of the sample.
• the digital aperture of the mirror 14 is of the order of 0.15 ° and the angle of incidence AI of the polarized incident ray 12 relative to the normal N2 to the sample 16 is of the order of 63.5 ° to 80.5 °.
• the sample 16 is for example made of a semiconductor material with at least one thin layer deposited on a transparent substrate.
• the sample comprises a front face FAV which receives the incident beam and a rear face FAR in contact with the sample holder.
• the invention obviously finds an application for samples of all kinds and made of any material.
• the sample 16 is placed on a sample holder 18.
• the sample holder 18 can be fixed and / or mobile in an orthonormal coordinate system along the axes X, Y, Z and / or mobile in rotation.
• the sample holder can also be hung.
• the ellipsometry measurement is carried out through a window or porthole 19, as described in the French Application filed on May 26, 2000 under number 00 06771 by the Applicant and entitled "Method and apparatus of ellipsometric metrology for sample contained in a chamber or the like".
• the window 19 is arranged in a plane substantially parallel to the surface of the sample 16.
• the window 19 at least partially closes the chamber (not shown) in which the sample is placed.
• the window 19 is a silica type material, isotropic and transparent in the ultraviolet.
• the incident 12 and reflected 20 rays pass through the window under oblique incidence.
• a refracting optical element 22 receives the ray reflected by the sample (if necessary, via the window 19). This refracting optical element 22 then focuses the reflected ray 20 through an analyzer 24.
• Placing a refracting element and a reflecting element on either side of the sample according to the invention makes it possible to ensure that the source and the detector are arranged on the same side with respect to the spot on the sample, which in particular reduces the size of the ellipsometer.
• the refracting optical element 22 replaces the collecting mirror and the tracking mirror placed between the sample and the analyzer.
• the refractive optical element 22 the spectroscopic ellipsometer according to the invention is therefore more compact and the transmission of the incident and / or reflected ray, in particular the transmission of the polarization state of the reflected ray, is improved in the extent to which the transmission lenses minimize the polarization phase change effects which are generally generated by the reflective elements.
• a blocking element of the slot type 30 is provided downstream of the analyzer 24.
• This slot 30 can be that of a spectrometer (not shown).
• the ray 28 from the analyzer 24 is conveyed in an optical fiber 32 via the slot 30.
• the opening of the slot 30 is adapted to the inlet 34 of the optical fiber 32.
• a blocking optical element of the slot type 26 is arranged downstream of the refracting optical element 22 in the direction of the propagation of the light in order to block certain radiations reflected by the sample.
• the width of the slit 26 determines the angles of incidence associated with the ray reflected by the sample and the arrangement of the center of the slit determines the average angle of incidence associated with the measurement of the reflected ray.
• actuator means are provided for controlling the width of the slot 26 as well as the arrangement of the center of the latter.
• the width and the center of the slot 26 are fixed.
• FIG 4 there is shown a variant of the spectroscopic ellipsometer of Figure 1 in which the refractor / transmitter optical element 22 is disposed in the outward path (i.e. between the polarizer and the 'sample) instead of being placed in the return path (i.e. between the sample and the analyzer).
• FIG. 4 we find the elements 2, 4, 6, 8 and 10 of the ellipsometer of FIG. 1.
• the polarized incident ray 12 is focused on the sample 16 through the refractor / transmitter optical element 22 according to a high angle of incidence AI with respect to the normal N2 of the sample (for example 71 °).
• the reflected ray 20 is collected by the mirror 14 to then be directed towards the analyzer 24.
• the blocking element 26 is placed near the mirror 14 in order to define the radiation of the reflected ray 20 intended to be analyzed by the analyzer 24.
• the refractor element 22 and the reflector element 14 are arranged on either side of the sample so as to place the illumination arm and the analysis arm of the ellipsometer on the same side.
• FIG. 5 there is shown a variant of the ellipsometer of Figure 1 in which another refractor / transmitter optical element 36 is disposed between the analyzer 24 and the input 34 of the optical fiber 32.
• This element refractor / transmitter optic 36 focuses the output ray 28 from the analyzer into the input 34 of the optical fiber 32.
• Such a refractor / transmitter optical element 36 has the advantage of allowing the adaptation of the output ray from the analyzer at the input of the optical fiber, and thus make up, if necessary, for a deviation in depth, that is to say at Z (in the case of an orthonormal reference frame XYZ) on the sample.
• the refractor / transmitter optical element 36 and / or 22 is a simple or compound transmission lens, preferably comprising a minimum of polarization effect, when it is composed, the lens 22 or 36 forms with its optics associated an achromatic set.
• the refractive optics may have an anti-reflective coating to improve the optical transmission of the system.
• the refractor / transmitter optical element 22 can be defined according to an opening suitable for letting the incident ray 12 coming from the polarizer pass towards the sample and for collecting the reflected ray 20 coming from the sample in order to focus it towards the analyzer 24.
• FIG 6 there is shown a variant of the ellipsometer described with reference to Figure 4 in which has been introduced a transmission lens 36 between the slot 30 and the inlet 34 of the optical fiber 32.
• FIG. 7 a variant of the ellipsometer of FIG. 1 is shown in which the polarizer 10 is placed between the mirror 14 and the sample 16. This arrangement can obviously be used in combination with the variants described in the other figures.
• FIG 8 there is shown another variant of the ellipsometer according to the invention, in which the lens 22 is arranged downstream of the analyzer 24 in the direction of the propagation of light.
• This arrangement also like the others, can obviously be used in combination with the variants described in the other figures.
• FIG. 9 another variant of the ellipsometer described with reference to FIG. 5 has been shown.
• the blocking element 26 is arranged upstream (in the direction of propagation of the light) of the transmission lens 22 instead of being disposed downstream as in the ellipsometer of FIG. 5.
• a blocking element 40 is disposed upstream of the analyzer 24.
• the blocking elements 26 and 40 as well as 30 make it possible to optimally block the reflected ray.
• FIG. 10 Another variant of the spectroscopic ellipsometer has been described in which, relative to the ellipsometer of FIG. 9, the blocking element 40 has been removed and the blocking element 8 has been placed in downstream of the polarizer 10 instead of being placed upstream as with reference to FIG. 9.
• the arrangement of the blocking element 8 downstream of the polarizer in the direction of the propagation of the light makes it possible to eliminate the parasitic radiations coming from the source and the polarizer and keep the source image fixed without the deflection, deflection and chromatism of the polarizer.
• FIG. 11 another variant of the spectroscopic ellipsometer of the invention has been shown.
• a blocking element 40 followed by a compensator 50 has been placed upstream of the analyzer 24.
• the compensating element 50 comprises a mirror.
• the compensating element 50 has the function of rotating the phase of the polarized light by a known value in order to be placed in optimal measurement conditions whatever the nature of the sample measured.
• FIG. 12 another variant of the spectroscopic ellipsometer according to the invention has been shown in which a compensating element 50 is disposed between the polarizer 10 and the blocking element 8.
• FIG. 13 there is shown a variant of the ellipsometer according to the invention in which a cross-dispersion function wavelength / angle of incidence AI is performed via a network 60 arranged downstream of the slot 30 in the direction of light propagation.
• the network 60 includes vertical lines 62 which make it possible to achieve a horizontal spectral dispersion 72 on a detector 70 of the matrix CCD type, and a vertical dispersion according to the angle of incidence 74.
• the assembly provides for a Michelson type 80 interferometer.
• the interferometer 80 comprises at least one movable mirror 82 on command 84.
• the polarizer 10 is here of the grid type and is IR compatible.
• a lens 22 On the detection side, a lens 22 is provided, an analyzer 24 preferably with a grid and a slot 90 disposed upstream of the analyzer 24.
• the slot 90 is of the knife or blocking element type to eliminate parasitic reflections from the rear face. of the sample, as described with reference to the French Application filed by the Applicant on July 17, 2000, under the number 00 09318, and entitled "Ellipsometer with high spatial resolution operating in the infrared".
• the detector 120 is preferably a detector of the Mercury-Cadmium-Tellurium type, liquid nitrogen or the like and compatible with infrared operation.
• a mirror 100 advantageously focuses the beam coming from the analyzer 24 on the detector 120.
• a device for selecting angles of incidence 110 is coupled to the mirror 100 in order to select, for measurements by the detector, only the radiation reflected by the sample under oblique incidence in a range of selected angles of incidence.
• the refractor 22 and reflector 14 elements are advantageously arranged on either side of the sample in order to arrange the source and the detector on the same side with respect to the spot on the sample, in particular to reduce the dimension of the ellipsometer and thus save space and weight.
• optical fibers on the source side and / or on the detection side also makes it possible to remotely deport optical devices and easily carry out multiplexing, which also saves time.
• the Applicant has observed that by placing the illumination arm and the analysis arm on the same side with respect to the sample, said illumination and analysis arms can be arranged in the same optical head housed in an ellipsometry box capable of being moved along X, Y, and / or Z axes.
• FIG. 15A to 15D there is shown such an optical head 200 containing the illumination and analysis arms of a spectroscopic ellipsometer according to the invention.
• the head or box 200 is of generally parallelepipedal shape, for example 220 mm in height, 315 mm in length and 83 mm in width.
• the box 200 further comprises a camera 210 intended to be placed at normal to the sample.
• the transmission lens 22 includes an opening capable of allowing the incident polarized ray 12 to pass towards the sample, and to collect / focus the ray reflected through the analyzer 24.
• the polarizer 10 and the associated elements of the illumination arm are placed in a first support 220.
• the support 220 is placed relative to the sample and to the mirror 14 so as to carry out an ellipsometry measurement as taught with reference to FIGS. 1 to 14.
• the support 220 is fixed in the box using suitable fixing means.
• the analyzer 24 and the associated elements of the analysis arm are placed in a second support 230.
• the support 230 is placed relative to the sample and to the lens 22 so as to carry out an ellipsometry measurement as taught with reference to FIGS. 1 to 14.
• the support 230 is fixed in the box using suitable fixing means.
• the support 220 comprises the polarizer 10 and the blocking element 8.
• the illumination arm is connected to the source 2 via an optical fiber 3 housed inside the box and one of the ends of which is connected to the source thus disposed outside of the box 200.
• the support 230 comprises the analyzer 24, the blocking element 26, the blocking element 40 and the lens 36.
• the spectrometer (not shown) is preferably placed outside the box and connected to the support 230 by an optical fiber 32.
• the detector and the processing means are arranged outside the box 200 and connected to the box via the optical fibers 3 and 32.
• the box 200 is movable in translation along the axes X, Y, and / or Z in order to move the ray incident on the sample longitudinally, laterally, and / or vertically.
• the sample holder 18 can be kept fixed.
• the sample holder 18 is also able to be movable in X, Y and / or Z translation.
• the sample holder is capable of being movable in rotation about a vertical axis (in Z) .
• the sample holder is able to support circular samples of 300 mm in diameter for example.
• Such an ellipsometry head or box supporting the illumination and analysis arms has the advantage of further improving the compactness of the ellipsometer according to the invention.
• Such a head 200 also has the advantage of being connected by optical fibers to optical devices (source, detector, remote, interchangeable, multiplexable spectrograph, processing means, etc.).
• the means for moving the head 200 in translation in X and / or in Y, and / or in Z, respectively 240, 250 and 260 can be belt, worm-gear or equivalent means.
• the travel in X is for example of the order of 300 mm, in Y of the order of 500 mm and in Z of the order of 100 mm.
• the head 200 and the sample holder 18 as well as the means for moving the head are arranged on a plate 270.
• the ellipsometer according to the invention may comprise another optical head (not shown) similar to the optical head 200 and able to move close to the optical head 200 in order to carry out another measurement of ellipsometry close to the measurement carried out by the optical head 200.

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• 2000
  • 2000-07-17 FR FR0009318A patent/FR2811761B1/fr not_active Expired - Fee Related
• 2001
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