Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes
  • G02B21/0004—Microscopes specially adapted for specific applications
  • G02B21/0016—Technical microscopes, e.g. for inspection or measuring in industrial production processes
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
  • G01B11/0616—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating
  • G01B11/0675—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of coating using interferometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/24—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures
  • G01B11/2441—Measuring arrangements characterised by the use of optical techniques for measuring contours or curvatures using interferometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
  • G01B9/02056—Passive reduction of errors
  • G01B9/02057—Passive reduction of errors by using common path configuration, i.e. reference and object path almost entirely overlapping
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/02—Interferometers
  • G01B9/0209—Low-coherence interferometers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B9/00—Measuring instruments characterised by the use of optical techniques
  • G01B9/04—Measuring microscopes
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B21/00—Microscopes

Definitions

• the present invention relates to a device for three-dimensional inspection of structured objects. It also relates to a method of inspection of structured objects implemented in this device.
• the field of the invention is more particularly but in a nonlimiting manner that of measurement and dimensional control of devices in the field of microsystems (MEMs) and in microelectronics.
• Manufacturing techniques in microelectronics and in microsystems evolve especially towards the realization of complex volumic structures, able to allow a better integration in volume of the functions of these systems.
• Optical measurement techniques are widely used for their ability to integrate into industrial environments and to provide accurate information in measurement ranges from a few millimeters to less than the nanometer. They have the advantage of allowing measurements without contact, without degradation or sample preparation, with devices whose cost remains reasonable.
• imaging techniques based on conventional microscopy, usually in reflection, which make it possible to inspect surfaces and patterns and to carry out dimensional measurements in a plane substantially perpendicular to the plane by image analysis. axis of observation.
• These devices usually include a light source, a camera and a magnified imaging optics adapted.
• Their lateral resolution, of the order of a micrometer, is essentially determined by the optical diffraction phenomenon, the magnification and the quality of the optics. Measurements are usually done in the visible part or near ultraviolet light spectrum, which limits the diffraction and use cameras and optics of reasonable cost.
• the imaging microscopy can be supplemented by interferential measurements, according to interferometric microscopy techniques.
• the device is then supplemented by an interferometer which allows to superpose on the camera the light coming from the surface of the object to be measured (the measurement wave) and a reference light wave coming from the same source and reflected by a surface reference. Interference between the measurement and reference waves is thus obtained, which makes it possible to measure the topology of a surface with a depth resolution of the order of one nanometer.
• measurements are usually made in the visible part of the light spectrum.
• Interferometric microscopy makes it possible, for example, to effectively measure topography on a first surface, or measurements of thicknesses of thin layers that are substantially transparent at the wavelengths used.
• it makes it difficult to measure thicknesses of material greater than a few tens of microns without the delicate optical compensations to be used, and of course it does not make it possible to measure silicon thicknesses, insofar as this material is not not transparent at visible wavelengths.
• interferometric measurement techniques in particular based on interferometry with low coherence in the infrared.
• materials widely used in microelectronics or in microsystems such as silicon or gallium arsenide are substantially transparent for wavelengths in the near infrared.
• FR 2892 188 Courteville describes a method and a device for measuring the height of patterns that have a high aspect ratio.
• the device comprises a substantially punctual measurement beam, which covers a zone limited to the surface of the object.
• the height measurement of the patterns covered by the beam is obtained by dividing the incident wavefront between the high and low parts of the patterns and interferometric measurement of the phase shifts induced between these fractions of wavefronts after a modal filtering step.
• the device described in FR 2892 188 can advantageously be implemented at infrared wavelengths for simultaneously measuring thicknesses of layers of semiconductor materials.
• the characterization of elements in microelectronics or in microsystems often requires simultaneous measurements of topology and measurements of height or thickness made at particular locations.
• the location of these measurements of height or thickness must sometimes be very precise, for example in "chip level packaging" applications where openings or vias of a few micrometers in width spaced several tens or hundreds of micrometers are drilled through semiconductor substrate.
• height or thickness measurements must be made in a limited extent area to take into account only certain patterns. In all these cases, the infrared measuring beam must therefore be precisely adjusted in position and / or in magnification on the surface of the object.
• Document FR 2718231 of Canteloup et al. which describes a method of measuring height or thickness using a spot measuring beam whose position is displayed on a camera.
• the beam of measurement passes through the imaging optics of the camera so as to appear in the visualized field.
• This device makes it possible to precisely position the measuring beam on the surface of the object.
• the interferometric measurement wavelength is in this case included in the imaging wavelengths for which the imaging optics is optimized.
• the method described in FR 2 718 231 can not be transposed to an interferometric measurement system in the infrared.
• the object of the present invention is to provide a structured object inspection device capable of simultaneously producing topography measurements, thickness measurements of layers and pattern height.
• a structured object inspection microscope device comprising:
• optical imaging means capable of producing on the camera an image of the object according to a field of view, which optical imaging means comprising a distal objective disposed on the object side, and
• a low-coherence infrared interferometer comprising a measurement beam with a plurality of infrared wavelengths, capable of producing measurements by interference between retro-reflections of said measuring beam and at least one distinct optical reference,
• the interferometer with low infrared coherence is balanced so that only the retro-reflections of the measuring beam occurring at optical distances close to the optical distance traveled by said beam to the object, defining a measurement range, produce measurements.
• the distal lens can be designed to produce images at visible wavelengths. It can include a microscope objective.
• the imaging system of the device according to the invention can thus comprise components conventionally used in microscopy, which has substantial advantages in terms of costs and industrial development.
• the camera can be a CCD camera.
• the device according to the invention can produce an image of the object at an optical wavelength or in a plurality of optical wavelengths substantially within a range of 200 to 1100 nanometers, ie in the near ultraviolet range. (Around 200 to 400 nm), the visible (around 400 to 780 nm) and / or the near infrared (around 780 to 1100 nm).
• the interferometer with low infrared coherence can produce, without limitation, dimensional measurements made along axes substantially parallel to the optical axis of the imaging system, such as, for example, thickness measurements of layers or height.
• dimensional measurements made along axes substantially parallel to the optical axis of the imaging system, such as, for example, thickness measurements of layers or height.
• these measurements can be made through materials that are not transparent at visible wavelengths such as silicon and gallium arsenide.
• the measurement beam of the low coherence interferometer may include wavelengths between 1100 and 1700 nanometers. It may in particular include wavelengths located near 1310 nm (nanometers) and / or 1550 nm.
• the device according to the invention thus makes it possible, simultaneously:
• the measurements with the infrared interferometer are carried out through the distal part of the imaging optics, which allows a real integration of all the measurements.
• This configuration raises a particular difficulty because the interferometers are in general very sensitive to parasitic reflections experienced by the measurement beam, which rapidly degrade the characteristics of measured phases. This is why in general they are implemented separately imaging systems, or in any case with optics optimized for their working wavelength, especially from the point of view of antireflection treatments.
• the device according to the invention may furthermore comprise first magnification means making it possible to change the magnification of the optical imaging means so as to simultaneously modify the field of view and the dimension of the measurement zone in substantially identical proportions.
• These first magnification means may be optical elements traversed simultaneously by the imaging beam and the measuring beam. They make it possible to simultaneously adjust the observed area (the field of view) and the measurement area covered by the measuring beam on the surface of the object, so as to adapt them to the characteristic dimensions of the patterns of the object to be measured. measure.
• These first magnification means may comprise at least one of:
• a turret equipped with optics of different magnifications, such as microscope objectives, and
• the device according to the invention may furthermore comprise second magnification means making it possible to modify the magnification of the measurement beam, so as to modify the dimension of the measurement zone relative to the field of view.
• These second magnification means which may be optical elements traversed only by the measuring beam, make it possible to give the device an additional degree of freedom for adjusting the size of the measurement zone.
• the device according to the invention may further comprise relative displacement means of the object and optical imaging means, for positioning the field of view at the desired location on the object.
• the device according to the invention may also comprise relative displacement means of the object and the measuring beam, that is to say, to move the measurement area in the field of view.
• the device according to the invention may further comprise lighting means, producing a lighting beam with visible wavelengths, arranged so as to illuminate the object through the distal lens.
• lighting means producing a lighting beam with visible wavelengths, arranged so as to illuminate the object through the distal lens.
• This configuration corresponds to a conventional configuration of reflection microscopy.
• the device according to the invention may furthermore comprise, at the level of the distal objective, a solid-field interferometer able to produce on the camera interference fringes superimposed on the image of the object. , so as to deduce a topography of the surface of the object.
• the solid field interferometer may comprise a substantially transparent dichroic element at the wavelengths of the measurement beam.
• This dichroic element can be for example, according to the type of interferometer used, a mirror, a splitter blade or a splitter cube. It can be arranged so that the infrared interferometric measurement beam undergoes a minimum of reflections through the solid field interferometer, which remains fully functional at the useful wavelengths of the imaging system.
• the device according to the invention makes it possible simultaneously to carry out profilometry measurements, that is to say of the three-dimensional shape of the surface of the object and measurements accessible only through interferometry. infrared.
• the device according to the invention may further comprise lighting means arranged opposite the object with respect to the imaging means, comprising a light source with longer wavelengths. at a micrometer.
• the measurements are therefore made in transmission.
• This embodiment is particularly interesting for making measurements with the infrared interferometer on the side of the rear face (that is to say the substrate) of microelectronic components for example. It is thus possible to visualize, in the form of variations in light density, particularly opaque areas such as metal tracks for positioning the measuring zone of the infrared interferometer precisely with respect to these elements. It is possible to implement this embodiment with cameras whose sensor is based on silicon, which retain sufficient sensitivity to wavelengths greater than 1 micrometer for which the silicon substrate of the object becomes transparent.
• the interferometer with low infrared coherence implemented in a device according to the invention may, in a non-limiting way, make it possible to measure in the measurement range at least one of the following elements:
• the optical thickness of at least one layer of substantially transparent material at wavelengths of the measuring beam is the optical thickness of at least one layer of substantially transparent material at wavelengths of the measuring beam
• the interferometer with low infrared coherence implemented in a device according to the invention can also make it possible to measure refractive indices, for example by measuring optical thicknesses of layers of materials whose geometrical thickness could be determined otherwise. This type of measurement can for example make it possible to verify the nature of a material.
• the device according to the invention may further comprise a viewing beam superimposed on the measurement beam, which viewing beam comprises at least one wavelength detectable by the camera.
• This viewing beam can be adjusted in such a way that it intercepts the surface of the object according to the measurement zone, which makes it possible to visualize the latter directly on the image produced by the camera.
• the device according to the invention may further comprise digital processing and display means capable of producing an image of the field of view comprising a display of the measurement zone.
• This display of the measurement zone can be generated by software means and superimposed on the image of the surface of the object.
• the low-coherence infrared interferometer is balanced so that only the retro-reflections of the measuring beam take place at optical distances close to the optical distance traveled by said beam to the object, defining a measurement range , produce measurements.
• the location of the measurement zone in the image of the field of view can be memorized during a prior calibration, in particular when the position of the measurement beam in the imaging means, therefore in the field of view, is fixed. .
• the information from the camera and the low coherence interferometer can be combined to produce a three-dimensional representation of the object.
• FIG. 1 illustrates an embodiment of an inspection device according to the invention
• FIG. 2 illustrates embodiments of solid field interferometers in an inspection device according to the invention, according to FIG. 2a, the so-called Michelson configuration and FIG. 2b, the so-called Mirau configuration,
• FIG. 3 illustrates an embodiment of a low-coherence infrared interferometer in an inspection device according to the invention
• FIG. 4b illustrates layer thickness measurements obtained with an inspection device according to the invention, for a position on the surface of an object illustrated in FIG. 4a,
• FIG. 5b illustrates measurements of pattern height obtained with an inspection device according to the invention, for a position on the surface of an object illustrated in FIG. 5a.
• an inspection device comprises an imaging channel and an interferometric measurement channel intended to provide measurements on an object to be inspected 4.
• the imaging path comprises a camera 1, equipped with a CCD matrix sensor 17. It also comprises optical imaging means 2 capable of forming an image 50 of the object 4 on the sensor 17 of the camera 1, according to a field of view substantially proportional to the magnification of the optical imaging means 2 and to the size of the sensor 17.
• the optical imaging means 2 comprise, in a conventional configuration in microscopy, a distal objective 3 disposed on the object side and an optical relay or tube lens 23, which are traversed by the imaging beam 22 consisting of the light from the object 4 and projected onto the sensor 17 of the camera 1.
• the distal lens 3 is a microscope objective optimized for visible wavelengths.
• the infrared interferometric measurement channel comprises an infrared measuring beam 6 inserted in the optical imaging means 2 by coupling means 7 so that it is incident on the object 4 according to a measurement zone essentially comprised in the field of view of the imaging path.
• the measuring beam 6 is derived from a low-coherence infrared interferometer 5 and brought by a monomode optical fiber 21 to a collimator 20.
• This collimator 20 forms a substantially collimated beam 6 which is inserted in the optical imaging means 2 by a separating plate, preferably dichroic 7.
• a dichroic plate which reflects the infrared radiation and transmits the visible light, is not essential to the operation of the device but it minimizes losses and parasitic reflections both in the imaging path and in the interferometric measurement pathway.
• the beam 6, substantially collimated and deflected by the dichroic plate 7, propagates in the optical imaging means 2 in a direction substantially parallel to their optical axis 24 to be focused on the object by the distal lens 3.
• the collimator 20 and the distal lens 3 constitute an imaging system which images the core of the fiber 21 from which the measurement beam 6 is drawn on the object 4.
• the measurement zone covered by the measuring beam 6 on the object 4 is determined by the magnification of the imaging system 20 and 3, the diffraction and the possible effect of a slight defocusing of the measuring beam 6.
• the measuring beam 6 When the measuring beam 6 is incident on the object 4 in a direction substantially perpendicular to the surface of the latter, within tolerance limits depending on its angular aperture at the distal lens 3, the reflections that occur on the The interfaces of the object 4 are recoupled in the optical fiber 21 and processed in the interferometer 5.
• the device according to the invention comprises displacement means 10 which make it possible to position the field of view at the desired location on the object 4.
• These displacement means comprise displacement means in the plane perpendicular to the optical axis 24. the sample holder supporting the object 4, and moving means in the direction of the optical axis 24 of the entire system relative to the object 4.
• the device according to the invention comprises means for changing the magnification, so as to:
• the magnification is adjusted by modifying the magnification of optical elements inserted between the dichroic plate 7 and the object 4 and traversed simultaneously by the measuring and imaging beams 6 and 22, so that simultaneously affecting the field of view and the dimension of the measurement zone in substantially identical proportions.
• the magnification is modified by changing the objective of microscope 3, so as to obtain on the imaging path magnifications of the order of x2 to x50 mainly.
• the device according to the invention is equipped with a turret lens holder, possibly motorized, which allows to change the objective 3 easily.
• the physical dimensions of the field of view (viewed on the camera 1) and the measurement area (of the infrared metrology) are simultaneously adjusted to the surface of the object in substantially similar proportions. .
• the object 4 is visualized on a field twice as small as with an objective x 10, and the size of the measurement zone on the object 4 is also substantially twice as small.
• the size in pixels of the measurement zone such as "seen" by the detector 17 of the camera 1 is substantially independent of the magnification of the lens 3, and therefore it can accurately position this measurement area using the imaging at all magnifications.
• the device according to the invention comprises a light source 12 whose emission spectrum comprises visible wavelengths.
• This light source 12 comprises white light-emitting diodes (LEDs). It emits a lighting beam 25 which illuminates the object 4 so as to allow reflection imaging.
• the illumination beam 25 is not shown in FIG. 1 after the blade 18.
• the interferometer 5 is a low-coherence interferometer operating in the infrared, at wavelengths for which many materials common in microelectronics such as silicon are substantially transparent.
• the interferometer 5 is intended to operate through the imaging means 2 and in particular the distal lens 3 which are optimized for visible wavelengths, which are standard in microscopy.
• optical antireflection treatments optimized for visible wavelengths tend to substantially increase the reflectivity of infrared surfaces, sometimes up to 30%, which constitutes very severe measurement conditions for infrared interferometry.
• the method implemented in the interferometer 5 makes it possible to make it practically insensitive to parasitic reflections.
• This result is achieved by implementing a principle of low coherence interferometry in which only the reflections of the measuring beam 6 have occurred in a zone or extent of measurement encompassing the interfaces of the object 4 (or at least one optical distance equivalent to the optical distance between the collimator 20 and the object 4 along the beam 6) can cause exploitable interference.
• the heart of the interferometer 5 is a double Michelson interferometer based on monomode optical fibers. It is illuminated by a fiber light source 42 which is a superluminescent diode (SLD) whose central wavelength is of the order of 1300 nm to 1350 nm and the spectral width of the order of 60 nm. The choice of this wavelength corresponds in particular to criteria of availability of the components.
• a fiber light source 42 which is a superluminescent diode (SLD) whose central wavelength is of the order of 1300 nm to 1350 nm and the spectral width of the order of 60 nm.
• SLD superluminescent diode
• the light from the source is directed through the coupler 40 and the fiber 21 to the collimator 20, to constitute the measurement beam 6.
• Part of the beam is reflected in the fiber 21 at the collimator 20, to constitute the reference wave.
• the retroreflections from the object 4 are coupled in the fiber 21 and directed with the reference wave towards the decoding interferometer built around the fiber coupler 41.
• This decoding interferometer has an optical correlator function whose two arms are, respectively, a fixed reference 44 and a time delay line 45.
• the signals reflected at the reference 44 and the delay line 45 are combined, through the coupler 41, on a detector 43 which is a photodiode.
• the function of the delay line 45 is to introduce an optical delay between the incident and reflected waves, variable over time in a known manner, obtained for example by the displacement of a mirror.
• the length of the arms 44 and 45 of the decoder interferometer 41 is adjusted so as to reproduce with the delay line 45 the differences in optical paths between the reference wave reflected at the collimator 20 and the retroreflections from of the object 4, in which case there is obtained at the detector 43 an interference peak 52 whose shape and Width depend on the spectral characteristics of the source 42 (the wider the spectrum of the source 42, the smaller the interference peak 52).
• the measuring range is determined by the difference in optical length between the arms 44 and 45 of the decoder interferometer 41, and the maximum stroke of the delay line 45.
• the reference wave is generated at the collimator 20 outside the imaging system 2, parasitic reflections in the optical system do not contribute significantly to interference.
• FIGS. 4 and 5 show examples of measurements illustrating the operation of the device after acquisition and processing on a computer 16.
• the spot measurements are made with the infrared interferometer at precise points on the surface of the object 4, at positions 51 displayed on the images 50 of the latter, so as to produce a representation of the object 4.
• FIG. 4b shows an interferometric signal 52 obtained with the interferometer 5, which corresponds to a thickness measurement of a silicon layer Ts followed by an air gap Tg.
• Each interface encountered by the measurement beam 6 and giving rise to a retro-reflection produces a peak of interference.
• the distances between the peaks correspond to the optical thickness of the layer, which must be divided by the refractive index to obtain the true thickness.
• Figure 4a shows the image 50 of the surface of the object 4 with the location 51 of the measurement location.
• FIG. 5 shows an exemplary pattern height measurement obtained with the interferometer 5 as implemented according to the method described in FR 2 892 188, by wavefront division.
• the patterns measured are holes.
• FIG. 5b shows an interferometric signal 52 obtained with the interferometer 5, for a height measurement H of a hole.
• the surface and the bottom of the hole each reflect a fraction of the wavefront of the incident measuring beam 6, thereby producing an interference peak.
• the distance between the peaks corresponds to the height H of the hole.
• Figure 5a shows the image 50 of the surface of the object 4 with the location 51 of the measurement site.
• the interferometer 5 can be used to measure absolute distances or altitudes on the object. Indeed, the position of the interference peaks 52 in the measurement range depends on the optical distance between the corresponding interface of the object 4 and the collimator 20 along the path traveled by the measuring beam 6. thus possible to measure the heights of patterns or other relief elements, or a topology, by moving the object 4 relative to the imaging system 2 and by noting the evolution of the position of the interference peaks 52 in the 'span.
• the location of the measurement zone in the image 50 is carried out by a prior calibration operation of the device, so that a mark corresponding to the position of this measurement zone can be superimposed on the image displayed. This mark is visible at the position 51 in the image 50 of FIG. 5a.
• Calibration can be performed for example by placing instead of the object an infrared viewing card that can see the camera on the infrared measuring beam 6.
• a light beam 15 with wavelengths detectable by the camera 1 is superimposed on the measuring beam 6.
• This superposition can be performed for example by means of a fiber coupler inserted at the level of the interferometer 5 before the collimator 20.
• This viewing beam 15 travels substantially the same path as the measuring beam 6 in the imaging system 2 and produces on the surface of the object 4 a task detectable by the camera 1, visible for example in Figure 5a. It is thus possible to display directly on the image 50 the position of the measurement zone without prior calibration.
• the device according to the invention further comprises a solid field interferometer 13, inserted at the distal lens 3.
• This solid field interferometer 13 can transform the device optical profilometer imaging device capable of producing an altitude map or a three-dimensional representation of the surface of the object 4.
• the altitude of the surface is obtained according to well-known methods, by superimposing on the light reflected by the object 4 on the sensor 17 of the camera 1 a reference wave from the same light source 12 and having traveled substantially the same optical distance to the sensor 17 as said light reflected by the object 4.
• This reference wave is generated by a reference mirror 31 located in one of the arms of the interferometer 13. It produces on the sensor 17 interference fringes whose shape depends on the difference in shape between the reference mirror 31 and the surface of the object 4.
• interferometers 13 can be used, depending in particular on the magnification and the working distance of the objectives 3.
• magnification and working distance of the objectives 3 can be used, depending in particular on the magnification and the working distance of the objectives 3.
• a splitter cube 30 (or a splitter plate) is inserted under the objective 3, and returns a fraction of the incident light beam 25 to a reference mirror 31;
• Linnik which is a variant of the Michelson configuration and which comprises an objective 3 in each arm of the interferometer 13;
• the illumination beam 25 is not shown in Figures 2a and 2b. Only the imaging beams 22 from the reflections on the mirror 31 and the object 4 are shown.
• the interferometer 5 into the profilometer, it is preferable to limit the reflection of the measuring beam 6 on the reference mirror 31.
• This condition is not essential but makes it possible to avoid the presence of a parasitic peak of strong intensity in the measurements.
• This result is achieved by using a dichroic 30 or 32 separator element substantially transparent to the wavelengths of the measuring beam 6, and which exhibits the desired reflectivity (for example of the order of 50%) at the wavelengths of the system imaging.
• a device according to the invention integrating an infrared interferometer and an optical profilometer makes it possible to construct a three-dimensional model of an object 4 by combining all the measurements in a single representation.
• This device is particularly effective for controlling narrow and deep engravings such as the holes shown in Figure 5a. Indeed, because of the numerical aperture of the imaging beam 22 (that is to say the half ratio between its width at the objective 3 and the distance from the objective 3 to the focusing point ), the optical profilometer can not access the bottom of the holes to measure the depth. This measurement is however accessible to the infrared interferometer 5 as illustrated in FIG. 5. The combination of measurements thus makes it possible to obtain a three-dimensional representation of the more complete surface, including the areas that are not accessible to the profilometer.
• the device according to the invention comprises a light source 14 which emits a beam 19 for illuminating the object 4 by transparency.
• a light source 14 which emits a beam 19 for illuminating the object 4 by transparency.
• This embodiment makes it possible to carry out transmission imaging of the object 4.
• the illumination beam 19 is not shown in FIG. 1 beyond the object 4.
• the light source 14 is designed so as to have an emission spectrum extending in the near infrared to wavelengths greater than 1 micrometer, for which the silicon does not is more completely opaque.
• This light source 14 may be a halogen lamp. It is then possible, even with a camera 1 whose sensor 17 is based on silicon, to obtain a transparency image making it possible, for example, to locate circuit elements on a wafer 4 to carry out with the infrared interferometer 12, measurements at specific locations by the back side of the wafer opposite the engraved elements.
• a light source 14 with an emission spectrum extending in the near infrared (wavelengths between 780 to 1100 nm ) and / or in the near-ultraviolet region (wavelengths between about 780 and 1100 nm), to make reflection imaging of the object 4 at one or a plurality of these wavelengths of the source 14.
• a solid field interferometer 13 with such a source 14.
• the camera 1 may comprise any device capable of acquiring images of an object 4, such as for example:
• the separating plates 7 and 18 may be replaced by any beam splitting means, such as separating cubes, polarized components, etc. ;
• the collimator 20 may comprise displacement means 11 which make it possible to move the position of the measuring beam 6, and therefore the position of the measurement zone on the object relative to the field of view covered by the imaging means 2;
• the device may comprise additional optics 8 with variable magnification, traversed simultaneously by the measurement beams
• magnification of this additional optic 8 can be adjusted continuously by moving optical elements, or discretely by replacing optical elements;
• the optical relay 23 may comprise a variable magnification optics, which makes it possible to vary on the camera 1 the field of view and the size of the measurement zone.
• the magnification can be continuously adjusted by moving optical elements, or discretely by replacing optical elements;
• the light source 12 may comprise a halogen source
• the light source 12 may comprise any light source having a spectral content detectable by the camera 1; the interferometer 5 can be implemented at any infrared wavelength, in particular between 1100 nm and 1700 nm, and especially in the vicinity of 1550 nm.
• the source 40 may be any type of source or combination of infrared sources, producing a plurality of wavelengths in a continuous or discontinuous spectrum;
• the interferometer 5 may include any type of low coherence interferometer. It can be a simple Michelson interferometer with a delay line in one of the arms, the optical delays can be decoded in the frequency domain by spectral analysis techniques;
• the interferometer 5 can be partially or totally realized with optics in free propagation.
• the interferometer 5 can also be partially or totally realized with integrated optics, based in particular on planar waveguides.

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• 2010
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  • 2011-04-19 WO PCT/FR2011/050900 patent/WO2011135231A1/fr active Application Filing
  • 2011-04-19 SG SG2012078218A patent/SG184974A1/en unknown
  • 2011-04-19 CN CN201180021226.4A patent/CN102893121B/zh active Active
  • 2011-04-19 EP EP11721347A patent/EP2564153A1/fr not_active Ceased
• 2016
  • 2016-12-02 JP JP2016235402A patent/JP2017096956A/ja active Pending

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