ELLIPSOMETER AND ELLIPSOMETRY METHOD

Abstract: An improved ellipsometry method and a self-correcting simultaneous multiple angle/multiple wavelength return path ellipsometer (20) are disclosed which allow for simultaneous measurement at multiple angles of incidence in a manner which permits separation of instrument error from the measured properties. Non-sample optical system ellipsometric effects of the ellipsometer are measured and the measured changes in polarization state are corrected to eliminate errors introduced thereby. The disclosed embodiment is self-correcting by way of a convex reflector (6) which can be inserted into and removed from the optical path of the beam of polarized light between a focusing optic (5) and the sample optical system (7) under study. The convex reflector (6) when inserted into the optical path causes the light rays of the beam of polarized light in each of the plurality of angles of incidence to retrace its path through the focusing optic (5) for detection by a detector array (10) without undergoing reflection and re-reflection as during a sample measurement configuration of the ellipsometer (20) is removed from the optical path.

Description: ELLIPSOMETER AND ELLIPSOMETRY METHOD TECHNICAL FIELD This application claims priority of the prior copendmg provisional application Serial No 60/1 15,354, filed January 8, 1999 The present invention relates to an eUipsometer and an ellipsometry method for elhpsometric measurements using a focused measurement beam at single or multiple nominal angles of incidence and/or multiple wavelengths, for measuring the change in polarization state of light upon interaction with a sample for determining characteristics of the sample DISCLOSURE OF THE INVENTION Ellipsometry is an optical technique for the characterization and observation of events at an interface or film between two media and is based on exploiting the polarization transformation that occurs as a beam of polarized light is reflected from or transmitted through the interface or film Ellipsometry has been particularly attractive because of its essential non-perturbmg character (when the wavelength and intensity of the light beam are properly chosen) hence its suitability for in-situ measurements, and its remarkable sensitivity to minute mterfacial effects, such as the formation of a sparsely distributed sub-monolayer of atoms or molecules One way in which the light wave can interact with an optical system under study is by being reflected by a surface of the optical system This reflection causes the state of polarization to be changed abruptly Such change can be explained using the Fresnel reflection coefficients for the two linear polarizations parallel (p) and perpendicular (s) to the plane of incidence Reflection ellipsometry has been recognized as an important tool for the study of surfaces and thm films Among the many useful applications of ellipsometry are (1) the measure of optical properties of materials and their frequency dependence (wavelength dispersion), the materials may be in liquid or solid phase, may be optically lsotropic or anisotropic, and can be either m bulk or thin-film form, (2) monitoπng of phenomena on surfaces that involve either the growth of thm films starting from a submono- layer (e g , by oxidation, deposition, absorption or diffusion of impurities), or the removal of such films (e g , by desorption, sputtering or diffusion), and (3) measurement of physical factors that affect the optical properties such as electric and magnetic fields, stress or temperature. When the polarization state change depends on the angle of interaction of the light beam and the sample under study, as for example with reflection from a sample, the incident light should be as colhmated as possible so only a single angle of incidence is measured at one time It is advantageous to measure as many angles of incidence on a particular sample as possible. However, in the past this was not done frequently because it is so cumbersome to get the data by making separate successive measurements at each angle through the use of a scanning technique or with multiple elhpsometers. This problem in the art has been overcome by the Assignee's simultaneous multiple angle/multiple wavelength eUipsometer and method as disclosed in its U.S. Patent No. 5, 166,752. The ellipsometry method and the eUipsometer disclosed therein permit the simultaneous illumination of a sample at a whole range of angles of incidence from a single beam of light and permit the rapid, easy collection of a large multiplicity of data for different angles or ranges of angles within the whole range of angles without requiring scanning or the use of multiple elhpsometers. However, a drawback of this known ellipsometry method and eUipsometer is that they do not provide a means for separation of instrument error from the measured properties. This instrument error can be significant, especially where the eUipsometer is vacuum compatible. The disclosure of Assignee's U.S. Patent No. 5,166,752 is incorporated herein by reference. Return path or folded-path elhpsometers are, per se, known. O'Bryan, for example, devised a folded-path eUipsometer for making measurements with colhmated light interacted with an optical system at a single angle of incidence, see Fig. 3.21 on page 253, and the related discussion, Ellipsometry and Polarized Light by R.A. Azzam and N. M. Bashara, published by North-Holland Physics Publishing, 1987 edition. However, this known return path eUipsometer does not allow for simultaneous measurements at multiple angles of incidence and/or multiple wavelengths. There is a need for an improved ellipsometry method and eUipsometer which overcome the aforementioned disadvantages and limitations of the prior art. An object of the present invention is to provide an improved ellipsometry method and eUipsometer which solve these problems and, at the same time, which offer more accurate measurements, more measurement capability and simplicity as compared with the prior art. These and other objects of the invention are attained by the ellipsometry method of the invention which comprises operating an eUipsometer to direct polaπzed light so that it interacts with a sample optical system under study, and measuring the change m polarization state of light interacted with the sample optical system, the polarized light from a single beam of light being simultaneously directed to interact with the sample optical system at different angles of incidence. The change of polarization state is measured for at least one, and preferably each of a plurality of the angles of incidence. The method further includes measuring non-sample optical system elhpsometric effects of the eUipsometer and using the results thereof to correct the measured changes in polarization state to eliminate error that is introduced by the non-sample optical system elhpsometric effects. In the disclosed embodiment, the step of measuring non-sample optical system elhpsometric effects of the eUipsometer includes operating the eUipsometer m an error correction mode during which the sample optical system under study is effectively removed from the optical path of the eUipsometer. As a result of the nature of the ellipsometry method and eUipsometer of the invention, the elhpsometric measurements made in the error correction mode and those made with the sample optical system under study, e.g. the sample, m the optical path of the eUipsometer differ only in that the measurement performed during sample measurement includes interactions with the measured sample. All aspects of the measurement which are related to imperfections in the apparatus, e.g. the non-sample optical system elhpsometric effects, are common to both measurements and are therefore subject to elimination by appropriate mathematical technique as discussed herein The ellipsometry method of the invention preferably involves operating a return-path eUipsometer with a polaπzer arm and an analyzer arm superimposed on or sharing components with the polanzer arm and wherein the step of directing the polaπzed light to interact with the sample optical system at a plurality of angles of incidence includes reflecting the light from a surface of the sample optical system and re-reflectmg the reflected light from the surface of the sample optical system so that it retraces its path in the arm of the eUipsometer. In this way, the light interacts twice with the surface of the sample. The step of measuπng non-sample optical system elhpsometric effects of the eUipsometer preferably includes inserting a reflector in the optical path of the beam of polarized light directed toward the sample optical system at different angles of incidence to cause the light rays at each of the plurality of angles of incidence in the beam to retrace its path in the arm of the eUipsometer without undergoing reflection and re -reflection from the surface of the optical system as m the sample measurement step. The reflector is removed from the optical path of the beam of polaπzed light directed toward the optical system to permit the measuπng of the change m polarization state of the light interacted with the sample optical system. In one example of the invention, a thin film under study is supported on a stage of the eUipsometer m a manner to permit adjustment of the position of the film with respect to the focusing optic of the eUipsometer. This enables the relative position of the film and focusing optic to be adjusted so that preferably the focused beam of polarized light is reflected and re -reflected from the same spot on the surface of the film Further, the disclosed embodiment of the method, the polarization state of the light beam is modulated during each of the measuring steps A portion of the light which is re-reflected to the focusing optic reaches a detector array of the eUipsometer where the intensity of a multiplicity of constituent rays, each corresponding to a different angle of incidence on the sample, is measured as a function of time This information is sufficient to determine the elhpsometric properties of the sample at each of the angles of incidence in accordance with standard practice. The improved eUipsometer of the invention comprises means for directing polarized light so that it interacts with a sample optical system under study, and means for measuπng the change m polarization state of the light interacted with the sample optical system under study, wherein the means for directing polarized light includes means for simultaneously directing polaπzed light from a single beam of light onto the optical system under study at different angles of incidence and wherein the means for measuring measures the change in polarization state of light interacted with the sample optical system under study for at least one, and preferably for each of a plurality, of the different angles of incidence. Further, the eUipsometer includes means for measuring non-sample optical system elhpsometric effects of the eUipsometer to allow correction of the measured changes in polaπzation state of the light interacted with the optical system to eliminate error introduced therein by the non- sample optical system elhpsometric effects. The means for measuπng non-sample optical system elhpsometric effects includes means for operating the eUipsometer in an error correction mode as mentioned above. More particularly, in the disclosed embodiment, the eUipsometer is a return-path eUipsometer having a polarizer arm and an analyzer arm supeπmposed on the polarizer arm and wherein the means for measuring the change m polaπzation state of light interacted with the sample optical system under study for each of the plurality of angles of incidence reflects the light from a surface of the optical system and re-reflects the reflected light from the surface of the sample optical system so that it retraces its path in the arm of the eUipsometer for detection by the detector array. In the disclosed embodiment, the means for measuring non-sample optical system elhpsometπc effects includes a reflector which can be automatically inserted in a position in the optical path of the beam of polarized light directed toward the sample optical system at different angles of incidence to cause the light rays at each of the plurality of angles of incidence in the beam to retrace its path in the arm of the eUipsometer without undergoing the reflection and re -reflection from the surface of the sample optical system The reflector in the disclosed embodiment is a convex mirror having a center of negative curvature thereof coincident with a focal point of a focusing optic of the eUipsometer focusing the single beam of light at a single point on the sample optical system with constituent light rays forming the plurality angles of incidence with the sample optical system. A mechanism is also provided for moving the reflector into and out of the position in the optical path The position is proximate the optical system under study the disclosed example. These and other objects, advantages and features of the present invention will become more apparent from the following detailed description of several embodiments of the invention taken with the accompanying drawings The method and eUipsometer of the invention are not limited to multi-angle ellipsometry but have applicability to return path ellipsometry and return path elhpsometers for allowing correcting for non-sample optical system elhpsometric effects such as that induced by a vacuum-window where the eUipsometer is vacuum compatible. BRIEF DESCRIPTION OF DRAWINGS Fig. 1 a schematic illustration of a self-correcting multiple angle return-path eUipsometer according to a preferred embodiment of the invention, the eUipsometer being shown in a sample measurement configuration thereof; Fig. 2 is a schematic illustration of the eUipsometer of Fig. 1 wherein the eUipsometer is depicted in an instrument error correction configuration, Fig. 3 is an enlarged schematic drawing of the portion of the eUipsometer of Figs. 1 and 2 showing the concave reflector and the location of its center of curvature; Fig. 4 is an enlarged schematic drawing of a portion of the disclosed eUipsometer showing the convex reflector positioned in the optical path of the focused, polarized light beam and the relationship of its center of negative curvature with a focal point of the focusing optic the eUipsometer; Fig. 5 is a schematic drawing of the mechanism for inserting and removing the convex reflector of the eUipsometer from the optical path of the focused, polarized beam of light, the mechanism including a beaπng and a hard stop for precisely positioning the convex reflector in a predetermined position in the optical path duπng ellipsometry measurements in the instrument error correction configuration thereof; Fig. 6 is a graph of elhpsometric measurements made with the eUipsometer according to the method of the invention including elhpsometπc measurements made in the sample measurement configuration and the resultant corrected elhpsometric measurements wherein the sample measurements have been corrected to eliminate the instrument errors therefrom, Fig. 7 is a schematic illustration of an eUipsometer like that in Fig. 1 , but with the convex mirror thereof being replaced by a concave mirror; and Fig. 8 is a schematic illustration of a further variation of the eUipsometer of Fig. 1, wherein the array detector and an analyzer are located between the sample and the polaπzation modulation section rather than further outward along the optical path from the light source as in the eUipsometer of Fig. 1 BEST MODE FOR CARRYING OUT THE INVENTION Referring now to the drawings, an eUipsometer 20, illustrated in Fig. 1-5 of the drawings is a self-correcting simultaneous multiple angle return-path eUipsometer. The eUipsometer 20 comprises a monochromatic or polychromatic colhmated light source 1, beam shaping optics including but not limited to a spatial filteπng beam expander 2, and a fixed polarizer 3, which provide a beam of polarized light. A polaπzation modulation section 4 of the eUipsometer includes a means for modulating the polarization state of the light beam, for example a rotating or oscillating retarder, a rotating or oscillating polarizer, or a photoelastic modulator. A focusing optic 5, consisting of one or more elements of either transmissive or reflective type, forms a focus at the surface of the sample 7 to be measured. The sample is held on a stage or chuck 16 of the eUipsometer. The angles of incidence in the focused beam vary over a range of angles of at least one or two degrees, and preferably as in the illustrated preferred embodiment, the range of angles of incidence is 30 degrees as discussed U.S. Patent No. 5,166,752. The focused beam is entirely oblique to the surface of the sample 7. The light is focused by the focusing optic 5 to a single small spot or point on the surface of sample 7. The diameter of the spot is preferably less than or equal to 10 microns. A convex reflector in the form of a convex mirror 6 is inserted into and removed from the optical path by means of an automated mechanism 12 controlled by a suitably programmed microprocessor 21. The mechanism 12 includes a beaπng 13 and a hard stop 14 for precisely positioning the convex reflector in the predetermined position in the optical path during operation of the eUipsometer m an instrument error correction configuration as depicted Figs. 2, 4 and 5. The stage or chuck 16 holding the sample 7 is preferably adjustable m the x, y and z directions as shown m Fig.1. A fixed concave reflector m the form of a concave mirror 8 is also provided in the eUipsometer along with a beam splitting optic 9 and a square or linear array detector 10 with associated imaging optics. The eUipsometer of the disclosed embodiment of the invention is operated m two configurations First, a sample measurement configuration (Fig. 1) during which the convex mirror 6 is removed from the optical path and second, and an instrument error correction configuration (Fig. 2), dunng which the convex mirror is inserted in the optical path effectively removing the measured sample 7 and concave mirror 8 from the optical system During operation in the sample measurement configuration (Fig. 1), light from the light source 1 passes through the beam shaping optics 2 and is linearly polaπzed by the fixed polaπzer 3 The polaπzation state of the light is modulated by the polarization modulation section 4. The light is then focused by the focusing optic 5 so as to arrive at a single point on the measured sample with the constituent light rays forming a multiplicity of incidence angles. The light is then reflected at a multiplicity of angles. The light then strikes the fixed concave mirror 8 This mirror is positioned such that its center of curvature is coincident with the illuminated point on the measured sample as illustrated in Fig. 3. This positioning allows each of the constituent rays reflected from the concave mirror to retrace its path through the above-described optical system in reverse order, e.g., it again passes through the optical sample. Accordingly, light reflected from the concave mirror 8 returns to the sample 7 arriving at a multiplicity of incidence angles. The light reflects from the measured sample and is collected by the focusing optic 5 where it is returned to a colhmated state. The light is then further modulated by the polaπzation modulation section 4 and then passes through the fixed polarizer 3. A portion of the light is then redirected by the beam splitting optic 9 to the array detector 10 where the intensity of a multiplicity of constituent rays, each corresponding to a different angle of incidence on the sample, are measured as a function of time. This information is sufficient to determine the elhpsometπc properties of the sample at each of the angles of incidence in accordance with standard practice. During operation of the eUipsometer 20 in the error instrument correction configuration (Fig. 2), the light proceeds in the apparatus in a manner identical to that described in the sample measurement configuration up to and including the first reference to the focusing optic 5. After passing through the focusing optic 5 the light is reflected from the convex mirror 6. This mirror is positioned such that the center of its negative curvature is coincident with the focal point of the focusing optic 5, see Fig. 4. This positioning allows each of the multiplicity of reflected constituent light rays to retrace its path through the optics of the eUipsometer for detection by the array detector 10 as described in the sample configuration commencing from and including the second reference to the focusing optic 5. According to the method of the invention, the eUipsometer enables contrasting measurements to be made at each of the two configurations described above In the sample measurement configuration, after passing through focusing optic 5 the light interacts with the sample 7. the concave mirror 8 and again with the measured sample 7 Alternately, in the instrument error correction configuration, after passing through the focusing optic 5, the light interacts with the convex mirror 6. In both configurations, the interaction of the light with the mirror, either concave or convex, is such that each of the multiplicity of constituent rays strikes the mirror perpendicular to the local surface. Such reflections where the light rays are perpendicular to the reflecting surface, ideally cause only a trivial phase reversal and do not impart elhpsometric light information to the light in a manner related to the detailed nature of the reflecting surface Therefore, elhpsometric measurements made in each of the two configurations described above differ only m that the measurement performed m the sample measurement configuration includes the two interactions with the measured sample. AU aspects of measurement which are related to imperfections in the eUipsometer are common to measurements made in each of the configurations are therefore subject to elimination by the appropriate mathematical technique. In the field of ellipsometry changes m polaπzation state are traditionally expressed in terms of two quantities: the relative phase of the s and p components is called delta. The arctangent of the relative amplitude of the s and p components is called psi. Delta errors accumulate in an additive manner. The sample measurement configuration described above measures a total delta equal to twice the delta of the sample plus the delta of the instrument. The error correction configuration measures the delta of the instrument only. Therefore, the error in delta is removed by subtraction of the error correction mode measurements from the sample measurement Psi errors accumulate by the product of the tangents. The sample measurement configuration measures the square of the tangent of the sample psi multiplied by the tangent of the psi due to instrument error. The error correction configuration measures the tangent of psi due to instrument error alone. Therefore, the error in psi is removed by dividing the tangent of the total psi measured m the sample measurement configuration by the tangent of the psi measured in the instrument correction configuration More specifically, by way of example, the eUipsometer 20 can be used to make elhpsometric measurements where the sample optical system is a thm film of silicon, 7 in Figs. 1 and 2, during the manufacture of semiconductor devices. The elhpsometπc measurements made m the instrument error correction configuration of the eUipsometer are preferably performed immediately prior to or after the ellipsometπc measurements made of the sample m the sample measurement configuration to minimize any changes in the error caused by the eUipsometer as a function of time, e g with temperature changes, for example The results of measurements using the eUipsometer 20 are depicted in Fig 6 of the drawing wherein measurements are shown before and after correction for non-sample optical system ellipsometπc effects. The sample optical system in this case is an 80 angstrom layer of silicon dioxide on a silicon substrate. The measured parameter is the thickness of silicon dioxide. In this experiment the focusing optic, 5 in Figures 1-4, was subjected to mechanical stress which is known to induce non-sample optical system elhpsometric errors into the eUipsometer. The induced stress is shown increasing across the horizontal axis from left to πght. The vertical axis shows the deviation from the expected result before and after correction of the measurement using the error correction mode. In this experiment the residual error of the corrected measurements is in part a result of making measurements before the induced mechanical stresses are fully redistributed in the focusing optic, 5. The eUipsometer 20, according to the invention, can also be provided with a dispersing element, not shown, as discussed with reference to Fig 5 in U S. Patent No 5,166,752 to enable the simultaneous detection of the beam as a function of angle of incidence and wavelength without scanning either. In the eUipsometer 20 depicted in the drawing as well as this vaπation thereof, the ellipsometry method and eUipsometer of the invention provide a method and means for separation of instrument error from the measured properties while at the same time allowing for simultaneous measurement of multiple angles of incidence and/or of multiple wavelengths of light The movement of the convex spherical mirror 6 into the optical path in front of the focusing optic 5 switches the eUipsometer to an error correction mode for the instrument error measurement Rapid, successive measurements can be made with and without this element in the optical path under the control of microprocessor 21 to allow for the determination and cancellation of all non- sample elhpsometric effects in the manner described. AU rays on both spherical mirrors 6 and 8 are at normal incidence The stage 16 at which the sample 7 is positioned is preferably adjustable m the x, y and z directions as shown schematically in Figs 1 and 4 as mentioned above. Fine adjusters can also be provided on the optical components of the eUipsometer, including the focusing optic 5 for ensuπng spot coincidence of the focused beam initially reflected from the surface of the sample 7 and that re-reflected by the concave mirror 8 As a result of these and other features of the invention, separation of instrument error from the measured properties can be accomplished to provide more accurate measurements and more measurement capability m a relatively simple manner as compared with conventional elhpsometers and elhpsometric methods. While I have shown and described only certain embodiments in accordance with the present invention, it is understood that the same is not limited thereto, but is susceptible to numerous changes and modifications as known to those skilled m the art. One possible vaπation is to replace the convex mirror 6 with a concave mirror, 22 in Fig 7, having a center of curvature coincident with a focal point of focusing optic 5 of the eUipsometer focusing the single beam of light at a single point on the sample optical system with constituent light rays forming the plurality of angles of incidence with the sample optical system. In such case, the concave mirror 22 would be fixed such that when the sample optical system 7 is removed from the optical path by stage 16 as shown in Fig 7, the rays after striking the concave mirror 22 retrace their path through the focusing optic 5. As noted above, the eUipsometer and ellipsometry method of the invention are also not limited to multi-angle ellipsometry, but have applicability to return path ellipsometry and elhpsometers including hybπd systems that can operate in a return path mode and another mode such as a single-pass eUipsometer, for example The error introduced by a vacuum wιndow(s) in a vacuum compatible eUipsometer according to the invention can be corrected with the method and eUipsometer of the invention. See vacuum window/chamber 24 shown schematically in Fig. 2. Therefore, I do not wish to be limited to the details shown and described herein, but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims

Claims: CLAIMS I claim: 1. An ellipsometry method comprising operating an eUipsometer to direct polaπzed light so that it interacts with a sample optical system under study more than once and measuring a change m polarization state of the light interacted with the sample optical system, wherein polaπzed light from a single beam of light is simultaneously directed to interact with the sample optical system at different angles of incidence and wherein a change in polaπzation state is measured for at least one of a plurality of said angles of incidence of the multiple interactions of the light with the sample optical system 2. The ellipsometry method according to claim 1, wherein said eUipsometer is a return-path eUipsometer with a polarizer arm and an analyzer arm superimposed on said polaπzer arm and wherein said step of directing said polarized light to interact with the optical system at different angles of incidence includes reflecting said light from a surface of the sample optical system and re-reflectmg said reflected light from said surface of said sample optical system so that it retraces its path in said arm of eUipsometer and is then separated from the originating beam to be measured 3. The ellipsometry method according to claim 1, wherein the nominal angle of said single beam of light with respect to said sample optical system is oblique 4. The ellipsometry method according to claim 1 , wherein the nominal angle of said single beam of light with respect to said sample optical system is normal 5. The ellipsometry method according to claim 1 , wherein the light source is monochomatic 6. The ellipsometry method according to claim 1 , wherein the light source is polychromatic or broadband 7. The ellipsometry method according to claim 1, wherein the polarized light is reflected and re -reflected from a surface of said sample optical system using one of a curved reflector, a combination of refracting and reflecting optics or a phase conjugate mirror 8. The ellipsometry method according to claim 1 , further comprising measuring non-sample optical system elhpsometric effects of said eUipsometer and correcting said measured change in polaπzation state of the light interacted with the sample optical system to eliminate error introduced therein by said non-sample optical system elhpsometric effects 9. An ellipsometry method comprising operating a return path eUipsometer to direct polaπzed light so that it interacts with a sample optical system under study and measuring a change in polaπzation state of the light interacted with the sample optical system, wherein polaπzed light is reflected back through a polarizing arm of the eUipsometer for measuπng non-sample optical elhpsometric effects of said eUipsometer and correcting said measured change in polarization state of the light interacted with the sample to eliminate error introduced therein by said non-sample optical system elhpsometric effects 10. A return path eUipsometer comprising means for directing polarized light so that it interacts with a sample optical system under study, means for measuring a change in polaπzation state of said light interacted with the sample optical system under study, and means for measuring non-sample optical system elhpsometric effects of said eUipsometer to allow correction of said measured change in polarization state of the light interacted with the sample optical system to eliminate error introduced therein by said non-sample optical system elhpsometric effects 11. An ellipsometry method comprising operating an eUipsometer to direct polarized light so that it interacts with a sample optical system under study and measuring a change polaπzation state of the light interacted with the sample optical system, wherein polaπzed light from a single beam of light is simultaneously directed to interact with the sample optical system at different angles of incidence and wherein a change m polaπzation state is measured for at least one of a plurality of said angles of incidence, said method including measuπng non-sample optical system ellipsometπc effects of said eUipsometer and correcting said measured change in polarization state of the light interacted with the sample optical system to eliminate error introduced therein by said non-sample optical system ellipsometπc effects 12. The ellipsometry method according to claim 11, wherein said step of measuπng non-sample optical system elhpsometric effects of said eUipsometer includes operating said eUipsometer m an error correction mode 13. The ellipsometry method according to claim 1 1, wherein said eUipsometer is a return-path eUipsometer with a polarizer arm and an analyzer arm supeπmposed on or sharing some components with said polaπzer arm and wherein said step of directing said polarized light to interact with the optical system at different angles of incidence includes reflecting said light from a surface of the sample optical system and re-reflectmg said reflected light from said surface of said sample optical system so that it retraces its path in said arm of said eUipsometer 14. The ellipsometry method according to claim 13, wherein said step of measunng non-sample optical system elhpsometric effects of said eUipsometer includes reflecting said beam of polaπzed light to cause the light rays at each of said plurality of angles of incidence in said beam to retrace its path in said arm of the eUipsometer without undergoing said reflection and re-reflection from said surface of said sample optical system 15. The ellipsometry method according to claim 14, including inserting and removing a reflector from said optical path of said beam of polarized light directed toward said sample optical system to permit said measuring of a change in polarization state of the light interacted with the sample optical system 16. The ellipsometry method according to claim 14, including removing said optical system under study from said optical path to perform said step of measuring non- sample optical system elhpsometπc effects to allow said beam to be reflected by a reflector to retrace its path m said arm of the eUipsometer without undergoing reflection and re- reflection from said surface of said sample optical system. 17. The ellipsometry method according to claim 11, including modulating the polaπzation state of said light beam during said measuπng steps. 18. The ellipsometry method according to claim 11, wherein said measuπng non-sample optical system elhpsometπc effects of said eUipsometer is performed prior to and/or after and in relatively close time sequence with said measuπng a change m polarization state of the light interacted with the sample optical system at different angles of incidence. 19. The ellipsometry method according to claim 1 1 , wherein each of said measuring steps includes detecting the intensity of reflected polaπzed light at each of a plurality of said angles of incidence 20. The ellipsometry method according to claim 1 1 , wherein said beam of polarized light directed to interact with the optical system at said different angles of incidence is entirely oblique with respect to the surface of said optical system with which it interacts 21. The ellipsometry method according to claim 1 1 , wherein the light is directed onto a surface of the optical system under study at a single spot with a cone of polarized light derived from a single beam 22. An eUipsometer compπsing means for directing polarized light so that it interacts with a sample optical system under study, and means for measuring a change in polarization state of said light interacted with the sample optical system under study, wherein said means for directing polarized light includes means for simultaneously directing polarized light from a single beam of light onto the optical system under study at different angles of incidence, and wherein said means for measuring measures a change m polaπzation state of light interacted with the sample optical system under study for at least one of a plurality of said different angles of incidence, and said eUipsometer including means for measuring non-sample optical system elhpsometric effects of said eUipsometer to allow correction of said measured change in polaπzation state of the light interacted with the sample optical system to eliminate error introduced therein by said non-sample optical system elhpsometric effects 23. An eUipsometer according to claim 22, wherein said means for measuπng non-sample optical system elhpsometric effects includes means for operating said eUipsometer in an error correction mode 24. An eUipsometer according to claim 22, wherein said eUipsometer is a return- path eUipsometer having a polarizer arm and an analyzer arm supeπmposed on said polarizer arm and wherein said means for measuπng a change in polaπzation state of light interacted with the sample optical system under study for at least one of said plurality of angles of incidence reflects said light from a surface of the sample optical system and re-reflects said reflected light from said surface of said sample optical system so that it retraces it path in said arm of said eUipsometer 25. An eUipsometer according to claim 24, wherein said means for measuring non-sample optical system elhpsometric effects includes a reflector which can be inserted in a position in the optical path of said beam of polarized light directed toward said sample optical system at different angles of incidence to cause the light rays at each of said plurality of angles of incidence m said beam to retrace its path in said arm of the eUipsometer without undergoing said reflection and re -reflection from said surface of said sample optical system 26. An eUipsometer according to claim 25, wherein said reflector is a convex mirror having a center of negative curvature thereof coincident with a focal point of a focusing optic of said eUipsometer focusing said single beam of light at a single point on the sample optical system with constituent light rays forming said plurality of angles of incidence with said sample optical system 27. An eUipsometer according to claim 25, further comprising means for moving said reflector into and out of said position in said optical path. 28. An eUipsometer according to claim 25 wherein said reflector is a concave mirror having a center of curvature thereof coincident with a focal point of a focusing optic of said eUipsometer focusing said single beam of light at a single point on the sample optical system with constituent light rays forming said plurality of angles of incidence with said sample optical system, said concave mirror being fixed such that when the sample optical system is removed from the optical path the rays after stπkmg said concave mirror retrace their path through the focusing optic. 29. An eUipsometer according to claim 22. including means for modulating the polarization of said polaπzed light. 30. A return path eUipsometer comprising a source of a beam of polaπzed light, a focusing optic for simultaneously focusing said beam of polarized light on a sample optical system under study at different angles of incidence for reflection therefrom, a concave reflector located in an optical path of the beam of light reflected from said sample optical system under study for re-reflectmg said reflected light from said sample optical system so that it retraces its path through said focusing optic, a detector array for detecting the intensity of said light re -reflected through said focusing optic for each of a plurality of said different angles of incidence, and a convex reflector which can be inserted into and remo\ ed from the optical path of said beam of polarized light between said focusing optic and said sample optical system under study, said convex reflector when inserted into said optical path causing the light rays of said beam of polarized light at each of said plurality of angles of incidence to retrace its path through said focusing optic without undergoing reflection and re-re flection from said sample optical system for detection by said detector array 31. A return path eUipsometer according to claim 30, further comprising a beam splitter for directing a portion of said light which has retraced its path through said focusing optic to said detector array 32. A return path eUipsometer according to claim 30, wherein said source of a beam of polaπzed light includes a light source, beam shaping optics including a spatial filtering beam expander, and a fixed polarizer arranged on an optical path of said light in said eUipsometer 33. A return path eUipsometer according to claim 30, wherein a center of curvature of said concave reflector is coincident with a point on said sample optical system illuminated by said focused beam while said convex reflector is removed from said optical path 34. A return path eUipsometer according to claim 30, wherein a center of negative curvature of said convex reflector is coincident with a focal point of said focusing optic when said convex reflector is inserted into said optical path 35. A return path eUipsometer according to claim 30, further compπsmg a modulator for modulating the polaπzation state of said polarized light from said light source before focusing said beam with said focusing optic 36. A return path eUipsometer according to claim 30, further compπsmg a mechanism for moving said convex reflector into and removing it from said optical path 37. A return path eUipsometer according to claim 32. further comprising a beam splitter located between said source of a beam of polaπzed light and said focusing optic for directing a portion of said light which has retraced its path through said focusing optic to an analyzer arm consisting of a second fixed polarizer and said detector array 38. The eUipsometer according to claim 10, wherein said eUipsometer can operate both m a return path mode and as a single pass eUipsometer. 39. The eUipsometer according to claim 10, wherein said eUipsometer is a vacuum compatible eUipsometer and said means for measuring non-sample optical system elhpsometric effects allows removing the error induced as a result of said vacuum compatibility. 40. The ellipsometry method according to claim 9, wherein said sample optical system is in a vacuum, said eUipsometer being vacuum compatible and said step of correcting including removing the error induced by the vacuum compatible eUipsometer

Inventors: WAGNER JEFF A, WAGNER, JEFF, A.
Applicants: RUDOLPH TECHNOLOGIES INC, RUDOLPH TECHNOLOGIES, INC.
Application year: 2001
Main classification: G01J4
IPC codes: G01J4, G01N21