Patent Publication Number: US-3874797-A

Title: Ellipsometer

Description:
United States Patent lll] 3,874,797  
 Kasai 5] Apr. 1, 1975 I ELLIPSOMETER Primary Examiner-Ronald L. Wibert 75 l t I T K a a Ann&#39;s-(mi! Exunziner-Paul K. Goodwin or 05 Ly l mdsd l hpm Attorney, Agent. or FirmFitzpatrick, Celia. Harper [73] Assignee: Nippon Kogaku K.K.. Tokyo. Japan &amp; Scinto 22 Filed: A r. 5, 1974 l 1 p r 57 ABSTRACT 1 Appl&#39; 458426 An ellipsometer includes a polarizing optical system, a  
  first and a second optical path changing total reflect- [30] Forei Appli ti P i it D ing prism. and an analyae Light from a light source A 973 J; a N 474135 passes through the polarizing optical system to leave it pr 1pm 7 in the form of elliptical polarized light. which in turn m 0.5. CI. 356/118 ass/mi Passes hmugh reflecim Prism which [5 l] hm CL d 21/40 the elliptical polarized light is given a phase skip dif- (581 Field of Search i 5 H6 1 l8 ference and deflected so as to impinge on the surface 156mm 5 6 of a sample obliquely with respect thereto. The light i i m i so reflected by the first total reflection prism further [56] References Cited passes through the second total reflection prism in which the light is given a phase skip difference and de- UNITED STATES PATENTS flected in a direction substantially parallel to the opti- WCHS i al axis of the polarizing optical system The FOREi N PATENTS 0 APPUCATIONS passed through the second total reflection prism is fii.i 16.824 5/1956 France 356/l is extinguished by the analyzer 4 Claims. 2 Drawing Figures Q P F O TEJEHTED APR 1 75 FIG.  
 FIG. 2  
 ELLIPSOMETER BACKGRUNI) ()F &#39;IHli INVEN&#39;I&#39;ION 1. Field of the Invention This invention relates to an ellipsometer for effecting polarization analysis. and more particularly. to a small ellipsometer pro\ided with total reflection prisms.  
 2. Description of the Prior Art Among the techniques of causing a light to impinge on the surface layer of a material to facilitate investigation and study of the kind of material by analysis of the light reflected by the surface layer. one technique which utilizes polarization is referred to as polarization analysis. and it employs an ellipsometer. or the like.  
  In the conventional ellipsometer however. the optical-mechanical systems forming the light incidence and emergence sides thereof have each occupied a very large space as compared with the area of a sample to be measured. thus making the entire device very bulky and accordingly inconvenient for transportation or like purposes. Also. when the ellipsometer was to be used in a metering room of a laboratory or factory. for esample. greater inconveniences have been encountered in the installation of the device because of the large space required by the same.  
 SUMMARY OF THE INVENTION By means of the present invention. l am able to redtlce the size of the ellipsometer and thus to avoid the foregoing difficulties and disadvantages. and I achieve this result by the use of total relfcction prisms.  
  According to the present invention. there is provided a small ellipsometer for measuring the thickness. optical constant. or the like. of a sample from the polarization with which light impinging on the surface of the sample is reflected thereform. The ellipsometer may comprise a polarizing optical system disposed on an optical asis substantially perpendicular to the surface of the sample to be measured and for providing an emergence of elliptical polarized light. a first optical path changing total reflection prism for imparting a phase skip differnce to the elliptical polarized light emergent from the polarizing optical system and for totally reflecting the polarized light to deflect the path thereof so as to cause it to impinge obliquely on the sample stirface. a second optical path changing total reflection prism for imparting a phase skip difference to the light reflected by the sample surface and for totally reflect ing the reflected light to deflect the path thereof so as to be sul&#39;istantially parallel to the optical axis of the polarizing optical system. and an analyser for extinguishing the light passed through the second total reflection prism.  
  The polarizing optical system may comprise a light source. a monochrome filter for passing therethrough the light from said source. a polarizer for converting the monochromatic light from the monochrome filter into rectilinear polarized light, and a A wavelength plate for converting the rectilinear polarized light from the polarizer into elliptical polarized light of an azimuth angle 45 with respect to the incidence surface of the sample.  
  The stun of the phase skip differences imparted by the first and second optical path changing total reflection prisms is 180. More particularly. the phase skip difference by the first total reflection prism is 135 and the phase skip difference imparted by the second total reflection prism is 45.  
  There has thus been outlined rather broadly the more important features ofthe invention in order that the detailed description thereof that follows may be better understood. and in order that the present contribution to the art may be better appreciated There are. of course. additional features ofthe invention that will be described hereinafter and which \vill form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes ofthe invention It is important. therefore. that the claims be regarded as including such equivalent construction as do not depart front the spirit and scope of the invention BRIEF DFSCRIP&#39;I&#39;ION ()F &#39;I&#39;Hli DRAWINGS Specific embodiments of the imention have been chosen for purposes of illustration and description. and are shown in the accompanying drawings forming a part of the specification wherein:  
  FIG. I is a schematic representation showing an arrangement according to one embodiment of the present invention. and  
  FIG. 2 is a view illustrating the principle of the measurement with the aid of a Poincare sphere.  
 DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. I. there is shown schematically an embodiment of the present invention including a light source 0. a monochrome filter F and a rotatable polarizer P. Light from the source 0. is converted by the filter and the polarizer into rectilinear polarized ntonochromatic light. A V4 wavelength plate 0, set to an azimuth angle of 45 with respect to the surface of incidence. is provided to convert the rectilinear polarized light into elliptical polarized light. A total reflection type deformed Fresnel prism II is provided for causing the light passed perpendicularly to the surface of a sam ple S to be measured (hereinafter referred to as the sample surface) to impinge obliquely on the sample surface. and is designed so that a single internal reflection provides a phase skip difference of 45 between the component in the surface of incidence and the component in the surface perpendicular to the surface of incidence.  
  Another total reflection type deformed Fresnel prism I2 is provided for causing the light reflected by the sample surface to be deflected into a path perpendicular to the sample surface. and is designed to provide a phase skip difference of45. Designated by letter A is an analyzer for extinguishing the rectilinear polarized light from the prism I2 and this analyzer is rotatable about its own axis.  
  The principle and operation of the measurement by the inventive ellipsometer will now be described with the aid of the Poincare sphere shown in FIG. 2. where P represents the surface of incidence (azimuth angle 0) and S represents the surface perpendicular to the surface of incidence (azimuth angle 90).  
  The rectilinear polarized light from the polarizer P of rotation angle a corresponding to P0 of the Poincare sphere travels through the A wavelength plate 0 to be thereby converted into elliptical polarized light of an azimuth angle 45 corresponding to El of the Poincare sphere. and further passes through the prism ll to undergo a phase variation of l35 as shown by [12 of the Poincare&#39;sphere. Such light then impinges on the sainple surface. Here. the light undergoes a phase skip and an amplitude ratio ill. so that a light corresponding to F3 in FIG. 2 leaves the sample surface to enter the prism l2. Here. the light further undergoes a phase variation of 45 to provide rectilinear polarized light corresponding to E4 in Fl(i. 2. (in the Poincare sphere. the rectilinear polarized light is shown on the equator. the lefthanded elliptical polarization is shown in the north hemisphere and the righthanded elliptical polarization is shown in the south hemisphere.) The light further passes through the prism l2 and is extinguished by the analyzer of rotation angle B The phase skip and the amplitude ratio ll! may be obtained directly from the Poincare sphere:  
 These may be analyzed in the conventional manner.  
  In the present embodiment. the combined phase skip differences imparted by the two prisms ll and I2 has been shown as I80&#34;. whereas. a phase skip difference other than this may result in the same effect as described above. in such cases. it would be necessary to direct the rectilinear polarized light to the analyzer A as by a compensator disposed behind the prism l2 and, in addition, the subsequent calculations would unavoidably be more cumbersome According to the present invention. as described hitherto. I am able to achieve a reduction in the space occupied by the entire device as compared with the prior art, and this means a greater facility for transporation as well as a greater ease with which the device is installed in a place desired. Further. the prisms being ofthe total reflection type permit complete elimination ofenergy loss and also permit the device to be available for other wavelengths by interchanging the filter F and the wavelength plate 0 accordingly.  
  I believe that the construction and operation of my novel ellipsometer will now be understood and that the advantages thereof will be fully appreciated by those persons skilled in the art.  
 I claim:  
  I. An ellipsometer for measuring the thickness optical constant or the like of a sample from the polariza tion with which light impinging on the surface of the sample is reflected therefrom. said ellipsometer com prising:  
 a polarizing optical system disposed on an optical axis substantially perpendicular to the surface of the sample to be measured and for providing an emergence of elliptical polarized light;  
 a first optical path changing total rellection prism for imparting a phase skip difference to the elliptical polarized light emergent from said polarizing optical system and for totally reflecting said polarized light to deflect the path thereof to cause it to im pinge obliquely on said sample surface.  
 a second optical path changing total reflection prism for imparting a phase skip difference to said light reflected by said surface of the sample and for totally reflecting said reflected light to deflect the path thereof to cause it to be substantially parallel to the optical axis of said polarizing optical system; and  
 an analyzer for extinguishing the light passed through said second total reflection prism.  
 2. An ellipsometer according to claim I, wherein said polarizing optical system comprises:  
 a light source.  
 a monochrome filter for passing therethrough the light from said source:  
 a polarizcr for converting the monochromatic light from said monochrome filter into rectilinear polarized light; and  
 a A wavelength plate for converting said rectilinear polarized light from said polarizer into elliptical polarized light of an azimuth angle 45 with respect to the incidence surface of the sample.  
  3. An ellipsometer according to claim I. wherein the sum of the phase skip differences imparted by said first and second optical path changing total reflection prisms is l8().  
  4. An ellipsometer according to claim 3. wherein the phase skip difference imparted by said first optical path changing total reflection prism is [35 and the phase skip difference imparted by said second optical path changing total reflection prism is 45.