FR2524982A1 - INFRARED SPECTROMETER FOR TRANSMISSION AND REFLECTION MEASURES WITHOUT TRANSFORMING THE APPARATUS AND WITHOUT CHANGING THE POSITION OF THE SAMPLE - Google Patents

Abstract

THIS APPARATUS INCLUDES TWO DETECTORS 28, 31 PLACES ON EACH OTHER OF SAMPLE 17, IN THE DIRECTION OF THE BEAM PATH. ONE 28 SERVES TO RECEIVE THE LIGHT 20 THROUGH THE SAMPLE, THE OTHER 31 TO RECEIVE THE LIGHT 21 REFLECTED BY THE SAMPLE. THIS SPECTROMETER ALSO ALLOWS ANALYSIS OF A SAMPLE AS ANY CHOICE, OR SIMULTANEOUSLY, IN TRANSMISSION AND REFLECTION, WITHOUT TRANSFORMATION OR CHANGE OF POSITION OF THE SAMPLE. THE INVENTION IS APPLICABLE IN PARTICULAR TO THE CONTROL OF THE MANUFACTURING OF INTEGRATED CIRCUITS.

Description

The invention relates to an infrared spectrometer comprising means

  optical means for producing a beam of rays which is focused on a section plane, which is located in a straight section of the beam and is intended to receive a sample to be analyzed in transmission, and which is directed on a detector device. The known infrared spectrometers include a

  source of infrared radiation and a monochromator or

  double-beam ironometer to produce the measurement signal To perform measurements on samples, two methods are known,

  called transmission measures and reflection measures.

  In transmission measurements, the spectrometer

  infrared system has optical means for focusing radiation

  of the infrared radiation source in a plane where the sample to be analyzed can be arranged in transmission, by means of a vat or other sample holder. Usually, a parallel beam is focused for this purpose by a parabolic mirror. and the diverging brush passing through the sample is again parallelized and refocused, but this time on an optical detector, by others

optical means.

  Many substances to be analyzed by spectroscopy in the infrared range are opaque, but it is known how to exploit the infrared radiation reflected as by a mirror and / or diffusely by the surface of these substances. Such so-called reflection measurements are known. for example, by the periodical

  "Analytical Chemistry", volume 50 (1978), pages 1906 to 1910 The spec-

  Infrared trometer described in this study is built only

for reflection measures.

  Since measuring devices using infrared are technically complicated and very expensive, the use is also known

  a separate part of the ray guide, so that the replacement

  placement of optical means makes it possible to use the infrared spectrometer of the choice, after a transformation in this sense, for transmission measurements or for reflection measurements An accessory device thus making it possible to pass from transmission measurements to reflection measurements is marketed for example, by Harrick Scientific Corporation of Ossining, NY, USA An accessory apparatus of this kind is also known from the firm

  Analect Instruments from Irvine, Ca, USA.

  Although these known accessory devices allow the use of the same means generating rays and the same unit to exploit the results of transmission measurements and reflection measurements, the transition from one to the other type of measurement requires

  a considerable transformation during the period of transformation

  the infrared spectrometer can not be used and the working time of qualified personnel who use it is lost In addition, since the transformation to switch from one type of action to another involves relatively long interruptions, sequential measurements on short-lived samples are not possible or are only possible under great difficulties Finally, the transformation of the optical unit inevitably leads to the change of the ray trajectory, so that the sample to be analyzed sequential measurements does not occupy the same location during the measurements, which may present considerable disadvantages, especially

non-homogeneous samples.

  The aim of the invention is to provide a spectrometer infra-

  with which the transmission measurements and the reflection measurements can be performed simultaneously or sequentially, that is to say one immediately after the others, and so that the two kinds of measurements are possible simultaneously or sequentially on one and the same sample remaining at the same position. The invention produces this result by arranging, on the side of the section plane towards which the brush is directed, a second detector device for receiving reflected light.

  by the sample in a direction at an angle to the direction

incident light.

  An infrared spectrometer according to the invention therefore comprises two detector devices, which are ready to operate simultaneously and make it possible to analyze, one the light

  crossing the sample and the other the light reflected by the sample.

  In the case of samples allowing light to pass through

  partially red, both analyzes can be performed simul-

  The field of application of such a spectrometer is thus

greatly expanded.

  Depending on the nature of the sample to be analyzed, it may be advantageous to arrange the sample perpendicular to the radius passing through it or at a given angle with the radius.

  incident and the reflected ray according to which it is necessary to work only

  in transmission and / or in mirror reflection or diffuse reflection For this purpose, it is possible to have in the region of the sectional plane a sample holder for orienting the surface of the sample perpendicularly to the right section of the brush and / or

  perpendicular to the bisector of the directions of light -

  incident and reflected light.

  Beams produced in optical devices

  are preferably parallel beams In a mode of realization

  According to the invention, such a parallel beam is condensed in such a way by a parabolic mirror that a focus is formed on the surface of the sample. It is thus possible, on the one hand, to produce a high radiation intensity. on the other hand, to obtain a sample area analyzed as limited and defined with as much

  as accurate as possible For the operation of the transmission signal

  reflection, the divergent brushes coming from the sample

  They are again parallelized and advantageously condensed again on a detector It is however quite possible to bring the measurement signals to a detector immediately at the detector.

following the sample.

  Like incident light and reflected light

  pass through the same half-space on one side of the surface of the sample

  One preferred refinement of the invention provides for the use of a common extra-axial paraboloid which, on the one hand, focuses the

  parallel beam incident on the sample and, on the other hand, parallel

  The reflective divergent brush is used. In this way, a high optical precision is obtained and it is not necessary to adjust the

  ray trajectories separately.

  The infrared spectrometer according to the invention finally makes it possible to obtain particularly good measurement results by the arrangement of the sample in a horizontal plane. This makes it possible to avoid disadvantages that may occur under the action of gravity when these are flat samples arranged on a slice. The spectrometer according to the invention makes it possible

  for the first time, to determine entire optical constants

  by simultaneous measurements in transmission and reflection in

  now the sample exactly at the same position This head pcssi-

  It is particularly advantageous in the manufacture of

  silicon, for example, where it is necessary to respect scrupulously

  production parameters The spectrometer according to the invention

  This allows the exact production parameters and properties of the material used to be

and simultaneous reflection.

  Other features and advantages of the invention

  will be clearer from the following description of a

  non-limiting embodiment, and the accompanying drawing, in which: Figure 1 is a perspective view of an embodiment of an infrared spectrometer according to the invention; and Figure 2 is a schematic representation of the ray path in the region of the sample on a

  spectrometer as in Figure 1.

  In the exemplary embodiment shown in FIG. 1, reference numeral 10 denotes a spectrometer unit (monochromator or

  interferometer) as those commonly used on

  infrared meters of the type in question here.

  optical and sample are arranged on a spectral table.

  meter 11 Unit 10 emits a parallel beam 12, which first falls on a first parabolic mirror 13 It is preferable that this mirror constitutes, with a fourth parabolic mirror 14 which it

  will still be discussed later, a common extra-axial paraboloid 15.

  The first parabolic mirror 13 transforms the parallel beam 12 into an incident convergent brush 16, as shown

  also Figure 2 The brush 16 falls on a sample 17 Dis

  laying horizontally on a sample holder which is not

  Figure 2 shows that the axis 18 of the incident brush 16 forms an angle f 'with the perpendicular 19 to the surface

of the sample 17.

  The incident brush 16 of the sample 17 produces, on the one hand, a diverging brush 20 which passes through the sample 17 and on the axis 22 coincides with the axis 18 of the incident brush, on the other hand, a divergent brush 21 reflected by the sample 17 and whose axis 23 forms the same angle% t with the perpendicular 19 if the surface of the sample returns the light in the manner of a mirror It goes without saying that one can also choose an angle that differs from the angle e if it is to exploit light reflected diffuse manner. The spectrometer according to the invention of FIGS. 1 and 2 comprises first guide-ray and detector optical means for the capture of the transmission signal and, at the same time, second optical guide-ray means and detectors for capturing the signal.

reflection.

  In a simple embodiment of the apparatus of the invention,

  the first of these means can be constituted by a first detector 24 which is located directly under the sample 17 and

  which directly receives the divergent brush 20 passing through the sample

  ple. However, in order to be able to perform more accurate measurements and to obtain a higher signal density on the surface of the optical detector, an improved and preferred embodiment of the invention provides that the brush 20 is again parallelized by a second one. parabolic mirror 25 delivering a parallel beam 26 that a third parabolic mirror 27 focuses on a

detector 28.

  At the same time, the reflected divergent brush 21 is parallelized by the fourth parabolic mirror 14 already mentioned at the beginning, which produces a parallel beam 29 that a fifth

  parabolic mirror focuses on a second detector 31.

  It goes without saying that the detectors 24, 28, 31 represented

  in FIG. 1 are connected to electromagnetic operating means

  in themselves known and not shown.

  It is easy to see the representation in perspec-

  FIG. 1 that the invention thus enables simulated measurements to be

  taned or sequential in transmission and reflection No transformation is necessary since the transmission and reflection rays are produced simultaneously and can be exploited at the same time Therefore, it is not necessary to transform optical means or to transport sample 17 from one point of analysis to another; the sample can be analyzed according to the two measurement methods by staying exactly in the same place and at the same time.

same position.

  Naturally, the optical means for guiding the spokes, in particular the mirrors 13, 14, 25, 27 and 30, establish a particularly advantageous ray path, which is only an example, it being understood that other paths are usable. also the layout shown as an example on

  Figure 1 is particularly suitable for measurements on samples

  17 horizontally and only held in place by gravity or depression Measurement on samples

  tilted or vertically oriented would be possible simply by

  11 of the table 11 around the axis of the parallel beam 12 or

  by known changes in the path of the rays.

Claims (7)

R E V E N D I C A T IO N S   An infrared spectrometer comprising optical means for producing a ray brush which is focused on a sectional plane, which is located in a straight section of the brush and is intended to receive a sample to be analyzed in transmission, and which is directed to a device detector, characterized in that   includes, on the side of the section plane towards which the pin-   a second sensor device (31) for receiving   of light reflected by the sample (17) in a direction   at an angle to the direction of the incident light (16).   Spectrometer according to claim 1 comprising   in the area of the section plane, a tank or other   sample to orient the surface of the sample   perpendicular to the straight section of the brush (16, 20) and / or perpendicular   bisecting (19) the directions of the incident brush (16) and the reflected brush (21).   Spectrometer according to claim 1 or 2, comprising   a parabolic mirror (13) spaced from the surface of the sample   (17) and focusing an incident parallel beam (12) on the surface of the sample.   4 Spectrometer according to any one of the claims   1 to 3 in which the brush (20) passing through the sample (17)   falls directly on a detector (24).   Spectrometer according to any one of claims 1 to 3 in which the brush (20) passing through the sample (17) falls on a second parabolic mirror (25) which parallels this brush   and a third parabolic mirror (27) focuses the beam parallel to read (26) on a detector (28).   Spectrometer according to any one of the claims   in which the diverging brush (21) reflected by the sample   (17) falls on a fourth parabolic mirror (14) which parallels   read the received light and direct it onto a fifth parabola-   (30), which focuses the parallelized beam (29) on a second optical detector (3 l).   Spectrometer according to claims 3 and 6 taken   together in which the first parabolic mirror (13) and the   third parabolic mirror (14) constitute a common subset,   preferably an extra-axial paraboloid (15).   8 Spectrometer according to any one of the claims   tions in which the sample (17) is horizontally on a sample holder.