Apparatus for measuring semiconductor layer thickness

Abstract: An apparatus for measuring a semiconductor layer thickness includes a light source emitting light for measurement, an interferometer emitting interference light modulated with time by applying modulation to the light from the light source, an optical system including a light transmission member for introducing the interference light into a measurement sample comprising at least one-layer film laminated on a substrate, light receiving means receiving interference light reflected from the laminated film of the sample, means for extracting only a film interference component from the reflected interference light and means for calculating a thickness of the laminated film from an interference intensity waveform of the film interference component. The receiving means comprises a plurality of photodetectors having respective photometric wavenumber ranges some parts of which are overlapped with each other. Thereby, a wavenumber range of the sum of the respective wavenumber ranges of the respective components is obtained as a whole wavenumber range and an optical measurement can be realized in a wide wavenumber range which could not be measured with a single material in each component.

Description: The present invention relates to an apparatus for measuring a semiconductor layer thickness and, more particularly, to an apparatus for measuring nondestructively and in noncontact a thickness of respective layers of a multiple-layer thin film structure. A description is given of a prior art apparatus for measuring a thickness of a semiconductor layer. Now, for example, as shown in Figure 12, a sample 11 comprising a plurality of semiconductor thin films (laminated films) 2, 3 and 4 disposed on a semiconductor substrate is supposed. A beam 5 having a certain wavelength is irradiated at incident angle  onto the surface of the sample 11. Numerals 6, 7, 8 and 9 designate respectively primary reflected light components at surfaces of the thin films 2, 3 and 4 and the substrate 1. The film thickness and the refractive index of the thin films 2, 3 and 4 are represented respectively as (d 1 , n 1 ), (d 2 , n 2 ) and (d 3 , n 3 ) and the refractive index of the substrate 1 is represented as n s . In this case, the reflected light components 6, 7, 8 and 9 at the surface of the respective thin film layers 2, 3 and 4 and the substrate 1 have phase differences therebetween due to their optical path lengths and these composite light beams are interfering with each other. Namely, the optical path difference δi between the reflected light component 6 at the surface of the uppermost layer of the sample and the reflected light component at an interface between an i-th layer and an (i+1)-th (i=1, 2, 3) layer both from the uppermost layer is represented as follows: where n o is a refractive index and  o is an incident angle of light into the uppermost surface of a wafer. Therefore, thicknesses of respective thin films 2, 3 and 4 can be obtained by analyzing an interference waveform of the reflected beams composed of the respective reflected light components 6 to 9 having these optical differences δi. In order to measure a layer thickness of laminated films, a method of analyzing a wavelength dispersion interference waveform of reflected interference light (hereinafter referred to as interference spectrum) is employed. However, since the interference spectrum is complicated when the sample is of laminated structure of plural layers, Fourier analysis method analyzing the reflection spectrum is employed. More particularly, Fourier-transformation spectroscopy having a high utilization efficiency of light energy and therefore superior in analysis of optically measured data is employed in an apparatus for measuring the above-described reflection spectrum. Figure 11 is a typical view showing a constitution of a prior art apparatus for measuring semiconductor layer thickness employing Fourier-transformation spectroscope, which is disclosed in Japanese Published Patent Application 3-110405. As shown in the figure, infrared light passing through a semiconductor crystal is emitted from a light source 10, is collimated to be a parallel beam by a collimating mirror 12 and enters into a Michelson interferometer 13. The Michelson interferometer 13 includes a beam splitter 14 dividing the parallel beam incident into two beams of transmitted and reflected, a fixed mirror 15 reflecting the transmitted beam from the beam splitter 14, a moving mirror 16 reflecting the reflected beam from the beam splitter 14 and a driver 17 for moving the moving mirror 16 at a constant speed in arrow directions in Figure 11. The beams reflected by the fixed mirror 15 and the moving mirror 16 returns to the beam splitter 14 and are synthesized as modulated interference light beams in which the optical path difference corresponding to a travelling distance of the moving mirror 16 varies with time. A part of the modulation interference light beam is output from the Michelson interferometer 13 and introduced into a reflection photometry system 18. The beam entered into the reflection photometry system 18 is reformed by an aperture 19 to be a beam having a predetermined area which is reflected by a plane mirror 20 so as to radiate beam in a predetermined area of the sample 11. The light irradiated to the sample 11 is subjected to interference according to film construction of the sample 11 as described above. The light beam reflected by the sample 11 advances changing its direction at a plane mirror 21, and is collected by a collecting mirror 22 to enter into a photodetector 23 at which an intensity of reflected interference light is detected. The intensity of the light beam detected at the photodetector 23 includes interference components according to the film construction of the sample 11 and this is modulated with the travelling distance accompanying with the constant speed moving of the moving mirror 16 in the above-described Michelson interferometer 13. The interference beam intensity modulated with the distance is transformed by Fourier transformation with the travelling distance, resulting in wavenumber dispersion spectrum of the light under measurement. This is a principle of so-called Fourier transformation optical spectrometry. In thus obtained reflected light spectrum, the film interference component of the sample 11 is superposed on the light intensity distribution which is determined dependent on the light source 10 in the apparatus and the transmission characteristics of all optical systems. Therefore, by dividing reflected light spectrum with film interference by reflected light spectrum which is measured with providing a comparative sample such as a semiconductor substrate having no film construction in place of the sample 11, only the film interference component can be taken out from the reflected light spectrum. Information on the film thickness can be obtained directly from the film interference spectrum. Or, the film thickness can be analyzed from the waveform of spatial interference intensity distribution (hereinafter referred to as Spatialgram) shown in Figure 13, which is obtained by executing reverse Fourier transformation to the film interference spectrum. In the graph of Figure 13, the abscissa represents travelling distance of the moving mirror 16 and the ordinate represents reflected light interference intensity. In the Spatialgram of Figure 13, there appear burst peaks 24 to 26 by that all beams interfere with each other and increase their strength at points where the optical path difference of the reflected light components at respective layer interfaces represented by the formula (1) coincides with an optical path difference due to a travelling position of the moving mirror 16. The distance between the respective bursts corresponds to the optical path difference of the reflected light components at the layer interfaces. In the example of Figure 13, the burst peak 24 corresponding to the reflected light component 6 at the surface of the sample 11 (refer to Figure 12) appears as a center burst peak and symmetrically at left and right relative thereto the reflected light components 7, 8, and 9 of respective layers produces respective side burst peaks 25 to 27 corresponding thereto. Provided that the distances from the center burst peak 24 to the respective side burst peaks be Li (i=1, 2, 3), an optical path difference δi of the respective reflected light components coincide with 2Li as a sum of going path and return path to and from the moving mirror 16. Therefore, the following equation is obtained from the above-described formula (1): Here, since the refractive index n j and incident angle  are known, respective layer thicknesses d i can be calculated from the distance Li between the bursts which is obtained from the Spatialgram. Next, a description is given of the operation of the apparatus for measuring a semiconductor layer thickness. Generally, a light beam collecting system shown in Figure 14(a) is employed as a reflection photometry system. This is to enhance utilization efficiency of light energy of the reflection photometry system. As a result, the signal to noise ratio (SN ratio) of a light detected signal is enhanced, the number of times of photometry integration is reduced to be effective in such as shortening the photometry time. As shown in Figure 14(a), however, since the incident angle of the collected beam is actually distributed continuously with a certain incident angle as a center value and the light beams 5'a and 5'b in the collected light beam incident on the sample 11 have different incident angles a and b, differences also appear in an optical path length of the respective beams advancing in the film as shown in the figure. This results in that a lot of interference waveforms overlap with each other in the film interference waveform accompanying with the distribution of incident angle and turbulence unfavorably occurs in the film interference waveform, further resulting in a problem in analyzing thin films or multi-layer films. Then, in Japanese Published Patent Application 3-110405, by employing as an irradiated beam to the sample 11 a parallel beam in a reflection photometry system, as shown in Figure 14(b), all light rays in the beam have the same optical path lengths and no turbulence occurs in the film interference waveform. This results in quite excellent photometry performance in measuring thin films and multi-layer films. By the way, in a method for measuring a film thickness from the analysis of the above-described film interference spectrum, the thin film measurement limit (d limit ) is mainly determined by a photometric wavenumber range (Δνcm -1 ), which is represented as follows: d limit = 1 Δν · 1 2n Here, n designates a refractive index of the film. However, unless the transmitting or reflecting conditions of light beam in all the optical systems constituting the spectroscope and in the measurement sample meet the photometric wavenumber range Δν, the spectroscope having a certain photometric wavenumber range Δν cannot be obtained, resulting in difficulty in optically measuring wide wavenumber range. As an example, a description is given of an application to measuring of a semiconductor film thickness by a combination of optical parts employed in Fourier-transformation infrared spectroscope (hereinafter referred to as FT-IR spectroscope). In Figure 11, a nichrome lamp is used as light source 10, potassium bromide (KBr) is used as beam splitter 14 and a photodetector employing mercury cadmium telluride (hereinafter referred to as MCT detector) is used as photodetector 23. In Figure 12 showing a film composition of the sample 11, a semiconductor film 2 comprising an Al 0.45 Ga 0.55 As layer having a refractive index and a thickness (n 1 , d 1 ) = (3.45, 0.42 microns), a semiconductor film 3 comprising an Al 0.15 Ga 0.85 As layer having (n 2 , d 2 ) = (3.56, 0.09 microns), a semiconductor film 4 comprising an Al 0.45 Ga 0.55 As layer having (n 3 , d 3 ) = (3.45, 1.55 microns) and a semiconductor substrate 1 comprising a GaAs substrate having a refractive index n s of 3.62 are employed. Figure 15 shows a fundamental reflection spectrum of GaAs semiconductor substrate, which is obtained by measuring a sensitivity wavenumber range of a whole spectroscope by the FT-IR spectroscope having the above-described combination. As shown in Figure 15, the sensitivity can be obtained in a range approximately from 5000cm -1 to 600cm -1 . Figure 16 shows a reflection spectrum, which is obtained by measuring film interference spectrum of the above-described three layer semiconductor film by the FT-IR spectroscope having the same combination. In the figure, there is a waveform accompanying with the film interference. Figure 17 shows a Spatialgram, which is obtained by taking out and transforming by reverse Fourier transformation, a wavenumber range from an arrow A (4300cm -1 ) to an arrow B (800cm -1 ) having photometric sensitivity in Figure 16. Judging from Figure 17, regardless of a waveform obtained by measuring a three-layer film, three side burst peaks do not appear and only a single side burst peak corresponding to the third layer appears. According to the formula (3), in the photometric wavenumber range Δν=4300-800=3500cm -1 , the thin film measurement limit d limit (3500) is 0.42 microns, which is equal to the thickness of the first layer semiconductor film 2, showing that it is difficult to distinguish the first layer from the second layer. Then, a description is given of an example which adopts the most suitable combination of optical systems capable of measuring a wavenumber range in a wider range. A tungsten halogen lamp is employed as light source 10, calcium fluoride is employed as beam splitter 14 and an MCT detector is employed as photodetector 23. Figure 18 shows a fundamental reflection spectrum of a GaAs substrate employing the optical system of this combination. As shown in Figure 18, it is admitted that there is the sensitivity in a range from about 11500cm -1 to 2500cm -1 . The limit at higher wavenumber side is a sensitivity limit of the MCT detector and the limit at lower wavenumber side is determined by the wavelength of emitted light from the tungsten halogen lamp. Figure 19 shows an interference spectrum of the semiconductor film of the above-described three layer structure, which is obtained by the optical measurement employing the optical system of this combination. Figure 20 shows a Spatialgram, which is obtained by taking out and transforming by reverse Fourier transformation, a wavenumber range from an arrow A (11000cm - 1 ) to an arrow B (2800cm -1 ) having photometric sensitivity shown in Figure 19. According to the formula (3), in the photometric wavenumber range Δν of 8200cm -1 , the thin film measurement limit d limit (8200) is 0.18 microns and the measurement limit (measurement sensitivity) is enhanced. However, since the second layer of the sample 11 has a half value thickness of the measurement limit (d 2 =0.09microns), the first and the second side burst peaks overlap with each other and only the third side burst peak clearly appears. The prior art apparatus for measuring a semiconductor layer thickness is constructed as described above, and there is a limit in optical measurement in a wide wavenumber range by Fourier spectroscopic photometry employing combination of present optical materials, resulting in a problem that thicknesses of thin semiconductor films cannot be measured. It is an object of the present invention to provide an apparatus for measuring a semiconductor layer thickness that, overcoming an optical measurement limit due to optical parts, can optically measure in a wider wavenumber range so as to measure nondestructively and in noncontact a thinner semiconductor multi-layer film thickness. Other objects and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific embodiment are given by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to the those skilled in the art from this detailed description. In an apparatus for measuring a semiconductor layer thickness according to the present invention, a photodetector, a light transmitting material or a light source are optically combined so that parts of respective wavenumber characteristic ranges may be overlapped with each other. In accordance with the present invention, the sum of respective wavenumber ranges of the respective components are obtained as a whole wavenumber range and an optical measurement can be realized in a wider wavenumber range than that by a single material of respective components. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1(a) to 1(c) are schematic diagrams showing a constitution of an apparatus for measuring a semiconductor layer thickness and a constitution of a complexed type photodetector used therein in accordance with a first embodiment of the present invention. Figure 2 is a diagram showing sensitivity characteristics of an MCT detector and a Si detector constituting the complexed type photodetector in the first embodiment of the present invention. Figure 3 is a diagram showing a sensitivity characteristic of the complexed type photodetector in the first embodiment of the present invention. Figure 4 is a diagram showing a film interference spectrum obtained in measuring laminated film thickness employing the complexed type photodetector in the first embodiment of the present invention. Figure 5 is a diagram showing a Spatialgram obtained by executing reverse Fourier-transformation to the film interference spectrum. Figure 6 is a diagram showing a constitution of a complexed type photodetector of an apparatus for measuring a semiconductor layer thickness in accordance with a second embodiment of the present invention. Figure 7 is a diagram showing a constitution of a complexed type photodetector of an apparatus for measuring a semiconductor layer thickness in accordance with a third embodiment of the present invention. Figure 8 is a diagram showing a table reciting wavenumber characteristic ranges of various kinds of light source, photodetector and beam splitter. Figures 9(a) to 9(c) are schematic diagrams showing a constitution of a complexed type beam splitter as a light transmission member of an apparatus for measuring a semiconductor layer thickness in accordance with a fourth embodiment of the present invention. Figure 10 is a schematic diagram showing a constitution of a light source of an apparatus for measuring a semiconductor layer thickness in accordance with a fifth embodiment of the present invention. Figure 11 is a schematic diagram showing a constitution of a prior art apparatus for measuring a semiconductor layer thickness by Fourier-transformation spectroscopy. Figure 12 is a schematic diagram showing optical paths of primary reflected light in a three-layer film formed on a substrate. Figure 13 is a graph showing a Spatialgram obtained by executing reverse Fourier transformation to the film interference spectrum which is obtained from the primary reflected light. Figures 14(a) and 14(b) are schematic diagrams showing optical paths of a collected light beam and a parallel light beam of primary reflected light in a three-layer film formed on a substrate. Figure 15 is a diagram showing a sensitivity characteristic of the prior art apparatus for measuring a semiconductor layer thickness employing Fourier-transformation spectroscopy. Figure 16 is a diagram showing film interference spectrum of a three-layer film measured by a prior art apparatus for measuring a semiconductor layer thickness employing Fourier-transformation spectroscopy. Figure 17 is a graph showing a Spatialgram obtained by executing reverse Fourier transformation to the film interference spectrum. Figure 18 is a diagram showing a sensitivity characteristic of a prior art apparatus for measuring a semiconductor layer thickness by Fourier-transformation spectroscopy employing an optimized combination of optical parts. Figure 19 is a graph showing a film interference spectrum of a three-layer film measured by the prior art apparatus for measuring a semiconductor layer thickness. Figure 20 is a graph showing a Spatialgram obtained by executing reverse Fourier transformation to the film interference spectrum. A first embodiment of the present invention will be described in detail with reference to Figures 1(a) to 1(c). In Figure 1(a) showing a photodetector corresponding to the photodetector 23 in Figure 11, a photodetector 300 in this first embodiment is of a complexed type one in which the light beam collected by the collecting mirror 22 in Figure 11 is divided into two beams so as to be incident to an MCT detector 31 and a silicon (Si) detector 32 through a beam splitter 30, the respective beams are transformed into electric signals at the same time, and they are synthesized to produce a signal in an electric signal synthesizer circuit 33. The output of the synthesizer circuit is processed to result in an interference spectrum. This construction makes it possible to obtain a detection signal in wavenumber sensitivity ranges of both of the MCT detector 31 and the Si detector 32. As a result, a photometric wavenumber range is enlarged to a range of the sum of the respective single detectors. Figure 1(b) shows a construction in which the complexed type photodetector 300 shown in Figure 1(a) is employed for the FT-IR spectroscope in Figure 11 to be applied to an actual measurement of a semiconductor layer thickness. In the figure, a tungsten halogen lamp is employed as light source 10 and calcium fluoride is employed as material of the beam splitter 14. Figure 2 shows sensitivity characteristics of the MCT detector and the Si detector respectively as A and B. As shown in Figure 3, the sensitivity characteristic of the photodetector 300 of complexed type incorporating the MCT detector and the Si detector is equal to the sum of the respective sensitivity characteristics of the photodetectors 31 and 32. Figure 4 shows a film interference spectrum of the above-described AlGaAs semiconductor three-layer film optically measured by the complexed type photodetector 300. In the figure, interference light is measured in a photometric wavenumber range Δν=12300cm -1 from about 15000cm -1 (arrow A) to about 2700cm -1 (arrow B). Figure 5 shows a Spatialgram obtained by transforming this wavenumber range Δν by reverse Fourier-transformation. Although from the formula (3), the thin film measurement limit d limit (12300) is 0.12 microns also in this case as described above, thicknesses obtained from the respective side burst peaks A, B and C are respectively 0.42 microns, 0.09 microns and 1.54 microns as shown in Figure 5, which represent approximately actual thicknesses. This corroborates how effective to enlarge the wavenumber range in measuring thin films. Here, a limit at higher wavenumber side of 15000cm -1 depends on a transmission characteristic of the beam splitter 30 comprising calcium fluoride in Figure 1(a) and it is possible to carry out an optical measurement of further higher wavenumber by improving this beam splitter. However, since band end gap absorption of Al 0.45 Ga 0.55 As crystal employed for the sample 11 is close to Eg=1.99eV, namely, 16000cm -1 , even if a further higher wavenumber photometry is employed, it must be noted that that sample can no longer provide any significance of measurement caused by the energy absorption or abnormal dispersion of a refractive index by AlGaAs as the sample. Still, as shown in Figure 1(c), the MCT detector 31 in Figure 1(a) can be replaced by a low cost tri-glycine sulfate (TGS) [(NH 2 CH 2 COOH) 3 H 2 SO 4 ] detector 43 which is generally used for simple photometry. In this case, since parts for the means cooling the MCT detector are not required, the apparatus can be simplified and a production cost can be reduced. In accordance with this embodiment, the light beam reflected by the sample 11 is received to be detected by two photodetectors such as the MCT detector 31 and the Si detector 32 having different wavenumber sensitivity combined with together, and therefore a whole photometric wavenumber range is enlarged to a range corresponding to the sum of those of the respective photodetectors, and a detected signal covering the both wavenumber sensitivity ranges can be obtained. Thus, a measurement of a semiconductor layer thickness which could not be measured in the prior art optical system is enabled. A second embodiment of the present invention will be described in detail with reference to Figure 6. As shown in Figure 6, in this embodiment the MCT detector 31 and the Si detector 32 are employed as a complexed type photodetector 301. These detectors are fixed in a liquid nitrogen cooler 50 which cools the MCT detector 31 with epoxy resin or the like to be arranged on the same plane. Photometric light beam is collected by the collecting mirror 22 in Figure 1(b) and enters directly into both of the photodetectors 31 and 32, and is detected at the same time. Then, the electric signals output from the detectors are synthesized in the electric signal synthesizer circuit 33. By employing such construction, influences due to the transmission characteristic of the beam splitter 30 in the photodetector 300 disappear and the photometric wavenumber ranges of both the photodetectors 31 and 32 are obtained more directly, resulting in enhancing the photometry preciseness. In Figure 7 showing a photodetector in accordance with a third embodiment of the present invention, three kinds of photodetectors are employed as a complexed type photodetector 302. More particularly, while the sensitivity characteristic of the above-described second embodiment becomes as shown in Figure 3 having a decline around 9000cm -1 and the photometric sensitivity in this vicinity has a lower value, this sensitivity dell is interpolated by arranging a germanium (Ge) detector 44 on the same plane as the MCT detector 31 and the Si detector 33, as shown in Figure 7. In this case, it is desirable to employ the MCT detector having a larger area than other detectors because the MCT detector is inferior a little in sensitivity to other detectors. By such construction, a photodetector having a high sensitivity and a wide photometric wavenumber range can be obtained. Figure 8 shows a table chart representing wavenumber characteristic ranges of various kinds of light sources, photodetectors and beam splitters. In the column of the light source, the wavenumber characteristic ranges of tungsten lamp, nichrome lamp and high pressure mercury arc lamp, respectively, are presented with some parts thereof overlapping with each other. In the column of the photodetector, the wavenumber characteristic ranges of the photodetectors respectively comprising silicon, indium arsenic, indium antimonide, MCT, TGS and liquid helium cooled type germanium are presented. In the column of the beam splitter, the wavenumber characteristic ranges of the beam splitters respectively comprising quartz, calcium fluoride, potassium bromide, cesium iodide, Mylar (polyethyleneterephthalate) [(OCH 2 CH 2 OCOC 6 H 4 CO) n ] of 5 microns, 12 microns and 25 microns, respectively, and wired grid polarizer are presented. In the column of the photodetector, according to the sum of the wavenumber characteristic ranges of both the MCT detector and the Si detector, possibility of detection over a wide range from around 25000cm -1 to 500cm -1 is shown. This suggests that a light in range from visible light (blue light) to far infrared ray can be detected by a photodetector of a complexed type incorporating an MCT detector and a Si detector for optimization. In Figure 8, subscripts of A, B or C in parentheses represent a photodetector comprising the same material but with different composition rate. While two or three kinds of photodetectors are employed in the first to the third embodiments, four or more kinds of photodetectors can be employed. A fourth embodiment of the present invention will be described in detail with reference to Figures 9(a) to 9(c). Figures 9(a) and 9(b) respectively show light transmission members corresponding to the beam splitter 14 in Figure 11 according to the fourth embodiment of the present invention. In both constructions of Figures 9(a) and 9(b), reference numeral 34 designates a region comprising calcium fluoride (CaF 2 ) and numeral 35 designates a region comprising quartz (SiO 2 ). By employing two materials having different light transmission bonds in each half of the light transmission area of the beam splitter, the characteristic wavenumber range thereof as a beam splitter is enlarged to the sum of the respective characteristic wavenumber ranges of the two materials employed singly. In the above-described construction, according to the column of the beam splitter in the table chart of Figure 8, the whole wavenumber characteristic range of the beam splitter employing calcium fluoride (CaF 2 ) and quartz (SiO 2 ) is approximately from 25000cm -1 to 2000cm -1 . In addition, the construction of Figure 9(b) having more than two different material regions for the plural sectioned areas arranged alternately can decrease the destruction of wavefront of transmission light beam to a larger extent than the construction of Figure 9(a) having two different material regions for the half sectioned areas, thereby providing a more uniform in-plane beam intensity. The beam splitter may comprise three materials as shown in Figure 9(c). In this construction of Figure 9(c), a calcium fluoride (CaF 2 ) region 34, a quartz (SiO 2 ) region 35 and a potassium bromide (KBr) region 42 are arranged at the trisected areas of the light transmission region. According to the column of the beam splitter of Figure 8, the beam splitter including three materials of calcium fluoride, quartz and potassium bromide makes it possible to conduct optical measurement in the wavenumber range of approximately from 25000cm -1 to 400cm -1 , thereby enlarging the long wavelength band to a larger extent than the construction employing two materials as shown in Figures 9(a) and 9(b). Further, while the beam splitter comprises three kinds of material in the fourth embodiment, the beam splitter can comprise four or more kinds of material. A fifth embodiment of the present invention will be described in detail with reference to Figure 10. Figure 10 shows a light source corresponding to light source 10 in Figure 11. In Figure 10, light beams from a tungsten halogen lamp 36 and a nichrome luminous lamp 37 are collected by collecting mirrors 38 and 39 respectively and they are synthesized through a beam splitter 40. Then, the synthesized beam is reformed for its wavefront by an aperture 41 so as to be a collected light source and it is introduced into the collimating mirror 12 of Figure 11. Since the optical path lengths from the aperture 41 to the respective lamps 36 and 37 are set to be equal, the respective light beams from the lamps which are synthesized at the beam splitter 40 have the same wavefronts at the aperture 41 and become the same parallel light beam at the collimating mirror 12. Thus, by combining the tungsten halogen lamp 36 and the nichrome luminous lamp 37 and synthesizing the outgoing beams therefrom, it is possible to irradiate light beam of the wavenumber range from 25000cm -1 to 200cm -1 as shown in the column of light sources of Figure 8. Further, while two kinds of light sources are employed in the fifth embodiment, three or more kinds of light sources can be employed. In addition, while the beam splitter 14 in the Michelson interferometer 13 (Figure 1(b)) is employed for illustrating the fourth embodiment, for other beam splitters in an optical path from the light source 10 to the photodetector 23 such as the beam splitter 30 in Figure 1(a) and the beam splitter 40 in Figure 10, the construction of the fourth embodiment can be employed. As described above, in an apparatus for measuring a semiconductor layer thickness according to the present invention, a photodetector, a light transmitting material, and a light source are optically combined so that parts of respective wavenumber characteristic ranges may be overlapped with each other. Thereby, a wavenumber range of the sum of respective wavenumber ranges of the respective components is obtained, enabling Fourier-transformation spectroscopy over a wavenumber range as wide as possible in conducting an optical measurement, thereby enhancing greatly the thin film measurement limit in semiconductor layer thicknesses measurement employing film interference spectrum analysis.

Claims: An apparatus for measuring a semiconductor layer thickness, comprising: a light source emitting light for measurement; an interferometer emitting interference light modulated with time by applying modulation to said light from said light source; an optical system including a light transmission member for introducing said interference light into a measurement sample comprising at least one-layer film laminated on a substrate; light receiving means receiving interference light reflected from said laminated film of said sample; means for extracting only a film interference component from said reflected interference light; means for calculating a thickness of said laminated film from an interference intensity waveform of said film interference component; and said light receiving means comprising a plurality of photodetectors having respective photometric wavenumber ranges some parts of which are overlapped with each other. An apparatus for measuring a semiconductor layer thickness, comprising: a light source emitting light for measurement; an interferometer emitting interference light modulated with time by applying modulation to said light from said light source; an optical system including a light transmission member for introducing a beam of said interference light into a measurement sample comprising at least one-layer film laminated on a substrate; light receiving means receiving interference light reflected from said laminated film of said sample and having a photometric wavenumber range wide enough to make feasible calculation, from signals corresponding to said reflected interference light, thickness values of said laminated film; means for extracting only a film interference component from said reflected interference light; means for calculating a thickness of said laminated film from an interference intensity waveform of said film interference component; and said light transmission member of said optical system incorporating a plurality of unit materials each transmitting a cross sectional portion of said beam of interference light, said unit materials having respective transmission wavenumber ranges some parts of which are overlapped with each other. An apparatus for measuring a semiconductor layer thickness, comprising: a light source emitting light for measurement; an interferometer emitting interference light modulated with time by applying modulation to said light from said light source; an optical system including a light transmission member for introducing said interference light into a measurement sample comprising at least one-layer film laminated on a substrate; light receiving means receiving interference light reflected from said laminated film of said sample and having a photometric wavenumber range wide enough to make feasible calculation, from signals corresponding to said reflected interference light, thickness values of said laminated film; means for extracting only a film interference component from said reflected interference light; means for calculating a thickness of said laminated film from an interference intensity waveform of said film interference component; and said light source comprising a plurality of unit light sources emitting respectively light of different wavelengths and the respective lights being optically synthesized to be emitted as said light for measurement. The apparatus for measuring a semiconductor layer thickness of claim 1 wherein said plurality of photodetectors constituting said light receiving means are arranged adjacent to each other on the same plane. The apparatus for measuring a semiconductor layer thickness of claim 1 wherein said plurality of photodetectors constituting said light receiving means are designed such that the interference light reflected from said laminated layer film of said sample is divided into plural through an optical member and the divided plural light beams are received by respective photodetectors. The apparatus for measuring a semiconductor layer thickness of claim 4 wherein a mercury cadmium telluride photodetector, a silicon photodetector and a germanium photodetector are employed as said plurality of photodetectors. The apparatus for measuring a semiconductor layer thickness of claim 5 wherein a mercury cadmium telluride photodetector and a silicon photodetector are employed as said plurality of photodetectors. The apparatus for measuring a semiconductor layer thickness of claim 5 wherein a tri-glycine sulfate photodetector and a silicon photodetector are employed as said plurality of photodetectors. The apparatus for measuring a semiconductor layer thickness of claim 2 wherein calcium fluoride and quartz are employed as said plurality of unit members having respective transmission wavenumber ranges of some parts of which are overlapped with each other. The apparatus for measuring a semiconductor layer thickness of claim 2 wherein calcium fluoride, quartz and potassium bromide are employed as said plurality of unit members having transmission wavenumber ranges some parts of which are overlapped with each other. The apparatus for measuring a semiconductor layer thickness of claim 3 wherein a tungsten halogen lamp and a nichrome luminous lamp are employed as said plurality of unit lights. An apparatus for measuring a semiconductor layer thickness, comprising: a light source emitting light for measurement; an interferometer emitting interference light modulated with time by applying modulation to said light from said light source; an optical system including a light transmission member for introducing said interference light into a measurement sample comprising at least one-layer film laminated on a substrate; light receiving means receiving interference light reflected from said laminated film of said sample and having a photometric wavenumber range wide enough to make feasible calculation, from signals corresponding to said reflected interference light, thickness values of said laminated film; means for extracting only a film interference component from said reflected interference light; means for calculating a thickness of said laminated film from an interference intensity waveform of said film interference component; and said light source, said optical system and said light receiving means respectively comprising a plurality of members optically combined having respective transmission wavenumber characteristic ranges some parts of which are overlapped with each other.

Inventors: FUKASAWA RYOICHI, HATTORI RYO, NISHIZAWA SEIZI, TAKAHASHI TOKUJI, FUKASAWA, RYOICHI, HATTORI, RYO, NISHIZAWA , SEIZI, TAKAHASHI, TOKUJI, FUKASAWA, RYOICHI, JASCO CORPORATION, HATTORI, RYO, C/O MITSUBISHI DENKI K.K., NISHIZAWA , SEIZI, JASCO CORPORATION, TAKAHASHI, TOKUJI, JASCO CORPORATION
Applicants: JASCO CORP, MITSUBISHI ELECTRIC CORP, JASCO CORPORATION, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1993
Main classification: G01B11
IPC codes: G01B11