Abstract

An automatic infrared ellipsometer for the study of surface and interface phenomena has been constructed. The system is based on a Fourier transform spectrometer that we equipped with an ellipsometer unit. Polarizers and analyzers are of the ion-etched wire-grid type. Their rotation is governed by means of a computer-controlled stepping-motor system. A discussion of calibration procedures for the infrared range is given, and special attention is given to the problem of selecting the best measurement strategy. The polarization state of the reflected beam is determined by measuring the intensity at 72 regularly spaced polarizer/analyzer settings. It is found that the effects of interferometric polarization, beam wandering, and detector dichroism cannot be neglected. However, these error sources have been eliminated by analyzing the zeroth, second, and fourth harmonic components of the azimuthally recorded intensity. Both the multiplex advantage of Fourier transform spectroscopy and the phase sensitivity of ellipsometry are combined in this instrument. Measurements on superconducting films, superlattices, and doped GaAs films are reported.

© 1992 Optical Society of America

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References

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  1. J. R. Beattie, “Optical constants of metals in the infrared—experimental methods,” Philos. Mag. 46, 235–245 (1955).
  2. O. Hunderi, J. Jensen, “Fourier-transform infrared ellipsometer for liquid crystal characterization,” SINTEF Rep. STF 34F84108 (SINTEF, Trondheim, Norway, 1984).
  3. M. J. Dignam, M. O. Baker, “Analysis of a polarizing Michelson interferometer,” Appl. Spectrosc. 35, 186–193 (1981).
    [CrossRef]
  4. A. Röseler, “Spectroscopic ellipsometry in the infrared,” Infrared Phys. 21, 349–353 (1981).
    [CrossRef]
  5. A. Röseler, “Spectroscopic infrared-ellipsometry with the Fourier-transform-spectrometer,” Preprint 85–4 (Zentralinstitut für Optik und Spectroskopie, Berlin, 1985).
  6. B. Drevillon, “Spectroscopic ellipsometry of ultrathin films: from UV to IR,” Thin Solid Films 163, 157–166 (1988).
    [CrossRef]
  7. D. L. Allara, J. D. Swalen, “An infrared reflection spectroscopy study of oriented cadmium arachidate monolayer films on evaporated silver,” J. Phys. Chem. 86, 2700–2704 (1982).
    [CrossRef]
  8. A. E. Dowrey, C. Marcott, “Approach to studying adsorbates on metal surfaces,” Appl. Spectrosc. 36, 414–416 (1982).
    [CrossRef]
  9. D. L. Allara, A. Raca, C. A. Pryde, “Distortions of band shapes in external reflection infrared spectra of thin polymer films on metal substrates,” Macromolecules 11, 1215–1220 (1978).
    [CrossRef]
  10. B. Jasse, J. L. Koenig, “Orientational measurements in polymers using vibrational spectroscopy,” J. Macromol. Sci. Rev. Macromol. Chem. C 17, 61–135 (1979).
    [CrossRef]
  11. F. Ferrieu, “Infrared spectroscopic ellipsometry using a Fourier transform infrared spectrometer: some applications in thin-film characterization,” Rev. Sci. Instrum. 60, 3212–3216 (1989).
    [CrossRef]
  12. J. Bremer, O. Hunderi, Fanping, “Ellipsometric characterization of thin films and superlattices,” Mater. Sci. Eng. B 5, 285–289 (1990).
    [CrossRef]
  13. R. M. A. Azzam, N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, Amsterdam, 1977).
  14. H. G. Liljenwall, A. G. Mathewson, “Two alignment methods for the polarizer and analyzer in an ellipsometer,” GIPR-028 (Department of Physics, Chalmers University of Technology, Gothenburg, Sweden, 1970).
  15. A. L. Fymat, “Polarization effects in Fourier spectroscopy. I: Coherency matrix representation,” Appl. Opt. 11, 160–173 (1972).
    [CrossRef] [PubMed]
  16. K. Leonhardt, “Gütezahlen und Gütefunktionen für Strahlenteiler und praktische Berechnung von Jonesmatrizen in Zweistrahlinterferometern,” Optik 36, 529–546 (1972).

1990

J. Bremer, O. Hunderi, Fanping, “Ellipsometric characterization of thin films and superlattices,” Mater. Sci. Eng. B 5, 285–289 (1990).
[CrossRef]

1989

F. Ferrieu, “Infrared spectroscopic ellipsometry using a Fourier transform infrared spectrometer: some applications in thin-film characterization,” Rev. Sci. Instrum. 60, 3212–3216 (1989).
[CrossRef]

1988

B. Drevillon, “Spectroscopic ellipsometry of ultrathin films: from UV to IR,” Thin Solid Films 163, 157–166 (1988).
[CrossRef]

1982

D. L. Allara, J. D. Swalen, “An infrared reflection spectroscopy study of oriented cadmium arachidate monolayer films on evaporated silver,” J. Phys. Chem. 86, 2700–2704 (1982).
[CrossRef]

A. E. Dowrey, C. Marcott, “Approach to studying adsorbates on metal surfaces,” Appl. Spectrosc. 36, 414–416 (1982).
[CrossRef]

1981

M. J. Dignam, M. O. Baker, “Analysis of a polarizing Michelson interferometer,” Appl. Spectrosc. 35, 186–193 (1981).
[CrossRef]

A. Röseler, “Spectroscopic ellipsometry in the infrared,” Infrared Phys. 21, 349–353 (1981).
[CrossRef]

1979

B. Jasse, J. L. Koenig, “Orientational measurements in polymers using vibrational spectroscopy,” J. Macromol. Sci. Rev. Macromol. Chem. C 17, 61–135 (1979).
[CrossRef]

1978

D. L. Allara, A. Raca, C. A. Pryde, “Distortions of band shapes in external reflection infrared spectra of thin polymer films on metal substrates,” Macromolecules 11, 1215–1220 (1978).
[CrossRef]

1972

A. L. Fymat, “Polarization effects in Fourier spectroscopy. I: Coherency matrix representation,” Appl. Opt. 11, 160–173 (1972).
[CrossRef] [PubMed]

K. Leonhardt, “Gütezahlen und Gütefunktionen für Strahlenteiler und praktische Berechnung von Jonesmatrizen in Zweistrahlinterferometern,” Optik 36, 529–546 (1972).

1955

J. R. Beattie, “Optical constants of metals in the infrared—experimental methods,” Philos. Mag. 46, 235–245 (1955).

Allara, D. L.

D. L. Allara, J. D. Swalen, “An infrared reflection spectroscopy study of oriented cadmium arachidate monolayer films on evaporated silver,” J. Phys. Chem. 86, 2700–2704 (1982).
[CrossRef]

D. L. Allara, A. Raca, C. A. Pryde, “Distortions of band shapes in external reflection infrared spectra of thin polymer films on metal substrates,” Macromolecules 11, 1215–1220 (1978).
[CrossRef]

Azzam, R. M. A.

R. M. A. Azzam, N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, Amsterdam, 1977).

Baker, M. O.

Bashara, N. M.

R. M. A. Azzam, N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, Amsterdam, 1977).

Beattie, J. R.

J. R. Beattie, “Optical constants of metals in the infrared—experimental methods,” Philos. Mag. 46, 235–245 (1955).

Bremer, J.

J. Bremer, O. Hunderi, Fanping, “Ellipsometric characterization of thin films and superlattices,” Mater. Sci. Eng. B 5, 285–289 (1990).
[CrossRef]

Dignam, M. J.

Dowrey, A. E.

Drevillon, B.

B. Drevillon, “Spectroscopic ellipsometry of ultrathin films: from UV to IR,” Thin Solid Films 163, 157–166 (1988).
[CrossRef]

Fanping,

J. Bremer, O. Hunderi, Fanping, “Ellipsometric characterization of thin films and superlattices,” Mater. Sci. Eng. B 5, 285–289 (1990).
[CrossRef]

Ferrieu, F.

F. Ferrieu, “Infrared spectroscopic ellipsometry using a Fourier transform infrared spectrometer: some applications in thin-film characterization,” Rev. Sci. Instrum. 60, 3212–3216 (1989).
[CrossRef]

Fymat, A. L.

Hunderi, O.

J. Bremer, O. Hunderi, Fanping, “Ellipsometric characterization of thin films and superlattices,” Mater. Sci. Eng. B 5, 285–289 (1990).
[CrossRef]

O. Hunderi, J. Jensen, “Fourier-transform infrared ellipsometer for liquid crystal characterization,” SINTEF Rep. STF 34F84108 (SINTEF, Trondheim, Norway, 1984).

Jasse, B.

B. Jasse, J. L. Koenig, “Orientational measurements in polymers using vibrational spectroscopy,” J. Macromol. Sci. Rev. Macromol. Chem. C 17, 61–135 (1979).
[CrossRef]

Jensen, J.

O. Hunderi, J. Jensen, “Fourier-transform infrared ellipsometer for liquid crystal characterization,” SINTEF Rep. STF 34F84108 (SINTEF, Trondheim, Norway, 1984).

Koenig, J. L.

B. Jasse, J. L. Koenig, “Orientational measurements in polymers using vibrational spectroscopy,” J. Macromol. Sci. Rev. Macromol. Chem. C 17, 61–135 (1979).
[CrossRef]

Leonhardt, K.

K. Leonhardt, “Gütezahlen und Gütefunktionen für Strahlenteiler und praktische Berechnung von Jonesmatrizen in Zweistrahlinterferometern,” Optik 36, 529–546 (1972).

Liljenwall, H. G.

H. G. Liljenwall, A. G. Mathewson, “Two alignment methods for the polarizer and analyzer in an ellipsometer,” GIPR-028 (Department of Physics, Chalmers University of Technology, Gothenburg, Sweden, 1970).

Marcott, C.

Mathewson, A. G.

H. G. Liljenwall, A. G. Mathewson, “Two alignment methods for the polarizer and analyzer in an ellipsometer,” GIPR-028 (Department of Physics, Chalmers University of Technology, Gothenburg, Sweden, 1970).

Pryde, C. A.

D. L. Allara, A. Raca, C. A. Pryde, “Distortions of band shapes in external reflection infrared spectra of thin polymer films on metal substrates,” Macromolecules 11, 1215–1220 (1978).
[CrossRef]

Raca, A.

D. L. Allara, A. Raca, C. A. Pryde, “Distortions of band shapes in external reflection infrared spectra of thin polymer films on metal substrates,” Macromolecules 11, 1215–1220 (1978).
[CrossRef]

Röseler, A.

A. Röseler, “Spectroscopic ellipsometry in the infrared,” Infrared Phys. 21, 349–353 (1981).
[CrossRef]

A. Röseler, “Spectroscopic infrared-ellipsometry with the Fourier-transform-spectrometer,” Preprint 85–4 (Zentralinstitut für Optik und Spectroskopie, Berlin, 1985).

Swalen, J. D.

D. L. Allara, J. D. Swalen, “An infrared reflection spectroscopy study of oriented cadmium arachidate monolayer films on evaporated silver,” J. Phys. Chem. 86, 2700–2704 (1982).
[CrossRef]

Appl. Opt.

Appl. Spectrosc.

Infrared Phys.

A. Röseler, “Spectroscopic ellipsometry in the infrared,” Infrared Phys. 21, 349–353 (1981).
[CrossRef]

J. Macromol. Sci. Rev. Macromol. Chem. C

B. Jasse, J. L. Koenig, “Orientational measurements in polymers using vibrational spectroscopy,” J. Macromol. Sci. Rev. Macromol. Chem. C 17, 61–135 (1979).
[CrossRef]

J. Phys. Chem.

D. L. Allara, J. D. Swalen, “An infrared reflection spectroscopy study of oriented cadmium arachidate monolayer films on evaporated silver,” J. Phys. Chem. 86, 2700–2704 (1982).
[CrossRef]

Macromolecules

D. L. Allara, A. Raca, C. A. Pryde, “Distortions of band shapes in external reflection infrared spectra of thin polymer films on metal substrates,” Macromolecules 11, 1215–1220 (1978).
[CrossRef]

Mater. Sci. Eng. B

J. Bremer, O. Hunderi, Fanping, “Ellipsometric characterization of thin films and superlattices,” Mater. Sci. Eng. B 5, 285–289 (1990).
[CrossRef]

Optik

K. Leonhardt, “Gütezahlen und Gütefunktionen für Strahlenteiler und praktische Berechnung von Jonesmatrizen in Zweistrahlinterferometern,” Optik 36, 529–546 (1972).

Philos. Mag.

J. R. Beattie, “Optical constants of metals in the infrared—experimental methods,” Philos. Mag. 46, 235–245 (1955).

Rev. Sci. Instrum.

F. Ferrieu, “Infrared spectroscopic ellipsometry using a Fourier transform infrared spectrometer: some applications in thin-film characterization,” Rev. Sci. Instrum. 60, 3212–3216 (1989).
[CrossRef]

Thin Solid Films

B. Drevillon, “Spectroscopic ellipsometry of ultrathin films: from UV to IR,” Thin Solid Films 163, 157–166 (1988).
[CrossRef]

Other

O. Hunderi, J. Jensen, “Fourier-transform infrared ellipsometer for liquid crystal characterization,” SINTEF Rep. STF 34F84108 (SINTEF, Trondheim, Norway, 1984).

A. Röseler, “Spectroscopic infrared-ellipsometry with the Fourier-transform-spectrometer,” Preprint 85–4 (Zentralinstitut für Optik und Spectroskopie, Berlin, 1985).

R. M. A. Azzam, N. M. Bashara, Ellipsometry and Polarized Light, (North-Holland, Amsterdam, 1977).

H. G. Liljenwall, A. G. Mathewson, “Two alignment methods for the polarizer and analyzer in an ellipsometer,” GIPR-028 (Department of Physics, Chalmers University of Technology, Gothenburg, Sweden, 1970).

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Figures (9)

Fig. 1
Fig. 1

Optical layout of the IR ellipsometer. The beam from the interferometer (IN) is intercepted by the polarizer (P1). After being reflected from the sample surface (SA) the beam is transmitted through the analyzer (P2) and focused toward either the DTGS or the mercury cadmium telluride (MCT) detector after reflections in mirrors M1–M3. The angular settings of P1 and P2 are governed by means of stepping motors, and the zero points for the azimuthal angle are found by means of a calibration routine that is discussed in the text. The smallest step size is 0.34 arc sec. Motors are usually run with a stepping frequency near 1 kHz. The angle of incidence can be varied in increments of 5° between 45° and 90°.

Fig. 2
Fig. 2

Infrared ellipsometry system (schematic). The ellipsometer attachment (see text and the caption to Fig. 1) is connected to a commercial unit containing a source (SO) and interferometer (IN). Step-motor control occurs through the driver (DR). The data transfer from the electronics module (EM) can take place either through a parallel interface or an IEEE-488 card. There are four peripherals: PC terminal (PC), spectrometer terminal (ST), printer (PR), and plotter (PL).

Fig. 3
Fig. 3

Extinction curves that show the zero-retardation signal (total intensity) as a function of an analyzer angle for two equivalent settings where the polarizer angle is 45° (upper curve) and −45° (lower curve), respectively. There is no sample in the ellipsometer.

Fig. 4
Fig. 4

Dichroic transmission ratio between the directly transmitted intensity in the horizontal p and vertical s directions as a function of energy for a DTGS detector. Analyzer angles are 0° and 90°, while the polarizer angle is constant and equal to 45°. Note that the intensity levels of both polarization directions also depend on beam-wandering effects (see text).

Fig. 5
Fig. 5

Wave-number-dependent polarization in the directly transmitted beam from the interferometer. The analyzer angle is constant and equal to 45°. The curve shows the ratio between the p and s polarizations in the interferometer as a function of energy.

Fig. 6
Fig. 6

Oscillating curve: the second-order sinusoidal Fourier coefficient as a function of energy in the mid-IR region. Smooth curve: coefficient after using the algorithm discussed in the text. There is no sample in the ellipsometer.

Fig. 7
Fig. 7

Ellipsometrically recorded phase (upper curve) and amplitude angles (lower curve) as a function of energy for a Pt/Al2O3 superlattice that is deposited on a glass substrate. The total thickness is 3750 Å, and the Pt and Al2O3 layers are 25 and 100 Å, respectively.

Fig. 8
Fig. 8

Upper curve: phase difference between the p and s components of light that is reflected from a doped GaAs sample. Lower curve: amplitude angle. The sample thickness is 0.45 mm, and the p-doped surface layer extends 0.5 μm into the surface region. The free-carrier concentration is 3.1 × 1019 cm−3.

Fig. 9
Fig. 9

Ellipsometric angles Δ (upper curve) and ψ (lower curve) for a sputtered YBa2Cu3O7 film. The crystalline, 1500-Å thick film is deposited on an yttrium-stabilized zirconium–oxide substrate.

Tables (1)

Tables Icon

Table I Change in Polarizer and Analyzer Setting during Calibrationa

Equations (24)

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tan ψ = | ρ | ,
ρ = | ρ | exp ( i Δ ) ,
E = J 2 J J 1 E 0
E 0 = [ E x E y ] 0
I = | t 0 | 2 [ ( r p * r s t * t 0 E x * E y + r p r s * t t 0 * E x E y * ) sin ϕ cos ϕ + | E y | 2 ( | t 0 | 2 | r s | 2 sin 2 ϕ ) ] .
Δ ϕ = | E x E y | | t t 0 | | r p r s | cos ( δ y δ x + δ 0 δ + δ s δ p )
I ( ϕ ) = ( α cos 2 ϕ + β sin 2 ϕ + γ ) S ( ϕ ) ,
α = ( | r p | 2 | r s | 2 ) / 2 ,
β = | r p r s | cos Δ ,
γ = ( | r p | 2 + | r s | 2 ) / 2 .
E 0 E 0 = | E x 0 | 2 cos 2 ϕ 1 + | E y 0 | 2 sin 2 ϕ 1 + E x 0 E y 0 cos ( δ y δ x ) sin 2 ϕ 1 .
S ( ϕ ) = 1 + n = 1 M a n cos n ϕ + n = 1 M b n sin n ϕ .
I ( ϕ ) = A 0 + n = 1 N A n cos n ϕ + n = 1 N B n sin n ϕ .
A n = γ a n + α ( a n + 2 + a n 2 ) / 2 + β ( b n + 2 b n 2 ) / 2 ,
B n = γ b n + α ( b n + 2 + b n 2 ) / 2 + β ( a n 2 a n + 2 ) / 2 .
A 2 A 0 = a 2 + α / γ 1 + ( α a 2 + β b 2 ) / ( 2 γ ) ,
B 2 A 0 = b 2 + β / γ 1 + ( α a 2 + β b 2 ) / ( 2 γ ) ,
A 4 A 0 = ( α a 2 + β b 2 ) / ( 2 γ ) 1 + ( α a 2 + β b 2 ) / ( 2 γ ) ,
B 4 A 0 = ( α b 2 + β a 2 ) / ( 2 γ ) 1 + ( α a 2 + β b 2 ) / ( 2 γ ) .
i = 1 4 [ x ( i ) x ( i ) s ] 2 < c i = 1 4 [ x ( i ) ] 2 ,
x ( 3 ) 2 B 4 / A 2 + A 4 / B 2 A 2 / B 2 + B 2 / A 2 ,
x ( 4 ) 2 B 4 / A 2 x ( 3 ) B 2 / A 2 .
ψ = tan 1 ( 1 α / γ 1 + α / γ ) 1 / 2 ,
Δ = cos 1 ( β / γ sin 2 ψ ) 1 / 2 .

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