Abstract

We measure the refractive index of thin films of TiO2 and SiO2 for given deposition parameters. Two complementary methods are used. The first is a postdeposition technique which uses the measurements of reflectance and transmittance in air. The second, in contrast, makes use of in situ measurements (under vacuum and during the actual deposition of the layer). The differences between the values deduced from the two methods can be explained by the amount of atmospheric moisture adsorbed by films. One tries to minimize these shifts for the two materials by choosing deposition parameters. The difficulties come from the absorption losses which must be as small as possible. We use the measured refractive indices of individual layers to give good numerical prediction of the wavelength shift (observed during the admittance of air after deposition in the vacuum chamber) of the transmittance peak of multidielectric Fabry-Perot filters.

© 1986 Optical Society of America

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References

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  1. P. Bousquet, E. Pelletier, “Optical Thin Film Monitoring: Recent Advances and Limitations,” Thin Solid Films 77, 165 (1981).
    [CrossRef]
  2. J. P. Borgogno et al., “Refractive Index and Inhomogeneity of Thin Films,” Appl. Opt. 23, 3567 (1984).
    [CrossRef] [PubMed]
  3. H. K. Pulker, G. Paesold, E. Ritter, “Refractive Indices of TiO2 Films Produced by Reactive Evaporation of Various Titanium–Oxygen Phases,” Appl. Opt. 15, 2986 (1976); J. P. Borgogno, P. Bousquet, F. Flory, B. Lazarides, E. Pelletier, P. Roche, “Inhomogeneity in Films: Limitations of the Accuracy of Optical Monitoring of Thin Films,” Appl. Opt. 20, 90 (1981).
    [CrossRef] [PubMed]
  4. H. A. Macleod, “The Microstructure of Optical Thin Films,” Proc. Soc. Photo-Opt. Instrum. Eng. 325, 21 (1982).
  5. H. A. Macleod, D. Richmond, “Moisture Penetration Patterns in Thin Films,” Thin Solid Films 37, 163 (1976).
    [CrossRef]
  6. F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).
  7. H. A. Macleod, “Turning Value Monitoring of Narrow-Band All Dielectric Thin-Film Optical Filters,” Opt. Acta 19, 1 (1972).
    [CrossRef]
  8. E. Pelletier, “Monitoring of Optical Thin Films During Deposition,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 74 (1983).
  9. J. P. Borgogno, B. Lazarides, E. Pelletier, “Automatic Determination of the Optical Constants of Inhomogeneous Thin Films,” Appl. Opt. 21, 4020 (1982).
    [CrossRef] [PubMed]
  10. J. P. Borgogno, B. Lazarides, P. Roche, “An Improved Method for the Determination of the Extinction Coefficient of Thin Film Materials,” Thin Solid Films 102, 209 (1983).
    [CrossRef]

1984

1983

F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).

E. Pelletier, “Monitoring of Optical Thin Films During Deposition,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 74 (1983).

J. P. Borgogno, B. Lazarides, P. Roche, “An Improved Method for the Determination of the Extinction Coefficient of Thin Film Materials,” Thin Solid Films 102, 209 (1983).
[CrossRef]

1982

J. P. Borgogno, B. Lazarides, E. Pelletier, “Automatic Determination of the Optical Constants of Inhomogeneous Thin Films,” Appl. Opt. 21, 4020 (1982).
[CrossRef] [PubMed]

H. A. Macleod, “The Microstructure of Optical Thin Films,” Proc. Soc. Photo-Opt. Instrum. Eng. 325, 21 (1982).

1981

P. Bousquet, E. Pelletier, “Optical Thin Film Monitoring: Recent Advances and Limitations,” Thin Solid Films 77, 165 (1981).
[CrossRef]

1976

1972

H. A. Macleod, “Turning Value Monitoring of Narrow-Band All Dielectric Thin-Film Optical Filters,” Opt. Acta 19, 1 (1972).
[CrossRef]

Borgogno, J. P.

Bousquet, P.

P. Bousquet, E. Pelletier, “Optical Thin Film Monitoring: Recent Advances and Limitations,” Thin Solid Films 77, 165 (1981).
[CrossRef]

Flory, F.

F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).

Lazarides, B.

J. P. Borgogno, B. Lazarides, P. Roche, “An Improved Method for the Determination of the Extinction Coefficient of Thin Film Materials,” Thin Solid Films 102, 209 (1983).
[CrossRef]

J. P. Borgogno, B. Lazarides, E. Pelletier, “Automatic Determination of the Optical Constants of Inhomogeneous Thin Films,” Appl. Opt. 21, 4020 (1982).
[CrossRef] [PubMed]

Macleod, H. A.

F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).

H. A. Macleod, “The Microstructure of Optical Thin Films,” Proc. Soc. Photo-Opt. Instrum. Eng. 325, 21 (1982).

H. A. Macleod, D. Richmond, “Moisture Penetration Patterns in Thin Films,” Thin Solid Films 37, 163 (1976).
[CrossRef]

H. A. Macleod, “Turning Value Monitoring of Narrow-Band All Dielectric Thin-Film Optical Filters,” Opt. Acta 19, 1 (1972).
[CrossRef]

Paesold, G.

Pelletier, E.

F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).

E. Pelletier, “Monitoring of Optical Thin Films During Deposition,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 74 (1983).

J. P. Borgogno, B. Lazarides, E. Pelletier, “Automatic Determination of the Optical Constants of Inhomogeneous Thin Films,” Appl. Opt. 21, 4020 (1982).
[CrossRef] [PubMed]

P. Bousquet, E. Pelletier, “Optical Thin Film Monitoring: Recent Advances and Limitations,” Thin Solid Films 77, 165 (1981).
[CrossRef]

Pulker, H. K.

Richmond, D.

H. A. Macleod, D. Richmond, “Moisture Penetration Patterns in Thin Films,” Thin Solid Films 37, 163 (1976).
[CrossRef]

Ritter, E.

Roche, P.

J. P. Borgogno, B. Lazarides, P. Roche, “An Improved Method for the Determination of the Extinction Coefficient of Thin Film Materials,” Thin Solid Films 102, 209 (1983).
[CrossRef]

Schmitt, B.

F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).

Appl. Opt.

Opt. Acta

H. A. Macleod, “Turning Value Monitoring of Narrow-Band All Dielectric Thin-Film Optical Filters,” Opt. Acta 19, 1 (1972).
[CrossRef]

Proc. Soc. Photo-Opt. Instrum. Eng.

E. Pelletier, “Monitoring of Optical Thin Films During Deposition,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 74 (1983).

H. A. Macleod, “The Microstructure of Optical Thin Films,” Proc. Soc. Photo-Opt. Instrum. Eng. 325, 21 (1982).

F. Flory, B. Schmitt, E. Pelletier, H. A. Macleod, “Interpretation of Wide Band Scans of Growing Optical Thin Films in Terms of Layer Microstructure,” Proc. Soc. Photo-Opt. Instrum. Eng. 401, 109 (1983).

Thin Solid Films

H. A. Macleod, D. Richmond, “Moisture Penetration Patterns in Thin Films,” Thin Solid Films 37, 163 (1976).
[CrossRef]

P. Bousquet, E. Pelletier, “Optical Thin Film Monitoring: Recent Advances and Limitations,” Thin Solid Films 77, 165 (1981).
[CrossRef]

J. P. Borgogno, B. Lazarides, P. Roche, “An Improved Method for the Determination of the Extinction Coefficient of Thin Film Materials,” Thin Solid Films 102, 209 (1983).
[CrossRef]

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Figures (9)

Fig. 1
Fig. 1

Titanium oxide. Values of refractive index as a function of thickness. The results are derived from the measurements recorded during deposition for several wavelengths. The optical thicknesses 4λ0/4 and 8λ0/4 are located on the thickness axis.

Fig. 2
Fig. 2

Refractive index of a 299.6-nm thick TiO2 film: the inside index ni is the extreme value of the film index at the substrate surface; the outside index n0 is the extreme value of the film index at the air surface; the mean index n ¯ is the half-sum of ni and n0 values. Errors bars for n ¯ assume that the errors in reflectance and transmittance are ±0.003.

Fig. 3
Fig. 3

Refractive index of TiO2 films as a function of wavelength: air measurements. Each curve is connected with a value of oxygen partial pressure (PO2) adjusted during reactive evaporation: 1, (PO2) > 5.0 × 10−4 Torr; 2, (PO2) = 5.0 × 10−4 Torr; 3, (PO2) = 3.5 × 10−4 Torr; 4, (PO2) = 3.0 × 10−4 Torr; 5, (PO2) = 2.5 × 10−4 Torr; 6, (PO2) = 2.0 × 10−4 Torr. Note: For each run the deposition rate was 0.3 nm/s, the substrate temperature during film formation was 325°C, the starting material was TiO, the substrate was glass.

Fig. 4
Fig. 4

Refractive index of the TiO2 films referred to in Fig. 3 as a function of wavelength: in situ measurements. Note: because of absorption, results concerning experiment 6 are not given.

Fig. 5
Fig. 5

Refractive index of SiO2 films as a function of wavelength: air measurements. Each curve is connected with a value of oxygen partial pressure (PO2) adjusted during reactive evaporation: 1, (PO2) = 5.0 × 10−4 Torr; 2, (PO2) = 0.2 × 10−4 Torr; 3, (PO2) = 1 × 10−6 Torr. Note: For each run the deposition rate was 0.5 nm/s, the substrate temperature during film formation was 325°C, the starting material was SiO2, the substrate was glass.

Fig. 6
Fig. 6

Refractive index of the SiO2 films referred to in Fig. 5 as a function of wavelength: in situ measurements.

Fig. 7
Fig. 7

Refractive index of TiO2 films as a function of wavelength when the layer is added on glass/H L H L. The results are derived from performed in situ measurements. Each curve is connected with a value of oxygen partial pressure (PO2) adjusted during reactive evaporation: 1, (PO2) = 5.0 × 10−4 Torr; 2, (PO2) = 3.0 × 10−4 Torr. Note: For each run the deposition rate was 0.3 nm/s, the substrate temperature during film formation was 325°C, the starting material was TiO.

Fig. 8
Fig. 8

Refractive index of SiO2 films as a function of wavelength when the layer is added on glass/H L H L H. The results are derived from performed in situ measurements. Each curve is connected with a value of oxygen partial pressure (PO2) adjusted during the reactive evaporation: 1, (PO2) = 5.0 × 10−4 Torr; 2, (PO2) = 0.2 × 10−4 Torr; 3, (PO2) = 1 × 10−6 Torr. Note: For each run the deposition rate was 0.5 nm/s, the substrate temperature during film formation was 325°C, the starting material was SiO2.

Fig. 9
Fig. 9

Computed (curve a) and measured in air (curve b) optical properties of a TiO2/SiO2 Fabry-Perot filter (design glass/H L H L H H L H L H). Computed curve: In a first step we compute the thicknesses of the layers assuming that they are quarterwaves at 632.6 nm and using the in situ refractive indices. In a second step we compute the optical properties using the thicknesses computed above and assuming that the relative indices increase between vacuum and air are 4.9% for TiO2 and 7.1% for SiO2 (see text).

Tables (4)

Tables Icon

Table I Optical Constants of TiO2 Films as a Function of Oxygen Partial Pressure (PO2) Adjusted During Reactive Evaporation

Tables Icon

Table II Optical Constants of SiO2 Films as a Function of Oxygen Partial Pressure (PO2) Adjusted During Reactive Evaporation

Tables Icon

Table III Comparison of Single and Multilayer Results for TiO2

Tables Icon

Table IV Comparison of Single and Multilayer Results for SiO2

Equations (2)

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n ¯ ( λ ) = A + ( B / λ 2 + ( C / λ 4 ) .
η = ( n air - n i n s i t u ) / [ ( n air + n i n s i t u ) / 2 ] .

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