Abstract

The plasma-assisted chemical vapor deposition technique was used to produce thin-film structures with both sinusoidally and stepwise varying refractive-index profiles. The refractive index of the SiOxNy system used in the fabrication was found to be time dependent following a stepwise change in reactant gas flows or initiation of the plasma. This time dependence has been quantified using in situ ellipsometry and was found to have components with exponential and linear dependences. The time dependence of water vapor partial pressure in the system was identified as the cause of the linear dependence. Allowance for the time-dependent effects has improved the agreement between the calculated spectral response and the measured result for a broadband high-reflectance mirror consisting of an arithmetic progression of discrete layers.

© 1995 Optical Society of America

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References

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  1. A. C. Gresham, B. A. Nichols, “Optical interference filters with continuous refractive index modulations by microwave plasma assisted chemical vapor deposition,” Opt. Eng. 32, 1018–1024 (1993).
    [CrossRef]
  2. S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
    [CrossRef]
  3. S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
    [CrossRef]
  4. P. H. Berning, “Theory and calculations of optical thin films,” Phys. Thin Films 1, 69–121 (1976).
  5. W. H. Southwell, “Spectral response calculations of rugate filters using coupled-wave theory,” J. Opt. Soc. Am. A 5, 1558–1564 (1988).
    [CrossRef]
  6. B. G. Bovard, “Rugate filter theory: an overview,” Appl. Opt. 32, 5427–5442 (1993).
    [CrossRef] [PubMed]
  7. W. H. Southwell, R. L. Hall, “Rugate filter sidelobe suppression using quintic and rugated quintic matching layers,” Appl. Opt. 28, 2949–2951 (1989).
    [CrossRef] [PubMed]
  8. W. H. Southwell, “Using apodization functions to reduce sidelobes in rugate filters,” Appl. Opt. 28, 5091–5094 (1989).
    [CrossRef] [PubMed]
  9. H. A. Abu-Safia, A. I. Al-Sharif, I. O. Abu Aljarayesh, “Rugate filter sidelobe suppression using half apodization,” Appl. Opt. 32, 4831–4835 (1993).
    [CrossRef] [PubMed]
  10. O. S. Heavens, H. M. Liddell, “Staggered broadband reflecting multilayers,” Appl. Opt. 5, 373–376 (1966).
    [CrossRef] [PubMed]
  11. J. S. Browder, S. S. Ballard, P. Klocek, “Physical properties of crystalline infrared materials,” in Handbook of Infrared Optical Materials, P. Klocek, ed. (Marcel Dekker, New York, 1991), Chap. 6, p. 352.

1994 (1)

S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
[CrossRef]

1993 (4)

A. C. Gresham, B. A. Nichols, “Optical interference filters with continuous refractive index modulations by microwave plasma assisted chemical vapor deposition,” Opt. Eng. 32, 1018–1024 (1993).
[CrossRef]

S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
[CrossRef]

H. A. Abu-Safia, A. I. Al-Sharif, I. O. Abu Aljarayesh, “Rugate filter sidelobe suppression using half apodization,” Appl. Opt. 32, 4831–4835 (1993).
[CrossRef] [PubMed]

B. G. Bovard, “Rugate filter theory: an overview,” Appl. Opt. 32, 5427–5442 (1993).
[CrossRef] [PubMed]

1989 (2)

1988 (1)

1976 (1)

P. H. Berning, “Theory and calculations of optical thin films,” Phys. Thin Films 1, 69–121 (1976).

1966 (1)

Abu Aljarayesh, I. O.

Abu-Safia, H. A.

Al-Sharif, A. I.

Ballard, S. S.

J. S. Browder, S. S. Ballard, P. Klocek, “Physical properties of crystalline infrared materials,” in Handbook of Infrared Optical Materials, P. Klocek, ed. (Marcel Dekker, New York, 1991), Chap. 6, p. 352.

Berning, P. H.

P. H. Berning, “Theory and calculations of optical thin films,” Phys. Thin Films 1, 69–121 (1976).

Bovard, B. G.

Browder, J. S.

J. S. Browder, S. S. Ballard, P. Klocek, “Physical properties of crystalline infrared materials,” in Handbook of Infrared Optical Materials, P. Klocek, ed. (Marcel Dekker, New York, 1991), Chap. 6, p. 352.

Casas, L. M.

S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
[CrossRef]

Gresham, A. C.

A. C. Gresham, B. A. Nichols, “Optical interference filters with continuous refractive index modulations by microwave plasma assisted chemical vapor deposition,” Opt. Eng. 32, 1018–1024 (1993).
[CrossRef]

Hall, R. L.

Heavens, O. S.

Klocek, P.

J. S. Browder, S. S. Ballard, P. Klocek, “Physical properties of crystalline infrared materials,” in Handbook of Infrared Optical Materials, P. Klocek, ed. (Marcel Dekker, New York, 1991), Chap. 6, p. 352.

Liddell, H. M.

Lim, S.

S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
[CrossRef]

S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
[CrossRef]

Nichols, B. A.

A. C. Gresham, B. A. Nichols, “Optical interference filters with continuous refractive index modulations by microwave plasma assisted chemical vapor deposition,” Opt. Eng. 32, 1018–1024 (1993).
[CrossRef]

Plant, T. K.

S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
[CrossRef]

Ryu, J. H.

S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
[CrossRef]

S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
[CrossRef]

Southwell, W. H.

Wager, J. F.

S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
[CrossRef]

S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
[CrossRef]

Appl. Opt. (5)

J. Opt. Soc. Am. A (1)

Opt. Eng. (1)

A. C. Gresham, B. A. Nichols, “Optical interference filters with continuous refractive index modulations by microwave plasma assisted chemical vapor deposition,” Opt. Eng. 32, 1018–1024 (1993).
[CrossRef]

Phys. Thin Films (1)

P. H. Berning, “Theory and calculations of optical thin films,” Phys. Thin Films 1, 69–121 (1976).

Thin Solid Films (2)

S. Lim, J. H. Ryu, J. F. Wager, L. M. Casas, “Inhomogeneous dielectrics grown by PECVD,” Thin Solid Films 236, 64–66 (1993).
[CrossRef]

S. Lim, J. H. Ryu, J. F. Wager, T. K. Plant, “Rugate filters grown by plasma-enhanced chemical vapor deposition,” Thin Solid Films 245, 141–145 (1994).
[CrossRef]

Other (1)

J. S. Browder, S. S. Ballard, P. Klocek, “Physical properties of crystalline infrared materials,” in Handbook of Infrared Optical Materials, P. Klocek, ed. (Marcel Dekker, New York, 1991), Chap. 6, p. 352.

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Figures (13)

Fig. 1
Fig. 1

Deposition system for PACVD of optical films under computer control.

Fig. 2
Fig. 2

Refractive index of films of SiO x N y deposited in the system as a function of the oxygen flow rate.

Fig. 3
Fig. 3

Response of the partial pressures of various gases in the RGA chamber of the system to a change in the flow rate of argon and oxygen and to the plasma being switched on and off. Note that the right-hand axis is for the H2O partial pressure.

Fig. 4
Fig. 4

Refractive index as determined by in situ ellipsometry during the growth of a three-layer film. The control signal given to the oxygen flow controller is shown on the same plot (dotted line). The response to a shut down in oxygen flow (at A) is more gradual than to its commencement (at B) and consists of an exponential and a linear part as discussed in the text.

Fig. 5
Fig. 5

Average compressive stress of silicon nitride films deposited at various flow rates of argon. A pronounced minimum occurs at approximately 1 sccm.

Fig. 6
Fig. 6

Center wavelength of the stop band for unapodized sinusoidal rugate layers as a function of the physical thickness of one period.

Fig. 7
Fig. 7

(a) Refractive-index profile generated by computer for an apodized sinusoidal rugate layer. (b) The reflectance profile predicted for the resulting layer. (c) The reflectance profile of the layer produced by PACVD using the computer-generated function of (a) to control the oxygen gas flow.

Fig. 8
Fig. 8

Reflectance of the structure of Fig. 7(c) during deposition using in situ white-light monitoring: (a) reflectance when the oxygen flow rate is minimum (refractive index of maximum), (b) reflectance when the oxygen flow rate is maximum (refractive index a minimum).

Fig. 9
Fig. 9

Two reflectance profiles selected form the data of Fig. 8 for (a) the structure when it terminates on a maximum of index, and (b) a minimum index. The two sets of sidelobes are alternatively enhanced and suppressed in turn.

Fig. 10
Fig. 10

Reflectance of 460 nm of the rugate structure of Fig. 7(c) during deposition as measured in situ.

Fig. 11
Fig. 11

Refractive-index profile of a broadband reflector design showing the modification introduced by the linear change in refractive index.

Fig. 12
Fig. 12

Reflectance profiles of the structure deposited by PACVD (solid curve) and calculated (dashed curve) using the refractive-index profile of Fig. 11.

Fig. 13
Fig. 13

Reflectance profile calculated for a step profile without considering the linear modification of the profile shown in Fig. 11.

Equations (4)

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Δ λ C λ C = n p 2 n a ,
λ C = 2 n a d ,
σ av = E Si 6 ( 1 - ν ) t s 2 t f ( 1 r c - 1 r u ) ,
r = Δ d 2 4 λ Δ m ,

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