William D. Partlow, Deborah P. Partlow, Robert M. Silva, and Jean M. Bennett, "Characterization of plasma-deposited and dip-coated films for critical optical applications," Appl. Opt. 26, 1537-1545 (1987)
Two types of coatings were evaluated with respect to their suitability for optical applications in which low scattering is required. The plasma-deposition technique produces dense pinhole-free films of refractory materials from a glow discharge plasma at typical substrate temperatures of 200–300°C. Plasma-deposited films of SiO2 and Si3N4, produced from reactions of SiH4 with N2O and NH3, respectively, were evaluated in this study. SiO2 films were also produced from metal-organic precursor solutions using dipping and spinning application techniques followed by pyrolysis at 600°C. Coatings were deposited on the highest quality substrates available, which were characterized prior to deposition so that the effects of the coatings could be separated from those of the substrates. Nomarski microscopy, surface profiling, total integrated scattering, ellipsometry, and photon backscattering techniques were used for characterization. The properties of these coatings and information on how the quality depends on coating conditions are reported in this paper.
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Reactant Gas Ratios and Deposition Rates for Plasma-Deposited Films
Coating
Reactant gas ratios
Deposition rate(Å/min)
SiO2
SiH4:N2O = 1:5.2
400
Si3N4
SiH4:NH3:N2 = 1:18.5:8.6
100
Table II
Total Integrated Scattering Measured Relative to the Incident Beam Intensity for Plasma-Deposited Films and Uncoated Substrates (λ6471 Å); Data are Averages of 19 Points on Each Sample
Si3N4 on silicon [1.9-cm (0.75-in.) diam]
1.94 ± 1.43 × 10−5
Uncoated silicon (1.9-cm diam)
2.64 ± 1.24 × 10−5
Si3N4 on silicon [3.86-cm (1.52-in.) diam]
2.63 ± 1. × 10−5
Uncoated silicon (3.86-cm diam)
2.76 ± 3. × 10−5
Silver on fused quartz
4.82 ± 1. × 10−5
Aluminum on Zerodur
1.11 ± 0. × 10−4
Table III
Test Solutions to Determine Maximum Practical Equivalent SiO2 Concentration with High Water of Hydrolysis
These solutions initially fell into the range of immiscibility between water and alcohol. However, as water was removed by chemical reactions, the solutions began to mix. Such solutions generally have a rather short shelf life (i.e., a few days) before gelling.
Dip coated.
Spin coated.
Solution made using propanol rather than ethanol.
Table V
Experiments to Test Certain Processing Variables
Solution A = 15 moles H2O/TEOS, 6% SiO2.
SiO2 substrate, polished by Zygo Corporation on one face only.
Si substrate, polished at VTI and characterized before coating.
Table VI
Talystep Surface Profile Measurements on Dip Coatings; Coating Parameters are Given In Table V
1 cm from substrate edge and 5 mm from upper edge of coating
4.7
63
1 cm from substrate edge and 5 mm from upper edge of coating
3.7
15
1 cm from substrate edge and 5 mm from upper edge of coating
3.3
Fused quartz substrate, polished by Zygo Corp.
Coating applied by spinning.
Silicon substrate.
Tables (6)
Table I
Reactant Gas Ratios and Deposition Rates for Plasma-Deposited Films
Coating
Reactant gas ratios
Deposition rate(Å/min)
SiO2
SiH4:N2O = 1:5.2
400
Si3N4
SiH4:NH3:N2 = 1:18.5:8.6
100
Table II
Total Integrated Scattering Measured Relative to the Incident Beam Intensity for Plasma-Deposited Films and Uncoated Substrates (λ6471 Å); Data are Averages of 19 Points on Each Sample
Si3N4 on silicon [1.9-cm (0.75-in.) diam]
1.94 ± 1.43 × 10−5
Uncoated silicon (1.9-cm diam)
2.64 ± 1.24 × 10−5
Si3N4 on silicon [3.86-cm (1.52-in.) diam]
2.63 ± 1. × 10−5
Uncoated silicon (3.86-cm diam)
2.76 ± 3. × 10−5
Silver on fused quartz
4.82 ± 1. × 10−5
Aluminum on Zerodur
1.11 ± 0. × 10−4
Table III
Test Solutions to Determine Maximum Practical Equivalent SiO2 Concentration with High Water of Hydrolysis
These solutions initially fell into the range of immiscibility between water and alcohol. However, as water was removed by chemical reactions, the solutions began to mix. Such solutions generally have a rather short shelf life (i.e., a few days) before gelling.
Dip coated.
Spin coated.
Solution made using propanol rather than ethanol.
Table V
Experiments to Test Certain Processing Variables
Solution A = 15 moles H2O/TEOS, 6% SiO2.
SiO2 substrate, polished by Zygo Corporation on one face only.
Si substrate, polished at VTI and characterized before coating.
Table VI
Talystep Surface Profile Measurements on Dip Coatings; Coating Parameters are Given In Table V
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