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Low-temperature PECVD-deposited silicon nitride thin films for sensor applications
Surface and Coatings Technology 142᎐144 Ž2001. 808᎐812
Low-temperature PECVD-deposited silicon nitride thin films for sensor applications G. SuchaneckU , V. Norkus, G. Gerlach Dresden Uni¨ ersity of Technology, Institute for Solid State Electronics, Mommsenstr. 13, Dresden D-10602, Germany
Abstract Polymer-like silicon-rich SiN x :H films suitable for transparent VISrNIRrMIR-range optical coatings were deposited by PECVD at a substrate temperature of 80 and 150⬚C. Optical properties and film microstructure were investigated by transmissionrreflection measurements and by FTIR. Air exposure for more than 1 year reveals no post-oxidation with time. The application as an antireflective coating for IR-sensor arrays is demonstrated. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma-enhanced CVD; Low temperature deposition; Silicon-rich silicon nitride
1. Introduction Low cost sensor fabrication for the consumer market requires inexpensive processing steps. One well established technique for patterning of metal films deposited at or near room temperature is the photolithographic lift-off process. In this case, the maximum deposition temperature is limited by a decrease of the photoresist solubility in removing solvents when exposed to temperatures above 110⬚C. Another limitation is the thermal stability of the glue used for fixing samples on a carrier which deteriorates, in our case, above 80⬚C. In sensor technology, patterned silicon nitride films serve as etch masks, phase-shifting masks for deepultraviolet lithography, antireflective coatings, interlayer dielectrics, resistive electric field shields, spacers etc. Usually, they are deposited by high temperature CVD processes, plasma-enhanced chemical vapor deposition ŽPECVD. processes at substrate temperatures in the range of 300᎐450⬚C, ECR-PECVD at temperatures as low as room temperature or r.f.-sputtering. In this work PECVD deposition of silicon-rich SiN x U
Corresponding author. Tel.; q49-351-463-5281; fax: q49-351463-2320.
films patternable by lift-off processing in standard PECVD equipment is presented. Previous work on PECVD of silicon-rich SiN x :H film w1᎐23x was mostly focused on substrate temperatures G 200⬚C in order to guarantee device quality. At substrate temperatures below 150⬚C the formation of a polymer-like film microstructure is expected, about which one knows still little. PECVD enables the deposition even at room temperature, while the optical properties of the material can be optimized for a particular substrate and wavelength by varying the relative amounts of precursor gases to control the composition of the material. For instance, the refractive index can be adjusted between the values of Si 3 N4 Ž2.0. and amorphous silicon Ž3.4..
2. Experimental Film deposition was performed on silicon, glass and NiCr covered substrates as well as on 128 element linear IR-sensor arrays in a Plasmalab 80q PECVD machine ŽOxford Plasma Technology. using a non-inflammable 2% SiH 4r98% N2 gas mixture at a total pressure of 0.8᎐1.05 mbar, a total gas flow of 800 and 1600 sccm, r.f. frequency of 13.56 MHz and r.f. power of 15᎐20 W. Considering a lift-off technique for optical
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 1 . 0 1 1 0 6 - 9
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
809
Fig. 1. Dependence of the film thickness of low temperature deposited SiN x :H films on deposition time.
coating patterning, most depositions were realized at a substrate temperature of 80⬚C. The optical characterization of the film was performed by transmissionr reflection measurements in the range of 200᎐2500 nm ŽShimadzu UV3100. to determine the film thickness, refractive index, refractive index dispersion, the absorption coefficient and the TAUC optical gap Eo . The hydrogen and nitrogen bonding configurations were obtained from FTIR measurements ŽPerkin-Elmer S2000. in the range of 370᎐4000 cmy1 . After correction of interference effects revealing thickness and refractive index in the FIR-range, the peaks in the spectra were fitted to Gaussians using software developed previously for the analysis of the C᎐H stretch modes of a-Si 1 ᎐ x C x :H w24x and different oxidation states of a-SiO x :H films w25x. Each Gaussian was specified by three coefficients: the peak position; peak width; and height. An initial guess for these coefficients was taken from our previous work and literature. A first run is obtained by allowing only peak heights to vary, except
in the last one, all coefficients are allowed to vary. The computer code performs, in all cases, iterative curvefitting in order to minimize a multi-dimensional error function. Supplementary, a film composition was also analyzed by AES.
3. Results and discussion A linear dependence of film thickness on deposition time ŽFig. 1. and the absence of a time lag enables tailoring of quarter-wavelength antireflection coatings for the VISrNIRrMIR spectral range Žcf. Fig. 2.. Good adhesion of the deposited SiN x :H films to silicon, glass and NiCr electrode coated substrates was obtained. Depending on deposition parameters, the refractive index covered the range from 2.0 to 2.6. The TAUC-gap was approximately 2.2 eV in good agreement with literature data for NrSi ratios of 0.5 to 0.7 w23x. The hydrogen content of silicon-rich SiN x :H films
Fig. 2. Spectral dependence of the absorption coefficient, deposited at a substrate temperature of 80⬚C SiN x :H films.
810
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
Fig. 3. Integrated absorption strength of Si᎐N stretching modes and Si᎐H 2 bending modes vs. deposition time. The lines are guides for the eye.
is mainly determined by hydrogen bonded to excess silicon w5,7,17x. Indeed, in our films no N᎐H stretching modes were detectable in the 3300᎐3500 cmy1 -wavenumber range. An estimation using the IR-absorption of the Si᎐H wagging and rocking modes consisting of two peaks at 650 and 685 cmy1 , gives 8 = 10 21 and 2 = 10 22 cmy3 using absorption strength constants of 2.1= 10 19 cmy2 for a-Si:H w26x and 5 = 10 19 cmy2 for a-SiN0.5 :H w14x, respectively. No oxygen and carbon incorporation was found by IR-analysis and AES. IR-analysis reveals sharp peaks with full width at half maximum ŽFWHM. values of 35 to 70 cmy1 . Dispersion analysis yields peaks at 730, 770, 805, 855, 890, 930 and 980 cmy1 in the 700᎐1000 cmy1 -wavenumber range and Si᎐H stretching vibration modes at 2070 cmy1 Žisolated Si᎐H stretching vibration w27x or Si᎐H in HSi᎐Si 2 N configuration w14,28x., at 2115 cmy1 Žisolated Si᎐H in a᎐SiN x :H w15x. and at 2150 cmy1 ŽSi᎐H in HSi᎐SiN2 or H 2 ᎐Si᎐N2 configuration w14,28x.. For short deposition times, the peaks at 805 and 855 cmy1 combine to one peak at 830 cmy1 . Three of the peaks
found in the 800 to 1000 cmy1 -wavenumber range were obtained earlier in PECVD a-SiN x :H films w14x and four of them in CVD ones w29x. However, the assignment of the peaks in the 800 to 1000 cmy1 wavenumber region is still an object of controversy. The correlation of the 2070 and 2150 cmy1 peak integrated absorption strengths with ones 730, 805, 855 and 930 cmy1 peaks, give evidence that these absorptions are due to Si᎐N stretching modes in different nitrogen containing complexes. Similarly, the 775 and 890 cmy1 peak absorption strengths are correlated with the 2070 cmy1 one and point to Si᎐H bonds in microcavities ŽFigs. 3 and 4.. The peak position of the isolated Si᎐H stretching vibration is consistent with the above given NrSi ratio of approximately 0.5 w15x. The splitting of the broad IR absorption peaks of amorphous thin films into a number of peaks with smaller FWHM values is characteristic for polymer-like film microstructures. Using absorption strength constants of stretching and bending modes for a-Si:H in w26,30x or a-SiN x :H w14x, an overestimation of hydrogen content by more than a
Fig. 4. Integrated absorption strength of Si᎐H stretching modes vs. deposition time. Each data point represents the mean of at least three samples. The lines are guides for the eye.
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
811
to silicon, glass and NiCr-electrode coated substrates and oxidation resistance for more than 1 year were demonstrated. Caution in the case of hydrogen content determination from IR absorption is demanded when using absorption strength constants estimated for amorphous SiN x :H. In summary, the antireflective coating developed in this work is a good alternative for optical coatings of sensor arrays matched to a given wavelength range. It can be patterned by means of lift-off technique and is compatible with the used chip technology. Fig. 5. Change of IR-transmission after exposure to air. Shown is the difference to the spectrum of the as-deposited film. For clarity, the curves were shifted by a value of 5% of transmission.
factor of two was observed. Therefore, integral absorption strengths were not converted to hydrogen content on Figs. 3 and 4. Similarly, a decrease of the absorption strength constant of C᎐H stretching modes in a-C:H films by more than a factor of four was reported when a polymer-like film structure was formed with increasing HrC ratios w31x. PECVD deposited at a substrate temperature of 320⬚C are known to have an unstable surface oxidizing with time w22x, films deposited using NH 3rSiH 4 gas mixtures at substrate temperatures less than 150⬚C tend to oxidize within 1 month because of their porous structure w21x. Our polymer-like film composition is long-term stable ŽFig. 5.. Due to the absence of the very sensitive H᎐Si᎐O peak at 980 cmy1 w25x in the spectrum difference, oxygen incorporation by air exposure for more than 1 year should be less than 0.5 at.%. This is attributed to the observed by positron annihilation spectroscopy w17x, strong hydrogen passivation of silicon dangling bonds, vacancy complexes or voids in silicon-rich SiN x :H films. Developed optical coatings were patterned by lift-off processing with structure dimensions as low as 10 m with a resolution of 2 m using an AZ 1514 photoresist. An example for application as an antireflective coating in uncooled IR sensor arrays is reported by us in w32x. Using the novel antireflective coating a 50% increase of the spectral responsivity for the 3᎐5 m and a 20% one for the 1.5᎐1.7 m wavelength ranges, respectively, were obtained.
4. Conclusions Polymer-like silicon-rich SiN x :H suitable for optical coatings in the VISrNIRrMIR-range were deposited by PECVD at substrate temperatures below the hardbaking temperature of photoresists. This enables lift-off processing for patterning. Good adhesion of the films
Acknowledgements This work was supported by the German Federal Ministry of Education, Science, Research and Technology under contract No. 16SV590r2. References w1x Y. Kuwano, Jpn. J. Appl. Phys. 8 Ž1969. 867. w2x R. Gereth, W. Scherber, J. Electrochem. Soc. 119 Ž1972. 1248᎐1254. w3x R.S. Rosler, W.C. Benzig, J. Baldo, Solid State Technol. 19 Ž1976. 45᎐50. w4x Y. Catherine, G. Turban, Thin Solid Films 41 Ž1977. L57᎐L60. w5x H. Dun, P. Pan, F.R. White, R.W. Douse, J. Electrochem. Soc. 128 Ž1981. 1550᎐1563. w6x M. Maeda, Y. Arita, J. Appl. Phys. 53 Ž1982. 6852᎐6856. w7x N.-S. Zhou, S. Fujita, A. Sasaki, J. Electron. Mater. 14 Ž1985. 55᎐72. w8x M. Shimozuma, K. Kitamore, H. Ohno, H. Hasegawa, H. Tagashita, J. Electron. Mater. 14 Ž1985. 575᎐586. w9x K. Allaert, A. van Calster, H. Loos, A. Lequesne, J. Electrochem. Soc. 132 Ž1985. 1763᎐1766. w10x H. Watanabe, K. Katoh, S. Imagi, Y. Shibata, J. Non-Cryst. Solids 77r78 Ž1985. 937᎐940. w11x V.S. Nguyen, W.A. Lanford, A.L. Rieger, J. Electrochem. Soc. 133 Ž1986. 970᎐974. w12x N. Voke, J. Kanicki, Mater. Res. Symp. Proc. 68 Ž1986. 175᎐181. w13x V.S. Nguyen, S. Fridmann, J. Electrochem. Soc. 134 Ž1987. 2324᎐2329. w14x E. Bustarret, M. Bensouda, M.C. Habrard, J.C. Bruyere, S. Poulin, S.C. Guirathi, Phys. Rev. B 38 Ž1988. 8171᎐8184. w15x J.W. Osenbach, J.L. Zell, W.R. Knolle, L.J. Howard, J. Appl. Phys. 67 Ž1990. 6830᎐6843. w16x R. Bredel, A. Debray, R. Hezel, J. Electrochem. Soc. 139 Ž1992. 827᎐831. w17x D. Landheer, G.C. Aers, G.I. Sproule, R. Khatri, P.J. Simpson, S.C. Gujrathi, J. Appl. Phys. 78 Ž1995. 2568᎐2574. w18x S.J. Bijlsma, H. van Kranenburg, K. Nieuwesteeg, M.G. Pitt, J.F. Verweij, IEEE Trans. ED 43 Ž1996. 1592᎐1601. w19x F. Demichelis, G. Crovini, F. Giorgis, C.F. Pirri, E. Tresso, J. Appl. Phys. 79 Ž1996. 1730᎐1735. w20x Z.-T. Jiang, T. Yamaguchi, K. Ohshimo, M. Aoyama, L. Asinovsky, Jpn. J. Appl. Phys. 37 Ž1998. 571᎐576. w21x W.-S. Liao, S.-C. Lee, J. Electrochem. Soc. 144 Ž1997. 1477᎐1481. w22x K. Matsuzaki, T. Horasawa, G. Tada, M. Saga, J. Electrochem. Soc. 145 Ž1998. 4296᎐4304. w23x B.G. Budaguan, A.A. Aivazov, D.A. Stryahilev, E.M. Sokolov, J.W. Metselaar, J. Non-Cryst. Solids 226 Ž1998. 217᎐224.
812
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
w24x G. Suchaneck, M. Albert, W. Beyer, H. Stotzel, K. Schade, J. ¨ Non-Cryst. Solids 137r138 Ž1991. 701᎐704. w25x G. Suchaneck, O. Steinke, B. Alhallani, K. Schade, J. Non-Cryst. Solids 187 Ž1995. 86᎐90. w26x A.A. Langford, M.L. Fleet, B.P. Nelson, W.A. Lanford, N. Maley, Phys. Rev. 45 Ž1992. 13367᎐13377. w27x G. Lucovsky, J. Yang, S.S. Chao, J.E. Tyler, W. Czubatyi, Phys. Rev. B 28 Ž1983. 3234᎐3240. w28x G. Lucovsky, Solid State Commun. 29 Ž1979. 571᎐576.
w29x M.L. Naiman, C.T. Kirk, R.J. Aucoin, F.L. Terry, P.W. Wyatt, S.D. Senturio, J. Electrochem. Soc. 131 Ž1984. 637᎐640. w30x J.D. Ouwens, R.E.I. Schropp, Mater. Res. Soc. Symp. Proc. 377 Ž1995. 419᎐424. w31x W. Jacob, M. Unger, Appl. Phys. Lett. 68 Ž1996. 475᎐477. w32x G. Suchaneck, V. Norkus, G. Gerlach, OPTOrIRS2 2000, 6th Conference and Exhibition Infrared Sensors and Systems, 2000, Erfurt Germany.
Low-temperature PECVD-deposited silicon nitride thin films for sensor applications G. SuchaneckU , V. Norkus, G. Gerlach Dresden Uni¨ ersity of Technology, Institute for Solid State Electronics, Mommsenstr. 13, Dresden D-10602, Germany
Abstract Polymer-like silicon-rich SiN x :H films suitable for transparent VISrNIRrMIR-range optical coatings were deposited by PECVD at a substrate temperature of 80 and 150⬚C. Optical properties and film microstructure were investigated by transmissionrreflection measurements and by FTIR. Air exposure for more than 1 year reveals no post-oxidation with time. The application as an antireflective coating for IR-sensor arrays is demonstrated. 䊚 2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma-enhanced CVD; Low temperature deposition; Silicon-rich silicon nitride
1. Introduction Low cost sensor fabrication for the consumer market requires inexpensive processing steps. One well established technique for patterning of metal films deposited at or near room temperature is the photolithographic lift-off process. In this case, the maximum deposition temperature is limited by a decrease of the photoresist solubility in removing solvents when exposed to temperatures above 110⬚C. Another limitation is the thermal stability of the glue used for fixing samples on a carrier which deteriorates, in our case, above 80⬚C. In sensor technology, patterned silicon nitride films serve as etch masks, phase-shifting masks for deepultraviolet lithography, antireflective coatings, interlayer dielectrics, resistive electric field shields, spacers etc. Usually, they are deposited by high temperature CVD processes, plasma-enhanced chemical vapor deposition ŽPECVD. processes at substrate temperatures in the range of 300᎐450⬚C, ECR-PECVD at temperatures as low as room temperature or r.f.-sputtering. In this work PECVD deposition of silicon-rich SiN x U
Corresponding author. Tel.; q49-351-463-5281; fax: q49-351463-2320.
films patternable by lift-off processing in standard PECVD equipment is presented. Previous work on PECVD of silicon-rich SiN x :H film w1᎐23x was mostly focused on substrate temperatures G 200⬚C in order to guarantee device quality. At substrate temperatures below 150⬚C the formation of a polymer-like film microstructure is expected, about which one knows still little. PECVD enables the deposition even at room temperature, while the optical properties of the material can be optimized for a particular substrate and wavelength by varying the relative amounts of precursor gases to control the composition of the material. For instance, the refractive index can be adjusted between the values of Si 3 N4 Ž2.0. and amorphous silicon Ž3.4..
2. Experimental Film deposition was performed on silicon, glass and NiCr covered substrates as well as on 128 element linear IR-sensor arrays in a Plasmalab 80q PECVD machine ŽOxford Plasma Technology. using a non-inflammable 2% SiH 4r98% N2 gas mixture at a total pressure of 0.8᎐1.05 mbar, a total gas flow of 800 and 1600 sccm, r.f. frequency of 13.56 MHz and r.f. power of 15᎐20 W. Considering a lift-off technique for optical
0257-8972r01r$ - see front matter 䊚 2001 Elsevier Science B.V. All rights reserved. PII: S 0 2 5 7 - 8 9 7 2 Ž 0 1 . 0 1 1 0 6 - 9
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
809
Fig. 1. Dependence of the film thickness of low temperature deposited SiN x :H films on deposition time.
coating patterning, most depositions were realized at a substrate temperature of 80⬚C. The optical characterization of the film was performed by transmissionr reflection measurements in the range of 200᎐2500 nm ŽShimadzu UV3100. to determine the film thickness, refractive index, refractive index dispersion, the absorption coefficient and the TAUC optical gap Eo . The hydrogen and nitrogen bonding configurations were obtained from FTIR measurements ŽPerkin-Elmer S2000. in the range of 370᎐4000 cmy1 . After correction of interference effects revealing thickness and refractive index in the FIR-range, the peaks in the spectra were fitted to Gaussians using software developed previously for the analysis of the C᎐H stretch modes of a-Si 1 ᎐ x C x :H w24x and different oxidation states of a-SiO x :H films w25x. Each Gaussian was specified by three coefficients: the peak position; peak width; and height. An initial guess for these coefficients was taken from our previous work and literature. A first run is obtained by allowing only peak heights to vary, except
in the last one, all coefficients are allowed to vary. The computer code performs, in all cases, iterative curvefitting in order to minimize a multi-dimensional error function. Supplementary, a film composition was also analyzed by AES.
3. Results and discussion A linear dependence of film thickness on deposition time ŽFig. 1. and the absence of a time lag enables tailoring of quarter-wavelength antireflection coatings for the VISrNIRrMIR spectral range Žcf. Fig. 2.. Good adhesion of the deposited SiN x :H films to silicon, glass and NiCr electrode coated substrates was obtained. Depending on deposition parameters, the refractive index covered the range from 2.0 to 2.6. The TAUC-gap was approximately 2.2 eV in good agreement with literature data for NrSi ratios of 0.5 to 0.7 w23x. The hydrogen content of silicon-rich SiN x :H films
Fig. 2. Spectral dependence of the absorption coefficient, deposited at a substrate temperature of 80⬚C SiN x :H films.
810
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
Fig. 3. Integrated absorption strength of Si᎐N stretching modes and Si᎐H 2 bending modes vs. deposition time. The lines are guides for the eye.
is mainly determined by hydrogen bonded to excess silicon w5,7,17x. Indeed, in our films no N᎐H stretching modes were detectable in the 3300᎐3500 cmy1 -wavenumber range. An estimation using the IR-absorption of the Si᎐H wagging and rocking modes consisting of two peaks at 650 and 685 cmy1 , gives 8 = 10 21 and 2 = 10 22 cmy3 using absorption strength constants of 2.1= 10 19 cmy2 for a-Si:H w26x and 5 = 10 19 cmy2 for a-SiN0.5 :H w14x, respectively. No oxygen and carbon incorporation was found by IR-analysis and AES. IR-analysis reveals sharp peaks with full width at half maximum ŽFWHM. values of 35 to 70 cmy1 . Dispersion analysis yields peaks at 730, 770, 805, 855, 890, 930 and 980 cmy1 in the 700᎐1000 cmy1 -wavenumber range and Si᎐H stretching vibration modes at 2070 cmy1 Žisolated Si᎐H stretching vibration w27x or Si᎐H in HSi᎐Si 2 N configuration w14,28x., at 2115 cmy1 Žisolated Si᎐H in a᎐SiN x :H w15x. and at 2150 cmy1 ŽSi᎐H in HSi᎐SiN2 or H 2 ᎐Si᎐N2 configuration w14,28x.. For short deposition times, the peaks at 805 and 855 cmy1 combine to one peak at 830 cmy1 . Three of the peaks
found in the 800 to 1000 cmy1 -wavenumber range were obtained earlier in PECVD a-SiN x :H films w14x and four of them in CVD ones w29x. However, the assignment of the peaks in the 800 to 1000 cmy1 wavenumber region is still an object of controversy. The correlation of the 2070 and 2150 cmy1 peak integrated absorption strengths with ones 730, 805, 855 and 930 cmy1 peaks, give evidence that these absorptions are due to Si᎐N stretching modes in different nitrogen containing complexes. Similarly, the 775 and 890 cmy1 peak absorption strengths are correlated with the 2070 cmy1 one and point to Si᎐H bonds in microcavities ŽFigs. 3 and 4.. The peak position of the isolated Si᎐H stretching vibration is consistent with the above given NrSi ratio of approximately 0.5 w15x. The splitting of the broad IR absorption peaks of amorphous thin films into a number of peaks with smaller FWHM values is characteristic for polymer-like film microstructures. Using absorption strength constants of stretching and bending modes for a-Si:H in w26,30x or a-SiN x :H w14x, an overestimation of hydrogen content by more than a
Fig. 4. Integrated absorption strength of Si᎐H stretching modes vs. deposition time. Each data point represents the mean of at least three samples. The lines are guides for the eye.
G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
811
to silicon, glass and NiCr-electrode coated substrates and oxidation resistance for more than 1 year were demonstrated. Caution in the case of hydrogen content determination from IR absorption is demanded when using absorption strength constants estimated for amorphous SiN x :H. In summary, the antireflective coating developed in this work is a good alternative for optical coatings of sensor arrays matched to a given wavelength range. It can be patterned by means of lift-off technique and is compatible with the used chip technology. Fig. 5. Change of IR-transmission after exposure to air. Shown is the difference to the spectrum of the as-deposited film. For clarity, the curves were shifted by a value of 5% of transmission.
factor of two was observed. Therefore, integral absorption strengths were not converted to hydrogen content on Figs. 3 and 4. Similarly, a decrease of the absorption strength constant of C᎐H stretching modes in a-C:H films by more than a factor of four was reported when a polymer-like film structure was formed with increasing HrC ratios w31x. PECVD deposited at a substrate temperature of 320⬚C are known to have an unstable surface oxidizing with time w22x, films deposited using NH 3rSiH 4 gas mixtures at substrate temperatures less than 150⬚C tend to oxidize within 1 month because of their porous structure w21x. Our polymer-like film composition is long-term stable ŽFig. 5.. Due to the absence of the very sensitive H᎐Si᎐O peak at 980 cmy1 w25x in the spectrum difference, oxygen incorporation by air exposure for more than 1 year should be less than 0.5 at.%. This is attributed to the observed by positron annihilation spectroscopy w17x, strong hydrogen passivation of silicon dangling bonds, vacancy complexes or voids in silicon-rich SiN x :H films. Developed optical coatings were patterned by lift-off processing with structure dimensions as low as 10 m with a resolution of 2 m using an AZ 1514 photoresist. An example for application as an antireflective coating in uncooled IR sensor arrays is reported by us in w32x. Using the novel antireflective coating a 50% increase of the spectral responsivity for the 3᎐5 m and a 20% one for the 1.5᎐1.7 m wavelength ranges, respectively, were obtained.
4. Conclusions Polymer-like silicon-rich SiN x :H suitable for optical coatings in the VISrNIRrMIR-range were deposited by PECVD at substrate temperatures below the hardbaking temperature of photoresists. This enables lift-off processing for patterning. Good adhesion of the films
Acknowledgements This work was supported by the German Federal Ministry of Education, Science, Research and Technology under contract No. 16SV590r2. References w1x Y. Kuwano, Jpn. J. Appl. Phys. 8 Ž1969. 867. w2x R. Gereth, W. Scherber, J. Electrochem. Soc. 119 Ž1972. 1248᎐1254. w3x R.S. Rosler, W.C. Benzig, J. Baldo, Solid State Technol. 19 Ž1976. 45᎐50. w4x Y. Catherine, G. Turban, Thin Solid Films 41 Ž1977. L57᎐L60. w5x H. Dun, P. Pan, F.R. White, R.W. Douse, J. Electrochem. Soc. 128 Ž1981. 1550᎐1563. w6x M. Maeda, Y. Arita, J. Appl. Phys. 53 Ž1982. 6852᎐6856. w7x N.-S. Zhou, S. Fujita, A. Sasaki, J. Electron. Mater. 14 Ž1985. 55᎐72. w8x M. Shimozuma, K. Kitamore, H. Ohno, H. Hasegawa, H. Tagashita, J. Electron. Mater. 14 Ž1985. 575᎐586. w9x K. Allaert, A. van Calster, H. Loos, A. Lequesne, J. Electrochem. Soc. 132 Ž1985. 1763᎐1766. w10x H. Watanabe, K. Katoh, S. Imagi, Y. Shibata, J. Non-Cryst. Solids 77r78 Ž1985. 937᎐940. w11x V.S. Nguyen, W.A. Lanford, A.L. Rieger, J. Electrochem. Soc. 133 Ž1986. 970᎐974. w12x N. Voke, J. Kanicki, Mater. Res. Symp. Proc. 68 Ž1986. 175᎐181. w13x V.S. Nguyen, S. Fridmann, J. Electrochem. Soc. 134 Ž1987. 2324᎐2329. w14x E. Bustarret, M. Bensouda, M.C. Habrard, J.C. Bruyere, S. Poulin, S.C. Guirathi, Phys. Rev. B 38 Ž1988. 8171᎐8184. w15x J.W. Osenbach, J.L. Zell, W.R. Knolle, L.J. Howard, J. Appl. Phys. 67 Ž1990. 6830᎐6843. w16x R. Bredel, A. Debray, R. Hezel, J. Electrochem. Soc. 139 Ž1992. 827᎐831. w17x D. Landheer, G.C. Aers, G.I. Sproule, R. Khatri, P.J. Simpson, S.C. Gujrathi, J. Appl. Phys. 78 Ž1995. 2568᎐2574. w18x S.J. Bijlsma, H. van Kranenburg, K. Nieuwesteeg, M.G. Pitt, J.F. Verweij, IEEE Trans. ED 43 Ž1996. 1592᎐1601. w19x F. Demichelis, G. Crovini, F. Giorgis, C.F. Pirri, E. Tresso, J. Appl. Phys. 79 Ž1996. 1730᎐1735. w20x Z.-T. Jiang, T. Yamaguchi, K. Ohshimo, M. Aoyama, L. Asinovsky, Jpn. J. Appl. Phys. 37 Ž1998. 571᎐576. w21x W.-S. Liao, S.-C. Lee, J. Electrochem. Soc. 144 Ž1997. 1477᎐1481. w22x K. Matsuzaki, T. Horasawa, G. Tada, M. Saga, J. Electrochem. Soc. 145 Ž1998. 4296᎐4304. w23x B.G. Budaguan, A.A. Aivazov, D.A. Stryahilev, E.M. Sokolov, J.W. Metselaar, J. Non-Cryst. Solids 226 Ž1998. 217᎐224.
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G. Suchaneck et al. r Surface and Coatings Technology 142᎐144 (2001) 808᎐812
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