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Etching behavior of optical thin films for different deposition techniques
TSF-34398; No of Pages 3 Thin Solid Films xxx (2015) xxx–xxx
Contents lists available at ScienceDirect
Thin Solid Films journal homepage: www.elsevier.com/locate/tsf
Etching behavior of optical thin films for different deposition techniques Thimotheus Alig ⁎, Stefan Günster, Detlev Ristau Laser Zentrum Hannover e.V., Hollerithallee 8, D-30419 Hannover, Germany
a r t i c l e
i n f o
Article history: Received 19 December 2014 Received in revised form 2 June 2015 Accepted 2 June 2015 Available online xxxx Keywords: Optical thin films Etching Coating deposition techniques
a b s t r a c t In view of extended applications of ion sources towards improved high precision multilayer structures, the etching behavior for different optical coating materials and deposition techniques as well as the performance of an etching process in a multilayer structure were investigated. Etching stabilities of the oxide materials Ta2O5, TiO2, HfO2, Al2O3, and SiO2 as well as the fluoride materials MgF2 and LaF3 were considered in dependence of material type, deposition technique, and etching process. For etching of the single layers a radio frequency pumped ion source operated with Argon or Oxygen plasma is employed. The ions are extracted from the plasma by means of a three grid extraction system with adjustable energy in the range between a few and several hundred eV. The etching behavior of the various single layer systems was associated to the etch rates and evaluated under consideration of the sputter power, to enable a selection of more and less stable materials. As an example for the influence of etched interfaces in a multilayer, a high reflective system at 532 nm with modification between high and low index materials will be discussed. A significant absorption decrease due to the plasma treatment could be determined without affecting the damage threshold and total scattering of the model system. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The application of ion sources in the production of optical thin films has various purposes. During Ion Beam Sputtering (IBS), ion sources are employed to sputter coating material towards the substrates, and during Ion Assisted Deposition (IAD) the sources are used to modify the evaporated material. In contrast to these applications, this work is focused on the etching of optical thin films by ion sources. The application of etching to single or multiple interfaces of an optical thin film during the production affects inter alia thickness control [1,2] as well as surface properties. Within this work, the influence of etching on optical thin films of various materials and structures was investigated. In a first step, oxide and fluoride single layers produced by different deposition methods are etched by an ion beam and controlled by broad band optical monitoring, to determine onset conditions and etch rates. Furthermore, the performance of etched interfaces in a multilayer structure with the objectives to achieve high stability and low losses is of interest. As an example, a high reflective system for the wavelength 532 nm with modification between high and low index materials is investigated. 2. Experimental details 2.1. Etching equipment and in situ control The experiments were performed in an IBS deposition system equipped with an additional ion source, to etch the optical thin films. ⁎ Corresponding author. E-mail address: [email protected] (T. Alig).
During deposition the primary source sputters target material towards the substrates mounted in a rotating calotte. The additional etch source points directly to the substrates and operates with radio frequency pumped Argon or Oxygen plasma. The ions are extracted from the plasma by means of a three grid extraction system with adjustable energy in the range between a few and several hundred eV. Etching can be performed in a reactive oxygen atmosphere at pressure levels between 2 and 9 10−2 Pa. Furthermore the setup comprises an optical broad band monitor, to control deposition and etching processes in situ. In this setup the spectral transmission of a defined sample position is recorded by a spectrometer covering the wavelength range from 420 to 950 nm. An associated program continuously calculates the thickness and deposition rate of the current layer from the recorded spectra with simultaneous consideration of the deposited design and the specified dispersion data. 2.2. Etching process and single layer systems For comparability reasons the various single layer systems were treated simultaneously in one etching process. Several treatment cycles with different mixtures of argon and oxygen combined with extraction voltages from 100 to 600 V were performed over a time period of 30 min. The beam current was varied from 40 to 70 mA by adjusting the gas flows between 1 and 5 sccm. The etching stabilities of the single layer systems are considered in respect to material type and deposition technique. Optical thin films presented in this study are made of high index materials Ta2O5, TiO2, HfO2 and Al2O3 as well as low index materials SiO2, MgF2 and LaF3 (see Table 1). All oxides were deposited by sputtering methods
http://dx.doi.org/10.1016/j.tsf.2015.06.004 0040-6090/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: T. Alig, et al., Etching behavior of optical thin films for different deposition techniques, Thin Solid Films (2015), http://dx.doi.org/10.1016/j.tsf.2015.06.004
2
T. Alig et al. / Thin Solid Films xxx (2015) xxx–xxx
Table 1 Parameters adjusted during the deposition process for different layer materials and deposition techniques. Layer material
Deposition technique
Substrate heating [°C]
Deposition rate [nm/s]
Base pressure [Pa]
Reactive gas
Sputter gas
TiO2 HfO2
IBS IBS E-beam/IAD IBS IBS IBS E-beam/IAD Thermal evap. Thermal evap.
50 50 250 50 50 50 150 350 350
0.05 0.10 0.30 0.16 0.13 0.30 0.60 0.20 0.20
10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4
O2 O2 O2 O2 O2 O2 O2
Ar Ar
Ta2O5 Al2O3 SiO2 LaF3 MgF2
Ar Ar Ar
performed in different deposition systems. Furthermore the oxides HfO2 and SiO2 were also deposited by evaporation techniques, whereas the fluorides were deposited by evaporation techniques only. The single layer systems were coated on 1 mm thick fused silica substrates with a diameter of 25 mm. An additional layer of Ta2O5 on the substrates avoids an insufficient index contrast for the low index materials.
Table 2 Differential rate and onset power adjusted during the etching process for different layer materials deposited by sputtering methods and/or evaporation techniques. Layer material
TiO2 HfO2 Ta2O5 Al2O3 SiO2 LaF3 MgF2
Differential rate [pm/Ws]
Onset power [W]
Sputtering
Sputtering
0.43 0.66 0.72 0.81 1.50
Evaporation 0.80
1.34 1.63 1.99
6.73 7.24 5.70 5.15 4.92
Evaporation 5.04
3.77 4.24 5.77
The model system is made of HfO2 as high and SiO2 as low index material deposited by ion beam sputtering. During the process an argon beam extracted with 1600 V at 180 mA is used to sputter the metallic targets. Subsequently the particles are oxidized in a reactive O2 atmosphere without plasma treatment. To compensate for the thinning effect of the etching process, a thicker coating design (1.1H 1.1L)14 1.1H (1.1L)2 was deposited. Due to the interface modification after each layer performed with 44 W sputter power, the original coating design was restored.
2.3. Etching process in multilayer structures 3. Results and discussion Besides the behavior of single layer materials, the application of etching in a multilayer structure is of interest. For this purpose a high reflection coating at 532 nm with interface modification between high and low index materials was deposited. For comparability reasons the same high reflection coating without interface modification was deposited as well. The coating design is specified by the sequence (HL)14 H 2L with H and L indicating high and low index layers of quarter wave optical thickness, respectively.
3.1. Etching behavior of single layer systems The etching behavior of the various single layer systems was associated to the etching rates of the in situ process control and evaluated under consideration of the sputter power used (see Fig. 1). The sputter power is determined from the extraction voltage and the beam current measured at the grid system of the ion source. In addition to the in situ
Fig. 1. Etching rates of different layer materials deposited by sputtering methods and/or evaporation techniques in dependence of the sputter power of the ion source used.
Please cite this article as: T. Alig, et al., Etching behavior of optical thin films for different deposition techniques, Thin Solid Films (2015), http://dx.doi.org/10.1016/j.tsf.2015.06.004
T. Alig et al. / Thin Solid Films xxx (2015) xxx–xxx
Fig. 2. Transmission spectrum of a high reflective system for the wavelength of 532 nm with interface modification between high and low index materials compared to a standard stack.
measurements of the optical broad band monitor, the single layer systems were investigated ex situ with spectrometers covering the band edge of the layer materials in the ultraviolet wavelength range. Evaluating the transmission spectra, no additional losses of the samples induced by the etching process could be determined. Furthermore selected surfaces were investigated using a scanning electron microscope, but no discrepancy of single layers with and without ion beam etching could be detected. The etching rates of the single layer systems increase with sputter power and reach at the maximum a tenth of the original deposition rates. In order to compare the different coating materials of the single layers, linear functions were fitted and slopes as well as onset values were determined (see Table 2). Considering plasma treatments, stable coating materials provide low etching rates in combination with high onset powers. For the investigated materials a correlation between high refractive index and low differential rate was observed. Except for MgF2, the onset power behaves inversely proportional to the differential rate. A general behavior difference between sputtered and evaporated samples could not be determined. While HfO2 shows higher stability deposited by sputtering methods, the stability of SiO2 is higher for evaporation techniques. Considering the fluorides deposited by evaporation techniques, MgF2 has a higher differential rate and onset power compared to LaF3. 3.2. Etching effects on multilayer structures The optical properties of a multilayer structure with interface modification by plasma treatment were investigated relative to a reference structure (see Fig. 2). The model system consists of a high reflection coating at 532 nm, to match the wavelength ranges of the measuring devices used. Ex situ measurements of the model system and reference structure in transmission mode confirm consistency in the high reflection range. Towards shorter wavelengths, deviations appear caused by small thickness variations of the etched layers. Both multilayer systems achieve the target reflectivity of more than 99.9% with a physical thickness of approximately 2.4 μm. One objective of the plasma treatment is an increased laser induced damage threshold [3]. The plasma treated multilayer structure reached a value of approximately 11 J/cm2 at 532 nm, for the onset threshold
3
extrapolated to an infinite number of pulses according to ISO 21254. Since the reference structure performed similarly, no significant effect of the interface modification regarding laser induced damage could be determined. Other work measuring laser induced damage threshold mainly describes processes using ion milling during deposition itself. The idea of etching down to quarter wave optical thickness is not presented [4]. Furthermore, absorption and scattering of the multilayer structure were investigated to provide information on the influence of etching on the optical losses. The absorption was determined by calorimetric measurements of the samples irradiated by laser light at 1064 nm [5]. With this arrangement, the plasma treated multilayer structure shows a lower absorption of 13 ppm compared to the reference sample with 39 ppm. The decreased absorption may be due to the heat accompanying the plasma treatment causing a post-oxidation of the coating material. To investigate the effect of plasma treatment regarding scattering, the model system was measured in a Fast Total Scattering facility at 532 nm [6]. Considering base levels of 440 ppm for the model system and 460 ppm for the reference structure, no significant effect of the plasma treatment regarding scattering could be determined. 3.3. Conclusions The impact of plasma treatments on single layers and model systems was investigated before the background of further improvements intended for high precision multilayer structures. The etching stability of single layers was considered in dependence of material type, deposition technique, and etching process. Furthermore, a high reflecting coating with plasma treatment between high and low index materials was investigated. Based on the single layer results, more and less stable materials could be identified, and for the multilayer structure with interface modification a significant absorption decrease compared to a reference structure could be determined. To reveal further potentials of plasma treatments in optical thin films, a comprehensive investigation in the process parameters and gas composition is necessary. Acknowledgments The work was performed in the framework of the project “Cell-UV”. The project Cell-UV is carried out in the framework of the European program “Eurostars”. The financial support of the German partners by the Federal Ministry of Education and Research (EUROSTARS E! 7721 CELL-UV) is gratefully acknowledged. References [1] D. Poitras, J.A. Dobrowolski, T. Cassidy, S. Moisa, Ion-beam etching for the precise manufacture of optical coatings, Appl. Opt. 42 (2003) 4037–4044. [2] W.C. Herrmann, J.R. McNeil, Ion beam milling as a diagnostic for optical coatings, Appl. Opt. 20 (1981) 1899–1901. [3] ISO 21254: Optics and Optical Instruments. Lasers and Laser Related Equipment, Test Methods for Laser-induced Damage Threshold, International Organization for Standardization, Geneva, 2011. [4] D.G. Golovach, V.I. Kantcel, Vadim I. Rakhovsky, Measurement of optical coating LIDT vs. their ion milling deposition parameters, Proc. SPIE 2428 (1995) 644–652. [5] ISO 11551: Optics and Optical Instruments. Lasers and Laser Related Equipment, Test Method for Absorptance of Optical Laser Components. International Standard, International Organisation for Standardisation, Geneva, 2003. [6] P. Kadkhoda, W. Sakiew, S. Günster, D. Ristau, Fast total scattering facility for 2D inspection of optical and functional surfaces, Proc. SPIE 7389 (2009) 73890S.
Please cite this article as: T. Alig, et al., Etching behavior of optical thin films for different deposition techniques, Thin Solid Films (2015), http://dx.doi.org/10.1016/j.tsf.2015.06.004
Contents lists available at ScienceDirect
Thin Solid Films journal homepage: www.elsevier.com/locate/tsf
Etching behavior of optical thin films for different deposition techniques Thimotheus Alig ⁎, Stefan Günster, Detlev Ristau Laser Zentrum Hannover e.V., Hollerithallee 8, D-30419 Hannover, Germany
a r t i c l e
i n f o
Article history: Received 19 December 2014 Received in revised form 2 June 2015 Accepted 2 June 2015 Available online xxxx Keywords: Optical thin films Etching Coating deposition techniques
a b s t r a c t In view of extended applications of ion sources towards improved high precision multilayer structures, the etching behavior for different optical coating materials and deposition techniques as well as the performance of an etching process in a multilayer structure were investigated. Etching stabilities of the oxide materials Ta2O5, TiO2, HfO2, Al2O3, and SiO2 as well as the fluoride materials MgF2 and LaF3 were considered in dependence of material type, deposition technique, and etching process. For etching of the single layers a radio frequency pumped ion source operated with Argon or Oxygen plasma is employed. The ions are extracted from the plasma by means of a three grid extraction system with adjustable energy in the range between a few and several hundred eV. The etching behavior of the various single layer systems was associated to the etch rates and evaluated under consideration of the sputter power, to enable a selection of more and less stable materials. As an example for the influence of etched interfaces in a multilayer, a high reflective system at 532 nm with modification between high and low index materials will be discussed. A significant absorption decrease due to the plasma treatment could be determined without affecting the damage threshold and total scattering of the model system. © 2015 Elsevier B.V. All rights reserved.
1. Introduction The application of ion sources in the production of optical thin films has various purposes. During Ion Beam Sputtering (IBS), ion sources are employed to sputter coating material towards the substrates, and during Ion Assisted Deposition (IAD) the sources are used to modify the evaporated material. In contrast to these applications, this work is focused on the etching of optical thin films by ion sources. The application of etching to single or multiple interfaces of an optical thin film during the production affects inter alia thickness control [1,2] as well as surface properties. Within this work, the influence of etching on optical thin films of various materials and structures was investigated. In a first step, oxide and fluoride single layers produced by different deposition methods are etched by an ion beam and controlled by broad band optical monitoring, to determine onset conditions and etch rates. Furthermore, the performance of etched interfaces in a multilayer structure with the objectives to achieve high stability and low losses is of interest. As an example, a high reflective system for the wavelength 532 nm with modification between high and low index materials is investigated. 2. Experimental details 2.1. Etching equipment and in situ control The experiments were performed in an IBS deposition system equipped with an additional ion source, to etch the optical thin films. ⁎ Corresponding author. E-mail address: [email protected] (T. Alig).
During deposition the primary source sputters target material towards the substrates mounted in a rotating calotte. The additional etch source points directly to the substrates and operates with radio frequency pumped Argon or Oxygen plasma. The ions are extracted from the plasma by means of a three grid extraction system with adjustable energy in the range between a few and several hundred eV. Etching can be performed in a reactive oxygen atmosphere at pressure levels between 2 and 9 10−2 Pa. Furthermore the setup comprises an optical broad band monitor, to control deposition and etching processes in situ. In this setup the spectral transmission of a defined sample position is recorded by a spectrometer covering the wavelength range from 420 to 950 nm. An associated program continuously calculates the thickness and deposition rate of the current layer from the recorded spectra with simultaneous consideration of the deposited design and the specified dispersion data. 2.2. Etching process and single layer systems For comparability reasons the various single layer systems were treated simultaneously in one etching process. Several treatment cycles with different mixtures of argon and oxygen combined with extraction voltages from 100 to 600 V were performed over a time period of 30 min. The beam current was varied from 40 to 70 mA by adjusting the gas flows between 1 and 5 sccm. The etching stabilities of the single layer systems are considered in respect to material type and deposition technique. Optical thin films presented in this study are made of high index materials Ta2O5, TiO2, HfO2 and Al2O3 as well as low index materials SiO2, MgF2 and LaF3 (see Table 1). All oxides were deposited by sputtering methods
http://dx.doi.org/10.1016/j.tsf.2015.06.004 0040-6090/© 2015 Elsevier B.V. All rights reserved.
Please cite this article as: T. Alig, et al., Etching behavior of optical thin films for different deposition techniques, Thin Solid Films (2015), http://dx.doi.org/10.1016/j.tsf.2015.06.004
2
T. Alig et al. / Thin Solid Films xxx (2015) xxx–xxx
Table 1 Parameters adjusted during the deposition process for different layer materials and deposition techniques. Layer material
Deposition technique
Substrate heating [°C]
Deposition rate [nm/s]
Base pressure [Pa]
Reactive gas
Sputter gas
TiO2 HfO2
IBS IBS E-beam/IAD IBS IBS IBS E-beam/IAD Thermal evap. Thermal evap.
50 50 250 50 50 50 150 350 350
0.05 0.10 0.30 0.16 0.13 0.30 0.60 0.20 0.20
10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4 10−4
O2 O2 O2 O2 O2 O2 O2
Ar Ar
Ta2O5 Al2O3 SiO2 LaF3 MgF2
Ar Ar Ar
performed in different deposition systems. Furthermore the oxides HfO2 and SiO2 were also deposited by evaporation techniques, whereas the fluorides were deposited by evaporation techniques only. The single layer systems were coated on 1 mm thick fused silica substrates with a diameter of 25 mm. An additional layer of Ta2O5 on the substrates avoids an insufficient index contrast for the low index materials.
Table 2 Differential rate and onset power adjusted during the etching process for different layer materials deposited by sputtering methods and/or evaporation techniques. Layer material
TiO2 HfO2 Ta2O5 Al2O3 SiO2 LaF3 MgF2
Differential rate [pm/Ws]
Onset power [W]
Sputtering
Sputtering
0.43 0.66 0.72 0.81 1.50
Evaporation 0.80
1.34 1.63 1.99
6.73 7.24 5.70 5.15 4.92
Evaporation 5.04
3.77 4.24 5.77
The model system is made of HfO2 as high and SiO2 as low index material deposited by ion beam sputtering. During the process an argon beam extracted with 1600 V at 180 mA is used to sputter the metallic targets. Subsequently the particles are oxidized in a reactive O2 atmosphere without plasma treatment. To compensate for the thinning effect of the etching process, a thicker coating design (1.1H 1.1L)14 1.1H (1.1L)2 was deposited. Due to the interface modification after each layer performed with 44 W sputter power, the original coating design was restored.
2.3. Etching process in multilayer structures 3. Results and discussion Besides the behavior of single layer materials, the application of etching in a multilayer structure is of interest. For this purpose a high reflection coating at 532 nm with interface modification between high and low index materials was deposited. For comparability reasons the same high reflection coating without interface modification was deposited as well. The coating design is specified by the sequence (HL)14 H 2L with H and L indicating high and low index layers of quarter wave optical thickness, respectively.
3.1. Etching behavior of single layer systems The etching behavior of the various single layer systems was associated to the etching rates of the in situ process control and evaluated under consideration of the sputter power used (see Fig. 1). The sputter power is determined from the extraction voltage and the beam current measured at the grid system of the ion source. In addition to the in situ
Fig. 1. Etching rates of different layer materials deposited by sputtering methods and/or evaporation techniques in dependence of the sputter power of the ion source used.
Please cite this article as: T. Alig, et al., Etching behavior of optical thin films for different deposition techniques, Thin Solid Films (2015), http://dx.doi.org/10.1016/j.tsf.2015.06.004
T. Alig et al. / Thin Solid Films xxx (2015) xxx–xxx
Fig. 2. Transmission spectrum of a high reflective system for the wavelength of 532 nm with interface modification between high and low index materials compared to a standard stack.
measurements of the optical broad band monitor, the single layer systems were investigated ex situ with spectrometers covering the band edge of the layer materials in the ultraviolet wavelength range. Evaluating the transmission spectra, no additional losses of the samples induced by the etching process could be determined. Furthermore selected surfaces were investigated using a scanning electron microscope, but no discrepancy of single layers with and without ion beam etching could be detected. The etching rates of the single layer systems increase with sputter power and reach at the maximum a tenth of the original deposition rates. In order to compare the different coating materials of the single layers, linear functions were fitted and slopes as well as onset values were determined (see Table 2). Considering plasma treatments, stable coating materials provide low etching rates in combination with high onset powers. For the investigated materials a correlation between high refractive index and low differential rate was observed. Except for MgF2, the onset power behaves inversely proportional to the differential rate. A general behavior difference between sputtered and evaporated samples could not be determined. While HfO2 shows higher stability deposited by sputtering methods, the stability of SiO2 is higher for evaporation techniques. Considering the fluorides deposited by evaporation techniques, MgF2 has a higher differential rate and onset power compared to LaF3. 3.2. Etching effects on multilayer structures The optical properties of a multilayer structure with interface modification by plasma treatment were investigated relative to a reference structure (see Fig. 2). The model system consists of a high reflection coating at 532 nm, to match the wavelength ranges of the measuring devices used. Ex situ measurements of the model system and reference structure in transmission mode confirm consistency in the high reflection range. Towards shorter wavelengths, deviations appear caused by small thickness variations of the etched layers. Both multilayer systems achieve the target reflectivity of more than 99.9% with a physical thickness of approximately 2.4 μm. One objective of the plasma treatment is an increased laser induced damage threshold [3]. The plasma treated multilayer structure reached a value of approximately 11 J/cm2 at 532 nm, for the onset threshold
3
extrapolated to an infinite number of pulses according to ISO 21254. Since the reference structure performed similarly, no significant effect of the interface modification regarding laser induced damage could be determined. Other work measuring laser induced damage threshold mainly describes processes using ion milling during deposition itself. The idea of etching down to quarter wave optical thickness is not presented [4]. Furthermore, absorption and scattering of the multilayer structure were investigated to provide information on the influence of etching on the optical losses. The absorption was determined by calorimetric measurements of the samples irradiated by laser light at 1064 nm [5]. With this arrangement, the plasma treated multilayer structure shows a lower absorption of 13 ppm compared to the reference sample with 39 ppm. The decreased absorption may be due to the heat accompanying the plasma treatment causing a post-oxidation of the coating material. To investigate the effect of plasma treatment regarding scattering, the model system was measured in a Fast Total Scattering facility at 532 nm [6]. Considering base levels of 440 ppm for the model system and 460 ppm for the reference structure, no significant effect of the plasma treatment regarding scattering could be determined. 3.3. Conclusions The impact of plasma treatments on single layers and model systems was investigated before the background of further improvements intended for high precision multilayer structures. The etching stability of single layers was considered in dependence of material type, deposition technique, and etching process. Furthermore, a high reflecting coating with plasma treatment between high and low index materials was investigated. Based on the single layer results, more and less stable materials could be identified, and for the multilayer structure with interface modification a significant absorption decrease compared to a reference structure could be determined. To reveal further potentials of plasma treatments in optical thin films, a comprehensive investigation in the process parameters and gas composition is necessary. Acknowledgments The work was performed in the framework of the project “Cell-UV”. The project Cell-UV is carried out in the framework of the European program “Eurostars”. The financial support of the German partners by the Federal Ministry of Education and Research (EUROSTARS E! 7721 CELL-UV) is gratefully acknowledged. References [1] D. Poitras, J.A. Dobrowolski, T. Cassidy, S. Moisa, Ion-beam etching for the precise manufacture of optical coatings, Appl. Opt. 42 (2003) 4037–4044. [2] W.C. Herrmann, J.R. McNeil, Ion beam milling as a diagnostic for optical coatings, Appl. Opt. 20 (1981) 1899–1901. [3] ISO 21254: Optics and Optical Instruments. Lasers and Laser Related Equipment, Test Methods for Laser-induced Damage Threshold, International Organization for Standardization, Geneva, 2011. [4] D.G. Golovach, V.I. Kantcel, Vadim I. Rakhovsky, Measurement of optical coating LIDT vs. their ion milling deposition parameters, Proc. SPIE 2428 (1995) 644–652. [5] ISO 11551: Optics and Optical Instruments. Lasers and Laser Related Equipment, Test Method for Absorptance of Optical Laser Components. International Standard, International Organisation for Standardisation, Geneva, 2003. [6] P. Kadkhoda, W. Sakiew, S. Günster, D. Ristau, Fast total scattering facility for 2D inspection of optical and functional surfaces, Proc. SPIE 7389 (2009) 73890S.
Please cite this article as: T. Alig, et al., Etching behavior of optical thin films for different deposition techniques, Thin Solid Films (2015), http://dx.doi.org/10.1016/j.tsf.2015.06.004