@misc{HaeberleHenkelGargourietal., author = {Haeberle, J{\"o}rg and Henkel, Karsten and Gargouri, Hassan and Naumann, Franziska and Gruska, Bernd and Arens, Michael and Tallarida, Massimo and Schmeißer, Dieter}, title = {Ellipsometry and XPS comparative studies of thermal and plasma enhanced atomic layer deposited Al2O3-films}, series = {Beilstein Journal of Nanotechnology}, volume = {2013}, journal = {Beilstein Journal of Nanotechnology}, number = {4}, issn = {2190-4286}, doi = {10.3762/bjnano.4.83}, pages = {732 -- 742}, abstract = {We report on results on the preparation of thin (<100 nm) aluminum oxide (Al2O3) films on silicon substrates using thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) in the SENTECH SI ALD LL system. The T-ALD Al2O3layers were deposited at 200 °C, for the PE-ALD films we varied the substrate temperature range between room temperature (rt) and 200 °C. We show data from spectroscopic ellipsometry (thickness, refractive index, growth rate) over 4" wafers and correlatethem to X-ray photoelectron spectroscopy (XPS) results. The 200°C T-ALD and PE-ALD processes yield films with similar refractive indices and with oxygen to aluminum elemental ratios very close to the stoichiometric value of 1.5. However, in both also fragments of the precursor are integrated into the film. The PE-ALD films show an increased growth rate and lower carbon contaminations. Reducing the deposition temperature down to rt leads to a higher content of carbon and CH-species. We also find a decrease of the refractive index and of the oxygen to aluminum elemental ratio as well as an increase of the growth rate whereas the homogeneity of the film growth is not influenced significantly. Initial state energy shifts in all PE-ALD samples are observed which we attribute to a net negative charge within the films.}, language = {en} } @misc{HenkelGargouriGruskaetal., author = {Henkel, Karsten and Gargouri, Hassan and Gruska, Bernd and Arens, Michael and Tallarida, Massimo and Schmeißer, Dieter}, title = {Capacitance and conductance versus voltage characterization of Al2O3 layers prepared by PE-ALD at 25°C ≤ T ≤ 200°C}, series = {Journal of Vacuum Science and Technology A}, volume = {1}, journal = {Journal of Vacuum Science and Technology A}, number = {32}, doi = {10.1116/1.4831897}, pages = {01A107-1 -- 01A107-10}, abstract = {In this work, plasma enhanced atomic layer deposited (PE-ALD) samples were prepared at substrate temperatures in the range between room temperature (RT) and 200 °C and investigated by capacitance-voltage and conductance-voltage recordings. The measurements are compared to standard thermal atomic layer deposition (T-ALD) at 200 °C. Very low interface state density (D it) ~1011 eV-1 cm-2 could be achieved for the PE-ALD process at 200 °C substrate temperature after postdeposition anneal (PDA) in forming gas at 450 °C. The PDA works very effectively for both the PE-ALD and T-ALD at 200 °C substrate temperature delivering also similar values of negative fixed charge density (N fix) around -2.5 × 1012 cm-2. At the substrate temperature of 150 °C, highest N fix (-2.9 × 1012 cm-2) and moderate D it (2.7 × 1011 eV-1 cm-2) values were observed. The as deposited PE-ALD layer at RT shows both low D it in the range of (1 to 3) × 1011 eV-1 cm-2 and low N fix (-4.4 × 1011 cm-2) at the same time. The dependencies of N fix, D it, and relative permittivity on the substrate temperatures and its adjustability are discussed.}, language = {en} } @inproceedings{HenkelTallaridaHaeberleetal., author = {Henkel, Karsten and Tallarida, Massimo and Haeberle, J{\"o}rg and Gargouri, Hassan and Naumann, Franziska and Gruska, Bernd and Arens, Michael and Schmeißer, Dieter}, title = {PE-ALD-Al2O3-Schichten f{\"u}r die Passivierung von Solarzellen}, series = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 16.04.2014}, booktitle = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 16.04.2014}, editor = {Gl{\"u}ck, Bernhard K. and Schmidt, Sindy and Stein, Erhard and Raschke, J{\"o}rg-Uwe and Richter, Hans}, publisher = {Cottbus-Senftenberg}, address = {BTU}, pages = {7 -- 14}, abstract = {D{\"u}nne Al2O3-Schichten wurden bei Substrattemperaturen zwischen Raumtemperatur und 200°C mittels PE-ALD auf Si-Substraten abgeschieden und ellipsometrisch, spektroskopisch und elektrisch charakterisiert. Ihr Potenzial f{\"u}r die chemische und Feldeffektpassivierung der Oberfl{\"a}chenrekombination wird bewertet.}, language = {de} } @misc{DasHenkelTallaridaetal., author = {Das, Chittaranjan and Henkel, Karsten and Tallarida, Massimo and Schmeißer, Dieter and Gargouri, Hassan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Gruska, Bernd and Arens, Michael}, title = {Thermal and plasma enhanced atomic layer deposition of TiO2: Comparison of spectroscopic and electric properties}, series = {Journal of Vacuum Science and Technology A}, volume = {2015}, journal = {Journal of Vacuum Science and Technology A}, number = {33}, issn = {1520-8559}, doi = {10.1116/1.4903938}, pages = {01A144-1 -- 01A144-8}, abstract = {Titanium oxide (TiO2) deposited by atomic layer deposition (ALD) is used as a protective layer in photocatalytic water splitting system as well as a dielectric in resistive memory switching. The way ALD is performed (thermally or plasma-assisted) may change the growth rate as well as the electronic properties of the deposited films. In the present work, the authors verify the influence of the ALD mode on functional parameters, by comparing the growth rate and electronic properties of TiO2 films deposited by thermal (T-) and plasma-enhanced (PE-) ALD. The authors complete the study with the electrical characterization of selected samples by means of capacitance-voltage and current-voltage measurements. In all samples, the authors found a significant presence of Ti3+ states, with the lowest content in the PE-ALD grown TiO2 films. The observation of Ti3+ states was accompanied by the presence of in-gap states above the valence band maximum. For films thinner than 10 nm, the authors found also a strong leakage current. Also in this case, the PE-ALD films showed the weakest leakage currents, showing a correlation between the presence of Ti3+ states and leakage current density.}, language = {en} } @inproceedings{HenkelDasSowinskaetal., author = {Henkel, Karsten and Das, Chittaranjan and Sowinska, Małgorzata and Tallarida, Massimo and Schmeißer, Dieter and Gargouri, Hassan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Gruska, Bernd and Arens, Michael}, title = {Charakterisierung von TiO2-ALD-Schichten und deren Nutzung f{\"u}r die Passivierung von Si-Photokathoden}, series = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 15.04.2015}, booktitle = {Tagungsband Photovoltaik-Meeting: Anwendungen-Qualit{\"a}t-Perspektiven, Senftenberg, 15.04.2015}, editor = {Gl{\"u}ck, B. K. and Schmidt, S. and Stein, E. and Raschke, J{\"o}rg-Uwe and Richter, H.}, publisher = {BTU Cottbus-Senftenberg}, address = {Senftenberg}, pages = {3 -- 8}, abstract = {Wir berichten zun{\"a}chst {\"u}ber den Einfluss der Methode der Atomlagenabscheidung auf die TiO2-Schichteigenschaften. Insbesondere wird der Zusammenhang zwischen Ti3+- sowie Interbandzust{\"a}nden mit elektrischen Kennlinien und deren Einfluss auf funktionale Schichteigenschaften diskutiert. Anschließend werden Mikrostrukturierung, Grenzfl{\"a}chen-Engineering und konforme Abscheidung einer TiO2-ALD-Schutzschicht effektiv zur Performance-Steigerung von p-Si-Photokathoden angewendet.}, language = {de} } @misc{SowińskaHenkelSchmeisseretal., author = {Sowińska, Małgorzata and Henkel, Karsten and Schmeißer, Dieter and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Naumann, Franziska and Gruska, Bernd and Gargouri, Hassan}, title = {Plasma-enhanced atomic layer deposition of titanium oxynitrides films: A comparative spectroscopic and electrical study}, series = {Journal of Vacuum Science and Technology A}, journal = {Journal of Vacuum Science and Technology A}, number = {34}, issn = {0734-2101}, doi = {10.1116/1.4936227}, pages = {01A127-1 -- 01A127-9}, abstract = {The process parameters' impact of the plasma-enhanced atomic layer deposition (PE-ALD) method on the oxygen to nitrogen (O/N) ratio in titanium oxynitride (TiOxNy) films was studied. Titanium(IV)isopropoxide in combination with NH3 plasma and tetrakis(dimethylamino) titanium by applying N2 plasma processes were investigated. Samples were characterized by the in situ spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and electrical characterization (current-voltage: I-V and capacitance-voltage: C-V) methods. The O/N ratio in the TiOxNy films is found to be very sensitive for their electric properties such as conductivity, dielectric breakdown, and permittivity. Our results indicate that these PE-ALD film properties can be tuned, via the O/N ratio, by the selection of the process parameters and precursor/coreactant combination.}, language = {en} } @inproceedings{TallaridaHenkelGargourietal., author = {Tallarida, Massimo and Henkel, Karsten and Gargouri, Hassan and Haeberle, J{\"o}rg and Gruska, Bernd and Arens, Matthias and Schmeißer, Dieter}, title = {New opportunities with Plasma enhanced atomic layer deposition (PE-ALD) of oxides}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, abstract = {Thermal Atomic layer deposition (T-ALD) of oxides is obtained by the pulsed alternation of a metal precursor and an oxygen source, typically H2O or O3, and the reactions leading to ALD are thermally activated. With plasma enhanced ALD (PE-ALD), instead, the oxygen source is represented by an oxygen-containing plasma. The higher reactivity of the plasma-generated species extend the capabilities of ALD: improved film quality and increased flexibility in process conditions, such as growth at low temperature, are typical advantages of PE-ALD over T-ALD. We report on results on the preparation of thin (<100 nm) aluminum oxide (Al2O3) films on silicon substrates using T-ALD and PE-ALD in the SENTECH SI ALD LL system. Films were deposited in the temperature range between room temperature (RT) and 200∘C. We characterized the films with spectroscopic ellipsometry (thickness, refractive index, growth rate) over 4" wafers and with X-ray photoelectron spectroscopy. All films resulted in a high degree of homogeneity, independent of the deposition temperature. Investigations with capacitance-voltage and conductance-voltage measurements showed a very low interface states density for the PE-ALD films.}, language = {en} } @misc{SowinskaBrizziDasetal., author = {Sowinska, Małgorzata and Brizzi, Simone and Das, Chittaranjan and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Naumann, Franziska and Gargouri, Hassan and Henkel, Karsten and Schmeißer, Dieter}, title = {Analysis of nitrogen species in titanium oxynitride ALD films}, series = {Applied Surface Science}, volume = {381}, journal = {Applied Surface Science}, issn = {0169-4332}, doi = {10.1016/j.apsusc.2016.02.096}, pages = {42 -- 47}, abstract = {Titanium oxynitride films are prepared by plasma enhanced atomic layer deposition method using two different precursors and nitrogen sources. Synchrotron radiation-based X-ray photoelectron spectroscopy and X-ray absorption spectroscopy are used to characterize the nitrogen species incorporated within these films depending on the deposition parameters. It is found that nitrogen atoms in these films are differently bonded. In particular, it can be distinguished between Ti-ON and Ti-N bonding configurations and molecular nitrogen species caused by precursor fragments.}, language = {en} } @misc{HenkelDasKotetal., author = {Henkel, Karsten and Das, Chittaranjan and Kot, Małgorzata and Schmeißer, Dieter and Naumann, Franziska and K{\"a}rkk{\"a}nen, Irina and Gargouri, Hassan}, title = {In-gap states in titanium dioxide and oxynitride atomic layer deposited films}, series = {Journal of Vacuum Science and Technology: A}, volume = {35}, journal = {Journal of Vacuum Science and Technology: A}, number = {1}, issn = {0734-2101}, doi = {10.1116/1.4972247}, pages = {01B135-1 -- 01B135-8}, abstract = {Valence band (VB) spectra of titanium dioxide (TiO2) and oxynitride (TiOxNy) films prepared by different atomic layer deposition (ALD) processes are compared and related to electrical characterization [current-voltage (JV) and capacitance-voltage (CV)] results. By increasing the nitrogen amount in the TiO2 film, band-gap narrowing is observed. The band-gap decrease is related to the contribution of the nitrogen density of states, which induces defects within the band-gap and thus reduces its optical band-gap. In-gap states are found in the VB spectra at 1 eV below the Fermi energy in all investigated ALD samples, i.e., in TiO2 as well as in TiOxNy films. An exponential correlation between leakage current density and in-gap state intensity is derived by the combination of JV measurements and VB spectra, whereas the in-gap states seem to have no influence on hysteresis and fixed oxide charges found in the CV data. It is argued that the in-gap states in TiO2 and TiOxNy have an excitonic or polaronic origin. Both, band-gap narrowing and in-gap state intensity can be tuned by the ALD process selection and the variation of its parameters.}, language = {en} } @misc{KotHenkelDasetal., author = {Kot, Małgorzata and Henkel, Karsten and Das, Chittaranjan and Brizzi, Simone and K{\"a}rkk{\"a}nen, Irina and Schneidewind, Jessica and Naumann, Franziska and Gargouri, Hassan and Schmeißer, Dieter}, title = {Analysis of titanium species in titanium oxynitride films prepared by plasma enhanced atomic layer deposition}, series = {Surface and Coatings Technology}, volume = {324}, journal = {Surface and Coatings Technology}, issn = {0257-8972}, doi = {10.1016/j.surfcoat.2016.11.094}, pages = {586 -- 593}, abstract = {A comparative study of thin titanium oxynitride (TiOxNy) films prepared by plasma enhanced atomic layer deposition using tetrakis(dimethylamino)titanium (TDMAT) and N2 plasma as well as titanium(IV)isopropoxide and NH3 plasma is reported. The comparison is based on the combination of Ti2p core level and valence band spectroscopy and current-voltage measurements. The TDMAT/N2 process delivers generally higher fractions of TiN and TiON within the Ti2p spectra of the films and stronger photoemissions within the bandgap as resolved in detail by high energy resolution synchrotron-based spectroscopy. In particular, it is shown that higher TiN contributions and in-gap emission intensities correlate strongly with increased leakage currents within the films and might be modified by the process parameters and precursor selection.}, language = {en} } @misc{KotŁobazaNaumannetal., author = {Kot, Małgorzata and Łobaza, Justyna and Naumann, Franziska and Gargouri, Hassan and Henkel, Karsten and Schmeißer, Dieter}, title = {Long-term ambient surface oxidation of titanium oxynitride films prepared by plasma-enhanced atomic layer deposition: An XPS study}, series = {Journal of Vacuum Science and Technology A}, volume = {36}, journal = {Journal of Vacuum Science and Technology A}, number = {1}, issn = {0734-2101}, doi = {10.1116/1.5003356}, abstract = {The surface oxidation of a titanium oxynitride (TiOxNy) film after long-time storage of 25 month in ambient conditions is investigated. The TiOxNy film is prepared by plasma-enhanced atomic layer deposition using etrakis(dimethylamino)titanium and nitrogen plasma, and the film is characterized by Ar+ ion sputtering of the film surface in combination with x-ray photoelectron spectroscopy (XPS) as well as by angle-resolved XPS. The total thickness of an oxygen-enriched layer at the surface of the TiOxNy films is found to be about 0.7 nm and it consists of a sequence of a 0.4 nm thick TiON/TiO2 enriched layer followed by a 0.3 nm thick TiO2 enriched layer underneath compared to the bulk composition of the film which shows constant values of 29\% TiN, 29\% TiO2, and 42\% TiON. The results suggest that the TiON enrichment takes place initially at the surface followed by a surface and subsurface oxidation.}, language = {en} } @inproceedings{KotNaumannGarainetal., author = {Kot, Małgorzata and Naumann, Franziska and Garain, Samiran and Po{\'{z}}arowska, Emilia and Gargouri, Hassan and Henkel, Karsten and Schmeißer, Dieter}, title = {Aluminum nitride films prepared by plasma atomic layer deposition using different plasma sources}, series = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Band 53,3}, booktitle = {Verhandlungen der Deutschen Physikalischen Gesellschaft, Reihe 6, Band 53,3}, publisher = {Deutsche Physikalische Gesellschaft}, address = {Bad Honnef}, issn = {0420-0195}, pages = {S. 170}, abstract = {Aluminum nitride (AlN) thin films are promising for versatile applications in optoelectronics, electronics, piezoelectrics, and acoustics due to their remarkable properties such as wide band gap, high dielectric constant, low electrical conductivity, good piezoelectric coefficient and high ultrasonic velocity. We present a comparative study of AlN films grown by plasma-enhanced atomic layer deposition at 350°C silicon wafers in the SENTECH SI ALD LL system using TMA and NH3 where either a capacitively coupled plasma (CCP) or a direct PTSA (planar triple spiral antenna) source was applied. The films were characterized by ellipsometry, XPS and electrical measurements. The layer properties are discussed concerning the varied ALD process parameters. In general, the process using the direct PTSA source delivered films with higher refractive index and better homogeneity over the wafer achieving also higher growth rates per cycle (GPC) in reduced total cycle durations. Films with refractive index in the range of 2.05 and permittivity around 8 could be realized with a GPC of 1.54 {\AA}/cycle.}, language = {en} } @misc{KotHenkelNaumannetal., author = {Kot, Małgorzata and Henkel, Karsten and Naumann, Franziska and Gargouri, Hassan and Tarnawska, Lidia Lupina and Wilker, Viola and Kus, Peter and Pożarowska, Emilia and Garain, Samiran and Rouissi, Zied and Schmeißer, Dieter}, title = {Comparison of plasma-enhanced atomic layer deposition AlN films prepared with different plasma sources}, series = {Journal of Vacuum Science and Technology A}, volume = {37}, journal = {Journal of Vacuum Science and Technology A}, number = {2}, issn = {0734-2101}, doi = {10.1116/1.5079628}, pages = {11}, abstract = {A comparative study of thin aluminum nitride (AlN) films deposited by plasma-enhanced atomic layer deposition in the SENTECH SI ALD LL system applying either a direct inductively coupled plasma (ICP) or an indirect capacitively coupled plasma (CCP) source is presented. The films prepared with the ICP source (based on a planar triple spiral antenna) exhibit improved properties concerning the growth rate per cycle, total cycle duration, homogeneity, refractive index, fixed and mobile electrical charges, and residual oxygen content compared to the CCP source, where the comparison is based on the applied plasma power of 200 W. The increase of the plasma power to 600 W in the ICP process significantly reduces the residual oxygen content and enhances the electrical breakdown field. The AlN layers grown under these conditions, with a growth rate per cycle of 1.54 {\AA}/cycle, contain residual oxygen and carbon concentrations of about 10\% and 4\%, respectively, and possess a refractive index of 2.07 (at 632.8 nm).}, language = {en} } @misc{NaumannReckGargourietal., author = {Naumann, Franziska and Reck, Johanna and Gargouri, Hassan and Gruska, Bernd and Bl{\"u}mich, Adrian and Mahmoodinezhad, Ali and Janowitz, Christoph and Henkel, Karsten and Flege, Jan Ingo}, title = {In situ real-time and ex situ spectroscopic analysis of Al₂O₃ films prepared by plasma enhanced atomic layer deposition}, series = {Journal of Vacuum Science and Technology B}, volume = {38}, journal = {Journal of Vacuum Science and Technology B}, number = {1}, issn = {0734-211X}, doi = {10.1116/1.5122797}, pages = {10}, abstract = {In situ real-time ellipsometry (irtE) with a very high time resolution of 24 ms was applied to monitor the inductively coupled plasma enhanced atomic layer deposition (ALD) process of Al₂O₃ thin films to precisely resolve each step of the ALD process and its complete cycle. The influence of plasma power, plasma pulse duration, and deposition temperature on the film growth characteristics was investigated. Ex situ ellipsometry [UV-VIS-NIR-SE (ultraviolet-visible-nearinfrared-spectroscopic ellipsometry) and IR-SE (infrared spectroscopic ellipsometry)] and x-ray photoelectron spectroscopy revealed the bulk properties (thickness, refractive index, chemical composition, and carbon incorporation) of the films, which together with the in situ results are compared to those of the films prepared by thermal ALD (T-ALD). The ICPEALD (inductively coupled plasma enhanced ALD) films were deposited at substrate temperatures between 80 and 250 °C and the role of plasma power (50-300 W) and its pulse duration (1-20 s) was investigated at 250 °C. The reference T-ALD layers were prepared at 200 °C. The ICPEALD process of Al₂O₃ shows an increased growth rate, and the produced films exhibit higher carbon contaminations than the T-ALD Al₂O₃ films. Plasma pulse times of up to 15 s further increase the content of carbon and CH species; at the same time, the refractive index decreases. The optical properties of ICPEALD deposited Al₂O₃ films are comparable with those of the T-ALD films for low plasma power and short plasma pulse durations. For the ICPEALD films, UV absorption is found and it is dependent on the deposition parameters. irtE resolves process effects that correlate with the bulk properties of Al₂O₃, such as impurities and oxygen deficiencies.}, language = {en} } @misc{MahmoodinezhadJanowitzNaumannetal., author = {Mahmoodinezhad, Ali and Janowitz, Christoph and Naumann, Franziska and Plate, Paul and Gargouri, Hassan and Henkel, Karsten and Schmeißer, Dieter and Flege, Jan Ingo}, title = {Low-temperature growth of gallium oxide thin films by plasma-enhanced atomic layer deposition}, series = {Journal of Vacuum Science and Technology A}, volume = {38}, journal = {Journal of Vacuum Science and Technology A}, number = {2}, issn = {0734-2101}, doi = {10.1116/1.5134800}, abstract = {Gallium oxide (Ga2O3) thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) applying a capacitively coupled plasma source where trimethylgallium (TMGa) as the gallium precursor and oxygen (O2) plasma were used in a substrate temperature (Ts)in the range of 80-200 °C. TMGa exhibits high vapor pressure and therefore facilitates deposition at lower substrate temperatures. The Ga2O3 films were characterized by spectroscopic ellipsometry (SE), x-ray photoelectron spectroscopy (XPS), and capacitance-voltage (C-V) measurements. The SE data show linear thickness evolution with a growth rate of ∼0.66 {\AA} per cycle and inhomogeneity of ≤2\% for all samples. The refractive index of the Ga2O3 thin films is 1.86 ± 0.01 (at 632.8 nm) and independent of temperature, whereas the bandgap slightly decreases from 4.68 eV at Ts of 80 °C to 4.57 eV at 200 °C. XPS analysis revealed ideal stoichiometric gallium to oxygen ratios of 2:3 for the Ga2O3 layers with the lowest carbon contribution of ∼10\% for the sample prepared at 150 °C. The permittivity of the layers is 9.7 ± 0.2 (at 10 kHz). In addition, fixed and mobile oxide charge densities of 2-4E12 and 1-2E12 cm-2, respectively, were observed in the C-V characteristics. Moreover, the Ga2O3 films show breakdown fields in the range of 2.2-2.7 MV/cm. Excellent optical and electrical material properties are maintained even at low substrate temperatures as low as 80 °C. Hence, the TMGa/O2 PEALD process is suitable for electronic and optoelectronic applications where low-temperature growth is required.}, language = {en} }