NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
G. Lupina, J. Kitzmann, I. Costina, M. Lukosius, C. Wenger, A. Wolff, S. Vaziri, M. Östling, I. Pasternak, A. Krajewska, W. Strupinski, S. Kataria, A. Gahoi, M. Lemme, Günther Ruhl, G. Zoth, O. Luxenhofer, W. Mehr
Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene
ACS Nano, vol. 9, no. 5, pp. 4776-4785
2015
DOI: 10.1021/acsnano.5b01261
Abstract anzeigen
Integration of graphene with Si microelectronics is very appealing by offering a potentially broad range of new functionalities. New materials to be integrated with the Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etching and electrochemical delamination methods with respect to residual submonolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection X-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 1013 atoms/cm2. These metal impurities appear to be partially mobile upon thermal treatment, as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics, these results reveal that further progress in synthesis, handling, and cleaning of graphene is required to advance electronic and optoelectronic applications.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
Günther Ruhl, W. Lehnert, M. Lukosius, C. Wenger, C. Baristiran Kaynak, T. Blomberg, S. Haukkac, P. Baumann, W. Besling, A. Roeste, B. Riou, S. Lhostif, A. Halimaou, F. Roozeboom, E. Langereis, W.M.M. Kessels, A. Zauner, S. Rushworth
Dielectric Material Options for Integrated Capacitors
ECS Journal of Solid State Science and Technology, vol. 3, no. 8
2014
DOI: 10.1149/2.0101408jss
Abstract anzeigen
Future MIM capacitor generations will require significantly increased specific capacitances by utilization of high-k dielectric materials. In order to achieve high capacitance per chip area, these dielectrics have to be deposited in three-dimensional capacitor structures by ALD or AVD (atomic vapor deposition) process techniques. In this study eight dielectric materials, which can be deposited by these techniques and exhibit the potential to reach k-values of over 50 were identified, prepared and characterized as single films and stacked film systems. To primarily focus on a material comparison, preliminary processes were used for film deposition on planar test devices. Measuring leakage current density versus the dielectric constant k shows that at low voltages (≤1 V) dielectrics with k-values up to 100 satisfy the typical leakage current density specification of <10−7 A/cm2 for MIM capacitors. At higher voltages (3 V) this specification is only fulfilled for dielectrics with k-values below 45. As a consequence, the maximum achievable capacitance gain by introducing high-k dielectrics depends on the operating voltage of the application, such as DRAM capacitors or RF and blocking capacitors. To meet the reliability requirements for RF and blocking capacitors, high-k dielectric film thicknesses of up to 50 nm are necessary.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
M. Lukosius, C. Wenger, T. Blomberg, Günther Ruhl
Properties of stacked SrTiO3/Al2O3 metal–insulator–metal capacitors
Journal of Vacuum Science & Technology B, vol. 31, no. 1
2013
DOI: 10.1116/1.4766183
Abstract anzeigen
The possibilities to grow thin films of SrTiO3 and Al2O3 by atomic layer deposition for stacked metal–insulator–metal capacitors have been investigated in this work. In order to tune the functional properties of the capacitors, different processing steps have been employed to realize different combinations of the dielectric stacks. Electrical properties, extracted after the postdeposition annealing and sputter deposition of the Au top electrodes, indicated that the metal–insulator–metal (MIM) structures with additional Al2O3 layer provided better leakage currents densities, compared to the ones with single SrTiO3 based MIM capacitors, but the dielectric constant values have also decreased if additional Al2O3 film was inserted. Attempts to optimize the properties of the MIM stacks have been done by manufacturing heterostructures of Al2O3/SrTiO3/Al2O3 as well as SrTiO3/Al2O3/SrTiO3. In the first case, Al2O3 prevented the crystallization of SrTiO3 in the multilayer dielectric structure and therefore reduced the total capacitance density of the particular MIM stack, whereas the SrTiO3/Al2O3/SrTiO3 stack was found to possess superior electrical properties. Leakage current density as low as ∼10−8 A/cm2 at 2 V and the dielectric constant value of 40 have been extracted.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
M. Lukosius, T. Blomberg, D. Walcyk, Günther Ruhl, C. Wenger
Metal-Insulator-Metal capacitors with ALD grown SrTiO3: Influence of Pt electrodes
IOP Conference Series: Materials Science and Engineering, vol. 41
2012
Abstract anzeigen
Metal-Insulator-metal (MIM) capacitors with atomic layer deposited (ALD) single SrTiO3 dielectric have been investigated in this work. Structural and electrical properties were studied after the formation of the MIM stack consisting of the platinum (Pt) bottom electrode, 50 nm SrTiO3 layer and the top Pt electrode. The as deposited films were amorphous and had a dielectric constant of ~ 10, whereas the annealing of the samples in the nitrogen (N2) or oxygen (O2) atmosphere at 550-600 °C led to the crystallization of the SrTiO3 and therefore to the increased dielectric constant of ~ 85. In addition, the electrical results revealed that the combination of SrTiO3 with the high work function electrode like Pt, provided better leakage current performance in comparison with TiN/ SrTiO3 stacks. The values as low as ~ 10−7 A/cm2 at 2 V were observed for both in N2 or O2 annealed SrTiO3 layers. On the other hand, the samples annealed in O2 atmosphere at 600 °C possessed lower capacitance-voltage nonlinearity coefficients (−645 ppm/V2) than the ones for N2 annealed samples (-2700 ppm/V2).
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
M. Lukosius, C. Baristiran Kaynak, S. Kubotsch, T. Blomberg, Günther Ruhl, C. Wenger
Properties of atomic-vapor and atomic-layer deposited Sr, Ti, and Nb doped Ta2O5 Metal–Insulator–Metal capacitors
Thin Solid Films, vol. 520, no. 14, pp. 4576-4579
2012
DOI: 10.1016/j.tsf.2011.10.199
Abstract anzeigen
Atomic Vapor Deposition and Atomic Layer Deposition techniques were applied for the depositions of Ta2O5, Ti–Ta–O, Sr–Ta–O and Nb–Ta–O oxide films for Metal–Insulator–Metal (MIM) capacitors used in back-end of line for Radio Frequency applications. Structural and electrical properties were studied. Films, deposited on the TiN bottom electrodes, in the temperature range of 225–400 °C, were amorphous, whereas the post deposition annealing at 600 °C resulted in the crystallization of Nb–Ta–O films. Electrical properties of MIM structures, investigated after sputtering Au top electrodes, revealed that the main characteristics were different for each oxide. On one hand, Ti–Ta–O based MIM capacitors possessed the highest dielectric constant (50), but the leakages currents were also the highest (~ 10− 5 A/cm2 at − 2 V). On the other hand, Sr–Ta–O showed the lowest leakage current densities (~ 10− 9 A/cm2 at − 2 V) as well as the smallest capacitance–voltage nonlinearity coefficients (40 ppm/V2), but the dielectric constant was the smallest (20). The highest nonlinearity coefficients (290 ppm/V2) were observed for Nb–Ta–O based MIM capacitors, although relatively high dielectric constant (40) and low leakage currents (~ 10− 7 A/cm2 at − 2 V) were measured. Temperature dependent leakage-voltage measurements revealed that only Sr–Ta–O showed no dependence of leakage current as a function of the measurement temperature.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
C. Wenger, M. Lukosius, T. Blomberg, A. Abrutis, P. Baumann, Günther Ruhl
ALD and AVD Grown Perovskite-type Dielectrics for Metal-Insulator-Metal Application
(Invited)
ECS Transactions, vol. 41, no. 2, pp. 53-61
2011
DOI: 10.1149/1.3633654
Abstract anzeigen
Atomic Vapor Deposition (AVD) and Atomic Layer Deposition (ALD) techniques were successfully applied for the depositions of perovskite type dielectrics, namely, Sr-Ta-O, Ti-Ta-O, Sr-Ti-O, Ba-Hf-O, Nb-Ta-O and Ce-Al-O. Thin films were investigated as alternative dielectrics for Metal-Insulator-Insulator (MIM) capacitors. Structural and electrical properties are investigated after depositing the metal oxides on 200 mm TiN/Si (100) substrates within the temperature range of 225-400 ºC. Electrical properties, investigated after sputtering Au top electrodes, revealed that the main characteristics are different for each dielectric. The highest dielectric constants were achieved for crystalline SrTiO3 (k=95), crystalline CeAlO3 (k = 60) and amorphous Ti-Ta-O (k = 50) films. However, Sr-Ta-O based MIM capacitors showed the lowest leakage current densities as well as the smallest capacitancevoltage linearity coefficients.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
M. Lukosius, C. Baristiran Kaynak, A. Abrutis, M. Skapas, V. Kubilius, A. Zauner, Günther Ruhl, C. Wenger
Metal-insulator-metal capacitors with MOCVD grown Ce-Al-O as dielectric
Microelectronic Engineering, vol. 88, no. 7, pp. 1529-1532
2011
DOI: 10.1016/j.mee.2011.03.044
Abstract anzeigen
Ce–Al–O thin films were prepared on 70 nm TiN/Si(1 0 0) substrates by pulsed injection metal organic chemical vapor deposition (PI-MOCVD) for metal–insulator–metal (MIM) applications. Depositions were carried out at 400 °C using two separate Ce and Al precursors. In order to get Ce–Al–O films with different stoichiometry, Al2O3 and CeO2 were mixed with different Ce:Al precursors’ ratios. According to the XRD analysis, the as deposited films were amorphous if more aluminum was injected than cerium, and crystalline – if they are cerium rich. Electrical properties have been investigated in MIM capacitors after e-beam evaporation of Au top electrodes. Oxides possess a dielectric constant of 10–20 in combination with leakage current densities as low as 10−5 A/cm2 at −2 V. The post deposition annealing (PDA) at 600 °C and 850 °C in N2 for 5 min lead to the diffusion of Ti from TiN bottom electrode and formation of the rutile TiO2 phase. Nevertheless, CeAlO3 films were obtained if the ratio of injected Ce:Al was 1:1. The k values increased to 60 in this case, but the leakage current density worsened to 10−3 A/cm2 at −2 V.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
C. Baristiran Kaynak, M. Lukosius, B. Tillack, C. Wenger, T. Blomberg, Günther Ruhl
Single SrTiO3 and Al2O3/SrTiO3/Al2O3 based MIM capacitors: Impact of the bottom electrode material
Microelectronic Engineering, vol. 88, no. 7, pp. 1521-1524
2011
DOI: 10.1016/j.mee.2011.03.022
Abstract anzeigen
Metal–Insulator–Metal (MIM) capacitors with atomic layer deposited (ALD) single SrTiO3 dielectric and Al2O3/SrTiO3/Al2O3 multilayer dielectric have been deposited on TaN and TiN bottom electrodes. The MIM stacks have been analyzed and compared in terms of electrical and structural properties. The results indicate that MIMs with multilayer dielectrics provide better leakage current performance than the ones with single dielectrics while capacitance density is decreased. Additional Al2O3 layers prevented the crystallization of SrTiO3 in the multilayer dielectric stack. The decreased capacitance density in MIMs with multilayer dielectric is attributed to the amorphous structure of SrTiO3 and the series capacitance of top and bottom Al2O3 layers. Furthermore, MIM capacitors with single SrTiO3 dielectric layer on TiN electrodes indicated better capacitance density compared to the one with TaN electrodes. The lower capacitance density of the single SrTiO3 dielectric on TaN electrodes is correlated to the interfacial layer formation between SrTiO3 and TaN electrodes.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
C. Baristiran Kaynak, M. Lukosius, I. Costina, B. Tillack, C. Wenger, Günther Ruhl, T. Blomberg
Enhanced leakage current behavior of Sr2Ta2O7-x/SrTiO3 bilayer dielectrics for metal-insulator-metal capacitors
Thin Solid Films, vol. 519, no. 17, pp. 5734-5739
2011
DOI: 10.1016/j.tsf.2011.01.001
Abstract anzeigen
Metal–Insulator–Metal (MIM) capacitors are one of the most essential components of radio frequency devices and analog/mixed-signal integrated circuits. In order to obtain high capacitance densities in MIM devices, high-k materials have been considered to be promising candidates to replace the traditional insulators. The challenging point is that the dielectric material must demonstrate high capacitance density values with low leakage current densities.
In this work, SrTiO3 based MIM capacitors have been investigated and the electrical performance of the devices have been optimized by using bilayered systems of Sr2Ta2O7−x/SrTiO3 with different thicknesses of Sr2Ta2O7−x. Sputtering X-Ray photoelectron spectroscopy (XPS) measurements have been applied to investigate the interfaces between the thin film constituents of the MIM stacks. The optimized bilayered system provides a leakage current density of 8∗10− 8 A/cm2 at 2 V (bottom electrode injection) and a high capacitance density of 13 fF/μm2.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
M. Lukosius, C. Baristiran Kaynak, C. Wenger, Günther Ruhl, S. Rushworth, P. Baumann
Atomic Vapor Depositions of Ti–Ta–O thin films for Metal–Insulator–Metal applications
Thin Solid Films, vol. 519, no. 11, pp. 3831-3834
2011
DOI: 10.1016/j.tsf.2011.01.239
Abstract anzeigen
Atomic Vapor Deposition technique was applied for the depositions of Ti–Ta–O oxide films for Metal–Insulator–Metal capacitors used in back-end of line for Radio Frequency applications. Composition, crystallinity, thermal stability and electrical properties were studied. Ti–Ta–O films, with the ratio of Ta/Ti ~ 1.5, deposited at 400 °C on TiN electrodes, were amorphous and possessed a dielectric constant of 50 with low voltage linearity coefficients and leakage currents densities as low as 10− 7 A/cm2 at 1 V. The films, deposited on Si wafers, were amorphous up to the annealing temperature of 700 °C and crystallized in orthorhombic Ta2O5 phase at higher temperatures.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
M. Lukosius, C. Baristiran Kaynak, C. Wenger, Günther Ruhl, S. Rushworth
Electrical characteristics of Ti-Ta-O based MIM capacitors
Journal of Vacuum Science & Technology B, vol. 29, no. 1
2011
DOI: 10.1116/1.3534020
Abstract anzeigen
Amorphous Ti–Ta–O thin films were deposited by the atomic-vapor deposition technique for metal-insulator-metal (MIM) applications. Depositions were carried out at 400 °C on 200-mm Si (100) wafers using TiN and TaN as bottom electrode materials. The comparison of electrical properties of MIM capacitors was done after physical-vapor deposited growth of different top electrodes, namely, Au, TiN, TaN, and Ti. Capacitance-voltage measurements revealed that the dielectric constant of 50 can be reached if Ti–Ta–O layers are deposited on TiN and if Au, TaN, or Ti is used as the top electrode. The k value is reduced to 37 if TaN is used as bottom electrode. However, if TiN is used as the top electrode, the k value of the stack is reduced by a factor of 3, from 50 to 17, independent of whether TiN or TaN are used as bottom electrodes. The lowest leakage current values (∼10−8 A/cm2) were observed when gold was used as the top electrode, whereas it increased by 3 orders of magnitude if the top electrode was changed to TiN and even more if the top electrode was changed to TaN or Ti.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
C. Baristiran Kaynak, M. Lukosius, I. Costina, B. Tillack, C. Wenger, Günther Ruhl, S. Rushworth
Investigations of thermal annealing effects on electrical and structural properties of SrTaO based MIM capacitor
Microelectronic Engineering, vol. 87, no. 12, pp. 2561-2564
2010
DOI: 10.1016/j.mee.2010.07.015
Abstract anzeigen
The annealing effects on dielectric and electrode materials in Ti/SrTaO/TaN/TiN/Ti/Si metal–insulator–metal (MIM) capacitors were studied. The electrical and structural properties were investigated after subjecting the samples to annealing temperatures of 500 °C, 700 °C and 900 °C. The electrical results revealed that the dielectric constant (k value) of Sr–Ta–O increased from 18 to 50 with increasing annealing temperature. This improvement in k value can be associated to the crystallization of dielectric layer. However, the leakage current density increased several orders of magnitudes with increase of the annealing temperatures. This observation was attributed to crystallization of dielectric, degradation of TaN electrode and out-diffusion of Si from the substrate.
NachhaltigAngewandte Naturwissenschaften und WirtschaftsingenieurwesenTAZ SpiegelauZeitschriftenartikel
C. Wenger, M. Lukosius, H.-J. Müssig, Günther Ruhl, S. Pasko, C. Lohe
Influence of the electrode material on HfO2 metal-insulator-metal capacitors
Journal of Vacuum Science & Technology B, vol. 27, no. 1, pp. 286-289
2009
DOI: 10.1116/1.3071843
Abstract anzeigen
TaN and TiN are investigated as bottom electrode materials for metal-insulator-metal (MIM) capacitor applications. Atomic vapor deposited HfO2 films are used as high-k dielectric. The influence of the interfacial layer between HfO2 and the bottom electrode on the electrical performance of MIM capacitors is evaluated. The capacitance density as well as the capacitance voltage linearity of high-k MIM capacitors is affected by the electrode material. There is also an impact by TaN and TiN on leakage current density and breakdown strength of the devices.
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