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Because of their superior performances to amorphous silicon (a-Si) semiconductors, amorphous oxide semiconductors have been attracting considerable attentions as backplanes for liquid crystal displays (LCDs) and organic light emitting diode displays (OLEDs). For mass production, the back channel etch (BCE)-type TFTs have considerable advantages owing to lesser process steps, lesser parasitic capacitances and shorter channel length than those of the etch stop layer (ESL)-type TFTs. However, the BCE-type TFTs often suffer from the unstable TFT operation against the transfer conditions and the various stress conditions due to the back channel damages to the oxide semiconductor [1-3]. Our study clearly demonstrates an addition of annealing process (post-annealing) that acts as recovery annealing is effective between SiNx deposition and SiOx deposition as passivation layer for the BCE-type TFTs application. The post-annealing effect to improve the stability of the BCE-type TFTs is investigated. The Oxide TFTs were fabricated on glass substrates with gate electrodes and gate insulator. The IGZO (Indium Gallium Zinc Oxide) thin film was deposited on the substrate by DC magnetron sputtering. Next, source and drain electrodes were formed by wet-etching process using a H2O2-based etchant. The passivation layer composed of double layered SiNx/SiOx was formed by PECVD, and some samples were treated with the aforementioned post-annealing at 300 ℃ in air during the passivation layer formation. It is confirmed that the stability under the negative bias thermal illumination stress (NBTIS) of the BCE-type TFTs with the post-annealing was superior to that of the BCE-type TFT without the post-annealing. In order to clarify the variation of the chemical composition of the IGZO thin film surfaces due to the post-annealing, X-ray Photoelectron Spectroscopy (XPS) was examined as well as electronic state analysis such as photoinduced transient spectroscopy (PITS) [4,5]. [1] G. Wang, Z. Song, X. Xiao, and S. Zhang; AM-FPD 2015 Symposium Digest, pp.111. [2] M. Nag, A. Bhoolokam, S. Steudel, A. Chasin, K. Myny, J. Maas, G. Groeseneken, and P. Heremans; Jpn. J. Appl. Phys, Vol. 53, No. 11, 111401 (2014). [3] R. Zhan, C. Dong, P.-T. Liu, and an H.-P. D. Shieh; Microelectronics Reliability, 53, pp.1879 (2013). [4] J. C. Balland, J. P. Zielinger, M. Tapiero, J. G. Gross, and C. Noguet; J. Phys. D: Appl. Physics, Vol. 19, No. 1 (1986). [5] A. Hino, Y. Takanashi, H. Tao, S. Morita, M. Ochi, H. Goto, K. Hayashi, and T. Kugimiya; J. Vac. Sci. Technol. B 32 (2014) 031210. Figure 1

In the present study, the sub-gap states of amorphous In-Ga-Zn-O (a-IGZO) thin films treated with various process conditions have been evaluated by means of capacitance-voltage (C-V) characteristics and isothermal capacitance transient spectroscopy (ICTS). It was found that the space-charge densities of the a-IGZO decreased as the oxygen partial pressure was increased during the sputtering of a-IGZO thin films. The ICTS spectra for the 4, 8, and 12 % samples were similar and the peak positions were found to be around 1 × 10-2 s at 180 K. On the other hand, the peak position for the 20 % sample shifted to a longer time regime and was located at around 2 × 10-1 s at 180 K. The total densities of the traps for the 4, 8, and 12 % samples were calculated to be 5−6 × 1016 cm-3, while that for 20 % was one order of magnitude lower than the others. From Thermal desorption spectrometer, it was found that desorption of Zn atoms started at a temperature higher than 300 °C for the 4 % sample, while desorption of Zn was not observed for the 20 % sample. The introduction of the sub-gap states could be attributed to oxygen-rich and/or Zn-deficient defects in the a-IGZO thin films formed during thermal annealing.

SUMMARY We have investigated the microwave-detected photoconductivity responses from the amorphous In–Ga–Zn–O (a-IGZO) thin films. The time constant extracted by the slope of the slow part of the reflectivity signals are correlated with TFT performances. We have evaluated the influences of the sputtering conditions on the quality of a-IGZO thin film, as well as the influences of gate insulation films and annealing conditions, by comparing the TFT characteristics with the microwave photoconductivity decay ( -PCD). It is concluded that the -PCD is a promising method for in-line process monitoring for the IGZO-TFTs fabrication.

In the present study, the electronic structure and film composition at the back channel surface of amorphous In-Ga-Zn-O (a-IGZO) thin films were characterized to discuss the origin of the threshold voltage shift in the a-IGZO TFTs under light negative bias and temperature stress (LNBTS) test. Photoelectron yield spectroscopy revealed that surface gap states were observed near the valence band maximum, but were not responsible for the hump observed in the transfer curve. By using photoelectron spectroscopy for chemical analysis (ESCA), it was found that the film composition was changed as it was approaching to the surface; the content of In increased while that of Ga decreased. A increase in oxygen deficiency was also observed near the back channel surface. In accordance with the change, downward band bending was detected by ultraviolet photoelectron spectroscopy near the surface (up to 5 ~ 7 nm) region. According to cathodoluminescence (CL) measurements, two broad bands were observed at around 1.8 and 2.4 eV. The gap states causing the luminescence were mainly located near the back channel surface. It is considered that the trap states due to the oxygen deficiency and/or the Zn interstitials could cause the hump effect in the transfer curve of a-IGZO TFTs.

A comparative study on light-induced negative-bias stress stabilities in amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) was performed by means of photoinduced transient spectroscopy (PITS). When the a-IGZO thin films were deposited with 4% O 2 partial pressure (P/P), a dominant peak with a maximum of around 100 K was clearly observed from the sample. There was a flow rate of SiH 4 /N 2 O of 4/100 sccm for the ESL deposition, while the PITS spectra from the sample with a flow rate of SiH 4 /N 2 O of 6/150 sccm possessed a broader peak of around 115 K and an apparent shoulder of around 200–280 K was observed. This shoulder of around the 200–280 K was clarified when the a-IGZO thin film was deposited with an O 2 P/P of 20 % In accordance with the changes in the electronic structures in the a-IGZO thin films due to the ESL deposition, the stability of the TFTs against the negative bias thermal Illumination stress (NBTIS) was degraded; the value of the V th shift after the 2h-NBTIS test was increased from 2.5 to 6.0 V The decreasing the compensating acceptors and/or the increasing the hydrogen-related donors could be the origin of the negative V th shift during the NBTIS test.

The double-layered Ti/Si barrier metal is demonstrated for the source/drain Cu interconnections in oxide semiconductor thin-film transistors (TFTs). The transmission electromicroscopy and ion mass spectroscopy analyses revealed that the double-layered barrier structure suppresses the interfacial reaction and the interdiffusion at the interface after thermal annealing at 350°C. The underlying Si layer was found to be very useful for the etch stopper during wet etching for the Cu/Ti layers. The oxide TFTs with a double-layered Ti/Si barrier metal possess excellent TFT characteristics. It is concluded that the present barrier structure facilitates the back-channel-etch-type TFT process in the mass production line, where the four- or five-mask process is used.

SUMMARY Microwave photoconductivity decay (μ-PCD) method was applied to evaluate the effects of chemical composition and Ar + plasma induced damage on the bulk and the surface states in amorphous In-Ga-ZnO (a-IGZO) films. It was found that the peak reflectivity signal in the photoconductivity response increased with decreasing the Ga content, and had a strong correlation with the a-IGZO transistor performances. In addition, the peak reflectivity signals obtained after various Ar + plasma treatment duration were well correlated with the transistor characteristics. With Ar + plasma treatment, the peak reflectivity signal decreased in accordance with degradation of transistor characteristics. The μ-PCD method was found to be a very useful tool not only to evaluate the bulk and the surface states, but also to predict the performance of a-IGZO transistors subjected to various plasma processes in the production.

Transparent amorphous oxide semiconductors (TAOSs) such as amorphous In-Ga-Zn-O (a-IGZO) are superior to the conventional semiconducting materials used in flat-panel displays (FPDs) because they have the advantages of high electron mobility, good uniformity, and a simple manufacturing process based on matured sputtering techniques [1]. To apply TAOS thin-film transistors (TFTs) to the mass production of next-generation displays, the stress stability during the a-IGZO TFT operation is a crucial issue that must be resolved. It has been reported that the concentration of the hydrogen atoms in the a-IGZO is huge and the diffusion coefficient of hydrogen is two orders of magnitude larger than that of oxygen [2]. It means that hydrogen atoms easily diffuse into the channel region of the a-IGZO TFTs from hydrogen-containing layers such as a passivation layer (PV) during the fabrication. Hydrogen atoms also easily absorb to the channel region during the fabrication. Therefore, clarification of the effect of hydrogen on the electronic properties of the a-IGZO is particularly important to improve the TFT performance such as various stress stabilities against negative bias thermal illumination stress (NBTIS), negative bias thermal stress (NBTS) and positive bias thermal stress (PBTS). The hump-shaped variation of the transfer curves under the NBTIS test was observed in both a-IGZO etch-stop layer (ESL)-type and back channel etch (BCE)-type TFTs. According to the results of photo-induced transient spectroscopy (PITS) analysis, it was observed that the density of hydrogen-related traps in the a-IGZO thin film was changed with the increase and/or decrease of hydrogen incorporated by the TFT manufacturing process [3, 4]. In this presentation, the impact of hydrogen-related trap levels on stress reliability with humps will be reviewed. Furthermore, the parallel-shaped variation of the transfer curves under the NBTS and PBTS test changed depending on the temperature of post-process annealing. It is believed that these behaviors are caused by interface defects due to dissociation and diffusion of hydrogen atoms at the interface [5, 6]. [1] K. Nomura, H. Ohta, A. Takagi, T. Kamiya, M. Hirano, and H. Hosono, Nature Vol. 432, pp. 488-492 (2004). [2] K. Nomura, T. Kamiya, and H. Hosono, ECS J. Solid State Sci. Technol. Vol. 2, No. 1, pp. 5-8 (2013). [3] K. Hayashi, M. Ochi, A. Hino, H. Tao, H. Goto, and T. Kugimiya, Jpn. J. Appl. Phys. 56, 03BB02 (2017). [4] M. Ochi, A. Hino, H. Goto, K. Hayashi, and T. Kugimiya, ECS J. Solid State Sci. Technol. 6, P247 (2017). [5] K. Hayashi, M. Ochi, A. Hino, H. Tao, H. Goto, and T. Kugimiya, Proc. IDW ’17, pp. 320-323 (2017). [6] M. Ochi, A. Hino, H. Goto, K. Hayashi, and T. Kugimiya, Jpn. J. Appl. Phys. 57, 02CB06 (2018). Figure 1

Total photoyield spectroscopy (TPYS) was applied to investigate the evolution of hydrogen-related defect states in amorphous In-Ga-Zn-O (a-IGZO) thin films. It was found that the defect states located at around 4.3 eV from the vacuum level were formed as a result of hydrogenation. After thermal annealing at 300 °C, the onset of the TPYS spectra shifted to 4.15 eV. As the annealing temperature was increased, the photoyield from the defect states decreased, implying that there was outdiffusion of hydrogen with Zn from the a-IGZO. These experiments produced direct evidence which shows the formation of defect states as a result of hydrogen incorporation into the a-IGZO thin films.

Detailed neutron diffraction measurements on a single crystalline ErB$_2$C$_2$ were performed. We observed magnetic diffuse scattering which consists of three components just above the transition temperatures, which is also observed in characteristic antiferroquadrupolar ordering compounds HoB$_2$C$_2$ and TbB$_2$C$_2$. The result of this experiments indicates that the antiferroquadrupolar interaction is not dominantly important as a origin of the magnetic diffuse scattering., Comment: 5 pages, 5 figures, submitted to J. Phys. Soc. Jpn

Electron traps in the channel region of amorphous In–Ga–Zn–O (a-IGZO) thin film transistors (TFTs) were evaluated using capacitance transient responses from thin (50 nm) metal-oxide-semiconductor diodes. It was found that the carrier transport was mainly dominated by the conduction band tail states. The trap density of a-IGZO deposited at 5 mTorr was higher than that at 1 mTorr, providing direct evidence that the trap density in the channel layer decreased by decreasing the sputtering pressure during the IGZO deposition. The defect states with activation energies of ∼0.2 eV were observed only a-IGZO deposited at 5 mTorr. The reduction of the corresponding TFT mobility should be originated from the increase in the conduction band tail states. The high pressure sputtering is suggested to enhance the structural fluctuation in a-IGZO films, at least in the structure surrounding defect, resulting in an increase of the concentration of the electron traps.

Fabrication process conditions of a passivation (PV) layer correlated with stress stabilities of amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). In etch-stop layer (ESL)-TFTs, by inserting a Si-based resin between SiN x and SiO x PV layers, the peak intensity in the photoinduced transient spectroscopy (PITS) spectrum was notably reduced. This suggested the suppression of hydrogen incorporation into a-IGZO, which led to the improvement of stability under negative bias thermal illumination stress (NBTIS). In contrast, the hydrogen-related defects in the a-IGZO were easily formed by the back-channel etch (BCE) process. Furthermore, it was found that, under NBTIS, the transfer curves of the BCE-TFTs shifted in parallel owing to the positive fixed charge located in the back channel of the a-IGZO TFTs. The hump-shaped shift increased with stress time. This is because hydrogen atoms located at the back-channel surfaces of the a-IGZO and/or PV layers were incorporated into the channel region of the BCE-TFTs and induced the hydrogen-related defects.

The magnetization processes along the principal [0 0 1] axis of an antiferromagnetic ErB 2 C 2 with T N = 15.9 K were examined by a capacitive Faraday method at temperatures down to 0.54 K in magnetic fields up to 5 T. The magnetization at 5.0 K increases up to the saturation magnetization with increasing field through five step-like transitions and decreases down to 0 μ B through five transitions showing clear hystereses. With increasing field at 0.54 K, the magnetization starts to increase at 1.7 T and gradually reaches the saturation without any step-like increase, although ErB 2 C 2 is suggested to be an Ising-like antiferromagnet from the strong anisotropic susceptibilities. Furthermore, the process with decreasing field shows a continuous decrease down to 1.6 T, a step-like decrease at 0.7 T and a residual magnetization of 0.4 μ B even at 0 T. It is presumed that this phenomenon may relate to the characteristic shape of Fermi surface that results in the broadest magnetic reflection with a nearly flat-top structure centered at the (1 0 0) reciprocal position.

We observed the profiles of anomalous magnetic diffuse scattering in ErB2C2 by neutron diffraction. The simple Lorentzian-type profiles along c * -axis indicate that the spin correlation along the c * -axis is an exponential type damping one with a correlation length of ∼ 15 A .

Negative bias thermal illumination stress (NBTIS) stabilities in amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs) were studied by photoinduced transient spectroscopy (PITS). The degradation of TFT performance correlated with trap states in the channel region of a-IGZO TFTs with an etch stop layer (ESL). A prominent peak at approximately 100 K was observed in a-IGZO formed under a partial pressure (p/p) of 4% O2. With increasing O2 p/p, an apparent shoulder of around 230 K appeared in PITS spectra. A higher flow rate of SiH4/N2O for the ESL deposition induced trap states associated with the 230 K peak. The peak at approximately 100 K could originate from the depletion of Zn by preannealing, while the peak at approximately 230 K should be attributed to the oxygen-deficient and/or Zn-rich defects due to the formation of OH in a-IGZO. The trap states in a-IGZO TFTs gave rise to degradation in terms of NBTIS. The threshold voltage shift (ΔV th) was 2.5 V, but it increased with the O2 p/p as well as the flow rate of SiH4/N2O for ESL deposition. The time dependence of ΔV th suggested that hydrogen from the ESL and/or in the a-IGZO thin films was incorporated and modified the trap states in the channel region of the a-IGZO TFTs.

High-resolution Rutherford backscattering spectrometry (HRBS) in combination with grazing angle argon sputtering was carried out to characterize the interface of aluminum-nickel (Al-Ni) alloy and amorphous-silicon films in a thin film transistor (TFT) for liquid crystal display (LCD). After thinning the top Al-Ni layer by a 1-keV Ar sputtering, the sensitivity of the interface oxygen was improved to be twice higher than that before sputtering. The results revealed that the oxygen at the interface relates to the contact characteristics.

Total photoyield emission spectroscopy (TPYS) was applied to study the evolution of sub-gap states in hydrogen-treated amorphous In-Ga-Zn-O (a-IGZO) thin films. The a-IGZO thin films were subjected to hydrogen radicals and subsequently annealed in ultra-high vacuum (UHV) conditions. A clear onset of the electron emission was observed at around 4.3 eV from the hydrogen-treated a-IGZO thin films. After successive UHV annealing at 300 °C, the onset in the TPYS spectra was shifted to 4.15 eV, and the photoelectron emission from the sub-gap states was decreased as the annealing temperature was increased. In conjunction with the results of thermal desorption spectrometer, it was deduced that the hydrogen atoms incorporated in the a-IGZO thin films induced metastable sub-gap states at around 4.3 eV from vacuum level just after the hydrogenation. It was also suggested that the defect configuration was changed due to the higher temperature UHV annealing, and that the hydrogen atoms desorbed with the involvement of Zn atoms. These experiments produced direct evidence to show the formation of sub-gap states as a result of hydrogen incorporation into the a-IGZO thin films.

Photoinduced transient spectroscopy (PITS) was applied to study the effects of thermal annealing in the thin-film transistor (TFT) fabrication process on the variations of the electron traps in the channel region of amorphous In-Ga-Zn-O (a-IGZO). A dominant peak with a maximum of around 130 K was observed in the PITS spectra, but the detailed features were varied depending on the annealing conditions. The six particular temperatures corresponding to the trap states were extracted at about 100, 140, 150, 210, 320, and 390 K from the differential PITS spectra, showing good correlation with the trap states observed in ZnO. The results of thermal desorption spectrometry suggested that the variation of electron traps in the a-IGZO thin films has its origin in the decomposition of O and Zn during the annealing process. The annealing after the etch-stop layer deposition was also examined. The peak at about 150 K extracted from the differential PITS spectra before and after the annealing was markedly decreased. The activation energy of the corresponding trap states was estimated to be around 0.3 eV, which was close to those known as the E3 center in ZnO. Secondary ion mass spectroscopy analysis suggested that the reduction of trap density was mainly due to a decrease in the number of defects which involve hydrogen atoms in their configuration. Considering these results, the variations in the electron traps in the a-IGZO thin films during the TFT fabrication process should be attributed to the introduction of Zn, O, and/or H-related defects into tetrahedra consisting of Zn-O bonds.

In this study, adhesion of the Cu/Cu-Mn stacked interconnections to glass (SiO2) substrates was evaluated and the results were correlated with a detailed analysis of the reaction layer between the Cu-Mn and the chemical vapour deposited SiO2. When the Mn concentrations were varied, an abrupt change in the adhesion properties was observed; the practical adhesion properties were obtained in the Cu/Cu-Mn interconnections with Mn concentrations at 8% and higher. To clarify the chemical nature and the microstructure of the reaction layer at the interface between the Cu-x Mn (x = 4, 10 at. %) and the SiO2 layers was analysed using angle-resolved x-ray photoelectron spectroscopy and transmission electron microscope-electron energy loss spectroscopy. These observations indicated that the cross-sectional structure along the reaction layer of the Cu–10 at. % Mn sample can be divided into two regions: in the high Mn region, the Mn-Si complex oxide and the SiO2 mixture phase are preferable due to a decrease in the ox...

The physical properties of amorphous In–Ga–Zn–O (a-IGZO) films deposited by DC sputtering under various sputtering pressures were investigated. The sputtering pressure was found to influence various physical properties. Lower sputtering pressures resulted in film densification and decreased both surface roughness and hydrogen concentration. In addition, transistor performance characteristics such as saturation mobility and sub-threshold swing improved as the sputtering pressure decreased. These results yield insight into the correlation between thin film transistor (TFT) performance and deposition conditions.

A magnetic short-range ordering has been found in ErB 2 C 2 near the transition temperatures by neutron diffraction experiments, which is the origin of anomalies in magnetisation.

Metal-oxide-semiconductor (MOS) diodes with various gate insulators (G/Is) were characterized by capacitance–voltage characteristics and isothermal capacitance transient spectroscopy (ICTS) to evaluate the effect of H and OH desorption and diffusion on the electronic structures in amorphous In–Ga–Zn–O (a-IGZO) thin films. The density and the distribution of the space charge were found to be varied depending on the nature of the G/I. In the case of thermally grown SiO2 (thermal SiO2) G/Is, a high space-charge region was observed near the a-IGZO and G/I interface. After thermal annealing, the space-charge density in the deeper region of the film decreased, whereas remained unchanged near the interface region. The ICTS spectra obtained from the MOS diodes with the thermal SiO2 G/Is consisted of two broad peaks at around 5 × 10−4 and 3 × 10−2 s before annealing, while one broad peak was observed at around 1 × 10−4 s at the interface and at around 1 × 10−3 s in the bulk after annealing. Further, the trap densi...

Electron traps in amorphous In–Ga–Zn–O (a-IGZO) thin films were studied using isothermal capacitance transient spectroscopy (ICTS). Broad peaks that shifted toward a longer elapsed time with an increase in the filling pulse width were detected from the ICTS spectra for metal-oxide-semiconductor diodes consisting of a Mo/SiO2/a-IGZO structure. The time constant of the peak position at 180 K was found to be from ∼1 m to ∼100 ms, corresponding to a range of energy level from ∼170 to ∼230 meV below the conduction band edge. The total trap density around the peak was estimated to be ∼1 × 1016 cm−3·eV−1. Further, according to the biasing voltage dependence of the ICTS signal, the density of the trap states increases by about three orders of magnitude near the interface between the a-IGZO and the gate dielectric layers. The electron transport in electronic devices using an a-IGZO could be influenced by the trap states detected in the present study.