Effect Of Post-metallization Annealing Research Articles

Ti/HfO2-Based RRAM with Superior Thermal Stability Based on Self-Limited TiOx

HfO2-based resistive random-access memory (RRAM) with a Ti buffer layer has been extensively studied as an emerging nonvolatile memory (eNVM) candidate because of its excellent resistive switching (RS) properties and CMOS process compatibility. However, a detailed understanding of the nature of Ti thickness-dependent RS and systematic thermal degradation research about the effect of post-metallization annealing (PMA) time on oxygen vacancy distribution and RS performance still needs to be included. Herein, the impact of Ti buffer layer thickness on the RS performance of the Al/Ti/HfO2/TiN devices is first addressed. Consequently, we have proposed a simple strategy to regulate the leakage current, forming voltage, memory window, and uniformity by varying the thickness of the Ti layer. Moreover, it is found that the device with 15 nm Ti shows the minimum cycle-to-cycle variability (CCV) and device-to-device variability (DDV), good retention (105 s at 85 °C), and superior endurance (104). In addition, thermal degradation of the Al/Ti(15 nm)/HfO2/TiN devices under different PMA times at 400 °C is carried out. It is found that the leakage current increases and the forming voltage and memory window decrease with the increase in PMA time due to the thermally activated oxidation of the Ti. However, when the PMA time increases to 30 min, the Ti can no longer capture oxygen from HfO2 due to the formation of self-limited TiOx. Therefore, the device shows superior thermal stability with a PMA time of 90 min at 400 °C and no degradation of the memory window, uniformity, endurance, or retention. This work demonstrates that the Ti/HfO2-based RRAM shows superior back-end-of-line compatibility with high thermal stability up to 400 °C for over an hour.

Resistive switching properties of amorphous Sm2Ti2O7 thin film prepared by RF sputtering for RRAM applications

The resistive switching (RS) characteristics of amorphous Sm2Ti2O7 thin films prepared by using RF sputtering were investigated and the effect of post-metallization annealing (PMA) on the RS properties were analysed. Comparison of as-deposited Sm2Ti2O7 thin film device and the device after PMA treatment, the latter exhibits better RS properties, including more uniform set voltages, switching cycle times and higher Ron/Roff ratio. The prepared samples all revealed bipolar resistive switching (BRS) behaviour. The results indicated that the conductive mechanism in terms of the concentration of oxygen vacancies can be controlled by different deposition atmosphere (Ar/O2) ratio and film thickness. Additionally, the resistive switching properties can be enhanced by PMA treatment due to the formation of AlOx interface layer, which prevents the oxygen ions from out-diffusion through the boundaries. At the PMA temperature of 350 °C, the two resistance states can be distinguished in a range of> 10 over 8099 switching cycles along with a retention of 104 s at room temperature and 85ºC, showing promise for non-volatile memory applications.

Investigation on the ohmic characteristic of Ni/Ti/4H-SiC

Ohmic contact is important for silicon carbide (SiC) devices such as Schottky diode, junction field effect transistor (JFET) and metal oxide transistor (MOSFET). The effect of post metallization annealing (PMA) on the ohmic characteristics of Ni/Ti/4H-SiC is investigated. The samples were annealed under different ambients of high vacuum, forming gas and N2 gas at 1050˚C for 3 minutes using rapid thermal process (RTP). Current-voltage (I-V) measurements taken for different distances of a transmission line model (TLM) structure have been utilized to extract the contact resistivity. The correlation between surface roughness and resistivity has been investigated. It was found that the involvement of nitrogen during the annealing process at 1050˚C was ineffective to reduce the contact resistivity. The resistivity is improved when the samples were annealed in forming gas (FG), (a mixture of H2+N2) environment, showing that the incorporation of H2 gas during the annealing process has produced a better result. On the other hand, high vacuum PMA was found to be effective to improve the ohmic characteristic with higher current level at lower voltage. Hence, the enhanced performance observed in high vacuum annealing samples is beneficial to get ohmic contact on Ni/Ti/4H-SiC for PMA process with a low thermal budget.

Effect of post deposition annealing and post metallization annealing on electrical and structural characteristics of Pd/Al2O3/6H-SiC MIS capacitors

PurposeAl2O3 used as gate dielectric enables exploitation of higher electric field capacity of SiC, improving capacitive coupling and memory retention in flash memories. Passivation of traps at interface and in bulk which causes serious threat is necessary for better performance. The purpose of this paper is to investigate the effect of post-deposition rapid thermal annealing (PDA) and post-metallization annealing (PMA) on the structural and electrical characteristics of Pd/Al2O3/6H-SiC capacitors.Design/methodology/approachAl2O3 film is deposited by ALD; PDA is performed by rapid thermal annealing (RTA) in N2 at 900°C for 1 min and PMA in forming gas for 10 and 40 min. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) measurements data are studied in addition to capacitance-voltage (C-V) and current-voltage (I-V) characteristics for the fabricated Pd/Al2O3/SiC capacitors. Conduction mechanism contributing to the gate leakage current is extracted for the entire range of gate electric field.FindingsRTA forms aluminum silicide at the interface causing an increase in the density of the interface states and gate leakage current for devices with an annealed film, when compared with an as-deposited film. One order improvement in leakage current has been observed for the devices with RTA, after subjecting to PMA for 40 min, compared with those devices for which PMA was carried out for 10 min. Whereas, no improvement in leakage current has been observed for the devices on as-deposited film, even after subjecting to PMA for 40 min. Conduction mechanisms contributing to gate leakage current are extracted for the investigated Al2O3/SiC capacitors and are found to be trapfilled limit process at low-field regions; trapassisted tunneling in the mid-field regions and Fowler–Nordheim (FN) tunneling are dominating in high-field regions.Originality/valueThe effect of PDA and PMA on the structural and electrical characteristics of Pd/Al2O3/SiC capacitors suitable for flash memory applications is investigated in this paper.

Improved interface characteristics of Mo/SiO2/4H-SiC metal-oxide-semiconductor with post-metallization annealing

The effects of post-metallization annealing (PMA) have been investigated for thermally-grown SiO2 on 4H-SiC metal-oxide-semiconductor (MOS) with a molybdenum (Mo) gate electrode. Mo is a great metal gate material for Silicon carbide (SiC) due to its high thermal budget and low thermal expansion coefficient, which allows high-temperature processing after the gate electrode formation. In this study, PMA process was carried out after Mo gate formation on thermally-grown SiO2/4H-SiC in the temperature range from 600 to 1000 °C in N2 or a forming gas ambient. The fabricated Mo/SiO2/4H-SiC MOS device annealed at 800 °C exhibited excellent interface characteristics with negligible hysteresis in comparison with as-grown or post-oxidation annealed samples.

Structural and electrical properties of ultra-thin high-k ZrO2 film on nitride passivated Ge(100) prepared by PEALD

The study of ultrathin ZrO2 films grown on surface passivated germanium substrates by plasma enhanced Atomic Layer Deposition (PEALD) has been carried out. Nitride passivation has been used to form an interfacial layer between ZrO2/Ge. The ultra-thin ZrO2 film deposited with thickness of ~5.75nm and refractive index of ~2.05 as observed through ellipsometry. The Ge3d, Zr3d, N1s and O1s are XPS core level spectra's confirm the formation of GeON and ZrO2 ultra-thin films. The AFM results show the roughness of deposited films as low as 0.3nm. The effect of post metallization annealing (PMA) on electrical properties of Au/Cr/ZrO2/GeON/Ge capacitors has been investigated. The improvement in k value (~38) and an EOT value (~0.5nm) after PMA on Ge/GeON/ZrO2 stack has been observed. The flat band voltage and hysteresis of post metallization annealed devices has been reduced as compared to that of without PMA GeON/ZrO2 stack.

Material and Device Characteristics of Metamorphic <formula formulatype="inline"> <tex Notation="TeX">${\rm In}_{0.53}{\rm Ga}_{0.47}{\rm As}$</tex></formula> MOSHEMTs Grown on GaAs and Si Substrates by MOCVD

We report a comparison of material and device characteristics of metamorphic In0.53Ga0.47As channel metal-oxide-semiconductor high-electron mobility transistors (MOSHEMTs) grown on GaAs and Si substrates by metal-organic chemical vapor deposition. A gate-last process was developed to simplify the fabrication of nanoscale channel length devices. Selective source/drain regrowth was incorporated to reduce parasitic resistances. Post-metallization annealing (PMA) was utilized to mitigate the weakened gate electrostatic control in the buried channel. The effect of PMA on the Ti/Al2O3 gate-stack was investigated in detail. Record-low ON-state resistance of 132 and 129 Ω·μm has been achieved in enhancement-mode InGaAs MOSHEMT on GaAs and on Si substrate, respectively. A 120-nm channel length device on GaAs exhibited a figure of merit Q(gm/SS) of 12, whereas a 60-nm channel length In0.53Ga0.47As MOSHEMT on Si demonstrated Q up to 14.

Characteristics of gadolinium oxide resistive switching memory with Pt–Al alloy top electrode and post-metallization annealing

The characteristics of gadolinium oxide (GdxOy) resistive switching memories (RRAMs) with a Pt–Al alloy (5.88 at% Al) top electrode (TE) and the effect of post-metallization annealing (PMA) were investigated. Resistance of high resistance state increased with increasing PMA temperature, achieving a resistance ratio of more than 104 owing to the increased Schottky barrier height between the TE and GdxOy film. The change in set and reset voltages corresponded to the concentration of oxygen vacancies at the TE/GdxOy interface, which was examined by x-ray photoelectron spectroscopy. At the PMA temperatures for higher than 350 °C, the GdxOy RRAMs with Pt–Al alloy TEs presented superior retention behaviour for more than 104 s at a testing temperature of 130 °C. Al diffusion into the GdxOy film to form AlxOy at the TE/GdxOy interface is responsible for the retention enhancement because it prevented the oxygen ions from out-diffusion through the Pt grain boundaries.

An accurate characterization of interface-state by deep-level transient spectroscopy for Ge metal-insulator-semiconductor capacitors with SiO2/GeO2 bilayer passivation

For Ge metal-insulator-semiconductor (MIS) capacitors with a GeO2 interfacial layer, interface-state density (Dit) was accurately characterized using deep-level transient spectroscopy. Elimination of the influence of slow-traps in the gate dielectric film on Dit characterization is described in detail. This was achieved by optimizing the injection pulse and quiescent reverse-bias voltages at each temperature. Dit values of approximately 5 × 1010 cm−2 eV−1 were observed at around mid-gap for both the n- and p-Ge-MIS capacitors with a TiN-gate, for which an asymmetric U-shape energy distribution in Dit was also observed. Furthermore, the effects of post-metallization annealing (PMA) on Dit improvement and slow-trap passivation were also investigated for Al-gated p-Ge-MIS capacitors, on which the defect passivation mechanism in Al-PMA is discussed. A reasonable correspondence was also observed between gate-film quality for Al-gated p-Ge-MIS capacitors and channel mobility in Ge-p-MIS field effect transistors with the gate fabricated by the same process as for p-Ge-MIS capacitors.

Effects of sputtering pressure and post-metallization annealing on the physical properties of rf-sputtered Y 2O 3 films

Y 2O 3 thin films were prepared by rf-sputtering under various sputtering pressures at room temperature. Spectroscopic ellipsometer, X-ray diffraction and semiconductor parameter analyzer were used to characterize the studied films. The results show the crystallinity and leakage current density of the films improved with decreasing sputtering pressure. The effects of post-metallization annealing (PMA) on optical, structural and electrical properties of the films were also evaluated. It is found that PMA can significantly enhance the electrical performance of Y 2O 3 film, and the lowest leakage current is found to be 1.54 × 10 −8 A/cm 2 at 1 MV/cm for the samples treated at 350 °C for 30 min. The leakage current mechanisms were discussed as well, which reveals that space charge limited current dominates the as-deposited films while Schottky mechanism describes the PMA treated ones well.

Hydrogen annealing effect on the properties of thermal Ta 2O 5 on Si

The effect of post-metallization annealing in H 2 at 723 K on the properties of MOS capacitors with thermally grown thin (13–26 nm) Ta 2O 5 layers was investigated. It was established that the annealing effect strongly depends on the properties of the as-grown oxides and in particular on the oxidation temperature. The oxidation at higher temperatures (823 and 873 K) is beneficial for improving the electrical, breakdown and insulating properties of the films after annealing. A dielectric constant of 32 was reached for these layers and the magnitude of leakage current guarantees their application in 64 Mbit DRAM. The hydrogen annealing, however, additionally generates slow states in the oxide with a density of about 5×10 11 cm −2.

Effect of post-metallization annealing on the ferroelectric properties of sol-gel derived PZT thin films

A series of monolithic Pt-PZT-Pt capacitors was prepared based on sol-gel derived PZT 53/47 films fired to 700 C. After deposition of top Pt electrodes, the capacitors were subjected to post-metallization annealing (PMA) temperatures of 100 C to 700 C. Dielectric and ferroelectric (FE) characterizations were performed. Increasing the PMA temperature produced lower values of spontaneous and remanent polarizations, dielectric constant and leakage currents. The observations are correlated with a proposed FE capacitor model.

Annealing and charging of slow and fast states in metal-tunnel oxide-silicon diodes measured using capacitance-voltage and current-voltage techniques

Capacitance-voltage (C-V) techniques are used to obtain new information on the effects of post-metallization annealing and charging of ultra-thin metal-tunnel oxide-silicon (MTOS) diodes, which we have previously characterized mainly using variations in the tunnel current density. The interrelationships between the annealing and charging and the nature of the defects are further illuminated in this work because of the ability of the C-V techniques to distinguish between charges contained in slow and fast states.

Effect of post-metallization annealing on W/Cr-metallized silicon junctions

The 1 μm “WAl” complementary metal-oxide-semiconductor process developed at CNET Grenoble uses a W/Cr bilayer as the first-level metal. In this paper the effects of the final (aluminium) anneal of the structures on the properties of W/Cr-metallized junction devices are discussed. By using several analytical techniques a direct correlation between junction leakage and structure has been established. The main cause of leakage current observed after annealing at above 400°C was found to be the generation of film-edge-induced dislocations associated with chromium disilicide formation.

Contrasts in electron and hole trapping phenomena in pyrogenic oxides grown with different H2O partial pressures on silicon

Trapping characteristics of both electrons and holes in pyrogenic oxides grown on silicon with different H2O partial pressures in the oxidizing ambient are studied by using the avalanche injection technique. The electron- and hole-trapping phenomena show opposite dependence on the pyrogenic oxide growth conditions. It is found that the electron-trap density increases with the H2O partial pressure, whereas the hole-trap density decreases. On the basis of the above, and from the results of further experiments on water-diffused oxides, the effect of post-metallization annealing, and infrared absorption, we examine different models of possible defects in silicon-dioxide films grown on Si for a consistent explanation. From the analysis SiH and SiOH centers appear to be the most likely hole and electron traps, respectively, in our pyrogenic oxides.