Characteristics Of HfO Research Articles

Annealing effect on physical and electrical characteristics of thin HfO 2, HfSi xO y and HfO yN z films on Si

We report the effect of annealing on electrical and physical characteristics of HfO 2, HfSi x O y and HfO y N z gate oxide films on Si. Having the largest thickness change of 0.3 nm after post deposition annealing (PDA), HfO y N z shows the lowest leakage current. It was found for both as-grown and annealed structures that Poole–Frenkel conduction is dominant at low field while Fowler–Nordheim tunneling in high field. Spectroscopic ellipsometry measurement revealed that the PDA process decreases the bandgap of the dielectric layers. We found that a decreasing of peak intensity in the middle HfO y N z layer as measured by Tof-SIMS may suggest the movement of N toward the interface region between the HfO y N z layer and the Si substrate during the annealing process.

Compositional, structural and electronic characteristics of HfO 2 and HfSiO dielectrics prepared by radio frequency magnetron sputtering

HfO 2 and HfSiO films were prepared on Si substrates by using radio frequency magnetron sputtering (RFMS). Compositional, structural and electronic properties of the two films were investigated completely. X-ray photoelectron spectroscopy (XPS) spectra showed that the atom ratio of Hf to O was about 1:2 in the HfO 2 film and the chemical composition of the HfSiO film was Hf 37Si 7O 56. Grazing incidence X-ray diffraction (GI-XRD) patterns indicated crystallization in the HfO 2 film after 400 °C annealing, but there is no detectable crystallization in the HfSiO film after 800 °C annealing. C– V measurements indicated that the dielectric constants for the HfO 2 and HfSiO film were 20.3 and 17.3, respectively. The fixed charge densities were found to be 6.0 × 10 12 cm −2 for the HfO 2 film and 3.7 × 10 12 cm −2 for the HfSiO film. I– V characteristics showed that the average leakage current densities were 2.4 μA/cm 2 for the HfO 2 film and 0.2 μA/cm 2 for the HfSiO film at the gate bias of 1 V.

Nonvolatile resistive switching characteristics of HfO2 with Cu doping

AbstractIn this work, resistive switching characteristics of hafnium oxide (HfO2) with Cu doping prepared by electron beam evaporation are investigated for nonvolatile memory applications. The top metal electrode/ hafnium oxide doped with Cu/n+ Si structure shows two distinct resistance states (high-resistance and low-resistance) in DC sweep mode. By applying a proper bias, resistance switching from one state to the other state can be achieved. Though the ratio of high/low resistance is less than an order, the switching behavior is very stable and uniform with nearly 100% device yield. No data loss is found upon continuous readout for more than 104 s. The role of the intentionally introduced Cu impurities in the resistive switching behavior is investigated. HfO2 films with Cu doping are promising to be used in the nonvolatile resistive switching memory devices.

Precise Depth Control and Low-Damage Atomic-Layer Etching of HfO[sub 2] using BCl[sub 3] and Ar Neutral Beam

The etch characteristics of HfO 2 by atomic-layer etching (ALET) were investigated using a BCl 3 /Ar neutral beam. The effect of ALET on surface modification and etch-depth control was also examined. Self-limited etching of HfO 2 could be obtained using BCl 3 ALET. This was attributed to the absorption of BCl 3 by the Langmuir isotherm during the absorption stage and the vaporization of hafnium-chlorides/boron oxychlorides formed on the surface during the desorption stage. In addition, the surface composition of HfO 2 was not altered by etching during ALET.

Resistance Switching Characteristics of HfO2 Film with Electrode for Resistance Change Random Access Memory

The electrode dependent resistance switching behaviors of amorphous HfO2 films grown by atomic layer deposition were systematically investigated. The low and high resistance states were successfully achieved for all the metal-insulator-metal resistor systems with Mo, Ru, and Pt symmetric electrodes. The characteristic reset and set voltages as well as the dynamic resistance ratio of the resistor device are strongly dependent on the electrode material with different work function. In addition, the different features for switching voltages with electrode are shown with annealing temperature.

Statistical modeling of the electrical characteristics for HfO 2 thin films grown by MOMBE for high- k dielectric applications

In this paper, the multiple regression model of electrical characteristics for HfO 2 thin films grown by metal organic molecular beam epitaxy (MOMBE) was investigated. The electrical properties, such as the accumulation capacitance and the hysteresis index, are the main factors to determine the characteristics of HfO 2. The input process parameters were extracted by analyzing the process conditions and the characterization of the films. X-ray diffraction was measured to analyze the variation of the characteristics on the various process conditions. In order to build the process model, the multiple regression models were carried out using the design of experiments. The analysis of variance and the effect plots were used to analyze the significance level and the relationship between the process parameters and the responses.

Characteristics of HfO2 and ZrO2 Mixed Oxide Film Grown by Atomic Layer Deposition

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Etch Properties of Hf-Based High- k Dielectrics Using Inductively Coupled Plasma

In this work, we investigated etching characteristics of HfO 2 thin film and Si using inductive coupled plasma (ICP) system. The maximum etch rate of HfO 2 is 85.5 nm/min at a BCl 3 /(Ar+BCl 3 ) of 20% and decreased with further addition of BCl 3 gas. From the QMS measurements, the most dominant positive ion energy distributions (IEDs) showed a maximum at 20% of BCl 3 . These tendency was very similar to the etch characteristics. This result agreed with the universal energy dependency of ion enhanced chemical etching yields. From the mass spectra, the Hf chloride and bromine oxide must be included in the etching by-products as volatile species.

Germanium MOS capacitors with hafnium dioxide and silicon dioxide dielectrics

Germanium (Ge) does not grow a suitable oxide for MOS devices. The Ge/dielectric interface is of prime importance to the operation of photo-detectors and scaled MOSTs. Therefore there is a requirement for deposited or bonded dielectric materials. MOS capacitors have been formed on germanium substrates with three different dielectric materials. Firstly, a thermally grown and bonded silicon dioxide (SiO 2) layer, secondly, SiO 2 deposited by atmospheric pressure CVD ‘silox’, and thirdly a hafnium oxide (HfO 2) high-k dielectric deposited by atomic layer deposition (ALD). Ge wafers used were p-type 〈1 0 0〉 2 Ω cm. C– V measurements have been made on all three types of capacitors to assess the interface quality. ALD HfO 2 and silox both display acceptable C– V characteristics. Threshold voltage and maximum and minimum capacitance values closely match expected values found through calculation. However, the bonded SiO 2 has non-ideal C– V characteristics, revealing the presence of a high density of interface states. A H 2/N 2 post metal anneal has a detrimental effect on C– V characteristics of HfO 2 and silox dielectrics, causing a shift in the threshold voltage and rise in the minimum capacitance value. In the case of hafnium dioxide, capacitor properties can be improved by performing a plasma nitridation of the Ge surface prior to dielectric deposition.

Effects of N[sub 2] RPN on the Structural and Electrical Characteristics of Remote Plasma Atomic Layer-Deposited HfO[sub 2] Films

The effect of remote plasma nitridation (RPN) pretreatment on the structural and electrical characteristics of remote plasma atomic layer-deposited HfO 2 films was investigated. An atomic change in the nitrogen's partial local coordination structure in the vicinity of Hf-O-Si was closely associated with the structural and electrical characteristics of the HfO 2 films. The HfO 2 film pretreated with RPN retained its amorphous structure after rapid thermal annealing at 600°C for 30 s. The RPN pretreated-HfO 2 film also showed significant enhancement of the gate capacitance and retained low leakage current densities (6.70 X 10 -8 A cm -2 at |V G - V FB | = 2 V).

Effects of Remote Plasma Pre-oxidation of Si Substrates on the Characteristics of ALD-Deposited HfO[sub 2] Gate Dielectrics

We investigated the physical and electrical characteristics of a HfO 2 /ultrathin SiO 2 (∼0.5 nm)/Si structure grown by a remote plasma atomic layer deposition (RPALD). The HF-cleaned Si substrate was oxidized by a remote plasma oxidation (RPO) process and yielded a ∼0.5 nm thick SiO 2 layer. HfO 2 films were deposited on both H-terminated and RPO-treated Si substrates by the RPALD. During HfO 2 film deposition, the RPO-treated sample showed more effectively retarded formation of initial Hf silicate layers than the sample on H-terminated Si. RPO treatment also improves electrical properties including hysteresis, effective fixed oxide charge density (Q f,eff ) and equivalent oxide thickness (EOT).

Improvement on the Electrical Characteristics of HfO[sub x]N[sub y]-Gated Metal-Oxide-Semiconductor Devices by High-Temperature Annealing

The electrical characteristics of HfO x N y -gated metal-oxide-semiconductor devices are significantly affected by the amount of defects in Si substrate. Devices with a low defect region near the Si surface were formed in this work using high-temperature annealing in a hydrogen ambient. Experimental results show longer minority carrier lifetime in silicon substrate, lower gate leakage current, and reduced interface trap density (D it ), which are attributable to the decrease in the interstitial oxygen (O i ) and crystal-originated-particle defects as well as better surface quality at HfO x N y /Si interface.

Current transport and high-field reliability of aluminum/hafnium oxide/silicon structure

The current transport mechanisms and the charge trapping characteristics of HfO 2 gate dielectrics prepared by different annealing conditions were studied. We found that the large leakage currents are mostly associated with the high trap density in the dielectric films. Taking into account the ionic nature of the metal oxide, the phonon-assisted trap ionization model should be used to explain this behavior. For samples with high temperature annealing in oxygen, large barriers of over 2 eV were found from the Fowler–Nordheim plots. These values were attributed to the existence of an interface silicon oxide layer. The effective interface barrier is also governed by the bulk properties of HfO 2 film, which modifies the field strength in the interface oxide layer according to the Gauss law. The reliability of the gate dielectric can be improved by the formation of interface SiO 2 layer but stoichiometric improvement in the HfO 2 layer has an adverse effect on the stressing induced charge trapping due to the interface barrier lowering effect.

Effects of Low-temperature NH3 Treatment on the Characteristics of HfO2 ∕ SiO2 Gate Stack

The effects of postdeposition low-temperature treatment (LTN treatment) on the characteristics of the gate stack with the TiN gate electrode were studied in this work. After the films were deposited using an AIXTRON Tricent atomic vapor deposition system, the LTN treatment was performed prior to the postdeposition annealing (PDA) step to prevent the growth of an additional interfacial layer, which is known to accompany the traditional high-temperature nitridation technique. The effective electrical oxide thickness for the devices annealed at 700°C PDA, either with or without LTN treatment, was estimated to be about 2.2 and 2.3 nm, respectively, without considering quantum effects. It was found that the LTN treatment effectively improves the characteristics of the stack gates, such as capacitance-voltage characteristics, frequency dispersion, trap generation rate, and dielectric breakdown voltage even at the high PDA temperature of 700°C.

Threshold voltage instability characteristics of HfO 2 dielectrics n-MOSFETs

In this paper, the threshold voltage instability characteristics of HfO 2 high- k dielectric are discussed. The results from various stress bias conditions including DC and AC with variations of frequency, duty cycle, and polarity provide additional insights into the intrinsic behavior and the trapping dynamics of high- k materials. A reduced threshold voltage shift was observed at higher frequency and lower duty cycle under AC positive unipolar stress compared to DC stress. Similarly, the degradation of maximum transconductance was also reduced with AC stress. However, subthreshold swing changes were found to be negligible and fairly independent of stress frequencies and duty cycles under AC positive unipolar stress. When different polarity of stress, such as positive, negative, and bipolar stress was applied, it was observed that frequency and duty cycle dependencies were still valid in all three conditions. In contrast to positive stress, negative stress showed a decrease in the threshold voltage shift. Bipolar stress resulted in the highest threshold voltage instability, but the degradation in transconductance and subthreshold swing was actually smaller than those in negative unipolar stress. The bulk trap of HfO 2 dielectric, which is proportional to its physical thickness, is believed to be the primary factor for threshold voltage shift. AC unipolar operation would allow a higher 10-year lifetime operating voltage than the DC condition. In addition to experimental results, a plausible mechanism has been proposed.

Electrical and reliability characteristics of HfO 2 gate dielectric treated in N 2 and NH 3 plasma atmosphere

As-grown HfO 2 films by plasma-enhanced chemical vapor deposition (PECVD) were treated by N 2 and NH 3 plasma at 70 W and 300 °C. The films treated by either N 2 or NH 3 plasma were crystallized at annealing temperature above 800 °C, resulting in 200 °C higher crystallization temperature than that of HfO 2 films without plasma treatment. The capacitors treated at the bottom side of HfO 2 by NH 3 plasma exhibited the lowest leakage current density, but the highest interface trap density. The capacitors treated at the bottom side of HfO 2 by N 2 plasma showed a comparable leakage current density to samples treated by NH 3 plasma and the lowest interface trap density. The N 2 plasma-treatment instead of NH 3 is a suitable method to improve the reliable characteristics of HfO 2 gate dielectric.

Reliability characteristics of high- k dielectrics

In this paper, recent results of Weibull slopes, area scaling factors, and breakdown behaviors observed for both soft breakdown and hard breakdown are discussed. These results would help to shed light on the breakdown mechanism of HfO 2 gate dielectrics. The Weibull slope β of the hard breakdown for both the area dependence and the time-to-dielectric-breakdown distribution was found to be β=2, whereas that of the soft breakdown was about 1.4 (EOT=14 Å). We also integrated the time-to-breakdown characteristics of HfO 2 under unipolar AC voltage stress on MOS capacitors. The results show that longer lifetime of HfO 2 has been observed when compared to constant voltage stress. Higher frequency and lower duty cycle in the AC stress resulted in longer lifetime. As thickness decreases, the amount of lifetime enhancement decreases. The enhancement of unipolar t BD is attributed to less charge trapping during the “on time”, t on and charge detrapping during the off time, t off. It is proposed that time ( τ in) for charge to be trapped in HfO 2 is longer than t on of unipolar stress under high frequency. In addition to experimental results, possible solutions are discussed.