Crystallization Of HfO2 Research Articles

Laser-induced spectral tuning of single quantum dots embedded into microposts cladded with HfO2

Our work investigates the precise tuning of InGaAs quantum dots (QDs) embedded into microposts by leveraging HfO2 crystallization-induced micro-strain via laser annealing. We investigate the efficacy of laser annealing power as a parameter for spectral control, achieving a notable blue shift of QD emissions of up to 5 meV. Through comprehensive Raman thermometry, we reveal consistent dependencies in laser-induced heating relative to micropost diameter, with larger microposts exhibiting superior heat dissipation capabilities and smaller tuning range. For instance, a 5.0 μm micropost demonstrates a maximum local temperature increase of 260 K at 1.82 mW of annealing power, compared to 435 K for a 1.1 μm diameter micropost under the same conditions. By correlating local temperatures derived from the longitudinal optical phonon linewidth of the Raman spectra, with QD emission line blue shift at specific laser powers, the tunability across differing post diameters is studied. Our findings underscore the potential of strain-tuning QDs through laser-induced HfO2 crystallization, offering avenues for scalable resonant single-photon sources applicable in superradiance and multi-photon interference scenarios.

Synthesis and growth mechanism of highly crystalized multi-branched HfB2 microrods with self-toughening effect

Development of strategies to toughen HfB2 ceramic, improve their mechanical properties is the key to promote their applications in extreme thermal environments. This study explores a kind of self-toughening method of HfB2 ceramic by incorporation the highly crystalized multi-branched HfB2 microrods. The multi-branched HfB2 microrods were synthesized by sol–gel process and carbothermal reduction, exhibiting length of 6–13 μm and diameter of 0.60–1.50 μm, respectively. Detailed analysis of the formation mechanism of HfB2 microrods reveals that the HfB2 multi-branched structure is a collaborative consequence of orientation attachment mechanism and reactive templates growth, in which process monoclinic HfO2 crystals transform into crystalized HfO2 microrods at ∼1000 °C, and worked as template to induce one-dimensional HfB2 microrods. Furthermore, spark plasma sintering experiments show that the optimal mechanical properties were attained by 6 wt% addition of HfB2 microrods, comparing with HfB2 ceramics free of self-toughening agent, the hardness and fracture toughness of self-toughened HfB2 ceramic improved by 8.82 % and 81.91 % respectively, demonstrating the effectiveness of self-toughening of the microrods without sacrificing the hardness of HfB2 ceramic. Thus, it can be seen that the work has important reference value for the synthesis of HfB2 powder with different morphologies and the toughening of HfB2 ceramics.

Interfacial stress engineering toward enhancement of ferroelectricity in Al doped HfO2 thin films

Abstract Ferroelectric HfO2 have attracted much attention owing to their superior ferroelectricity at an ultra-thin thickness and good compatibilities with Si-based complementary-metal-oxide-semiconductor (CMOS) technology. However, the crystallization of polar orthorhombic phase (o-phase) HfO2 is less competitive, which greatly limits the ferroelectricity of as-obtained ferroelectric HfO2 thin films. Fortunately, the crystallization of o-phase HfO2 can be thermodynamically modulated via interfacial stress engineering. In this paper, the growth of improved ferroelectric Al doped HfO2 (HfO2:Al) thin films on (111)-oriented Si substrate have been reported. Structural analysis has suggested that non-polar monoclinic HfO2:Al grown on (111)-oriented Si substrate suffered from a strong compressive strain, which promoted the crystallization of (111)-oriented o-phase HfO2 in the as-grown HfO2:Al thin films. In addition, the in-plane lattice of (111)-oriented Si substrate matches well with that of (111)-oriented o-phase HfO2, which further thermally stabilized the o-phase HfO2. Accordingly, an improved ferroelectricity with a remnant polarization (2P r) of 26.7 μC/cm2 has been obtained. The results shown in this work provide a simple way toward the preparation of improved ferroelectric HfO2 thin films.

Quantum Mechanical Simulation of Polarization Switching in HfO2 Crystals

Quantum Mechanical Simulation of Polarization Switching in HfO2 Crystals

Quantum mechanical simulation of polarization switching in HfO2 crystals

The work is devoted to the study of the process of changing the polarization of hafnium oxide crystals in the orthorhombic phase associated with the gradual weakening of the polarization effects in FeRAM elements based on thin films of hafnium oxide HfO2. To solve the problem, quantum-mechanical calculations of the structure of orthorhombic hafnium oxide were carried out, a possible way of crystal rearrangement during a change in polarization upon application of voltage was identified, and its optimization was carried out using the elastic band method. The values of the polarization change and the energy barrier of the corresponding transition are obtained. A study of the stability of this transition has been carried out. The results of a series of computational experiments using high-performance computing systems of hybrid architecture based on the Center for Collective Use of the FRC IU RAS are presented. An analysis of the results shows that, despite the low energy barrier of the transition, the probability of a spontaneous change in polarization is low due to the impossibility of changing the polarization of an individual cell without taking into account the influence of the polarizations of neighboring cells.

Spark plasma sintered Si(Hf)OC nanocomposites exhibiting thermally stable dielectric behavior processed through precursor route

This work uses hafnium n tetra butoxide precursor to modify silicon oxycarbide (SiOC) with an easy, novel, and economical procedure to synthesize Si(Hf)OC nanocomposites. FTIR analysis confirmed the formation of Si–O-Hf linkages during cross-linking. The as-pyrolyzed powders were sintered using the spark plasma sintering technique. X-ray diffractograms confirmed the in-situ crystallization of tetragonal HfO2 in an amorphous SiOC matrix. The morphological features were imaged using electron microscopy. The dielectric properties of sintered Si(Hf)OC nanocomposites were investigated at varied temperatures (25 °C–250 °C) and frequency ranges (10−1 Hz–106 Hz) for the first time. At room temperature, the ε՚ value at 1 kHz is found to be 14, which is almost double the value of pure sintered SiOC (ε՚∼5). The dielectric loss (tanδ) is less than 0.07 at 1 kHz at room temperature, which is significantly less than sintered SiOC (tanδ ∼0.5). An increase in permittivity is associated with high permittivity t-HfO2 nanocrystals and additional interfacial/space charge polarization at the interfaces between the t-HfO2 and SiOC matrix. At high-frequency regions (>1 kHz), the dielectric properties of nanocomposites were found to be thermally stable (up to 250 °C). At low-frequency regions (<70 Hz), the material exhibits a rise in dielectric permittivity with increasing temperature, most likely due to charge carrier accumulation at the interfaces of t-HfO2, SiO2, and carbon in the SiOC matrix through the migration of thermally activated charge carriers.

Multi-Layer High-K Gate Stack Materials for Low D&lt;sub&gt;it&lt;/sub&gt; 4H-SiC Based MOSFETs

Metal-oxide-semiconductor capacitors with single and multi-layer high-K gate dielectrics on Si (0001) face of n-type 4H-SiC substrates have been investigated. Multi-layered nanolaminated gate-stack comprises alternating ultrathin (6nm) Al2O3 and HfO2. A 5nm thick interfacial silicon oxynitride is deposited prior to laminated films to investigate interface trap properties and tuning of flat band voltage. Total thickness of gate-stack films including interfacial layer is 55nm. The thermal stability of multi-layered nanolaminated film is investigated using XTEM. Localized crystallization of HfO2 is visible after RTA at 900°C while Al2O3 remains fully amorphous. Some of HfO2 grains have extended into Al2O3 layer but was not able to crossover. The measured accumulation capacitance of 55nm thick gate dielectric gives an effective dielectric constant value of 9.6 and an equivalent oxide thickness of 22nm from high-frequency capacitance-voltage measurements. A positive flat band voltage ( of 12.2V and 10.6V are observed from both single layer HfO2 and Al2O3 dielectrics, respectively due to presence of negatively charged oxygen interstitial defects generated during atomic layer deposition process. However, VFB shifted towards negative voltage-7.6V for multi-layered Al2O3/HfO2 stacks probably associated with positive Al and Hf interstitials at interface of Al2O3/HfO2. Ultrathin interfacial oxynitride films is effective to reduce Dit to 3×1011/eVcm2 and tuning of VFB. The breakdown field of stacked gate dielectric on 4H-SiC is 10.0 MV/cm.

Vibrational fingerprints of ferroelectric HfO2

Hafnia (HfO2) is a promising material for emerging chip applications due to its high-κ dielectric behavior, suitability for negative capacitance heterostructures, scalable ferroelectricity, and silicon compatibility. The lattice dynamics along with phononic properties such as thermal conductivity, contraction, and heat capacity are under-explored, primarily due to the absence of high quality single crystals. Herein, we report the vibrational properties of a series of HfO2 crystals stabilized with yttrium (chemical formula HfO2: xY, where x = 20, 12, 11, 8, and 0%) and compare our findings with a symmetry analysis and lattice dynamics calculations. We untangle the effects of Y by testing our calculations against the measured Raman and infrared spectra of the cubic, antipolar orthorhombic, and monoclinic phases and then proceed to reveal the signature modes of polar orthorhombic hafnia. This work provides a spectroscopic fingerprint for several different phases of HfO2 and paves the way for an analysis of mode contributions to high-κ dielectric and ferroelectric properties for chip technologies.

Phase transformation of sputtered hafnium oxide by post annealing treatment and its effect on the amorphous Si-In-Zn-O thin film transistor

The effect of post annealing treatment on the phase transformation and the electrical properties of the sputtered hafnium oxide (HfO2) is investigated. As-deposited HfO2 films were annealed at 200 and 400 ∘C in ambient conditions. Film annealed at 200 ∘C is amorphous, but further annealing at 400 ∘C crystallizes it into the monoclinic structure. Amorphous films exhibit a higher bandgap (≥ 5.8 eV) than the monoclinic film (≈ 5.65 eV). The electrical characteristics of the Metal-Insulator-Metal devices reveal a nonlinear capacitance with respect to the voltage. The nonlinearity is predominant in the as-deposited film due to the oxygen vacancy related defects formed during the deposition. However, excess Hf-O bond formation occurs with annealing at higher temperatures, reducing the capacitance-voltage curve’s nonlinearity. The dielectric constant of the as-deposited, 200, and 400 ∘C annealed films are estimated as 22.35, 22.64, and 20.57, respectively. The increment in the dielectric constant at 200 ∘C is due to its amorphous phase and reduced defects. Amorphous Si-In-Zn-O thin film transistors fabricated using the as-deposited and annealed hafnium oxide as gate insulator show almost similar threshold voltage of ≈ −1 V. The transistor with hafnium oxide annealed at 200 ∘C shows the highest on current (1.04 × 10−6 A) followed by as-deposited (6.82 × 10−7 A) and 400 ∘C annealed device (5.86 × 10−7 A), respectively. Moreover, the interface state density increases monotonically from 3.98 × 1012 to 1.11 × 1013 cm−2 for as-deposited and 400 ∘C, respectively. The increment in the interface state density is due to the grain boundary formation due to the crystallization of HfO2.

Density functional modeling of structural and electronic properties of amorphous high temperature oxides

Ab initio molecular dynamics modeling in the NPT ensemble is used to obtain amorphous states by melting SiO2, ZrO2 and HfO2 crystals. A wide range of melt stabilization temperatures are used. Two types of SiO2 amorphous states are obtained. For melt temperatures below 4500 K, a perfect silica glass is obtained without any point defects. For melt temperatures above 4500 K, silica point defects such as threefold coordinated oxygen atoms, edge-sharing SiO4-tetrahedra, and others together with a wide range of Si-O-Si rings including 3-, and 4-membered rings appear. When the temperature of the melt exceeds the ZrO2 and HfO2 crystal melting point by 100 – 400 K, a sharp drop in the density of amorphous states is observed, accompanied by a decrease in atomic coordination, but this does not lead to the formation of defect states in the depth of the band gap of hafnium and zirconium dioxides.

Non-doped HfO2 crystallization controlled by dwell time in laser annealing

Laser annealing is performed to crystallize a 10 nm thick non-doped hafnium dioxide (HfO2) thin film. The influence of the laser annealing dwell time on the crystallization process is investigated considering the Gibbs free energy diagram of various HfO2 phases (i.e. monoclinic, cubic, tetragonal, and orthorhombic). Progressive phase transformations as a function of the dwell time are evidenced and discussed. Furthermore, for the sample showing ferroelectricity, the endurance property is much improved compared to the previously reported ferroelectric non-doped HfO2.

A nanoscale continuous transition from the monoclinic to ferroelectric orthorhombic phase inside HfO2 nanocrystals stabilized by HfO2 capping and self-controlled Ge doping

A transition from the monoclinic to ferroelectric orthorhombic phase, takes place within a region of few atomic layers of single HfO2 crystals. Atomic calculations show high stability of the ferroelectric orthorhombic phase.

Self-induced ferroelectric 2-nm-thick Ge-doped HfO2 thin film applied to Ge nanowire ferroelectric gate-all-around field-effect transistor

This paper reports a self-induced ferroelectric 2-nm-thick Ge-doped HfO2 (Ge:HfO2) thin film. Ge thermal desorption, incorporation into HfO2, and further Ge:HfO2 crystallization were all performed through rapid thermal annealing simultaneously. The ferroelectric property of a 2-nm-thick Ge:HfO2/2-nm-thick Al2O3 dielectric stack was confirmed using the polarization-electric field measurement. X-ray photoelectron spectroscopy was used to confirm that Ge bonded to HfO2 as Hf-germanates. Piezoresponse force microscopy was used to demonstrate the piezoelectric property of Ge:HfO2/Al2O3. Furthermore, a dielectric stack of Ge:HfO2/Al2O3 was applied as a gate insulator in a Ge nanowire gate-all-around ferroelectric field-effect transistor (Ge NW Fe-GAAFET). The device exhibited a minimum steep-sub-threshold slope of 47 mV/dec, a high ION/IOFF ratio of &amp;gt;106, and low gate leakage current; moreover, it was free of a drain-induced barrier lowering effect. The proposed self-induced ferroelectric Ge:HfO2 Ge NW Fe-GAAFET is feasible for future ultra-low power integrated circuit applications.

A simple approach to room-temperature synthesis of cubic Al-doped HfO2 nanoparticles and their toxicity evaluation in normal prostate cells

Al-doped HfO2 nanoparticles were prepared at room-temperature using a novel one-step, straightforward, high-yield, efficient and green process. It includes a mechanically activated metathesis reaction that promotes the direct crystallization of cubic HfO2 (c-HfO2) in milling. Al-cation was used as dopant, achieving c-HfO2 stabilization at low content (5% mol). The c-HfO2 is stable up to 380 °C without exhibiting transformation from the cubic to monoclinic polymorph. The c-HfO2 showed spherical-like morphology with diameter below 7 nm. Human Prostate Epithelial Cells (HPrEC) were used to evaluate nanoparticles toxicity. Cells viability and survival were determined performing MTS and colony formation assays. Nanoparticles were found harmless for cells metabolic activity at concentrations up to 1000 μg/mL. A decrease of ~30% on HPrEC plating efficiency was observed at the highest concentration.

NiSi2 as a bottom electrode for enhanced endurance of ferroelectric Y-doped HfO2 thin films

We exploit the uniform silicidation of an ultra-thin Ni film deposited on crystalline silicon that upon rapid thermal annealing transforms into NiSi2 and then is used as a bottom electrode (BE) with the right structure for orthorhombic crystallization of Y-doped HfO2 (YHO) during an additional post deposition annealing (PDA) process. Compared to a standard TiN BE in metal–insulator–metal structures, the use of NiSi2 and PDA promotes a more reproducible and stable ferroelectric behavior of YHO thin films. In contrast to YHO/TiN, high reproducibility in the current–voltage characteristics as well as lower leakage currents for the YHO/NiSi2 structures (after PDA below 600 °C) enable these devices to withstand up to 10e9 stressing cycles without significantly changing the magnitude of its original remanent polarization (Pr), thus ensuring small wake-up and/or fatigue behavior. All this is possible by the seemingly passivation effect of an interfacial layer developed at the YHO/NiSi2 interface during PDA.

Crystallization of HfO2 thin films and their influence on laser induced damage

We present our investigation on the crystallization of IBS HfO2 on (0001) SiO2. The crystallization was studied by in-situ XRD. The activation energy was 2.6±0.5 eV. The growth follows a two-dimensional mode. LIDT measurements (5000-on-1) with 10 ns pulses at 355 nm on 3QWT HfO2 layers shows that the crystallization leads to increase of the laser irradiation resistance. The 0%-LIDT of the as coated sample was 3.1 J/cm2 and increased to 3.7 J/cm2 after 5h @ 500°C.

Intriguing morphological evolution during chemical vapor deposition of HfS2 using HfCl4 and S on sapphire substrate

For chemical vapor deposition (CVD) of HfS2, HfCl4 is commonly used as the Hf precursor, and a sapphire (Al2O3) substrate is preferred to improve film crystallinity. During the HfS2 CVD process using HfCl4 and S precursors on the sapphire substrate, we observed an anomalous morphological evolution due to the chemical interaction between the Al2O3 substrate and HfCl4, particularly when the substrate was exposed to HfCl4 vapor too early, prior to the introduction of S. The excessive HfCl4-induced local chemical etching produced a serrated surface on the substrate, while pyramid-shaped HfO2 crystals (a by-product of chemical etching) and CVD-HfS2 flakes formed on the unetched and etched substrate surface regions, respectively. A mechanism for the observed morphological evolution is proposed based on thermodynamic and kinetic considerations, which emphasizes the importance of precursor supply timing to minimize the potential process-related defects.

Synthesis of HfO2 from hafnium hydroxide hydrate

A comprehensive study of processes taking place during synthesis and subsequent thermal treatment of hafnium oxide was performed. Synthesis of HfO2 involves following stages: stepwise dehydration of hydrated hafnium hydroxide, crystallization of metastable tetragonal phase of HfO2 and subsequent irreversible transition to the stable monoclinic modification. Preliminary heat treatment lowered temperature of crystallization of HfO2 and resulted in changing process mechanism.

Advanced Millisecond Annealing Approaches for High-k Metal Gate and Contact Scaling

Scaling of semiconductor devices over past decades has been made possible by continuous innovations in materials engineering as well as device geometries and integration [1,2]. Shrinking device features necessitate precise engineering of various materials and interfaces. Thermal processing plays a key role in engineering of ever-evolving materials and processes governed by thermodynamics and kinetics. High-k metal gate (HKMG) and contact to source-drain present key challenges in meeting device performance and yield requirements for continued logic CMOS scaling. In this paper, we will present equipment and process innovations in millisecond annealing that enable HKMG and source-drain contact scaling. Key requirements for HKMG architecture include EOT scaling, device reliability, maintaining desired effective work function, and minimal Vfb roll-off effect. Thermal treatment of HKMG film stack leads to HfO2 crystallization, reaction of HfO2 with the SiO2 interface layer (IL), diffusion of nitrogen (N) and reaction with HfO2, and displacement of oxygen vacancies from HfO2. In addition, nitridation of HfO2 suppresses charge traps, improving reliability. Nitrogen placement in the HKMG stack is a function of annealing conditions, and needs to be controlled precisely to meet device performance and reliability requirements. HKMG integration can benefit greatly from millisecond annealing that offers high temperature processing but in millisecond time scales. In this paper, we will introduce millisecond annealing in ammonia (NH3) ambient. We will demonstrate that millisecond annealing in NH3 ambient offers unique capabilities in controlling the N dose and placement in the HKMG stack. It is extremely important to control the N profile since N penetration to the interface layer degrades PMOS reliability. Fig 1 shows the three film stacks investigated in this work. Millisecond annealing was performed using a scanning continuous wave laser to reach desired surface temperature of a wafer placed on a heated stage. This approach allows for millisecond scale control of thermal energy delivery to the wafer. Fig 2 shows the N concentration as a function of millisecond anneal peak temperature for different heater temperatures. N incorporation increases with peak temperature. Lower heater temperature enables higher N incorporation. As shown in Fig 3, lower heater temperature also results in lesser IL thickening, which is desirable for EOT scaling. Fig 4 shows angle-resolved X-Ray Photoelectron Spectroscopy (AR-XPS) profiles for HfO2/IL film stack annealed at the same peak temperature but with different heater temperatures. Clearly, lower heater temperature leads to shallower, Gaussian-like N profile contained within HfO2. In this paper, we will also demonstrate nitridation of other HKMG film stacks such as TiN/HfO2/IL, and TaN/HfO2/IL with excellent control over N dose and depth profile. We will show that this approach leads to conformal nitridation of HKMG film stack. We will also present MOSCAP data complementing the physical characterization and demonstrating device performance and reliability benefits of millisecond annealing in NH3 ambient. Continued CMOS scaling requires geometric shrinking of device features such as contact to source and drain. Smaller contact dimensions necessitate reduction of bulk and interface resistivity of various materials deposited in the contact structure. Advanced logic devices beyond 10nm node are expected to use Cobalt as contact fill metal [3]. Oxidation of barrier TiN is detrimental to the quality of subsequent Cobalt metal fill and introduces an additional contributor to the overall external resistance of the device. Silicidation anneal after Ti liner/TiN barrier deposition results in oxidation of TiN surface due to the presence of trace amounts of O2 in the anneal chamber. Hence, it is paramount to minimize surface oxidation of TiN to enable optimal contact metal fill. In this paper, we will demonstrate that TiN oxidation can be minimized by improving millisecond anneal chamber background O2 level and cooling down wafers in controlled ambient. The importance of ambient control during silicide anneal was investigated by comparing surface oxidation resulting from annealing with various ambient control schemes. Fig. 5 shows that a silicide anneal run with X ppm ambient O2 during the anneal resulted in significant oxidation of TiN, and oxidation was reduced with reduced ambient O2 during anneal. The least degree of TiN oxidation was achieved with improved ambient control during both the anneal process and wafer cooldown. Improvement in chamber O2 level along with cooler wafer extraction also resulted in better Co adhesion to TiN and ~17% reduction in contact resistivity (Fig 6). Enhanced ambient control capability in the millisecond anneal system is expected to provide further benefits in HKMG EOT scaling and reliability in combination with NH3 thermal processing. Figure 1

Study of Lanthanum Diffusion in HfO2-Based High-k Gate Stack

La2O3 has been selected as a threshold voltage (Vt) tuning material for advanced nodes because of its uniqueness of reducing effective work function towards NFET band edge by creating dipoles at SiO2/HfO2 interface [1,2]. In this paper, we study the factors which influence the diffusion of Lanthanum (La) atoms through HfO2 during anneal. These factors include: (1) Crystallization state of HfO2; (2). HfO2 thickness; (3) Drive-in anneal temperature; (4) TiN capping material during drive-in anneal. We prepare the following stack: Si/SiO2/ HfO2/ La2O3 /TiN/a-Si, and anneal the stack to diffuse the La atoms into HfO2 layer. Then a-Si, cap TiN and excessive La2O3 were sequentially removed by wet etch. Final structure Si/SiO2/La-doped HfO2 is measured by XPS/XRF to determine the amount of La atoms that were diffused in. The diffusion of La is governed by its initial dosage (La2O3 deposition thickness), its adjacent layers (bottom HfO2, and top cap TiN), and the annealing temperature. By varying these parameters, we systematically study the effects of each factor, and correlate them to final Vt shift in the devices. The Vt shift in the MOSFET device is found to be proportional to the final diffused La amount in HfO2. The Vt shift shows obvious dependence on initial La dosage, annealing temperature and HfO2 thickness. On the other hand, the crystallization of HfO2 display a surprising blocking effect for La diffusion, indicating that La diffusion doesn’t follow the common grain-boundary diffusion mechanism. We found that HfO2 starts to crystallize when post-deposition anneal temperature is greater than 880C. La diffusion through crystallized HfO2 is significantly reduced compared to the case when HfO2 is still amorphous. On the contrary, Nitrogen atoms, which were incorporated during cap TiN deposition process, shows enhanced diffusion through HfO2. Fig.1 (a) shows the La signal in gate stack prior to and after La diffusion. The final La amount is much less for crystallized HfO2 (Hk PDA temp =900C and 950C) than for amorphous HfO2 (Hk PDA temp =800C and 850C). However, N signal, in Fig.1 (b) shows increased value for crystallized HfO2. Fig. 1(c) (d) show the Vt shift from NFET and PFET devices respectively, confirming less La diffusion (less Vt shift) in crystallized HfO2. The Vt of NFET is reduced while the Vt of PFET is enhanced because of the unipolar nature of the La-Si-O dipoles. We also conducted Angle-resolved XPS (AR-XPS) and TEM/EELS analysis and they both show that in crystallized HfO2, the La distribution is away from HfO2/SiO2 interface, while in amorphous HfO2, more La reside at HfO2/SiO2 interface. The capping material is also crucial for La diffusion in HfO2. We tested two types of TiN: (1) ALD TiN using a metalorganic precusor, tetrakis (dimethylamido) titanium and Nitrogen (TDMAT-TiN), (2) ALD TiN using TiCl4 precursor and NH3 (TiC4-TiN). We observe significant Vt difference between devices using these two TiN materials. The final diffused La is much less for TiC4-TiN based cap than TDMAT-TiN based cap. This is attributed to different La diffusion rate in the capping TiN material which in turn affects the La diffusion into HfO2. In summary, we evaluate the factors that influence La diffusion in HfO2-based Hk gate stack. Both crystallization of HfO2 and the absorption of La in top TiN material have great contributions to the effectiveness of La diffusion in HfO2. Some of these factors for La diffusion are especially intertwined with the growth of SiO2 interfacial layer (IL) which affects the Tinv and Toxgl of the MOSFET devices. Cares have to be taken to engineer the stack structure and integration scheme to achieve desired Vt shift and device performance. REFERENCE: [1] H. N. Alshareef et.al. Appl. Phys. Lett. 89, 232103 (2006) [2] Koji Kita and Akira Toriumi, Appl. Phys. Lett. 94, 132902 (2009) Figure 1