Characteristics of high-k gate oxides prepared by oxidation of 1.4 nm multi-layered Hf/Al metal film

We investigated the physical and electrical properties of high-k gate oxide formed by oxidizing multi-layered Hf and Al metal films. We demonstrated that oxidation of multi-layered metal films results in two distinctive amorphous layers: That is, Hf- and Al-doped metal oxide films were formed on the top of silicate film. The thickness of silicate layer and therefore equivalent oxide thickness (EOT) value were dependent on the number of metal films. To reduce the EOT value, higher number of metal layers is desirable. In addition, annealing has to be done at 600 °C to obtain the minimum value of EOT. Hysteresis phenomenon usually observed in high-k oxide was not observed in this work.     

HfO2 gate insulator formed by atomic layer deposition for thin-film-transistors

We have investigated the effects of annealing temperature on the physical and electrical properties of the HfO₂ film deposited by an atomic layer deposition (ALD) method for high-k gate oxides in thin-film-transistors (TFTs). The ALD deposition of HfO₂ directly on the Si substrate at 300 °C results in the formation of thin HfSi_xO_y interfacial layer between Si and HfO₂. The subsequent low temperature N₂-annealing of HfO₂ films (i.e., 300 °C) using a rapid thermal processor (RTP) improves the overall electrical characteristics of HfSi_xO_y-HfO₂ films. Based on the current work, we suggest that HfO₂ film deposited by the ALD method is suitable for high-k gate oxides in TFTs, which have to be fabricated at low temperature.     

Plasma etching of high-k and metal gate materials

Etching characteristics of high-k dielectric materials (HfO₂) and metal electrode materials (Pt, TaN) have been studied in high-density chlorine-containing plasmas at pressures around 10 mTorr. The etching of HfO₂ was performed in BCl₃ without rf biasing, giving an etch rate of about 5 nm/min with a high selectivity of >10 over Si and SiO₂. The etching of Pt and TaN was performed in Ar/O₂ with high rf biasing and in Ar/Cl₂ with low rf biasing, respectively, giving a Pt etch rate of about several tens nm/min and a TaN etch rate of about 200 nm/min with a high selectivity of >8 over HfO₂ and SiO₂. The etched profiles were outwardly tapered for Pt, owing to the redeposition of etch or sputter products on feature sidewalls, while the TaN profiles were almost anisotropic, probably owing to the ion-enhanced etching that occurred.     

Effects of annealing temperature on the characteristics of ALD-deposited HfO2 in MIM capacitors

We have investigated the annealing effects of HfO₂ films deposited by an atomic layer deposition (ALD) method on the electrical and physical properties in the Si/SiO₂/Pt/ALD-HfO₂/Pd metal-insulator-metal (MIM) capacitors. If the annealing temperature for HfO₂ films was restricted below 500 °C, an annealing step using a rapid thermal processor (RTP) improves the electrical properties such as the dissipation factor and the dielectric constant. On the other hand, annealing at 700 °C degrades the electrical characteristics in general; the dissipation factor increases over the frequency range of 1∼4 MHz, and the leakage current increases up to 2 orders at the low electric field regions. We found that the degradation of electrical properties is due to the grain growth in the HfO₂ film (i.e., poly-crystallization of the film) by the high temperature annealing processing. We suggested that the annealing temperature must be restricted below 500 °C to obtain the high quality high-k film for the MIM capacitors.     

Characteristics of high-k dielectric ECR-ALD lanthanum hafnium oxide (LHO) films

In this study, we investigated the characteristics of various lanthanum hafnium oxide (LHO) films with different lanthanum (La) concentrations deposited by an electron cyclotron resonance plasma-enhanced atomic layer deposition (ECR-ALD). Tris(isopropyl-cyclopentadienyl)lanthanum (La(iPrCp)₃) and tetrakis(ethylmethylamino)hafnium (TEMAHf) were utilized as the La and hafnium (Hf) precursors, respectively. When the La/(La + Hf) atomic percent ratio was 49.1%, the growth rate of the LHO film was 0.5 Å/cycle, with a dielectric constant of 16.3. As the La concentration was increased, the dielectric constant decreased. In addition, we found that a La-hydrate phase (La-O-H) can be easily formed when the La/(La + Hf) is over about 50%.     

A polymer-network gel route to oxide composite nanoparticles with core/shell structure

A modified polymer-network gel route has been developed to prepare oxide composite nanoparticles with core/shell structure. The core particles, which are prepared firstly using an acrylamide gel method, are dispersed in the solution of the shell material to form a uniform suspension, and then the suspension system is gelled by the polymerization of acrylamide. The gel is calcined to remove the organic phase, consequently leading to the coating of the shell material on the core particles. The versatility of this sol-gel method in preparing core/shell nanocomposites is evidenced by the example of MgO-coated La_0.67Ca_0.33MnO₃ system. The preparation process has been discussed in detail.     

Electrical and materials properties of AlN/ HfO2 high-k stack with a metal gate

In this study, aluminum nitride (AlN) was grown by molecular layer deposition on HfO₂ that had been deposited on 200 mm Si (100) substrates. The AlN was grown on HfO₂ using sequential exposures of trimethyl-aluminum and ammonia (NH₃) in a batch vertical furnace. Excellent thickness uniformity on test wafers from the top of the furnace to the bottom of the furnace (across the furnace load) was obtained. The equivalent oxide thickness was 16.5-18.8 Å for the AlN/HfO₂ stack on patterned device wafers with a molybdenum oxynitride metal gate with leakage current densities from low 10^− 5 to mid 10^− 6 A/cm² at threshold voltage minus one volt. There was no change in the work function with the AlN cap on HfO₂ with the MoN metal gate, even with a 1000 °C anneal.     

Gas sensitivity of metal oxide mixed tin oxide films prepared by spray pyrolysis

Various kinds of SnO₂ films, modified with the addition of iron, antimony, copper, titanium, manganese, nickel, cobalt or calcium oxides, were fabricated by using the spray pyrolysis technique and their gas-sensing characteristics were studied. From electrical measurements in air, the relative sensitivity towards inflammable gas of these SnO₂-based film sensors was compared. It was observed that SnO₂-based films of higher electrical resistance had a tendency to have higher sensitivity towards ethanol than the SnO₂-based films of lower resistance. The addition of p-type metal oxides, such as NiO and MnO, to the SnO₂ matrix was found to be effective in increasing the sensitivity towards inflammable gas.     

Magnetic and photoconductive properties of the CoxPt1−x-Pt-TiO2 nanocomposite films prepared by reactive sputter-deposition

Co-Pt-Ti-O films were prepared on SiO₂ glass substrate by sputtering of a Co-Pt-Ti composite target in Ar+O₂ atmosphere with the total pressure of 4 Pa and then in situ annealed at an elevated temperature T_a to form the Co_xPt_1−x-TiO₂ films. It is found that the ferromagnetic films grow in the form of fiber-like columnar grain about 10 nm in diameter when sputtered in the pressure ratio of O₂/Ar=1/133 followed by in situ annealing at The films contain Pt and amorphous anatase-type TiO₂ phases besides the ferromagnetic fcc-Co_xPt_1−x phase. Thus, such nanocomposite films show photoconductive properties due to the anatase-type TiO₂ phase as well as ferromagnetic properties due to the Co_xPt_1−x phase.     

Integrations and challenges of novel high-k gate stacks in advanced CMOS technology

Due to the limitations in conventional complementary metal-oxide-semiconductor (CMOS) scaling technology in recent years, innovation in transistor structures and integration of novel materials has been a key to enhancing the performance of CMOS field-effect transistors (FETs) of past technology generations. Tremendous progress of high dielectric constant (high-k) gate stacks has been made in recent years and some of them have come into application in CMOS devices. However, many challenges remain, such as: (a) suitable permittivity, band gap and band alignment for dielectrics, on Si, (b) thermodynamic stability and interface engineering at both high-k/Si interface and metal/metal interface, (c) depletion effect, high gate resistance and its incompatibility with high-k for metal gate, and (d) low performance attributed to threshold voltage instability. Based on current progress and fundamental considerations, we review the current status and challenges in novel high-k dielectrics and metal gates research for planar CMOS devices and alternative device technologies to provide insights for future research. Finally, this review concludes with perspectives towards the future gate stack technology and challenges in advanced CMOS devices.     

Dielectric properties of sol-gel derived high-k titanium silicate thin films

High-k dielectric titanium silicate (Ti_xSi_1 − xO₂) thin films have been deposited by means of an optimized sol-gel process. At the optimal firing temperature of 600 °C, the Ti_0.5Si_0.5O₂ films are shown to exhibit not only a dielectric constant (k) as high as ∼ 23 but more importantly the lowest leakage current and dielectric losses. Fourier transform infrared spectroscopy shows an absorbance peak at 930 cm^− 1, which is a clear signature of the formation of Ti-O-Si bondings in all the silicate films. The developed sol-gel process offers the required latitude to grow Ti_xSi_1 − xO₂ with any composition (x) in the whole 0 ≤ x ≤ 1 range. Thus, the k value of the Ti_xSi_1 − xO₂ films can be tuned at any value between that of SiO₂ (3.8) to that of TiO₂ (k ∼ 60) by simply controlling the TiO₂ content of the films. The composition dependence of the dielectric constant of the Ti_xSi_1 − xO₂ films is analyzed in the light of existing models for dielectric composites.     

基于磁控溅射的金属氧化物气敏薄膜的研究进展

气体传感器的应用越来越广泛,对气敏材料的研究也越来越深入。磁控溅射法是生产气敏薄膜的一种主要方法,本文重点介绍了用磁控溅射法制备的几种金属氧化物薄膜(SnO2、WO3、ZnO、TiO2、In2O3和NiO等)的气敏性能及其研究进展,对其它薄膜做了简要概述,并提出了目前在气敏薄膜研究中存在的问题。     

P-type tin–indium oxide films prepared by thermal oxidation of metallic InSn alloy films

P-type transparent conducting tin–indium oxide (TIO) films were successfully fabricated on quartz substrates by thermal oxidation of InSn alloy (In / Sn = 0.2) films that were deposited by magnetron sputtering at room temperature (R.T.). Structural and electrical properties of TIO films were investigated. X-ray diffraction studies showed that all TIO films were polycrystalline with an orthorhombic structure. The surface morphology of TIO films viewed by field emission scanning electron microscope (SEM) revealed that the films are composed of uniformly distributed submicron grains. Hall effect measurement results indicated that hole concentration as high as 9.61 × 10¹⁸ cm^− 3 was achieved. It's found that 600 °C was the optimum thermal oxidation temperature to get p-type TIO films with highest hole concentration.     

Pulsed laser deposition and characterization of Hf-based high-k dielectric thin films

The continuous downward scaling of the complementary metal oxide semiconductor (CMOS) devices has enabled the Si-based semiconductor industry to meet the technological requirements such as high performance and low power consumption. However, the ever-shrinking dimensions of the active device, metal-oxide-semiconductor-field-effect-transistor (MOSFET), in the circuit create other physical challenges. The industry standard SiO₂ for the gate region is reaching to its physical limits. New materials with higher dielectric constant are needed to replace the silicon dioxide in these gate regions. One of the candidates for this replacement is Hf-based oxides. In this project, we have used pulsed laser deposition (PLD) to synthesize Hf-based high-k dielectric films on Si single crystal substrates with varying deposition parameters and mixtures of HfO₂ and ZrO₂ then used X-ray absorption fine-structure spectroscopy (XAFS) in order to probe the local structure around the Hf metal. The local structural information extracted through XAFS has been correlated with the deposition parameters such as the substrate temperature and the HfO₂, to ZrO₂ ratio in the mixtures.     

Chemical/mechanical polishing of diamond films assisted by molten mixture of LiNO3 and KNO3

Chemical/mechanical polishing can be used to polish the rough surface of diamond films prepared by chemical vapor deposition (CVD). In this paper, a mixture of oxidizing agents (LiNO₃ + KNO₃) has been introduced to improve the material removal rate and the surface roughness in chemical/mechanical polishing because of its lower melting point. It had been shown that by using this mixture the surface roughness R_a (arithmetic average roughness) could be reduced from 8-17 to 0.4 μm in 3 h of polishing, and the material removal rate can reach 1.7-2.3 mg/cm²/h at the temperature of 623 K. Pure aluminium is compared with cast iron as the contact disk material in the polishing. Although the material removal rate of aluminiumdisk is lower than that of cast iron, it can eliminate the carbon contamination from the contact disk to the surface of diamond films, and facilitate the analysis of the status of diamond in the chemical/mechanical polishing. The surface character and material removal rate of diamond films under different polishing pressure and rotating speed have also been studied. Graphite and amorphous carbon were detected on the surface of polished diamond films by Raman spectroscopy. It has been found that the oxidization and graphitization combined with mechanical cracking account for the high material removal rate in chemical/mechanical polishing of diamond films.     

Properties of indium oxide/tin oxide multilayered films prepared by ion-beam sputtering

The preparation and characterization of indium oxide (InO _x )/tin oxide (SnO _y ) multilayered films deposited by ion-beam sputtering are described and compared with indium tin oxide (ITO) films. The structure and the optoelectrical properties of the films are studied in relation to the layered structures and the post-deposition annealing. Low-angle X-ray diffraction analysis showed that most films retained the regular layered structures even after annealing at 500° C for 16 h. As an example, we obtained a resistivity of 6×10^–4 cm and a transparency of about 85% in the visible range at a thickness of 110 nm in a multilayered film of InO _x (2.0 nm)/SnO _y (0.2 nm)×50 pairs when annealed at 300° C for 0.5 h in air. Hall coefficient measurements showed that this film had a mobility of 17 cm² V^–1 sec^–1 and a carrier concentration (electron density) of 5×10²⁰ cm^–3.     

Thin cuprous oxide films prepared by thermal oxidation of copper foils with water vapor

We present an improved preparation method for the growth of high quality crystals of cuprous oxide films grown by thermal oxidation of cupper foils with water vapor. This method proved to be good for preparing cuprous oxide films with high purity and large grain size. X-ray diffraction studies revealed the formation of Cu₂O films with preferred (111) orientation. The cuprous oxide diodes fabricated by the above technique have been studied using current-voltage method.     

Chemical vapor deposition of SiO2 films by TEOS/O2 supermagnetron plasma

A TEOS/O₂ supermagnetron double electrode plasma system was used to deposit SiO₂ films. Deposition rates were measured as a function of rf power and substrate stage temperature. With an increase of rf power on both electrodes from 40 to 80W, the deposition rate increased; however, with a further increase of rf power from 80 to 120W, the deposition rate ceased to increase or decreased only a small amount. The presence of O-H bonds from bonded water in the film was evaluated using buffered HF (BHF) etching solution. With an increase of rf power from 40 to 120W, the BHF etch rate decreased; i.e., the number of O-H bonds were reduced. A minimum BHF etch rate was observed at a rf phase difference of 180° between the two rf power sources. A SiO₂ film was deposited on a trench-patterned quartz substrate. A flat surface SiO₂ layer with air gaps (voids) was formed on the high-aspect ratio (depth/width=1.5-2) trench area.     

Study of (Zr,Ti)CN, (Zr,Hf)CN and (Zr,Nb)CN films prepared by reactive magnetron sputtering

(Zr,Ti)CN, (Zr,Hf)CN and (Zr,Nb)CN coatings, in which Ti, Hf and Nb were added to ZrCN base compound, have been prepared by reactive magnetron sputtering. The coatings, with two different non-metal/metal ratios, were comparatively investigated in terms of elemental and phase composition, texture, surface morphology, hardness and friction performance. It has been shown that the films exhibit nanocomposite structures, consisting of a mixture of crystalline metal carbonitride and amorphous carbon. As compared with ternary ZrCN coatings, the quaternary coatings were found to exhibit superior mechanical and friction characteristics. In general, the films with higher non-metal content revealed finer morphologies, higher hardness and lower friction coefficient. Depending on the coating type and non-metal/metal ratio, the hardness values ranged from about 21 to 29 GPa, being higher than those of ZrCN reference films. The coefficients of friction varied from 0.2 to 0.5, the lowest values being obtained for the coatings with the highest non-metal content.     

Further work function and interface quality improvement on Al2O3 capped high-k/metal gate p-type metal-oxide-semiconductor field-effect-transistors by incorporation of fluorine

The impact of fluorine (F) incorporation into TiN/HfO₂/SiO₂ on work function has been investigated. By process scheme optimization, F implanted through sacrificial oxide layer reveals sufficient the flat-band voltage (V_FB) shift ~ 170 mV without an equivalent oxide thickness (EOT) penalty. On the contrary, apparent EOT increasing was observed if F implanted directly through Si. Moreover, F incorporation into TiN/Al₂O₃/HfO₂/SiO₂, the V_FB shift can be up to about 250 mV or 410 mV at 10 keV with a dose of 2 × 10¹⁵ cm^− 2 or 5 × 10¹⁵ cm^− 2, respectively. Effective work function has been boosted to 4.95 eV closer to the valence band edge. Besides, interface defect density also can be improved ~ 20% by F incorporation from charge pumping result.