Kyu-Jeong Choi

Effect of Annealing Conditions on a Hafnium Oxide Reinforced SiO2 Gate Dielectric Deposited by Plasma-Enhanced Metallorganic CVD

Hafnium oxide thin films for gate dielectric were deposited at 300°C on p-type Si(100) substrates by plasma-enhanced metallorganic chemical vapor deposition (PE-MOCVD) and annealed in O 2 and N 2 ambients at various temperatures, As-deposited HfO 2 films showed an almost amorphous structure, but samples annealed at 800°C in O 2 showed an increase of crystallinity compared with those in the N 2 ambient. The flatband voltage shifts and interface trap densities of HfO 2 capacitors annealed in an O 2 ambient are larger and lower, respectively, than those in N 2 ambient. Interface trap densities of HfO 2 thin films annealed at 800°C in O 2 were about 5.5 × 10 11 cm -2 eV -1 . The capacitance equivalent oxide thicknesses of HfO 2 thin films annealed at 800°C were approximately 30 A independent of N 2 and O 2 ambients. Hysteresis of as-deposited gate dielectric was quite large, but that of gate dielectric annealed at 800°C in O 2 and N 2 ambients was reduced to a negligible level of about 20 mV without increase of the equivalent oxide thickness. The leakage current densities of HfO 2 thin films annealed at 800°C in O 2 and N 2 ambient were about 8 × 10 -5 and 3 × 10 -6 A/cm 2 , respectively, at -1 V.

Metal/ferroelectric/insulator/semiconductor structure of Pt/SrBi2Ta2O9/YMnO3/Si using YMnO3 as the buffer layer

The ferroelectric SrBi2Ta2O9 (SBT) and YMnO3 buffer layers for the metal/ferroelectric/ insulator/semiconductor (MFIS) structure were deposited using pulsed-laser ablation and metalorganic chemical vapor deposition, respectively. Memory windows of the MFIS structure were in the range of 0.3–1.5 V when the gate voltage varied from 2 to 6 V. There were no reactions between ferroelectric SBT and Si in the MFIS structure annealed at 900 °C. The YMnO3 buffer layer plays an important role in alleviating the interdiffusion between elements of SBT and Si. The proposed MFIS structure of Pt/200 nm–SBT/25 nm–YMnO3/Si is attractive for nondestructive read-out ferroelectric random access memory applications.

Ferroelectric YMnO3 thin films grown by metal-organic chemical vapor deposition for metal/ferroelectric/semiconductor field-effect transistors

Abstract Ferroelectric thin films of YMnO 3 and Y 2 O 3 insulator were deposited on Si(100) substrates by metal-organic chemical vapor deposition. When the YMnO 3 thin films were annealed in ambient oxygen, the secondary phases of orthorhombic YMnO 3 (o-YMO), Y 2 O 3 and Y 2 Mn 2 O 7 were observed, along with the primary phase of hexagonal YMnO 3 (h-YMO). On the other hand, the films annealed in vacuum (100 mtorr) crystallized to an h-YMO single phase, without an apparent secondary phase. When the gate voltage swept from +5 to −5 V, the capacitor had a hysteresis curve with a clockwise rotation, which indicates ferroelectric polarization switching behavior. The memory window of the Pt/YMnO 3 /Y 2 O 3 /Si gate capacitor annealed in vacuum at 850°C is 1.8 V. The typical leakage current density of the films annealed in ambient oxygen and vacuum are approximately 10 −3 and 10 −7 A/cm 2 at an applied voltage of 5 V, respectively. The annealing atmosphere plays a critical important in the crystallinity and electrical properties of YMnO 3 thin films.

Characterization of HfO2 and HfO x N y Gate Dielectrics Grown by PE Metallorganic CVD with a TaN Gate Electrode

HfO x N y films were prepared using hafnium tertiary-butoxide {Hf]OC(CH 3 ) 3 ] 4 } in a plasma and N 2 ambient to improve the thermal stability of hafnium-based gate dielectrics. The incorporation of 10% nitrogen into HfO 2 films resulted in a smooth surface morphology and a crystallization temperature as high as 200°C compared with pure HfO 2 films. TaN/HfO x N y /Si capacitors showed stable capacitance-voltage characteristics even at a postmetal annealing (PMA) temperature of 1000°C in a N 2 ambient and a constant value of 1.6 nm equivalent oxide thickness irrespective of an increase in the postdeposition annealing (PDA) and PMA temperatures. The leakage current densities of HfO x N y capacitors annealed at PDA and PMA temperatures of 800 and 900°C, respectively, were approximately one order of magnitude lower than that of HfO 2 capacitors.

Control of the Interfacial Layer Thickness in Hafnium Oxide Gate Dielectric Grown by PECVD

The HfO 2 thin films for use in gate dielectric applications were deposited at 300°C onto p-type Si(100) substrates using Hf[OC(CH 3 ) 3 ] 4 as the precursor in the absence of oxygen by plasma-enhanced chemical vapor deposition (PECVD). The HfO 2 films deposited in the absence of O 2 show excellent electrical properties such as low equivalent oxide thickness (EOT) and good thermal stability. The deposited films have an interfacial layer of approximately 10 A in thickness, resulting in a decrease in the thickness of the interfacial layer by about 50% compared to films deposited in the presence of oxygen. The leakage current density of HfO 2 films was approximately four orders of magnitude lower than an electrically comparable SiO 2 at the same EOT. The improvement of electrical properties can be attributed to the decrease in the SiO 2 interfacial layer. The thickness of the interfacial layer can be controlled by deposition in the absence of oxygen after evacuation of the reaction chamber by means of an ultrahigh vacuum.

Characteristics of Pt and TaN Metal Gate Electrode for High-κ Hafnium Oxide Gate Dielectrics

TaN gate electrodes for HfO 2 gate dielectric were prepared using dc magnetron sputtering and compared with Pt gate electrode in terms of thermal stability at a post metal annealing (PMA) temperature of 900°C for 1 min inN 2 . The increase of nitrogen content in Ta 1 - x N x electrode produces an increase of resistivity and Ta 0 . 4 6 3 N 0 . 5 3 7 electrodes showed a good thermal stability of resistivity even at an annealing temperature of 1000°C for 1 min in N 2 ambient. TaN/HfO 2 /Si capacitors showed superior properties to Pt/HfO 2 /Si capacitors in capacitance-voltage and current-voltage characteristics. TaN gate electrodes are suitable for application to high-K hafnium oxide gate dielectrics.

Low Voltage Switching Characteristics of 60 nm Thick SrBi2Ta2 O 9 Thin Films Deposited by Plasma-Enhanced ALD

60 nm thick SrBi 2 Ta 2 O 9 (SBT) thin films were fabricated using plasma-enhanced atomic layer deposition (ALD) with an alternating supply of single cocktail source and oxygen plasma. The linear relationship between the number of cycles and film thickness and a constant deposition rate with source pulse time suggests that a self-limiting process that has distinct characteristics of ALD was achieved. The 60 nm thick SrBi 2 Ta 2 O 9 films that were annealed at 750°C completely crystallized to the layer-structured perovskite phase. The SBT capacitors showed excellent ferroelectric switching properties. Low voltage switching below 1.5 V was achieved successfully in the 60 nm SBT capacitor.

Liquid-delivery metal-organic CVD of strontium bismuth tantalate thin films using Sr[Ta(OC2H5)5(OC2H4OCH3)]2 and Bi(C6H5)3 precursors

SrBi 2 Ta 2 O 9 (SBT) thin films were deposited onto Pt/Ti/SiO 2 /Si substrates by liquid-delivery metal-organic (MO) CVD using Sr[Ta(OC 2 H 5 ) 5 (OC 2 H 4 OCH 3 )] 2 and Bi(C 6 H 5 ) 3 precursors. The film composition was primarily controlled by varying the deposition temperature and the concentration of the single-mixture solution. The stoichiometric SBT thin films deposited at 540°C were well crystallized, and showed a relatively high intensity of α-axis orientation of (200), as well as the main peaks of (115) and (008). The SBT films, annealed at 750°C in ambient oxygen showed a good ferroelectric property, a saturated hysteresis loop even at an applied voltage of 2 V. The remanent polarization (2P r ) and coercive field (E c ) of SBT films annealed at 750°C were 12 μC cm -2 and 60 kV cm -1 , respectively, at an applied voltage of 5 V.

(Bi, La)4Ti3O12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices

Using nanocrystalline perovskite nuclei, (117) oriented-(Bi,La)4Ti3O12(BLT) thin films were grown using a noble bake process for nonvolatile ferroelectric memory devices. The c-axis oriented BLT thin films have a remanent polarization (2Pr) of 8.0μC∕cm2 at a 3V driving voltage, and the (117) oriented films have a 2Pr value of about 25μC∕cm2. The BLT capacitors, grown on a platinum electrode via nanocrystalline perovskite nuclei, had fatigue and imprint free characteristics after applying 1×1011 switching cycles and for ten years at a 125°C stress. The average sensing margin of the (117) oriented BLT thin films was approximately 700mV for a 0.65μm2 cell size and a sufficient signal margin for ten years was indicated, based on the extrapolation of the measured data for high density ferreoelectric random access memory applications.

Low-temperature Crystallization of SrBi 2 Ta 2 O 9 Thin Filmswith Bi 2 O 3 Interfacial Layers by Liquid-delivery Metalorganicchemical Vapor Deposition

Ferroelectric SrBi 2 Ta 2 O 9 (SBT) thin films and Bi 2 O 3 interfacial layers were deposited onto the Pt/Ti/SiO 2 /Si substrates via liquid-delivery metalorganic chemical vapor deposition. The SBT films with a 5-nm-thick Bi 2 O 3 interfacial layer were well crystallized without c-axis orientation, even at deposition temperature of 540 °C and showed a stronger (115) orientation than those without a Bi 2 O 3 layer with increasing annealing temperature. The remanent polarizations of SBT films with Bi 2 O 3 interfacial layer were significantly improved in comparison with those without Bi 2 O 3 layer. The remanent polarization (2P r ) and coercive field (E c ) of SBT films without and with a Bi 2 O 3 interfacial layer annealed at 750 °C were 12 and 21 μC/cm 2 and 60 and 38 kV/cm, respectively, at an applied voltage of 5 V.