Hiroshi Miki

Rutile-type TiO2 thin film for high-k gate insulator

Abstract We investigated rutile-type titanium dioxide (TiO2) films for possible use as a high-k gate insulator. The TiO2 thin films were directly deposited on Si substrates using a RF magnetron sputtering method with a sintered oxide target. A single phase of rutile-type TiO2 whose dielectric constant of approximately 75 was obtained when the film was deposited in an inert gas atmosphere and annealed at 800 °C in an oxidizing gas atmosphere. The oxygen ions were deficient in the as-deposited film, and consequently, a sufficient oxygen supply was needed to crystallize the film to a single phase of rutile during the post-annealing. However, the interfacial SiO2 layer between the TiO2 and the Si substrate simultaneously grew thicker than 2 nm. As the interfacial SiO2 grew, the leakage current was decreased and the equivalent oxide thickness was increased, in the Au/rutile-type TiO2/Si capacitor. Therefore, we concluded that the growth of the interfacial SiO2 layer thicker than 2 nm is inevitable to form the single phase of rutile-type TiO2 and to decrease the leakage.

H2 DAMAGE OF FERROELECTRIC PB(ZR,TI)O3 THIN-FILM CAPACITORS : THE ROLE OF CATALYTIC AND ADSORPTIVE ACTIVITY OF THE TOP ELECTRODE

Large-scale integrated fabrication in a H2 containing atmosphere, for example, during the passivation process, can cause serious damage in metal/Pb(Zr,Ti)O3/metal capacitors (i.e., Pt/PZT/Pt capacitors). To reveal the cause of the H2 damage, we investigated the behavior of hysteresis curves and the leakage current of capacitors with a top electrode of Pt, Pd, Au, or Ag. Capacitors with a top electrode of Au or Ag are more resistant to the H2 annealing damage than those of Pt or Pd. We found that the H2 damage was strongly affected by the catalytic activity and adsorptive properties of the top electrode when exposed to H2.

Electrode‐induced degradation of Pb(ZrxTi1−x)O3 (PZT) polarization hysteresis characteristics in Pt/PZT/Pt ferroelectric thin‐film capacitors

One of the most serious forms of damage that occurs during the integration of Pt/PZT/Pt ferroelectric capacitors [where PZT is Pb(ZrxTi1−x)O3] is the disappearance of polarization hysteresis characteristics during the passivation process. The hydrogen content of the atmosphere during this process affects the ferroelectric capacitor characteristics. However, the PZT film itself is not damaged by annealing in a hydrogen‐containing atmosphere even at 400 °C, whereas the Pt/PZT/Pt ferroelectric capacitor loses its polarization hysteresis characteristics at 300 °C. The top Pt electrode was found to induce this damage. Possible mechanisms such as stress and a chemical reaction with the Pt catalyst are discussed.

Anomalously Large Threshold Voltage Fluctuation by Complex Random Telegraph Signal in Floating Gate Flash Memory

A threshold voltage fluctuation (DeltaVth) due to random telegraph signal (RTS) in a floating-gate (FG) flash memory was investigated. From statistical analysis of the DeltaVth, we found an anomalously large DeltaVth at high percentage region of the DeltaVth distribution, which is caused by a complex RTS. Since the ratio of the complex RTS among the RTS is increased by charge injection to tunnel oxide, the dispersion of the DeltaVth distribution increases after program/erase (P/E) cycle. Since the DeltaVth due to the complex RTS is much larger than the simple RTS, the complex RTS become one of the reliability issues in larger capacity flash memory, especially after P/E cycle

Impact of threshold voltage fluctuation due to random telegraph noise on scaled-down SRAM

The impact of a random telegraph noise (RTN) on a scaled-down SRAM is shown for the first time. To estimate the impact on SRAM, we statistically analyzed a threshold voltage fluctuation (DeltaVth) of n-and p-MOSFETs. It is revealed that DeltaVth of the p-MOSFET is larger than that of the n-MOSFET. This difference can be explained by considering the followings: (i) number- and mobility-fluctuation models of RTN (ii) the difference in the capture cross section between electron and hole. In addition, based on these results, SRAM margin enclosed by read / write Vth curves with or without RTN was simulated. We consequently found that Vth margin comes close to Vth window of the SRAM by considering the effect of RTN on DeltaVth, even at hp 65. Moreover, DeltaVth due to RTN of the p-MOSFET is comparable with DeltaVth due to the random dopant fluctuation (RDF) at hp 45 because DeltaVth due to the RDF is inversely proportional to square root of the gate area (S), while DeltaVth due to RTN is inversely proportional to S.

The effects of the catalytic nature of capacitor electrodes on the degradation of ferroelectric Pb(Zr,Ti)O3 thin films during reductive ambient annealing

The disappearance of ferroelectricity in Pb(Zr0.52,Ti0.48)O3 (PZT) thin-film capacitors, which is caused by heat treatment in a reductive ambience, is investigated. Bare PZT films are not damaged by annealing in a hydrogen-containing atmosphere (H2 annealing) up to 400 °C, whereas a PZT capacitor with Pt electrodes loses its ferroelectricity during annealing at less than 300 °C. We have found that the degradation of ferroelectricity depends upon the metal used for the top electrode of the PZT capacitor. The increased degradation in the case of a PZT capacitor with Pt electrodes can be explained by a catalytic reaction on the Pt surface. We have made the ferroelectricity of a Pt/PZT/Pt capacitor retained even after the H2 annealing at 300 °C, or above, simply by oxidizing it before the H2 annealing.

Statistical measurement of random telegraph noise and its impact in scaled-down high-κ/metal-gate MOSFETs

This paper presents results of statistical analysis of RTN in highly scaled HKMG FETs. A robust algorithm to extract multiple-trap RTN is proposed and applied to show that RTN can cause serious variation even when HKMG and undoped channel are introduced. We further focus on hysteretic behavior caused by RTN with time constants much longer than the circuit timescale. This reveals that RTN also induces novel instabilities such as short-term BTI and logic delay uncertainty. Extraction of RTN in SRAM arrays is also presented to discuss its impact on operational stability.

Pt/PbZrxTi1−xO3 interfacial reaction and Schottky barrier formation studied by x-ray photoelectron spectroscopy: Effect of H2 and O2 annealing

The Pt/PbZrxTi1−xO3 (PZT) interfacial reaction caused by low-temperature (320 °C) annealing and resulting change in the surface Fermi level position (Schottky barrier height) has been studied by using in vacuo x-ray photoelectron spectroscopy (XPS). A thin (2 nm) Pt layer was deposited on a polycrystalline PZT film and annealed in 0.5-Torr H2 and O2 in a chamber connected to the XPS chamber. For the PZT samples annealed prior to Pt deposition, a small amount of metallic Pb was produced after the Pt deposition. The annealing also moved the surface Fermi level (EF) at the Schottky interface toward the conduction band minimum (EC) of PZT by 0.4 eV, as evidenced by the band-bending shift of the PZT core levels. Excess metallic states appeared in the valence-band spectra of an annealed bare PZT surface. There was no appreciable annealing-atmosphere dependence in the amount of metallic Pb produced and surface EF position at the PT/PZT interface. However, a clear annealing-atmosphere dependence was observed for ...

Evaluation methodology for random telegraph noise effects in SRAM arrays

We propose a novel method to evaluate the impact of RTN on SRAM, and have demonstrated and proved the RTN effects are indeed present in SRAM by both simulation and experiments. Our results also determine the necessary voltage guard band to prevent SRAM yield loss.

Reduction of random telegraph noise in High-к / metal-gate stacks for 22 nm generation FETs

This work demonstrates, for the first time, the reduction of random telegraph noise (RTN) in high-к / metal gate (HK / MG) stacks incorporated in 22 nm generation FETs. Many thousands of such FETs have been fabricated, measured, and analyzed using a statistical technique to separate RTN as a major noise component from 1/f noise as a minor component. Based on a statistical comparison of these FETs, we find that high temperature forming gas annealing can suppress RTN threshold voltage variation (ΔVth). In addition, properly annealed HK FETs have smaller RTN ΔVth than SiON FETs, due mostly to fewer traps and partly to thinner inversion thickness in HK / MG. Based on these results, we project that random dopant fluctuations will have a greater impact on SRAM yield than RTN until at least the 15 nm generation, for doped channel FETs.