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Amorphous thin Ge 2 Sb 2 Te 5 films were deposited by MOCVD (metal organic chemical vapor deposition) on three-dimensional structures. Ammonium gas, used as a reactant, reduced the deposition temperature to 150 °C, which is lower than that of metal-organic precursors. Introducing nitrogen and hydrogen radicals made by decomposition of the ammonium gas further reduced the growth temperature. The lowest growth temperature producing a realistic growth rate was 100 °C. Phase-change memory cells made of MOCVD-grown films were confirmed to have operation and reliability characteristics as good as those of conventional cells made of sputter-deposited films.

We developed high-performance metal-ferro-electric-insulator-semiconductor (MFIS) structures with a thin Al 2 O 3 layer deposited on Si 3 N 4 buffer layer. The Al 2 O 3 were deposited by atomic layer deposition technique and the Si 3 N 4 were made by the direct nitridation of Si substrate using atomic nitrogen radicals. Since the buffer Si 3 N 4 was made perfectly damage-free and hydrogen-free, we can perform high temperature oxidation to eliminate defects in Al 2 O 3 and ferroelectric films down to the negligible level. On the stacked buffer layer, we deposited highly c-axis oriented Bi 3.25 La 0.75 Ti 3 O 12 film and fabricated MFIS structure. With the help of the high insulating property of a buffer layer and a highly c-axis oriented ferroelectric film, we succeeded to realize the large memory windows together with the long retention characters in the Pt/Bi 3.25 La 0.75 Ti 3 O 12 /Al 2 O 3 /Si 3 N 4 /Si MFIS structure.

In the stacked structure of PbZr1-xTixO3(PZT)/Pt/TiN/poly-Si for a ferroelectric random access memory (RAM), the mechanism of TiN barrier-metal oxidation was investigated by transmission electron microscopy (TEM). In the cross-sectional TEM images of PZTyPtyTiNySi, titanium oxide was observed beneath the Pt grain boundary. The oxygen was diffused through the Pt grain boundary during the heat treatment in an oxygen atmosphere for crystallization of PZT films. The annealing of the TiN film in ammonia resulted in the suppression of the oxidation during the crystallization annealing of PZT. The minimum required Pt film thickness to protect TiN from oxidation can be reduced from 200 nm to 100 nm.

The role of ozone in the reactive coevaporation of the lead zirconate titanate thin film was investigated by depositing films at various growth rates with various ozone fluxes or molecular oxygen fluxes on unheated substrates and then crystallizing them using rapid thermal annealing. The oxidation state of lead in the as-deposited film was determined from the ratio of the ozone to the total metal fluxes. The amount of atomic oxygen supplied to the surface of the film was at least 103 times larger when the deposition was done using ozone rather than molecular oxygen. When the ozone flux was more than one-third of the total metal flux, well-oxidized films were obtained. To ensure obtaining well-oxidized film, the ozone flax should be more than twice as much.

A one-mask-patterned ferroelectric capacitor test structure designed with a 0.5-μm feature size was fabricated. Oxygen plasma treatment after dry etching decreased the leakage current to as low as that of as-deposited film. These one-mask-patterned ferroelectric capacitors, with switching charge almost equal to as-deposited film, were successfully fabricated. Ferroelectric memories as dense as dynamic random access memories will become possible with this technology. However, the leakage current density for micron-sized capacitors is 2 to 10 times that of large capacitors. The leakage current in small capacitors is increased due to perimeter leakage that runs through the damaged region on the capacitor sidewall. © Scripta Technica, Inc. Electr Eng Jpn, 121(1): 43–50, 1997

The mechanism of TiN barrier metal oxidation of Pt/TiN electrodes are investigated for planarized stacked memory utilizing lead zirconate titanate (PZT). Thinner (

We developed high-performance metal–ferroelectric–insulator–semiconductor (MFIS) structures with a damage-free and hydrogen-free Si3N4 buffer layer as an insulator. We fabricated Si3N4 films by nitriding Si substrates with N2 and/or atomic N radicals generated by an rf radical cell. In contrast to conventional Si3N4 films, the radical-nitride Si3N4 films showed no hysteresis or flat-band shift in the capacitance–voltage (C–V) characteristics even after high-temperature treatments, such as crystallization annealing of ferroelectric thin films deposited on the buffer Si3N4. Using this radical nitride Si3N4 as a buffer layer, we fabricated MFIS diodes with a Pt/Bi3.25La0.75Ti3O12/Si3N4/Si structure. These diodes had good hysteresis in their C–V characteristics, resulting from remnant polarization of the ferroelectric films. However, no other parasitic effects originating in charge trapping and/or detrapping were observed.

with platinum electrodes subjected to hydrogen annealing using strain imaging. The polarization remains downward, when the applied voltage is below 3Vpp. This is caused by a positive internal electric field produced by space charges created in areas with upper platinum electrodes. The freezing of polarization induces a significant reduction in remanent polarization but does not cause large changes in permittivity.

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.

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.

A new contactless characterization technique based on microwave impedance measurement was developed and applied to the nondestructive measurement of deep level concentration in semi‐insulating GaAs crystals. Using this new technique, the nonuniform distribution of EL2 was measured in GaAs wafers used for IC fabrication. Taking advantage of the nondestructive and contactless feature of this new technique, both the EL2 concentration and the threshold voltage (Vth) of metal semiconductor field effect transistors were measured in the same sample. By analyzing the relation of these two quantities, it is found that the activation efficiency of implanted Si atoms is lower in the EL2 richer region, and vice versa. A possible mechanism to explain the experimental data is discussed in relation with crystal nonstoichiometry.

Tungsten‐related deep levels in a silicon crystal are investigated using microwave and conventional deep level transient spectroscopy. It is found that tungsten atoms have two diffusion constants. Most tungsten atoms stay near the surface of Si crystal, but the remainder go deeper than 1 μm from the surface. It is also found that tungsten atoms make both a hole trap of 0.41 eV and an electron trap of 0.22 eV. Device characteristics are found to be seriously degraded due to deep levels made of deeply diffused tungsten atoms.