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To realize the full potential of high density embedded ferroelectric memory, ferroelectric film thickness must be scaled below 100 nm to ensure that the capacitor operating voltage is compatible with advanced, low voltage logic transistors. In this article, we describe recent progress in the preparation of sub-100 nm thick Pb(Zr,Ti)O3 (PZT) thin films by metalorganic chemical vapor deposition on 200 mm wafers using an industry-standard processing platform. Within the full range of thicknesses investigated, 134–52 nm, capacitor operating voltage scales linearly with film thickness, yielding 71 nm thick films with a switched polarization (Psw) of ∼40 μC/cm2 at 1.2 V. Below ∼50 nm, PZT surface roughness makes further thickness scaling difficult. With improved surface morphology, however, even lower operating voltages should be feasible.

This paper describes amorphous Pb(Zr, Ti)O3 (PZT) thin films deposited by cosputtering Pb(Zr0.5 Ti0.5)O3 and PbO targets. By optimizing the amount of the excess Pb and the deposition temperature, PZT thin films with a single perovskite phase were obtained successfully on Ir substrates and Pt substrates at 520°C. 250-nm-thick PZT films crystallized by rapid thermal annealing (RTA) at 600°C for 20 s exhibited excellent ferroelectric properties: a coercive voltage of 1.0 V, a remanent polarization density of about 40 μC/cm2, and a polarization switching endurance over 1x109 cycles. Although a heat treatment in a reductive ambient causes degradation of ferroelectric properties of PZT thin films, their degraded ferroelectric properties can be easily recovered from by a 1-min RTA in an oxygen at 400°C.

The reduction of the oxidation temperature is effective for atomically-controlled gate oxide growth. We focus the effects of post-oxidation annealing on oxides grown at a low temperature from 650 to 850°C. The N 2 annealing drastically decreased the leakage current at the low gate voltage below 1.5 V. The interface trap density was also reduced by the N 2 annealing. We confirmed the correlation between the interface trap density and the leakage current at a low voltage below 1.5 V. We also found that the stressing immunity of the ultrathin oxides grown at a low temperature, 650°C, is dramatically improved by post-oxidation annealing at 850°C.

The measured switched polarization properties of integrated Pb(Zr,Ti)O3 (PZT) capacitors arrays have been found to show a small dependence on individual capacitor size in the range from 0.17 and 100 μm2. These thin (90 nm) PZT capacitors have low voltage switching properties with polarization saturation of

Summary form only given. High-density, embedded ferroelectric memory (FeRAM) has the potential to replace embedded flash, embedded DRAM, and non-cache SRAM and could be a key enabler for future system-on-a-chip applications. Despite this appeal, the evidence that ferroelectric capacitors can be scaled to the submicron regime has been limited. In this paper, we report the fabrication and electrical properties of submicron PZT capacitors formed using both planar bottom electrodes and W plug contact structures. We observe that the aggregate saturation polarization value is nearly independent of individual capacitor area in the measured range from the contact-limited size of 0.12 /spl mu/m/sup 2/ to 10/sup 4/ /spl mu/m/sup 2/. This result suggests that high-density, embedded FeRAM technology may be feasible.

Sputtered Pb(Zr, Ti)O3 thin films with superior ferroelectric properties were successfully obtained by controlling the grain structure and the film compositions. We found that amorphous PbTiO3 buffer layers are effective in forming PZT thin films with fine dense grains. The sputtered PZT thin films with Ti-rich phase showed excellent ferroelectric properties. The polarization retention properties of PZT capacitors with Ti-rich phase are remarkable, and the value of the retained polarization density after 10 years is expected to be larger than 40 μC/cm2. Further, 150-nm-thick PZT capacitors with Zr/Ti=30/70 showed 2P, at 1.5 V of more than 30 μC/cm2, and good retention property. These results indicate the potential of the lower voltage operation of sputtered PZT capacitors by optimizing the film composition and thickness.

The low temperature oxidation is effective for the atomically-controlled gate oxide growth. We focused the effects of post-oxidation annealing (POA) and attempted to improve the properties of the low-temperature-grown ultrathin oxides with a thickness of 3nm by POA. POA abruptly reduced the leakage current at a low gate voltage below 1.5V and the interface trap density. The correlation between the interface trap and the leakage current at a low applied voltage region were confirmed. We found that the stressing immunity of the ultrathin oxides grown at a low temperature, 650°C, is drastically improved by POA at 850°C.

A novel technique has been proposed for selective and in-situ excimer-laser crystallization and doping to thin poly-Si films. Dopant atoms are supplied, during the Si laser crystallization process, to the Si film on glass from the doped SOG (spin-on-glass) film coated on the top. Conductivity of the processed film was increased to more than 10S/cm from about 10−8S/cm of the starting film. This technique has been applied to the bottom gate Amorphous-Si TFTs with self-aligned poly-Si source and drain. The electron field-effect mobility was 1.0cm2/Vs and the on/off current ratio was more than 106. No parasitic effects were observed, and the hole conduction was effectively suppressed. This in-situ crystallization and doping technique can also be applied to the top gate a-Si TFT process.

We have demonstrated that the scaling of IrO x (Pb(Zr, Ti)O3:PZT)/Ir capacitors can be extended into the submicron regime. The submicron IrO x /PZT/Ir capacitors were fabricated using a one-mask stack-etch process, integrated with an SiO2 interlayer dielectric, and contacted with Al metallization. The aggregate electrical properties of integrated PZT capacitor arrays are shown to be nearly independent of individual capacitor area in the range between 102 µm2 and 0.12 µm2. In particular, switched polarization values of more than 30 µC/cm2 were obtained for PZT capacitors with an individual capacitor area of 0.12 µm2. This result suggests that the lateral scaling can be achieved down to 0.1 µm2. Through the use of appropriate diffusion barriers, hydrogen-robust submicron PZT capacitors are obtained. No degradation in ferroelectric properties of submicron PZT capacitors was observed under the test conditions. These results suggest that PZT capacitors can be integrated into a standard complementary metal oxide semiconductor (CMOS) process flow with minimal degradation.

Crystalline lead-zirconate-titanate (PZT) films of perovskite structure with fine grains were successfully obtained on Ir substrates using an amorphous lead-titanate (a-PTO) buffer layer. The grain size of PZT ranged from 100 to 150 nm. The results of the temperature dependence of the X-ray diffraction patterns of PZT films prepared on a-PTO buffer layer revealed that PZT films with a single perovskite phase were obtained at 500°C. In addition, 250-nm-thick PZT films fabricated with a-PTO buffer layer and crystallized at 600°C showed excellent ferroelectric properties. The 2P r values of Ir/PZT/Ir capacitors with a-PTO buffer layer satisfactorily saturated at the applied voltage of 3.5 V. No degradation in the polarization density was observed for switching cycles up to 1×109.

Switching behaviors of lead-zirconate-titanate thin-film capacitors with Ti/Zr ratios of 60/40 and 75/25 were successfully characterized by observing their switching transient currents. The capacitor with 60/40 showed the remanent polarization density of 24.0 µ/cm2 independent of the frequency of the external switching biases. On the other hand, the remanent polarization density of the capacitor with 75/25 was reduced markedly with increasing the frequency. The remanent polarization density was lowered from 23.6 µC/cm2 at 100 Hz to 13.0 µC/cm2 at 12.5 kHz. While the switching transient currents were observed as a function of time, the lead-zirconate-titanate thin-film capacitor with 60/40 showed the typical sharp switching transient current. In sharp contrast, the capacitor with 75/25 ratio showed a monotonous transient current which suggests the presence of ferroelectric domains having long time constants. Consequently, the lead-zirconate-titanate thin film with the Ti/Zr ratio of 60/40 showed better switching behavior as compared to that with the Ti/Zr ratio of 75/25.

In this paper, the recovery of the ferroelectric properties of Ir/Pb(Zr,Ti)O3/Ir thin film capacitors damaged by annealing in a hydrogen ambient has been described. The ferroelectric properties of the capacitors markedly degrade as a result of heat treatment in a hydrogen ambient at 400°C. These properties can be easily recovered to their initial state by post annealing using a rapid thermal annealing process in an oxygen ambient at 400°C for 1 min.