Koukou Suu

Preparation of (Pb, La) (Zr, Ti)O3 ferroelectric films by RF sputtering on large substrate

(Pb, La)(Zr, Ti)O 3 (PLZT) thin films were deposited on 6-inch Pt/Ti/SiO 2 /Si substrates by rf magnetron sputtering using a multichamber production system. The Pb content in PLZT films deposited at low temperature was measured by inductively coupled plasma (ICP) spectroscopy, and the structural properties of crystallized PLZT films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). A novel method for Pb content control was developed and it was found that Pb content in PLZT film could be changed by changing the electric potential of the substrate. For ferroelectric properties, only small differences were observed between the rapid thermally annealed PLZT film and furnace- annealed ones. Good uniformities of film thickness, Pb content and remanent polarization were achieved on 6-inch wafers.

Stability Control of Composition of RF-Sputtered Pb(Zr, Ti)O3 Ferroelectric Thin Film

The process stability of Pb(Zr, Ti)O3 (PZT) sputtering was studied by observing film composition change as a function of the process duration ( e.g. integrating sputtering time). A useful method of controlling compositional stability was developed. It was found that the existence of a potentially grounded anode was effective to prevent the large variation of Pb contents in PZT thin films and improve the process stability of PZT sputtering.

Reactive Ion Etching Process of Transition-Metal Oxide for Resistance Random Access Memory Device

The reactive ion etching (RIE) of the binary transition-metal oxides (TMOs) NiO, CuO and CoO, which are expected to be key materials of resistance random access memory (RRAMTM), was investigated. We found that inductively coupled plasma using CHF3-based discharge, which is highly compatible with conventional semiconductor RIE, is effective for the TMOs studied here. Furthermore, device fabrication using Pt/CoO/Pt trilayers is carried out, and a large change in resistance, which is an essential functionality of RRAM, was successfully observed. This should be definite evidence of a successful RIE realized in the present device fabrication.

Lead content control of PLZT thin films prepared by RF magnetron sputtering

Abstract PLZT thin films were deposited on 6-inch Pt/Ti/SiO2/Si substrates by radio frequency (RF) magnetron sputtering using a multichamber type production system. The lead (Pb) content in low temperature deposited PLZT films was measured by ICP spectroscopy and structural properties of rapid thermally annealed PLZT films were characterized by X-ray diffraction and scanning electron microscopy. It is found that several sputtering parameters such as RF power, argon (Ar) gas flow and magnetic field were very effective to control the Pb content which is essential for obtaining good ferroelectric properties.

Preparation of SrBi2(Ta, Nb)2O9 thin films by rf sputtering for ferroelectric memory production

Abstract Ferroelectric SrBi2(Ta, Nb)2O9 (SBTN) thin films were prepared by rf magnetron sputtering utilizing a multi-chamber type production tool (ULVAC CERAUS ZX1000). Accurate and dynamic compositional control results in excellent ferroelectric performances such as large 2Pr up to 15μC/cm2, fatigue free at least 109 cycles as well as good uniformity and process repeatability. These results indicate that the SBTN sputtering process is promising for ferroelectric memory production.

Quantum Chemical Investigation for Chemical Dry Etching of SiO2 by Flowing NF3 into H2 Downflow Plasma

A quantum chemical investigation of the chemical dry etching of SiO2 using H2 downflow plasma with flowing NF3 was carried out using the B3LYP/6-31+G(d,p) method. The results provide a reasonable interpretation of how the chemical dry etching of SiO2 takes place in a down flow area. Experimentally, it was found that the etch rates of thermal silicon oxide film range from 1 to 10 nm/min depending on the etching conditions, and white powder was produced on the etched surface. It was deduced that the etchants were HF and NH3 produced by the reaction of H+ NF3, and that the white powder on the etched surface was produced by the decomposition of (NH4)2SiF6 formed on the etched surface. The calculated results support the HF and NH3 production mechanism and clarify the molecular structures of (NH4)2SiF6 and the white powder. Another important point in the chemical dry etching of SiO2 was the realization of a high etching selectivity to Si. As the F atom was deduced to be the main etchant of Si, its generation mechanism in H2 down flow plasma with the addition of NF3 was also studied and a method of suppressing F atom production was proposed in this research.

Quantum Chemical Investigation of Si Chemical Dry Etching by Flowing NF3 into N2 Downflow Plasma

A quantum chemical investigation of the chemical dry etching of N2 downflow plasma and NF3 flow into the downflow area was carried out by the B3LYP/6-31+G(d) method. The results provide a reasonable interpretation of how the chemical dry etching of Si takes place. Experimentally, it was reported that single-crystal silicon was etched in the N2 downflow plasma with NF3 flow and the etch rate depended on the etching conditions, and it had been deduced that the etchant was F atoms produced by the reaction of N*+ NF3. It was found through our calculations that there were three reaction routes of NF3 proceeding F production in the initial reaction step, with N(2Do) and N2(A3Σu+) and by electron attachment, and it is thought that the most probable F production reaction in the downflow area is N(2Do) + NF3→N=NF2+ F and the next probable reaction is N2(A3Σu+) + NF3(3E)→N2(1Σg+) + NF2+F.

Preparation of SrBi2Ta2O9 ferroelectric thin film by rf magnetron sputtering

Abstract SrBi2Ta2O9 (SBT) thin films were deposited on 6-inch Pt/Ti/SiO2/Si substrates by rf magnetron sputtering using a 12-inch ceramic SBT single target. It is found that several sputtering parameters such as argon (Ar) pressure and rf power were very effective to control the Bi content of SBT thin films which is essential for obtaining good ferroelectric properties.

Preparation of SrBi2Ta1.5Nb0.5O9 Ferroelectric Thin Films by RF Sputtering on Large Substrate.

Ferroelectric SrBi2(Ta, Nb)2O9(SBTN) thin films were prepared by RF magnetron sputtering utilizing a multichamber production tool (ULVAC CERAUS ZX1000). Accurate and dynamic compositional control provided by this method results in excellent ferroelectric performances such as large Pr up to 15 µC/cm2, at least 109 cycles fatigue free and good 6-inch wafer uniformity. Good process reproducibility was also confirmed in terms of deposition rate, composition, and electrical properties through a 30-wafer nonstop sputtering test. These results indicate that the SBTN sputtering process is promising for ferroelectric memory production.

Dissociation Channels of c-C4F8 to CF2 Radical in Reactive Plasma

It has been generally assumed that octafluorocyclobutane (c-C4F8) is mainly decomposed to CF2 via C2F4 in etching process plasma. However, the detailed mechanism for the dissociations is yet ambiguous. In this paper we have calculated the probable dissociation pathways by using ab initio molecular orbital method. The results show that c-C4F8 is dissociated via the first triplet excited state T1(3A2), the fourth triplet excited state T4(32E) and the fourth singlet excited state S4(12E). One of the degenerate excited states of T4 and S4 is constituted by antibonding combination of two π bonding orbital of C2F4. T1 state is constituted by antibonding combination of b1u antibonding σ orbital of C2F4. Therefore, in the case of the dissociation via S4 and T4 excited states c-C4F8 may dissociate to two C2F4, and in the case of the dissociation via T1 excited state c-C4F8 may dissociate to four CF2 radicals. It is also found that C3F5+ ion observed as the main peak in c-C4F8 process plasma is produced by electron collision with the slightly larger energy than the ionization threshold value. The main dissociation path of C2F4 is a vertical electron attachment. However, it is also found that dissociation pathways via 1B2g, 3B1u, and 3B2g excited states are very important and should not be ignored.