Thin silicon dioxide and nitrided oxide using rapid thermal processing for trench capacitors
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Electrical characteristics of trench capacitors using RTO (Rapid Thermal Oxidation) oxides, nitroxides, and reoxidized nitroxides as the gate insulators are discussed. High temperature RTO is effective in preventing oxide thinning at the trench corner, and so the dielectric strength of trench capacitors is improved drastically. The mean time to failure (MTTF) of trench capacitors using RTO is more than ten times longer than that of trench capacitors using conventional furnaces. Using reoxidized nitroxides as the gate insulator, superior charge to breakdown (
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INJECTED CHARGE=IC/cm2 -19
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IOOK TRENCHES AREA = 2mm2
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FURNACE RTO RTO/RTN RTO/RTN/RTO
Gate Area=0.13mm
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10"* 10"' 10° S T R E S S CURRENT DENSITY (A/cm2) FIG. 8. Electron trapping rate versus stress current density characteristics of trench capacitor.
troxide (RTO/RTN) films is caused by the nitrogen pileup at the surface of the film. The electron trapping rate of reoxidized nitroxide (RTO/RTN/RTO) films is significantly lower than that of nitroxide (RTO/RTN) films. The reduction of electron traps corresponds to the decrease of the nitrogen concentration at the surface of the film. F. Interface-state density To clarify the charge injection immunity of insulator films, the interface-state density was measured after the charge injection into the insulator films. After the initial interface-state density measurement, the charge injection (0.03-0.09 C/cm 2 ) by applying the positive bias to the gate electrode was carried out. We measured interface-state density at E — Ev — 0.8 eV, because the measurement at E — Ev — 0.8 eV is sensitive for charge injection. Figure 9 shows the interface-state density at E — Ev = 0.8 eV as a function of the injected charge for furnace controlled oxide, RTO oxide, nitroxide (RTO/RTN), and reoxidized nitroxide (RTO/RTN/RTO) films. After the charge injection the interface-state density at 0.8 eV was increased with increasing the charge injection. For RTO oxides, the increase of the interface-state density is smaller than that of furnace controlled oxides. However, for nitroxide (RTO/RTN) films, the interface-state density was increased significantly with increasing the charge injection. On the other hand, for reoxidized nitroxide films the increase of the interface-state density after the charge injection was suppressed compared with oxide and nitroxide films. For interface-state generation in thermal oxide (both furnace controlled and RTO), the mechanism was explained as the interactions of the hot carrier and weak bonds near the Si-SiO 2 interface. Two types of centroide as the origins of weak bonds have
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0.2 0.4 0.6 0.8 1.0 INJECTED CHARGE (C/cm2)
FIG. 9. Interface-state density at E - Ev — 0.8 eV as a function of injected charge.
been proposed. One is hydrogen-containing centroide and the other is strained S i - 0 bonds near the Si-SiO 2 interface. Hori et al. have reported that nitroxide films have a large amount of hydrogen in the film
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