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With the aim of improving flash-memory retention characteristics, we investigated threshold voltage shift (AV,,,) due to charge detrap from tunnel oxide. Accordingly we propose new parameter that can reveal the main origin of detrap (hole/electron) and the detrap centroid. We found that the main origin of detrap changes from holes to electrons depending on the degree of tunnel-oxide degradation. Since the hole detrap increases V, of a programmed memory cell, this V,,, increase must be considered, especially when designing a multi-level flash memory.Introduction In a flash memory, the prograderase (PE) operation not only injectdejects charges in the floating.gate but also generates traps in the tunnel oxide that capture charges during P E operation. Since the captured charges are gradually detrapped during charge retention, the detrap shifts V,,, in a programmed memory cell and can cause retention error [2]. The retention error due to detrap must be considered especially when designing a multi-level flash memory, because the threshold voltage differences in a multi-level flash memory are narrower than conventional in a flash memory. So far, the detrap phenomenon has been mainly studied by analysis of detrap current (Jd) [3]. Consequently, Jd is known to be inversely proportional to the detrap period (t), and this dependence can be explained by a tunneling-front (TF) model [4]. However, the mechanism by which V, changes (AV,) due to charge detrap is not yet fully understood. In this study, we thus analyzed AV,,, by comparing AV, and Jd, and we propose a new parameter that is useful for analyzing detrap phenomenon. We consequently found that the sign of AV,,, can be negative as well as positive, depending on the degree of tunnel-oxide degradation.Since the programmed Vth has one level in a conventional flash memory, only V, decrease should be considered for analyzing retention characteristics. However, the V,,, increase must be

Change in the cross-sectional profile of a photoresist (PR) pattern due to shrinkage was evaluated to investigate the mechanism of electron beam-induced shrinkage. A scanning transmission electron microscope (STEM) was used to observe the cross-sectional profiles of PR lines after atomic-layer deposition of metal oxide and carbon deposition on the sample surface. A HfO 2 thin layer enhanced the profile contrast in the STEM measurements without blurring the edge, which enabled the precise cross-sectional measurement of the PR patterns. We found interesting features associated with shrinkage from the detailed profile change obtained using this method, such as a rounding of the pattern top, a necking of the sidewall profile, a rounding of the foot in the pattern on the organic underlying layer, and voltage-independent sidewall shrinkage under a large electron beam dose. These behaviors along with the results from a Monte Carlo simulation are discussed. Consequently, these observations experimentally clarified that the elastic deformation effect and the impact of the secondary electrons emitted from the spaces around the pattern into the sidewall are important to interpret the change in the shape of the pattern induced by shrinkage.

A basic process to fabricate Ru/rutile-Co-doped TiO 2 /Ru capacitors for 20 nm-technology generation of DRAMs and beyond was developed. The aim of this study is that the basic process provides foresights into EOT and leakage-current density requirements. We chose rutile-TiO 2 for the insulators to meet the requirement of relative permittivity and Ru to suppress leakage-current density. We found the as-deposited lower electrode of Ru crystallized into the rutile phase of TiO 2 with a relative permittivity of 109 due to the similarity of crystal structures and lattice constants between rutile-TiO 2 and rutile-RuO 2 , which was generated by oxidizing Ru with ambient oxygen. Furthermore, we confirmed that doping elements that had a small-ionic radius, such as Co, decreased leakage-current density. The dependence of the leakage current of Ru/Co-doped-TiO 2 /Ru capacitors on temperature and analysis of the band structure with X-ray photoelectron spectroscopy revealed that leakage-current density is determined by a balance between thermionic current and tunneling current through the Schottky barrier. Through calculations using a theoretical equation for these currents, the optimum percentage of Co was estimated to range from 0.3-0.6 % to meet requirement of leakage current for 20 nmDRAMs. The major requirements of memory-cell capacitors for dynamic random access memories (DRAMs) have been set for equivalent oxide thickness (EOT) and leakage-current density. Capacitors need capacitance of 25fF regardless of what generation they are to avoid reading error.1 Less EOT is necessary to maintain capacitance with shrunken memory-cell areas. Twenty-nanometer DRAMs require capacitors with EOTs of less than 0.45 nm.1 Therefore, the permittivity of insulators must be larger than 60 assuming their physical thickness is 7 nm.1 The leakage-current density, on the other hand, needs to be less than 10 −7 A/cm 2 regardless of the generation when 1 V is applied between electrodes.1 This requirement is to maintain a refresh time as long as 64 ms.Major candidates for insulators fulfilling target permittivity are rutile-TiO 2 and perovskite-SrTiO 3 .1 We face difficulties with deposition despite the potential large permittivity of SrTiO 3 . Atomic layer deposition (ALD) is necessary to fabricate DRAM capacitors due to their high conformity and ability to control thickness. Although their precursors needs vapor pressures of more than 100 Torr at deposition temperatures around 200-400• C, the vapor pressures of strontium such as Sr(thd) 2 are insufficient being less than 1 Torr.2 Therefore, it is still difficult to commercialize SrTiO 3 . However, there are precursors of TiO 2 such as titanium tetraisopropoxide (TTIP) that have vapor pressures higher than that of strontium. Thus, TiO 2 is the most likely material for the capacitor insulators of 20 nm-technology generation of DRAMs and beyond.Insulators with large permittivity tend to have smaller band gaps. 3 The candidate material for electrodes should have a large work function, which is kn...