Toshihisa Nozawa

Damage mechanism in low-dielectric (low-k) films during plasma processes

Plasma is extensively used for the etching/ashing of low-dielectric (low-k) films. However, since low-k films, such as SiOC films, are vulnerable to plasma irradiation, they are severely damaged during plasma processes, such as the extraction of methyl groups from low-k films. As a result, plasma irradiation increases the dielectric constant of low-k films and reduces the reliability of Cu/low-k interconnects. In previous work, the authors achieved highly selective and low-damage etching processes for low-k films by using their developed neutral beam process instead of the conventional plasma process. They have now investigated the damage mechanism in low-k films (porous SiOC films) during plasma processes by clarifying the effects of ions, radicals, and photons in plasma. First, they compared the damage in SiOC films etched by the conventional plasma process and the neutral beam process. Their results show that plasma processes change the structure of the SiOC film deeply within the film (over 100nm in d...

Conformal doping of topographic silicon structures using a radial line slot antenna plasma source

Fin extension doping for 10 nm front end of line technology requires ultra-shallow high dose conformal doping. In this paper, we demonstrate a new radial line slot antenna plasma source based doping process that meets these requirements. Critical to reaching true conformality while maintaining fin integrity is that the ion energy be low and controllable, while the dose absorption is self-limited. The saturated dopant later is rendered conformal by concurrent amorphization and dopant containing capping layer deposition followed by stabilization anneal. Dopant segregation assists in driving dopants from the capping layer into the sub silicon surface. Very high resolution transmission electron microscopy-Energy Dispersive X-ray spectroscopy, used to prove true conformality, was achieved. We demonstrate these results using an n-type arsenic based plasma doping process on 10 to 40 nm high aspect ratio fins structures. The results are discussed in terms of the different types of clusters that form during the pl...

A new metallic complex reaction etching for transition metals by a low-temperature neutral beam process

We investigated a new oxidation reaction at a low temperature (−30 °C) as a result of O2 neutral beam bombardment at a low activation energy (<0.025 eV), which can efficiently form a thin oxide film of all transition metals, such as tantalum, ruthenium and platinum. Meanwhile, a new neutral beam enhanced chemical etching for the neutral beam oxidized transition metals that uses a new metallic complex reaction process and does not cause chemical or physical damage at low temperatures was also proposed. As a result, a highly anisotropic etching profile without re-deposition on the sidewall could be achieved with just the pure chemical reaction between ethanol and metallic oxide at a low kinetic energy using the neutral beam process.

Non-porous ultra-low-k SiOCH (k = 2.3) for damage-free integration and Cu diffusion barrier

Pores in ultra-low-k carbon-doped silicon oxide (SiOCH) film have been a serious problem because they produce fragile film strength, with the film incurring damage from integration and diffusion of Cu atoms in thermal annealing. To address this problem, we developed a practical large-radius neutral-beam-enhanced chemical vapour deposition process to precisely control the film structure so as to eliminate any pores in the film. We used the process with dimethoxy-tetramethyl-disiloxane (DMOTMDS) as a precursor to form a SiOCH film on an 8 inch Si wafer and obtained a non-porous film having an ultra-low k-value of 2.3 with sufficient modulus (>10 GPa). Analysing the film structure by experimental and theoretical techniques showed that symmetric linear Si–O molecular chains were grown and cross-linked to each other in the film. This particular film did not incur any damage from acid or alkali solution or oxygen plasma. Furthermore, the dense film almost completely resisted Cu diffusion into it during thermal annealing.

Electrical Characteristics of Novel Non-porous Low-

A novel non-porous low-k dielectric, fluorocarbon, deposited by new microwave excited plasma enhanced chemical vapor deposition was successfully integrated into Cu damascene interconnects for the first time. Electrical characteristics of fluorocarbon/Cu damascene lines are investigated. A compatible line to line leakage current to the one with porous low-k carbon doped silicon oxide and a low effective dielectric constant as a value of 2.5 are achieved. The novel non-porous ultralow-k dielectric, fluorocarbon, is considered as a promising candidate to extendible for 22 nm generation and beyond.

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The plasma enhanced chemical vapor deposition (PECVD) of extremely high-quality SiO2 at low temperature below 400 °C has been developed using tetraethoxysilane (TEOS). Plasma of TEOS and Ar, O2 gases was generated by a microwave (2.45 GHz) radial-line-slot-antenna (RLSA) system. The RLSA Plasma is a sort of surface-wave-plasma (SWP) and it realizes lower electron temperature (Te) with higher electron density (Ne) at the wafer position compared with conventional PECVD reactors. The physical properties were examined by 5% HF wet etching rates and thermal desorption spectroscopy. It was confirmed that the RLSA TEOS film were much better than conventional PECVD films and a high temperature oxide (HTO) with 900 °C N2 anneal treatment. Electrical properties of dielectric leakage, breakdown and negative bias charge-to-breakdown (Qbd) test also performed. The RLSA TEOS films showed far better properties among the conventional films and in much the same quality as a wet-thermal oxide grown at 950 °C. It was considered that all these properties were owing to the RLSA plasmas uniqueness of lower plasma damage and oxidization efficiency for precursors.

Dielectric Fluorocarbon on Cu Interconnects for 22 nm Generation and Beyond

The mechanism of CO2 plasma ashing process was evaluated. CO2 plasma is a good candidate for the ashing process for photoresists because it generates a lot of CO2 ions. These ions can ash equivalent amounts of carbon film with less low-k damage than can oxygen radicals. A high ratio of CO2 ions to oxygen radicals in CO2 plasma can make the ashing process efficient with less low-k damage. The ratio can be controlled by changing the CO2 flow rate, chamber pressure, and radio frequency (RF). When a lower RF frequency of 2 MHz as a plasma generator was used, the authors reduced sidewall low-k damage in patterned structures. CO2 ions can perform anisotropic ashing because the velocity distribution of CO2 ions is directional due to acceleration with a plasma sheath.

High-Quality SiO2 Film Formation below 400 °C by Plasma Enhanced Chemical Vapor Deposition Using Tetraethoxysilane Source Gas

The authors developed a ceramic upper shower plate used in the microwave-excited high-density plasma process equipment incorporating a dual shower-plate structure to establish a very uniform gas-flow pattern in the process chamber. Thousands of very fine gas-injection holes are implemented on this Al2O3 upper shower plate with optimized allocation to establish a uniform gas-flow pattern of plasma-excitation gases and radical-generation gases for generating intended radicals in the plasma-excitation region. The size of these fine holes must be 50μm or less in diameter and 8mm or more in length because these holes perform an essential role: They completely avoid the plasma excitation in these fine holes and upper gas-supply regions resulting from the plasma penetration into these regions from excited high-density plasma, even if very high-density plasma greater than 1×1012cm−3 is excited just under the ceramic upper shower plate by microwaves supplied from the radial line slot antenna. On the other hand, va...

Characterization of CO2 plasma ashing for less low-dielectric-constant film damage

In recent ultra large-scale integration (ULSI), Cu wiring and low-k dielectrics are used to reduce resistive capacitive (RC) delay in interconnects. Cu diffusion barrier layers, such as SiC and SiCN, have relatively high k-values, thus they decrease effective k-values (keff) of dielectrics. For this issue, we propose a new amorphous hydrocarbon film (a-CHx) as a Cu barrier dielectric deposited using a microwave-excited plasma reactor with a showerhead. Low ion bombardments and optimum deposition gases gave an excellent film, which achieved low leakage current and thermal resistance simultaneously. This film showed Cu diffusion barrier ability at 350 °C and a lifetime of more than 10 years lifetime at 0.2 MV/cm, which is sufficient for next-generation interlayer dielectric films.

Establishment of very uniform gas-flow pattern in the process chamber for microwave-excited high-density plasma by ceramic shower plate

A new oxidation reaction at ultralow temperature (-30°C) by bombardment of O2 neutral beam can be enhanced at the extremely low activation energy, which can efficiently form a thin oxide film of all transition metal, such as platinum and ruthenium. Meanwhile, a novel neutral beam enhanced chemical etching for transition metals and magnetic materials was proposed without chemical and physical damages at ultralow temperature through Metallic Complex Reaction process. Highly anisotropic etching profile without both any sidewall re-deposition and damages on magnetic properties could be achieved just with a pure chemical reaction between ethanol and metallic oxide with low kinetic energy by neutral beam for the first time. This new etching technology has been considered as a breakthrough technology to develop next generation MRAM devices.