Seigo Takashima

Plasma damage mechanisms for low-k porous SiOCH films due to radiation, radicals, and ions in the plasma etching process

Low dielectric constant (low-k) films have been widely used as insulating materials in ultra-large-scale integrated circuits. Low-k films receive heavy damage during the plasma processes of etching or ashing, resulting in an increase in their dielectric constant. In order to realize damage-free plasma processes for low-k films, it is essential to determine the influence of radiation, radicals, and ions emitted in the plasma process on the characteristics of low-k films. We have developed a technique to evaluate the influence of radiation, radicals, ions, and their synergies on films in real plasma processes and have named it pallet for plasma evaluation (PAPE). Using the PAPE, plasma-induced damage on porous SiOCH films were investigated in dual-frequency capacitively coupled H2∕N2 plasmas. The damage was characterized by ellipsometry, Fourier-transform infrared spectroscopy, and thermal desorption spectroscopy. On the basis of the results, the damage mechanisms associated with vacuum ultraviolet (VUV) and UV radiation, radicals, and ions were clarified. The damage was caused not only by ions and radicals but also by VUV and UV radiation emitted by the plasmas. Moreover, it was found that the synergy between the radiation and the radicals enhanced the damage.Low dielectric constant (low-k) films have been widely used as insulating materials in ultra-large-scale integrated circuits. Low-k films receive heavy damage during the plasma processes of etching or ashing, resulting in an increase in their dielectric constant. In order to realize damage-free plasma processes for low-k films, it is essential to determine the influence of radiation, radicals, and ions emitted in the plasma process on the characteristics of low-k films. We have developed a technique to evaluate the influence of radiation, radicals, ions, and their synergies on films in real plasma processes and have named it pallet for plasma evaluation (PAPE). Using the PAPE, plasma-induced damage on porous SiOCH films were investigated in dual-frequency capacitively coupled H2∕N2 plasmas. The damage was characterized by ellipsometry, Fourier-transform infrared spectroscopy, and thermal desorption spectroscopy. On the basis of the results, the damage mechanisms associated with vacuum ultraviolet (VUV) an...

Development of measurement technique for carbon atoms employing vacuum ultraviolet absorption spectroscopy with a microdischarge hollow-cathode lamp and its application to diagnostics of nanographene sheet material formation plasmas

This study describes the development of a compact measurement technique for absolute carbon (C) atom density in processing plasmas, using vacuum ultraviolet absorption spectroscopy (VUVAS) employing a high-pressure CO2 microdischarge hollow-cathode lamp (C-MHCL) as the light source. The characteristics of the C-MHCL as a resonance line source of C atoms at 165.7 nm for VUVAS measurements of the absolute C atom density are reported. The emission line profile of the C-MHCL under typical operating conditions was estimated to be the Voigt profile with a ΔνL/ΔνD value of 2.5, where ΔνL is the Lorentz width and ΔνD is the Doppler width. In order to investigate the behavior of C and H atoms in the processing plasma used for the fabrication of two-dimensional nanographene sheet material, measurements of the atom densities were carried out using the VUVAS technique. The H atom density increased with increasing pressure, while the C atom density was almost constant at 5×1012 cm−3. The density ratio of C to H atoms ...

Development of atomic radical monitoring probe and its application to spatial distribution measurements of H and O atomic radical densities in radical-based plasma processing

Atomic radicals such as hydrogen (H) and oxygen (O) play important roles in process plasmas. In a previous study, we developed a system for measuring the absolute density of H, O, nitrogen, and carbon atoms in plasmas using vacuum ultraviolet absorption spectroscopy (VUVAS) with a compact light source using an atmospheric pressure microplasma [microdischarge hollow cathode lamp (MHCL)]. In this study, we developed a monitoring probe for atomic radicals employing the VUVAS with the MHCL. The probe size was 2.7 mm in diameter. Using this probe, only a single port needs to be accessed for radical density measurements. We successfully measured the spatial distribution of the absolute densities of H and O atomic radicals in a radical-based plasma processing system by moving the probe along the radial direction of the chamber. This probe allows convenient analysis of atomic radical densities to be carried out for any type of process plasma at any time. We refer to this probe as a ubiquitous monitoring probe for atomic radicals.

Mechanism of plasma-induced damage to low-k SiOCH films during plasma ashing of organic resists

Plasma-induced damage to porous SiOCH (p-SiOCH) films during organic resist film ashing using dual-frequency capacitively coupled O2 plasmas was investigated using the pallet for plasma evaluation method developed by our group. The damage was characterized by ellipsometry and Fourier-transform infrared spectroscopy. Individual and synergetic damage associated with vacuum ultraviolet (VUV) and UV radiation, radicals, and ions in the O2 plasma were clarified. It was found that the damage was caused not only by radicals but also by synergetic reactions of radicals with VUV and UV radiation emitted by the plasmas. It is noteworthy that the damage induced by plasma exposure without ion bombardment was larger than the damage with ion bombardment. These results differed from those obtained using an H2/N2 plasma for resist ashing. Finally, the mechanism of damage to p-SiOCH caused by O2 and H2/N2 plasma ashing of organic resist films is discussed. These results are very important in understanding the mechanism of...

Evaluation of Property Changes due to Radiation, Radicals, and Ions on Organic Low-k Films in H2/N2 Plasma Etching

An organic low-dielectric constant (low-k) film, polyallylene (PAr), is a prospective candidate for low-k interlayer films for ultra large-scale integrated circuits (ULSIs). PAr films are caused the property changes such as increases of the dielectric constant during plasma etching and ashing. In a previous study, we have developed a novel technique called pallet for plasma evaluation (PAPE) for separately evaluating the property changes caused by radiation, radicals, and ions in process plasmas and clarified the mechanism of plasma-induced property changes on low-k porous SiOCH films. In this study, using the PAPE technique, we investigated the changes on the surface of a PAr film due to radiation, radicals, radiation with radicals, and ions in dual-frequency capacitively coupled H2/N2 plasmas. The property changes were characterized by ellipsometry and X-ray photoelectron spectroscopy. The property changes on the PAr films due to radiation and radicals were considerably smaller compared to those on the low-k porous SiOCH films.

Direct current superposed dual-frequency capacitively coupled plasmas in selective etching of SiOCH over SiC

Superpositioning of negative dc bias in dual-frequency capacitively coupled plasmas (dc-superposed (DS)-CCP) was realized for the selective etching of carbon-doped silicon oxide (SiOCH) films over carbon-doped amorphous silicon (SiC) films, while the dc bias exceeded about ?800?V. When a dc bias of ?1200?V was superposed on 60?MHz VHF power on the top electrode opposed to a wafer on the bottom electrode biased with 13.56?MHz power, a selectivity of above 50 for SiOCH over SiC was obtained. From characterization of the plasma density and various chemical species in the gaseous phase, such as CF2, CF and atomic N, the density of CF2 significantly decreased with the application of dc bias ranging from ?800 to ?1200?V. This indicated that CF2 radicals were consumed at the surface of the counter electrode which was made of silicon. The bulk densities of the species including CF2 were decreased, especially due to excess surface loss caused by the bombardment of highly energetic ions accelerated by the superposed dc bias, as well as the rf sheath for the superposition of the negative dc bias. The DS-CCP technology is thus concluded to be indispensable for yielding highly selective etching of SiOCH over SiC.

Surface loss probabilities of H and N radicals on different materials in afterglow plasmas employing H2 and N2 mixture gases

Surface loss probabilities of hydrogen (H) and nitrogen (N) radicals on different wall materials in H2/N2 mixture plasmas have been investigated by employing vacuum ultraviolet (VUV) absorption spectroscopy with a high pressure microdischarge hollow cathode lamp as a light source. The surface loss probability of a radical was calculated by using the lifetime obtained from the decay curve of the radical density in afterglow plasmas. The surface loss probabilities on different walls in the H2/N2 mixture plasmas were higher than those in a pure H2 or N2 plasma. The behaviors of species such as ions and VUV photons as a function of the gas mixture ratio were measured to investigate those influences on plasma-surface interactions. In addition, changes on the surface exposed to the plasma were analyzed by x-ray photoelectron spectroscopy. Quantitative measurements of surface loss probabilities of radicals on various wall materials are expected to be crucially important in achieving good understanding of the int...

Surface reactions during low-k etching using H2∕N2 plasma

We investigated the relationship between the hard mask faceting that occurs during organic low-k etching and the ion energy distribution function of a capacitively coupled plasma reactor. We minimized the hard mask faceting by precisely controlling the ion energy. This precise control was obtained by selecting the optimum bottom frequency and bias power. We measured the amount of damage done to a SiOCH film exposed to H2∕N2 plasma in order to find the H2∕N2 ratio at which the plasma caused the least damage. The amount of moisture uptake by the damaged SiOCH film is the dominant factor controlling the dielectric constant increase (Δk). To suppress Δk, the incident ion species and ion energies have to be precisely controlled. This reduces the number of adsorption sites in the bulk SiOCH and maintains the hydrophobic surface that suppresses water permeation during air exposure.

Simultaneous monitoring of multimetallic atom densities in plasma processes employing a multimicrohollow cathode lamp

The authors have developed a simultaneous measurement technique of multimetallic atom densities in process plasmas using absorption spectroscopy employing a multimicrohollow cathode plasma as a light source. The optical emissions of four metallic atoms of Cu, Zn, Fe, and Mo were simultaneously produced from the multimicrohollow cathode plasma of millimeter size. The absolute densities of Cu and Mo in the magnetron sputtering plasma were simultaneously measured using this technique. The simultaneous monitoring of multimetallic atoms is very useful for controlling the plasma processes precisely.

Preparation of Aqueous Dispersion of Titanium Dioxide Nanoparticles using Plasma on Liquid Surface

A method for preparing an aqueous dispersion of titanium dioxide (TiO2) nanoparticles by generating plasma on the liquid surface was developed. The plasma was generated between the tip of a needle electrode in the gas phase and the liquid surface. A 0.01 wt % aqueous dispersion of TiO2 was prepared by plasma treatment with ultrasonication. Dynamic light scattering measurements indicated that the average TiO2 nanoparticle sizes in the dispersions with plasma treatment in air and Ar atmosphere were approximately 150 and 180 nm, respectively. Although the pH of the dispersion prepared by Ar plasma treatment was fairly close to the isoelectric point of TiO2, the dispersion maintained a finely dispersed state. The surface potentials of TiO2 nanoparticles in the dispersions treated with plasma were confirmed to be positively charged. This suggests that the dispersions formed by plasma treatment were stabilized by electrostatic repulsion between the particles.