Itsuko Sakai

Sub-55 nm Etch Process Using Stacked-Mask Process

Using a stacked mask process (S-MAP) with spun-on carbon (SOC) film, 56 nm line and space patterns of SiO2 were successfully etched. It was found that deformation of the SOC line pattern which occurred at line dimensions under 60 nm during SiO2 reactive ion etching (RIE) using fluorocarbon gas, originates from fluorination of the SOC film. By decreasing the hydrogen content of the SOC film, this cause of line pattern deformation was suppressed effectively.

Mechanism of Etch Stop in High Aspect-Ratio Contact Hole Etching

The mechanism of etch stop in contact hole etching has been studied. It was found that in high aspect ratio holes, even though the incident ions lose charge due to collision with the sidewall, they are able to bombard the bottom of the hole maintaining their high energy. It was also confirmed that the redeposition of sputtered species from the fluorocarbon polymer on the hole sidewall induces the etch stop at the bottom of the high-aspect hole. Furthermore, it was observed that etch stop occurs at higher aspect ratios for the same hole diameter in oxide films with higher boron and phosphorous dopant concentrations. This is explained by the effective removal of etch-inhibiting carbon species due to the release of more oxygen at a higher etch rate in highly doped oxide film. In conclusion, the etch stop in a high-aspect-ratio hole is determined by the balance between the effects of high-energy-species bombardment and etch inhibition of carbon species.

Chemical bond modification in porous SiOCH films by H2 and H2/N2 plasmas investigated by in situ infrared reflection absorption spectroscopy

The modification of porous low-dielectric (low-k) SiOCH films by ashing plasma irradiation and subsequent exposure to air was investigated by in situ characterizations. Porous blanket SiOCH film surfaces were treated by a H2 or H2/N2 plasma in a 100-MHz capacitively coupled plasma reactor. The individual or combined effects of light, radicals, and ions generated by the plasmas on the chemical bonds in the porous SiOCH films were characterized using an in situ evaluation and by in situ Fourier-transform infrared reflection absorption spectroscopy (IR-RAS). In situ IR-RAS analysis revealed that the number of Si-OH, Si-H, and Si-NH2 bonds increased while the number of Si-CH3 bonds decreased during exposure to a H2 or H2/N2 plasma. Subsequent air exposure increased the number of Si-OH bonds by modifying Si-O-Si structures. The experimental results indicate that light emitted from a H2 or H2/N2 plasma can break Si-CH3 and Si-O-Si bonds and thereby generate dangling bonds. Radicals (e.g., NxHy and H radicals) c...

H2/N2 plasma damage on porous dielectric SiOCH film evaluated by in situ film characterization and plasma diagnostics

This study investigates the mechanism of H2/N2 plasma ashing damage of porous SiOCH films. Porous SiOCH films were treated by a H2/N2 plasma using a 100-MHz capacitively coupled plasma etcher. The impact of ions, radicals, and vacuum ultraviolet radiation on the porous SiOCH films was investigated using in situ bulk analysis techniques such as spectroscopic ellipsometry and Fourier-transform infrared spectroscopy and ex situ film characterization techniques such as dynamic secondary ion mass spectrometry and x-ray photoelectron spectroscopy. In addition, plasma analysis including vacuum ultraviolet absorption spectroscopy was performed. The film characterization and plasma analysis show that the extraction of methyl by H radicals was enhanced by light while N radicals were responsible for inhibit the extraction of Si-CH3 bonds by forming nitride layer. The H2/N2 plasma damage mechanism is discussed based on characterization of the film and plasma diagnostics.

Sub-45 nm SiO2 Etching with Stacked-Mask Process Using High-Bias-Frequency Dual-Frequency-Superimposed RF Capacitively Coupled Plasma

By using a stacked mask process (S-MAP) with spun-on-carbon (SOC) film, 38 nm line patterns were successfully etched by controlling the ion energy using high-bias-frequency dual-frequency-superimposed (DFS) rf capacitively coupled plasma in combination with the low hydrogen content SOC film. It was found that ions with higher energy enhance the fluorination of SOC and induce pattern wiggling under fluorine exposure. By using a higher bias frequency to control the ion energy distribution and reduce the maximum ion energy, the SOC pattern wiggling was effectively suppressed.

Dual-Frequency Superimposed RF Capacitive-Coupled Plasma Etch Process

A dual-frequency superimposed (DFS) 100 MHz and 3.2 MHz rf capacitive-coupled plasma etch process for sub-90 nm devices has been developed. The electron density of DFS reactive ion etching (RIE) plasma at 40 mTorr was controlled from 4.0×1010 to 3.6×1011 cm-3 by adjusting the 100 MHz rf power, and the self-bias voltage (-Vdc) was controlled from 20 to 760 V by adjusting the superimposed 3.2 MHz rf power. DFS RIE demonstrated independent control of electron density and self-bias voltage in a wide range. In the damascene etch process of SiOC film using Si3N4 as an etch mask, it was found that mask edge erosion is dependent on ion energy regardless of the selectivity of SiOC to Si3N4. DFS RIE offers the most suitable process for damascene etching of SiOC, which requires precise ion energy control.

Highly selective etch gas chemistry design for precise DSAL dry development process

Dry development process for directed-self assembly lithography (DSAL) hole shrink process has been studied with focus on etch selectivity of poly(methyl methacrylate) (PMMA) to polystyrene (PS) and suppression of etch stop. Highly selective etch of PMMA to PS was achieved using CO gas chemistry. However, it was found that PMMA etching stopped proceeding beyond a certain depth. Scanning Transmission Electron Microscopy (STEM) and X-ray Photoelectron Spectroscopy (XPS) analysis indicated that a deposition layer formed not only on PS but also on PMMA. H2 addition to CO plasma proved effective in controlling the deposition layer thickness and suppressing etch stop. CO/H2 plasma process combined with ion energy control was applied to the dry development process for hole shrink. DSAL dry development process for hole shrink process was successfully realized by designing the etch gas chemistry and controlling ion energy.

Selective etch of poly(methyl methacrylate) in block copolymer based on control of ion energy and design of gas chemistry for directed self assembly lithography

The selective etching of poly(methyl methacrylate) (PMMA) in a block copolymer was studied with a focus on the material structures of polystyrene (PS) and PMMA. Based on our predictions, we investigated the effect of ion bombardment and designed a carbon-containing gas plasma to improve selectivity. The etching characteristics of the carbon-containing gas plasma on the polymers were examined. Highly selective etching of PMMA to PS was achieved using the carbon-containing gas plasma. The carbon species in the plasma increased with increasing carbon-containing gas ratio and suppressed the PS etch rate drastically. The CO plasma process was successfully applied to a dry development process for directed-self assembly lithography.

High rate deep Si etching for through-silicon via applications

High rate deep Si etching for through-silicon via (TSV) applications is reported. The requirements for the Si etch process is discussed from the viewpoint of TSV size and productivity, and the effective processes are described. For “small” TSV a few microns in diameter and up to 10 μm deep, profile control is the most important requirement, For “large” TSV with diameters of more than 50 μm and depths up to 100 μm and more, an ultrahigh Si etch rate is indispensable. The “medium” TSV with diameters and depths several tens of microns requires both high etch rate and profile control. Capacitively coupled plasma MERIE at high pressure is shown to be effective, by using HBr gas chemistry for small TSV, and by using SF6 gas chemistry and high rf frequency for large and medium TSV where an extremely high etch rate can be obtained.

Organic Film Reactive Ion Etching Using 100 MHz rf Capacitive Coupled Plasma

A new reactive ion etching (RIE) process using a 100 MHz rf capacitive coupled plasma (CCP), where the wafer is placed on the cathode, has been studied. The electron densities obtained in the 100 MHz Ar plasma process were higher than those obtained in the 13.56 MHz Ar plasma process, and self-bias voltages (-Vdc) obtained in the 100 MHz plasma process were less than 1/3 of those obtained in the 13.56 MHz plasma process. The resist etch process in the 100 MHz plasma process using hydrogen-based gas chemistry showed high selectivity to SiO2 above 50. Also, the stacked mask process (S-MAP) in the 100 MHz plasma process showed a great improvement of the carbon film etch profile with less faceting of the spin-on-glass (SOG) mask, compared with that in the 13.56 MHz plasma process. Furthermore, the 100 MHz organic low-k film etch process using a SiO2 etch mask showed less erosion of the SiO2 mask edge and straight sidewall profile of the organic low-k film. The 100 MHz rf CCP process has a great advantage in organic film etching.