Tokuhisa Ohiwa

SiO2 Tapered Etching Employing Magnetron Discharge of Fluorocarbon Gas

SiO2 tapered etching has been studied with special emphasis on the substrate temperature. A tapered etching profile was formed accompanying a polymer deposition on the side wall, and a high etching rate was obtained by lowering the substrate temperature. The polymer film deposited on the side wall was easily removed together with photoresist by O2 plasma ashing to yield a very smooth side wall in the via hole without any residual films. Experiments on polymer deposition revealed that the polymerization at as low a temperature as -70°C gives a fluorine-rich polymer film with poor durability in a plasma environment, and the etchants for SiO2 are released by ion bombardments at the interface between the polymer and the underlying SiO2 to enhance SiO2 etching.

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.

Sub-45nm resist process using stacked-mask process

The stacked-mask process (S-MAP) is a tri-level resist process by lithography and dry etching, which consists of thin resist, spin-on-glass (SOG), and spun-on carbon (SOC). However, as design rules progress below 60nm, two problems arise in the conventional S-MAP: 1) the deformation of SOC line pattern during SiO2 reactive ion etching (RIE), 2) the degradation of lithography performance due to high reflectivity at the interface between resist and SOG in high NA. In this study, we clarified the origin of the above problems and improved S-MAP materials and processes. Firstly, we found that the pattern deformation is induced by the inner stress due to volume expansion by fluorination during RIE, and that the deformation is suppressed by decreasing hydrogen content of SOC. Secondly, we developed new carbon-containing SOG that coexists with low reflectivity and acceptable etching performance. Using the above SOG and SOC, we developed a new S-MAP that shows an excellent lithography / etching performance in sub-45nm device fabrication.

Application of polysilanes for deep-UV antireflective coating

Application of polysilanes for a deep UV (DUV) bottom anti- reflective coating (BARC), in order to resolve the problem posed by the insufficient anti-reflection with thin conventional organic BARC applied on transparent dielectric film, is described. The newly developed polysilane anti- reflective coating has the real part of refractive index, n equals 2.00, and the imaginary part, k equals 0.23 at 248 nm. The polysilane coating is immiscible with a chemically amplified photoresist, and is not removable during normal wet development of photoresist. Etching rate of the polysilane is 2 times faster than that of DUV resist during BARC etching, and lower than that of DUV resist during dielectric film etching. The polysilane layer is easily removed by ashing using O2 gas process. Using thick polysilane coating, it can realize both the suppression of the interface reflection between the resist and BARC and good critical dimension control on dielectric film.

Resist and Sidewall Film Removal after Al Reactive Ion Etching (RIE) Employing F+H2O Downstream Ashing

The sidewall residue seen after Al etching and via-hole etching on an Al pattern was investigated. X-ray photo-electron spectroscopy (XPS) after O2 plasma ashing revealed that this sidewall residue contained a large number of Al atoms sputtered from the Al film surface. A downstream ashing technique employing F atoms and water vapor has already been developed to remove the persistent resist after plasma processing or ion implantation, but even this downstream ashing could not remove the sidewall residue containing Al. It has been found that the downstream process changed Al and Al oxide in the residue to Al fluoride, a water-soluble compound. Thus, rinsing with DI water successfully removed the sidewall residue after downstream ashing.

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.