Makoto Sekine

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...

Analysis of GaN Damage Induced by Cl2/SiCl4/Ar Plasma

GaN-based optical devices are fabricated using a GaN/InGaN/GaN sandwiched structure. The effect of radicals, ions, and UV light on the GaN optical properties during Cl2/SiCl4/Ar plasma etching was evaluated using photoluminescence (PL) analysis. The samples were exposed to plasma (radicals, ions, and UV light) using an inductively coupled plasma (ICP) etching system and a plasma ion beam apparatus that can separate the effects of UV and ions both with and without covering the SiO2 window on the surface. Etching damage in an InGaN single quantum well (SQW) was formed by exposing the sample to plasma. The damage, which decreases PL emission intensity, was generated not only by ion beam irradiation but also by UV light irradiation. PL intensity decreased when the thickness of the upper GaN layer was etched to less than 60 nm. In addition, simultaneous irradiation of UV light and ions slightly increased the degree of damage. There seems to be a synergistic effect between the UV light and the ions. For high-quality GaN-based optoelectronics and power devices, UV light must be controlled during etching processes in addition to the etching profile, selectivity, and ion bombardment damage.

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.

Feature Profiles on Plasma Etch of Organic Films by a Temporal Control of Radical Densities and Real-Time Monitoring of Substrate Temperature

The precise etching of organic films with a low dielectric constant (low-k) in a dual-frequency capacitively coupled plasma etching reactor with a plasma generation of 100 MHz and an applied bias of 2 MHz employing a gas mixture of hydrogen and nitrogen was performed by real-time control of the densities of hydrogen (H) and nitrogen (N) radicals based on real-time measurement of the Si substrate temperature. H and N radical densities were monitored near the sidewall of the reactor by vacuum ultraviolet absorption spectroscopy, and temperature was monitored by an optical fiber-type low-coherence interferometer. On the basis of the results of surface analysis by X-ray photoelectron spectroscopy, etched profiles were effectively determined from the chemical component of protection layers on the sidewall of the etched pattern affected by the ratio of H/(H+N) and substrate temperature. As the etching feature evolves, the ratio of radical density should be controlled temporally to maintain vertical profiles according to the change in substrate temperature. As a result, we have successfully realized an organic film with a vertical feature. These results indicate the need for autonomous control of the etch process based on real-time information on the plasma process for the next-generation ultrafine etching.

Vacuum Ultraviolet and Ultraviolet Radiation-Induced Effect of Hydrogenated Silicon Nitride Etching: Surface Reaction Enhancement and Damage Generation

Photon-enhanced etching of SiNx:H films caused by the interaction between vacuum ultraviolet (VUV)/ultraviolet (UV) radiation and radicals in the fluorocarbon plasma was investigated by a technique with a novel sample setup of the pallet for plasma evaluation. The simultaneous injection of UV radiation and radicals causes a dramatic etch rate enhancement of SiNx:H films. Only UV radiation causes the film shrinkage of SiNx:H films owing to hydrogen desorption from the film. Capacitance–voltage characteristics of SiNx:H/Si substrates were studied before and after UV radiation. The interface trap density increased monotonically upon irradiating the UV photons with a wavelength of 248 nm. The estimated effective interface trap generation probability is 4.74 ×10-7 eV-1photon-1. Therefore, the monitoring of the VUV/UV spectra during plasma processing and the understanding of its impact on the surface reaction, film damage and electrical performance of underlying devices are indispensable to fabricate advanced devices.

Quantum Chemical Investigation for Chemical Dry Etching of SiO2 by Flowing NF3 into H2 Downflow Plasma

A quantum chemical investigation of the chemical dry etching of SiO2 using H2 downflow plasma with flowing NF3 was carried out using the B3LYP/6-31+G(d,p) method. The results provide a reasonable interpretation of how the chemical dry etching of SiO2 takes place in a down flow area. Experimentally, it was found that the etch rates of thermal silicon oxide film range from 1 to 10 nm/min depending on the etching conditions, and white powder was produced on the etched surface. It was deduced that the etchants were HF and NH3 produced by the reaction of H+ NF3, and that the white powder on the etched surface was produced by the decomposition of (NH4)2SiF6 formed on the etched surface. The calculated results support the HF and NH3 production mechanism and clarify the molecular structures of (NH4)2SiF6 and the white powder. Another important point in the chemical dry etching of SiO2 was the realization of a high etching selectivity to Si. As the F atom was deduced to be the main etchant of Si, its generation mechanism in H2 down flow plasma with the addition of NF3 was also studied and a method of suppressing F atom production was proposed in this research.

Quantum Chemical Investigation of Si Chemical Dry Etching by Flowing NF3 into N2 Downflow Plasma

A quantum chemical investigation of the chemical dry etching of N2 downflow plasma and NF3 flow into the downflow area was carried out by the B3LYP/6-31+G(d) method. The results provide a reasonable interpretation of how the chemical dry etching of Si takes place. Experimentally, it was reported that single-crystal silicon was etched in the N2 downflow plasma with NF3 flow and the etch rate depended on the etching conditions, and it had been deduced that the etchant was F atoms produced by the reaction of N*+ NF3. It was found through our calculations that there were three reaction routes of NF3 proceeding F production in the initial reaction step, with N(2Do) and N2(A3Σu+) and by electron attachment, and it is thought that the most probable F production reaction in the downflow area is N(2Do) + NF3→N=NF2+ F and the next probable reaction is N2(A3Σu+) + NF3(3E)→N2(1Σg+) + NF2+F.

Impacts of CF+, CF2+, CF3+, and Ar Ion Beam Bombardment with Energies of 100 and 400 eV on Surface Modification of Photoresist

Photoresists used in advanced ArF-excimer laser lithography are not tolerant enough for plasma etching processes. Degradation of photoresists during etching processes might cause not only low selectivity, but also line edge roughness (LER) on the sidewalls of etched patterns. For a highly accurate processing, it is necessary to understand the mechanisms of etching photoresists and to construct a new plasma chemistry that realizes a nano scale precise pattern definition. In this study, the modified layers formed on the surface of a photoresist by the bombardment of fluorocarbon ions of CF+, CF2+, and CF3+, and argon (Ar) ions were analyzed by X-ray photoelectron spectroscopy (XPS). The etching yield of the modified steady-state surface was almost dependent on the mass of incident ion species. The surface composition was modified with increasing dosage of each ion species, and reached a specific steady state that was dependent on the ion species. The bombardment of F-rich ion species such as CF2+ and CF3+ resulted in the formation of not only fluorocarbon layers, but also graphite like structures on the surface. On the basis of these results, the surface reaction for the ion-beam-induced modification was discussed.

Spatial Distributions of Electron, CF, and CF2 Radical Densities and Gas Temperature in DC-Superposed Dual-Frequency Capacitively Coupled Plasma Etch Reactor Employing Cyclic-C4F8/N2/Ar Gas

On a plasma etch reactor for a wafer of 300 mm in diameter, the spatial distributions of the absolute densities of CF and CF2 radicals, electron density (ne), and the gas temperature (Tg) of N2 were measured employing the dual frequency of negative dc voltage superposed to a very high frequency (VHF) of 60 MHz capacitively coupled plasma (DS-2f-CCP) with the cyclic- (c-)C4F8/Ar/N2 gas mixture. The dc bias was superposed on the upper electrode with a frequency of 60 MHz. The distributions of electron and radical densities were uniform within a diameter of about 260 mm, and took a monotonic decay in regions outside a diameter of 260 mm on the reactor for 300 mm wafers in the reactor. It was found that only CF2 density at the radial position between 150 and 180 mm, corresponding to the position of the Si focus ring, dropped, while CF density took a uniform distribution over a diameter of 260 mm. Additionally, at this position, the rotational temperature of N2 gas increased to be 100 K larger than that at the center position. CF2 radical density was markedly affected by the modified surface loss probability of the material owing to coupling with surface temperature.

Dissociation Channels of c-C4F8 to CF2 Radical in Reactive Plasma

It has been generally assumed that octafluorocyclobutane (c-C4F8) is mainly decomposed to CF2 via C2F4 in etching process plasma. However, the detailed mechanism for the dissociations is yet ambiguous. In this paper we have calculated the probable dissociation pathways by using ab initio molecular orbital method. The results show that c-C4F8 is dissociated via the first triplet excited state T1(3A2), the fourth triplet excited state T4(32E) and the fourth singlet excited state S4(12E). One of the degenerate excited states of T4 and S4 is constituted by antibonding combination of two π bonding orbital of C2F4. T1 state is constituted by antibonding combination of b1u antibonding σ orbital of C2F4. Therefore, in the case of the dissociation via S4 and T4 excited states c-C4F8 may dissociate to two C2F4, and in the case of the dissociation via T1 excited state c-C4F8 may dissociate to four CF2 radicals. It is also found that C3F5+ ion observed as the main peak in c-C4F8 process plasma is produced by electron collision with the slightly larger energy than the ionization threshold value. The main dissociation path of C2F4 is a vertical electron attachment. However, it is also found that dissociation pathways via 1B2g, 3B1u, and 3B2g excited states are very important and should not be ignored.