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Title: Effect of oxygen concentration on the spike formation during reactive ion etching of SiC using the mixed gas plasma of NF{sub 3} and O{sub 2}

Abstract

Reactive ion etching (RIE) of poly-{beta}-SiC was investigated in the NF{sub 3}/O{sub 2} mixture gas plasma. The addition of 10% oxygen concentration to the NF{sub 3} plasma increased the etching rate to {approx}80 nm/min at a total pressure of 10 Pa and 997 nm/min at a total pressure of 20 Pa. The ratio of increase in etching rate against that in the pure NF{sub 3} plasma was {approx}43%. RIE for longer than 30 min in the 90% NF{sub 3} and 10% O{sub 2} mixture gas plasma gave a much smoother surface than that etched in the pure NF{sub 3} plasma. However, the further addition of O{sub 2} decreased the etching rate. Optical-emission spectra indicated the presence of an oxygen radical, in addition to fluorine radical and molecular nitrogen cations, in the NF{sub 3}/O{sub 2} mixture gas plasma. X-ray photoemission spectroscopy analysis of the etched samples revealed that the SiO{sub 2} layer was formed on the surface at the higher O{sub 2} concentration. The role of oxygen in the NF{sub 3}/O{sub 2} mixture gas plasma was elucidated. Scanning electron microscopy observation revealed that many thornlike substances, i.e., spikes, were formed on the SiC surface during RIE at the total pressure ofmore » 10 Pa. Images of the cross section of spike formed during RIE at the total pressure of 2 Pa also indicated that the sputtered aluminum particle from a mask may be preferentially deposited on the top of carbon-rich island formed on the SiC surface and act as a micromask together with carbon on the carbon-rich island to form a thornlike spike. An etching model of the SiC surface and the mechanism on formation and growth of the spike on the SiC surface in the NF{sub 3}/O{sub 2} mixture gas plasma are proposed.« less

Authors:
; ; ; ; ; ; ; ; ;  [1];  [2];  [2];  [2];  [2];  [2]
  1. Department of Applied Chemistry, Graduate School of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321 (Japan) and Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20979399
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films; Journal Volume: 25; Journal Issue: 2; Other Information: DOI: 10.1116/1.2699473; (c) 2007 American Vacuum Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ALUMINIUM; CARBON; CATIONS; EMISSION SPECTRA; ETCHING; LAYERS; LUMINESCENCE; MIXTURES; NITROGEN FLUORIDES; OXYGEN; PLASMA; RADICALS; SCANNING ELECTRON MICROSCOPY; SEMICONDUCTOR MATERIALS; SILICA; SILICON CARBIDES; SILICON OXIDES; SURFACES; X-RAY PHOTOELECTRON SPECTROSCOPY

Citation Formats

Tasaka, A., Watanabe, E., Kai, T., Shimizu, W., Kanatani, T., Inaba, M., Tojo, T., Tanaka, M., Abe, T., Ogumi, Z., Department of Applied Chemistry, Graduate School of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321, Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321, Toyo Tanso Co., Ltd., 5-7-2 Takeshima, Nishi Yodogawa-ku, Osaka 555-0011, Sumitomo Osaka Cement Co., Ltd., 6-28 Rokubancho, Chiyoda-ku, Tokyo 102-8465, and Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510. Effect of oxygen concentration on the spike formation during reactive ion etching of SiC using the mixed gas plasma of NF{sub 3} and O{sub 2}. United States: N. p., 2007. Web. doi:10.1116/1.2699473.
Tasaka, A., Watanabe, E., Kai, T., Shimizu, W., Kanatani, T., Inaba, M., Tojo, T., Tanaka, M., Abe, T., Ogumi, Z., Department of Applied Chemistry, Graduate School of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321, Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321, Toyo Tanso Co., Ltd., 5-7-2 Takeshima, Nishi Yodogawa-ku, Osaka 555-0011, Sumitomo Osaka Cement Co., Ltd., 6-28 Rokubancho, Chiyoda-ku, Tokyo 102-8465, & Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510. Effect of oxygen concentration on the spike formation during reactive ion etching of SiC using the mixed gas plasma of NF{sub 3} and O{sub 2}. United States. doi:10.1116/1.2699473.
Tasaka, A., Watanabe, E., Kai, T., Shimizu, W., Kanatani, T., Inaba, M., Tojo, T., Tanaka, M., Abe, T., Ogumi, Z., Department of Applied Chemistry, Graduate School of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321, Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321, Toyo Tanso Co., Ltd., 5-7-2 Takeshima, Nishi Yodogawa-ku, Osaka 555-0011, Sumitomo Osaka Cement Co., Ltd., 6-28 Rokubancho, Chiyoda-ku, Tokyo 102-8465, and Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510. Thu . "Effect of oxygen concentration on the spike formation during reactive ion etching of SiC using the mixed gas plasma of NF{sub 3} and O{sub 2}". United States. doi:10.1116/1.2699473.
@article{osti_20979399,
title = {Effect of oxygen concentration on the spike formation during reactive ion etching of SiC using the mixed gas plasma of NF{sub 3} and O{sub 2}},
author = {Tasaka, A. and Watanabe, E. and Kai, T. and Shimizu, W. and Kanatani, T. and Inaba, M. and Tojo, T. and Tanaka, M. and Abe, T. and Ogumi, Z. and Department of Applied Chemistry, Graduate School of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321 and Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, 1-3 Miyako-dani, Tadara, Kyotanabe, Kyoto 610-0321 and Toyo Tanso Co., Ltd., 5-7-2 Takeshima, Nishi Yodogawa-ku, Osaka 555-0011 and Sumitomo Osaka Cement Co., Ltd., 6-28 Rokubancho, Chiyoda-ku, Tokyo 102-8465 and Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510},
abstractNote = {Reactive ion etching (RIE) of poly-{beta}-SiC was investigated in the NF{sub 3}/O{sub 2} mixture gas plasma. The addition of 10% oxygen concentration to the NF{sub 3} plasma increased the etching rate to {approx}80 nm/min at a total pressure of 10 Pa and 997 nm/min at a total pressure of 20 Pa. The ratio of increase in etching rate against that in the pure NF{sub 3} plasma was {approx}43%. RIE for longer than 30 min in the 90% NF{sub 3} and 10% O{sub 2} mixture gas plasma gave a much smoother surface than that etched in the pure NF{sub 3} plasma. However, the further addition of O{sub 2} decreased the etching rate. Optical-emission spectra indicated the presence of an oxygen radical, in addition to fluorine radical and molecular nitrogen cations, in the NF{sub 3}/O{sub 2} mixture gas plasma. X-ray photoemission spectroscopy analysis of the etched samples revealed that the SiO{sub 2} layer was formed on the surface at the higher O{sub 2} concentration. The role of oxygen in the NF{sub 3}/O{sub 2} mixture gas plasma was elucidated. Scanning electron microscopy observation revealed that many thornlike substances, i.e., spikes, were formed on the SiC surface during RIE at the total pressure of 10 Pa. Images of the cross section of spike formed during RIE at the total pressure of 2 Pa also indicated that the sputtered aluminum particle from a mask may be preferentially deposited on the top of carbon-rich island formed on the SiC surface and act as a micromask together with carbon on the carbon-rich island to form a thornlike spike. An etching model of the SiC surface and the mechanism on formation and growth of the spike on the SiC surface in the NF{sub 3}/O{sub 2} mixture gas plasma are proposed.},
doi = {10.1116/1.2699473},
journal = {Journal of Vacuum Science and Technology. A, International Journal Devoted to Vacuum, Surfaces, and Films},
number = 2,
volume = 25,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • In this paper, the authors performed a reactive ion etch of a 4H-SiC substrate with a gas mixture of NF{sub 3}, HBr, and O{sub 2}, resulting in a microtrenching-free etch. The etch rate was 107.8 nm/min, and the selectivity over the oxide hard mask was ∼3.85. Cross-sectional scanning electron microscopy showed no microtrenching compared with etches using plasmas of NF{sub 3}, NF{sub 3}/HBr, and NF{sub 3}/O{sub 2}. Analyzing a variety of HBr/O{sub 2} mixing ratios, the authors discuss the additive effect of each gas and their respective potential mechanisms for alleviating microtrenching. To increase the radius of gyration of the bottommore » corners, they introduced a second etch step with Cl{sub 2}/O{sub 2} plasma. Fabricating simple metal-oxide-semiconductor capacitors on the two-step etched surface, the authors found that the electrical characteristics of the etched sample were nearly the same as the nonetched sample.« less
  • In pure NF{sub 3} plasma, the etching rates of four kinds of single-crystalline SiC wafer etched at NF{sub 3} pressure of 2 Pa were the highest and it decreased with an increase in NF{sub 3} pressure. On the other hand, they increased with an increase in radio frequency (RF) power and were the highest at RF power of 200 W. A smooth surface was obtained on the single-crystalline 4H-SiC after reactive ion etching at NF{sub 3}/Ar gas pressure of 2 Pa and addition of Ar to NF{sub 3} plasma increased the smoothness of SiC surface. Scanning electron microscopy observation revealed that the numbermore » of pillars decreased with an increase in the Ar-concentration in the NF{sub 3}/Ar mixture gas. The roughness factor (R{sub a}) values were decreased from 51.5 nm to 25.5 nm for the As-cut SiC, from 0.25 nm to 0.20 nm for the Epi-SiC, from 5.0 nm to 0.7 nm for the Si-face mirror-polished SiC, and from 0.20 nm to 0.16 nm for the C-face mirror-polished SiC by adding 60% Ar to the NF{sub 3} gas. Both the R{sub a} values of the Epi- and the C-face mirror-polished wafer surfaces etched using the NF{sub 3}/Ar (40:60) plasma were similar to that treated with mirror polishing, so-called the Catalyst-Referred Etching (CARE) method, with which the lowest roughness of surface was obtained among the chemical mirror polishing methods. Etching duration for smoothing the single-crystalline SiC surface using its treatment was one third of that with the CARE method.« less
  • Polycrystalline {beta}-SiC and single-crystalline 4H-SiC surfaces were etched by reactive ion etching (RIE) using NF{sub 3} gas plasma. A smooth surface was obtained on the polycrystalline SiC after RIE at NF{sub 3} gas pressures of 2 and 10 Pa for 10 min, and neither spikes nor pillars were formed on it. On the other hand, some pillars were formed on the single-crystalline SiC surface by RIE at NF{sub 3} gas pressures of 2 and 10 Pa. Though the absence of carbon-rich regions and SiO{sub x} on the outermost surface before etching was confirmed by x-ray photoelectron spectroscopy and Raman analysis,more » x-ray diffraction analysis revealed that graphite crystallites were present in the single-crystalline SiC bulk. It was concluded that the graphite crystallites acted as masks and the pillars grew up from the graphite crystallites in the single crystalline SiC during RIE.« less
  • Ions and neutrals sampled from a NF/sub 3//O/sub 2/ etching plasma were observed by a quadrupole mass spectrometer and cylindrical mirror ion energy analyzer to investigate ion-bombardment-enhanced etching of tungsten. Dc biasing of a 13.56 MHz, 2.7 Pa, 1.24 W/cm/sup 2/ , 3/1 NF/sub 3//O/sub 2/ glow discharge raised the average ion energy bombarding the grounded electrode from 35 to 172 eV concurrent with an increase in the ion current by a factor of 3. Total conversion of NF/sub 3/ to N/sub 2/ and F/sub 2/ occurred under these conditions yielding a typical etch rate of polycrystalline tungsten of 150more » nm/min. The primary ion observed was WF/sup +//sub 5/. The WF/sub 6/ etch product concentration was independent of ion energy, but correlated strongly with ion current. The results support a damage-induced chemical reaction as the enhancement mechanism.« less