Mitigation of accumulated electric charge by deposited fluorocarbon film during SiO2 etching

Shimmura, Tadashi; Suzuki, Yuya; Soda, S.; Samukawa, Seiji; Koyanagi, Mitsumasa; Hane, Kazuhiro

doi:10.1116/1.1649347

Cited by 29 publications

(15 citation statements)

References 15 publications

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“…The electrical potential and electric fields produced by charge deposited on sidewalls and the etch front can deviate the trajectories of subsequent ions while reducing their energy, resulting in twisting and an etch stop. Pulsed power excitation can address many of the detriments of charging by elevating the ion energy, 20 reducing the thickness of fluorocarbon films on sidewalls, 21 and enabling the injection of negative ions to neutralize positive charge inside the feature. 22,23 Optimizing plasma etching of HAR features requires precise control of both the fluxes of ions and neutrals.…”

Section: Introductionmentioning

confidence: 99%

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

Huang

Huard

Shim

et al. 2019

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Plasma etching of high aspect ratio (HAR) features, typically vias, is a critical step in the fabrication of high capacity memory. With aspect ratios (ARs) exceeding 50 (and approaching 100), maintaining critical dimensions (CDs) while eliminating or diminishing twisting, contact-edge-roughening, and aspect ratio dependent etching (ARDE) becomes challenging. Integrated reactor and feature scale modeling was used to investigate the etching of HAR features in SiO 2 with ARs up to 80 using tri-frequency capacitively coupled plasmas sustained in Ar/C 4 F 8 /O 2 mixtures. In these systems, the fluxes of neutral radicals to the wafer exceed the fluxes of ions by 1-2 orders of magnitude due to lower threshold energies for dissociation compared with ionization. At low ARs (<5), these abundant fluxes of CF x and C x F y radicals to the etch front passivate the oxide to form a complex which is then removed by energetic species (ions and hot neutrals) through chemically enhanced reactive etching, resulting in the formation of gas phase SiF x , CO x , and COF. As the etching proceeds into higher ARs, the fractional contribution of physical sputtering to oxide removal increases as the fluxes of energetic species to the etch front surpass those of the conduction constrained CF x and C x F y radicals. The instantaneous etch rate of oxide decreases with increasing aspect ratio (ARDE effect) due to decreased fluxes of energetic species and decreased power delivered by these species to the etch front. As the etch rate of photoresist (PR) is independent of AR, maintaining CDs by avoiding undercut and bowing requires high SiO 2-over-PR selectivity, which in turn requires a minimum thickness of the PR at the end of etching. Positive ions with narrow angular distributions typically deposit charge on the bottom of low AR features, producing a maximum in positive electric potential on the bottom of the feature. For high AR features, grazing incidence collisions of ions on sidewalls depositing charge produce electric potentials with maxima on the sidewalls (as opposed to the bottom) of the feature.

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Section: Introductionmentioning

confidence: 99%

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

Huang

Huard

Shim

et al. 2019

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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“…The conductive film dissipates charge more quickly than the underlying SiO 2 . 16 This technique has been specifically applied to the control of twisting by reducing intrafeature charging. 17 A third method is injecting negative charge into the feature to neutralize accumulated positive charge.…”

Section: Fig 1 ͑Color Online͒ Scanning Electron Micrograph Of An Hamentioning

confidence: 99%

“…If the polymer has a finite conductivity, it may be possible to dissipate some of the accumulated charge and so lessen the likelihood of twisting. 16 We investigated this possibility by specifying the conductivity of the polymer to be 0.01 ⍀ −1 cm −1 . The incidence of twisting decreased from 49% to 38%, an improvement on but not an elimination of twisting.…”

mentioning

confidence: 99%

High energy electron fluxes in dc-augmented capacitively coupled plasmas. II. Effects on twisting in high aspect ratio etching of dielectrics

Wang¹,

Kushner²

2010

Journal of Applied Physics

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In high aspect ratio ͑HAR͒ plasma etching of holes and trenches in dielectrics, sporadic twisting is often observed. Twisting is the randomly occurring divergence of a hole or trench from the vertical. Many causes have been proposed for twisting, one of which is stochastic charging. As feature sizes shrink, the fluxes of plasma particles, and ions in particular, into the feature become statistical. Randomly deposited charge by ions on the inside of a feature may be sufficient to produce lateral electric fields which divert incoming ions and initiate nonvertical etching or twisting. This is particularly problematic when etching with fluorocarbon gas mixtures where deposition of polymer in the feature may trap charge. dc-augmented capacitively coupled plasmas ͑dc-CCPs͒ have been investigated as a remedy for twisting. In these devices, high energy electron ͑HEE͒ beams having narrow angular spreads can be generated. HEEs incident onto the wafer which penetrate into HAR features can neutralize the positive charge and so reduce the incidence of twisting. In this paper, we report on results from a computational investigation of plasma etching of SiO 2 in a dc-CCP using Ar/ C 4 F 8 / O 2 gas mixtures. We found that HEE beams incident onto the wafer are capable of penetrating into features and partially neutralizing positive charge buildup due to sporadic ion charging, thereby reducing the incidence of twisting. Increasing the rf bias power increases the HEE beam energy and flux with some indication of improvement of twisting, but there are also changes in the ion energy and fluxes, so this is not an unambiguous improvement. Increasing the dc bias voltage while keeping the rf bias voltage constant increases the maximum energy of the HEE and its flux while the ion characteristics remain nearly constant. For these conditions, the occurrence of twisting decreases with increasing HEE energy and flux.

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“…Furthermore, the conductivity of a-CF x films has also been reported, where associated features may induce charging at the bottoms of the high-AR holes during the RIE process. [18][19][20][21] This charge-up phenomenon is reported to infer the twisting of holes. 22) These reports suggest that controlling the thickness of the a-CF x film and the AR region where the a-CF x film is deposited can overcome the various hole shape problems, which occur during the high-aspect-ratio-contact (HARC) process.…”

mentioning

confidence: 93%

Analysis of formation mechanism of deposited film in a high-aspect-ratio hole during dry etching using fluorocarbon gas plasmas

Hiwasa¹,

Kataoka²,

Sasao³

et al. 2022

Appl. Phys. Express

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In the dry etching process using fluorocarbon (FC) gas, deposited amorphous-CFx (a-CFx) films in patterns, such as holes and trenches, strongly affect the etching performance. The influence of the FC gas molecular structures and their atomic compositions on the formation of a-CFx films at different positions in the holes were investigated. It was found that the deposition region and thickness of the a-CFx film strongly depend on the molecular structures of the FC gas, such as double bonds, benzene rings, and the atomic ratio of fluorine to carbon.

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Mitigation of accumulated electric charge by deposited fluorocarbon film during SiO2 etching

Cited by 29 publications

References 15 publications

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

Plasma etching of high aspect ratio features in SiO2 using Ar/C4F8/O2 mixtures: A computational investigation

High energy electron fluxes in dc-augmented capacitively coupled plasmas. II. Effects on twisting in high aspect ratio etching of dielectrics

Analysis of formation mechanism of deposited film in a high-aspect-ratio hole during dry etching using fluorocarbon gas plasmas

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