In situ measurement of plasma charging on SiO2 hole bottoms and reduction by negative charge injection during etching

Ohmori, Takeshi; Makabe, Toshiaki

doi:10.1016/j.apsusc.2007.10.070

Cited by 29 publications

(22 citation statements)

References 52 publications

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“…We note that there are several other strategies to control charging of features that rely on pulsed plasmas. 22,23 In this approach, the source power is pulsed producing an active glow discharge, followed by an afterglow in which electrons rapidly attach to form a positive ion-negative ion plasma. Application of a bias during the afterglow then accelerates negative ions into the feature to neutralize excess positive charge.…”

Section: Charging Of Featuresmentioning

confidence: 99%

“…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. In fluorocarbon plasmas, fluxes of CF x neutrals are produced by electron impact dissociation followed by diffusion to the wafer.…”

Section: Introductionmentioning

confidence: 99%

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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: Charging Of Featuresmentioning

confidence: 99%

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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“…One approach utilizes pulsed ion-ion plasmas to inject negative ions into the feature. 18,19 The second approach, investigated here, produces and injects a narrow angle, high energy electron ͑HEE͒ flux into the feature.…”

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

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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“…In the etching of a nanometer-scale trench, local charge accumulation is one of the origins of anomalous process. The influence of a local charging on the etching rate of SiO 2 is very important in an arranged trench pattern, and the angular distribution of ions or neutrals must be discussed from the viewpoint of the local charging [8,9] . Experimental evidence of bottom charging in arranged holes during etching is demonstrated in Ar and CF4 plasma [10,11] .…”

Section: Introductionmentioning

confidence: 99%

Feature Profile Evolution During Etching of SiO₂in Radio-Frequency or Direct-Current Plasmas

Zhao¹,

Dai²,

Wang³

2012

Plasma Sci. Technol.

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We have developed a plasma etching simulator to investigate the evolution of pattern profiles in SiO2 material under different plasma conditions. This model focuses on energy and angular dependent etching yield (physical sputtering in this paper), neutral and ion angular distributions, and reflection of ions or neutrals on the surface of a photoresist or SiO2. The effect of positive charge accumulation on the surface of insulated mask or SiO2 is studied and the charge accumulation contributes to a deflection of ion trajectory. The wafer profile evolution has been simulated using a cellular-automata-like method under radio-frequency (RF) bias and direct-current (DC) bias, respectively. On the basis of the critical role of angular distribution of ions or neutrals, the wafer profile evolution has been simulated for different variances of angles. Observed microtrenching has been well reproduced in the simulator. The ratio of neutrals to ions has been considered and the result shows that because the neutrals are not accelerated by an electric field, their energy is much lower compared with ions, so they are easily reflected on the surface of SiO2, which makes the trench shallower.

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In situ measurement of plasma charging on SiO2 hole bottoms and reduction by negative charge injection during etching

Cited by 29 publications

References 52 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

Feature Profile Evolution During Etching of SiO₂in Radio-Frequency or Direct-Current Plasmas

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In situ measurement of plasma charging on SiO2 hole bottoms and reduction by negative charge injection during etching

Cited by 29 publications

References 52 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

Feature Profile Evolution During Etching of SiO2in Radio-Frequency or Direct-Current Plasmas

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Feature Profile Evolution During Etching of SiO₂in Radio-Frequency or Direct-Current Plasmas