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

Abstract

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.

Modeling of Charging on Unconventional Surface Morphologies of PMMA Substrates During Ar Plasma Etching

“…[25,27] However, in reality, the surface is floating with a radio frequency bias which is taken into account to the ion energy distribution function (IEDF); the IEDF depends on the sheath potential. [27] In order to mirror the simulation domain, [22,39] the following condition is imposed on both left (x ¼ a) and right (x ¼ b) boundary,…”

“…Kenney and Hwang [44] investigated the stochastic behavior of charging by studying the oscillation of charging potential in high AR dielectric nanostructures. Wang and Kushner [25] investigated the role of charging on the twisting of high AR SiO 2 holes etched by fluorocarbon chemistries. All of the works described above are studies for the surface charging and its consequences, i.e., profile irregularities and etching artifacts, on conventional surface morphologies or structures met in semiconductor industry, i.e., trenches or holes.…”

“…Consequently, the ion deflection caused by surface charging, lead to profile irregularities such as notching, [22] microtrenching, [23] etching lag, [24] and twisting. [25,26] The notching effect describes the formation of long narrow wedge in a conductive material at the interface with an underlying insulator. It commonly appears at the inner sidewall foot of the outermost feature in a line and space pattern adjacent to an open area.…”

Heating mode transition in a hybrid direct current/dual-frequency capacitively coupled CF4 discharge

“…Therefore, this kind of hybrid dc/RF plasma source has received increased attention recently in both industrial and academic fields. [11][12][13][14][15][16][17][18][19][20] When a negative dc voltage is applied to the electrode, the sheath structure is determined by the superposition of a dc sheath and an RF sheath. 12,13 Under the effect of the large potential drop in the dc/RF sheath, ions are attracted to bombard the dc electrode continuously, and abundant secondary electrons are thus emitted and accelerated toward the plasma.…”

Modeling of implantation and mixing damage during etching of SiO2 over Si in fluorocarbon plasmas

“…Higher energy ions also tend to be more anisotropic and so are better able to maintain critical dimensions (CD). 3 An example of this process is fluorocarbon plasma etching of trenches and vias in SiO 2 and stopping on a crystalline Si layer. The fluorocarbon radicals produced in the plasma deposit a polymer layer on the SiO 2 which is partially consumed during the etching process, thereby thinning the layer.…”