Radial Etch Rate Nonuniformity in Reactive Ion Etching

Nagy, A. G.

doi:10.1149/1.2115981

Cited by 20 publications

(13 citation statements)

References 4 publications

(9 reference statements)

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“…Silicon wafers processed with a plasma dry-etching process can show structures with unexpected deviations due to non-uniform plasma density, so that individual wafers made with the same recipe can differ from each other. Similar non-uniformities have been reported in the literature (Nagy 1984;Kao & Stenger 1990).…”

Section: Visualization Of the Nucleating Areasupporting

confidence: 91%

Heat-flux enhancement by vapour-bubble nucleation in Rayleigh–Bénard turbulence

et al. 2015

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We report on the enhancement of turbulent convective heat transport due to vapour-bubble nucleation at the bottom plate of a cylindrical Rayleigh-Bénard sample (aspect ratio 1.00, diameter 8.8 cm) filled with liquid. Microcavities acted as nucleation sites, allowing for well-controlled bubble nucleation. Only the central part of the bottom plate with a triangular array of microcavities (etched over an area with diameter of 2.5 cm) was heated. We studied the influence of the cavity density and of the superheat T b − T on (T b is the bottom-plate temperature and T on is the value of T b below which no nucleation occurred). The effective thermal conductivity, as expressed by the Nusselt number Nu, was measured as a function of the superheat by varying T b and keeping a fixed difference T b − T t 16 K (T t is the top-plate temperature). Initially T b was much larger than T on (large superheat), and the cavities vigorously nucleated vapour bubbles, resulting in two-phase flow. Reducing T b in steps until it was below T on resulted in cavity deactivation, i.e. in one-phase flow. Once all cavities were inactive, T b was increased again, but they did not reactivate. This led to one-phase flow for positive superheat. The heat transport of both one-and two-phase flow under nominally the same thermal forcing and degree of superheat was measured. The Nusselt number of the two-phase flow was enhanced relative to the one-phase system by an amount that increased with increasing T b . Varying the cavity density (69, 32, 3.2, 1.2 and 0.3 mm −2 ) had only a small effect on the global Nu enhancement; it was found that Nu per active site decreased as the cavity density increased. The heat-flux enhancement of an isolated nucleating site was found to be limited by the rate at which the cavity could generate bubbles. Local bulk temperatures of one-and two-phase flows were measured at two positions along the vertical centreline. Bubbles increased the liquid temperature (compared to one-phase † Email address for correspondence: daniela.narezo@gmail.com 332 D. Narezo Guzman and others flow) as they rose. The increase was correlated with the heat-flux enhancement. The temperature fluctuations, as well as local thermal gradients, were reduced (relative to one-phase flow) by the vapour bubbles. Blocking the large-scale circulation around the nucleating area, as well as increasing the effective buoyancy of the two-phase flow by thermally isolating the liquid column above the heated area, increased the heat-flux enhancement.

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Section: Visualization Of the Nucleating Areasupporting

confidence: 91%

Heat-flux enhancement by vapour-bubble nucleation in Rayleigh–Bénard turbulence

et al. 2015

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“…Again, only model results were given with no experimental data. Experimental work has been published by Nagy (2) and Peccoud et al (5).…”

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confidence: 99%

Analysis of Nonuniformities in the Plasma Etching of Silicon with CF 4 / O 2

Kao

Stenger

1990

J. Electrochem. Soc.

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Experimental and modeling work has been performed to examine the effects of reactor pressure, etchant gas flow rate, and wafer location on the uniformity of plasma etching silicon using CF4/O2 in a parallel-plate-radial flow reactor. Intrawafer etch rates were measured at 12 points across a 3 in. wafer at pressures between 125 and 200 mtorr, 70~ and gas residence times between 1.28 and 2.14s. Depending on the operating conditions, an edge-to-center decrease in etch rate of 5-25% was observed. A combined reactor/reaction model is able to predict this degree of nonuniformity. Uniformity was improved by increasing the reactor pressure and decreasing the flow rate of the etchant gas. Etch uniformity was also found to be a function of wafer location within the reactor. Data are presented which show the influences of process parameters on both etch rate magnitude and uniformity.Intrawafer nonuniform etching in plasma and reactive ion etching systems is a major problem in current IC processing technology. The result of intrawafer nonuniformities is a direct decrease in circuit yields or overdesign to compensate for etch rate variations. In particular, the plasma etching of silicon, silicon dioxide, and aluminum in a parallel plate radial flow system often displays an edge-to-center decrease in etch rate, a phenomenon sometimes referred to as the "bullseye effect" (1, 2). Clearly, the inability to etch consistent circuits on each chip of a wafer will continue unless the causes of the bullseye effect are better understood and corrections are made.Several papers have been published which discuss the problem of etch nonuniformities. Stenger et al.(1) studied the interwafer nonuniformities of NF3 etching silicon in a radial flow reactor. The etch rates for this system were found to be more uniform at lower flow rates holding pressure, feed gas composition, and temperature constant.Since they evaluated etch rates by measuring the decrease in wafer mass after etching, intrawafer nonuniformities could not be examined. Dalvie et al.(3) have developed a model of CF4 etching silicon in a radial flow reactor. Their model assumes uniformly distributed silicon on the lower electrode, low CF4 dissociation rates, and radially constant electron density. The effects of pressure, flow rate, and discharge power on etch rate were simulated. They found that average etch rates increased as the flow rate decreased or the reactor pressure increased. The primary effect of increasing the discharge power in their model was to increase the average electron density, which resulted in higher etch rates. Their model also predicted intrawafer as well as interwafer etch nonuniformities; however, no experimental data were offered for comparison. Alkire and Economou (4) examined the nonuniform stripping of photoresist with 02 in a barrel reactor, which is a common application of barrel etchers. The transport of etching species to the wafer in barrel reactors relies predominantly on diffusion, with little convective influences. This results in a depletion ...

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“…Results of the plasma reactor mode] are first presented in terms of important dimensionless parameters of the system. ported experimentally at boundaries where two surfaces having different etch rates met (29,30). For the case under examination, ion-assisted etching was uniform over the etching surface since the electron (and hence the positive ion) density distribution was assumed uniform.…”

Section: Resultsmentioning

confidence: 99%

“…One observes that when the reactivity of the surface being etched is comparable to that of the surrounding surface, etch uniformity is greatly improved. Using a substrate electrode that etches as fast as the wafer itself (29), however, causes the etch rate to decrease be- cause the etchable surface area is larger (loading). This effect may be seen in Fig.…”

Section: Resultsmentioning

confidence: 99%

A Mathematical Model for a Parallel Plate Plasma Etching Reactor

Economou

Alkire

1988

J. Electrochem. Soc.

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A mathematical model was formulated for predicting species concentration profiles and etch rate distribution in a parallel plate plasma reactor. Explicit account was taken of the ion-assisted component of etching by considering ion transport in the sheath. For the case of oxygen discharge, convective diffusion and chemical reactions of the etchant species were included as well as the electron density and energy variations in the bulk plasma. Important dimensionless system parameters were identified and their effect on etch rate, degree of etch anisotropy, and uniformity was examined. The model predictions were evaluated by comparison with experimental data on etch rate of polymer in an oxygen plasma as a function of pressure, power, and flow rate. For each, the model captured the salient features observed experimentally, although quantitative comparisons were not possible owing to the lack of accurate rate reaction kinetics data.

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Radial Etch Rate Nonuniformity in Reactive Ion Etching

Cited by 20 publications

References 4 publications

Heat-flux enhancement by vapour-bubble nucleation in Rayleigh–Bénard turbulence

Heat-flux enhancement by vapour-bubble nucleation in Rayleigh–Bénard turbulence

Analysis of Nonuniformities in the Plasma Etching of Silicon with CF 4 / O 2

A Mathematical Model for a Parallel Plate Plasma Etching Reactor

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