High rate anisotropic etching

Bruce, Richard H.; Malafsky, Geoffrey P.; Reinberg, A. R.; Yao, Wenqian

doi:10.1109/iedm.1981.190150

Cited by 1 publication

(7 citation statements)

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“…Behavior with pressure and power density.--While many plasma etch experiments describe resul~ (3,4,5) in qualitative agreement with the predictions of this model, there are only three reports of experimental results with respect to pressure and rf power density (1,2,6) on etch profiles that are sufficiently detailed to permit reasonably quantitative comparison. At 13.56 MHz, the rf power density of 0.4 W/cm z produces an increased undercut with increased pressure of CF4 for the plasma etching of doped polysilicon (1).…”

Section: Comparison With Experimentsmentioning

confidence: 65%

“…The ion transport would be expected to be much more anisotropic, both because of the larger fields at similar rf.powers and because the smaller sheath thickness decreases the number of collisions the ions can make while in such a higher field. The observed increase in etch anisotropy with lower excitation frequencies at the same power is well documented (3,4). The effect of these lower frequencies in increasing the resist erosion (3,4,6), and reducing the process selectivity (or increasing the sputtering) is also well known.…”

Section: Comparison With Experimentsmentioning

confidence: 89%

“…For a << 1, Eq. [4] reduces to .p2 ___ I --a 2 and for a >> 1, to p2 ___ l/a, so that as a ~ 0, p2 --> 1, or isotropic ion transport directionality, and as a --) ~, p2 -> 0, or anisotropic (strongly directional) ion transport. This is summarized schematically in Fig.…”

Section: -Co Qmentioning

confidence: 98%

“…Squaring this expression and defining ~ = (1 + u2/ <w2>)-1 as the ion kinetic energy transport directionality, for which we obtain an expression in terms of the parameter p2 = 2/(1 -4-X/1 4-(2a) 2) [4] Replacing ~ = 1/noQ, where no is the neutral scatterer number density, Q is the ion-neutral collision cross section, and recognizing that m+<wf>/2 : 3kT+/2 is the ion thermal energy, the parameter a is…”

Section: Relating the Sheath Electric Field And Gas Pressure To The I...mentioning

confidence: 99%

“…The following four experimental results are somewhat inconsistent with or, at least, show some incompleteness in our understanding of the mechanisms of anisotropic plasma etching: (i) the wide variety of conditions yielding anisotropic plasma etching at pressures too high to preclude collision dominated charged particle transport across the plasma sheath (1)(2)(3)(4)(5)(6); (ii) the increase in etch anisotropy as rf power density increases (2,6), excitation frequency decreases (3,4) and/or etch gas pressure decreases (1,5,6); (iii) the observed ability to modify etch profiles at constant rf power, pressure, and frequency by application of d-c voltages to one of the reactor electrodes (2); and, finally, (iv) that the ratio of the isotropic and anisotropic vertical etch rates, under conditions of (iii) above, are significantly less than that of the etch depth to mask undercut (2).…”

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confidence: 99%

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Plasma Etch Anisotropy—Theory and Some Verifying Experiments Relating Ion Transport, Ion Energy, and Etch Profiles

Zarowin

1983

J. Electrochem. Soc.

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A model of plasma etch anisotropy is presented which shows that the ionic component of the chemical etch process produces etch profiles that vary with E/p , where E is the electric field controlling the ion transport to the etch surface and p is the etch gas pressure. From a relation derived here between E and the observable rf current density, Jnormalrf , this model predicts that the profiles will vary continuously from isotropically to anisotropically produced as the parameter Jnormalrf/p is increased. This behavior reflects the directionality of the ion kinetic energy transported to the etch surface and the effect of the ion energy in reducing the surface reaction activation energy. The one‐to‐one correspondence between ion energy and ion transport or etch directionality shown by this model clarifies the compromise required between etch anisotropy and the adverse effects of such high ion energy, such as reduced resist survival and selectivity against other materials in addition to the possibility of increased substrate damage. Another important practical consequence of this work is the establishment of a theoretical basis for extending the conventional wisdom that low pressures (<10 Pa) are required for anisotropic plasma etching to the more general requirement of a sufficiently high E/p ratio. Thus, this theory shows, and a wide range of experiments verify, that equally anisotropic etch profiles are obtainable at high (e.g., 1000 Pa) or low pressures from the same Jnormalrf/p ratios. Alternatively, it will be shown that reactive ion etching is a low pressure limiting case of plasma etching, both of which are able to produce identically anisotropic etch profiles, although the latter is capable of considerably higher etch rates. Finally, this model predicts a dependence of the anisotropy on the ion‐neutral scatterer collision cross section and/or mass ratio, which is experimentally confirmed here by previously unpublished data.

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Section: Comparison With Experimentsmentioning

confidence: 65%

Section: Comparison With Experimentsmentioning

confidence: 89%

Section: -Co Qmentioning

confidence: 98%

Section: Relating the Sheath Electric Field And Gas Pressure To The I...mentioning

confidence: 99%

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confidence: 99%

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