Laser Induced Fluorescence and Optical Emission Studies of Fluorocarbon Plasmas

Booth, Jean-Paul; Hancock, Christopher P.; Perry, N. D.; Blaikleye, D. C. W.; Cairns, J.A.; Smailes, R.

doi:10.1557/proc-98-135

Cited by 21 publications

(5 citation statements)

References 14 publications

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“…Furthermore, it has been shown that, under strongly polymerizing conditions ͑for ex-ample, in CF 4 plasma with a high H 2 content͒, the lifetime of the CF 2 radical becomes extremely long. [31][32][33] This implies that its reaction probability on the wafer and reactor wall surfaces becomes vanishingly small, and thus that the polymer film is not formed by direct incorporation of incident CF 2 radicals.…”

Section: B the Role Of Cf X Radicalsmentioning

confidence: 99%

CF 2 production and loss mechanisms in fluorocarbon discharges: Fluorine-poor conditions and polymerization

Cunge

Booth

1999

Journal of Applied Physics

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176

117

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Articles you may be interested inStudy of Ti etching and selectivity mechanism in fluorocarbon plasmas for dielectric etchThe study of CF and CF 2 radical production and loss mechanisms in capacitively-coupled 13.56 MHz CF 4 plasmas has been extended to CF 4 plasmas with an Si substrate, and to C 2 F 6 plasmas, conditions where the atomic fluorine concentration is lower and where more polymer deposition occurs on the reactor surfaces. Processes in the gas phase and at the reactor surfaces were investigated by time resolved axial concentration profiles obtained by laser induced fluorescence, combined with absolute calibration techniques. The results for CF were similar to those observed in the fluorine rich case, whereas the results for CF 2 were strikingly different and more complex. This paper focuses on the CF 2 radical, which, under these conditions is produced at all of the surfaces of the reactor, apparently via a long-lived surface precursor. The results can only be explained if large polymeric ions and/or neutrals are produced by polymerization in the gas phase. The gas-phase CF 2 concentration is high, causing the otherwise slow gas-phase concatenation reactions C X F Y (CF 2 ) n ϩCF 2 →C X F Y (CF 2 ) nϩ1 to occur. These processes produce high-mass neutrals ͑and ions͒ which are the real polymer precursors. The CF 2 radical therefore circulates in a closed cycle between the surface and the gas phase. The degree of polymerization is controlled by the fluorine atom concentration, which simultaneously controls the concentrations of CF 2 , of chain initiating species such as CF 3 and of dangling bonds on the growing oligomers. This model appears to apply to fluorocarbon discharges in general, and agrees well with other results presented in the literature.

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Section: B the Role Of Cf X Radicalsmentioning

confidence: 99%

CF 2 production and loss mechanisms in fluorocarbon discharges: Fluorine-poor conditions and polymerization

Cunge

Booth

1999

Journal of Applied Physics

Self Cite

176

117

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“…However, CF2 did not show a dependence on percent oxygen. This is a surprising result since others have found a marked decrease in CF2 with oxygen, both experimentally and theoretically (6,14,15). This may be due to the underlying spectral continuum centered at 250 nm which is observed in the presence of oxygen.…”

Section: Model Developmentmentioning

confidence: 78%

Development of Techniques for Real‐Time Monitoring and Control in Plasma Etching: I . Response Surface Modeling of and Etching of Silicon and Silicon Dioxide

McLaughlin

Butler

Edgar

et al. 1991

J. Electrochem. Soc.

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A systematic modeling analysis of reactive ion etching of silicon and silicon dioxide using CF4/O2 and CF4/H2 was performed. A parallel plate reactor was employed to obtain relationships among manipulated variables (power, pressure, etchant composition, flow rate), measured process variables ([F], false[CF2false] , false[COxfalse] , [H], dc bias), and performance variables (Si and SiO2 etch rates, selectivity, anisotropy, uniformity). Using a fractional factorial experimental design, empirical models were fitted in order to facilitate comparison with experimental trends noted by other investigators, as well as analysis of variable interactions. This is the first paper in the literature that considers the full range of multivariable interactions, covering four manipulated variables, four process variables, and seven performance variables. In addition, this work demonstrates the importance of performing an analysis of variance in order to determine goodness of fit of the empirical model. A high value of the squared multiple correlation coefficient R2 does not guarantee an adequate model and may lead to erroneous conclusions.

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“…This has led recently to the development of industrial reactors that incorporate hot silicon reactor walls in order to increase and control the polymerization. However, under strongly polymerizing conditions (for example, in CF 4 plasmas with a high H 2 content), the lifetime of the CF 2 radical becomes extremely long [32][33][34]. This implies that its reaction probability on the wafer and reactor wall surfaces becomes very small, and thus that the polymer film is not formed by direct incorporation of incident CF 2 radicals.…”

Section: Cf X Radicalsmentioning

confidence: 99%

“…The pump-out rate (about 1 s −1 ) is also negligible. In contrast, under conditions where the F atom concentration is high, CF x radicals are efficiently destroyed at the grounded reactor walls [27,32,65] (see table 2). This leads to loss rates of the order of 100-1000 s −1 , depending on the radical, the plasma conditions and (especially) the reactor geometry.…”

Section: Fluorine-rich Conditionsmentioning

confidence: 99%

Optical and electrical diagnostics of fluorocarbon plasma etching processes

Booth

1999

Plasma Sources Sci. Technol.

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This article reviews recent work concerning the role of CF and CF 2 radicals in etching and polymerization processes occurring in capacitively coupled radio-frequency plasmas in fluorocarbon gases used for the selective etching of SiO 2 layers in microelectronic device fabrication. Laser-induced fluorescence (LIF) was used to determine time-resolved axial concentration profiles of these species in continuous and pulse-modulated CF 4 and C 2 F 6 plasmas. Calibration techniques, including broad-band UV absorption spectroscopy, were developed to put the LIF measurements on an absolute scale. A novel technique was used to determine the ion flux to the reactor walls in these polymerizing environments. The mass distribution of the ions arriving at the reactor walls was determined using a quadrupole mass spectrometer.It was found that CF x radicals are produced predominantly by the reflection of neutralized and dissociated CF +x ions at the powered electrode surface. When the fluorine atom concentration is high, the CF x radicals are destroyed effectively by recombination catalysed by the reactor walls. When the fluorine atom concentration is lowered, the CF 2 concentration rises markedly, and it participates in gas-phase oligomerization processes, forming large C x F y molecules and, after ionization, large C x F + y ions. These species appear to be the true polymer precursors. This mechanism explains the well known correlation between high CF 2 concentrations, polymer deposition and SiO 2 over Si etch selectivity.

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Laser Induced Fluorescence and Optical Emission Studies of Fluorocarbon Plasmas

Cited by 21 publications

References 14 publications

CF 2 production and loss mechanisms in fluorocarbon discharges: Fluorine-poor conditions and polymerization

CF 2 production and loss mechanisms in fluorocarbon discharges: Fluorine-poor conditions and polymerization

Development of Techniques for Real‐Time Monitoring and Control in Plasma Etching: I . Response Surface Modeling of and Etching of Silicon and Silicon Dioxide

Optical and electrical diagnostics of fluorocarbon plasma etching processes

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