Polymer deposition and etching mechanisms in C2F6 radio-frequency plasma as studied by laser-induced fluorescence

Kitamura, Mamoru; Akiya, Hideo; Urisu, Tsuneo

doi:10.1116/1.584438

Cited by 30 publications

(17 citation statements)

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“…Kitamura et al 19 reported that the rate was proportional to 2.5 to third power of the CF 2 partial pressure. Accordingly, it is certain that the rate of R 3 is not linearly dependent on the CF x partial pressure, unlike in the case of R 1 .…”

Section: Resultsmentioning

confidence: 98%

Expression of the Si Etch Rate in a CF 4 Plasma with Four Internal Process Variables

Cho

Hwang

Kim

et al. 1999

J. Electrochem. Soc.

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Prediction of the Si etch rate in a fluorocarbon plasma is important in finding the optimal process condition for highly selective SiO 2 etching over Si which is essential for ultralarge-scale integration (ULSI) fabrication. [1][2][3][4] The best tool in making such a prediction is the etch-rate equation with the rate expressed as a function of the process variables. However, the relations between the etch rate and the external process variables such as total pressure, power density, and gas flow rate are strongly dependent on the hardware configuration of the etching system and do not guarantee run-to-run reproducibility in different etchers. The internal process variables such as the partial pressures of radicals, the sheath bias voltage, and the ion current density, which are set in response to the external variables, eventually determine the etching characteristics independent of the etcher configuration. 5 Therefore, they are more useful than the external variables for etch-rate prediction. The internal variables in the etch rate equation are not necessarily independent of each other but should be measurable in the process with proper diagnostic tools.Several research groups have expressed the Si etch rate in a fluorine-based plasma with the internal process variables. [6][7][8][9][10][11] The F concentration is the most important because F atoms are the main etchant species in the system. Ninomiya et al. 6 observed that the Si etch rate increased linearly with the F concentration. Flamm et al., 7 who expressed the etch rate as a function of the F concentration and the substrate temperature, also reported that the rate was proportional to the F concentration. However, these two groups excluded the influence of reactive ions in their experiments by locating the Si substrate outside the F 2 plasma. Therefore, these equations represent the thermal etch rate due to F atoms but not the rate in the ion-enhanced plasma etching where the thermal rate is relatively small.The mechanisms of the ion-enhanced etching are still debated but are summarized into four categories: chemical sputtering, 12 chemically enhanced physical sputtering, 13 damage-enhanced chemical reaction, 14 and increased spontaneous etching. 15 Enhancement of the etch rate by ions is related to two internal variables: the sheath bias voltage and the ion current density. The former represents the kinetic energy of incident ions and the latter the number flux of ions. Although the ionic kinetic energy is determined by the difference between the plasma and the electrode potentials, it is usually dependent on the electrode potential only, because the plasma potential is relatively small enough to be neglected. 16 Mayer and Barker 17 observed that the Si etch yield, the etch rate per incident ion, increased with the kinetic energy of the ions in their study with reactive ion beam etching (RIBE) apparatus. Moreover, Steinbrüchel 18 reported that the ionenhanced chemical etch yield increased linearly with the square root of the ion energy. A few groups, in...

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Section: Resultsmentioning

confidence: 98%

Expression of the Si Etch Rate in a CF 4 Plasma with Four Internal Process Variables

Cho

Hwang

Kim

et al. 1999

J. Electrochem. Soc.

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“…Polymer layers on the surface are easily formed in fluorocarbon discharges with high concentrations of radical species, like CF, CF 2 , and CF 3 . [10][11][12] However, generally these radicals themselves do not contribute to the polymer film formation. Contrariwise, in many cases a net radical flux from the surface into the plasma glow has been observed.…”

Section: Introductionmentioning

confidence: 99%

Polymerization of fluorocarbons in reactive ion etching plasmas

Stoffels

Tachibana

1998

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

153

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Polymerization reactions in radio frequency fluorocarbon plasmas of CF 4 , C 2 F 6 , and C 4 F 8 have been studied by electron attachment mass spectrometry ͑EAMS͒. In these plasmas polymerization occurs readily and molecules containing up to ten carbon atoms ͑the mass limit of the mass spectrometer͒ have been found. The densities of large polymers increase with increasing size of the parent gas. In a fluorine-rich environment like a CF 4 plasma the detected polymers are mainly fully saturated with F ͑C n F 2nϩ2 ). As the amount of fluorine in the parent gas decreases, also the degree of saturation of the polymers decreases, which is clearly seen in C 2 F 6 and C 4 F 8 plasmas. The unsaturated polymers are more reactive, so they can stick more easily to surfaces and possibly create thick polymer films, which are often observed after discharge operation. The polymerization rate depends on the chemical activity of the plasma, which can be easily enhanced by increasing the radio frequency power. The positive ions, extracted from the plasma, are generally somewhat smaller than the neutral polymers and their fluorine content is lower. This is probably due to dissociation of neutrals during their ionization by plasma electrons and to ion collisions in the sheath region. Finally, we have shown that EAMS has considerable advantages in the study of electronegative plasmas and polymerization processes in comparison with traditional mass spectrometry. Unlike the traditional mass spectrometry, employing ionization by high energy electrons, EAMS much better preserves the structure of high polymers, allowing us to detect them as large negative ions.

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“…5 The CF 2 radical is an important species in halocarbon plasmas because it influences the balance between polymer deposition and etching, and hence selectivity, in silicon/silicon dioxide etching applications. 1,2 As a result, a number of previous experimental studies have reported 1D measurements of CF 2 density using mass spectrometry, 6 infrared diode laser-absorption, [7][8][9][10] and laser-induced fluorescence, [11][12][13][14][15][16][17][18][19] but, to our knowledge, the present results are the first complete 2D measurements of CF 2 density in any reactor. In addition to yielding information on the relative magnitude of CF 2 concentration at various conditions, these measurements are of interest because they provide insight into the plasma uniformity through 2D visualization of the CF 2 spatial distribution.…”

Section: Introductionmentioning

confidence: 72%

Two-dimensional imaging of CF2 density by laser-induced fluorescence in CF4 etching plasmas in the gaseous electronics conference reference cell

McMillin

Zachariah

1997

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

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Spatially resolved two-dimensional maps of the relative CF 2 density in low-pressure radio-frequency Ar/CF 4 /O 2 discharges generated within a parallel-plate Gaseous Electronics Conference reference cell have been obtained using planar laser-induced fluorescence imaging. The experiments cover a wide range of pressure, composition, flow rate, and power deposition conditions ͑13.3-133.3 Pa, 1%-100% CF 4 , 1%-10% O 2 , 5-100 sccm, 3-35 W͒. Typically, the centerline (r ϭ 0) axial CF 2 distribution was symmetric with the local peak occurring near the center of the electrode gap, but, in all cases, significant radial variations in CF 2 density were observed ͑14%-45% standard deviation from the mean͒ with the peak density occurring near the edge of the discharge region. Varying the pressure led to significant changes in both the magnitude and spatial distribution of CF 2 density, while varying the composition, flow rate, and power primarily affected only the magnitude of the CF 2 density, with only modest changes in the spatial distribution. Based on image-averaged comparisons, the CF 2 density increased with power, pressure, and CF 4 mole fraction, decreased with addition of oxygen, and varied nonmonotonically with flow rate.

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Polymer deposition and etching mechanisms in C2F6 radio-frequency plasma as studied by laser-induced fluorescence

Cited by 30 publications

References 0 publications

Expression of the Si Etch Rate in a CF 4 Plasma with Four Internal Process Variables

Expression of the Si Etch Rate in a CF 4 Plasma with Four Internal Process Variables

Polymerization of fluorocarbons in reactive ion etching plasmas

Two-dimensional imaging of CF2 density by laser-induced fluorescence in CF4 etching plasmas in the gaseous electronics conference reference cell

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