Tungsten etching mechanisms in low-pressure SF6 plasma

Abstract

A detailed study of tungsten low-pressure etching in a helicon source reactor was performed. In correlation with surface analyses (transmission electronic microscope, Rutherford backscattering, nuclear reaction analysis), a complete parametric study of the plasma and etching parameters versus the macroscopic parameters [gas pressure, radio frequency (rf) power, substrate bias voltage) has been carried out. Using a model developed by Hoffman and Heinrich for silicon etching (Proceedings of the 9th ISPC, Pugnochiuso, Italy, 1989, p. 1003), and taking into account the experimental results, it has been shown that tungsten etching mechanisms can be expressed by the formation and destruction of a low-density reactive top layer. Sputtering of this layer under argon-ion bombardment has been studied by optical emission spectroscopy. Consequently, the tungsten etch rate can be expressed as an analytical function of the macroscopic parameters such as gas pressure, rf power, and substrate bias voltage.

Kinetics and crystal orientation dependence in high aspect ratio silicon dry etching

“…For TEM cross-sectional analysis the substrate is covered by 200 nm aluminum to protect the surface during sample preparation. 15 The surface roughness is investigated by AFM ͑Park Autoprobe M5͒ and the topography with a surface profiler ͑Tencor Alpha-step 500͒. Sample inspection is done with optical microscopy and scanning electron microscopy ͑SEM͒, the latter to make cross-sectional images of cleaved structures.…”

Measurement of the amount of oxygen generated by quartz source walls in a SF6 dense plasma: Application to a helicon reactor

“…[8][9][10] The plasma source has been extensively described in previous articles. 7,11 Plasma production is briefly described as follows. A transverse electromagnetic rf wave ͑13.56 MHz͒ H͑͒, generated by an antenna located outside the quartz source tube, is coupled with a steady state longitudinal magnetic field B 0 ͑around 100 G͒.…”

“…As we were working at low pressure, the gas phase chemistry and optical absorption by metastable atoms are negligible and the intensity of the above mentioned lines can also be used for actinometry measurements. 11 Mass spectroscopic analysis has been achieved by using a quadrupole mass spectrometer ͑QMG 112͒. The gas inside the diffusion chamber was sampled through a 0.3-mm-diam knife edge pinhole located on the diffusion chamber wall.…”

“…11 In the low pressure regime ͑pϽ2 bar͒ the etch rates increase quasilinearly with the pressure, showing that the etch rates were limited by the concentration of reactive species ͑F atoms͒ in the plasma. For pressures higher than 2 bar, a saturation regime occurs, which indicates that the reactive species are no longer the limiting factor.…”

“…In fact, in our reactor, an increase in pressure results in a decrease of the ion density and, consequently, a decrease of the ion flux to the walls, which leads to the ion current density control of the etch rate. 11 In order to verify that point for the etch of the reactor walls, experiments were carried out at two different rf powers applied to the antenna for the same SF 6 pressure ͑2.5 bar, corresponding to 11.5 sccm͒. From results shown in Fig.…”