Tungsten etching in low-pressure SF6 plasma: Influence of the surface temperature

Abstract

The influence of the surface temperature on tungsten etching in a SF6 plasma diffusing from a helicon source has been studied in detail. The surface temperature dependence of the etching kinetics has been analyzed. The influence of the other parameters such as oxygen content of the plasma and ion energy have also been considered. The etching mechanism depends on the temperature range: the etching is partly spontaneous at higher temperatures (T≳−20 °C), becomes a chemical sputtering type at intermediate temperature (−20 °C<T<−40 °C), and a chemically enhanced physical sputtering at lower temperature (T<−40 °C). Surface analyses by x-ray photoelectron spectroscopy provide an understanding of how the surface chemistry is modified with temperature.

Interactive effects in reactive ion etching of W1−xGex

“…The shift from anisotropy (Ϫ10°C) to isotropy ͑30°C͒ is indicative for the transition from an ion-induced to a ͑predominantly͒ thermally activated etch process. This result compares well with etch profile studies on W. 5 Finally, we consider the etch rate enhancement of W 1Ϫx Ge x which is also found to vary with temperature. See Fig.…”

“…4 Corresponding XPS measurements revealed WF 4 O and WF 4 species at the etched surface. 5 the larger etch rate enhancement of W 1Ϫx Ge x in F/Oplasmas compared to F plasma could be attributed to enhanced formation of volatile W etch products under ͑at least equally͒ efficient attack of the W-Ge bond. In an attempt to quantify this more precisely we used model B, taking the fraction ( f ) of W involved in the bond breaking the same as found in the SF 6 case.…”

“…One essential question is the possible impact of the Ge component on the dry etch behavior of the WGe alloy compared to that of pure W. Previously, the RIE characteristics of pure W in CF 4 , CF 4 /O 2 , SF 6 , SF 6 /O 2 , CF 2 Cl 2 , and Cl 2 plasmas have been investigated. [3][4][5][6][7][8][9] The general picture emerging from these studies is temperature dependent dry etch behavior. There is a gradual shift from ion-induced anisotropic etching below 0°C to much more chemical etching with isotropic features at room temperature ͑RT͒ and higher temperatures.…”

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

“…It is well known, for example, that the presence of oxygen decreases the selectivity between silicon and the photoresist mask, but it can also improve some etching characteristics such as etch rate, 4,5 or anisotropy. 6,7 Thus, it is important to determine precisely the amount of oxygen coming from the source walls under standard processing conditions. Therefore, we used two complementary techniques.…”

Single-order lamellar multilayer gratings

“…The resulting Arrhenius plots are shown in figure 4.6 and clearly indicate the difference in volatility with fluorine between silicon and tungsten. Where silicon has an E act of only 2 meV, meaning this reaction can be considered spontaneous [75], E act of tungsten was determined to be 60 meV [84,86]. As the thermal energy in the temperature range used is between 13 and 25 meV, additional energy is required to initiate the etching of tungsten.…”