Mechanism of Tungsten Atom Formation in Tungsten Etchback Using SF 6/Ar Helicon Plasma

The formation mechanism of tungsten (W) atoms in tungsten etching has been investigated with the /Ar helicon plasma. The etch rate of W films decreases with increasing flow rate of Ar in the /Ar gas mixture while the density of tungsten atoms increases as measured by optical emission spectroscopy. Tungsten films are rarely etched with pure Ar plasma. The density of tungsten atoms generated by a direct sputtering is much less than the one in /Ar plasma. By comparing the etch rate with the relative intensity of W atom as a function of source power and bias power, it was found that tungsten atoms are mainly formed through the dissociation reaction of stable product, , and further by electron impact. The loading effect in tungsten etchback can be suppressed by enhancing the redeposition of (y and z ⩾ 0) by‐products by increasing the source power. The suppression mechanism of the loading effect is investigated by an in situ monitoring of optical emission of tungsten atoms generated during overetching in tungsten etchback.