Atomic Layer Deposition (ALD) was conventionally developed as a purely thermal process to deposit two-element films such as oxides and nitrides. ALD of single-element films (metals and semiconductors), with a few exceptions, is still a difficult task. Plasma-enhanced ALD (PEALD) can enable deposition of certain single-element films but has a reduced step coverage compared to thermal ALD, can cause damage to the wafer under treatment and involve a large variety of chemical reactions. As a result, the wafer surface may be exposed to many ions, radicals and atoms, as well as UV photons. This makes the composition and structure of the growing film not trivial to predict and control.
This work explores alternative techniques to generate radicals without plasma. We choose processes where dissociation of a certain precursor, to form radicals, can be achieved by collisions with a hot tungsten wire heated up to a temperature in the range of 1600-2000 oC. We use in situ real-time spectroscopic ellipsometry in combination with ex-situ techniques, to characterize deposition. The successful generation of atomic hydrogen (at-H) by the hot wire and its delivery to the substrate over a distance of 70 cm have been confirmed by etching of tellurium (Te) films at room temperature.
In this presentation, the concept will be explained and discussed; several examples of the radical-enhanced processes, enabled by utilizing a hot wire instead of using a plasma, will be given. The main example concerns hot-wire atomic layer deposition (HWALD) of tungsten (W) films. The films were grown on a 100-nm thick thermal SiO2 with a proper seed layer. Two different reactor configurations were employed: a large-volume reactor (70 cm distance between the HW and the substrate) and a small-volume reactor (3-5 cm distance between the HW and the substrate). In my presentation, I will further look into the chemistry behind these and other examples.