Plasma-assisted atomic layer deposition of HfNx: Tailoring the film properties by the plasma gas composition

Plasma-Assisted ALD of Highly Conductive HfNx: On the Effect of Energetic Ions on Film Microstructure

“…The ions with a larger mass and higher < E ion > leads to a minimum in the electrical resistivity of 4.1 × 10 -4 Ωcm. To best of our knowledge, this value represents the lowest resistivity reported in the literature for HfN x films grown by either CVD or ALD, and is comparable to the resistivity of PVD grown films [13,14,[21][22][23]. This low resistivity is achieved for films as thin as ~ 35 nm.…”

“…We demonstrated that the application of an external RF substrate bias during the H 2 plasma exposure and an increase in the timeaveraged substrate potential (|V bias |) from 0 to 130 V resulted in a major decrease in electrical resistivity (ρ e ) from 0.9 to 3.3 × 10 -3 Ωcm [14]. The decrease in ρ e was found to be correlated with a major increase in the fraction of Hf(III) oxidation state from 0.65 ± 0.02 to 0.82 ± 0.02 [13,14]. These results demonstrated that the impingement of energetic ions during the film growth can significantly improve the chemical and associated electrical properties of HfN x thin films prepared by ALD.…”

“…HfN x predominantly exists in two crystal phases: highly resistive Hf 3 N 4 with Hf(IV) oxidation state [9,10], and low resistivity δ-HfN with Hf(III) oxidation state [11,12]. The control of the oxidation state of Hf is therefore essential to synthesize conductive HfN x layers [13][14][15]. Physical vapor deposition (PVD) methods have been widely adopted for the synthesis of low resistivity HfN x films [8,11,12,[16][17][18][19].…”

“…(1-2)•10 -4 Ωcm for a typical film thickness of ~ 200 nm [17,19,20]. On the other hand, the growth of low resistivity HfN x films by techniques employing a metal-organic precursor, such as chemical vapor deposition (CVD) or atomic layer deposition (ALD), is very challenging [13,14,[21][22][23]. A major challenge is the reduction of Hf(IV) oxidation state in the precursor to Hf(III) oxidation state in the deposited film, as highlighted in our previous work [13,14].…”

“…These requirements motivate the synthesis of low resistivity HfN x films by ALD. We have recently shown that the δ-HfN phase can be achieved by adopting CpHf(NMe 2 ) 3 as Hf(IV) precursor and H 2 plasma as reducing co-reactant in a plasma-assisted ALD process [13]. We demonstrated that the application of an external RF substrate bias during the H 2 plasma exposure and an increase in the timeaveraged substrate potential (|V bias |) from 0 to 130 V resulted in a major decrease in electrical resistivity (ρ e ) from 0.9 to 3.3 × 10 -3 Ωcm [14].…”