Spontaneous etching of B2O3 by HF gas studied using infrared spectroscopy, mass spectrometry, and density functional theory

Abstract

The spontaneous etching of boron oxide (B 2 O 3 ) by hydrogen fluoride (HF) gas is important during thermal atomic layer etching after BCl 3 converts the surface of various metal oxides to a B 2 O 3 layer. In this study, the chemical vapor etching (CVE) of B 2 O 3 by HF was experimentally monitored using Fourier transform infrared (FTIR) spectroscopy and quadrupole mass spectrometry (QMS). The spontaneous etching of B 2 O 3 by HF gas was also analyzed using density functional theory (DFT). B 2 O 3 films were grown using B 2 O 3 atomic layer deposition with BCl 3 and H 2 O as the reactants at 40 °C. FTIR spectroscopy then observed the CVE of B 2 O 3 by HF at 150 °C. B 2 O 3 etching was monitored by the loss of absorbance for B-O stretching vibration in B 2 O 3 films. FTIR spectroscopy studies also observed B-F stretching vibrations from BF x species on the B 2 O 3 surface after HF exposures. In addition, the QMS analysis was able to identify the etch products during the spontaneous etching of B 2 O 3 by HF gas at 150 °C. The QMS studies observed the main volatile etch products as BF 3 , BF 2 (OH), and H 2 O. Additional volatile etch products were also detected including B 3 O 3 F 3 and other boroxine ring compounds. The DFT predictions were consistent with the spontaneous etching of B 2 O 3 by HF gas. DFT confirmed that CVE was likely because the energetics of the spontaneous etching reaction B 2 O 3 (s) + 6HF(g) → 2BF 3 (g) + 3H 2 O(g) were more favorable than the self-limiting reaction B 2 O 3 (s) + 6HF(g) → 2BF 3 (s) + 3H 2 O(g). The spontaneous etching of B 2 O 3 was predicted at temperatures above −163 °C for an HF reactant pressure of 0.2 Torr and BF 3 and H 2 O product pressure of 0.01 Torr.

Volatile Products from Ligand Addition of P(CH3)3 to NiCl2, PdCl2, and PtCl2: Pathway for Metal Thermal Atomic Layer Etching

“…Spontaneous thermal etching is also important in thermal atomic layer etching (ALE) processes. , Thermal ALE is defined by sequential surface modification and volatile release reactions that remove material with atomic layer control. , To obtain atomic layer control, at least one of the reactions must be self-limiting. , For the known thermal ALE processes, the surface modification reaction is the self-limiting reaction . The volatile release reaction in thermal ALE can be non-self-limiting, i.e., continuous or spontaneous, if the surface modification reaction is self-limiting. − Many thermal ALE reactions have been developed recently for a variety of materials . Thermal ALE has been defined for metal oxides including Al 2 O 3 , − HfO 2 , , ZnO, and Ga 2 O 3 .…”

“…11,12 For the known thermal ALE processes, the surface modification reaction is the self-limiting reaction. 13 The volatile release reaction in thermal ALE can be non-self-limiting, i.e., continuous or spontaneous, if the surface modification reaction is self-limiting. 11−13 Many thermal ALE reactions have been developed recently for a variety of materials.…”

Thermal Atomic Layer Etching of Al2O3 Using Sequential HF and BCl3 Exposures: Evidence for Combined Ligand-Exchange and Conversion Mechanisms

“…This spontaneous etching of B 2 O 3 by HF has been investigated by earlier studies. 10,39 Thermochemical calculations for this reaction at 300 °C yield a negative standard free energy change of ΔG 0 = −16.4 kcal/mol. 47 This negative standard free energy change predicts a spontaneous reaction under equilibrium conditions at the standard state.…”

“…Following conversion to a B 2 O 3 layer, the B 2 O 3 can be spontaneously etched using HF exposures. 10,39 Spontaneous etching is chemical vapor etching as defined by continuous volatilization of material resulting from precursor exposure. 39−41 BCl 3 was used previously during WO 3 thermal ALE for the conversion of the surface of WO 3 to a B 2 O 3 layer.…”

“…There is also a gain of absorbance for B−O vibrations at 1370 cm −1 with an increasing number of BCl 3 exposures. 39 47 This reaction should not be spontaneous under equilibrium conditions at standard state. However, this reaction may be possible at the nonstandard and nonequilibrium conditions for this surface reaction.…”