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

NiCl2, PdCl2, and PtCl2can be spontaneouslyetched by ligand addition with P(CH3)3(P(Me)3, trimethylphos-phine). Ligand addition of P(Me)3to these group 10 metalchlorides can form stable and volatile complexes. These ligand-addition reactions are suggested by the covalent bond classification(CBC) method. The CBC method provides guidelines fordetermining probable transition metal complexes based upon thestoichiometry of the metal (M), one-electron donor ligands (X),and electron-pair donor ligands (L). The CBC model predicts thata complex with a stoichiometry of MX2L2is most frequentlyobserved for Ni, Pd, and Pt. This prediction suggests thatMCl2(P(Me)3)2is a likely stable product after exposing Ni, Pd, and Pt to chlorination and then ligand-addition reactions withP(Me)3. In accordance with these expectations,in situQMS studies revealed that NiCl2(P(Me)3)2+, PdCl2(P(Me)3)2+, andPtCl2(P(Me)3)2+were observed as volatile metal complexes resulting from P(Me)3exposure to NiCl2, PdCl2, and PtCl2.Thermochemical calculations also indicated that addition of P(Me)3to MCl2and MCl2(P(Me)3) was favorable where M = Ni, Pd,and Pt. The identification of these volatile products and the theoretical verification of their stability suggest that pathways for Ni, Pd,and Pt thermal atomic layer etching (ALE) are possible based on sequential chlorination and ligand-exchange reactions.

Automated summary

NiCl2, PdCl2, and PtCl2 can form stable and volatile complexes by adding the ligand P(Me)3. In these ligand-addition reactions, MCl2(P(Me)3)2 is the most common product. In situ QMS studies confirmed the formation of volatile metal complexes after exposing the metal chlorides to P(Me)3. Thermochemical calculations also showed that adding P(Me)3 to MCl2 and MCl2(P(Me)3) is favorable. These findings suggest that thermal atomic layer etching of Ni, Pd, and Pt may be possible based on sequential chlorination and ligand-exchange reactions.