Optimization of substrate-selective atomic layer deposition of zirconia on electroplated copper using ethanol as both precursor reactant and surface pre-deposition treatment

Abstract

Recent developments on the further optimization of the selective atomic layer deposition (ALD) of zirconium oxide (ZrO2) onto silicon over electroplated copper are reported with tris(dimethylamino)cyclopentadienyl zirconium as the zirconium precursor and ethanol as both oxygen source for precursor and pretreatment of copper surface to reduce surface oxides. A comparison between the electroplated (EP) and e-beam deposited (EB) copper before ALD using high-resolution X-ray photoelectron spectroscopy (XPS) showed EP Cu having more oxides on the surface and unexpectedly the EP Cu was found to have higher selectivity of ALD. In addition, a comparison of deposition of zirconia on silicon over EP and EB copper substrates for 70 ALD cycles show experimental conditions can impact the degree of selective deposition with the electroplated copper. With further optimization of the substrate pretreatment and ALD process parameters, both XPS survey analysis and ellipsometry showed ALD selectivity was enhanced up to 100 cycles on electroplated copper samples which is higher than ever previously reported forming an amorphous ZrO2 film of ~ 3 nm thickness on silicon and no deposition on copper. Lack of crystallinity of the ALD ZrO2 films is manifested by X-ray absorption fine structure and grazing incidence X-ray diffraction. Atomic force microscopy and scanning electron microscopy performed on the samples indicated no significant changes of the roughness and topography on the samples before and after ZrO2 ALD. Both thermodynamic calculations and experimental data presented here show that ALD selectivity is mainly dictated by the balance of the total amounts of oxygen and carbon in the reactor along with the ALD conditions and reactor design. These studies show pre-deposition ethanol exposure of the substrate, deposition/adsorption of reduction byproducts formed, and the total oxygen and carbon in the ALD reactor are important contributors to whether ALD selectivity can be significantly enhanced or even achieved at all.