The atomic layer deposition of SrB₂O₄ films using the thermally stable precursor Bis(tris(pyrazolyl)borate)strontium

The atomic layer deposition (ALD) of strontium borate films is carried out using bis(tris(pyrazolyl)borate)strontium (SrTp₂) and water as precursors. Self-limiting ALD growth is established at 350°C with SrTp₂ and water pulse lengths of ≥ 2.0 s and ≥ 0.3 s, respectively. An ALD window is observed from 300 to 375 °C, in which the growth rate is 0.47A per cycle. The thin film compositions are assessed by elastic recoil detection analysis (ERDA) and X-ray photoelectron spectroscopy (XPS). ERDA suggests compositions of SrB₂O₄ at growth temperatures of <350 °C, but the boron/strontium and oxygen/strontium ratios are lower than those of SrB₂O₄ at 350 and 400 °C.Within the ALD window, hydrogen concentrations range from 0.37(42) to 0.87(7) at.-%, and the carbon and nitrogen concentrations are below the detection limits. XPS analyses on representative strontium borate thin films show all expected ionizations. X-ray diffraction (XRD) experiments reveal that the as-deposited films are amorphous. The surface morphology is assessed by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The rms surface roughness of typical 2µm x 2 µm areas for films deposited at 325 and 350 °C are 0.3 and 0.2 nm, respectively. SEM images of these films show no cracks or pinholes.