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 (SrTp(2)) and water as precursors. Self-limiting ALD growth is established at 350 degrees C with SrTp(2) and water pulse lengths of >= 2.0 s and >= 0.3 s, respectively. An ALD window is observed from 300 to 375 degrees C, in which the growth rate is 0.47 angstrom 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 degrees C, but the boron/strontium and oxygen/strontium ratios are lower than those of SrB2O4 at 350 and 400 degrees 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 2 mu m x 2 mu m areas for films deposited at 325 and 350 degrees C are 0.3 and 0.2 nm, respectively. SEM images of these films show no cracks or pinholes.