Hf0.5Zr0.5O2 based ferroelectric capacitors are deposited via atomic layer deposition with different oxygen content by tuning the ozone dose time during the oxidation step. The impact of the oxygen content in the layer is evaluated in terms of crystalline phase formation and electrical properties. Outstanding device performance and good reliability are demonstrated for the devices with the highest polar orthorhombic phase fraction which only can be reached for an optimized oxygen content. Accordingly, the right oxygen amount is essential for an optimized device performance.