Optical beam steerers on InP integrated photonics have not been able to offer high angular resolution, due to the technological challenges in realizing a large emission aperture. In this paper, we propose the creation of waveguide-based grating antennas fabricated in SiO2 super-cladding on InP membrane on silicon (IMOS) to achieve simultaneously high resolution and good compatibility with InP-based active devices. By exploiting the high dry etch selectivity between SiO2 and InP, a tolerant fabrication process is proposed and demonstrated, allowing for high controllability in the process. Device parameters including buffer thickness and pitch have been explored to obtain an optimized design. A 2-mm long grating antenna is fabricated and shows a record narrow full-width-half-maximum angular beam width of 0.05° and a high spatial resolution of more than 250 points when the wavelength is tuned over a range of 100 nm.