Quantum devices based on optically addressable spin qubits in diamond are promising platforms for quantum technologies such as quantum sensing and communication. Nano- and microstructuring of the diamond crystal is essential to enhance device performance, yet fabrication remains challenging and often involves trade-offs in surface quality, aspect ratio, device size, and uniformity. We tackle this hurdle with an approach producing millimeter-scale, thin (down to 70 nm), and highly parallel (< 0.35 nm/μm) membranes from single-crystal diamond. The membranes remain contamination free and possess atomically smooth surfaces (Rq < 200 pm) as required by state-of-the-art quantum applications. We demonstrate the benefits and versatility of our method by fabricating large fields of free-standing and homogeneous photonic nano- and microstructures. Leveraging a refined photolithography-based strategy, our method offers enhanced scalability and produces robust structures suitable for direct use, while remaining compatible with heterogeneous integration through pick-and-place transfer techniques.