The ability to fabricate micro/nanostructures on large surface areas would enhance product performance in optics and solar energy systems, where maintaining high productivity is also critical. Recently, diamond tools structured with nanoscale features have been used to machine ductile materials such as copper and electroless nickel. This study uses engineered diamond tools featuring multi-tip cutting edges to investigate nanoscale grooving of silicon. Multi-tip cutting edges create a certain level of pressure and temperature at the cutting zone, which leads to phase transformations in silicon. Experiments were performed using an ultra-precision machining setup to identify conditions leading to nanoscale ductile-mode machining of silicon. As nanogrooves reach 300 nm depth, hexagonal-Si (Si-IV) phase formation was observed based on laser Raman spectroscopy measurements. Hexagonal allotropes of silicon are known to improve light absorption of silicon. Additional experiments with non-structured diamond tools did not yield any Si-IV phase transformation, indicating the importance of obtaining necessary pressure and temperature conditions at the cutting zone.