Chemically assisted ion beam etching using Cl-2 has been used to fabricate InP-based arrayed waveguide filters that demonstrate full polarization independence and excellent performance characteristics. The process is carried out at elevated temperatures of approximately 250 degrees C to avoid difficulties associated with the low volatility of indium chlorides at lower temperatures. Optimization of the process for smooth, vertical etching is discussed. InP regrowth is successfully carried out on the etched InGaAsP guides, and measurements of the fabricated devices are presented. The adaptation of the process for angled etching is also demonstrated.