Mechanical strength of low-k material greatly decreases; material composition change will also give dry etching a lot of problems which have never met before. This paper explores the approaches to solve new problems when plasma etching low-k material, such as avoiding low-k damage and other defects, keeping anisotropic and needed selectivity; finding out the process parameters with the biggest influence, such as gas species, pressure, RF frequency, power, etc. Applies the process trend to plasma etching low-k material (BD) of 40nm dual damascene trench etch and achieves the critical target.