A method for manufacturing a diffuser for a backlight module is disclosed. The method includes providing a transparent substrate; forming a first transparent photoresist layer on the transparent substrate; spreading a plurality of masking particles on the first transparent photoresist layer; exposing and developing the first transparent photoresist layer; removing the masking particles; etching the exposed region of the first transparent photoresist layer to form a first scattering array; and optionally forming a passivation layer on the first transparent photoresist layer.