Apparatus and method for adjusting an ion beam between a mass analyzer and a substrate holder. Herein, one or more bended, such as arch-shaped, curved or zigzag shaped, bar magnets are configured to apply one or more magnetic fields to adjust the shape or cross section of an ion beam passing through a space partially surrounded by the one or more bended bar magnets. At least one of the gap width between neighbor bended bar magnets, the curvature of each bended bar magnet and the current flowing through each bended bar magnet may be fixed or adjusted dependently or independently. Therefore, the Lorentz force applied on the ion beam along different directions may be changed in a desired manner, and then the ion beam may be flexibly elongated, compressed or shaped to meet the process requirement.