A method of controlling surface non-uniformity of a process layer includes receiving a first lot of wafers, and polishing a process layer of the first lot of wafers. A control variable of the polishing operations is measured after the polishing is performed on the process layer. A first adjustment input for an arm oscillation length of a polishing tool is determined based on the measurement of the control variable. A process layer of a second lot of wafers is polished using the adjustment input for the arm oscillation length. A controller for controlling surface non-uniformity of a process layer includes an optimizer and an interface. The optimizer is adapted to determine a first adjustment input for arm oscillation length of a polishing tool based on a measurement of a control variable from a first lot of wafers. The interface is adapted to provide the first adjustment input to the polishing tool for polishing a second lot of wafers.