seating a substrate having a substrate radius on an electrostatic chuck;

applying first radio-frequency power to the electrostatic chuck to induce plasma in a region at least above the electrostatic chuck, wherein the first radio-frequency power is provided by a first radio-frequency power supply; and

generating a magnetic field in the region at least above the electrostatic chuck using a magnet having a ring-shape and disposed above the electrostatic chuck by applying second radio-frequency power to the magnet, wherein the second radio-frequency power is applied to the magnet by a second radio-frequency power supply including a power source generating a source voltage, and a modulator connected between the power source and the magnet, and wherein the modulator is configured to generate a pulse through modulation of the source voltage,

wherein the magnet has an inner radius ranging from about one-half to about one-fourth of the substrate radius,

wherein the modulator comprises:

a pulse generator configured to generate the pulse; and

a peak generator connected to the pulse generator and configured to generate a peak of the pulse,

wherein the pulse generator comprises:

first delay cells connected in series to the power source; and

a first gate driver connected to the first delay cells to provide a trigger signal to the first delay cells, and

wherein the peak generator comprises:

an additional power source;

second delay cells connected in series to the additional power source, and

a second gate driver connected to the first gate driver and the second delay of cells to provide the trigger signal to the second delay of cells.