Method for controlling in-plane uniformity of substrate processed by plasma-assisted process

A method for controlling in-plane uniformity of a substrate processed by plasma-assisted process in a reactor comprising:

• a susceptor and a showerhead disposed in parallel facing each other and conductively coupled for plasma discharge in a reaction space formed between the susceptor and the showerhead;
• and an annular duct circularly surrounding the susceptor, said method comprising:
• supplying a principal gas for plasma-assisted process of a substrate placed on the susceptor, to the reaction space through the showerhead, and discharging radially the principal gas from the reaction space through the annular duct;
• and
• while supplying the principal gas to the reaction space, supplying a secondary gas to the reaction space from an area in close proximity to an outer periphery of the susceptor, outside an outer circumference of the substrate as viewed from above, so as to flow at least partially in an inward direction passing the outer circumference of the substrate, reversing the direction of the secondary gas to flow toward the annular duct in a vicinity of the outer circumference of the substrate, and discharging radially the secondary gas together with the principal gas from the reaction space through the annular duct,
• wherein the reactor comprises a reaction chamber and a transfer chamber under the reaction chamber, wherein the reaction chamber and the transfer chamber are separated by a separation ring having an opening in which the susceptor is disposed and a top surface of the susceptor is approximately flush with the separation ring during the plasma-assisted process, wherein the secondary gas is supplied to the reaction space through a clearance between the separation ring and the susceptor at a flow rate such that the secondary gas enters the reaction space partially in the inward direction passing the outer circumference of the substrate, reverses direction to flow toward the annular duct in a vicinity of the outer circumference of the substrate, and is discharged radially together with the principal gas from the reaction space through the annular duct,
• wherein the clearance between the separation ring and the susceptor varies along the outer periphery of the susceptor to change the flow rate of the secondary gas along the outer periphery of the susceptor,
• wherein a center of the separation ring is shifted from a center of the susceptor toward a gate valve disposed in a side wall of the transfer chamber, through which gate valve the substrate is taken into and out of the transfer chamber.