Select transistor, method for making select transistor, memory device, and method for manufacturing memory device

A method for manufacturing a memory device including a plurality of memory transistors connected in series and select transistors disposed in both ends of the plurality of memory transistors, comprising:

• forming a tunnel insulating layer on a semiconductor substrate;
• forming a charge storage layer on the tunnel insulating layer;
• forming a blocking insulating layer on the charge storage layer;
• selectively irradiating the blocking insulating layer in a region where the select transistor is to be formed, with a gas cluster ion beam containing argon as source gas;
• forming a gate electrode on the blocking insulating layer;
• patterning the tunnel insulating layer, the charge storage layer, blocking insulating layer and the gate electrode;
• and
• forming a source/drain region within the semiconductor substrate at both sides of the patterned gate electrode.