High efficiency photoresist coating

A method of applying a coating of photoresist to a circular semiconductor wafer, the wafer having a top surface, a center, a diameter, and an outer edge, the method comprising the steps of

• (a) mounting the wafer on a chuck, the top surface of the wafer aligned horizontally and oriented upward,
• (b) positioning an extrusion head adjacent to the outer edge of the wafer and above the top surface of the wafer, the extrusion head configured to extrude photoresist out an extrusion slot, the extrusion slot having a length bounded by a first end and a second end, the extrusion head positioned with the extrusion slot aligned radially with respect to the wafer, the first end of the extrusion slot located adjacent to the outer edge of the wafer, and the second end of the extrusion slot outside the outer edge of the wafer,
• (c) rotating the wafer about its center, wherein with the wafer rotating at a rotational speed, and the extrusion head moving at a radial speed, the motion of a radially moving extrusion head with respect to the rotating wafer is at a tangential velocity which is a constant tangential velocity.
• (d) extruding a ribbon of photoresist from the extrusion slot, the ribbon having a width which is substantially equal to the length of the slot, wherein the photoresist is extruded from the extrusion slot at a rate which is a constant extrusion rate, and
• (e) while extruding photoresist from the extrusion slot, and maintaining the extrusion slot aligned radially with respect to the wafer, moving the extrusion head radially inward from the outer edge of the wafer toward the center of the wafer until the photoresist covers the entire top of the surface of the wafer.

A method of applying a coating of photoresist to a circular semiconductor wafer, the wafer having a top surface, a center, a diameter, and an outer edge, the method comprising the steps of

• (a) mounting the wafer on a chuck,
• (b) positioning an extrusion head at the center of the wafer and above the top surface of the wafer, the extrusion head configured to extrude photoresist out an extrusion slot, the extrusion slot having a length bounded by a first end and a second end, the extrusion head positioned with the extrusion slot aligned radially with respect to the wafer, the first end of the extrusion slot located at the center of the wafer and the second end of the extrusion slot located between the center of the wafer and the outer edge of the wafer,
• (c) rotating the wafer about its center wherein with the wafer rotating at a rotational speed, and the extrusion head moving at a radial speed, the motion of a radially moving extrusion head with respect to the rotating wafer is at a tangential velocity which is a constant tangential velocity,
• (d) extruding a ribbon of photoresist from the extrusion slot, the ribbon having a width substantially equal to the length of the slot, wherein the photoresist is extruded from the extrusion slot at a rate which is a constant extrusion rate, and
• (e) while extruding photoresist from the extrusion slot, and maintaining the extrusion slot aligned radially with respect to the wafer, moving the extrusion head radially outward toward the outer edge of the wafer until the photoresist covers the entire top surface of the wafer.