Overlay Measurement Device, Focus Control Method of Overlay Measurement Device for Tool-induced Shift Measurement, and Focus Control Program of Overlay Measurement Device for Tool-induced Shift Measurement

An overlay measurement device, comprising:

• an objective lens;
• a lens focus actuator configured to adjust a distance between the objective lens and a wafer by moving the objective lens;
• an auto-focus device configured to output a signal according to the distance between the objective lens and the wafer;
• and
• a controller communicatively coupled to the lens focus actuator and the auto-focus device, wherein the controller comprises a memory in which instructions are stored, and a processor configured to execute the instructions, and the instructions enable the processor to perform the following:
• obtaining, for each site of a reference field of a reference wafer in an unrotated state, a first signal that is a signal from the auto-focus device when the corresponding site is in focus, wherein illumination of the auto-focus device is illumination extending spatially beyond an overlay mark formed at the site;
• obtaining, for each site of the reference field after the reference wafer is rotated by 180 degrees, a second signal that is a signal from the auto-focus device when the corresponding site is in focus, wherein illumination of the auto-focus device is illumination extending spatially beyond the overlay mark formed at the site;
• matching the corresponding site with the first signal and the second signal for storage;
• positioning a measurement target site of a measurement target wafer within a field of view of the overlay measurement device;
• and
• adjusting a focus by moving the objective lens on the basis of the first signal matched with the measurement target site when the measurement target wafer is in an unrotated state, or adjusting a focus by moving the objective lens on the basis of the second signal matched with the measurement target site when the measurement target wafer is in a 180-degree rotated state.

A program for controlling a focus of an overlay measurement device, the program being stored in a storage medium to enable a method of controlling the focus of the overlay measurement device to be executed using a computing device, wherein the method includes:

• obtaining, for each site of a reference field of a reference wafer in an unrotated state, a first signal that is a signal from an auto-focus device when the corresponding site is in focus, wherein illumination of the auto-focus device is illumination extending spatially beyond an overlay mark formed at the site;
• obtaining, for each site of the reference field after the reference wafer is rotated by 180 degrees, a second signal that is a signal from the auto-focus device when the corresponding site is in focus, wherein illumination of the auto-focus device is illumination extending spatially beyond the overlay mark formed at the site;
• matching the corresponding site with the first signal and the second signal for storage;
• positioning a measurement target site of a measurement target wafer within a field of view of the overlay measurement device;
• and
• adjusting a focus on the basis of the first signal matched with the measurement target site when the measurement target wafer is in an unrotated state, or adjusting a focus on the basis of the second signal matched with the measurement target site when the measurement target wafer is in a 180-degree rotated state.