Scanning Magneto-Optic Kerr Effect Microscope for Inspection of MRAM Manufacturing

Spin transfer torque Magneto-resistive random access memory (STT-MRAM) is becoming next-generation non-volatile memory, for example, replacement of embedded Flash and static random access memory (SRAM) in logic devices. In semiconductor device manufacturing, the inspection process is very important for yield management. Optical inspection equipment is often used to detect defects in device patterns; however, as for MRAM inspection, it is desirable to detect not only device patterns but also magnetic properties at the same time. The magneto-optic Kerr effect (MOKE) microscope is a 2-D evaluation method for the magnetic property using MOKE. In this article, a high-speed inspection method for evaluating magnetic property called scan MOKE is proposed by combining a MOKE microscope with a time delay integration (TDI) camera, a scan stage, and an electromagnet that enables a position-dependent magnetic field in the scan direction (gradient magnet). This method shows to provide a high-speed evaluation of the magnetic properties based on the thickness and the annealing conditions of the perpendicular magnetic anisotropy (PMA) STT-MRAM.