Mirror electron microscope for inspecting nanometer-sized defects in magnetic media

We developed a mirror electron microscope (MEM) for the highly sensitive inspection of defects on the magnetic storage disks of commercial hard disk drives (HDDs). Magnetic fields recorded on a magnetic disk do not affect the MEM images for inspection. We used artificial defects in a detection sensitivity evaluation to test the effectiveness of our MEM inspection tool and found that it was sensitive enough to detect defects that were 67 nm in diameter and 7 nm in height. The size of a MEM image for a defect was eight times larger than the physical size measured by an atomic force microscope. The obtained sensitivity is beyond the resolution power of the objective lens of the MEM itself. This is because MEM images the distortion of static electrical potentials spread over a larger area than the physical size of a defect itself and the image is obtained in out-of-focus condition of an objective lens. The image acquisition time was 50 ms, which corresponded to the inspection time of 4 h for the full surface inspection of a 2.5 in. magnetic disk. MEM is a promising technique for conducting a highly sensitive defect inspection and a high throughput inspection simultaneously as compared with an SEM-based inspection.