8820

The Hitachi 8820 is a CD-SEM manufactured by Hitachi. The system accepts wafers of 200 mm (8-inch) or 150 mm (6-inch) diameter, with a special carrier available for 50 mm (2-inch) to 125 mm (5-inch) wafers. The CD measurement range is 0.1 to 10 μm, with a measurement reproducibility of ±1 % or 0.005 μm (3 sigma), whichever is larger. Throughput is specified as 20 wafers per hour in continuous measurement with 1 point per chip and 5 chips per wafer. The secondary electron image resolution is 5 nm at an accelerating voltage of 0.8 kV, using a dedicated reference specimen. Magnification covers the range ×1000 to ×150,000 for the SEM image, and approximately ×110 for the optical microscope image.^[1]

The Hitachi 8820 uses a Schottky emission electron gun with an accelerating voltage variable from 700 V to 1300 V in 10 V steps. The lens system consists of an electromagnetic condenser lens system and an FCM (final condenser and objective) objective lens. Secondary electrons are detected by a 1-stage detection system. The objective lens aperture is a heating-type movable aperture with four openings selectable from outside the column, allowing fine adjustment. A two-stage deflection scanning coil and an 8-pole electromagnetic stigmator coil (X, Y) are employed. Probe current can be monitored via an incorporated Faraday cup with automatic measurement. The system also includes an optical microscope providing a 1.2 mm square visual field with monochrome image.^[1]

Wafer handling in the Hitachi 8820 is performed by a cassette-to-cassette auto loader. Wafers are transferred from an open cassette to the loader chamber by an arm-type robot with random access capability using two cassettes. Vacuum chucking is used on the back of the wafer, and orientation flat detection is done by a non-contact optical sensor. After loading, the loader chamber is automatically evacuated and the wafer is transferred to the stage. The stage has a movement range of X and Y from 0 to 200 mm, driven by pulse motors with computer control up to a maximum speed of 50 mm/s.^[1]