Differential pumping apparatus and focused charged particle beam system

A focused charged particle beam system, comprising:

• a differential pumping apparatus, including:
• a head movable relative to a surface to be processed of a substrate to be processed to face any area on the surface to be processed,
• the head having closed-loop grooves (10A, 10B, 10C, 10D) in its surface adapted to face the surface to be processed, each of the closed-loop grooves surrounding the center of the surface adapted to face the surface to be processed,
• the closed-loop grooves including the innermost closed loop-groove (10A) and other closed-loop grooves (10B, 10C, 10D),
• the head having, within the area surrounded by the innermost closed-loop groove (10A), among the closed-loop grooves an aperture defining a space for conducting processing of the surface to be processed,
• the innermost closed-loop groove (10A) being connectable to a deposition gas supply to deliver a deposition gas to the space for conducting processing of the surface to be processed, the closed-loop grooves including at least one closed-loop groove, selected from the other closed-loop grooves (10B, 10C, 10D), to which a vacuum pump is connectable to suck air from the one closed-loop groove to create high vacuum within the space under the condition that the surface of the head faces the surface to be processed;
• a focused energy beam column, which is on the side of the head opposite to the surface adapted to face the surface to be processed, having a lens barrel, the lens barrel having a focused energy beam system built-in for emitting a focused energy beam to pass through the aperture;
• a displacement drive unit configured to move the head or the surface to be processed to adjustably control the parallelism and distance between the surface to be processed and the surface of the head;
• gap measurement devices placed at least three locations along the periphery of the surface of the head, each of the gap measurement devices being configured to detect the distance between the surface of the head and the surface to be processed and to provide the distance information, and
• a gap control unit configured to control the displacement drive unit in response to the distance information measured by each of the gap measurement devices so that the surface of the head and the surface to be processed will be parallel to each other with a predetermined distance kept therebetween.