A measured force resolution of 5.6×10-18 at 4.8 K in vacuum using a single-crystal silicon cantilever only 600 Å thick is demonstrated. The spring constant of this cantilever was 6.5×10-6 N/m, or more than 1000 times smaller than that of typical atomic force microscope cantilevers. The cantilever fabrication includes the integration of in-line tips so that the cantilever can be oriented perpendicular to a sample surface. This orientation helps suppress cantilever snap-in so that high force sensitivity can be realized for tip-sample distances less than 100 Å. © 1997 American Institute of Physics.