Surface charge on insulating samples can be a significant source of error for scanning probe microscopes. We have found that it is possible to operate a scanning force microscope in a manner that makes it relatively immune to charge-induced forces while still allowing the probe tip to nondestructively follow the surface topography. The need to maintain close charge balance on the sample is thus obviated. We have used this strategy to perform critical dimension measurements on optical photomasks with the Surface/Interface Stylus NanoProfilometer. This instrument incorporates a servoed force-balance sensor. Surface topography is determined by touching the surface with contact forces between 0.1 and 1 μN.

Accurate stylus control and automatic tip characterization has enabled a new level of performance from scanning probe microscopy, This technology has the potential to aid the leading edge of CD-SEM metrology and is widely applicable in processes with high-aspect-ratio structures in which wall angles and profile details are critical.

One of the fundamental requirements for reliable critical dimension measurement with a scanning probe microscope is stability of the stylus against flexing and against erosion. We report on the wear of an etched optical fiber when scanned across a variety of surfaces. The optical fiber probe tip was used in a novel scanning probe microscope employing a balance beam force sensor.

To measure the angle of a wall, the probe of a stylus profiler must be able to reach the wall. Sample tilting substantially expands the range of wall angles accessible to a profiler. Tilting also allows flared probe tip characterizers to be used more efficiently. The balance beam force sensor used for this work was designed to permit significant sample tilting.

Measurements were made of the sticking coefficient γ of CO2 molecules on a H2O ice substrate as a function of time. A molecular beam was used with a flux of 7.7 × 1013 molecules cm−2 sec−1. The H2O surface temperature Ts was varied between 72.4 and 74.4 K. The behavior of γ as a function of time was interpreted in terms of a microscopic nucleation theory. γ was also measured for Ts decreasing at a constant rate b from above 78 K to 72 K. These data, taken with different beam fluxes, showed that nucleation processes are continuous for this system rather than discontinuous at some critical temperature. Analysis of the data for Ts = constant and b = constant gave a critical cluster size of four CO2 molecules and an activation energy equal to 22 ± 2.4 kcal mole−1. Thermal desorption rate measurements yielded an activation energy of desorption for CO2 on solid H2O equal to 6007 cal mole−1.