Inspection method for contact/via-holes using a low-energy electron microcolumn

摘要

Further scaling of semiconductor devices is limited by the increasing number of defects in contactor via-holes that occur as the aspect ratio increases. Inspection of the bottom of a via-hole, to check for complete clearance, becomes problematical for aspect ratios greater than about 5. Such an inspection is extremely important to circuit yield, as any residue in the hole will result in device failure. At present, holes are inspected from the top using conventional scanning electron microscope imaging, but this method is ineffective for hole diameters <100 nm. Smaller holes need to be observed by this method in cross section to ensure clearance; a method that is not suitable for manufacturing. To resolve the problem, the authors propose a novel method of inspecting small contact/via-holes using a low voltage microcolumn, where the image formed by the specimen current is very sensitive to the presence of residues in the hole. Simply when the beam is place over the hole, the presence of a residual thin film at the bottom of the hole can be reliably detected simply by measuring the sample current due to a stationary electron probe. This inspection method is been demonstrated with a patterned SiO_2 layer on a Si substrate. Preliminary results for currents measured from this sample show that the Si substrate and the SiO_2 residual layer are clearly distinguished. The inspection method and test results for a submicrometer pattern will be discussed in detail.