Robust and efficient image processing scheme for electron beam LSI wafer pattern inspection

Abstract

Electron beam-based wafer pattern inspection systems have the major advantage of allowing for the inspection of internal electric properties. However, charge-up of the wafer resulting from the use of an electron beam significantly influences inspection and remains a challenging issue. As an alternative approach to strict charge control, the authors propose a new inspection method that is capable of error-free, one-time inspection for recipe preparation, and which provides high-efficiency defect review and low error ratio inspection. Inspection is carried out at a higher-than-expected sensitivity, and defect candidate images are stored by a defect image analyzer (DIA). After inspection, the stored information contains both actual defects and nuisance defects. The distribution of candidate defects is displayed on a wafer map and the operator reviews the stored images and high-resolution review images on demand in order to check whether defects are true or nuisance defects. If necessary, the operator then adjusts the detection sensitivity and the system re-judges the stored data, displaying the modified wafer map to screen. In this way, the proposed system is robust against sensitivity drift caused by charge-up, and offers efficient, low error ratio inspection.

Robust defect detection method using reference image averaging for high-throughput SEM wafer pattern inspection system

“…[4] The pattern on the wafer consists of many grating dies that will later be diced into final LSI products. An example of a defect detected by the inspection system and a cross-section of the defect are shown in Figures 2(a) and (b) [4] . The product shown is a memory chip, with a dark insulator (background) and bright conductive material (pattern).…”

“…[4] An electron beam from an electron source irradiates the wafer via a deflector and an objective lens. A sensor detects secondary electrons emitted from the wafer, which are generated by the bombardment of primary electrons.…”

“…For this reason, a scanning electron microscopy (SEM) inspection system offering high resolution and the ability to evaluate electric properties was developed in 1991. [4] Although the system is able to detect defects of interest (DOI), the throughput has remained 100 mega pixels per second (Mpps), which means that the duration of inspection is about 17 hours per wafer. Limiting inspection time to an hour per wafer is a fundamental requirement for semiconductor production.Therefore, throughput remains far less than desired.…”