Background and applications of electron beam test techniques

Abstract

The use of electron beams for contactless testing of electrical functions and electrical integrity of different active devices in VLSI chips has been demonstrated over the past years. This method of testing electronic networks is based on an electron probe which is deflected from point to point in the network. A current of secondary electrons emitted in response to the impingement of the electron probe is converted to a signal indicating the presence of a voltage or varying potential at the different points. Voltage contrast, electron beam induced current, dual potential approach, stroboscopic techniques and other methods have been developed and are used to detect different functional failures in devices. Besides the VLSI application, the contactless testing of three-dimensional conductor networks of a 10 cm x 10 cm x 0.8 cm multilayer ceramic module poses a different and new application for the electron beam test technique as reported in [1–5]. A dual potential electron beam test system allows to generate electron beam induced voltage contrast and also to detect this voltage contrast over the large area without moving the substrate and test for the electrical integrity of the networks. Less attention in most of the applications has been paid to the electron optical environment; mostly, SEMs were upgraded or converted to do the job of a “voltage contrast” machine. This by no means will satisfy all requirements and more thoughts have to be given to aspects such as: low voltage electron guns: thermal emitter, Schottky emitter, field emitter; low voltage electron optics; two-lens systems; different means of detection; signal processing; storage and others.