Electron beam induced voltage and injected charge modes of testing

Abstract

IntroductionThe usefulness of the electron beam testing in the semiconductor industry has been described and substantiated by many workers (Wolfgang 1980, Menzel andKubalek 1981). Several testing modes have been well described and analyzed. Recently, one of the less known modes of operation is gaining popularity. It is the no-contact version of beam utilization in the induced voltage mode.Consideration for contactless mode is given when conventional methods can not satisfy testing needs. Typical testing requirements to be satisfied are:No mechanical contacts Probing of small areas No damage to the device tested Speed of testing operation. The other testing technique available beside electron beam (E-beam) is mechanical probing. However, mechanical probing is slow, usually it is destructive, it poorly accesses devices, its needles are too large for VLSI type device sizes, and it disrupts operation of some dynamic circuits.Focused electron beams, in different modes of utilization, do satisfy the above requirements. Processes in Voltage InductionsAn impinging electron beam produces several effects' three of which are used in the charge deposition for induction of voltages utilized for testing. The effects are: production of surface charges, induction of bulk charges, and injection of negative charges. All these effects take place on every irradiated specimen; however, their relative importance, in producing detectable signals, depends on the specimen materials and structural configuration.An important issue is the ability to produce potentials in selected places for testing purposes. The mechanism of voltage induction depends on the material and structure of the specimen. In general, there are three types of materials present in the semiconductor devices: semiconductors, metals, and insulators. SemiconductorsVoltage induction in semiconductors depends on the presence or absence of junctions. When junctions are present, induced charges produce a self biasing effect. When there are no junctions, semiconductors act similarly to metals. Under special conditions, junctions can be biased in the ways required by the test. MetalsAn impinging beam, depending on its energy, produces surface charges, which propagate throughout the conductor and reveal themselves through corresponding positive or negative potentials. Thus surface charging is the predominant effect. 54 G. V. Lukianoff, G. O. Langner: Electron beam induced voltage and injected charge modes of testing InsulatorsCharging effects on an insulator are governed by the secondary emission yield curve. Depending on the beam energy, either positive or negative charges can be produced at the top surface.Semiconductor devices are frequently layered structures of different materials. In such cases, each structure has to be analyzed individually. Semiconductors Operational conditionsProduction of the induced potentials and their detection define operational conditions for the electron beam. Energy of the beam, for testing of semiconductors with the junctions, is selected so a...

Thermal field emission for low voltage scanning electron microscopy

“…Low voltage scanning electron microscopy (LVSEM) is a technique long recognized as offering the possibility of high resolution (< 10 nm) imaging of biological specimens, but has been little used because of instrumental difficulties. Recently, LVSEM has become important for inspection and testing of semiconductor devices and interest in these applications has accelerated greatly (Lukianoff & Langner, 1983;Menzel & Kubalek, 1983;Wolfgang, 1983). In biological applications high resolution is important and beam current less so.…”