Novel electron beam technology using InGaN photocathode for high-throughput scanning electron microscope imaging

Abstract

An InGaN photocathode with a negative electron affinity (NEA) surface is suitable for industrial use because of features such as a long quantum efficiency lifetime, availability with a visible laser as an excitation light source, and the presence of a transmission-type structure. The first objective is the development of an InGaN photocathode electron gun that can be mounted on a scanning electron microscope (SEM) and the evaluation of the electron beam size at the emission point, maximum emission current, and transverse energy of the electron beam, which are important factors for realizing a high probe current in the SEM. The second objective is the evaluation of emission current stability, while the third objective is the generation of a pulsed electron beam and multi-electron beam from the InGaN photocathode. The parameters of the electron beam from the photocathode electron gun were an emission beam radius of 1 μm, transverse energy of 44 meV, and an emission current of up to 110 μA. Using a high beam current with low transverse energy from the photocathode, a 13 nA probe current with 10 nm SEM resolution was observed with 15 μA emission. At 15 μA, the continuous electron beam emission for 1300 h was confirmed; at 30 μA, the cycle time between the NEA surface reactivations was confirmed to be 90 h with 0.043% stability. Moreover, a 4.4 ns pulsed e-beam with a 4.7 mA beam current was generated, and a 5 × 5 multielectron beam with 12% uniformity was then obtained. The advantages of the InGaN photocathode, such as high electron beam current, low transverse energy, long quantum efficiency lifetime, pulsed electron beam, and multi-electron beam, are useful in industries including semiconductor device inspection tools.

Photoelectron beam from semiconductor photocathodes leading to new inspection technologies

“…We have achieved SEM imaging of the electrical operation process of MOS transistors in flash memory devices and clear SEM imaging of particles at the bottom of high aspect ratio trench by using the selective electron beaming technology with the PC-SEM [12], [13], [14]. Here, as a basic performance evaluation of the PC-SEM, we describe the results of the evaluation of the brightness and angular current density of the electron beam on the specimen in the SEM.…”