The influence of small-scale magnetic field on the heating of J0250+5854 polar cap

The influence of surface small-scale magnetic field on the heating of PSR J0250+5854 polar cap is considered. It is assumed that the polar cap is heated only by reverse positrons accelerated in pulsar diode. It is supposed that pulsar diode is located near the star surface (polar cap model) and operates in the steady state space charge-limited flow regime. The reverse positron current is calculated in the framework of two models: rapid and gradually screening. To calculate the production rate of electron-positron pairs we take into account only the curvature radiation of primary electrons and its absorption in magnetic field. It is assumed that some fraction of electron-positron pairs may be created in bound state that can later be photoionized by thermal photons from star surface.

Generation of plasma in low-pressure discharge

A hydrodynamic model of plasma has been developed, which takes into account both secondary and primary electrons. It has been shown that a solution with a plasma potential higher than the anode potential is possible if the ionization frequency is higher than some critical value. At lower ionization frequencies, it is possible to obtain a solution with a plasma potential below the anode potential

Estimating Step Heights from Top-Down SEM Images

Scanning electron microscopy (SEM) is one of the most common inspection methods in the semiconductor industry and in research labs. To extract the height of structures using SEM images, various techniques have been used, such as tilting a sample, or modifying the SEM tool with extra sources and/or detectors. However, none of these techniques focused on extraction of height information directly from top-down images. In this work, using Monte Carlo simulations, we studied the relation between step height and the emission of secondary electrons (SEs) resulting from exposure with primary electrons at different energies. It is found that part of the SE signal, when scanning over a step edge, is determined by the step height rather than the geometry of the step edge. We present a way to quantify this, arriving at a method to determine the height of structures from top-down SEM images. The method is demonstrated on three different samples using two different SEM tools, and atomic force microscopy is used to measure the step height of the samples. The results obtained are in qualitative agreement with the results from the Monte Carlo simulations.

Impact of secondary electron emission noise in SEM

In semiconductor-device inspection using scanning electron microscopes (SEMs), the irradiation dose of the electron beam becomes lower because of increasing needs for higher throughput and lower damage to the samples. Therefore, it is necessary to form images using fewer primary electrons, making noise reduction of SEM images one of the main challenges. We have modeled the imaging process of SEMs, which consists of the generation of primary, secondary and tertiary electrons (PEs, SEs and TEs, respectively), and detection. Furthermore, a method to accurately evaluate the fluctuation in the number of SEs and TEs are proposed. We found that SEM-image noise can be minimized by directly detecting SEs generated in the sample, in which case the fluctuation in the number of SEs determines the image quality. The variance number of SEs emitted from a 500-eV PE irradiation onto a Si wafer is 1.9 times as large as the value derived assuming a Poisson process. A Monte-Carlo simulation result was used to explain the experimental results and predict that PE energy less than 1 keV suppresses the fluctuation in the number of SEs, and consequently, the SEM-image noise level. These findings provide a method for determining imaging conditions that improve the throughput of SEMs.