By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Shirahata, Kaori (Tokyo, JP); Bizen, Daisuke (Tokyo, JP); Sakakibara, Makoto (Tokyo, JP); Sohda, Yasunari (Tokyo, JP); Kawano, Hajime (Tokyo, JP); Kazumi, Hideyuki (Tokyo, JP), filed on April 20, 2015, was published online on July 3, 2018.
The assignee for this patent, patent number 10014160, is Hitachi High-Technologies Corporation (Tokyo, JP).
Reporters obtained the following quote from the background information supplied by the inventors: "Currently, the scanning electron microscope (hereinafter, SEM) is widely used in observation of submicron- and nano-sized samples. The SEM is designed to form an image by irradiating a sample with primary electrons emitted from an electron source while scanning the primary electrons, and by detecting secondary electrons that are generated in the sample. Here, the secondary electrons can be grouped into 'true' secondary electrons characterized by having an energy of 50 eV or less, and backscattered electrons having an energy nearly equal to the incident energy of the primary electron. It is possible to obtain the contrast that reflects the differences in the shape of the pattern surface, the potential, the work function, and the like from the 'true' secondary electron. On the other hand, it is possible to obtain the contrast that reflects the difference in the pattern material from the backscattered electron (See Non-patent Literature 1).
"Recently, SEMs developed by different companies have included a plurality of detectors, enabling users to obtain images with various contrasts. On the other hand, it is difficult to interpret the image contrast and there is an increased demand for a quantitative analysis of the energy of secondary electrons detected by the SEM. In addition, it is necessary to perform an energy analysis on the secondary electrons under the condition in which the energy of the primary electrons is low, in order to reduce the damage to the sample caused by primary electron irradiation. As a method for performing the energy dispersion of secondary electrons in SEM, for example there is known a method described in Patent Literature 1."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "Technical Problem
"In the method disclosed in Patent Literature 1, the energy dispersion of the secondary electron is performed by placing a spectrometer between an objective lens of an SEM and a sample. However, in such a configuration, it is difficult to reduce the distance between the objective lens and the sample. As a result, there is a problem that the spatial resolution of a primary electron is deteriorated.
"The retarding method that applies a negative voltage V.sub.r (<0) to a sample to decelerate the primary electron immediately above the sample is an effective method for obtaining a high spatial resolution under the condition in which the energy of the primary electron is low. In the retarding method, a voltage V.sub.r of several kV is typically applied to the sample. In this case, the secondary electrons generated in the sample are accelerated by the retarding voltage V.sub.r, and most of the secondary electrons pass through the objective lens which is the converging lens. In other words, when the retarding method is applied to the configuration disclosed in Patent Literature 1, there would be very few secondary electrons injected into the spectrometer.
"Thus, in order to perform an energy analysis of secondary electrons in the SEM to which the retarding method is applied, the secondary electrons passing through the objective lens should be deflected to the outside of the optical axis and then are injected into the spectrometer. Further, the secondary electrons passing through the objective lens are spatially scattered, thus requiring a convergence mechanism in order to increase the number of secondary electrons to be injected into the spectrometer.
"On the other hand, in the retarding optical system, changing the energy injected into the sample of the primary electron to change the observation target is achieved by changing the retarding voltage V.sub.r. Here, the energy of the secondary electron changes when V.sub.r is changed, and there is a problem that the focus position of the secondary electron changes. Further, the relationship between the energy resolution .DELTA.E of the spectrometer, and the energy E.sub.p of the secondary electron, which is detected passing through the spectrometer, is expressed by the following equation.
"Here, R is a unique constant determined by the size and shape of the spectrometer as well as the dimensions of the slit. When the retarding method is used, the secondary electron is accelerated by the voltage V.sub.r applied to the sample. In other words, there is a problem that when V.sub.r is changed for a change in the observation target or the like, the energy of the secondary electron injected into the spectrometer also changes, resulting in a change in the energy resolution .DELTA.E.
"An object of the present invention is to provide an SEM using a retarding method and having an electron spectroscopy system, in which the number of electrons injected into a spectrometer and the energy resolution do not change even if the retarding voltage V.sub.r is changed, and to provide a control method of the SEM.
"Solution to Problem
"In order to achieve the above object, the present invention provides an SEM including: an electron source; a first deflector that deflects a primary electron beam emitted from the electron source; a converging lens that focuses the primary electron beam deflected by the first deflector; a second deflector that deflects a secondary electron from a sample, which is generated by the first electron beam focused by the converging lens, to the outside of the optical axis of the primary electron beam; a voltage applying unit that applies a negative voltage to the sample to decelerate the primary electron beam; a spectrometer for dispersing the secondary electron; a detector that detects the secondary electron passing through the spectrometer; an electrostatic lens provided between the second deflector and the spectrometer; and a voltage control unit that controls the voltage applied to the electrostatic lens based on the negative voltage applied to the sample. The electrostatic lens allows the deflecting action to be overlapped with the converging action.
"Further, in order to achieve the above object, the present invention provides a control method of an SEM including: a deflector that deflects a secondary electron from a sample, which is generated by focusing a primary electron beam emitted from an electron source and by irradiating the sample with the primary electron beam, to the outside of the optical axis of the primary electron beam; a spectrometer for dispersing the secondary electron; a detector that detects the secondary electron passing through the deflector; and an electrostatic lens provided between the deflector and the spectrometer, allowing the deflecting action to be overlapped with the converging action. The control method applies a negative voltage to the sample to decelerate the primary electron beam, to control a first bias voltage applied to the electrostatic lens based on the negative voltage applied to the sample.
"Advantageous Effects of Invention
"According to the present invention, it is possible to perform the energy dispersion of the secondary electron, without changing the number of electrons injected into the electrometer and the energy resolution even if the retarding voltage V.sub.r is changed, by using the retarding method."
For more information, see this patent: Shirahata, Kaori; Bizen, Daisuke; Sakakibara, Makoto; Sohda, Yasunari; Kawano, Hajime; Kazumi, Hideyuki. Scanning Electron Microscope and Method for Controlling Same. U.S. Patent Number 10014160, filed April 20, 2015, and published online on July 3, 2018. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=10014160.PN.&OS=PN/10014160RS=PN/10014160
Keywords for this news article include: Asia, Japan, Business, Technology Companies, Hitachi High-Technologies Corporation, Semiconductor Equipment and Materials Companies.
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