Radiant energy – Inspection of solids or liquids by charged particles – Electron probe type
Reexamination Certificate
2000-12-13
2003-06-10
Lee, John R. (Department: 2881)
Radiant energy
Inspection of solids or liquids by charged particles
Electron probe type
C250S306000, C250S307000, C250S311000, C250S492200, C250S442110, C250S398000
Reexamination Certificate
active
06576902
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a correction method of a scanning electron microscope. In particular, the present invention relates to a correction method of a scanning electron microscope employed for dimensional measurement or the like of a highly integrated circuit semiconductor.
2. Description of the Related Art
Currently, measurement of pattern dimensions in a semiconductor device is performed by a scanning electron microscope (hereinafter, SEM). This SEM is an apparatus for observing a surface of a micro (minute) sample by scanning an electron beam on the surface of the minute sample instead of light. The SEM has a merit in that the sample can be observed in a wide range from scores of magnifications to hundreds of thousands of magnifications (the magnification in which a molecular level can be observed).
In general, in the SEM, an electron generated by an electron gun is converged to an electron beam by a group of electromagnetic lenses. This electron beam is adjusted by means of an electromagnetic lens for focal position control so as to be converged at one point on a stage. This electron beam is scanned on the stage in a two-dimensional manner by controlling a magnetic field caused by a beam-scanning electrode.
When a sample is placed on the stage, and irradiated by the electron beam, secondary electrons according to a rugged state of a sample surface are discharged from the sample surface targeted for measurement. In the SEM, the discharged secondary electrons are collected, and are detected by means of a detector such as a scintillator or a photo multiplier (photoelectric multiplier) to be electrically converted. The electrically converted electron is synchronized with a scan signal of a scanning radiation of a display section such as a CRT, whereby a secondary electron image (hereinafter, referred to as an SEM image) according to the rugged state of the sample surface is obtained. Since the scanning range of the electron beam is narrow, the stage is moved in a X-Y plane direction by means of a stage movement system, whereby the SEM image of the entire sample targeted for measurement is obtained.
In addition, the SEM enables observation of a minutely small region, and thus, it is used as an apparatus for dimensional measurement as well as sample observation. In this case, it is required to perform the correction work of dimensional measurement precision, thereby maintaining the measurement precision. Conventionally, for example, correction has been performed by obtaining how many dots on the screen the SEM image of a standard sample whose dimensions are obtained in advance correspond to.
Conventionally, it is presumed that the electron beams of the SEM are always converged at one point on the sample surface, and that an ideal irradiation position caused by an electron beam control signal coincides with an irradiation position of actual electron beam. However, it is not actually verified as to whether or not the electron beam is converged on the sample surface and as to whether or not the ideal irradiation position caused by the electron beam control signal coincides with the actual irradiation position of electron beams.
Because of this, actually, if the electron beam is not always converged at one point on the sample surface or if the ideal irradiation position of electron beam does not coincide with the irradiation position of actual electron beam, these cannot be detected. Thus, there is a problem that a displacement between an actual sample surface and a detected image occurs, and the detection precision is impaired.
In addition, since the ideal irradiation position caused by the electron beam control signal does not coincide with the actual irradiation position of the electron beam, the electron beam is not actually irradiates a user-specified irradiation position. That is, the electron beam is irradiates a different position. Thus, there is a problem that an SEM image at the irradiation position that is not specified by the user is recognized as an SEM image at the user-specified irradiation position.
SUMMARY OF THE INVENTION
From the foregoing, it is an object of the present invention to provide a method of correction of a scanning electron microscope capable of performing correction with high precision by causing the user-specified irradiation position of the electron beam to coincide with the actual irradiation position of the electron beam.
In order to achieve the foregoing object, according to a first aspect of the present invention, there is provided a scanning electron microscope correction method comprising the steps of: setting a detection sample for producing light of an intensity corresponding to an electron density of an electron beam irradiating a surface of the detection sample; irradiating with the electron beam a predetermined position of the detection sample placed on a movable stage of the scanning electron microscope; detecting the intensity of the light produced from the detection sample; and performing correction relating to the scanning electron microscope on the basis of the intensity of the detected light.
In the scanning electron microscope correction method according to the first aspect of the present invention, correction relevant to the scanning electron microscope is performed by, for example, utilizing the fact that the density of the electron beam irradiated to the surface of the detection sample is a maximum and the detected light intensity is a maximum when the focal position of the electron beam irradiating the detection sample is precisely converged on the surface of the detection sample. For example, at least one of the movement amount of the focal position of the electron beam and the movement amount of the stage is corrected.
In this way, for example, the user-specified focal position of the electron beam can coincide with an actual focal position of the electron beam accurately, and the focal position of the electron beam can be corrected with high precision.
A focal position can be corrected by correcting, for example, the movement amount of the focal position so that the detected light intensity is always a maximum at each of the different positions on the detection sample on an inactive stage or the movement amount of the stage so that the detected light intensity is always a maximum in a state in which the movement amount of the focal position is constant (fixed). In addition, the focal position is moved in an optical axial direction so that the detected light intensity during electron beam scanning is always a maximum, whereby the focal position can be corrected.
According to a second aspect of the present invention, there is provided a scanning electron microscope correction method, wherein one of a movement control amount of a focal position of the electron beam in an optical axis direction and a movement control amount of the stage in the optical axis direction is corrected at a plurality of positions on the stage. In this manner, the focal position is corrected corresponding to an inclination of the stage. Thus, the displacement of the focal position due to such inclination of the stage is prevented, and an error caused by the inclination of the stage can be eliminated.
First, an electron beam irradiates a predetermined position, and the movement control amount of the focal position in the optical axis direction is corrected. Then, the stage is moved, and the irradiation position of the electron beam is changed to another position, whereby the electron beam irradiates another position. If the stage is inclined, the focal position is shifted from the surface of the detection sample, and the maximum optical intensity is not obtained.
In order to maximize the light intensity, there can be employed a method of adjusting the movement control amount of the focal position in the optical axis direction at each position after the stage has been moved; and a method of adjusting the inclination of the stage at each position after the stage has been moved.
According to the
Oki Electric Industry Co. Ltd.
Rabin & Berdo P.C.
Wells Nikita
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