JP2964597B2 - Correction method of fluctuation of irradiation current in surface analysis - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a sample with an electron beam, spectrally analyzing X-rays radiated from the sample, and changing the irradiation current with time in mapping measurement for obtaining the concentration distribution of elements on the sample surface. And a correction method for

[Prior art]

In the electron beam microanalyzer (EPMA), it takes a long time to perform mapping measurement, so that the irradiation current may fluctuate during mapping, but there is no mechanism to monitor the fluctuation and provide feedback. Was. For this reason, at present, the measurement is started after confirming that the irradiation current does not fluctuate for a certain period of time. However, even if such a check is performed, there is no guarantee that the irradiation current does not fluctuate during mapping, and there has been a problem that the reliability of the measurement result is poor.

SUMMARY OF THE INVENTION It is an object of the present invention to check a change in irradiation current during mapping, correct the change, and improve measurement accuracy.

[Means for Solving the Problems]

As a method of correcting the fluctuation of the irradiation current in mapping,
Before analyzing the sample surface, the characteristic X-ray intensity of the analysis element is initially measured at at least two analysis points on the sample surface, the measured value is stored in a storage device, and then the mapping measurement of the sample surface is performed. The characteristic X-ray intensity of the analysis element in the initial measurement and the characteristic X-ray intensity of the analysis element in the mapping measurement at the same point as the analysis point in the initial measurement are read out from the storage device. An extrapolation correction function was obtained, and the measured value of the mapping measurement was corrected using the correction function.

[Operation]

In the present invention, at a plurality of points in the analysis area, the characteristic X-ray intensity of the analysis element is initially measured in advance, and the measurement result at that point obtained at the time of mapping measurement and the measurement result obtained at the reference measurement are used. , A correction function, and the mapping measurement value is corrected by the correction function to correct the variation of the irradiation current during the mapping. Since the initial measurement is performed only at several points, it does not take much time, and the irradiation current during that time can be regarded as constant. In general, the fluctuation of the irradiation current can be considered to be smooth within the time required for mapping, so the ratio of the initial measurement value at the same point as the initial measurement and the measurement value at the time of mapping is smoothly connected by interpolation. The result indicates a change over time in the measured value. Therefore, by using this, it is possible to correct the influence of the fluctuation of the irradiation current.

【Example】

FIG. 1 shows a flowchart of one embodiment of the present invention.
In FIG. 1, a sample is set on a stage so that the sample surface is positioned horizontally, and first, an analysis region and an analysis element to be subjected to mapping measurement are designated (A). Initially, the characteristic X-ray intensity is measured at least at two locations (Xa, Xb) for the analysis element, and the measured value Ic (Xi) is stored in a storage device (a). For example, as shown in FIG. 3, the analysis points of the initial measurement are square analysis points, and A near the start point and B near the end point.
Set to. Perform mapping measurement of the analysis area, and
Im (Xi) [where i = a or b] is stored in the storage device (c). From the measurement values obtained in the mapping measurement,
X-ray intensity Im (Xi) at the same analysis point measured in the initial measurement
Then, the measurement value Ic (Xi) of the initial measurement is called out, and a correction function Y (Xi) is created by the arithmetic unit (D). For example, if the correction function is represented by a linear function as shown in FIG. 2, it can be set as in the following equation (1). Where Xi is the analysis point (in the order of measurement), and the correction function Y (X
i) represents the ratio between the measured value that would be obtained by the irradiation current in the initial measurement at the point i and the measured value Im (Xi), and by multiplying the measured value by this value, the irradiation in the initial measurement is performed. The measured value (correction value) that will be obtained by the current is a value obtained. Therefore, Y (Xa) indicates the ratio Ic (Xa) / Im (Xa) between the initial measured value Ic (Xa) at the point a and the measured value Im (Xa) at the time of mapping, and Y (Xb)
Indicates Ic (Xb) / Im (Xb). Since the correction function changes gradually with time, it is considered that the correction function changes linearly in a simple manner, and the correction function Y (Xi) is changed to the coordinates [Xa, Y (Xa)] of the correction function at points a and b. And [Xb, Y (Xb)] can be expressed as the following equation (1). Y (Xi) = [(Y (Xb) −Y (Xa)) / (Xb−Xa)] × (Xi−Xa) + Y (Xa) (1) In the arithmetic unit, the measured value Im at the analysis point Xi
By multiplying (Xi) by the above correction function Y (Xi) as in the following equation (2), I ′ (Xi) = Im (Xi) × Y (Xi) (2) The measured value is corrected to the measured value I '(Xi) corresponding to the irradiation current (e). Mapping display is performed using the correction value I '(Xi) (f). In the above embodiment, a linear equation based on two-point measurement is used as the correction function. However, if a large number of analysis points are measured in the reference measurement instead of the two-point measurement, a more accurate correction function using a multi-dimensional equation can be used. Corrections can be made.

[Effect]

ADVANTAGE OF THE INVENTION According to this invention, it became possible to correct | amend the mapping measurement value by the fluctuation | variation of an irradiation current, and the measurement accuracy improved further.

[Brief description of the drawings]

FIG. 1 is a flowchart of one embodiment of the present invention, FIG. 2 is a correction function diagram, and FIG. 3 is an explanatory diagram of analysis points.

Claims (1)

(57) [Claims] In a mapping measurement for irradiating a sample surface with an electron beam and dispersing X-rays emitted from the sample to obtain a concentration distribution of elements on the sample surface, at least two points on the sample surface are analyzed before the sample surface analysis. Initially measure the characteristic X-ray intensity of the analyzed element at the analysis point, store the measured value in the storage device, then perform mapping measurement of the sample surface, store the measured value in the storage device, and store the measured value in the initial measurement. Characteristic X-ray intensity,
The characteristic X-ray intensity of the analysis element in the mapping measurement at the same point as the analysis point of the initial measurement is read from the storage device, an interpolative correction function is obtained from the difference between the two, and the measured value of the mapping measurement is corrected by the correction function. A method for correcting a variation in irradiation current in a plane analysis, characterized in that: