1. Field of the Invention
The present invention relates to a contaminating-element analyzing method using a total reflection X-ray fluorescence analysis and an apparatus of the same, in particular, to a contaminating-element analyzing method for allowing contaminating elements to be detected and the concentrations thereof to be precisely calculated and an apparatus of the same.
2. Description of the Related Art
Thus far, as a method for nondestructively analyzing elements contained in samples, a fluorescent X-ray have been used. In addition, to improve the sensitivity of the analysis, total reflection X-ray fluorescence analyzing methods have been developed. The application of this method to contamination control for semiconductor production lines are being studied.
Among the total-reflection X-ray fluorescence analyzing methods, since energy dispersive-type fluorescent X-ray analyzing method allows a spectrum of a wide energy region to be measured, multi elements can be measured simultaneously with a single solid-state detector (SSD) disposed just above a sample. In addition, since the energy dispersive-type fluorescent X-ray analyzing method does not require a crystal monochromator, the SSD can be disposed at a position very close to a sample. Thus, the energy dispersive-type fluorescent X-ray analyzing method can provide higher sensitivity than for example wave dispersive-type fluorescent X-ray analyzing method.
In the conventional energy dispersive-type fluorescent X-ray analyzing method, if the concentration of a contaminating-element is high (for example, around 10.sup.11 atoms/cm.sup.2), the peak and escape peak of the element can be easily identified in the measured waveform of the fluorescent X-ray. An integrated intensity for obtaining the concentration of an element can be calculated with a low error.
However, when a contaminating-element in the level ranging from 10.sup.8 to 10.sup.9 atoms/cm.sup.2 which is required in the semiconductor production lines is quantified by the energy dispersive-type fluorescent X-ray analyzing method, the following problems will take place.
(1) Since the total count number is small, if the concentration of a contaminating element is low, the peak of the element in the measured waveform of a fluorescent X-ray disappears in the background. Thus, the identification of the peak of the element becomes very difficult.
(2) Even if the peak of an element can be identified, it may be difficult to separate this peak from the escape peak of the element. Thus, when the integrated intensity is calculated, an error may take place. In addition, since the escape peak of an element also depends on the intensity of primary X-ray, the amount of contamination, and so forth, it is difficult to quantify the escape peak and feedback it.
(3) In the semiconductor production lines, if a sample is Si substrate, it is difficult to identify the peaks of elements (such as Mg and Al) whose atomic numbers are close to the atomic number of Si regardless of the concentrations of their contaminations. In addition, sum peaks which are present at peak positions of n.times.Si--K.alpha. (where n is any integer) become interfering peaks.
(4) To raise the sensitivity of analysis, an Primary X-ray which is provided with a rotating target is used so as to increase the output power. In this case, since the effect of Compton scattering of a primary X-ray is large, the peak of an element may disappear in the spectrum of the primary X-ray. For example, in W-L.beta..sub.1 of a Primary X-ray, which has a high excitation efficiency against a transition metal, the identification of the peak of Zn may be difficult.
The present invention is made from the abovedescribed point of view.