JPH04143642A - Total reflection fluorescent x-ray analyser - Google Patents

Abstract

PURPOSE:To measure the concn. of impurity with high sensitivity by making it possible to change the incident direction of X-ray irradiating the sample held to a sample holder within a horizontal surface. CONSTITUTION:The sample wafer 12 held to a sample holder 11 is arranged directly under a semiconductor X-ray detector 14. The integrated intensity of fluorescent X-rays generated by irradiating the surface of a water with X-rays at a low angle is measured by a detector 14. At this time, since the horizontal incident direction of X-rays can be changed, by changing said incident direction to a direction becoming max. in diffraction intensity, the measuring intensity of fluorescent X-ray due to the detector 14 becomes max. By this method, the concn. of the impurity on the surface of the wafer 12 can be measured with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a total internal reflection fluorescent X-ray spectrometer capable of measuring the impurity concentration on the surface of a wafer with high sensitivity.

<Prior Art> As the degree of integration of semiconductor devices progresses, it is required to improve the cleanliness of the surface of silicon wafers. Therefore, even minute amounts of contaminants adhering to the surface of the silicon wafer must be precisely controlled.

A total internal reflection fluorescent X-ray spectrometer is a device for detecting and evaluating trace metal contamination on silicon wafers.

This device utilizes the fact that when X-rays are incident on a material surface at a very low angle, the X-rays are totally reflected at the material surface.

In other words, excitation X-rays are irradiated onto the sample at a very low angle (for example, 0.03 degrees), X-rays that do not contribute to excitation are totally reflected on the sample holder surface, and fluorescent X-rays are transferred to the semiconductor X-ray detector. (SSD).

<Problems to be Solved by the Invention> However, in such conventional total internal reflection fluorescent X-ray analyzers, the X-ray incidence device has a fixed positional relationship with respect to the sample wafer in the horizontal direction. Therefore, it was not possible to measure the intensity of the fluorescent X-rays by changing the crystal orientation to the sample wafer. Therefore, there was a problem that the impurity concentration could not be measured with high sensitivity. For example, it was not possible to accurately measure impurities at low concentrations.

<Points of focus for solving the problem> Therefore, the inventor has developed a total internal reflection fluorescent X-ray analyzer that
By changing the incident direction of the X-rays on the sample (the angle of incidence on the sample in the horizontal direction), the sensitivity to surface impurities changes, and the diffraction intensity of the incident X-rays on the sample surface changes, and the maximum sensitivity to surface impurities changes. It has been found that the incident direction showing the sensitivity coincides with the incident direction giving the maximum X-ray diffraction intensity.

Therefore, the present invention allows X-rays to be incident from any direction,
The present invention provides a total internal reflection fluorescent X-ray analyzer that can measure impurity concentration with high sensitivity.

Means for Solving the Problems> The present invention provides a sample holder that holds a sample, an X-ray irradiation mechanism that irradiates the sample held in the sample holder with X-rays at a low angle, and a In a total internal reflection fluorescence X-ray analyzer equipped with an X-ray detector placed directly above the sample and detecting fluorescent X-rays generated from the sample, the horizontal surface of the X-rays irradiated onto the sample held in the sample holder. This is a total internal reflection fluorescent X-ray analyzer with variable incidence direction.

<Function> Total reflection fluorescent X-ray analyzer (TXRF device) according to the present invention
In this case, a sample wafer held in a sample holder is placed directly below the semiconductor X-ray detector.

Then, the X-ray irradiation mechanism irradiates the surface of the sample wafer with X-rays at a low angle, and the integrated intensity of the generated fluorescent X-rays is measured by the detector.

In this case, in the present invention, the incident direction of the irradiated X-rays (the incident direction in the horizontal direction with respect to the sample wafer) can be changed. Then, by changing this incident direction, for example, to the direction where the diffraction intensity of the incident X-ray is maximum,
The intensity of fluorescent X-rays measured by the detector becomes maximum. That is, it is possible to measure the impurity concentration on the wafer surface with high sensitivity.

Figure 1 shows the angle of incidence of X-rays (incident X-rays; WLβ1) kept constant (
An example is shown in which measurements were taken at several points in the center of a sample wafer under conditions of 0.1°). As shown in this figure, the integrated intensity of W (horizontal axis) and the integrated intensity of impurities on the wafer surface (vertical axis) are synchronized. That is, the greater the integrated intensity of W, the greater the integrated intensity of impurities (F e, N i ).

On the other hand, it is known that the integrated intensity of W changes depending on its incident direction. For example, in the case of 5j (100), the integrated intensity becomes maximum due to incidence from the (110) direction.

As a result, regarding the measurement point on the wafer surface, the wafer is rotated around this measurement point to find the direction in which the integrated intensity of W is maximum, and from this direction
By irradiating a beam and measuring the integrated intensity of impurities, it becomes possible to measure with high sensitivity. Furthermore, if the diffraction intensity of W is to be monitored, since the intensity of W is large, the data can be compared in a short time.

<Example> The total internal reflection fluorescent X-ray analyzer according to the present invention will be described below based on an example.

FIG. 2 is a block diagram showing a schematic configuration of a total internal reflection fluorescent X-ray analyzer.

In this figure, 1 is a sample holder, and a sample wafer 2 is fixed and placed on the sample holder 11 by, for example, an electrostatic chuck mechanism. Also,
This sample holder 11 is rotatably provided around its central axis by a sample position control mechanism 13.

14 is a semiconductor X-ray detector (SSD) disposed directly above this sample holder 11, and its count value is input to a counting circuit 15.

Reference numeral 16 denotes an X-ray irradiation tube through which primary X-rays excited from a target such as W are incident on the sample wafer 12 held in the sample holder 11 at a predetermined low angle. 17 is a scintillation counter used to determine the angle of the sample wafer 12 with respect to the incident X-rays.

These X-ray irradiation tube 16 and scintillation counter 1
7 and 7 are arranged at positions 180 degrees apart from each other with the sample holder 11 in between in a horizontal plane.

Note that 18 and 19 are slits.

Here, 20 is a computer to which signals from the counting circuit 15 and scintillation counter 17 are input, and controls and drives the sample position control mechanism 13 based on these input signals.

The computer 20 has a well-known configuration and has Ilo, R
It is composed of AM, ROM, CPU, etc.

Therefore, when the Lβ1 ray of W, for example, is incident on the surface of the sample wafer 12 from the X-ray irradiation tube 16 through the slit 18 at a low angle, the fluorescence A line will appear.

The 5SD 14 counts the integrated intensity of this fluorescent X-ray and outputs it to the computer 20 via the counting circuit 15.

The computer 20 compares the count value of the 5SD 14 based on a predetermined incident direction with the count value obtained from other incident directions, and drives the sample position control mechanism 13 to obtain count data from multiple directions. Then, the concentration of impurities on the surface of the sample wafer 12 is measured based on data regarding the incident direction showing the maximum sensitivity (count value).

Note that the sample holder 11 is configured to be fixed or movable, and the X-ray irradiation tube 16 is attached to this sample holder 110.
It can also be configured to be movable along the circumferential direction.

Note that, as a conventional total reflection fluorescent X-ray analyzer, for example, one manufactured by Technos Co., Ltd. is known. This device had two systems for transporting and driving the sample wafer. In other words, a transport system that moves the wafer in parallel in one direction, and an S
It had a drive system that rotated the wafer directly below the SD.

However, with this device, it was not possible to measure any point on the wafer surface by changing the incident direction. For example, point A (x L
Regarding y1), first, rotate the wafer and move point A onto the Y axis. Next, by moving the wafer in parallel along this Y axis, point A is brought directly below the SSD. In this case, the wafer center is offset from the SSD center, so the wafer cannot be rotated and
It was not possible to measure point A by changing the incident direction of the line.

Therefore, it is advantageous to configure the TXRF apparatus so that the center of the wafer can be moved not only in the Y-axis direction but also in the X-axis direction. For example, point A (xi
, yl), first, the wafer is translated in parallel so that the SSD position coincides with this point A. Next, the wafer moves in parallel on a circumference centered on this point A and whose radius is the distance to the wafer center. Furthermore, the tool is rotated so that this point A does not shift from the position directly below the SSD. As a result, measurement can be performed at any point on the wafer by changing only the incident direction of the X-rays.

This improvement also allows input of measurement points, for example, to be changed from conventional (x,
It may also be possible to do this by inputting (r, θ) from the y) input.

By measuring the diffraction intensity of incident X-rays, S
The direction of incidence on the wafer at which the SD exhibits maximum sensitivity can be determined.

For example, when a silicon wafer with a (100) orientation is irradiated with W Lβ1 rays from different directions, the (110)
) direction, both the intensity of the diffraction line and the impurity sensitivity are maximum.

Therefore, for a silicon wafer with the (100) orientation, the SSD can measure the impurity concentration with maximum sensitivity by injecting X-rays from the (110) orientation.

<Effects> As described above, according to the present invention, the total internal reflection fluorescent X-ray analyzer can measure the intensity of fluorescent X-rays generated by impurities on the surface of a sample with maximum sensitivity. As a result, the impurity concentration can be measured accurately.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the integrated intensity of W and the integrated intensity of impurities according to the present invention, and FIG. 2 is a block diagram showing a total internal reflection fluorescent X-ray analyzer according to an embodiment of the present invention. 11... Sample holder, 12...
......Sample wafer, 14...
・Detector, 16......X-ray irradiation tube.

Claims (1)

[Claims] A sample holder that holds a sample; an X-ray irradiation mechanism that irradiates the sample held in the sample holder with X-rays at a low angle; In a total internal reflection fluorescence X-ray analyzer equipped with an X-ray detector that detects fluorescent X-rays generated from A total internal reflection fluorescent X-ray analyzer characterized by: