JPH06324009A - Heavy metal analysis method - Google Patents

Abstract

PURPOSE:To simultaneously analyze the heavy metal contained near and inside the surface of a semiconductor substrate. CONSTITUTION:A slit 16 is provided at a rotary plate 14. The width of a slit 16 is determined by the time while X rays 13 are applied to a semiconductor substrate 11. The rotary plate 14 is rotated by controlling a motor 15. An X-ray detector 17 is positioned at the upper part of the semiconductor substrate 11. A semiconductor detector, for example, one where lithium is diffused on silicon, is generally used for the X-ray detector 17. A micro wave generation part 18 and a micro wave detector 19 are installed on the upper part of the substrate. The X rays 13 applied from an X-ray generation part 12 enter the semiconductor substrate 11 at a small angle of theta below 0.1 degrees.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a heavy metal analysis method.

[0002]

2. Description of the Related Art A total reflection fluorescent X-ray analysis method, which is one of heavy metal analysis methods, reduces unintended heavy metals generated in a semiconductor device manufacturing process, and improves device characteristics and device manufacturing yield. Therefore, it is used to identify the type of heavy metal element near the surface of the semiconductor substrate and quantitatively obtain the surface concentration.

FIG. 4 shows a conceptual diagram for explaining a measuring method of total reflection X-ray fluorescence analysis. The X-ray 2 generated from the X-ray generator 1 is incident on the surface of the semiconductor substrate 3 at a very shallow incident angle θ.
Is illuminated by. Normally, the X-ray 2 is a characteristic X-ray made of tungsten, molybdenum or copper. When the incident angle θ is silicon as the semiconductor substrate 3 and X-rays having a wavelength of about 0.13 nm (W-Lβ1 rays) are used as the X-rays 2,
Set to about 0.05 to 0.15 degrees. The X-rays 2 incident on the semiconductor substrate 3 are totally reflected on the surface of the semiconductor substrate 3 due to the difference in refractive index between the atmosphere (or vacuum) and the semiconductor substrate 3, and most of the incident X-rays 2 are incident on the semiconductor substrate 3. Go out. At this time, the heavy metal existing in the vicinity of the surface of the semiconductor substrate 3 receives the X-rays 2 and the fluorescent X-rays 4 are generated.
The fluorescent X-rays 4 are incident on the X-ray detector 5 installed on the semiconductor substrate 3. The fluorescent X-ray 4 has an energy value peculiar to the type of heavy metal, and the fluorescent X-ray 4 is detected by the X-ray detector 5.
The type of heavy metal element can be specified by measuring the energy value of. Further, the concentration of the heavy metal element near the surface can be obtained from the detection intensity of the fluorescent X-ray 4.

[0004]

However, in the method as described above, the X-rays 2 applied to the semiconductor substrate 3 are
Since the light is incident on the semiconductor substrate 3 at an extremely shallow incident angle θ,
The light is incident only from the surface of the semiconductor substrate 3 to a depth of several nm to several tens of nm. Therefore, several n from the surface of the semiconductor substrate 3
For heavy metals contained in a depth of m to several tens of nm, the type and concentration of the element can be determined, but the concentration of heavy metals contained in a depth larger than that could not be obtained.

In view of the above problems, the present invention is a semiconductor substrate 3
Is a heavy metal analysis method which can quantitatively obtain not only the heavy metal in the vicinity of the surface but also the concentration of the heavy metal contained inside the semiconductor substrate 3 at the same time.

[0006]

In order to solve the above problems, the heavy metal analysis method of the present invention is a fluorescent X-ray generated from a heavy metal in the semiconductor substrate by intermittently irradiating the semiconductor substrate with X-rays. Then, the electrons generated in the semiconductor substrate are measured, and the concentration of the heavy metal is measured from the time change of the density of the electrons.

Further, the irradiation time of the X-rays once is shorter than the lifetime of the electrons, and the non-irradiation time of the X-rays is longer than the lifetime of the electrons.

[0008]

The X-ray is intermittently irradiated to one place on the semiconductor substrate and the fluorescent X-ray generated from the heavy metal is detected to detect the heavy metal element near the surface of the semiconductor substrate from the energy value and intensity of the fluorescent X-ray. The type and concentration can be obtained.
Further, by monitoring the time change of the electron density generated in the semiconductor substrate, the lifetime of the electron can be obtained, and the heavy metal concentration inside the semiconductor substrate can be known.

[0009]

EXAMPLES Examples of the present invention will be described below with reference to FIGS.
Will be described with reference to.

A semiconductor substrate 1 having a mirror-polished surface
The X-ray 13 from the X-ray generator 12 is applied to the measurement point 1
Irradiate intermittently. The X-rays are incident on the surface of the semiconductor substrate 11 at a very shallow angle (0 degrees to 0.5 degrees). Then, the rotary plate 14 is arranged in the middle of the irradiation optical path of the X-rays 13 and is rotated to interrupt the X-ray irradiation.

The shape of the rotary plate 14 is shown in FIG. The rotary plate 14 is provided with slits 16. The width of the slit 16 is determined by the time for which the X-ray 13 is applied to the semiconductor substrate 11. The rotation of the rotary plate 14 is performed by controlling the motor 15. The X-ray detector 17 is the semiconductor substrate 1.
Located at the top of 1. As the X-ray detector 17, it is general to use a semiconductor detector, for example, one in which lithium is diffused in silicon. Reference numeral 18 is a microwave generator. Reference numeral 19 is a microwave detector.

First, the X-rays 13 emitted from the X-ray generator 12 are incident on the semiconductor substrate 11 at a shallow angle θ of 0.1 degrees or less.

The center point of the rotary plate 14 is attached to the motor 15 and is driven by the motor 15 to rotate. The semiconductor substrate 11 is irradiated with the X-rays 13 only when the rotating plate 14 rotates and the slits 16 intersect the irradiation optical path of the X-rays 13, and otherwise the X-rays 13 are blocked by the rotating plate 14, The substrate 11 is not irradiated. When the semiconductor substrate 11 is intermittently irradiated with the X-rays 13, electrons are excited near the surface of the semiconductor substrate 11 only while the X-rays 13 are being irradiated. The excited electrons become conduction electrons, diffuse inside the semiconductor substrate 11, and recombine with holes to disappear. The life of the electron at this time is called a lifetime. If a heavy metal is present inside the semiconductor substrate 11, the generated electrons are captured by the heavy metal and the lifetime is shortened.

During the measurement, the microwave is always emitted from the microwave irradiating section 18 to the semiconductor substrate 11 at an angle close to a vertical angle, with an error of 10 degrees or less with respect to the vertical angle.
The microwave applied to the semiconductor substrate 11 is reflected by the electrons generated by the X-rays 13, and the reflection intensity is proportional to the electron density. The intensity of the reflected microwave is measured by the microwave detector 19.

FIG. 3 shows the change over time of the reflected microwave intensity. That is, by measuring the reflected microwave intensity, the time change of the electron density inside the semiconductor substrate 11 can be obtained, and the electron lifetime is obtained. The lifetime is the time until the intensity of the microwave reflected by the semiconductor substrate 11 becomes 1 / e of the maximum value, or the time from the intensity of 1 / e to the intensity of 1 / e ^2. Yes (e is the base of the natural logarithm). Since the lifetime decreases as the concentration of heavy metals contained in the semiconductor substrate 11 increases, the concentration of heavy metals contained in the semiconductor substrate 11 can be calculated if the lifetime is obtained.

In this way, the lifetime of the electrons excited by the X-rays 13 is measured until the electrons are recombined with the holes and returned to the ground state. However, the X-rays 13 may enter the semiconductor substrate 11 again during the lifetime measurement,
If the irradiation time for one time is long, the electrons are excited from the semiconductor substrate 11 again while the electrons are recombined with the holes, and the time change of the electron density cannot be obtained. X-ray 1 on the semiconductor substrate 11
It is necessary to block it by the rotating plate 14 so that 3 does not enter. It is necessary to set the time for shutting off the X-rays 13 to a time that is sufficiently longer than the lifetime, and to make the irradiation time for each X-ray 13 once shorter than the lifetime. If the time to shut off the X-ray 13 is determined in this way, the rotating plate 14
The rotation speed of is determined. In addition, X-ray 1 is applied to the semiconductor substrate 11.
The time for irradiating 3 is determined by the width of the slit 16 provided in the rotary plate 14.

Next, the necessity of intermittently irradiating the semiconductor substrate 11 with X-rays 13 will be described. In the total reflection fluorescent X-ray analysis, fluorescent X-rays generated from heavy metals are detected, so if the measurement time is short, the statistical fluctuation of the fluorescent X-ray intensity becomes large. Usually, a measurement time of hundreds to thousands of seconds is required. When the X-ray 13 is blocked by the rotating plate 14 to measure the electron lifetime, the fluorescent X-rays are not generated from the heavy metal on the surface of the semiconductor substrate 11 during that time. Therefore, the fluorescence X
In order to reduce the statistical fluctuation of the line intensity, it is necessary to intermittently irradiate the surface of the semiconductor substrate 11 with the X-rays 13 and prolong the time for generating the fluorescent X-rays from the heavy metal.

In the usual total reflection X-ray fluorescence analysis, only the heavy metal near the surface of the semiconductor substrate 11 can obtain the type and surface concentration of the element. By using the method of this embodiment, not only the concentration of heavy metals in the vicinity of the surface of the semiconductor substrate 11 but also the concentration of heavy metals contained in the entire semiconductor substrate 11 can be measured at the same time.

[0019]

Industrial Applicability According to the present invention, a semiconductor substrate is intermittently irradiated with X-rays, and a fluorescent X-ray generated from a heavy metal and an electron generated by the X-ray irradiation are monitored to change the density with time. Not only the heavy metal concentration near the surface of the substrate,
It is possible to simultaneously determine the concentration of heavy metals contained in the entire semiconductor substrate. By using the heavy metal analysis method of the present invention, the cleanliness of the semiconductor element manufacturing process can be increased and the manufacturing yield can be increased.

[Brief description of drawings]

FIG. 1 is a schematic view of a heavy metal analysis method according to an embodiment of the present invention.

FIG. 2 is a view showing a shape of a rotary plate for intermittently blocking X-rays.

FIG. 3 is a diagram showing a time change of conduction electron density generated in a semiconductor substrate.

FIG. 4 is a schematic diagram for explaining total reflection X-ray fluorescence analysis.

[Explanation of symbols]

 11 semiconductor substrate 12 X-ray generator 13 X-ray 14 rotating plate 15 motor 16 slit 17 X-ray detector 18 microwave generator 19 microwave detector

Claims (2)

[Claims] 1. A semiconductor substrate is intermittently irradiated with X-rays, fluorescent X-rays generated from a heavy metal in the semiconductor substrate and electrons generated in the semiconductor substrate are measured, and the time density of the electrons changes. A method for analyzing heavy metals, which comprises measuring the concentration of the heavy metals further. 2. The X-ray irradiation time of one time is shorter than the lifetime of the electron, and the non-irradiation time of the X-ray is longer than the lifetime of the electron. Heavy metal analysis method.