JPH0933460A - Apparatus and method for evaluating semiconductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate an in-plane distribution of impurities in a short time, by detecting fluorescent X rays generated from a surface of a semiconductor wafer. SOLUTION: When a semiconductor wafer 3 is arranged on a holder 5 within a measuring chamber 1, a monochromatic light of a specific wavelength enters a surface of the wafer 3 from an incidence optical system 7, whereby fluorescent X rays corresponding to a concentration of impurities to a depth where the incident light can enter from the surface of the wafer 3 are generated. As a result, a photosensitive surface of an imaging plate 11 (referred to as an IP herein) immediately above the wafer 3 is exposed to the X rays correspondingly to an intensity of the fluorescent X rays. At this time, as a distance between the IP 11 and the wafer 3 is smaller, a positional resolving power for an in-plane distribution of impurities can be improved more. The distribution of impurities within the surface plane of the wafer 3 is thus obtained by evaluating the photosensitive surface of the exposed IP 11. When the invention is employed in an actual production line, the contamination of the wafer 3 in a manufacturing process of semiconductor elements can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor evaluation apparatus used for analyzing trace impurities on the surface of a semiconductor wafer and an evaluation method therefor.

[0002]

2. Description of the Related Art With the miniaturization, high integration and thinning of semiconductor devices, surface contamination of semiconductor wafers has come to seriously affect characteristics such as deterioration of breakdown voltage of a gate oxide film. Therefore, development of an analysis technique for detecting impurities that cause defects is indispensable for device development. However, the impurity concentration that causes these problems is
As the device becomes more highly integrated, the level becomes lower, and it is now necessary to keep it below 10 ⁹ atoms / cm ² .

Conventionally, as a method for analyzing trace impurities on the surface of a semiconductor wafer, total reflection X-ray fluorescence analysis (Total reflec
ction X-Ray Fluorescence, hereinafter referred to as the TXRF method. ) Is used (Matsushita, Tsuchiya: Nikkei Microdevice, October 1990 issue, pp99-106). TXR
The F method is characterized in that impurities on the wafer surface can be evaluated nondestructively and further the distribution of impurities in the wafer surface can be evaluated. However,
The detection sensitivity is 10 ⁹ to 10 ¹⁰ atoms / cm ² , which is not sufficient for the current level.

Therefore, a radioluminography method (hereinafter referred to as RLG method) having a detection sensitivity of 10 ⁸ atoms / cm ² and capable of evaluating the in-plane distribution of a wafer has been proposed (Muraoka: No. 22). Proceedings of the 28th Ultra LSI Ultra Clean Technology Symposium, pp28
7-296). The RLG method is a method in which a radioactive isotope such as ⁶⁴ Cu is adsorbed by impurities on the surface of a semiconductor wafer, and radiation generated from this radioactive isotope is imaged on an imaging plate.
This is a method of detecting impurities on the wafer surface by recording on a radiation-sensitive plate called “Imaging Plate” (hereinafter referred to as “IP”).

However, it is impossible to adsorb the radioactive isotope on the semiconductor wafer in the actual production line, and there is a problem in using it in the actual production line at present. It is also impossible to identify the type of impurities.

[0006]

As described above,
The conventional TXRF method does not have sufficient detection sensitivity to evaluate the level of impurity concentration currently required, while the conventional RLG method cannot be used in an actual production line, and the type of impurities is I could not identify.

The present invention has been made in view of the above circumstances, and an object thereof is to analyze impurities on the surface of a semiconductor wafer with a detection sensitivity of a level of 10 ⁹ atoms / cm ² or less in an actual production line. It is an object of the present invention to provide a semiconductor evaluation apparatus and an evaluation method therefor capable of identifying impurities.

[0008]

In order to achieve the above object, a first invention is to provide a measuring chamber in which a semiconductor wafer is evaluated, and a holder installed in the measuring chamber for fixing the semiconductor wafer. An incident optical means for injecting an X-ray flux of an arbitrary wavelength on the surface of the semiconductor wafer, an adjusting means for adjusting an incident angle of the X-ray flux and a position of the semiconductor wafer, and a fluorescent X-ray generated from the surface of the semiconductor wafer. An X-ray detecting means for detecting is provided.

In a second invention, the incident optical means has an X-ray source and a monochromator for extracting only monochromatic light of a specific wavelength from the X-rays generated by the X-ray source, and the X-ray of the X-ray source. It is characterized in that the wire tube target material is replaceable.

In a third aspect of the invention, the incident optical means has an X-ray source and a monochromator for extracting only monochromatic light of a specific wavelength from the X-ray generated by the X-ray source, and the monochromator is rotatable. Is characterized in that.

In a fourth aspect of the invention, the incident optical means includes an X-ray source, a monochromator for extracting only monochromatic light of a specific wavelength from the X-ray generated by the X-ray source, and an X-ray generated by the X-ray source. It is characterized by having a total reflection mirror that removes unnecessary short wavelength components other than the specific wavelength component from the line.

A fifth aspect of the invention is characterized in that an absorbing material is inserted between the surface of the semiconductor wafer and the X-ray detecting means.

A sixth invention is a semiconductor evaluation method for evaluating impurities on the surface of an analysis sample by using the semiconductor evaluation apparatus of the first invention, wherein a semiconductor wafer having the same structure, orientation and composition as the analysis sample is used. The surface of the analytical sample is cleaned to prepare a comparative sample, and the analytical sample is evaluated by subtracting the measured result of the comparative sample from the measured result of the analytical sample.

According to the above construction, the X-ray detecting means collectively detects the intensity of the fluorescent X-rays generated from the semiconductor wafer over the entire surface of the wafer, so that the in-plane distribution of impurities can be evaluated in a short time. The detection sensitivity and resolution can be improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor evaluation device according to a first embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of a semiconductor evaluation device according to the present embodiment.

In FIG. 1, the semiconductor evaluation apparatus according to the present embodiment comprises a measurement chamber 1 in which a semiconductor wafer 3 is evaluated, a holder 5 for fixing the semiconductor wafer 3, and a holder 5.
An incident optical system 7 for injecting an X-ray flux of monochromatic light on the surface of the semiconductor wafer 3, a variable slit 9 for adjusting the incident width of the X-ray flux, and an IP installed directly on the semiconductor wafer 3.
11, an IP cassette 13 that stores the IP 11, and a controller 15 that adjusts the coordinates and angle of the semiconductor wafer 3.
And a computer 17 that manages the controller 15, and a scintillation counter 19 that monitors the reflection state of the X-ray flux on the surface of the semiconductor wafer 3.

The inside of the measurement chamber 1 is usually atmospheric air,
When analyzing impurities of light elements such as Na and Al,
A vacuum state may be used to prevent absorption of fluorescent X-rays by air.

The holder 5 is provided with a chuck for fixing the semiconductor wafer 3 and securely fixes the semiconductor wafer 3.

The incident optical system 7 is shown in FIGS. 2 (a), (b),
It is composed of one or a combination of at least two selected from the three mechanisms shown in (c), and monochromatic light of an arbitrary wavelength can be incident on the surface of the semiconductor wafer 3. The mechanism shown in Fig. 2 (a) is an X-ray source (60kV / 60kV /
500 mA) 21 and a monochromator 23 that extracts only monochromatic light of a specific wavelength from the X-rays generated by the X-ray source 21. The monochromator 21 is also rotatable so that monochromatic light of an arbitrary wavelength can be extracted.
The mechanism shown in FIG. 2B is a total reflection mirror 25 that removes unnecessary short wavelength components other than the specific wavelength component from the X-ray source 21, the monochromator 23, and the X-rays generated by the X-ray source 21. have. The mechanism shown in FIG. 2 (c) has the X-ray source 21 and the monochromator 23,
The X-ray tube target material 27 of the X-ray source 21 is replaceable so that monochromatic light of a required wavelength can be obtained.

The IP 11 is for being exposed to fluorescent X-rays generated from the semiconductor wafer 3 to detect and store the in-wafer distribution of the intensity of the fluorescent X-rays. An X-ray film, a multi-channel plate, a CCD or the like can be used as the X-ray detection medium replacing the IP11.

The controller 15, the computer 17 and the scintillation counter 19 are held so that the monochromatic light from the incident optical system 7 is accurately incident on the surface of the semiconductor wafer 3 at a low angle of 0 to 1 degree and is totally reflected. Adjust the angle and coordinates of the container 5.

Next, the operation of the semiconductor evaluation apparatus according to this embodiment will be described.

When the semiconductor wafer 3 is placed on the holder 5 in the measuring chamber 1, monochromatic light having a desired wavelength is incident on the surface of the semiconductor wafer 3 from the incident optical system 7. The controller 15 and the computer 17 set the incident angle in the range of 0 to 1 degree, and move the coordinates of the holder 5 so that the incident light is irradiated on the surface of the semiconductor wafer 3. At this time, the controller 15, the computer 17, and the scintillation counter 19 adjust the incident light so that the incident light is totally reflected on the surface of the semiconductor wafer 3. By reducing the incident angle to 0.01 degree, it becomes possible to irradiate the entire surface of the semiconductor wafer 3 in a lump, and it is possible to weaken the scattering of fluorescent X-rays and incident light from the semiconductor wafer 3 itself. it can. On the other hand, if the incident angle is 1 degree or more, the scattered X-ray intensity in the semiconductor wafer 3 becomes high, and the fluorescent X-ray intensity of impurities near the surface becomes relatively low, so the incident angle is 1 degree or less. It is necessary to.

When incident light is incident on the surface of the semiconductor wafer 3, fluorescent X-rays are generated according to the impurity concentration up to the depth at which the incident light can penetrate from the surface of the semiconductor wafer 3. For example, when the semiconductor wafer 3 is a silicon wafer, when the incident angle is 1 degree or less, the penetration depth of incident light is about 1 μm.

When fluorescent X-rays are generated from the surface of the semiconductor wafer 3, the IP1 placed directly above the semiconductor wafer 3
The photosensitive surface of No. 1 is exposed according to the intensity of the fluorescent X-ray. At this time, as the distance between the IP11 and the semiconductor wafer 3 is shorter, the positional resolution of the in-wafer distribution of impurities can be improved. The incident width needs to be adjusted by the variable slit 9 so that the photosensitive surface of the IP 11 is not directly exposed to the incident light.

By evaluating the photosensitive surface of the IP11 thus exposed, the in-wafer distribution of impurities on the surface of the semiconductor wafer 3 can be obtained.

Next, the results of comparative experiments by the semiconductor evaluation apparatus according to this embodiment and the conventional total reflection X-ray fluorescence analysis apparatus will be shown.

The sample is a 125 mmφ silicon wafer, the cut surface is the (001) plane, and the orientation flat is cut parallel to the [110] direction.
The accuracy of these crystal planes and crystal directions is controlled to 1 degree or less.

Using the above sample, 10 ¹² was formed on the wafer surface.
A sample contaminated by adsorbing atoms / cm ² level of Cr, Fe, Ni, Cu, Zn and a reference with extremely suppressed surface contamination were prepared by washing with acid and alkali.

FIG. 3 and FIG. 4 show the analysis results of the sample and the reference by the conventional total reflection X-ray fluorescence analysis method.
FIG. 3 (a) is a diagram showing the spectral intensities of the respective measurement elements on the reference surface by a conventional total reflection X-ray fluorescence analyzer, and FIG. 3 (b) is each measurement on the sample surface by a conventional total reflection X-ray fluorescence analyzer. A diagram showing the spectral intensities of the elements,
FIG. 4 (a) is a diagram showing the in-plane distribution of the Cu spectrum intensity on the sample surface by the conventional total reflection X-ray fluorescence analyzer, and FIG. 4 (b) is the sample surface by the conventional total reflection X-ray fluorescence analyzer. It is a figure which shows the in-plane distribution of the spectrum intensity of Fe.

As shown in FIG. 3 (a), only the fluorescent X-rays of the silicon wafer and the scattering of the incident light are observed on the reference surface, while the spectrum of all the contaminating elements is observed on the sample surface as shown in (b). Intensity is observed.

FIGS. 4 (a) and 4 (b) show an example of the results obtained by observing the in-wafer distribution of the spectral intensity for each element. The diagrams shown in FIGS. 4A and 4B can be obtained by moving the position of the sample silicon wafer and evaluating the entire surface of the wafer. Since this evaluation requires 300 seconds per point, the larger the number of points to be evaluated, the longer the evaluation time, and the whole surface mapping of a large-diameter wafer requires 1-2 days. In addition, the resolution is the interval of this one point and is about 1 cm.

On the other hand, FIG. 5 shows the analysis results of the sample and the reference by the semiconductor evaluation apparatus according to this embodiment. Here, as the incident light, a monochromatic characteristic X-ray is used. FIG. 5A is an IP image in which the reference surface is evaluated by the semiconductor evaluation apparatus according to the present embodiment,
(b) is an IP image in which the sample surface is evaluated by the semiconductor evaluation apparatus according to the present embodiment.

As shown in FIG. 5 (a), only the fluorescent X-rays of the silicon wafer and the scattering of incident light are observed on the reference surface, while as shown in FIG. A high concentration region of is observed.

Since this evaluation can be obtained with an exposure time of 1200 seconds, and the entire surface of the wafer can be evaluated in a lump, it should be carried out in a significantly shorter time than the evaluation by the conventional total reflection fluorescent X-ray analysis method described above. You can Further, the resolution is 100 μm or less, which is remarkably improved as compared with the conventional one.

Here, the IP image of the reference surface shown in FIG. 5 (a) is always necessary when the evaluation is performed by the semiconductor evaluation apparatus according to the present embodiment.

As shown in FIG. 5A, scattering of fluorescent X-rays and incident light of the silicon wafer is observed even in the IP image of the reference with suppressed surface contamination. This is because not only the fluorescent X-rays from the contaminants but also the fluorescent X-rays of the silicon wafer and the scattering of the incident light are observed in the IP image shown in ().

Therefore, when the presence / absence of impurities on the wafer surface is determined by the semiconductor evaluation apparatus according to the present embodiment, each position on the wafer surface is determined from the intensity of the fluorescent X-ray shown in FIG. 5 (b). It is necessary to obtain it by subtracting the intensity of the fluorescent X-ray shown in 5 (a). Also, I
From P, the intensity of the fluorescent X-ray was measured by the PSL value (Photo-stimulated
Since it can be read as luminesceuce), the intensity of the fluorescent X-ray can be easily obtained from the IP. The reference and the sample are wafers manufactured in the same crystal orientation, and the setting error of the incident angle of the incident light is 0.001.
It must be below the degree.

Next, the result of the contamination element identification experiment by the semiconductor evaluation apparatus according to the present embodiment will be described. In this experiment, as shown in FIG. 6, the solid state detector 29 and the counting circuit 31 are added to the semiconductor evaluation device according to the present embodiment.
In addition, a conventional semiconductor evaluation apparatus capable of performing total reflection X-ray fluorescence analysis is used, and the same sample and reference are used as those used in the above experiment.

FIG. 7 is a diagram showing the evaluation results of samples and references by total reflection fluorescent X-ray analysis by the semiconductor evaluation device, and FIG. 8 is an IP image by the semiconductor evaluation device. 7 (a) and 8 (a) show the result of the reference, and FIG. 7 (b) and FIG. 8 (b) show the result of the sample, respectively. Here, the incident light is monochromatic light having a wavelength of 1.9 Å.

As shown in FIG. 7 (b), Fe and C are among the pollutant elements in the incident light having a wavelength of 1.9 Å.
It can be seen that only r fluorescent X-rays are generated.

Therefore, only Fe and Cr among the polluting elements are observed in the IP image shown in FIG. 8B. Therefore, comparing FIG. 5B with FIG. The high concentration region is narrowed down to Ni, Cu or Zn other than Fe and Cr.

Similarly, the wavelength of the incident light is 1.5,
Contamination elements can be identified by changing to 1.6, 1.9 and 2.5 angstroms and sequentially obtaining IP images excluding Zn, Cu, Ni and Fe.

FIG. 9 is a diagram showing a Cr calibration curve of the semiconductor evaluation apparatus according to the present embodiment. The surface concentration of Cr is 10
It was obtained by evaluating wafers that had been changed to ⁸ , 10 ⁹ , 10 ¹⁰ , 10 ¹¹ , 10 ¹² atoms / cm ² .
From FIG. 9, it was confirmed that the detection sensitivity reached 10 ⁸ atoms / cm ² .

It should be noted that instead of changing the wavelength of incident light, a filter for absorption is inserted between the wafer surface and the IP and the contaminant element is identified by utilizing the difference in absorption coefficient of the fluorescent X-ray absorbing material. You can also do it. Here, as the absorbing material, a material in which transition metal impurities such as silicon, amorphous carbon, and high-purity quartz are controlled to an extremely small amount, or
Gases such as N ₂ , Ar, Kr and Xe are suitable.

[0046]

As described above, according to the present invention, the in-plane distribution of impurities on the surface of a semiconductor wafer can be obtained in a shorter time than the conventional total reflection X-ray fluorescence analysis method. Further, its detection sensitivity and resolution can be greatly improved.

Further, by using it in an actual production line, it is possible to control contamination of the semiconductor wafer in the manufacturing process of the semiconductor element.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a semiconductor evaluation device according to an embodiment.

FIG. 2 is a diagram showing a configuration of an incident optical system shown in FIG.

FIG. 3A is a diagram showing the spectral intensities of respective measurement elements on a reference surface by a conventional total reflection X-ray fluorescence analyzer, and FIG. 3B is each measurement on a sample surface by a conventional total reflection X-ray fluorescence analyzer. It is a figure which shows the spectrum intensity of an element.

4A is a diagram showing an in-plane distribution of Cu spectral intensities on a sample surface by a conventional total reflection X-ray fluorescence analyzer, and FIG. 4B is a diagram showing a sample surface by a conventional total reflection X-ray fluorescence analyzer. It is a figure which shows the in-plane distribution of the spectrum intensity of Fe.

5A is an IP image in which a reference surface is evaluated by the semiconductor evaluation apparatus according to the present embodiment, and FIG. 5B is an IP image in which a sample surface is evaluated by the semiconductor evaluation apparatus according to the present embodiment.

FIG. 6 is a diagram showing another configuration of the semiconductor evaluation device according to the present embodiment.

7A is a diagram showing the spectral intensities of the respective measurement elements on the reference surface by total reflection X-ray fluorescence analysis of the semiconductor evaluation device shown in FIG. 6, and FIG. 7B is a total reflection of the semiconductor evaluation device shown in FIG. It is a figure which shows the spectrum intensity of each measurement element of the sample surface by a fluorescent X-ray analysis.

8A is a diagram showing an IP image in which a reference surface is evaluated by the semiconductor evaluation device shown in FIG. 6, and FIG. 8B is a diagram showing an IP image in which a sample surface is evaluated by the semiconductor evaluation device shown in FIG. Is.

FIG. 9 is a diagram showing a Cr calibration curve of the semiconductor evaluation device according to the present embodiment.

[Explanation of symbols]

 1 Measurement Chamber 3 Semiconductor Wafer 5 Holder 7 Incident Optical System 9 Variable Slit 11 IP 13 IP Cassette 15 Controller 17 Computer 19 Scintillation Counter 21 X-ray Source 23 Monochromator 25 Total Reflection Mirror 27 X-ray Tube Target Material 29 Solid-state Detection Vessel 31 counting circuit

Claims (6)

[Claims] 1. A measuring chamber in which a semiconductor wafer is evaluated, a holder installed in the measuring chamber for fixing the semiconductor wafer, and an incident optical means for injecting an X-ray flux of an arbitrary wavelength on the surface of the semiconductor wafer. A semiconductor evaluation device comprising: an adjusting means for adjusting an incident angle of the X-ray flux and a position of the semiconductor wafer; and an X-ray detecting means for detecting a fluorescent X-ray generated from the surface of the semiconductor wafer. 2. The incident optical means comprises an X-ray source and the X-ray source.
The semiconductor evaluation device according to claim 1, further comprising a monochromator for extracting only monochromatic light having a specific wavelength from the X-ray generated by the radiation source, and the X-ray tube target material of the X-ray source is replaceable. . 3. The incident optical means includes an X-ray source and the X-ray source.
The semiconductor evaluation device according to claim 1, further comprising a monochromator for extracting only monochromatic light having a specific wavelength from the X-ray generated by the radiation source, and the monochromator being rotatable. 4. The incident optical means comprises an X-ray source and the X-ray source.
A monochromator that extracts only monochromatic light of a specific wavelength from the X-rays generated by the radiation source, and a total reflection mirror that removes unnecessary short wavelength components other than the specific wavelength component from the X-rays generated by the X-ray source. The semiconductor evaluation apparatus according to claim 1, which is characterized in that. 5. An absorbing material is inserted between the surface of the semiconductor wafer and the X-ray detecting means.
The semiconductor evaluation device described. 6. A semiconductor evaluation method for evaluating impurities on the surface of an analysis sample using the semiconductor evaluation apparatus according to claim 1, wherein a semiconductor wafer having the same structure, orientation and composition as the analysis sample is surface cleaned and compared. A semiconductor evaluation method, wherein a sample is prepared, and the analysis sample is evaluated by subtracting the measurement result of the comparative sample from the measurement result of the analysis sample.