JP3341649B2 - High sensitivity detection method for Cu in silicon wafer bulk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon wafer used for manufacturing a semiconductor device such as an IC or an LSI, and more particularly to a heavy metal impurity mixed in a wafer bulk in a wafer manufacturing process or a semiconductor device manufacturing process. And a detection method having the ability to detect Cu with high sensitivity.

[0002]

2. Description of the Related Art In a wafer manufacturing process and a semiconductor device manufacturing process, heavy metal impurities such as iron, copper, and nickel may be mixed into a wafer surface or a bulk, and these heavy metals exist in an operation region of a semiconductor device. It is known that when a state occurs, the operation of the semiconductor device is hindered. As a method for analyzing heavy metal impurities in such a bulk, a chemical analysis method, a secondary ion mass spectrometry method, or the like is used.

[0003] Among them, the chemical analysis method is basically limited to a case where the sample is a solution. To evaluate a solid sample such as a semiconductor wafer, for example, the surface of the wafer is chemically treated with an HF solution or the like, and the solution is subjected to a chemical treatment. Collected by atomic absorption analysis or ICP
(Inductively Coupled Plas
ma) A method of specifying an element by emission analysis or the like. In particular, in the field of semiconductors, gas phase decomposition / flameless atomic absorption spectrometry or gas phase decomposition / inductively coupled plasma mass spectrometry has been used. These methods have a problem that contamination coming from a sample pretreatment step or the like greatly affects the reliability of analysis values. The pre-treatment process takes time and labor, and the person who performs the process requires a technology of a certain level or more.

Further, heat treatment is performed on the silicon wafer,
A technique has been reported in which impurities in the bulk are aggregated on the surface and in the vicinity of the surface to analyze the impurities in the bulk by chemical analysis, but the problem of contamination has not been solved.

[0005] The secondary ion analysis method is a highly sensitive local elemental analysis method and is used for analyzing trace impurities in semiconductors. In this method, several hundreds eV to several tens keV are applied to the surface.
When irradiating an ion beam (primary ion) such as O ₂ ⁺ , Cs ⁺ , Ga ⁺ or the like or a neutral particle such as Ar having the energy, atoms on the sample surface are released into a vacuum by sputtering. This method evaluates the types and concentrations of elements contained in the sample surface by extracting ionized substances (secondary ions) from the sputtered particles with an electric field and performing mass analysis using a magnetic field or a high-frequency electric field. . It is mainly applied to the analysis in the depth direction such as the measurement of the dopant profile in a semiconductor material and the behavior analysis of impurity analysis. However, this device is expensive and requires complicated handling in terms of maintenance of the device, such as necessity of an ultra-vacuum.

[0006] Impurity analysis is also evaluated by total reflection X-ray fluorescence. The total reflection X-ray fluorescence analysis is a technique for non-destructively analyzing trace elements that are unevenly distributed on the “surface” or “near the surface” of a substance, and cannot detect the inside of a bulk in principle.

[0007]

The analysis of impurities in a bulk by chemical analysis has high detection sensitivity but requires pretreatment, and is not convenient. In addition, when heat treatment is performed, secondary contamination due to the heat treatment may occur. The analysis of impurities in the bulk by secondary ion mass spectrometry has a disadvantage that the sensitivity varies depending on the element and the measurement condition setting and adjustment are not easy. The total reflection X-ray fluorescence is a method for evaluating the surface and the vicinity of the surface, but is not for evaluating the inside of the bulk. However, the operability is extremely good and the method is easy to use. Here, the depth near the surface that can be evaluated by total reflection fluorescent X-rays is up to about 100 ° (the X-ray incident angle at this time is about 0.
(2 degrees), and in the case of normal analysis, evaluation is made at a depth of 20 to 30 degrees (the X-ray incident angle at this time is about 0.09 degrees).

In particular, contamination by Cu tends to diffuse into the bulk even if the wafer surface is contaminated for some reason.
In the evaluation means for evaluating the surface and the vicinity of the surface, the contamination may not be detected in spite of the presence of contamination, or may be underestimated than the actual contamination. As described above, since contamination by Cu is hard to be detected by ordinary surface analysis, even if inspection of heavy metals is performed, contamination of heavy metals may be overlooked and defects may occur in subsequent device processes and the like.

In general, the means for analyzing a wafer surface cannot be detected unless impurities present on the wafer surface are present at or below the detection limit of the analyzer. That is, even if there is contamination inside the bulk, it cannot be detected only by surface analysis.
In the case of Cu, for example, about 10 ¹⁵ atoms /
Even if there is about ³ cm ³ of contamination, it may not be detected on the wafer surface.

The present invention has been made in view of such a problem, and does not require a pretreatment such as heat treatment which easily causes secondary contamination, and detects Cu in a simple silicon wafer bulk with high sensitivity. It is an object of the present invention to provide a detection method capable of performing the detection.

[0011]

In order to solve the above-mentioned problems, the invention described in claim 1 of the present invention is to irradiate the surface of a silicon wafer with X-rays so that Cu in the wafer bulk is exposed to the surface or surface. A highly sensitive method for detecting Cu in a silicon wafer bulk, characterized in that it is aggregated in the vicinity and analyzed using a total reflection X-ray fluorescence analyzer.

As described above, the surface of a silicon wafer is irradiated with X-rays scattered below the lower limit of detection of the total reflection X-ray fluorescence spectrometer so as to be higher than the lower limit of detection. By aggregating and analyzing Cu in the surface or near the surface, it is possible to detect Cu easily and with high sensitivity without contamination.

According to a second aspect of the present invention, the time for irradiating the surface of the silicon wafer with X-rays is set to 30 minutes or more, and in the third aspect, the X-ray irradiating condition is set at a tube voltage of 20 kV. As described above, the tube current is set to 20 mA or more, and the incident angle of the X-rays to the wafer is set to 0.2 degree or less in claim 4. As described above, when the X-ray irradiation conditions are specified, Cu is sufficiently aggregated on the surface by the strong X-ray intensity of the tube voltage of 20 kV or more and the tube current of 20 mA or more, and it is possible to detect Cu in the deep portion with sufficient irradiation time. It can be aggregated on or near the surface. Further, in order to aggregate at a shallow place, it is preferable to set the incident angle of the X-ray to 0.2 degrees or less. Therefore,
Cu in the wafer bulk can be detected with high sensitivity and can be analyzed very easily.

The present inventors have conducted intensive studies on a method of detecting heavy metal impurities in a silicon wafer bulk, particularly Cu, which was difficult to detect, which could not be detected by conventional wafer surface analysis means. When X-rays are irradiated for a long time under specific conditions using a total reflection X-ray fluorescence spectrometer, Cu aggregates on the wafer surface, and it is found that X-ray analysis should be performed on the aggregated region. Thus, the present invention has been completed.

According to the present invention, an X-ray is applied to, for example, one point or the whole surface of a mirror surface of a silicon wafer to cause Cu in the wafer bulk to agglomerate on the surface or in the vicinity of the surface. Is analyzed by a total reflection X-ray fluorescence analyzer. Here, the means for irradiating X-rays may be a total reflection X-ray fluorescence spectrometer used for analysis or an X-ray capable of receiving high-intensity X-rays
A line diffractometer can be used. Surface depth that can be evaluated by total reflection X-ray fluorescence by irradiation of X-rays by these devices (approximately 20 to 50 ° and near the surface within 100 °)
Impurities are agglomerated. In this case, it is preferable to use a total reflection X-ray fluorescence spectrometer for X-ray irradiation, since subsequent analysis can be performed by the same device, which is simple and is preferable because the depth at which Cu aggregates matches the depth to be evaluated. However, since the X-ray irradiation intensity is for analysis, it may be insufficient. In such a case, the X-ray irradiation device may be used separately from the total reflection X-ray fluorescence analyzer for analysis.

In the present invention, it has been found that it is extremely effective to perform high-power X-ray irradiation for a long time in order to agglomerate Cu in the wafer bulk on the surface. That is, conventionally, when impurity analysis is performed using total reflection fluorescent X-rays, X-rays are also emitted when evaluating impurities. In general, when impurity analysis is performed using total reflection fluorescent X-rays, the measurement time, that is, the time for irradiating X-rays for evaluation is as long as 10 seconds.
~ 17 minutes. However, in the case where no impurity at or above the lower detection limit was present on the wafer surface in advance, it was not possible to detect aggregation of Cu from the inside of the bulk to the surface only by irradiation during this analysis time.

However, by repeatedly performing the impurity analysis using the total reflection fluorescent X-rays, those which cannot be detected until then can be gradually detected. Depending on the Cu contamination status and the output of X-rays, etc.
It can be detected by X-ray irradiation for about a minute. Further, even if the contamination inside the bulk is small, the detection can be performed by extending the irradiation time of the X-ray. This is the first time that such a phenomenon has been virtually captured.

It is preferable that the intensity of the X-ray irradiated to coagulate Cu is as high as possible. For example, when an enclosed X-ray tube is used as an X-ray generator and the X-ray intensity is output at a tube voltage of 40 kV and a tube current of 40 mA, a silicon wafer that can be detected by irradiation for about 5 hours (another analysis method) 1.1 × 10 ¹¹
wafers where atoms / cm ² of Cu were detected)
1/4 output of X-ray intensity (tube voltage about 20 kV, tube current 20
When measured at mA), Cu was detected after 25 hours or more. This means that the higher the X-ray intensity, the more preferable, and that the aggregation of Cu is promoted and the evaluation can be performed in a short time.

The term "high sensitivity" as used in the present invention does not mean that the apparatus to be evaluated is made to have a high sensitivity. However, the sample cannot be detected by a conventional inspection method by subjecting the sample to X-ray irradiation to aggregate impurities. Is to be able to detect that By performing such an X-ray irradiation treatment, impurities in the wafer surface layer can be stably aggregated for a long time, and the impurities can be evaluated even after being left for one week or more. it can. This means that even if processing is performed at another place and time using an X-ray irradiator that is more powerful than the total reflection fluorescent X-ray, stable evaluation can be performed thereafter. Wire devices can be utilized.

In the present invention, X for coagulating Cu is used.
The line intensity is preferably such that the tube voltage is 20 kV or more and the tube current is 20 mA or more. This is because the X-ray intensity varies depending on the type of the X-ray tube used or the setting of the monochromator, but if the tube voltage or the tube current is lower than these values, the X-ray intensity becomes insufficient and Cu cannot be aggregated, This is because, as described above, the X-ray irradiation time required for detection becomes extremely long.

The incident angle of X-rays may be any number of times in principle, but is preferably 0.2 degrees or less. If it exceeds 0.2 degrees, X-rays can easily reach deep inside the wafer.
Cu may aggregate to a depth that is not detected by total reflection fluorescent X-rays used for measurement. When this occurs, there is a possibility that high-sensitivity analysis cannot be performed. Therefore, it is preferable that the incident angle of the X-rays on the wafer be 0.2 degrees or less. Here, the incident angle of X-rays refers to the angle between the wafer surface and the incident X-rays. Also, when analyzing with total reflection X-ray fluorescence, the angle is preferably 0.2 degrees or less. This is because if the angle is larger than this, the X-rays may reach deep inside the wafer, the background X-ray intensity may increase, and analysis may not be performed with high sensitivity.

The irradiation time of the X-rays on the wafer is appropriately determined according to the intensity of the X-rays, the concentration distribution of Cu inside the bulk in the depth direction, and the like.
The irradiation time of X-rays at an X-ray intensity of V or more and a tube current of 20 mA or more is preferably 30 minutes or more. If the time is less than 30 minutes, even if the X-ray intensity is high, Cu may not sufficiently aggregate on the surface. After performing the above-mentioned aggregation treatment on the surface of Cu by X-ray irradiation, surface impurity analysis is performed by a total reflection X-ray fluorescence analyzer.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to examples, but the present invention is not limited to these.

【Example】

Example 1 Two single-crystal silicon wafers having a diameter of 200 mm and a thickness of 725 μm were prepared, and the center of the mirror surface was irradiated with X-rays for a long time. X-ray irradiation was performed using a total reflection X-ray fluorescence spectrometer (TREX610 manufactured by Technos).
The X-ray source was a tungsten sealed tube, and a tube voltage of 40 kV, a tube current of 40 mA, and an X-ray incident angle of 0.09 degrees were selected as conditions for evaluation.

Of the two single-crystal silicon wafers used for evaluation, one is non-contaminated as it is, and the other is contaminated with a Cu-containing solution and then heat-treated.
Was diffused inside the wafer bulk to lower the surface concentration below the lower detection limit of the total reflection X-ray fluorescence spectrometer. That is, even if the silicon wafer is intentionally contaminated,
If Cu is diffused by heat treatment, contamination near the surface cannot be detected. Note that the lower detection limit of the apparatus of this embodiment is 8.
It is 1 × 10 ⁹ atoms / cm ² .

The two types of wafers were irradiated with X-rays under the above-mentioned conditions. The analysis of Cu aggregated on the surface was performed simultaneously with X-ray irradiation by a total reflection X-ray fluorescence analyzer. The integration of X-rays was performed hourly, and the conversion of concentration was also performed using the X-ray intensity integrated for one hour. FIG. 1 shows the change with time in the concentration of Cu detected by this analysis.

FIG. 1 (a) shows the temporal change of Cu of the non-contaminated wafer. Even when the X-ray was irradiated for 35 hours, the lower limit of detection (8.1 × 10 ⁹ atoms / cm) was obtained as in the initial measurement.
² ) It is below. FIG. 1 (b) shows the change with time of the detected Cu in the wafer intentionally contaminated with copper. The concentration of Cu exceeded the lower limit of detection by X-ray irradiation for 5 hours, and the total reflection fluorescent X-ray The detection can be performed by the analyzer, and thereafter, the detection amount of Cu increases with the irradiation time.

Example 2 X-ray irradiation for 60 hours (output voltage: 30 kV, current: 200 mA, incident angle :) was performed on the center of a wafer intentionally contaminated with copper under the same conditions as in Example 1.
0.090 °), and the in-plane distribution was measured by a total reflection X-ray fluorescence analyzer. FIG. 2 shows that Cu was detected only in the central portion of the wafer irradiated with X-rays. This indicates that Cu was aggregated from the bulk to the surface at a depth that can be evaluated by total reflection X-ray fluorescence analysis due to long-time irradiation of X-rays.

The present invention is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the scope of the claims of the present invention. It is included in the technical scope of the invention.

For example, in the above-described embodiment, an example has been described in which the X-ray is irradiated only to one point of the wafer. However, the present invention is not limited to such a case, and the wafer may be used in accordance with the purpose. Irradiation may be performed on a plurality of points on the surface, on a predetermined area or on the entire surface, and the average value may be obtained, or the distribution in the wafer plane may be analyzed.

In the above embodiment, the mirror surface (the mirror surface of the polished wafer) was irradiated with X-rays.
The X-ray irradiation for aggregating u is not particularly limited to the surface state of the wafer, but may be performed on any surface state such as after lapping, after etching, or after surface grinding. However, in order to analyze with high sensitivity by total reflection X-ray fluorescence, it is preferable to irradiate the mirror surface for measurement.

[0031]

According to the present invention, it is possible to detect Cu in a wafer bulk with high sensitivity and easily without the necessity of a pretreatment such as a heat treatment that easily causes secondary contamination.

[Brief description of the drawings]

FIG. 1 is a graph showing a change over time of a detected amount of Cu in a wafer bulk according to the present invention. (A) is a time-dependent change on a non-contaminated wafer as a reference, and (b) is a time-dependent change on a wafer which is intentionally contaminated with copper and heat-treated so that the surface concentration is lower than the lower limit of detection of total reflection X-ray fluorescence. It is shown.

[Fig. 2] Intentional contamination of copper and surface density of total reflection X
4 is a graph showing the in-plane distribution of the detected amount of Cu after irradiating a central portion with X-rays for 60 hours for a wafer that has been subjected to a heat treatment so as to be below the line detection lower limit.

[Explanation of symbols]

 C: Center of wafer E: Outer edge of wafer

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-4-136738 (JP, A) JP-A-6-283583 (JP, A) JP-A-9-64133 (JP, A) JP-A-9-133 82769 (JP, A) JP-A-9-82770 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 23/00-23/227 H01L 21/66

Claims (4)

(57) [Claims] 1. A silicon wafer characterized by irradiating a surface of a silicon wafer with X-rays to agglomerate Cu in the wafer bulk on or near the surface, and analyzing the Cu using a total reflection X-ray fluorescence analyzer. Cu in wafer bulk
High sensitivity detection method. 2. The method for detecting Cu in a silicon wafer bulk with high sensitivity according to claim 1, wherein the time for irradiating the surface of the silicon wafer with X-rays is 30 minutes or more. 3. The X-ray irradiation conditions include a tube voltage of 20 kV.
The method for detecting Cu in a silicon wafer bulk according to claim 1 or 2, wherein the tube current is 20 mA or more. 4. An X-ray incident angle on a wafer of 0.2
The method for detecting Cu in a silicon wafer bulk with high sensitivity according to any one of claims 1 to 3, wherein the temperature is not higher than the temperature.