JP7247907B2 - Method for evaluating organic matter adhering to the surface of a semiconductor substrate - Google Patents

Description

The present invention relates to a method for evaluating a semiconductor substrate, and more particularly to a method for evaluating an organic substance on the surface of a semiconductor substrate.

In the manufacturing process of a semiconductor device, when organic matter adheres to the surface of an insulating film formed on a semiconductor substrate, it adversely affects the electrical characteristics of the semiconductor device, such as an increase in leakage current and a decrease in dielectric strength. It is described in US Pat. It is known that such deterioration in quality is closely correlated with atmospheric organic matter adhering to the surface. Therefore, if there is an analytical method for evaluating the organic contamination that adheres to the surface, it will be possible to estimate the origin of this contamination. It is possible to take countermeasures such as cleaning the substrate surface to remove attached organic matter before reaching the limit of occurrence.

Conventionally, as a method for evaluating such organic matter contamination, organic compound molecules are desorbed from the sample wafer surface by a temperature programmed desorption method. This desorbed gaseous organic compound (desorbed organic compound) is sampled by a predetermined method, and the sampled gaseous desorbed organic compound is measured by ultraviolet absorption spectrum, gas chromatography, or mass spectrometry. (Patent Document 1 and Patent Document 2). In the temperature programmed desorption method, the temperature of the semiconductor substrate is raised to a high temperature to desorb organic substances. There is a problem that is difficult.

Another known method for evaluating the surface contamination of a semiconductor substrate with organic matter is to measure it by an X-ray photoelectron spectroscopy (XPS) method. The XPS method qualitatively and quantitatively analyzes the elements present on the sample surface by irradiating a measurement sample with soft X-rays in a high vacuum and measuring the energy and number of photoelectrons that escape from the sample surface with a spectrometer. In the evaluation of a very small amount of surface organic matter contamination by the XPS method, the amount of organic matter contamination is the ratio of the number of carbon atoms to the total number of atoms in the analysis area of several tens of angstroms in depth from the surface, or the known amount of carbon atoms present in the analysis area. It is expressed by the ratio of the number of carbon atoms to the number of atoms of the element. The XPS method requires spectral separation, and error occurs depending on the separation method. In particular, a minute spectrum is hidden in a very strong (large number of photoelectrons) spectrum. There is a problem of overlooking

JP-A-9-171002 JP-A-6-347445 JP-A-2005-121493 JP-A-8-220030

Masaru Usami, "Semiconductor Evaluation Technology Seen in 100 Examples, 7th Edition", p26-27 (1996) Industrial Research Institute

As described above, conventionally, the thermal desorption method and the XPS method have been used as methods for evaluating organic matter contamination on the surface of a semiconductor substrate. However, the methods for evaluating organic contamination on the surface of semiconductor substrates using the thermal desorption method and the XPS method each have the above-described problems.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a highly sensitive method for evaluating organic substances existing on the surface of a semiconductor substrate.

The present invention has been made to achieve the above objects, and is a method for evaluating an organic matter attached to a surface of a semiconductor substrate, wherein the ions are accelerated to the surface of the semiconductor substrate at an acceleration voltage of 200 keV or more and 600 keV or less. Provided is a method for evaluating organic matter adhering to the surface of a semiconductor substrate, characterized by measuring Rutherford backscattering after incident light.

With such a method for evaluating organic matter adhering to the surface of a semiconductor substrate, it is possible to suppress the destruction of the organic matter adhering to the surface of the semiconductor substrate by ions, reduce the influence of the semiconductor substrate, which is the base material, and detect the vicinity of the surface with high sensitivity. evaluation becomes possible.

At this time, in the measurement of the Rutherford backscattering, the incident angle of the ions to the surface of the semiconductor substrate is set to be 5° or more and 15° or less, and the outermost surface at a depth of 0.2 nm from the semiconductor substrate surface is Measurement is preferred.

By doing so, it is possible to further suppress the destruction of the organic substances adhering to the surface of the semiconductor substrate by the ions, and to further reduce the influence of the semiconductor substrate, which is the base material, and to evaluate the vicinity of the surface with higher sensitivity. be possible.

As described above, according to the method for evaluating organic matter attached to the surface of a semiconductor substrate according to the present invention, it is possible to measure and evaluate minute amounts of organic matter contamination on the surface of a semiconductor substrate nondestructively and with high sensitivity. The method of the present invention for evaluating organic matter adhering to the surface of a semiconductor substrate is very effective for evaluating clean rooms and boxes for transporting and storing wafers, and contributes to improving the yield of semiconductor devices manufactured using semiconductor substrates. it becomes possible to

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows an example of embodiment of the Rutherford backscattering method in the evaluation method of the organic substance adhering to the semiconductor substrate surface of this invention. FIG. 3 is a schematic diagram showing a case where the incident angles of ions are set to a low inclination angle (θ ₁ ) and a high inclination angle (θ ₂ ) in Rutherford backscattering spectroscopy. FIG. 4 is a diagram showing organic substance measurement results of Example 1 and Comparative Example 1 (acceleration voltage dependence). FIG. 10 is a diagram showing the incident angle dependence of the amount of organic matter detected in Example 2. FIG. FIG. 11 shows an embodiment of Rutherford backscattering spectroscopy in Example 2; FIG. 10 is a diagram showing the amounts of organic substances detected in Example 3 and Comparative Example 2; FIG. 3 shows an embodiment of general Rutherford backscattering spectroscopy.

The present invention will be described in detail below, but the present invention is not limited to these.

As described above, there has been a demand for a highly sensitive method for evaluating organic substances existing on the surface of a semiconductor substrate.

As a result of intensive studies on the above problems, the present inventors have found that the acceleration voltage of the ions is reduced, for example, from 200 keV to 500 keV, and, for example, the accelerator is placed within 5 to 10 degrees from the horizontal with respect to the semiconductor substrate. Evaluate organic compounds adhering to the surface of a semiconductor substrate by means of Rutherford backscattering spectroscopy, which conducts elemental analysis by irradiating ions onto the surface of the semiconductor substrate and measuring the energy and number of backscattered ions. The present inventors have found that it is possible to measure and evaluate trace amounts of organic matter contamination on the surface of a semiconductor substrate non-destructively and with high sensitivity, thereby completing the present invention.

Description will be made below with reference to the drawings.

First, the Rutherford Backscattering Spectroscopy (RBS) method will be described. The RBS method is called Rutherford Backscattering Spectrometry. For example, high-energy accelerated probe ions (for example, light ions such as helium ions (He ⁺ ) and hydrogen ions (H ⁺ )) are implanted into the surface of a semiconductor to form a semiconductor substrate. The mass of the nuclei in the semiconductor material that caused the scattering from the energy spectrum and the number of ions when Rutherford scattered by the nuclei of the constituent atoms, bending the direction of travel and ejecting in the opposite direction (backward, i.e., incident direction) and the density and the location of nuclei (eg depth from the surface). According to Non-Patent Document 1, the detection depth from the surface can be measured with an accuracy of approximately 100 angstroms to a depth of several μm from the semiconductor surface.

In addition, the RBS method is an excellent evaluation method because quantitative analysis is possible without preparing a standard sample containing impurities, analysis is possible almost non-destructively, and depth direction distribution can also be measured. (Non-Patent Document 1).

The conventional RBS method as shown in FIG. 7 uses a semiconductor substrate 1, an accelerator 2, a mass spectrometer 3, and a position detector 4. In the conventional RBS method, for light elements such as carbon and oxygen present in a heavy base material, signals of scattering particles from these light elements are hidden in strong signals from the base material. Scattered particles from light elements cannot be distinguished from those from the matrix. In particular, it has been said that this difficulty is significant when performing analysis at a depth of several tens of micrometers from the surface (for example, Patent Document 3).

FIG. 1 shows an example of a schematic diagram of the evaluation method for organic matter adhering to the surface of a semiconductor substrate according to the present invention. In the evaluation method of the organic substance adhering to the semiconductor substrate surface of the present invention, the acceleration voltage of ions during RBS measurement is 200 keV or more and 600 keV or less, ions are incident on the semiconductor substrate surface, and Rutherford backscattering is measured. This is a method for evaluating adhering organic matter.

If the acceleration voltage is less than 200 keV, the ions will not be sufficiently accelerated and the measurement sensitivity will not be obtained. . If the acceleration voltage of ions during RBS measurement is 200 keV or more and 600 keV or less, it becomes possible to evaluate the vicinity of the surface with high sensitivity while reducing the influence of the semiconductor substrate which is the base material.

At this time, if the acceleration voltage is in the range of 200 keV or more and 600 keV or less, the acceleration voltage may be set to an optimum value according to conditions such as the molecular weight of the organic matter, the measuring device, and the object to be evaluated. Optimal values include, for example, 200 keV to 500 keV, more preferably 400 keV to 450 keV.

At this time, in the measurement of Rutherford backscattering, the incident angle of the ions to the surface of the semiconductor substrate is set to an inclination of 5° or more and 15° or less, and the outermost surface at a depth of 0.2 nm from the semiconductor substrate surface can be measured. preferable. The inclination angle is the angle from the horizontal plane of the semiconductor substrate surface to the central axis of the semiconductor substrate surface (the angle from the semiconductor substrate surface to the incident ion beam). Specifically, they are θ ₁ and θ ₂ in FIG. 2, which will be described later in detail.

If the angle of incidence of the ions on the surface of the semiconductor substrate is set to an inclination angle of 5° or more and 15° or less, the damage of the organic matter adhering to the surface of the semiconductor substrate due to the ions is suppressed, and the influence of the semiconductor substrate, which is the base material, is further reduced. This makes it possible to evaluate with higher sensitivity. That is, it is preferable to install the probe ion accelerator just above the surface of the substrate to be evaluated (with an inclination angle of 5° or more and 15° or less). If the angle of inclination is too large, organic substances on the surface will be removed by ions, and if the angle of inclination is too small, the probe ions will not sufficiently strike the semiconductor substrate surface. Further, by measuring the outermost surface at a depth of 0.2 nm from the surface of the semiconductor substrate, it becomes possible to evaluate the vicinity of the surface more. Patent document 4 describes a surface analysis method as an analysis method in which ions are incident on the surface of the substrate to be evaluated and measurements are made. This surface analysis method is a method for analyzing light elements such as hydrogen. Specifically, it is a method for analyzing by knocking out atoms on the outermost surface of the substrate to be evaluated. It cannot be analyzed non-destructively.

Here, the angle of incidence of ions on the surface of the semiconductor substrate will be described in more detail with reference to FIG. FIG. 2 is a diagram showing two incident angles θ ₁ and θ ₂ of ions when ions are incident on the surface of organic matter 5 on semiconductor substrate 1 . Between θ ₁ and θ ₂ , θ ₂ has a larger dip.

When the incident angle is _{a high angle of inclination such as θ 2 in} FIG. is suppressed from being pushed into the semiconductor substrate 1, the effect of the base material is reduced. Also, if the incident angle is too low, the ions may not hit the semiconductor substrate 1 or the organic substance 5 . Therefore, it is preferable to set the incident angle of ions to the surface of the semiconductor substrate to the dip angle of 5° or more and 15° or less.

Since the measurement depth generally depends on both the acceleration voltage and the angle, if the acceleration voltage is in the range of 200 keV or more and 600 keV or less, the incident angle of ions on the surface of the semiconductor substrate can be measured by measuring the molecular weight of the organic substance, the measuring device, You may adjust according to conditions, such as a to-be-evaluated object.

According to the method for evaluating organic matter adhering to the surface of a semiconductor substrate of the present invention, the RBS method can be used to measure light elements such as carbon that constitute organic matter and exist on the surface of the semiconductor substrate. become. In the analysis of organic matter present on the surface of a semiconductor substrate, the analysis can be performed without the need to desorb the organic matter from the semiconductor substrate, and non-destructive and highly sensitive analysis is possible.

EXAMPLES The present invention will be described in detail below with reference to examples, but these are not intended to limit the present invention.

(Example 1)
A boron-doped normal resistance silicon wafer with a diameter of 300 mm was prepared, and the surface of the silicon wafer was cleaned with 0.5% HF for initialization and then subjected to normal SC1 cleaning at 70°C. After that, seven silicon wafers were placed in a wafer case and left for one week. At this time, 5 dummy wafers were placed before and after the 7 wafers used for measurement so that the wafer surfaces did not directly face the case. After left for one week, the evaluation of the organic matter adhering to the surface of the semiconductor substrate was carried out by changing the acceleration voltage to 200 keV, 400 keV, 450 keV, 500 keV, and 600 keV to evaluate the organic matter on the surface. The incident angle at this time was set to an inclination angle of 10°. As a result, it was possible to measure organic matter with the highest sensitivity when the acceleration voltage was 450 keV. The results are shown in FIG.

(Comparative example 1)
The evaluation described in Example 1 was performed by changing the acceleration voltage to 100 keV and 1000 keV. However, at acceleration voltages of 100 keV and 1000 keV, the organic matter adhering to the surface of the semiconductor substrate could not be detected. The results are also shown in FIG.

(Example 2)
A boron-doped normal resistance silicon wafer with a diameter of 300 mm was prepared, and the surface of the silicon wafer was cleaned with 0.5% HF for initialization and then subjected to normal SC1 cleaning at 70°C. After that, 9 silicon wafers were placed in a wafer case and left for one week. At this time, 5 dummy wafers were placed before and after the 9 wafers used for the measurement so that the surfaces of the wafers did not directly face the case. After left for one week, the evaluation of the organic matter adhering to the surface of the semiconductor substrate was performed with the incident angle of ions (θ ₃ in FIG. 5) set to the dip angles of 2°, 4°, 6°, 8°, 10°, 12°, and 16°. Shake to assess surface organics. The acceleration voltage at this time was set to 450 keV. As a result, it was possible to measure the organic substance with the highest sensitivity when the incident angle was 10 degrees of the dip. The results are shown in FIG.

(Example 3)
A boron-doped normal resistance silicon wafer with a diameter of 300 mm was prepared, and the surface of the silicon wafer was cleaned with 0.5% HF for initialization and then subjected to normal SC1 cleaning at 70°C. After that, the silicon wafer was placed in a wafer case and allowed to stand for one week, after which the surface organic matter was evaluated by the method according to the present invention. At this time, 5 dummy wafers were placed before and after the 2 wafers used for the measurement, so that the surfaces of the wafers did not directly face the case. The evaluation of the organic matter adhering to the surface of the semiconductor substrate was carried out at an acceleration voltage of 450 keV and an incident angle of 10 degrees of dip. As a result, a surface density of 0.89 g/cm ³ of organic matter was observed. The depth from the surface at this time is 0.1 nm. The results are shown in FIG.

(Comparative example 2)
Another silicon wafer was taken out from the wafer case of Example 3 and analyzed for organic matter by the conventional evaluation method, the temperature programmed desorption method (TDS method), but no organic matter could be detected. The temperature was raised from room temperature to 500° C., and GC-MS was used for analysis. The results are also shown in FIG.

As in Comparative Example 1, when the ion acceleration voltage was 100 keV and 1000 keV, the organic substance attached to the surface of the semiconductor substrate could not be detected. In addition, as in Comparative Example 2, in the method for evaluating organic matter adhering to the surface of the semiconductor substrate by the thermal desorption method, the organic matter adhering to the surface of the semiconductor substrate could not be detected.

On the other hand, according to the method for evaluating organic matter adhering to the surface of a semiconductor substrate of the present invention, as shown in Example 1, organic matter can be measured with high sensitivity when the ion acceleration voltage is 200 keV or more and 600 keV or less. It was possible. Also, as shown in Example 2, when the incident angles of ions are 2°, 4°, 6°, 8°, 10°, 12°, and 16°, it is possible to measure organic matter with high sensitivity. Met. In addition, as shown in Example 3, the organic matter adhering to the surface of the semiconductor substrate, which could not be detected by the thermal desorption method, could be detected and evaluated.

As described above, according to the method for evaluating organic matter adhering to the surface of a semiconductor substrate according to the present invention, it is possible to measure and evaluate minute amounts of organic matter contamination on the surface of a semiconductor substrate non-destructively and with high sensitivity.

It should be noted that the present invention is not limited to the above embodiments. The above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of

DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Accelerator, 3... Mass spectrometer, 4... Position detector,
5... Organic substances.

Claims (1)

A method for evaluating organic matter adhering to the surface of a semiconductor substrate,
The ions are incident on the semiconductor substrate surface at an acceleration voltage of 200 keV or more and 600 keV or less, and Rutherford backscattering is measured ;
In the measurement of the Rutherford backscattering, the incident angle of the ions to the surface of the semiconductor substrate is set to an inclination angle of 5° or more and 15° or less, and the outermost surface is measured at a depth of 0.2 nm from the semiconductor substrate surface. A method for evaluating organic matter adhering to the surface of a semiconductor substrate, characterized by:

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