JP2011060861A - Surface layer evaluating method for semiconductor wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface layer evaluating method for a semiconductor wafer, wherein the method can evaluate distribution of electrically active defects and contaminations in the depth direction of a surface layer of a semiconductor wafer. <P>SOLUTION: A plurality of depth dependency graphs by temperatures of photoluminescence intensity of a semiconductor wafer of good quality and a reference temperature dependence graph are generated, and a dominant wafer depth region of photoluminescence intensity is obtained for each of the depth dependency graphs by the temperatures to generate a measured temperature dependence graph. Then, the measured temperature dependence graph is contrasted with the reference temperature dependence graph to evaluate defects and contaminations. Further, the temperature of a part where a shift quantity is large is obtained, and depth regions of defects and contaminations of the measured wafer are estimated from dominant wafer depth regions of one of the depth dependency graphs by the temperatures that corresponds thereto. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for evaluating a surface layer of a semiconductor wafer, and more particularly to a method for evaluating a surface layer of a semiconductor wafer capable of evaluating defects and contamination existing on the surface layer of a semiconductor wafer by photoexcitation spectroscopy.

  As a technique for evaluating defects and contamination of a silicon wafer, a photoluminescence method, which is a kind of photoexcitation spectroscopy, is known. This method irradiates a silicon wafer with light of energy higher than the band gap (forbidden band), and measures the light (luminescence) emitted when the excited electron-hole pairs (excess carriers) recombine. Then, defects and impurities existing in the silicon wafer are detected and evaluated.

Conventionally, a method for detecting and evaluating the distribution state of electrically active defects and contamination in the wafer surface by obtaining the distribution of photoluminescence emission intensity in a minute area of a silicon wafer is known. (For example, Patent Document 1).
In general, if there are defects or contamination in the crystal, electron levels corresponding to them are formed in the band gap. If these electronic levels are present in the band gap, the excited excess carriers are recombined through the electronic levels. For this reason, the ratio of band edge emission due to direct recombination between bands is relatively reduced. As a result, when there is a defect or contamination, the band edge emission intensity is lower than when there is no defect or contamination.

  Further, in Non-Patent Document 1, when a short wavelength laser such as 532 nm was used, it was considered that only a region near a maximum of a few um from the wafer surface corresponding to the light penetration length was evaluated. . However, according to the inventor's calculation simulation, a considerable amount of excess carriers injected into the wafer surface layer is diffused deep into the silicon wafer, where light is emitted. Therefore, even when a short wavelength laser is used, the evaluation was actually performed to a considerably deep region of the silicon wafer (FIG. 3). In such a case, it has been difficult to obtain information on the wafer surface layer with high sensitivity.

Special table 2004-511104 gazette Journal of The Electrochemical Society, 150 (8) G436-G442 (2003), Photoluminescence Intensity Analysis in Contact to Conduct Characterization.

  As described above, in Patent Document 1, in a silicon wafer, a planar distribution state of electrically active defects and contamination is obtained by obtaining a distribution in the wafer surface of the photoluminescence emission intensity in a minute region. It was possible to detect and evaluate it. However, in the evaluation method disclosed in Patent Document 1, the distribution of defects and contamination in the depth direction of the silicon wafer was detected and could not be evaluated.

  An object of the present invention is to provide a method for evaluating the surface layer of a semiconductor wafer that can evaluate the distribution of electrically active defects and contamination in the depth direction of the semiconductor wafer.

  According to the first aspect of the present invention, an electrically active defect on the surface layer of the semiconductor wafer is generated by generating photoluminescence by photoexcitation of a short wavelength laser on the surface layer of the semiconductor wafer and measuring the photoluminescence. A method for evaluating the surface layer of a semiconductor wafer for evaluating contamination, and creating a plurality of depth dependence graphs by temperature simulating the relationship between the depth position and the photoluminescence intensity for a good semiconductor wafer according to temperature, For the temperature-dependent depth dependence graph, obtain the dominant wafer depth region of photoluminescence intensity, and create a reference temperature dependence graph that simulates the relationship between temperature and photoluminescence intensity for the above-mentioned non-defective semiconductor wafer. In addition, the relationship between temperature and photoluminescence intensity for the measured semiconductor wafer The measured temperature dependence graph is created, and then the reference temperature dependence graph and the measured temperature dependence graph are compared. If the two graphs match, it is evaluated that there are no defects and contamination in the measured semiconductor wafer. On the other hand, if the measured temperature dependence graph is shifted to a lower photoluminescence intensity than the reference temperature dependence graph, it is evaluated that the measured semiconductor wafer has defects or contamination, and the measured semiconductor wafer In the depth region where the defect or contamination is present, the temperature of the measured temperature dependence graph where the shift amount from the reference temperature dependence graph is larger than the normal portion is obtained, and then the temperature corresponding to this temperature is obtained. Depth dependency graph by temperature is selected, and the wafer depth region where the photoluminescence intensity of the selected graph is controlled A surface evaluation method of al obtaining semiconductor wafer.

According to the first aspect of the present invention, first, the relationship between the depth position and the photoluminescence intensity with respect to a non-defective semiconductor wafer is simulated for each temperature, and a temperature-dependent depth dependence graph for each temperature is created. Thereafter, a wafer depth region in which the photoluminescence intensity is dominant is obtained for each temperature-dependent depth dependence graph.
Next, for non-defective semiconductor wafers, the relationship between temperature and photoluminescence intensity is simulated, a reference temperature dependence graph is created, and temperature and photoluminescence intensity are measured for a measured semiconductor wafer. Create a measured temperature dependence graph showing the relationship.

  Thereafter, the reference temperature dependency graph is compared with the actually measured temperature dependency graph. At this time, if both graphs match, it is evaluated that there is no defect or contamination in the actually measured semiconductor wafer. On the other hand, when the measured temperature dependence graph is shifted to a lower photoluminescence intensity than the reference temperature dependence graph, it is evaluated that there is a defect or contamination in the measured semiconductor wafer. This indicates that the photoluminescence intensity has decreased due to the presence of defects or contamination inside the semiconductor wafer.

  Next, when detecting the depth region where defects or contamination exist in the surface layer of the actually measured semiconductor wafer, first, the shift amount from the reference temperature dependency graph in the actually measured temperature dependency graph is larger than the normal part. Find the temperature of the part. Next, the temperature-dependent depth dependence graph corresponding to this temperature is selected, and from the wafer depth region where the photoluminescence intensity of the selected graph is governed, the depth at which there is a defect or contamination of the measured semiconductor wafer. Guess the area. As a result, it is possible to detect and evaluate the distribution of electrically active defects and contamination in the depth direction of the semiconductor wafer, which is difficult to detect by the conventional method.

As the semiconductor wafer, for example, a single crystal silicon wafer, a polycrystalline silicon wafer, a gallium arsenide wafer, or the like can be employed.
Examples of the diameter of the semiconductor wafer include 200 mm, 300 mm, and 450 mm.

As a method for evaluating defects and contamination of a semiconductor wafer accompanied by photoexcitation, a photoluminescence method which is a kind of photoexcitation spectroscopy is employed.
Photoluminescence can be measured with high sensitivity to shallow level impurities. For example, a microanalysis of about 1 × 10 ¹¹ atoms / cm ³ can be performed on many impurities.
The measurement conditions for photoluminescence by the photoluminescence method are arbitrary.
The configuration of the photoluminescence measuring device is also arbitrary. Generally, an excitation light source, a cryostat on which a semiconductor wafer is set, a converging lens, a spectroscope, and a photodetector are provided. Various lasers (argon laser, helium-neon laser, krypton laser, etc.) can be employed as the excitation light source. As the short wavelength laser, for example, a laser beam of 532 nm can be adopted. Other excitation light sources may be a xenon arc lamp, a tungsten lamp, or the like.

A crystal defect can be adopted as the “electrically active defect”. As the “contamination”, metal contamination can be adopted. Evaluated is at least one of electrically active defects and contamination.
The “non-defective semiconductor wafer” refers to a dummy semiconductor wafer having no defects or contamination on the surface layer, for example. “Actually measured semiconductor wafer” means a wafer actually measured by a photoluminescence method.

The “wafer depth region where photoluminescence intensity is dominant” means the wafer depth position at which the emission intensity reaches a predetermined ratio with respect to the entire emission intensity (depth direction) of photoluminescence. To the depth position where the emission intensity reaches a predetermined ratio. Alternatively, the ratio of the photoluminescence emission intensity at the measurement depth of the semiconductor wafer refers to a wafer depth region where the maximum emission intensity decreases from a surface where the emission intensity is maximum to a predetermined ratio.
Here, the “predetermined ratio” refers to 50 to 90%. If it is less than 50%, it cannot be said that it is dominant over the whole, and since the depth distribution of the emission intensity of photoluminescence becomes a skirt shape, the dominant wafer depth region exceeds 90%. In other words, even if the measurement temperature is changed, the dominant wafer depth region does not change so much, and a considerably deep region is included. A preferred ratio for light emission over the entire depth of the semiconductor wafer is 50%. If it is this range, it can be said that it is dominant with respect to the whole, and also the difference with each measurement temperature is easy to see.
The temperature of the semiconductor wafer at the time of measuring the photoluminescence intensity here is, for example, 50K, 100K, 200K, 300K, 400K or the like.
“The reference temperature dependence graph and the measured temperature dependence graph are compared and the two graphs match” means that all the data values in the reference temperature dependence graph and all the data values in the measured temperature dependence graph are the same, and the two graphs overlap. That means.

“The measured temperature dependency graph is shifted to a lower photoluminescence intensity than the reference temperature dependency graph” means that the measured temperature dependency graph is directed toward the lower photoluminescence intensity with reference to the reference temperature dependency graph. That is, the transition is made on a line parallel to or nearly parallel to the reference temperature dependence graph. Such a phenomenon occurs because the distribution of defects and contamination in the semiconductor wafer in the depth direction is almost uniform, and the photoluminescence intensity decreases as a whole. However, if defects or contamination are present on the surface layer of the semiconductor wafer, a portion greatly deviating from the line of the reference temperature dependency graph is generated in a part of the actually measured temperature dependency graph.
“The part of the measured temperature dependence graph where the shift amount from the reference temperature dependence graph is larger than the normal part” means the shift amount of the measured temperature dependence graph from the reference temperature dependence graph due to the influence of defects or contamination on the wafer surface layer. The shift amount is larger than that of the “normal part” in which is constant, and the part greatly deviates from the line representing the reference temperature dependence graph. The measured temperature of the deviated portion of the semiconductor wafer is obtained.

“Selecting a temperature-dependent depth-dependent graph corresponding to this temperature” means selecting a temperature-dependent depth-dependent graph created for the same temperature as the “temperature of the part greatly deviating”.
“Determine the depth region where defects or contamination of the measured semiconductor wafer exists from the wafer depth region where the photoluminescence intensity of the selected graph is dominated” means that the defect or contamination of the measured semiconductor wafer is This means that the depth of the existing surface layer is determined on the assumption that the selected wafer depth region is controlled by the photoluminescence intensity of the selected temperature-dependent depth dependence graph.
Specifically, for example, in FIG. 4, the photoluminescence intensity in the vicinity of 50K is greatly deviated, and if the profile of 50K is confirmed in FIG. 3, the photoluminescence intensity of the surface layer with respect to the whole becomes 50%. Since it reaches around 20 μm, assuming that defects or contamination are distributed in a region shallower than 20 μm, it is possible to obtain a depth region where defects or contamination of the actually measured semiconductor wafer exists.

According to the first aspect of the present invention, a plurality of temperature-dependent depth dependency graphs and a reference temperature dependency graph are created for the photoluminescence intensity of a non-defective semiconductor wafer. A wafer depth region in which the sense intensity is dominant is obtained. In addition, an actually measured temperature dependence graph is created for the actually measured semiconductor wafer. Then, the reference temperature dependence graph and the measured temperature dependence graph are compared, and if both graphs match, it is evaluated that there are no defects and contamination, while if the measured temperature dependence graph is shifted in the low photoluminescence intensity direction, Assess that there is a defect or contamination. When evaluating defects and contamination in the depth direction of a semiconductor wafer, the temperature of the portion where the shift amount of the measured temperature dependence graph is large is obtained, and the photoluminescence intensity of the temperature-dependent depth dependence graph corresponding to this temperature is obtained. From the dominant wafer depth region, the depth region where defects or contamination of the actually measured semiconductor wafer exists is estimated.
Since it comprised in this way, the distribution of the electrically active defect in the depth direction of a semiconductor wafer and the contamination which were difficult to detect with the conventional method can be detected, and it can be evaluated.

It is a flow sheet of the surface layer evaluation method of the semiconductor wafer concerning Example 1 of this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a whole block diagram of the photo-luminescence measuring apparatus in which the surface evaluation method of the semiconductor wafer which concerns on Example 1 of this invention is used. In the surface layer evaluation method of the semiconductor wafer which concerns on Example 1 of this invention, it is the depth dependence graph classified by temperature which simulated the relationship between the depth position with respect to a good semiconductor wafer and photoluminescence intensity according to temperature. In the surface layer evaluation method of the semiconductor wafer concerning Example 1 of this invention, it is a graph which shows the state where the measurement temperature dependence graph has shifted on the basis of the reference temperature dependence graph which simulated the relation between temperature and photoluminescence intensity. is there. In the semiconductor wafer surface layer evaluation method according to Example 1 of the present invention, the reference temperature dependence graph simulating the relationship between temperature and photoluminescence intensity is used as a reference, and another measured temperature dependence graph is shifted. It is a graph.

  Examples of the present invention will be specifically described below. Here, a silicon wafer is employed as the semiconductor wafer.

A silicon wafer (semiconductor wafer) has a diameter of 300 mm obtained by processing a silicon single crystal pulled by the CZ (Czochralski) method and a specific resistance by boron doping of 1.0 Ω · cm. A silicon oxide film having a thickness of about 1 nm is formed over the entire region.
Next, the silicon wafer is transferred to a photoluminescence measuring apparatus, and the surface of the silicon wafer is evaluated for defects or contamination.
First, with reference to FIG. 2, the photoluminescence measuring apparatus 10 will be specifically described. This photoluminescence measuring device 10 is a defect detection device based on a strong excitation microscopic photoluminescence method. Specifically, the trade name SiPHER manufactured by Nanometrics is adopted.
The photoluminescence measuring apparatus 10 includes laser light sources 12 and 13 for irradiating the surface of a silicon wafer 11 with laser light, half mirrors 14 and 15, an output meter 16, a surface scattered light detector 17, and an autofocusing device. A detector 18, a movable mirror 19, a white light source 20, a CCD camera 21, a microscope objective lens 22, a long wave path filter 23, a photoluminescence light detector 24, and an autofocus mirror 25. I have.

  The laser light emitted from the laser light sources 12 and 13 is irradiated to the surface of the silicon wafer 11 from the microscope objective lens 22 through the half mirrors 14 and 15 while being output and measured by the output meter 16, and photoluminescence is generated. Part of the generated photoluminescence passes through the half mirror 15 and is detected by the photoluminescence light detector 24 through the long wave pass filter 23. The detected light is amplified in output and recorded in a recorder, and used for defect evaluation of the silicon wafer 11.

Next, based on the flow sheet of FIG. 1, photoluminescence is generated by photoexcitation on the surface layer of the silicon wafer 11 using the photoluminescence measuring apparatus 10 of Example 1, and silicon is measured by measuring photoluminescence. A method for evaluating electrically active defects and contamination on the surface layer of the wafer 11 will be described.
Specifically, first, a plurality of temperature-dependent depth dependence graphs are created by simulating the relationship between the depth position of the non-defective silicon wafer 11 and the photoluminescence intensity for each temperature (S101, FIG. 3).

Next, for each temperature-dependent depth dependence graph, a wafer depth region in which the photoluminescence intensity is dominant is obtained (S102). That is, using the temperature-dependent depth dependence graph, for example, the depth position reaching 50% with respect to the entire photoluminescence intensity (depth direction) is obtained.
Next, a reference temperature dependence graph simulating the relationship between the temperature and the photoluminescence intensity is created for the non-defective silicon wafer 11 (S103, FIG. 4), and the temperature and photoluminescence are measured for the measured semiconductor wafer. An actually measured temperature dependence graph showing the relationship with the sense intensity is created (S104, FIG. 4).
Thereafter, the reference temperature dependence graph and the measured temperature dependence graph are compared (S105, FIG. 4). If the two graphs match, it is evaluated that the measured silicon wafer 11 is free from defects and contamination, while the measured temperature dependence graph. If the graph is shifted to a lower photoluminescence intensity than the reference temperature dependence graph, it is evaluated that there is a defect or contamination in the actually measured silicon wafer 11 (S106, FIG. 4).

Next, a depth region where defects or contamination of the actually measured silicon wafer 11 exists is obtained. Specifically, first, the temperature (50 K in this case) of the portion where the shift amount from the reference temperature dependency graph is larger than the normal portion in the actually measured temperature dependency graph is obtained (S107, FIG. 4). Thereafter, a temperature-dependent depth dependency graph (50K graph) corresponding to this temperature is selected (S108, FIG. 3). Thereafter, a wafer depth region in which the photoluminescence intensity of the selected graph is controlled is obtained (S109, FIG. 3), and a depth region where defects or contamination of the actually measured silicon wafer 11 exists is evaluated. That is, the region from the surface of the actually measured silicon wafer 11 to 20 μm is, for example, 50% of the photoluminescence emission of the entire depth of the silicon wafer 11. Therefore, the depth region around 20 μm is estimated as a depth region where defects or contamination of the actually measured silicon wafer 11 exists.
Since it comprised in this way, the distribution of the electrically active defect and contamination in the depth direction of the silicon wafer 11 which was difficult to detect by the conventional method can be detected and evaluated.

Next, a surface evaluation method for a semiconductor wafer according to Embodiment 2 of the present invention will be described with reference to FIG.
As shown in FIG. 5, in Example 2, as the actually measured silicon wafer 11, the measured temperature dependence graph in which the temperature of the portion where the shift amount from the reference temperature dependence graph is larger than the normal portion is 400 K is adopted. This is an example. In this case, the area near 100 μm from the surface of the actually measured silicon wafer 11 is 50% of the photoluminescence emission of the entire depth of the silicon wafer 11. As a result, a region deeper than the vicinity of 100 μm is estimated as a depth region where defects or contamination of the actually measured silicon wafer 11 exists.
Others are the same as in the first embodiment, and a description thereof will be omitted.

  The present invention is useful for wafers in which the quality of the wafer surface layer is important, such as epitaxial wafers.

11 Silicon wafer (semiconductor wafer).

Claims (1)

Evaluation of the surface layer of a semiconductor wafer for evaluating electrically active defects and contamination of the surface layer of the semiconductor wafer by generating photoluminescence on the surface layer of the semiconductor wafer by photoexcitation of a short wavelength laser and measuring the photoluminescence A method,
Creates multiple temperature-dependent depth dependence graphs that simulate the relationship between depth position and photoluminescence intensity for a good semiconductor wafer by temperature, and controls the photoluminescence intensity for each temperature-dependent depth dependence graph. A typical wafer depth region,
Create a reference temperature dependence graph that simulates the relationship between temperature and photoluminescence intensity for the above-mentioned non-defective semiconductor wafer, and measure the relationship between temperature and photoluminescence intensity for the measured semiconductor wafer. Create a temperature dependence graph
Then, the reference temperature dependence graph and the measured temperature dependence graph are compared, and if the two graphs match, the measured semiconductor wafer is evaluated as having no defects and contamination, while the measured temperature dependence graph is If the photoluminescence intensity is shifted to a lower side than the reference temperature dependence graph, it is evaluated that there is a defect or contamination in the measured semiconductor wafer, and
For the depth region where the defect or contamination of the measured semiconductor wafer exists, the temperature of the measured temperature dependence graph is determined as the temperature of the portion where the shift amount from the reference temperature dependence graph is larger than the normal part, and then A method for evaluating a surface of a semiconductor wafer, wherein a temperature-dependent depth-dependent graph corresponding to a temperature is selected and a wafer depth region in which the photoluminescence intensity of the selected graph is controlled is obtained.

Images