JP5742742B2 - Metal contamination assessment method - Google Patents

Description

  The present invention relates to a metal contamination evaluation method for evaluating metal contamination of various heat treatment furnaces used in a silicon substrate manufacturing process or a device manufacturing process.

  In the manufacturing process of a semiconductor silicon substrate (wafer) and the manufacturing process of a semiconductor device, if the wafer is contaminated with metal impurities or the like, the performance of the product is adversely affected. Therefore, reduction of metal contamination is a very important issue.

  As a method for evaluating metal contamination during a silicon substrate manufacturing process or a device manufacturing process, measurement of a recombination lifetime by a microwave photoconductive decay method (μ-PCD method) is widely used. In this μ-PCD method, a light pulse having an energy larger than the band gap of a silicon single crystal is first irradiated to generate excess carriers in the wafer. The electrical conductivity of the wafer increases due to the generated excess carriers, but thereafter, the electrical conductivity decreases with the lapse of time because excess carriers disappear due to recombination. By detecting this change as a time change of the reflected microwave power and analyzing it, the recombination lifetime can be obtained. The recombination lifetime is shortened when there are metal impurities or defects that form a level that becomes a recombination center in the forbidden band. From this, metal impurities, crystal defects, and the like in the wafer can be evaluated by measuring the recombination lifetime (for example, Non-Patent Document 1).

  When the sample to be evaluated has a wafer shape, excess carriers generated by the light pulse are not only recombined inside the wafer and disappear, but also diffused to the front and back surfaces of the wafer and disappear due to surface recombination. Therefore, in order to evaluate metal contamination inside the wafer, it is necessary to suppress surface recombination on the front surface and the back surface. As a method for suppressing surface recombination, thermal oxidation treatment (oxide film passivation) and electrolytic solution treatment (sometimes abbreviated as chemical passivation treatment or CP treatment) are generally used. In oxide film passivation, care must be taken not to generate metal contamination or crystal defects in a heat treatment process for forming an oxide film. Therefore, when evaluating metal contamination in a heat treatment furnace other than the oxidation furnace, for example, an epitaxial growth furnace for manufacturing an epitaxial wafer, a chemical passivation treatment is used.

  Known solutions for chemical passivation treatment include iodine alcohol solution (for example, Non-Patent Document 2) and quinhydrone alcohol solution (for example, Patent Document 1). In the case of a quinhydrone alcohol solution, it takes time until the surface passivation effect is stabilized (for example, Non-Patent Document 3). Therefore, iodine alcohol solution is used when it is desired to obtain the evaluation result of metal contamination as soon as possible.

JP 2002-329692 A

JEIDA-53-1997 “Method for measuring recombination lifetime of silicon wafer by reflection microwave photoconductive decay method” T. T. et al. S. Horanyi et al. , Appl. Surf. Sci. 63 (1993) 306. H. Takato et al. , Jpn. J. et al. Appl. Phys. 41 (2002) L870.

  As the performance of semiconductor devices increases, even a small amount of metal contamination has an adverse effect on device performance, and reducing metal contamination is an extremely important issue. In particular, in an image sensor such as a CCD (Charge Coupled Device) or CIS (CMOS Image Sensor), a weak white flaw or dark current becomes a problem as the light receiving sensitivity and resolution are improved, and a very small amount of metal contamination is adversely affected. Is concerned. For this reason, in an epitaxial wafer widely used as a substrate for an image sensor, it is strongly desired to reduce not only metal contamination in the device manufacturing process but also metal contamination in the process of manufacturing the epitaxial wafer.

  In order to reduce metal contamination in a silicon substrate manufacturing process or a device manufacturing process, a method for evaluating a very small amount of metal contamination with high sensitivity and high accuracy is required.

  As described above, the recombination lifetime measurement by the μ-PCD method is widely used as a method for evaluating metal contamination. In order to evaluate metal contamination with high sensitivity by this method, it is desirable to use a silicon substrate having a high initial value of the recombination lifetime at a stage before metal contamination as a silicon substrate for metal contamination evaluation. This is because even when the amount of metal contamination is the same, the higher the initial value of the recombination lifetime, the greater the degree of decrease in the recombination lifetime due to metal contamination.

  Conventionally, as a metal contamination evaluation method, for example, a silicon substrate for metal contamination evaluation with a limited resistivity is heat-treated in a heat treatment furnace to be evaluated, and metal contamination is evaluated based on the measured recombination lifetime after the heat treatment. It was. However, the measurement value of the recombination lifetime after the heat treatment differs depending on the initial value even if the metal contamination concentration is the same, so that the metal contamination cannot be strictly evaluated only from the measurement value of the recombination lifetime after the heat treatment. was there. Moreover, in order to evaluate metal contamination strictly, it was necessary to obtain | require the variation | change_quantity before and behind the heat processing used as evaluation object.

  However, the initial value of the recombination lifetime of the silicon substrate is not determined only by the resistivity, but the grown-in defect (crystal growth introduction defect) formed during crystal growth becomes a carrier recombination center. (Hereinafter, recombination centers formed during crystal growth may be referred to as grown-in recombination centers). Therefore, the initial value before the heat treatment to be used as a reference for the measured value after the heat treatment differs depending on the crystal lot (that is, the initial value before the heat treatment is different between silicon substrates manufactured from silicon single crystal ingots grown separately). There was a problem of different).

  On the other hand, the grown-in recombination center is thermally unstable and may disappear in the heat treatment process for evaluating metal contamination. Therefore, for example, in the epitaxial growth process, the grown-in recombination center disappears, so that the measured value of the recombination lifetime is improved, and metal contamination may not be evaluated. Of course, there is no problem if a silicon crystal having a very low density of grown-in recombination centers is produced. However, in order to produce such a silicon crystal, the production conditions are extremely limited, and the productivity is lowered. The problem of high costs arises.

  The present invention has been made in view of such problems, and provides a metal contamination evaluation method capable of evaluating metal contamination of a heat treatment furnace used in a silicon substrate manufacturing process or a device manufacturing process with high sensitivity and high accuracy. The purpose is to provide.

  The present invention was made in order to solve the above problems, and is a method for evaluating metal contamination of a heat treatment furnace to be evaluated using a measurement value of a recombination lifetime of a silicon substrate for metal contamination evaluation, A step of preparing a plurality of metal contamination evaluation silicon substrates by producing a plurality of silicon substrates from the same silicon single crystal ingot, and one of the plurality of metal contamination evaluation silicon substrates is not an evaluation target. A step of performing a heat treatment A in which heat treatment is performed in a heat treatment furnace; a step of performing a heat treatment B in which the silicon substrate not subjected to the heat treatment A among the plurality of metal contamination evaluation silicon substrates is heat treated in the heat treatment furnace to be evaluated; Performing a surface passivation treatment on the surface of each silicon substrate after the heat treatment A or the heat treatment B, and the heat treatment A and the table The step of obtaining the measurement value A by measuring the recombination lifetime of the silicon substrate after the passivation treatment by the microwave photoconductive decay method, and the recombination of the silicon substrate after the heat treatment B and the surface passivation treatment are performed. The metal lifetime of the heat treatment furnace to be evaluated is evaluated by comparing the measured value B with the step of obtaining the measured value B by measuring the coupling lifetime by the microwave photoconductive decay method and the measured value A A metal contamination evaluation method characterized by comprising the steps of:

  If the metal contamination evaluation method is as described above, based on the measurement value (measurement value A) of the recombination lifetime of the silicon substrate in which the thermally unstable Grown-in recombination center is extinguished by the heat treatment A, Since the measurement value A and the measurement value B are compared, the influence on the recombination lifetime due to the grown-in recombination center can be eliminated, and the metal contamination of the heat treatment furnace to be evaluated can be accurately evaluated.

  In this case, the heat treatment A is preferably performed at a heat treatment temperature of 1000 ° C. or higher and 1200 ° C. or lower and a heat treatment time of 1 minute or longer and 60 minutes or shorter.

  By performing heat treatment under such heat treatment conditions, the grown-in recombination centers can be effectively eliminated in the heat treatment A.

  Moreover, in the metal contamination evaluation method according to the present invention, the evaluation of metal contamination by comparison of the measurement value B with the measurement value A as a reference is performed as measurement value B−measurement value A, measurement value B / measurement value A, or ( It can be performed based on the calculated value obtained by the calculation of 1 / measured value B) − (1 / measured value A).

  By such calculation, a calculated value excluding the influence of the Grown-in recombination center can be obtained.

  The surface passivation treatment can be performed by chemical passivation treatment or by forming an oxide film on the surface of the silicon substrate.

  Since the chemical passivation treatment has a high passivation effect, it is preferable to perform the surface passivation treatment by the chemical passivation treatment because the influence of surface recombination can be more effectively suppressed. The surface passivation treatment can also be performed by forming an oxide film on the surface of the silicon substrate. Further, when an oxide film is formed on the surface of the silicon substrate by the heat treatment (heat treatment A or heat treatment B), the oxide film can also be used as an oxide film for surface passivation.

  Moreover, when performing a surface passivation process by a chemical passivation process, it is preferable to perform the said chemical passivation process using an iodine alcohol solution.

  Such a chemical passivation treatment has a high passivation effect and stabilizes soon after the treatment, so that the recombination lifetime can be measured quickly.

  With the metal contamination evaluation method according to the present invention, it is possible to evaluate the metal contamination of the heat treatment furnace to be evaluated by eliminating the influence of thermally unstable grown-in recombination centers. As a result, metal contamination of the heat treatment furnace can be evaluated with high sensitivity and high accuracy in the silicon substrate manufacturing process and the device manufacturing process.

It is the flowchart which showed an example of the outline of the metal contamination evaluation method concerning this invention. It is the graph which showed the relationship between the heat processing temperature and recombination lifetime in an experiment example. It is the graph which showed the relationship between the heat processing time and recombination lifetime in an experiment example. 4 is a graph showing a relationship between a measured value A of recombination lifetime and measured value B−measured value A in Example 1. FIG. 6 is a graph showing a relationship between an initial value of a recombination lifetime and a measured value B-initial value in Comparative Example 1. 4 is a graph showing a relationship between a recombination lifetime measurement value A and a measurement value B / measurement value A in Example 1. FIG. 6 is a graph showing a relationship between an initial value of a recombination lifetime and a measured value B / initial value in Comparative Example 1.

  Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings, but the present invention is not limited thereto.

  FIG. 1 shows an example of an outline of the metal contamination evaluation method according to the present invention.

  First, as shown in FIG. 1A, a plurality of silicon substrates for metal contamination evaluation are prepared by preparing a plurality of silicon substrates from the same silicon single crystal ingot (step a). The diameter of the silicon substrate for metal contamination evaluation prepared here is preferably the same as the diameter of the wafer processed in the heat treatment furnace to be evaluated, for example, 6 to 12 inches (150 to 300 mm). . The thickness of the metal contamination evaluation silicon substrate may be a standard thickness, for example, 0.5 to 1.0 mm. The processing conditions on the surface of the metal contamination evaluation silicon substrate may be standard conditions, but it is preferable to avoid a process that lowers the recombination lifetime, such as a sandblast process or a formation of a polycrystalline silicon film.

  In the present invention, the method for preparing the silicon single crystal ingot before cutting the silicon substrate is not particularly limited. For example, it can be produced by the Czochralski method (CZ method) or the floating zone method (FZ method). The “silicon single crystal ingot” in the present invention refers to an ingot-shaped single crystal rod made of a silicon single crystal, as long as it can be produced by cutting a wafer-shaped silicon substrate from the ingot. For example, the “silicon single crystal ingot” in the present invention is a concept including a single crystal rod (often referred to as a silicon single crystal block) in a state where a silicon single crystal ingot produced by the CZ method or the FZ method is divided.

  Note that the plurality of silicon substrates manufactured from the same silicon single crystal ingot are not necessarily manufactured at the same time, and may be manufactured separately as long as they are manufactured from the same silicon single crystal ingot.

  After the metal contamination evaluation silicon substrate is prepared as described above, as shown in FIG. 1B, at least one of the plurality of metal contamination evaluation silicon substrates is heat-treated in a heat treatment furnace that is not an evaluation target. (Heat treatment A, step b). As the heat treatment furnace used in the heat treatment A, various heat treatment furnaces that can heat-treat the semiconductor substrate can be used, and an epitaxial growth furnace can also be used. By this heat treatment A, thermally unstable Grown-in recombination centers are eliminated. The heat treatment furnace used in the heat treatment A preferably has a low metal contamination level.

  In the heat treatment A, the heat treatment temperature is preferably set to 1000 ° C. or more and 1200 ° C. or less, and the heat treatment time is preferably set in a range of 1 minute or more and 60 minutes or less. The heat treatment A is more preferably performed in an oxidizing atmosphere. The fact that such heat treatment conditions are preferable in the heat treatment A is based on knowledge obtained by experimental examples described later.

  In the heat treatment A, if the heat treatment temperature is 1000 ° C. or higher, the grown-in recombination centers can be effectively eliminated. If heat processing temperature is 1200 degrees C or less, the fall of the recombination lifetime by metal contamination and a lattice defect being newly introduce | transduced by the heat processing can be suppressed. If the heat treatment time is 1 minute or longer, the grown-in recombination centers can be effectively eliminated. There is no problem even if the heat treatment time is long, but if it is too long, it becomes inefficient, and therefore it is preferably 60 minutes or less.

  In the heat treatment A, when the heat treatment atmosphere is an oxidizing atmosphere, an oxide film is formed on the surface of the silicon substrate. By forming the oxide film, interstitial silicon is injected into the silicon substrate, and Grown-in recombination centers caused by vacancies can be effectively eliminated. In addition, by forming an oxide film, metal contamination in the heat treatment can be suppressed, and further, the oxide film can be used as an oxide film for passivation, so that an independent chemical passivation treatment is performed as described later. The recombination lifetime can be measured without performing

  In addition, a silicon substrate that is not subjected to the heat treatment A among the plurality of metal contamination evaluation silicon substrates prepared in the step a is subjected to a heat treatment in a heat treatment furnace that is an object for evaluating the metal contamination (heat treatment B, step c). The metal contamination evaluation method according to the present invention can be applied to the evaluation of various heat treatment furnaces capable of heat treating a semiconductor substrate, and can also be applied to an epitaxial growth furnace.

  When the heat treatment furnace to be evaluated is an epitaxial growth furnace, an epitaxial layer is preferably grown on the surface of the metal substrate for metal contamination evaluation during the heat treatment B. The thickness, conductivity type, resistivity, etc. of the epitaxial layer are not particularly limited. For example, a non-doped epitaxial layer can be grown with a thickness of about 1 to 10 μm, or the specification of the manufactured product should be the same. Can do. Further, only the heat treatment can be performed without growing the epitaxial layer.

  Next, as shown in FIG. 1D, a surface passivation treatment is performed on the surface of each silicon substrate after the heat treatment A or the heat treatment B (step d). This surface passivation treatment is preferably performed by chemical passivation treatment, but can also be performed by forming an oxide film on the surface of the silicon substrate (oxide film passivation). When performing surface passivation by oxide film passivation, the heat treatment A (step b) or the heat treatment B (step c) and the surface passivation treatment (step d) can be performed simultaneously.

  In this surface passivation treatment, the silicon substrate after the heat treatment A and the silicon substrate after the heat treatment B may be treated simultaneously or individually.

  Chemical passivation has a higher passivation effect than oxide film passivation and can suppress the effects of surface recombination more effectively. By adopting chemical passivation in this surface passivation treatment process, the recombination lifetime due to metal contamination is achieved. Can be evaluated with higher sensitivity. In addition, in the heat treatment A or the heat treatment B, when a heat treatment in which an oxide film is not formed is performed, such as a heat treatment using an epitaxial growth furnace, chemical passivation is easier than oxide film passivation in which an oxide film is formed later. There is an advantage that it is not affected by the heat treatment for forming the oxide film.

  The chemical passivation treatment is preferably performed using an iodine alcohol solution. Thus, the chemical passivation treatment using an iodine alcohol solution has a high passivation effect and stabilizes quickly after the treatment, so that the recombination lifetime can be measured quickly.

  When the heat treatment furnace for performing the heat treatment A or the heat treatment B is a heat treatment furnace capable of forming an oxide film, an oxide film is formed by the heat treatment, and the oxide film is used as an oxide film for passivation and recombination without performing chemical passivation treatment. Lifetime can be measured. Although the oxide film passivation has a lower passivation effect than the chemical passivation process, the oxide film passivation can also be adopted as the surface passivation process if the evaluation does not affect the oxide film passivation. In particular, in the case of a heat treatment furnace that can be oxidized, an oxide film is formed by heat treatment, and the oxide film is used as a passivation film, so that the recombination lifetime can be measured as it is without chemical passivation treatment. Can do.

  Next, as shown in FIG. 1 (e), the recombination lifetime of the silicon substrate after the heat treatment A and the surface passivation treatment is measured by the microwave photoconductive decay method (μ-PCD method). The value A is obtained (step e). Further, as shown in FIG. 1 (f), the recombination lifetime of the silicon substrate after the heat treatment B and the surface passivation treatment is measured by the microwave photoconductive decay method to obtain a measurement value B (step f ). The measurement conditions in these μ-PCD methods may be those generally used. For example, the measurement can be performed under the conditions described in Non-Patent Document 1. A commercially available measuring apparatus can be used. When the surface passivation treatment is performed by the chemical passivation treatment, if a natural oxide film is formed on the surface of the silicon substrate for metal contamination evaluation, the natural oxide film is removed with a hydrofluoric acid aqueous solution before the chemical passivation treatment. . When the heat treatment furnace used in the heat treatment A or the heat treatment B is an epitaxial growth furnace, the recombination lifetime of the silicon substrate for metal contamination evaluation after epitaxial growth can be measured.

  The lifetime measurement of the silicon substrate subjected to the heat treatment A (step e) and the lifetime measurement of the silicon substrate subjected to the heat treatment B (step f) may be measured simultaneously or individually. . Moreover, the lifetime measurement of the silicon substrate which performed heat processing A used as the reference | standard of evaluation in the below-mentioned process g measured at least once with at least one silicon substrate with respect to one silicon single crystal ingot. It ’s fine.

  Next, as shown in FIG. 1 (g), the metal contamination of the heat treatment furnace to be evaluated is compared by comparing the measurement value B obtained in step f with the measurement value A obtained in step e as a reference. Evaluate (step g). Here, the evaluation of metal contamination by comparison of the measured value (measured value B) of the silicon substrate subjected to the heat treatment B on the basis of the measured value (measured value A) of the silicon substrate subjected to the heat treatment A is described as a measured value B−. Measurement value A, measurement value B / measurement value A, or (1 / measurement value B) − (1 / measurement value A) can be performed based on the calculated value. By such calculation, a calculated value excluding the influence of the Grown-in recombination center can be obtained.

  The measured value A is compared with the measured value B with reference to the measured value (measured value A) of the recombination lifetime of the silicon substrate in which the thermally unstable Grown-in recombination center is eliminated by performing the heat treatment A. Therefore, the influence of the grown-in recombination center on the recombination lifetime can be eliminated, and the metal contamination of the heat treatment furnace to be evaluated can be evaluated. As described above, according to the metal contamination evaluation method according to the present invention, a very small amount of metal contamination that adversely affects the performance of recent high-performance devices can be evaluated with high sensitivity and high accuracy.

  Next, in the present invention, in the heat treatment A aiming to eliminate the grown-in recombination centers, the heat treatment temperature is set to 1000 ° C. or more and 1200 ° C. or less, and the heat treatment time is set in the range of 1 minute or more and 60 minutes or less. The reason why is preferable is explained by the knowledge obtained by the following experiment.

(Experimental example)
By a floating zone method, a silicon single crystal ingot having a conductivity type of p-type, a resistivity of 4500 Ω · cm (crystal a), a conductivity type of n-type, and a resistivity of 43 Ω · cm (crystal b) was grown. Each silicon single crystal ingot has a diameter of 200 mm and a crystal axis orientation of <100>. Then, from these silicon single crystal ingots, a mirror-polished silicon substrate was produced by a standard wafer processing process.

  Next, in order to investigate the value of the recombination lifetime before the heat treatment on the fabricated silicon substrate, the chemical passivation treatment using iodine ethanol solution to remove the natural oxide film with hydrofluoric acid aqueous solution and suppress the surface recombination Then, the recombination lifetime was measured by the μ-PCD method. As a result, the recombination lifetime of crystal a was 1067 μsec, and the recombination lifetime of crystal b was 619 μsec.

  Next, the heat treatment time is fixed to 30 minutes for the silicon substrates manufactured from the same silicon single crystal ingot, and the heat treatment temperatures are 500 ° C., 600 ° C., 700 ° C., 800 ° C., 900 ° C., 1000 ° C., 1100 ° C. The temperature was changed to 1200 ° C. and heat treatment was performed in an oxygen atmosphere. The heat treatment temperature was fixed at 1000 ° C., and the heat treatment time was changed to 10 seconds, 1 minute, 10 minutes, 30 minutes, and 60 minutes, and the heat treatment was performed in an oxygen atmosphere.

  Next, the oxide film formed on the surface of the heat-treated silicon substrate is removed with a hydrofluoric acid aqueous solution and subjected to chemical passivation using an iodine ethanol solution to suppress surface recombination, and then μ-PCD. The recombination lifetime was measured by the method. When the heat treatment condition was 1000 ° C. for 30 minutes, the recombination lifetime was measured using the oxide film formed by the heat treatment as an oxide film for passivation before removing the oxide film.

  The measurement results of the recombination lifetime when the heat treatment time is fixed at 30 minutes and the heat treatment temperature is changed are shown in FIGS. The graph in FIG. 2A corresponds to the crystal a, and the graph in FIG. 2B corresponds to the crystal b.

  As shown in FIG. 2A, in the case of the crystal a, it was found that when the heat treatment temperature was 1000 ° C. or higher, the recombination lifetime value was higher than that before the heat treatment. This result shows that the grown-in recombination centers disappeared by heat treatment at 1000 ° C. or higher. In the case of the crystal b, as shown in FIG. 2B, it was found that when the heat treatment temperature was 900 ° C. or higher, the recombination lifetime value was higher than that before the heat treatment. The reason why the recombination lifetime of the crystal b is higher than the temperature of the crystal a is considered to be that the grown-in recombination center of the crystal b is thermally unstable.

  As a result of measuring the lifetime before removing the oxide film on a silicon substrate subjected to heat treatment at 1000 ° C. for 30 minutes, the result was 6320 μsec for crystal a and 2368 μsec for crystal b. In either case, although the recombination lifetime was slightly lower than the recombination lifetime measured by removing the oxide film with a hydrofluoric acid solution and then performing chemical passivation, the recombination lifetime was higher than before the heat treatment. I found out.

  The measurement results of the recombination lifetime when the heat treatment temperature is fixed at 1000 ° C. and the heat treatment time is changed are shown in FIGS. The graph in FIG. 3A corresponds to the crystal a, and the graph in FIG. 3B corresponds to the crystal b.

  As shown in FIG. 3, it was found that for any crystal, when the heat treatment time was 1 minute or longer, the recombination lifetime value was higher than that before the heat treatment. This result shows that the Grown-in recombination center can be sufficiently eliminated if the heat treatment time is 1 minute or longer.

  From these results, when the heat treatment temperature is at least 1000 ° C. and the heat treatment time is 1 minute or longer, the grown-in recombination centers can be more effectively eliminated, and the value of the recombination lifetime is increased. I understood it.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, these do not limit this invention.

Example 1
Five silicon single crystal ingots having different conductivity types, resistivity, and oxygen concentration were grown by the Czochralski method (CZ method) or the floating zone method (FZ method). The crystal diameters are all 200 mm and the crystal axis orientations are all <100>. Then, from these silicon single crystal ingots, a mirror-polished silicon substrate was produced by a standard wafer processing process.

  Next, the manufactured silicon substrate was subjected to a heat treatment (heat treatment A) in a hydrogen atmosphere at 1130 ° C. for 3 minutes in a heat treatment furnace that is not an evaluation target. Thereafter, the natural oxide film was removed with an aqueous hydrofluoric acid solution, and after chemical passivation treatment using an iodine ethanol solution was performed to suppress surface recombination, the recombination lifetime was measured by the μ-PCD method. In the measurement, mapping measurement at intervals of 2 mm was performed on the entire surface of the wafer, and the average value was defined as a measurement value A.

  Further, the other prepared silicon substrate was placed in an epitaxial growth furnace to be subjected to metal contamination evaluation, and an undoped epitaxial layer having a thickness of about 10 μm was grown (heat treatment B). Thereafter, the natural oxide film was removed with an aqueous hydrofluoric acid solution, a chemical passivation treatment was performed using an iodine ethanol solution, and the recombination lifetime was measured by the μ-PCD method. In the measurement, mapping measurement was performed at intervals of 2 mm on the entire surface of the wafer, and the average value was defined as a measurement value B.

  The relationship between measured value A and measured value B−measured value A is shown in FIG. For any measured value A, the value of measured value B-measured value A is negative, and it can be seen that the value of recombination lifetime is reduced due to metal contamination in heat treatment B. Moreover, since the absolute value of measured value B-measured value A is larger as measured value A is higher, the higher the value of recombination lifetime after extinguishing the Grown-in recombination center, the more metal contamination occurs. It can be seen that it can be evaluated with high sensitivity.

  The relationship between measured value A and measured value B / measured value A is shown in FIG. For any measured value A, the value of measured value B / measured value A is smaller than 1, and it can be seen that the value of recombination lifetime is reduced due to metal contamination in heat treatment B. Moreover, since the value of measured value B / measured value A is smaller as measured value A is higher, the higher the value of recombination lifetime after extinguishing the Grown-in recombination center, the higher the metal contamination. It can be seen that the sensitivity can be evaluated.

As a result of calculating the value of (1 / measured value B) − (1 / measured value A), it was 5 × 10 ⁻⁵ to 8 × 10 ⁻⁵ . The value of (1 / measured value B) − (1 / measured value A) is a value relatively indicating the concentration of metal contamination in heat treatment B, and the positive value indicates that metal contamination can be evaluated. It shows that.

(Comparative Example 1)
In order to measure the initial value of the recombination lifetime when heat treatment is not performed on a silicon substrate manufactured from the same silicon single crystal ingot as in Example 1, the natural oxide film is removed with a hydrofluoric acid aqueous solution, and surface recombination is performed. In order to suppress, chemical passivation treatment using iodine ethanol solution was performed, and then recombination lifetime was measured by μ-PCD method. In the measurement, mapping measurement at intervals of 2 mm was performed on the entire surface of the wafer, and the average value was used as the initial value. And it compared with the measured value B after the heat treatment B of Example 1.

  The relationship between the initial value and the measured value B-initial value is shown in FIG. From this result, it can be seen that the value of “measured value B−initial value” may be positive, and metal contamination in the heat treatment B may not be evaluated.

  The relationship between the initial value and the measured value B / initial value is shown in FIG. From this result, it is understood that the value of “measured value B / initial value” may be greater than 1, and metal contamination in the heat treatment B may not be evaluated.

As a result of calculating the value of (1 / measured value B) − (1 / initial value), it is −4 × 10 ^{−4 to} 6 × 10 ⁻⁵ , which may be a negative value. It can be seen that contamination may not be evaluated.

  From the results of the above Examples and Comparative Examples, it was found that according to the present invention, metal contamination of the heat treatment furnace can be evaluated with high sensitivity and high accuracy.

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

Claims (4)

A method for evaluating metal contamination of a heat treatment furnace to be evaluated using a measurement value of a recombination lifetime of a silicon substrate for metal contamination evaluation,
Preparing a plurality of silicon substrates for metal contamination evaluation by preparing a plurality of silicon substrates from the same silicon single crystal ingot;
A heat treatment A in which one of the plurality of silicon contamination evaluation silicon substrates is heat-treated in a heat treatment furnace that is not the object of evaluation and the grown-in recombination centers disappear, and the heat treatment temperature is set to 1000 ° C. to 1200 ° C. Performing the time as a range of 1 minute to 60 minutes ;
Performing a heat treatment B in which the silicon substrate not subjected to the heat treatment A among the plurality of metal contamination evaluation silicon substrates is subjected to a heat treatment in the heat treatment furnace to be evaluated;
Performing a surface passivation treatment on the surface of each silicon substrate after performing the heat treatment A or the heat treatment B;
Measuring the recombination lifetime of the silicon substrate after performing the heat treatment A and the surface passivation treatment by a microwave photoconductive decay method to obtain a measurement value A;
Measuring the recombination lifetime of the silicon substrate after the heat treatment B and the surface passivation treatment by a microwave photoconductive decay method to obtain a measurement value B;
A method for evaluating metal contamination of the heat treatment furnace to be evaluated by comparing the measurement value B with the measurement value A as a reference. Evaluation of metal contamination by comparison of the measured value B with the measured value A as a reference is measured value B−measured value A, measured value B / measured value A, or (1 / measured value B) − (1 / measured value. The metal contamination evaluation method according to claim 1, wherein the metal contamination evaluation method is performed based on a calculated value obtained by the calculation of A). The metal contamination evaluation method according to claim 1 or 2 , wherein the surface passivation treatment is performed by chemical passivation treatment or by forming an oxide film on the surface of the silicon substrate. The metal contamination evaluation method according to claim 3 , wherein the chemical passivation treatment is performed using an iodine alcohol solution.

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