Heat treatment method for silicon wafers

Abstract

To provide a silicon wafer heat treatment method that can suppress the formation of OSF due to metal contamination when performing oxidation heat treatment on a silicon wafer contaminated with metal.SOLUTION: A heat treatment method for performing oxidation heat treatment on a metal-contaminated silicon wafer includes first heat treatment of dissolving metal precipitates on the surface of a silicon wafer by carrying the silicon wafer into a heat treatment furnace at room temperature, and performing heat treatment on the silicon wafer at a temperature equal to or higher than the higher one of a solid solubility limit temperature at which the solid solubility matches the estimated contamination concentration of a contaminant metal in the silicon wafer and the highest temperature in the thermal history of the silicon wafer after metal contamination, and lower than the melting point of silicon after replacing the atmosphere with a non-oxidizing atmosphere, and a second heat treatment of replacing the atmosphere with an oxidizing atmosphere without lowering the temperature, and heat-treating and oxidizing the silicon wafer at a temperature higher than the heat treatment temperature of the first heat treatment and lower than the melting point of silicon.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a heat treatment method for performing an oxidation heat treatment on a silicon wafer contaminated with metal. In particular, when performing the above oxidation heat treatment, the present invention relates to a heat treatment method for a silicon wafer that can suppress the formation of oxidation-induced stacking faults (hereinafter also referred to as OSF) caused by metal contamination.

Background Art

[0002] In the manufacturing process of semiconductor integrated circuits, the presence of OSF is cited as a cause of yield reduction. OSF is caused by minute defects introduced during crystal growth or metal contamination of the silicon wafer, becomes apparent in oxidation processes and the like in the manufacture of semiconductor devices, increases the leakage current of the semiconductor device, and causes device failure. From the above, in order to prevent deterioration of the electrical characteristics of semiconductor devices due to OSF, it is necessary to reduce OSF formation. As a method for reducing OSF, it has been proposed to perform rapid heating and rapid cooling heat treatment (RTA) in a reducing atmosphere (for example, Patent Document 1). In addition, a method has also been proposed in which heat treatment in an oxygen-containing atmosphere, an argon atmosphere, a hydrogen-containing atmosphere, etc. is performed before the OSF manifestation heat treatment, so that even when heat treatment is performed under conditions where OSF becomes apparent thereafter, it becomes OSF-free (for example, Patent Document 2).

[0003] However, Patent Document 1 may be subject to metal contamination that causes OSF generation during the RTA heat treatment. Furthermore, since equipment for performing rapid heating and rapid cooling is required, it is not simple. In addition, the method described in Patent Document 2 avoids metal contamination and also avoids the formation of OSF caused by minute defects introduced during crystal growth, and does not reduce the occurrence of OSF caused by metal contamination in a silicon wafer contaminated with metal.

[0004] In order to reduce the formation of OSF caused by metal contamination, methods such as avoiding metal contamination itself and avoiding the influence on the surface layer of the silicon wafer used to fabricate the device by gettering can be considered. However, it is difficult to completely prevent metal contamination, and it takes time and cost to utilize the gettering mechanism.

[0005] In Patent Document 3, it is proposed to reduce the formation of OSF caused by crystal by performing a pre-heat treatment of heat treatment at a temperature of 400°C to 500°C for 10 minutes to 100 hours in a non-oxidizing atmosphere. However, there is no description regarding the temperature rise, and in the specified temperature range, the reduction effect of the formation of OSF caused by metal contamination may not be expected.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a heat treatment method for a silicon wafer capable of suppressing the formation of OSF caused by metal contamination when performing an oxidation heat treatment on a silicon wafer contaminated with metal.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention is a heat treatment method for performing an oxidation heat treatment on a silicon wafer contaminated with metal, Carry the silicon wafer into a heat treatment furnace at room temperature. After replacing the inside of the heat treatment furnace with a non-oxidizing atmosphere, under the non-oxidizing atmosphere, at a temperature higher than the higher of the solid solubility limit temperature at which the solubility coincides with the estimated contamination concentration of the contaminating metal in the silicon wafer and the highest temperature in the heat history after metal contamination of the silicon wafer, and lower than the melting point of silicon, perform a heat treatment on the silicon wafer to dissolve the metal deposits on the surface of the silicon wafer, which is the first heat treatment, After the first heat treatment, without lowering the temperature, replace the inside of the heat treatment furnace with an oxidizing atmosphere, and perform a heat treatment on the silicon wafer at a temperature not lower than the heat treatment temperature of the first heat treatment and lower than the melting point of silicon under the oxidizing atmosphere to oxidize the silicon wafer, which is the second heat treatment, A heat treatment method for a silicon wafer is provided, which is characterized by including the above.

[0009] According to such a heat treatment method for a silicon wafer of the present invention, when performing an oxidation heat treatment on a silicon wafer contaminated with metal, it is possible to suppress the formation of OSF caused by metal contamination even when there is no gettering mechanism or the like.

[0010] At this time, the contamination concentration of the contaminating metal in the silicon wafer can be estimated from the impurity analysis of the silicon wafer or the environmental contamination test of the process to which the silicon wafer has been subjected.

[0011] In this way, the contamination concentration of the contaminating metal can be estimated, and the solid solubility limit temperature at which the solubility coincides with the contamination concentration can be obtained. As a result, the heat treatment temperature in the first heat treatment can be determined.

Effects of the Invention

[0012] According to the heat treatment method for a silicon wafer of the present invention, even when performing an oxidation heat treatment on a silicon wafer after metal contamination, it is possible to suppress the formation of OSF caused by metal contamination.

Brief Description of the Drawings

[0013]

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Best Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited thereto. As described above, a silicon wafer may be contaminated with metal due to the environment or heat treatment during the manufacturing process, and when an oxidation heat treatment is performed, OSF caused by metal contamination may be formed. As a countermeasure, as described above, methods for suppressing OSF formation have been explored and various methods have been proposed. However, as a method for avoiding OSF formation caused by metal contamination, all of them are methods for avoiding metal contamination itself. Therefore, the present inventor investigated the OSF formation mechanism caused by metal contamination in order to find a method for suppressing OSF formation even in a silicon wafer after metal contamination. As a result of the investigation, it was found that OSF formation depends not on the contamination concentration of the contaminated metal in the silicon wafer itself, but on the density of metal precipitates on the surface of the silicon wafer before the oxidation heat treatment. From this, it was considered that it might be possible to suppress OSF formation by performing a heat treatment in a non-oxidizing atmosphere for the purpose of dissolving the metal precipitates on the surface of the silicon wafer before the oxidation heat treatment, and the idea of the present invention was reached.

[0015] The heat treatment method for a silicon wafer of the present invention is a heat treatment method for performing an oxidation heat treatment on a metal-contaminated silicon wafer, and FIG. 1 is a flowchart showing an example of the steps. As shown in Fig. 1, the heat treatment method of the present invention includes steps of performing a first heat treatment and a second heat treatment. Note that, as will be described later, the second heat treatment includes an oxidation heat treatment step. First, as shown in S1 of Fig. 1, prepare a silicon wafer contaminated with metal. The silicon wafer (hereinafter, also simply referred to as a wafer) itself is not particularly limited. For example, it may be manufactured by the Czochralski method or may be manufactured by the floating zone method. If it is contaminated with metal, the resistivity, oxygen concentration, etc. are not particularly limited. However, when performing an oxidation heat treatment on a silicon wafer having no gettering ability such as a high-resistivity silicon wafer with a high resistivity and a low-oxygen concentration, OSF caused by metal contamination is likely to occur. Therefore, it is particularly preferable to apply the present invention.

[0016] Examples of the types of contaminating metals include those that are not normally treated as dopants but are treated as contaminating metals, such as Fe, Ni, Co, Cu, etc., but are not limited thereto.

[0017] Also, the manner of contamination is not particularly limited. It may be a wafer intentionally contaminated for testing or the like, or a wafer that has been contaminated with metal during the wafer manufacturing process (for example, during the heat treatment process) before the preparation step of this wafer. Note that, for the former, since it is intentionally contaminated, its contamination concentration can be easily estimated. For the latter, for example, by routinely performing inspections (impurity analysis) on metal contamination for each manufacturing process, it is possible to obtain quantitative data on whether metal contamination has occurred in the processed silicon wafer (the timing of metal contamination), the type of contaminating metal, and the degree of contamination, regardless of the use or treatment of any device. Of course, inspections may be performed not only in cases where inspections are routinely performed but also separately using a silicon wafer when necessary. Here, such inspections are also referred to as environmental contamination tests. By this environmental contamination test, it is possible to estimate the contamination concentration of the contaminating metal in the prepared silicon wafer. Alternatively, the contamination concentration of the contaminating metal can also be estimated by subjecting the prepared silicon wafer to impurity analysis. Examples of the analysis method include total reflection X-ray fluorescence analysis and SIMS measurement on silicon wafers that have undergone the same process.

[0018] Next, as shown in S2 of FIG. 1, before performing the heat treatment in an oxidizing atmosphere, a first heat treatment is performed in a non-oxidizing atmosphere for the purpose of dissolving the metal precipitates on the wafer surface. During this heat treatment in a non-oxidizing atmosphere, in order to prevent the generation of OSF due to oxidation by the oxygen in the air that slightly enters the heat treatment furnace when the silicon wafer is carried into the furnace, the silicon wafer is carried into the heat treatment furnace at room temperature, and after replacing the furnace atmosphere with a non-oxidizing atmosphere, the temperature is raised to a predetermined heat treatment temperature and then heat treatment is performed. The room temperature can be, for example, 20 to 25°C.

[0019] The heat treatment temperature in the non-oxidizing atmosphere is set to be equal to or higher than the higher of the solid solubility limit temperature at which the solubility coincides with the contamination concentration of the contaminating metal estimated in the silicon wafer and the highest temperature in the heat history of the silicon wafer after metal contamination. The principle that heat treatment at a temperature equal to or higher than the highest temperature in the heat history after metal contamination is effective in suppressing OSF formation has not been clearly elucidated in detail, but stress during heat treatment after metal contamination and point defects such as interstitial silicon and vacancies are involved in metal precipitation and its nucleation, and it is presumed that a temperature equal to or higher than the formation temperature is required for the dissolution of the metal precipitates. Therefore, if no heat treatment has been particularly performed on the silicon wafer after metal contamination (if there is no particular heat history), the heat treatment temperature can be set to be equal to or higher than the solid solubility limit temperature. Also, the upper limit of the heat treatment temperature is set to be lower than the melting point of silicon. By performing heat treatment within such a temperature range, the contaminating metal changes from an unsaturated state to a stable state dissolved in silicon, and the contaminating metal precipitated on the surface (surface layer) dissolves in silicon. Since the deposits on the silicon wafer surface of the contaminating metal are nuclei in OSF formation, by dissolving the metal deposits on the silicon wafer surface through the first heat treatment (heat treatment in a non-oxidizing atmosphere), it becomes possible to suppress the formation of OSF caused by metal contamination during the second heat treatment (oxidation heat treatment) in the subsequent process.

[0020] Here, regarding the estimated contamination concentration and contamination timing of the contaminating metal, as described in the wafer preparation process of S1 in FIG. 1, they can be obtained from impurity analysis, environmental contamination tests, etc. Also, regarding the solid solubility limit temperature, it can be obtained from the relational expressions between the solid solubility and the solid solubility limit temperature of various contaminating metals in silicon, which have been known conventionally. For example, in the case of Ni, the following formula 1 is known. By substituting the estimated contamination concentration into the Ni solid solubility [Ceq] of this formula 1 and solving for the temperature [T], it can be obtained. Ceq = 1.2×10 24 exp(-1.68 / k B T) [Here, Ceq: Ni solid solubility (atoms / cm 3 ), k B : Boltzmann constant (eV / K), T: temperature (K)]…(Formula 1) (Weber, E. R.: Appl. Phys. A30 (1983) 1. Refer to.) Also, for Fe, Co, Cu, etc., relational expressions such as the following are known. Fe: Ceq = 4.3×10 22 exp(-2.1 / k B T) (Aoki, M., Hara, A., Ohsawa, A. : J. Appl. Phys. 72 (1992) 895. Refer to.) Co: Ceq = 1.0×10 26 exp(-2.83 / k B T) (Weber, E. R. : Appl. Phys. A 30 (1983) 1. Refer to.) Cu: Ceq = 5.5×10 23 exp(-1.49 / k B T) (Weber, E. R., Wiehl, N. : Mater. Res. Soc. Svmp. Proc. 14 (1983) 19. See reference)

[0021] Next, an example will be given and explained for the case where another heat treatment is performed on a metal-contaminated silicon wafer after the metal contamination. In this case, as described above, the heat treatment temperature in a non-oxidizing atmosphere shall be set to be higher than either the solid solubility limit temperature or the highest temperature in the heat history after the metal contamination. For example, as a contaminating metal, when deliberately contaminated with Ni at a concentration of about 10 13 atoms / cm 3 and then heat-treated at 800 °C (heat treatment H A ), consider the case of a silicon wafer. At this time, the solid solubility of Ni in Si corresponding to about 10 13 atoms / cm 3 is about 500 °C from the above formula 1 (solid solubility limit temperature = about 500 °C). On the other hand, the highest temperature in the heat history after the metal contamination is 800 °C of the above heat treatment H A . Therefore, since the temperature of the heat treatment H A received so far after the metal contamination is higher than the solid solubility limit temperature of the contaminating metal (Ni), the heat treatment temperature under a non-oxidizing atmosphere shall be set to a temperature that satisfies 800 °C or higher and less than the silicon melting point.

[0022] Note that the deliberate contamination of Ni mentioned here is only to clarify the contamination amount and clearly show the effect of the present invention. As described above, the metal contamination referred to in the present invention includes not only deliberate contamination but also environmental contamination that the silicon wafer undergoes during the manufacturing process.

[0023] Also, the heat treatment time in a non-oxidizing atmosphere is not limited, but in particular, it can depend on the diffusion coefficient of the contaminating metal. The higher the temperature, the shorter the heat treatment time to exhibit the effect, but it is preferably set to be longer than the heat treatment time when the diffusion length of the contaminating metal corresponds to the thickness of the metal-contaminated silicon wafer. In this way, it can be appropriately determined according to the type of contaminating metal, heat treatment temperature, thickness of the silicon wafer, etc.

[0024] Further, as shown in S3 of FIG. 1, after the first heat treatment, a second heat treatment is performed. At this time, in order to prevent metal precipitates from being formed again during the cooling process, the atmosphere is replaced from the non-oxidizing atmosphere in the first heat treatment to an oxidizing atmosphere without lowering the temperature, and heat treatment is performed at a temperature equal to or higher than the heat treatment temperature of the first heat treatment (and less than the melting point of silicon) in the oxidizing atmosphere. In this way, the oxidation heat treatment of the silicon wafer is performed. By performing the second heat treatment continuously in an oxidizing atmosphere without lowering the furnace temperature after the first heat treatment in this way, it is possible to avoid the metal precipitates that become the nuclei of OSF formation dissolved in the first heat treatment from precipitating again during the cooling process and OSF being formed in the second heat treatment step.

[0025] Note that the second heat treatment time is not particularly limited, and for example, it can be 1 minute or more. Also, the upper limit is not particularly limited, and it can be appropriately determined according to the required oxide film thickness and the like.

[0026] Even if an oxidation heat treatment is performed on a silicon wafer after metal contamination by the heat treatment method as described above, it is possible to extremely effectively and more reliably prevent the formation of OSF due to metal contamination compared to the conventional method.

Example

[0027] Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. (Example 1) A silicon wafer used for device fabrication was produced by slicing and polishing in a normal manner from a CZ-grown silicon single crystal ingot with a diameter of 150 mm, an initial oxygen concentration of 18 ppma (JEIDA), and an orientation of <100>. Next, as shown in FIG. 2, about 10 Ni was deposited on the surface of this silicon wafer. 13 atoms / cm 2It was deliberately contaminated at a concentration of. Specifically, it was carried out by spin-coating a solution obtained by diluting a standard solution for Ni atomic absorption (1000 mg / L = 1000 ppm) with pure water on the wafer surface. The silicon wafer was carried into the heat treatment furnace at room temperature, and after heat treatment at 1000 °C for 1 h in a nitrogen atmosphere (hereinafter also referred to as diffusion heat treatment), it was cooled to room temperature (25 °C) at -220 °C / min, and the silicon wafer was taken out after cooling. In this way, Ni silicide was formed on the surface of the silicon wafer.

[0028] The volume concentration of Ni in this silicon wafer is about 10 13 atoms / cm 2 at the surface contamination concentration, and since the thickness is 675 μm, it is about 1.5×10 14 atoms / cm 3 . From Equation 1, when the solubility limit corresponding to about 1.5×10 14 atoms / cm 3 was determined, the solubility limit temperature was about 580 °C. That is, the highest temperature in the heat history after deliberate contamination (1000 °C in the above diffusion heat treatment) > the solubility limit temperature (about 580 °C). In addition, another similar silicon wafer was prepared, and the same heat treatment was performed in the same heat treatment furnace as above. When the Ni concentration of the silicon wafer before and after the heat treatment was analyzed, the increase in the Ni concentration was extremely small compared to the above deliberate contamination amount: about 1.5×10 14 atoms / cm 3 and was negligible. Therefore, the increase in Ni contamination from the outside of the silicon wafer during this diffusion heat treatment can be ignored.

[0029] Next, in order to dissolve the Ni silicide on the surface, the silicon wafer was carried into the heat treatment furnace at room temperature (25 °C). After sufficiently replacing the inside of the heat treatment furnace with a nitrogen atmosphere, the temperature was raised to 1000 °C in the nitrogen atmosphere, and the first heat treatment was performed for 3 h. Thereafter, while maintaining the temperature, the atmosphere was replaced with oxygen, and the second heat treatment (oxidation heat treatment) was performed at 1000 °C for 4 h in an oxygen atmosphere.

[0030] The oxide film on the silicon wafer after the second heat treatment was removed with 5% hydrofluoric acid, and selective etching was performed for 1 minute using a selective etching solution (IT solution) to form etch pits on the wafer surface. The surface of the silicon wafer was observed with an optical microscope, and the OSF density was measured.

[0031] (Comparative Example 1) As shown in Fig. 3, heat treatment was performed in the same manner as in Example 1 except that the first heat treatment in Example 1 was not performed and the loading method during the second heat treatment (oxidation heat treatment) was different. More specifically, after performing intentional contamination, diffusion heat treatment, cooling, and wafer removal similar to Example 1, the wafer was loaded at room temperature, the inside of the heat treatment furnace was replaced with an oxygen atmosphere, the temperature was raised to 1000 °C in the oxygen atmosphere, and heat treatment (oxidation heat treatment) was performed for 4 h. Thereafter, the OSF density was measured in the same manner as in Example 1.

[0032] (Comparative Example 2) As shown in Fig. 4, heat treatment was performed in the same manner as in Example 1 except that the silicon wafer was heated from 800 °C to 1000 °C when it was introduced into the heat treatment furnace during the first heat treatment in Example 1, and the OSF density was measured.

[0033] (Comparative Example 3) As shown in Fig. 5, heat treatment was performed in the same manner as in Example 1 except that the first heat treatment temperature in Example 1 was set to 800 °C, which is lower than the diffusion heat treatment temperature, and the OSF density was measured.

[0034] The measurement results of the respective OSF densities are shown in Fig. 6. Comparing Example 1 with Comparative Example 1, it can be seen that by performing the first heat treatment in a non-oxidizing atmosphere in the present invention (that is, Example 1), the formation of OSF due to metal contamination is suppressed. Also, comparing Example 1 with Comparative Example 2, it can be seen that in the first heat treatment, when the silicon wafer is introduced into a high-temperature heat treatment furnace (that is, Comparative Example 2), the OSF reduction effect is low. Furthermore, when comparing Example 1 and Comparative Example 3, it can be seen that when the first heat treatment is not performed at a high temperature equal to or higher than the diffusion heat treatment temperature (i.e., the heat treatment temperature that the silicon wafer received after contamination), which is higher than the solid solubility limit temperature (i.e., Comparative Example 3), the OSF reduction effect is low. Therefore, according to the present invention, when performing an oxidation heat treatment on a silicon wafer contaminated with metal, it is possible to effectively suppress the formation of OSF caused by metal contamination even without a gettering mechanism.

[0035] Incidentally, the diffusion heat treatment in Example 1 is a process of diffusing intentionally contaminated Ni on the wafer surface from the surface into silicon. This time, the diffusion heat treatment temperature was higher than the solid solubility limit temperature. Conversely, when the diffusion heat treatment is performed at a temperature lower than the solid solubility limit temperature, since only the Ni on the wafer surface enters the silicon up to the solid solubility at the heat treatment temperature in the diffusion heat treatment, by setting the temperature of the first heat treatment to be equal to or higher than the solid solubility limit temperature of Ni, OSF caused by metal contamination hardly occurs.

[0036] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Claims

1. A heat treatment method for performing an oxidation heat treatment on a silicon wafer contaminated with a metal selected from Fe, Ni, Co, and Cu, wherein the silicon wafer is carried into a heat treatment furnace at room temperature, and after replacing the inside of the heat treatment furnace with a non-oxidizing atmosphere, a solid solubility limit temperature at which the solid solubility coincides with the contamination concentration of the contaminated metal estimated in the silicon wafer and a first heat treatment for dissolving metal precipitates on the surface of the silicon wafer by performing a heat treatment on the silicon wafer at a temperature higher than the higher of the maximum temperature in the heat history after the metal contamination of the silicon wafer and lower than the melting point of silicon in the non-oxidizing atmosphere; after the first heat treatment, without lowering the temperature, the inside of the heat treatment furnace is replaced with an oxidizing atmosphere, and a second heat treatment for oxidizing the silicon wafer by performing a heat treatment on the silicon wafer at a temperature not lower than the heat treatment temperature of the first heat treatment and lower than the melting point of silicon in the oxidizing atmosphere; A heat treatment method for a silicon wafer, comprising the steps of:

2. The heat treatment method for a silicon wafer according to claim 1, wherein the contamination concentration of the contaminated metal in the silicon wafer is estimated from impurity analysis of the silicon wafer or an environmental contamination test of the process to which the silicon wafer has been subjected.

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