JP2010263009A - Silicon wafer and manufacturing method thereof - Google Patents

Abstract

A silicon wafer in which no crystal defects exist in the surface layer portion of the wafer and oxygen precipitates and other crystal defects are reduced inside the wafer, and a method for manufacturing the same are provided.
(1) A step of forming a polysilicon layer on the outer surface of a silicon wafer consisting of a defect-free region cut out from a silicon single crystal ingot grown by the Czochralski method, and forming the polysilicon layer A manufacturing method comprising a step of performing an RTA process on a wafer and a step of removing a polysilicon layer on at least one main surface of the wafer after the RTA process. The RTA treatment is desirably performed in a nitriding atmosphere or an oxidizing atmosphere. (2) A silicon wafer in which oxygen precipitates inside the wafer are reduced and can be manufactured by the above-described manufacturing method. It is desirable that a polysilicon layer be formed on one main surface of the wafer.
[Selection figure] None

Description

  The present invention relates to a silicon wafer suitably used for a semiconductor device substrate and the like and a method for manufacturing the same.

  A silicon wafer used as a substrate for a semiconductor device is generally cut out from a silicon single crystal ingot grown by the Czochralski method (hereinafter referred to as “CZ method”) and manufactured through a process such as polishing.

  A silicon wafer contains oxygen as an impurity, and this oxygen impurity forms an oxygen precipitate (hereinafter also referred to as “BMD (Bulk Micro Defect)”) that causes dislocations, defects, and the like. It is known that BMD is formed by growing minute nuclei (oxygen precipitation nuclei) introduced into a crystal when pulling up a silicon single crystal, for example, by a heat treatment such as an oxidation heat treatment in a device manufacturing process. If this BMD is near the surface (surface layer part) of the wafer on which the semiconductor device is formed, it will greatly affect device characteristics such as an increase in leakage current and a decrease in oxide insulation (oxide breakdown voltage). Effect.

  On the other hand, the BMD formed inside the wafer serves as a gettering site that captures contaminant impurities (particularly metal impurities) and removes them from the wafer surface layer. In the device manufacturing process, an apparatus that generates metal contamination, such as a dry etching process, may be used, and it is extremely important that the wafer has an excellent gettering capability.

  Therefore, conventionally, defects such as oxygen precipitates do not exist in the surface layer portion of the wafer, and oxygen precipitates, a polycrystalline silicon (polysilicon) layer, a high-concentration phosphorus diffusion layer, or the like is present on the inside or the back surface of the wafer. A method for manufacturing a silicon wafer in which a gettering site exists has been developed.

For example, Patent Document 1, after the injection of vacancies in the wafer by heat-treating the wafer in an atmosphere containing nitriding gas such as NH _3, and subjected to a high-temperature heat treatment, a defect-free layer on the wafer surface (hereinafter, " A method of manufacturing a silicon wafer is described in which a DZ layer (referred to as a “DZ layer”) is formed, and thereafter, oxygen precipitation heat treatment is performed to deposit BMD therein. Thus, a silicon wafer having a DZ layer in the surface layer portion and having a sufficient BMD density inside and excellent gettering ability can be manufactured.

JP 2003-31582 A

Certainly, as described in the above-mentioned Patent Document 1, if the RTA process is performed in a nitriding gas atmosphere, for example, vacancies are injected into the wafer, and the gettering ability having a sufficient BMD density inside the wafer is excellent. A silicon wafer can be provided.
In recent years, development of an insulated gate bipolar transistor (IGBT) has been promoted. IGBTs are elements that use the wafer in the vertical direction (wafer thickness direction) instead of elements that use only the vicinity of the wafer surface in the horizontal direction, like LSIs such as memories, and their characteristics affect the quality of the bulk of the wafer. Is done. For this reason, it has become necessary to reduce not only the COP and BMD in the wafer surface layer but also the COP and BMD inside the wafer. In addition to the wafers for IGBTs, in recent years, further improvements have been made in the device manufacturing process, and the risk of impurity contamination has been greatly reduced, so that the quality required for wafers is limited to COPs and dislocation clusters. In addition, it is expected that a silicon wafer in which even BMD, which is a kind of crystal defect, is reduced as much as possible will be required in the future as a next-generation wafer.
When the oxygen concentration in the silicon wafer is low, the formation of BMD precipitation nuclei itself can be suppressed and the BMD can be reduced. However, since the oxygen is low inside the wafer, there is a problem that the strength of the wafer is weakened. .

  It is an object of the present invention to provide a silicon wafer in which no crystal defects exist in the surface layer portion of the wafer and BMD and other crystal defects are reduced inside the wafer, and a method for manufacturing the same.

In order to solve the above problems, the present inventor has rapidly heated a polysilicon layer formed in advance on the entire surface composed of the front surface, back surface and chamfered surface of the silicon wafer (hereinafter referred to as “outer surface”). An attempt was made to perform heat treatment for rapid cooling (hereinafter referred to as “RTA (Rapid Thermal Annealing) treatment”).
As a result, by forming a polysilicon layer in advance on the outer surface of the silicon wafer, it was confirmed that metal impurity contamination inside the wafer can be suppressed and that the BMD density can be reduced over the entire thickness direction of the wafer. It came to.

  The gist of the present invention is the following (1) silicon wafer production method and the following (2) silicon wafer produced by the method.

(1) A step of forming a polysilicon layer on the outer surface of a silicon wafer composed of a defect-free region cut out from a silicon single crystal ingot grown by the CZ method, and an RTA process is performed on the wafer on which the polysilicon layer is formed. A method for manufacturing a silicon wafer, comprising: a step; and a step of removing a polysilicon layer on at least one main surface of the wafer after the RTA treatment.
In the method for producing a silicon wafer of the present invention, if the RTA treatment is performed in a nitriding atmosphere or an oxidizing atmosphere, there is no concern that metal contamination will occur.

(2) A silicon wafer comprising a defect-free region cut out from a silicon single crystal ingot grown by the CZ method, wherein oxygen precipitates (BMD) inside the wafer are reduced.
If the silicon wafer of the present invention is a wafer in which a polysilicon layer is formed on at least one main surface, it is desirable because it has a gettering function.

  According to the silicon wafer manufacturing method of the present invention, the metal impurity concentration inside the wafer is extremely low, there is no crystal defect in the surface layer portion of the wafer, and BMD and other crystal defects are reduced inside the wafer. A silicon wafer can be manufactured.

  The silicon wafer of the present invention is a wafer in which no crystal defects exist in the surface layer portion of the wafer and BMD and other crystal defects are reduced inside the wafer, and as a next-generation silicon wafer that does not adversely affect device characteristics. It is valid.

It is the figure which showed the relationship between V (the pulling speed of a silicon single crystal) / G (temperature gradient of the growth direction in the single crystal immediately after pulling) and the interstitial silicon type point defect density | concentration and vacancy type point defect density | concentration. It is a figure which shows the measurement result of the BMD density in the silicon wafer manufactured with the manufacturing method of this invention by the result of an Example, and contrasts with a comparative example.

  The method for producing a silicon wafer according to the present invention includes a step of forming a polysilicon layer on the outer surface of a silicon wafer consisting of a defect-free region cut out from a silicon single crystal ingot grown by the CZ method, and forming the polysilicon layer. The method comprises a step of subjecting the wafer to RTA treatment, and a step of removing a polysilicon layer on at least one main surface of the wafer after the RTA treatment. Hereinafter, each step will be described in detail.

(A) Step of forming a polysilicon layer on the outer surface of a silicon wafer As a material of the silicon wafer of the present invention, a silicon wafer consisting of a defect-free region cut out from a silicon single crystal ingot grown by the CZ method is used. . The defect-free region here is a crystal region where COP, OSF, and dislocation clusters do not exist.

  A silicon single crystal ingot used for the production of a silicon wafer composed of this defect-free region has a V / G of V / G, where V is the pulling speed of the single crystal and G is the temperature gradient in the growth direction in the single crystal immediately after pulling. It is obtained by maintaining within the proper range described below.

  FIG. 1 is a diagram shown in the above-mentioned Patent Document 1, and graphically represents the relationship between V / G, interstitial silicon type point defect concentration, and vacancy type point defect concentration. This figure explains that the boundary between the vacancy region and the interstitial silicon region is determined by V / G, and is called the Boronkov theory.

In FIG. 1, the region where V / G on the horizontal axis is smaller than the critical point is a region where interstitial silicon type point defects exist predominantly, and further, a region [I] where V / G is smaller than (V / G) _I Is a region where agglomerates of interstitial silicon type point defects (called “dislocation clusters”) exist. On the other hand, a region where V / G is larger than the critical point is a region where vacancy type point defects exist predominantly, and a region [V] where V / G is larger than (V / G) _V is a vacancy type point defect. Are aggregates (referred to as “COP”). The region [P] between (V / G) _I and (V / G) _V is a perfect region where there are no interstitial silicon type point defect aggregates or vacant type point defect aggregates. Of the region [P], the side where the interstitial silicon-type point defects are dominant from the critical point is the region [P _I ], and the side where the vacancy-type point defects are dominant is the region [P _V ]. In addition, an OSF nucleus forming region where an OSF (Oxidation Induced Stacking Fault) nucleus is formed exists in the region [V] adjacent to the region [P].

As shown in FIG. 1, by adjusting the pulling rate of the single crystal and maintaining V / G within the range of (V / G) _I to (V / G) _V , the entire perfect region [P] A silicon single crystal ingot made of is obtained, and a silicon wafer made of a defect-free region can be cut out from this ingot.

Since this wafer does not contain crystal defects of COP, OSF and dislocation clusters from the beginning, it is possible to eliminate the deterioration of device characteristics caused by these crystal defects. The oxygen concentration in the wafer is preferably 7 × 10 ^{17 to} 16 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979). If the oxygen concentration is less than 7 × 10 ¹⁷ atoms / cm ³ , the formation of BMD precipitation nuclei itself is suppressed, but since the oxygen is low up to the inside of the wafer, there arises a problem that the strength of the wafer becomes weak. In the present invention, since oxygen diffuses outward by performing the RTA process, the oxygen concentration inside the wafer excluding the surface layer portion is high, so that there is an advantage that the wafer strength is excellent.

  Next, a polysilicon layer is formed over the entire outer surface of the silicon wafer consisting of this defect-free region. When forming the polysilicon layer, first, an oxide film is formed in advance on the outer surface of the wafer (attaching an oxide film), and then a polysilicon layer is formed by, for example, a CVD method.

  The oxide film deposition may be performed by thermal oxidation or the like as employed in the embodiments described later. Specifically, heating is performed at 600 to 700 ° C. for about 10 minutes in an atmosphere (air) containing oxygen.

The polysilicon layer is formed by introducing a source gas such as monosilane (SiH ₄ ) into the reaction furnace, and depositing and growing polysilicon on the surface of the wafer heated to 600 to 700 ° C. The thickness of the polysilicon layer is preferably 0.1 to 10 μm. The polysilicon layer can be made to function as a gettering site by removing the polysilicon layer so as to leave only one main surface in a final process described later. In addition, if the layer thickness is 0.1 μm or more, sufficient gettering capability can be obtained, and diffusion of metal impurities and hole injection into the surface portion of the silicon wafer during the RTA process described later can be suppressed. On the other hand, when the layer thickness exceeds 10 μm, productivity decreases.

(B) RTA processing step RTA processing is performed on the silicon wafer on which the polysilicon layer is formed. This RTA treatment is introduced into the crystal in the process of pulling up the silicon single crystal ingot, and is newly introduced inside the wafer in the process of forming a fine oxygen precipitation nucleus incorporated into the wafer and a polysilicon layer on the outer surface of the silicon wafer. This is performed to eliminate the introduced minute oxygen precipitation nuclei.

  The temperature and time for the RTA treatment may be set to an appropriate temperature and time so that minute oxygen precipitation nuclei existing inside the wafer can be eliminated. If the treatment temperature is too low, it takes time for the treatment, and if it is too high, the silicon melts. The treatment time depends on the treatment temperature, but is preferably 60 seconds or less from the viewpoint of reducing the occurrence of slip. Further, in the temperature rising process of the RTA process, it is desirable that the temperature rising rate be in the range of 10 to 150 ° C./sec. If it is less than 10 ° C./sec, the productivity is poor, and if it exceeds 150 ° C./sec, slip dislocation tends to occur in the wafer. From the same viewpoint as the temperature increase rate, the temperature decrease rate in the temperature decrease step is preferably in the range of 10 to 150 ° C./sec.

  For the RTA process, it is desirable to use a lamp annealing furnace capable of rapidly raising and lowering temperature because the temperature can be raised and lowered quickly and the process can be performed without applying an excessive amount of heat to the wafer.

Examples of the gas atmosphere in the RTA treatment include a gas atmosphere such as a nitriding gas atmosphere containing ammonia or nitrogen, an oxidizing gas atmosphere containing oxygen or the like, or a reducing gas atmosphere containing hydrogen or the like. The oxygen precipitation nuclei form minute silicon oxide (SiO ₂ ), and are dissolved (solid solution) to the inside of the wafer if the processing temperature and time in the RTA processing are appropriate regardless of the gas atmosphere. be able to.

  However, when the RTA treatment is performed in a reducing atmosphere such as hydrogen gas, the polysilicon layer is reduced by hydrogen and the thickness of the polysilicon layer is reduced. The metal in the atmosphere attached to the surface is likely to thermally diffuse inside the wafer, and as a result, the risk of contamination of metal impurities such as Cu and Ni inside the wafer increases. Therefore, it is desirable that the atmosphere during the RTA treatment is a nitriding gas atmosphere or an oxidizing gas atmosphere that avoids a reducing atmosphere and has a low risk of metal impurity contamination.

  For example, when an RTA process is performed in a nitriding gas atmosphere on a silicon wafer whose outer surface is not covered with a polysilicon layer, vacancies that promote BMD precipitation are usually injected into the wafer. However, since the polysilicon layer is formed over the entire outer surface of the silicon wafer, even if the RTA treatment is performed in the nitriding gas atmosphere, the introduction of vacancies into the wafer is hindered. Formation of minute oxygen precipitation nuclei can be prevented.

  Further, when COP is contained inside the silicon wafer, it is necessary to extinguish COP by heating in a reducing atmosphere. In the present invention, a wafer composed of a defect-free region that does not contain COP is used. Since it is used, the RTA treatment can be performed in a nitriding gas atmosphere.

(C) Removal process of polysilicon layer on outer surface of silicon wafer After the RTA treatment, the polysilicon layer formed on the outer surface of the silicon wafer is removed. All of the polysilicon layer formed on the outer surface of the wafer may be removed, or the polysilicon layer may be removed so that only one main surface (for example, the main surface on the back side of the wafer) remains. Good. The remaining polysilicon layer functions as a gettering site.

  The removal of the polysilicon layer may be performed by mechanical polishing, but is not limited thereto. Any method that can remove the polysilicon layer without affecting the flatness of the surface of the silicon wafer is applicable.

  Since the formation of the polysilicon layer causes damage (distortion) in the vicinity of the wafer surface in contact with the polysilicon layer, the surface layer portion of the wafer is removed by a machining process such as polishing or a chemical process such as etching. Desirably, the thickness to be removed is preferably several times greater than the thickness of the formed polysilicon layer. For example, as shown in the examples described later, when a polysilicon layer having a thickness of 1.5 μm is formed, it is desirable to remove about 10 μm from the surface.

  According to the method for producing a silicon wafer of the present invention, since a RTA process is performed with a silicon layer formed on the outer surface of a silicon wafer having a defect-free region, the surface layer portion and the inside are In addition, a silicon wafer in which BMD and other crystal defects are reduced in the wafer can be manufactured.

  The silicon wafer of the present invention is a silicon wafer composed of a defect-free region cut out from a silicon single crystal ingot grown by the CZ method, wherein oxygen precipitates (BMD) inside the wafer are reduced. It is a silicon wafer. This wafer can be manufactured by applying the silicon wafer manufacturing method of the present invention described above.

  In the silicon wafer of the present invention, it is desirable that a polysilicon layer functioning as a gettering site is formed on one main surface (that is, the back surface). In the silicon wafer of the present invention, BMD is reduced inside the wafer, and since the wafer itself does not have a gettering function, metal contamination in a process in which this wafer is used as a material, such as a semiconductor device manufacturing process, etc. This is because it is necessary to avoid or eliminate the concern.

  BMD is a crystal defect that inherently hinders device characteristics. However, in the silicon wafer of the present invention, this BMD is reduced not only in the surface layer but also in the inside. Since minute oxygen precipitation nuclei for precipitating BMD have disappeared, BMD is not formed after being subjected to the semiconductor device manufacturing process. Therefore, if the silicon wafer of the present invention is used, the device formation layer can be further expanded in the depth direction of the wafer without being affected by device characteristics such as an increase in leakage current and a reduction in oxide film breakdown voltage, The wafer can be used effectively.

A silicon wafer having a defect-free region with a diameter of 200 mm and having an oxygen concentration of 11 × 10 ¹⁷ atoms / cm ³ and 15 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979) is used. After forming the layer, RTA treatment was performed in a nitriding gas atmosphere using an RTA furnace. The wafer was subjected to precipitation heat treatment for forming BMD, and then the wafer cross section was selectively etched to measure the BMD density. For comparison, the same measurement is performed for the case where only the polysilicon layer is formed (Comparative Example 1) and for the case where the polysilicon layer is formed after the RTA process by changing the process order (Comparative Example 2). went. The silicon wafers having an oxygen concentration of 11 × 10 ¹⁷ atoms / cm ³ were designated as Sample B1, Sample A1, and Sample C1 in the present invention example, Comparative Example 1, and Comparative Example 2, respectively. Moreover, the silicon wafer of 15 × 10 ¹⁷ atoms / cm ³ was designated as sample B2, sample A2, and sample C2 in the present invention example, comparative example 1, and comparative example 2, respectively.

  In forming the polysilicon layer, an oxide film was previously applied to the outer surface of the wafer. Subsequently, a polysilicon layer was formed on the outer surface of the wafer by CVD using monosilane as a raw material. Table 1 shows the implementation conditions for forming the oxide film and forming the polysilicon layer.

  A lamp annealing furnace was used for the RTA treatment. Table 2 shows temperature rising conditions, processing temperature and time, temperature lowering conditions, and the like.

  In order to measure the BMD density inside the wafer, a heat treatment was performed at 1000 ° C. for 16 hours in an air atmosphere as a precipitation heat treatment for precipitating BMD. By this precipitation heat treatment, if minute oxygen precipitation nuclei exist inside the wafer, it can be grown to a size detectable as BMD.

  The BMD density is measured by cleaving the wafer after the precipitation heat treatment, selectively etching this cleaved cross section to a depth of 2 μm with Secco liquid, and then measuring the wafer in three thickness directions (1/3 of the thickness from the wafer surface). (4, 1/2 and 3/4 sites) were observed with a microscope, and the BMD density was calculated based on the observation results.

  In Table 3 and FIG. 2, the measurement result of BMD density (the average value of said 3 places) is shown.

  As shown in Table 3 and FIG. 2, BMD was reduced in the present invention example (sample B1 and sample B2: polysilicon layer formation → RTA treatment). In contrast, in Comparative Example 1 (Sample A1 and Sample A2: Polysilicon layer formation only) and Comparative Example 2 (Sample C1 and Sample C2: RTA treatment → polysilicon layer formation), formation of BMD was observed in both cases. . In Comparative Example 1, the minute oxygen precipitates introduced into the crystal during the pulling process of the silicon single crystal and the minute oxygen precipitate nuclei incorporated inside the wafer and the minute layer generated inside the wafer during the process of forming the polysilicon layer on the outer surface of the silicon wafer. It is considered that BMD was formed due to the oxygen precipitation nuclei. On the other hand, in the present invention, it is considered that BMD was reduced as a result of the above-described oxygen precipitation nuclei disappearing by the RTA treatment. On the other hand, in Comparative Example 2, it is considered that when the silicon wafer was subjected to the RTA process, holes were injected into the wafer, and BMD was formed due to the holes.

For the purpose of investigating impurity contamination, a silicon wafer consisting of a defect-free region having a diameter of 200 mm and having an oxygen concentration of 11 × 10 ¹⁷ atoms / cm ³ and 15 × 10 ¹⁷ atoms / cm ³ (ASTM F-121, 1979) The following three types of treatment were performed. That is, after forming a polysilicon layer on the outer surface of the wafer, an RTA treatment was performed in an NH ₃ gas atmosphere using an RTA furnace (example of the present invention). In the present invention example, RTA treatment was performed in a hydrogen gas atmosphere instead of NH ₃ gas (Comparative Example 3). Further, in Comparative Example 3, RTA treatment was performed without forming a polysilicon layer on the outer surface of the wafer (Comparative Example 4). The conditions for the RTA treatment were in accordance with Table 2. For Comparative Example 3 and Comparative Example 4, in Table 2, hydrogen gas was used instead of NH ₃ gas. In the present invention example and the comparative example 3, the thickness of the polysilicon layer was 1.5 μm. The Cu, Fe, and Ni concentrations inside the wafers were analyzed without performing a precipitation heat treatment for depositing BMD on these wafers. ICP-MS (Inductively Coupled Plasma-Mass Spectroscopy) was used for the analysis. The silicon wafers having an oxygen concentration of 11 × 10 ¹⁷ atoms / cm ³ were designated as sample B1, sample D1, and sample E1 in the present invention example, comparative example 3, and comparative example 4, respectively. The silicon wafer 15 × 10 ¹⁷ atoms / cm ^3, an example the present invention, in Comparative Examples 3 and 4, respectively, the sample B2, was used as a sample D2 and sample E2.
Table 4 shows the impurity concentration measurement results.

As shown in Table 4, in the example of the present invention, the impurity concentration was most reduced. In contrast, in Comparative Example 3 in which RTA treatment was performed in a hydrogen gas atmosphere instead of NH ₃ gas, the concentrations of Cu, Fe, and Ni were higher than those of the inventive examples. Since the RTA treatment is performed in a reducing atmosphere, the polysilicon layer is reduced and the thickness of the polysilicon layer is reduced. As the layer thickness decreases, the metal in the atmosphere attached to the surface of the polysilicon layer is removed from the wafer. This is thought to be because the heat diffused easily inside. Among these, the concentration of Cu is the highest because Cu is easily diffused inside the wafer. In Comparative Example 4 in which RTA treatment was performed in a hydrogen gas atmosphere without forming a polysilicon layer on the outer surface of the wafer, the amount of impurity contamination was the highest. It is considered that because the RTA treatment was performed in a reducing atmosphere, the natural oxide film on the wafer surface was reduced and silicon was exposed to the surface, and the metal in the atmosphere adhered to the exposed surface and thermally diffused inside the wafer.
From the above investigation, by applying the silicon wafer manufacturing method of the present invention, impurity contamination is reduced, BMD is reduced inside the wafer, and the defect-free region is greatly expanded in the depth direction from the wafer surface. It could be confirmed.

According to the silicon wafer manufacturing method of the present invention, it is possible to manufacture a silicon wafer in which impurity contamination is reduced and BMD and other crystal defects are reduced not only in the surface layer portion of the wafer but also in the wafer. In addition, the silicon wafer of the present invention is a silicon wafer in which BMD is reduced, and can be manufactured by the manufacturing method of the present invention. If necessary, gettering can be applied to one main surface of the wafer. Since the device formation layer can be expanded in the depth direction of the wafer, the wafer can be used effectively.
Therefore, the present invention can be widely used in the manufacture of silicon wafers and semiconductor devices.

Claims (4)

Forming a polysilicon layer on the outer surface of a silicon wafer consisting of a defect-free region cut out from a silicon single crystal ingot grown by the Czochralski method;
Applying RTA treatment to the wafer on which the polysilicon layer is formed;
And a step of removing a polysilicon layer on at least one main surface of the wafer after the RTA treatment.   The method for producing a silicon wafer according to claim 1, wherein the RTA treatment is performed in a nitriding atmosphere or an oxidizing atmosphere. A silicon wafer consisting of a defect-free region cut out from a silicon single crystal ingot grown by the Czochralski method,
A silicon wafer characterized in that oxygen precipitates inside the wafer are reduced.   The silicon wafer according to claim 3, wherein a polysilicon layer is formed on one main surface of the silicon wafer.

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