JP2011037678A - Method for producing silicon single crystal, method for producing silicon wafer, and method for producing epitaxial wafer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing, in a method for growing a silicon single crystal from a silicon melt containing added carbon, a silicon single crystal, whereby a decrease in a carbon concentration around the outer periphery of the silicon single crystal can be suppressed and to provide methods for producing a silicon wafer and an epitaxial wafer which has a uniform plane bulk micro defect density (BMD density) and which have high gettering capability. <P>SOLUTION: What are provided are a method for producing a silicon single crystal 16 comprising preparing a silicon melt 13 containing added carbon in a crucible 12, and pulling up under rotation at a rotation speed of 0.52-0.84 rad/s a silicon seed crystal 17 kept in contact with the silicon melt 13 while applying a magnetic field of a magnetic flux density of 0.2-0.4 T to the silicon melt 13 in the crucible 12 to grow the silicon single crystal 16 on the silicon seed crystal 17 and a method for producing a silicon wafer and an epitaxial wafer by using an ingot of the silicon single crystal 16 produced by the method. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a method for manufacturing a silicon single crystal, a method for manufacturing a silicon wafer, and a method for manufacturing an epitaxial wafer, and in particular, a method for manufacturing a silicon single crystal that can be suitably used for manufacturing a substrate for an image sensor (CIS). In addition, the present invention relates to a method for manufacturing a silicon wafer and an epitaxial wafer that can be suitably used for manufacturing an imaging device.

  Conventionally, as a semiconductor substrate used to manufacture a semiconductor device such as an image sensor, a silicon wafer cut out from a silicon single crystal ingot grown by the Czochralski method (CZ method), or epitaxially formed on the surface of the silicon wafer is used. A layered epitaxial wafer is used. As such silicon wafers and epitaxial wafers (hereinafter sometimes simply referred to as “wafers”), with the recent miniaturization of semiconductor devices, crystal defects caused by heavy metals (for example, white defects in imaging elements). In particular, there is a demand for a material having a high gettering ability that is difficult to generate.

  Here, in general, as a factor that affects the gettering ability of a wafer, interstitial oxygen (enters between the lattices) into the oxygen precipitation nuclei existing in the wafer by a heat treatment performed in a semiconductor device manufacturing process or the like. There are known oxygen precipitates (BMD: Bulk Micro Defects) formed by bonding oxygen atoms). When this BMD is present inside the wafer, it exhibits a gettering action for heavy metals and becomes a gettering site (IG effect: Internal Gettering). In order to obtain a wafer with high gettering ability, It is considered effective to promote the formation of BMD.

  Therefore, studies have been made on a method capable of promoting the formation of BMD to increase the BMD density and enhancing the gettering ability of the wafer. As such a method, carbon is added to the wafer during the heat treatment. A method for promoting the formation of oxygen precipitates (BMD) and increasing the BMD density has been proposed. Specifically, as a method of adding carbon into the wafer, a method of implanting carbon ions into the wafer using an ion implantation facility, or a silicon single crystal by heating the outer peripheral surface of the single crystal being pulled up with a carbon heater. A method has been proposed in which carbon is added to the outer peripheral portion of the wafer and a wafer is manufactured using the silicon single crystal ingot (see, for example, Patent Document 1).

  However, the method of implanting carbon ions into a wafer using an ion implantation facility requires the introduction of the ion implantation facility and requires a long processing time, which causes a problem that the production cost increases. Further, the method using a carbon heater has a problem that heavy metal contamination may occur due to heavy metals existing in the carbon heater or in the apparatus.

  In contrast, as a method for adding carbon to a wafer at low cost without using a carbon heater, a silicon single crystal is grown using a silicon-added silicon melt, and the wafer is removed from the silicon single crystal ingot. A method of cutting out has been proposed.

  However, in this method using carbon-added silicon melt, the carbon concentration and oxygen concentration in the outer peripheral portion of the grown silicon single crystal are lower than in the central portion, and as a result, carbon is added in the outer peripheral portion of the silicon single crystal. As a result, the BMD density at the outer periphery of the wafer manufactured using the silicon single crystal ingot is lowered (that is, a difference in BMD density occurs in the surface of the wafer). It was.

Japanese Patent No. 3055458

  Therefore, in the method of growing a silicon single crystal using carbon-added silicon melt, it is possible to suppress a decrease in carbon concentration in the outer peripheral portion of the silicon single crystal (ie, manufacturing using the silicon single crystal ingot). It has been demanded to develop a method for producing a silicon single crystal that can suppress the decrease in the BMD density at the outer peripheral portion of the wafer and make the in-plane BMD density uniform. Further, it has been demanded to develop a method for producing a wafer having a high gettering ability, particularly an epitaxial wafer, in which the in-plane BMD density is made uniform.

An object of the present invention is to advantageously solve the above-mentioned problems, and a method for producing a silicon single crystal according to the present invention comprises preparing a silicon melt added with carbon in a crucible, and silicon in the crucible. While applying a magnetic field having a magnetic flux density of 0.2 to 0.4 T to the melt, rotating the silicon seed crystal in contact with the silicon melt at a rotational speed of 0.52 to 0.84 rad / s. And pulling up and growing a silicon single crystal on the silicon seed crystal. Thus, the silicon seed crystal is rotated at a rotational speed of 0.52 to 0.84 rad / s (5 to 8 rpm) while applying a magnetic field having a magnetic flux density of 0.2 to 0.4 T (2000 to 4000 gauss). If the pulling is performed while lowering the carbon concentration, it is possible to suppress a decrease in carbon concentration in the outer peripheral portion of the silicon single crystal.
Further, according to the above, the carbon concentration in the outer peripheral portion within 50 mm from the outer peripheral surface of the silicon single crystal toward the center becomes higher than the carbon concentration at the center position of the silicon single crystal, and the outer peripheral surface of the silicon single crystal Since the carbon concentration at a position of 10 mm from the center to the center is 1.2 times or more the carbon concentration at the center position of the silicon single crystal, the oxygen concentration at the outer peripheral portion of the grown silicon single crystal is lower than that at the center portion. Even if it becomes, the fall of the BMD density in the outer peripheral part of the wafer manufactured using this silicon single crystal ingot can be suppressed.
Here, in the present invention, “carbon concentration” refers to the concentration measured by the FT-IR method, and “carbon concentration in the outer peripheral portion of the silicon single crystal” refers to the average of the outer peripheral portion measured by the FT-IR method. Refers to carbon concentration. The “carbon concentration at the center position of the silicon single crystal” refers to the carbon concentration at the center position of the cross section of the silicon single crystal measured by the FT-IR method.

Here, in the method for producing a silicon single crystal of the present invention, it is preferable that the oxygen concentration in the silicon single crystal is 13 × 10 ^{17 to} 17 × 10 ¹⁷ atoms / cm ³ . This is because the in-plane distribution of BMD can be made uniform even if the oxygen concentration in the outer peripheral portion is lowered due to the effect of promoting the formation of BMD by adding carbon. Here, in the present invention, “oxygen concentration in silicon single crystal” refers to an average oxygen concentration measured by the FT-IR method.

In the method for producing a silicon single crystal of the present invention, carbon is added to the silicon melt so that the carbon concentration in the pulled silicon single crystal is 1 × 10 ^{15 to} 1.3 ¹⁷ atoms / cm ^3. It is preferable. This is because the effect of promoting the formation of BMD by adding carbon can be sufficiently obtained.

  Furthermore, the method for producing a silicon wafer according to the present invention includes cutting out a silicon wafer from a silicon single crystal ingot produced by the production method described above.

  And the manufacturing method of the epitaxial wafer of this invention includes cutting out a silicon wafer from the ingot of the silicon single crystal manufactured with the manufacturing method mentioned above, and forming an epitaxial layer on the surface of the silicon wafer. In this way, if an epitaxial wafer is manufactured using a silicon single crystal ingot that suppresses a decrease in carbon concentration in the outer peripheral portion by manufacturing by the above method, the in-plane BMD density is made uniform and high gettering ability is obtained. An epitaxial wafer having the same can be obtained.

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing a silicon single crystal using the silicon melt which added carbon, the manufacturing method of the silicon single crystal which can suppress the fall of the carbon concentration in the outer peripheral part of a silicon single crystal is provided. can do. Further, it is possible to provide a method for producing a wafer having a high gettering ability, particularly an epitaxial wafer, in which the in-plane BMD density is uniform.

It is explanatory drawing which shows an example of the single crystal manufacturing apparatus suitable for using for the manufacturing method of the silicon single crystal of this invention. It is sectional drawing which shows the cross section of the silicon single crystal manufactured using an example of the manufacturing method of the silicon single crystal of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Here, an example of the method for producing a silicon single crystal of the present invention can be carried out using a single crystal production apparatus 10 as shown in FIG.

  This single crystal manufacturing apparatus 10 is an apparatus for manufacturing a silicon single crystal by a magnetic field application type Czochralski method, and accommodates polycrystalline silicon and carbon, which are raw material materials of the silicon single crystal, in a chamber 11. The crucible 12, the heater 14 for heating the raw material in the crucible 12 to form a melt 13, and the crucible 12 provided at the lower part of the crucible 12 are circumferentially (see from above the apparatus in FIG. 1). A crucible rotating mechanism 15 that rotates clockwise), a wire rope 19 to which a seed crystal holder (seed chuck) 18 for holding a silicon seed crystal 17 for growing a silicon single crystal 16 is attached to the tip; A silicon single crystal is wound up while rotating the wire rope 19 in a direction opposite to the rotation direction of the crucible 12 (counterclockwise in FIG. 1 when viewed from above the apparatus). 6, and a take-up mechanism 20 to raise while rotating the silicon seed crystal 17 and the seed crystal holder 18.

  The single crystal manufacturing apparatus 10 includes a magnetic field applicator 21 for applying a magnetic field having a magnetic flux density of 0.2 to 0.4 T to the melt 13 in the crucible 12. It is arranged so as to surround it.

  And in the single crystal manufacturing apparatus 10, a silicon single crystal is manufactured as follows, for example, using the silicon single crystal manufacturing method according to the present invention.

First, polycrystalline silicon and carbon are accommodated in the crucible 12 so that the carbon concentration in the pulled silicon single crystal is, for example, 1 × 10 ^{15 to} 1.3 ¹⁷ atoms / cm ^3, and heated by the heater 14. A magnetic field having a magnetic flux density of 0.2 T to 0.4 T is applied to the melt 13 by the magnetic field applicator 21 while using the melt 13. Carbon is not particularly limited, and pure carbon, graphite, and the like can be used.

  Next, with the magnetic field applied to the melt 13, the silicon seed crystal 17 held in the seed crystal holder 18 attached to the tip of the wire rope 19 is brought into contact with the melt 13. Then, while applying a magnetic field to the melt 13, the crucible 12 using the crucible rotating mechanism 15 is rotated at a rotational speed of 0.01 to 0.31 rad / s, for example, and the wire rope 19 is rotated in the rotational direction of the crucible 12. Is wound by the winding mechanism 20 while rotating in the opposite direction at a rotational speed of 0.52 to 0.84 rad / s, and the silicon seed crystal 17 and the silicon single crystal 16 grown on the silicon seed crystal 17 are obtained. Pull up while rotating. Since the silicon seed crystal 17 and the silicon single crystal 16 rotate integrally with the wire rope 19, the rotation speed of the silicon seed crystal 17 and the silicon single crystal 16 at the time of pulling is equal to the rotation speed of the wire rope 19. .

Here, in the silicon single crystal 16 pulled up as described above, the carbon concentration in the silicon single crystal does not decrease even at the outer periphery. Therefore, even if the oxygen concentration in the outer peripheral portion of the grown silicon single crystal is lower than that in the central portion, the decrease in BMD density in the outer peripheral portion of the wafer manufactured using the silicon single crystal ingot is suppressed. Can do. From the viewpoint of sufficiently obtaining the effect of promoting BMD formation by adding carbon, the oxygen concentration of the pulled silicon single crystal 16 is preferably 13 × 10 ^{17 to} 17 × 10 ¹⁷ atoms / cm ³ . Incidentally, the oxygen concentration of the silicon single crystal can be controlled by a known method.

The silicon single crystal 16 manufactured by the single crystal manufacturing apparatus 10 as described above has a cross section (radius R) of the ingot of the manufactured silicon single crystal 16 as shown in FIG. average carbon concentration in the outer peripheral surface O _S peripheral portion within 50mm toward the center C of O (portion indicated by hatching in FIG. 2) is higher than the carbon concentration in the center C of the silicon single crystal 16. Further, the carbon concentration at a position of 10 mm from the outer peripheral surface of the silicon single crystal 16 toward the center C becomes 1.2 times or more the carbon concentration at the center position of the silicon single crystal.

  Then, the silicon wafer cut out from the silicon single crystal ingot manufactured as described above using a wire saw or the like is used as it is or after forming an epitaxial layer on the surface by a known method to form an epitaxial wafer, for example, imaging It can be used as a semiconductor substrate for an element (CIS).

  EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not limited to the following Example.

(Comparative Example 1)
A single crystal manufacturing apparatus shown in FIG. 1 using a silicon melt to which carbon is added so that the carbon concentration in the pulled silicon single crystal is 1 × 10 ¹⁶ atoms / cm ³ or more. A magnetic field is applied and the silicon seed crystal is rotated and pulled up while changing the rotation speed within a range of 0.52 to 1.04 rad / s, and the oxygen concentration in the longitudinal direction of the crystal is 12 × 10 ^{17 to} 17 × 10 ^17. A silicon single crystal ingot was produced in the range of atoms / cm ³ .
Then, a sample wafer is cut out with a wire saw from the manufactured silicon single crystal ingot, and the oxygen concentration at the center of each of the sample wafers 1 to 5 having different oxygen concentrations (different positions in the longitudinal direction of the single crystal), and in the wafer plane The oxygen concentration distribution and carbon concentration distribution were evaluated by the following methods. The results are shown in Table 1.
Further, the sample wafers 1 to 5 were subjected to a heat treatment at a temperature of 800 ° C. for 3 hours in a dry oxidation atmosphere, and then further subjected to a heat treatment at a temperature of 1000 ° C. for 16 hours. Then, after removing the oxide film formed on the surface of each wafer with a hydrofluoric acid aqueous solution, the wafer was opened, the cross section was selectively etched using a light solution, and the BMD density of the cross section was measured by the following method. . The results are shown in Table 1.

(Comparative Example 2)
A silicon single crystal ingot was manufactured in the same manner as in Comparative Example 1 except that the magnetic flux density of the applied magnetic field was changed to 0.18T.
Then, the sample wafer was cut out in the same manner as in Comparative Example 1, and the oxygen concentration at the center of the sample wafers 6 to 10 having different oxygen concentrations, and the oxygen concentration distribution and the carbon concentration distribution in the wafer surface were evaluated by the following methods. .
Moreover, the heat processing etc. similar to the comparative example 1 were performed with respect to the sample wafers 6-10, and BMD density was measured. These results are shown in Table 1.

Example 1
Comparative example except that the magnetic flux density of the magnetic field to be applied was changed in the range of 0.2 to 0.3 T, and the rotational speed of the silicon seed crystal at the time of pulling was changed in the range of 0.52 to 0.84 rad / s. In the same manner as in Example 1, a silicon single crystal ingot was produced.
Then, the sample wafer was cut out in the same manner as in Comparative Example 1, and the oxygen concentration at the center of the sample wafers 12 to 15 having different oxygen concentrations, and the oxygen concentration distribution and the carbon concentration distribution in the wafer surface were evaluated by the following methods. .
Further, the sample wafers 12 to 15 are subjected to the same heat treatment as in Comparative Example 1,
BMD density was measured. These results are shown in Table 1.

(Example 2)
Comparative example except that the magnetic flux density of the magnetic field to be applied was changed in the range of 0.3 to 0.4 T, and the rotation speed of the silicon seed crystal at the time of pulling was changed in the range of 0.52 to 0.84 rad / s. In the same manner as in Example 1, a silicon single crystal ingot was produced.
Then, the sample wafer was cut out in the same manner as in Comparative Example 1, and the oxygen concentration at the center of each of the sample wafers 16 to 20 having different oxygen concentrations, and the oxygen concentration distribution and the carbon concentration distribution in the wafer surface were evaluated by the following methods. .
Further, the sample wafers 16 to 20 are subjected to the same heat treatment as in Comparative Example 1,
BMD density was measured. These results are shown in Table 1.

(Measurement of oxygen concentration)
The oxygen concentration at the center of the wafer was measured by an FT-IR (Fourier transform infrared absorption) method using an FT-IR apparatus (manufactured by Bio-Rad).
(Evaluation of in-plane oxygen concentration distribution)
Using an FT-IR apparatus (manufactured by Bio-Rad), the oxygen concentration was measured at a pitch of 5 mm from the center of the wafer to the outer periphery by the FT-IR (Fourier transform infrared absorption) method. And the ratio (oxygen concentration in-plane ratio) of the oxygen concentration in the position of 10 mm (140 mm) from the outer periphery with respect to the oxygen concentration of the central part (0 mm) was obtained.
(Evaluation of in-plane carbon concentration distribution)
Using an FT-IR apparatus (manufactured by Bio-Rad), the carbon concentration was measured at a pitch of 5 mm from the center of the wafer to the outer periphery by the FT-IR (Fourier transform infrared absorption) method. And the ratio (carbon concentration in-plane ratio) of the carbon concentration in the position of 10 mm (140 mm) from the outer periphery with respect to the carbon concentration of the central part (0 mm) was obtained.
(Measurement of BMD density)
Using an optical microscope, the BMD density was measured at a pitch of 5 mm from the wafer center to the outer peripheral direction. And the ratio (BMD density in-plane ratio) of the BDM density in the position of 10 mm (140 mm) from the outer periphery with respect to the BMD density of a center part (0 mm) was calculated | required.

  From Comparative Examples 1 and 2 and Examples 1 and 2 in Table 1, using a silicon single crystal ingot manufactured according to the method for manufacturing a silicon single crystal of the present invention, a silicon wafer having a uniform in-plane distribution of BMD is obtained. You can see that

  ADVANTAGE OF THE INVENTION According to this invention, when manufacturing a silicon single crystal using the silicon melt which added carbon, the manufacturing method of the silicon single crystal which can suppress the fall of the carbon concentration in the outer peripheral part of a silicon single crystal is provided. can do. Further, it is possible to provide a method for producing a wafer having a high gettering ability, particularly an epitaxial wafer, in which the in-plane BMD density is uniform.

DESCRIPTION OF SYMBOLS 10 Single crystal manufacturing apparatus 11 Chamber 12 Crucible 13 Melt 14 Heater 15 Crucible rotating mechanism 16 Silicon single crystal 17 Silicon seed crystal 18 Seed crystal holder 19 Wire rope 20 Winding mechanism 21 Magnetic field applicator

Claims (5)

  Silicon seed added with carbon is prepared in a crucible, and a silicon species in contact with the silicon melt while applying a magnetic field with a magnetic flux density of 0.2 to 0.4 T to the silicon melt in the crucible. A method for producing a silicon single crystal, comprising raising the crystal while rotating the crystal at a rotational speed of 0.52 to 0.84 rad / s, and growing the silicon single crystal on the silicon seed crystal. 2. The method for producing a silicon single crystal according to claim 1, wherein an oxygen concentration in the silicon single crystal is 13 × 10 ^{17 to} 17 × 10 ¹⁷ atoms / cm ³ . The carbon is added to the silicon melt so that the carbon concentration in the pulled silicon single crystal is 1 × 10 ^{15 to} 1.3 ¹⁷ atoms / cm ^3. A method for producing a silicon single crystal.   The manufacturing method of a silicon wafer including cutting out a silicon wafer from the ingot of the silicon single crystal manufactured with the manufacturing method in any one of Claims 1-3.   A method for producing an epitaxial wafer, comprising cutting a silicon wafer from a silicon single crystal ingot produced by the production method according to claim 1, and forming an epitaxial layer on the surface of the silicon wafer.

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