Method for producing silicon single crystal and silicon single crystal semiconductor wafer

Abstract

The present invention relates to a semiconductor wafer made of single crystal silicon and to a method for producing a single crystal silicon by pulling the single crystal from a melt contained in a crucible and containing phosphorus and boron as dopants in a ratio of not more than 0.41, in which the melt contains boron in a concentration of not less than 5.0 * 1014 atoms / cm3 and not more than 2.2 * 1015 atoms / cm3, and the melt contains boron in a concentration of not less than 5.0 * 1014 atoms / cm3 and not more than 2.2 * 1015 atoms / cm3. And the single crystal comprises a cylindrical portion having a diameter of at least 300 mm and a length and surrounded by a heat shield when lifted from the melt; the distance between the lower edge of the heat shield and the surface of the melt is not less than 18 mm; the method comprises: rotating a single crystal at a speed of not less than 8 rpm and not greater than 13 rpm; and applying a horizontal magnetic field to the melt, wherein the magnetic flux density of the horizontal magnetic field is not less than 2000 Gs and not more than 3000 Gs.

Description

Technical Field

[0001] The present invention provides a method for producing a silicon single crystal by pulling the single crystal from a melt, the melt being present in a crucible and containing phosphorus and boron as dopants, wherein the single crystal is mainly p-doped and has a cylindrical section (cylindrical section or cylindrical part) having a diameter and a length. The present invention also provides a single crystal silicon semiconductor wafer. Background Art

[0002] Pulling a silicon single crystal from a melt by the Czochralski method involves pulling a cylindrical section having a uniform diameter, from which single crystal silicon semiconductor wafers are generally separated.

[0003] In order to avoid reducing the specific resistance (or resistivity) of a silicon single crystal doped with boron due to the segregation of boron along the length of the single crystal, counter-doping with phosphorus may be performed.

[0004] US 2005 0 252 442 A1 describes a method for producing a silicon single crystal, wherein the single crystal is pulled from a melt which is present in a crucible and contains phosphorus and boron as dopants in a ratio of 0.31 and wherein the single crystal is predominantly p-doped and has a cylindrical section with a diameter of approximately 200 mm.

[0005] It is also important to observe a target resistance over the length of the cylindrical section of the single crystal that the resistance from the center to the edge of the single crystal at any length position on the cylindrical section differs from the target resistance to a minimum.

[0006] EP 2 607 526 A1 describes a method for producing a silicon single crystal, wherein the single crystal is pulled from a melt which is present in a crucible and contains phosphorus and boron as dopants in a ratio of 0.42, and wherein the single crystal is predominantly p-doped and has a cylindrical section with a diameter of about 200 mm. Based on the maximum resistance measured, the radial variation in resistance is 1.5%. Summary of the invention

[0007] One object of the invention is to achieve, for a relatively large and relatively long silicon single crystal, a minimum variation of its specific resistance in the axial and radial directions in a cylindrical section.

[0008] The object of the present invention is achieved by a method for producing a silicon single crystal by pulling a single crystal from a melt, the melt being present in a crucible and containing phosphorus and boron as dopants in a ratio of not more than 0.41, wherein the melt contains phosphorus in a concentration of not less than 5.0×10 14 atoms / cm3 3 ) and not more than 2.2×10 15atoms / cubic centimeter of boron, and the single crystal has a cylindrical section and is surrounded by a heat shield (or heat shield) during pulling from the melt, the cylindrical section having a diameter of at least 300 mm (millimeters) and a length, and wherein the distance between the lower edge of the heat shield and the surface of the melt is not less than 18 mm, the method comprising:

[0009] Pulling the single crystal at a speed of not less than 8 rpm and not more than 13 rpm; and

[0010] A horizontal magnetic field is applied to the melt, and the magnetic flux density of the horizontal magnetic field is not less than 2000 Gs (Gauss) and not more than 3000 Gs.

[0011] The inventors have identified the features required to achieve this objective.

[0012] The melt must contain a concentration of not less than 5.0×10 14 atoms / cm3 and not more than 2.2×10 15 atoms / cm3 of boron and has been counter-doped with phosphorus so that the ratio of phosphorus to boron (or phosphorus to boron) is no greater than 0.41. This ratio is preferably no greater than 0.35 and no less than 0.1.

[0013] The single crystal has a diameter of at least 300 mm in a cylindrical section and is pulled from the melt by the Czochralski method while being surrounded by a heat shield. The distance between the lower edge of the heat shield and the melt cannot be less than 18 mm. The distance is preferably 19 to 25 mm.

[0014] As the growing crystal is pulled from the melt, it is rotated at a speed of not less than 8 rpm and not more than 13 rpm.

[0015] During the pulling of the single crystal, a horizontal magnetic field is applied to the melt, and the magnetic flux density of the horizontal magnetic field is not less than 2000 Gauss and not more than 3000 Gauss.

[0016] If the above characteristics are met, semiconductor wafers can be separated from the pulled single crystal, in which the change in specific resistance from the center to the edge based on the minimum resistance is no more than 1%. In the case of measuring the resistance of the semiconductor wafer separated from the cylindrical section, the 6mm edge exclusion is not considered. Based on the average resistance of the first semiconductor wafer separated from the cylindrical section, the change in resistance over the axial length of the cylindrical section of the single crystal is no more than 18%.

[0017] The cylindrical section of the single crystal has a diameter of at least 300 mm and preferably a length of at least 1500 mm.

[0018] Therefore, the present invention also provides a single-crystal silicon semiconductor wafer with a diameter of at least 300 mm, which is mainly p-doped and contains phosphorus and boron as dopants, and whose specific resistance varies by no more than 1% from the center to the edge of the semiconductor wafer based on the minimum resistance.

[0019] The specific resistance of the semiconductor wafer is preferably not less than 6 ohm-centimeter (ohmcm) and not more than 30 ohm-centimeter.

[0020] The semiconductor wafer is preferably used for producing electronic components having NAND logic.

[0021] The invention is further described with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A device suitable for carrying out the method according to the invention is shown, the illustration being limited to features useful for understanding the invention.

[0023] Figure 2 The development (variation) of the specific resistance relative to the average resistance at the beginning of the cylindrical section is shown in the case of the example and the comparative example, depending on the crystallization amount (FS) of the silicon.

[0024] Figure 3 The radial variation of the specific resistance as a function of the crystallization amount of silicon in the case of the example and the comparative example is shown.

[0025] Reference numerals list

[0026] 1 Reactor chamber

[0027] 2 Crucible

[0028] 3 Axis

[0029] 4 Drivers

[0030] 5 Melt

[0031] 6 Heating device

[0032] 7 Magnetic coil

[0033] 8 Single crystal

[0034] 9. Lifting device

[0035] 10 Heat shield

[0036] 11 Distance DETAILED DESCRIPTION

[0037] Detailed description of a working example of the invention

[0038] according to Figure 1The device comprises a reactor chamber 1 containing a crucible 2. The crucible 2 is supported on an axis 3 and can be raised, lowered and rotated by means of a drive 4. The crucible 2 contains a melt 5 and is heated by means of a heating device 6 surrounding it. The melt contains phosphorus and boron as dopants in a ratio of not more than 0.41, and the concentration of boron is not less than 5.0×10 14 atoms / cm3 and not more than 2.2×10 15 Atoms / cubic centimeter. A magnetic coil 7 is arranged outside the reactor chamber 1, and the magnetic coil 7 generates a horizontal magnetic field to which the melt is subjected. The magnetic flux density of the horizontal magnetic field is not less than 2000Gs and not more than 3000Gs. A single crystal 8 of silicon is pulled from the melt 5 by means of a pulling device 9, during which the single crystal 8 rotates around its longitudinal axis at a speed of not less than 8rpm and not more than 13rpm. This forms a cylindrical section with increasing length and substantially (or basically) uniform diameter, from which a single crystal silicon semiconductor wafer is cut at a subsequent stage. In order to be protected from thermal radiation from the heating device 6, the single crystal 8 is surrounded by a heat shield 10. The distance 11 between the lower edge of the heat shield 10 and the surface of the melt 5 is not less than 18mm.

[0039] The present invention was tested in examples and compared with comparative examples.

[0040] Based on Figure 1 Two silicon single crystals with a nominal diameter of 300 mm were pulled in a device characterized by the invention. In the example case, the dopant present in the melt is a concentration of 4.8×10 14 atoms / cm3 of phosphorus and a concentration of 1.29×10 15 atoms / cm3 of boron, and in the case of the comparative example, only 1.2×10 15 atoms / cubic centimeter of boron.

[0041] In both cases, a horizontal magnetic field with a flux density of 2400 Gs was applied to the melt, the lower edge of the heat shield was at a distance of 20 mm from the surface of the melt, and the single crystal was rotated at a speed of 10 rpm.

[0042] Figure 2 It is shown that in the case of the example and the comparative example, the specific resistance (R rel ) relative to the development of the average resistance at the beginning of the cylindrical section.

[0043] In the case of this example, up to a crystallization level of 80%, the resistance drops by only slightly more than 10% of the value at the beginning of the cylindrical section.

[0044] Figure 3The radial variation (RV) of the specific resistance as a function of the crystallization amount (SF) of silicon is shown for the example and comparative examples. The resistance was measured according to ASTM C and the edge exclusion of 6 mm was left out of consideration.

[0045] RV is calculated by the following formula:

[0046] RV=((R max -R min ) / R min )×100%

[0047] Where R max and R min Represent the maximum resistance and minimum resistance respectively.

[0048] In the exemplary case, the radial variation starting from the cylindrical section up to 80% of the crystallinity, based on the minimum resistance, remains less than 1%.

[0049] Single crystal silicon semiconductor wafers cut from cylindrical sections of the exemplary single crystal have an average specific resistance in the range of 14 ohm-cm to 17 ohm-cm.

Claims

1. A method for producing a silicon single crystal by pulling the single crystal from a melt present in a crucible and containing phosphorus and boron as dopants in a ratio of not more than 0.41, wherein: The melt contains a concentration of not less than 5.0×10 14 atoms / cm3 and not more than 2.2×10 15 atoms / cubic centimeter of boron, and the single crystal has a cylindrical section and is surrounded by a heat shield during pulling from the melt, the cylindrical section having a diameter of at least 300 mm and a length, and wherein the lower edge of the heat shield is at a distance of not less than 18 mm from the surface of the melt, the method comprising: Pulling the single crystal at a speed of not less than 8 rpm and not more than 13 rpm; and A horizontal magnetic field is applied to the melt, wherein the magnetic flux density of the horizontal magnetic field is not less than 2000 Gs and not more than 3000 Gs.

2. The method according to claim 1, characterized in that The length is at least 1500 mm.

3. The method according to claim 1 or claim 2, characterized in that: The ratio is not greater than 0.35 and not less than 0.

1.

4. The method according to any one of claims 1 to 3, characterized in that The distance is 19 to 25 mm.

5. A monocrystalline silicon semiconductor wafer having a diameter of at least 300 mm, which is predominantly p-doped and includes phosphorus and boron as dopants and whose specific resistance, based on minimum resistance and taking into account an edge exclusion of 6 mm, does not vary by more than 1% from the center to the edge of the semiconductor wafer.

6. The semiconductor wafer according to claim 5, characterized in that It has a specific resistance of not less than 6 ohm-cm and not more than 30 ohm-cm.

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