Method for manufacturing epitaxially coated semiconductor wafers from single-crystal silicon

Abstract

1. A method for producing epitaxially coated semiconductor wafers from single crystal silicon, comprising: Providing a melt of silicon in a crucible; pulling a single crystal of silicon from the surface of the melt at a pulling rate v by the CZ method, oxygen and boron are incorporated into the single crystal, and the concentration of oxygen in the single crystal is 6.4×10 17 atoms / cm 3 Above 8.0×10 17 atoms / cm 3 pulling a single crystal of silicon, the single crystal having a resistivity of 10 mΩcm to 25 mΩcm, and the melt being free of nitrogen and carbon doping; applying a cusp magnetic field to the melt during the pulling of the single crystal of silicon surrounded by a thermal shield; The pulling rate v and the axial temperature gradient G at the phase boundary between the single crystal and the melt are defined as follows: v / G is 0.13 mm 2 / ℃ min or more 0.20mm 2 / °C or less; heating the single crystal using a ring heater disposed above the melt and surrounding the single crystal; producing a substrate wafer from single crystal silicon having a polished horizontal surface by processing said single crystal of silicon; depositing an epitaxial layer of silicon on the polished horizontal surface of the substrate wafer, the depositing of the epitaxial layer being a first heat treatment in which the substrate wafer is heated to a temperature of 700° C. or greater; A method comprising:

Description

[Technical Field]

[0001] The present invention provides a method for manufacturing an epitaxially coated semiconductor wafer from single-crystal silicon, which is particularly suitable for further processing to obtain electronic components such as CMOS image sensors (CIS). [Background technology]

[0002] Prior Art / Challenges For the above-mentioned applications, metallic impurities must not reach the electronic structure contained within the epitaxial layer.

[0003] U.S. Patent Application Publication 2014 / 0374861 states that if oxygen precipitates called BMDs (bulk microdefects) are present in a substrate wafer on which an epitaxial layer has been deposited, then the concentration of BMDs is at least 1.0 × 10⁻⁶. 9 / cm 3 Therefore, they state that typical component defects caused by contamination with metallic impurities will be suppressed.

[0004] To enable such a relatively high BMD inclusion, it is often proposed to dope the single crystal providing the substrate wafer with nitrogen or carbon, and / or subject the substrate wafer to a heat treatment before the deposition of the epitaxial layer to stabilize nuclei where BMDs can form in a later stage.

[0005] However, due to doping with nitrogen or carbon, surface defects can also occur in the epitaxial layer, and the heat treatment of the substrate wafer constitutes an additional method step that increases manufacturing costs.

[0006] German Patent No. 102014221421 describes a method that does not require nitrogen doping and does not require any heat treatment before the deposition of the epitaxial layer. However, a drawback of this method is that it requires at least 1.0 × 10 9 / cm 3The necessary BMD density is not achieved, is not uniformly distributed, and decreases towards the edge of the semiconductor wafer having an epitaxial layer.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide a semiconductor wafer having an epitaxial layer capable of generating a BMD density reaching at least 1.0×10 9 / cm 3 and to provide such a method for providing the same.

Means for Solving the Problems

[0008] An object of the present invention is a method for manufacturing a semiconductor wafer epitaxially coated from single crystal silicon, providing a melt of silicon in a crucible, pulling up a single crystal of silicon from the surface of the melt at a pulling speed v by the CZ method, wherein oxygen and boron are incorporated into the single crystal, and the concentration of oxygen in the single crystal is 6.4×10 17 atoms / cm 3 or more and 8.0×10 17 atoms / cm 3 or less, the resistivity of the single crystal is 10 mΩcm or more and 25 mΩcm or less, and pulling up a single crystal of silicon without doping the melt with nitrogen and carbon, applying a CUSP magnetic field to the melt during the pulling up of the single crystal of silicon surrounded by a thermal shield, controlling the pulling speed v and the axial temperature gradient G at the phase boundary between the single crystal and the melt such that the quotient v / G is 0.13 mm 2 / °C min or more and 0.20 mm 2 / °C min or less, heating the single crystal using a ring heater disposed above the melt and surrounding the single crystal, By processing a single crystal of silicon, a substrate wafer is manufactured from a single-crystal silicon having a polished horizontal surface, The process involves depositing an epitaxial layer of silicon on a polished horizontal surface of a substrate wafer, wherein the deposition of the epitaxial layer is the first heat treatment in the process of heating the substrate wafer to a temperature of 700°C or higher, and This is achieved by methods including,

[0009] Having p / p+ doping, epitaxially coated semiconductor wafers of single-crystal silicon manufactured by this method are particularly suitable for the manufacture of CIS components due to the radially uniform BMD distribution that can be generated by heat treatment directly beneath the epitaxial layer. The heat treatment preferably involves heating the epitaxially coated semiconductor wafer to a temperature of 780°C for 3 hours, and then to a temperature of 1000°C for 16 hours. Alternatively, heat treatment with an equivalent thermal budget can be performed in the process of further processing the epitaxially coated semiconductor wafer to obtain electronic components.

[0010] In this method, the single crystals from which the epitaxially coated substrate wafer is split are produced by the MCZ method, in which the single crystals are generated in a crucible and pulled from the molten material exposed to a magnetic field using a seed crystal. The magnetic field used in the axially symmetric magnetic field is a cusp magnetic field. The cusp magnetic field preferably reaches a maximum magnetic field strength of 105 mT to 116 mT, and the plane of the cusp magnetic field with a magnetic field strength of 0 mT is preferably 30 mm to 80 mm, more preferably 50 mm, below the surface of the molten material.

[0011] It is preferable that the single crystal be actively cooled. The cooling rate in the temperature range of 1000°C to 800°C is preferably between 0.7°C / min and 1°C / min.

[0012] The distance from the surface of the molten material to the lower edge of the heat shield is preferably 35 mm to 45 mm.

[0013] The amount of oxygen entering the single crystal during the pulling process is controlled by adjusting process parameters. These process parameters include, in particular, the strength of the cusp magnetic field, the rotation speed of the crucible, and the pressure of the purge gas passing through the molten material to remove silicon dioxide leaking from the single crystal environment. The rotation speed of the crucible is preferably between 3.5 rpm and 6.0 rpm. The pressure of the purge gas, such as argon, hydrogen, or a mixture of these two gases, is preferably between 2500 Pa and 8500 Pa.

[0014] The point defect distribution in a single crystal particularly affects the ability of subsequent BMD formation in an epitaxially coated semiconductor wafer. As is well known, the point defect distribution depends on the value of the quotient v / G during single crystal pulling. Therefore, the material coefficients are the ratio of the pulling rate v to the axial temperature gradient G, and the phase boundaries between single crystals during growth on the molten material. The method according to the present invention is 0.13 mm 2 / ℃ min or more 0.20mm 2 A quotient v / G of less than or equal to / ℃ / min is required. The pulling speed is preferably 0.4 mm / min or more and 0.48 mm / min or less.

[0015] The axial temperature gradient G in the edge region of a growing single crystal is further affected by heating the single crystal using a ring-shaped heater positioned above the molten material and surrounding the single crystal. For a single crystal with a diameter of 300 mm, the output of the ring-shaped heater is preferably between 7 kW and 13 kW.

[0016] The pulled single crystal preferably has a diameter of at least 200 mm, more preferably at least 300 mm, and is processed to obtain a substrate wafer of single crystal silicon. The working steps include, in addition to dividing the single crystal into wafers, further mechanical processing steps such as lapping and / or grinding of the horizontal plane of the wafer, and rounding of the edges of the wafer. The substrate wafer is also preferably chemically etched, particularly preferably chemically mechanically polished. Thus, the substrate wafer has a polished edge and at least one polished horizontal plane. Preferably, the polishing step includes simultaneous polishing (DSP) of the front and back surfaces of the substrate wafer and chemical mechanical polishing (CMP) of the front surface of the substrate wafer.

[0017] The epitaxial layer of silicon is preferably deposited on the polished surface of the substrate wafer. This step is preferably carried out in a single wafer reactor, for example a Centura® type reactor supplied by Applied Materials. The deposition gas preferably contains a hydrogen-containing silane, such as trichlorosilane (TCS). When TCS is used, the deposition temperature is preferably within a temperature range of 1000 °C or higher and 1250 °C or lower. The thickness of the epitaxial layer is preferably at least 1 μm. The deposition of the epitaxial layer is the first heat treatment in the process in which the substrate wafer is heated to a temperature of 700 °C or higher. Therefore, there is no heat treatment for the nucleation of BMD species before the deposition of the epitaxial layer. The substrate wafer is also not intentionally doped with nitrogen and / or carbon.

[0018] The semiconductor wafer coated with an epitaxial layer of single crystal silicon manufactured in this way has, in the region of the substrate wafer, the concentration of interstitial oxygen and the resistivity of the original single crystal of the substrate wafer. Therefore, the oxygen concentration is 6.4×10 17 atoms / cm 3 or more and 8.0×10 17 atoms / cm 3 or less (according to the new standard ASTM), and the resistivity is 10 mΩcm or more and 25 mΩcm or less.

[0019] When a semiconductor wafer epitaxially coated with single-crystal silicon is subjected to a standard heat treatment including heating to a temperature of 780 °C over 3 hours and then to a temperature of 1000 °C over 16 hours, or a heat treatment having an equivalent thermal budget, BMD is formed directly under the epitaxial layer at a density of at least 1×10 9 / cm 3 . The variation in BMD density across the radius, calculated by the formula ((BMDmax - BMDmin) / BMDmean)×100%, is less than 170%, where BMDmax, BMDmin, and BMDmean represent the measured maximum, minimum, and average BMD densities, respectively.

[0020] The present invention will be further described below with reference to the drawings.

Brief Description of the Drawings

[0021] [Figure 1] Shows the characteristics of an apparatus suitable for performing the method according to the present invention. [Figure 2] The average BMD density of an epitaxially coated semiconductor layer manufactured according to the present invention after a standard heat treatment is shown as a function of the relative axial position (raP) for the corresponding substrate wafer in the single crystal. [Figure 3] The average BMD density of five epitaxially coated semiconductor wafers manufactured according to the present invention is shown according to the radial position (Pos) at which the BMD density was measured.

Modes for Carrying Out the Invention

[0022] Detailed Description of Embodiments of the Invention Figure 1 shows a schematic diagram of the environment surrounding a single crystal (hot zone) during single crystal production using an apparatus suitable for carrying out the method according to the present invention. The growing single crystal 1 is surrounded by a heat shield 2, the lower end of which is a short distance from the molten material 3. Furthermore, in the region of the lower end of the heat shield 2, there is a ring-shaped heater 4 that supplies heat to the edge of the phase boundary between the single crystal 1 and the molten material 3. The ring-shaped heater 4 assists in controlling the temperature gradient at the edge of the phase boundary between the growing single crystal 1 and material 3, and is preferably also part of a system for controlling the diameter of the single crystal. At the height of the central and upper regions of the heat shield 2, and at a certain distance from the ring-shaped heater 4, the single crystal 1 is also surrounded by a device 5 for cooling the single crystal, preferably a water cooler. The molten material 3 is contained in a crucible 6 made of quartz, which is then held by an outer crucible 7 made of graphite. The crucibles 6, 7 and the molten material 3 are mounted on the end of a rotatable, vertically movable, and vertically movable shaft 8. The molten material 3 is heated primarily through resistance heaters 9 positioned around the outer crucible 7. Devices 10 for generating the cusp magnetic field applied to the molten material 3 surround the resistance heaters 9 in sequence.

[0023] Multiple silicon single crystals are pulled in the manner of the present invention in a device having the characteristics shown in Figure 1, and further processed to obtain an epitaxially coated semiconductor wafer having a diameter of 300 mm.

[0024] Figure 2 shows the average BMD density (BMD-D) of a semiconductor wafer after standard heat treatment, depending on the relative axial position (raP) of the corresponding substrate wafer within the single crystal.

[0025] Figure 3 shows the average BMD density (BMD-D) of five epitaxially coated semiconductor wafers manufactured according to the present invention, according to the radial position (Pos) where the BMD density was measured. [Explanation of Symbols]

[0026] List of codes used 1 Single crystal 2 Heat Shield 3. Molten material 4. Ring-shaped heater 5. Single-crystal cooling devices 6 Crucible 7. External crucible 8 shafts 9. Resistance Heater 10. Cusp magnetic field generating devices

Claims

1. A method for manufacturing an epitaxially coated semiconductor wafer from single-crystal silicon, To provide molten silicon in a crucible, The CZ method involves pulling up a silicon single crystal from the surface of the molten material at a pulling speed v, thereby incorporating oxygen and boron into the single crystal, with the oxygen concentration in the single crystal being 6.4 × 10⁻¹⁰. １７ atoms / cm ３ The above 8.0 x 10 １７ atoms / cm ３ The following conditions apply: the resistivity of the single crystal is 10 mΩcm or more and 25 mΩcm or less; and the molten material is not doped with nitrogen and carbon; and the silicon single crystal is pulled. Applying a cusp magnetic field to the molten silicon single crystal during the pulling process, surrounded by a heat shield, The pulling speed v and the axial temperature gradient G at the phase boundary between the single crystal and the molten material are given by a ratio v / G of 0.13 mm. ２ / ℃ min or more 0.20mm ２ Controlling the temperature to be below / ℃ minutes, The single crystal is heated using a ring-shaped heater placed above the molten material and surrounding the single crystal, and the single crystal, after being removed from the molten material, is cooled at a cooling rate of 0.7°C / min or more and 1°C / min or less within a temperature range of 1000°C to 800°C. By processing the aforementioned silicon single crystal, a substrate wafer is manufactured from single-crystal silicon having a polished horizontal surface, The process involves depositing an epitaxial layer of silicon on the polished horizontal surface of the substrate wafer, wherein the deposition of the epitaxial layer is the first heat treatment in the process of heating the substrate wafer to a temperature of 700°C or higher, and Methods that include...

2. The method according to claim 1, characterized in that the distance from the surface of the molten material to the lower edge of the heat shield is 35 mm or more and 45 mm or less.

3. The method according to claim 1, characterized in that the cusp magnetic field reaches a maximum magnetic field strength of 105 mT or more and 116 mT or less, and the plane of the cusp magnetic field having a magnetic field strength of 0 mT is 30 mm or more and 80 mm or less below the surface of the molten material.

4. The method according to claim 1, characterized in that the crucible is rotated at a speed of less than 3.5 rpm and 6.0 rpm or less.

5. The method according to claim 1, characterized in that the single crystal is pulled in a purge gas atmosphere having a pressure of 2500 Pa or more and 8500 Pa or less.

6. The method according to claim 1, characterized in that the single crystal has a diameter of 300 mm, and the output of the ring-shaped heater is 7 kW or more and 13 kW or less.

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