Process for thermal treatment of a wafer of monocrystalline silicon and wafer of monocrystalline silicon

Abstract

The invention relates to a process for thermal treatment of a wafer of monocrystalline silicon comprising the steps of: (i) heating the wafer to a target temperature of not less than 1280°C and not more than 1300°C; (ii) holding the target temperature for not less than 5 s and not more than 60 s; and (iii) cooling the wafer at a cooling rate of not less than 10°C / s and not more than 50°C / s, characterized in that steps (i) to (iii) are performed in an atmosphere having an oxygen partial pressure of not less than 40% and not more than 90%. The invention further relates to a wafer of monocrystalline silicon composed of N-region, characterized in that the concentration of interstitial oxygen is not more than 2.5 x 1017 atoms / cm3; and the concentration of COPs having a size of not less than 15 nm is not more than 2.0 x 106 cm-3.

Description

[0001] Method for the thermal treatment of a single-crystal silicon wafer and single-crystal silicon wafer. Technical field

[0002] The invention relates to a method for the thermal treatment of a disk of single-crystal silicon and a disk of single-crystal silicon.

[0003] State of the art

[0004] For certain electronic components, single-crystal silicon wafers with a low concentration of COPs are advantageous as a starting material. Particularly for the production of insulated-gate bipolar transistors (IGBTs), low concentrations of COPs, preferably not exceeding a certain size, are required to achieve good gate-oxide integrity (GOI).

[0005] It is known that the size and concentration of COPs can be influenced by thermal treatment, particularly by RTA treatment. The term “Rapid Thermal Annealing” (RTA) describes a heat treatment in which a disk is heated relatively quickly to a relatively high temperature, held at that temperature for a relatively short time, and then cooled relatively quickly. A device suitable for performing RTA treatment is described in US 2003 / 0029859 A1. During the RTA treatment, the disk rests on a ring within the device, is rotated, and exposed to thermal radiation from above.

[0006] US 2020 / 0181802 A1 describes a method for the thermal treatment of a silicon wafer in which the oxygen partial pressure during the RTA treatment depends on the temperature and the cooling rate. RTA treatments often take place at temperatures above 1300°C, as described, for example, in US 2012 / 0139088 A1. JP 2009-170656 A describes a thermal treatment at 1100 to 1300°C, in which various gas flows and gas compositions are used. Technical problem of the invention and its solution

[0007] The object of the present invention is to provide a single-crystal silicon wafer with a relatively low concentration of interstitial oxygen, a lower concentration of COPs, and simultaneously a low dislocation density. Furthermore, the single-crystal silicon wafer should preferably also exhibit a very low concentration of BMDs (bulk microdefects).

[0008] The inventors have surprisingly discovered that, through thermal treatment under very specific process conditions, the concentration of COPs and BMDs can be further reduced, thus enabling the production of a single-crystal silicon wafer with improved gate-oxide integrity (GOI). At the same time, this thermal treatment is relatively gentle, so that the resistance to thermally induced dislocations is not impaired by the thermal treatment.

[0009] According to the first aspect, the present invention relates to a method for the thermal treatment of a wafer of single-crystal silicon. The method comprises the following steps:

[0010] (i) Heating the disc to a target temperature of not less than 1280°C and not more than 1300°C;

[0011] (ii) Maintaining the target temperature for not less than 5 s and not more than 60 s; and (iii) Cooling the disk at a cooling rate of not less than 10°C / s and not more than 50°C / s;

[0012] characterized in that steps (i) to (iii) are carried out in an atmosphere with an oxygen partial pressure of not less than 40% and not more than 90%.

[0013] According to the second aspect, the present invention relates to a method for producing wafers from single-crystal silicon, comprising the following steps:

[0014] Drawing a single-crystal rod from single-crystal silicon according to the Czochralski method; grinding the single-crystal rod;

[0015] Sawing the polished single-crystal rod into slices;

[0016] Grinding and / or lapping of the discs;

[0017] chemical etching and / or cleaning of the discs;

[0018] Carrying out the thermal treatment method according to the first aspect of the present invention; and

[0019] Polishing the discs.

[0020] According to the third aspect, the present invention relates to a disk of single-crystal silicon consisting of N-region, characterized in that the concentration of interstitial oxygen is not more than 2.5 x 10 17 atoms / cm² 3 is; and

[0021] the concentration of COPs with a size of not less than 15 nm not more than 2.0 x 10 6 cm -3 amounts.

[0022] The disc according to the third aspect can be produced by thermal treatment according to the method according to the first aspect and by the method according to the second aspect of the present invention.

[0023] Brief description of the characters

[0024] Fig. 1 shows, for embodiments 1 to 4 (A1 to A4) and comparative example 1 (R), the COP values ​​s determined by IR-LST, measured along a slit edge in a radial direction at a distance r from the disk center.

[0025] Fig. 2 shows, for embodiments 1 to 4 (A1 to A4) and comparative example 1 (R), the concentrations c of COPs with a size of not less than 15 nm determined by IR-LST, measured along a slit edge in the radial direction at a distance r from the disk center.

[0026] Fig. 3 shows maps of the mechanical stress at the disk edge of the disks produced in comparative examples 1 and 2. The mechanical stress was determined using SIRD. Fig. 4 shows maps of the mechanical stress at the disk edge of the disks produced in embodiments 1 and 2. The mechanical stress was determined using SIRD.

[0027] Fig. 5 shows QBD measurements for comparison example 1 (R) and embodiments 1 and 2 (A1 and A2).

[0028] Fig. 6 shows the density d of GOI defects for embodiments 1 to 4 (A1 to A4) and comparison example 1 (R).

[0029] Fig. 7 shows the radial distribution of the BMD concentration determined by IR-LST, measured along a slit edge in a radial direction at radial intervals of 5 mm, where d is the BMD concentration and r is the radial distance from the disk center.

[0030] Detailed description of the invention

[0031] According to the first aspect, the present invention relates to a method for the thermal treatment of a disk made of single-crystal silicon.

[0032] In step (i) of the inventive method according to the first aspect, a wafer of single-crystal silicon is heated to a target temperature of not less than 1280°C and not more than 1300°C, preferably not less than 1280°C and not more than 1295°C, more preferably not less than 1285°C and not more than 1295°C, and most preferably not less than 1285°C and not more than 1290°C. A temperature in this range is sufficiently high, on the one hand, to enable the resolution of some of the COPs and thus reduce the concentration of COPS with a size of 15 nm or larger. On the other hand, a temperature in this range is not so high that thermally induced dislocations (slips) occur on a large scale in wafers of single-crystal silicon with a relatively low concentration of interstitial oxygen.Flat wafers of single-crystal silicon with a relatively low concentration of interstitial oxygen are susceptible to the formation of thermally induced dislocations. Preferably, the heating of the single-crystal silicon wafer in step (i) is carried out at a heating rate of not less than 10°C / s and not more than 100°C / s. Particularly preferably, the heating in a first step up to a temperature of 1200°C is carried out at a rate of not less than 50°C / s and not more than 100°C / s; and the heating in a second step from a temperature of 1200°C to the target temperature is carried out at a rate of not less than 10°C / s and not more than 45°C / s. Preferably, the second heating step is carried out immediately after the first heating step.

[0033] In step (ii), the single-crystal silicon wafer is held at the target temperature for not less than 5 s and not more than 60 s, preferably for not less than 20 s and not more than 50 s, most preferably for not less than 25 s and not more than 45 s. In one embodiment, the target temperature is held for not less than 30 s and not more than 40 s.

[0034] The cooling of the single-crystal silicon wafer in step (iii) is carried out at a cooling rate of not less than 10°C / s and not more than 50°C / s. The cooling of the single-crystal silicon wafer in step (iii) preferably takes place immediately after step (ii). Preferably, the cooling of the single-crystal silicon wafer in step (iii) from the target temperature down to 1200°C is carried out at a cooling rate of not less than 10°C / s and not more than 27°C / s, and the cooling from 1200°C down to a final temperature is carried out at a cooling rate of not less than 30°C / s and not more than 50°C / s. Cooling at a relatively lower rate down to 1200°C and at a relatively higher rate above 1200°C leads to the dissolution of larger COPs without the formation of thermally induced dislocations.

[0035] Particularly preferably, in step (iii) the cooling of the single-crystal silicon wafer from the target temperature to 1200°C is carried out at a cooling rate of not less than 15°C / s and not more than 25°C / s, and the cooling from 1200°C to a final temperature is carried out at a cooling rate of not less than 30°C / s and not more than 40°C / s. In another particularly preferred embodiment, the cooling of the single-crystal silicon wafer in step (iii) from the target temperature to 1200°C is carried out at a cooling rate of not less than 20°C / s and not more than 25°C / s, and the cooling from 1200°C to a final temperature is carried out at a cooling rate of not less than 30°C / s and not more than 35°C / s. The aforementioned, particularly preferred embodiments of cooling enable improved resolution of the COPs and thus the production of discs with particularly low concentrations of COPs.

[0036] The final temperature is preferably not more than 1000°C, particularly preferably not more than 850°C, and most preferably not more than 700°C. Preferably, the final temperature is not less than 500°C, and particularly preferably not less than 600°C. With further cooling, the cooling rate decreases continuously.

[0037] Steps (i) to (iii) of the thermal treatment process according to the first aspect are carried out in an atmosphere with an oxygen partial pressure of not less than 40% and not more than 90%, preferably not less than 50% and not more than 80%, and most preferably not less than 60% and not more than 80%. If the oxygen partial pressure is at least 40%, the increased generation of Si interstitials by oxidation on the wafer surfaces can lead to the dissolution of large agglomerates into smaller COPs. However, a high oxygen partial pressure of more than 90% can lead to an increased thickness of the oxide layer on the wafer surface, which necessitates an additional chemical oxide removal step, for example using HF, to allow subsequent wafer polishing.Furthermore, if the oxygen partial pressure near the surface exceeds 90%, the oxygen concentration in the single crystal can be increased, which in turn can promote oxygen-induced stacking faults (OSFs). Particularly good agglomerate resolution can be achieved if the oxygen partial pressure is not less than 60% and not more than 80%. The absolute pressure during steps (i) to (iii) is preferably not less than 200 mbar and not more than 1500 mbar, more preferably not less than 500 mbar and not more than 1100 mbar. The atmosphere during steps (i) to (iii) of the thermal treatment process according to the first aspect preferably consists of oxygen and argon.

[0038] The inventive method does not require nitrogen doping. Doping with nitrogen has the disadvantage that a comparatively high concentration of nitrogen promotes the formation of OSF defects.

[0039] According to the second aspect, the present invention relates to a method for producing wafers from single-crystal silicon, which comprises the following steps:

[0040] Pulling a single-crystal rod from single-crystal silicon according to the Czochralski method;

[0041] Grinding of the single crystal rod;

[0042] Sawing the polished single-crystal rod into slices;

[0043] Grinding and / or lapping of the discs;

[0044] chemical etching and / or cleaning of the discs;

[0045] Carrying out the thermal treatment method according to the first aspect of the present invention; and

[0046] Polishing the discs.

[0047] Preferably, the steps are carried out in this order. Optionally, an epitaxial layer can also be deposited on the disc, preferably after polishing the discs.

[0048] In the inventive process for producing wafers of single-crystal silicon, a single crystal is first pulled using the Czochralski method. When pulling the single crystal from a silicon melt contained in a crucible, in an atmosphere of argon and optionally hydrogen, care must be taken to control the ratio of pulling speed v to axial temperature gradient G at the interface between the single crystal and the melt such that the cylindrical section of the single crystal consists only of the nitrogen region. This creates flow conditions and a temperature field in the melt that hinder the dissolution of oxygen from the crucible material and promote the escape of SiO₂ from the melt via its surface, thus ensuring that oxygen is absorbed homogeneously from the center to the edge of the growing single crystal.Furthermore, when pulling the single crystal, the pulling speed and the cooling rate of the single crystal are controlled to keep the concentration of thermal donors in the single crystal low.

[0049] The silicon melt, preferably containing an n-type or p-type dopant, is preferably prepared by melting polycrystalline silicon and an n-type dopant, for example phosphorus, or polycrystalline silicon and a p-type dopant, for example boron, in a quartz crucible. However, the silicon melt can also be prepared without any dopants.

[0050] During the pulling of a single crystal, heat is preferably supplied to the melt from at least three points, as described in DE 102016209008 B4. This occurs from above in the region of the phase boundary between the growing single crystal and the melt, from above in the region of the melt's surface, and selectively from the side towards the upper half of the melt. Furthermore, the melt can also be heated from below, for example, to reduce the heating load at at least one of the three points while maintaining the overall heating power. For instance, it may be advantageous to reduce the heat supply from the side to protect the quartz crucible and to prevent the upper part of the crucible wall from losing its shape and tipping towards the melt.

[0051] The heat supply to the melt is preferably such that the ratio of the heating power to the total heating power is not less than 5% and not more than 15% when the melt is heated from above in the region of the phase boundary, and not less than 5% and not more than 15% when the melt is heated from above in the region of the surface. If the melt is additionally heated from below, the ratio of the heating power expended for this purpose to the heating power expended to heat the melt from the side is preferably not more than 5%. The heat supply from the side must be selectively directed to an upper portion of the volume of the melt. In other words, intentional heating from the side of a lower portion of the volume of the melt does not occur at the beginning of the crystal growth and preferably not until 70% of the initial volume of the melt has become part of the single crystal.Otherwise, the desired flow conditions and temperature field in the melt cannot be generated. Accordingly, the method comprises the selective supply of heat to an upper volume of the melt, which has an initial height hm, where the height hm is less than the initial height hM of the melt. The ratio hm:hM is preferably no more than 0.75. The settling of the melt caused by the crystallization of the single crystal is compensated for by raising the quartz crucible.

[0052] Furthermore, heating of the melt preferably takes place from above, both in the region of the phase boundary between the growing single crystal and the melt, and in the region of the melt's surface, more precisely in the region of the melt's surface between a heat shield surrounding the growing single crystal and the wall of the quartz crucible. Both processes are carried out by means of two heating devices that are almost independent of each other, because the heat shield blocks additional heating of the other region by either of the two heating devices.

[0053] Heating the melt from above in the region of the phase boundary between the growing single crystal and the melt serves primarily to control the axial temperature gradient G at this boundary. It is known that the formation of eigenpoint defects (silicon interstitial atoms and vacancies) and their agglomerates depends significantly on the ratio V / G of the growing speed V and the axial temperature gradient G. The axial temperature gradient G can be approximately calculated using simulations and substantially influenced by the design of the immediate surroundings of the growing single crystal, the hot zone.The single crystal of silicon is grown at a pulling rate V according to the CZ method, preferably at a pulling rate V which results in a V / G that does not cause agglomerates to form in the growing single crystal of silicon interstitial atoms and that the concentration of free vacancies, the presence of which promotes the formation of thermal donors, is as low as possible, preferably not more than 3 x 10. 14 / cm 3 Accordingly, it is particularly preferred to control the V / G ratio such that vacancies dominate from the center to the edge of the single crystal without forming agglomerates that are detectable as COP defects (crystal originated particles) and / or that silicon interstitial atoms dominate from the center to the edge of the single crystal without forming agglomerates that are detectable as Lpit defects (large etch pits).

[0054] Heating the melt from above in the area of ​​a surface of the melt helps to create the flow conditions and temperature field in the melt that are necessary to reduce the oxygen concentration in the single crystal of silicon to less than 2.2 x 10 17 atoms / cm² 3 to limit.

[0055] Furthermore, a magnetic field is applied to the melt, preferably a CUSP field, i.e., a magnetic field with a field line structure that is axially symmetric to the axis of rotation of the quartz crucible. The magnetic field preferably has a maximum flux density of 700–1300 gauss. The plane of the magnetic field with the lowest magnetic flux density is preferably located 80 mm to 160 mm above the surface of the melt or 120 mm to 220 mm below the surface of the melt.

[0056] The crucible is preferably rotated during the pulling of the cylindrical section of the single crystal, particularly preferably at a rotational speed of not less than 0.5 and not more than 10 revolutions per minute. The rotation of the growing single crystal rod is preferably not less than 4 and not more than 20 revolutions per minute. The vertical distance from the underside of a heat shield arranged above the melt and surrounding the growing single crystal rod to the surface of the melt is preferably not less than 10 mm and not more than 30 mm. The pulling speed is preferably not less than 0.35 mm / min and not more than 0.6 mm / min. Due to the conditions chosen during pulling with respect to the v / G ratio, the crystal lattice consisted exclusively of N-region, with a proportion of Nv domain and a proportion of Ni domain. The single crystal is not intentionally doped with nitrogen.The concentration of nitrogen in the cylindrical section of the single crystal is therefore preferably not more than 1.0 x 10. 12 atoms / cm² 3 The cylindrical section of the single crystal preferably has a diameter in the range of 312 to 315 mm.

[0057] The fabrication process described above yields wafers consisting exclusively of N-regions, in which no agglomerates of silicon interstitial atoms or vacancies with a diameter greater than 20 nm are present. Preferably, the N-region comprises at least one Ni domain in which silicon interstitial atoms predominate as the point defect type, and at least one Nv domain in which vacancies predominate as the point defect type.

[0058] The cylindrical portion of the single crystal is then ground, and the ground single-crystal rod is sawn into wafers. The resulting wafers are ground and / or lapped, and subsequently etched and / or chemically cleaned. Following this, the process for the thermal treatment of a wafer of single-crystal silicon according to the first aspect of the present invention is carried out, and the thermally treated wafers are subsequently polished.

[0059] In the third aspect, the present invention relates to a disk of single-crystal silicon consisting of N-region, characterized in that the concentration of interstitial oxygen is not more than 2.5 x 10 17 atoms / cm² 3 is; and

[0060] the concentration of COPs with a size of not less than 15 nm not more than 2.0 x 10 6 cm -3 amounts.

[0061] Preferably, no COPs with a size greater than 35 nm are present. This means that no COPs with a size of 35 nm or greater can be detected using any of the methods known to those skilled in the art. The disk according to the invention, made of single-crystal silicon, can have a diameter of not less than 200 mm and not more than 450 mm, and preferably has a diameter of not less than 300 mm and not more than 310 mm, particularly preferably not less than 301 mm and not more than 305 mm. The disk according to the invention preferably has a thickness of not less than 500 mm and not more than 1500 mm, particularly preferably not less than 700 mm and not more than 1000 mm. The disk can have a <100> -orientation, a <110> -orientation or a <111 >-orientation and particularly preferably has a <100> -Orientation.

[0062] The single-crystal silicon wafer according to the invention has a front and a back side. The front side is preferably the side of the wafer that faces upwards during the thermal treatment and on which electronic components are to be deposited. The single-crystal silicon wafer according to the invention can have an oxide layer on its back side with a thickness of preferably no more than 100 nm, more preferably no more than 50 nm, and most preferably no less than 5 nm and no more than 30 nm.

[0063] The N-region is characterized in that it contains no agglomerates of silicon interstitial atoms or vacancies with a diameter greater than 30 nm, preferably no such agglomerates with a diameter greater than 20 nm. Preferably, the concentration of agglomerates of silicon interstitial atoms and vacancies with a diameter of no more than 20 nm in the N-region is no more than 3.0 x 10 5 cm -3 .

[0064] During the Czochralski method of growing a single crystal, oxygen is largely incorporated at interstitial sites within the crystal. This interstitial oxygen is referred to as interstitial oxygen. In a wafer of single-crystal silicon according to the third aspect of the present invention, the concentration of interstitial oxygen is no more than 2.5 x 10⁻⁶. 17 atoms / cm² 3 , preferably not more than 2.2 x 10 17atoms / cm² 3 and most preferably no more than 2.0 x 10 17 atoms / cm² 3 Preferably, the concentration of interstitial oxygen is not less than 1.0 x 10 17 atoms / cm² 3 In one embodiment, the concentration of interstitial oxygen is not less than 1.0 x 10 17 atoms / cm² 3 and no more than 2.0 x 10 17 atoms / cm² 3 The concentration of interstitial oxygen can be measured using LT-FTIR. The determination of the interstitial oxygen content of single-crystal silicon is preferably carried out by measuring an infrared absorption band at room temperature using a short baseline between 10⁴⁰ cm⁻¹. -1 and 1160 cm -1This reduces uncertainties caused by IR absorption disturbances in the endpoint regions of longer baselines, which arise from effects other than absorption by interstitial oxygen. Using the short baseline leads to improved precision of the method.

[0065] The concentration of interstitial oxygen is preferably determined according to standard SEMI MF1188-1107. In order to measure the concentration of interstitial oxygen at a specific depth in the inner region of the disk, the near-surface area can either be removed by etching, or the disk can be fractured, cut, or split, preferably split or fractured, and the concentration measured along the fracture, cut, or split edge on the cross-sectional profile, i.e., on a surface arranged perpendicular to the main surfaces and running along the split edge.

[0066] The concentration of COPs with a size of not less than 15 nm is not more than 2.0 x 10 6 cm -3 The concentration of COPs can be detected using IR-LST (infrared light scattering tomography).

[0067] In an IR-LST measurement, the incident light is scattered by COPs, and the scattered light is detected by a CCD camera. COPs form peaks on the intensity map of the detected scattered light. This map could be quantified using a computer program to determine concentrations, for example, by an automated defect detection algorithm. The computer program can determine the number of defects, their concentration, and their size distribution. Preferably, calibration is performed using latex particles of known size.

[0068] In one embodiment of the semiconductor disk according to the third aspect of the present invention, IR-LST measurements are taken at radial intervals of 5 mm along a surface of a fracture, slit, or cut edge that is perpendicular to the main surfaces of the semiconductor disk. For each measurement point at 5 mm radial intervals, a dark-field image of the scattered light, preferably 2000 pm x 350 pm, is recorded. The incident light is preferably laser light with a power of 74 mW. For each dark-field image, the concentration of COPs, preferably those with a size of at least 15 nm, and the size of the COPs can be determined using a computer program. The determination of the COPs by IR-LST measurement and the subsequent evaluation can be performed on an LST-2500HD instrument manufactured by Semilab.

[0069] The concentration of COPs within the meaning of the present invention is therefore the concentration determined at a specific location (a measurement point), preferably obtained from the evaluation of a dark-field image. The mean concentration of the COPs corresponds to the arithmetic mean of the COP concentrations measured at various locations along the edge. The mean concentration is therefore preferably obtained from the evaluation of all measurement points, i.e., all dark-field images.

[0070] Preferably, the average concentration of COPs with a size of not less than 15 nm is not more than 1.0 x 10 6 cm -3 Preferably no more than 8 x 10 5 cm -3 , preferably no more than 5 x 10 5 cm -3 The mean concentration of COPs corresponds to the arithmetic mean of the concentrations of COPs determined along the fracture, cleavage or cut edge.

[0071] The size of the COPs according to the present invention corresponds to the arithmetic mean of the sizes of the COPs detected at a single location (a measurement point), preferably obtained from the evaluation of a dark-field image. The mean size of the COPs corresponds to the arithmetic mean of the sizes of the COPs measured at various locations along the edge. The mean size is therefore preferably obtained from the evaluation of all measurement points, i.e., all dark-field images. Preferably, the size of the COPs is no more than 25 nm, and particularly preferably no more than 20 nm. Preferably, the mean size of the COPs is no more than 20 nm, and particularly preferably no more than 18 nm.

[0072] In a preferred embodiment, the average concentration of COPs with a size of not less than 15 nm is not more than 1.0 x 10 6 cm -3 and the average size of the COPs is no more than 20 nm.

[0073] The concentration of BMDs (Bulk Micro Defects) of the disk according to the invention is preferably no more than 3.0 x 10 after heat treatment. 8 cm -3 , preferably no more than 5.0 x 10 7 cm -3 , preferably no more than 5.0 x 10 6 cm -3 In a particularly preferred embodiment, the concentration of BMDs after heat treatment is not less than 2 x 10 5 cm -3 and no more than 5.0 x 10 6 cm -3 .

[0074] For modern IGBT applications, such low BMD densities are advantageous. The production of interposer wafers requires both the lowest possible concentrations of COPs and the lowest possible concentrations of BMDs.

[0075] The heat treatment for the formation of BMDs comprises a first and a second step. In the first step, the disk is exposed to an atmosphere of an oxygen-nitrogen mixture with a volume ratio of 1:10 (O₂:N₂) for 3 hours at a temperature of 780 °C. In the second step, the disk is exposed to an atmosphere of an oxygen-nitrogen mixture with a volume ratio of 1:10 (O₂:N₂) for 16 hours at a temperature of 1000 °C. A similar heat treatment is also described in EP 4 151 782 B1.

[0076] The concentration of BMDs can be detected using IR-LST (infrared light scattering tomography). Preferably, a device from the manufacturer Semilab, for example an LST-2500HD, with a laser power of 0.13 mW and a scan window of 208 pm x 337 pm, is used for the IR-LST measurement. Preferably, measurement points are recorded at 5 mm intervals in the radial direction along a slit edge, particularly preferably over the entire diameter of the disk. Preferably, the measurement is taken along the centerline of the surface at the slit edge, with the surface at the slit edge being perpendicular to the main surfaces. For each point, the arithmetic mean of the size distribution of the BMDs detected in the scan window is reported. The mean size of the BMDs corresponds to the arithmetic mean of all sizes measured at different locations along the edge.

[0077] The following procedure for testing resistance to thermally induced dislocations can be used to assess whether single-crystal silicon wafers are free of thermally induced dislocations (slips). This procedure comprises the following steps (a) to (c).

[0078] (a) The discs of the present invention can be subjected to heat treatment in a vertical furnace, for example, a device from ASM International NV, wherein each disc rests on three fingers of a boat (long finger boat, for example, from the manufacturer Ferrotec Materials Technologies Corporation). During the heat treatment, there is therefore contact between the disc and the fingers of the boat. In the heat treatment, the disc is heated to 1100°C according to the temperature program specified in Table 1 and held at this temperature in an oxygen atmosphere for 2 hours before the disc is cooled again.

[0079] (b) A BFA analysis is performed using a SIRD system from PVA Metrology & Plasma Solutions GmbH on circular sub-surfaces with a radius of 40 mm around the contact points where the disc and the boat fingers were in contact during heat treatment. The shortest distance of the three sub-surfaces to the edge of the disc was not less than 1 mm and not more than 33% of the disc's diameter, preferably not less than 1 mm and not more than 6 mm.

[0080] (c) The high-pass filtered depolarization map provided by the SIRD system is evaluated in the sub-areas, and a depolarization threshold range of ± 40 DU (depolarization units) is defined to distinguish between good and bad cells. During the BFA analysis, the depolarization is determined for cells of a grid that is virtually overlaid on the depolarization map. The grid preferably consists of square cells with a side length of preferably 2 mm. The result of the BFA analysis is the percentage ratio bcf (bad cell fraction). This ratio corresponds to the ratio of the number of bad cells that lie outside the threshold range in the three sub-areas to the total number of cells in the three sub-areas. Cells that do not lie completely within a sub-area are only counted if the area of ​​the affected cell that overlaps with the sub-area is at least 50%.Preferably, the disk made of single-crystal silicon according to the third aspect of the present invention has an electrical resistance of not less than 10 ohms cm and not more than 500 ohms cm, particularly preferably not less than 40 ohms cm and not more than 120 ohms cm, most preferably not less than 60 and not more than 100 ohms cm.

[0081] Preferably, the single-crystal silicon wafer according to the third aspect of the present invention has a maximum GOI defect density of 0.30 defects cm' 2 , preferably a maximum GOI defect density of no more than 0.20 defects cm' 2 , most preferred is a maximum GOI defect density of no more than 0.15 defects cnr 2 on.

[0082] Detailed description of exemplary implementations and comparative examples.

[0083] Examples

[0084] Example 1

[0085] First, a single crystal of silicon was prepared in an atmosphere of argon according to the Czochralski method. <100> -Orientation was used. A device with a heating element for heating the quartz crucible from below, as described in patent DE 102016209008 B4, was employed. A quartz crucible with a wall height of over 58 cm and a diameter of 32 inches was used. The argon pressure in the drawing machine was maintained in the range of 10 mbar to 30 mbar, and the argon flow rate was set to more than 5000 l / h. During the drawing process, a CUSP magnetic field was applied with a zero line above the phase boundary of the melt. The crystal rotation was reduced during the drawing process from an initial value of over 12 U / rnin to a value of less than 10 U / rnin and then held constant at this value.The counter-rotation of the crucible was reduced during pulling from a value of not less than 5 ll / min and not more than 7 ll / min to a value of not more than 4 ll / min and not less than 2 ll / min. The cylindrical section of the single crystal was pulled at a pulling speed of not less than 0.45 mm / min and not more than 0.55 mm / min. Due to the conditions chosen during pulling regarding the v / G ratio, the crystal lattice consisted exclusively of N-region, with a proportion of Nv domain and a proportion of Ni domain.

[0086] The cylindrical portion of the single crystal was subsequently ground and sawn into wafers. The resulting wafers were ground or lapped, then etched and chemically cleaned. Following this, the thermal treatment process according to the first aspect of the present invention was carried out, and the thermally treated wafers were subsequently polished.

[0087] In the thermal treatment, the single-crystal silicon wafer was treated in an atmosphere of 75% oxygen and 25% argon at a pressure of 1000 mbar. The wafer was heated in this atmosphere to a temperature of 1290 °C, with the heating rate decreasing to 75 °C / s up to 1200 °C and then to the target temperature of 1290 °C at 25 °C / s. The target temperature was held for 30 seconds, after which the wafer was cooled back down to 1200 °C at a rate of 25 °C / s. From 1200 °C, the wafer was then cooled at a rate of 30 °C / s down to 600 °C. Finally, it was cooled to room temperature.

[0088] The following embodiments 2 to 4 differ from embodiment 1 only by the different thermal treatment, in particular by the different target temperature and holding time of the target temperature.

[0089] Example 2

[0090] In the thermal treatment, the single-crystal silicon wafer was heated to a temperature of 1290 °C in an atmosphere of 75% oxygen and 25% argon at a pressure of 1000 mbar. The target temperature was maintained for 40 s. Otherwise, the procedure was exactly the same as in embodiment 1.

[0091] Example 3

[0092] In the thermal treatment, the single-crystal silicon wafer was heated to a temperature of 1295 °C in an atmosphere of 75% oxygen and 25% argon at a pressure of 1000 mbar. The target temperature was maintained for 40 s. Otherwise, the procedure was exactly the same as in embodiment 1.

[0093] Example 4

[0094] In the thermal treatment, the single-crystal silicon wafer was heated to a temperature of 1300 °C in an atmosphere of 75% oxygen and 25% argon at a pressure of 1000 mbar. The target temperature was maintained for 25 s. Otherwise, the procedure was exactly the same as in embodiment 1.

[0095] Comparative example 1

[0096] The comparative example 1 differs from embodiment 1 only in that the thermal treatment was carried out in an atmosphere of 25% oxygen and 75% argon, with identical temperature control.

[0097] Comparative example 2

[0098] A polished disc was produced from the same crystal rod as the discs used in the exemplary embodiment; this disc was not subjected to any thermal treatment.

[0099] IR-LST

[0100] For the disks according to embodiments 1 to 4 and comparative example 1, the sizes and concentrations of the COPs along a slit edge in the radial direction at intervals of 5 mm from the disk center to the disk edge were determined using IR-LST. For each measurement point in the radial direction, a 2000 pm x 350 pm dark-field image of the scattered light was acquired. The laser light of the infrared light scattering tomograph had a power of 74 mW. From the dark-field image, both the size and the concentration of the COPs with a size of at least 15 nm could be determined.

[0101] Figure 1 shows, for embodiments 1 to 4 (A1-A4) and comparative example 1 (R), the sizes of the COPs determined radially from the disk center to the disk edge along a surface at the slit edge. Preferably, measurements were taken along the centerline of the surface at the slit edge, with the surface at the slit edge being perpendicular to the main surfaces. For each point, the arithmetic mean of the size distribution of the COPs detected on the respective dark-field image is given ("size of the COPs" as defined in the third aspect of the present invention). The mean size of the COPs, i.e., the arithmetic mean of all sizes measured at different locations along the edge, was in the range of 17.5 pm to 18.5 pm for all embodiments and comparative example.

[0102] Figure 2 shows the concentrations determined along the slit edge for embodiments 1 to 4 (A1-A4) and comparative example 1 (R). For embodiments 1 to 4 (A1-A4), a concentration of COPs with a size of not less than 15 nm of not more than 2.0 x 10⁻⁶ was determined for each measurement point (each acquired dark-field image). 6 cm -3 determined. In contrast, higher concentrations of more than 1.0 x 10 were found for the comparison example (R). 7 cm -3 This shows that the concentration of COPs can be significantly reduced by the thermal treatment method according to the invention, while the size distribution of the COPs remains largely unchanged.

[0103] SIRD measurement and thermal stress test

[0104] SIRD measurements with subsequent BFA analysis were performed in an annular edge region of the disk with a width of 15 mm (depolarization threshold range ± 40 DU). A SIRD system from PVA Metrology & Plasma Solutions GmbH was used for the measurements. The mechanical stress was determined using SIRD. Fig. 3 shows maps of the mechanical stress at the disk edge of the disks produced in comparative examples 1 and 2. Fig. 4 shows maps of the mechanical stress at the disk edge of the disks produced in exemplary embodiments 1 and 2. The SIRD measurements show that only minimal stress was generated in the edge region after a thermal stress test. The stress test was performed in a vertical furnace from ASM International NV, in which each disk rested on three fingers of a long-finger boat from Ferrotec Materials Technologies Corporation.The thermal stress test and its evaluation can be carried out and evaluated according to the procedure described in EP 4 386819 A1 for testing the resistance of wafers made of single-crystal silicon.

[0105] Following thermal stress testing according to the program specified in Table 1, the depolarization is evaluated limited to one or more sub-areas around the contact points where contact existed between the disc and the fingers of the boat during heat treatment.

[0106] Table 1 below shows the temperature program of the thermal stress test with the respective target temperatures (left column), the respective heating and cooling rates (middle column), and the holding time at the respective target temperature (right column). All steps were performed in an atmosphere of oxygen and nitrogen. Only the holding step at 1100°C for 2 hours was carried out in a pure oxygen atmosphere.

[0107] Table 1

[0108]

[0109] Table 2 shows that for all embodiments and comparative examples in the above-described method for testing resistance to thermally induced dislocations, i.e., after the stress test according to the temperature program specified in Table 1 on a long finger boat, a bfc percentage of more than 2% and less than 4% was determined (depolarization threshold range ± 40 DU). Thus, comparable values ​​were achieved in the embodiments and comparative examples. This shows that the inventive thermal treatment method does not impair resistance to thermally induced dislocations compared to disks that have not undergone any or a different RTA treatment.

[0110] Table 2

[0111]

[0112] It was thus shown that the inventive method makes accessible a disk of single-crystal silicon which has the desired concentration of interstitial oxygen and COPs of a certain size, without deteriorating the resistance to thermally induced dislocations.

[0113] Furthermore, after heat treatment, a low concentration of BMDs of no more than 5.0 x 10 was detected using IR-LST. 6 cm -3 detected (see Fig. 7). For this purpose, a Semilab LST-2500HD device with a laser power of 0.13 mW and a scan window of 208 pm x 337 pm was used. Measurement points were recorded at 5 mm intervals in the radial direction along the slit edge.

[0114] In the first step of the heat treatment, the disk was exposed to an atmosphere of an oxygen-nitrogen mixture with a volume ratio of O₂:N₂ of 1:10 for a period of 3 hours at a temperature of 780 °C. In the second step of the heat treatment, the disk was exposed to an atmosphere of an oxygen-nitrogen mixture with a volume ratio of O₂:N₂ of 1:10 for a period of 16 hours at a temperature of 1000 °C.

[0115] GOI

[0116] Figure 5 shows QBD measurements for embodiments 1 and 2 (A1 and A2) and the comparison example (R). A QBD measurement is a determination of the charge to breakdown. It is a standard destructive test method used to determine the quality of gate oxides in MOS devices. It corresponds to the total charge that flows through the dielectric layer immediately before failure. Thus, QBD is a measure of time-dependent gate oxide breakdown. As a measure of oxide quality, QBD can also be a useful indicator of the product's reliability under certain electrical stress conditions. The QBD measurement shows the improved electrical properties of the disks produced in embodiments 1 and 2 compared to the comparison example. These are due to the significantly lower GOI densities detected in embodiments 1 and 2.

[0117] Fig. 6 shows that the disks produced in embodiments 1 to 4 (A1 to A4) have a GOI density of less than 0.4 defects cnr 2 exhibited, while in the comparison example (R) GOI densities of more than 0.8 defects cnr 2 were observed.

Claims

24 Patent claims 1. Method for the thermal treatment of a wafer of single-crystal silicon, comprising the following steps: (i) Heating the disc to a target temperature of not less than 1280°C and not more than 1300°C; (ii) Maintaining the target temperature for not less than 5 s and not more than 60 s; and (iii) Cooling the disk at a cooling rate of not less than 10°C / s and not more than 50°C / s; characterized in that steps (i) to (iii) are carried out in an atmosphere with an oxygen partial pressure of not less than 40% and not more than 90%.

2. Method for the thermal treatment of a disk of single-crystal silicon according to claim 1 , characterized in that the heating in step (i) takes place at a heating rate of not less than 10°C / s and not more than 100°C / s.

3. Method for the thermal treatment of a disk of single-crystal silicon according to claim 1 or 2, characterized in that the heating in step (i) up to a temperature of 1200°C is carried out at a rate of not less than 50°C / s and not more than 100°C / s; and the heating from a temperature of 1200°C up to the target temperature is carried out at a rate of not less than 10°C / s and not more than 45°C / s.

4. Method for the thermal treatment of a disk of single-crystal silicon according to any one of claims 1 to 3, characterized in that the cooling in step (iii) from the target temperature up to 1200°C is carried out at a cooling rate of not less than 10°C / s and not more than 27°C / s, and the cooling from 1200°C up to a final temperature is carried out at a cooling rate of not less than 30°C / s and not more than 50°C / s.

5. Method for the thermal treatment of a wafer of single-crystal silicon according to any one of claims 1 to 4, characterized in that the target temperature in step (ii) is maintained for not less than 20 s and not more than 50 s.

6. Method for the thermal treatment of a disk of single-crystal silicon according to any one of claims 1 to 5, characterized in that steps (i) to (iii) are carried out in an atmosphere with an oxygen partial pressure of not less than 50% and not more than 80%.

7. Method for producing wafers from single-crystal silicon, comprising the following steps in this order: Drawing a single-crystal rod from single-crystal silicon according to the Czochralski method; Grinding of the single crystal rod; Sawing the polished single-crystal rod into slices; Grinding and / or lapping of the discs; chemical etching and / or cleaning of the discs; Performing the thermal treatment method according to any one of claims 1 to 6; and Polishing the discs.

8. Method for producing wafers from single-crystal silicon according to claim 7, characterized in that in the step of drawing a single-crystal rod from single-crystal silicon according to the Czochralski method, during the drawing of the section with the target diameter the rotational speed of the crucible is not less than 0.5 and not more than 10 revolutions per minute, the rotation of the single crystal rod is not less than 4 and not more than 20 revolutions per minute, and The vertical distance between the underside of a heat shield arranged above the melt and surrounding the growing single-crystal rod and the surface of the melt is not less than 10 mm and not more than 30 mm.

9. A method for producing wafers of single-crystal silicon according to claim 8, characterized in that, in the step of drawing a single-crystal rod of single-crystal silicon according to the Czochralski method, a CUSP magnetic field with a maximum flux density of not less than 700 gauss and not more than 1300 gauss acts on the melt.

10. Slice of single-crystal silicon consisting of N-region characterized by the fact that the concentration of interstitial oxygen not more than 2.5 x 10 17 atoms / cm² 3 amounts to; and the concentration of COPs with a size of not less than 15 nm not more than 2.0 x 10 6 cm -3 amounts.

11. A disk of single-crystal silicon according to claim 10, characterized in that the mean size of the COPs is not more than 20 nm.

12. Slice of single-crystal silicon according to claim 10, characterized in that the mean concentration of COPs with a size of not less than 15 nm not more than 1.0 x 10 6 cm -3 and the average size of the COPs is no more than 20 nm.

13. Slice of single-crystal silicon according to one of claims 10 to 12, wherein the N-region is characterized in that it contains no agglomerates of silicon interstitial atoms or vacancies with a diameter of more than 20 nm.

14. A disk made of single-crystal silicon according to any one of claims 10 to 13, characterized in that the disk has a diameter of not less than 300 mm and not more than 310 mm and a thickness of not less than 500 pm and not more than 1500 pm.27 15. Disc made of single-crystal silicon according to one of claims 10 to 14, characterized in that the disc has an electrical resistance of not less than 40 ohm cm and not more than 120 ohm cm.

16. Single-crystal silicon wafer according to any one of claims 10 to 15, characterized in that the wafer has a maximum GOI defect density of 0.30 defects cm' 2 exhibits.

17. Slice of single-crystal silicon according to one of claims 10 to 16, characterized in that the concentration of BMD after heat treatment is not more than 5.0 x 10 6 cm -3 amounts, the heat treatment includes the following steps: a first step in which the single-crystal silicon disk is exposed to an atmosphere of a mixture of oxygen and nitrogen with a volume ratio of O2:N2 of 1:10 for a period of 3 hours at a temperature of 780°C; and a second step in which the disk of single-crystal silicon is exposed to an atmosphere of a mixture of oxygen and nitrogen with a volume ratio of O2:N2 of 1:10 for a period of 16 hours at a temperature of 1000°C.

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