Method for determining crystal defects in a workpiece made of monocrystalline silicon

Abstract

The invention relates to a method for determining crystal defects in a workpiece made of monocrystalline silicon, comprising the following steps: (i) reactive ion etching at least one surface of the workpiece in a gas mixture comprising oxygen and one or more halogen-containing compounds selected from the group consisting of elemental halogen X2, hydrogen halide HX and nitrogen halide NHnX3-n, wherein X is selected from the group of Cl and Br, and 0 ≤ n ≤ 2, the flow rate of oxygen and of each of the one or more halogen-containing compounds is not less than 5 sccm and not more than 100 sccm, and the at least one surface of the workpiece to be etched is exposed to the gas mixture for no less than 10 seconds and no more than 20 minutes; and (ii) identifying defects on the etched surface of the workpiece by means of light scattering measurement.

Description

[0001] Method for determining crystal defects in a workpiece made of single-crystal silicon

[0002] Technical field

[0003] The present invention relates to a method for determining crystal defects in a workpiece made of single-crystal silicon and a method for producing wafers made of single-crystal silicon.

[0004] State of the art

[0005] Monocrystalline silicon wafers are manufactured through a variety of processes, including drawing a single-crystal rod from a melt, sawing the crystal into wafers, grinding and / or lapping, edge rounding, chemical etching, polishing, and chemical cleaning. During the fabrication of devices on these semiconductor wafers, thermal processes and complex coating steps are performed, requiring a high degree of surface purity and, in particular, the near-complete absence of crystal defects and foreign material on the surface. To ensure these requirements are met, methods are needed that allow for the identification of defects as small as a few nanometers.

[0006] Conventional surface analysis methods such as transmission electron microscopy (TEM) are complex in sample preparation and measurement and are also limited to small areas, making such methods unsuitable for examining the entire surface of a larger area of ​​a workpiece made of single-crystal silicon, for example the entire front face of a disk made of single-crystal silicon.

[0007] Reactive ion etching (RIE) removes defect-free single-crystal material from the surface of a single-crystal silicon workpiece, while defects, such as oxides, remain as etch residues in the form of raised areas on the surface. In the prior art, a gas mixture of HBr, NF3, O2, and helium is used for this purpose (see K. Nakashima et al.).

[0008] Journal of The Electrochemical Society, 147 (11) 4294-4296 (2000) and K. Nakashima et al. Journal of The Electrochemical Society, 152 (5) G339-G344 (2005)).

[0009] Methods for reactive ion etching are further described in the publications JP 2007-123542 A, JP 2000-58509A, JP4121643 and JP4888632B2.

[0010] The raised areas can be detected using a light microscope or a scanning electron microscope. Their number can be measured by a data processor or a particle counter. However, the methods described in the prior art usually require thermal treatment before and / or chemical treatment after the actual RIE process. Such additional treatments can alter the morphology and shape of the defects. Furthermore, the RIE process in the prior art is designed in such a way that a relatively large amount of material is removed. Both the additional treatment steps and the relatively harsh conditions of the RIE process itself lead to a significant change in the morphology and geometry of the surface of the workpiece under investigation, which makes it difficult to identify the causes of the defects.

[0011] Furthermore, the methods described in the prior art lead to a relatively high surface roughness, which greatly reduces the sensitivity of optical measurement methods, for example, measurement methods based on light scattering.

[0012] Technical problem of the invention and its solution

[0013] The object of the present invention is to provide a gentler method for identifying crystal defects on or near the surface of a workpiece made of single-crystal silicon, which exhibits high sensitivity and enables the reliable determination of the positions and sizes of the identified defects. Changes to the shape and morphology of the defects should be kept to a minimum. Furthermore, the method should be suitable for process control.

[0014] The problem is solved by a method for determining crystal defects in a workpiece made of single-crystal silicon according to the first aspect of the present invention. The method comprises the following steps: (i) Reactive ion etching of at least one surface of the workpiece in a gas mixture comprising oxygen and one or more halogenated compounds selected from the group consisting of elemental halogens X₂, hydrogen halides HX, and nitrogen halides NHₙXₙ, wherein

[0015] X is selected from the group of CI and Br, and 0 < n < 2, the flow rate of oxygen and of each of the one or more halogenated compounds is not less than 5 sccm and not more than 100 sccm (sccm - standard cubic centimeters per minute), and at least one surface of the workpiece to be etched is exposed to the gas mixture for not less than 10 seconds and not more than 20 minutes; and

[0016] (ii) Identification of defects on the etched surface of the workpiece by means of light scattering measurement.

[0017] It was surprisingly found that the inventive method can, on the one hand, identify defects in the form of raised areas on the etched surface, but, on the other hand, alter their geometry and morphology less than in the RIE methods described in the prior art. The inventive method enables the identification of defects without the need for thermal treatment or additional chemical treatment before or after reactive ion etching.

[0018] Due to the lower surface roughness after reactive ion etching compared to prior art methods, it is possible to identify defects on the etched surface of the workpiece with high sensitivity using light scattering measurement. Thus, a relatively large area of ​​a single-crystal silicon workpiece can be quickly and efficiently examined for defects in the nanometer range. Therefore, the inventive method is suitable for use in process control during the production of single-crystal silicon wafers.

[0019] Since the process according to the first aspect of the present invention alters defects in their geometry and morphology less than the RIE processes described in the prior art, the process is well suited for investigating and identifying the causes of the defects. In a second aspect, the present invention relates to a process for producing wafers from single-crystal silicon, the process comprising the following steps:

[0020] Drawing a single-crystal rod from single-crystal silicon according to the Czochralski method;

[0021] Grinding of the single crystal rod;

[0022] Sawing the polished single-crystal rod into slices;

[0023] Grinding and / or lapping of the discs; chemical etching of the discs;

[0024] Polishing the discs; and chemical cleaning of the discs, characterized in that the method for determining crystal defects according to the first aspect of the present invention is carried out on a sample basis as part of process control.

[0025] This method makes it possible to evaluate the quality of the manufactured disks made of single-crystal silicon in an industrial process and to more easily identify the cause of defects.

[0026] Brief description of the characters

[0027] Fig. 1 shows the positions of the defects determined in step (ii) of embodiment 1 by means of light scattering measurement on a disk of single-crystal silicon. The defects are marked as white dots.

[0028] Fig. 2 shows an image of a typical elevation (defect) on the surface of a disk of single-crystal silicon, taken with a scanning electron microscope in step (iii) of embodiment 1.

[0029] Fig. 3a shows a top view of a raised area (defect) on the surface of a single-crystal silicon wafer, taken with a scanning electron microscope in step (iii) of embodiment 2. Fig. 3b shows a scanning electron microscope image of the same defect as in Fig. 3a after tilting the sample in the scanning electron microscope. Fig. 4 shows the positions of the defects on a single-crystal silicon wafer, determined by light scattering measurement in step (ii) of embodiment 3. The defects are marked as black and gray dots.

[0030] Fig. 5a shows an image of a raised area (defect) on the surface of a single-crystal silicon wafer, taken with an atomic force microscope in step (iii) of embodiment 3. Fig. 5b shows the height profile of the raised area recorded in Fig. 5a.

[0031] Fig. 6 shows the positions of the defects determined in step (iii) of embodiment 4 by light scattering measurement on a disk of single-crystal silicon. The defects are marked as black and gray dots.

[0032] Detailed description of the invention

[0033] The method for determining crystal defects in a workpiece made of single-crystal silicon according to the first aspect of the present invention is preferably used for determining crystal defects in wafers made of single-crystal silicon. The workpiece is therefore preferably a wafer made of single-crystal silicon. The wafer made of single-crystal silicon can be doped, for example, with one or more elements selected from the group consisting of oxygen, nitrogen, boron, phosphorus, arsenic, and antimony. The wafer can have a diameter of 150 mm to 450 mm, more preferably a diameter of 200 mm to 300 mm. The thickness of the wafer is preferably not less than 500 pm, more preferably not less than 700 pm, and more preferably not more than 1000 pm.

[0034] In step (i) of the process according to the invention, defect-free, single-crystal material is removed from the surface of the workpiece made of single-crystal silicon by reactive ion etching, leaving behind defects, for example oxides, as raised areas on the surface. These raised areas can have an almost circular or oval cross-section and taper upwards. For example, the raised areas can be conical. Crystal defects within the meaning of the present invention remain after reactive ion etching as raised areas on the etched surface of the workpiece, preferably as raised areas with a height of not less than 20 nm, more preferably not less than 50 nm, and most preferably not less than 100 nm. Preferably, the raised areas have a height of not more than 1000 nm. The terms "defect" and "crystal defect" are used synonymously in the present invention.Crystal defects within the meaning of the present invention are both defects in the crystal lattice of the silicon single crystal and deposits of foreign material on or at the surface of the silicon single crystal.

[0035] The reactive ion etching (RIE) according to step (i) of the process according to the invention is an ion-assisted reactive etching process. In this process, gases are decomposed into free electrons, ions, and radicals in a plasma, preferably between two electrodes. The etching of the surface of the workpiece made of single-crystal silicon is carried out by ions and / or charge-neutral radicals. In reactive ion etching, the chemical etching reaction is triggered by the kinetic energy of the impacting ions. Preferably, the reactive ion etching takes place in a chamber with two electrodes and a vacuum system. The vacuum system allows the removal of volatile products formed during etching, for example, silanes or halosilanes.The reactive ion etching according to step (i) of the method according to the invention can, for example, be carried out in a commercially available reactive ion etching device of the type PlasmaPro System 133 RIE from the manufacturer Oxford Instruments.

[0036] In the present invention, the plasma is preferably generated by a high-frequency magnetic field. The high-frequency magnetic field preferably has a magnetic flux density of not less than 0.5 and not more than 20 mT. The pressure during the reactive ion etching step is preferably not less than 0.5 and not more than 20 Pa. This pressure refers to the pressure in the chamber of the device in which the plasma is generated and brought into contact with the surface of the workpiece.

[0037] The surface of the workpiece to be etched is preferably the front face of a single-crystal silicon wafer. The front face is the side of the wafer on which components will later be manufactured. However, the surface to be etched can also be the surface at a fracture edge of a workpiece, for example, a single-crystal silicon wafer.

[0038] The gas mixture comprises oxygen and one or more halogenated compounds selected from the group consisting of elemental halogens X₂, hydrogen halides HX, and nitrogen halides NHnXs-n, wherein X is selected from the group consisting of chlorine and brinochloride, and 0 < n < 2. Preferably, the gas mixture comprises oxygen and one or more halogenated compounds selected from the group consisting of chlorine, bromine, hydrogen chloride, and bromine. In a particularly preferred embodiment, the gas mixture comprises oxygen and one or more compounds selected from the group consisting of chlorine and hydrogen bromide. Furthermore, the gas mixture preferably comprises at least one inert gas selected from the group consisting of helium, argon, and nitrogen, more preferably helium and / or argon, and most preferably argon.In one embodiment, the gas mixture consists of (a) oxygen; (b) one or more halogen-containing compounds selected from the group consisting of elemental halogen X2, hydrogen halide HX and nitrogen halide NH. n X3- n , wherein X is selected from the group consisting of Cl and Br, and 0 < n < 2; and (c) an inert gas selected from the group consisting of helium, argon, and nitrogen. The gas mixture thus more preferably comprises oxygen and hydrogen bromide, oxygen and chlorine, or oxygen, hydrogen bromide, and chlorine. Most preferably, the gas mixture consists of oxygen, hydrogen bromide, and argon; oxygen, chlorine, and argon; or oxygen, hydrogen bromide, chlorine, and argon. In a particularly preferred embodiment, the gas mixture consists of oxygen, chlorine, hydrogen bromide, and argon.

[0039] The flow rate of oxygen and of each of the one or more halogenated compounds is not less than 5 sccm and not more than 100 sccm, preferably not less than 10 sccm and not more than 50 sccm, and most preferably not less than 20 sccm and not more than 40 sccm. The flow rate of argon is preferably not less than 10 sccm and not more than 300 sccm, more preferably not less than 20 sccm and not more than 200 sccm, and most preferably not less than 50 sccm and not more than 150 sccm. The unit standard cubic centimeters per minute (sccm) represents the volumetric flow rate under standard conditions (T=0°C; p=1013 mbar).If the gas mixture consists of oxygen, chlorine, bromine, hydrogen and argon, the flow rates of oxygen, chlorine and hydrogen bromide are preferably not less than 10 sccm and not more than 50 sccm each, and the flow rate of argon is preferably not less than 20 sccm and not more than 200 sccm.

[0040] The at least one surface of the workpiece to be etched is exposed to the gas mixture for not less than 10 seconds and not more than 20 minutes, preferably for not less than 20 seconds and not more than 10 minutes, more preferably for not less than 30 seconds and not more than 5 minutes, and most preferably for not less than 30 seconds and not more than 2 minutes. Hereinafter, the time for which the surface of the workpiece is exposed to the gas mixture is referred to as the etching time.

[0041] If the workpiece surface is exposed to the gas mixture for at least 10 seconds, the etching process reveals the majority of defects as raised areas on the etched surface. If the etching time is at least 15 seconds, preferably at least 20 seconds, and more preferably at least 30 seconds, the number of defects with a height of at least 20 nm, and preferably at least 50 nm, can be further increased.

[0042] If the etching time does not exceed 20 minutes, it is ensured that the surface is not excessively roughened, thus enabling light scattering measurements to identify the size and position of the defects, which are identified as raised areas. By reducing the etching time to no more than 10 minutes, preferably no more than 5 minutes, the surface roughening can be further reduced, thereby increasing the sensitivity of the light scattering measurement. Step (i) does not require any subsequent chemical treatment of the surface, for example with hydrofluoric acid, so the morphology and geometry of the defects are altered less.In a preferred embodiment of the present invention, the time for which the at least one surface of the workpiece to be etched is exposed to the gas mixture, i.e., the etching time, is set such that the profile on the etched surface of the workpiece has a depth of no more than 1000 nm, preferably a depth of no more than 500 nm, and most preferably a depth of no more than 300 nm. The depth corresponds to the arithmetic mean of the heights of the measured elevations, which can be determined, for example, in step (iii) by electron microscopy or atomic force microscopy, taking into account at least 20 elevations, preferably at least 50 elevations.

[0043] In one embodiment, after reactive ion etching in step (i), at least 80% of the defects identified in step (ii) have a height of at least 20 nm and at least 1000 nm. Preferably, at least 80% of the defects identified in step (ii) have a height of at least 50 nm and at least 500 nm. The proportion of defects with the required height can be determined in step (iii) by examining at least 20, preferably at least 50, defects identified in step (ii) on the etched surface using electron microscopy or atomic force microscopy. The height of a defect thus corresponds to the local profile depth.

[0044] Optionally, the workpiece can undergo thermal treatment prior to reactive ion etching, for example, to simulate thermal process steps in the manufacturing process of electronic components and to investigate the associated formation of defects. However, thermal pretreatment is not necessary.

[0045] In step (ii), defects on the etched surface of the workpiece are identified using light scattering measurement. This measurement can be performed with a device from KLA Tencor Corp. or Hitachi High-Tech Corp.

[0046] The surface inspection in step (ii) is therefore based on the principle of light scattering, whereby a changed scattered light signal occurs in the cross-section of a defect. The inspection of semiconductor wafers for contamination and damage using optical methods is described, for example, in US RE37,740 E, which describes a scattered light inspection device with which the surface of a rapidly rotating wafer is scanned with a laser. Such scattered light measurement systems provide, among other things, information about the position of the defects on the wafer surface as well as their size. This information can be stored electronically, preferably in a standardized file format, so that this information is also available for subsequent analytical measurements of the wafer on other measuring instruments.One such standardized file format is KLARF (KLA Review File Format), which stores information about the positions of defects on the surface of a workpiece, preferably a single-crystal silicon wafer, and additionally the position of these defects relative to various measuring instruments. In step (ii) of the method according to the invention, the positions and sizes of the identified defects, determined by light scattering measurement, can thus be stored in an electronic format, preferably in the KLARF file format. By referencing the light scattering measurement system using polystyrene latex spheres of known diameter, the sizes of the defects can be determined in step (ii). For example, defects with a size of 50 nm to 60 nm can be identified in step (ii).

[0047] To determine the causes of the identified defects, an additional step (iii) can be performed in which specific defects identified in step (ii) are selected and examined using electron microscopy and / or atomic force microscopy. For this purpose, a Zeiss Auriga scanning electron microscope and / or an atomic force microscope from Park or Semilab can be used. Preferably, in step (iii), the geometry and / or morphology of the selected defects is examined. Particularly preferably, the geometry, i.e., the shape of the elevations, is investigated. However, the chemical composition of the defects can also be analyzed, for example, using scanning electron microscopy (SEM) with coupled analyzers such as EDX (energy-dispersive X-ray spectroscopy) or a SIMS instrument (secondary ion mass spectrometry) coupled to a scanning electron microscopy (SEM) instrument.For example, a Zeiss Auriga 60 scanning electron microscope coupled with an AMETEK EDAX Octane Elite EDX instrument and / or a Hiden Analytical EQS SIMS instrument can be used to determine the chemical composition of the selected defects.

[0048] In a second aspect, the present invention relates to a method for producing wafers from single-crystal silicon, the method comprising the following steps:

[0049] Drawing a single-crystal rod from single-crystal silicon according to the Czochralski method;

[0050] Grinding of the single crystal rod;

[0051] Sawing the polished single-crystal rod into slices;

[0052] Grinding and / or lapping of the discs; chemical etching of the discs;

[0053] Polishing the discs; and chemical cleaning of the discs, characterized in that the method according to the first aspect of the present invention is carried out on a sample basis as part of process control.

[0054] Preferably, the method according to the first aspect of the present invention is carried out after polishing the disc. The polishing of the disc preferably comprises two steps. First, double-sided polishing (DSP) is performed, followed by chemical-mechanical polishing (CMP) in a second step. The method according to the first aspect of the present invention is preferably carried out after the first polishing step, i.e., after DSP, and particularly preferably after the second polishing step, i.e., after DSP and CMP.

[0055] By performing the procedure according to the first aspect of the present invention on a sample basis as part of process control, the quality of the manufactured wafers made of single-crystal silicon, in particular the number, distribution, and size of crystal defects, can be evaluated with high sensitivity. Furthermore, by examining the morphology and geometry using step (iii) of the procedure according to the first aspect, the cause of the defects can be more easily identified. This makes it possible to intervene in the process and eliminate the cause of the defects. This ensures consistently high wafer quality.

[0056] Examples of implementation

[0057] Example 1

[0058] A polished and chemically cleaned single-crystal silicon wafer was etched in an Oxford Instruments PlasmaPro System 133 RIE refractory etching system using a gas mixture of oxygen, hydrogen bromide, chlorine, and argon. Flow rates were 20 sccm for oxygen and chlorine, 30 sccm for hydrogen bromide, and 100 sccm for argon. The etching time in the main RIE step was 5 minutes. Subsequently, the front surface of the etched wafer was examined for defects using light scattering measurements, thus identifying the position and size of surface defects. The positions and sizes of the surface defects were recorded and saved electronically as a KLARF file, as described above. An inner, circular region with a high defect density was identified (see Fig. 1). The annular, outer region of the front surface was largely defect-free.The front surface of the disc under investigation was roughened by the reactive ion network, which reduced the sensitivity of the light scattering system.

[0059] The KLARF file was then transferred to a computer connected to a Zeiss Sigma 300 scanning electron microscope. Images of defects at specific locations were acquired using the scanning electron microscope (see Fig. 2). The cone of a typical defect in the disk has a height of approximately 260 nm. The defect height is therefore significantly smaller than in the processes described in the prior art. The cones were not attacked at their tips during the reactive ion etching; that is, the defects were preserved. No subsequent chemical treatment was performed. Thus, it is possible to examine the defects subsequently using further analytical methods such as transmission electron microscopy. Example 2

[0060] Segments were produced from a single-crystal silicon wafer using a commercially available slitting device from the manufacturer SELA. The segments can be produced from polished and chemically cleaned semiconductor wafers, as well as from wafers sawn from a single-crystal rod that have not undergone any further treatment. Without further processing, the segments were subjected to the reactive ion etching process described in Exemplary Example 1, with the difference that the etching time was 10 minutes.

[0061] The cleavage edge of the etched segment was then examined using a Zeiss Sigma 300 scanning electron microscope. A typical cone at the cleavage edge is shown in Fig. 3a, and after tilting in the scanning electron microscope in Fig. 3b.

[0062] Example 3

[0063] A polished and chemically cleaned single-crystal silicon wafer was etched in a RIE system as described in Exemplary Example 1. Exemplary Example 3 differs from Exemplary Example 1 only in that the etching time was reduced to 30 seconds. Subsequently, the front surface of the etched wafer was examined for defects using light scattering measurement, thus identifying the position and size of surface defects on the wafer. The positions and sizes of the surface defects were recorded and saved in an electronic format as a KLARF file, as described above. In contrast to Exemplary Example 1, defects were identified across the entire front surface, as shown in Fig. 4. An inner, circular area was identified whose defect density is comparable to the defect density identified in the inner area in Exemplary Example 1.In addition, defects were also identified in the outer annular region extending to the edge of the disk (see Fig. 4). This demonstrates that an etching time of 30 seconds in step (i) of the inventive method is sufficient to create defects as elevations with the height required for subsequent detection in step (ii). At the same time, shortening the etching time reduces the roughening of the disk surface, thus improving the sensitivity of the light scattering measurement and enabling better detection of the existing defects. A photograph of a typical defect on the disk treated in this embodiment, taken with an atomic force microscope, is shown in Fig. 5a. Fig. 5b shows the height profile of this defect. Figs. 5a and 5b demonstrate that an etching time of just 30 seconds in step (i) of the inventive method is sufficient to make defects visible as elevations with a height of more than 20 nm.

[0064] Example 4

[0065] Exemplary embodiment 4 differs from exemplary embodiment 3 only in that the etching time was further reduced from 30 seconds to 15 seconds. Surface inspection of the front side of the etched disc using light scattering measurement revealed a lower defect density on the front side compared to exemplary embodiment 3 (see Fig. 6). This shows that shortening the etching time results in not all defects being detectable by light scattering measurement. This is presumably due to insufficient etching of the defects and a consequent lower proportion of defects with sufficient height.

Claims

Patent claims 1. Method for determining crystal defects in a workpiece made of single-crystal silicon, comprising the following steps (i) Reactive ion etching of at least one surface of the workpiece in a gas mixture comprising oxygen and one or more halogenated compounds selected from the group consisting of elemental halogen X2, hydrogen halide HX and nitrogen halide NHnXs-n, wherein X is selected from the group consisting of CI and Br, and 0 < n < 2, the flow rate of oxygen and of each of the one or more halogenated compounds is not less than 5 sccm and not more than 100 sccm, and at least one surface of the workpiece to be etched is exposed to the gas mixture for not less than 20 seconds and not more than 20 minutes; and (ii) Identifying defects on the etched surface of the workpiece using light scattering measurement.

2. Method for determining crystal defects in a workpiece made of single-crystal silicon according to claim 1, wherein the gas mixture comprises oxygen and one or more halogen-containing compounds selected from the group consisting of chlorine, bromine, hydrogen chloride and hydrogen bromide.

3. Method for determining crystal defects in a workpiece made of single-crystal silicon according to claim 1, wherein the gas mixture comprises oxygen and one or more compounds selected from the group consisting of chlorine and bromine, hydrogen.

4. Method for determining crystal defects in a workpiece made of single-crystal silicon according to one of claims 1 to 3, wherein the gas mixture additionally comprises at least one inert gas selected from the group consisting of helium, argon and nitrogen.

5. Method for determining crystal defects in a workpiece made of single-crystal silicon according to claim 1, wherein the gas mixture consists of oxygen, chlorine, bromine, hydrogen and argon.

6. Method for determining crystal defects in a workpiece made of single-crystal silicon according to any one of claims 1 to 5, wherein the flux rate of oxygen and of each of the one or more halogen-containing compounds is not less than 10 sccm and not more than 50 sccm.

7. Method for determining crystal defects in a workpiece made of single-crystal silicon according to claim 5, wherein the flux rates of oxygen, chlorine and hydrogen bromide are each not less than 10 sccm and not more than 50 sccm, and the flux rate of argon is not less than 20 sccm and not more than 200 sccm.

8. Method for determining crystal defects in a workpiece made of single-crystal silicon according to any one of claims 1 to 7, wherein the surface to be etched is exposed to the flow of the gas mixture for not less than 20 seconds and not more than 10 minutes.

9. Method for determining crystal defects in a workpiece made of single-crystal silicon according to any one of claims 1 to 8, wherein in step (ii) the positions and sizes of the identified defects are stored in an electronic format.

10. Method for determining crystal defects in a workpiece made of single-crystal silicon according to any one of claims 1 to 9, wherein an additional step (iii) is carried out in which certain defects identified in step (ii) are selected and examined by means of electron microscopy and / or atomic force microscopy.

11. Method for determining crystal defects in a workpiece made of single-crystal silicon according to claim 10, wherein in step (iii) the geometry and / or morphology of the determined, selected defects is examined.

12. Method for determining crystal defects in a workpiece made of single-crystal silicon according to one of claims 1 to 11, wherein the surface to be etched is exposed to the flow of the gas mixture for not less than 30 seconds and not more than 5 minutes.

13. Method for determining crystal defects in a workpiece made of single-crystal silicon according to one of claims 1 to 12, wherein in step (i) a plasma is generated by a high-frequency magnetic field.

14. Method for determining crystal defects in a workpiece made of single-crystal silicon according to claim 13, wherein the high-frequency magnetic field has a magnetic flux density of not less than 0.5 mT and not more than 20 mT.

15. Method for determining crystal defects in a workpiece made of single-crystal silicon according to any one of claims 1 to 14, wherein in step (i) a pressure of not less than 0.5 and not more than 20 Pa prevails.

16. Method for determining crystal defects in a workpiece made of single-crystal silicon according to any one of claims 1 to 15, wherein in step (i) the time for which the at least one surface of the workpiece to be etched is exposed to the gas mixture is adjusted such that the profile produced by the etching on the surface of the workpiece has a depth of no more than 1000 nm, preferably no more than 500 nm.

17. Method for producing wafers from single-crystal silicon, comprising the following steps: 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 of the discs; Polishing the discs; and Chemical cleaning of the discs, characterized in that the method according to one of claims 1 to 16 is carried out on a random sample basis as part of process control.

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