Method for determining crystal defects in a monocrystalline silicon workpiece and method for producing monocrystalline silicon wafers

Abstract

A method for determining crystal defects in a single-crystal silicon workpiece, comprising the steps of: (i) reactive ion etching at least one surface of the workpiece in a gas mixture containing oxygen and one or more halogen-containing compounds, the halogen-containing compounds being selected from elemental halogen X2, hydrogen halides HX, and nitrogen halides NHnX3-n, wherein X is selected from Cl and Br, and NHn2, the flow rate of oxygen and the flow rate of each of the one or more halogen-containing compounds being not less than 5 sccm and not more than 100 sccm, and the at least one surface of the workpiece to be etched being 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 by light scattering measurement.

Description

[Technical Field]

[0001] This invention relates to a method for determining crystal defects in a single-crystal silicon workpiece and a method for producing single-crystal silicon wafers. [Previous Technology]

[0002] Single-crystal silicon wafers (silicon wafers) are produced in multiple process steps, including pulling single-crystal ingots, dicing the crystal into wafers, grinding and / or lapping, edge rounding, chemical etching, and polishing and chemical cleaning of the wafers. During the production of components on the semiconductor wafers, heat treatment and complex coating steps are performed, requiring high surface purity, particularly the absence of crystal defects and foreign materials at the surface. The ability to ensure these requirements necessitates methods capable of identifying defects with dimensions in the nanometer range.

[0003] Traditional surface analysis techniques such as transmission electron microscopy (TEM) not only involve complex sample preparation and measurement, but are also limited to small areas, making this technique unsuitable for studying the entire surface of large-area single-crystal silicon workpieces, such as the entire front side of a single-crystal silicon wafer.

[0004] Reactive ion etching (RIE) removes defect-free single-crystal material from the surface of a single-crystal silicon workpiece, while defects (e.g., oxides) remain on the surface as etching residues in the form of protrusions. For this type of etching, prior art has used, for example, a gas mixture consisting of HBr, NF3, O2, and helium (see K. Nakashima et al., 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)). Reactive ion etching methods are further described in publications JP 2007-123542 A, JP 2000-58509 A, JP4121643, and JP4888632 B2.

[0005] Protrusions can be captured using an optical microscope or a scanning electron microscope. The number of protrusions can be measured by a data processor or a particle counter. However, the methods described in the prior art typically require heat treatment before the RIE method itself and / or chemical treatment after the RIE method itself. This additional treatment may alter the morphology and shape of the defect. Furthermore, in the prior art, the RIE method is configured to achieve a relatively high material removal rate. The additional processing steps and relatively harsh conditions of the RIE method itself lead to significant changes in the surface morphology and geometry of the workpiece under study, making it more difficult to identify the cause of the defect.

[0006] The methods described in the prior art also result in relatively rough surfaces, which greatly reduces the sensitivity of optical measurement techniques, such as light scattering-based optical measurement techniques. [Summary of the Invention]

[0007] Technical Problems and Corresponding Solutions of the Invention

[0008] The object of this invention is to provide a relatively benign method for identifying crystal defects on or near the surface of a single-crystal silicon workpiece. This method exhibits high sensitivity and allows for reliable determination of the location and size of the identified defects. Changes in the shape and morphology of the defects should be minimized. This method is also suitable for program control.

[0009] This objective is achieved by a method for determining crystal defects in a single-crystal silicon workpiece according to a first aspect of the invention. The method comprises the following steps: (i) reactively ion etching at least one surface of the workpiece in a gas mixture containing oxygen and one or more halogen-containing compounds selected from elemental halogens X2, hydrogen halides HX, and nitrogen halides NHnX3-n, wherein X is selected from Cl and Br, and 0 ≤ n ≤ 2, the flow rate of each of the oxygen and one or more halogen-containing 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 (ii) identifying defects on the etched surface of the workpiece by means of light scattering measurements.

[0010] It has been surprisingly determined that, on the one hand, the method of the present invention can identify defects in the form of protrusions on the etched surface, but on the other hand, their geometry and morphology are less altered compared to the RIE methods described in the prior art. The method of the present invention can identify defects without requiring heat treatment or additional chemical treatment before or after reactive ion etching.

[0011] Because the surface roughness is relatively low after reactive ion etching compared to methods described in the prior art, defects on the etched surface of the workpiece can be identified with high sensitivity via light scattering measurements. Therefore, defects in relatively large areas of single-crystal silicon workpieces, in the nanometer range, can be studied quickly and effectively. As a result, the method of the present invention is suitable for use as part of process control in single-crystal silicon wafer manufacturing.

[0012] Since the changes in wafer geometry and morphological defects are less severe in the method according to the first aspect of the invention compared to the RIE method described in the prior art, this method is well-suited for studying and identifying the causes of defects.

[0013] In a second aspect, the present invention relates to a method for producing single-crystal silicon wafers, the method comprising the steps of: pulling a single-crystal silicon ingot by the Czochralski method; grinding the single-crystal ingot; slicing the ground single-crystal ingot into wafers; grinding and / or refining the wafers; chemically etching the wafers; polishing the wafers; and chemically cleaning the wafers, which includes, on the basis of random samples, a method for determining crystal defects according to the first aspect of the present invention as part of process control.

[0014] This method can evaluate the quality of the produced single-crystal silicon wafers in the industrial process and more easily identify the causes of defects.

Implementation Method

[0016] The method for determining crystal defects in a single-crystal silicon workpiece according to the first aspect of the present invention is preferably used for determining crystal defects in a single-crystal silicon wafer. Therefore, the workpiece is preferably a single-crystal silicon wafer. The single-crystal silicon wafer may be doped with, for example, one or more elements selected from oxygen, nitrogen, boron, phosphorus, arsenic, and antimony. The wafer may have a diameter of 150 mm to 450 mm, more preferably 200 mm to 300 mm. The thickness of the wafer is preferably not less than 500 μm, more preferably not less than 700 μm, and preferably not greater than 1000 μm.

[0017] In step (i) of the method of the present invention, defect-free single-crystal material at the surface of a single-crystal silicon workpiece is removed by reactive ion etching, such that defects (e.g., oxides) are retained as protrusions at the surface. The protrusions may have an almost circular or elliptical cross-section and an upward taper. For example, the protrusions may be conical. In the context of the present invention, crystal defects are retained as protrusions on the etched surface of the workpiece after reactive ion etching, preferably as protrusions with a height of not less than 20 nm, more preferably not less than 50 nm, and most preferably not less than 100 nm. The protrusions preferably have a height of not more than 1000 nm. When used in the present invention, defect and crystal defect are synonymous terms. In the context of the present invention, crystal defects are not only defects in the lattice of single-crystal silicon, but also deposits of foreign material on the surface of single-crystal silicon or on the surface.

[0018] Step (i) of the method according to the invention is reactive ion etching (RIE), which is an ion-assisted reactive etching process. In this process, the gas is decomposed into free electrons, free ions, and free radicals in the plasma, preferably between two electrodes. The surface of the single-crystal silicon workpiece is etched by ions and / or electrically neutral groups. In reactive ion etching, the chemical etching reaction is initiated by the kinetic energy of the colliding ions. Reactive ion etching is preferably carried out in a chamber having two electrodes and a vacuum system. The vacuum system allows for the removal of volatile products formed during etching, such as silanes or halosilanes. The reactive ion etching in step (i) of the method according to the invention can be carried out, for example, in a commercially available PlasmaPro System 133 RIE reactive ion etching apparatus from the manufacturer Oxford Instruments.

[0019] In this invention, 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 mT (millitalas) and not more than 20 mT. The pressure during the reactive ion etching step is preferably not less than 0.5 Pa and not more than 20 Pa. This pressure refers to the pressure in the chamber of the device through which plasma is generated and comes into contact with the surface of the workpiece.

[0020] Here, the surface of the workpiece to be etched is preferably the front side of the monocrystalline silicon wafer. The front side is the side of the wafer on which components will later be produced. Alternatively, the surface to be etched can be the surface of a workpiece such as, for example, the cut edge of a monocrystalline silicon wafer.

[0021] The gas mixture comprises oxygen and one or more halogen-containing compounds selected from elemental halogens X2, hydrogen halides HX, and nitrogen halides NHnX3-n, wherein X is selected from Cl and Br, and 0 ≤ n ≤ 2. The gas mixture preferably comprises oxygen and one or more halogen-containing compounds selected from chlorine, bromine, hydrogen chloride, and hydrogen bromide. In a particularly preferred embodiment, the gas mixture comprises oxygen and one or more compounds selected from chlorine and hydrogen bromide. Furthermore, the gas mixture preferably comprises at least one inert gas selected from helium, argon, and nitrogen, more preferably helium and / or argon, and most preferably argon. In one embodiment, the gas mixture comprises: (a) oxygen; (b) one or more halogenated compounds selected from elemental halogens X2, hydrogen halides HX, and nitrogen halides NHnX3-n, wherein X is selected from Cl and Br, and 0 ≤ n ≤ 2; and (c) an inert gas selected from helium, argon, and nitrogen. Therefore, the gas mixture preferably comprises oxygen and hydrogen bromide, oxygen and chlorine, or oxygen, hydrogen bromide, and chlorine. Most preferably, the gas mixture comprises: oxygen, hydrogen bromide, and argon; oxygen, chlorine, and argon; or oxygen, hydrogen bromide, chlorine, and argon. In a particularly preferred embodiment, the gas mixture comprises oxygen, chlorine, hydrogen bromide, and argon.

[0022] The flow rate of each of oxygen and one or more halogen-containing compounds shall be 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 shall preferably be 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, hydrogen bromide and argon, the flow rates of oxygen, chlorine and hydrogen bromide shall preferably be not less than 10 sccm and not more than 50 sccm, and the flow rate of argon shall preferably be not less than 20 sccm and not more than 200 sccm.

[0023] 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 not less than 20 seconds and not more than 10 minutes, more preferably not less than 30 seconds and not more than 5 minutes, and most preferably not less than 30 seconds and not more than 2 minutes. The time during which the workpiece surface is exposed to the gas mixture is referred to hereinafter as the etching time.

[0024] If the surface of the workpiece is exposed to the gas mixture for not less than 10 seconds, the etching identifies most of the defects that appear as protrusions on the etched surface. If the etching time is not less than 15 seconds, preferably not less than 20 seconds, and more preferably not less than 30 seconds, the number of defects with a height of not less than 20 nm, preferably not less than 50 nm, can be further increased.

[0025] An etching time of no more than 20 minutes ensures that the surface does not become too rough, allowing light scattering measurements to identify the size and location of defects identified as protrusions. By reducing the etching time to no more than 10 minutes, preferably no more than 5 minutes, surface roughening can be further reduced, thereby allowing for further improvement in the sensitivity of light scattering measurements. Step (i) does not require any downstream chemical treatment of the surface, such as with hydrofluoric acid, so the morphology and geometry of the defects are not significantly altered.

[0026] In a preferred embodiment of the invention, the time (i.e., etching time) during which at least one surface of the workpiece to be etched is exposed to the gas mixture is determined such that the profile on the etched surface of the workpiece has a depth of not more than 1000 nm, preferably not more than 500 nm, and most preferably not more than 300 nm. Here, the depth corresponds to the arithmetic mean of the measured heights of the protrusions, which can be determined, for example, in step (iii), considering at least 20 protrusions, preferably at least 50 protrusions, by means of an electron microscope or an atomic force microscope.

[0027] In one embodiment, after reactive ion etching in step (i), at least 80% of the defects identified in step (ii) have a height of not less than 20 nm and not more than 1000 nm. Preferably, at least 80% of the defects identified in step (ii) have a height of not less than 50 nm and not more than 500 nm. The proportion of defects with the desired height can be determined in step (iii) by studying at least 20, preferably at least 50, defects on the etched surface identified in step (ii) using an electron microscope or an atomic force microscope. Therefore, the height of the defect corresponds to the local profile depth.

[0028] Prior to reactive ion etching, the workpiece may be subjected to heat treatment as needed to, for example, simulate the thermal steps in the electronic component manufacturing process and study the relevant development of defects. However, heat pretreatment is not required.

[0029] Finally, in step (ii), defects on the etched surface of the workpiece are identified by light scattering measurement. Light scattering measurement can be performed using instruments from manufacturers such as KLA Tencor or Hitachi High-Tech. Therefore, the surface inspection in step (ii) is based on the principle of light scattering, where the scattered light signal is altered in the effective cross-section of the defect. For example, US RE37,740 E describes the inspection of contamination and damage to semiconductor wafers using optical methods, describing a light scattering inspection instrument used for laser scanning of the surface of a high-speed rotating wafer. This light scattering measurement system provides information including the location and size of defects on the wafer surface. This information can be stored electronically, preferably in a standardized file format, so that it can also be used for subsequent analytical measurements of the wafer on different measuring instruments. One such standardized file format is KLARF (KLA Review File Format), which stores information about the location of defects on the surface of the workpiece, preferably a single-crystal silicon wafer, and additionally stores the positions of these defects relative to different measuring instruments. Therefore, in step (ii) of the method of the present invention, the size and location of the identified defect, determined by light scattering measurement, can be stored electronically, preferably in KLARF file format. The size of the defect can be determined in step (ii) by referring to a light scattering measurement system using polystyrene latex spheres of known diameter. In this way, for example, defects with a size of 50 nm to 60 nm can be identified in step (ii).

[0030] To be able to state the cause of the discovered defects, an additional step (iii) may be performed, in which the specific defects identified in step (ii) are selected and studied via electron microscopy and / or atomic force microscopy. This can be done using an Auriga scanning electron microscope from manufacturer Zeiss and / or an atomic force microscope from manufacturer Park or Semilab. Preferably, the geometry and / or morphology of the selected specific defects are studied in step (iii). Here, the geometry, i.e., the shape of the protrusion, is particularly preferred to be studied. However, the chemical composition of the defects may also be analyzed via, for example, a scanning electron microscope (SEM) coupled with an analyzer such as EDX (energy-dispersive X-ray spectroscopy) or a SIMS (secondary-ion mass spectrometry) instrument coupled to a scanning electron microscope. For example, an Auriga 60 scanning electron microscope from Zeiss, coupled with an Octane Elite EDX instrument from manufacturer AMETEK EDAX and / or an EQS SIMS instrument from manufacturer Hiden Analytical, can be used to determine the chemical composition of the selected defect.

[0031] In a second aspect, the present invention relates to a method for producing single-crystal silicon wafers, the method comprising the steps of: pulling a single-crystal silicon ingot by the Tchaikovsky method; grinding the single-crystal ingot; dicing the ground single-crystal ingot into a wafer; grinding and / or refining the wafer; chemically etching the wafer; polishing the wafer; and chemically cleaning the wafer, which comprises performing the method according to the first aspect of the invention on a random sample basis as part of the process control.

[0032] The method according to the first aspect of the invention is preferably performed after wafer polishing. The wafer polishing preferably comprises two steps. First, in the first step, double-sided polishing (DSP) is performed, followed by chemical mechanical polishing (CMP) in the second step. The method according to the first aspect of the invention is preferably performed after the first polishing step, i.e., after DSP, and more preferably after the second polishing step, i.e., after both DSP and CMP.

[0033] Because the method according to the first aspect of the invention is performed on random samples as part of a program control, the quality of the produced single-crystal silicon wafers can be evaluated with high sensitivity, particularly the number, distribution, and size of crystal defects. Furthermore, as a result of studying the morphology and geometry via step (iii) of the method according to the first aspect, the causes of defects can be more easily identified. This allows for intervention in the process and elimination of the causes of defects. As a result, it can be ensured that the wafers consistently maintain high quality.

[0034] Working Example

[0035] Working Example 1

[0036] Polished and chemically cleaned single-crystal silicon wafers were etched in a PlasmaPro System 133 RIE unit from Oxford Instruments in a gas mixture of oxygen, hydrogen bromide, chlorine, and argon. The flow rates of oxygen and chlorine were 20 sccm each, hydrogen bromide was 30 sccm, and argon was 100 sccm. The etching time in the main step of the RIE method was 5 minutes. Defects on the front side of the etched wafer were then studied by light scattering measurements, and the location and size of surface defects on the wafer were identified accordingly. The location and size of surface defects were maintained in electronic format and stored as KLARF files as described above. Inner circular regions with high defect density were identified (see Figure 1). The annular outer region of the front surface showed essentially no defects. The front side of the studied wafer was roughened by reactive ion etching, which reduced the sensitivity of the light scattering system.

[0037] The KLARF file was then transferred to a computer connected to a Sigma 300 scanning electron microscope from the manufacturer, Zeiss. The scanning electron microscope was used to record images of the defects at specific locations (see Figure 2). The cone of a typical wafer defect has a height of approximately 260 nm. Therefore, the defect height is much lower than that described in the processes of the prior art. During reactive ion etching, the peak of the cone was not etched, meaning the defect was preserved. No downstream chemical processing was performed. Therefore, the defect can then be studied by further analytical techniques such as transmission electron microscopy.

[0038] Working Example 2

[0039] Silicon segments are produced from monocrystalline silicon wafers using commercially available dicing equipment from manufacturer SELA. Segment production can begin with polished and chemically cleaned semiconductor wafers, or with wafers diced from monocrystalline ingots without further processing. Without further processing, the silicon segments are subjected to the reactive ion etching process described in Working Example 1, except that the etching time is 10 minutes.

[0040] The cut edges of the etched silicon segments were then studied using a Sigma 300 scanning electron microscope from the manufacturer Zeiss. A typical cone at the cut edge is shown in Figure 3a, and a typical cone after tilting in the scanning electron microscope is shown in Figure 3b.

[0041] Working Example 3

[0042] As described in Working Example 1, a polished and chemically cleaned single-crystal silicon wafer is etched in a RIE unit. Working Example 3 differs from Working Example 1 only in that the etching time is reduced to 30 seconds. Defects on the front side of the etched wafer are then studied by light scattering measurements, thus identifying the location and size of surface defects on the wafer. The location and size of the surface defects are maintained in electronic format and stored as a KLARF file as described above. In contrast to Working Example 1, defects are identified across the entire front side, as shown in FIG4. An inner circular region is identified, with a defect density comparable to that identified in the inner region in Working Example 1. However, defects are also identified in the outer annular region extending to the wafer edge (see FIG4). This indicates that the 30-second etching time in step (i) of the method of the present invention is sufficient to generate defects as protrusions, which have the height required for detection in subsequent step (ii). Simultaneously, as a result of the reduced etching time, the roughness of the wafer surface is reduced, thus improving the sensitivity of light scattering measurements and more effectively detecting existing defects. Figure 5a shows an image of a typical defect on a wafer processed in this working embodiment, taken using an atomic force microscope. Figure 5b shows the height profile of the defect. Figures 5a and 5b demonstrate that an etching time of only 30 seconds in step (i) of the method of the present invention is sufficient to expose the defect as a protrusion with a height greater than 20 nm.

[0043] Working Example 4

[0044] The only difference between Working Example 4 and Working Example 3 is that the etching time is further reduced from 30 seconds to 15 seconds. When performing surface inspection of the front side of the etched wafer via light scattering measurement, a lower defect density was found on the front side compared to Working Example 3 (see Figure 6). This indicates that the reduction in etching time means it is no longer possible to detect all defects via light scattering measurement. This may be due to insufficient etching of defects and a smaller proportion of defects with sufficient height. [Simplified Explanation of the Diagram]

[0015] Figure 1 shows the location of a defect on a single-crystal silicon wafer determined by light scattering measurement in step (ii) of Working Example 1. The defect is characterized as a white spot. Figure 2 shows an image of a typical protrusion (defect) on the surface of a single-crystal silicon wafer recorded by scanning electron microscopy in step (iii) of Working Example 1. Figure 3a shows a top view of a protrusion (defect) on the surface of a single-crystal silicon wafer recorded by scanning electron microscopy in step (iii) of Working Example 2. Figure 3b shows a scanning electron micrograph of the same defect as in Figure 3a after tilting the sample in a scanning electron microscope. Figure 4 shows the location of a defect on a single-crystal silicon wafer determined by light scattering measurement in step (ii) of Working Example 3. The defect is characterized as a black spot and a gray spot. Figure 5a shows an image of a protrusion (defect) on the surface of a single-crystal silicon wafer recorded by atomic force microscopy in step (iii) of Working Example 3. Figure 5b shows the height profile of the protrusion recorded in Figure 5a. Figure 6 shows the location of defects on the single-crystal silicon wafer determined by light scattering measurements in step (iii) of working example 4. The defects are characterized as black spots and gray spots.

Claims

1. A method for determining crystal defects in a single-crystal silicon workpiece, comprising the steps of: (i) reactive ion etching at least one surface of the workpiece in a gas mixture containing oxygen and one or more halogen-containing compounds, the halogen-containing compounds being selected from elemental halogen X2, hydrogen halides HX, and nitrogen halides NHnX3-n, wherein X is selected from Cl and Br, and 0 ≤ n ≤ 2, the flow rate of oxygen and the flow rate of each of the one or more halogen-containing compounds being not less than 5 sccm (standard cubic centimeters per minute) and not more than 100 sccm, and the at least one surface of the workpiece to be etched being 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 by light scattering measurement.

2. The method for determining crystal defects in a single-crystal silicon workpiece as described in claim 1, wherein the gas mixture comprises oxygen and one or more halogen-containing compounds selected from chlorine, bromine, hydrogen chloride, and hydrogen bromide.

3. The method for determining crystal defects in a single-crystal silicon workpiece as described in claim 1, wherein the gas mixture comprises oxygen and one or more halogen-containing compounds selected from chlorine and hydrogen bromide.

4. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, wherein the gas mixture further comprises at least one inert gas selected from helium, argon and nitrogen.

5. The method for determining crystal defects in a single-crystal silicon workpiece as described in claim 1, wherein the gas mixture is composed of oxygen, chlorine, hydrogen bromide and argon.

6. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3 and 5, wherein the flow rate of oxygen and the flow rate of each of the one or more halogen-containing compounds are not less than 10 sccm and not more than 50 sccm.

7. The method for determining crystal defects in a single-crystal silicon workpiece as described in claim 5, wherein the flow rates of oxygen, chlorine and hydrogen bromide are not less than 10 sccm and not more than 50 sccm, and the flow rate of argon is not less than 20 sccm and not more than 200 sccm.

8. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein the surface to be etched is exposed to the gas mixture stream for not less than 20 seconds and not more than 10 minutes.

9. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein in step (ii), the location and size of the identified defects are stored in an electronic format.

10. A method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein step (iii) is performed in which the specific defects identified in step (ii) are selected and studied by means of an electron microscope and / or an atomic force microscope.

11. The method for determining crystal defects in a single-crystal silicon workpiece as described in claim 10, wherein in step (iii), the geometry and / or morphology of a selected particular defect is studied.

12. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein the surface to be etched is exposed to the gas mixture stream for not less than 30 seconds and not more than 5 minutes.

13. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein in step (i), plasma is generated by a high-frequency magnetic field.

14. The method for determining crystal defects in a single-crystal silicon workpiece as described in claim 13, wherein the high-frequency magnetic field has a magnetic flux density of not less than 0.5 mT (millitalas) and not more than 20 mT.

15. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein in step (i), the pressure is not less than 0.5 Pa and not more than 20 Pa.

16. The method for determining crystal defects in a single-crystal silicon workpiece as claimed in any one of claims 1 to 3, 5 and 7, wherein in step (i), the time for which at least one surface of the workpiece to be etched is exposed to the gas mixture is determined such that the profile formed by etching on the surface of the workpiece has a depth of not more than 1000 nm.

17. A method for producing single-crystal silicon wafers, comprising the following steps: pulling a single-crystal silicon ingot using the Czochralski method; grinding the single-crystal ingot; slicing the ground single-crystal ingot into wafers; grinding and / or lapping the wafers; chemically etching the wafers; polishing the wafers; and chemically cleaning the wafers, wherein, The method described in any one of requests 1 to 16 may be performed randomly as part of program control.

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