Evaluation method for silicon single crystal substrate

Abstract

To provide a method for performing an OSF inspection accurately with high sensitivity even on a silicon single crystal having a {111} plane as a principal plane.SOLUTION: Provided is a method for evaluating a silicon single crystal substrate. The method includes: cleaving a silicon single crystal substrate having a {111} plane as a principal plane to expose a {110} plane; performing, on the silicon single crystal substrate with an exposed {110} plane, first stage heat treatment at 900-1,050°C for 30-540 minutes and, following the first stage heat treatment, second stage heat treatment at 1,100-1,200°C for 30-200 minutes under an oxidizing atmosphere; and thereafter, selectively etching the silicon single crystal substrate with an exposed {110} plane to perform an OSF inspection on the {110} plane.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for evaluating the OSF of a silicon single crystal substrate with a main surface of {111} surface. [Background technology]

[0002] Semiconductor devices such as transistors and ICs mainly use silicon single crystal wafers (hereinafter sometimes simply referred to as wafers) cut from silicon single crystals. Silicon single crystals are generally manufactured by the Czochralski method (CZ method), in which a seed crystal is immersed in a molten semiconductor material contained in a crucible and then pulled up to obtain a large-diameter, high-quality single crystal. In the CZ method, quartz (SiO2) is used for the crucible that contains the raw material, so oxygen dissolves in the raw material melt and is mixed into the crystal as interstitial oxygen atoms during crystal growth. This interstitial oxygen brings about an intrinsic gettering effect due to the pinning action of dislocations and the formation of precipitates during device processing, so controlling the concentration and distribution of interstitial oxygen in the crystal is important for semiconductor device characteristics.

[0003] On the other hand, when the interstitial oxygen in the crystal is supersaturated, the interstitial oxygen precipitates as oxygen precipitates. Furthermore, some of these precipitates become large oxygen precipitates, which may form oxidation-induced stacking faults (hereinafter referred to as OSFs) near the wafer surface after device processing, degrading device characteristics and reducing yields. Therefore, it is important to understand the OSFs in silicon single crystals before device processing.

[0004] In recent years, wide-gap semiconductors such as GaN have been used in power devices, and as one of the substrates for GaN devices, wafers with a Si{111} surface as the main surface, which has a relatively small difference in lattice constant from GaN, are used. Since the generation of OSFs after device processing on the Si{111} surface also leads to deterioration of device characteristics and reduced yields, it is important to understand the OSFs in single crystals on the Si{111} surface before device processing, just as with the Si{100} surface.

[0005] However, it is known that the OSF growth rate is slower on the Si{111} surface compared to Si{100} and {110}. This is generally understood to be due to the high kink density on the {111} surface, which traps interstitial Si generated during oxidation heat treatment. Therefore, there is a problem with OSF inspection on the {111} surface, where the etch pits produced during selective etching are small and can be overlooked during OSF inspection. If OSF inspection is overlooked, it can degrade the customer's device characteristics and have a negative impact on yield. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 6-97251 [Patent Document 2] JP 2009-302142 A [Patent Document 3] International Publication No. 2021 / 246101 Summary of the Invention [Problem to be solved by the invention]

[0007] A conventionally known method for inspecting OSFs in silicon single crystal wafers involves subjecting the wafer to a specified heat treatment to generate OSFs on the wafer surface, and then counting the density of the generated OSFs using an optical microscope.

[0008] In Patent Document 1, OSF inspection is performed by performing a first heat treatment at 900 to 1050° C. for 30 to 300 minutes, followed by a second heat treatment at 1100 to 1200° C. for 30 to 200 minutes. However, this method is based on the results of the {100} plane and cannot be applied to the {111} plane, which has a slow OSF growth rate.

[0009] Patent Document 2 shows a method of performing OSF inspection on a {100} plane in a silicon single crystal having a {110} plane as the main surface by cleaving the silicon single crystal so that the {100} plane appears in the thickness direction of the wafer (cleavage plane) and then performing selective etching. However, since the {111} plane is not perpendicular to the {100} plane, it is impossible to cleave the {111} plane to expose the {100} plane in the thickness direction, and this method cannot be applied to wafers having a {111} plane as the main surface.

[0010] Patent Document 3 provides a wafer with a main surface of {100} surface. <110> It is described that there is a method to obtain the defect density by cleaving the wafer in the {100} direction, etching the cleaved surface, and then observing the etch pits with an optical microscope. <110> If you cleave it in the direction, the {110} plane appears as a cleaved plane in the thickness direction, but in the case of the {111} plane, <110> When cleaved in the direction, the {110} plane does not appear, but the {211} plane is exposed. Since the {211} plane is not a cleavage plane, the actual surface is not flat and roughness occurs, making it difficult to observe the pits under a microscope after etching.

[0011] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for performing OSF inspection with high accuracy and high sensitivity even in silicon single crystals whose main surface is the {111} plane. [Means for solving the problem]

[0012] The present invention has been made to achieve the above-mentioned object, and provides a method for evaluating a silicon single crystal substrate, comprising: cleaving a silicon single crystal substrate having a {111} plane as a main surface to expose the {110} plane; subjecting the silicon single crystal substrate with the {110} plane exposed to a first-stage heat treatment at 900-1050°C for 30-540 minutes; and subsequently to the first-stage heat treatment, subjecting the silicon single crystal substrate with the {110} plane exposed to a second-stage heat treatment at 1100-1200°C for 30-200 minutes in an oxidizing atmosphere; and then selectively etching the silicon single crystal substrate with the {110} plane exposed, and performing an OSF inspection of the {110} plane.

[0013] By using this method for evaluating silicon single crystal substrates, it is now possible to perform accurate and highly sensitive OSF inspection even on wafers whose principal surface is the {111} plane, for which OSF inspection was previously difficult.

[0014] In this case, the method for evaluating a silicon single crystal substrate may use, as the silicon single crystal substrate, a silicon single crystal wafer cut out from a silicon single crystal or a silicon single crystal slab for inspection.

[0015] The method for evaluating a silicon single crystal substrate according to the present invention is particularly suitable for evaluating such a silicon single crystal substrate.

[0016] At this time, the oxygen concentration of the silicon single crystal substrate is 8.0×10 17 atoms / cm 3 The above can be used as an evaluation method for a silicon single crystal substrate.

[0017] With such an oxygen concentration, an OSF nucleus of sufficient density is formed after the first stage heat treatment, making OSF inspection easier and highly sensitive. Effect of the Invention

[0018] As described above, in the evaluation method for silicon single crystal substrates according to the present invention, when performing an OSF inspection using a slab or wafer cut from a silicon single crystal having a {111} plane as the main surface, the slab or wafer is cleaved in a direction selected so that the {110} plane appears on the cleavage surface thereof, and a first stage heat treatment is performed at 900 to 1050°C for 30 to 540 minutes, followed by a second stage heat treatment at 1100 to 1200°C for 30 to 200 minutes in an oxidizing atmosphere, followed by selective etching, and then performing an OSF inspection on the {110} plane. This makes it possible to perform an accurate and highly sensitive OSF inspection even on wafers having a {111} plane as the main surface, which reduces the OSF inspection sensitivity, and thus makes it possible to prevent deterioration of device characteristics and a decrease in yield for customers. [Brief description of the drawings]

[0019] [Figure 1] 1 is an evaluation flow chart of the evaluation method and the embodiment of the silicon single crystal substrate according to the present invention. [Diagram 2] 3 shows the evaluation flow charts for Comparative Examples 1 and 2. [Diagram 3] 4 shows an optical microscope image of the etch pit of the {110} plane (cleavage plane) observed in Example 1-3. [Figure 4] 3 shows an optical microscope image of the {111} plane (main surface) observed in Comparative Examples 1 and 2. [Diagram 5] 110 is an optical microscope image of the {110} plane (cleavage plane) observed in Comparative Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] The present invention will be described in detail below, but the present invention is not limited to these.

[0021] As described above, there has been a demand for an evaluation method for silicon single crystal substrates that can perform OSF inspection accurately and with high sensitivity, even for silicon single crystals whose principal surface is the {111} plane.

[0022] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that a method for evaluating a silicon single crystal substrate, which comprises cleaving a silicon single crystal substrate having a {111} plane as a main surface to expose the {110} plane, subjecting the silicon single crystal substrate with the {110} plane exposed to a first-stage heat treatment at 900 to 1050°C for 30 to 540 minutes, and subsequently to the first-stage heat treatment, subjecting the silicon single crystal substrate with the {110} plane exposed to a second-stage heat treatment at 1100 to 1200°C for 30 to 200 minutes in an oxidizing atmosphere, and then selectively etching the silicon single crystal substrate with the {110} plane exposed, and inspecting the OSF of the {110} plane, makes it possible to perform an OSF inspection with high accuracy and sensitivity even on a wafer having a {111} plane as a main surface, for which the OSF inspection sensitivity is reduced, and have completed the present invention.

[0023] The following description will be given with reference to the drawings.

[0024] (Single crystal silicon substrate) In this specification, the term "silicon single crystal substrate" refers to a plate-like object cut from a silicon single crystal ingot, and there are no particular limitations on the thickness, shape, size (area of ​​the main surface), etc. The silicon single crystal substrate includes silicon single crystal wafers that are commonly distributed as semiconductor materials, and slabs for inspection cut from an ingot. The silicon single crystal substrate targeted by the silicon single crystal substrate evaluation method according to the present invention has a {111} plane as the main surface. The silicon single crystal substrate to be evaluated at this time is a substrate having an oxygen concentration of 8.0×10 17 atoms / cm 3 It is preferable to use an oxygen concentration of at least ASTM'79, because such an oxygen concentration allows OSF nuclei to be formed at a sufficient density after the first heat treatment, making OSF testing easier and more sensitive.

[0025] (Method of evaluating silicon single crystal substrates) Next, the evaluation method for silicon single crystal substrates according to the present invention will be described below. An evaluation flow diagram of the evaluation method for silicon single crystal substrates according to the present invention is shown in FIG.

[0026] (cleavage) First, a silicon single crystal substrate with a {111} surface as the main surface is cleaved to expose the {110} surface. When cleaving a silicon single crystal substrate with a main surface of the {111} plane, <110> Even if the cleavage is made in the direction, the {110} surface does not appear, and the {211} surface is exposed. Therefore, a direction is selected so that the {110} surface is exposed on the cleavage surface and cleaves. Specifically, <211> By cleaving in the direction, the {110} surface can be exposed.

[0027] (Heat treatment) Next, heat treatment is performed. The silicon single crystal substrate with the {110} plane exposed is subjected to a first heat treatment at 900-1050°C for 30-540 minutes, and a second heat treatment at 1100-1200°C for 30-200 minutes in an oxidizing atmosphere. In the first heat treatment, oxygen precipitates with relatively large grain sizes are grown to form OSF nuclei. For this reason, the atmosphere for the first heat treatment is not particularly limited. In the subsequent second heat treatment, the wafer surface is oxidized and interstitial silicon is injected from the interface between the oxide film and the wafer to form OSF. For this reason, the atmosphere for the second heat treatment is an oxidizing atmosphere. The injected interstitial silicon gathers around the OSF nuclei formed in the first heat treatment to form OSF. With such heat treatment, OSF grows sufficiently on the {110} plane that appears after cleavage, making it easy to inspect the OSF with an optical microscope after etching. If the temperature or time of the first and second heat treatment stages is lower or shorter than the above conditions, the diffusion distance of oxygen decreases, OSF nuclei and OSFs do not grow sufficiently, making observation with an optical microscope after etching difficult.

[0028] (OSF Inspection) After the heat treatment, the silicon single crystal substrate with the {110} plane exposed is selectively etched to inspect the OSF of the {110} plane. A known chemical can be used for the selective etching. Note that, since an oxide film is formed on the sample surface by the above heat treatment, it is preferable to remove the oxide film using hydrofluoric acid or the like before the selective etching.

[0029] The method of observing OSFs is not particularly limited as long as it is possible to measure the number (density) of OSFs so that samples can be compared and pass / fail judged. For example, any known method may be used, such as counting the number of OSFs observed in the field of view using an optical microscope. EXAMPLES

[0030] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0031] Example 1 Evaluations were carried out according to the evaluation flow shown in FIG. 1. Diameter 300mm with a main surface of {111} surface produced by the CZ method, oxygen concentration 8.0×10 17 atoms / cm 3 , using a silicon single crystal wafer in the Nv region, the {110} plane appears on the cleaved plane, <211> The wafer was cleaved in the axial direction. The cleaved wafer was subjected to a first heat treatment at 900℃ for 540 min in dry O2, followed by a second heat treatment at 1150℃ for 100 min in wet O2. The heat-treated wafer was immersed in dilute hydrofluoric acid to remove the oxide film formed during the heat treatment, and then selectively etched by immersing it in a mixed solution of hydrofluoric acid, nitric acid, and acetic acid. The cleaved {110} surface was then observed with an optical microscope to confirm the presence of etch pits.

[0032] Example 2 A sample was prepared under the same conditions as in Example 1, except that the first heat treatment was performed at 1000°C for 180 min in dry O2, followed by the second heat treatment at 1150°C for 100 min in wet O2. The cleavage surface, {110}, was observed with an optical microscope to confirm the presence of etch pits.

[0033] Example 3 A sample was prepared under the same conditions as in Example 1, except that the atmosphere in the first heat treatment was nitrogen. The {110} plane, which is the cleavage surface, was observed under an optical microscope to confirm the presence of etch pits.

[0034] Comparative Example 1 The evaluation was performed according to the evaluation flow shown in Figure 2. Using a silicon single crystal wafer with the {111} plane as the main surface, which was produced by the CZ method, similar to Example 1, a first stage heat treatment was performed at 900°C for 540 min in dry O2, followed by a second stage heat treatment at 1150°C for 100 min in wet O2. After the heat treatment, the wafer was immersed in dilute hydrofluoric acid to remove the oxide film formed by the heat treatment, and then selective etching was performed by immersing it in a mixed acid solution of hydrofluoric acid, nitric acid, and acetic acid. Then, the {111} plane, which was the main surface, was observed with an optical microscope to confirm etch pits.

[0035] Comparative Example 2 A sample was prepared under the same conditions as in Comparative Example 1, except that the first heat treatment was performed at 1000°C for 180 min in dry O2, followed by the second heat treatment at 1150°C for 100 min in wet O2. The main surface, {111}, was then observed with an optical microscope to confirm the presence of etch pits.

[0036] Comparative Example 3 A sample was prepared under the same conditions as in Example 1, except that the first heat treatment was performed at 800°C for 240 min in N2, followed by the second heat treatment at 1000°C for 960 min in dry O2. The cleavage surface, {110}, was then observed with an optical microscope to confirm the presence of etch pits.

[0037] The conditions for Examples 1-3 and Comparative Examples 1-3 are summarized in Table 1. Fig. 3 shows optical microscope images of etch pits on the {110} plane observed in Examples 1-3, Fig. 4 shows optical microscope images of the {111} plane observed in Comparative Examples 1 and 2, and Fig. 5 shows optical microscope images of the {110} plane observed in Comparative Example 3.

[0038] [Table 1]

[0039] As shown in Figure 3, linear etch pits were confirmed on the {110} plane in Examples 1-3, whereas no etch pits were confirmed on the {111} plane in Comparative Examples 1 and 2, which were subjected to the same heat treatment, as shown in Figure 4. In other words, while OSF inspection was impossible by observing the {111} plane, it was possible to perform OSF inspection accurately and with high precision by observing the {110} plane that appeared after cleavage.

[0040] In both Examples 1 and 3, OSFs grew sufficiently and were observed as etch pits. In other words, the atmosphere in the first heat treatment step, whether it was an acidic atmosphere or an inert atmosphere, did not affect the OSF inspection sensitivity.

[0041] As shown in Comparative Example 3, when the first heat treatment was performed at 800°C for 240 min in N2 and the second heat treatment was performed at 1000°C for 960 min in dry O2, OSF nuclei and OSFs did not grow sufficiently, and no OSFs were observed even on the {110} plane exposed by cleavage, as shown in Figure 5, making OSF inspection impossible.

[0042] As described above, according to the embodiment of the present invention, it is possible to perform accurate and highly sensitive OSF inspection even on wafers whose main surface is the {111} plane, for which OSF inspection has been conventionally difficult.

[0043] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention.

Claims

1. A method for evaluating a silicon single crystal substrate, comprising the steps of: a silicon single crystal substrate having a {111} plane as a main surface is cleaved to expose a {110} plane, and the silicon single crystal substrate with the {110} plane exposed is subjected to a first stage heat treatment at 900 to 1050° C. for 30 to 540 minutes, and subsequently to the first stage heat treatment, a second stage heat treatment at 1100 to 1200° C. for 30 to 200 minutes in an oxidizing atmosphere; Thereafter, the silicon single crystal substrate with the {110} plane exposed is selectively etched, and an OSF inspection of the {110} plane is performed.

2. 2. The method for evaluating a silicon single crystal substrate according to claim 1, wherein a silicon single crystal wafer cut out from a silicon single crystal or a silicon single crystal slab for inspection is used as the silicon single crystal substrate.

3. The silicon single crystal substrate has an oxygen concentration of 8.0×10 １７ atoms / cm ３ 3. The method for evaluating a silicon single crystal substrate according to claim 1, further comprising the steps of:

Images