Silicon epitaxial substrate and heat treatment method of silicon substrate

Abstract

To provide a Si{110} substrate in which a generation of a recess-shaped defect is suppressed, and a heat treatment method of the Si{110} substrate.SOLUTION: A silicon substrate has a main plane with a plane orientation of {110} and does not include a recess shaped defect with a length of 50 nm or more and 2000 nm or less in a longitudinal direction on a surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a silicon substrate and a method for heat treating a silicon substrate. [Background technology]

[0002] Instead of the fin structure currently used in logic ICs, GAA (Gate-All-Around) structures and CFETs (Complementary Field Effect Transistors) stacking NMOS and CMOS have been proposed for next-generation semiconductors and are being actively researched and developed. In this regard, the use of the (110) plane orientation of silicon (hereinafter also referred to as "Si"), one of several available, is being considered as a method for improving hole mobility (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-091887 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-100596 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-088045 [Patent Document 4] Japanese Patent Application Laid-Open No. 2014-239184 [Patent Document 5] Japanese Patent Application Laid-Open No. 2008-091891 [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-253797 [Non-patent literature]

[0004] [Non-Patent Document 1] The 1st Workshop of the Industry-Academia Collaboration Committee on Crystal Growth, Processing, and Evaluation of Semiconductors of the Japan Society of Applied Physics: "Crystal Technology Supporting the Revival of Semiconductors" [Non-patent document 2] Yamada et al., "Fabrication of Si(110)-16×2 Single Domain Surface," Surface Science, 29(7), 401(2008) [Non-patent document 3] Miyaji et al., "Observation of Si(110) reconstructed surface by ultra-high vacuum non-contact atomic force microscopy," Journal of the Japan Institute of Metals, 72(4), 290(2008) Summary of the Invention [Problem to be solved by the invention]

[0005] However, problems with Si(110) substrates have been pointed out, such as high surface roughness and haze (Non-Patent Document 1). Haze, also known as the degree of cloudiness of the surface, is a measure of surface roughness expressed as the degree of light scattering, with higher haze indicating a rougher surface. Furthermore, the most stable structure of the Si(110) outermost surface has only been identified relatively recently (Non-Patent Documents 2 and 3).

[0006] Furthermore, as described in Non-Patent Documents 2 and 3, in the surface structure of Si(110), the most stable structure, 16x2 domain (a region with a single structural unity), is said to undergo a phase transition depending on the temperature, as shown in Figure 2, and the structure changes in the range of 600 to 800°C.

[0007] This structural change also leads to the phenomenon of step bunching. Step bunching is a phenomenon in which atomic-level steps exist on the wafer surface of semiconductor materials such as silicon, and when the atoms on the surface move due to heat treatment or other processes, these steps gather together, forming larger steps. Furthermore, for example, SiGe, which is stacked in GAA and CFETs, is often processed at temperatures exactly within this range, making it easy to imagine that this makes understanding the surface structure even more difficult. The phenomenon associated with this phase change creates a large bias, hindering our understanding of other phenomena (such as defects and contamination behavior).

[0008] This unique top surface structure of the Si(110) surface also affects the surface structure after etching. The step edges of the 16x2 domain surface structure are not single-atom structures like Si(100), but have a two-atom step. When the energy of the reaction system is low (equilibrium reaction), the reaction proceeds at the top surface atoms, resulting in a linear structure of the surface after etching surrounded by the first-nearest-neighbor Si(111) atoms. On the other hand, when the energy of the reaction system is high, the top surface and atoms below it become involved in the reaction, resulting in a square shape surrounded by the second-nearest-neighbor Si(111) atoms.

[0009] For Si(110) with such a surface state, Patent Document 1 discloses a method for reducing surface roughness by tilting the orientation during epitaxial growth. Patent Document 2 discloses the same epitaxial growth method, but with the specification of the cooling rate and surface protection. Furthermore, Patent Document 3 discloses a method for similarly reducing surface roughness by specifying the surface orientation during crystal growth rather than during epitaxial growth. Patent Document 4 discloses polishing the epitaxial surface. Patent Document 5 discloses a technology that differs from Patent Document 1 in the LPD detection size. Furthermore, Patent Document 6 discloses a method for reducing surface roughness that forms in a circular ring shape around the periphery, even when the epitaxial film thickness is very thick at 30 μm or more, by setting the off-angle during slicing to 0.5 to 7°.

[0010] On the other hand, the inventors have clarified that in addition to defects caused by such surface roughness and crystal defects, Si(110) substrates, unlike Si(100) substrates, have a special structure with a most stable structure of 16x2, and therefore have unstable regions (referred to as "disordered regions" in Non-Patent Document 2) adjacent to the most stable structure 16x2. From these regions, minute protrusion-like defects are generated by heat treatments such as hydrogen baking before epitaxial growth and epitaxial growth, and form the in-plane distribution of the Si(110) substrate, and have presented countermeasures for this.

[0011] As described above, the surface of a Si(110) substrate has a very complex shape, and various methods have been published to reduce the surface roughness. However, as mentioned above, the Si(110) substrate, in particular, differs from the Si(100) substrate in that its most stable structure is a special 16x2 structure. Therefore, the inventors discovered that there are unstable regions adjacent to the most stable 16x2 structure, and that relatively large depression-like defects are generated from these regions by performing heat treatments such as hydrogen baking before epitaxial growth or epitaxial growth.

[0012] The present invention has been made to solve the above problems, and aims to provide a Si{110} substrate and a heat treatment method for a Si{110} substrate in which the generation of pit-like defects is suppressed. [Means for solving the problem]

[0013] The present invention has been made to achieve the above-mentioned object, and provides a silicon substrate characterized in that the principal surface has a plane orientation of {110} and does not contain depression-like defects with a longitudinal length of 50 nm or more and 2000 nm or less on the surface.

[0014] Such a silicon substrate is of high quality with no pit-like defects and improved surface roughness, and therefore, device characteristics can be improved.

[0015] In this case, the silicon substrate may have a principal surface {110} with an off-angle of 0.23° or more.

[0016] This further improves the surface roughness and further improves the device characteristics.

[0017] The present invention has also been made to achieve the above-mentioned object, and provides a heat treatment method for a silicon substrate having a principal surface with a plane orientation of {110}, the heat treatment method comprising: a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C; a heat treatment step of performing heat treatment at the heat treatment temperature; and a cooling step of cooling the silicon substrate to a temperature lower than 570°C, wherein the sum of the products of the temperature and time of the silicon substrate during the period from when the temperature of the silicon substrate reaches 570°C in the heating step to when the temperature of the silicon substrate reaches 570°C in the cooling step is 60,000 (°C·sec) or less.

[0018] According to this method of heat treating a silicon substrate, it is possible to suppress the generation of depression-like defects.

[0019] In this case, the off angle of the main surface of the silicon substrate can be set to 0.23° or more.

[0020] This makes it possible to further suppress the generation of depression-like defects. [Effects of the Invention]

[0021] As described above, the silicon substrate of the present invention is of high quality, free from pit-like defects and having improved surface roughness, which leads to improved device characteristics. Furthermore, the heat treatment method for a silicon substrate of the present invention makes it possible to suppress the generation of pit-like defects. [Brief explanation of the drawings]

[0022] [Figure 1] The results of AFM measurement of the surface of the Si(110) substrate of the example are shown. [Figure 2] 1 shows the results of AFM measurement of the surface of the Si(110) substrate of Comparative Example 1. [Figure 3] 1 shows the results of AFM measurement of the surface of the Si(110) substrate of Comparative Example 2. [Figure 4] 1 shows a cross-sectional structure diagram of an example of a Si(110) (Si{110}) substrate. DETAILED DESCRIPTION OF THE INVENTION

[0023] The present invention will be described in detail below, but the present invention is not limited thereto.

[0024] As described above, there has been a demand for a Si{110} substrate and a method of heat treating a Si{110} substrate that suppresses the generation of pit-like defects.

[0025] As a result of extensive research into the above-mentioned problems, the present inventors have found that a silicon substrate having a principal surface with a plane orientation of {110} and free of dent-like defects having a longitudinal length of 50 nm or more and 2000 nm or less on the surface can provide a high-quality silicon substrate free of dent-like defects and improved surface roughness, thereby enabling improved device characteristics to be achieved, and have completed the present invention.

[0026] As a result of extensive research into the above-mentioned problems, the present inventors have found that it is possible to suppress the generation of dent-like defects by a heat treatment method for a silicon substrate having a principal surface with a plane orientation of {110}, the heat treatment method comprising a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at that heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C, wherein the sum of the products of the temperature and time of the silicon substrate during the period from when the temperature of the silicon substrate reaches 570°C in the heating step to when the temperature of the silicon substrate reaches 570°C in the cooling step is set to 60,000 (°C·sec) or less, and have completed the present invention.

[0027] [Silicon substrate] In the present invention, a plane orientation of {110} includes a plane equivalent to (110), and also includes a plane having an off angle of 0.23 to 0.5 degrees from the {110} plane.

[0028] Fig. 4 shows a cross-sectional structure of an example of a Si(110) substrate. As shown in Fig. 4, a Si(110) substrate 2 has a surface 3 (the outermost surface of the surface stable structure). It is on surface 3 that pit-like defects with longitudinal lengths of 50 nm to 2000 nm (hereinafter simply referred to as "pit-like defects"), which are the subject of the present invention, exist.

[0029] When a Si(110) substrate is subjected to hydrogen annealing before epitaxial growth, or when epitaxial growth (silicon, SiGe, etc.) or heat treatment is performed, depression-like defects such as those shown in Figure 2 may occur.

[0030] As described in Patent Document 2 and Non-Patent Documents 2 and 3, this defect is generated due to differences in the stable structure of Si(110). In particular, the investigations and research of this researcher revealed that such long defects can exist only when stable structures such as 16 × 2 domains are connected.

[0031] To generate such long defects, atomic interactions must occur over a long distance. In other words, when considering a pit-like defect, an interaction of (surface energy) x (thermal energy) is required.

[0032] As shown in FIG. 4, the silicon {110} substrate 2 of the present invention does not contain such depression-like defects on the surface 3 of the surface stable structure.

[0033] In addition, pit defects are affected not only by heat treatment conditions but also by the off-angle of the substrate's main surface. In other words, when considering pit defects, understanding that it is an interaction between (surface energy) and (thermal energy) can help prevent defects.

[0034] Here, the surface energy corresponds to the step-terrace width formed by the off-angle of the silicon (110) substrate, and as the off-angle decreases and the terrace width decreases, the surface energy becomes relatively large.

[0035] In the present invention, the off-angle of the main surface of the silicon {110} substrate 2 can be 0.23° or more. The upper limit of the off-angle is not particularly limited, but may be 0.5°.

[0036] Such silicon substrates have improved surface roughness and device characteristics. This is because the large off-angle causes the ES effect (Ehrlich-Schwebel effect: wider terraces allow for greater atomic diffusion, suppressing step motion), which suppresses the generation of defects.

[0037] [Silicon substrate heat treatment method] The heat treatment method for a silicon {110} substrate according to the present invention includes a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at the heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C.

[0038] Here, the heat treatment refers to a heat treatment in which the silicon substrate is treated at a temperature of 570° C. or higher, and includes annealing, epitaxial growth, and other layer formation processes. The heat treatment does not have to be performed at a constant temperature.

[0039] To reduce the above-mentioned pit-like defects, it is necessary to keep the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reaches 570°C in the heating process to the time when the silicon substrate temperature reaches 570°C in the cooling process to 60,000 (°C·sec) or less.

[0040] That is, when a Si(110) substrate with an off-angle of 0.26° on the main surface was subjected to hydrogen annealing at a temperature of 1080°C for 60 seconds in the heat treatment process, a depression-shaped defect with a longitudinal length of 1 μm was generated, as shown in Figure 2. In this case, the sum of the product of the temperature and time of the silicon substrate from the time when the temperature of the silicon substrate reached 570°C in the heating process to the time when the temperature of the silicon substrate reached 570°C in the cooling process was 65000 (°C·sec).

[0041] Next, when a Si(110) substrate with the same principal surface off-angle of 0.26° as above was subjected to hydrogen annealing at a temperature of 900°C for 60 seconds in the heat treatment process, no pit-like defects were generated, as shown in Figure 1. In this case, the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reached 570°C in the heating process to the time when the silicon substrate temperature reached 570°C in the cooling process was 57,000 (°C·sec).

[0042] In this way, by taking into consideration the heat treatment temperature and time, and performing heat treatment so that the sum of the product of the silicon substrate temperature and time during the period from when the silicon substrate temperature reaches 570°C in the heating process to when the silicon substrate temperature reaches 570°C in the cooling process is 60,000 (°C·sec) or less, it is possible to suppress the generation of pit-like defects.

[0043] The lower limit of the sum of the products of the temperatures and times is not particularly limited, but may be 5400 (°C·sec).

[0044] In the heat treatment method for a Si{110} substrate according to the present invention, the off-angle of the main surface of the silicon substrate can be set to 0.23° or more. This makes it possible to further suppress the generation of pit-like defects. The upper limit of the off-angle is not particularly limited, but may be set to 0.5°. [Example]

[0045] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0046] (Example) A silicon single crystal substrate with a diameter of 300 mm, a (110) orientation, boron doping, a resistivity of 10 Ω·cm, and an off-angle of 0.26° to the (110) major surface was prepared and subjected to hydrogen annealing at a temperature of 900°C for 60 seconds at atmospheric pressure. During this time, the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reached 570°C in the heating process to the time when the silicon substrate temperature reached 570°C in the cooling process was 57,000 (°C·sec).

[0047] After this, the angle of view was adjusted so that one side of the acquired image was 1 μm, and AFM measurement was performed. The measurement results are shown in Figure 1. As shown in Figure 1, no dent-like defects were observed on the surface of the silicon substrate.

[0048] (Comparative Example 1) The same silicon single crystal substrate as in the example was prepared and subjected to hydrogen annealing at 1080°C for 60 seconds at atmospheric pressure. During this process, the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reached 570°C in the heating process to the time when the silicon substrate temperature reached 570°C in the cooling process was 65000 (°C·sec).

[0049] The angle of view was then adjusted so that one side of the acquired image was 1 μm, and AFM measurement was performed. The measurement results are shown in Figure 2. A depression-like defect with a longitudinal length of 1 μm, as shown in Figure 2, was observed on the surface of the silicon substrate.

[0050] (Comparative Example 2) The same silicon single crystal substrate as in the example was prepared, except that the off-angle of the main surface was 0.24°, and this was subjected to hydrogen annealing at a temperature of 1030°C for 60 seconds at atmospheric pressure. During this time, the sum of the product of the silicon substrate temperature and time from the time when the silicon substrate temperature reached 570°C in the heating process to the time when the silicon substrate temperature reached 570°C in the cooling process was 65000 (°C·sec).

[0051] After this, the angle of view was adjusted so that one side of the acquired image was 1 μm, and AFM measurement was performed. The measurement results are shown in Figure 3. A 0.8 μm depression-like defect, as shown in Figure 3, was observed on the surface of the silicon substrate.

[0052] As described above, according to the examples of the present invention, the heat treatment of the Si(110) substrate can be performed without generating pit-like defects on the surface, and a Si(110) substrate without pit-like defects of 50 nm to 2000 nm on the surface can be obtained.

[0053] The present invention is not limited to the above-described embodiments, which are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that provides similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0054] 1...pit-like defect, 2...Si(110) (Si{110}) substrate, 3...Surface (surface stable structure).

Claims

1. A silicon substrate having a principal surface with a {110} plane orientation, characterized in that the silicon substrate does not contain depression-like defects having a longitudinal length of 50 nm or more and 2000 nm or less on the surface.

2. 2. The silicon substrate according to claim 1, wherein the main surface has a plane orientation of {110} and has an off-angle of 0.23° or more.

3. A method for heat treating a silicon substrate having a principal surface with a {110} plane orientation, comprising the steps of: The heat treatment method includes a heating step of heating the silicon substrate to a heat treatment temperature higher than 570°C, a heat treatment step of performing heat treatment at the heat treatment temperature, and a cooling step of cooling the silicon substrate to a temperature lower than 570°C, A heat treatment method for a silicon substrate, characterized in that the sum of the product of the temperature and time of the silicon substrate during the period from the time when the temperature of the silicon substrate reaches 570°C in the heating step to the time when the temperature of the silicon substrate reaches 570°C in the cooling step is 60,000 (°C·sec) or less.

4. 4. The method for heat treating a silicon substrate according to claim 3, wherein the off-angle of the main surface of the silicon substrate is set to 0.23° or more.

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