Single-crystal silicon substrate and method for producing single-crystal silicon substrate

Abstract

The present invention relates to a single-crystal silicon substrate characterized in that the plane orientation is (110) and the surface of the single-crystal silicon substrate has a surface stable structure of 1×1 in a room-temperature environment. Thus, the haze of a silicon (110) substrate is reduced, and a single-crystal silicon substrate having a stable surface structure and a method for producing the single-crystal silicon substrate are provided.

Description

Silicon single crystal substrate and method for manufacturing the same

[0001] The present invention relates to a silicon single crystal substrate and a method for manufacturing the silicon single crystal substrate.

[0002] As an alternative to the Fin structure currently used in logic ICs, GAA (Gate All Around) and CFET (Complementary Field Effect Transistor), which stacks NMOS and CMOS, have been proposed for the next generation and beyond, and are being actively researched and developed. In this case, the use of a silicon (hereinafter also referred to as Si) substrate with a (110) surface orientation is considered as a method for improving hole mobility (Non-Patent Document 1).

[0003] However, problems with silicon (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 silicon (110) outermost surface has only been identified relatively recently (Non-Patent Documents 2 and 3).

[0004] According to the descriptions in Non-Patent Documents 2 and 3, the 16x2 domain, which is the most stable surface stable structure, undergoes a phase transition depending on the temperature, and the structure changes in the range of 900 K (627°C) to 1043 K (770°C), as shown in Figure 2 (hereinafter referred to as the 600-800°C range). This temperature range, for example, is used in hydrogen baking to grow a silicon epitaxial layer (hereinafter simply referred to as epi or epitaxial), and the subsequent silicon epi exceeds 1000°C. Therefore, the stable surface stable structure 1x1 is initially formed at high temperatures. However, during the subsequent cooling, the phase transition occurs as the temperature gradually passes through the 600-800°C range, and the surface structure changes depending on the time of passage. For example, SiGe, which is stacked in GAA and CFETs, often uses exactly this temperature range, making it even more difficult to understand the surface structure.

[0005] This unique surface structure of the silicon (110) surface also affects the surface structure after etching. The step edges of the 16x2 surface structure are not monoatomic like silicon (100), but have a two-atom step. As a result, when the energy of the reaction system is low (equilibrium reaction), the reaction proceeds with the atoms on the outermost surface, resulting in a linear structure of the surface after etching surrounded by silicon (111) atoms that are first-nearest to the surface. On the other hand, when the energy of the reaction system is high, the atoms on the outermost surface and below are also involved in the reaction, resulting in a square shape surrounded by silicon (111) atoms that are second-nearest to the surface.

[0006] For such silicon (110) surface conditions, Patent Document 1 discloses a method for reducing surface roughness by tilting the orientation during epitaxial growth. Patent Document 2 discloses the regulation of the cooling rate and surface protection. Furthermore, Patent Document 3 discloses a method for similarly reducing surface roughness by regulating the plane orientation during crystal growth rather than epitaxial growth. Patent Document 4 discloses polishing the epitaxial surface. Furthermore, Patent Document 5 discloses a combination of Patent Documents 1 and 3.

[0007] Japan Society of Applied Physics, Industry-Academia Collaboration Committee on Crystal Growth, Processing and Evaluation of Semiconductors, 1st Workshop "Crystal Technology Supporting the Revival of Semiconductors" Yamada et al., "Fabrication of Si(110)-16x2 Single Domain Surface", Surface Science, 29(7), 401 (2008) Miyaji et al., "Observation of Si(110) Reconstructed Surface by Ultra-High Vacuum Non-Contact Atomic Microscopy", Journal of the Japan Institute of Metals, 72(4), 290 (2008)

[0008] JP 2008-091887 A JP 2006-100596 A JP 2008-088045 A JP 2014-239184 A JP 2008-091891 A

[0009] As described above, the surface of a silicon (110) substrate has a very complex shape, and various methods have been disclosed to alleviate the surface roughness. However, unlike a silicon (100) substrate, the most stable surface structure of a silicon (110) substrate is a special 16x2 structure (a structure with a step of two atoms). Furthermore, the structural transition temperature is 600-800°C, and during processes that pass through this temperature range, such as epitaxial growth, the surface structure changes, resulting in unavoidable haze.

[0010] The present invention has been made in consideration of the above-mentioned problems of the conventional technology, and has an object to provide a silicon single crystal substrate that suppresses haze on a silicon (110) substrate and has a stable surface structure, and a method for manufacturing the silicon single crystal substrate.

[0011] In order to solve the above problems, the silicon single crystal substrate of the present invention has a plane orientation of (110), and the surface of the silicon single crystal substrate has a stable surface structure of 1x1 in a room temperature environment.

[0012] In such a silicon (110) substrate with a stable surface structure of 1 × 1 in a room temperature environment, firstly, the stable surface structure is 1 × 1, and therefore haze is suppressed, unlike a structure with a step of two atoms such as a stable surface structure of 16 × 2. Secondly, because it is in a room temperature environment, it is far from the structural transition temperature (600 to 800°C) of the silicon (110) substrate, and the structure is less likely to change, resulting in a stable surface structure.

[0013] In addition, the method for manufacturing a silicon single crystal substrate of the present invention is a method for forming a surface stable structure 1x1 in a room temperature environment by preparing a silicon single crystal substrate having a (110) plane orientation and rapidly annealing the silicon single crystal substrate.

[0014] In this method of forming a surface stabilized structure 1x1 in a room temperature environment by rapid annealing, first, the rapid annealing is a method of rapidly annealing only the outermost surface of the substrate, rapidly raising the temperature of only the outermost surface of the substrate, without raising the temperature of areas other than the outermost surface of the substrate, thereby allowing only the outermost surface of the substrate to reach the desired temperature in an extremely short time, thereby forming the surface stabilized structure 1x1. Because it is a surface stabilized structure 1x1, haze can be suppressed, unlike a structure having a two-atom step such as a surface stabilized structure 16x2. Next, since the rapid annealing is performed in a room temperature environment, areas other than the outermost surface of the substrate are maintained at room temperature, and after the rapid annealing is completed, the outermost surface of the substrate can be returned to room temperature in an extremely short time. Therefore, both during heating and cooling after the rapid annealing, the temperature of the outermost surface of the substrate can instantly pass through the structural transition temperature (600-800°C), making it difficult for the structure to change and allowing for a stable surface structure.

[0015] The silicon single crystal substrate of the present invention is a silicon (110) substrate with a surface stable structure of 1 x 1 in a room temperature environment, and unlike a structure with a two-atom step such as a surface stable structure of 16 x 2, haze is suppressed. Secondly, because it is in a room temperature environment, it is far from the structural transition temperature (600-800°C) of the silicon (110) substrate, and the structure is less likely to change, resulting in a stable surface structure.

[0016] Furthermore, the method for producing a silicon single crystal substrate of the present invention is a method for forming a surface stable structure 1x1 in a room temperature environment by rapid annealing, and unlike a structure having a step of two atoms, such as a surface stable structure 16x2, haze can be suppressed. Furthermore, both during heating for rapid annealing and during cooling after completion of the rapid annealing, the temperature of the outermost surface of the substrate can instantaneously pass through the structural transition temperature (600 to 800°C), making it possible to obtain a surface structure that is less likely to change and is stable.

[0017] 1 is a schematic diagram of a silicon single crystal substrate in a first embodiment of the present invention; FIG. 2 is a schematic diagram showing the relationship between the surface temperature of a silicon (110) substrate and the surface stable structure; FIG. 3 is a flow diagram of a method for manufacturing a silicon single crystal substrate in a first embodiment of the present invention; FIG. 4 is a schematic diagram of a conventional silicon single crystal substrate;

[0018] The present invention will be described in detail below, but the present invention is not limited thereto.

[0019] As described above, there has been a need to provide a silicon single crystal substrate that suppresses haze on a silicon (110) substrate and has a stable surface structure, and a method for manufacturing the silicon single crystal substrate.

[0020] As a result of extensive research into the above-mentioned problems, the inventors discovered that the stable surface structure does not undergo a phase change by instantaneously passing through the temperature range of 600 to 800°C, which is the structural transition temperature of a silicon (110) substrate, and thus completed the present invention.

[0021] That is, the silicon single crystal substrate of the present invention has a plane orientation of (110), and the surface of the silicon single crystal substrate has a stable surface structure of 1x1 in a room temperature environment.

[0022] In addition, the method for manufacturing a silicon single crystal substrate of the present invention is a method for forming a surface stable structure 1x1 in a room temperature environment by preparing a silicon single crystal substrate having a (110) plane orientation and rapidly annealing the silicon single crystal substrate.

[0023] Specifically, as a means of obtaining a stable surface with little haze, a surface stable structure 1x1 is formed at high temperature, and rapid annealing (flash lamp annealing) is performed to instantly pass through the structural transition temperature (600-800°C).

[0024] Annealing here is usually done to activate dopants introduced by ion implantation and to repair defects, but conventional annealing using a general halogen lamp takes several seconds to heat up, and the steep profile formed by ion implantation can be disrupted by dopant diffusion during this time. Lowering the annealing temperature can suppress diffusion, but this has the disadvantage of insufficient activation and defect repair, which are the original purposes.

[0025] On the other hand, if flash lamp annealing using a xenon flash lamp is used as rapid annealing, this dilemma can be resolved by applying heat only to the substrate surface in an extremely short time (on the order of milliseconds). This method is used in the present invention.

[0026] By using such flash lamp annealing, it takes only a few milliseconds to heat the surface temperature of the substrate from room temperature (e.g., 25°C) to approximately 1,200°C, and after heating is complete, it also takes a short time to return from approximately 1,200°C to room temperature. This allows the temperature of the outermost surface of the substrate to instantly pass through the structural transition temperature (600-800°C), providing no time for structural change and maintaining an extremely stable surface structure. In this case, a surface stable structure 1x1 is formed at approximately 1,200°C, and the surface stable structure 1x1 can be maintained even when cooled to room temperature. Furthermore, a surface stable structure 1x1 can suppress haze, unlike a structure with a two-atom step such as a surface stable structure 16x2.

[0027] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0028] 1 is a schematic diagram of a silicon single crystal substrate according to a first embodiment of the present invention. The silicon single crystal substrate 1 has a (110) plane orientation and has two stable surface structures 1x1 on its surface in a room temperature environment. More specifically, the substrate surface alone is heated to approximately 1,200°C by rapid annealing (flash lamp annealing) for an extremely short time of a few milliseconds to form the stable surface structures 1x1, and then the substrate surface alone is returned to room temperature in an extremely short time.

[0029] On the other hand, Figure 4 is a schematic diagram of a conventional silicon single crystal substrate. Using a conventional annealing method, the entire substrate was heated to 1,200°C in an epitaxial furnace over a long period of time (several seconds or more), and then returned to room temperature over a similarly long period of time. In this case, only the surface stable structure 1x1 shown in Figure 1 was formed in the 1,200°C environment of the epitaxial furnace. However, because it took a long time to return to a room temperature environment, the surface structure underwent a phase change as it passed through the structural transition temperature (600-800°C), and not only the surface stable structure 1x1 shown in Figure 2 but also the surface stable structure 16x2 shown in Figure 3 and the surface stable structure (17,15,1)2x1 shown in Figure 4 were formed. The presence of various structures on the surface resulted in increased haze.

[0030] Figure 2 is a schematic diagram showing the relationship between the surface temperature of a silicon (110) substrate and the stable surface structure. This diagram summarizes the information from Non-Patent Documents 2 and 3, as well as what has become clear through further investigation. Silicon (110) is prone to form the stable surface structure 16x2 at low temperatures below 900 K (627 °C), the stable surface structure 1x1 at high temperatures above 1043 K (770 °C), and the stable surface structure (17,15,1)2x1 in the temperature range from 900 K (627 °C) to 1043 K (770 °C). For example, the stable surface structure (17,15,1)2x1 is formed at 1003 K (730 °C).

[0031] Among these, the stabilized surface structure 16x2 has a step of two atoms, and the stabilized surface structure (17,15,1)2x1 is said to have a stepped structure. The stabilized surface structure 1x1, which has fewer steps, is more preferable. The stabilized surface structure 1x1 can most effectively suppress haze.

[0032] According to Figure 2, the surface stable structure 1x1 is formed at a temperature of 1043 K (770°C) or higher, so although the explanation above using Figures 1 and 4 used an example of approximately 1,200°C, this is not limited to this and the temperature can be selected arbitrarily within the range of 770°C or higher.

[0033] FIG. 3 is a flow diagram of a method for manufacturing a silicon single crystal substrate according to the first embodiment of the present invention.

[0034] First, in step S1, a silicon single crystal substrate with a (110) plane orientation is prepared.

[0035] Next, in step S2, the silicon single crystal substrate is rapidly annealed to form a surface stabilized structure 1x1 at room temperature. This is a method in which only the outermost surface of silicon (110) is heated instantaneously by rapid annealing, forming the surface stabilized structure 1x1 at high temperature, and then rapid cooling is performed to suppress the structural transition.

[0036] Here, as a method for this rapid annealing, flash lamp annealing using a flash lamp filled with a rare gas such as xenon can be used. This flash lamp has a radiant energy of, for example, several tens of J / cm. ２ The method can be such that the above high energy is irradiated as pulsed light of 0.1 to 100 milliseconds.

[0037] The room temperature is expected to be between 0 and 40°C depending on the season, and can be kept at, for example, 25°C using air conditioning equipment.

[0038] Furthermore, based on Non-Patent Documents 2 and 3 and findings gained through further research, the surface temperature of silicon (110) when forming the surface stabilized structure 1x1 should be 850°C or higher, but can also be set to, for example, 1,200°C or lower, specifically 1,200°C.

[0039] As described above, within these conditions, the heating and cooling times are only a few milliseconds, and the structural transition temperature (600-800°C) can be instantaneously reached. As a result, a silicon single crystal substrate with a stable 1x1 surface structure can be produced in a room temperature environment.

[0040] EXAMPLES The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited thereto.

[0041] [Example 1] Silicon single crystal substrates with a diameter of 300 mm, a plane orientation of (110), doped with boron, and a resistance of 10 Ω cm were prepared, and 25 substrates were subjected to flash lamp annealing in a room temperature environment. Here, flash lamp energy: 30 J / cm ２・Flash lamp pulse width: 5 milliseconds (1 pulse) ・Surface temperature of single crystal silicon substrate: 1,200°C on average ・Room temperature: 25°C ・Time to pass through the structural transition temperature (600-800°C): 5 milliseconds on average

[0042] The haze was then measured using an optical defect inspection device (KLA-Tencor's SurfScan-SP3, hereinafter also referred to as KLA / SP-3). The haze values ​​from the first to 25th sheets were stable at a low value between 0.7 and 0.8 ppm. Examination with an atomic force microscope (AFM) revealed a surface stable structure of 1x1.

[0043] [Comparative Example 1] Silicon single crystal substrates with a diameter of 300 mm, a plane orientation (110), doped with boron, and a resistance of 10 Ω cm were prepared, and 25 substrates were subjected to hydrogen annealing in an epitaxial furnace at 1,140°C. Here, the following conditions were met: Surface temperature (and overall temperature) of the single crystal silicon substrate: 1,140°C Room temperature: 25°C Time to pass through the structural transition temperature (600-800°C): 10 seconds on average

[0044] Thereafter, the haze was measured using a KLA / SP-3. The haze values ​​for the first to 25th sheets were 1 to 2.5 ppm, which were larger than those in Example 1 and tended to vary more widely. When examined with an AFM, the surface stabilized structure was 16 x 2.

[0045] As described above, it was found that Example 1 had a lower and more stable haze value than Comparative Example 1.

[0046] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to 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.

Claims

1. A silicon single crystal substrate having a (110) surface orientation and a surface stable 1x1 structure at room temperature.

2. A method for manufacturing a silicon single crystal substrate, comprising: preparing a silicon single crystal substrate having a (110) surface orientation; and rapidly annealing the silicon single crystal substrate to form a 1x1 surface stable structure in a room temperature environment.

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