Heat treatment method for silicon substrate

Abstract

To provide a method for suppressing / controlling roughness of a principal surface of an Si{110} substrate, especially, a defect in a fine projection shape.SOLUTION: The present invention relates to a heat treatment method that performs film forming heat treatment for forming a film on a principal surface of a silicon substrate, the principal surface having a plane direction {110}. The heat treatment method includes the processes of: feeding the silicon substrate having the plane direction {110} on the principal surface in a heat treatment furnace of 540°C in in-furnace temperature; raising the temperature of the silicon substrate while forming a passivation film on the principal surface of the silicon substrate fed in the heat treatment furnace; and performing the film forming heat treatment on the silicon substrate after raising the temperature.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to 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, the most stable structure of the Si(110) surface, a 16x2 domain (a structurally cohesive region), undergoes a phase transition depending on the temperature. Figure 3 is a schematic diagram showing the relationship between the surface temperature of a silicon (110) substrate and the most stable surface structure. As shown in Figure 3, the most stable surface structure of a silicon (110) substrate is believed to change in the range of approximately 600 to 800°C. For example, hydrogen baking to grow a silicon epitaxial (hereinafter simply referred to as "epitaxial") layer and the subsequent silicon epitaxial growth exceed 1000°C, so the surface structure initially becomes a 1x1 structure. However, at this temperature range, a phase change occurs during cooling, and the surface structure also changes depending on the time spent cooling.

[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 specifying 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 that is the measurement target. 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 (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 in which the most stable structure is 16 × 2 domains, and therefore there are unstable regions (referred to as "disordered regions" in Non-Patent Document 2) adjacent to the most stable 16 × 2 domain structure, and that minute protrusion-like defects are generated from these regions by heat treatments such as hydrogen baking before epitaxial growth and epitaxial growth, thereby forming the in-plane distribution of defects on 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 surface roughness. As mentioned above, Patent Document 2 discloses that surface roughness can be reduced by forming a passivation film at a temperature of 720°C or higher during cooling after epitaxial growth. However, even if surface roughness is reduced by forming a passivation film after epitaxial growth, in actual device processes using wafers, this passivation film must be removed before film formation, and the effect of this method is limited. Therefore, measures are required for the actual process, especially during film formation.

[0012] The present invention has been made to solve the above problems, and aims to provide a method for suppressing and controlling the roughness of the main surface, particularly micro-protrusion defects, on a Si{110} substrate during film formation. [Means for solving the problem]

[0013] The present invention has been made to achieve the above-mentioned object, and provides a heat treatment method for performing a film-forming heat treatment to form a film on a main surface of a silicon substrate having a plane orientation of {110}, the heat treatment method comprising the steps of: loading the silicon substrate having a plane orientation of {110} on the main surface into a heat treatment furnace at a furnace temperature of 540°C or less; raising the temperature of the silicon substrate while forming a passivation film on the main surface of the silicon substrate loaded into the heat treatment furnace; and performing a film-forming heat treatment on the silicon substrate after the temperature is raised.

[0014] This heat treatment method for silicon substrates makes it possible to prevent dislocations from the most stable structure of the Si{110} surface, and to produce high-quality silicon {110} substrates with uniform surfaces and films formed thereon without the generation of in-plane step bunching or protrusion-like defects.

[0015] In this case, the passivation film can be any one of an oxide film, a nitride film, and an oxynitride film.

[0016] This allows the production of a high-quality silicon {110} substrate with a more uniform surface and film formation without the generation of step bunching or protruding defect distribution within the surface. [Effects of the Invention]

[0017] As described above, the heat treatment method for silicon substrates of the present invention makes it possible to produce high-quality silicon {110} substrates with uniform surfaces and films formed thereon without generating step bunching or protruding defect distribution within the surface. [Brief explanation of the drawings]

[0018] [Figure 1] 1 shows AFM images of the substrate surface of Example 1 (measurement area: (a) 1 μm square, (b) 0.1 μm square, (c) 0.8 μm square). [Figure 2] 1 shows AFM images of the substrate surface of Example 2 (measurement area: (a) 1 μm square, (b) 0.1 μm square, (c) 0.8 μm square). [Figure 3] FIG. 1 is a schematic diagram showing the relationship between the surface temperature of a Si(110) substrate and the most stable surface structure. [Figure 4] A cross-sectional structure diagram of a Si(110) single crystal substrate is shown. [Figure 5] 1 shows AFM images of the substrate surface of Comparative Example 1 (measurement area: (a) 1 μm square, (b) 0.1 μm square, (c) 0.8 μm square). [Figure 6]1 shows AFM images of the substrate surface of Comparative Example 2 (measurement area: (a) 1 μm square, (b) 0.1 μm square, (c) 0.8 μm square). DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention will be described in detail below, but the present invention is not limited thereto.

[0020] As mentioned above, there has been a demand for a method to suppress and control the roughness of the main surface of a Si{110} substrate during film formation, particularly the formation of minute protrusion-like defects.

[0021] As a result of extensive investigations into the above-mentioned problems, the present inventors have found that a high-quality silicon {110} substrate on which a film has been formed and which has a uniform surface can be fabricated without in-plane step bunching or protrusion-like defects, by using a heat treatment method for performing a film-forming heat treatment on a main surface of a silicon substrate having a {110} plane orientation, the heat treatment method comprising the steps of: loading the silicon substrate having a {110} plane orientation on a main surface into a heat treatment furnace at a furnace temperature of 540°C or less; raising the temperature of the silicon substrate while forming a passivation film on the main surface of the silicon substrate loaded into the heat treatment furnace; and performing a film-forming heat treatment on the silicon substrate after the temperature increase, thereby completing the present invention.

[0022] In the present invention, a plane orientation of {110} includes a plane whose orientation is equivalent to (110), and also includes a plane having an off angle of 0.23 to 0.5 degrees from the {110} plane.

[0023] Figure 4 shows a cross-sectional structure diagram of a Si(110) single crystal substrate. As shown in Figure 4, Si(110) single crystal substrate 1 has surface 2 (the outermost surface with a stable surface structure). As shown in Figure 3, the structure (atomic arrangement) of outermost surface 2 of Si(110) varies depending on the temperature. Dislocations in the temperature range of 570 to 800°C shown in Figure 3 not only cause step bunching, which affects surface roughness, but also generate tiny protrusion-like defects associated with changes in surface morphology.

[0024] These step bunching and protrusion defects are caused by the rearrangement of the atomic arrangement on the top surface, so in reactions and processes in which the top surface atoms are exposed, such as epitaxial growth, hydrogen baking, and etching, the temperature drop conditions after the process have a significant effect in addition to the temperature of the process itself. In other words, dislocations occur when the temperature slowly passes through the dislocation temperature range of 570 to 800°C.

[0025] On the other hand, when the surface is covered with a passivation film, the atoms on the silicon surface bond with other atoms (oxygen and nitrogen) to form a network, making them less mobile than when there is no film. Therefore, it is thought that the temperature increase, before the film-forming atoms bond with the silicon surface atoms, has a greater impact on the generation of defects in the form of minute protrusions on the surface than the temperature decrease after film formation. The composition of the film to be formed is not particularly limited. Examples include oxide films and nitride films.

[0026] From this, it is thought that, when the temperature of a Si{110} substrate is raised, forming a passivation film on the substrate surface as the substrate passes through the transition temperature of 570 to 800°C can suppress the generation of in-plane step bunching and protruding defect distribution. It is more preferable to form a passivation film on the substrate surface during temperature rise, especially before the temperature reaches 570°C.

[0027] In an embodiment of the heat treatment method of the present invention for performing a film-forming heat treatment to form a film on a main surface of a silicon substrate having a main surface with a plane orientation of {110}, first, the silicon substrate having a main surface with a plane orientation of {110} is placed in a heat treatment furnace at a furnace temperature of 540°C or less (a step of placing in a heat treatment furnace).

[0028] The lower limit of the furnace temperature is not particularly limited, but taking into consideration the time required for temperature rise, it can be set to, for example, 450° C. or higher, at which rearrangement of the surface structure does not occur.

[0029] Next, the temperature of the silicon substrate is raised while a passivation film is formed on the main surface of the silicon substrate placed in a heat treatment furnace (a temperature raising step).

[0030] In this case, the passivation film can be any one of an oxide film, a nitride film, and an oxynitride film.

[0031] This allows the production of a high-quality silicon {110} substrate with a more uniform surface and film formation without the generation of step bunching or protruding defect distribution within the surface.

[0032] After the temperature is raised, the silicon substrate is subjected to a film-forming heat treatment. At this time, the passivation film formed in the previous temperature-raising step can be removed by hydrogen baking. Note that if the passivation film and the film to be formed are of the same type, the passivation film does not need to be removed. The film-forming heat treatment is preferably performed after the temperature has risen past the transition temperature of 570 to 800°C.

[0033] In fact, when a Si(110) substrate was placed in a heat treatment furnace at an internal temperature of 570°C (above this temperature, dislocations occur as shown in Figure 3), and a surface passivation film was not formed during heating, and when the temperature reached 1000°C, oxygen was added and the substrate was heat treated, and then rapidly cooled, step bunching 3 and minute protrusion-like defects 4 were observed to form on the substrate surface, as shown in Figure 5.

[0034] Figure 5 shows the results of AFM (atomic force microscope) measurements of the Si(110) substrate surface after heat treatment under the above-mentioned conditions. By observing the image of the measurement area (a) 1 μm square, it is possible to determine whether or not there are minute protrusion-like defects. Furthermore, by comparing the image of the measurement area (b) 0.1 μm square and the image of the measurement area (c) 0.8 μm square, it is possible to determine whether or not there is step bunching. If the step directions in images (b) and (c) are the same, step bunching has not occurred. However, in Figure 5, the steps in (b) are tilted at approximately 70°, which indicates that step bunching 3 has occurred.

[0035] On the other hand, when a Si(110) substrate was placed in a heat treatment furnace at 540°C, which is lower than 570°C (dislocations are less likely to occur at temperatures below this, as shown in Figure 3), a passivation film was formed on the surface as the temperature rose, and when it reached 1000°C, it was subjected to heat treatment with the addition of oxygen or nitrogen, and then rapidly cooled. As shown in Figures 1 and 2, no step bunching or minute protrusion-like defects were observed on the substrate surface.

[0036] In addition, when a Si(110) substrate was placed in a heat treatment furnace at an internal temperature of 570°C, a surface passivation film was formed during the heating process, and when the temperature reached 1000°C, oxygen was added and the substrate was then rapidly cooled. As shown in Figure 6, the formation of minute protrusion-like defects 4 was observed on the substrate surface. [Example]

[0037] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0038] Example 1 A boron-doped single-crystal silicon substrate with a (110) major surface, a diameter of 300 mm, a resistivity of 10 Ω·cm, and an off-axis angle of 0.26° was prepared. It was placed in a heat treatment furnace set at 540°C and heated to 1000°C at a rate of 5°C / min while flowing oxygen at 0.1 sccm. It was then heat-treated at 1000°C for 60 seconds while flowing oxygen at 10 sccm, after which it was rapidly cooled to 540°C.

[0039] The substrate surface was then subjected to AFM measurement, and the measurement results are shown in Figure 1. As shown in Figure 1, no step bunching or protrusion-like defects were observed on the substrate surface.

[0040] Example 2 The same single crystal silicon substrate as in Example 1 was prepared and placed in a heat treatment furnace set at 540°C. While flowing nitrogen at 0.1 sccm, the substrate was heated to 1000°C at a rate of 5°C / min, and heat treated at 1000°C for 60 seconds while flowing nitrogen at 10 sccm, and then rapidly cooled to 540°C.

[0041] The substrate surface was then subjected to AFM measurement, and the measurement results are shown in Figure 2. As shown in Figure 2, no step bunching or protrusion-like defects were observed on the substrate surface.

[0042] (Comparative Example 1) The same single crystal silicon substrate as in Example 1 was prepared and placed in a heat treatment furnace set at 570°C. The substrate was placed in a vacuum state and heated to 1000°C at a rate of 5°C / min. Heat treatment was performed at 1000°C for 60 seconds while flowing oxygen at 10 sccm, and then the substrate was rapidly cooled to 540°C.

[0043] The substrate surface was then subjected to AFM measurement, and the measurement results are shown in Figure 5. As shown in Figure 5, the formation of step bunching 3 and protrusion-like defects 4 was observed on the substrate surface.

[0044] (Comparative Example 2) The same single crystal silicon substrate as in Example 1 was prepared and placed in a heat treatment furnace set at 570°C. While flowing oxygen at 0.1 sccm, the substrate was heated to 1000°C at a rate of 5°C / min, and heat treated at 1000°C for 60 seconds while flowing oxygen at 10 sccm, and then rapidly cooled to 540°C.

[0045] The substrate surface was then subjected to AFM measurement, and the measurement results are shown in Figure 6. As shown in Figure 6, no step bunching was observed, but slight protrusion-like defects 4 were observed.

[0046] As described above, according to the examples of the present invention, in the film formation heat treatment of the silicon (110) substrate, it was possible to produce a silicon (110) substrate on which a high-quality film was formed with a uniform surface without generating step bunching or a distribution of protruding defects within the surface.

[0047] The present invention is not limited to the above-described embodiments. The above-described embodiments 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 exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0048] 1...Si(110) single crystal substrate, 2...surface (surface stabilized structure), 3...Step bunching, 4...Micro-protrusion defects.

Claims

1. A heat treatment method for forming a film on a main surface of a silicon substrate having a {110} plane orientation, the heat treatment method comprising: a step of placing a silicon substrate having a {110} plane orientation on its main surface into a heat treatment furnace at a furnace temperature of 540° C. or less; a step of increasing the temperature of the silicon substrate while forming a passivation film on a main surface of the silicon substrate placed in the heat treatment furnace; a step of performing a film-forming heat treatment on the silicon substrate after the temperature increase;

2. 2. The heat treatment method according to claim 1, wherein the passivation film is one of an oxide film, a nitride film, and an oxynitride film.

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