PRODUCTION METHOD FOR SiGe SUBSTRATE

Abstract

The present invention is a production method for an SiGe substrate that involves growing an SiGe layer on a silicon substrate. The production method is characterized in that growth of the SiGe layer is begun at a temperature that is at or above room temperature and at or below the lowest glass transition temperature of the most stable structure at the surface of the silicon substrate in accordance with the crystal plane orientation at the surface of the silicon substrate, and the SiGe layer is grown as the temperature is raised above the lowest glass transition temperature. The present invention thereby provides a method for producing a high-quality SiGe substrate that has a good-quality SiGe layer formed on a silicon substrate.

Description

Method for producing SiGe substrate

[0001] The present invention relates to a method for producing a SiGe substrate.

[0002] SiGe is a material that is widely used in various devices, including electronic, optical, and RF devices. Recently, instead of 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 next-generation semiconductors, and SiGe plays an important role in the manufacturing process of these devices (Non-Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2002-329664 Japanese Patent Application Laid-Open No. 2008-513979 Japanese Patent Application Laid-Open No. 2004-531889

[0004] The 1st Workshop of the Industry-Academia Collaboration Committee on Crystal Growth, Processing, and Evaluation of Semiconductors, Japan Society of Applied Physics, "Crystal Technology Supporting the Revival of Semiconductors," Yonenaga, "Growth of High-Quality SiGe Crystals and Elucidation of Their Fundamental Properties," Materia, 47(1), 3 (2008); Sato, "Fundamentals and Challenges of Heteroepitaxy: 1st Workshop of the 3C-SiC Technology Study Group for IoT in Harsh Environments" (2019); Wong, L. H. "Strain Relaxation in SiGe / Si Heteroepitaxy." Doctoral Thesis, Nanyang Technological University, Singapore, (2007). E. A. Fitgerald, et. al. , “Totally relaxed GexSi1-x layers with low threading dislocation densities grows on Si substrares”, App. Phys. Lett. , 59, 811 (1991). F. K. Le Geues, et. al. , “Mechanism and conditions for anomalous strain relaxation in graded thin films and superlattices”, App. Phys. Lett. , 71, 4230 (1992). T. Taniguchi, et. al., Abstract of SAP Spring Meeting, 17a-F102-9 (2018). T. Taniguchi, et. al., Abstract of JSAP Autumn Meeting, 20p-234-10 (2018). Ueba, "Fundamentals of Epitaxial Growth - Strain, Diffusion, and Step Motion", Journal of the Japanese Society for Crystal Growth, 43 (4), 213 (2016).

[0005] However, in the equilibrium phase diagram, the liquidus and solidus of SiGe are widely separated, and the distribution coefficient is 2 to 5, which is greater than 1, making it known that SiGe is prone to polycrystallization. Even if single crystals can be grown, the growth rate is slow and it is difficult to grow them consistently (Non-Patent Document 2).

[0006] Therefore, for semiconductor devices, SiGe is grown on Si substrates, sometimes referred to as virtual SiGe substrates. In this SiGe growth (heteroepitaxial), how to mitigate the difference in lattice constants between Si and Ge is crucial. The lattice constant of Si crystals is 0.5431 nm, while that of Ge crystals is 0.56754 nm, resulting in a difference of approximately 4.5%. To mitigate this difference in lattice constants, SiGe uses a SiGe alloy. If the Ge composition ratio is x, the lattice constant of the SiGe alloy is 0.5431 nm + x × 0.02 nm + x squared × 0.0027 nm. For example, assuming x is 0.3, the lattice constant is 0.5493 ​​nm, resulting in a minimal lattice mismatch of 0.14%. This lattice mismatch can lead to dislocations and defects in the subsequently grown epitaxial layer, resulting in degradation of quality. However, it is believed that there is a critical thickness, and even if there is lattice mismatch, defects will not occur unless the critical thickness is exceeded (Non-Patent Document 3).

[0007] Therefore, various intermediate layers have been proposed that utilize this critical thickness to form a buffer layer. For example, there is a method in which the Ge concentration is varied from the silicon substrate to a SiGe layer with a predetermined Ge concentration, which is called a graded buffer layer (Non-Patent Documents 4, 5, 6). Another method has been proposed, which involves stacking multiple layers with thicknesses below the critical thickness, called a superlattice buffer layer (Non-Patent Documents 6, 7, 8).

[0008] In addition to these techniques, various techniques have been disclosed for growing a SiGe layer epitaxially on a silicon substrate. Patent Document 1 discloses a method for growing a SiGe layer epitaxially on a wafer in a perfect region that is free of vacancy-type point defects and interstitial Si-type point defects.

[0009] Patent Document 2 discloses a method for growing Si—Ge materials on Si(100), in which a new hydride with direct Si—Ge bonds is used to grow uniform, relayed, and highly planar films with low defect densities at low temperatures of about 300-450° C., completely eliminating the need for thick, compositionally graded buffer layers and lift-off techniques. At temperatures of about 500-700° C., SiGe quantum dots are grown with narrow diameter distributions, defect-free microstructures, and highly uniform elemental contents at the atomic level, thereby enabling precise control of morphology, composition, structure, and strain.

[0010] Patent Document 3 discloses a manufacturing method in which an initial layer of germanium is formed on a silicon substrate, rounded S-K ridges are formed due to lattice mismatch, silicon dioxide is formed between the ridges by oxidation, and the peaks of the ridges are exposed by a subsequent reduction step, which are almost completely released and free of strain, and these peaks become nucleation sites for the subsequent growth of a final layer of germanium, which is formed as single crystals extending from the nucleation sites.

[0011] Although various methods have been investigated, none of them take into consideration the stable structure of the silicon outermost surface. It is known that the most stable structure and its temperature range for the silicon outermost surface differ depending on the surface orientation (Non-Patent Document 9). In other words, if film formation is initiated at a temperature higher than the temperature range in which the most stable structure is formed, when the substrate surface passes through the transition temperature during subsequent cooling, the transition to the most stable structure occurs, causing disturbances in the crystallinity, and no improvement in crystallinity can be expected no matter how many buffer structures or other measures are used.

[0012] The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for producing a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon substrate.

[0013] The present invention has been made to achieve the above-mentioned object, and provides a method for producing a SiGe substrate by growing a SiGe layer on a silicon substrate, characterized in that growth of the SiGe layer is initiated at a temperature above room temperature and below the lowest transition temperature of the most stable structure of the silicon substrate surface, depending on the crystal plane orientation of the surface of the silicon substrate, and the temperature is raised to a temperature higher than the lowest transition temperature during growth to grow the SiGe layer.

[0014] According to this method for producing a SiGe substrate, a high-quality SiGe substrate can be produced by forming a high-quality SiGe layer on a silicon substrate.

[0015] At this time, the crystal plane orientation of the surface of the silicon substrate can be set to {110}.

[0016] This makes it possible to fabricate a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon substrate having a surface crystal plane orientation of {110}.

[0017] At this time, the growth of the SiGe layer can be started at a temperature of 540° C. or lower.

[0018] This makes it possible to more stably fabricate a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon {110} substrate.

[0019] At this time, the growth of the SiGe layer can be started at a temperature of 510° C. or less.

[0020] This makes it possible to more stably produce a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon {110} substrate.

[0021] As described above, according to the method for producing a SiGe substrate of the present invention, it is possible to produce a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon substrate.

[0022] 1 is a schematic diagram showing the relationship between the surface temperature of a silicon (110) substrate and the most stable surface structure. 2 is a schematic diagram showing a SiGe substrate obtained by a method for producing a SiGe substrate according to the present 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 method for producing a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon substrate.

[0025] As a result of extensive research into the above-mentioned problems, the inventors have found that a high-quality SiGe substrate can be produced by a method for producing a SiGe substrate by growing a SiGe layer on a silicon substrate, the method comprising starting growth of the SiGe layer at a temperature above room temperature and below the lowest transition temperature of the most stable structure of the surface of the silicon substrate, depending on the crystal plane orientation of the surface of the silicon substrate, and then raising the temperature to a temperature higher than the lowest transition temperature during growth to grow the SiGe layer, and have completed the present invention.

[0026] 2 is a schematic diagram of a SiGe substrate obtained by the SiGe substrate fabrication method according to the present invention. The SiGe substrate 1, in which a SiGe layer 3 is formed on a silicon single crystal substrate 2, is sometimes called a virtual SiGe substrate. The composition of the SiGe layer 3 is not particularly limited, but the Ge content can be 10 to 35 atomic %.

[0027] The low-index faces of silicon (100), (110), and (111) each have a surface structural transition temperature. Si(100) does not undergo a surface phase transition at temperatures above room temperature, but Si(110) changes from a 16x2 structure to a more complex structure such as a 17x2 structure at 540°C, as shown in Figure 1. Furthermore, Si(111) changes from a 7x7 structure to a 1x1 structure at 860°C (Non-Patent Document 9).

[0028] That is, for a surface orientation other than Si(100), film formation (growth) is started at a temperature equal to or lower than the lowest transition temperature among the transition temperatures of this stable structure, and during the growth, the temperature is raised to a temperature higher than the lowest transition temperature. When the temperature is returned to room temperature after film formation, the interface distortion due to the structural change disappears. By growing the film across the transition temperature in this way, it is possible to specifically reduce the surface defect density by about two orders of magnitude.

[0029] When a CVD apparatus is used, the growth temperature of SiGe is often in the range of 600°C to 700°C. Si(100) has a low transition temperature, and the transition temperature of Si(111) is 860°C, which is higher than the growth temperature range. However, as mentioned above, the transition occurs in Si(110) at 540°C. Therefore, a silicon substrate whose surface has a crystal plane orientation of {110} can be suitably applied to the SiGe substrate fabrication method according to the present invention.

[0030] The starting temperature for growing the SiGe layer is set lower than the temperature (540°C) at which the substrate surface with a Si{110} orientation assumes the most stable structure, and while growing the SiGe film, the temperature is raised to a temperature higher than the transition temperature. After growth is completed, the temperature is returned to room temperature, and there is no distortion at the interface due to the structural change. Therefore, a high-quality SiGe substrate can be produced in which a good-quality SiGe layer is formed on a silicon substrate with a surface crystal plane orientation of {110}.

[0031] 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 1 degree or less from the {110} plane (just plane).

[0032] In this case, the growth of the SiGe layer can be started at a temperature of 540° C. or lower, which makes it possible to more stably produce a high-quality SiGe substrate in which a high-quality SiGe layer is formed on a silicon {110} substrate.

[0033] The growth start temperature should be lower than the transition temperature, but it is preferable to start film formation at a temperature 30° C. lower than the transition temperature, since there is naturally variation in the transition phenomenon.

[0034] That is, in the case of a silicon substrate having a {110} crystal plane orientation on the surface, it is preferable to start growing the SiGe layer at a temperature of 510° C. or lower. This makes it possible to more stably produce a high-quality SiGe substrate in which a good-quality SiGe layer is formed on a silicon {110} substrate.

[0035] As an example of the embodiment, SiH, which is a gas necessary for SiGe growth, is used at temperatures below 510° C. ２ Cl ２ and GeH ４The temperature is increased while introducing gas into the reactor, and the growth temperature is reached at about 600° C., whereby growth is carried out.

[0036] The rate of temperature rise at this time is not particularly limited, but can be set within a range that allows for sufficient temperature control in a general growth apparatus. If the temperature rises too rapidly, an overshoot of the temperature occurs when the predetermined growth temperature is reached. Generally, the rate is set to about 1°C / sec to 0.1°C / sec.

[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 A boron-doped single crystal silicon substrate having a surface crystal plane orientation of (110), a diameter of 300 mm, and a resistivity of 10 Ω·cm was prepared and placed in an epitaxial growth reactor.

[0039] SiH ２ Cl ２ Gas and GeH ４ The gases were used as raw materials and introduced at 1000 sccm into an epitaxial growth reactor whose pressure was reduced to 1333 Pa (10 Torr). When forming a film on a silicon substrate, the growth temperature (substrate temperature) was raised from 510°C to 610°C at a rate of 0.5°C / sec while the gases were flowing, and then the temperature was held at 610°C for 60 minutes to grow a SiGe layer (Ge concentration = 30 atomic %), thereby producing a SiGe substrate.

[0040] The SiGe substrate was cooled to room temperature, and the surface was etched with a fluorine-nitric acid mixture. The defect density on the surface was evaluated using an optical microscope. The defect density was 1×10 ５ / cm ２ It was.

[0041] Comparative Example A SiGe layer was formed under the same conditions as in the example, except that the growth gas was introduced into the epitaxial growth reactor at 610° C. to start growth.

[0042] The SiGe substrate was cooled to room temperature, and the surface was etched with a fluorine-nitric acid mixture. The defect density on the surface was evaluated using an optical microscope. The defect density was 1×10 ７ / cm２ It was.

[0043] As described above, according to the examples of the present invention, it was possible to form a SiGe layer on a silicon substrate, the surface defect density of which was two orders of magnitude lower than that of the comparative example.

[0044] This specification includes the following aspects. [1]: A method for producing a SiGe substrate by growing a SiGe layer on a silicon substrate, the method comprising: starting growth of the SiGe layer at a temperature above room temperature and below the lowest transition temperature of the most stable structure of the silicon substrate surface, depending on the crystal plane orientation of the surface of the silicon substrate; and raising the temperature to a temperature higher than the lowest transition temperature during growth to grow the SiGe layer. [2]: A method for producing a SiGe substrate according to [1] above, which includes setting the crystal plane orientation of the surface of the silicon substrate to {110}. [3]: A method for producing a SiGe substrate according to [1] or [2] above, which includes starting growth of the SiGe layer at 540°C or lower. [4]: ​​A method for producing a SiGe substrate according to [1], [2], or [3] above, which includes starting growth of the SiGe layer at 510°C or lower.

[0045] 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.

Claims

1. A method for producing a SiGe substrate by growing a SiGe layer on a silicon substrate, characterized in that growth of the SiGe layer is initiated at a temperature above room temperature and below the lowest transition temperature of the most stable structure of the silicon substrate surface, depending on the crystal plane orientation of the surface of the silicon substrate, and the temperature is raised to a temperature higher than the lowest transition temperature during growth to continue growing the SiGe layer.

2. The method for producing a SiGe substrate according to claim 1, wherein the crystal plane orientation of the surface of the silicon substrate is {110}.

3. The method for producing a SiGe substrate according to claim 2, wherein the growth of the SiGe layer is started at a temperature of 540° C. or less.

4. The method for producing a SiGe substrate according to claim 2 or 3, wherein the growth of the SiGe layer is started at a temperature of 510° C. or lower.

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