A method for forming a silicon-germanium epitaxial layer

Abstract

The present invention relates to the field of semiconductor technology and proposes a method for forming a silicon-germanium epitaxial layer, comprising the following steps: S1, cleaning and drying a substrate, and then sputtering a transition layer to obtain a substrate covered with the transition layer; S2, subjecting the transition layer substrate to a first selective epitaxial growth process at 700-800°C, a second selective epitaxial growth process at 450-500°C, and finally a third selective epitaxial growth process at 150-200°C; the transition layer material in S1 is composed of graphite and / or carbon nanotubes. This technical solution solves the prior art problems of poor quality and low uniformity of epitaxially grown silicon-germanium materials on silicon-based substrates.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for forming a silicon germanium epitaxial layer. Background Art

[0002] In recent years, silicon-germanium alloys have attracted widespread attention due to their potential applications in optoelectronic devices. On the one hand, silicon-germanium materials have high carrier mobility, continuously tunable bandgap depending on the germanium composition, and are compatible with currently mature silicon planar processes. On the other hand, their high absorption coefficient in the near-infrared region of the solar spectrum makes them suitable for applications in modulation-doped field-effect transistors, photodetectors, and solar cells.

[0003] Currently, the main methods for growing SiGe epitaxial layers are molecular beam epitaxy (MBE) and ultra-high vacuum chemical vapor deposition (UHV / CVD). MBE has inherent advantages in growing quantum well structures with abrupt interfaces. As a growth technique for high-purity source materials, MBE can produce strained silicon quantum wells with low background impurities and steeper interfaces. Therefore, MBE is the primary method for growing SiGe epitaxial layers. However, a significant challenge in heteroepitaxially growing SiGe thin films on silicon substrates is the 4.18% lattice mismatch between SiGe and SiGe. This lattice mismatch results in a rough, uneven surface with significant undulations and a high dislocation density. Dislocations generated during epitaxial growth provide recombination centers for electron-hole pairs, resulting in significant dark current and impacting the device's light detection performance. Furthermore, SiGe also has a significant thermal mismatch between SiGe and SiGe. Therefore, epitaxially growing high-quality, highly uniform SiGe on silicon substrates is a technical challenge that those skilled in the art urgently need to address. Summary of the Invention

[0004] The present invention provides a method for forming a silicon germanium epitaxial layer, which solves the problems of poor quality and low uniformity of silicon germanium materials epitaxially grown on a silicon-based substrate in the related art.

[0005] The technical solutions of the present invention are as follows:

[0006] A method for forming a silicon germanium epitaxial layer comprises the following steps:

[0007] S1, cleaning the substrate, drying it, and then sputtering a transition layer to obtain a substrate covered with a transition layer;

[0008] S2. The transition layer substrate is first subjected to a first selective epitaxial growth process at 700-800° C., then subjected to a second selective epitaxial growth process at 450-500° C., and finally subjected to a third selective epitaxial growth process at 150-200° C.

[0009] As a further technical solution, the material of the transition layer in S1 is composed of graphite and / or carbon nanotubes.

[0010] As a further technical solution, the material of the transition layer in S1 is composed of graphite and carbon nanotubes.

[0011] As a further technical solution, the carbon nanotubes are multi-walled carbon nanotubes.

[0012] As a further technical solution, the multi-walled carbon nanotubes have a diameter of 10 to 20 nm and a length of 5 to 15 μm.

[0013] As a further technical solution, the mass ratio of the graphite to the carbon nanotubes is 3:1.

[0014] As a further technical solution, the sputtering gas pressure is 0.5 Pa, the sputtering temperature is 650° C., the sputtering rate is 1.2 nm / min, and the sputtering time is 60 min.

[0015] As a further technical solution, the step S2 further includes pre-annealing, and the pre-annealing temperature is 700°C.

[0016] As a further technical solution, the pressure in the first selective epitaxial growth process, the second selective epitaxial growth process and the third selective epitaxial growth process is 5 to 10 torr, and the reaction gases used include silicon-containing gas, germanium-containing gas and hydrogen chloride gas.

[0017] As a further technical solution, the silicon-containing gas includes one of silane, silane, and dichlorosilane; and the germanium-containing gas includes germane.

[0018] As a further technical solution, the flow rate of the silicon-containing gas is 50-150 sccm; the flow rate of the germanium-containing gas is 200-270 sccm; and the flow rate of the hydrogen chloride gas is 100-150 sccm.

[0019] As a further technical solution, the flow rate of the silicon-containing gas is 135 sccm; the flow rate of the germanium-containing gas is 250 sccm; and the flow rate of the hydrogen chloride gas is 120 sccm.

[0020] As a further technical solution, the time for the first selective epitaxial growth process is 30 seconds, the time for the second selective epitaxial growth process is 100 seconds, and the time for the third selective epitaxial growth process is 700 seconds.

[0021] The working principle and beneficial effects of the present invention are:

[0022] 1. On the one hand, the present invention sputters graphite and / or carbon nanotubes on a substrate as a transition layer to transition the lattice constant between silicon and germanium, thereby reducing surface roughness and dislocation density, thereby improving the uniformity of the silicon-germanium epitaxial layer; on the other hand, a three-stage epitaxial growth process is adopted, namely, first performing a first selective epitaxial growth process at 700-800°C, performing a second selective epitaxial growth process at 450-500°C, and finally performing a third selective epitaxial growth process at 150-200°C to form the silicon-germanium epitaxial layer. The obtained silicon-germanium epitaxial layer has high uniformity and a fast growth rate.

[0023] 2. The present invention uses graphite and multi-walled carbon nanotubes as transition layer materials. Graphite and multi-walled carbon nanotubes have a layered structure, and there are weak van der Waals forces between their layers, which makes interlayer slip more likely to occur. This can improve the 4.18% lattice mismatch between silicon and germanium, and reduce the defects in the formation of silicon-germanium epitaxial layers.

[0024] 3. The present invention further controls the diameter of the multi-walled carbon nanotubes to 10-20 nm and the length to 5-15 μm, thereby further improving the quality and uniformity of the silicon germanium epitaxial layer. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0026] Example 1

[0027] S1. After cleaning the silicon substrate with RCA, blow it dry with nitrogen and place it in the main sputtering chamber of the magnetron sputtering system. Pump the vacuum to 2×10 -5 Pa, argon gas was introduced, and the transition material was sputtered at a rate of 1.2 nm / min for 60 min at a sputtering pressure of 0.5 Pa and a sputtering temperature of 650 ° C to obtain a substrate covered with a transition layer, wherein the transition material was graphite;

[0028] S2. After pre-annealing the obtained transition layer-covered substrate at 700°C under nitrogen protection, the pressure in the chamber is adjusted to 5 torr, and a first selective epitaxial growth is performed at 750°C for 30s, a second selective epitaxial growth is performed at 450°C for 100s, and a third selective epitaxial growth is performed at 200°C for 700s to obtain a silicon-germanium epitaxial layer. In the first selective epitaxial growth, the second selective epitaxial growth, and the third selective epitaxial growth, the flow rate of silane is 135sccm, the flow rate of germane is 250sccm, and the flow rate of hydrogen chloride gas is 120sccm.

[0029] Example 2

[0030] S1. After cleaning the silicon substrate with RCA, blow it dry with nitrogen and place it in the main sputtering chamber of the magnetron sputtering system. Pump the vacuum to 2×10 -5 Pa, argon gas was introduced, and the transition material was sputtered at a rate of 1.2 nm / min for 60 min at a sputtering pressure of 0.5 Pa and a sputtering temperature of 650°C to obtain a substrate covered with a transition layer, wherein the transition material was multi-walled carbon nanotubes, and the diameter of the multi-walled carbon nanotubes was 10-20 nm and the length was 5-15 μm;

[0031] S2 is the same as S2 in Example 1.

[0032] Example 3

[0033] S1. After cleaning the silicon substrate with RCA, blow it dry with nitrogen and place it in the main sputtering chamber of the magnetron sputtering system. Pump the vacuum to 2×10 -5 Pa, argon gas was introduced, and a transition material was sputtered at a rate of 1.2 nm / min for 60 min at a sputtering pressure of 0.5 Pa and a sputtering temperature of 650°C to obtain a substrate covered with a transition layer, wherein the transition material was composed of graphite and multi-walled carbon nanotubes in a mass ratio of 3:1, and the multi-walled carbon nanotubes had a diameter of 10-20 nm and a length of 5-15 μm;

[0034] S2 is the same as S2 in Example 1.

[0035] Example 4

[0036] S1 is the same as S1 in Example 3;

[0037] S2. After pre-annealing the obtained transition layer-covered substrate at 700°C under nitrogen protection, the pressure in the chamber is adjusted to 10 torr, and a first selective epitaxial growth is performed at 700°C for 30s, a second selective epitaxial growth is performed at 480°C for 100s, and a third selective epitaxial growth is performed at 150°C for 700s to obtain a silicon germanium epitaxial layer. In the first selective epitaxial growth, the second selective epitaxial growth, and the third selective epitaxial growth, the flow rate of silicon ethane is 50sccm, the flow rate of germane is 200sccm, and the flow rate of hydrogen chloride gas is 100sccm.

[0038] Example 5

[0039] S1 is the same as S1 in Example 3;

[0040] S2. After pre-annealing the obtained transition layer-covered substrate at 700°C under nitrogen protection, the pressure in the chamber is adjusted to 8 torr, and a first selective epitaxial growth is performed at 800°C for 30s, a second selective epitaxial growth is performed at 500°C for 100s, and a third selective epitaxial growth is performed at 180°C for 700s to obtain a silicon germanium epitaxial layer. In the first selective epitaxial growth, the second selective epitaxial growth, and the third selective epitaxial growth, the flow rate of dichlorosilane is 150sccm, the flow rate of germane is 270sccm, and the flow rate of hydrogen chloride gas is 150sccm.

[0041] Example 6

[0042] The only difference from Example 3 is that the diameter of the multi-walled carbon nanotubes is 15-25 nm and the length is 5-15 μm.

[0043] Example 7

[0044] The only difference from Example 3 is that the multi-walled carbon nanotubes are replaced with an equal amount of single-walled carbon nanotubes.

[0045] Comparative Example 1

[0046] S1 is the same as S1 in Example 3;

[0047] S2. After pre-annealing the obtained transition layer-covered substrate at 700°C under nitrogen protection, the pressure in the chamber is adjusted to 5 torr, and a first selective epitaxial growth is performed at 750°C for 30s, and a second selective epitaxial growth is performed at 450°C for 800s to obtain a silicon-germanium epitaxial layer. In the first selective epitaxial growth and the second selective epitaxial growth, the flow rate of silane is 135sccm, the flow rate of germane is 250sccm, and the flow rate of hydrogen chloride gas is 120sccm.

[0048] Comparative Example 2

[0049] The silicon-based substrate was cleaned by RCA and dried with nitrogen, and then pre-annealed at 700°C under nitrogen protection. The pressure in the chamber was adjusted to 5 torr, and a first selective epitaxial growth was performed at 750°C for 30 seconds, a second selective epitaxial growth was performed at 450°C for 100 seconds, and a third selective epitaxial growth was performed at 200°C for 700 seconds to obtain a silicon-germanium epitaxial layer. During the first selective epitaxial growth, the second selective epitaxial growth, and the third selective epitaxial growth, the flow rate of silane was 135 sccm, the flow rate of germane was 250 sccm, and the flow rate of hydrogen chloride gas was 120 sccm.

[0050] Ten silicon germanium epitaxial layers obtained in Examples 1 to 7 and Comparative Examples 1 to 2 were respectively taken to measure their thickness, and the results are recorded in Table 1.

[0051] Table 1 Silicon Germanium epitaxial layer thickness

[0052]

[0053]

[0054] It can be seen from Table 1 that the silicon germanium epitaxial layer obtained by the method for forming a silicon germanium epitaxial layer provided by the present invention has high quality, high yield and high uniformity.

[0055] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for forming a silicon germanium epitaxial layer, characterized in that: The following steps are involved: S1, cleaning the substrate, drying it, and then sputtering a transition layer to obtain a substrate covered with a transition layer; S2, first performing a first selective epitaxial growth process on the transition layer substrate at 700-800° C., performing a second selective epitaxial growth process at 450-500° C., and finally performing a third selective epitaxial growth process at 150-200° C.; The material of the transition layer in S1 is composed of graphite and carbon nanotubes; The carbon nanotubes are multi-walled carbon nanotubes; The mass ratio of the graphite to the carbon nanotubes is 3:

1.

2. The method for forming a silicon germanium epitaxial layer according to claim 1, wherein: The sputtering pressure was 0.5 Pa, the sputtering temperature was 650° C., the sputtering rate was 1.2 nm / min, and the sputtering time was 60 min.

3. The method for forming a silicon germanium epitaxial layer according to claim 1, wherein: The step S2 also includes pre-annealing, and the pre-annealing temperature is 700°C.

4. The method for forming a silicon germanium epitaxial layer according to claim 1, wherein: The pressure in the first selective epitaxial growth process, the second selective epitaxial growth process and the third selective epitaxial growth process is 5-10 Torr, and the reaction gases used include silicon-containing gas, germanium-containing gas and hydrogen chloride gas.

5. The method for forming a silicon germanium epitaxial layer according to claim 4, wherein: The flow rate of the silicon-containing gas is 50-150 sccm; the flow rate of the germanium-containing gas is 200-270 sccm; and the flow rate of the hydrogen chloride gas is 100-150 sccm.

6. The method for forming a silicon germanium epitaxial layer according to claim 5, wherein: The flow rate of the silicon-containing gas is 135 sccm; the flow rate of the germanium-containing gas is 250 sccm; and the flow rate of the hydrogen chloride gas is 120 sccm.

7. The method for forming a silicon germanium epitaxial layer according to claim 1, wherein: The time for the first selective epitaxial growth process is 30 seconds, the time for the second selective epitaxial growth process is 100 seconds, and the time for the third selective epitaxial growth process is 700 seconds.

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