A method for fabricating a germanium-silicon epitaxial structure

Abstract

This invention provides a method for preparing a germanium-silicon epitaxial structure. By adjusting the flow ratio of germane to silane in different reaction stages, a gradient change in germanium composition from 0 to a target value is achieved between different epitaxial layers in the epitaxial structure. This effectively alleviates the mismatch stress caused by the difference in lattice constant. Furthermore, the porous silicon buffer layer formed on the substrate surface can further release the mechanical stress at the interface. Since low-temperature annealing is performed after each reaction stage, it promotes the orderly rearrangement of atoms and significantly reduces the dislocation defect density. In addition, by using lasers of specific wavelengths and power densities, the surface dangling bonds of different epitaxial layers are selectively excited, promoting the two-dimensional layered growth of the epitaxial layers. Finally, a high-quality germanium-silicon epitaxial structure with low defect density is obtained, providing a high-quality material basis for the manufacture of high-performance silicon-based optoelectronic devices.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology and relates to a method for preparing a germanium-silicon epitaxial structure. Background Technology

[0002] With the rapid development of integrated circuit technology, the demand for epitaxial wafers used to improve circuit performance has increased significantly. Silicon-based epitaxial wafers have become a hot research topic in the semiconductor industry due to their compatibility with mature silicon process platforms and reduced costs. Among them, germanium-silicon (GeSi) alloys have become a core material for next-generation semiconductor devices due to their tunable bandgap, high carrier mobility, and compatibility with silicon-based processes.

[0003] However, traditional germanium-silicon epitaxial growth technology on silicon substrates faces the following problems: silicon has a lattice constant of 0.543 nm, while germanium has a lattice constant of 0.566 nm, resulting in a lattice mismatch of approximately 4.2%. When a germanium-silicon epitaxial layer is grown directly on a silicon substrate, atoms tend to aggregate to form three-dimensional islands rather than spreading uniformly into two-dimensional layers. Furthermore, to release the enormous stress caused by the lattice mismatch, a high density of mismatch dislocations and punch-through dislocations is generated inside the germanium-silicon epitaxial layer. The uneven distribution of dislocations not only severely reduces carrier lifetime and leads to non-uniform electrical performance, but also significantly reduces the yield and reliability during chip manufacturing. Moreover, since germanium-silicon epitaxial layers are usually formed at high temperatures, during the cooling process from the growth temperature to room temperature after epitaxial growth, the significant difference in the thermal expansion coefficients of silicon and germanium results in different degrees of shrinkage, generating tensile stress inside the germanium-silicon epitaxial layer. The presence of this stress can cause cracks on the surface of the epitaxial layer, ultimately leading to severe bending of the wafer.

[0004] In existing technologies, the problems of traditional germanium-silicon epitaxial technology are usually solved by setting a low-temperature buffer layer or forming a composition gradient layer. Among them, the low-temperature buffer layer process first grows a low-temperature germanium buffer layer on the substrate, using the low atomic mobility at low temperature to suppress the growth of three-dimensional islands, followed by high-temperature annealing; however, this process often fails to completely eliminate dislocations, and the high-temperature annealing process can easily introduce new thermal stress defects; 2) The composition gradient layer process achieves a smooth transition of lattice constant by gradually increasing the germanium composition. Although this process can effectively reduce dislocation density, the traditional linear gradient process has a long growth time, complex process, and extremely high requirements for temperature control. If the temperature is not properly controlled, it will still cause the problem of large surface roughness of the formed germanium-silicon epitaxial structure. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a method for preparing germanium-silicon epitaxial structures, which solves the problems of complex processes and difficulty in controlling dislocation defect density in existing low-temperature buffer layer technology and composition gradient layer technology.

[0006] To achieve the above and other related objectives, the present invention provides a method for preparing a germanium-silicon epitaxial structure, comprising the following steps:

[0007] A substrate is provided, the substrate is pretreated to form a porous silicon buffer layer, and the pretreated substrate is placed in a reaction chamber;

[0008] A first precursor gas, a second precursor gas, and a carrier gas are sequentially introduced into the reaction chamber. The different ratios of the first precursor gas and the second precursor gas are controlled to form an epitaxial structure on the substrate surface. The epitaxial structure includes at least a first epitaxial film layer, a second epitaxial film layer, a third epitaxial film layer, and a fourth epitaxial film layer. After each epitaxial film layer is formed, the reaction chamber is cooled and the carrier gas is introduced into the reaction chamber separately for annealing.

[0009] After each epitaxial film layer is formed, dopant source gas is synchronously introduced into the reaction chamber in a pulse mode to achieve in-situ doping of the epitaxial structure and to form a passivation layer on the surface of the epitaxial structure using an atomic layer deposition process.

[0010] Optionally, the pretreatment process for the substrate includes electrochemical etching of the substrate, wherein the thickness of the porous silicon buffer layer is 30-50 nm and the porosity of the porous silicon buffer layer is 20%-40%.

[0011] Optionally, the first precursor gas is GeH4, the second precursor gas is SiH4, the carrier gas source gas is H2, and the flow rate ratio of the first precursor gas to the second precursor gas is 0~50%.

[0012] Optionally, when forming the first epitaxial film, the second epitaxial film, the third epitaxial film, and the fourth epitaxial film, the flow ratio of GeH4 and SiH4 increases linearly from 0 to 50%.

[0013] Optionally, the thickness of the first epitaxial film, the second epitaxial film, the third epitaxial film, and the fourth epitaxial film is 20~100nm.

[0014] Optionally, the thicknesses of the first epitaxial film, the second epitaxial film, the third epitaxial film, and the fourth epitaxial film are equal.

[0015] Optionally, the temperature at which each epitaxial film layer is formed is 600℃~750℃, and the temperature at which each epitaxial film layer is formed increases in a gradient.

[0016] Optionally, the doping source gas is B2H6 or PH3, and the in-situ doping process of the epitaxial structure includes simultaneously introducing B2H6 or PH3 into the reaction chamber and performing laser irradiation, wherein the wavelength of the laser is 532 nm and the power density is 10~50 mW / cm². 2 .

[0017] Optionally, the material forming the passivation layer is aluminum oxide, hafnium oxide, or silicon nitride, and the thickness of the passivation layer is 2~10 nm.

[0018] Optionally, the annealing temperature after forming each epitaxial film layer shall not exceed 400°C, and the annealing time shall be controlled to be 2~10 min.

[0019] As described above, in the method for preparing the germanium-silicon epitaxial structure of the present invention, by adjusting the flow ratio of germane and silane in different reaction stages, a gradient change of germanium composition from 0 to the target value is achieved between different epitaxial layers in the epitaxial structure. This effectively alleviates the mismatch stress caused by the difference in lattice constant. Furthermore, the porous silicon buffer layer formed on the substrate surface can further release the mechanical stress at the interface. Since low-temperature annealing is performed after each reaction stage, it promotes the orderly rearrangement of atoms and significantly reduces the dislocation defect density. In addition, by using lasers of specific wavelengths and power densities, the surface dangling bonds of different epitaxial layers are selectively excited, promoting the two-dimensional layered growth of the epitaxial layers. Finally, a high-quality germanium-silicon epitaxial structure with low defect density is obtained, providing a high-quality material basis for the manufacture of high-performance silicon-based optoelectronic devices. Attached Figure Description

[0020] Figure 1 The diagram shows the process flow of the method for preparing germanium-silicon epitaxial structures in an embodiment of the present invention.

[0021] Figure 2 The diagram shown is a cross-sectional view of the substrate provided in an embodiment of the present invention.

[0022] Figure 3 The diagram shown is a top view of the structure after the porous silicon buffer layer is formed in an embodiment of the present invention.

[0023] Figure 4 The diagram shown is a top view of the structure after the strain relaxation layer is formed in an embodiment of the present invention.

[0024] Figure 5 The diagram shows the temperature gradient changes at various stages during the formation of the epitaxial film in an embodiment of the present invention.

[0025] Figure 6 The diagram shown is a cross-sectional view of the epitaxial film layer after its formation in an embodiment of the present invention.

[0026] Figure 7The diagram shown is a cross-sectional view of the structure after the passivation layer is formed in an embodiment of the present invention.

[0027] Component designation explanation

[0028] 10. Substrate; 11. Porous silicon buffer layer; 12. Strain relaxation layer; 13. First epitaxial film layer; 14. Second epitaxial film layer; 15. Third epitaxial film layer; 16. Fourth epitaxial film layer; 17. Passivation layer; S1~S3: Steps. Detailed Implementation

[0029] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0030] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0031] This invention provides a method for preparing germanium-silicon epitaxial structures to address the shortcomings of the prior art. Figure 1 The diagram shown is a process flow chart of a method for preparing a germanium-silicon epitaxial structure according to an embodiment of the present invention. (See attached diagram.) Figure 1 The present invention provides a method for preparing a germanium-silicon epitaxial structure, comprising:

[0032] S1: A substrate 10 is provided, the substrate 10 is pretreated to form a porous silicon buffer layer 11, and the pretreated substrate 10 is placed in the reaction chamber.

[0033] Among them, such as Figure 2 As shown, the substrate 10 can be any suitable semiconductor substrate, such as a silicon substrate, a silicon carbide substrate, or a gallium nitride substrate, but is not limited thereto. In this embodiment of the invention, the preparation method of the germanium-silicon epitaxial structure will be introduced using a silicon substrate 10 as an example.

[0034] In some embodiments, before electrochemically etching the silicon substrate 10, the process further includes completely removing the natural oxide layer on the surface of the silicon substrate 10 using a diluted acid solution, followed by rinsing with deionized water, and finally drying with high-purity nitrogen gas to ensure that contaminants on the surface of the silicon substrate 10 can be completely removed.

[0035] As an example, the pretreatment process for the substrate 10 includes electrochemical etching of the substrate 10, wherein the thickness of the porous silicon buffer layer 11 is 30~50 nm and the porosity of the porous silicon buffer layer 11 is 20%~40%.

[0036] In some embodiments, such as Figure 3 As shown, before placing the substrate 10 in the CVD chamber, the surface of the substrate 10 is first subjected to an electrochemical etching process to form a porous silicon buffer layer 11. Specifically, the substrate 10 is placed in a fluorinated electrolyte, typically a mixture of hydrofluoric acid and ethanol. A current is applied with the substrate 10 as the anode, causing silicon atoms to undergo oxidation and dissolution at the anode, ultimately forming a nanoscale porous silicon buffer layer 11 on the surface of the silicon substrate 10. The formed porous silicon buffer layer 11 can absorb stress through its pores. By controlling the current density and corrosion time during electrochemical corrosion, the porosity and thickness of the porous silicon buffer layer 11 can be precisely controlled. Specifically, in this embodiment, the porosity of the porous silicon buffer layer 11 is 20% to 40%, for example, 20%, 30% or 40%, and the thickness of the porous silicon buffer layer 11 is 30 to 50 nm, for example, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm, but not limited to these.

[0037] In some embodiments, such as Figure 4 As shown, due to the relatively rough surface of the formed porous silicon buffer layer 11, it cannot be directly used as a nucleation surface for high-quality epitaxy. Therefore, a strain relaxation layer 12 needs to be formed on the surface of the porous silicon buffer layer 11. The strain relaxation layer 12 can fill the surface undulations of the porous silicon buffer layer 11, making the epitaxial nucleation surface a smooth surface. The strain relaxation layer 12 can also cover a large number of dangling bonds on the surface of the porous silicon buffer layer 11, significantly reducing the interface state density. Specifically, in this embodiment, the strain relaxation layer 12 is Ge 0.8 Si 0.2 / Si superlattice structure.

[0038] In some embodiments, the substrate 10, on which a porous silicon buffer layer 11 and a strain relaxation layer 12 are formed on the surface, is placed in the reaction chamber of a metal chemical vapor deposition apparatus, and the reaction chamber is evacuated.

[0039] S2: A first precursor gas, a second precursor gas, and a carrier gas are sequentially introduced into the reaction chamber. The different ratios of the first precursor gas and the second precursor gas are controlled to form an epitaxial structure on the surface of the substrate 10. The epitaxial structure includes at least a first epitaxial film layer 13, a second epitaxial film layer 14, a third epitaxial film layer 15, and a fourth epitaxial film layer 16. After each epitaxial film layer is formed, the reaction chamber is cooled and the carrier gas is introduced into the reaction chamber separately for annealing.

[0040] In some embodiments, after evacuating the reaction chamber, a first precursor gas, a second precursor gas, and a carrier gas are introduced into the reaction chamber. The carrier gas carries the first and second precursor gases into the reaction chamber. Specifically, the first precursor gas is GeH4, the second precursor gas is SiH4, and the carrier gas is H2. The flow rate ratio of GeH4 to SiH4 is 0-50%. Silane and germanane, as raw materials for epitaxial film growth, react within the reaction chamber.

[0041] In some embodiments, by controlling different flow ratios between the first precursor gas and the second precursor gas, the reaction process of silane and germane forming an epitaxial structure in the deposition chamber is divided into at least four reaction stages, wherein the flow ratio of germane and silane in the four reaction stages can increase linearly from 0 to 50%, such as... Figure 5The diagram illustrates the temperature changes at various stages during the chemical vapor deposition process in this embodiment of the invention. Specifically, in the first reaction stage of chemical vapor deposition, the substrate 10 is pretreated and placed in the reaction chamber. The reaction chamber is evacuated and heated, with the flow ratio of germane to silane controlled at 0 (i.e., the flow rate of germane is 0). The temperature of the first reaction stage is controlled at 600°C to 650°C, and the temperature increases gradually. After the first epitaxial film 13 reaches the required thickness, the reaction chamber is cooled and the carrier gas is introduced separately for annealing. The annealing temperature is 400°C, and the annealing time is controlled at 5 minutes. Then, the second reaction stage of chemical vapor deposition is performed, with the flow ratio of germane to silane controlled at 5%. The temperature of the second reaction stage is controlled at 600°C to 685°C, and the temperature increases gradually. After the second epitaxial film 14 reaches the required thickness, the reaction chamber is cooled and the carrier gas is introduced separately for annealing. The annealing temperature is 400°C, and the annealing time is controlled at 5 minutes. The time is 5 minutes; then, the third reaction stage of chemical vapor deposition is carried out, controlling the flow ratio of germane to silane at 15%, and controlling the temperature of the third reaction stage at 600℃~715℃, with the temperature increasing in a gradient. After the third epitaxial film 15 reaches the required thickness, the reaction chamber is cooled and the carrier gas is introduced separately for annealing at 400℃ for 5 minutes; then, the fourth stage of chemical vapor deposition is carried out, controlling the flow rates of germane and silane. The ratio is 30%, and the temperature of the fourth reaction stage is controlled at 600℃~750℃, with the temperature change increasing in a gradient. After the fourth epitaxial film 16 reaches the required thickness, the reaction chamber is cooled and the carrier gas source is introduced separately for annealing. The annealing temperature is 400℃ and the annealing time is controlled at 5 minutes. Finally, the first epitaxial film 13, the second epitaxial film 14, the third epitaxial film 15 and the fourth epitaxial film 16 of the required thickness are formed on the surface of the strain relaxation layer 12.

[0042] In some embodiments, the thicknesses of the first epitaxial layer 13, the second epitaxial layer 14, the third epitaxial layer 15, and the fourth epitaxial layer 16 are 20~100 nm, for example, as... Figure 6 As shown, the thicknesses of the first epitaxial film 13, the second epitaxial film 14, the third epitaxial film 15, and the fourth epitaxial film 16 are all 50 nm. In other embodiments, the thickness of the first epitaxial film 13 may also be 30 nm, the thickness of the second epitaxial film 14 may also be 50 nm, the thickness of the third epitaxial film 15 may also be 70 nm, and the thickness of the fourth epitaxial film 16 may also be 90 nm.

[0043] S3: After each epitaxial film layer is formed, doping source gas is synchronously introduced into the reaction chamber in a pulse mode to achieve in-situ doping of the epitaxial structure and to form a passivation layer 17 on the surface of the epitaxial structure using an atomic layer deposition process.

[0044] As an example, the doping source gas is B2H6 or PH3, and the in-situ doping process of the epitaxial structure includes simultaneously introducing B2H6 or PH3 into the reaction chamber and performing laser irradiation, wherein the wavelength of the laser is 532 nm and the power density is 10~50 mW / cm². 2 .

[0045] Specifically, to perform n-type or p-type doping on the first epitaxial layer 13, the second epitaxial layer 14, the third epitaxial layer 15, and the fourth epitaxial layer 16, after forming each epitaxial layer, a dopant source gas is pulsed into the CVD chamber. When the dopant source gas is B₂H₆, it corresponds to p-type doping; when the dopant source gas is PH₃, it corresponds to n-type doping. Simultaneously, laser irradiation is applied during the pulsed introduction of the dopant source gas into the CVD chamber. The laser irradiation selectively excites dangling bonds on the surfaces of the first epitaxial layer 13, the second epitaxial layer 14, the third epitaxial layer 15, and the fourth epitaxial layer 16, promoting their two-dimensional layered growth. The laser wavelength is 532 nm, and the power density is 10~50 mW / cm². 2 .

[0046] In some embodiments, the presence of numerous dangling bonds on the surface of the epitaxial structure, which act as centers for nonradiative recombination of charge carriers, severely reduces minority carrier lifetime. To reduce surface recombination of charge carriers in the epitaxial structure, such as... Figure 7 As shown, an atomic layer deposition process is used to form a passivation layer 17 on the surface of the fourth epitaxial film layer 16. The material forming the passivation layer 17 is aluminum oxide, hafnium oxide, or silicon nitride, and the thickness of the passivation layer 17 is 2~10nm. For example, the passivation layer 17 is an aluminum oxide layer and the thickness of the aluminum oxide layer is 5nm. On the one hand, this avoids stress accumulation caused by the excessive thickness of the passivation layer 17. On the other hand, the high density of the aluminum oxide layer effectively blocks the intrusion of external water vapor, oxygen, and metal ions, preventing the surface of the epitaxial structure from being oxidized or contaminated.

[0047] In summary, the method for preparing germanium-silicon epitaxial structures of the present invention achieves a gradient change in germanium composition from 0 to the target value among different epitaxial layers by adjusting the flow ratio of germanane and silane in different reaction stages. This effectively alleviates the mismatch stress caused by differences in lattice constants. Furthermore, the porous silicon buffer layer formed on the substrate surface can further release the mechanical stress at the interface. Low-temperature annealing after each reaction stage promotes the ordered rearrangement of atoms, significantly reducing the dislocation defect density. The strain relaxation layer formed between the substrate and the epitaxial structure effectively blocks the propagation of dislocation defects between the interfaces, significantly reducing the interface state density between the silicon substrate and the germanium-silicon epitaxial layers. In addition, by selectively exciting surface dangling bonds in different epitaxial layers with lasers of specific wavelengths and power densities, the two-dimensional layered growth of the epitaxial layers is promoted, ultimately obtaining a high-quality, low-defect-density germanium-silicon epitaxial structure, providing a superior material basis for the manufacture of high-performance silicon-based optoelectronic devices. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0048] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a germanium-silicon epitaxial structure, characterized in that, Includes the following steps: A substrate is provided, the substrate is pretreated to form a porous silicon buffer layer, and the pretreated substrate is placed in a reaction chamber; A first precursor gas, a second precursor gas, and a carrier gas are sequentially introduced into the reaction chamber. The different ratios of the first precursor gas and the second precursor gas are controlled to form an epitaxial structure on the substrate surface. The epitaxial structure includes at least a first epitaxial film layer, a second epitaxial film layer, a third epitaxial film layer, and a fourth epitaxial film layer. After each epitaxial film layer is formed, the reaction chamber is cooled and the carrier gas is introduced into the reaction chamber separately for annealing. After each epitaxial film layer is formed, dopant source gas is synchronously introduced into the reaction chamber in a pulse mode to achieve in-situ doping of the epitaxial structure and to form a passivation layer on the surface of the epitaxial structure using an atomic layer deposition process.

2. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The pretreatment process for the substrate includes electrochemical etching of the substrate, wherein the thickness of the porous silicon buffer layer is 30~50nm and the porosity of the porous silicon buffer layer is 20%~40%.

3. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The first precursor gas is GeH4, the second precursor gas is SiH4, the carrier gas is H2, and the flow rate ratio of the first precursor gas to the second precursor gas is 0~50%.

4. The method for preparing a germanium-silicon epitaxial structure according to claim 3, characterized in that: When forming the first epitaxial film, the second epitaxial film, the third epitaxial film, and the fourth epitaxial film, the flow ratio of GeH4 and SiH4 increases linearly from 0 to 50%.

5. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The thicknesses of the first epitaxial film, the second epitaxial film, the third epitaxial film, and the fourth epitaxial film are 20~100nm.

6. The method for preparing a germanium-silicon epitaxial structure according to claim 5, characterized in that: The first epitaxial film, the second epitaxial film, the third epitaxial film, and the fourth epitaxial film have the same thickness.

7. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The temperature at which each epitaxial film layer is formed is 600℃~750℃, and the temperature at which each epitaxial film layer is formed increases in a gradient.

8. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The doping source gas is B₂H₆ or PH₃. The in-situ doping process of the epitaxial structure includes simultaneously introducing B₂H₆ or PH₃ into the reaction chamber and performing laser irradiation, wherein the wavelength of the laser is 532 nm and the power density is 10~50 mW / cm². 2 .

9. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The material forming the passivation layer is aluminum oxide, hafnium oxide, or silicon nitride, and the thickness of the passivation layer is 2~10 nm.

10. The method for preparing a germanium-silicon epitaxial structure according to claim 1, characterized in that: The annealing temperature after each epitaxial film layer is formed shall not exceed 400℃, and the annealing time shall be controlled to be 2~10min.

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