Method for improving concentration uniformity and surface defect pits of P-type low doping

Abstract

The invention discloses a method for improving concentration uniformity and surface defect pits of P-type low doping. The method comprises the following steps: S1, putting a silicon carbide substrate on a graphite base in a silicon carbide epitaxial reaction cavity; s2, then hydrogen is introduced into the reaction cavity, and in-situ etching is carried out; s3, growing an N-type buffer layer by using a chemical vapor deposition method; s4, after the growth of the buffer layer is completed, stopping introducing ethylene, trichlorosilane and nitrogen, and introducing a fourth flow of HCl gas to assist hydrogen for etching; s5, the ethylene with the fifth flow, the trichlorosilane with the sixth flow and the trimethyl aluminum gas with the seventh flow are introduced again, and growth of the follow-up low-doped P-type epitaxial layer is completed; and S6, after the growth is finished, turning off ethylene, trichlorosilane and trimethylaluminum gases, and automatically conveying the wafer to a wafer taking area by an epitaxial reaction cavity system. According to the invention, the P-type doping concentration can be reduced, the doping uniformity can be improved, and the pits defect generated by adjusting the carbon-silicon ratio, the temperature and other conditions can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor, in particular to a method for improving the concentration uniformity and surface defect pits of P-type low doping. BACKGROUND

[0002] Currently, the industry mainly reduces the P-type doping concentration by adjusting the carbon silicon ratio, temperature, pressure and growth rate and other process parameters, but such methods are difficult to ensure good doping uniformity when the concentration is reduced to 5e14 or less. For example, if the P-type low doping concentration is reduced to 5e14 or less, the trace TMA used in the low doping process will cause poor doping uniformity due to the easy agglomeration of trimethylaluminum (TMA). At the same time, in order to achieve the goal of P-type low doping to 5e14, it is usually necessary to reduce the carbon silicon ratio or increase the temperature, and these adjustments will cause the imbalance of the carbon silicon ratio, thereby significantly increasing the number of surface pits defects. SUMMARY

[0003] The purpose of the present application is to overcome the above-mentioned defects in the prior art, and to provide a method for improving the concentration uniformity and surface defect pits of P-type low doping. By introducing HCl gas, the present application reduces the incorporation of Al atoms into the SiC lattice and the agglomeration of trace trimethylaluminum, which can further reduce the P-type doping concentration and improve the uniformity of doping. On the other hand, it can improve the pits defects caused by the imbalance of the carbon silicon ratio and reduce the number of pits defects.

[0004] To achieve the above-mentioned purpose, the present application provides a method for improving the concentration uniformity and surface defect pits of P-type low doping, comprising the following steps:

[0005] S1, placing a silicon carbide substrate on a graphite susceptor in a silicon carbide epitaxial reaction chamber by a mechanical hand of an epitaxial device;

[0006] S2, then introducing hydrogen into the reaction chamber, and slowly heating the temperature of the reaction chamber to a first temperature, and then performing in-situ etching while keeping the first temperature constant;

[0007] S3, introducing a first flow rate of ethylene, a second flow rate of trichlorosilane and a third flow rate of nitrogen into the reaction chamber, and growing a 1um thick N-type buffer layer with a doping concentration of 1E18 by chemical vapor deposition;

[0008]

[0008] S4, after the growth of the buffer layer is completed, stop introducing ethylene, trichlorosilane and nitrogen, and introduce a fourth flow rate of HCl gas assisted hydrogen for etching, which is used to reduce the memory effect of P-type doping;

[0009] S5. After etching, keep the HCl gas flowing in, and then introduce ethylene gas at a fifth flow rate, trichlorosilane gas at a sixth flow rate, and trimethylaluminum gas at a seventh flow rate to maintain a fixed growth rate and complete the subsequent growth of the low-doped P-type epitaxial layer, wherein the fifth flow rate is greater than the first flow rate, and the sixth flow rate is greater than the second flow rate.

[0010] S6. After growth is complete, the ethylene, trichlorosilane and trimethylaluminum gases are turned off, and then the reaction chamber is automatically cooled. When the temperature of the reaction chamber slowly decreases to the second temperature, the epitaxial reaction chamber system automatically transfers the wafer to the wafer pick-up area.

[0011] Furthermore, in steps S2-S6, the flow rate of hydrogen is 100~140 slm, and the pressure of the introduced gas is controlled to be 80~120 mbar.

[0012] Furthermore, the first temperature is 1600~1640℃, and the etching time in step S2 is controlled to be 5~10 minutes.

[0013] Furthermore, in step S3, the first flow rate is 24~35 sccm, the second flow rate is 60~80 sccm, and the third flow rate is 150~180 sccm.

[0014] Furthermore, in step S5, the fifth flow rate is 90~140 sccm, the sixth flow rate is 250~320 sccm, and the seventh flow rate is 20~60 sccm.

[0015] Furthermore, the fourth flow rate is 600~2000 sccm.

[0016] Furthermore, in step S4, the etching time using HCl gas to assist hydrogen gas is 60 seconds.

[0017] Furthermore, in step S5, the growth rate of the low-doped P-type epitaxial layer is controlled at 50~70µm / h, and its growth thickness is 5.5~10µm.

[0018] Furthermore, steps S3 to S6 all require the continuous flow of hydrogen gas while maintaining the temperature inside the reaction chamber at the first temperature.

[0019] Furthermore, the second temperature in step S6 is 700°C.

[0020] Compared to existing technologies, the advantages of this invention are as follows: by introducing HCl gas, aluminum atoms in trimethylaluminum can form Al-Cl bonds; these Al-Cl bonds have a relatively large bond energy, which can reduce the incorporation of Al atoms in the SiC lattice and the agglomeration of trace amounts of trimethylaluminum. Therefore, this method can not only further reduce the p-type doping concentration and improve doping uniformity, but also improve the pits defects caused by the carbon-silicon ratio imbalance and reduce their number. Attached Figure Description

[0021] To more clearly illustrate the technology in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Fig. 1 This is a schematic flowchart of a method for improving the concentration uniformity of low-doped P-type materials and reducing surface defects (pits) according to the present invention.

[0023] Fig. 2 This is a schematic diagram comparing the uniformity of doping concentration distribution on the wafer surface between the present invention and existing technologies;

[0024] Fig. 3 This is a schematic diagram comparing the number of pits on a wafer in this invention with that in the prior art. Detailed Implementation

[0025] The technology of this embodiment of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiment is one embodiment of the present invention, and not all embodiments thereof. Based on this embodiment of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0027] Furthermore, if the embodiments of the present invention involve descriptions such as "first" or "second", such descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated.

[0028] like Figs. 1 to 3The present invention discloses a method for improving the concentration uniformity of low-doped P-type materials and reducing surface defects (pits), comprising the following steps:

[0029] S1. The silicon carbide substrate is placed onto the graphite base inside the silicon carbide epitaxial reaction chamber by the robotic arm of the epitaxial equipment;

[0030] S2. Then hydrogen gas is introduced into the reaction chamber, and the temperature of the reaction chamber is slowly raised to the first temperature. While keeping the first temperature constant, in-situ etching is performed.

[0031] Preferably, in this embodiment, the flow rate of hydrogen gas introduced in step S2 is 100~140 slm, the pressure of the reaction chamber is controlled at 80~120 mbar, the first temperature is 1600~1640℃, and when the temperature of the reaction chamber reaches the first temperature of 1600~1640℃, the temperature of the reaction chamber is kept constant, and in-situ etching is performed, with the etching time controlled between 5~10 min.

[0032] Preferably, the temperature rise rate of the reaction chamber is 50~55℃ / min to ensure uniform heating of the silicon carbide substrate surface and reduce crystal defects caused by thermal stress.

[0033] It is understandable that by controlling the flow rate and pressure within the above range to uniformly etch the surface of the silicon carbide substrate, the optimal effect of removing surface contaminants and reshaping the surface atomic arrangement can be achieved. During operation, adjustments can be made according to the actual situation. Generally speaking, the ideal surface reconstruction effect can be achieved by controlling it within the above range.

[0034] S3. Introduce ethylene at a first flow rate, trichlorosilane at a second flow rate, and nitrogen at a third flow rate into the reaction chamber to grow an N-type buffer layer with a thickness of 1 μm and a doping concentration of 1E18 using chemical vapor deposition.

[0035] Preferably, in this embodiment, the first flow rate of ethylene is 24-35 sccm, the second flow rate of trichlorosilane is 60-80 sccm, and the third flow rate of nitrogen is 150-180 sccm. By precisely controlling the flow rate ratio of each gas, the consistency of doping concentration is ensured, forming a high-quality N-type buffer layer. For example, the first flow rate can be set to 24 sccm, 25 sccm, 30 sccm, or 35 sccm; the second flow rate can be set to 60 sccm, 70 sccm, or 80 sccm; and the third flow rate can be set to 150 sccm, 160 sccm, 170 sccm, or 180 sccm, to achieve precise control of the N-type doping concentration and ensure the uniformity of the epitaxial layer and crystal quality. This buffer layer helps to reduce the defect density in subsequent P-type epitaxial growth and improves the overall material performance.

[0036] Through the synergistic effect of the gas flow ratio and the temperature and pressure within the reaction chamber, the generation of defects such as micropipes and stacking faults in the epitaxial layer was effectively suppressed, further improving the crystal quality. Simultaneously, this buffer layer provides a good interface foundation for subsequent P-type epitaxial growth, significantly improving doping uniformity and surface pit defect density.

[0037] It should be noted that in step S3, the pressure inside the reaction chamber is controlled at 100~120 mbar, and the temperature is maintained at 1600~1640℃. This temperature and pressure window ensures the complete pyrolysis and surface reaction of the precursors (ethylene, trichlorosilane). Throughout the process, hydrogen is used as the carrier gas and reaction auxiliary gas, and the hydrogen flow rate is kept stable between 100~140 slm to maintain a stable flow field and thermal field uniformity inside the reaction chamber, promote the thorough mixing and uniform delivery of the reaction gases, effectively remove chlorine-containing byproducts, and inhibit gas-phase nucleation, thereby ensuring a smooth epitaxial layer surface.

[0038] By precisely controlling the flow ratio of nitrogen to trichlorosilane (N / Si), the N-type doping concentration was stabilized at 1×10⁻⁶. 18 cm -3 During the growth process, the proportions of all gas components and core process parameters remain constant to ensure the stability of the deposition rate and doping concentration, laying a solid foundation for the high-quality epitaxy of the subsequent P-type layer.

[0039] S4. After the buffer layer has grown, stop the flow of ethylene, trichlorosilane and nitrogen, and introduce HCl gas at a fourth flow rate to assist hydrogen in etching, in order to reduce the memory effect of P-type doping.

[0040] Preferably, the flow rate of HCl gas is controlled between 600 and 2000 sccm; and the etching time using HCl gas to assist hydrogen etching is 60 s. The etching process effectively removes surface oxides and impurities, while simultaneously controlling the surface morphology and improving the crystal quality of the subsequent P-type layer.

[0041] In addition, in this embodiment, the temperature inside the reaction chamber is maintained at 1600~1640℃, and the pressure is maintained at 100~120mbar to ensure the uniformity and stability of the etching process. The hydrogen flow rate is maintained at 100~140slm to ensure the stable delivery of the etching atmosphere and the timely removal of reaction byproducts.

[0042] Understandably, in this step, HCl gas is introduced. HCl gas, in combination with H2 at high temperature, has a very strong chemical etching ability and can etch the SiC surface. It reacts with the contaminated cavity wall component surface and the N-type buffer layer surface to generate volatile chlorides. These volatile chlorides are promptly discharged from the reaction chamber with the gas flow, thereby effectively purifying the growth interface.

[0043] S5. After etching, keep the HCl gas flowing in, and then introduce ethylene gas at a fifth flow rate, trichlorosilane gas at a sixth flow rate, and trimethylaluminum gas at a seventh flow rate to maintain a fixed growth rate and complete the subsequent growth of the low-doped P-type epitaxial layer, wherein the fifth flow rate is greater than the first flow rate, and the sixth flow rate is greater than the second flow rate.

[0044] Preferably, in this embodiment, the fifth flow rate is 90-140 sccm, the sixth flow rate is 250-320 sccm, and the seventh flow rate is 20-60 sccm to ensure a reasonable distribution of the P-type doping concentration gradient. By increasing the flow rate ratio of ethylene to trichlorosilane, the carbon-silicon ratio is adjusted to optimize crystal quality. The amount of trimethylaluminum introduced is slightly controlled to achieve controlled P-type doping, allowing aluminum atoms to be uniformly integrated into the crystal lattice and forming a high-quality P-type epitaxial layer. During the growth process, the temperature inside the reaction chamber is stabilized at a high temperature of 1600-1640℃, the pressure is maintained at 80-120 mbar, and the hydrogen flow rate is continuously controlled within the range of 100-140 slm.

[0045] In the p-type low-doping process, the reaction SiHCl3 + H2 ⇌ Si + 3HCl is endothermic. Cooling reduces Si formation. According to Si-Al competitive growth, the reduction of Si leads to an increase in p-type concentration, which is detrimental to the growth of p-type low-doped epitaxy. Therefore, in this embodiment, a high-temperature environment is maintained to ensure sufficient Si formation and suppress excessive Al doping, thereby effectively controlling the p-type doping concentration. Simultaneously, continuous HCl gas introduction further suppresses parasitic phase deposition, improves epitaxial layer interface clarity and crystal integrity, and ensures high-quality growth of the low-doped p-type layer.

[0046] By increasing the flow ratio of ethylene to trichlorosilane and adjusting the carbon-silicon ratio to optimize crystal quality, and by slightly controlling the amount of trimethylaluminum introduced, the growth rate of the low-doped P-type epitaxial layer is controlled at 50~70µm / h, and its growth thickness is 5.5~10μm. The obtained low-doped P-type epitaxial layer has excellent electrical uniformity and interface smoothness.

[0047] S6. After growth is complete, the ethylene, trichlorosilane and trimethylaluminum gases are shut off, and then the reaction chamber is automatically cooled. When the temperature of the reaction chamber slowly decreases to the second temperature, the epitaxial reaction chamber system automatically transfers the wafer to the wafer pick-up area.

[0048] It should be noted that before the wafer is transferred to the next process step, hydrogen gas must still be supplied to protect the high-temperature wafer from external environmental influences during the cooling process, preventing oxidation or contamination. Hydrogen gas is continuously supplied until the furnace temperature drops below a second temperature, which is 700°C, ensuring the wafer surface remains in an inert atmosphere until the cooling stage is complete, preventing any crystal defects caused by thermal stress. Once the temperature drops below 700°C, the hydrogen flow rate is gradually reduced and the heating system is shut down. At this point, the wafer structure is stable, and the surface is smooth with no signs of oxidation.

[0049] The temperature in the reaction chamber is reduced from a first temperature to a second temperature. This cooling process needs to be controlled at a rate of 40-45°C / min to avoid thermal stress cracking of the wafer due to rapid cooling, while ensuring the interface stability between the epitaxial layer and the substrate. This cooling rate has been optimized and verified to minimize crystal defect formation while maintaining production efficiency. Throughout the cooling process, a hydrogen atmosphere is continuously maintained to prevent the intrusion of any trace amounts of oxygen or moisture, ensuring a clean wafer surface.

[0050] This embodiment achieves low-doping of P-type silicon by reducing the carbon-to-silicon ratio, increasing the temperature, and adding HCl gas. It was found that without HCl, the agglomeration of trace amounts of trimethylaluminum leads to excessive concentration uniformity, and the imbalance of the carbon-to-silicon ratio increases pit defects in the epitaxial layer. The addition of HCl serves two purposes: firstly, it forms Al-Cl bonds with aluminum atoms in trimethylaluminum. The relatively high Al-Cl bond energy reduces the incorporation of Al atoms into the SiC lattice and the agglomeration of trace amounts of trimethylaluminum, thus lowering the doping concentration and improving concentration uniformity. Secondly, in silicon carbide epitaxy, trichlorosilane (SiHCl3) provides the silicon source through the decomposition reaction SiHCl3 → SiClx + HCl in a high-temperature hydrogen atmosphere. The addition of HCl can mitigate the excessive Si cluster aggregation caused by reducing the carbon-to-silicon ratio and increasing the temperature, thereby reducing localized carbon enrichment, making the reaction more balanced, and reducing pit defect formation. Therefore, the introduction of HCl not only optimizes the gas-phase reaction equilibrium but also smooths the surface step flow morphology through chemical etching, significantly suppressing the propagation of defects such as microtubes and stacking faults.

[0051] like Fig. 2 and Fig. 3 As shown, the comparison after the introduction of HCl gas shows that the concentration uniformity of the prior art process without adding HCl is 76.56%, while the concentration uniformity of the present invention is 4.93% after adding HCl, and the number of pits is reduced from 3360 / cm² to 20 / cm². Thus, the present application achieves low doping of P-type while improving its concentration uniformity and surface pit defects through the combined regulation of HCl gas, reducing the carbon-silicon ratio, and increasing the temperature.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the concentration uniformity of low-doped p-type materials and reducing surface defects (pits), characterized in that, Includes the following steps: S1. The silicon carbide substrate is placed onto the graphite base inside the silicon carbide epitaxial reaction chamber by the robotic arm of the epitaxial equipment; S2. Then hydrogen gas is introduced into the reaction chamber, and the temperature of the reaction chamber is slowly raised to the first temperature. While keeping the first temperature constant, in-situ etching is performed. S3. Introduce ethylene at a first flow rate, trichlorosilane at a second flow rate, and nitrogen at a third flow rate into the reaction chamber to grow an N-type buffer layer with a thickness of 1 μm and a doping concentration of 1E18 using chemical vapor deposition. S4. After the buffer layer has grown, stop the flow of ethylene, trichlorosilane and nitrogen, and introduce HCl gas at a fourth flow rate to assist hydrogen in etching, in order to reduce the memory effect of P-type doping. S5. After etching, keep the HCl gas flowing in, and then introduce ethylene gas at a fifth flow rate, trichlorosilane gas at a sixth flow rate, and trimethylaluminum gas at a seventh flow rate to maintain a fixed growth rate and complete the subsequent growth of the low-doped P-type epitaxial layer, wherein the fifth flow rate is greater than the first flow rate, and the sixth flow rate is greater than the second flow rate. S6. After growth is complete, the ethylene, trichlorosilane and trimethylaluminum gases are turned off, and then the reaction chamber is automatically cooled. When the temperature of the reaction chamber slowly decreases to the second temperature, the epitaxial reaction chamber system automatically transfers the wafer to the wafer pick-up area.

2. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, The flow rate of hydrogen in steps S2-S6 is 100~140 slm, and the pressure is controlled to be 80~120 mbar.

3. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, The first temperature is 1600~1640℃, and the etching time in step S2 is controlled to be 5~10min.

4. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, In step S3, the first flow rate is 24~35 sccm, the second flow rate is 60~80 sccm, and the third flow rate is 150~180 sccm.

5. The method for improving the concentration uniformity of low-doped p-type materials and reducing surface defects (pits) according to claim 4, characterized in that, In step S5, the fifth flow rate is 90~140 sccm, the sixth flow rate is 250~320 sccm, and the seventh flow rate is 20~60 sccm.

6. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, The fourth flow rate is 600~2000 sccm.

7. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, In step S4, the etching time using HCl gas to assist hydrogen gas is 60 seconds.

8. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, In step S5, the growth rate of the low-doped P-type epitaxial layer is controlled at 50~70µm / h, and its growth thickness is 5.5~10µm.

9. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, In steps S3 to S6, hydrogen gas must be continuously introduced while maintaining the temperature inside the reaction chamber at the first temperature.

10. The method for improving the concentration uniformity and surface defects (pits) of low-doped p-type materials according to claim 1, characterized in that, The second temperature in step S6 is 700°C.

Images