CN116288733A - Method for reducing silicon carbide epitaxial basal plane dislocation - Google Patents
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- 229910010271 silicon carbide Inorganic materials 0.000 title claims abstract description 49
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- 238000000034 method Methods 0.000 title claims abstract description 34
- 239000000758 substrate Substances 0.000 claims abstract description 65
- 238000000137 annealing Methods 0.000 claims abstract description 51
- 238000000407 epitaxy Methods 0.000 claims abstract description 21
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 20
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 20
- 239000013078 crystal Substances 0.000 claims abstract description 20
- 238000005498 polishing Methods 0.000 claims abstract description 19
- 239000000126 substance Substances 0.000 claims abstract description 12
- 239000012300 argon atmosphere Substances 0.000 claims abstract description 9
- 238000000227 grinding Methods 0.000 claims abstract description 8
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- 239000007789 gas Substances 0.000 claims description 6
- 238000011534 incubation Methods 0.000 claims description 2
- 238000002360 preparation method Methods 0.000 claims description 2
- 238000006243 chemical reaction Methods 0.000 abstract description 17
- 239000000463 material Substances 0.000 abstract description 8
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 26
- 229910052786 argon Inorganic materials 0.000 description 13
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- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 2
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- 230000015556 catabolic process Effects 0.000 description 2
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- 229910052710 silicon Inorganic materials 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- 238000005482 strain hardening Methods 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- 102000029749 Microtubule Human genes 0.000 description 1
- 108091022875 Microtubule Proteins 0.000 description 1
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- 238000005516 engineering process Methods 0.000 description 1
- 239000003344 environmental pollutant Substances 0.000 description 1
- 239000000374 eutectic mixture Substances 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
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- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
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- C30B25/00—Single-crystal growth by chemical reaction of reactive gases, e.g. chemical vapour-deposition growth
- C30B25/02—Epitaxial-layer growth
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Abstract
The invention discloses a method for reducing silicon carbide epitaxial basal plane dislocation, belonging to the technical field of silicon carbide crystal materials; the method comprises the following steps: grinding and mechanically polishing the silicon carbide crystal substrate; then, covering the surface of the substrate with a carbon film, and then carrying out annealing treatment or carrying out annealing treatment on the substrate in argon atmosphere to release the residual processing stress during thickness removal; the heat preservation time of the annealing treatment is 3-4 hours; after annealing, removing the carbon film from the substrate covered with the carbon film, and then performing chemical mechanical polishing; directly performing chemical mechanical polishing on the substrate annealed in the argon atmosphere; performing epitaxy after chemical mechanical polishing; the substrate after annealing has 100% of conversion rate of epitaxial basal plane dislocation, and solves the problems of high basal plane dislocation density in the center of the wafer after epitaxy and low conversion rate of basal plane dislocation in the center of the wafer during epitaxy.
Description
Technical Field
The invention belongs to the technical field of silicon carbide crystal materials, and relates to a method for reducing silicon carbide epitaxial basal plane dislocation, which is used for improving the conversion rate of substrate basal plane dislocation in the epitaxial process.
Background
The silicon carbide material is used as one of the most popular wide-bandgap semiconductor materials at present, has the excellent performances of large forbidden bandwidth, large critical breakdown electric field, large electron saturation drift velocity, high thermal conductivity and the like, thereby determining the wide application of the silicon carbide material in the fields of smart grids, electric automobiles, rail transit, new energy grid connection, switching power supplies, industrial motors, household appliances and the like, and showing good development prospects. Unlike conventional silicon power device fabrication processes, silicon carbide power devices cannot be fabricated directly on silicon carbide single crystal materials, and require high quality epitaxial layers to be grown on conductive silicon carbide single crystal substrates, on which various devices are fabricated. The development of silicon carbide related devices is not separated from the development of silicon carbide substrate epitaxy technology, and defects in the silicon carbide substrate can influence the yield of the epitaxy process and have larger influence on the performance of the devices. Therefore, how to obtain a high quality silicon carbide epitaxial layer by precisely controlling defects in a silicon carbide substrate becomes very important.
Silicon carbide substrate surface treatment is one of the important problems faced by silicon carbide epitaxy. The problems of scratches, sub-damage layers, pollutant residues and the like caused by the silicon carbide substrate cutting and polishing process in the early stage are more, and researchers adopt wet corrosion to reduce the influence of substrate surface defects on the quality of an epitaxial film before epitaxy. Effectively regulating defects in silicon carbide epitaxial layers is critical to ensuring the performance and reliability of silicon carbide power devices. Defects in silicon carbide epitaxial layers are largely classified as faults, dislocations, surface defects, and point defects. The Stacking Faults (SFs) exist in a variety of configurations, including the Shockley SFs and the Frank-type SFs, the dislocations in 4H silicon carbide include threading dislocations (TSDs), edge dislocations (TEDs), basal Plane Dislocations (BPDs), micropipes (MP), etc., which can be observed by defect selective etching. The screw dislocation mainly comes from the propagation of the substrate screw dislocation to the epitaxial layer, which affects the breakdown voltage of the device and reduces the reliability of the device. Edge dislocations are primarily derived from the extension of substrate edge dislocations, while the density of edge dislocations in the epitaxial layer increases due to the conversion of basal plane dislocations to edge dislocations, with less impact on device performance. Microtubule defects are currently well controlled. The base plane dislocation causes forward voltage drift of the bipolar device, and influences the stability of the device. The main reasons for the generation of basal plane dislocation in combination with the production process of silicon carbide from crystal to substrate include Wen Changre stress in the crystal growth process, impurity atoms in the raw material, and processing stress aggregation generated in the cutting, grinding and polishing of the processing process. The main reasons for the generation of basal plane dislocations from the substrate to the epitaxial production process include basal plane dislocations of the substrate itself and basal plane dislocations newly generated by thermal stress in the epitaxial process.
The basal plane dislocation slides along the (0001) plane in the crystal growth process, and more than 99% of the basal plane dislocation is converted into edge dislocation at the interface between the silicon carbide epitaxial layer and the substrate. But some of the basal plane dislocations still extend to the epitaxial layer, which has a fatal effect on device performance. Converting basal plane dislocations into edge dislocations is one of the focus of silicon carbide epitaxy research. The growth temperature has no effect on the evolution of the basal plane dislocation, and the high C/Si ratio and low growth rate are beneficial to inhibiting the propagation of the basal plane dislocation of the substrate to the silicon carbide epitaxial layer. The conversion of the basal plane dislocation to the edge dislocation is related to the included angle alpha between the dislocation line and the growth direction, the substrate inclination angle is reduced, the included angle between the basal plane dislocation and the growth direction can be increased, and the included angle between the edge dislocation and the growth direction is reduced, so that the conversion efficiency of the basal plane dislocation to the edge dislocation is increased. And (3) obtaining the epitaxial layer with the BPD conversion efficiency of more than or equal to 97% on the silicon carbide substrate with the inclination angle of 4 degrees. The low doping concentration n-silicon carbide epitaxial layer is favorable for converting BPD into TED, and the n doping concentration is that< 10 16 𝑐𝑚 -3 When the BPD conversion efficiency reaches 96% -99%. The conversion efficiency of BPDs can be improved by epitaxy on the silicon carbide substrate etched in molten KOH, and a silicon carbide epitaxial layer without BPD defects is obtained in this way. In addition, the method of adopting KOH-NaOH-MgO eutectic mixture to etch the substrate, hydrogen in-situ etching the substrate, interval regrowth method, introducing buffer layer and the like can also effectively improve the conversion efficiency of BPDs and even achieve 100 percent conversion.
In practical epitaxial production, the problem that the basal plane dislocation density of the center of the wafer after epitaxy is higher and the basal plane dislocation conversion rate of the center of the epitaxial process is low is often found.
Disclosure of Invention
The invention overcomes the defects of the prior art and provides a method for reducing the plane dislocation of a silicon carbide epitaxial substrate; the problem that the basal plane dislocation density of the center of the wafer after epitaxy is high and the conversion rate of the basal plane dislocation of the center of the wafer during epitaxy is low is solved.
In order to achieve the above purpose, the present invention is realized by the following technical scheme.
A method of reducing dislocation of epitaxial basal planes of silicon carbide comprising the steps of:
1) And grinding and mechanically polishing the silicon carbide crystal substrate.
2) In the conventional annealing process, as the boiling point of silicon is lower than that of carbon, carbonization occurs on the surface, and the annealing treatment is performed after the surface of the substrate is covered with a carbon film or the substrate is annealed in an argon atmosphere, so that high-temperature carbonization can be avoided and the residual processing stress during thickness removal can be released; the heat preservation time of the annealing treatment is 3-4 hours.
3) After annealing, removing the carbon film from the substrate covered with the carbon film, and then performing chemical mechanical polishing; the substrate annealed in the argon atmosphere was directly subjected to chemical mechanical polishing.
4) The chemical mechanical polishing is followed by epitaxy.
Preferably, the incubation time of the annealing treatment is 3 hours.
Preferably, the heat preservation temperature of the annealing treatment is 1000 ℃.
Preferably, the argon atmosphere is added with SiH 4 And (3) gas.
Preferably, the preparation method of the silicon carbide crystal is PVT method.
Preferably, the substrate is epitaxially grown by CVD.
Compared with the prior art, the invention has the following beneficial effects:
the invention carries out carbon film covering annealing on the mechanically polished substrate or adds a proper amount of SiH into the mechanically polished substrate under the protection of argon 4 Annealing, and regulating and controlling the annealing time of the substrate covered carbon film or the argon protection annealing time; the conversion rate of the epitaxial basal plane dislocation of the annealed substrate reaches 100%, and the method can effectively solve the problem that internal stress exists in the material after work hardening in the processes of cutting, grinding and mechanical polishing of crystals, and improves the conversion rate of the basal plane dislocation.
Drawings
FIG. 1 is an annealing temperature setting curve used in examples 1 and 2.
FIG. 2 is a graph showing the dislocation tendency of the substrate and epitaxial wafer substrate surface annealed for 0, 1, 2, and 3 hours with the carbon film of example 1.
Fig. 3 is a graph showing the substrate and epitaxial wafer basal plane dislocation trends for example 2 argon shield anneals for 0, 1, 2, and 3 hours.
Fig. 4 is a schematic view of an apparatus structure for argon protection annealing in example 2.
FIG. 5 is a graph showing the density distribution of epitaxial basal plane dislocations at different annealing times for the film of example 1.
FIG. 6 is a graph showing the density of epitaxial basal plane dislocations at different anneal times under argon shield of example 2.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the invention is further described in detail by combining the embodiments and the drawings. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention. The following describes the technical scheme of the present invention in detail with reference to examples and drawings, but the scope of protection is not limited thereto.
Example 1
The embodiment provides a method for reducing silicon carbide epitaxial basal plane dislocation; in this embodiment, the substrate covered with the carbon film is annealed to release the processing stress remaining during the thickness removal, thereby reducing the dislocation of the epitaxial base plane of silicon carbide. In this embodiment, the same crystal is cut into four identical substrates for processing.
As shown in fig. 2, the same crystal is cut into four adjacent substrates, which are subjected to the same grinding and mechanical polishing process.
And covering the surfaces of the four substrates with a carbon film.
And annealing the substrate with the carbon film covered on the surface for different time, and releasing the residual processing stress when the thickness is removed, wherein the first piece close to the C surface is not annealed, the second piece is annealed for 1 hour, the third piece is annealed for 2 hours, the fourth piece is annealed for 3 hours, the annealing temperature is 1000 ℃, the annealing temperature curves are as shown in figure 1, only the difference exists in the heat preservation time, and the temperature rise and the temperature reduction are consistent.
And removing the carbon film on the surface after annealing, and performing chemical mechanical polishing to obtain the substrate with good surface state. Epitaxy was performed using the same epitaxy process and the dislocation density after epitaxy was examined, and the results are shown in table 5.
Referring to fig. 5, the substrate after annealing for 3 hours with the carbon film had a basal plane dislocation density of 0, and it was reached that the annealed substrate had a 100% conversion rate of the epitaxial basal plane dislocation.
Example 2
The embodiment provides a method for reducing silicon carbide epitaxial basal plane dislocation; in the embodiment, the substrate is placed in an annealing furnace protected by argon gas for annealing treatment, and the residual processing stress during thickness removal is released, so that the planar dislocation of the epitaxial base of the silicon carbide is reduced. In this embodiment, the same crystal is cut into four identical substrates for processing.
As shown in FIG. 4, a schematic structural diagram of an annealing furnace according to the present embodiment is shown, in which a furnace body 1 is provided with an argon gas inlet 2 and SiH 4 An air inlet 3; a vacuum exhaust port 4 is also arranged; the furnace body 1 is used for placing a wafer 5 to be annealed. The annealing furnace is vacuumized and filled with argon, and a proper amount of SiH is added in the argon atmosphere 4 Annealing is performed.
As shown in fig. 3, after the operation of evacuating and argon-filling the substrate with few basal plane dislocations near the first basal plane dislocation of the C-plane of crystal growth, the annealing furnace does not perform the temperature-raising and temperature-lowering annealing.
And annealing the second sheet close to the C surface for 1 hour, annealing the third sheet for 2 hours and annealing the fourth sheet for 3 hours under the protection of argon, wherein the annealing temperature is 1000 ℃, the annealing temperature curves are as shown in figure 1, only the difference in the heat preservation time exists, and the temperature rise and the temperature reduction are consistent. And carrying out chemical mechanical polishing after annealing to obtain the substrate with good surface state. Carrying out epitaxy by using the same epitaxy process and detecting dislocation density after epitaxy; as shown in fig. 6, the density distribution diagram of the epitaxial basal plane dislocation under the protection of argon gas at different annealing times is shown.
Referring to fig. 6, the substrate after annealing for 3 hours under the protection of argon gas has a basal plane dislocation density of 0, and the conversion rate of the annealed substrate through the epitaxial basal plane dislocation is 100%.
In order to effectively control the basal plane dislocation density after silicon carbide epitaxy, examples 1 and 2 ensure the purity of the raw materials, and annealing is performed after crystal growth; under the condition of adjusting proper temperature field and C/Si ratio of epitaxial furnace, cutting, grinding and mechanically polishing the crystal, reducing stress in the substrate by annealing, covering and annealing the surface of the substrate with carbon film, or adding proper amount of SiH into the mechanically polished substrate under the protection of argon 4 Annealing, and performing chemical mechanical polishing after annealing; because energy cannot be generated by blank or vanish in the processes of cutting, grinding and mechanical polishing of the crystal, internal stress exists in the material after work hardening, and the substrate covering carbon film annealing time or argon protection annealing time is regulated and controlled, so that the basal plane dislocation density of the center of the wafer is effectively regulated and controlled.
While the invention has been described in detail in connection with specific preferred embodiments thereof, it is not to be construed as limited thereto, but rather as a result of a simple deduction or substitution by a person having ordinary skill in the art to which the invention pertains without departing from the scope of the invention defined by the appended claims.
Claims (6)
1. A method for reducing dislocation of epitaxial basal planes of silicon carbide, comprising the steps of:
1) Grinding and mechanically polishing the silicon carbide crystal substrate;
2) Then, covering the surface of the substrate with a carbon film, and then carrying out annealing treatment or carrying out annealing treatment on the substrate in argon atmosphere to release the residual processing stress during thickness removal; the heat preservation time of the annealing treatment is 3-4 hours;
3) After annealing, removing the carbon film from the substrate covered with the carbon film, and then performing chemical mechanical polishing; directly performing chemical mechanical polishing on the substrate annealed in the argon atmosphere;
4) The chemical mechanical polishing is followed by epitaxy.
2. A method of reducing dislocation of epitaxial basal planes of silicon carbide as claimed in claim 1 wherein the incubation time of the annealing treatment is 3 hours.
3. A method of reducing dislocation of epitaxial basal planes of silicon carbide as claimed in claim 1 or claim 2 wherein the soak temperature of the annealing treatment is 1000 ℃.
4. The method for reducing planar dislocation of epitaxial substrate of silicon carbide as claimed in claim 1, wherein the argon atmosphere is added with SiH 4 And (3) gas.
5. The method for reducing dislocation of epitaxial base of silicon carbide as claimed in claim 1, wherein the preparation method of silicon carbide crystal is PVT method.
6. A method of reducing dislocation of epitaxial basal planes of silicon carbide as claimed in claim 1 wherein the method of epitaxial growth of the substrate is CVD.
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