CN108796616B - Method for improving uniformity of p-type doping concentration in silicon carbide epitaxial wafer - Google Patents
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Abstract
The invention discloses a method for improving the uniformity of p-type doping concentration in a silicon carbide epitaxial wafer, which is based on a chemical vapor deposition growth technology, a small amount of silicon source, carbon source, hydrogen chloride, trimethylaluminum and the like are added into air flotation gas of a base, and then the air flotation gas is used as carrier gas to push a small amount of process gas to the edge of a graphite base so as to finely adjust the p-type doping efficiency of the edge of a substrate. The method effectively reduces the deviation of the doping concentration of the edge point and the central point of the epitaxial wafer caused by nonlinear depletion, and effectively optimizes the uniformity of the in-wafer doping concentration of the epitaxial wafer on the premise of not changing key process parameters. The process is compatible with the conventional SiC epitaxial process and has higher popularization value.
Description
Technical Field
The invention belongs to the technical field of semiconductor materials, and particularly relates to a method for improving uniformity of p-type doping concentration in a silicon carbide epitaxial wafer.
Background
In recent years, with the continuous development of power electronic technology, the physical limitations of traditional power electronic devices based on silicon (Si) materials are increasingly appearing, and the improvement of the working voltage (<8kV), the working current, the working frequency, the working temperature (<175 ℃), the dissipation power, the radiation resistance and other performances of the devices are severely restricted.
Currently, silicon carbide (SiC) materials are internationally recognized as next generation power electronic device materials. The SiC power electronic device has unique performance potentials of ultrahigh voltage (up to 4 ten thousand volts), ultrahigh current (up to thousands of amperes), ultrahigh junction temperature (over 500 ℃), high reliability and the like, and is a core element of a power electronic device in large-capacity application. As a bipolar fully-controlled switch device, an insulated gate field effect transistor (IGBT) is the dominant structure of a high-voltage large-capacity power electronic device. The IGBT device is different from a Schottky diode device, a high-quality p-type epitaxial layer is contained in an epitaxial structure of the Schottky diode device, and the obtained p-type SiC epitaxial layer with low defect density and high uniformity is the basis for developing the SiC IGBT.
In recent years, n-type SiC epitaxy technology has been greatly developed, and both defect suppression and uniformity control technology have been broken through, but p-type SiC epitaxy technology is far less mature than n-type SiC epitaxy technology. In the patent "a method for improving the uniformity of n-type doping concentration in silicon carbide epitaxial wafer" (ZL201310615586.8), "it is proposed that the uniformity of n-type doping concentration in the epitaxial wafer is improved by adding process gas into air floating gas on the premise of not changing the key process parameters of epitaxy. The mechanism of adjusting the edge doping of the epitaxial wafer by adding process gas into the air flotation gas is also applicable to improving the uniformity in the p-type doped wafer, but the control rules of the p-type doping and the n-type doping are completely different, and the method provided by the patent is not applicable to p-type SiC epitaxy.
Aluminum is an effective p-type dopant for silicon carbide, and occupies silicon crystal sites in silicon carbide, so that a competitive mechanism of Al impurity atoms and Si atoms exists, the p-type doping efficiency is proportional to a carbon-to-silicon ratio (C/Si ratio), and the p-type doping efficiency can be changed by adjusting the C/Si ratio in the process gas. When the difference between the p-type doping concentration at the edge and the center of the epitaxial wafer is not large, a silicon source or a carbon source is added into the gas floatation, and the C/Si ratio at the edge of the epitaxial wafer is locally adjusted, so that the purpose of optimizing the uniformity in the wafer is achieved. When the difference between the doping concentration of the p-type epitaxial wafer edge and the doping concentration of the p-type epitaxial wafer center is large, if the C/Si ratio of the edge is further adjusted, the C/Si ratio of the edge deviates from a process window, and the number of epitaxial defects is increased. The doping efficiency of the edge needs to be adjusted in other ways. The hydrogen chloride can also greatly reduce the probability of Al entering crystal lattices and reduce the p-type doping efficiency. The p-type doping efficiency at the edge of the epitaxial wafer can be reduced by adding hydrogen chloride in the air flotation. And the p-type doping concentration of the edge of the epitaxial wafer can be directly improved by directly adding trimethylaluminum into the air flotation gas.
Disclosure of Invention
The purpose of the invention is as follows: aiming at the problems, the invention provides a method for improving the uniformity of the p-type doping concentration in a silicon carbide epitaxial wafer.
The technical scheme is as follows: in order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows: a method for improving the uniformity of p-type doping concentration in a silicon carbide epitaxial wafer comprises the following steps:
(1) placing a silicon surface silicon carbide substrate on a graphite base in a reaction chamber of a silicon carbide epitaxial system;
(2) replacing the gas in the reaction chamber for multiple times by adopting argon, introducing hydrogen into the reaction chamber, gradually increasing the hydrogen flow to 60-120L/min, setting the pressure of the reaction chamber to be 80-200 mbar, gradually heating the reaction chamber to the growth temperature of 1550-1700 ℃, maintaining the temperature of the reaction chamber for 5-15 minutes after the growth temperature is reached, and etching the substrate by adopting pure hydrogen;
(3) introducing a silicon source and a carbon source with small flow into the reaction chamber, controlling the flow ratio of the silicon source to the hydrogen gas to be less than 0.03%, and introducing a p-type doping source of trimethylaluminum with the growth thickness of0.5-5 μm, and the doping concentration is 1-5E 18cm-3The highly doped buffer layer;
(4) changing the flow rates of a silicon source, a carbon source and a p-type doping source to a set value required by the growth of an epitaxial structure in a linear gradual change mode, and selecting the type of process gas added into the air flotation gas according to the distribution mode of the doping concentration of a typical epitaxial wafer along the diameter direction of the substrate under the process condition;
(5) after the epitaxial structure growth is completed, the growth source and the doping source are closed, the temperature of the reaction chamber is reduced to room temperature in the hydrogen atmosphere, after the temperature of the reaction chamber reaches the room temperature, hydrogen is discharged, gas in the reaction chamber is replaced for many times through argon, finally, the pressure of the reaction chamber is inflated to atmospheric pressure through the argon, and then the chamber is opened to take the wafer.
In the step (4), when the p-type doping concentration of the epitaxial wafer is high at two sides and low in the middle and is distributed in a bowl shape, and the edge doping concentration does not exceed the doping concentration of the central point by 20%, a silicon source is added into the air flotation gas, and the flow rate of the silicon source added into the air flotation gas does not exceed 15% of the flow rate of the silicon source used for the process.
In the step (4), when the p-type doping concentration of the epitaxial wafer is high at two sides and low in the middle and is distributed in a bowl shape, and the edge doping concentration exceeds the doping concentration of the central point by 20%, a silicon source and hydrogen chloride are added into the air flotation gas, the flow rate of the silicon source added into the air flotation gas is not more than 15% of that of the silicon source used for the process, and the flow rate of the hydrogen chloride is not more than 0.05% of that of the hydrogen flow in the reaction chamber.
In the step (4), when the p-type doping concentration of the epitaxial wafer is low at two sides and high in the middle and is distributed in an arch bridge shape, and the edge doping concentration exceeds the doping concentration of the central point by 20%, adding a carbon source into the air flotation gas, wherein the flow rate of the carbon source added into the air flotation gas is not more than 15% of the flow rate of the process carbon source.
In the step (4), when the p-type doping concentration of the epitaxial wafer is low at two sides and high in the middle and is distributed in an arch bridge shape, and the doping concentration at the edge exceeds the doping concentration at the central point by 20%, a carbon source and trimethylaluminum are added into the air flotation gas, the flow rate of the carbon source added into the air flotation gas is not more than 15% of the flow rate of the process carbon source, and the actual flow rate of the trimethylaluminum is not more than 0.02% of the hydrogen flow rate of the reaction chamber.
In the step (1), a silicon surface silicon carbide substrate deviated to the <11-20> direction by 4 degrees or 8 degrees is selected.
In the step (4), the silicon source is silane, dichlorosilane, trichlorosilane or tetrachlorohydrogensilicon; the carbon source is methane, ethylene, acetylene or propane.
Has the advantages that: compared with the common epitaxy technology, the invention realizes the optimization of the doping concentration uniformity of the epitaxial wafer by adding a small amount of process gas into the air flotation gas under the condition of not changing the key process parameters, thereby enlarging the selection window of the key process parameters and realizing more excellent key indexes such as background concentration, surface appearance, defect density and the like.
Drawings
FIG. 1 is a schematic diagram of the fine tuning of the substrate edge gas distribution by adding an assist gas to the pedestal gas bearing;
FIG. 2 is a comparison graph of doping concentration distribution of epitaxial wafers along the radial direction, after 3.5ml/min propane is added into the air flotation gas, and different flow rates of trimethylaluminum are added into the air flotation gas.
Detailed Description
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
In order to improve the uniformity of the p-type doping concentration in the silicon carbide epitaxial wafer and reduce the doping concentration deviation of the central point and the edge point of the silicon carbide epitaxial wafer on the premise of not changing the key epitaxial process parameters, the invention provides a method for improving the uniformity of the p-type doping concentration in the silicon carbide epitaxial wafer.
The invention discloses a method for improving the uniformity of p-type doping concentration in a silicon carbide epitaxial wafer, which comprises the following steps:
(1) selecting a silicon surface silicon carbide substrate deflected to the <11-20> direction by 4 degrees or 8 degrees, and placing the substrate on a graphite base in a reaction chamber of the SiC epitaxial system;
(2) the argon is adopted to replace the gas in the reaction chamber for many times, and hydrogen (H) is introduced into the reaction chamber2) Gradually increasing the hydrogen flow to 60-120L/min, and using hydrogen as the air-floating gas to push the graphite baseRotating, setting the pressure of the reaction chamber to be 80-200 mbar, gradually heating the reaction chamber to the growth temperature of 1550-1700 ℃, maintaining the temperature of the reaction chamber for 5-15 minutes after the temperature reaches the growth temperature, and carrying out pure hydrogen H on the substrate2Etching;
(3) introducing a small-flow silicon source and a carbon source into the reaction chamber, and controlling the flow ratio (Si/H) of the silicon source and the hydrogen gas2Ratio) is less than 0.03 percent, p-type doping source Trimethylaluminum (TMA) is introduced, the growth thickness is 0.5-5 mu m, and the doping concentration is 1-5E 18cm-3The highly doped buffer layer;
(4) changing the flow rates of the silicon source, the carbon source and the p-type doping source to a set value required by the growth of an epitaxial structure in a linear gradual change mode, and selecting the type of the process gas added into the air flotation gas according to the distribution mode of the typical epitaxial wafer doping concentration along the diameter direction of the substrate under the process condition, as shown in fig. 1, wherein the specific selection method comprises the following steps:
(4.1) adding a silicon source into the air flotation gas under the condition that the p-type doping concentration of the epitaxial wafer is high at two sides and low in the middle and is bowl-shaped and distributed, and the edge doping concentration does not exceed the doping concentration of the central point by 20%, wherein the flow of the silicon source added into the air flotation gas does not exceed 15% of the flow of the silicon source used for the process;
(4.2) adding a silicon source and hydrogen chloride into the air flotation gas under the process condition that the p-type doping concentration of the epitaxial wafer is high at two sides and low in the middle and is distributed in a bowl shape, and the edge doping concentration exceeds the doping concentration of the central point by 20%, wherein the flow of the silicon source added into the air flotation gas is not more than 15% of that of the silicon source used for the process, and the flow of the hydrogen chloride is not more than 0.05% of that of the hydrogen flow in the reaction chamber;
(4.3) adding a carbon source into the air flotation gas under the process condition that the p-type doping concentration of the epitaxial wafer is low at two sides and high in the middle and is distributed in an arch bridge shape, and the edge doping concentration exceeds the doping concentration of the central point by 20%, wherein the flow rate of the carbon source added into the air flotation gas is not more than 15% of that of the process carbon source;
(4.4) under the process condition, when the p-type doping concentration of the epitaxial wafer is low at two sides and high in the middle and is distributed in an arch bridge shape, and the edge doping concentration exceeds the doping concentration of the central point by 20%, adding a carbon source and trimethylaluminum into the air flotation gas, wherein the flow rate of the carbon source added into the air flotation gas is not more than 15% of the flow rate of the process carbon source, and the actual flow rate of the trimethylaluminum is not more than 0.01% of the hydrogen flow rate of the reaction chamber.
The flow rate of the auxiliary gas added into the air flotation gas is set according to key process conditions, and the actual value needs to be determined through multiple experimental comparison, so that the flat radial distribution of the doping concentration is realized as a selection standard. The epitaxial growth time is set according to the actual epitaxial rate and the required epitaxial layer thickness.
(5) After the epitaxial structure growth is completed, the growth source and the doping source are closed, the temperature of the reaction chamber is reduced to room temperature in the hydrogen atmosphere, after the temperature of the reaction chamber reaches the room temperature, the hydrogen is discharged, the gas in the reaction chamber is replaced for many times through argon, finally, the pressure of the reaction chamber is inflated to the atmospheric pressure through the argon, and then the chamber is opened to take the wafer.
The technical solution of the present invention is explained in detail by a specific embodiment.
The method for improving the uniformity of the p-type doping concentration in the silicon carbide epitaxial wafer in the SiC chemical vapor deposition epitaxial system comprises the following steps:
1. selecting a silicon surface silicon carbide substrate deflected to the direction of <11-20> by 4 degrees, and placing the substrate on a graphite base in a reaction chamber of the SiC epitaxial system;
2. the argon is adopted to replace the gas in the reaction chamber for many times, and hydrogen (H) is introduced into the reaction chamber2) Gradually increasing hydrogen flow to 100L/min, selecting hydrogen as air-floating gas to push the graphite base to rotate, setting the pressure of the reaction chamber at 100mbar, gradually heating the reaction chamber to 1650 deg.C, maintaining the temperature of the reaction chamber for 5 min, and carrying out pure hydrogen H on the substrate2Etching;
3. silane and propane are introduced into the reaction chamber at the flow rates of 20ml/min and 10ml/min respectively, and a doping source of trimethylaluminum is introduced at the flow rate of 20ml/min for 12 minutes, the growth thickness of the trimethylaluminum is 1 mu m, and the doping concentration is 3E18cm-3The p-type highly doped buffer layer;
4. setting the flow rate of trimethylaluminum to 10ml/min, increasing the flow rates of silane and propane to 50ml/min and 25ml/min in 30 seconds by adopting a linear gradual change mode, adding propane into air flotation gas, setting the flow rates of the trimethylaluminum to 3.5ml/min and 3ml/min respectively, setting the time to 30 minutes, and growing a 12-micron p-type doped epitaxial layer;
5. after the epitaxial structure growth is completed, the growth source and the doping source are closed, the temperature of the reaction chamber is reduced to room temperature in the hydrogen atmosphere, after the temperature of the reaction chamber reaches the room temperature, the hydrogen is discharged, the gas in the reaction chamber is replaced for many times through argon, finally, the pressure of the reaction chamber is inflated to the atmospheric pressure through the argon, and then the chamber is opened to take the wafer.
The reason why the flow rates of propane and trimethylaluminum in the aerosol gas in the step 4 are set to 3.5ml/min and 3ml/min, respectively, is as follows: under typical process conditions of silane flow 50ml/min, propane flow 25ml/min, growth temperature 1650 ℃, reaction chamber pressure 100mbar and hydrogen gas floatation flow 1000ml/min, the epitaxial wafer has p-type doping concentration with two low sides and high middle, is distributed in an arch bridge, and has p-type doping concentration deviation of the edge and the center point larger than 20%. According to the method provided by the invention, as the propane adopted by the process is 25ml/min, the flow rate of the propane added in the air flotation gas should not be more than 3.75ml/min, and 3.5ml/min propane is selected to be added in the air flotation gas in the embodiment. And then adjusting by adding trimethylaluminum into the air flotation gas. FIG. 2 is a comparison graph of doping concentration distribution of epitaxial wafers along the radial direction, after 3.5ml/min propane is added into the air flotation gas, and different flow rates of trimethylaluminum are added into the air flotation gas. Under the process condition, the flat p-type doping concentration can be realized by selecting the trimethylaluminum flow of 3 ml/min.
By adding a small amount of process gas into the air flotation gas, the uniformity of the in-chip doping concentration of the epitaxial wafer can be effectively optimized under the condition of not changing key process parameters. Therefore, the window of key process parameters is enlarged, and more excellent key indexes such as background concentration, surface appearance, defect density and the like are realized.
Claims (5)
1. A method for improving the uniformity of p-type doping concentration in a silicon carbide epitaxial wafer is characterized in that: the method comprises the following steps:
(1) placing a silicon surface silicon carbide substrate on a graphite base in a reaction chamber of a silicon carbide epitaxial system;
(2) replacing the gas in the reaction chamber for multiple times by adopting argon, introducing hydrogen into the reaction chamber, gradually increasing the hydrogen flow to 60-120L/min, setting the pressure of the reaction chamber to be 80-200 mbar, gradually heating the reaction chamber to the growth temperature of 1550-1700 ℃, maintaining the temperature of the reaction chamber for 5-15 minutes after the growth temperature is reached, and etching the substrate by adopting pure hydrogen;
(3) introducing a silicon source and a carbon source with small flow into the reaction chamber, controlling the flow ratio of the silicon source to the hydrogen gas to be less than 0.03%, introducing a p-type doping source of trimethylaluminum, wherein the growth thickness is 0.5-5 mu m, and the doping concentration is 1-5E 18cm-3The highly doped buffer layer;
(4) changing the flow rates of a silicon source, a carbon source and a p-type doping source to a set value required by the growth of an epitaxial structure in a linear gradual change mode, and selecting the type of process gas added into the air flotation gas according to the distribution mode of the doping concentration of a typical epitaxial wafer along the diameter direction of the substrate under the process condition; the method specifically comprises the following steps: the epitaxial wafer p-type doping concentration is high at two sides and low in the middle and is distributed in a bowl shape, when the edge doping concentration exceeds the center point doping concentration by 20%, a silicon source and hydrogen chloride are added into air flotation gas, the flow of the silicon source added into the air flotation gas is not more than 15% of the flow of a silicon source for a process, and the flow of the hydrogen chloride is not more than 0.05% of the flow of hydrogen in a reaction chamber;
(5) after the epitaxial structure growth is completed, the growth source and the doping source are closed, the temperature of the reaction chamber is reduced to room temperature in the hydrogen atmosphere, after the temperature of the reaction chamber reaches the room temperature, hydrogen is discharged, gas in the reaction chamber is replaced for many times through argon, finally, the pressure of the reaction chamber is inflated to atmospheric pressure through the argon, and then the chamber is opened to take the wafer.
2. The method of claim 1, wherein the p-type doping concentration uniformity within the silicon carbide epitaxial wafer is improved by: in the step (1), a silicon surface silicon carbide substrate deviated to the <11-20> direction by 4 degrees or 8 degrees is selected.
3. The method of claim 1, wherein the p-type doping concentration uniformity within the silicon carbide epitaxial wafer is improved by: in the step (4), the silicon source is silane, dichlorosilane, trichlorosilane or tetrachlorohydrogensilicon; the carbon source is methane, ethylene, acetylene or propane.
4. A method for improving the uniformity of p-type doping concentration in a silicon carbide epitaxial wafer is characterized in that: the method comprises the following steps:
(1) placing a silicon surface silicon carbide substrate on a graphite base in a reaction chamber of a silicon carbide epitaxial system;
(2) replacing the gas in the reaction chamber for multiple times by adopting argon, introducing hydrogen into the reaction chamber, gradually increasing the hydrogen flow to 60-120L/min, setting the pressure of the reaction chamber to be 80-200 mbar, gradually heating the reaction chamber to the growth temperature of 1550-1700 ℃, maintaining the temperature of the reaction chamber for 5-15 minutes after the growth temperature is reached, and etching the substrate by adopting pure hydrogen;
(3) introducing a silicon source and a carbon source with small flow into the reaction chamber, controlling the flow ratio of the silicon source to the hydrogen gas to be less than 0.03%, introducing a p-type doping source of trimethylaluminum, wherein the growth thickness is 0.5-5 mu m, and the doping concentration is 1-5E 18cm-3The highly doped buffer layer;
(4) changing the flow rates of a silicon source, a carbon source and a p-type doping source to a set value required by the growth of an epitaxial structure in a linear gradual change mode, and selecting the type of process gas added into the air flotation gas according to the distribution mode of the doping concentration of a typical epitaxial wafer along the diameter direction of the substrate under the process condition; the method specifically comprises the following steps: the epitaxial wafer p-type doping concentration is high at two sides and low in the middle and is distributed in a bowl shape, when the edge doping concentration does not exceed the center point doping concentration by 20%, a silicon source is added into air flotation gas, and the flow rate of the silicon source added into the air flotation gas does not exceed 15% of the flow rate of a silicon source used for the process;
(5) after the epitaxial structure growth is completed, the growth source and the doping source are closed, the temperature of the reaction chamber is reduced to room temperature in the hydrogen atmosphere, after the temperature of the reaction chamber reaches the room temperature, hydrogen is discharged, gas in the reaction chamber is replaced for many times through argon, finally, the pressure of the reaction chamber is inflated to atmospheric pressure through the argon, and then the chamber is opened to take the wafer.
5. A method for improving the uniformity of p-type doping concentration in a silicon carbide epitaxial wafer is characterized in that: the method comprises the following steps:
(1) placing a silicon surface silicon carbide substrate on a graphite base in a reaction chamber of a silicon carbide epitaxial system;
(2) replacing the gas in the reaction chamber for multiple times by adopting argon, introducing hydrogen into the reaction chamber, gradually increasing the hydrogen flow to 60-120L/min, setting the pressure of the reaction chamber to be 80-200 mbar, gradually heating the reaction chamber to the growth temperature of 1550-1700 ℃, maintaining the temperature of the reaction chamber for 5-15 minutes after the growth temperature is reached, and etching the substrate by adopting pure hydrogen;
(3) introducing a silicon source and a carbon source with small flow into the reaction chamber, controlling the flow ratio of the silicon source to the hydrogen gas to be less than 0.03%, introducing a p-type doping source of trimethylaluminum, wherein the growth thickness is 0.5-5 mu m, and the doping concentration is 1-5E 18cm-3The highly doped buffer layer;
(4) changing the flow rates of a silicon source, a carbon source and a p-type doping source to a set value required by the growth of an epitaxial structure in a linear gradual change mode, and selecting the type of process gas added into the air flotation gas according to the distribution mode of the doping concentration of a typical epitaxial wafer along the diameter direction of the substrate under the process condition; the method specifically comprises the following steps: the epitaxial wafer p-type doping concentration is low on two sides and high in the middle and is distributed in an arch bridge shape, when the edge doping concentration exceeds the doping concentration of the central point by 20%, a carbon source and trimethylaluminum are added into air flotation gas, the flow of the carbon source added into the air flotation gas does not exceed 15% of the flow of a process carbon source, and the actual flow of the trimethylaluminum does not exceed 0.02% of the hydrogen flow of a reaction chamber;
(5) after the epitaxial structure growth is completed, the growth source and the doping source are closed, the temperature of the reaction chamber is reduced to room temperature in the hydrogen atmosphere, after the temperature of the reaction chamber reaches the room temperature, hydrogen is discharged, gas in the reaction chamber is replaced for many times through argon, finally, the pressure of the reaction chamber is inflated to atmospheric pressure through the argon, and then the chamber is opened to take the wafer.
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| CN111029250B (en) * | 2019-12-09 | 2022-07-22 | 中国电子科技集团公司第五十五研究所 | Method for realizing SiC epitaxial curve-shaped doping distribution |
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| CN112490117B (en) * | 2020-12-08 | 2021-08-10 | 瀚天天成电子科技（厦门）有限公司 | Method for improving growth quality of silicon carbide epitaxial film |
| CN112853491A (en) * | 2020-12-31 | 2021-05-28 | 山西烁科晶体有限公司 | Doped silicon carbide single crystal and preparation method thereof |
| CN113564710B (en) * | 2021-07-19 | 2022-08-23 | 瀚天天成电子科技（厦门）有限公司 | Control method for silicon carbide epitaxial growth |
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