Epitaxial growth process for n-type doped silicon carbide

Abstract

The invention provides an epitaxial growth process for improving doping uniformity of n-type doped silicon carbide, and relates to the technical field of semiconductors. The method is based on a chemical vapor deposition growth technology; 11 to 20 gt; the silicon carbide epitaxial growth is carried out by taking silicon carbide with a 4-degree silicon surface in the direction as a substrate, taking trichlorosilane (TCS) and ethylene (C2H4) as growth sources and taking ammonia gas (NH3) as a doping source. Ammonia gas is adopted as an n-type dopant, the decomposition efficiency of the n-type dopant is close to 100% at the temperature of 700 DEG C or above, and the energy of N-H bond breakage of ammonia gas molecules is 390 KJ / mo which is far lower than 946 KJ / mo needed by N-N bond breakage of nitrogen molecules. Therefore, compared with a traditional doping source such as nitrogen, the ammonia gas has higher doping efficiency, residues of excessive nitrogen-containing precursors in the reaction chamber can be reduced, the memory effect is reduced, and thus more excellent in-chip uniformity and stable inter-chip repeatability of the epitaxial wafer are obtained. The selection range of the doping source is widened, the accurate control of the doping concentration is realized, and the stability of the doping concentration in the continuous growth process is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor materials, and in particular to an epitaxial growth process for n-type doped silicon carbide. Background Art

[0002] Silicon carbide (SiC), as a wide bandgap semiconductor material, has the characteristics of high critical breakdown electric field, high thermal conductivity and high electron saturation mobility. It is an ideal material for preparing high-temperature, high-frequency, high-voltage and strong radiation power electronic devices.

[0003] The doping concentration uniformity of SiC epitaxial materials seriously affects the performance of SiC devices. Good doping uniformity can improve the reliability of devices. Generally speaking, SiC devices have specific requirements for epitaxial doping concentration. 600V~10kVn-type doped 4H-SiC devices require the control range of epitaxial doping concentration to be 1×10 14 ~2×10 16 cm -3 . In the prior art, high-purity nitrogen (N2) is used as an n-type dopant to achieve this doping value. The doping concentration and distribution uniformity of the epitaxial wafer can be changed by adjusting the flow rate of the dopant. However, since nitrogen itself is very stable, its decomposition efficiency and doping efficiency are low at high temperatures, and a large amount of N2 is usually introduced, making it difficult to accurately control its doping concentration, affecting the doping uniformity within the wafer. In addition, during the process, a large amount of N elements will remain in the cavity environment, affecting the doping concentration during continuous epitaxial growth, causing it to deviate from the target value, resulting in the problem of low repeatability during continuous growth. Summary of the invention

[0004] The object of the present invention is to provide an epitaxial growth process for improving the uniformity of doping of n-type doped silicon carbide. Compared with the traditional N2 as an n-type doping source, the decomposition efficiency and doping efficiency of ammonia at high temperature are extremely high, and the decomposition efficiency is close to 100% above 700 degrees Celsius, and the energy of breaking the NH bond of the NH3 molecule is 390KJ / mol, which is much lower than the 946KJ / mol required for breaking the NN bond of the N2 molecule. When other process conditions are the same, N2 and NH3 are used as doping sources respectively, and the partial pressures in the mixed gas are set to be consistent, and the NH3 doping concentration is about 100 times the N2 doping concentration. Therefore, in the epitaxial growth process using ammonia as an n-type doping source, only a trace amount of ammonia is needed to hit the doping value, which can avoid the chamber memory effect caused by excessive doping sources. This solution can effectively solve the problem of unstable doping concentration repeatability during continuous growth when N2 is currently used as an n-type doping source.

[0005] The present invention adopts the following scheme:

[0006] An epitaxial growth process of n-type doped silicon carbide comprises the following steps:

[0007] S1. Place the silicon carbide substrate in a high-temperature standby reaction chamber through a wafer transfer device: the silicon carbide substrate is a 4H silicon carbide conductive substrate with a bias of 4 to 8 degrees in the <11-20> direction;

[0008] S2, charging the reaction chamber with a carrier gas to a set pressure according to a set flow rate, and heating the reaction chamber to a set temperature, wherein the carrier gas is hydrogen;

[0009] S3, perform in-situ hydrogen etching: raise the temperature of the reaction chamber to 1500-1750° C., maintain the temperature constant and perform in-situ etching for 5-60 minutes;

[0010] S4, buffer layer growth, set the buffer layer growth conditions, and start to grow the silicon carbide buffer layer at a low speed:

[0011] (1) Maintaining a constant pressure in the reaction chamber, setting the buffer layer growth temperature to a range of 1500 to 1750° C.;

[0012] (2) introducing Si source, C source and doping source; wherein the Si source is TCS, the C source is C2H4, and the doping source is NH3;

[0013] (3) According to the requirements of the doping concentration and thickness of the buffer layer material, the carbon-silicon ratio C / Si is ensured to be in the range of 0.4 to 0.7, the C source flow rate is controlled to be 10 to 50 sccm, the Si source flow rate is set according to the C / Si ratio, the actual effective flow rate of NH3 is between 40 and 100 sccm, and the growth rate is controlled to be below 8 μm / h; according to the designed values ​​of the buffer layer thickness and doping concentration, the buffer layer growth at a low growth rate is started;

[0014] S5, epitaxial layer growth: set the epitaxial layer growth conditions, start to grow the silicon carbide epitaxial layer at a high speed, and maintain the temperature and pressure of the reaction chamber during the epitaxial growth process; according to the requirements of the doping concentration and thickness of the epitaxial layer, set the flow rate of C2H4 to 170-250sccm, control the C / Si ratio between 0.7-1, and set the flow rate of TCS according to the C / Si ratio. The actual effective flow rate of NH3 is 90-180sccm; the epitaxial growth time is 10-30min, the growth rate is 30-120μm / h, and the epitaxial layer growth with a high growth rate is started until the doping concentration of the epitaxial layer is 1e16cm -3 ;

[0015] S6, turning off the growth source and the doping source, and obtaining an n-type doped silicon carbide epitaxial wafer after cooling.

[0016] Furthermore, in step S2, the carrier gas is set to have a flow rate of 80 to 200 s lm, a set pressure of 60 to 150 mbar, and a set temperature of 1500 to 1700°C.

[0017] Furthermore, in step S4, the thickness of the final buffer layer is controlled to be 0.5-2 μm, and the doping concentration is controlled to be 1.0e17-1.0e18 cm -3 within the range.

[0018] Furthermore, a two-stage dilution pipeline is provided on the intake path of the NH3, which passes through the reaction chamber after being diluted by the carrier gas.

[0019] Furthermore, in step S6, after the epitaxial growth is completed, the growth source and doping source gases are turned off, the temperature is gradually lowered to 600-1000°C and the pressure is increased to 900-1100 mbar, and then the silicon carbide epitaxial wafer is taken out of the reaction chamber using a transmission device, and is purged with an inert gas and cooled to room temperature before being taken out.

[0020] Beneficial effects:

[0021] Compared with the prior art, the advantages of the present invention are as follows: ammonia is used as a doping source, which has a lower decomposition temperature and higher decomposition efficiency. Compared with doping sources such as N2, it has a higher doping efficiency, reduces the residual N atoms in the graphite chamber, reduces the memory effect, and improves the stability of the doping concentration during the continuous growth process. It can obtain better uniformity within the epitaxial wafer and stable inter-wafer repeatability. It broadens the selection range of doping sources and realizes precise control of doping concentration. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the arrangement of carrier gas and doping source inlet pipelines in an epitaxial growth process of n-type doped silicon carbide according to an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of doping source concentration in Example 2;

[0024] Figure 3 is a schematic diagram of doping source concentration of Comparative Example 1;

[0025] Figure 4 These are the uniformity data at different doping source concentrations in Example 2 and Comparative Example 1. DETAILED DESCRIPTION

[0026] Example 1

[0027] Combination Figure 1 , this embodiment provides an epitaxial growth process of n-type doped silicon carbide, comprising the following steps:

[0028] Step 1: Place the silicon carbide substrate in the reaction chamber through a high temperature transfer plate: The silicon carbide substrate is a 4H silicon carbide conductive substrate with a bias of 4 to 8 degrees in the <11-20> direction;

[0029] Step 2: Filling the reaction chamber with a carrier gas at a set flow rate to a set pressure, and heating the reaction chamber to a set temperature, wherein the carrier gas is hydrogen; the carrier gas set flow rate is 80 to 200 s lm, the set pressure is 60 to 150 mbar, and the set temperature is 1500 to 1750° C.;

[0030] Step 3: Perform in-situ hydrogen etching: raise the temperature of the reaction chamber to 1500-1750°C, maintain the temperature constant and perform in-situ etching for 5-60 minutes;

[0031] Step 4: Buffer layer growth, set the buffer layer growth conditions, and start growing the silicon carbide buffer layer at a low speed:

[0032] (1) Maintaining a constant pressure in the reaction chamber, setting the buffer layer growth temperature to a range of 1500 to 1750° C.;

[0033] (2) introducing Si source, C source and doping source; wherein the Si source is TCS, the C source is C2H4, and the doping source is NH3;

[0034] (3) According to the requirements of the doping concentration and thickness of the buffer layer material, the carbon-silicon ratio C / Si is guaranteed to be in the range of 0.4-0.7, the C source flow rate is controlled to be 10-50 sccm, the Si source flow rate is set according to the C / Si ratio, the actual effective flow rate of NH3 is between 40-100 sccm, and the growth rate is controlled to be below 8 μm / h; according to the designed values ​​of the buffer layer thickness and doping concentration, the buffer layer growth with a low growth rate is started; the final buffer layer thickness is controlled to be 0.5-2 μm, and the doping concentration is controlled to be 1.0e17-1.0e18 cm -3 within the scope;

[0035] Step 5: Epitaxial layer growth, set the epitaxial layer growth conditions, start to grow the silicon carbide epitaxial layer at a high speed, and maintain the temperature and pressure of the reaction chamber during the epitaxial growth process; according to the epitaxial layer doping concentration and thickness requirements, set the C2H4 flow rate to 170-250sccm, control the C / Si ratio between 0.7-1, and the TCS flow rate is set according to the C / Si ratio. The actual effective flow rate of NH3 is 90-180sccm; the epitaxial growth time is 10-30min, the growth rate is 30-120μm / h, and the epitaxial layer growth at a high growth rate is started until the epitaxial layer doping concentration is 1e16cm -3 ;

[0036] Step 6: Turn off the growth source and the doping source, and obtain an n-type doped silicon carbide epitaxial wafer after cooling; after the epitaxial growth is completed, turn off the growth source and the doping source and other gases, gradually reduce the temperature to 600-1000°C and increase the pressure to 900-1100 mbar, use the transmission device to take the silicon carbide epitaxial wafer out of the reaction chamber, and use inert gas to purge and cool to room temperature before taking it out.

[0037] When the carrier gas and the doping source are introduced, a two-stage dilution pipeline is provided on the intake path of the NH3, and the NH3 passes through the reaction chamber after being diluted by the carrier gas. Figure 1 In the carrier gas and doping source inlet pipeline shown, the doping source NH3 and the carrier gas are mixed through MFC01 and MFC02 to the primary dilution pipeline for preliminary dilution, and then the mixed gas of NH3 and the carrier gas is diluted again by hydrogen through MFC03 to the secondary dilution pipeline and then enters the reaction chamber through the main pipeline. The reaction chamber here is the process chamber. The two-stage dilution can make the concentration of the doping source too high when it enters.

[0038] Example 2

[0039] This example specifically describes the epitaxial growth process of n-type doped silicon carbide of Example 1:

[0040] A 4H silicon carbide conductive substrate with a silicon surface tilted 4° in the <11-20> direction was selected, and the substrate was placed on a graphite tray in the loading chamber. The graphite tray and the substrate were transferred as a whole to a graphite rotating base in the reaction chamber by a robot.

[0041] The hydrogen flow rate was gradually increased to 150 s lm, and argon was selected as the flotation gas to drive the graphite base to rotate. The argon flow rate was 3 s lm, the reaction chamber pressure was set to 100 mbar, and the reaction chamber temperature was set to 1620 °C.

[0042] After reaching the growth temperature and growth pressure, in-situ etching is performed for 5 minutes.

[0043] For the growth of the buffer layer, ammonia was used as the n-type doping source. TCS and C2H4 were introduced into the reaction chamber. The C2H4 flow rate was 35 sccm. The TCS flow rate was calculated based on the C / Si ratio. The C / Si ratio was controlled at 0.6. 40 sccm of ammonia was introduced. The growth time was 5 min, and the growth doping concentration was 1e18 cm -3 buffer layer.

[0044] Epitaxial layer growth, increase TCS flow and C2H4 flow, where C2H4 flow is 210sccm, TCS flow is calculated according to C / Si, C / Si is controlled at 0.81, and 100sccm ammonia is introduced. Epitaxial growth is 10min, and the growth doping concentration is 1e16cm -3 epitaxial layer.

[0045] After the epitaxial growth is completed, the growth source and doping source are turned off, the temperature of the reaction chamber is lowered to the wafer removal temperature and pressure in a hydrogen atmosphere, and the graphite tray and the epitaxial wafer are transferred to the loading chamber as a whole using a robot; after cooling to room temperature in an argon atmosphere, the chamber is opened to remove the wafer.

[0046] Repeat the above steps of epitaxial growth process, and use the same process parameters to continuously grow 10 furnaces of n-type doped silicon carbide epitaxial wafers. The doping concentration is as follows: Figure 2 shown.

[0047] Comparative Example 1

[0048] A 4H silicon carbide conductive substrate with a silicon surface tilted 4° in the <11-20> direction was selected, and the substrate was placed on a graphite tray in the loading chamber. The graphite tray and the substrate were transferred as a whole to a graphite rotating base in the reaction chamber by a robot.

[0049] The hydrogen flow rate was gradually increased to 150 s lm, and argon was selected as the flotation gas to drive the graphite base to rotate. The argon flow rate was 3 s lm, the reaction chamber pressure was set to 100 mbar, and the reaction chamber temperature was set to 1620 °C.

[0050] After reaching the growth temperature and growth pressure, in-situ etching is performed for 5 minutes.

[0051] For the growth of the buffer layer, nitrogen was used as the n-type doping source. TCS and C2H4 were introduced into the reaction chamber. The C2H4 flow rate was 35 sccm. The TCS flow rate was calculated based on the C / Si ratio. The C / Si ratio was controlled at 0.6. 70 sccm of nitrogen was introduced. The growth time was 5 min, and the growth doping concentration was 1e18 cm -3 buffer layer.

[0052] Epitaxial layer growth, increase TCS flow and C2H4 flow, where C2H4 flow is 210sccm, TCS flow is calculated according to C / Si, C / Si is controlled at 0.81, and 120sccm nitrogen is introduced. The epitaxial time is consistent with Example 1, and the target value of epitaxial doping concentration is 1e16cm -3 .

[0053] After the epitaxial growth is completed, the growth source and doping source are turned off, the temperature of the reaction chamber is lowered to the wafer removal temperature and pressure in a hydrogen atmosphere, and the graphite tray and the epitaxial wafer are transferred to the loading chamber as a whole using a robot; after cooling to room temperature in an argon atmosphere, the chamber is opened to remove the wafer.

[0054] Repeat the epitaxial growth process of the comparative example 1, and use the same process parameters to continuously grow 10 furnaces of n-type doped silicon carbide epitaxial wafers. The doping concentration is as follows: Figure 3 shown.

[0055] Figure 2 , Figure 3 The doping value distribution of the epitaxial wafer along the diameter is shown, and 15 points are measured for a single diameter. The horizontal axis is the radial position, and the vertical axis is the doping concentration. Figure 4 It is a data arrangement table of Example 2 and Comparative Example 1. Figure 2 and Figure 3 It can be seen that the doping concentration curves of the 10 batches of n-type doped epitaxial wafers obtained in Example 2 have a high overlap, ranging from 9.81e15 to 1.02e16cm -3 The deviation is 1.4e14cm -3 The data is more stable, indicating that the doping concentration stability during continuous growth is high. However, the doping concentration curve of the 10-furnace n-type doped silicon carbide epitaxial wafer obtained in Comparative Example 1 has a larger fluctuation range, ranging from 9.94 to 1.09 cm -3 Between, standard deviation 2.9e14cm -3 And the overall uniformity is worse, which means that it is more affected by the background concentration, the stability of the doping concentration is low, and it is more difficult to control the doping uniformity during the continuous growth process.

[0056] Therefore, using ammonia as a doping source improves the stability of the doping concentration during the continuous growth process.

[0057] It should be understood that the above are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention.

[0058] The above description of the drawings used in the implementation manner only illustrates certain embodiments of the present invention and should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

Claims

1. A process for epitaxial growth of n-type doped silicon carbide, characterized in that: The steps include: S1. Place the silicon carbide substrate in a high-temperature standby reaction chamber through a wafer transfer device: the silicon carbide substrate is a 4H silicon carbide conductive substrate with a bias of 4 to 8 degrees in the <11-20> direction; S2, charging the reaction chamber with a carrier gas to a set pressure according to a set flow rate, and heating the reaction chamber to a set temperature, wherein the carrier gas is hydrogen; S3, perform in-situ hydrogen etching: raise the temperature of the reaction chamber to 1500-1750° C., maintain the temperature constant and perform in-situ etching for 5-60 minutes; S4, buffer layer growth, set the buffer layer growth conditions, and start to grow the silicon carbide buffer layer at a low speed: (1) Maintaining a constant pressure in the reaction chamber, setting the buffer layer growth temperature to a range of 1500 to 1750° C.; (2) introducing Si source, C source and doping source; wherein the Si source is TCS, the C source is C2H4, and the doping source is NH3; (3) According to the requirements of the doping concentration and thickness of the buffer layer material, the carbon-silicon ratio C / Si is ensured to be in the range of 0.4 to 0.7, the C source flow rate is controlled to be 10 to 50 sccm, the Si source flow rate is set according to the C / Si ratio, the actual effective flow rate of NH3 is between 40 and 100 sccm, and the growth rate is controlled to be below 8 μm / h; according to the designed values ​​of the buffer layer thickness and doping concentration, the buffer layer growth at a low growth rate is started; S5, epitaxial layer growth: set epitaxial layer growth conditions, start high-speed growth of silicon carbide epitaxial layer, maintain the temperature and pressure of the reaction chamber during epitaxial growth; according to the requirements of epitaxial layer doping concentration and thickness, set the flow rate of C2H4 to 170-250sccm, control the C / Si ratio between 0.7-1, set the flow rate of TCS according to the C / Si ratio, and the actual effective flow rate of NH3 to 90-180sccm; the epitaxial growth time is 10-30min, the growth rate is 30-120μm / h, and start epitaxial layer growth with a high growth rate; S6, turning off the growth source and the doping source, and obtaining an n-type doped silicon carbide epitaxial wafer after cooling.

2. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: In step S2, the carrier gas is set to have a flow rate of 80 to 200 slm, a pressure of 60 to 150 mbar, and a temperature of 1500 to 1700°C.

3. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: A two-stage dilution pipeline is arranged on the intake path of the NH3, and the NH3 passes through the reaction chamber after being diluted by the carrier gas.

4. The epitaxial growth process of n-type doped silicon carbide according to claim 1, characterized in that: In step S6, after the epitaxial growth is completed, the growth source and doping source gases are turned off, the temperature is gradually reduced to 600-1000°C and the pressure is increased to 900-1100 mbar, and the silicon carbide epitaxial wafer is taken out of the reaction chamber using a transmission device, and is purged with an inert gas and cooled to room temperature before being taken out.

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