Epitaxial wafer and preparation method thereof

Abstract

The present application discloses an epitaxial wafer and a method for preparing the same. The epitaxial wafer preparation method comprises: providing a heterojunction epitaxial layer; forming a cap layer on the heterojunction epitaxial layer to obtain an epitaxial wafer; the cap layer comprises a first sublayer, a second sublayer, and a third sublayer stacked in sequence, and the first sublayer is bonded to the heterojunction epitaxial layer. The present application prepares a cap layer on the heterojunction epitaxial layer, wherein the cap layer comprises a first sublayer, a second sublayer, and a third sublayer stacked in sequence; wherein the first sublayer can reduce the diffusion of magnesium atoms in the cap layer to the heterojunction epitaxial layer; the second sublayer can compensate for the diffusion damage of magnesium atoms in the first sublayer during annealing; therefore, the present application can effectively improve the two-dimensional electron gas damage problem caused by the diffusion of magnesium atoms in the current conventional cap layer, as well as the problem of decreased and uneven hole concentration in the cap layer, by setting the cap layer as a stacked first sublayer, a second sublayer, and a third sublayer.

Description

Technical Field

[0001] The present application relates to the field of semiconductor manufacturing technology, and in particular to an epitaxial wafer and a method for preparing the same. Background Art

[0002] Compared to first-generation semiconductors like silicon and germanium, third-generation semiconductor materials, primarily gallium nitride (GaN) and silicon carbide (SiC), offer wide bandgap, high breakdown electric field, high thermal conductivity, high electron saturation velocity, and enhanced radiation resistance, making them more suitable for the fabrication of high-temperature, high-frequency, radiation-resistant, and high-power devices. GaN's high withstand voltage, high current density, and high-frequency characteristics have drawn significant attention in lighting, lasers, electronic power devices, and microwave power devices.

[0003] In III-V compound semiconductors such as gallium nitride, ionic and covalent bonds coexist. Ionic bonds make Group V atoms more attractive to electrons, resulting in a misalignment of the centers of positive and negative charge within the material, leading to spontaneous polarization. When aluminum gallium nitride (AlGaN), with a smaller lattice spacing, is grown on gallium nitride, the barrier layer experiences lateral tensile stress. Based on the principle of elastic invariance, the barrier layer experiences vertical compressive stress, increasing the distance between the centers of positive and negative charge within the barrier layer and forming piezoelectric polarization. The dual-polarization interface generates a two-dimensional electron gas, making the GaN / AlGaN heterojunction the core component of GaN-based high electron mobility transistors (HEMTs). Consequently, conventional GaN-based HEMTs are depletion-mode devices, also known as normally-on devices.

[0004] Depletion-mode devices require a negative voltage supply to shut down the device, which not only increases the risk of the circuit being accidentally turned on, but also increases the power consumption of the entire circuit. To improve safety and reduce circuit power consumption, various techniques are commonly used to deplete the two-dimensional electron gas under the gate to produce enhancement-mode devices, also known as normally-off devices. The main methods for producing enhancement-mode devices on the epitaxial end include recessed gate structure technology, fluorine ion implantation technology, and p-type cap layer technology. Both recessed gate structure and fluorine ion implantation are prone to damaging the barrier layer and causing current collapse. P-type cap layer technology is more suitable for producing high-reliability GaN-based HEMT devices. Therefore, preparing a high-quality p-type gallium nitride cap layer is a critical step in the preparation of high-reliability GaN-based enhancement-mode power devices. Summary of the Invention

[0005] The purpose of this application is to provide an epitaxial wafer and a preparation method thereof, which can effectively improve the two-dimensional electron gas damage problem caused by magnesium atom diffusion in the current conventional cap layer, as well as the problem of decreased and uneven hole concentration in the cap layer.

[0006] The first aspect of the present application provides a method for preparing an epitaxial wafer, comprising:

[0007] providing a heterojunction epitaxial layer;

[0008] forming a cap layer on the heterojunction epitaxial layer to obtain an epitaxial wafer;

[0009] The cap layer includes a first sublayer, a second sublayer, and a third sublayer stacked in sequence, and the first sublayer is bonded to the heterojunction epitaxial layer.

[0010] In some embodiments, the step of forming the first sub-layer includes:

[0011] introducing a first gallium source and a first nitrogen source into a reaction chamber, and growing a gallium nitride layer on the heterojunction epitaxial layer in a hydrogen atmosphere;

[0012] The first gallium source is turned off, and a first magnesium source is introduced to dope the gallium nitride layer, and the first sublayer is grown on the heterojunction epitaxial layer.

[0013] In some embodiments, during the process of growing the first sub-layer,

[0014] The first magnesium source has a first gas flow rate Q1, and the range of the first gas flow rate Q1 is 100 to 800 sccm; the first sublayer has a first growth temperature T1, and the range of the first growth temperature T1 is 900 to 1100°C; the first sublayer has a first growth pressure P1, and the range of the first growth pressure P1 is 200 to 800 mbar; the gallium nitride layer has a first growth time t1, and the first growth time t1 is 30 to 90 seconds, and the doping time is 10 to 50 seconds; the number of growth cycles of the first sublayer is 1 to 2 cycles.

[0015] In some embodiments, the step of forming the second sub-layer includes:

[0016] Simultaneously, a second gallium source, a second nitrogen source, and a second magnesium source are introduced into the reaction chamber, and the second sub-layer is grown on the first sub-layer in the hydrogen atmosphere.

[0017] In some embodiments, during the process of growing the second sub-layer,

[0018] The second magnesium source has a second gas flow rate Q2, satisfying: 1≤Q2 / Q1≤2; the second sublayer has a second growth temperature T2, and the range of the second growth temperature T2 is 900~1100℃; the second sublayer has a second growth pressure P2, and the range of the second growth pressure P2 is 200~800mbar; the second sublayer has a second growth time t2, and the second growth time t2 is 30~120s.

[0019] In some embodiments, the step of forming the third sub-layer includes:

[0020] Simultaneously, a third gallium source, a third nitrogen source, and a third magnesium source are introduced into the reaction chamber, and the third sub-layer is grown on the second sub-layer in the hydrogen atmosphere.

[0021] In some embodiments, during the process of growing the third sub-layer,

[0022] The third magnesium source has a third gas flow rate Q3, satisfying: 0.5≤Q3 / Q1≤1.2; the third sublayer has a third growth temperature T3, and the range of the third growth temperature T3 is 900~1100℃; the third sublayer has a third growth pressure P3, and the range of the third growth pressure P3 is 200~800mbar; the third sublayer has a third growth time t3, and the third growth time t3 is 5~20min.

[0023] In some embodiments, the gas flow rate of the first gallium source is 20 to 100 sccm; the gas flow rate of the first nitrogen source is 5,000 to 50,000 sccm.

[0024] In some embodiments, the gas flow rate of the second gallium source is 20 to 100 sccm; the gas flow rate of the second nitrogen source is 5,000 to 50,000 sccm.

[0025] In some embodiments, the gas flow rate of the third gallium source is 20 to 100 sccm; the gas flow rate of the third nitrogen source is 5,000 to 50,000 sccm.

[0026] In some embodiments, the first gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the first nitrogen source is selected from ammonia; and the first magnesium source is selected from bismuth magnesium.

[0027] In some embodiments, the second gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the second nitrogen source is selected from ammonia; and the second magnesium source is selected from bismuth magnesium.

[0028] In some embodiments, the third gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the third nitrogen source is selected from ammonia; and the third magnesium source is selected from bismuth magnesium.

[0029] In some embodiments, after growing the first sub-layer, the method further includes:

[0030] The first sub-layer is subjected to a first annealing treatment. During the first annealing treatment, a first annealing temperature is 800-1000° C., and a first annealing time is 30-90 seconds.

[0031] In some embodiments, after forming a cap layer on the heterojunction epitaxial layer to obtain an epitaxial wafer, the method further includes:

[0032] The epitaxial wafer is subjected to a second annealing treatment in a nitrogen atmosphere.

[0033] In some embodiments, during the second annealing process, the second annealing temperature is 650-850° C.; the second annealing pressure is 400-1000 mbar; and the second annealing time is 10-30 min.

[0034] A second aspect of the present application provides an epitaxial wafer, which is prepared using the epitaxial wafer preparation method as described above.

[0035] In some embodiments, the epitaxial wafer includes a cap layer, the cap layer includes a first sublayer, a second sublayer, and a third sublayer stacked in sequence, the first sublayer has a first thickness D1, the second sublayer has a second thickness D2, and the third sublayer has a third thickness D3, satisfying: D1 <D3,D2<D3。

[0036] In some embodiments, the first thickness D1 is in the range of 1 to 15 nm; and / or,

[0037] The second thickness D2 is in the range of 1 to 10 nm; and / or,

[0038] The third thickness D3 ranges from 50 nm to 500 nm.

[0039] In some embodiments, the concentration of magnesium atoms in the cap layer is 0.5 to 5E19 atoms / cm 3 .

[0040] The beneficial effects of this application are:

[0041] The present application provides a method for preparing an epitaxial wafer, comprising: providing a heterojunction epitaxial layer; forming a cap layer on the heterojunction epitaxial layer to obtain an epitaxial wafer; the cap layer comprising a first sublayer, a second sublayer, and a third sublayer stacked in sequence, the first sublayer being bonded to the heterojunction epitaxial layer. The present application prepares a cap layer on the heterojunction epitaxial layer, the cap layer comprising a first sublayer, a second sublayer, and a third sublayer stacked in sequence; wherein the first sublayer can reduce the diffusion of magnesium atoms in the cap layer into the heterojunction epitaxial layer; the second sublayer can compensate for the diffusion damage of magnesium atoms in the first sublayer during annealing; therefore, the present application can effectively improve the two-dimensional electron gas damage problem caused by the diffusion of magnesium atoms in the current conventional cap layer, as well as the problem of decreased and uneven hole concentration in the cap layer, by configuring the cap layer as a stacked first sublayer, a second sublayer, and a third sublayer. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 Flowchart of the epitaxial wafer preparation method provided in this application;

[0043] Figure 2This is a schematic diagram of the structure of the epitaxial wafer provided in this application.

[0044] In the accompanying drawings, the components represented by the reference numerals are as follows:

[0045] 100. Heterojunction epitaxial layer; 101. Substrate; 102. Nucleation layer; 103. Buffer layer; 104. Channel layer; 105. Barrier layer; 200. Cap layer; 201. First sublayer; 202. Second sublayer; 203. Third sublayer; 300. Epitaxial wafer. DETAILED DESCRIPTION

[0046] The technical solutions of the present application will be described clearly and completely below in conjunction with the embodiments and drawings of the present application. Obviously, the embodiments described are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present application. The various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be understood as a rigid limitation on the scope of the present application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the numbered range, such as 1, 2, 3, 4, 5 and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any quoted number (fractional or integer) within the indicated range.

[0047] The p-type cap layer is usually prepared by doping with magnesium (Mg), but the diffusion of Mg can easily cause damage to the two-dimensional electron gas (2DEG) and a decrease in the hole concentration at the bottom of the p-type cap layer.

[0048] like Figure 1-Figure 2 As shown, the first aspect of the present application provides a method for preparing an epitaxial wafer, comprising:

[0049] S1: providing a heterojunction epitaxial layer 100;

[0050] S2: forming a cap layer 200 on the heterojunction epitaxial layer 100 to obtain an epitaxial wafer 300; the cap layer 200 includes a first sublayer 201, a second sublayer 202 and a third sublayer 203 stacked in sequence, and the first sublayer 201 is bonded to the heterojunction epitaxial layer 100.

[0051] Specifically, the cap layer 200 is a p-type cap layer 200. The present application prepares the cap layer 200 on the heterojunction epitaxial layer 100, and the cap layer 200 includes a first sublayer 201, a second sublayer 202, and a third sublayer 203 stacked in sequence; wherein the first sublayer 201 can reduce the diffusion of magnesium atoms in the cap layer 200 into the heterojunction epitaxial layer 100; and the second sublayer 202 can compensate for the diffusion damage of magnesium atoms in the first sublayer 201 during annealing; therefore, the present application can effectively improve the two-dimensional electron gas (2DEG) damage problem caused by the diffusion of magnesium atoms in the current conventional cap layer, as well as the problem of decreased and uneven hole concentration in the cap layer 200, by configuring the cap layer 200 to include the first sublayer 201, the second sublayer 202, and the third sublayer 203 stacked in sequence.

[0052] In some embodiments, the heterojunction epitaxial layer 100 includes a substrate 101, a nucleation layer 102, a buffer layer 103, a channel layer 104, and a barrier layer 105, which are sequentially stacked. The nucleation layer 102, the buffer layer 103, the channel layer 104, and the barrier layer 105 can be formed by in-situ deposition using a metal organic chemical deposition system (MOCVD).

[0053] Specifically, the material of the substrate 101 is (111) oriented single crystal silicon.

[0054] The material of the nucleation layer 102 is selected from at least one of aluminum nitride, gallium nitride, and silicon nitride.

[0055] The buffer layer 103 is composed of at least one of one aluminum gallium nitride layer, two aluminum gallium nitride layers, three aluminum gallium nitride layers, four aluminum gallium nitride layers, and five aluminum gallium nitride layers.

[0056] The material of the channel layer 104 is gallium nitride.

[0057] The barrier layer 105 is made of at least one material selected from aluminum gallium nitride, aluminum scandium nitride, and indium aluminum gallium nitride.

[0058] In some embodiments, the step of forming the first sub-layer 201 includes:

[0059] A first gallium source and a first nitrogen source are introduced into the reaction chamber to grow a gallium nitride layer on the heterojunction epitaxial layer 100 in a hydrogen atmosphere;

[0060] The first gallium source is turned off, and the first magnesium source is introduced to dope the gallium nitride layer, and a first sub-layer 201 is grown on the heterojunction epitaxial layer 100 .

[0061] In some embodiments, the first sub-layer 201 may be formed by in-situ deposition using a metal organic chemical vapor deposition system (MOCVD).

[0062] In some embodiments, during the growth of the first sublayer 201, the first magnesium source has a first gas flow rate Q1, and the first gas flow rate Q1 ranges from 100 to 800 sccm; the first sublayer 201 has a first growth temperature T1, and the first growth temperature T1 ranges from 900 to 1100°C; the first sublayer 201 has a first growth pressure P1, and the first growth pressure P1 ranges from 200 to 800 mbar; the gallium nitride layer has a first growth time t1, and the first growth time t1 is 30 to 90 s, and the doping time is 10 to 50 s; the number of growth cycles of the first sublayer 201 is 1 to 2 cycles.

[0063] Specifically, the first gas flow rate Q1 is any one of 100 sccm, 200 sccm, 300 sccm, 400 sccm, 500 sccm, 600 sccm, 700 sccm, and 800 sccm, or a range consisting of any two values; the first growth temperature T1 is any one of 900°C, 1000°C, and 1100°C, or a range consisting of any two values; the first growth pressure P1 is any one of 200 mbar, 300 mbar, 400 mbar, 500 mbar, 600 mbar, 700 mbar, and 800 mbar, or a range consisting of any two values; the first growth time t1 is any one of 30s, 40s, 50s, 60s, 70s, 80s, and 90s, or a range consisting of any two values; the doping time is any one of 10s, 20s, 30s, 40s, and 50s, or a range consisting of any two values.

[0064] In some embodiments, the step of forming the second sub-layer 202 includes:

[0065] At the same time, a second gallium source, a second nitrogen source, and a second magnesium source are introduced into the reaction chamber, and the second sub-layer 202 is grown on the first sub-layer 201 in a hydrogen atmosphere.

[0066] In some embodiments, during the growth of the second sub-layer 202, the second magnesium source has a second gas flow rate Q2, satisfying: 1≤Q2 / Q1≤2; the second sub-layer 202 has a second growth temperature T2, and the second growth temperature T2 ranges from 900 to 1100°C; the second sub-layer 202 has a second growth pressure P2, and the second growth pressure P2 ranges from 200 to 800 mbar; the second sub-layer 202 has a second growth time t2, and the second growth time t2 is 30 to 120s.

[0067] Specifically, in the process of growing the second sub-layer 202, the second growth temperature T2 is any one of 900°C, 1000°C, and 1100°C, or a range consisting of any two values; the second growth pressure P2 is any one of 200mbar, 300mbar, 400mbar, 500mbar, 600mbar, 700mbar, and 800mbar, or a range consisting of any two values; the second growth time t2 is any one of 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s, and 120s, or a range consisting of any two values.

[0068] In some embodiments, the step of forming the third sub-layer 203 includes:

[0069] At the same time, a third gallium source, a third nitrogen source, and a third magnesium source are introduced into the reaction chamber, and a third sub-layer 203 is grown on the second sub-layer 202 in a hydrogen atmosphere.

[0070] In some embodiments, during the growth of the third sublayer 203, the third magnesium source has a third gas flow rate Q3, satisfying: 0.5≤Q3 / Q1≤1.2; the third sublayer 203 has a third growth temperature T3, and the range of the third growth temperature T3 is 900~1100℃; the third sublayer 203 has a third growth pressure P3, and the range of the third growth pressure P3 is 200~800mbar; the third sublayer 203 has a third growth time t3, and the third growth time t3 is 5~20min.

[0071] Specifically, in the process of growing the third sublayer 203, the third growth temperature T3 is any one of 900°C, 1000°C, and 1100°C, or a range consisting of any two values; the third growth pressure P3 is any one of 200mbar, 300mbar, 400mbar, 500mbar, 600mbar, 700mbar, and 800mbar, or a range consisting of any two values; the third growth time t3 is any one of 5min, 8min, 10min, 12min, 15min, 18min, and 20min, or a range consisting of any two values.

[0072] In some embodiments, the gas flow rate of the first gallium source is 20-100 sccm; the gas flow rate of the first nitrogen source is 5000-50000 sccm.

[0073] Specifically, the gas flow rate of the first gallium source is any one of 20sccm, 30sccm, 40sccm, 50sccm, 60sccm, 70sccm, 80sccm, 90sccm, and 100sccm, or a range consisting of any two values; the gas flow rate of the first nitrogen source is any one of 5000sccm, 10000sccm, 15000sccm, 20000sccm, 25000sccm, 30000sccm, 35000sccm, 40000sccm, 45000sccm, and 10000sccm, or a range consisting of any two values.

[0074] In some embodiments, the gas flow rate of the second gallium source is 20-100 sccm; the gas flow rate of the second nitrogen source is 5000-50000 sccm.

[0075] Specifically, the gas flow rate of the second gallium source is any one of 20sccm, 30sccm, 40sccm, 50sccm, 60sccm, 70sccm, 80sccm, 90sccm, and 100sccm, or a range consisting of any two values; the gas flow rate of the second nitrogen source is any one of 5000sccm, 10000sccm, 15000sccm, 20000sccm, 25000sccm, 30000sccm, 35000sccm, 40000sccm, 45000sccm, and 10000sccm, or a range consisting of any two values.

[0076] In some embodiments, the gas flow rate of the third gallium source is 20-100 sccm; the gas flow rate of the third nitrogen source is 5000-50000 sccm.

[0077] Specifically, the gas flow rate of the third gallium source is any one of 20sccm, 30sccm, 40sccm, 50sccm, 60sccm, 70sccm, 80sccm, 90sccm, and 100sccm, or a range consisting of any two values; the gas flow rate of the third nitrogen source is any one of 5000sccm, 10000sccm, 15000sccm, 20000sccm, 25000sccm, 30000sccm, 35000sccm, 40000sccm, 45000sccm, and 10000sccm, or a range consisting of any two values.

[0078] In some embodiments, the first gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the first nitrogen source is selected from ammonia; and the first magnesium source is selected from bismuth magnesium.

[0079] In some embodiments, the second gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the second nitrogen source is selected from ammonia; and the second magnesium source is selected from bismuth magnesium.

[0080] In some embodiments, the third gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the third nitrogen source is selected from ammonia; and the third magnesium source is selected from bismuth magnesium.

[0081] In some embodiments, after growing the first sub-layer 201, the method further includes:

[0082] A first annealing treatment is performed on the first sublayer 201. During the first annealing treatment, the first annealing temperature is 800-1000° C., and the first annealing time is 30-90 seconds. Specifically, the first annealing temperature is any one of 800° C., 850° C., 900° C., 950° C., and 1000° C., or a range consisting of any two values; and the first annealing time is any one of 30 seconds, 40 seconds, 50 seconds, 60 seconds, 70 seconds, 80 seconds, and 90 seconds, or a range consisting of any two values.

[0083] It can be understood that performing the first annealing treatment on the first sub-layer 201 can eliminate the stress of the first sub-layer 201 .

[0084] In some embodiments, after forming the cap layer 200 on the heterojunction epitaxial layer 100 to obtain the epitaxial wafer 300, the method further includes:

[0085] The epitaxial wafer 300 is subjected to a second annealing process in a nitrogen atmosphere.

[0086] It is understandable that performing a second annealing treatment on the epitaxial wafer 300 in a nitrogen atmosphere can eliminate the Mg—H complex and activate the Mg acceptor.

[0087] In some embodiments, during the second annealing process, the second annealing temperature is 650-850° C.; the second annealing pressure is 400-1000 mbar; and the second annealing time is 10-30 min.

[0088] Specifically, the second annealing temperature is any one of 650° C., 700° C., 750° C., 800° C., and 850° C., or a range consisting of any two values; the second annealing pressure is any one of 400 mbar, 500 mbar, 600 mbar, 700 mbar, 800 mbar, 900 mbar, and 1000 mbar, or a range consisting of any two values; and the second annealing time is any one of 10 min, 15 min, 20 min, 25 min, and 30 min, or a range consisting of any two values.

[0089] In a second aspect of the present application, an epitaxial wafer is provided, and the epitaxial wafer 300 is prepared by the epitaxial wafer preparation method as described above.

[0090] In some embodiments, the epitaxial wafer 300 includes a cap layer 200, and the cap layer 200 includes a first sub-layer 201, a second sub-layer 202, and a third sub-layer 203 that are sequentially stacked. The first sub-layer 201 has a first thickness D1, the second sub-layer 202 has a second thickness D2, and the third sub-layer 203 has a third thickness D3, satisfying: D1 < D3, D2 < D3.

[0091] It can be understood that by controlling the first thickness D1, the second thickness D2, and the third thickness D3 to satisfy: D1 < D3, D2 < D3, the problem of damage to the two-dimensional electron gas (2DEG) caused by the diffusion of magnesium atoms in the cap layer 200, as well as the problems of the decrease and non-uniformity of the hole concentration in the cap layer 200, can be improved.

[0092] In some embodiments, the range of the first thickness D1 is 1 - 15 nm. Specifically, the first thickness D1 is any value or the range composed of any two values among 1 nm, 3 nm, 5 nm, 8 nm, 10 nm, 13 nm, and 15 nm.

[0093] It can be understood that the first sub-layer 201 has the function of reducing the diffusion of magnesium atoms in the cap layer 200 to the heterojunction epitaxial layer 100, and by controlling the range of the first thickness D1 to be 1 - 15 nm, the diffusion of magnesium atoms in the cap layer 200 to the heterojunction epitaxial layer 100 can be effectively inhibited.

[0094] In some embodiments, the range of the second thickness D2 is 1 - 10 nm. Specifically, the second thickness D2 is any value or the range composed of any two values among 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm.

[0095] It can be understood that the second sub-layer 202 can compensate for the diffusion damage of magnesium atoms in the first sub-layer 201 during annealing, and by controlling the range of the second thickness D2 to be 1 - 10 nm, the diffusion damage of magnesium atoms in the first sub-layer 201 during annealing can be effectively supplemented.

[0096] In some embodiments, the range of the third thickness D3 is 50 - 500 nm. Specifically, the range of the third thickness D3 is any value or the range composed of any two values among 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, and 500 nm.

[0097] It is understandable that the third sublayer 203 is of great significance to the device performance. By controlling the third thickness D3 to be in the range of 50-500 nm, a cap layer structure with uniform hole concentration distribution can be obtained, thereby increasing the stability of the device.

[0098] In some embodiments, the concentration of magnesium atoms in the cap layer 200 is 0.5 to 5E19 atoms / cm 3 Specifically, 0.5 atoms / cm 3 , 1atoms / cm 3 、1E1atoms / cm 3 、1E5atoms / cm 3 、1E10atoms / cm 3 、1E15atoms / cm 3 、1E19atoms / cm 3 、2E19atoms / cm 3 、3E19atoms / cm 3 、4E19atoms / cm 3 、5E19atoms / cm 3 Any value or any two values ​​in the range.

[0099] It can be understood that, in the epitaxial wafer prepared by the method for preparing an epitaxial wafer provided in the present application, the concentration uniformity of magnesium atoms in the cap layer 200 is good, and thus the hole concentration in the cap layer 200 is high.

[0100] The present application will be described below with reference to specific embodiments.

[0101] Example 1

[0102] A heterojunction epitaxial layer 100 is provided. The heterojunction epitaxial layer 100 includes a substrate 101, a nucleation layer 102, a buffer layer 103, a channel layer 104, and a barrier layer 105, which are stacked in sequence. The heterojunction epitaxial layer 100 is placed in a reaction chamber. The substrate 101 is made of single-crystalline silicon; the nucleation layer 102 is made of aluminum nitride; the buffer layer 103 is made of a layer of aluminum gallium nitride; the channel layer 104 is made of gallium nitride; and the barrier layer 105 is made of aluminum gallium nitride.

[0103] A first gallium source and a first nitrogen source are introduced into the reaction chamber, and a gallium nitride layer is grown on the heterojunction epitaxial layer 100 under a hydrogen atmosphere. The first gallium source is turned off, and a first magnesium source is introduced to dope the gallium nitride layer, and a first sublayer 201 is grown on the heterojunction epitaxial layer 100. During the growth of the first sublayer 201, the first gallium source is trimethylgallium, and the gas flow rate of the first gallium source is 60 sccm; the first nitrogen source is ammonia, and the gas flow rate of the first nitrogen source is 30,000 sccm; the first magnesium source is cyclopentadienyl magnesium, and the first gas flow rate Q1 is 500 sccm; the first growth temperature T1 is 1000° C.; the first growth pressure P1 is 500 mbar; the first growth time t1 is 60 s, and the doping time is 45 s; and the number of growth cycles for the first sublayer 201 is 1 cycle.

[0104] After the first sub-layer 201 is grown, the first sub-layer 201 is subjected to a first annealing treatment. During the first annealing treatment, the first annealing temperature is 1000° C., the first annealing pressure is 500 mbar, and the first annealing time is 45 seconds.

[0105] At the same time, a second gallium source, a second nitrogen source, and a second magnesium source are introduced into the reaction chamber. In a hydrogen atmosphere, the second sublayer 202 is grown on the first sublayer 201. During the growth of the second sublayer 202, the second gallium source is trimethylgallium, and the gas flow rate of the second gallium source is 60 sccm; the second nitrogen source is ammonia, and the gas flow rate of the second nitrogen source is 30,000 sccm; the second magnesium source is bismuth magnesium, and the second gas flow rate Q2 is 500 sccm; the second growth temperature T2 is 1000°C; the second growth pressure P2 is 500 mbar; and the second growth time t2 is 60 s.

[0106] At the same time, a third gallium source, a third nitrogen source and a third magnesium source are introduced into the reaction chamber, and the third sublayer 203 is grown on the second sublayer 202 under a hydrogen atmosphere. During the growth of the third sublayer 203, the third gallium source is trimethylgallium, and the gas flow rate of the third gallium source is 60 sccm; the third nitrogen source is ammonia, and the gas flow rate of the third nitrogen source is 30,000 sccm; the third magnesium source is bismuth magnesium, and the third gas flow rate Q3 is 500 sccm; the third growth temperature T3 is 1000°C; the third growth pressure P3 is 500 mbar; and the third growth time t3 is 10 min.

[0107] The epitaxial wafer was obtained and subjected to a second annealing treatment in a nitrogen atmosphere. During the second annealing treatment, the second annealing temperature was 800° C., the second annealing pressure was 800 mbar, and the second annealing time was 30 minutes.

[0108] Example 2

[0109] The preparation method of Example 2 is the same as that of Example 1, except that the value of the third growth time t3 is adjusted.

[0110] Comparative Examples 1-2

[0111] The preparation methods of Examples 2 and 3 are the same as those of Example 1, except that only the third sub-layer is grown, and the value of the third growth time t3 is adjusted.

[0112] Test Method

[0113] 1. SIMS test

[0114] A secondary ion mass spectrometer is used to detect the Mg atomic content in the epitaxial wafer, to detect a first depth in which the Mg atomic content in the epitaxial wafer is greater than 1E19, and to detect a second depth in which the Mg atomic content in the epitaxial wafer is greater than 1E17.

[0115] 2. Hall test

[0116] The bulk hole concentration in the cap layer was measured using a contact-type Hall effect tester HL9900.

[0117] Table 1 shows the parameter settings of Examples 1-2 and Comparative Examples 1-2.

[0118]

[0119] Table 2 shows the test results of Examples 1-2 and Comparative Examples 1-2.

[0120]

[0121]

[0122] Result analysis:

[0123] It can be seen from the results of Example 1, Comparative Example 1 and Table 2 that by setting the cap layer as a stacked first sublayer, a second sublayer and a third sublayer, the diffusion of magnesium atoms into the barrier layer can be greatly reduced, the uniformity of Mg in the cap layer is improved, and the barrier layer is protected at the same time, thereby improving the stability and yield of the device.

[0124] It can be seen from the results of Example 2, Comparative Example 2 and Table 2 that by setting the cap layer as a stacked first sublayer, a second sublayer and a third sublayer, the uniformity of magnesium atoms in the cap layer can be improved, thereby increasing the hole concentration in the cap layer.

[0125] The above is a detailed introduction to the present application. Specific examples are used herein to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for those skilled in the art, based on the idea of ​​the present application, there may be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for preparing an epitaxial wafer, characterized in that: include: Providing a heterojunction epitaxial layer (100); forming a cap layer (200) on the heterojunction epitaxial layer (100) to obtain an epitaxial wafer (300); The cap layer (200) comprises a first sublayer (201), a second sublayer (202), and a third sublayer (203) stacked in sequence, and the first sublayer (201) is bonded to the heterojunction epitaxial layer (100); Forming a cap layer (200) on the heterojunction epitaxial layer (100), comprising: introducing a first gallium source and a first nitrogen source into the reaction chamber to grow a gallium nitride layer on the heterojunction epitaxial layer (100); The first gallium source is turned off, a first magnesium source is introduced to dope the gallium nitride layer, and the first sublayer (201) is grown on the heterojunction epitaxial layer (100); during the process of growing the first sublayer (201), the first magnesium source has a first gas flow rate Q1; performing a first annealing treatment on the first sub-layer (201); A second gallium source, a second nitrogen source, and a second magnesium source are simultaneously introduced into the reaction chamber to grow the second sublayer (202) on the first sublayer (201); during the process of growing the second sublayer (202), the second magnesium source has a second gas flow rate Q2, satisfying the following: 1≤Q2 / Q1≤2; A third gallium source, a third nitrogen source and a third magnesium source are simultaneously introduced into the reaction chamber to grow the third sublayer (203) on the second sublayer (202). During the process of growing the third sublayer (203), the third magnesium source has a third gas flow rate Q3, which satisfies the following: 0.5≤Q3 / Q1≤1.

2.

2. The method for preparing an epitaxial wafer according to claim 1, wherein: The step of growing a gallium nitride layer on the heterojunction epitaxial layer (100) is performed in a hydrogen atmosphere.

3. The method for preparing an epitaxial wafer according to claim 2, wherein: During the process of growing the first sub-layer (201), The first gas flow rate Q1 ranges from 100 to 800 sccm; the first sublayer (201) has a first growth temperature T1, which ranges from 900 to 1100°C; the first sublayer (201) has a first growth pressure P1, which ranges from 200 to 800 mbar; the gallium nitride layer has a first growth time t1, which ranges from 30 to 90 seconds, and the doping time is 10 to 50 seconds; the number of growth cycles of the first sublayer (201) is 1 to 2 cycles.

4. The method for preparing an epitaxial wafer according to claim 3, wherein: The step of forming the second sub-layer (202) is performed under the hydrogen atmosphere.

5. The method for preparing an epitaxial wafer according to claim 4, wherein: The second sublayer (202) has a second growth temperature T2, which ranges from 900 to 1100°C; the second sublayer (202) has a second growth pressure P2, which ranges from 200 to 800 mbar; and the second sublayer (202) has a second growth time t2, which ranges from 30 to 120 seconds.

6. The method for preparing an epitaxial wafer according to claim 3, wherein: The step of forming the third sublayer (203) is performed under the hydrogen atmosphere.

7. The method for preparing an epitaxial wafer according to claim 6, wherein: During the process of growing the third sub-layer (203), The third sublayer (203) has a third growth temperature T3, and the range of the third growth temperature T3 is 900-1100°C; the third sublayer (203) has a third growth pressure P3, and the range of the third growth pressure P3 is 200-800mbar; the third sublayer (203) has a third growth time t3, and the third growth time t3 is 5-20min.

8. The method for preparing an epitaxial wafer according to claim 7, wherein: The gas flow rate of the first gallium source is 20 to 100 sccm; the gas flow rate of the first nitrogen source is 5000 to 50000 sccm; and / or, The gas flow rate of the second gallium source is 20 to 100 sccm; the gas flow rate of the second nitrogen source is 5000 to 50000 sccm; and / or, The gas flow rate of the third gallium source is 20 to 100 sccm; the gas flow rate of the third nitrogen source is 5000 to 50000 sccm.

9. The method for preparing an epitaxial wafer according to claim 7, wherein: The first gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the first nitrogen source is selected from ammonia; the first magnesium source is selected from bismuth magnesium; and / or The second gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the second nitrogen source is selected from ammonia; the second magnesium source is selected from bismuth magnesium; and / or, The third gallium source is selected from at least one of trimethyl gallium and triethyl gallium; the third nitrogen source is selected from ammonia; and the third magnesium source is selected from bismuth magnesium.

10. The method for preparing an epitaxial wafer according to claim 2, wherein: During the first annealing treatment, the first annealing temperature is 800-1000° C., and the first annealing time is 30-90 seconds.

11. The method for preparing an epitaxial wafer according to claim 1, wherein: After forming a cap layer (200) on the heterojunction epitaxial layer (100) to obtain an epitaxial wafer (300), the method further comprises: The epitaxial wafer (300) is subjected to a second annealing process in a nitrogen atmosphere.

12. The method for preparing an epitaxial wafer according to claim 11, wherein: During the second annealing process, the second annealing temperature is 650-850° C.; the second annealing pressure is 400-1000 mbar; and the second annealing time is 10-30 minutes.

13. An epitaxial wafer, characterized in that: The epitaxial wafer (300) is prepared by using the epitaxial wafer preparation method according to any one of claims 1 to 12.

14. The epitaxial wafer according to claim 13, wherein: The epitaxial wafer (300) includes a cap layer (200), the cap layer (200) includes a first sublayer (201), a second sublayer (202), and a third sublayer (203) stacked in sequence, the first sublayer (201) having a first thickness D1, the second sublayer (202) having a second thickness D2, and the third sublayer (203) having a third thickness D3, satisfying: D1 <D3,D2<D3。 15. The epitaxial wafer according to claim 14, characterized in that: The first thickness D1 is in the range of 1 to 15 nm; and / or, The second thickness D2 is in the range of 1 to 10 nm; and / or, The third thickness D3 is in the range of 50 to 500 nm.

16. The epitaxial wafer according to claim 14, characterized in that The concentration of magnesium atoms in the cap layer (200) is 0.5 to 5E19 atoms / cm 3 .

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