CN109378371B - LED epitaxial wafer growth method - Google Patents

Abstract

The present application discloses a method for growing an LED epitaxial wafer. The method includes treating a sapphire substrate with an AlN thin film on the surface, growing a first graded AlGaN layer, growing a second graded AlGaN layer, and growing a first graded AlGaN layer on the sapphire substrate in sequence. Three graded AlGaN layers, growth of low temperature buffer layer, growth of undoped GaN layer, growth of Si-doped N-type GaN layer, periodic growth of active layer MQW, growth of P-type AlGaN layer, growth of Mg-doped P-type GaN layer , cooling down. Sequentially growing the first graded AlGaN layer, the second graded AlGaN layer and the third graded AlGaN layer reduces the dislocation density, reduces the warpage of the epitaxial wafer, and improves the pass rate of the GaN epitaxial wafer, the luminous efficiency of the LED and the antistatic ability. Annealing the graded AlGaN layer makes the surface of the entire epitaxial layer smoother, with fewer surface hexagonal defects and pits, and the overall appearance is better.

Description

LED epitaxial wafer growth method

technical field

The invention relates to the technical field of LED epitaxial wafer growth, in particular to a LED epitaxial wafer growth method.

Background technique

The currently commonly used GaN growth method is patterning on a sapphire substrate. Sapphire crystal is one of the best substrate materials for the growth of the third-generation semiconductor material GaN epitaxial layer, and its single crystal preparation process is mature. GaN is the base material for blue LEDs. Among them, SiC, the substrate material of the GaN epitaxial layer, has a small lattice mismatch with GaN, only 3.4%, but its thermal expansion coefficient is quite different from that of GaN, which is easy to cause the GaN epitaxial layer to break, and the manufacturing cost is high, which is 10% of that of sapphire. The cost of the substrate material Si is low, and the mismatch degree with GaN lattice is large, reaching 17%. It is difficult to grow GaN, and the luminous efficiency is too low compared with sapphire; the substrate material sapphire has the same crystal structure (hexagonally symmetric wurtzite crystal) structure), and the lattice mismatch with GaN is 13% larger, which easily leads to high dislocation density in the GaN epitaxial layer. For this reason, adding AlN or low-temperature GaN epitaxial layer or SiO2 layer on the sapphire substrate can reduce the dislocation of the GaN epitaxial layer. density.

There is a large lattice mismatch (13-16%) and thermal mismatch between sapphire and GaN, which makes the misfit dislocation density in the GaN epitaxial layer high (~10 ¹⁰ cm ^-2 ), which affects the quality of the GaN epitaxial layer , thereby affecting the quality of the device (luminous efficiency, drain electrode, lifetime, etc.).

The traditional method is to use a low-temperature buffer layer to improve the crystal quality of the GaN epitaxial layer by adjusting the nitridation of the sapphire substrate, the growth temperature of the low-temperature buffer layer, and the thickness of the buffer layer. However, since the low-temperature buffer layer is still heteroepitaxy, its improved crystal quality is limited. In addition, due to the large lattice mismatch between each epitaxial thin film layer, the epitaxial crystal thin film is always subjected to stress during the growth process, resulting in the bending and warping of the epitaxial wafer. When the traditional low-temperature buffer layer method is used for epitaxial crystal growth on a large-size sapphire substrate, the warpage of the epitaxial wafer is large, resulting in a high grinding fragmentation rate and a low product yield in the subsequent chip fabrication process.

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to provide a method for growing an LED epitaxial wafer, comprising the steps of:

Treat a sapphire substrate with an AlN film on the surface;

A first graded AlGaN layer, a second graded AlGaN layer, and a third AlGaN layer are grown sequentially on the sapphire substrate, wherein,

The growing of the first graded AlGaN layer includes: controlling the reaction chamber pressure of 400-600 mbar, feeding NH ₃ with a flow rate of 60-70 L/min, N ₂ with a flow rate of 90-95 L/min, TMGa of 100-110 sccm, 230-250sccm TMAl source, the growth temperature is gradually reduced from 550°C to 500°C by 0.1°C per second during the growth process, and a first graded AlGaN layer with a thickness D1 of 8-10nm is grown on the sapphire substrate, Wherein the molar composition of Al is 10-12%;

The growing of the second graded AlGaN layer includes: increasing the growth temperature to 700° C., keeping the pressure of the reaction chamber and the gas flow rate unchanged, and gradually increasing the growth temperature from 700° C. at a rate of 0.2° C. per second during the growth process to 800° C., growing a second graded AlGaN layer with a thickness D2 of 8-10 nm on the first graded AlGaN layer, wherein the molar composition of Al is 10-12%, and D2=D1;

The growing of the third AlGaN layer includes: increasing the pressure of the reaction chamber to 850-900 mbar, reducing the growth temperature from 800° C. to 480° C., keeping the gas flow rate unchanged, maintaining the pressure of the reaction chamber at 850-900 mbar during the growth process, and growing Keeping the temperature constant at 480°C, a third AlGaN layer with a thickness D3 of 8-10 nm is grown on the second graded AlGaN layer, wherein the molar composition of Al is 10-12%, and D3=D2;

Keep the pressure of the reaction chamber between 850-900 mbar, control the flow rate of N ₂ to be 150-160 L/min, and control the temperature of the reaction chamber to be between 680-720 ° C. For the first graded AlGaN layer, the second graded AlGaN layer and the first graded AlGaN layer The three AlGaN layers are annealed for 20s;

Growth of low temperature buffer layer;

Growth of undoped GaN layers;

growing a Si-doped N-type GaN layer;

Periodically grow the active layer MQW;

Growth of P-type AlGaN layer;

growing a Mg-doped P-type GaN layer;

and cooling down.

Preferably, the sapphire substrate with the AlN thin film on the surface is treated at a high temperature for 5-10 minutes at 1000-1200° C. and the pressure of the reaction chamber is maintained in a hydrogen atmosphere of 100-150 mbar.

Preferably, for the growth of the low temperature buffer layer, the temperature is further lowered to 550-650 ℃, the pressure of the reaction chamber is maintained at 400-600 mbar, and the flow rate of NH ₃ , 50-100 sccm TMGa, 100-130 L/ min of H ₂ , and a low temperature buffer layer with a thickness of 20-50 nm is grown on the third AlGaN layer.

Preferably, for the growth of the undoped GaN layer, the temperature is increased to 1000-1200° C., the pressure of the reaction chamber is maintained at 150-300 mbar, and the flow rate of NH ₃ of 30,000-40,000 sccm, TMGa of 200-400 sccm, 100-130 L/min of H ₂ , continuously growing an undoped GaN layer of 2-4 μm on the low temperature buffer layer.

Preferably, for the growth of the Si-doped N-type GaN layer, the pressure of the reaction chamber is kept at 150-300 mbar, the temperature is kept at 1000-1100° C., and the flow rate of NH ₃ and 200-300 sccm is 40-60 L/min. TMGa, 50-90 L/min H ₂ and 20-50 sccm SiH ₄ , a 2-4 μm Si-doped N-type GaN layer was continuously grown on the undoped GaN layer, and the Si doping concentration was 5E+18- 1E+19 atoms/cm ³ .

Preferably, the periodically grown active layer MQW is further:

The pressure of the reaction chamber is maintained at 300-400 mbar, the low temperature is 700-750 ℃, and NH ₃ of 50,000-60,000 sccm, TEGa of 100-150 sccm, and TMIn are introduced, and the flow rate of TMIn increases gradually from 150-170 sccm to 25-52 sccm per second. 1500-1700sccm, grow In _y1 Ga _(1-y1) N for 30-50s, grow thickness D4, In doping concentration increases from 1E+19atoms/ ^cm3 to 4E+17-7E+17atoms/ ^cm3 per second It is 3E+19atoms/cm ³ ;

Maintain the growth conditions unchanged, the flow rate of stable TMIn is 1500-1700sccm, the growth of In _y2 Ga _(1-y2) N for 100-150s, the growth thickness is D5, the In doping concentration is 1E+20-3E+20atoms/cm ³ , The range of D4+D5 is 3-3.5nm, and the range of y1 and y2 is 0.015-0.25, where y1 and y2 are not equal;

Raise the temperature to 800-850℃, maintain the pressure at 300-400mbar, pass 50000-60000sccm NH3, 400-500sccm TEGa, grow a 10nm GaN layer, In _y1 Ga _(1-y1) N/In _y2 Ga _{( 1-y2)} The number of N/GaN cycles is 10-15.

Preferably, for growing the P-type AlGaN layer, the temperature is increased to 900-1000° C., the pressure in the reaction chamber is maintained at 200-400 mbar, and the P-type AlGaN layer of 20-50 nm is continuously grown on the active layer MQW , the Al doping concentration is 1E+20-3E+20 atoms/cm ³ , and the Mg doping concentration is 5E+18-1E+19 atoms/cm ³ .

Preferably, for the growth of the Mg-doped P-type GaN layer, the temperature is increased to 930-950° C., the pressure of the reaction chamber is maintained at 200-600 mbar, and the P-type AlGaN layer is continuously grown on the P-type AlGaN layer of 100-300 nm. Mg-doped P-type GaN layer, Mg doping concentration 1E+19-1E+20atoms/cm ³ .

Preferably, in the cooling and cooling, the temperature is further lowered to 700-800° C., maintained for 20-30 min, and then cooled in the furnace.

Compared with the prior art, the LED epitaxial wafer growth method provided by the present invention achieves the following beneficial effects:

First, by growing the first graded AlGaN layer with a slightly lower crystal quality on the sapphire substrate of the AlN film, it can better match the substrate, has a smaller lattice mismatch, and can make the epitaxial atom filling uniform Up, the intra-chip uniformity is improved.

Second, a second graded AlGaN layer with high crystalline quality is grown on the first graded AlGaN layer. The atoms in the epitaxial layer will release the intra-chip stress and block the upward extension of the defects caused by the lattice mismatch in the early stage. When the growth continues, it will be blocked again. The upward extension of the defect when it is directly parallel to the upward movement reduces the dislocation density and improves the crystal quality.

Third, growing the third AlGaN layer at low temperature and high pressure on the second graded AlGaN layer improves the doping efficiency of Al and the crystalline quality of the layer, which is beneficial to eliminate the stress accumulation effect of the sapphire substrate on the GaN thin film, and significantly increases the The stress control window of the epitaxial film material is enlarged, thereby reducing the warpage of the epitaxial wafer, which is beneficial to improve the pass rate of the GaN epitaxial wafer, and improves the luminous efficiency and antistatic ability of the LED.

Fourth, the first graded AlGaN layer, the second graded AlGaN layer and the third AlGaN layer are briefly annealed for 20 s, so that the lattices of the first graded AlGaN layer, the second graded AlGaN layer and the third AlGaN layer are heated under the action of heat. A new regular arrangement is obtained, a tidy surface is obtained, which is beneficial to the growth of the low-temperature buffer layer in the next step, and the surface of the entire epitaxial layer is smoother, with fewer surface hexagonal defects and concave pits, and the overall appearance is better.

Description of drawings

The drawings described herein are used to provide further understanding of the present application and constitute a part of the present application. The schematic embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation of the present application. In the attached image:

FIG. 1 is a flowchart of a method for growing an LED epitaxial wafer in Embodiment 1 of the present invention.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. It should be noted that the described embodiments are in fact only some, not all, of the embodiments of the present invention, and are merely illustrative in fact and in no way intended to limit the present invention and its application or use. The scope of protection of this application should be determined by the appended claims.

Example 1:

Referring to FIG. 1, a specific embodiment of the LED epitaxial wafer growth method described in the present application is shown, and the method includes:

Step 101 , treating the sapphire substrate with the AlN film on the surface, specifically, at 1000° C., the sapphire substrate with the AlN film on the surface is treated at a high temperature for 5 minutes in a hydrogen atmosphere where the pressure of the reaction chamber is maintained at 100 mbar.

Step 102, sequentially growing a first graded AlGaN layer, growing a second graded AlGaN layer and a third AlGaN layer on the sapphire substrate:

The growing of the first graded AlGaN layer includes: controlling a reaction chamber pressure of 400 mbar, feeding NH ₃ with a flow rate of 60 L/min, N ₂ with a flow rate of 90 L/min, TMGa with a flow rate of 100 sccm, and a TMAl source with a flow rate of 230 sccm into the reaction chamber. The growth temperature is gradually reduced from 550°C to 500°C by 0.1°C per second, and a first graded AlGaN layer with a thickness D1 of 8 nm is grown on the sapphire substrate, wherein the molar composition of Al is 10%;

The growing of the second graded AlGaN layer includes: increasing the growth temperature to 700° C., keeping the pressure of the reaction chamber and the gas flow rate unchanged, and gradually increasing the growth temperature from 700° C. at a rate of 0.2° C. per second during the growth process to 800° C., growing a second graded AlGaN layer with a thickness D2 of 8 nm on the first graded AlGaN layer, wherein the molar composition of Al is 10%;

The growing of the third AlGaN layer includes: the growing of the third AlGaN layer includes: increasing the pressure of the reaction chamber to 850 mbar, reducing the growth temperature from 800° C. to 480° C., keeping the gas flow rate unchanged, and maintaining the reaction chamber during the growth process. The pressure is 850 mbar, the growth temperature is kept unchanged at 480 °C, and a third AlGaN layer with a thickness D3 of 8 nm is grown on the second graded AlGaN layer, wherein the molar composition of Al is 10%;

Keep the pressure of the reaction chamber at 850mbar, control the flow rate of N ₂ to be 150L/min, and control the temperature of the reaction chamber to be between 680°C. 20s annealing treatment.

Step 103, growing a low-temperature buffer layer: the temperature is lowered to 550° C., the pressure of the reaction chamber is maintained at 400 mbar, the flow rate is 10000 sccm NH ₃ , 50 sccm TMGa, and 100 L/min H ₂ , and the thickness is grown on the third AlGaN layer. 20nm low temperature buffer layer.

Step 104 , growing an undoped GaN layer: raising the temperature to 1000° C., maintaining the pressure of the reaction chamber at 150 mbar, and feeding NH ₃ with a flow rate of 30,000 sccm, TMGa with a flow rate of 200 sccm, and H ₂ with a flow rate of 100 L/min. A 2μm undoped GaN layer was continuously grown on the top.

Step 105, growing the Si-doped N-type GaN layer: keep the pressure of the reaction chamber at 150 mbar, keep the temperature at 1000 °C, and feed NH ₃ with a flow rate of 40 L/min, TMGa with 200 sccm, H ₂ with 50 L/min, and SiH with 20 sccm. _4. Continuously grow a 2 μm Si-doped N-type GaN layer on the undoped GaN layer, and the Si doping concentration is 5E+18 atoms/cm ³ .

Step 106, periodically growing the active layer MQW:

The pressure of the reaction chamber was maintained at 300 mbar, the low temperature was 700 ℃, 50000 sccm of NH ₃ , 100 sccm of TEGa, and TMIn were introduced, and the flow rate of TMIn increased gradually from 150 sccm to 1500 sccm at a rate of 45 sccm per second, and In _0.015 Ga _0.985 N was grown for 30 s, and the growth The thickness is 1 nm, and the In doping concentration is gradually increased from 1E+19 atoms/cm ³ to 3E+19 atoms/cm ³ with an increase of 6.7E+17 atoms/cm ³ per second;

Maintain the growth conditions unchanged, the flow rate of stable TMIn is 1500sccm, the growth of In _0.25 Ga _0.75 N for 100s, the growth thickness is 2nm, and the In doping concentration is 1E+20atoms/cm ³ ;

The temperature was raised to 800°C, the pressure was maintained at 300mbar, NH3 of 50000sccm, TEGa of 400sccm were fed, and a GaN layer of 10 nm was grown, and the In _0.015 Ga _0.985 N/In _0.25 Ga _0.75 N/GaN cycle number was 10.

Step 107, growing a P-type AlGaN layer: raising the temperature to 900° C., maintaining the reaction chamber pressure at 200 mbar, and continuously growing a 20-nm P-type AlGaN layer on the active layer MQW, with an Al doping concentration of 1E+20atoms/cm ^3. The Mg doping concentration is 5E+18 atoms/cm ³ .

Step 108 , growing a Mg-doped P-type GaN layer: raising the temperature to 930° C., maintaining the reaction chamber pressure at 200 mbar, and continuously growing a 100 nm magnesium-doped P-type GaN layer on the P-type AlGaN layer, Mg-doped The concentration was 1E+19 atoms/cm ³ .

Step 109 , cooling down: cooling to 700° C., holding for 20 minutes, and then cooling in the furnace.

Example 2:

This embodiment provides a method for growing an LED epitaxial wafer, and the method includes:

Step 201 , treating the sapphire substrate with the AlN film on the surface, specifically, at 1200° C., under a hydrogen atmosphere with the pressure of the reaction chamber maintained at 150 mbar, high temperature treatment of the sapphire substrate with the AlN film on the surface for 10 minutes.

Step 202, sequentially growing a first graded AlGaN layer, growing a second graded AlGaN layer and a third AlGaN layer on the sapphire substrate:

The growing of the first graded AlGaN layer includes: controlling the pressure of the reaction chamber at 600 mbar, feeding NH ₃ with a flow rate of 70 L/min, N ₂ with a flow rate of 95 L/min, TMGa with a flow rate of 110 sccm, and a TMAl source with a flow rate of 250 sccm into the reaction chamber. The growth temperature is gradually reduced from 550°C to 500°C by 0.1°C per second, and a first graded AlGaN layer with a thickness D1 of 10 nm is grown on the sapphire substrate, wherein the molar composition of Al is 12%;

The growing of the second graded AlGaN layer includes: increasing the growth temperature to 700° C., keeping the pressure of the reaction chamber and the gas flow rate unchanged, and gradually increasing the growth temperature from 700° C. at a rate of 0.2° C. per second during the growth process to 800° C., growing a second graded AlGaN layer with a thickness D2 of 10 nm on the first graded AlGaN layer, wherein the molar composition of Al is 12%;

The growing of the third AlGaN layer includes: the growing of the third AlGaN layer includes: increasing the pressure of the reaction chamber to 900 mbar, reducing the growth temperature from 800° C. to 480° C., keeping the gas flow rate unchanged, and maintaining the reaction chamber during the growth process. The pressure is 900 mbar, the growth temperature is kept unchanged at 480 °C, and a third AlGaN layer with a thickness D3 of 10 nm is grown on the second graded AlGaN layer, wherein the molar composition of Al is 12%;

Keep the pressure of the reaction chamber at 900 mbar, control the flow rate of N ₂ to be 160 L/min, and control the temperature of the reaction chamber to be between 720 ° C. The first graded AlGaN layer, the second graded AlGaN layer and the third AlGaN layer are subjected to 20s annealing treatment.

Step 203, growing a low temperature buffer layer: the temperature is lowered to 650°C, the pressure of the reaction chamber is maintained at 600mbar, the flow rate is 20000sccm NH ₃ , 100 sccm TMGa, 130 L/min H ₂ , and the thickness is grown on the third AlGaN layer 50nm low temperature buffer layer.

Step 204 , growing an undoped GaN layer: raising the temperature to 1200° C., maintaining the pressure of the reaction chamber at 300 mbar, and feeding NH ₃ with a flow rate of 40,000 sccm, TMGa with a flow rate of 400 sccm, and H ₂ with a flow rate of 130 L/min. A 4μm undoped GaN layer was continuously grown on the top.

Step 205 , growing Si-doped N-type GaN layer: keep the pressure of the reaction chamber at 300 mbar, keep the temperature at 1100° C., and feed NH ₃ with a flow rate of 60 L/min, TMGa with 300 sccm, H ₂ with 90 L/min and SiH with 50 sccm. _4. Continuously grow a 4 μm Si-doped N-type GaN layer on the undoped GaN layer, and the Si doping concentration is 1E+19 atoms/cm ³ .

Step 206, periodically growing the active layer MQW:

The pressure of the reaction chamber was maintained at 400 mbar, the low temperature was 750 ℃, and 60000 sccm of NH ₃ , 150 sccm of TEGa, and TMIn were introduced. The flow rate of TMIn increased gradually from 170 sccm to 1700 sccm at a rate of 30.6 sccm per second, and In _0.010 Ga _0.990 N was grown for 50 s. The growth thickness is 1.5 nm, and the In doping concentration is gradually increased from 1E+19 atoms/cm ³ to 3E+19 atoms/cm ³ with an increase of 4E+17 atoms/cm ³ per second;

Keep the growth conditions unchanged, the flow rate of stable TMIn is 1700sccm, the growth of In _0.2 Ga _0.8 N for 150 s, the growth thickness of 2 nm, and the In doping concentration of 3E+20atoms/cm ³ ;

The temperature was raised to 850°C, the pressure was maintained at 400mbar, NH3 of 60000sccm, TEGa of 500sccm were fed, and a GaN layer of 10 nm was grown, and the In _0.010 Ga _0.990 N/In _0.2 Ga _0.8 N/GaN cycle number was 15.

Step 207 , growing a P-type AlGaN layer: raising the temperature to 1000° C., maintaining the reaction chamber pressure at 400 mbar, and continuously growing a 50 nm P-type AlGaN layer on the active layer MQW, and the Al doping concentration is 3E+20 atoms/cm ^3. The Mg doping concentration is 1E+19 atoms/cm ³ .

Step 208 , growing a Mg-doped P-type GaN layer: raising the temperature to 950° C., maintaining the pressure of the reaction chamber at 600 mbar, and continuously growing a 300 nm magnesium-doped P-type GaN layer on the P-type AlGaN layer, Mg-doped The concentration was 1E+20 atoms/cm ³ .

Step 209 , cooling down: cooling down to 800° C., keeping the temperature for 30 minutes, and then cooling in the furnace.

Example 3

Step 301 , treating the sapphire substrate with the AlN film on the surface, specifically, at 1100° C., the sapphire substrate with the AlN film on the surface is treated at a high temperature for 7 minutes in a hydrogen atmosphere with the pressure of the reaction chamber maintained at 125 mbar.

Step 302, growing a first graded AlGaN layer, growing a second graded AlGaN layer and a third AlGaN layer in sequence on the sapphire substrate:

The growing of the first graded AlGaN layer includes: controlling the reaction chamber pressure of 500 mbar, feeding NH ₃ with a flow rate of 65 L/min, N ₂ with a flow rate of 93 L/min, TMGa with a flow rate of 105 sccm, and a TMAl source with a flow rate of 240 sccm into the reaction chamber. The growth temperature is gradually reduced from 550°C to 500°C by 0.1°C per second, and a first graded AlGaN layer with a thickness D1 of 9 nm is grown on the sapphire substrate, wherein the molar composition of Al is 11%;

The growing of the second graded AlGaN layer includes: increasing the growth temperature to 700° C., keeping the pressure of the reaction chamber and the gas flow rate unchanged, and gradually increasing the growth temperature from 700° C. at a rate of 0.2° C. per second during the growth process to 800° C., growing a second graded AlGaN layer with a thickness D2 of 9 nm on the first graded AlGaN layer, wherein the molar composition of Al is 11%;

The growing of the third AlGaN layer includes: the growing of the third AlGaN layer includes: increasing the pressure of the reaction chamber to 870 mbar, reducing the growth temperature from 800° C. to 480° C., keeping the gas flow rate unchanged, and maintaining the reaction chamber during the growth process. The pressure is 870 mbar, the growth temperature is kept unchanged at 480 °C, and a third AlGaN layer with a thickness D3 of 9 nm is grown on the second graded AlGaN layer, wherein the molar composition of Al is 11%;

Keep the pressure of the reaction chamber at 870 mbar, control the flow rate of N ₂ to be 155 L/min, and control the temperature of the reaction chamber to be between 700 ° C. The first graded AlGaN layer, the second graded AlGaN layer and the third AlGaN layer are subjected to 20s annealing treatment.

Step 303 , growing a low-temperature buffer layer: the temperature is lowered to 600° C., the pressure of the reaction chamber is maintained at 500 mbar, the flow rate is 15000 sccm NH ₃ , 70 sccm TMGa, 115 L/min H ₂ , and the thickness is grown on the third AlGaN layer 35nm low temperature buffer layer.

Step 304 , growing an undoped GaN layer: raising the temperature to 1100° C., maintaining the pressure of the reaction chamber at 225 mbar, and feeding NH ₃ with a flow rate of 35,000 sccm, TMGa with a flow rate of 300 sccm, and H ₂ with a flow rate of 115 L/min. A 3 μm undoped GaN layer was continuously grown on the top.

Step 305 , growing Si-doped N-type GaN layer: keep the pressure of the reaction chamber at 225 mbar, keep the temperature at 1050° C., and feed NH ₃ with a flow rate of 50 L/min, TMGa with 250 sccm, H ₂ with 70 L/min and SiH with 35 sccm. _4. Continuously grow a 3 μm Si-doped N-type GaN layer on the undoped GaN layer, and the Si doping concentration is 7E+18 atoms/cm ³ .

Step 306, periodically growing the active layer MQW:

The pressure of the reaction chamber was maintained at 350 mbar, the low temperature was 725 °C, and 55000 sccm of NH ₃ , 125 sccm of TEGa, and TMIn were introduced. The flow rate of TMIn increased gradually from 160 sccm to 1600 sccm at a rate of 36 sccm per second, and In _0.1 Ga _0.9 N was grown for 40 s. The thickness is 1.15 nm, and the In doping concentration is gradually increased from 1E+19 atoms/cm ³ to 3E+19 atoms/cm ³ with an increase of 5E+17 atoms/cm ³ per second;

Maintain the growth conditions unchanged, the flow rate of stable TMIn is 1600sccm, the growth of In _0.15 Ga _0.85 N for 125s, the growth thickness is 2.1nm, and the In doping concentration is 2E+20atoms/cm ³ ;

The temperature was raised to 825°C, the pressure was maintained at 350mbar, NH3 of 55000sccm, TEGa of 450sccm were fed, and a GaN layer of 10 nm was grown. The number of cycles of In _0.1 Ga _0.9 N/In _0.15 Ga _0.85 N/GaN was 13.

Step 307 , growing a P-type AlGaN layer: raising the temperature to 950° C., maintaining the reaction chamber pressure at 300 mbar, and continuously growing a 35 nm P-type AlGaN layer on the active layer MQW, with an Al doping concentration of 2E+20atoms/cm ^3. The Mg doping concentration is 7.5E+18 atoms/cm ³ .

Step 308 , growing a Mg-doped P-type GaN layer: raising the temperature to 940° C., maintaining the reaction chamber pressure at 400 mbar, and continuously growing a 200 nm magnesium-doped P-type GaN layer on the P-type AlGaN layer, Mg-doped The concentration was 5E+19 atoms/cm ³ .

Step 309 , cooling down: cooling down to 750° C., keeping the temperature for 25 minutes, and then cooling in the furnace.

Example 4

Step 401 , treating the sapphire substrate with AlN thin film on the surface, specifically, at 1050° C., the sapphire substrate with AlN thin film on the surface is treated at a high temperature for 6 minutes in a hydrogen atmosphere where the pressure of the reaction chamber is maintained at 110 mbar.

Step 402, growing a first graded AlGaN layer, growing a second graded AlGaN layer and a third AlGaN layer in sequence on the sapphire substrate:

The growing of the first graded AlGaN layer includes: controlling the reaction chamber pressure of 450 mbar, feeding NH ₃ with a flow rate of 63 L/min, N ₂ with a flow rate of 91 L/min, TMGa of 102 sccm, and TMAl source of 235 sccm into the reaction chamber, and during the growth process The growth temperature is gradually reduced from 550°C to 500°C by 0.1°C per second, and a first graded AlGaN layer with a thickness D1 of 8.5 nm is grown on the sapphire substrate, wherein the molar composition of Al is 10.5%;

The growing of the second graded AlGaN layer includes: increasing the growth temperature to 700° C., keeping the pressure of the reaction chamber and the gas flow rate unchanged, and gradually increasing the growth temperature from 700° C. at a rate of 0.2° C. per second during the growth process to 800° C., growing a second graded AlGaN layer with a thickness D2 of 8.5 nm on the first graded AlGaN layer, wherein the molar composition of Al is 10.5%;

The growing of the third AlGaN layer includes: the growing of the third AlGaN layer includes: increasing the pressure of the reaction chamber to 860 mbar, reducing the growth temperature from 800° C. to 480° C., keeping the gas flow rate unchanged, and maintaining the reaction chamber during the growth process. The pressure is 860 mbar, the growth temperature is kept unchanged at 480 °C, and a third AlGaN layer with a thickness D3 of 8.5 nm is grown on the second graded AlGaN layer, wherein the molar composition of Al is 10.5%;

Keep the pressure of the reaction chamber at 860mbar, control the flow rate of N ₂ to be 152L/min, and control the temperature of the reaction chamber to be between 690°C. 20s annealing treatment.

Step 403 , growing a low-temperature buffer layer: the temperature is lowered to 560° C., the pressure of the reaction chamber is maintained at 450 mbar, the flow rate is 13000 sccm NH ₃ , 60 sccm TMGa, and 110 L/min H ₂ , and the thickness is grown on the third AlGaN layer. 30nm low temperature buffer layer.

Step 404 , growing an undoped GaN layer: raising the temperature to 1050° C., maintaining the pressure of the reaction chamber at 180 mbar, and feeding in NH ₃ with a flow rate of 33000 sccm, TMGa with 250 sccm, and H ₂ with 110 L/min, and in the low temperature buffer layer A 2.5 μm undoped GaN layer was continuously grown on top.

Step 405 , growing Si-doped N-type GaN layer: keep the pressure of the reaction chamber at 190 mbar, keep the temperature at 1010° C., and feed NH ₃ with a flow rate of 45 L/min, TMGa at 220 sccm, H ₂ at 60 L/min, and SiH at 25 sccm _4. Continuously grow a 2.5 μm Si-doped N-type GaN layer on the undoped GaN layer, and the Si doping concentration is 6E+18 atoms/cm ³ .

Step 406, periodically growing the active layer MQW:

The pressure of the reaction chamber was maintained at 330 mbar, the low temperature was 710 ℃, and 53000 sccm of NH ₃ , 110 sccm of TEGa, and TMIn were introduced. The flow rate of TMIn increased gradually from 155 sccm to 1550 sccm at a rate of 39.8 sccm per second, and In _0.2 Ga _0.8 N was grown for 35 s. The growth thickness is 1.2 nm, and the In doping concentration is gradually increased from 1E+19 atoms/cm ³ to 3E+19 atoms/cm ³ with an increase of 5.7E+17 atoms/cm ³ per second;

Maintain the growth conditions unchanged, the flow rate of stable TMIn is 1550sccm, the growth of In _0.22 Ga _0.78 N for 110s, the growth thickness is 2.15nm, and the In doping concentration is 1.5E+20atoms/cm ³ ;

The temperature was raised to 810°C, the pressure was maintained at 330mbar, NH3 of 53000sccm, TEGa of 430sccm were fed, and a GaN layer of 10 nm was grown. The In _0.2 Ga _0.8 N/In _0.22 Ga _0.78 N/GaN cycle number was 11.

Step 407 , growing a P-type AlGaN layer: raising the temperature to 930° C., maintaining the reaction chamber pressure at 250 mbar, and continuing to grow a 25 nm P-type AlGaN layer on the active layer MQW, with an Al doping concentration of 1.5E+20atoms/ cm ³ , the Mg doping concentration is 6E+18 atoms/cm ³ .

Step 408 , growing a Mg-doped P-type GaN layer: raising the temperature to 910° C., maintaining the reaction chamber pressure at 300 mbar, and continuously growing a 150 nm magnesium-doped P-type GaN layer on the P-type AlGaN layer, Mg-doped The concentration was 3E+19 atoms/cm ³ .

Step 409 , cooling down: cooling down to 720° C., keeping the temperature for 22 minutes, and then cooling in the furnace.

Comparative Experiment:

The following is a traditional process LED structure epitaxial growth method, the specific steps are:

1. The sapphire substrate with AlN film on the surface is treated at a high temperature for 5-10 minutes at 1000-1200°C and the pressure of the reaction chamber is maintained at a hydrogen atmosphere of 100-150mbar.

2. The temperature is lowered to 550-650℃, the pressure of the reaction chamber is maintained at 400-600mbar, and the flow rate is 10000-20000sccm NH ₃ , 50-100 sccm TMGa, 100-130L/min H ₂ , and grow on a sapphire substrate Low temperature buffer layer GaN with a thickness of 20-50nm.

3. Raise the temperature to 1000-1200°C, maintain the pressure of the reaction chamber at 150-300mbar, pass in NH ₃ with a flow rate of 30,000-40,000 sccm, TMGa with a flow rate of 200-400 sccm, and H ₂ with a flow rate of 100-130 L/min, and continue to grow 2- 4μm undoped GaN;

4. Continuously grow Si-doped N-type GaN, the Si doping concentration is 5E+18-1E+19 atoms/cm ³ , and the total thickness is controlled at 2-4 μm.

5. Periodically growing the active layer MQW, including steps,

The pressure of the reaction chamber was maintained at 300-400 mbar, the low temperature was 700-750 ℃, NH ₃ of 50,000-60,000 sccm, TEGa of 100-150 sccm, and TMIn were introduced. 50s of In _y1 Ga _(1-y1) N, the growth thickness is D6, and the In doping concentration is gradually changed from 1E+19 atoms/cm ³ to 3E+19 atoms/cm ³ ;

Maintain the growth conditions unchanged, the flow rate of stable TMIn is 1500-1700sccm, the growth of In _y2 Ga _(1-y2) N for 100-150s, the growth thickness is D7, the In doping concentration is 1E+20-3E+20atoms/cm ³ , The range of D6+D7 is 3-3.5nm, and the range of y1 and y2 is 0.015-0.25, where y1 and y2 are not equal;

Raise the temperature to 800-850℃, maintain the pressure at 300-400mbar, pass 50000-60000sccm NH3, 400-500sccm TEGa, grow a 10nm GaN layer, In _y1 Ga _(1-y1) N/In _y2 Ga _{( 1-y2)} The number of N/GaN cycles is 10-15.

6. Raise the temperature to 900-1000°C again, maintain the pressure of the reaction chamber at 200-400mbar, continue to grow a 20-50nm P-type AlGaN layer, Al doping concentration 1E+20-3E+20atoms/cm ³ , Mg doping Concentration 5E+18-1E+19 atoms/cm ³ .

7. Raise the temperature to 930-950°C again, maintain the pressure of the reaction chamber at 200-600mbar, and continue to grow a 100-300nm Mg-doped P-type GaN layer with a Mg-doped concentration of 1E+19-1E+20atoms/cm ³ .

8. Finally, lower the temperature to 700-800℃, keep the temperature for 20-30min, and then cool in the furnace.

A group of epitaxial wafer samples W1 are grown by using the growth method provided by the present invention, and a group of epitaxial wafer samples W2 are grown by using the traditional growth method. The epitaxial wafer sample W1 was made into a chip sample C1 with a size of 254 μm×686 μm according to the standard process on the production line, and the epitaxial wafer sample W2 was made into a chip sample C2 with a size of 254 μm×686 μm according to the standard process on the production line.

The crystalline quality of the GaN epitaxial wafer samples was characterized by a high-resolution X-ray diffractometer (HRXRD) model D8 Discover, and a semi-integrating sphere automatic wafer spotting machine model LEDA-8F P7202 was used to test the optoelectronic properties of the chip samples. Features, as shown in Table 1:

Table 1 FWHM (full width at half maximum) and dislocation density of XRD rocking curves of samples W1 W2

By analyzing Table 1, the following conclusions can be drawn: Compared with the sample W2, the screw dislocation density and the edge dislocation density of the sample W1 are significantly reduced, and the width at half maximum is smaller, indicating that the method of the present invention can effectively improve the epitaxial film. crystal quality. In addition, statistics on the appearance yield of samples W1 and W2 show that the proportion of hexagonal defects and concave pits on the surface of the W2 sample is 0.7%, and the proportion of hexagonal defects and concave pits on the surface of the W1 sample is 0.3%, which shows the present invention The method can obviously improve the appearance of the epitaxial wafer surface.

The warpage BOW value data (um) of the epitaxial wafer samples W1 and W2 are counted. The average warpage of the W1 sample is 5.6um, and the average warpage of the W2 sample is 6.4um. The LED epitaxial wafer produced by the method of the present invention The warpage of the sample is obviously smaller, which shows that the method of the present invention can obviously reduce the warpage of the epitaxial wafer and improve the product qualification rate.

In order to clarify the influence of the crystal quality of the GaN epitaxial wafers grown by the method of the present invention and the traditional method on the optoelectronic parameters of the LED device, the samples W1 and W2 were fabricated into chips respectively. Specifically, the sample W1 was fabricated into a chip to obtain a chip sample C1 with a size of 254 μm×686 μm; the sample W2 was fabricated into a chip to obtain a chip sample C2 with a size of 254 μm×686 μm; a spot tester was used to test the luminescence under the forward direction of 150 mA. Power (LOP), leakage current (IR) under reverse -5V, antistatic capability (ESD pass rate) under Human Body Model (HBM) 2000V and 4000V, and the average value of all core photoelectric parameters, such as Table 2 shows:

Table 2 Test values of main photoelectric parameters of chip samples C1 and C2

By analyzing Table 2, the following conclusions can be drawn: the chip samples prepared by the growth method provided by the present invention have high luminous power, significantly lower leakage and high antistatic yield. Among them, the main reasons for high luminous power, low leakage and strong antistatic ability are that the method of the present invention increases the blocking and isolation mechanism of defects during epitaxial crystal growth, reduces dislocation ascending layer by layer, gradually improves lattice matching, and reduces dislocations. Density, reduce defect ratio, improve crystal quality, thereby improving LED luminous efficiency and antistatic ability.

It can be known from the above embodiments that the beneficial effects of the present application are:

First, by growing the first graded AlGaN layer with a slightly lower crystal quality on the sapphire substrate of the AlN film, it can better match the substrate, has a smaller lattice mismatch, and can make the epitaxial atom filling uniform Up, the intra-chip uniformity is improved.

Second, a second graded AlGaN layer with high crystalline quality is grown on the first graded AlGaN layer. The atoms in the epitaxial layer will release the intra-chip stress and block the upward extension of the defects caused by the lattice mismatch in the early stage. When the growth continues, it will be blocked again. The upward extension of the defect when it is directly parallel to the upward movement reduces the dislocation density and improves the crystal quality.

Third, growing the third AlGaN layer at low temperature and high pressure on the second graded AlGaN layer improves the doping efficiency of Al and the crystalline quality of the layer, which is beneficial to eliminate the stress accumulation effect of the sapphire substrate on the GaN thin film, and significantly increases the The stress control window of the epitaxial film material is enlarged, thereby reducing the warpage of the epitaxial wafer, which is beneficial to improve the pass rate of the GaN epitaxial wafer, and improves the luminous efficiency and antistatic ability of the LED.

Fourth, the first graded AlGaN layer, the second graded AlGaN layer and the third AlGaN layer are briefly annealed for 20 s, so that the lattices of the first graded AlGaN layer, the second graded AlGaN layer and the third AlGaN layer are heated under the action of heat. A new regular arrangement is obtained, a tidy surface is obtained, which is beneficial to the growth of the low-temperature buffer layer in the next step, and the surface of the entire epitaxial layer is smoother, with fewer surface hexagonal defects and concave pits, and the overall appearance is better.

Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are provided for illustration only and not for the purpose of limiting the scope of the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention. The scope of the invention is defined by the appended claims.

Claims (9)

1. A method for growing an LED epitaxial wafer is characterized by comprising the following steps:

processing a sapphire substrate with an AlN thin film on the surface;

sequentially growing a first gradient AlGaN layer, a second gradient AlGaN layer and a third AlGaN layer on the sapphire substrate, wherein,

first gradual change of growthThe AlGaN layer includes: controlling the pressure of the reaction cavity with the pressure of 400-600mbar, and introducing NH with the flow rate of 60-70L/min into the reaction cavity₃90-95L/min N₂100-110sccm TMGa and 230-250sccm TMAl source, gradually reducing the growth temperature from 550 ℃ to 500 ℃ by reducing the temperature by 0.1 ℃ per second in the growth process, and growing a first gradient AlGaN layer with the thickness D1 of 8-10nm on the sapphire substrate, wherein the molar composition of Al is 10-12%;

the growing a second graded AlGaN layer includes: increasing the growth temperature to 700 ℃, keeping the pressure of a reaction cavity and the gas inlet flow constant, gradually increasing the growth temperature from 700 ℃ to 800 ℃ by increasing the temperature by 0.2 ℃ per second in the growth process, and growing a second gradient AlGaN layer with the thickness of D2 being 8-10nm on the first gradient AlGaN layer, wherein the molar composition of Al is 10-12%, D2 is D1, and the crystalline quality of the first gradient AlGaN layer is lower than that of the second gradient AlGaN layer;

the growing a third AlGaN layer includes: increasing the pressure of the reaction cavity to 850-;

keeping the pressure of the reaction cavity between 850 and 900mbar, and controlling N₂The flow rate is 150-;

growing a low-temperature buffer layer;

growing an undoped GaN layer;

growing an N-type GaN layer doped with Si;

periodically growing an active layer MQW;

growing a P-type AlGaN layer;

growing a P-type GaN layer doped with Mg;

and cooling.

2. The method for growing the LED epitaxial wafer according to claim 1, wherein the sapphire substrate with the AlN thin film on the surface is processed at a high temperature for 5-10 minutes at 1000-1200 ℃ and under a hydrogen atmosphere with a reaction chamber pressure of 100-150 mbar.

3. The method as claimed in claim 1, wherein the growth of the low temperature buffer layer is further characterized by cooling to 550-650 ℃, maintaining the pressure in the reaction chamber at 400-600mbar, and introducing a flow of 10000-20000sccmnH₃TMGa 50-100sccm, H100-130L/min₂And growing a low-temperature buffer layer with the thickness of 20-50nm on the third AlGaN layer.

4. The method as claimed in claim 1, wherein the growing of the undoped GaN layer is further performed by raising the temperature to 1000-₃200-400sccm TMGa, 100-130L/min H₂And continuously growing an undoped GaN layer of 2-4 mu m on the low-temperature buffer layer.

5. The method as claimed in claim 1, wherein the Si-doped N-type GaN layer is grown by maintaining the pressure in the reaction chamber at 150-₃200-300sccm TMGa, 50-90L/min H₂And 20-50sccm SiH₄Continuously growing a 2-4 μm Si-doped N-type GaN layer on the undoped GaN layer, wherein the doping concentration of Si is 5E +18-1E +19atoms/cm³。

6. The LED epitaxial wafer growth method according to claim 1, wherein the active layer MQW is periodically grown, further,

the pressure of the reaction chamber is maintained at 300-400mbar, the low temperature is 700-750 ℃, NH of 50000-60000sccm is introduced₃100-150sccm TEGa and TMIn, the flow rate of TMIn is gradually increased from 150-170sccm to 1500-1700sccm by increasing 25-52sccm per second, and 30-50s of In are grown_y1Ga_(1-y1)N with a growth thickness of D4, and In doping concentration increased by 4E +17-7E +17atoms/cm per second³From 1E +19atoms/cm³Gradually changed into 3E +19atoms/cm³；

The growth condition is maintained unchanged, the flow rate of the stable TMIn is 1500-1700sccm, and 100-150s of In is grown_y2Ga_(1-y2)N, the growth thickness is D5, the In doping concentration is 1E +20-3E +20atoms/cm³D4+ D5 in the range of 3-3.5nm, y1 and y2 in the range of 0.015-0.25, wherein y1 and y2 are not equal;

raising the temperature to 800-_y1Ga_(1-y1)N/In_y2Ga_(1-y2)The number of N/GaN cycles is 10-15.

7. The method as claimed in claim 1, wherein the P-type AlGaN layer is grown by raising the temperature to 900-1000 ℃ and maintaining the pressure in the reaction chamber at 200-400mbar, and the P-type AlGaN layer with a thickness of 20-50nm is continuously grown on the MQW of the active layer, wherein the Al doping concentration is 1E +20-3E +20atoms/cm³Mg doping concentration of 5E +18-1E +19atoms/cm³。

8. The method as claimed in claim 1, wherein the growing of the Mg-doped P-type GaN layer is further performed by raising the temperature to 930-³。

9. The method as claimed in claim 1, wherein the temperature is lowered to 800 ℃ for 20-30min, and then the epitaxial wafer is cooled in a furnace.

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