A high-uniformity gallium nitride heterojunction material structure and an epitaxial growth method

Abstract

The application discloses a high-uniformity gallium nitride heterojunction material structure and an epitaxial growth method, and relates to the technical field of semiconductor single crystal thin films.The material structure comprises, from bottom to top, a SiC substrate, an AlN nucleation layer, a GaN buffer layer, an InAlGaN interlayer and an AlGaN barrier layer.The material is prepared on the substrate by a metal organic chemical vapor deposition method.The InAlGaN interlayer can enhance the confinement of carriers in the heterojunction quantum well and improve the two-dimensional electron gas mobility.Compared with a conventional AlN interlayer, the InAlGaN interlayer has a smaller lattice mismatch degree with the GaN buffer layer, is not prone to lattice relaxation, has a larger thickness selection window, is easy to control in process, and the increase of the number of atomic layers of the interlayer is beneficial to improving the uniformity and consistency of the electrical characteristics of the gallium nitride high electron mobility transistor material.The InAlGaN interlayer is grown by a gradual temperature rising process, so that the surface quality of the interlayer can be effectively improved and the influence of temperature rising on the material performance can be avoided.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of semiconductor single crystal thin films, in particular to a high-uniformity gallium nitride heterojunction material structure and an epitaxial growth method. BACKGROUND

[0002] A gallium nitride (GaN) high electron mobility transistor (HEMT) is a new type of electronic device, adopts aluminum gallium nitride (AlGaN) as a potential barrier, and forms an AlGaN / GaN heterojunction with a GaN buffer layer, which is a relatively common material system at present, and benefits from the strong polarization characteristics and band gap difference of the AlGaN / GaN heterojunction, a high-density two-dimensional electron gas (2DEG) is formed in the heterojunction quantum well, and the channel electrons are controlled by a Schottky gate voltage to realize work. The GaN HEMT device has excellent characteristics of high frequency and large power, is widely used in information transmission, energy conversion and other fields such as wireless communication base stations and power electronic devices, and meets the current development concept of energy saving, environmental protection and green low carbon.

[0003] The AlGaN / GaN heterojunction two-dimensional electron gas mobility is one of the key factors affecting the power characteristics of the device, and a higher carrier mobility is beneficial to improve the working current of the device. The two-dimensional electron gas mobility of the AlGaN / GaN heterojunction is restricted by multiple scattering mechanisms, mainly including: lattice scattering (also known as phonon scattering), interface scattering and alloy disorder scattering. At room temperature, the two-dimensional electron gas mobility of the AlGaN / GaN heterojunction is generally 1300-1600 cm 2 / Vs, which is related to the Al component and the two-dimensional electron gas concentration. By inserting a layer of aluminum nitride (AlN) about 1 nm between the AlGaN / GaN heterojunction, the two-dimensional electron gas mobility can be increased to 2000-2200 cm 2 / Vs, and the two-dimensional electron gas concentration is also improved, and the improvement amplitude is closely related to the thickness of the AlN insertion layer.

[0004] Although the AlN insertion layer can improve the material and device performance, due to the large lattice mismatch with the AlGaN barrier layer above and the GaN buffer layer below, the thickness thereof generally cannot exceed 2 nm, otherwise strain relaxation, surface quality deterioration and other problems will occur, and the effect of improving the channel electron transport characteristics cannot be achieved. At present, the process difficulty of growing an AlN insertion layer of about 1 nm (two atomic layers) by a metal organic chemical vapor deposition (MOCVD) method is relatively large, and it is difficult to accurately control the thickness and ensure the uniformity of the whole wafer. Therefore, for the AlGaN / GaN heterojunction material used for a microwave power device, how to effectively improve the channel two-dimensional electron gas mobility, at the same time, realize accurate controllability of the epitaxial process and uniformity in the wafer is an important topic. SUMMARY

[0005] The technical problem solved by the present application: In the prior art, the two-dimensional electron gas channel of the AlGaN / GaN heterojunction epitaxial material without an AlN insertion layer has low mobility, and the AlGaN / GaN heterojunction epitaxial material with an AlN insertion layer has the problems of high internal stress and high difficulty in uniformity control. The present application provides a high-uniformity gallium nitride heterojunction material structure and an epitaxial growth method. The use of InAlGaN as an insertion layer can effectively improve the channel two-dimensional electron gas concentration and mobility. Compared with the AlN insertion layer, the lattice mismatch degree between the InAlGaN insertion layer and the GaN is smaller, the critical thickness of strain relaxation of the insertion layer is larger, the selection window of the insertion layer thickness is increased, the difficulty of the epitaxial process is reduced, and the increase in the number of atomic layers is beneficial to improving the uniformity and consistency of the material. At the same time, the use of a gradual temperature rising process to grow the InAlGaN insertion layer can effectively improve the surface quality of the insertion layer and avoid the influence of temperature rising on the material performance.

[0006] Technical solution: A high-uniformity gallium nitride heterojunction material structure, the high-uniformity gallium nitride heterojunction material structure is sequentially arranged from bottom to top as a substrate, an AlN nucleation layer, a GaN buffer layer, an InAlGaN insertion layer, and an AlGaN barrier layer, wherein the thickness of the AlN nucleation layer is 10-100 nm, the thickness of the GaN buffer layer is 500-2500 nm, the thickness of the InAlGaN insertion layer is 2-4 nm, and the thickness of the AlGaN barrier layer is 10-30 nm.

[0007] As a preferred, the substrate is a SiC substrate.

[0008] As a preferred, in the InAlGaN insertion layer, the In component range interval is (0, 0.1], the Al component range interval is (0.5, 0.9], and the Ga component range interval is (0, 0.5]. The InAlGaN insertion layer material in this range will not significantly increase the stress of the AlGaN / GaN heterojunction, cause lattice relaxation, and also has a relatively strong polarization strength, so as to keep the channel two-dimensional electron gas concentration and mobility at a relatively high level.

[0009] As a preferred, the Al component range in the AlGaN barrier layer is between 0.15 and 0.35.

[0010] Based on the epitaxial growth method of the above-mentioned high-uniformity gallium nitride heterojunction material structure, the steps are as follows:

[0011] Step one. Select a substrate and place it in a metal organic chemical vapor deposition (MOCVD) equipment reaction chamber;

[0012] Step two. Increase the temperature of the reaction chamber to 1000-1200℃, introduce hydrogen, and perform baking treatment on the substrate for 5-10 minutes;

[0013] Step three. Adjust the temperature of the reaction chamber to 1000-1200℃, set the pressure of the reaction chamber to 50-100Torr, introduce ammonia and trimethylaluminum, and grow a 10-100 nm thick AlN nucleation layer;

[0014] Step four. Close the trimethylaluminum, adjust the temperature of the reaction chamber to 950-1100℃, set the pressure of the reaction chamber to 100-500Torr, introduce trimethylgallium, and grow a 500-2500 nm thick GaN buffer layer;

[0015] Step five. Adjust the temperature of the reaction chamber to 850-900℃, set the pressure of the reaction chamber to 50-150Torr, introduce trimethylindium and trimethylaluminum, and grow a 2-4 nm thick InAlGaN interlayer on the buffer layer, with the temperature gradually increasing to 950-1000℃ during the growth process;

[0016] Step six. Close the trimethylindium, keep the temperature and pressure of the reaction chamber unchanged, and grow a 10-30 nm thick AlGaN barrier layer;

[0017] Step seven. Close the ammonia, trimethylaluminum, and trimethylgallium, and reduce to room temperature.

[0018] Preferably, the rate of the temperature gradually increasing in step five is 40-80℃ / min.

[0019] Beneficial effects: The InAlGaN interlayer proposed in the present application has a strong polarization effect when the In component is low and the Al component is high, which can raise the energy level of the AlGaN barrier layer, enhance the confinement of channel electrons, effectively reduce the probability of channel electrons entering the barrier layer, and improve the channel two-dimensional electron gas concentration and mobility. Compared with the AlN interlayer, the lattice mismatch degree between the InAlGaN interlayer and the GaN is smaller, so that the critical thickness of strain relaxation of the interlayer increases, the selection window of the interlayer thickness increases, the difficulty of the epitaxial process is reduced, and the increase in the number of atomic layers is beneficial to improve the uniformity and consistency of the material.

[0020] Compared with AlGaN, the growth of InAlGaN quaternary alloy requires a lower temperature to improve the incorporation efficiency of In. Therefore, growing AlGaN on InAlGaN requires increasing the temperature of the reaction chamber, which can cause damage to the surface of the InAlGaN interlayer and cause a decrease in material performance. The present application proposes a gradual temperature rising process for growing the InAlGaN interlayer, which can effectively improve the surface quality of the interlayer and avoid the influence of temperature rising on material performance. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1A high-uniformity gallium nitride heterojunction epitaxial material structure diagram.

[0022] Figure 2 A high-uniformity gallium nitride heterojunction epitaxial material preparation flow chart.

[0023] Figure 3 An AlN and InAlGaN two insertion layer and GaN buffer layer lattice mismatch degree comparison diagram. DETAILED DESCRIPTION

[0024] The application will be further described below in conjunction with the drawings and specific embodiments.

[0025] A high-uniformity gallium nitride heterojunction material, as shown in Figure 1 The structure includes:

[0026] A substrate 1, the substrate material is SiC;

[0027] An AlN nucleation layer 2, which is grown on the substrate 1, functions to wet the substrate 1, provide nucleation points for the subsequent buffer layer, and adjust the stress between the substrate 1 and the epitaxial layer, the AlN nucleation layer 2 has a thickness of 10-100 nm;

[0028] A GaN buffer layer 3, which is grown on the AlN nucleation layer 2, releases the lattice mismatch between the epitaxial layer and the substrate 1, and provides a substrate for heterojunction preparation, the GaN buffer layer 3 has a thickness of 500-2500 nm;

[0029] An InAlGaN insertion layer 4, which is grown on the GaN buffer layer 3, uses InAlGaN quaternary alloy, has a small lattice mismatch degree with the GaN buffer layer, a large relaxation critical thickness, a large number of atomic layers, and good thickness uniformity, the InAlGaN insertion layer 4 has a thickness of 2-4 nm, an In component range interval of (0, 0.1], an Al component range interval of (0.5, 0.9], and a Ga component range interval of (0, 0.5];

[0030] An AlGaN barrier layer 5, which is grown on the InAlGaN insertion layer 4, forms a quantum well with the GaN buffer layer, generates a high-concentration two-dimensional electron gas through the polarization effect, and has a thickness of 10-30 nm and an Al component range of 0.15-0.35.

[0031] Wherein the InAlGaN quaternary alloy mentioned in the application is actually a combination of InN, AlN, GaN three materials, the sum of the number of atoms of three III group elements in the alloy is equal to the number of atoms of V group element. The proportion of the number of atoms of each III group element in the total number of atoms of III group elements is the component of the III group element, assuming that the In component is x, the Al component is y, and the Ga component is z, then x+y+z=1.

[0032] Similarly, the AlGaN mentioned in the application is a combination of AlN and GaN two materials, the sum of the number of atoms of two III group elements in the alloy is equal to the number of atoms of V group element. The proportion of the number of atoms of each III group element in the total number of atoms of III group elements is the component of the III group element, assuming that the Al component is y and the Ga component is z, then y+z=1.

[0033] Figure 2 The preparation flow chart of the application, combined Figure 1 The schematic diagram, the epitaxial growth method of the above-mentioned high-uniformity gallium nitride heterojunction material structure adopts MOCVD, wherein the V group source used is ammonia, the III group source used is trimethyl gallium, trimethyl aluminum, and trimethyl indium, and the carrier gas is hydrogen or nitrogen. According to experimental research, the preferred preparation process and steps are as follows:

[0034] Step one. Selecting a substrate 1, placing it in the reaction cavity of the MOCVD equipment;

[0035] Step two. The reaction cavity is heated to 1000-1200℃, hydrogen is introduced, and the substrate 1 is subjected to baking treatment for 5-10 minutes;

[0036] Step three. Adjust the reaction cavity temperature to 1000-1200℃, set the reaction cavity pressure to 50-100Torr, introduce ammonia and trimethyl aluminum, and grow a 10-100 nm thick AlN nucleation layer 2;

[0037] Step four. Close the trimethyl aluminum, adjust the reaction cavity temperature to 950-1100℃, set the reaction cavity pressure to 100-500Torr, introduce trimethyl gallium, and grow a 500-2500 nm thick GaN buffer layer 3;

[0038] Step five. Adjust the reaction cavity temperature to 850-900℃, set the reaction cavity pressure to 50-150Torr, introduce trimethyl indium and trimethyl aluminum, and grow a 2-4 nm thick InAlGaN insertion layer on the buffer layer. The temperature gradually increases to 950-1000℃ during the growth process, and the rate of temperature gradual increase is 40-80℃ / min;

[0039] Step six. Close the trimethyl indium, keep the reaction cavity temperature and pressure unchanged, and grow a 10-30 nm thick AlGaN barrier layer;

[0040] Step seven. Turn off ammonia, trimethylaluminum and trimethylgallium, and reduce to room temperature. Take out the wafer.

[0041] Example 1

[0042] Step 1, select the substrate 1, and place it in the reaction chamber of the MOCVD equipment;

[0043] Step 2, the reaction chamber is heated to 1050℃, the growth pressure is 100 Torr, and the substrate 1 is pretreated in situ under hydrogen atmosphere, the time is 10 minutes;

[0044] Step 3, grow a nucleation layer on the substrate 1, adjust the temperature of the reaction chamber, and introduce ammonia and trimethylaluminum, grow an AlN nucleation layer 2 with a thickness of 50 nm under the conditions of a growth temperature of 1100℃ and a growth pressure of 100 Torr;

[0045] Step 4, grow a buffer layer on the nucleation layer, turn off the trimethylaluminum, adjust the temperature of the reaction chamber, introduce trimethylgallium under the conditions of a growth temperature of 1050℃ and a growth pressure of 200 Torr, and grow a GaN buffer layer 3 with a thickness of 2000 nm;

[0046] Step 5, grow an insertion layer on the buffer layer, adjust the temperature and pressure of the reaction chamber, introduce trimethylindium and trimethylaluminum, and grow an InAlGaN insertion layer 4 with a thickness of 3 nm under the conditions of a growth temperature gradually changing from 900℃ to 1000℃ at a heating rate of 60℃ / min, a growth pressure of 100 Torr, and a molar ratio of ammonia, trimethylindium, trimethylaluminum and trimethylgallium of 1600:4:3:1, wherein the In component gradually changes from 0.05 to 0.01, the Al component gradually changes from 0.6 to 0.63, and the Ga component gradually changes from 0.35 to 0.36;

[0047] Step 6, grow a barrier layer on the insertion layer, turn off the trimethylindium, and grow an AlGaN barrier layer 5 with a thickness of 20 nm under the conditions of a growth temperature of 1000℃ and a growth pressure of 100 Torr, wherein the Al component is 0.25;

[0048] Step 7, turn off ammonia, trimethylaluminum and trimethylgallium, and reduce to room temperature.

[0049] Example 2

[0050] Step 1, select the substrate 1, and place it in the reaction chamber of the MOCVD equipment;

[0051] Step 2, the reaction chamber is heated to 1050℃, the growth pressure is 100 Torr, and the substrate 1 is pretreated in situ under hydrogen atmosphere, the time is 10 minutes;

[0052] Step 3, growing a nucleation layer on the substrate 1, adjusting the temperature of the reaction chamber, introducing ammonia and trimethylaluminum, under the conditions of a growth temperature of 1100℃ and a growth pressure of 100 Torr, growing an AlN nucleation layer 2 with a thickness of 50 nm;

[0053] Step 4, growing a buffer layer on the nucleation layer, closing the trimethylaluminum, adjusting the temperature of the reaction chamber, introducing trimethylgallium under the conditions of a growth temperature of 1050℃ and a growth pressure of 200 Torr, growing a GaN buffer layer 3 with a thickness of 2000 nm;

[0054] Step 5, growing an insertion layer on the buffer layer, adjusting the temperature and pressure of the reaction chamber, introducing trimethylindium, trimethylaluminum, under the conditions of a growth temperature gradually changing from 870℃ to 970℃ at a rate of 60℃ / min, a growth pressure of 100 Torr, and a molar ratio of ammonia, trimethylindium, trimethylaluminum, and trimethylgallium of 2000:5:3.5:1, growing an InAlGaN insertion layer 4 with a thickness of 3 nm, wherein the In component gradually changes from 0.08 to 0.02, the Al component gradually changes from 0.7 to 0.74, and the Ga component gradually changes from 0.22 to 0.24;

[0055] Step 6, growing a barrier layer on the insertion layer, closing the trimethylindium, under the conditions of a growth temperature of 970℃ and a growth pressure of 100 Torr, growing an AlGaN barrier layer 5 with a thickness of 20 nm, wherein the Al component is 0.25;

[0056] Step 7, closing the ammonia, trimethylaluminum, and trimethylgallium, and cooling to room temperature.

[0057] Example 3

[0058] Step 1, selecting a substrate 1 and placing it in the reaction chamber of the MOCVD equipment;

[0059] Step 2, heating the reaction chamber to 1050℃, growing the substrate 1 in situ under a hydrogen atmosphere with a growth pressure of 100 Torr for 10 minutes;

[0060] Step 3, growing a nucleation layer on the substrate 1, adjusting the temperature of the reaction chamber, introducing ammonia and trimethylaluminum, under the conditions of a growth temperature of 1100℃ and a growth pressure of 100 Torr, growing an AlN nucleation layer 2 with a thickness of 50 nm;

[0061] Step 4, growing a buffer layer on the nucleation layer, closing the trimethylaluminum, adjusting the temperature of the reaction chamber, introducing trimethylgallium under the conditions of a growth temperature of 1050℃ and a growth pressure of 200 Torr, growing a GaN buffer layer 3 with a thickness of 2000 nm;

[0062] Step 5, growing the insertion layer on the buffer layer, adjusting the temperature and pressure of the reaction cavity, introducing trimethyl indium and trimethyl aluminum, growing the InAlGaN insertion layer 4 with a thickness of 3 nm under the conditions that the growth temperature gradually changes from 850°C to 950°C at a rate of 60°C / min, the growth pressure is 100 Torr, and the molar ratio of ammonia, trimethyl indium, trimethyl aluminum and trimethyl gallium is 2400:6:4:1, wherein the In component gradually changes from 0.1 to 0.03, the Al component gradually changes from 0.8 to 0.86, and the Ga component gradually changes from 0.1 to 0.11;

[0063] Step 6, growing the barrier layer on the insertion layer, closing the trimethyl indium, growing the AlGaN barrier layer 5 with a thickness of 20 nm under the conditions that the growth temperature is 950°C and the growth pressure is 100 Torr, wherein the Al component is 0.25;

[0064] Step 7, closing the ammonia, trimethyl aluminum and trimethyl gallium, and cooling to room temperature.

[0065] Comparative Example 1

[0066] The same as Example 2, except that:

[0067] Step 5, growing the insertion layer on the buffer layer, adjusting the pressure of the reaction cavity, closing the trimethyl gallium, introducing the trimethyl aluminum, growing the AlN insertion layer 4 with a thickness of 1 nm under the conditions that the growth temperature is 1050°C and the growth pressure is 100 Torr, and the molar ratio of ammonia and trimethyl aluminum is 800:1.

[0068] Step 6, growing the barrier layer on the insertion layer, opening the trimethyl gallium, growing the AlGaN barrier layer 5 with a thickness of 20 nm under the conditions that the growth temperature is 1050°C and the growth pressure is 100 Torr, wherein the Al component is 0.25.

[0069] Comparative Example 2

[0070] The same as Example 2, except that:

[0071] Step 5, growing the insertion layer on the buffer layer, adjusting the temperature and pressure of the reaction cavity, introducing trimethyl indium and trimethyl aluminum, growing the InAlGaN insertion layer 4 with a thickness of 3 nm under the conditions that the growth temperature is constant at 870°C, the growth pressure is 100 Torr, and the molar ratio of ammonia, trimethyl indium, trimethyl aluminum and trimethyl gallium is 2000:5:3.5:1, wherein the In component is constant at 0.08, the Al component is constant at 0.7, and the Ga component is constant at 0.22.

[0072] Step 6, growing the barrier layer on the insertion layer, closing trimethyl indium, adjusting the reaction cavity temperature, growing the AlGaN barrier layer 5 with a thickness of 20 nm under the condition that the growth temperature is 970℃ and the growth pressure is 100 Torr, wherein the Al component is 0.25.

[0073] In order to improve the barrier height and realize effective isolation of the channel carriers, the Al component of the InAlGaN insertion layer needs to be not less than 0.5, the higher the Al component, the better the isolation effect, but the larger the lattice mismatch with the GaN buffer layer. The In component design mainly considers the difficulty of process implementation, and a high In component requires a lower growth temperature, which has poor process matching with the barrier layer. Therefore, the In component is generally less than 0.1. Figure 3 The lattice mismatch degree of AlN and InAlGaN two insertion layers with the GaN buffer layer is compared in the graph, and it can be seen from the graph that compared with the AlN insertion layer, the lattice mismatch degree of the InAlGaN insertion layer with the GaN buffer layer is lower, and in the preferred range of the Al component of 0.6-0.8 and the In component of 0-0.1, the matching degree of the InAlGaN insertion layer with the GaN buffer layer is less than 2%. The matching degrees of embodiments 1-3 are about 1.2%, 1.2% and 1.3% respectively, which are half of that of comparative example 1.

[0074] The characteristics of the 4-inch AlGaN / GaN heterojunction materials grown by the structures and processes of the five epitaxial materials of embodiments 1-3 and comparative examples 1-2 are shown in the following table.

[0075]

[0076] As can be seen from the results in comparative example 1 and embodiment 2, the InAlGaN insertion layer can significantly improve the sheet resistance uniformity of the material without significantly reducing the electrical characteristics of the material. As can be seen from the results in comparative example 2 and embodiment 2, the InAlGaN insertion layer needs to be grown at a low temperature and the AlGaN barrier layer needs to be grown at a high temperature, and the temperature rise will cause the surface quality of the material to decrease, affecting the electrical characteristics and uniformity of the material. The process of gradually changing the temperature can overcome this problem.

[0077] The above embodiments are only used to illustrate the technical solutions of the present application and not to limit them, and there are many practical manufacturing solutions for the manufacturing method, and any equivalent changes and decorations made according to the claims of the present application all belong to the scope of the present application.

Claims

1. A method for epitaxial growth of a high uniformity gallium nitride heterojunction material structure, comprising: The high-uniformity gallium nitride heterojunction material structure is sequentially arranged from bottom to top as a substrate (1), an AlN nucleation layer (2), a GaN buffer layer (3), an InAlGaN insertion layer (4) and an AlGaN barrier layer (5), wherein the thickness of the AlN nucleation layer (2) is 10-100 nm, the thickness of the GaN buffer layer (3) is 500-2500 nm, the thickness of the InAlGaN insertion layer (4) is 2-4 nm, and the thickness of the AlGaN barrier layer (5) is 10-30 nm. The epitaxial growth method comprises the following steps: Step one. Selecting a substrate (1) and placing it in a metal organic chemical vapor deposition device reaction chamber; Step two. Heating the reaction chamber to 1000-1200℃, introducing hydrogen, and baking the substrate (1) for 5-10 minutes; Step three. Adjusting the reaction chamber temperature to 1000-1200℃, setting the reaction chamber pressure to 50-100Torr, introducing ammonia and trimethylaluminum, and growing a 10-100 nm thick AlN nucleation layer (2); Step four. Closing the trimethylaluminum, adjusting the reaction chamber temperature to 950-1100℃, setting the reaction chamber pressure to 100-500Torr, introducing trimethylgallium, and growing a 500-2500 nm thick GaN buffer layer (3); Step five. Adjusting the reaction chamber temperature to 850-900℃, setting the reaction chamber pressure to 50-150Torr, introducing trimethylindium and trimethylaluminum, and growing a 2-4 nm thick InAlGaN insertion layer (4) on the buffer layer, and gradually increasing the temperature to 950-1000℃ during the growth process; Step six. Closing the trimethylindium, keeping the reaction chamber temperature and pressure unchanged, and growing a 10-30 nm thick AlGaN barrier layer (5); Step seven. Closing the ammonia, trimethylaluminum and trimethylgallium, and cooling to room temperature.

2. The method of claim 1, wherein the method further comprises: The substrate is a SiC substrate.

3. The method of claim 1, wherein the method further comprises: The In component of the InAlGaN insertion layer (4) ranges from (0, 0.1], the Al component ranges from (0.5, 0.9], and the Ga component ranges from (0, 0.5].

4. The method of claim 1, wherein the method further comprises: The Al component of the AlGaN barrier layer (5) ranges from 0.15 to 0.

35.

5. The method of claim 1, wherein the method further comprises: The temperature gradually increases at a rate of 40-80℃ / min in step five. The temperature gradually increases at a rate of 40-80℃ / min in step five.

Images