CN104532209B - A kind of method that wafer scale large scale hexagonal boron nitride is prepared in substrate - Google Patents

Abstract

A kind of method that wafer scale large scale hexagonal boron nitride is prepared in substrate, is related to hexagonal boron nitride.The controllable growth hexagonal boron nitride thin layer on Cu paper tinsels；After carrying Borazane gas leaves quartz ampoule, Cu paper tinsel substrates are bent to semi-cylindrical and rolled over and insert quartz boat, push-in heating warm area, vacuumized, heat, H is passed through when temperature reaches setting value₂, surface de-oxidation thing processing is carried out, continues to raise the growth temperature in 3rd area, when being heated to area's predecessor, while reaching the area's temperature of setting value one and three area's temperature, H is passed through from quartz ampoule₂With Ar conveying caused by Borazane gases reacted into reaction chamber, until Cu paper tinsels are completely covered, reaction takes out Cu paper tinsels after terminating, the growing large-area hexagonal boron nitride thin layer i.e. on Cu paper tinsels, spin coating pmma layers again, Cu substrates are dissolved, pmma/ hexagonal boron nitride films are transferred on substrate, the pmma layers of sample surfaces are removed again, that is, are completed.

Description

A method for preparing wafer-level large-size hexagonal boron nitride on a substrate

technical field

The invention relates to hexagonal boron nitride, in particular to a method for preparing wafer-level large-size hexagonal boron nitride on a substrate.

Background technique

Because sapphire has a wide range of applications, such as LEDs, solar cells, MOS tubes, monocrystalline silicon chips, diodes, etc. If h-BN can be stably transferred directly on the sapphire substrate, it will be more conducive to the performance test of h-BN and the preparation of new optoelectronic devices.

Because h-BN has very good properties, such as high thermal conductivity, high mechanical strength, high chemical stability, high electrical resistance, etc., h-BN has very broad application prospects, and it can be used in thermal interface materials , such as LEDs, LCDs, TVs, mobile phones, computers, telecommunication equipment, etc., can also be used as substrates for coatings and graphene. Now h-BN nano-films can be synthesized in different ways, such as: micro-mechanical exfoliation method, solution method, MOCVD, APCVD, LPCVD and so on. At present, in the process of synthesizing h-BN by CVD method, different kinds of metals are used as substrates.

In the new generation of optoelectronic devices and microprocessor applications, there is an increasingly strong demand for large-area high-quality hexagonal boron nitride. Therefore, if the growth of boron nitride can be well controlled, it will be of great significance to obtain boron nitride with a large area of precisely controllable layers.

Contents of the invention

The purpose of the present invention is to solve the problems of small area, low coverage and poor uniformity of the existing hexagonal boron nitride, and to provide a large-area, high-quality, precise and controllable layer thickness method for preparing wafer-level large A method for dimensioning hexagonal boron nitride.

The present invention comprises the following steps:

1) Controlled growth of hexagonal boron nitride thin layer on Cu foil, the specific method is as follows: use three-temperature zone LPCVD system, use Borazane powder as the reaction source, first, put the Cu foil into the quartz boat, push it into the CVD reaction chamber for heating In the temperature zone, Borazane powder is placed in the built-in quartz tube, the cavity is evacuated, and then the tube furnace is used to heat the quartz reaction cavity. When the temperature of the three-zone reaction chamber reaches the set value (800-1000°C), H2 is introduced first, the surface is deoxidized, and the growth temperature of the three-zone is continued to be raised, and the precursor of the first zone is heated at the same time. When the set temperature of the first zone (60-80°C) and the third zone (1000-1050°C) are reached, the Borazane gas generated by _H2 and Ar transport from the quartz tube enters the reaction chamber for reaction. The sample was pulled out of the heating zone, and _H2 and Ar were used as protective gases at the same time, and finally the sample was taken out when it dropped to room temperature; after optical microscopy and SEM tests on the surface, hexagonal nitrogen grown on the Cu foil could be observed Boron thin layer;

2) After the gas carrying Borazane leaves the quartz tube, bend the Cu foil substrate into a semi-cylindrical shape with the quartz tube as the central axis and fold it into the quartz boat, push it into the heating temperature zone of the CVD reaction chamber, and pump the air pressure in the chamber to 10 ^-3 torr, and then use a tube furnace to heat the quartz reaction chamber. When the temperature reaches the set value, first pass H ₂ into the surface for deoxidation treatment, and then continue to increase the growth temperature of the three zones, and at the same time, a Zone precursors are heated, and when the set temperature of zone 1 (60-80°C) and zone 3 (1000-1050°C) are reached at the same time, _H2 and Borazane gas generated by Ar transport are introduced into the reaction chamber from the quartz tube Carry out the reaction until the Cu foil is completely covered. After the reaction, the Cu foil is taken out, and the surface of the Cu foil is tested by optical microscopy and SEM. A large-area hexagonal boron nitride thin layer grown on the Cu foil can be observed;

3) Spin-coat the pmma layer on the Cu foil with the hexagonal boron nitride thin layer, then use ammonium persulfate to dissolve the Cu substrate, and then use the transfer tool to transfer the pmma/hexagonal boron nitride film to the substrate, and finally Soak in acetone solution to remove the pmma layer on the surface of the sample, which completes the preparation of wafer-scale large-size hexagonal boron nitride on the substrate.

In step 1), the chamber is evacuated, and the air pressure in the chamber can be pumped to about 10 ^-3 torr by using a mechanical pump and a molecular pump; the time for the surface deoxidation treatment can be 10 to 30 minutes; the The amounts of H ₂ and Ar introduced from the quartz tube are 4-8 sccm and 10-20 sccm respectively; the amounts of H ₂ and Ar introduced simultaneously are 8-15 sccm and 10-20 sccm respectively.

In step 2), the chamber is evacuated, and the air pressure in the chamber can be evacuated to about 10 ^-3 torr by using a mechanical pump and a molecular pump; the time for the surface deoxidation treatment can be 10 to 30 minutes; The amounts of H ₂ and Ar introduced into the tube are 4-8 sccm and 10-20 sccm respectively; the diameter of the large-area hexagonal boron nitride thin layer can be 2-4 inches.

In step 3), the transfer tool can use a flat spatula, especially a large-sized flat spatula; the diameter of the substrate can be 2 to 4 inches; the substrate can be a sapphire substrate, Si sheet, quartz Glass, metal, plastic flexible film, etc., preferably sapphire substrate.

In order to better improve the quality of the obtained h-BN and further expand the application of sapphire in optoelectronic devices, the present invention proposes to grow and transfer wafer-level large-size hexagonal boron nitride, which can greatly improve the quality and output of h-BN, Thereby obtaining high-quality optoelectronic devices. From the application point of view, the application of this material in optoelectronic devices such as LEDs and solar cells is expected to improve their light output and light absorption efficiency, thereby improving their external quantum efficiency, and can also prolong the life of LEDs and work stability.

The invention adopts a small quartz tube built into the CVD large quartz tube heating chamber, utilizes the principle of gas spherical diffusion in vacuum, and combines with a symmetrical semi-cylindrical copper foil substrate to realize the growth of a large-area and uniform h-BN atomic layer film with few raw materials. At the same time, the quartz magnetic rod is used to achieve the purpose of rapid heating and cooling, so that the surface of the hexagonal boron nitride can be kept flat during the cooling process. Design a complete set of large-size flat shovel tools, which have the functions of solution filtration and flat support, respectively, to achieve stable and flat atomic film transfer. Stable transfer of large-area ultra-thin hBN to any target substrate by PMMA transfer method. The invention uses LPCVD to grow large-area hexagonal boron nitride on copper foil and successfully transfers it to the target substrate. This method can realize large output with few raw materials, and provides possibility for mass production.

Description of drawings

Fig. 1 is a schematic diagram of a three-temperature-zone LPCVD system according to an embodiment of the present invention.

Figure 2 is a SEM image of hexagonal boron nitride grown on Cu foil at 1050°C.

Fig. 3 is the SEM image of the graphene grown on the Cu foil with the growth time of 5min, 10min, 30min and 40min respectively.

Figure 4 is the Raman spectrum of hexagonal boron nitride transferred to silicon wafer.

Figure 5 is the XPS spectrum (B1s) of hexagonal boron nitride transferred onto silicon wafers.

Figure 6 is the XPS spectrum (N1s) of hexagonal boron nitride transferred onto silicon wafers.

Figure 7 is a SEM image of hexagonal boron nitride successfully transferred to sapphire.

detailed description

Embodiment one:

First, hexagonal boron nitride is grown controllably on Cu foil.

1) Put 0.5mg Borazane powder in a quartz boat into a slender quartz tube, and put it into a three-temperature zone CVD device, as shown in Figure 1. Adjust the position so that the Borazane powder is in the middle of the first temperature zone, connect the slender small quartz tube to the vent, and then put the cleaned Cu foil into the third temperature zone of the CVD device, and ensure that it is in the third temperature zone. In the middle of the temperature zone, there are Borazane powder and Cu foil in sequence along the direction of airflow. The vacuum chamber is sealed with a rubber ring flange, and the predetermined temperature rise parameters and ventilation parameters are input into the computer to prepare for the subsequent heating of the three temperature zones of CVD. Start to vacuumize the cavity, first use the mechanical oil pump, turn on the molecular pump when the vacuum degree reaches 2×10 ^-2 Torr, and start the heating temperature zone according to the predetermined parameters when the vacuum degree is lower than 9×10 ^-3 Torr heating. When the temperature of the substrate in the third temperature zone reaches 800°C, 12sccm of H ₂ with a pressure of 30psi and 20sccm of Ar with a pressure of 30psi are introduced. The aeration process lasts for 30 minutes. This aeration process can clean the oxides and impurities on the Cu surface. According to the parameters set by the temperature control program, after ventilation for 30 minutes, stop feeding the gas, and the temperature of the three-zone reaction chamber continues to increase. When the temperature of the three-zone reaction chamber reaches 1050°C, the temperature of the first zone Borazane just reaches the set temperature of 70°C. The mixture of H ₂ and Ar gas is used as the carrier gas, the gas flow rate is 8sccm/15sccm, and the air pressure is 30psi. At this time, the growth process starts, and the Borazane powder in the first area produces Borazane gas at a temperature of 70°C. Under the action of the carrier gas Next, the Borazane gas is transported to the high temperature reaction area, and part of the Borazane gas is deposited on the surface of the Cu foil to nucleate and grow into a h-BN nano film.

2) PMMA transfer steps:

Prepare ammonium persulfate solution, 6g ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ )+210ML(H ₂ O). After cutting the sample, place it on a small glass slide, seal the sample with adhesive strips, and Prevent PMMA from entering the back of the sample. Apply PMMA evenly on the surface of the sample through a glue spreader. After drying naturally in the air for 30 minutes, place it on a heating platform at 100°C for 20 minutes (put a clean glass slide underneath), and tear off the sample from the glass slide after cooling, and cut off the part of the edge of the sample that is not coated with PMMA. Put the PMMA layer of the sample upwards, float in the ammonium persulfate solution prepared in the first step, and clean the back of the sample. Rinse the dissolved Cu and the hexagonal boron nitride on the back to prevent the hexagonal boron nitride on the back from affecting the front. Rinse with deionized water every 10 minutes, rinse 2 to 3 times before and after, and then float the sample in the solution for about 3 hours to melt all the Cu. Transfer the sample to deionized water with a glass slide and soak for 30 minutes, and the sample floats on the surface of deionized water. Clean the Si sheet, place the Si sheet in acetone solution for 30 min, and then use absolute ethanol for 30 min. Si piece salvage, pay attention to make the sample loaded in the middle of the Si piece when salvaging, dry the water, prevent the air bubbles between the sample and the Si piece due to moisture. For drying treatment, after the cleaned samples are naturally dried, put them into a drying oven at 150°C for 1 hour. Soak in acetone for 10 minutes, remove PMMA, change the acetone solution 3 times, then soak for a long time, change the solution once a day, 2D-3D. When changing the solution, draw the acetone solution with a syringe, and do not expose the sample to the air. Rinse with absolute ethanol and remove.

Example 2: Growing large-area continuous boron nitride

1) As in Example 1, put the precursor in a quartz boat with 1 mg of Borazane powder in a small elongated quartz tube, and put it into a three-temperature-zone CVD device, as shown in FIG. 1 . Adjust the position so that the Borazane powder is in the middle of the first temperature zone, connect the slender small quartz tube to the air vent, take a 7cm×7cm copper foil to clean, and then bend the cleaned Cu foil into the CVD device. The third temperature zone, and ensure that it is in the middle of the third temperature zone, Borazane powder and Cu foil along the direction of airflow. The remaining steps are the same as in Example 1, and the growth time is increased to 40 minutes.

2) The transfer procedure is the same as above. Due to the large increase in the transfer sample area, the original tool can no longer be used for stable transfer. When the Cu foil is completely melted, use a large-area flat shovel transfer tool to transfer the sample to deionized water, and then Carry out 2-inch sapphire slice salvage, fix the sapphire slice on a large-area porous transfer tool, and then salvage the sample in deionized water, and the next steps are the same as the above transfer process, so that the large-area continuous growth area with a diameter of 2 inches Thin films of hexagonal boron nitride were stably transferred onto sapphire substrates with a diameter of 2 inches.

The above sample transferred to the silicon wafer was tested by Raman spectrum, and it was found that a strong hexagonal boron nitride peak appeared at 1371.6 cm ⁻¹ . In addition, the sample was tested for XPS spectrum, and it was found that the B1s peak was at 190.08ev, and the N1s peak was at 397.8ev, which once again proved that high-quality hexagonal boron nitride had been grown. A series of samples grown above were characterized by SEM. The characterization results are shown in Figures 2 to 7, indicating that a large-area continuous hexagonal boron nitride film has been successfully grown. The diameter of the hexagonal boron nitride film is 2 inches, and the successful transfer onto a substrate with a diameter of 2 inches.

The invention provides a method for preparing wafer-level large-size hexagonal boron nitride on a substrate (the large size refers to ≥ 2 inches). It mainly uses low-pressure chemical vapor deposition (LPCVD) to grow large-sized h-BN nano-films on copper foil substrates, and transfer them stably to large-sized sapphire substrates, making it easier to measure various characteristics of samples, for novel optoelectronic devices and other large-area applications. Firstly, by adjusting various parameters, h-BN can be grown controllably on the surface of Cu; then, using the diffusion principle of vacuum air flow and the semi-roll method of copper foil substrate, the ultra-large area can be obtained with less reaction raw materials. Atomic layer h-BN thin films. And design a complete set of stainless steel flat shovel tools, use the PMMA transfer method to evenly transfer the wafer-level large-size h-BN film to a 2-inch or larger sapphire substrate to complete van der Waals bonding. Through this technology, high-yield, high-quality, super-large-area h-BN atomic thin films can be obtained, which can be applied to the industrial wafer production of optoelectronic devices to obtain new devices with excellent performance.

The controllable growth of hexagonal boron nitride on Cu foil needs to be able to stably control the number of layers, single crystal size and coverage area of hexagonal boron nitride. The temperature of the precursor, the growth temperature and the growth time are respectively controlled, and at the same time, the sample is rapidly cooled by the magnetic rod after the growth is completed, thereby improving the growth quality of hexagonal boron nitride.

In the invention, the growth area is increased by adjusting factors, so that a large-area substrate can be stably covered, and a series of experiments are carried out by changing experimental conditions. In addition, the mechanical pump and molecular pump are used to pump the vacuum to below 9×10 ^-3 , and the magnetic rod is used to pull the sample out of the sample when the growth is completed, and the temperature is rapidly lowered. When the system is cooled to room temperature, the sample is opened and taken out. This method can Keep the surface of grown hexagonal boron nitride flat and obtain high-quality samples. It is found that by increasing the reaction time, the coverage area of hexagonal boron nitride can be effectively increased until the Cu foil substrate is completely covered. The inner diameter of the reaction chamber of the CVD equipment is 2 inches. By bending the copper foil, a maximum size of 4 inches can be grown. , effectively increasing the yield of an experiment.

After the hexagonal boron nitride is successfully transferred to the sapphire substrate, it is convenient to do a series of characterizations, and can be more effectively used in the industrial production of electronic devices. After a large area of hexagonal boron nitride is grown on Cu foil, use the solution transfer method to transfer hexagonal boron nitride to a 2-inch sapphire substrate, and use a large-size flat shovel tool to achieve a stable and flat atomic film transfer; pmma To intermediate transition, ammonium persulfate was used to dissolve Cu foil, and acetone was used to remove PMMA. Using this transfer method, the hexagonal boron nitride film can be well transferred to various wafer substrates, such as Si wafers, quartz glass, metal, plastic flexible films, etc.

Claims (6)

1. A kind of 1. method that wafer scale large scale hexagonal boron nitride is prepared in substrate, it is characterised in that comprise the following steps：

   1) controllable growth hexagonal boron nitride thin layer, specific method are as follows on Cu paper tinsels：With three-temperature-zone LPCVD systems, use Cu paper tinsels first, are put into quartz boat, push-in CVD reaction chamber heating warm areas, by Borazane by Borazane powder as reaction source Powder is placed in built-in quartz ampoule, and intracavitary is vacuumized, and then quartz reaction chamber is heated with tube furnace；When 3rd area react When chamber temperature reaches 800~1000 DEG C of setting value, H is first passed through₂, surface de-oxidation thing processing is carried out, continues to raise the life in 3rd area Long temperature, and area's predecessor is heated simultaneously, and reach the area's temperature of one area's temperature of setting value, 60~80 DEG CHe tri- simultaneously At 1000~1050 DEG C, H is passed through from quartz ampoule₂With Ar conveying caused by Borazane gases reacted into reaction chamber, Sample is pulled out heating zone by question response after terminating, while is passed through H₂It is used as protective gas with Ar, is finally taken out when room temperature is dropped to Sample；By carrying out light microscope and SEM tests to its surface, it is observed that the hexagonal boron nitride being grown on Cu paper tinsels is thin Layer；

   It is described that H is passed through from quartz ampoule₂Amount with Ar is respectively 4~8sccm and 10~20sccm；

   It is described while be passed through H₂Amount with Ar is respectively 8~15sccm and 10~20sccm；

   2) after carrying Borazane gas leaves quartz ampoule, Cu paper tinsel substrates are bent to the semicolumn of the axle centered on quartz ampoule Shape and folding insert quartz boat, push-in CVD reaction chamber heating warm areas, intracavitary are vacuumized, then with tube furnace to quartz reaction chamber Heating, when temperature reaches setting value, is first passed through H₂, surface de-oxidation thing processing is carried out, continues to raise the growth in 3rd area afterwards Temperature, and area's predecessor is heated simultaneously, while reach the area's temperature 1000 of one area's temperature of setting value, 60~80 DEG CHe tri- At~1050 DEG C, H is passed through from quartz ampoule₂With Ar conveying caused by Borazane gases reacted into reaction chamber, up to Cu paper tinsels are completely covered, and reaction takes out Cu paper tinsels after terminating, and light microscope is carried out to Cu paper tinsels surface and SEM is tested, can be observed To the large area hexagonal boron nitride thin layer being grown on Cu paper tinsels；H is passed through from quartz ampoule₂Amount with Ar be respectively 4~8sccm and 10~20sccm；

   A diameter of 2~4 inches of the large area hexagonal boron nitride thin layer；

   3) there are spin coating pmma layers on the Cu paper tinsels of hexagonal boron nitride thin layer in growth, then dissolve Cu substrates using ammonium persulfate, Recycle transfer tool that pmma/ hexagonal boron nitride films are transferred on substrate, be finally putting into acetone soln immersion, remove sample The pmma layers on surface, that is, complete to prepare wafer scale large scale hexagonal boron nitride in substrate；

   A diameter of 2~4 inches of the substrate.
2. A kind of 2. method that wafer scale large scale hexagonal boron nitride is prepared in substrate as claimed in claim 1, it is characterised in that Step 1) and 2) in, it is described to vacuumize intracavitary, be that intracavitary air pressure is evacuated to 10 using mechanical pump and molecular pump^-3torr。
3. A kind of 3. method that wafer scale large scale hexagonal boron nitride is prepared in substrate as claimed in claim 1, it is characterised in that In step 1) and 2) in, the time of surface de-oxidation thing processing is 10~30min.
4. A kind of 4. method that wafer scale large scale hexagonal boron nitride is prepared in substrate as claimed in claim 1, it is characterised in that In step 3), the transfer tool is grafter.
5. A kind of 5. method that wafer scale large scale hexagonal boron nitride is prepared in substrate as claimed in claim 1, it is characterised in that In step 3), the substrate is using Sapphire Substrate, Si pieces, quartz glass, metal, plastic flexible films.
6. A kind of 6. method that wafer scale large scale hexagonal boron nitride is prepared in substrate as claimed in claim 5, it is characterised in that In step 3), the substrate is Sapphire Substrate.