阅读说明：本技术 一种蓝宝石模板上GaN单晶衬底高温激光剥离装置及剥离方法 (High-temperature laser stripping device and method for GaN single crystal substrate on sapphire template ) 是由 张雷 刘磊 张百涛 王国栋 叶帅 何京良 徐明升 俞娇仙 王守志 胡小波 徐现刚 于 2021-07-28 设计创作，主要内容包括：本发明提供一种蓝宝石模板上GaN单晶衬底高温激光剥离装置及剥离方法,包括固定加热炉和括激光器、光束整形器、振镜系统和成像设备,固定加热炉用于固定、加热待剥离样品,激光器发出的激光依次经过光束整形器、振镜系统照射到待剥离样品上,待剥离样品反射的照明光成像至成像设备上,实现剥离过程的实时监察。本发明的装置固定加热炉用于控制剥离的温度,缓解由激光照射与非照射区域温差引起的应力,提高完整剥离整片GaN单晶衬底的良率,可通过调整激光能量、光斑直径、剥离温度、扫描速度与扫描路径等参数调整剥离工艺,通过显微成像系统实现剥离过程的实时观察,可随时反馈剥离情况,调整剥离工艺,实现完整GaN单晶衬底的剥离。(The invention provides a high-temperature laser stripping device and a high-temperature laser stripping method for a GaN single crystal substrate on a sapphire template, and the device comprises a fixed heating furnace, a laser, a beam shaper, a vibrating mirror system and an imaging device, wherein the fixed heating furnace is used for fixing and heating a sample to be stripped, laser emitted by the laser is irradiated onto the sample to be stripped through the beam shaper and the vibrating mirror system in sequence, and illuminating light reflected by the sample to be stripped is imaged onto the imaging device, so that the real-time monitoring of the stripping process is realized. The device of the invention fixes the heating furnace for controlling the stripping temperature, relieves the stress caused by the temperature difference between the laser irradiation area and the non-irradiation area, improves the yield of the complete stripping of the whole GaN single crystal substrate, can adjust the stripping process by adjusting the parameters such as laser energy, spot diameter, stripping temperature, scanning speed, scanning path and the like, realizes the real-time observation of the stripping process through a microscopic imaging system, can feed back the stripping condition at any time, adjusts the stripping process and realizes the stripping of the complete GaN single crystal substrate.)

1. A high-temperature laser stripping device for a GaN single crystal substrate on a sapphire template comprises a fixed heating furnace and a laser processing imaging device, wherein the fixed heating furnace is used for fixing and heating a sample to be stripped;

the laser processing imaging equipment comprises a laser, a beam shaper, a galvanometer system and imaging equipment; laser emitted by the laser sequentially passes through the beam shaper and the galvanometer system to be irradiated on the sample to be stripped, and illuminating light reflected by the sample to be stripped is imaged on imaging equipment, so that real-time monitoring of the stripping process is realized.

2. The device for high-temperature laser lift-off of GaN single crystal substrate on sapphire template as described in claim 1, wherein the laser is an all-solid-state semiconductor laser, a KrF excimer laser or a lamp-pumped laser, and the emission wavelength of the laser is 248-355nm, preferably 248nm, 266nm or 355 nm.

3. The high-temperature laser lift-off device of GaN single crystal substrates on sapphire templates of claim 1, wherein the beam shaper comprises: aspheric convex and concave lenses; a concave lens is positioned between the laser and the convex lens, the focal length of the concave lens being 1/3 the focal length of the convex lens; the beam shaper is used for shaping the Gaussian beam emitted by the laser, adjusting the size of a laser spot emitted by the laser, and enabling the shaped uniform flat-top beam to be incident on the stripped sample.

4. The device for high-temperature laser lift-off of a GaN single crystal substrate on a sapphire template according to claim 1, wherein the galvanometer system is a three-dimensional (3D) galvanometer or a two-dimensional (2D) galvanometer.

5. The device for high-temperature laser separation of a GaN single crystal substrate on a sapphire template as claimed in claim 1, wherein the fixed heating furnace comprises a heating furnace shell, a heating furnace cavity is arranged in the furnace shell, a sample supporting platform to be separated is arranged in the heating furnace cavity, a separation window is arranged at the top of the furnace shell, a water cooling flange is arranged between the furnace shell and the separation window, the separation window and the furnace shell are fixedly connected through the water cooling flange, and a supporting plate is arranged at the bottom of the furnace shell and used for supporting the heating furnace.

6. The device for high-temperature laser lift-off of GaN single crystal substrates on sapphire templates of claim 5, wherein the fixed heating furnace is connected with a temperature control system for controlling the temperature of the heating furnace, the temperature of the fixed heating furnace is continuously adjustable from room temperature to 900 ℃, and the heating rate is adjusted and controlled at 1-15 ℃/min.

7. The device for high-temperature laser lift-off of GaN single crystal substrates on sapphire templates as claimed in claim 6, wherein the lift-off window is shaped to match the furnace shell, and is a sapphire window sheet or CaF₂Window sheets or quartz glass.

8. The device for high-temperature laser lift-off of a GaN single crystal substrate on a sapphire template according to claim 1, wherein the sample stage to be lifted off is an adjustable-height sample stage.

9. The device for high-temperature laser peeling of the GaN single crystal substrate on the sapphire template as claimed in claim 1, wherein a heating resistance wire is arranged on the furnace shell, and a wind cooling device is further arranged at the upper part of the furnace shell.

10. A high-temperature laser lift-off method of a GaN single crystal substrate on a sapphire template is carried out by the device of claim 1, and comprises the following steps:

1) turning on a laser red light indicator lamp for calibration, scanning the whole surface of a sample to be stripped by laser, setting the scanning speed of a laser line to be 1.5mm/min, and adjusting the diameter of a light spot to be 2 mm;

2) opening the fixed heating furnace, heating the fixed heating furnace to 820-;

3) and after the stripping is finished, fixing the heating furnace for cooling, and taking out the stripped sample when the temperature is reduced to the room temperature.

Technical Field

The invention relates to a high-temperature laser stripping device and a high-temperature laser stripping method for a GaN single crystal substrate on a sapphire template, and belongs to the technical field of semiconductor material preparation.

Background

Gallium nitride (GaN) is one of the core materials of the third generation semiconductor, the forbidden band width, the electron saturation migration speed, the breakdown voltage and the working temperature of the GaN-based high-power semiconductor are far higher than those of Si and GaAs, and the GaN-based high-power semiconductor is expected to be widely applied to the fields of high-power electronic devices and high-frequency radio-frequency devices on the basis of the excellent physical and chemical properties of the GaN-based high-power semiconductor. However, due to the lack of high-quality and low-cost GaN homogeneous substrates, most GaN-based devices are prepared on heterogeneous substrate epitaxy at present. Due to lattice mismatch and thermal mismatch between the GaN material and the foreign substrate material, stress and a large amount of dislocation are inevitably generated in the epitaxial layer, and the performance and the service life of the GaN-based device are seriously influenced. Therefore, the preparation of high-quality and low-cost GaN homogeneous substrates is an indispensable component for promoting the development of GaN-based devices.

GaN has a particular thermal stability, with a melting point of up to 2000 ℃ or higher and a decomposition pressure at the melting point of up to 4.5 GPa. Decomposition already takes place at normal pressure without heating to the melting point. Therefore, the growth of GaN single crystal by using the traditional melt method requires not only high pressure resistance of equipment, but also corrosion resistance, and extremely strict growth conditions. GaN single crystal substrates currently in commercial use are mostly grown by Hydride Vapor Phase Epitaxy (HVPE). Compared with the liquid phase method, the HVPE method has the advantages of being capable of growing under normal pressure or micro negative pressure, fast in growth speed, simple in equipment, capable of achieving commercial application and the like.

However, sapphire is often used as a template for growing GaN single crystal substrates by HVPE. Therefore, it is a great challenge to remove the sapphire template behind the GaN single crystal after growth to obtain a complete self-supporting GaN single crystal substrate. The use of sapphire-transparent uv laser lift-off to obtain self-supporting GaN single crystals is an effective way. However, no mature laser stripping equipment exists at present, and a sample is generally stripped at normal temperature, temperature difference exists between a laser irradiation area and a non-irradiation area, thermal stress is generated, and cracking is easy to occur in the stripping process, so that the stripping yield is very low, and the stripping yield is one of the reasons that the cost of the GaN single crystal substrate is high. How to improve the peeling yield of the self-supporting GaN single crystal substrate is a problem which needs to be solved urgently at present.

Disclosure of Invention

Aiming at the problems of the existing laser stripping, the invention provides a high-temperature laser stripping device and a high-temperature laser stripping method for a GaN single crystal substrate on a sapphire template, aiming at improving the stripping yield of a self-supporting GaN single crystal substrate.

The invention is realized by the following technical scheme:

a high-temperature laser stripping device for a GaN single crystal substrate on a sapphire template comprises a fixed heating furnace and a laser processing imaging device, wherein the fixed heating furnace is used for fixing and heating a sample to be stripped;

the laser processing imaging equipment comprises a laser, a beam shaper, a galvanometer system and imaging equipment; laser emitted by the laser sequentially passes through the beam shaper and the galvanometer system to be irradiated on the sample to be stripped, and illuminating light reflected by the sample to be stripped is imaged on imaging equipment, so that real-time monitoring of the stripping process is realized.

Preferably, the laser is an all-solid-state semiconductor laser, a KrF excimer laser or a lamp-pumped laser, and the emission wavelength of the laser is 248-355 nm.

All-solid-state semiconductor lasers, KrF excimer lasers or lamp-pumped lasers are all prior art.

Preferably, according to the invention, the emission wavelength of the laser is 248nm, 266nm or 355 nm.

The laser used in the invention can emit 355nm or 266nm ultraviolet laser or 248nm ultraviolet laser. A laser having a wavelength transparent to sapphire can be used for the lift-off of the GaN single crystal substrate on the sapphire template.

According to a preferred embodiment of the present invention, the beam shaper includes: aspheric convex and concave lenses; a concave lens is positioned between the laser and the convex lens, the focal length of the concave lens being 1/3 the focal length of the convex lens; the beam shaper is used for shaping the Gaussian beam emitted by the laser, adjusting the size of a laser spot emitted by the laser, and enabling the shaped uniform flat-top beam to be incident on the stripped sample.

Preferably according to the invention, the galvanometer system is a three-dimensional (3D) galvanometer or a two-dimensional (2D) galvanometer.

The introduction of the galvanometer system is to replace a moving platform and eliminate the vibration of a sample to be stripped caused in the moving process of the moving platform. And the scanning path of the laser light path is adjusted by controlling the galvanometer system software, so that the whole scanning of the sample to be stripped is realized. Meanwhile, the scanning precision of the galvanometer system is higher than the movement precision of the movement platform, so that the purposes of accurate scanning, improvement of stripping precision and complete stripping of the GaN single crystal substrate are achieved.

According to the optimization of the invention, the fixed heating furnace comprises a heating furnace shell, a heating furnace cavity is arranged in the furnace shell, a sample supporting platform to be peeled is arranged in the heating furnace cavity, a peeling window is arranged at the top of the furnace shell, a water cooling flange is arranged between the furnace shell and the peeling window, the peeling window and the furnace shell are fixedly connected together through the water cooling flange, and a supporting plate is arranged at the bottom of the furnace shell and used for supporting the heating furnace.

Preferably, the fixed heating furnace is connected with a temperature control system for controlling the temperature of the heating furnace, the temperature of the fixed heating furnace is continuously adjustable from room temperature to 900 ℃, and the heating speed is regulated and controlled at 1-15 ℃/min.

According to the invention, the shape of the stripping window is matched with the furnace shell, and the stripping window is a sapphire window sheet or CaF₂Window sheets or quartz glass.

Sapphire window sheet or CaF₂The window piece is transparent to 355nm ultraviolet laser.

According to the invention, the sample tray to be stripped is preferably an adjustable-height sample tray.

The height of the height-adjustable sample support platform can be adjusted up and down.

According to the invention, the furnace shell is preferably provided with heating resistance wires, and the upper part of the furnace shell is also provided with a wind cooling device.

The temperature of the fixed heating furnace can be continuously adjusted from room temperature to 900 ℃, and the temperature rise speed can be adjusted and controlled at 1-15 ℃/min. The temperature control of the heating furnace can be realized by a temperature control meter arranged on the heating furnace, and can also be realized by software integrated with a laser. The heating furnace is used for regulating and controlling the stripping temperature of the sample to be stripped in the stripping process. A supporting platform for placing a sample to be stripped is fixed in the heating furnace cavity, and the height of the supporting platform can be manually finely adjusted; the top of the heating furnace is provided with a water-cooling flange, the temperature diffused by the heating furnace is reduced through the water-cooling flange, and meanwhile, an air cooling device is introduced, so that the surrounding temperature of the heating furnace is controlled within 30 ℃. A stripping window is fixed on the upper part of the water-cooling flange and transmits ultraviolet laser to enter the surface of a sample to be stripped. The lift-off window being made of sapphire, quartz glass or CaF₂And other materials which can be penetrated by ultraviolet laser can be used for stripping the window.

The imaging device monitors the stripping process in real time, and the stripping process is adjusted according to the actual stripping condition, so that the success rate of stripping the self-supporting GaN single crystal is improved.

A high-temperature laser lift-off method of a GaN single crystal substrate on a sapphire template is carried out by adopting the device, and comprises the following steps:

1) turning on a laser red light indicator lamp for calibration, scanning the whole surface of a sample to be stripped by laser, setting the scanning speed of a laser line to be 1.5mm/min, and adjusting the diameter of a light spot to be 2 mm;

2) opening the fixed heating furnace, heating the fixed heating furnace to 820-;

3) and after the stripping is finished, fixing the heating furnace for cooling, and taking out the stripped sample when the temperature is reduced to the room temperature.

The invention has the advantages that:

1. the high-temperature laser stripping device provided by the invention replaces a motion platform with a 3D galvanometer system, so that the stripping precision is greatly improved.

2. The high-temperature laser stripping device adopts the fixed heating furnace to control the temperature of the stripping process, ensures a uniform temperature zone in a certain range, and improves the stability of the laser stripping temperature.

3. The high-temperature laser stripping device provided by the invention is introduced with the microscopic imaging equipment, so that the real-time monitoring of the whole stripping process can be realized.

4. The high-temperature laser stripping device adopts two cooling measures, namely a water-cooling flange is arranged at the top of a heating furnace; and secondly, an air cooling device is additionally arranged at the left lower side of the galvanometer system.

Drawings

FIG. 1 is a schematic structural view of a laser lift-off apparatus for a GaN-on-sapphire single crystal substrate of the present invention;

FIG. 2 is a schematic view showing the structure of a heating furnace of the peeling apparatus;

in the figure, 1 laser, 2 beam shaper, 3 galvanometer system, 4 fixed heating furnace, 5 supporting plate, 6 imaging equipment, 7 air cooling device, 41 stripping window, 42 water cooling flange, 43 sample pallet to be stripped and 44 sample to be stripped.

Detailed Description

In order to further explain the structural features and technical modes of the present invention in detail and achieve specific objects and functions, the present invention is further explained in detail with reference to the accompanying drawings and the detailed description.

Example 1:

a high-temperature laser lift-off device for GaN single crystal substrate on sapphire template has structure shown in FIG. 1 and FIG. 2. The device comprises a fixed heating furnace 4 and a laser processing imaging device, wherein the fixed heating furnace 4 is used for fixing and heating a sample 44 to be stripped, the laser processing imaging device is positioned above the fixed heating furnace 4, and the laser processing imaging device is of a closed structure;

the laser processing imaging device comprises a laser 1, a beam shaper 2, a galvanometer system 3 and an imaging device 6; laser emitted by the laser 1 is irradiated onto the sample to be peeled 44 through the beam shaper 2 and the galvanometer system 3 in sequence, and illumination light reflected by the sample to be peeled 44 is imaged on the imaging device 6, so that real-time monitoring of the peeling process is realized.

The laser 1 is a lamp-pumped compact 355nm nanosecond ultraviolet laser. The maximum single pulse energy reaches 40mJ, the repetition frequency is 1-20Hz, the diameter of the original laser spot is 6mm, and the laser spot can be adjusted within the range of 1-3mm after being adjusted by the beam shaper 2. The galvanometer system 3 adopts a three-dimensional (3D) galvanometer, and can realize the adjustment of the light path in the directions of an x axis, a y axis and a z axis.

The beam shaper includes: aspheric convex and concave lenses; a concave lens is positioned between the laser and the convex lens, the focal length of the concave lens being 1/3 the focal length of the convex lens; the beam shaper is used for shaping the Gaussian beam emitted by the laser, adjusting the size of a laser spot emitted by the laser, and enabling the shaped uniform flat-top beam to be incident on the stripped sample.

The fixed heating furnace comprises a heating furnace shell, a heating furnace cavity is arranged in the furnace shell, a sample supporting platform 43 to be peeled is arranged in the heating furnace cavity, a peeling window 41 is arranged at the top of the furnace shell, a water cooling flange 42 is arranged between the furnace shell and the peeling window 41, the peeling window 41 is fixedly connected with the furnace shell by the water cooling flange 42, and a supporting plate 5 is arranged at the bottom of the furnace shell and used for supporting the heating furnace. The oven cavity, which has a diameter of 60mm and a height of 120mm, can be stripped to a 2 inch sample. The shape of the stripping window 41 is matched with the furnace shell, the stripping window 41 is a sapphire window sheet and can penetrate 355nm ultraviolet laser, and the supporting plate is made of a heat-insulating material and fixed on the optical platform.

The sample holder 43 to be peeled is an adjustable-height sample holder. The furnace shell is provided with a heating resistance wire, the upper part of the furnace shell and the left lower side of the galvanometer system are provided with an air cooling device 7.

The sample to be stripped is bulk GaN single crystal grown on a sapphire template by an HVPE method, and the thickness of the bulk GaN single crystal is more than 500 mu m.

Example 2:

a method of peeling using the high-temperature laser peeling apparatus for a GaN single crystal substrate on a sapphire template of example 1:

1) turning on a laser red light indicator lamp for calibration, scanning the whole surface of a sample to be stripped by laser, setting the scanning speed of a laser line to be 1.5mm/min, and adjusting the diameter of a light spot to be 2 mm;

2) opening a fixed heating furnace and a temperature control system, heating the fixed heating furnace to 850 ℃ at the heating rate of 5 ℃/min, opening a laser to emit laser, sequentially irradiating the laser emitted by the laser onto the sample to be stripped through a beam shaper and a galvanometer system according to a set scanning path and a set scanning speed, and imaging illumination light reflected by the sample to be stripped onto imaging equipment to realize real-time monitoring of the stripping process;

3) and after the stripping is finished, the heating furnace starts to cool, and when the temperature is reduced to the room temperature, the stripped sample is taken out.

Example 3

The apparatus for high-temperature laser lift-off of a GaN single crystal substrate on a sapphire template described in example 1 is different in that:

the laser 1 is a KrF excimer laser with 248nm, the repetition frequency is 1-10Hz, the single pulse energy can reach 50mJ, and the diameter of the laser spot is fixed to be 3 mm. The laser beam is converted into a flat-top beam by the beam shaper 2. The galvanometer system 3 adopts a two-dimensional (2D) galvanometer to realize the adjustment of the light path in the directions of an x axis and a y axis, and the scanning path of the laser beam is controlled by software to complete the whole scanning of the sample to be stripped.

The heating furnace cavity has the diameter of 110mm and the height of 150mm, and can strip a 4-inch (compatible with 2 inches) sample. The shape of the stripping window 41 is matched with the furnace shell, and the stripping window is CaF₂The optical plate can transmit 355nm ultraviolet laser, and the supporting plate is fixed on the optical platform by using a heat insulating material. The sample to be peeled 44 was a bulk GaN single crystal grown on a sapphire seed crystal by HVPE method or a thick film GaN single crystal grown on sapphire by MOCVD method.

Example 4:

a method of peeling using the high-temperature laser peeling apparatus for a GaN single crystal substrate on a sapphire template of example 3:

1) and (3) turning on a laser red light indicator lamp for calibration, enabling the laser to scan the whole surface of the sample to be stripped, setting the scanning speed of a laser line to be 1.5mm/min, and adjusting the diameter of a light spot to be 3 mm.

2) Opening a fixed heating furnace and a temperature control system, heating the fixed heating furnace to 800 ℃ at a heating rate of 5 ℃/min, opening a laser to emit laser, sequentially irradiating the laser emitted by the laser onto the sample to be stripped through a beam shaper and a galvanometer system according to a set scanning path and a set scanning speed, and imaging illuminating light reflected by the sample to be stripped onto imaging equipment to realize real-time monitoring of the stripping process;

3) and after the stripping is finished, the heating furnace starts to cool, and when the temperature is reduced to the room temperature, the stripped sample is taken out.

It should be understood that the above are only preferred embodiments of the present invention, and are not intended to limit the present invention, but all modifications made within the spirit and principle of the present invention should be included in the scope of the present invention.