Epitaxial structure for preparing nano-film device through electrochemical stripping and stripping method
By designing an epitaxial structure including substrate, sacrificial layer and device structure layer on the GaN substrate, and using an electrochemical peeling method of inclined field plate and insulating dielectric buried layer, the cost of removing GaN substrate in the prior art is solved. The problem of device layer damage has achieved stable and lossless nano-thin film device peeling and high success rate.
Patent Information
- Application Number
- CN202411410145.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-10
- Publication Date
- 2024-12-27
AI Technical Summary
The prior art is costly when removing GaN substrates, which is prone to damage the device layer and is not suitable for materials such as SiC and Si. In addition, electrochemical peeling technology has damage problems in the aspect-transverse etching ratio, making it difficult to achieve lossless nano-scale device peeling.
An epitaxial structure including substrate, sacrificial layer and device structure layer was designed, using insulating field plate structure and insulating dielectric buried layers such as SiO2. The corrosion removal of the sacrificial layer is achieved through an electrochemical corrosion device, and the device structure layer is released to ensure vertical and horizontal. The etch ratio is 0, protecting device layer integrity.
Stable and lossless nano-film device stripping is achieved, which improves the peeling success rate, enhances electrode stability and device layer integrity.
Smart Images
Figure CN119208359A_ABST
Abstract
Description
Technical Field
[0001] The invention particularly relates to an epitaxial structure and a stripping method for preparing a nano film device by electrochemical stripping, and belongs to the technical field of semiconductor devices. Background Art
[0002] GaN has the advantages of high electron mobility, wide bandgap, critical breakdown field strength and stable physical and chemical properties, which are very beneficial to power electronic devices such as light-emitting diodes (LEDs), field effect transistors (FETs), and Schottky diodes (SBDs). Due to the lack of natural substrates, group III nitrides are generally grown on foreign substrates, such as sapphire, silicon, silicon carbide, etc. However, the low thermal conductivity of general substrates will cause serious thermal degradation of the device under high-power working conditions, so it is particularly important to develop a low-cost and gentle (without damaging the epitaxial layer of the device) substrate removal technology. The prepared ultra-thin devices can be bonded to flexible substrates to prepare flexible devices, and bonded to high thermal conductivity substrates (such as diamond) to improve the thermal reliability of the device.
[0003] Hydride vapor phase epitaxy (HVPE) is considered a promising method for commercial preparation of self-supporting GaN substrates due to its fast growth rate and large wafer size. However, the cost of independent GaN substrates grown by this method is very high, which is not conducive to large-scale application. At present, the laser lift-off (LLO) method has been developed to separate sapphire substrates to prepare independent GaN substrates. The LLO method uses a high-power ultraviolet laser to decompose GaN at the interface between sapphire and GaN to separate the substrate from the epitaxial layer. The cost of this method is high, and high temperature will cause GaN to crack, and it is not suitable for separation on SiC and Si. The method of removing the substrate by ICP etching. The etching rate is difficult to control and it is very easy to damage the upper device layer.
[0004] Electrochemical stripping is a selective etching technology using semiconductor doping. This gentle and non-destructive stripping technology is more appropriate for preparing nano-scale device films and does not consider the type of substrate. However, horizontal and vertical etching is more related to the problem of device layer damage, and generally acidic corrosive solutions will etch longitudinally along dislocations throughout the entire device layer, so it is particularly important to design an epitaxial structure suitable for electrochemical stripping to prepare nano-thin film devices. Stable and reliable anode contact is the prerequisite for long-term wafer-level electrochemical etching, so the design of the electrode structure is the key to electrochemical etching. Summary of the invention
[0005] The main purpose of the present invention is to provide an epitaxial structure and a stripping method for preparing a nano film device by electrochemical stripping, thereby overcoming the deficiencies in the prior art.
[0006] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention includes: A first aspect of an embodiment of the present invention provides an epitaxial structure suitable for preparing a nano-thin film device by electrochemical stripping, comprising: an epitaxial structure body and an anode field plate, The epitaxial structure body includes a substrate, a sacrificial layer and a device structure layer, wherein the sacrificial layer is stacked on the substrate, and the device structure layer includes an insulating buried layer, a device layer and an insulating protection layer which are sequentially stacked on the sacrificial layer along the longitudinal direction of the epitaxial structure body, wherein the surface of the sacrificial layer facing away from the substrate has a first region and a second region sequentially arranged along the lateral direction of the epitaxial structure body, the first region is covered by the device structure layer, a side of the device structure layer close to the second region forms a step structure with the sacrificial layer, and a selected side wall of the device structure layer close to the second region is inclined, and the anode field plate continuously covers the step structure and forms an ohmic contact with the device structure layer and the sacrificial layer.
[0007] A second aspect of an embodiment of the present invention provides a method for preparing a nano-thin film device by electrochemical stripping, comprising: Provide an electrochemical etching device and the epitaxial structure suitable for electrochemical stripping to prepare nano-thin film devices, The epitaxial structure is immersed in the electrolyte of the electrochemical etching device, and the anode field plate of the epitaxial structure is electrically connected to the anode of the electrochemical etching device, and the cathode of the electrochemical etching device is placed in the electrolyte, so that the sacrificial layer is corroded and removed, thereby releasing the device structure layer.
[0008] Compared with the prior art, the advantages of the present invention include: the inclined field plate structure adopted by the present invention can alleviate the electric field concentration effect at the electrode edge, improve the stability of the electrode under long-term operation, and the insulating dielectric buried layer such as SiO2 can avoid longitudinal etching to damage the device layer, so that the vertical and horizontal etching ratio of electrochemical etching can reach 0, which is very important for stripping nano-thin films and effectively protects the integrity of the device layer. In addition, the present invention can achieve non-destructive stripping of stable nano-thin film devices and improve the success rate of stripping. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Figure 1 It is a schematic structural diagram of an epitaxial structure suitable for preparing a nano-thin film device by electrochemical stripping provided in a typical implementation case of the present invention; Figure 2 It is a top view of an epitaxial structure suitable for preparing a nano-thin film device by electrochemical stripping provided in a typical implementation case of the present invention; Figure 3 This is an electron microscope image of an epitaxial structure suitable for preparing a nano-thin film device by electrochemical stripping provided in a typical implementation case of the present invention; Figure 4It is a structural diagram of the selected sidewalls and anode field plate metal coordination of the epitaxial structure body at different inclination angles. DETAILED DESCRIPTION
[0010] In view of the deficiencies in the prior art, the inventor of this case has proposed the technical solution of the present invention after long-term research and extensive practice. The technical solution, its implementation process and principle will be further explained as follows.
[0011] A first aspect of an embodiment of the present invention provides an epitaxial structure suitable for preparing a nano-thin film device by electrochemical stripping, comprising: an epitaxial structure body and an anode field plate, The epitaxial structure body includes a substrate, a sacrificial layer and a device structure layer, wherein the sacrificial layer is stacked on the substrate, and the device structure layer includes an insulating buried layer, a device layer and an insulating protection layer which are sequentially stacked on the sacrificial layer along the longitudinal direction of the epitaxial structure body, wherein the surface of the sacrificial layer facing away from the substrate has a first region and a second region sequentially arranged along the lateral direction of the epitaxial structure body, the first region is covered by the device structure layer, a side of the device structure layer close to the second region forms a step structure with the sacrificial layer, and a selected side wall of the device structure layer close to the second region is inclined, and the anode field plate continuously covers the step structure and forms an ohmic contact with the device structure layer and the sacrificial layer.
[0012] Furthermore, the inclination angle of the selected sidewall of the device structure layer close to the second region is 30° to 75°.
[0013] Furthermore, the side of the device structure layer close to the second region is used as the positioning edge of the epitaxial wafer / epitaxial structure, that is, a portion of the device structure layer is cut off as the positioning edge (because each wafer needs to cut a small portion as the positioning edge, for example, the area lost by cutting the positioning edge for 2, 4, 6, and 8 inch wafers is 189 mm respectively 2 、757 mm 2 、1684mm 2 、2677mm 2 ), at the same time, the sacrificial layer below the removed portion is exposed, and the remaining device structure layer and the sacrificial layer form a step structure.
[0014] Furthermore, the thickness of the anode field plate is uniform, and the portion of the anode field plate covering the inclined selected sidewall of the device structure layer is also inclined as a whole.
[0015] Furthermore, the anode field plate includes a first part, a second part and a third part which are arranged in sequence, the first part covers the second area of the sacrificial layer, the second part covers the inclined selected side wall of the device structure layer, the third part is arranged on the top end surface of the device structure layer facing away from the sacrificial layer, the second part is inclined as a whole, and the inclination angle of the second part is the same as the inclination angle of the selected side wall of the device structure layer.
[0016] Furthermore, the thickness of the insulating buried layer and the insulating protection layer is not less than 200 nm.
[0017] Furthermore, the thickness of the insulating buried layer is 200-500nm.
[0018] Furthermore, the thickness of the insulating protective layer is 200-500nm.
[0019] Furthermore, the material of the insulating buried layer and the insulating protection layer includes silicon oxide.
[0020] Furthermore, the step structure is formed by removing a portion of the device structure layer by etching.
[0021] Furthermore, the sacrificial layer is heavily n-doped, and the n-type doping concentration of the sacrificial layer is ≥ 5*e18 / cm 3 .
[0022] Furthermore, under the premise of ensuring the crystal quality, the n-type doping concentration of the sacrificial layer is as high as possible. Considering the process conditions and other factors, the n-type doping concentration of the sacrificial layer is preferably 5*e18 / cm 3 ~5*e19 / cm 3 .
[0023] Furthermore, the thickness of the sacrificial layer is 1.5 μm to 3 μm.
[0024] Furthermore, the sacrificial layer is an n++ GaN sacrificial layer.
[0025] Furthermore, the epitaxial structure body also includes a buffer layer, and the buffer layer is stacked on the substrate.
[0026] Furthermore, the buffer layer includes a GaN buffer layer.
[0027] A second aspect of an embodiment of the present invention provides a method for preparing a nano-thin film device by electrochemical stripping, comprising: Provide an electrochemical etching device and the epitaxial structure suitable for electrochemical stripping to prepare nano-thin film devices, The epitaxial structure is immersed in the electrolyte of the electrochemical etching device, and the anode field plate of the epitaxial structure is electrically connected to the anode of the electrochemical etching device, and the cathode of the electrochemical etching device is placed in the electrolyte, so that the sacrificial layer is corroded and removed, thereby releasing the device structure layer.
[0028] The technical solution, its implementation process and principles, etc. will be further explained below in conjunction with the accompanying drawings and specific implementation cases. Unless otherwise specified, the preparation process of the epitaxial structure, the etching process and its equipment, the electrochemical corrosion device, etc. used in the embodiments of the present invention are all known to those skilled in the art.
[0029] In a more specific implementation, see Figure 1 , Figure 2 and Figure 3 , an epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping, comprising an epitaxial structure body and an anode field plate, wherein the epitaxial structure body comprises a substrate, a buffer layer, a sacrificial layer, and a device structure layer which are sequentially stacked along the longitudinal direction thereof, wherein the surface of the sacrificial layer facing away from the buffer layer comprises a first region and a second region which are sequentially adjacently arranged along the lateral direction of the epitaxial structure body, the first region is completely covered by the device structure layer, a side of the device structure layer close to the second region forms a step structure with the sacrificial layer, and a selected side wall of the device structure layer close to the second region is inclined, the anode field plate continuously covers the step structure, and forms ohmic contact with the device structure layer and the sacrificial layer.
[0030] Specifically, the thickness of the anode field plate is uniform, and the portion of the anode field plate covering the selected sidewall of the device structure layer is also tilted as a whole, and the tilt angle of the tilted portion of the anode field plate is the same as the tilt angle of the selected sidewall of the device structure layer. More specifically, the anode field plate includes a first portion, a second portion, and a third portion that are sequentially arranged, the first portion covers the second region of the sacrificial layer, the second portion covers the tilted selected sidewall of the device structure layer, the third portion is arranged on the top end surface of the device structure layer that is opposite to the sacrificial layer, the second portion is tilted as a whole, and the tilt angle of the second portion is the same as the tilt angle of the selected sidewall of the device structure layer.
[0031] More specifically, the selected sidewall of the device structure layer close to the second region has an inclination angle of 30° to 75°. It should be noted that the inclination angle of the selected sidewall is the angle between the extension direction of the selected sidewall and the lateral direction of the epitaxial structure body. The inclined field plate structure can alleviate the electric field concentration effect at the electrode edge and improve the stability of the electrode under long-term operation. Figure 4As shown, if the selected side wall inclination angle is too small, the contact area between the electrode and the heavily doped sacrificial layer surface becomes smaller, resulting in uneven current expansion. If the selected side wall inclination angle is too large, the adhesion of the contact electrode is reduced, resulting in a break at the connection between the field plate and the contact electrode, thereby causing failure of the field plate.
[0032] Specifically, the device structure layer includes an insulating buried layer, a device layer and an insulating protection layer which are sequentially stacked on the sacrificial layer along the longitudinal direction of the epitaxial structure body. The insulating buried layer can make the longitudinal and transverse etching ratio of electrochemical etching reach 0, which can avoid longitudinal etching damaging the device layer during electrochemical stripping and effectively protect the integrity of the device layer, which is crucial for stripping nanoscale films.
[0033] Specifically, the buried insulating layer and the insulating protective layer are both silicon oxide layers. More specifically, the buried insulating layer has a thickness of 200-500 nm, and the insulating protective layer has a thickness of 200-500 nm.
[0034] Specifically, the sacrificial layer is heavily n-type doped. For example, the sacrificial layer may be an n++ GaN sacrificial layer. Specifically, the n-type doping concentration of the sacrificial layer is ≥ 5*e18 / cm 3 Under the premise of ensuring the crystal quality, the n-type doping concentration of the sacrificial layer is as high as possible. Considering the process conditions and other factors, the n-type doping concentration of the sacrificial layer is preferably 5*e18 / cm 3 ~5*e19 / cm 3 , the thickness of the sacrificial layer is 1.5 μm~3 μm.
[0035] Specifically, the buffer layer includes a GaN buffer layer, etc., and the substrate may be a homogeneous substrate or a heterogeneous substrate, for example, the substrate may be a sapphire substrate or a gallium nitride substrate, etc.
[0036] In a more specific embodiment, a method for preparing an epitaxial structure suitable for electrochemical stripping to prepare a nano-thin film device may include the following steps: First, a buffer layer, a sacrificial layer (n-type doping concentration of 5*e18 / cm 3 ~5*e19 / cm 3 , thickness 1.5~3 µm or more), insulating buried layer, device layer and insulating protection layer; The ICP etching technology is used to etch away a portion of the buried insulating layer, a portion of the device layer and a portion of the insulating protective layer at the edge of the wafer, thereby exposing the sacrificial layer, and making the side walls of one side of the buried insulating layer, the device layer and the insulating protective layer as a whole present an inclined state, and one side of the buried insulating layer, the device layer and the insulating protective layer and the exposed sacrificial layer form a step structure; illustratively, the ICP etching atmosphere is BCl3: Cl2 = 20 slm: 10 slm, the pressure of the etching chamber is 10 mtorr, the RF power = 100 W, and the DC voltage is 120 V; An anode field plate structure is manufactured, and the anode field plate structure is made to continuously cover the top surface of the insulating buried layer, the insulating buried layer, the inclined side wall formed by etching the device layer and the insulating protection layer, and the exposed sacrificial layer. Through annealing treatment, the anode field plate structure forms an ohmic contact with the device layer and the sacrificial layer. Annealing forms an ohmic contact and improves the reliability of the long-term etching of the gold-semiconductor contact interface.
[0037] The present invention prepares anode electrodes in a large area on the transverse plane to ensure the uniformity of the etching current. The inclined field plate structure can alleviate the electric field concentration effect at the edge of the electrode and improve the stability of the electrode (the electrode refers to the entire anode, that is, the sacrificial layer surface electrode + table electrode + anode field plate) under long-term operation. Annealing is used to form an ohmic contact and improve the reliability of the gold semi-contact interface during long-term etching. The buried layer of insulating dielectrics such as SiO2 avoids longitudinal etching to damage the device layer, and can make the longitudinal and transverse etching ratio of electrochemical etching reach 0, which is crucial for stripping nano-scale films and effectively protects the integrity of the device layer. In addition, the present invention can achieve non-destructive stripping of stable nano-thin film devices and improve the success rate of stripping.
[0038] It should be understood that the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.
Claims
1. An epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping, characterized in that: include: Epitaxial structure body and anode field plate, The epitaxial structure body includes a substrate, a sacrificial layer and a device structure layer, wherein the sacrificial layer is stacked on the substrate, and the device structure layer includes an insulating buried layer, a device layer and an insulating protection layer which are sequentially stacked on the sacrificial layer along the longitudinal direction of the epitaxial structure body, wherein the surface of the sacrificial layer facing away from the substrate has a first region and a second region sequentially arranged along the lateral direction of the epitaxial structure body, the first region is covered by the device structure layer, a side of the device structure layer close to the second region forms a step structure with the sacrificial layer, and a selected side wall of the device structure layer close to the second region is inclined, and the anode field plate continuously covers the step structure and forms an ohmic contact with the device structure layer and the sacrificial layer.
2. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 1, characterized in that: The inclination angle of the selected side wall of the device structure layer close to the second region is 30° to 75°.
3. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 1 or 2, characterized in that: The thickness of the anode field plate is uniform, and the portion of the anode field plate covering the inclined selected sidewall of the device structure layer is also inclined as a whole.
4. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 3, characterized in that: The anode field plate includes a first part, a second part and a third part which are arranged in sequence, the first part covers the second area of the sacrificial layer, the second part covers the inclined selected side wall of the device structure layer, the third part is arranged on the top end surface of the device structure layer facing away from the sacrificial layer, the second part is inclined as a whole, and the inclination angle of the second part is the same as the inclination angle of the selected side wall of the device structure layer.
5. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 1, characterized in that: The thickness of the insulating buried layer and the insulating protective layer is not less than 200 nm; Preferably, the thickness of the insulating buried layer is 200-500 nm; Preferably, the thickness of the insulating protective layer is 200-500 nm.
6. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 5, characterized in that: The material of the insulating buried layer and the insulating protection layer includes silicon oxide.
7. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 1, characterized in that: The step structure is formed by removing a portion of the device structure layer by etching.
8. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 1, characterized in that: The sacrificial layer is heavily n-doped, and the n-doping concentration of the sacrificial layer is ≥ 5*e18 / cm 3 ; Preferably, the n-type doping concentration of the sacrificial layer is 5*e18 / cm 3 ~5*e19 / cm 3 ; Preferably, the thickness of the sacrificial layer is 1.5 μm to 3 μm; Preferably, the sacrificial layer is an n++ GaN sacrificial layer.
9. The epitaxial structure suitable for preparing nano-thin film devices by electrochemical stripping according to claim 1, characterized in that: The epitaxial structure body further includes a buffer layer, and the buffer layer is stacked on the substrate; Preferably, the buffer layer comprises a GaN buffer layer.
10. A method for preparing nano-thin film devices by electrochemical stripping, characterized in that: include: Provide an electrochemical etching device and an epitaxial structure suitable for electrochemical stripping to prepare a nano-thin film device as described in any one of claims 1 to 9, The epitaxial structure is immersed in the electrolyte of the electrochemical etching device, and the anode field plate of the epitaxial structure is electrically connected to the anode of the electrochemical etching device, and the cathode of the electrochemical etching device is placed in the electrolyte, so that the sacrificial layer is corroded and removed, thereby releasing the device structure layer.