Schottky diode with transverse structure, in-situ sample preparation method and processing technology

Abstract

The invention discloses a Schottky diode with a transverse structure, an in-situ sample preparation method and a processing technology. The cathode and the anode of the Schottky diode are in the same plane, the cathode ohmic contact layer is arranged on the periphery of the structure, the anode Schottky metal layer is arranged in the center of the structure, and the AlGaN barrier layer and the GaN substrate layer are sequentially arranged between the cathode ohmic contact layer and the anode Schottky metal layer. According to the in-situ sample preparation method, the FIB sample preparation technology and the selected area circuit breaking method are adopted to complete connection of the sample and the chip, the failure behavior of the device can be observed in real time under a transmission electron microscope, and the processing technology achieves effective isolation of the anode and the two-dimensional electron device through silicon oxide in the sample preparation process. Meanwhile, silicon oxide isolation can prevent short circuit of a power supply, so that a current passing path is shorter, the efficiency is higher, and the surface of a sample and a metal functional area below the sample can be effectively prevented from being damaged when ion beams are operated. The problems of low device power conversion efficiency, electrode short circuit and the like are solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor devices, and further relates to a Schottky diode with a lateral structure, an in-situ sample preparation method and a processing technology thereof in the technical field of wide bandgap semiconductor devices. The present invention can be applied to high-power devices, switching power supplies and rectifier circuits. Background Art

[0002] Among semiconductor devices, Schottky diodes are an important rectifying device. Among them, fast recovery Schottky diodes have the advantages of wide bandgap, high switching frequency, low reverse leakage current, and low reverse leakage time, and are widely used in power, electronics, communications and other fields. Schottky diodes can be used in certain high-voltage areas by increasing their breakdown voltage, and can be used in communications and other fields by reducing their leakage current, reducing the hidden dangers caused by high temperature. In order to further improve the rectification efficiency of the device, reduce the static power consumption of the device, and meet the application of the device in higher voltage fields, Schottky diodes need to have a smaller turn-on voltage, a smaller reverse leakage and a higher breakdown voltage at the same time. At present, the reverse withstand voltage of vertical structure Schottky diodes is generally low, generally not higher than 100V. Although technological development has enabled the maximum reverse bias withstand voltage of some diodes to reach 200V, compared with other diodes, the reverse withstand voltage capability of vertical structure diodes is still limited, which limits the use of vertical structure Schottky diodes in some occasions requiring high voltage applications. Secondly, the reverse leakage current of the vertical Schottky diode has a positive temperature characteristic, that is, as the temperature rises, the reverse leakage current will increase sharply, which may cause thermal breakdown of the device and the risk of thermal runaway. Moreover, the vertical diode will cause great damage to the sample during the sample preparation process due to the way the circuit is designed, making the sample more fragile.

[0003] Chen Jiabo et al. proposed a Schottky diode for GaN-based power electronic devices in their paper "Research on GaN Quasi-vertical Schottky Diode and Planar Complementary Logic Inverter" (PhD Dissertation of Xidian University, June 2022). The diode is a GaN quasi-vertical Schottky diode structure that combines a sidewall cathode structure and a F ion-implanted field-limiting ring structure. The structure improves the breakdown voltage and power while also reducing resistance under the premise that the turn-on voltage remains unchanged. However, the structure still has the following three shortcomings. First, the sidewall cathode structure and the F ion-implanted field-limiting ring structure will face reliability issues under long-term working conditions. For example, F ion implantation may cause changes in material properties, and the sidewall cathode structure may degrade under high temperature or high voltage conditions. Second, although the F ion-implanted field-limiting ring structure helps to increase the breakdown voltage, the introduced sidewall cathode structure will affect this. At the same time, the sidewall cathode structure may increase the forward on-resistance, thereby reducing the power conversion efficiency of the device. Third, due to the complexity and reliability of the preparation process, the cost of this structure is high, which limits its promotion in certain low-cost application fields.

[0004] Dexing Yifa Power Semiconductor Co., Ltd. proposed a planar Schottky diode and its preparation method in its patent application "A planar Schottky diode and its preparation method" (application number 202211646174.6, application publication number CN 11577828 A). Since the structure of the diode is a Schottky diode device with an N-type substrate, its preparation method is to set a doping region to improve its reverse surge current capability. The shortcomings of the preparation method of the diode are that, first, in the process of high-energy ion implantation of boron, the ion beam energy is too high to easily damage the sample structure; second, the sample preparation process cannot perform real-time analysis of its reliability, and cannot directly link the performance failure of the device with microstructural damage. Summary of the invention

[0005] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and to propose a lateral structured Schottky diode and an in-situ sample preparation method, so as to solve the problems of low power conversion efficiency of Schottky diode devices and difficulty in connecting electrodes to MEMS chips and electrode short circuits during the sample preparation process of Schottky diode in-situ powered samples.

[0006] To achieve the above purpose, the idea of ​​the present invention is that the Schottky diode of the present invention adopts a lateral structure, that is, the positive and negative electrodes are in the same plane, the outer periphery of the structure is the cathode ohmic contact layer, the center is the anode Schottky metal layer, and the material structures of the layers between the two are AlGaN barrier layer and GaN substrate layer in sequence. By optimizing the metal layer ratio and thickness of the cathode ohmic electrode, the contact resistance can be effectively reduced. The barrier layer adopts AlGaN material, and its two-dimensional electron gas is formed by spontaneous polarization and piezoelectric polarization, so that the carrier migration rate is less affected by temperature, and even increases at low temperatures, thereby obtaining a higher carrier migration speed. The above two special features make the lateral structure diode of the present invention have lower contact resistance and higher carrier migration speed. Lower contact resistance can reduce the loss of energy at the contact interface, allowing the current to pass through the diode more smoothly, and the higher carrier migration speed increases the transmission speed of carriers inside the diode. In this way, the problem of low power conversion efficiency of Schottky diode devices in the prior art is solved. The in-situ sample preparation method of the present invention adopts FIB sample preparation technology and selective disconnection method to complete the connection between the sample and the chip. The failure behavior of the device can be observed in real time by observing its electrical characteristics under a transmission electron microscope TEM (Transmission Electron Microscope), thereby improving the reliability of the device, thereby avoiding the problem that the prior art cannot perform real-time analysis of its reliability during the sample preparation process. A direct connection between device performance failure and material microstructure damage is established. The technology enables the device to be observed at the atomic scale in the real-time service state of the device when it is powered on, directly establishing the physical nature of material structure damage, element diffusion, etc. related to the degradation of electrical characteristics, and providing guidance for further realizing high-performance diode devices. The processing method of the present invention can block the ion beam from directly bombarding the sample surface by depositing a Pt protective layer on the top of the device, which can fully reduce the damage of the ion beam to the sample and achieve the effect of protecting the device. The processing method of the present invention isolates the metal layers between different layers through silicon oxide isolation, prevents current leakage and short circuit, can control the current flow direction, and effectively prevents the metal functional area from contacting the electrode in the subsequent connection process to cause a short circuit. The processing technology of the lateral structure Schottky diode of the present invention. During the sample preparation process, silicon oxide isolation is designed to achieve effective isolation between the anode and the two-dimensional electronic device, and at the same time achieve short circuit between the chip and the electrode. Silicon oxide isolation prevents power short circuit, makes the current path shorter and more efficient, and can effectively prevent the ion beam from damaging the sample surface and the metal functional area below during operation. This solves problems such as low device power conversion efficiency and electrode short circuit.

[0007] The Schottky diode of the lateral structure of the present invention comprises an ohmic metal layer and a Schottky metal layer, wherein the ohmic metal layer and the Schottky metal layer are both arranged in the same plane, the periphery of the structure is an ohmic contact layer, the center is a Schottky metal layer, and the material structures of the layers between the two are sequentially an AlGaN barrier layer and a GaN substrate layer, and the effect of reducing resistance is achieved by optimizing the thickness and proportion of each metal layer.

[0008] Furthermore, the anode radius of the Schottky metal layer is 100 μm, and the distance between the cathode of the ohmic contact layer and the anode of the Schottky metal layer is 15 μm.

[0009] Furthermore, the barrier layer is made of AlGaN material and has a thickness of 25 nm.

[0010] Furthermore, the substrate layer is made of GaN material and has a thickness of 200 nm.

[0011] The in-situ sample preparation method of the lateral structure Schottky diode of the present invention adopts FIB sample preparation technology and a selective area disconnection method to complete the connection between the sample and the chip, so as to realize real-time observation of the failure behavior of the electrical characteristics of the device under a transmission electron microscope.

[0012] Furthermore, the FIB sample preparation technology is to fix the AlGaN / GaN heterojunction Schottky diode and the DENS thermoelectric chip and place them in a vacuum environment for in-situ sample preparation, and determine the sampling position by adjusting the working distance and the concentric height.

[0013] Furthermore, the selective disconnection method refers to selecting a part of the sample by U-cutting and transferring it to the chip by a robot to complete the connection between the sample and the chip.

[0014] The in-situ sample preparation process of the lateral structure Schottky diode of the present invention comprises the following steps:

[0015] Step 1, sampling and determining the sampling location;

[0016] Step 2, depositing the Pt protective layer:

[0017] Using an electron beam, a Pt protective layer is deposited between the Ohmic metal layer and the Schottky metal layer; an ion beam is used to machine a groove next to the anode Pt protective layer, the groove depth reaching the GaN substrate layer; silicon oxide is deposited in the groove;

[0018] Step 3, U-shaped cutting of samples:

[0019] The sample is cut using a U-cut method; after being completely cut, the manipulator is adjusted to be close to the sample, and the manipulator and the sample are connected by depositing a Pt layer, and the other side of the sample is completely cut off, and the sample is extracted by the manipulator and connected to the chip, and Pt is deposited to connect the Schottky metal layer of the device to the electrode 1 of the chip, and the ohmic metal layer to the electrode 2;

[0020] Step 4, cutting the Pt thinned sample:

[0021] The Pt layer between the cathode and anode is cut off by an ion beam, and the thickness of the diode sample is thinned by real-time observation in an electron beam until the thickness of the sample in the observation area in the electron beam is less than 100 nm.

[0022] Furthermore, the sampling and determining the sampling position refers to fixing the AlGaN / GaN heterojunction Schottky diode and the DENS thermoelectric chip, placing them in a vacuum environment for in-situ sample preparation, and placing the Schottky diode device in the center of the field of view by adjusting the working distance and the concentric height.

[0023] Furthermore, the size of the Pt protective layer is the length, width and height of the Pt protective layer set according to the sample sizes of the Ohmic metal layer and the Schottky metal layer.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] First, the Schottky diode of the present invention adopts a lateral structure, which overcomes the defect of low power conversion efficiency of the Schottky diode device in the prior art, so that the lateral structure diode of the present invention has lower contact resistance and higher carrier migration speed, which can better improve the performance of the device, so that the structure can achieve a higher on-current and smaller reverse leakage while having a device with a smaller Schottky metal width, such as controlling the current flow direction by depositing silicon oxide isolation, thereby obtaining a higher on-current. While having a high on-current, it also has the advantage of resisting high breakdown voltage. Moreover, the lateral structure diode is easier to achieve specific doping and process treatment during the preparation process.

[0026] Second, the in-situ sample preparation method of the Schottky diode of the present invention overcomes the defect of the prior art that the reliability of the Schottky diode cannot be analyzed in real time during the sample preparation process, so that the present invention can observe the preparation process of the lateral structure Schottky diode sample in real time, thereby improving the reliability of the device.

[0027] Third, the Schottky diode processing technology of the present invention can fully reduce the damage of the ion beam to the sample by depositing a Pt protective layer on the top of the device, thereby achieving the effect of protecting the device. Moreover, the device failure behavior can be observed in real time under a transmission electron microscope (TEM), so that the present invention fully establishes the connection between device performance failure and material microstructure damage.

[0028] Fourthly, the Schottky diode processing technology of the present invention can control the current flow direction through silicon oxide isolation, and prevent the problem of short circuit caused by contact between the functional area and the electrode during the subsequent connection process, so that the present invention further optimizes the performance of the Schottky diode device.

[0029] Fifth, the lateral structure sampling method of the present invention is not only applicable to the lateral structure sampling that is more difficult to operate, but also applicable to the sampling of longitudinal vertical structure devices. It also causes less damage to the sample structure, while reducing the research and sampling costs, and has a wider range of applications and is more universal. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the structure of a lateral Schottky diode used in the present invention;

[0031] Figure 2 A schematic diagram of an in-situ sample preparation method for a lateral structure Schottky diode of the present invention;

[0032] Figure 3 The figure is a process flow chart of the processing of the lateral structure Schottky diode of the present invention. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand and implement the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0034] Reference Figure 1 , the structure of the lateral Schottky diode according to the embodiment of the present invention is further described.

[0035] The lateral structure Schottky diode of the present invention comprises a cathode at the periphery of the structure, an anode (Schottky metal layer) at the center, a functional area (including AlGaN and GaN) at the bottom and a GaN substrate layer.

[0036] Take AlGaN / GaN heterojunction Schottky diode and DENS thermoelectric chip for example, Figure 2 , the in-situ sample preparation method of the lateral structure Schottky diode of the present invention is further described.

[0037] Step 1, injection.

[0038] Step 1.1, confirm that the electron beam source and ion beam source of the FIB-SEM are turned off. In the control software, click the Vent button and wait for the venting to complete.

[0039] Step 1.2: Pull open the hatch of the FIB-TEM horizontally, insert the nail stand with the AlGaN / GaN heterojunction Schottky diode and the DENS thermoelectric chip into the workbench of the FIB-TEM chamber, and confirm that it is fixed.

[0040] Step 1.3, click the Pump button in the control software and wait for the chamber pressure to be evacuated to below 5×10-3Pa to obtain a vacuum environment.

[0041] Step 2: Determine the sampling location.

[0042] Step 2.1, working distance adjustment: After vacuuming, turn on the electron beam and ion beam Beam keys, locate the area where the sample needs to be prepared, adjust the Focus key to more than 5000 times and click the Link key, adjust the sample stage height several times, and gradually raise it so that the working distance between the sample and the ion beam source is 4mm.

[0043] Step 2.2, concentric height adjustment: When the sample stage is at 0°, move the position where the sample needs to be prepared to the center of the electron beam window, tilt the sample stage to 15°, and use the StageZ up / down key of the software to adjust the position where the sample needs to be prepared to the center of the electron beam observation window. Tilt it to 52° and further adjust the sample preparation position to the center;

[0044] Step 2.3: Move the FIB-SEM sample stage and place the Schottky diode device in the center of the field of view.

[0045] Reference Figure 3 , the steps of a processing technology for a lateral Schottky diode according to an embodiment of the present invention are further described.

[0046] Step 1, depositing a Pt layer.

[0047] Step 1.1, use electron beam (2kv, 1.6-3.2nA) to deposit a Pt protective layer with a size of 10μm×2μm×0.5μm between the cathode (ohmic contact) and the anode (Schottky contact). The size can be adjusted according to the size of the sample. This causes the anode and cathode to be short-circuited, such as Figure 2 (a) shown.

[0048] Step 1.2, a groove is machined by ion beam next to the anode Pt protective layer, such as Figure 2 As shown in (b), the groove depth should reach the GaN substrate layer.

[0049] Step 2, deposit silicon oxide isolation.

[0050] Depositing silicon oxide in the grooves, e.g. Figure 2 As shown in (c), short circuits caused by direct contact between the functional area (anode metal) and the channel electron area can be prevented. Silicon oxide isolation can also better protect the sample structure and reduce the damage to the sample caused by ion beam and electron beam during FIB-SEM processing, greatly reducing the damage to the sample.

[0051] Silicon oxide is deposited in the groove to the extent that the entire groove is almost covered, and is filled in the ion beam using a Si gas needle in the chamber.

[0052] Step 3, U-shaped cutting.

[0053] The U-cut method (30 kV, 2.4-5.0 nA) is used. The U-cut area should completely include the silicon oxide isolation area. The sample is cut, such as Figure 2 (d) As shown. The ion beam starts cutting at about 0.5 to 1 μm from the sample surface to ensure that the sample has a complete device structure. After complete cutting, adjust the manipulator close to the sample, connect the manipulator and the sample by depositing Pt, completely cut off the other side of the sample, and use the manipulator to extract the sample. The position is shown in Figure 2 (e) and connected to the chip, depositing Pt to connect the anode of the device to electrode 1 of the chip and the cathode to electrode 2, as shown in Figure 2 (f) is shown, the purpose is to be able to observe in real time in the transmission electron microscope when conducting subsequent research on its electrical properties. The use of deposited Pt to connect the manipulator and the sample means that the sample is extracted and transferred to the chip using the manipulator of the transmission electron microscope, which is conducive to the subsequent verification of its electrical properties.

[0054] Step 4, cut off the Pt and thin the sample.

[0055] Step 4.1, use an ion beam (30kv, 2.4-3.0nA). The size of the ion beam can be adjusted as needed to cut off the Pt layer between the cathode and anode, such as Figure 2 As shown in (g), the Pt layer is cut off to prevent the device from losing its original electrical properties due to short circuit between the anode and cathode.

[0056] Step 4.2, use ion beam to thin, real-time observation can be carried out in the electron beam, the values ​​required for ion beam thinning can be adjusted to 30kv, 0.44-0.26nA / 30kv, 46-90pA / 5kv, 63pA / 2kv, 44pA. Until the thickness of the observation area is less than 100nm, it meets the requirements of transmission electron microscope observation. The final result is as follows Figure 2 (h) shown.

[0057] Thinning a sample means using an ion beam to cut the extracted sample into a wedge-shaped portion that is thin on the top and thick on the bottom. The thinning of the sample is to meet the needs of real-time observation under a transmission electron microscope. The thickness must be less than 100nm so that it can be observed in real time under a transmission electron microscope when studying its electrical properties.

Claims

1. A lateral Schottky diode, comprising an ohmic metal layer and a Schottky metal layer, characterized in that: The ohmic metal layer and the Schottky metal layer are both arranged in the same plane. The outer periphery of the structure is the ohmic contact layer, the center is the Schottky metal layer, and the material structures of the layers between the two are the AlGaN barrier layer and the GaN substrate layer in sequence. The effect of reducing resistance is achieved by optimizing the thickness and proportion of each metal layer.

2. The Schottky diode according to claim 1, characterized in that: The anode radius of the Schottky metal layer is 100 μm, and the distance between the cathode of the ohmic contact layer and the anode of the Schottky metal layer is 15 μm.

3. The Schottky diode according to claim 1, characterized in that: The barrier layer is made of AlGaN material and has a thickness of 25 nm.

4. The Schottky diode according to claim 1, characterized in that: The substrate layer is made of GaN material and has a thickness of 200nm.

5. The in-situ preparation method of a Schottky diode with a lateral structure according to claim 1, characterized in that: The FIB sample preparation technology and the method of selective disconnection are used to complete the connection between the sample and the chip, so as to realize the real-time observation of the failure behavior of the device's electrical characteristics under a transmission electron microscope.

6. The in-situ sample preparation method of a lateral Schottky diode according to claim 5, characterized in that: The FIB sample preparation technology is to fix the AlGaN / GaN heterojunction Schottky diode and the DENS thermoelectric chip and place them in a vacuum environment for in-situ sample preparation, and determine the sampling position by adjusting the working distance and the concentric height.

7. The in-situ sample preparation method of a lateral Schottky diode according to claim 5, characterized in that: The selective disconnection method refers to selecting a part of the sample by U-cutting and transferring it to the chip by a robot to complete the connection between the sample and the chip.

8. The process for manufacturing a Schottky diode with a lateral structure according to claim 1, characterized in that: The steps of the processing technology include the following: Step 1, sampling and determining the sampling location; Step 2, depositing the Pt protective layer: Using an electron beam, a Pt protective layer is deposited between the Ohmic metal layer and the Schottky metal layer; an ion beam is used to machine a groove next to the anode Pt protective layer, the groove depth reaching the GaN substrate layer; silicon oxide is deposited in the groove; Step 3, U-shaped cutting of samples: The sample is cut using a U-cut method; after being completely cut, the manipulator is adjusted to be close to the sample, and the manipulator and the sample are connected by depositing a Pt layer, and the other side of the sample is completely cut off, and the sample is extracted by the manipulator and connected to the chip, and Pt is deposited to connect the Schottky metal layer of the device to the electrode 1 of the chip, and the ohmic metal layer to the electrode 2; Step 4, cutting the Pt thinned sample: The Pt layer between the cathode and anode is cut off by an ion beam, and the thickness of the diode sample is thinned by real-time observation in an electron beam until the thickness of the sample in the observation area in the electron beam is less than 100 nm.

9. The process for manufacturing a Schottky diode with a lateral structure according to claim 8, characterized in that: The sampling and determining of the sampling position described in step 1 refers to fixing the AlGaN / GaN heterojunction Schottky diode and the DENS thermoelectric chip, placing them in a vacuum environment for in-situ sample preparation, and placing the Schottky diode device in the center of the field of view by adjusting the working distance and the concentric height.

10. The process for manufacturing a Schottky diode with a lateral structure according to claim 9, characterized in that: The size of the Pt protective layer is the length, width and height of the Pt protective layer set according to the sample sizes of the Ohmic metal layer and the Schottky metal layer.

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