A GaN-based lateral charge balance power diode and a method for manufacturing the same

Abstract

The application belongs to the technical field of semiconductor integrated circuits and devices, and discloses a GaN-based lateral charge balance power diode and a preparation method thereof. The diode comprises a hetero-substrate, a patterned template arranged on the hetero-substrate, a high-aspect-ratio curved channel formed by the patterned template, and a GaN active region formed by lateral epitaxy on the top of the curved channel. The GaN active region comprises a p-GaN region, a lightly-doped n ‑ -GaN drift region, and a heavily-doped n + -GaN region. The p-GaN region is located below the bottom or side of the lightly-doped n ‑ -GaN drift region, and is mutually depleted with the lightly-doped n-GaN drift region to form in-body charge balance under reverse bias. The application can adjust the size and doping concentration of the p region and the n region through a one-time epitaxy combined with etching process, so as to improve the n-type drift region doping concentration and reduce the specific on-resistance while maintaining the breakdown voltage.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor integrated circuits and devices technology, specifically relating to a GaN-based lateral charge-balanced power diode and its fabrication method. Background Technology

[0002] GaN, as a third-generation semiconductor material, possesses advantages such as a wide bandgap, high electron mobility, high critical breakdown electric field, and high chemical stability, making it a power semiconductor material with great development potential. Breakdown voltage and on-resistance are two of the most important parameters of power devices, and there is an inherent constraint between them, known as the one-dimensional limit of the material. With the development of power devices, this one-dimensional limit has begun to restrict their application in high-voltage fields. Therefore, breaking through this one-dimensional limit will help further improve the performance of power devices.

[0003] Charge-balanced devices (such as superjunction devices and RESURF devices) are an effective technical means to overcome the above-mentioned constraints. By simultaneously introducing n-type and p-type semiconductor materials into the device structure, the pn junction is depleted under reverse bias, so that the electric field is uniformly distributed in the device body, thereby improving the device's breakdown voltage performance. At the same time, by increasing the doping concentration of the n-type region, the on-resistance of the device can be effectively reduced, ultimately realizing the fabrication of high-current and high-voltage power devices.

[0004] Currently, research on GaN charge-balancing devices is still in its early stages. GaN charge-balancing devices mainly include two types: lateral and vertical structures. In lateral structures, the anode and cathode are typically located on the device surface or in the lateral region, and the current mainly propagates laterally. Compared to vertical structures, lateral structures are more compatible with planar fabrication processes. They allow for optimization of the device's breakdown voltage and conduction characteristics by adjusting the length of the lateral drift region, the relative positions of the p-type and n-type regions, and the doping concentration. Therefore, they offer better fabrication feasibility and structural tunability in GaN power devices.

[0005] However, existing lateral GaN charge-balanced structures are mostly based on the AlGaN / GaN polarization effect to form super heterojunctions. For example, p-GaN is placed on the surface of the AlGaN / GaN electron channel, and charge balance is achieved by utilizing the holes in p-GaN and the two-dimensional electron gas at the AlGaN / GaN interface; or Mg is δ-doped at the bottom of the channel to form charge balance with the channel electrons. Although this type of lateral structure can improve the electric field distribution to some extent, its conductive channel mainly depends on the two-dimensional electron gas. Limited by the channel electron concentration, interface scattering, and charge balance adjustment range, it still suffers from problems such as high on-resistance and limited forward output current.

[0006] Vertical structures typically withstand reverse voltage along the thickness direction of the epitaxial layer, which theoretically benefits high voltage withstand and high current output, and can also achieve charge balance through structures such as superjunctions. However, in GaN materials, the fabrication of vertical charge-balanced structures usually relies on processes such as multiple ion implantations, multiple epitaxy, deep trench etching followed by secondary epitaxial backfilling, or sidewall ion implantation. These processes are not only complex and costly, but also present significant challenges in quality control of p-type doping, ion implantation activation, and deep trench backfilling in GaN, easily leading to interface damage, increased leakage current, and decreased voltage withstand performance.

[0007] Therefore, an improved charge-balancing structure is still needed for lateral GaN power devices. This structure should retain the process compatibility and tunability of the lateral structure while further improving the electric field distribution in the lateral drift region, increasing the device breakdown voltage, and reducing the on-resistance. This application addresses the aforementioned problems of existing lateral GaN charge-balancing devices by setting a p-GaN region and a lightly doped n-region within the lateral GaN active region. - -GaN drift regions allow the two to deplete each other under reverse bias, thereby achieving bulk charge balance and electric field homogenization. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a GaN-based lateral charge-balanced power diode and its fabrication method. This method requires only one epitaxial growth step, is simple in process, low in cost, and produces high-quality crystal material, which is beneficial for fabricating high-performance devices. Optimizing the device structure allows for high doping in the n-type region, resulting in low on-resistance. This solves the problem of low output current in traditional AlGaN / GaN-based lateral charge-balanced devices, laying an important foundation for the application of GaN-based charge-balanced devices in high-voltage, high-power power electronic systems.

[0009] The present invention discloses a GaN-based lateral charge-balanced power diode, comprising a heterogeneous substrate; the upper end of the heterogeneous substrate is provided with parallel silicon nitride layers spaced apart in the lateral direction, and silicon dioxide is provided between the two silicon nitride layers, and the two silicon nitride layers are arranged in a lateral staggered manner to form a curved channel. GaN is grown within the curved channel, and an epitaxial layer with a core-shell structure is grown on the GaN. The structure of the epitaxial layer, from the inside to the outside, consists of a p-GaN region, an n-GaN region, and an epitaxial layer. - -GaN drift region, the n - -One end of the GaN drift region is n + -GaN region; Where, n + -The GaN region forms an ohmic contact with the cathode metal; n - The other end of the -GaN drift region and the p-GaN region together come into contact with the anode metal, forming a Schottky contact.

[0010] Furthermore, the n- - The GaN drift region has a drift region length W1, wherein n + The p-GaN region has a length W2, where W1 is greater than W2, and the p-GaN region has a length W3; W1 is used to adjust the breakdown voltage and on-resistance of the device, W2 is used to reduce the cathode ohmic contact resistance, and W3 is used to adjust the charge balance between the p-GaN region and the n⁻-GaN drift region and the electric field distribution inside the device.

[0011] Furthermore, the n - The thickness of the -GaN drift region is Hn, and the thickness of the p-GaN region is Hp, where n - The doping concentration Nd and thickness Hn of the GaN drift region are approximately equal to the doping concentration Na and thickness Hp of the p-GaN region, so that the n-GaN drift region under reverse bias is approximately equal to the thickness Hn of the p-GaN drift region. - - The GaN drift region and the p-GaN region mutually deplete each other and homogenize the electric field distribution in the drift region.

[0012] This invention also provides a method for fabricating a GaN-based lateral charge-balanced power diode, comprising the following steps: (a) Fabricating a Si3N4 / SiO2 / Si3N4 patterned template on a substrate, constructing a depth H c Greater than the opening width W c The curved channels are designed to form high aspect ratio curved channels that allow the inclined growth of penetrating dislocations to terminate at the channel sidewalls; GaN aspect ratio trapping (ART) epitaxial growth is performed in the curved channels using metal-organic chemical vapor deposition (MOCVD). (b) A core-shell structured GaN epitaxial layer is grown, consisting of p-GaN and n-GaN layers from the inside out. - -GaN and n + -GaN layer; (c) Dry etching exposes the p-GaN region on the left and the n-GaN region above. - -GaN region; (d) Masking, vapor deposition of Cr / Au metal, and n on the right side. + -GaN contact, forming a cathode ohmic contact; (e) Masking, evaporating Ni / Au metal, and then reacting it with the p-GaN and n-metal on the left side. - -GaN interface contact, forming Schottky contact.

[0013] Furthermore, the width W of the opening of the curved channel cLess than 10μm.

[0014] Furthermore, the aspect ratio of the curved channel is less than 0.5.

[0015] The beneficial effects of this invention are as follows: (1) The diode of the present invention is formed by providing lightly doped n in the lateral GaN active region. - -GaN drift region, p-GaN region vertically located at its bottom, and heavily doped n on one side. + - In the GaN region, the forward current of the device flows along the lightly doped n-axis. - - The GaN drift region translocates laterally between the anode and cathode. Under reverse bias, the bottom p-GaN region and the top lightly doped n-GaN region... - - Vertical mutual depletion occurs in the GaN drift region; when the thickness and doping concentration of both satisfy the charge balance relationship, the space charge and electric field distribution in the entire lateral drift region can be adjusted, thereby allowing for the increase of lightly doped n - The doping concentration of the GaN drift region, while considering the breakdown voltage and on-resistance of the device, allows the p-GaN region to be combined with the lightly doped n-GaN region. - - The GaN drift region forms a charge balance under reverse bias, thereby improving the breakdown voltage and reducing the on-resistance; (2) The present invention uses the ART lateral epitaxy method to terminate some of the tilted through dislocations at the channel sidewall, which is beneficial for growing GaN materials with low dislocation density and high crystal quality on a heterogeneous substrate; within the GaN active region formed by the ART lateral epitaxy of the curved channel, a p-GaN region and lightly doped n are set. - -GaN drift region and heavily doped n + -GaN region, where the p-GaN region is located in the lightly doped n - -The bottom or lower side of the GaN drift region, when reverse biased, is adjacent to lightly doped n - - The GaN drift regions are mutually depleted, resulting in a more uniform electric field distribution in the drift regions. This structure is formed through a single epitaxial etching process, allowing adjustment of the size, relative height, and doping concentration of the p-region and n-region to meet charge balance conditions, further resolving the problem of mutual constraint between breakdown voltage and drift region on-resistance in conventional SBDs; (3) The present invention achieves the process by epitaxy combined with etching in one step. Compared with multiple epitaxy, ion implantation or deep trench backfilling, the process is simpler, the interface damage is smaller, and it is more suitable for GaN material system. It avoids the problems of complex process, high cost and poor crystal quality of traditional structure. It breaks the one-dimensional limit of the material and effectively improves the breakdown voltage of the device under the same on-resistance. Attached Figure Description

[0016] Figure 1This is a schematic diagram of a GaN lateral charge balance diode; Figure 2 This is a flowchart of the fabrication process for a GaN lateral charge-balanced diode; Figure 3 This is a schematic diagram of the active region structure of a GaN lateral charge balance diode; Figure 4 This is a schematic diagram of the curved channel structure in a GaN lateral charge balance diode; Figure 5 It is lightly doped at the top (n) - -Thickness H of GaN drift region n Adjusting the p-GaN region with lightly doped n - Schematic diagram of the charge balance relationship between GaN drift regions; Figure 6 It is lightly doped n - -Doping concentration N in the GaN drift region d Adjusting the p-GaN region with lightly doped n - Schematic diagram of the charge balance relationship between GaN drift regions; Figure 7 It is lightly doped n - -Doping concentration N in the GaN drift region d The doping concentration N of the p-GaN region a Relationship diagram; Wherein: 1-heterogeneous substrate, 2-silicon nitride, 3-silicon dioxide, 4-GaN grown in the channel, 5-P-type GaN region, 6-lightly doped n-type GaN, 7-heavily doped n-type GaN, 8-anode metal, 9-cathode metal. Detailed Implementation

[0017] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0018] like Figure 1 and Figure 4 As shown, the GaN-based lateral charge-balanced power diode of the present invention includes a heterogeneous substrate 1, which may be sapphire, silicon, etc.; the upper end of the heterogeneous substrate 1 is provided with parallel silicon nitride 2 at intervals along the lateral direction, and silicon dioxide 3 is provided between the two layers of silicon nitride 2, and the two layers of silicon nitride 2 are arranged in a lateral staggered manner to form a curved channel. GaN4 is grown within a curved channel, featuring a core-shell epitaxial layer consisting of p-GaN regions 5 and n from the inside out. - -GaN drift region (i.e., lightly doped n-type GaN) 6, the n - -One end of the GaN drift region 6 is n + -GaN region (i.e., heavily doped n-type GaN) 7; Where, n + -GaN region 7 contacts the cathode metal 9 to form a cathode ohmic contact; n - - The other end of the GaN drift region 6 and the p-GaN region 5 are in contact with the anode metal 8, forming a Schottky contact.

[0019] like Figure 2 As shown, the present invention also provides a method for fabricating a GaN-based lateral charge-balanced power diode, which includes the following steps: (a) A patterned Si3N4 / SiO2 / Si3N4 template is fabricated on a substrate, and the lower Si3N4 layer, SiO2 layer, and upper Si3N4 layer are patterned using photolithography and etching processes, so that the openings in the upper and lower layers are staggered laterally, thereby forming a curved channel with a depth greater than the opening width; for example... Figure 4 As shown, the width W of the curved channel opening c Less than 10 μm, with a curved channel depth of H c The aspect ratio of the curved channel is less than 0.5; (b) Using MOCVD process, GaN ART epitaxial growth is performed in the curved channel, so that GaN grows selectively along the curved channel and the penetrating dislocations that extend at an angle during the epitaxial growth process terminate at the sidewall of the curved channel. (c) A core-shell structured GaN epitaxial layer is grown, consisting of p-GaN and n-GaN layers from the inside out. - -GaN and n + -GaN layer; (d) Dry etching exposes the p-GaN region on the left and the n-GaN region above. - -GaN region; (e) Masking, vapor deposition of Cr / Au metal, and n on the right side. + -GaN contact, forming a cathode ohmic contact; (f) Masking, evaporating Ni / Au metal, and then reacting it with the p-GaN and n-metal on the left side. - -GaN interface contact, forming Schottky contact.

[0020] This invention utilizes curved channel ART lateral epitaxy to obtain a low-dislocation GaN active region, and simultaneously introduces a p / n charge balance structure within this active region, thereby achieving both material quality optimization and electric field distribution optimization. For example... Figure 3As shown, in the lateral structural parameters of this invention, the drift region length W1 is a crucial parameter affecting the device's breakdown voltage and on-resistance. Specifically, under reverse bias and with the drift region fully depleted, the electric field within the device tends to be uniformly distributed, and the breakdown voltage is positively correlated with the drift region length W1. Therefore, increasing the drift region length W1 is beneficial for improving the device's withstand voltage capability. Simultaneously, the drift region length W1 is also the primary transport path for charge carriers during forward conduction; as the drift region length W1 increases, the device's forward conduction resistance increases accordingly. Therefore, the drift region length W1 can be optimized according to the target withstand voltage level and conduction loss requirements. The length W2 on the right is n. + The length of the p-GaN region is primarily used to form low-resistance cathode ohmic contacts and reduce contact resistance; its impact on device breakdown voltage is relatively small. Increasing W2 expands the lateral extension region during current injection or collection from the cathode metal, reducing cathode-side contact resistance and series resistance, and alleviating local current congestion. The p-GaN region length W3 is used to adjust the charge balance between the p-GaN region and the n⁻-GaN drift region, further influencing depletion region expansion and the internal electric field distribution of the device. W3 determines the lateral coverage of the p-GaN region. Under reverse bias, acceptor ions in the p-GaN region are negatively charged, while donor ions in the lightly doped n⁻-GaN drift region are positively charged; both form a space charge region after depletion. Increasing W3 increases the lateral range of the p-GaN region participating in depletion and charge compensation, thus altering the total charge matching relationship between the p-region and the n⁻ region, and changing the lateral extension range of the depletion region within the drift region.

[0021] Longitudinal structural parameter H n and H p These represent the top lightly doped n - -Thickness of the GaN drift region and the thickness of the bottom p-GaN region. H n and H p Used to adjust the p-GaN region and lightly doped n - The charge balance relationship between the p-GaN drift regions. Under reverse bias, the p-GaN region and the lightly doped n-region... - -GaN drift regions are mutually depleted; when lightly doped with n - -Doping concentration N in the GaN drift region d and thickness H n The doping concentration N in the p-GaN region a and thickness H p Satisfying N d ×H n With N a ×H pWhen the values ​​are approximately equal, the space charge distribution within the drift region becomes more uniform, which can reduce the electric field concentration at the anode side and device edges. Through this charge balance design, the lightly doped n-type voltage can be improved while maintaining a high reverse breakdown voltage. - - The doping concentration of the GaN drift region reduces the specific on-resistance of the device.

[0022] Regarding the structural parameters of this device, the present invention has made some design modifications, as shown in the following examples: I. In different lightly doped n - -Doping concentration N in the GaN drift region d (i.e., silicon doping concentration) at which the top is lightly doped with n - -Thickness H of GaN drift region n The effect on breakdown voltage. For example... Figure 5 As shown, it can be seen that when the doping concentration (i.e., magnesium doping concentration) N in the p-GaN region is higher than that of the magnesium doping concentration, the overall doping concentration is lower than that of the magnesium doping concentration. a Fixed at 1×10 17 cm -3 Lightly doped n - -Doping concentration N in the GaN drift region d Fixed at 1×10 17 cm -3 The thickness H of the p-GaN region p It is 1.6 μm, with light n-doped top. - -Thickness H of GaN drift region n The thickness H of the p-GaN region is less than p At that time, H n The increase in size allows for the expansion of the p-GaN region and the lightly doped n-region. - -Depletion between GaN drift regions improves the device's breakdown voltage. H n The thickness H of the p-GaN region is greater than p At that time, H n The increase in size makes the p-GaN region more compatible with the lightly doped n-region. - Depletion between GaN drift regions becomes more difficult, reducing the device's breakdown voltage. The doping concentration N in the p-GaN region... a Fixed at 1×10 17 cm -3 With light doping of n - -Doping concentration N in the GaN drift region d (i.e., silicon doping concentration) decreases until it reaches 5 × 10 16 cm -3 At that time, lightly doped n - -Doping concentration N in the GaN drift region d The reduction in size decreases the dependence of the p-GaN region on lightly doped n - The difficulty of depleting the GaN drift region makes it possible to lightly dope thicker top layers with n-type magnets.- -The GaN drift region is fully depleted, and the peak breakdown voltage corresponds to the top lightly doped n. - -Thickness H of GaN drift region n Therefore, it is improved.

[0023] II. Lightly doped n under different p-GaN region lengths W3 - -Doping concentration N in the GaN drift region d The effect of silicon doping concentration on breakdown voltage. For example... Figure 6 As shown, when the length W3 of the p-GaN region is fixed, the doping concentration N of the p-GaN region... a 1×10 17 cm -3 Lightly doped n - -Doping concentration N in the GaN drift region d The doping concentration N is less than that of the p-GaN region. a At that time, due to the doping concentration N in the p-GaN region a Relatively lightly doped n - -Doping concentration N in the GaN drift region d Larger, when N d As the value increases, the p-GaN region responds better to lightly doped n - - The GaN drift region can be fully depleted, improving the device's breakdown voltage. Meanwhile, the doping concentration N in the p-GaN region... d The doping concentration N greater than that of the p-GaN region a At that time, N d The increase in size makes the p-GaN region more compatible with the lightly doped n-region. - Depletion between the p-GaN drift regions becomes more difficult, weakening the device's breakdown voltage. The drift region length W1 is 16 μm. As the p-GaN region length W3 increases, up to 15 μm, approaching the drift region length W1, the increase in p-GaN region length W3 makes the p-GaN region more susceptible to depletion by lightly doped n-type regions. - -GaN has a larger depletion region in its drift region, and the peak breakdown voltage corresponds to a lightly doped n - -Doping concentration N in the GaN drift region d It has been improved.

[0024] III. Doping concentration N in different p-GaN regions a Below, lightly doped n - -Doping concentration N in the GaN drift region d Impact. For example... Figure 7 As shown, the doping concentration N in the p-GaN region a 5×10 16 cm -3 At that time, lightly doped n - -Doping concentration N in the GaN drift regiond The closer to 5×10 16 cm -3 p-GaN region for lightly doped n - - The GaN drift region can be fully depleted, improving the device's breakdown voltage. Meanwhile, the doping concentration N in the p-GaN region... a The larger the value, the more lightly doped n is required to reach the maximum breakdown voltage. - -Doping concentration N in the GaN drift region d The larger.

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to further limit the present invention. All equivalent changes made based on the description and drawings of the present invention are within the protection scope of the present invention.

Claims

1. A GaN-based lateral charge-balanced power diode, characterized in that, It includes a heterogeneous substrate (1); the upper end of the heterogeneous substrate (1) is provided with parallel silicon nitride (2) in the lateral direction, and silicon dioxide (3) is provided between the two silicon nitride layers. The two silicon nitride layers are arranged in a lateral staggered manner to form a curved channel. GaN (4) is grown within the curved channel, and an epitaxial layer with a core-shell structure is grown on the GaN. The structure of the epitaxial layer, from the inside to the outside, consists of a p-GaN region (5) and an n-GaN region (6). - -GaN drift region (6), the n - -One end of the GaN drift region is n + -GaN region (7); Where, n + - The GaN region (7) forms an ohmic contact with the cathode metal (9); n - The other end of the -GaN drift region (6) and the p-GaN region (5) come into contact with the anode metal (8) to form a Schottky contact.

2. The GaN-based lateral charge-balanced power diode according to claim 1, characterized in that, The n - -The GaN drift region (6) has a drift region length W1, wherein the n + -GaN region (7) has a length W2, where W1 is greater than W2, and p-GaN region (5) has a length W3; W1 is used to adjust the breakdown voltage and on-resistance of the device, W2 is used to reduce the cathode ohmic contact resistance, and W3 is used to adjust the charge balance relationship between p-GaN region and n⁻-GaN drift region and the electric field distribution inside the device.

3. The GaN-based lateral charge-balanced power diode according to claim 1, characterized in that, The n - The thickness of the GaN drift region (6) is Hn, and the thickness of the p-GaN region (5) is Hp, wherein the n - The doping concentration Nd and thickness Hn of the GaN drift region (6) are approximately equal to the doping concentration Na and thickness Hp of the p-GaN region (5), so that the n-GaN region under reverse bias is approximately equal to the thickness Hn of the p-GaN drift region (6). - -GaN drift region (6) and p-GaN region (5) mutually deplete each other and homogenize the electric field distribution of the drift region.

4. A method for fabricating a GaN-based lateral charge-balanced power diode, characterized in that, The process for preparing the diode according to any one of claims 1-3 includes the following steps: (a) Fabricating a Si3N4 / SiO2 / Si3N4 patterned template on a substrate, constructing a depth H c Greater than the opening width W c A curved channel is formed to create a high aspect ratio curved channel that allows the inclined growth of penetrating dislocations to terminate at the channel sidewall; GaN aspect ratio-constrained epitaxial growth is performed in the curved channel using organometallic chemical vapor deposition. (b) A core-shell structured GaN epitaxial layer is grown, consisting of p-GaN and n-GaN layers from the inside out. - -GaN and n + -GaN layer; (c) Dry etching exposes the p-GaN region on the left and the n-GaN region above. - -GaN region; (d) Masking, vapor deposition of Cr / Au metal, and n on the right side. + -GaN contact, forming a cathode ohmic contact; (e) Masking, evaporating Ni / Au metal, and then reacting it with the p-GaN and n-metal on the left side. - -GaN interface contact, forming Schottky contact.

5. The method for fabricating a GaN-based lateral charge-balanced power diode according to claim 4, characterized in that, In step 1, the width W of the curved channel opening c Less than 10μm.

6. The method for fabricating a GaN-based lateral charge-balanced power diode according to claim 4, characterized in that, In step 1, the aspect ratio of the curved channel is less than 0.5.

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