KR100770132B1 - Gan semiconductor device - Google Patents

Abstract

A GaN semiconductor device is provided to increase a reverse breakdown voltage and to reduce leakage current by simultaneously designing a floating metal ring and a field plate. An epi-wafer(110) includes at least GaN-based semiconductor layer. A source electrode(120) and a drain electrode(130) are disposed apart from each other on the epi-wafer. A gate electrode(140) is arranged on the epi-wafer between the source electrode and the drain electrode. At least, one conductive floating metal ring(150) is positioned on the epi-wafer between the gate electrode and the drain electrode. A bias is not applied to the conductive floating metal ring. An insulating passivation layer(160) is formed to expose partially the gate electrode, the source electrode, and the drain electrode. A conductive field plate(170) is disposed on the passivation layer in order to be connected to the exposed gate electrode. The conductive field plate is formed to diffuse electric field concentrated on the gate electrode in an inverse bias state.

Description

Nitride-based semiconductor device {GaN SEMICONDUCTOR DEVICE}

1 is a cross-sectional view of an AlGaN / GaN high electron mobility transistor according to a first embodiment of the present invention;

FIG. 2 is a diagram illustrating leakage current characteristics of the AlGaN / GaN high mobility transistor of FIG. 1;

3 is a view showing switching characteristics of an AlGaN / GaN high electron mobility transistor according to an embodiment of the present invention;

4 is a cross-sectional view of a GaN metal semiconductor field effect transistor according to a second embodiment of the present invention;

5 is a cross-sectional view of a horizontal GaN Schottky barrier diode, according to a third embodiment of the present invention;

6 is a cross-sectional view of a horizontal GaN Schottky barrier diode formed over an AlGaN / GaN heterojunction epi wafer structure with high forward current characteristics, in accordance with a fourth embodiment of the present invention;

7 is a cross-sectional view of a vertical GaN Schottky barrier diode, in accordance with a fifth embodiment of the present invention;

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to nitride semiconductor devices, and more particularly, to a structure for increasing breakdown voltage and reducing leakage current of GaN semiconductor devices.

Recently, wide band-gap materials, such as gallium nitride (GaN) and silicon carbide (SiC), are in the spotlight in electric power systems. In particular, GaN has superior physical properties compared to other semiconductor materials. Previous studies have been made in semiconductor devices.

For example, GaN Schottky barrier diodes (SBDs) have high breakdown voltage, low leakage current and fast switching speed due to wide band-gap material characteristics and high critical field (> 3 MV / cm) characteristics. Excellent electrical properties. Accordingly, development of horizontal and vertical GaN Schottky barrier diodes having higher breakdown voltage and lower ON-resistance characteristics than conventional silicon devices is under development.

In order to improve the forward and reverse characteristics of GaN Schottky junction diodes, metals such as Pt, Ir, and Pd are used as the Schottky junction metals, and the characteristics of Schottky barrier diodes mainly affect Schottky metals and surface conditions. Because I receive.

However, since metals exhibiting excellent characteristics as Schottky junctions are expensive, a method of improving the operating characteristics of Schottky junctions using a general metal such as Ni is required.

Meanwhile, a planar floating guard ring is mainly used as an edge termination technique for increasing the breakdown voltage of a semiconductor device.

However, since GaN devices are difficult to do with P-type doping, it is difficult to design horizontal floating guard rings at the current technology level.

Therefore, the present invention has been made to solve the above problems of the prior art, an object of the present invention is to provide a GaN-based semiconductor device that significantly improves the breakdown voltage characteristics of the nitride-based semiconductor device and reduces the leakage current .

In order to achieve the above object, a GaN-based semiconductor device according to an embodiment of the present invention, an epi wafer having at least a GaN-based semiconductor layer; Source and drain electrodes spaced apart from each other on the epi wafer; A gate electrode disposed on the epi wafer between the source electrode and the drain electrode; At least one conductive floating metal ring disposed on the epi wafer between the gate electrode and the drain electrode and to which no bias is applied; An insulating passivation layer formed to expose at least a portion of the gate electrode, the source electrode, and the drain electrode; And a conductive field plate disposed on the passivation layer so as to contact the exposed gate electrode and dissipating an electric field concentrated at the gate electrode during reverse biasing.

When the nitride semiconductor device is a high electron mobility transistor, the epi wafer comprises a substrate; An epitaxial wafer including an AlN layer, a GaN buffer layer, an AlGaN barrier layer, and a GaN cap layer, which are sequentially stacked on the substrate, and wherein the nitride wafer is a metal semiconductor field effect transistor; It characterized in that it comprises an AlN layer, GaN buffer layer sequentially stacked on the substrate.

According to another embodiment of the present invention, a GaN semiconductor device includes: an epi wafer including at least a GaN semiconductor layer; An anode electrode and a cathode electrode spaced apart from each other on the epi wafer; At least one conductive floating metal ring disposed on the epi wafer between the anode electrode and the cathode electrode and free from bias; An insulating passivation layer formed to expose at least a portion of the anode electrode and the cathode electrode; And a conductive field plate disposed on the passivation layer so as to contact the exposed anode electrode and dispersing an electric field concentrated on the anode electrode during reverse biasing.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the same components in the drawings are denoted by the same reference numerals and symbols as much as possible even if shown on different drawings. In addition, in describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

1 is a cross-sectional view of an AlGaN / GaN high electron mobility transistor 100 showing an embodiment of a GaN semiconductor device according to the present invention.

Referring to FIG. 1, an AlGaN / GaN high electron mobility transistor 100 according to the present invention may include a source electrode 120 and a drain electrode 130 spaced apart from each other on an AlGaN / GaN heterojunction epitaxial wafer 110. ; A gate electrode 140 formed between the source electrode 120 and the drain electrode 130; A floating metal ring (FMR) 150 formed between the gate electrode 140 and the drain electrode 130; A passivation film 160 formed on the entire surface except the electrode portion and a field plate 170 formed on the passivation film 160 to be connected to the gate electrode 130.

The AlGaN / GaN heterojunction epitaxial wafer 110 is formed of AlN crystal nucleation layer 102, GaN buffer layer 103, and AlGaN barrier grown by metal organic chemical vapor deposition (MOCVD) on a substrate 101 such as sapphire or SiC. Layer 104 and GaN cap layer 105.

The AlN crystal nucleation layer 102 is for minimizing defects due to mismatch of crystal lattice between the substrate and the GaN-based semiconductor, and growing the GaN-based semiconductor epistructure on the substrate.

GaN buffer layer 103 and AlGaN barrier layer 104 is a hetero-structure, AlGaN has a wider bandgap than GaN, the two-dimensional electron gas between the GaN buffer layer 103 and AlGaN barrier layer 104 form a channel having a (two-dimensional electron gas; 2DEG) concentration. 2DEG has high electron mobility and provides very high trans-conductance for HEMT at high frequencies.

The GaN cap layer 105 is an epitaxial layer for improving breakdown voltage and reducing surface leakage current. The GaN cap layer 105 may further increase the breakdown voltage of the device by not doping the AlGaN barrier layer 104 and the GaN cap layer 105. The GaN cap layer 105 may not be designed depending on the device application.

The source electrode 120 and the drain electrode 130 are ohmic junctions of Ti / Al / Ni / Au (5/20/20/300 nm thick) and are deposited by an e-beam evaporator. And a pattern is formed by a lift-off process.

The gate electrode 140 is a Schottky junction, which is a stacked structure of Pt / Mo / Ti / Au (5/20/20/300 nm thick, respectively) and is deposited by an e-beam evaporator like an ohmic junction. The pattern is formed by a lift-off process. Pt during Schottky junction has high breakdown voltage and low gate leakage current due to high metal work function, and Mo has the advantage of enabling stable operation at high temperature due to high melting point.

The floating metal ring 150 is a Schottky junction and has a laminated structure of Pt / Mo / Ti / Au (each of 5/20/20/300 nm thickness). The floating metal ring 150 is intended to prevent breakdown due to a high electric field being caught at the Schottky junction edge by depletion region of the GaN device being concentrated at the Schottky junction during reverse bias. In other words, the breakdown voltage of the GaN device is improved by diffusing the depletion region of the GaN device along the floating metal ring to mitigate the field concentration at the Schottky junction edge. In the drawing of this embodiment, the case of one floating metal ring is shown as an example, but as the number of floating metal rings increases, the electric field concentration under the main Schottky junction decreases, so that the leakage current decreases. Therefore, many designs are designed at optimized intervals in consideration of the distance between the source electrode and the drain electrode, the width of the floating metal ring, and the yield resistance.

The passivation film 160 may be implemented as a dielectric film such as a silicon oxide film or a silicon nitride film.

A field plate 170 is formed on the passivation film 160 to connect with the gate electrode 130, and reduces the leakage current by dispersing the concentration of the electric field under the main Schottky junction. The thickness and length of the field plate are closely related to the thickness of the passivation film 160, the length of the floating metal ring 150, the spacing between the gate electrode 140 and the drain electrode 130, and the breakdown voltage of the device. Therefore, the field plate 170 is optimized in consideration of the maximum value of the electric field applied to the end of the passivation film 160, the thickness of the field plate can be connected at least the step between the gate electrode 130 and the passivation film 160. It is preferable to form so much.

The manufacturing process of the AlGaN / GaN high electron mobility transistor having the above structure is as follows.

Referring back to FIG. 1, 40 μm thick AlN was deposited on a C-plane sapphire substrate 101, a 3 μm thick unintentionally doped GaN buffer layer 103, a 33 nm thick undoped layer. An AlGaN barrier layer 104 and a 5 nm thick undoped GaN cap layer 105 are deposited one after the other. The AlGaN barrier layer 104 and the GaN cap layer 105 do not dope for high breakdown voltage of the device.

By inductively coupled plasma etching, the AlGaN / GaN heterojunction epi wafer is etched about 300 nm to form a mesa structure, which serves to separate devices.

Subsequently, a photoresist pattern to be used as a mask for forming the source electrode 120 and the drain electrode 130 is formed on the GaN cap layer 105, and then a solution in which HCl and DI water are mixed at a 1: 1 ratio is formed. To remove the natural oxide film on the surface. In this case, the photoresist pattern is formed to expose the upper portion of the GaN cap layer 105 of the predetermined source electrode 120 and the drain electrode 130.

Subsequently, an ohmic junction having a Ti / Al / Ni / Au structure (5/20/20/300 nm thickness) structure on the GaN cap layer 105 exposed through a deposition process using an e-beam evaporator. After the formation of the photoresist, the source electrode 120 and the drain electrode 130 are formed by removing the photoresist by a lift-off process. After ohmic junction deposition, annealing is performed at 850 ° C. using RTA for 30 seconds in an N ₂ gas atmosphere.

The photoresist pattern to be used as a mask is formed on the GaN cap layer 105 when the gate electrode 140 and the floating metal ring 150 are formed. In this case, the photoresist pattern is formed such that the predetermined gate electrode 140 and the upper portion of the GaN cap layer 105 of the floating metal ring 150 are exposed.

A Schottky junction with a Pt / Mo / Ti / Au (5/20/20 / 300nm thickness) structure is formed on the GaN cap layer 105 exposed through a deposition process using an e-beam evaporator. After the photoresist is removed by a lift-off process, the gate electrode 140 and the floating metal ring 150 are formed. In this embodiment, the coating metal ring 150 is formed by the Schottky junction in the gate electrode 140 forming step, but may be formed by the ohmic bonding when the source electrode 120 and the drain electrode 130 are formed. have. In this case, the floating metal ring 150 is formed to have a length similar to that of the gate electrode 140 (for example, 3 μm), and the distance from the gate electrode 140 is about 3 μm. A distance between the gate electrode 140 and the drain electrode 130 is about 20 μm, and a distance between the gate electrode 140 and the source electrode 120 is about 3 μm.

After the gate electrode 140 is formed, a 350 nm-thick silicon oxide layer 160 is deposited using the passivation layer 160 by inductively coupled plasma-chemical vapor deposition (ICP-CVD).

The passivation layer 160 is etched to expose the source electrode 120, the drain electrode 130, and the gate electrode 140, and then a Schottky junction is formed on the passivation layer 160 to be connected to the gate electrode 140. The material is deposited to form the metal field plate 170. At this time, the length of the metal field plate 170 is about 9um.

FIG. 2 illustrates leakage current characteristics of the AlGaN / GaN high electron mobility transistor of FIG. 1 according to an embodiment of the present invention, and shows the measured results while increasing the reverse voltage from 0V to 200V. For reference, the solid line display shows the leakage current characteristics when the metal field plate 170 is provided, and the dotted line shows the leakage current characteristics when the metal field plate 170 is not provided.

Referring to FIG. 2, the metal field plate 170 has a leakage current of 8.5 mA at a reverse voltage of 200V. In contrast, when the metal field plate 170 is not provided, the reverse voltage has a leakage current of 88 mA at 200V. That is, the additional metal field plate design has a reduced leakage current characteristic.

On the other hand, the breakdown voltages are 484 V and 250 V, respectively, with and without the metal field plate 170. Three of the electric field peaks present in the device at the time of reverse bias have a floating metal ring, but four additional metal field plates are designed to further increase the breakdown voltage. The measured on-resistance are each 4.2mΩ-cm ² and 4.5mΩ-cm ^2, the difference between the two values is negligible levels.

3 illustrates switching characteristics of an AlGaN / GaN high electron mobility transistor according to an exemplary embodiment of the present invention, and illustrates an inductor load switching operation. The gate-source voltages applied to the device are 0V (on-state) and -6V (off-state), the drain voltage is 20V, and the current has a switching characteristic of the device at 0.2A.

When the operating frequency is 200 kHz, the turn-on time and turn-off time of the AlGaN / GaN high electron mobility transistor according to the present invention are 40ns and 36ns, respectively. That is, it can be seen that it has a fast switching characteristic without the RF dispersion effect due to the GaN trap. The proposed device can be used for power semiconductors that require high-speed switching.

Meanwhile, the present invention can be applied to GaN metal semiconductor field effect transistors (MESFET), horizontal GaN diodes, and vertical GaN diodes as well as AlGaN / GaN high electron mobility transistors as a design for increasing breakdown voltage and reducing leakage current. .

4 is a cross-sectional view of a GaN metal semiconductor field effect transistor (MESFET) according to a second embodiment of the present invention.

Referring to FIG. 4, the metal semiconductor field effect transistor 200 according to the present invention may include a source electrode 220 and a drain electrode 230 spaced apart from each other on the epi wafer 210; A gate electrode 240 formed between the source electrode 220 and the drain electrode 230; A floating metal ring (FMR) 250 formed between the gate electrode 240 and the drain electrode 230; A passivation film 260 is formed on the entire surface except the electrode portion, and a field plate 270 is formed on the passivation film 260 to be connected to the gate electrode 230.

The epi wafer 210 includes an AlN crystal nucleation layer 202 and a GaN buffer layer 203 grown by metal organic chemical vapor deposition (MOCVD) on a substrate 201 such as sapphire, SiC, or the like.

This embodiment is the same as the structure of the first embodiment except that the epi wafer 210 is not provided with the AlGaN barrier layer and the GaN cap layer, and thus the detailed description thereof will be omitted.

5 is a cross-sectional view of a horizontal GaN Schottky barrier diode, in accordance with a third embodiment of the present invention.

Referring to FIG. 5, the horizontal GaN Schottky barrier diode 300 according to the present invention includes an anode electrode 320 and a cathode electrode 330 spaced apart from each other on an epi wafer 310; A floating metal ring (FMR) 350 formed between the anode electrode 320 and the cathode electrode 330; A passivation film 360 and a field plate 370.

6 is a cross-sectional view of a horizontal GaN Schottky barrier diode formed over an AlGaN / GaN heterojunction epi wafer 410 structure with high forward current characteristics in accordance with a fourth embodiment of the present invention.

7 is a cross-sectional view of a vertical GaN Schottky barrier diode, in accordance with a fifth embodiment of the present invention.

Referring to FIG. 7, the vertical GaN Schottky barrier diode 500 according to the present invention includes an anode electrode 520 and a cathode electrode 530 disposed on and under the GaN bulk wafer 510, respectively; A floating metal ring (FMR) 550 disposed to be spaced apart from the anode electrode 520; A passivation film 560 and a field plate 570.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention.

As described above, the present invention designs the floating metal ring and the field plate simultaneously in the GaN semiconductor device structure to increase the reverse breakdown voltage and reduce the leakage current.

In addition, the present invention has the advantage that does not deteriorate other electrical characteristics of the GaN device.

The present invention is also applicable to GaN metal semiconductor effect transistors and GaN Schottky barrier diodes as well as AlGaN / GaN high electron mobility transistors. Therefore, the present invention can be usefully used to increase breakdown voltage and decrease leakage current of GaN devices used as rectifier diodes, micro amplifiers or power switches.

Claims (7)

An epi wafer having at least GaN-based semiconductor layers; Source and drain electrodes spaced apart from each other on the epi wafer; A gate electrode disposed on the epi wafer between the source electrode and the drain electrode;  At least one conductive floating metal ring disposed on the epi wafer between the gate electrode and the drain electrode and to which no bias is applied; An insulating passivation layer formed to expose at least a portion of the gate electrode, the source electrode, and the drain electrode; And a conductive field plate disposed over the passivation layer so as to contact the exposed gate electrode and disperse an electric field concentrated at the gate electrode during reverse biasing. The semiconductor wafer of claim 1, wherein the nitride semiconductor device is a high electron mobility transistor. A substrate; A nitride-based semiconductor device comprising an AlN layer, a GaN buffer layer, an AlGaN barrier layer and a GaN cap layer sequentially stacked on the substrate. The semiconductor wafer of claim 1, wherein the nitride semiconductor device is a metal semiconductor field effect transistor. A substrate; A nitride-based semiconductor device comprising an AlN layer, GaN buffer layer sequentially stacked on the substrate. An epi wafer having at least GaN-based semiconductor layers; An anode electrode and a cathode electrode spaced apart from each other on the epi wafer;  At least one conductive floating metal ring disposed on the epi wafer between the anode electrode and the cathode electrode and free from bias; An insulating passivation layer formed to expose at least a portion of the anode electrode and the cathode electrode; And a conductive field plate disposed on the passivation layer so as to contact the exposed anode electrode, and having a conductive field plate for dispersing an electric field concentrated on the anode electrode during reverse biasing. The epitaxial wafer of claim 4, wherein the nitride semiconductor device is a horizontal GaN Schottky barrier diode. A substrate; A nitride-based semiconductor device comprising an AlN layer, GaN buffer layer sequentially stacked on the substrate. 6. The epi wafer of claim 5, wherein the epi wafer is The nitride-based semiconductor device further comprises an AlGaN barrier layer and a GaN cap layer sequentially stacked on the GaN buffer layer. GaN bulk wafers; An anode electrode and a cathode electrode disposed on an upper surface and a lower surface of the GaN bulk wafer, respectively; At least one conductive floating metal ring spaced apart from the anode and not biased; An insulating passivation layer formed to expose at least a portion of the anode electrode; And a conductive field plate disposed on the passivation layer so as to contact the exposed anode electrode and disperse an electric field concentrated on the anode electrode in reverse bias.

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