KR101103775B1 - GaN SEMICONDUCTOR DEVICE AND METHOD FOR FABRICATING THE SAME - Google Patents

Abstract

The present invention relates to a structure for increasing a breakdown voltage of a nitride semiconductor device and reducing a leakage current and a manufacturing method thereof.

A nitride-based semiconductor device of the present invention comprises: a nitride semiconductor substrate; A dielectric layer formed on the nitride semiconductor substrate and having at least one contact hole; A first electrode connected to the nitride semiconductor substrate through the contact hole and extending on the dielectric layer; And a second electrode connected to the nitride semiconductor substrate, wherein the first electrode includes a sloped field plate for uniformly spreading an electric field on the nitride semiconductor substrate under the corner of the first electrode when biased in the reverse direction The first electrode sidewall formed in the contact hole is formed to be inclined at an acute angle with respect to the upper surface of the nitride semiconductor substrate.

Nitride based semiconductor device, leakage current, yield resistance, field plate, depletion region

Description

TECHNICAL FIELD [0001] The present invention relates to a nitride semiconductor device and a method of manufacturing the same. BACKGROUND ART [0002]

The present invention relates to a nitride semiconductor device, and more particularly, to a structure and a manufacturing method thereof for increasing a breakdown voltage of a GaN semiconductor device and reducing a leakage current.

Gallium nitride (GaN) materials with wide band-gap characteristics are attracting much attention in the power semiconductor field because of their excellent forward characteristics, high breakdown voltage and low intrinsic carrier density, which are suitable for power switch applications. GaN material based semiconductor devices include Schottky barrier diodes, metal semiconductor field effect transistors, and high electron mobility transistors.

On the other hand, reverse leakage current characteristics are important characteristics not only in GaN devices but also in other semiconductor devices, and a large reverse leakage current increases the power consumption of the device and reduces the breakdown voltage. The most common cause of leakage currents in GaN devices is known as various defects due to lattice mismatch occurring during GaN substrate growth. In reverse operation of the device, the electric field is concentrated on the edge of the Schottky gate. Defects and dislocations on the GaN wafer accelerate the tunneling phenomenon of the Schottky gate edge, causing large leakage current and low yielding of the device. do. Therefore, when the field concentration at the Schottky gate edge is relaxed, the leakage current decreases and the breakdown voltage increases.

Methods for suppressing the leakage current of a GaN device include a floating gate, a field-modulating plate, an overlapping gate structure, a source extended field palette, Various field concentration mitigation structures such as multiple field plates are being developed.

FIG. 1 is a cross-sectional view schematically showing a general structure of an AlGaN / GaN high electron mobility transistor to which a field plate according to the related art is applied.

1, an AlGaN / GaN high electron mobility transistor to which a conventional field plate is applied includes a source electrode 120 and a drain electrode 130 spaced apart from each other on an AlGaN / GaN heterojunction epitaxial layer 110, A passivation layer 140 formed on the epitaxial layer 110 between the source electrode 120 and the drain electrode 130 and having a contact hole and a gate field plate 140 connected to the epitaxial layer through the contact hole. 150). The gate field plate 150 includes a field plate extension 150 'extending toward the drain on the passivation layer 140.

When the gate field plate is applied in this way, a depletion layer D is formed not only in the gate electrode but also in the lower end of the field plate extension 150 'when a reverse voltage is applied to the device, thereby alleviating and dispersing the electric field concentration at the edge portion of the gate electrode .

However, under the conventional field plate structure, as shown in FIG. 1, the depletion layer expands at a lower end (E) of the edge portion of the gate electrode in a sector shape, thereby limiting a leakage current and a breakdown voltage characteristic of the device.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a nitride-based semiconductor device capable of effectively alleviating electric field concentration at a corner portion of a gate electrode and a method of manufacturing the same.

To this end, the nitride-based semiconductor device of the present invention comprises a nitride semiconductor substrate; A dielectric layer formed on the nitride semiconductor substrate and having at least one contact hole; A first electrode connected to the nitride semiconductor substrate through the contact hole and extending on the dielectric layer; And a second electrode connected to the nitride semiconductor substrate, wherein the first electrode includes a sloped field plate for uniformly spreading an electric field on the nitride semiconductor substrate under the corner of the first electrode when biased in the reverse direction The sidewall of the contact hole is formed to have an inclined angle inclined at an acute angle with respect to the upper surface of the nitride semiconductor substrate, and the inclination angle of the sidewall of the contact hole is controlled by the etching selectivity.

Wherein the etch selectivity is determined by controlling the dilution rate of the etchant for etching the dielectric layer.

The nitride based semiconductor device is a high electron mobility transistor, wherein the first electrode is a gate electrode, and the second electrode is a source / drain electrode.

Wherein the nitride semiconductor substrate comprises an AlGaN / GaN heterojunction structure, wherein the nitride semiconductor device comprises a horizontal diode using a GaN heterojunction wafer, a GaN metal-semiconductor field effect transistor, a GaN Schottky barrier diode, a vertical GaN Schottky A barrier diode, and a GaN metal-insulator-semiconductor field-effect transistor.

A method of manufacturing a nitride semiconductor device according to the present invention includes: forming a nitride semiconductor layer on a substrate; And forming a contact hole by partially etching the dielectric layer through a photolithography and etching process after forming a dielectric layer on the nitride semiconductor layer, wherein a sidewall of the contact hole is formed in an inclined surface contact hole having an inclined angle inclined at an acute angle with respect to a surface of the nitride semiconductor layer ; Depositing a first electrode material on the sloped contact hole and the dielectric layer, and patterning the first electrode material to form a first electrode having a sloped side wall; And forming a second electrode, wherein an inclination angle of the inclined surface contact hole is controlled by an etch selectivity ratio.

Wherein the etch selectivity is determined by controlling the dilution rate of the etchant for etching the dielectric layer.

The first electrode is patterned by a lift-off process.

According to the present invention, since the depletion layer extends close to a straight line along the inclined plane at the lower end of the gate electrode corner, electric field concentration is significantly reduced as compared with the expansion in the conventional sector form. As a result, the leakage current is reduced, the breakdown voltage is increased, and the reverse characteristic of the device can be effectively improved without deteriorating the forward current-voltage characteristic.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the same components in the drawings are denoted by the same reference numerals and symbols as possible even if they are shown in different drawings. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

FIG. 2 is a schematic cross-sectional view of an AlGaN / GaN high electron mobility transistor (HEMT) 200 showing the structure of a first embodiment of a nitride semiconductor device to which an inclined surface field plate according to the present invention is applied.

2, an AlGaN / GaN high electron mobility transistor 200 according to the present invention includes a source electrode (not shown) disposed on a nitride semiconductor substrate 210 formed of an AlGaN / GaN heterojunction epitaxial layer 210, A dielectric layer 240 formed on the epitaxial layer 210 between the source electrode 220 and the drain electrode 230 and having a contact hole, And a gate electrode 250 (first electrode) formed to be connected to the epitaxial layer through a contact hole. The gate electrode 250 includes a field plate extension 250 'extending from the dielectric layer 240 toward the source electrode 220 and the drain electrode 230. The sidewall portion S' And an inclined surface structure inclined with respect to the upper surface of the epitaxial layer 210. The gate electrode 250 having the field plate extension 250 'may be a tapered field plate for uniformly developing an electric field to the nitride semiconductor substrate under the edge of the gate electrode in reverse bias In particular, when the side wall S is formed to be inclined, the depletion layer D 'under the edge of the gate electrode at the edge of the gate electrode is extended to a straight line E' Can be effectively mitigated.

FIG. 3 is a graph simulating the effect of field concentration relaxation according to the inclined plane structure. The AlGaN / GaN HEMT (.circle-solid.) With no field plate and the AlGaN / GaN HEMT And an AlGaN / GaN HEMT (DELTA) element to which a slope (30 DEG) field plate according to the present invention is applied. In this simulation, the length of the gate electrode is equal to 4 mu m, and the field plate extends 1 mu m toward the source electrode and 2 mu m toward the drain electrode, and the angle of the slope is 30 DEG.

As shown in FIG. 3, the electric field of the gate edge is reduced from 1.16e7 V / cm to 8.48e6 V / cm when the field plate is applied, and the electric field is decreased to 6.06e6 V / cm when the field plate is sloped do. That is, application of a field plate having a side wall perpendicular to that of a field plate is mitigated, and concentration of an electric field at a gate edge is further alleviated by applying an inclined field plate to the field plate having a side wall perpendicular Simulation can be confirmed.

A detailed structure and manufacturing method of the AlGaN / GaN high electron mobility transistor 200 having the slope field plate according to the present invention having the above-described structure will be described below.

2, the AlGaN / GaN heterojunction epitaxial layer 210 is formed on a semi-insulating 4H-SiC substrate 201 by a metal organic chemical vapor deposition (MOCVD) process, Layer 202, a GaN buffer layer 203, an AlGaN barrier layer 204, and a GaN cap layer 205.

In addition to the semi-insulating substrate, the substrate 201 may have a high resistance, be doped with n-type or p-type, and may use silicon carbide, silicon, sapphire or other suitable substrate material.

The crystal nucleation layer 202 is for minimizing defects due to crystal lattice mismatch between the substrate 201 and the nitride semiconductor layer 203 to be formed thereon.

The GaN buffer layer 203 and the AlGaN barrier layer 204 have a hetero structure such that AlGaN has a wider bandgap than that of GaN and a two dimensional electron barrier layer is formed between the GaN buffer layer 203 and the AlGaN barrier layer 204. [ To form a channel with a two-dimensional electron gas (2DEG) concentration. 2DEG has a high electron mobility and provides very high trans-conductance to HEMTs at high frequencies.

The GaN cap layer 205 is an epitaxial layer for improving the breakdown voltage and reducing the surface leakage current and the AlGaN barrier layer 204 and the GaN cap layer 205 are formed of an unintentionally doped (UID) Lt; RTI ID = 0.0 > breakdown voltage. ≪ / RTI > The GaN cap layer 205 may be omitted depending on the application field of the device.

The source electrode 220 and the drain electrode 230 are formed using an e-beam evaporator having a stacked structure of Ti / Al / Ni / Au (10 nm / 80 nm / 20 nm / And then a pattern is formed by a lift-off process.

The dielectric layer 240 is formed by, for example, depositing a silicon oxide film, a silicon nitride film, or the like by an ICP-CVD process, and then etching through a normal photolithography process and an etching process so that the side walls of the contact hole are inclined. By forming the contact hole sidewalls in such a manner as to be inclined, the lower sidewall of the gate field plate formed in the contact hole also has an inclined surface, and the angle of the inclined surface is determined by the inclination angle of the sidewall of the contact hole. The tilt angle of the contact hole sidewall is determined by the etch selectivity of the wet etch, and the etch selectivity can be easily controlled, for example, by changing the dilution rate of the etchant. For example, when the silicon oxide film is etched with an etchant diluted with a ratio of HF: NH ₄ F of 1:10, the inclination angle of the contact hole side wall is about 20 Degrees. If, rest of the processing conditions are the same, and HF: NH ₄ F was diluted biyueul 1: When 5 change in inclination angle of the contact hole, the side wall is about 35 ° ((b) of Fig. _4), HF: NH 4 F of the When the dilution analog is changed to 1:15, the inclination angle becomes about 15 (Fig. 4 (c)). Therefore, the inclination angle of the side wall of the contact hole is adjusted by changing the dilution ratio of the dielectric etchant according to the inclination angle of the gate field plate to be implemented. It is needless to say that the inclination of the sidewalls of the contact hole can be realized not only by the wet etching described in this embodiment but also by the dry etching process.

In the present embodiment, the gate electrode 250 has a sloped surface formed by inclining the bottom edge (contact hole sidewall portion) by about 20 DEG. By this sloped surface structure, when the reverse voltage is applied (reverse bias) And the depletion layer D 'extends near the straight line along the inclined surface at the edge portion E'. That is, by forming the lower edge portion of the gate electrode 250 to be inclined, a tapered field plate for uniformly developing an electric field on the nitride semiconductor substrate under the edge of the electrode during reverse bias is formed.

The gate electrode 250 forms a schottky contact with the epitaxial layer 210 through a contact hole and is formed on the contact hole and the dielectric layer 240 by an electron-beam evaporator in the same manner as the ohmic contact Ni / Au / Ni (Each having a thickness of 50 nm / 270 nm / 50 nm) is deposited, and then a pattern is formed by a lift-off process.

The inclined structure and the inclination angle of the bottom edge of the gate electrode 250 are optimized and set according to the device design such as the distance between the first electrode and the second electrode, the length of the field plate, the thickness of the dielectric layer, The side walls of the dielectric layer 240 can be easily adjusted by inclining them at a corresponding angle.

FIG. 5 is a graph illustrating the relationship between the gate leakage current of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 and the AlGaN / GaN high electron mobility transistor without a field plate according to the prior art, Fig.

5, when the gate-source voltage V _GS is -5 V and the drain-source voltage V _DS is 100 V, the leakage currents are 29.58 μA / mm and 49.18 nA / mm, respectively, The leakage current of the electron mobility transistor is reduced by about 1000 times as compared with the leakage current of the conventional high electron mobility transistor. From these results, it can be seen that the inclined surface field plate according to the present invention effectively suppresses the electric field concentration at the edge portion of the gate electrode compared to the conventional vertical surface field plate.

6 is a graph comparing the breakdown voltage characteristics of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 according to the present invention and an AlGaN / GaN high electron mobility transistor without a field plate according to the prior art . The breakdown voltage of the high electron mobility transistor according to the present invention is about 1400 V, whereas the breakdown voltage of the conventional high electron mobility transistor is about 1000 V, which indicates that the breakdown voltage characteristic is greatly improved by the present invention.

FIG. 7 is a graph comparing transmission characteristics of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 according to the present invention and an AlGaN / GaN high electron mobility transistor without a field plate according to the prior art. When the gate-source voltage is 0V, the maximum transconductances are 104.2mS / mm and 106.6mS / mm, respectively, and the drain currents are 294.1mA / mm and 293.7mA / mm, respectively.

FIG. 8 is a current-voltage characteristic curve of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 according to the present invention and an AlGaN / GaN high electron mobility transistor without a field plate according to the prior art. The drain voltage-current was measured while the gate voltage was lowered from 1V to -5V by 2V. Both devices maintained the pinch-off characteristic up to 20V and the maximum drain current was also similar.

5, 6, 7 and 8, when the slope field plate structure according to the present invention is applied, the leakage current can be effectively reduced and the breakdown voltage can be increased without deteriorating the forward characteristics of the GaN device have.

The slope field plate structure according to the present invention can be applied to a GaN metal-semiconductor field effect transistor (MESFET), a GaN Schottky barrier diode, a vertical GaN Schottky barrier diode, an AlGaN / GaN high electron mobility transistor, And a nitride-based semiconductor device such as a metal-insulator-semiconductor field-effect transistor (MOSFET).

FIG. 9 is a cross-sectional view of a horizontal diode using a GaN heterojunction wafer, showing a structure of a nitride semiconductor device according to a second embodiment of the present invention; FIG.

9, the horizontal diode includes a cathode 320 and an anode 330 spaced apart from each other on the AlGaN / GaN heterojunction epitaxial layer 310, a cathode 320 and an anode 330, And a dielectric layer (340) formed on the epitaxial layer (310). The anode electrode 330 has an inclined surface formed at an angle (preferably at an acute angle) with respect to the surface of the epitaxial layer 310 (the contact hole bottom surface) at the lower edge portion (the contact hole side wall portion) According to such an inclined surface structure, the anode electrode forms an inclined surface field plate which expands the electric field from the epitaxial layer 310 under the edge of the node electrode toward a straight line when a reverse voltage is applied (reverse bias).

10 is a cross-sectional view of a GaN metal-semiconductor field-effect transistor, showing a structure of a nitride-based semiconductor device to which an inclined field plate structure according to the present invention is applied, according to a third embodiment of the present invention.

10, the metal-semiconductor field effect transistor includes a source electrode 420 and a drain electrode 430 spaced apart from each other on a GaN substrate 410 and a source electrode 420 and a drain electrode 430 disposed between the source electrode 420 and the drain electrode 430, A dielectric layer 440 formed on the substrate 410 and having a contact hole and a gate electrode 450 having an inclined surface field plate structure connected to the GaN substrate 410 through the contact hole.

11 is a cross-sectional view of a GaN Schottky barrier diode showing the structure of a fourth embodiment of a nitride semiconductor device to which an inclined field plate structure according to the present invention is applied.

11, the GaN Schottky barrier diode includes a cathode electrode 520 and an anode electrode 530 having a slope field plate structure disposed on the GaN substrate 510 and a cathode electrode 520 and an anode electrode 530 And a dielectric layer formed on the GaN substrate 510.

FIG. 12 is a cross-sectional view of a vertical GaN Schottky barrier diode of a fifth embodiment of a nitride-based semiconductor device to which an inclined field plate structure according to the present invention is applied.

12, the vertical GaN Schottky barrier diode includes a dielectric layer 620 formed with a contact hole on a GaN substrate 610, a dielectric layer 620 formed of a sloped field plate structure formed to be connected to the GaN substrate 610 through a contact hole And an anode electrode 630 and a cathode electrode 640 connected to the back surface of the GaN substrate 610 by ohmic contact.

13 is a sectional view of a GaN metal-insulator-semiconductor field-effect transistor (MOSFET) showing the structure of a sixth embodiment of a nitride-based semiconductor device to which an inclined field plate structure according to the present invention is applied.

13, the GaN metal-insulator-semiconductor field-effect transistor includes a first dielectric layer 720 formed on a GaN substrate 710, a source electrode 730 disposed on the first dielectric layer 720, And a drain electrode 740 and a second dielectric layer 750 formed on the first dielectric layer 720 between the source electrode 730 and the drain electrode 740 and having a contact hole, And a gate electrode 760 having an inclined surface field plate structure extending over the second dielectric layer 750.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

FIG. 1 schematically shows a general structure of an AlGaN / GaN high electron mobility transistor to which a field plate according to the related art is applied,

2 is a view showing a first embodiment of a nitride semiconductor device to which an inclined surface field plate according to the present invention is applied,

FIG. 3 is a graph simulating the effect of field concentration mitigation according to a slope structure,

4 is a scanning electron microscope (SEM) photograph showing the inclination angle of the dielectric layer according to the dilution ratio of the etching agent,

FIG. 5 is a graph illustrating the relationship between the gate leakage current of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 and the AlGaN / GaN high electron mobility transistor without a field plate according to the prior art, FIG.

6 is a graph comparing breakdown voltage characteristics of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 according to the present invention and an AlGaN / GaN high electron mobility transistor without a field plate according to the prior art,

FIG. 7 is a graph comparing transmission characteristics of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 according to the present invention and an AlGaN / GaN high electron mobility transistor without a field plate according to the prior art,

FIG. 8 is a graph showing current-voltage characteristic curves of an AlGaN / GaN high electron mobility transistor (HEMT) of FIG. 2 according to the present invention and an AlGaN / GaN high electron mobility transistor without a field plate according to the prior art,

9 is a view showing a structure of a nitride semiconductor device according to a second embodiment of the present invention;

10 is a view showing a structure of a third embodiment of a nitride-based semiconductor device to which an inclined field plate structure according to the present invention is applied,

11 is a view showing a structure of a nitride semiconductor device according to a fourth embodiment of the present invention;

12 is a view showing a structure of a nitride semiconductor device according to a fifth embodiment of the present invention;

13 is a cross-sectional view of a GaN metal-insulator-semiconductor field-effect transistor (MOSFET) showing the structure of a nitride-based semiconductor device according to a sixth embodiment to which an inclined field plate structure according to the present invention is applied.

Claims (9)

A nitride semiconductor substrate; A dielectric layer formed on the nitride semiconductor substrate and having at least one contact hole; A first electrode connected to the nitride semiconductor substrate through the contact hole and extending on the dielectric layer; And And a second electrode connected to the nitride semiconductor substrate, Wherein the first electrode is formed so as to form an inclined surface field plate that uniformly spreads an electric field on the nitride semiconductor substrate under the corner of the first electrode when the first electrode is biased in a reverse direction, Wherein the inclined angle of the sidewall of the contact hole is controlled by the etching selectivity ratio and the angle between the sidewall of the contact hole and the upper surface of the dielectric layer is not perpendicular Semiconductor device. 2. The nitride based semiconductor device of claim 1, wherein the etch selectivity is determined by controlling a dilution rate of the etchant for etching the dielectric layer. The nitride based semiconductor device according to claim 1, wherein the nitride based semiconductor device is a high electron mobility transistor, wherein the first electrode is a gate electrode, and the second electrode is a source / drain electrode. The nitride based semiconductor device according to claim 3, wherein the nitride semiconductor substrate includes an AlGaN / GaN heterojunction structure. The nitride based semiconductor device of claim 1, wherein the nitride based semiconductor device comprises a GaN heterojunction wafer, a GaN metal-semiconductor field effect transistor, a GaN Schottky barrier diode, a vertical GaN Schottky barrier diode, a GaN metal- Wherein the nitride-based semiconductor device is one of a field-effect transistor and a field-effect transistor. Claims [1] An AlGaN / GaN heterojunction epitaxial layer formed on the substrate; A source electrode and a drain electrode spaced apart from each other on the epitaxial layer; A dielectric layer formed on the epitaxial layer between the source electrode and the drain electrode, the dielectric layer having a contact hole; And A Schottky junction with the epitaxial layer through the contact hole and a gate electrode extending onto the dielectric layer, The side walls of the contact holes are inclined at an acute angle with respect to the upper surface of the epitaxial layer so as to form an inclined surface field plate that uniformly spreads an electric field on the epitaxial layer below the corner of the gate electrode when reverse biased, Wherein an inclination angle of the sidewall of the contact hole is adjusted by an etching selection ratio, And an angle formed by a side wall of the contact hole and an upper surface of the dielectric layer is not perpendicular. Forming a nitride semiconductor layer on a substrate; And forming a contact hole by partially etching the dielectric layer through a photolithography and etching process after forming a dielectric layer on the nitride semiconductor layer, wherein a sidewall of the contact hole is formed in an inclined surface contact hole having an inclined angle inclined at an acute angle with respect to a surface of the nitride semiconductor layer ; Depositing a first electrode material on the sloped contact hole and the dielectric layer, and patterning the first electrode material to form a first electrode having a sloped side wall; And And forming a second electrode, The inclination angle of the inclined surface contact hole is controlled by the etching selectivity, Wherein an angle formed by a side wall of the contact hole and an upper surface of the dielectric layer is not perpendicular. 8. The method of claim 7, wherein the etch selectivity is determined by controlling a dilution rate of the etchant for etching the dielectric layer. 8. The method of claim 7, wherein the first electrode is patterned by a lift-off process.

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