KR101008272B1 - Normally off nitride high electron mobility transistor and method for manufacturing thereof - Google Patents

Abstract

The present invention relates to a high electron mobility transistor and a method of manufacturing the same, and more particularly, to form a low Al content of the lower portion of the gate electrode of the barrier layer (AlGaN) to locally prevent the formation of the 2DEG layer to improve the normal off characteristics. The present invention relates to a nitride-based high electron mobility transistor having a normal off characteristic that can be implemented and a method of manufacturing the same.

A nitride-based high electron mobility transistor having a normal-off characteristic of the present invention and a method for manufacturing the same include: a buffer layer formed on a substrate and including a 2DEG layer discontinuously present; The buffer layer is formed on a predetermined region of the upper, Al _y Ga _{1 -} a first barrier layer made of _y N; A second barrier layer formed on the buffer layer except for the region where the first barrier layer is formed and formed of Al _x Ga _{1- x} N; A gate electrode formed on the first barrier layer; And a source electrode and a drain electrode formed at both sides of the gate electrode.

 High electron mobility transistor (HEMT), nitride system, normal off

Description

Nitride-based high electron mobility transistor having a normal off characteristic and a method for manufacturing the same

The present invention relates to a high electron mobility transistor and a method of manufacturing the same, and more particularly, to form a low Al content of the lower portion of the gate electrode of the barrier layer (AlGaN) to locally prevent the formation of the 2DEG layer to improve the normal off characteristics. The present invention relates to a nitride-based high electron mobility transistor having a normal off characteristic that can be implemented and a method of manufacturing the same.

In general, semiconductor devices such as field effect transistors (FETs) and high electron mobility transistors (HEMTs) for the application of semiconductor materials such as Si and GaAs to low power and low frequency (in the case of Si) Used extensively in

However, Si has a low electron mobility, resulting in high source resistance, which severely degrades the high-performance gain. GaAs has higher electron mobility and lower source resistance than Si, allowing it to operate at higher frequencies, but with a relatively narrow bandgap and breakdown. Because of the low breakdown voltage, GaAs-based HEMTs cannot provide high power at high frequencies.

Therefore, in high power and high frequency applications, attention has been paid to nitrides of group III elements, that is, wide bandgap semiconductor materials such as GaN-based compound semiconductors. GaN compound semiconductor has higher breakdown voltage, electron saturation rate and thermal / chemical stability than other semiconductor materials. Therefore, next generation wireless and satellite communication system requiring high power and high frequency characteristics, high temperature and heat resistance The application range is expanding to the field which has limitation with existing semiconductor materials such as engine control system which is required.

In particular, HEMTs using GaN / Al _x Ga _{1 - x} N have high electron density (above 1 × 10 ¹³ / cm ² ), high breakdown voltage, wide bandgap, large conduction band offset, It shows high electron mobility (1500cm ² / Vs at room temperature) and electron saturation rate.

In a high electron mobility transistor (HEMT), a 2DEG (two-dimensional electron gas) layer is formed by heterojunction of two semiconductor materials having different band gap energies. The 2DEG layer is used as a current channel between the drain electrode and the source electrode, and the current flowing through the current path is controlled by a bias voltage applied to the gate electrode.

However, a typical HEMT device has a normally on characteristic. In order to turn off the HEMT element of the normal-on characteristic, a negative power source for negative potential of the gate electrode is required, and the electric circuit becomes expensive. In addition, the HEMT of the normal-on characteristic may cause excessive current to flow when the power is turned on, and thus a special circuit for suppressing the excessive current is required.

1 is a view showing the structure of a conventional high electron mobility transistor.

In the conventional HEMT, the substrate 110, the transition layer 120, the buffer layer 130, the 2DEG layer 140, and the barrier layer 150 are sequentially formed, and the source electrode 160, The drain electrode 170 and the gate electrode 180 are included.

The charges accumulated by the polarity difference of the stacked AlGaN / GaN epi form 2DEG (2-dimensional electron gas) and the amount of current flowing through the 2DEG layer is controlled by the gate. Due to the characteristics of the HEMT structure, there is always a 2DEG layer, so that the device is normally on, and the device is always on. Therefore, voltage must be applied to write the device. There is a point.

2 is a view showing the structure of another conventional high electron mobility transistor.

In the past, it has been attempted to obtain normal off characteristics by forming a thin barrier layer made of AlGaN. When the barrier layer is formed thin, the electric field due to piezo polarization based on the heterojunction between the barrier layer and the 2DEG layer is weakened, and the electron concentration of the 2DEG layer is reduced. At this time, if an electric field based on a potential difference in the absence of a bias voltage is applied between the 2DEG layer having a reduced electron concentration and the gate electrode, the 2DEG layer immediately below the gate electrode is lost. For this reason, in a state where a bias voltage is not applied to the gate electrode, no current flows between the drain and the source, and the state is turned off.

However, when the barrier layer is formed as a whole, there is a problem that the electron concentration is lowered even in the 2DEG layer other than directly under the gate electrode, and the on-resistance between the drain and the source is increased.

Therefore, in order to solve such a problem, as shown in FIG. 2, only the barrier layer 150 under the gate electrode 180 is thinned to obtain a normal off characteristic. However, if this method is adopted, damage to the semiconductor crystals occurs when the barrier layer 150 is formed thin by etching, thereby deteriorating the electrical characteristics of the HEMT. In addition, it is difficult to achieve the selective etching of the barrier layer 150 easily and accurately, and there exist technical difficulties such as unnecessary insulating film formation. Because of this problem, HEMT of normal off has not been put to practical use at present.

The present invention devised to solve the problems of the prior art as described above is to form a low Al content of the lower portion of the gate electrode of the barrier layer (AlGaN) to locally prevent the formation of the 2DEG layer to implement the normal off characteristics It is an object of the present invention to provide a nitride-based high electron mobility transistor having a normal off characteristic and a method of manufacturing the same.

In addition, the present invention enables the generation and control of the 2DEG layer according to the gate voltage by locally suppressing the formation of the 2DEG layer only in the lower region of the gate electrode, and minimizing the resistance by keeping the 2DEG layer still in the source-drain region. Another object of the present invention is to provide a nitride-based high electron mobility transistor having a normal-off characteristic for forming a high output device, and a method of manufacturing the same.

The object of the present invention is formed on top of the substrate, the buffer layer comprising a discontinuous 2DEG layer; A first barrier layer formed on a predetermined region above the buffer layer and formed of Al _y Ga _1-y N; A second barrier layer formed on the buffer layer except for the region where the first barrier layer is formed and formed of Al _x Ga _{1 - x} N; A gate electrode formed on the first barrier layer; And a nitride-based high electron mobility transistor having normal-off characteristics including source and drain electrodes formed on both sides of the gate electrode.

In addition, the composition of Al _x Ga _{1 - x} N and Al _y Ga _{1 - y} N of the present invention preferably satisfies x>y> 0, and x is made to satisfy 0 <x <1.

In addition, the 2DEG layer of the present invention is preferably formed in the lower portion of the gate electrode discontinuously.

In addition, the height of the first barrier layer and the height of the second barrier layer of the present invention is preferably formed to be the same.

In addition, the first barrier layer of the present invention is preferably made in the form covering the upper portion of the second magnetic barrier layer.

In addition, another object of the present invention is a first step of forming a buffer layer made of a nitride-based semiconductor on the substrate; Forming a patterned oxide film on a predetermined region over the buffer layer; A third step of forming a second barrier layer by growing Al _x Ga _{1 - x} N to the oxide layer height on the exposed buffer layer because the oxide layer is not formed; A fourth step of removing the oxide film; A fifth step of growing a _y N forming the first barrier _layer, the oxide film is removed Al _y Ga ₁ in the exposed areas; A sixth step of depositing a metal on the second barrier layer and then performing heat treatment to form source and drain electrodes; And a seventh step of forming a gate electrode by depositing a metal on the first barrier layer, thereby manufacturing a nitride-based high electron mobility transistor having a normal off characteristic.

In addition, the composition of Al _x Ga _{1 - x} N and Al _y Ga _{1 - y} N of the present invention preferably satisfies x>y> 0, and x is made to satisfy 0 <x <1.

In addition, the first barrier layer of the present invention is preferably formed by selectively growing Al _y Ga _{1 - y} N to the height of the second barrier layer.

In addition, the first barrier layer of the present invention is preferably formed to grow Al _y Ga _{1 - y} N to cover the second barrier layer.

In addition, it is preferable that the first barrier layer and the second barrier layer of the present invention are formed on the buffer layer to form a discontinuous 2DEG layer on the lower portion of the gate electrode.

In addition, the source electrode and the drain electrode of the present invention is preferably located on both sides of the gate electrode and formed in contact with the 2DEG layer.

In addition, the heat treatment of the sixth step of the present invention is preferably carried out at 600 to 1200 ℃.

In addition, the fourth step of removing the oxide film of the present invention is preferably carried out by wet etching using HF.

Accordingly, the nitride-based high electron mobility transistor having a normal off characteristic of the present invention and a method of manufacturing the same have a low Al content in the lower portion of the gate electrode of the barrier layer (AlGaN), thereby preventing the formation of the 2DEG layer and improving the normal off characteristics. There is a significant and advantageous effect of enabling this.

In addition, the nitride-based high electron mobility transistor having a normal-off characteristic of the present invention and a method of manufacturing the same are capable of generating and adjusting the 2DEG layer according to the gate voltage by locally removing only the lower region of the gate electrode. There is a significant and advantageous effect of maintaining a 2DEG layer in the source-drain electrode region to minimize the resistance to form a high output device.

The terms or words used in this specification and claims are not to be construed as being limited to their ordinary or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best describe their invention. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

Therefore, the embodiments described in the specification and the drawings shown in the drawings are only the most preferred embodiment of the present invention and do not represent all of the technical idea of the present invention, various modifications that can be replaced at the time of the present application It should be understood that there may be equivalents and variations.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

3 to 8 are cross-sectional views illustrating a method of manufacturing a nitride-based high electron mobility transistor according to a first embodiment of the present invention.

The nitride-based high electron mobility transistor of the present invention includes a substrate 210, a transition layer 220, a buffer layer 230, a 2DEG layer (two-dimensional electron gas layer 240), and a barrier layer 250. The source electrode 260, the drain electrode 270, and the gate electrode 280 are provided.

The barrier layer 250 is composed of a first barrier layer 252 and a second barrier layer 251. The barrier layer 250 has a composition in which the first barrier layer 252 and the second barrier layer 251 are formed differently so that electrons move. The 2DEG layer 240 may be partially discontinuous so that the nitride-based high electron mobility transistor of the present invention exhibits a normal off characteristic. The lower the Al composition, the smaller the lattice constant difference between the barrier layer 250 and the buffer layer 230 is, thereby reducing the band gap and the polarity difference, thereby suppressing the formation of the 2DEG 240.

Looking at the manufacturing method of the nitride-based high electron mobility transistor having a normal off characteristics of the present invention.

First, as shown in FIG. 3, after forming a buffer layer 230 having a high resistance on the substrate 210, a patterned oxide layer 290 is formed on a predetermined region above the buffer layer 230. In this case, the portion where the oxide film 290 is formed is the same range as the portion where the gate electrode 280 is formed.

The transition layer 220 may be further formed before the buffer layer 230 is formed on the substrate 210. The transition layer 210 is composed of several layers including GaN, AlGaN, AIN, InGaAIN, etc. in various orders to alleviate stress due to mismatch between the substrate and the hetero-epitaxial layer. There may be.

The substrate 210 may be any one selected from substrates such as silicon (Si), sapphire (Al ₂ O ₃ ), silicon carbide (SiC), and the like, and the silicon substrate may be a substrate such as (100) or (111). 3C, 4H, 6H and 15R polytypes and the like can be used as the silicon carbide substrate.

The buffer layer 230 is made of a nitride semiconductor and is preferably formed of undoped gallium nitride (GaN) to which impurities are not added. The gallium nitride buffer layer 230 may be formed by an epitaxial growth method, for example, trimethylgallium (TMG) and ammonia as sources of Ga and N, respectively, and hydrogen as a carrier gas at a temperature of 800 to 1200 ° C. The epitaxial layer of gallium nitride is grown using.

In the case where the substrate is a sapphire substrate, due to the difference in lattice constant and thermal expansion coefficient with the gallium nitride buffer layer, the cleaning conditions and the growth of the low temperature buffer layer at the initial stage of film growth become important.

The thickness of the buffer layer 230 is preferably adjusted within the range of 0.5 to 15 μm, and the buffer layer 230 may be formed of a group 3-5 compound semiconductor other than gallium nitride.

Next, as shown in FIG. 4, the second barrier layer 251 is formed by growing Al _x Ga _{1 - x} N to the height of the oxide film 290 on the exposed buffer layer 230 because no oxide film 290 is formed. do. After removing the oxide film 280 by wet etching using a solution containing HF as shown in FIG. 5, Al _y Ga _{1 - y} N is grown in the exposed region by removing the oxide film 290 as shown in FIG. 6. One barrier layer 252 is formed.

An epitaxial growth method is used to grow Al _y Ga _{1 - y} N, and it is preferable to selectively grow to grow to the height of the second barrier layer 251 without being overgrown. When the first barrier layer 252 is overgrown, a step of selectively planarizing using an etchbag process or a chemical mechanical polishing (CMP) process may be further added.

In the present invention, the first barrier layer 252 and the second barrier layer 251 are formed through the process of FIGS. 4 to 6 to form a barrier layer 250 having a partly different Al content.

The barrier layer 250 formed on the buffer layer 230 is formed of a nitride semiconductor having a lattice constant different from that of the buffer layer 230. Preferably, an AlGaN-based material is used and serves to supply electrons.

In the present invention, the barrier layer 250 is composed of Al _x Ga _{1 - x} N (251) and Al _y Ga _{1 - y} N (252) components so that the Al content of the lower region of the gate electrode 280 is formed to be low. to be. That is, the gate electrode 280, the lower region is Al _y Ga ₁ of the barrier layer ₍₂₅₀₎ to _x N film _{(251) y} N film 252 is made and the gate region other than the electrode lower portion is Al _x Ga ₁ to And satisfy x>y> 0. At this time, x is a numerical value which satisfies 0 <x <1, Preferably it is 0.1-0.9.

This does not mean only the case where the mole fractions of Al, Ga, and N exactly match. If the molar fraction of Al is too high, it will increase the electron density, but cracks will degrade the crystal quality and make the growth of AlGaN difficult. Therefore, it is preferable to increase the mole fraction of Al if there is no problem of crystal or transient current.

In an embodiment of the present invention, x is adjusted to 0.3 and y to 0.1 to form a barrier layer, and the present invention is not limited thereto.

The 2DEG layer (2D Electromagnetic Gas) 240 is generated while the barrier layer 250 is formed on the buffer layer 230. AlGaN-based material, which forms the barrier layer 250, has a larger bandgap than GaN, which is the material of the buffer layer 230, and when the two materials are bonded together, the discontinuity in the energy bandgap results in a larger band gap. The free band moves into a small bandgap material. These electrons accumulate at the interface between these layers to form the 2DEG layer 240, and act as a channel for allowing current to flow between the source and drain electrodes. As the Al content increases, the 2DEG 240 is formed at a higher concentration.

In the present invention, a part of the barrier layer 250, that is, a part of the barrier layer under the gate electrode, is formed to have a different composition to implement a normal off characteristic. The Al content of the lower region of the gate electrode 280 of the barrier layer 250 is formed to be low.

When the Al content decreases, the stress is released due to the reduction of the lattice constant difference between the buffer layer 230 and the barrier layer 250, and the threshold voltage is increased while the piezoelectric effect disappears, thereby preventing the formation of the 2DEG layer 240. Because. Only the lower region of the gate electrode can locally remove the 2DEG layer, thereby realizing a normal off state, and the 2DEG layer can be generated and controlled according to the gate voltage. In addition, it is possible to maintain a high concentration of 2DEG layer in the source-drain electrode region, thereby minimizing the resistance and forming a high output device.

As the Al concentration of the barrier layer 250 decreases, the surface potential of the Schottky barrier completely depletes the AlGaN layer in the gate electrode 280 which is in Schottky contact with the barrier layer 250, and the GaN layer serving as the buffer layer 230. The electrons of the 2DEG layer 240 formed on the surface are depleted.

The depletion of the portion of the gate electrode breaks the 2DEG layer, which serves as a channel through which the current flows between the source electrode and the gate electrode, so that current cannot flow between the source and drain electrodes. For this reason, the drain-source electrode is turned off in the state in which the bias voltage is not applied to the gate electrode, and the high electron mobility transistor is operated in the normal off state.

The barrier layer 250 is made of undoped AlGaN but exhibits n-type semiconductor characteristics. Instead of the undoped barrier layer made of AlGaN, a barrier layer made of AlGaN to which n-type impurities are added may be formed.

The barrier layer 250 may be formed by an epitaxial growth method, and may be formed to have a thickness thinner than that of the buffer layer 230. For example, it may be made by MOCVD using TMG (Trimethylgallium), TMA (Trimethylalluminium), and ammonia as sources of Ga, Al, and N at a temperature of 900 ° C. or higher, but is not limited thereto.

The thickness of the barrier layer 250 is preferably adjusted in the range of 200 kPa to 1000 kPa. The thicker the barrier layer, the better the 2DEG layer can be formed to form a high concentration of 2DEG layer, it is possible to minimize the leakage current of the gate electrode. However, if it is too thick, it will crack and degrade the quality of the crystal, so it should not exceed 1000Å.

Lastly, as shown in FIG. 7, metal is deposited on portions of the second barrier layer 251 where the source electrode 260 and the drain electrode 270 are to be formed to form the source electrode 260 and the drain electrode 270. It is then possible to heat treatment to complete the ohmic junction. The heat treatment may be performed at 600 to 1200 ° C. and a rapid thermal process (RTP) may be used to shorten the process time.

In this manner, the source electrode 260 and the drain electrode 270 are formed as shown in FIG. 8, and the gate electrode 280 is formed on the first barrier layer 251 to complete the high electron mobility transistor.

As a material of the source electrode 260 and the drain electrode 270, an alloy of titanium (Ti), aluminum (Al), nickel (Ni), or gold (Au) may be used. The material of the gate electrode 280 may be used. Is a material capable of Schottky contact with a nitride-based semiconductor material, such as nickel (Ni), platinum (Pt), tungsten (W), palladium (Pd), chromium (Cr), copper (Cu), and gold ( Metals such as Au), metal silicides, alloys thereof, and the like can be used.

In addition, although the gate electrode 280 having a T-type structure is illustrated in FIG. 8, a structure of a Γ type, a field plate, or the like may be used in addition to the T-type.

Optionally, a passivation layer made of GaN, Sin, or the like may be further formed on the barrier layer 250 to prevent cracks during heat treatment when forming an ohmic junction.

[Other Embodiments]

9 through 11 are cross-sectional views illustrating a method of manufacturing a nitride-based high electron mobility transistor according to a second exemplary embodiment of the present invention.

3 to 5 are commonly applied to the second embodiment, and the series of processes and principles up to FIG. 5 are the same as the first embodiment.

In the high electron mobility transistor according to the second embodiment of the present invention, as shown in FIG. 4, Al _x Ga _{1 - x} N is raised to the height of the oxide film 290 on the exposed buffer layer 230 because the oxide film 290 is not formed. The second barrier layer 251 is grown to grow. In addition, as shown in FIG. 5, after the oxide film 280 is removed by wet etching using a solution including HF, Al _y Ga _{1 - y} N is grown to form the first barrier layer 252. Other processes are the same except for.

As shown in Figure 9, the oxide film 290 is removed, the Al _y Ga ₁ in the exposed areas _- not by growing _y N in forming the first barrier layer 252, not selectively grown Al _x Ga _{1-a x} N The first barrier layer 252 made of Al _y Ga _{1 - y} N is also formed on the second barrier layer 251. Even if it is formed in this way, it is possible to manufacture a high electron mobility transistor having a normal-off characteristic by reducing the content of Al in the present invention and preventing the formation of the 2DEG layer.

10 to 11, the source electrode 260, the drain electrode 270, and the gate electrode 280 are formed in the same manner as in the first embodiment to complete the high electron mobility transistor.

Although the present invention has been shown and described with reference to the preferred embodiments as described above, it is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Various changes and modifications will be possible.

1 to 2 are cross-sectional views showing the structure of a conventional high electron mobility transistor,

3 to 8 are manufacturing process diagrams of the nitride-based high electron mobility transistor according to the first embodiment of the present invention,

9 to 11 are manufacturing process diagrams of a nitride-based high electron mobility transistor according to a second embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

210: substrate 220: transition layer

230: buffer layer 240: 2DEG layer

250: barrier layer 260: source electrode

270: drain electrode 280: gate electrode

290: oxide film

Claims (13)

A buffer layer formed on the substrate and including a 2DEG layer discontinuously present; A first barrier layer formed on a predetermined region above the buffer layer and formed of Al _y Ga _1-y N; A second barrier layer formed on the same layer as the first barrier layer and formed on the buffer layer except for a region where the first barrier layer is formed, and formed of Al _x Ga _1-x N; A gate electrode formed on the first barrier layer; And A source electrode and a drain electrode formed on both sides of the gate electrode; The composition of Al _x Ga _1-x N and Al _y Ga _1-y N satisfies x>y> 0, x satisfies 0 <x <1, and y satisfies 0 <y <1. A nitride-based high electron mobility transistor having an off characteristic. delete The method of claim 1, And the 2DEG layer has a normal off characteristic in which a lower portion of the gate electrode is discontinuously formed. The method of claim 1, A nitride-based high electron mobility transistor having a normal off characteristic of the height of the first barrier layer and the height of the second barrier layer. The method of claim 1, The nitride-based high electron mobility transistor having a normal off characteristics of the first barrier layer covering the upper portion of the second barrier layer. A first step of forming a buffer layer of a nitride-based semiconductor on the substrate; Forming a patterned oxide film on a predetermined region over the buffer layer; A third step of forming a second barrier layer by growing Al _x Ga _1-x N to the oxide layer height on the exposed buffer layer because the oxide layer is not formed; A fourth step of removing the oxide film; Forming a first barrier layer on the same layer as the second barrier layer by growing Al _y Ga _1-y N in the exposed region by removing the oxide film; A sixth step of depositing a metal on the second barrier layer and then performing heat treatment to form source and drain electrodes; And And depositing a metal on the first barrier layer to form a gate electrode. and x is 0 <x <1, and y is 0 <y <1. The method of claim 6, And a composition of Al _x Ga _1-x N and Al _y Ga _1-y N having a normal off characteristic satisfying x>y> 0. The method of claim 6, The first barrier layer is Al _y Ga _{1 - y} N a method of the first nitride-based high electron mobility transistor having a normally-off characteristic of forming selectively grown to the second barrier storey. The method of claim 6, The first barrier layer is Al _y Ga _{1 - y} N grown by the method for manufacturing a nitride based high electron mobility transistor having a normally-off characteristic formed so as to cover the second barrier layer. The method of claim 6, The first barrier layer and the second barrier layer is formed on the buffer layer to form a nitride-based high electron mobility transistor having a normal off characteristics that the discontinuous 2DEG layer is formed in the lower portion of the gate electrode. The method of claim 6, The source electrode and the drain electrode are disposed on both sides of the gate electrode, the method of manufacturing a nitride-based high electron mobility transistor having a normal off characteristics formed in contact with the 2DEG layer. The method of claim 6, The heat treatment of the sixth step is a method of manufacturing a nitride-based high electron mobility transistor having a normal off characteristics performed at 600 to 1200 ℃. The method of claim 6, The fourth step of removing the oxide film is a method of manufacturing a nitride-based high electron mobility transistor having a normal off characteristics to proceed by wet etching using HF.

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