CN103872145A - GaN heterojunction power diode - Google Patents

Abstract

The invention relates to the technical field of semiconductor devices, and relates to a GaN heterojunction power diode. In the present invention, the Schottky metal of the anode is deposited in the groove rather than directly on the surface of the heterojunction, and a dielectric is deposited on the lower right side of the groove near the cathode side to form a junction terminal structure at the anode, and through engraving The etch barrier layer reduces the concentration of two-dimensional electron gas (2DEG) in the channel below the Schottky metal to achieve an extremely low forward turn-on voltage of the device. The beneficial effect of the present invention is that it has the advantages of low turn-on voltage, low conduction resistance, high conduction current, high reverse withstand voltage and low power consumption, and its manufacturing process is compatible with traditional GaN heterojunction HEMT devices, which can realize Monolithic integration with conventional GaN heterojunction HEMT devices. The invention is especially suitable for GaN heterojunction power diodes.

Description

A GaN heterojunction power diode

technical field

The invention relates to the technical field of semiconductor devices, and relates to a GaN heterojunction power diode.

Background technique

As a typical representative of the third-generation wide-bandgap semiconductor, gallium nitride (GaN) has many excellent characteristics: high critical breakdown electric field (~3.5×10 ⁶ V/cm), high electron mobility (~2000cm ² /vs ), high two-dimensional electron gas (2DEG) concentration (~10 ¹³ cm ^-2 ) and good high temperature working ability, etc. High Electron Mobility Transistor (HEMT) based on AlGaN/GaN heterojunction (or heterojunction field effect transistor HFET, modulation doped field effect transistor MODFET, hereinafter collectively referred to as HEMT devices) has been applied in the semiconductor field, especially in The field of radio frequency/microwave has been applied in wireless communication, satellite communication, etc. In addition, such devices based on wide-bandgap GaN materials have the characteristics of high reverse blocking voltage, low forward conduction resistance, high operating frequency, and high efficiency, which can meet the requirements of the system for semiconductor devices with higher power, higher frequency, and smaller size. The requirements of volume, lower power consumption and harsher working environment.

Diodes play an extremely important role in the semiconductor field. In recent years, diodes based on GaN heterojunction materials have also achieved great development. However, the traditional GaN heterojunction Schottky diode has a large turn-on voltage due to the Schottky contact barrier and its withstand voltage capability depends on the metal-semiconductor contact between the Schottky metal and the GaN semiconductor. A larger turn-on voltage will increase the forward operating loss of the device, so it is of great significance to develop a GaN power diode with low forward turn-on voltage and high reverse withstand voltage for practical applications. Literature Jae-Gil Lee, et.al., "Low Turn-on VoltageAlGaN/GaN-on-Si Rectifier With Gated Ohmic Anode", IEEE Electron Device Letters, vol.34, no.2, Feb2013 proposed a groove structure with 0.37 The turn-on voltage of V is much smaller than the turn-on voltage of the Schottky barrier diode>1.0V, but in terms of reverse withstand voltage, this structure is limited by the reverse leakage of the traditional Schottky contact. Literature Silvia Lenci, et.al., "Au-Free AlGaN/GaN Power Diode on8-in Si Substrate With Gated EdgeTermination", IEEE Electron Device Letters, vol.34, no.8, Aug2013 proposed a Xiao Teky diode. This structure utilizes the junction terminal structure to reduce the reverse leakage of the Schottky contact, but the forward conduction current of the device is limited by the current carrying capacity of the Schottky contact.

Contents of the invention

What the present invention aims to solve is to propose a new type of diode with low turn-on voltage, low on-resistance, high on-current, high reverse withstand voltage and low power consumption for the above-mentioned problems existing in the traditional GaN heterojunction power diode. GaN heterojunction diodes.

The technical solution adopted by the present invention to solve the above technical problems is: a GaN heterojunction power diode, comprising a substrate substrate 1, a GaN layer 2 arranged on the upper end surface of the substrate substrate 1, and a GaN layer arranged on the upper end surface of the GaN layer 2. The AlMN layer 3, the GaN layer 2 and the AlMN layer 3 form a heterojunction, the two sides of the upper end surface of the AlMN layer 3 are respectively provided with a first Schottky metal 5 and a second Schottky metal 9, the A passivation layer 7 is arranged between the first Schottky metal 5 and the second Schottky metal 9, and a first ohmic contact layer 4 is arranged between the first Schottky metal 5 and the AlMN layer 3, and its characteristic That is, the contact surface between the AlMN layer 3 and the second Schottky metal 9 is provided with a groove 8, and the side of the groove 8 close to the first Schottky metal 5 is provided with a dielectric 6, and the other side is provided with a The second ohmic contact layer 10 .

The general technical solution of the present invention is based on etching the AlMN barrier layer to locally reduce the thickness of the AlMN barrier layer so as to reduce the concentration of the two-dimensional electron gas (2DEG) of the heterojunction to realize the modulation of the forward turn-on voltage of the diode so as to obtain a higher The device has a low forward turn-on voltage, and the dielectric is introduced into the anode junction terminal to reduce the reverse leakage to improve the reverse withstand voltage of the device, forming a GaN heterojunction lateral diode based on the junction terminal to achieve high withstand voltage. The diode has an extremely low turn-on voltage and a high withstand voltage capability. It should be pointed out that when the thickness of the AlMN barrier layer, the composition of the AlMN barrier layer Al, or the AlN layer is inserted in the heterojunction, or there is doping in the AlMN barrier layer and the distribution of the doping is different, The depth of the groove corresponding to the same low forward turn-on voltage will vary

Specifically, M in the AlMN layer 3 is one of Ga, In and a mixture of Ga and In.

Specifically, the dielectric 6 is one of SiO ₂ , Si ₃ N ₄ , AlN, Al ₂ O ₃ , MgO and HfO ₂ .

Specifically, the depth of the groove 8 is 20nm.

The beneficial effect of the present invention is that it has the advantages of low turn-on voltage, low conduction resistance, high conduction current, high reverse withstand voltage and low power consumption, and its manufacturing process is compatible with traditional GaN heterojunction HEMT devices, which can realize Monolithic integration with conventional GaN heterojunction HEMT devices.

Description of drawings

Fig. 1 is the structural representation of GaN heterojunction power diode of the present invention;

2 is a schematic diagram of device isolation in the process flow of the GaN heterojunction power diode of the present invention;

3 is a schematic diagram of depositing ohmic contacts in the process flow of the GaN heterojunction power diode of the present invention;

4 is a schematic diagram of etching AlMN and forming grooves in the process flow of the GaN heterojunction power diode of the present invention;

Fig. 5 is a schematic diagram of depositing a dielectric in the process flow of the GaN heterojunction power diode of the present invention;

Fig. 6 is a schematic diagram of depositing and depositing Schottky metal in the process flow of the GaN heterojunction power diode of the present invention;

7 is a schematic diagram of passivation of the active region in the process flow of the GaN heterojunction power diode of the present invention;

Fig. 8 is a schematic diagram of the structure of a groove lateral field effect diode;

Figure 9 is a simulation schematic diagram of the structure shown in Figure 8, when the depth of the groove is 20nm, there is a positive turn-on voltage, which is about 0.25V (when Ia=1mA/mm is defined as the device is turned on in the forward direction);

Figure 10 is a schematic diagram of the turn-on voltage of the device structure shown in Figure 8 (defined as Ia=1mA/mm when the device is turned on in the forward direction) as a function of the depth of the groove;

Fig. 11 is a schematic diagram of the structure of a traditional Schottky barrier diode SBD;

Figure 12 is a schematic diagram of the comparison of forward current capabilities of the three structures;

Fig. 13 is a schematic diagram of comparison of forward turn-on voltages of three structures;

Fig. 14 is an electric field distribution diagram of the structures shown in Fig. 8 and Fig. 1 during reverse withstand voltage;

Fig. 15 is a current distribution diagram of the structure shown in Fig. 8 under a reverse withstand voltage of 522.5V;

Fig. 16 is a current distribution diagram of the structure shown in Fig. 1 under a reverse withstand voltage of 522.5V;

FIG. 17 is a schematic diagram showing the comparison of reverse leakage and withstand voltage of the two structures described in FIGS. 1 and 8 .

Detailed ways

Below in conjunction with accompanying drawing, describe technical scheme of the present invention in detail:

The present invention proposes a high-performance GaN heterojunction power diode. Different from conventional lateral field effect rectifiers, the Schottky metal of the anode in the present invention is deposited in the groove rather than directly on the surface of the heterojunction, and A dielectric is deposited on the lower right side of the groove near the cathode to form a junction termination structure at the anode. The invention reduces the concentration of two-dimensional electron gas (2DEG) in the channel below the Schottky metal by etching the barrier layer to realize the device has an extremely low forward turn-on voltage, and the dielectric is only on the lower right side of the groove close to the cathode side There is deposition, and does not cover the entire groove, so the turn-on voltage will not be affected by the dielectric; and the diode provided by the present invention adopts an Ohm/Schottky mixed anode design at the anode, wherein the Schottky contact controls the opening of the device /off, the ohmic contact is the conduction path of the device. Therefore, the diode provided by the present invention has extremely low anode contact resistance, so that the conduction resistance of the whole device is greatly reduced and the conduction current is greatly increased. On the other hand, when the device is in the directional mode, the electric field is concentrated on the edge of the Schottky metal near the cathode side. When the junction termination structure is introduced, the reverse leakage current flowing through the Schottky metal can be effectively reduced, thereby improving the device’s response. to withstand pressure. Therefore, the GaN heterojunction diode provided by the present invention has the advantages of low turn-on voltage, low on-resistance, high on-current, high reverse withstand voltage and low power consumption. The GaN HEMT process is compatible, and the monolithic integration of GaN diodes and HEMTs can be realized.

As shown in Figure 1, the GaN heterojunction power diode of the present invention comprises substrate substrate 1, the GaN layer 2 that is arranged on the upper end surface of substrate substrate 1, the AlMN layer 3 that is arranged on the upper end surface of GaN layer 2, so The GaN layer 2 and the AlMN layer 3 form a heterojunction, and the two sides of the upper end surface of the AlMN layer 3 are respectively provided with a first Schottky metal 5 and a second Schottky metal 9, and the first Schottky metal A passivation layer 7 is provided between the first Schottky metal 5 and the second Schottky metal 9, a first ohmic contact layer 4 is provided between the first Schottky metal 5 and the AlMN layer 3, and the AlMN layer 3 and the second A groove 8 is provided on the contact surface of the Schottky metal 9 , a dielectric 6 is provided on one side of the groove 8 close to the first Schottky metal 5 , and a second ohmic contact layer 10 is provided on the other side.

Working principle of the present invention is:

Since the AlMN barrier layer under the Schottky metal is etched, the corresponding two-dimensional electron gas (2DEG) concentration in the channel is reduced. When the voltage applied to the anode is lower than the turn-on voltage, there is no electron accumulation in the channel under the Schottky metal, the 2DEG conductive channel is disconnected, and no current path can be formed; Electrons accumulate in the channel beneath the base metal, forming a current path from the anode to the cathode, and the device turns on. Fig. 8 is a comparison diagram. By simulating the structure of Fig. 8, the relationship between the turn-on voltage and the groove depth is obtained, as shown in Fig. 9 . Through the simulation of the structure in Figure 8, when the depth of the groove is 20nm (the thickness of the AlGaN barrier layer is 25nm, and the Al composition is 26%), it has a positive turn-on voltage, which is about 0.25V. Figure 11 is a comparative structure, a traditional Schottky barrier diode SBD. Figures 12 and 13 are comparison diagrams of the forward characteristics of the three structures, wherein the groove depth of the GaN heterojunction power diode proposed by the present invention is 20nm. When the device is turned on when Ia=1mA/mm, the turn-on voltage of the proposed device is also 0.25V. However, the turn-on voltage of the Schottky barrier diode SBD is 1.5V. It can be seen that the turn-on voltage of the proposed device is much smaller than that of the traditional Schottky barrier diode SBD.

When a reverse voltage is applied to the anode, as shown in Figure 14, the electric field is concentrated on the side of the Schottky metal close to the cathode. Compared with the situation without a junction terminal structure, the present invention can effectively reduce the reverse voltage flowing through the Schottky contact. To leakage, as shown in Figures 15 and 16, and then improve the reverse withstand voltage of the device. Fig. 17 is a comparison diagram of leakage and withstand voltage of the structures shown in Fig. 1 and Fig. 8 .

The present invention can adjust the forward turn-on voltage of the device by optimizing the depth of the groove 8 . In order to achieve a low positive turn-on voltage, the method of etching the AlMN barrier layer to reduce the two-dimensional electron gas concentration in the channel below the Schottky metal is adopted, and the dielectric is only deposited on the lower right side of the groove near the cathode, so that the dielectric introduction did not change the turn-on voltage. In the simulation, the Al composition of the barrier layer is 26%, the thickness is 25nm, the thickness of the dielectric is 10nm, and the length of the dielectric 6 in the groove 8 is 0.5um.

The invention provides an optional preparation process flow chart, comprising the following steps:

Step 1: As shown in Figure 2, prepare the substrate to realize device isolation.

The second step: as shown in Figure 3, deposit ohmic contact metal.

Step 3: as shown in Figure 4, wet or dry etch the AlMN layer to realize the positive turn-on voltage of the rectifier.

The fourth step: as shown in Figure 5, deposit dielectric SiO ₂ , Si ₃ N ₄ , AlN, Al ₂ O ₃ , MgO or HfO ₂ by means of atomic layer deposition (ALD) or plasma enhanced chemical vapor deposition (PECVD) etc. and the patterning of the medium layer.

Step 5: as shown in Figure 6, deposit Schottky metal.

Step 6: As shown in Figure 7, the active area of the device is passivated.

The anode adopts a mixed anode method, which is composed of ohmic metal and Schottky metal connected.

The structure proposed by the present invention is simulated and analyzed by using the device simulation software Sentaurus. In the simulation, the thickness of the AlGaN barrier layer is 25nm, the Al composition is 26%, and the distance between cathode and anode is Lac=5μm. The depth of the groove in the AlGaN barrier layer is trecess, the dielectric material at the bottom right of the groove is HfO ₂ , the thickness is 10nm, and the bottom length is 0.5μm. When simulating the effect of the trench depth on the forward turn-on voltage of the device, it can be seen from Figure 9 that when the trench depth trecess is 20nm, the forward turn-on voltage of the device is only 0.25V, which is much smaller than that shown in Figure 11 The turn-on voltage of the traditional Schottky barrier diode SBD1.5V. From the comparison diagrams of Figures 12 and 13, it can be seen that when the forward conduction current Ia=1mA/mm is defined as the device is turned on in the forward direction, then the turn-on voltage of the structure in Figure 1 and the structure in Figure 8 is both 0.25V, and the introduction of the junction terminal structure The forward turn-on voltage and conduction current are not changed, and the conduction current of the device mainly flows through the ohmic contact in the mixed anode structure. From the comparison of the reverse characteristics in Figures 15 and 16 and Figure 17, it can be found that the introduction of the junction terminal structure in the diode proposed by the present invention greatly reduces the reverse leakage of the device and significantly improves the reverse withstand voltage of the device. The above simulation results illustrate the effectiveness and practicability of the device proposed by the present invention.

Claims (4)

1. A GaN heterojunction power diode, comprising a substrate substrate (1), a GaN layer (2) arranged on the upper end surface of the substrate substrate (1), and an AlMN layer arranged on the upper end surface of the GaN layer (2) (3), the GaN layer (2) and the AlMN layer (3) form a heterojunction, and the two sides of the upper end surface of the AlMN layer (3) are respectively provided with a first Schottky metal (5) and a second Schottky metal A special base metal (9), a passivation layer (7) is arranged between the first Schottky metal (5) and the second Schottky metal (9), and the first Schottky metal (5) A first ohmic contact layer (4) is provided between the AlMN layer (3), characterized in that a groove (8) is provided on the contact surface between the AlMN layer (3) and the second Schottky metal (9) , the side of the groove (8) close to the first Schottky metal (5) is provided with a dielectric (6), and the other side is provided with a second ohmic contact layer (10). 2. A GaN heterojunction power diode according to claim 1, characterized in that M in the AlMN layer (3) is one of Ga, In and a mixture of Ga and In. 3. A GaN heterojunction power diode according to claim 2, characterized in that the dielectric (6) is SiO ₂ , Si ₃ N ₄ , AlN, Al ₂ O ₃ , MgO and HfO ₂ A sort of. 4. A GaN heterojunction power diode according to any one of claims 1-3, characterized in that the depth of the groove (8) is 20 nm.

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