CN101252088A - A Realization Method of a Novel Enhanced AlGaN/GaN HEMT Device - Google Patents

Abstract

The invention discloses a method for realizing a novel enhanced AlGaN/GaN HEMT device, which relates to the technical field of microelectronics. The realization method has the advantages of low cost, simple process, good repeatability, high reliability and little damage to materials. Enhanced HEMT devices with high threshold voltage and nanoscale effective channel length can be obtained. In the present invention, after the growth of the AlN nucleation layer and the GaN epitaxial layer, and before the secondary growth of the GaN epitaxial layer and the AlGaN layer, the method of etching the mesa is used to make the heterojunction material on the side of the mesa grow along the non-polarization direction , thereby greatly weakening the two-dimensional electron gas density in the heterojunction material on the side of the mesa. In this way, the gate of the device is made on the side of the mesa. When no voltage is applied to the gate, the conductive channel will not conduct or weakly conduct; when a certain positive bias is applied to the gate, the conductive channel will conduct Pass. The invention can be used in high-temperature, high-frequency, high-power occasions, high-power switches and digital circuits.

Description

A Realization Method of a Novel Enhanced AlGaN/GaN HEMT Device

technical field

The invention belongs to the technical field of microelectronics, and relates to semiconductor materials and device manufacturing technology. Specifically, it is a new type of enhanced AlGaN/GaN HEMT device implementation method, which can be used in high-temperature, high-frequency, high-power occasions, high-power switches, and digital circuits.

Background technique

As a typical representative of wide bandgap semiconductor materials, GaN-based materials have the characteristics of large bandgap width, high electron saturation drift velocity, high breakdown field strength and good thermal conductivity, and can be used to make high-temperature, high-frequency and high-power electronic devices. More importantly, GaN-based materials can form modulation-doped AlGaN/GaN heterostructures, which can obtain high electron mobility, extremely high peak electron velocity and saturation electron velocity at room temperature, and obtain better than the first Higher two-dimensional electron gas density in second-generation compound semiconductor heterostructures. Therefore, the high electron mobility transistor HEMT based on AlGaN/GaN heterojunction has very good application prospects in high-power microwave devices. Since 1994, the growth of AlGaN/GaN heterojunction materials and the development of AlGaN/GaN HEMT devices have always occupied the main position in the research of GaN electronic devices. However, most of the research on GaN-based electronic devices for more than a decade has focused on depletion-mode AlGaN/GaN HEMT devices, because the AlGaN/GaN heterostructures are stronger than those based on InP and GaAs. The existence of polarization charges makes it very difficult to fabricate GaN-based enhancement devices, and there are few reports on this aspect.

Enhanced AlGaN/GaN HEMT devices have broad application prospects. Firstly, the inverter formed by the combination of enhancement mode HEMT device and depletion mode HEMT device has a great application prospect in digital circuits such as high temperature and radiation resistance. At the same time, enhanced AlGaN/GaN HEMT devices also have great application potential and good circuit compatibility in microwave high-power devices and circuits, because most of the current microwave power amplifiers use Si-based and GaAs-based enhanced devices. And as a power switch application, enhanced AlGaN/GaN HEMT devices have also attracted much attention. Therefore, it is of great significance to study high-performance enhancement mode AlGaN/GaN HEMT devices.

At present, no matter domestically or internationally, few people use the traditional barrier layer P-type Mg doping technology to develop enhanced AlGaN/GaN HEMT devices. This is because, firstly, the Mg doping process technology is not yet mature; secondly, the activation energy of Mg in AlGaN is very high, and a high annealing temperature is required to activate it. Therefore, the current international reports on AlGaN/GaN enhanced HEMT devices also avoid the method of P-type heavily doped barrier layer, but adopt some new methods. These methods include:

In 2001, Kurnar and others at the University of Illinois in the United States also successfully developed an AlGaN/GaN enhanced HEMT device using concave gate technology. They made a slight change in the structure of the traditional depletion-mode AlGaN/GaN HEMT device, that is, after growing the AlGaN/GaN heterostructure on the sapphire substrate, there is no direct electron beam evaporation to form the gate, but the pre-growth In the gate area, a groove is etched by ICP-RIE in Cl ₂ /Ar plasma, and a Ni/Au Schottky contact gate is made on the concave gate window after rapid thermal annealing. The two-dimensional electron gas in the channel can be greatly depleted by adjusting the groove depth. This method has been used ever since. See the literature Kumar, V., et al.: 'Recessed 0.25mm gateAlGaN＝GaN HEMTs on SiC with high gate-drain breakdown voltage using ICP-RIE', Electron. Lett.2001, 37, pp.1483-1485. 2003 , They also used concave gate technology and through structural optimization, successfully fabricated a high transconductance enhanced AlGaN/GaN HEMT with a gate length of one micron on a SiC substrate by MOCVD. The device has a peak intrinsic transconductance of 248mS/mm, a current density of 470mA/mm, a threshold voltage of 75mV, _fT of 8GHz, and _fMax of 26GHz. See literature V.Kumar, A.Kuliev, T.Tanaka, Y.Otoki, and I.Adesida, "Hightransconductance enhancement-mode AlGaN/GaN HEMTs on SiC substrate," Electron.Lett., vol.39, no.24, pp.1758-1760, Nov.2003.

In recent years, foreign countries have discovered a new technology in the development of enhanced AlGaN/GaN HEMT devices, that is, fluoride-based plasma implantation technology. It was found in the research that due to the strong electronegativity of F ions implanted in the AlGaN barrier layer, the F ions in the barrier layer will provide stable negative charges, which can effectively deplete the strong two-dimensional electrons in the channel region. gas. When the number of implanted F ions reaches a certain amount, the two-dimensional electron gas in the channel is completely depleted, and the original depletion-type AlGaN/GaN HEMT is converted into an enhancement-type HEMT. In 2005, Y.CAI and others from the Electronic Engineering Department of Hong Kong University of Science and Technology successfully developed high-performance enhanced AlGaN/GaN HEMT devices using fluoride-based plasma processing technology. It is reported that the carrier concentration of the thin layer at room temperature is 1.3×10 ¹³ cm ^-2 , the mobility is 1000cm ² /Vs, the threshold voltage of the device is 0.9V, the maximum drain current is 310mA/mm, and the peak transconductance is 148mS /mm, the cut-off frequency f _T is 10.1GHz, and the maximum resonant frequency f _max is 34.3GHz. See Y.Cai, YGZhou, KJChen, and KMLau, "High-performance enhancement-mode AlGaN/GaN HEMTs using fluoride-based plasmatreatment," IEEE Electron Device Lett., vol.26, no.7, pp.435-437 .

Afterwards, reports on enhanced AlGaN/GaN HEMT devices were all based on recessed gate technology and fluoride-based plasma implantation technology, and their performance was constantly refreshed. In 2006, PALACOS and others at the University of California in the United States effectively combined these two technologies to develop a high-performance enhanced AlGaN/GaN HEMT device. The gate length of this device is 160nm, the threshold voltage is 0.1V, the peak transconductance exceeds 400mS/mm, the maximum drain current reaches 1.2A/mm, the cutoff frequency f _T reaches 85GHz, and the maximum resonance frequency f _max is 150GHz . See literature T. Palacios, A. Chakraborty, S. Keller, SPDenBaars, "High-performance E-mode AlGaN/GaN HEMT," IEEE Electron Device Lett.vol.27, no.6, JUNE 2006.

To sum up, at present, the fabrication of enhanced AlGaN/GaN HEMT devices in the world mainly adopts concave gate technology and fluoride-based plasma implantation technology. There are still great shortcomings in the existing technology. First, the threshold voltage is not high. The highest reported value is only 0.9V, which is far from enough for switching applications. Second, whether etching to form grooves or fluorine ion implantation will affect the material Although some damage can be eliminated after annealing, the residual damage will still affect the performance and reliability of the device. At the same time, the repeatability of this process is not high; the third is to form short-channel devices for microwave applications. It is necessary to use high-end process equipment such as electron beam direct writing to produce short grid lengths, and the process is relatively difficult.

content of the invention

The object of the present invention is: in order to overcome the shortcoming of prior art, propose a kind of realization method of the novel enhanced AlGaN/GaN HEMT device. The realization method has the advantages of low cost, simple process, good repeatability, high reliability and no damage to materials. Enhanced HEMT devices with high threshold voltage and nanoscale effective channel length can be obtained.

The object of the present invention is achieved in this way: the present invention uses the epitaxial growth process, after the growth of the AlN nucleation layer and the GaN epitaxial layer, before the secondary GaN epitaxial layer and the AlGaN layer growth, the method of etching the mesa is adopted to make the side of the mesa The heterojunction material on the mesa grows along the non-polarization direction, which greatly weakens the two-dimensional electron gas density in the heterojunction material on the side of the mesa. In this way, the gate of the device is made on the side of the mesa. When no voltage is applied to the gate, the conductive channel will not conduct or weakly conduct; when a certain positive bias is applied to the gate, the conductive channel will conduct Pass. The preparation of the enhanced AlGaN/GaN HEMT device is carried out in the following steps:

(1) On the sapphire or silicon carbide substrate, use MOCVD or MBE process to grow AlN nucleation layer;

(2) On the AlN nucleation layer, grow a GaN epitaxial layer;

(3) ICP or RIE process is used to etch the mesa on the GaN epitaxial layer;

(4) After etching the mesa, put the sample made above into the reaction chamber, and grow the GaN epitaxial layer for the second time;

(5) After the secondary growth of the GaN epitaxial layer, the epitaxial growth of the AlGaN barrier layer;

(6) On the AlGaN barrier layer, a gate dielectric layer is deposited by LPCVD or PECVD process, and the gate dielectric layer can be SiO ₂ or SiN _x ;

(7) After the gate dielectric layer is formed, the source and drain regions are photolithographically obtained to obtain the source and drain region windows;

(8) Using electron beam evaporation process, evaporating ohmic contact metal on the windows of source and drain regions to form source and drain electrodes;

(9) After the source and drain electrodes are formed, photoetching the gate area window on the gate dielectric layer, and using an electron beam evaporation process to evaporate the gate metal on the gate window to form a gate;

(10) After the gate is formed, a thickened electrode pattern is obtained by photolithography. After that, the electron beam evaporation process is used to thicken the electrode and complete the device manufacturing.

In the implementation method of the above-mentioned novel enhanced AlGaN/GaN HEMT device, the growth conditions for growing the AlN nucleation layer are as follows: the temperature of the reaction chamber is controlled between 450°C and 550°C, and the reaction rate is less than 5nm/min. The thickness is 20nm-40nm.

The realization method of the above-mentioned novel enhanced AlGaN/GaN HEMT device, the growth condition of the said growth GaN epitaxial layer is: the temperature of the reaction chamber is controlled between 900°C and 1050°C, the reaction rate is less than 20nm/min, The thickness of the epitaxial layer can be controlled, generally in the range of 1 to 3 μm.

The implementation method of the above-mentioned novel enhanced AlGaN/GaN HEMT device is to etch the mesa on the GaN epitaxial layer. In the process of etching the mesa, the etching depth depends on the gate length required by the device. The purpose of etching the mesa is to change the growth direction of the AlGaN/GaN heterojunction material under the gate grown on it later, so that the heterojunction material in this region grows along the non-polarized direction. Thus, the two-dimensional electron gas density in the heterojunction under the gate is greatly weakened.

The implementation method of the above-mentioned novel enhanced AlGaN/GaN HEMT device, the so-called secondary growth GaN epitaxial layer, not only effectively improves the surface quality of the material after mesa etching, but more importantly, through the secondary GaN The adjustment of the thickness of the epitaxial layer can change the inclination angle of the non-polarization surface, thereby obtaining enhanced HEMT devices with different threshold voltages, because the inclination angle directly affects the two-dimensional electron gas density in the non-polarization surface area.

The implementation method of the above-mentioned novel enhanced AlGaN/GaN HEMT device is said to photoetch the gate region window on the gate dielectric layer, and the gate region window is selected on the side of the gate dielectric layer. Since there is only a very weak two-dimensional electron gas density in the heterojunction below the gate region, when no voltage is applied to the gate, the conductive channel will not conduct or weakly conduct; when a certain positive bias is applied to the gate , the conduction channel conducts.

Compared with the prior art, the present invention has the following advantages:

(1) The method proposed by the present invention is to etch the mesa before the growth of the heterojunction material, so that the heterojunction material on the side of the mesa grows along the non-polarization direction, thereby greatly weakening the polarization on the side of the mesa. The two-dimensional electron gas in the heterojunction material, so the depletion rate of the two-dimensional electron gas is high, and the threshold voltage of the enhanced device formed is higher, which can reach more than 1V.

(2) The process steps in the implementation of the present invention are relatively mature in China at present, the process is relatively simple, the cost is low, and it is completely compatible with the mature depletion-mode GaN-based HEMT device preparation process. In particular, micron-scale lithography tools can be used to form nanoscale effective channel lengths, which greatly reduces the process difficulty of devices with short channel lengths.

(3) The method proposed in the present invention is obtained by direct growth using an epitaxial growth process. Compared with the currently commonly used groove etching and ion implantation technology abroad, this method effectively avoids material damage caused by etching and ion implantation, so the process repeatability is better and the device reliability is higher.

(4) the present invention proposes a kind of realization method of novel enhanced AlGaN/GaN HEMT device at home for the first time, and provides the realization method of monolithic integrated enhanced type and depletion type HEMT inverter, which will be extremely Greatly expand the application field of GaN-based HEMT devices.

Description of drawings

Fig. 1 is a schematic diagram of the cross-sectional structure of a single-gate enhanced AlGaN/GaN HEMT device completed in Embodiment 1 of the present invention

Fig. 2 is a schematic diagram of the cross-sectional structure of the dual-gate enhanced AlGaN/GaN HEMT device completed in Embodiment 2 of the present invention

Fig. 3 is a schematic diagram of the cross-sectional structure of the monolithic integrated enhancement mode and depletion mode AlGaN/GaN HEMT inverter completed in Embodiment 3 of the present invention

Detailed ways

Referring to Fig. 1, it is a schematic cross-sectional structure diagram of a single-gate enhanced AlGaN/GaN HEMT device completed in Embodiment 1 of the present invention. In this embodiment, a 0001-plane sapphire substrate was selected as the growth substrate, and a single-gate enhanced AlGaN/GaN HEMT device was prepared according to the following process:

1. Place the sapphire substrate in the reaction chamber of the metal organic chemical vapor deposition MOCVD equipment, pump the vacuum of the reaction chamber to below 1×10 ^-2 Torr, and treat the sapphire under the protection of the mixed gas of hydrogen and ammonia. The substrate is subjected to high-temperature heat treatment and surface nitriding, the heating temperature is 1050°C, the heating time is 5min, the pressure of the reaction chamber is 40Torr, the flow rate of hydrogen gas is 1500 sccm, and the flow rate of ammonia gas is 1500 sccm;

2. Lower the substrate temperature to 500°C, keep the growth pressure at 40Torr, the flow rate of hydrogen gas at 1500 sccm, the flow rate of ammonia gas at 1500 sccm, and feed the aluminum source with a flow rate of 30 μmol/min into the reaction chamber to grow low-temperature AlN with a thickness of 30 nm nucleation layer;

3. Increase the growth temperature to 1000°C, keep the growth pressure at 40Torr, the flow rate of hydrogen gas at 1500 sccm, the flow rate of ammonia gas at 1500 sccm, and feed a gallium source with a flow rate of 50 μmol/min into the reaction chamber to grow GaN epitaxy with a thickness of 2000 nm. layer;

4. Deposit silicon dioxide SiO ₂ : use electron evaporation equipment to deposit a SiO ₂ layer with a thickness of about 150 nm. This step is added to form a double-layer mask pattern in which SiO ₂ and photoresist act together to protect the sample, which is more conducive to protecting the surface of the unetched area;

5. Photolithography table: Swing the positive glue on the sample at a speed of 5000 rpm, and then bake it in an oven at a temperature of 80°C for 10 minutes, and form the window required for etching through photolithography and development;

6. ICP etching: ICP dry etching is used to etch the GaN layer to form a mesa. The electrode power used during etching is 600W, the bias voltage is 120V, the pressure is 1Pa, and the etching time is 200s;

7. Remove the etched mask: use acetone to remove the etched positive resist, then soak in BOE for 1 min to remove the SiO ₂ mask, and finally clean it with deionized water and dry it with nitrogen;

8. Place the sample again in the reaction chamber of the metal organic chemical vapor deposition MOCVD equipment, pump the vacuum of the reaction chamber to below 1×10 ^-2 Torr, and conduct the sample under the protection of the mixed gas of hydrogen and ammonia. For heat treatment, the heating temperature is 1000°C, the heating time is 5min, the pressure of the reaction chamber is 40Torr, the flow rate of hydrogen gas is 1500sccm, and the flow rate of ammonia gas is 1500sccm;

9. Repeat step 3 to grow a GaN epitaxial layer with a thickness of 100nm for the second time;

10. Feed the aluminum source and the gallium source into the reaction chamber at the same time, control the flow rate and the reaction temperature, and grow a 3nm undoped AlGaN isolation layer, a 15nm Si-doped AlGaN barrier layer and a 5nm undoped AlGaN cap layer in sequence. The doping concentration of the barrier layer is 2×10 ¹⁸ cm ^-3 ;

11. Form silicon nitride SiN gate dielectric layer: use PECVD equipment to deposit a SiN layer with a thickness of about 5nm, then use the same method as step 5 to form windows in the source and drain regions, and use wet etching to remove the SiN dielectric film in the source and drain regions ;

12. Source and drain areas of photolithography: In order to better peel off the metal, first shake the adhesive on the sample at a speed of 8000 rpm for 30s, and bake in a high-temperature oven at 160°C for 20 minutes; The positive glue was cast on the sample at a rotation speed of 5000 rpm, and finally baked in a high-temperature oven at 80°C for 10 minutes, and the source and drain area windows were obtained by photolithography;

13. Primer film: Use DQ-500 plasma stripping machine to remove the undeveloped photoresist thin layer in the window area, which greatly improves the stripping yield;

14. Evaporation source and drain metal: use VPC-1100 electron beam evaporation equipment to deposit Ti/Al/Ni/Au four-layer metal;

15. Metal stripping and annealing: Soak in acetone for more than 20 minutes, then perform ultrasonic treatment, and then blow dry with nitrogen. Put the sample into the rapid annealing furnace for annealing: first, pass nitrogen into the annealing furnace for about 7 minutes, and then perform high-temperature annealing at 850°C for 30s under nitrogen atmosphere;

16. Photolithographic gate area window: throw the adhesive on the sample at a speed of 8000 rpm for 30s; bake in a high-temperature oven at a temperature of 160°C for 20 minutes; then throw the positive glue on the sample at a speed of 5000 rpm, and finally baked in a high-temperature oven at 80°C for 10 minutes, and obtained the gate window by photolithography;

17. Evaporate grid metal: Use VPC-1100 electron beam evaporation equipment to evaporate Ni/Au two-layer metal, and then soak the sample in the stripping solution for 2 minutes to obtain the grid;

18. Thickened electrode by photolithography: The sample is shaken and the rotation speed is 5000 rpm, and then baked in a high-temperature oven at a temperature of 80°C for 10 minutes, and then the pattern of the thickened electrode is obtained by photolithography;

19. Thickened electrode by evaporation and stripping: Use VPC-1100 electron beam evaporation equipment to evaporate Ti/Au two-layer metal, and then use stripping process to get thickened electrode. So far, the device fabrication is completed.

Referring to Fig. 2, it is a schematic diagram of the cross-sectional structure of the dual-gate enhanced AlGaN/GaN HEMT device completed in Embodiment 2 of the present invention. The manufacturing process of the dual-gate enhanced AlGaN/GaN HEMT device is essentially the same as that of Embodiment 1. The dual-gate enhanced AlGaN/GaN HEMT device shares one source, and the two gates, drains and AlGaN barrier layers are left-right symmetrical structures with respect to the source. The source and drain metals of the device are completed once by electron beam evaporation Ti/Al/Ni/Au, and then the two gates are completed once by electron beam evaporation Ti/Au.

Referring to FIG. 3 , it is a schematic diagram of a cross-sectional structure of a monolithic integrated enhancement mode and depletion mode AlGaN/GaN HEMT inverter completed in Embodiment 3 of the present invention. The sapphire substrate is still used as the growth substrate, and the previous preparation process is basically the same as that of Example 1, except that the subsequent process has some changes.

The main changes in the follow-up process are: first, the depletion-mode and enhancement-mode HEMT devices share the same drain, and their source and drain electrodes are completed by electron beam evaporation of Ti/Al/Ni/Au at one time; second, for depletion-mode HEMT devices , in the above step 11, the SiN dielectric in the source, drain metal region and gate metal region is removed at the same time, the depletion type device uses a Ni/Au double-layer metal Schottky gate, and the enhancement mode HEMT device uses a dielectric gate.

For those skilled in the art, after understanding the content and principles of the present invention, they can make various amendments and changes in form and details according to the methods of the present invention without departing from the principles and scope of the present invention. But these amendments and changes based on the present invention are still within the protection scope of the claims of the present invention.

Claims (6)

1. the implementation method of a novel enhancement type AlGaN/GaN HEMT device, implementation step is as follows:

(1) on sapphire or silicon carbide substrates substrate, utilizes MOCVD or MBE technology, the growing AIN nucleating layer;

(2) on the AlN nucleating layer, the growing GaN epitaxial loayer;

(3) on the GaN epitaxial loayer, adopt ICP or RIE technology etching table top;

(4) behind the etching table top, the above-mentioned sample of making is put into reative cell, diauxic growth GaN epitaxial loayer;

(5) after the diauxic growth GaN epitaxial loayer, epitaxial growth AlGaN barrier layer;

(6) on the AlGaN barrier layer, adopt LPCVD or pecvd process deposit gate dielectric layer, gate dielectric layer can be SiO ₂Perhaps SiN _x

(7) after gate dielectric layer forms, photolithographic source, drain region, acquisition source, drain region window;

(8) adopt electron beam evaporation process, on source, drain region window, evaporate metal ohmic contact, formation source, drain electrode;

(9) after source, drain electrode form, photoetching area of grid window on gate dielectric layer, and on this gate window, adopt electron beam evaporation process evaporation gate metal, form grid;

(10) after grid formed, photoetching obtained the thickening electrode pattern, adopts electron beam evaporation process afterwards, adds thick electrode, finishes the device manufacturing.

2. the manufacture method of a kind of enhanced AlGaN according to claim 1/GaN HEMT device, said its growth conditions of growing AIN nucleating layer is: the temperature of reative cell is controlled between 450 ℃～550 ℃, reaction rate was less than 5nm/ minute, and thickness is 20nm～40nm.

3. the manufacture method of enhanced AlGaN according to claim 1/GaN HEMT device, said growing GaN epitaxial loayer, its growth conditions is: the temperature of reative cell is controlled between 900 ℃～1050 ℃, reaction rate was less than 20nm/ minute, epitaxy layer thickness can be controlled, generally at 1～3 μ m.

4. the manufacture method of enhanced AlGaN according to claim 1/GaN HEMT device, said on the GaN epitaxial loayer etching table top, in the process of etching table top, the needed grid of the degree of depth visual organ spare of etching are grown and are decided, the purpose of mesa etch is the direction of growth for the AlGaN/GaN heterojunction material that is in the grid below thereon of growth after changing, this regional heterojunction material is grown along non-polarised direction, thereby weakened the two-dimensional electron gas density in the heterojunction of grid below greatly.

5. the manufacture method of enhanced AlGaN according to claim 1/GaN HEMT device, said diauxic growth GaN epitaxial loayer, it has not only improved the material surface quality behind the mesa etch effectively, the more important thing is, adjustment by secondary GaN epitaxy layer thickness, can change non-polarized angle of inclination, thereby obtain to have the enhancement mode HEMT device of different Fujian threshold voltage, because the angle of inclination directly influences the two-dimensional electron gas density in non-polarized zone.

6. the manufacture method of enhanced AlGaN according to claim 1/GaN HEMT device, said on gate dielectric layer photoetching area of grid window, the area of grid window is chosen on the side of gate dielectric layer, owing to have only extremely weak two-dimensional electron gas density in the heterojunction of area of grid below, when not having making alive on the grid, conducting channel can conducting or weak conducting; When adding certain positive bias on the grid, the conducting channel conducting.

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