CN103996707B - Add grid field plate enhanced AlGaN/GaN HEMT device structure and preparation method thereof - Google Patents

Abstract

The invention discloses a grid field plate enhanced AlGaN/GaN HEMT device structure and a manufacturing method thereof. The structure includes a substrate, an intrinsic GaN layer, an AlN isolation layer, an intrinsic AlGaN layer, an AlGaN doped layer, a p Type GaN layer, gate electrode, source electrode, drain electrode, gate field plate, insulating layer, passivation layer and silicide used to adjust the concentration of two-dimensional electron gas. The source electrode, the drain electrode and the insulating layer are located on the AlGaN doped layer, the gate electrode is located on the p-type GaN layer, and the silicide is located on the insulating layer. The grid field plate is electrically connected to the gate electrode. The silicide introduces compressive stress to the insulating layer and the AlGaN layer, and the AlGaN layer between the silicides is subjected to tensile stress. By making the block spacing smaller than the block width, the overall AlGaN layer obtains tension. Stress increases the concentration of 2DEG.

Description

Structure and Fabrication Method of AlGaN/GaN HEMT Device Enhanced by Adding Gate Field Plate

technical field

The invention belongs to the field of microelectronics technology, and relates to the manufacture of semiconductor devices, in particular to a grid field plate enhanced AlGaN/GaN HEMT device structure and manufacturing method, which can be used to manufacture low on-resistance, high frequency, high breakdown voltage Enhancement Mode High Electron Mobility Transistor.

Background technique

In recent years, the third bandgap semiconductor represented by SiC and GaN has the characteristics of large bandgap, high breakdown electric field, high thermal conductivity, high saturated electron velocity and high concentration of two-dimensional electron gas at the heterojunction interface. It has received widespread attention. In theory, high electron mobility transistor HEMT, light emitting diode LED, laser diode LD and other devices made of these materials have obvious superior characteristics than existing devices, so in recent years, researchers at home and abroad have conducted extensive and in-depth research on them. research and achieved remarkable results.

AlGaN/GaN heterojunction high electron mobility transistor HEMT has shown unique advantages in high-temperature devices and high-power microwave devices. The pursuit of high-frequency, high-voltage, and high-power devices has attracted a lot of research. In recent years, fabrication of higher frequency and high voltage AlGaN/GaN HEMTs has become another research focus. After the growth of the AlGaN/GaN heterojunction is completed, there will be a large amount of two-dimensional electron gas 2DEG at the interface of the heterojunction. When the resistivity at the interface is reduced, we can obtain higher device frequency characteristics. AlGaN/GaN heterojunction electron mobility transistors can achieve very high frequencies, but often at the expense of high-voltage withstand characteristics. The current method of increasing the frequency of AlGaN/GaN heterojunction transistors is as follows:

1. Combining dielectric-free passivation with regrown ohmic contacts to reduce resistivity. See Yuanzheng Yue, Zongyang Hu, Jia Guo et al. InAlN/AlN/GaNHEMTsWithRegrownOhmicContactsandf _T of 370GH. EDL.Vol33.NO.7, P1118-P1120. The approach uses a 30nm gate length and combines dielectric-freepassivation with regrown ohmic contacts to reduce source-drain resistivity. The frequency can reach 370GHz. It is also possible to continue to increase the frequency to 500GHz by reducing the channel length.

2. Re-grow a two-dimensional electron gas channel from the heavily doped source-drain to the gate. See Shinohara, K. Regan, D. Corrion, A. Brown et al. self-aligned-gateGaN-HEMTswithheavily-dopedn ⁺ -GaNohmiccontactsto2DEG; IEDM, IEEE; 2012. In the past, the re-growth of n ⁺ GaN ohmic contact was effective in reducing the channel contact resistance, but the heavily doped source-drain contact directly to the two-dimensional electron gas channel close to the gate electrode can obtain better frequency characteristics and current characteristics. The method reported in the paper makes the frequency f _T /fmax = 342/518 GHz. At the same time, the breakdown voltage is 14V.

Contents of the invention

The purpose of the present invention is to address the shortcomings of the above high-frequency devices, to provide a method based on silicide-induced stress on the channel, so as to simultaneously improve the frequency characteristics and withstand voltage characteristics of the enhanced AlGaN/GaN high-mobility transistor, and enhance the reliability of the process. Controllability and repeatability, meeting the application requirements of GaN-based electronic devices for high frequency and high voltage.

The present invention is achieved like this:

The technical idea of the present invention is: use the method of epitaxial growth and etching to grow an insulating layer on AlGaN, form a stepped insulating layer with one thick and one thin insulating layer by etching, and then grow multiple massive silicides on the thin insulating layer , the silicide block spacing is smaller than the block width, and the silicide is also grown on the thick insulating layer to form a field plate and connect to the gate electrode. Because the thermal expansion coefficient of the silicide is greater than that of the insulating layer and AlGaN. When the epitaxial growth cools, the silicide will introduce compressive stress to the insulating layer and the AlGaN layer, and at the same time, the AlGaN layer located between the silicide will be subjected to tensile stress. When the AlGaN layer is subjected to compressive stress, the 2DEG concentration at the AlGaN/GaN interface decreases, and when the AlGaN layer is subjected to tensile stress, the 2DEG concentration at the AlGaN/GaN interface increases. The magnitude of the compressive stress (tensile stress) on the AlGaN layer is related to the length of the silicide (silicide spacing). This relationship is not a linear relationship, but the stress on the AlGaN layer versus the polarization when the action distance is reduced. The influence of charge increases rapidly (as shown in Figure 2 below), so we can make the width of the silicide and the spacing between the silicides different to realize the adjustment of the two-dimensional electron gas concentration. On the whole, the increase or decrease of the 2DEG concentration depends on Depending on the size relationship between the two, in this invention, we choose to increase the concentration of the two-dimensional electron gas to reduce the channel resistance. Therefore, the tensile stress is greater than the compressive stress, so the silicide width is greater than the silicide spacing. As shown in Figure 2, if the width of the silicide is 1 μm, and the silicide spacing is 0.25 μm, then the tension experienced by the silicide spacing (0.25 μm) region makes the polarized charge finally larger than the pole of the silicide region (1 μm). The polarized charge is two orders of magnitude larger, so the overall effect is that the AlGaN layer is subjected to tensile stress, that is, the polarized charge concentration increases, so the concentration of 2DEG between the gate source and the gate drain also increases due to the increase in the polarized charge. the result of. Therefore, the resistance of this region is reduced. See IEICETRANS.ELECTON, VOL.E93-C, NO.8AUGUST2010. Analysis of Passivation-Film-Induced Stress Effect on Electrical Properties in AlGaN/GaNHEMTs. By choosing to make the spacing between silicides smaller than the length of silicides, the increase in 2DEG concentration is much greater than the decrease in 2DEG concentration Therefore, the resistance between the gate-drain and the gate-source is reduced, and the frequency characteristic of the high-mobility transistor is improved without changing the distance between the gate and the drain. The field plate on the thick insulating layer has a negligible effect on the 2DEG due to its thick dielectric, but it can play the role of a field plate after being connected to the gate electrode, which can improve the withstand voltage characteristics of the present invention.

According to the above technical idea, a gate field plate enhanced AlGaN/GaN HEMT device structure, the structure includes a substrate, an intrinsic GaN layer, an AlN isolation layer, an intrinsic AlGaN layer, an AlGaN doped layer, a p-type GaN layer, Gate electrode, source electrode, drain electrode, gate field plate, insulating layer, passivation layer and silicide for adjusting two-dimensional electron gas concentration; the AlGaN doped layer is located on the intrinsic AlGaN layer, and the p-type GaN layer Located on the AlGaN doped layer, the source and drain electrodes and the insulating layer are located on the AlGaN doped layer, the gate electrode is located on the p-type GaN layer, and the silicide is located on the insulating layer; an enhanced AlGaN is epitaxially grown on the substrate /GaN heterojunction material, and form the source electrode and the drain electrode on the heterojunction material, and then deposit a layer of insulating layer, wherein the thick insulating layer is located between the gate electrode and the drain electrode, close to the gate electrode, the thickness of 200nm-700nm; the thin insulating layer is respectively located between the thick insulating layer and the drain electrode and between the gate electrode and the source electrode, with a thickness of 5-10nm, and a silicide is formed between the gate-drain region and the gate-source region on the insulating layer The silicide is blocky, which will introduce compressive stress to the insulating layer and the AlGaN layer, and the AlGaN layer located between the silicides will be subjected to tensile stress. By making the block spacing smaller than the block width, the AlGaN layer will obtain tensile stress as a whole, so that 2DEG is enhanced in the channel, the silicide includes NiSi, TiSi ₂ or Co ₂ Si, the silicide on the thick insulating layer is electrically connected to the gate electrode to form a gate field plate; there is a p-GaN epitaxial layer under the gate electrode, forming Enhanced device. Finally, a passivation layer is deposited to passivate the device.

The substrate material in the present invention is sapphire, silicon carbide, GaN or MgO, the composition of Al and Ga in the intrinsic AlGaN layer and the AlGaN doped layer can be adjusted, x=0～1 in AlxGa1 _{- xN} , the intrinsic GaN layer can be replaced by an AlGaN layer, and the Al composition in the AlGaN is smaller than the Al composition in the intrinsic AlGaN layer and the AlGaN doped layer, and the p-type GaN material can be replaced by a p-type AlGaN material or a p-type InGaN Material. According to the above technical idea, the structure of improving the performance of enhanced AlGaN/GaN HEMT devices by using metal silicide includes the following process:

(1) The epitaxially grown enhanced p-GaN/AlGaN/GaN material is organically cleaned, cleaned with flowing deionized water, and etched in a solution with a volume ratio of HCl:H ₂ O = 1:1 for 30-60s , and finally washed with flowing deionized water and dried with high-purity nitrogen;

(2) Perform photolithography and dry etching on the cleaned p-GaN/AlGaN/GaN material to form active region mesas;

(3) Perform photolithography on the p-GaN/AlGaN/GaN material prepared on the mesa to form an etching region of p-GaN;

(4) and put the material into the ICP dry etching reaction chamber, the process conditions are: the power of the upper electrode is 200W, the power of the lower electrode is 20W, the pressure of the reaction chamber is _1.5Pa , the flow of Cl is 10sccm, and the flow of Ar gas The flow rate is 10sccm, the etching time is 10min, and the p-GaN epitaxial layer outside the gate electrode area is etched away;

(5) Perform photolithography on the etched p-GaN/AlGaN/GaN material to form a source-drain ohmic contact area, and put it into an electron beam evaporation table to deposit ohmic contact metal Ti/Al/Ni/Au=20/120/ 45/50nm and peel off, and finally perform rapid thermal annealing at 850°C for 35s in a nitrogen environment to form an ohmic contact;

(6) Put the device into a magnetron sputtering reaction chamber to prepare Al ₂ O ₃ thin films, the process conditions are: the DC bias voltage of the Al target is 100V, the Ar gas flow is 30 sccm, the O flow is 10 sccm, the pressure of the reaction chamber 0.5Pa, deposit a 300nm thick Al ₂ O ₃ film;

(7) Perform photolithography and development on the deposited device to form a wet etching area of _Al2O3 film, put the material into a solution with a volume ratio of HF _{: H2O} =1:10, etch for 3-5min, Etch Al ₂ O ₃ to 5-10nm;

(8) Then put the device into the magnetron sputtering reaction chamber to sputter Ni and Si simultaneously. The process conditions are: the DC bias voltage of the Ni target is 100V, the RF bias voltage of the Si target is 450V, and the carrier gas Ar The flow rate is 30sccm, and a mixed metal film with a thickness of 100nm to 150nm is co-deposited;

(9) Perform photolithography on the device with the deposited film to form the etching window area of the mixed film, and put it into the ICP dry etching reaction chamber. The process conditions are: the power of the upper electrode is 200W, and the power of the lower electrode is 20W , the reaction chamber pressure is 1.5Pa, the flow rate of CF ₄ is 20sccm, the flow rate of Ar gas is 10sccm, and the etching time is 5min. the spacing between the blocks is smaller than the silicide block width;

(10) Put the device into a rapid annealing furnace, and perform rapid thermal annealing at 450°C for 30s in a nitrogen atmosphere to form a NiSi alloy. The silicide will introduce compressive stress to the insulating layer and the AlGaN layer, and the AlGaN between the silicide The layer will be subjected to tensile stress. By making the block spacing smaller than the block width, the AlGaN layer will obtain tensile stress as a whole, thereby enhancing the 2DEG in the channel;

(11) Perform photolithography on the completed alloy device to form the gate electrode and the gate field plate region, and put the device into a solution with a volume ratio of HF:H ₂ O = 1:1 to complete the Al ₂ O ₃ in the gate electrode region Etch to form gate electrode and grid field plate window, then put Ni/Au=20/200nm into the electron beam evaporation station to deposit and lift off, and complete the preparation of gate electrode and grid field plate;

(12) Put the device with the gate electrode prepared into the PECVD reaction chamber to deposit the SiN passivation film. The specific process conditions are: the flow rate of SiH ₄ is 40 sccm, the flow rate of NH ₃ is 10 sccm, the pressure of the reaction chamber is 1-2Pa, radio frequency With a power of 40W, deposit a SiN passivation film with a thickness of 200nm to 300nm;

(13) The device is cleaned again, photolithographically developed, and the etching area of the SiN film is formed, and put into the ICP dry etching reaction chamber. The process conditions are: the power of the upper electrode is 200W, and the power of the lower electrode is 20W. The chamber pressure is 1.5 Pa, the flow rate of CF ₄ is 20 sccm, the flow rate of Ar gas is 10 sccm, and the etching time is 10 min, and the SiN and Al ₂ O ₃ films covered on the source electrode, drain electrode and gate electrode are etched away;

(14) The device is cleaned, photolithographically developed, and placed in an electron beam evaporation station to deposit a thickened electrode with Ti/Au=20/200nm to complete the preparation of the overall device.

The present invention has the following advantages:

(1) The device of the present invention adopts the method of depositing an insulating layer and silicide to generate stress on AlGaN and adjust the electron gas concentration and electric field strength in the channel. Improve device frequency characteristics.

(2) The silicide prepared in the present invention is located between the gate-drain and the gate-source, which improves the frequency characteristics without reducing the distance between the gate and the drain, thus without sacrificing the high-voltage resistance characteristics.

(3) In the present invention, the size and spacing of the silicide can be adjusted between the gate-drain and the gate-source as required, thereby adjusting the magnitude of the stress. The electron gas concentration between gate-source and gate-drain and frequency characteristics can be adjusted as required.

(4) The addition of the gate field plate in the present invention improves the withstand voltage characteristics of the device.

Description of drawings

The above and other aspects and advantages of the invention will become more readily apparent by describing in more detail exemplary embodiments of the invention with reference to the accompanying drawings, in which:

Fig. 1 is the sectional structure schematic diagram of device of the present invention;

Figure 2 is an illustration of the physical principle (the change of polarization charge with the width of the silicide);

Fig. 3 is a schematic diagram of the manufacturing process flow of the device of the present invention.

detailed description

Hereinafter, the invention will now be described more fully with reference to the accompanying drawings, in which various embodiments are shown. However, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

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

Referring to FIG. 1 , a gate field plate enhanced AlGaN/GaN HEMT device structure, the structure includes a substrate, an intrinsic GaN layer, an AlN isolation layer, an intrinsic AlGaN layer, an AlGaN doped layer, a p-type GaN layer, a gate electrode, source electrode, drain electrode, gate field plate, insulating layer, passivation layer, and silicide for adjusting the two-dimensional electron gas concentration; the AlGaN doped layer is located on the intrinsic AlGaN layer, and the p-type GaN layer is located on the On the AlGaN doped layer, the source and drain electrodes and the insulating layer are located on the AlGaN doped layer, the gate electrode is located on the p-type GaN layer, and the silicide is located on the insulating layer; an enhanced AlGaN/ GaN heterojunction material, and form the source electrode and the drain electrode on the heterojunction material, and then deposit a layer of insulating layer, wherein the thick insulating layer is located between the gate electrode and the drain electrode, close to the gate electrode, with a thickness of 200nm-700nm, the thin insulating layer is respectively located between the thick insulating layer and the drain electrode and between the gate electrode and the source electrode, with a thickness of 5-10nm, and silicide is formed between the gate-drain region and the gate-source region on the insulating layer , the silicide will introduce compressive stress to the insulating layer and the AlGaN layer, and the AlGaN layer located between the silicides will be subjected to tensile stress, and the block spacing is smaller than the block width so that the AlGaN layer generally obtains tensile stress, thereby enhancing the 2DEG in the channel. The silicide includes NiSi, TiSi ₂ or Co ₂ Si, and the silicide on the thick insulating layer is electrically connected to the gate electrode to form a gate field plate; there is a p-GaN epitaxial layer under the gate electrode to form an enhancement device. Finally, a passivation layer is deposited to passivate the device.

The above descriptions are only examples of the present invention, and are not intended to limit the present invention. Various suitable modifications and variations are possible in the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. A grid field plate enhanced AlGaN/GaN HEMT device structure, characterized in that: the structure includes a substrate, an intrinsic GaN layer, an AlN spacer, an intrinsic AlGaN layer, an AlGaN doped layer, and a p-type GaN layer , gate electrode, source electrode, drain electrode, gate field plate, insulating layer, passivation layer, and silicide for adjusting the channel electric field; the AlGaN doped layer is located on the intrinsic AlGaN layer, and the p-type GaN layer is located on the On the AlGaN doped layer, the source and drain electrodes and the insulating layer are located on the AlGaN doped layer, the gate electrode is located on the p-type GaN layer, and the silicide is located on the insulating layer; an enhanced AlGaN/ GaN heterojunction material, and form the source electrode and the drain electrode on the heterojunction material, and then deposit a layer of insulating layer, wherein the thick insulating layer is located between the gate electrode and the drain electrode, close to the gate electrode, with a thickness of 200nm-700nm, the thin insulating layer is respectively located between the thick insulating layer and the drain electrode and between the gate electrode and the source electrode, with a thickness of 5-10nm, and silicide is formed between the gate-drain region and the gate-source region on the insulating layer , the silicide is blocky, which will introduce compressive stress to the insulating layer and the AlGaN layer, and the AlGaN layer between the silicides will be subject to tensile stress. 2DEG is enhanced. The silicide includes NiSi, TiSi ₂ or Co ₂ Si. The silicide on the thick insulating layer is electrically connected to the gate electrode to form a gate field plate; there is a p-GaN epitaxial layer under the gate electrode to form an enhanced Devices, and finally deposit a passivation layer to achieve device passivation. 2. The device structure of field plate enhanced AlGaN/GaN HEMT according to claim 1, wherein the substrate material is sapphire, silicon carbide, GaN or MgO. 3. The device structure of the grid field plate enhanced AlGaN/GaN HEMT according to claim 1, characterized in that: the composition of Al and Ga in the intrinsic AlGaN layer and the AlGaN doped layer can be adjusted, Al _x Ga _1-x x=0~1 in N. 4. The device structure of grid field plate enhanced AlGaN/GaN HEMT according to claim 1, characterized in that: the intrinsic GaN layer is replaced by an AlGaN layer, and the composition of Al in the AlGaN is smaller than the intrinsic AlGaN layer and AlGaN layer Al composition in the doped layer. 5 . The device structure of enhanced gate field plate AlGaN/GaN HEMT according to claim 1 , wherein the p-type GaN layer material is replaced by p-type AlGaN material or p-type InGaN material. 6. The device structure of enhanced AlGaN/GaN HEMT with gate field plate according to claim 1, characterized in that: the silicide on the thick insulating layer is electrically connected with the gate electrode to form a gate field plate, which increases the breakdown voltage of the device. 7. A fabrication method based on a field plate enhanced AlGaN/GaN HEMT device structure comprising the following steps: (1) The epitaxially grown enhanced p-GaN/AlGaN/GaN material is organically cleaned, cleaned with flowing deionized water, and etched in a solution with a volume ratio of HCl:H ₂ O = 1:1 for 30-60s , and finally washed with flowing deionized water and dried with high-purity nitrogen; (2) Perform photolithography and dry etching on the cleaned p-GaN/AlGaN/GaN material to form active region mesas; (3) Perform photolithography on the p-GaN/AlGaN/GaN material prepared on the mesa to form an etching region of p-GaN; (4) and put the material into the ICP dry etching reaction chamber, the process conditions are: the power of the upper electrode is 200W, the power of the lower electrode is 20W, the pressure of the reaction chamber is _1.5Pa , the flow of Cl is 10sccm, and the flow of Ar gas The flow rate is 10sccm, the etching time is 10min, and the p-GaN epitaxial layer outside the gate electrode area is etched away; (5) Perform photolithography on the etched p-GaN/AlGaN/GaN material to form a source-drain electrode contact area, and put it into an electron beam evaporation table to deposit ohmic contact metal Ti/Al/Ni/Au=20/120/ 45/50nm and peel off, and finally perform rapid thermal annealing at 850°C for 35s in a nitrogen environment to form an ohmic contact; (6) Put the device into a magnetron sputtering reaction chamber to prepare Al ₂ O ₃ thin films, the process conditions are: the DC bias voltage of the Al target is 100V, the Ar gas flow is 30 sccm, the O flow is 10 sccm, the pressure of the reaction chamber 0.5Pa, deposit a 300nm thick Al ₂ O ₃ film; (7) Perform photolithography and development on the deposited device to form a wet etching area of _Al2O3 film, put the material into a solution with a volume ratio of HF _{: H2O} =1:10, etch for 3-5min, Etch Al ₂ O ₃ to 5-10nm; (8) Then put the device into the magnetron sputtering reaction chamber to sputter Ni and Si simultaneously. The process conditions are: the DC bias voltage of the Ni target is 100V, the RF bias voltage of the Si target is 450V, and the carrier gas Ar The flow rate is 30sccm, and a mixed metal film with a thickness of 100nm to 150nm is co-deposited; (9) Perform photolithography on the device with the deposited film to form the etching window area of the mixed film, and put it into the ICP dry etching reaction chamber. The process conditions are: the power of the upper electrode is 200W, and the power of the lower electrode is 20W , the reaction chamber pressure is 1.5Pa, the flow rate of CF ₄ is 20sccm, the flow rate of Ar gas is 10sccm, and the etching time is 5min. the spacing between the blocks is smaller than the silicide block width; (10) Put the device into a rapid annealing furnace, and perform rapid thermal annealing at 450°C for 30s in a nitrogen atmosphere to form a NiSi alloy. The silicide will introduce compressive stress to the insulating layer and the AlGaN layer, and the AlGaN between the silicide The layer will be subjected to tensile stress. By making the block spacing smaller than the block width, the AlGaN layer will obtain tensile stress as a whole, thereby enhancing the 2DEG in the channel; (11) Perform photolithography on the completed alloy device to form the gate electrode and the gate field plate region, and put the device into a solution with a volume ratio of HF:H ₂ O = 1:1 to complete the Al ₂ O ₃ in the gate electrode region Etch to form gate electrode and grid field plate window, then put Ni/Au=20/200nm into the electron beam evaporation station to deposit and lift off, and complete the preparation of gate electrode and grid field plate; (12) Put the device with the gate electrode prepared into the PECVD reaction chamber to deposit the SiN passivation film. The specific process conditions are: the flow rate of SiH ₄ is 40 sccm, the flow rate of NH ₃ is 10 sccm, the pressure of the reaction chamber is 1-2Pa, radio frequency With a power of 40W, deposit a SiN passivation film with a thickness of 200nm to 300nm; (13) The device is cleaned again, photolithographically developed, and the etching area of the SiN film is formed, and put into the ICP dry etching reaction chamber. The process conditions are: the power of the upper electrode is 200W, and the power of the lower electrode is 20W. The chamber pressure is 1.5 Pa, the flow rate of CF ₄ is 20 sccm, the flow rate of Ar gas is 10 sccm, and the etching time is 10 min, and the SiN and Al ₂ O ₃ films covered on the source electrode, drain electrode and gate electrode are etched away; (14) The device is cleaned, photolithographically developed, and placed in an electron beam evaporation station to deposit a thickened electrode with Ti/Au=20/200nm to complete the preparation of the overall device.