CN112993019A - GaN HEMT radio frequency device with air bridge field plate structure and preparation method thereof - Google Patents

GaN HEMT radio frequency device with air bridge field plate structure and preparation method thereof Download PDF

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CN112993019A
CN112993019A CN202110182884.7A CN202110182884A CN112993019A CN 112993019 A CN112993019 A CN 112993019A CN 202110182884 A CN202110182884 A CN 202110182884A CN 112993019 A CN112993019 A CN 112993019A
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layer
electrode
gan
field plate
plate structure
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孙慧卿
王鹏霖
黄志辉
丁霄
郭志友
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South China Normal University
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
    • H01L29/76—Unipolar devices, e.g. field effect transistors
    • H01L29/772—Field effect transistors
    • H01L29/778—Field effect transistors with two-dimensional charge carrier gas channel, e.g. HEMT ; with two-dimensional charge-carrier layer formed at a heterojunction interface
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/40—Electrodes ; Multistep manufacturing processes therefor
    • H01L29/402—Field plates
    • H01L29/404—Multiple field plate structures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
    • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
    • H01L29/66007—Multistep manufacturing processes
    • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
    • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
    • H01L29/66409—Unipolar field-effect transistors
    • H01L29/66446—Unipolar field-effect transistors with an active layer made of a group 13/15 material, e.g. group 13/15 velocity modulation transistor [VMT], group 13/15 negative resistance FET [NERFET]
    • H01L29/66462—Unipolar field-effect transistors with an active layer made of a group 13/15 material, e.g. group 13/15 velocity modulation transistor [VMT], group 13/15 negative resistance FET [NERFET] with a heterojunction interface channel or gate, e.g. HFET, HIGFET, SISFET, HJFET, HEMT

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Abstract

The invention relates to a GaN HEMT radio frequency device with an air bridge field plate structure and a preparation method thereof, wherein the GaN HEMT radio frequency device comprises a buffer layer, a channel layer, an AlN insert layer and a barrier layer which are sequentially laminated on a substrate; the source electrode and the drain electrode are positioned on the barrier layer; the GaN cap layer is positioned between the source electrode and the drain electrode, and the grid electrode is positioned on the cap layer; the passivation layer continuously spans and covers between the source electrode and the grid electrode, between the grid electrode and the drain electrode; one end of the air bridge field plate structure with the symmetrical step-shaped section extends across the space between the source electrode and the grid electrode, the space between the grid electrode and the drain electrode along the surface of the source electrode, and the other end of the air bridge field plate structure is positioned between the grid electrode and the drain electrode; an air region is arranged between the passivation layer and the symmetrical step-shaped air bridge field plate structure. The design of inserting an AlN thin layer between the heterojunction and combining the symmetrical step-shaped air bridge field plate structure obviously improves the radio frequency performance and the high-temperature stability of the device, and in addition, the preparation method is simple, the process reliability is high, and the industrial application prospect is good.

Description

GaN HEMT radio frequency device with air bridge field plate structure and preparation method thereof
Technical Field
The invention relates to the field of radio frequency devices, in particular to a GaN HEMT radio frequency device with an air bridge field plate structure and a preparation method thereof.
Background
In recent years, GaN-based HEMT devices have attracted attention in the power electronics field due to their excellent properties, particularly excellent dc breakdown voltage and ac frequency properties, and thus, research into methods for improving the radio frequency characteristics of GaN devices has become a major focus in this field. The introduction of methods and structures such as gradual channel changing, doping and the like promotes the improvement of the overall performance of the HEMT device, and lays a foundation for the current wider application requirements. However, in the prior art, the contradiction between the high frequency and other performance parameters of the device is still outstanding, and the reliability and the stability in a high-temperature state are also insufficient, so how to better solve the problems and further improve the radio frequency comprehensive performance of the device is a focus of current internal and external concerns.
The field plate structure refers to a metal plate which is connected with the device electrode, can be synchronously prepared with the preparation of the device electrode and interconnection metal, and has the advantage that the overall electrical performance of the device can be changed by changing the electric field distribution on one side of the grid. The invention is based on an air bridge field plate structure, is used in a radio frequency device, optimizes the performance of the radio frequency device by improving the air bridge field plate structure, and provides a scheme of the invention based on the scheme.
Disclosure of Invention
Based on the structure, the GaN HEMT radio frequency device with the air bridge field plate structure and the preparation method thereof are provided, the radio frequency device adopts a symmetrical step-shaped air bridge field plate structure, one end of the field plate structure extends from the surface of a source electrode to cross a region between the source electrode and a grid electrode, the grid electrode and a region between the grid electrode and a drain electrode, the other end of the field plate structure is positioned between the grid electrode and the drain electrode, the region crossing the grid electrode is provided with a thickened metal layer, and the step-shaped structure is approximately equivalent to a symmetrical inverted V shape with an inclined angle in mechanics. The arrangement of the structure can effectively adjust the distribution condition of the electric field of the device channel, and the air bridge structure adopts a medium bridge structureThe generation of parasitic capacitance can be reduced more remarkably, thereby improving the radio frequency performance of the device. Specifically, the HEMT device cutoff frequency fMAnd the highest oscillation frequency fMAXThe structure is closely related to the gate-source parasitic capacitance, especially the parasitic capacitance generated between the source end bridging part and the gate, so that the parasitic capacitance can be effectively reduced and the radio-frequency performance of the device can be improved by adopting the air bridge gate field plate structure with a high bridge floor. Further, the symmetrical step-shaped air bridge gate field plate can bear more severe temperature change and larger pressure compared with a parallel plate air bridge structure which is easy to collapse and short-circuit. The stepped structure is similar to symmetrical inverted V-shaped structure with inclined angle in mechanics, and has certain inclined angle to expand the metal volume at high temperature to produce great elasticity in the metal bridge structure and horizontal component FsVertical component force F due to horizontal symmetry of air bridgecBut also can well balance the tendency that the metal bridge collapses downwards due to the self weight, and achieve the effects of more reliability and stability. Meanwhile, the symmetrical steps avoid adopting an arch structure or other semi-annular structures with high-temperature stability, the preparation process is suitable for the neutral and comprehensive performances of devices, the preparation process is simpler, and the process stability is better.
In addition, the radio frequency device adopts the AlGaN/GaN heterojunction 2DEG as an electronic channel layer, an AlN thin layer is inserted between the AlGaN/GaN heterojunction, the effective conduction band step is improved, the potential well can be deepened, the confinement property of the 2DEG is improved, the stability of the quantum property of the AlGaN/GaN heterojunction is kept, factors such as parallel conductance outside the channel caused by thermal activation and the like are inhibited, and on the other hand, the AlN layer is inserted between the barrier layer and the GaN channel layer, so that the barrier layer has the lowest density of threading dislocation and the most uniform stress distribution, the extension defect of the barrier layer is reduced, and the growth quality of the AlGaN is obviously improved. Based on the above purpose, the invention at least adopts the following scheme:
GaN HEMT radio frequency device with air bridge field plate structure includes: the buffer layer, the GaN channel layer, the AlN insertion layer and the AlGaN barrier layer are sequentially stacked on the substrate; a source and a drain on the AlGaN barrier layer; the p-type GaN cap layer is positioned between the source electrode and the drain electrode, and the grid electrode is positioned on the p-type GaN cap layer; the passivation layer continuously spans and covers the region between the source electrode and the grid electrode, the grid electrode and the region between the grid electrode and the drain electrode; one end of the air bridge field plate structure with the symmetrical step-shaped section extends across the region between the source electrode and the grid electrode, the grid electrode and the partial region between the grid electrode and the drain electrode along the surface of the source electrode, and the other end of the air bridge field plate structure is positioned on the passivation layer of the partial region between the grid electrode and the drain electrode; an air region is arranged between the passivation layer and the symmetrical step-shaped air bridge field plate structure.
Preferably, the air bridge field plate structure has a thickened metal layer in a region crossing the gate; the width of the end face of the air bridge field plate structure, which is contacted with the source electrode, is equal to the width of the source electrode.
Preferably, the air bridge field plate structure takes a vertical bisector of a cross section of the gate electrode as a symmetry axis in the horizontal direction.
Preferably, the cross section of the air region between the passivation layer and the air bridge field plate structure is in a gate hole shape with a flat top shape.
Preferably, the AlN insert layer has a thickness of 1 to 2 nm; the thickness of the AlGaN barrier layer is preferably 10-20 nm, and the Al component is 0.25-0.3; the thickness of the GaN channel layer is 10-20 nm.
Preferably, the thickness of the p-type GaN cap layer region is 2-2.5 nm, and the doping concentration is 1-2 multiplied by 1018cm-3。
Preferably, the buffer layer is a GaN buffer layer, and an AlN nucleation layer disposed on the substrate and a GaN transition layer disposed on the AlN nucleation layer are further included between the substrate and the GaN buffer layer; the thickness of the GaN transition layer is 150-250 nm, and the thickness of the GaN buffer layer is 1.5-2 mu m.
Preferably, the passivation layer is preferably SiN, and the thickness of the passivation layer near the gate is at least equal to the thickness of the passivation layer in the region between the source or drain and the gate.
The invention also provides a preparation method of the GaN HEMT radio frequency device with the air bridge field plate structure, which comprises the following steps:
sequentially epitaxially growing a GaN buffer layer, a GaN channel layer, an AlN insert layer and an AlGaN barrier layer on a substrate;
depositing a passivation layer on the AlGaN barrier layer, and etching the passivation layer to form a source electrode window, a grid electrode window and a grid electrode window positioned between the source electrode and the grid electrode window;
epitaxially growing a p-type GaN cap layer in the gate window, forming a gate on the GaN cap layer, and forming a source electrode and a drain electrode in the source electrode and drain electrode windows;
depositing a passivation layer to cover the region between the source electrode and the grid electrode and the region between the grid electrode and the drain electrode;
photoetching the surface of the passivation layer to form a gate hole-shaped sacrificial layer with a flat-top section;
depositing a metal layer on the surface of the source electrode and the surface of a part of the passivation layer between the grid electrode and the drain electrode to form a flat-top gate-opening-shaped metal layer;
removing the gate-hole-shaped sacrificial layer;
symmetrical rectangular sacrificial layers with the width equal to that of the source electrode are formed on the two end sides of the surface of the door-opening-shaped metal layer respectively, thickened metal layers are deposited among the sacrificial layers, and then the sacrificial layers are removed to form an air bridge field plate structure with a symmetrical step-shaped cross section.
Preferably, the thickness of the passivation layer in the vicinity of the gate is at least equal to the thickness of the passivation layer in the region between the source or drain electrode and the gate.
Drawings
Fig. 1 is a schematic cross-sectional structure diagram of a GaN HEMT radio-frequency device with an air-bridge field plate structure according to an embodiment of the present invention.
FIG. 2 is a flow chart of a method of making an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings, and the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by persons of ordinary skill in the art without any creative effort belong to the protection scope of the present invention.
The present invention will be described in further detail below. Referring to fig. 1, an embodiment of the present invention provides a GaN HEMT rf device with an air bridge field plate structure, which includes a substrate 11, a GaN buffer layer 22, a GaN channel layer 23, an AlN insertion layer 31, and an AlGaN barrier layer 41 stacked on the substrate 11 in sequence, a source 61 and a drain 62 are respectively located at two end sides of a surface of the AlGaN barrier layer 41, a p-type GaN cap 51 is located between the source 61 and the drain 62, the p-type GaN cap 51 is close to the source 61, and a gate 63 is located on a surface of the p-type GaN cap 51.
The substrate 11 is preferably a semi-insulating 4H-SiC type or 6H-SiC type substrate, which can be back-thinned to about 150 to 200 μm. The substrate 11 and the GaN buffer layer 22 further include an AlN nucleation layer 12 disposed on the substrate 11 and a GaN transition layer 21 disposed on the AlN nucleation layer. The thickness of the GaN transition layer 21 is 150-250 nm, and the thickness of the GaN buffer layer is 1.5-2 μm. The thickness of the p-type GaN cap layer area is 2-2.5 nm, and the doping concentration is 1-2 multiplied by 1018cm-3。
In a preferred embodiment, the AlN insert layer has a thickness of 1 to 2 nm. The AlGaN barrier layer 41 preferably has a thickness of 10 to 20nm, and has an Al component of 0.25 to 0.3. The thickness of the GaN channel layer is 10-20 nm. The heterojunction 2DEG formed by AlGaN/GaN is used as an electron channel layer, and compared with the traditional GaN device, the electron mobility can be improved, and the high-frequency performance can be enhanced. In addition, an AlN thin layer is inserted between the AlGaN/GaN heterojunction, so that the effective conduction band order is improved, the confinement property of 2DEG can be improved while the potential well is deepened, the stability of the quantum property of the potential well is kept, and factors such as parallel conductance outside a channel caused by thermal activation are inhibited. On the other hand, inserting AlN between the barrier layer and the GaN channel layer can enable the barrier layer to have lowest density of threading dislocation and most uniform stress distribution, thereby reducing the extension defect of the barrier layer and obviously improving the growth quality of AlGaN.
The passivation layer 64 is disposed between the source electrode 61 and the drain electrode 62. The passivation layer 64 continuously spans the region covered between the source electrode 61 and the gate electrode 63, and the region between the gate electrode 63 and the drain electrode 62. The thickness of the passivation layer near the gate is at least equal to the thickness of the passivation layer in the region between the source or drain and the gate. Specifically, the passivation layer near the gate can be thickened according to the requirements of the actual process to gradually adjust the electric field distribution nearby, and the passivation layer is in a convex shape and is higher than the source electrode and the drain electrode. An ellipsometer can be used for monitoring parameters of the passivation layer, and the parameters such as the thickness, the electric leakage and the like of the passivation layer can be ensured to meet requirements.
One end of the air-bridge field plate structure 71 extends across the region between the source and gate, the gate and a portion of the region between the gate and drain along the surface of the source electrode 61. As shown in fig. 1, the section of the air bridge field plate structure 71 is in a symmetrical step shape, and the air bridge field plate structure uses the vertical bisector of the cross section of the gate electrode as a symmetry axis in the horizontal direction to offset the horizontal elastic force component generated by heating the metal, so as to maintain high stability. One end of the air-bridge field plate structure 71 is disposed on the surface of the source electrode 61, and the width of the end surface is equal to the width of the source electrode. The other end is arranged on the surface of the passivation layer between the grid electrode 63 and the drain electrode 62. An air dielectric region 72 is present between the air bridge field plate structure 71 and the passivation layer 64, and the cross section of the air dielectric region is in a gate-hole shape with a flat top shape. As shown in fig. 1, the air bridge field plate structure 71 has a thickened metal layer in a region crossing the gate, the step-shaped structure is designed to be approximately equivalent to a symmetrical inverted "V" shape with an inclined angle in mechanics, and due to a certain inclined angle, the metal volume expands at high temperature, so that a large elastic force is generated in the metal bridge structure, and the horizontal component F of the elastic forcesVertical component force F due to horizontal symmetry of air bridgecBut also can well balance the tendency that the metal bridge collapses downwards due to the self weight, and achieve the effects of more reliability and stability. Meanwhile, the symmetrical steps avoid adopting an arch structure or other semi-annular structures with high-temperature stability, the preparation process is suitable for neutral and the comprehensive performance of the device can be better considered, and the preparation process is simpler.
Based on the device structure, an embodiment of the invention also provides a preparation method of the GaN HEMT radio-frequency device with the air bridge field plate structure, which comprises the following steps:
and selecting a semi-insulating SiC substrate, and carrying out epitaxial growth by adopting a Metal Organic Chemical Vapor Deposition (MOCVD) process. Firstly, cleaning a high-temperature substrate at about 1000 ℃, and introducing hydrogen into a reaction chamber to remove pollutants on the surface of the substrate. Is connected withAnd an AlN nucleating layer with the thickness of 20-100 nm is epitaxially grown by adopting an indirect ammonia supply growth mode at 1000 ℃, so that the residual stress of the GaN obtained at the later stage is reduced, and the possibility of pre-reaction of reactants is reduced in a time-sharing transportation mode. Wherein the intermittent ammonia supply can adopt TMA continuous feeding and NH3The flow rate of TMA is 13sccm and NH is performed in a cycle of 20s introduction and 20s stop introduction3The flow rate was 800 sccm. The nucleation center is formed through the step, so that the adhesion of the GaN and the substrate can be increased, and the surface appearance and the growth structure are perfected.
The growth of the nucleation layer is then annealed and resurfaced, and the variation in temperature facilitates the formation of high quality GaN epitaxial layers.
Continuously growing a GaN transition layer with the thickness of about 150-250 nm on the AlN nucleating layer at the temperature of 1000-1100 ℃, and introducing H2、NH3A gallium source with pressure of 5300-5500 Pa and H2Flow rate 500sccm, NH3The flow rate of the gallium source is 5000sccm, the flow rate of the gallium source is 220sccm, and the doping is not performed intentionally. After the growth of the transition layer, in NH3And reducing the temperature in the atmosphere to ensure that the GaN layer is not decomposed.
Then epitaxially growing a GaN buffer layer of 1.5-2 μm on the GaN transition layer, doping C, and adopting N2As carrier gas, CCl4The flow rate is 0.015-0.02 mu mol/min.
Then, a GaN channel layer with the thickness of 10-20 nm is grown on the GaN transition layer, and H is introduced2、NH3The growth temperature of the gallium source is set to 900-920 ℃, the gallium source is unintentionally doped, the pressure is 5300-5500 Pa, and H is2Flow rate 500sccm, NH3The flow rate of (1) is 5000sccm, and the flow rate of the gallium source is 220 sccm.
And then growing an AlN insert layer with the thickness of about 1-2 nm on the GaN channel layer by an intermittent ammonia supply mode, wherein the thickness is optimally 1.2 nm. The intermittent ammonia supply can adopt TMA continuous introduction and NH3The flow rate of TMA is 13sccm and NH is performed in a cycle of 20s introduction and 20s stop introduction3The flow rate is 800sccm, and the temperature is preferably 1000-1050 ℃;
then, H is introduced2、NH3Gallium source and aluminum source, the growth temperature is set to 900-920 ℃, and the growth is carried out by unintentional dopingThe AlGaN barrier layer is 10-20 nm thick and contains 25-30% of Al, and the AlGaN layer and the GaN channel layer form an AlGaN/GaN heterojunction.
And depositing a SiN passivation layer on the AlGaN barrier layer by adopting a Plasma Enhanced Chemical Vapor Deposition (PECVD) method. Wherein the power is set to 20-30W, N2O flow rate of 800sccm, SiH4The flow rate was 150sccm and the temperature was 250 ℃. The whole thickness range of the passivation layer is 20-40 nm. And simultaneously, carrying out forward baking and soft baking on the surface of the passivation layer by adopting a wet etching method, then forming a window through exposure and development, and etching the growth window of the p-GaN cap layer.
Carrying out epitaxial growth on a p-GaN growth window by adopting a Metal Organic Chemical Vapor Deposition (MOCVD) process with the doping concentration of 1-2 multiplied by 1018cm-3And the p-GaN cap layer with the thickness of 2-2.5 nm adopts the same growth temperature and pressure as those of the GaN buffer layer, the pressure is set to be 5300-5500 Pa, and the temperature range is 1000-1100 ℃.
And manufacturing a source electrode, a drain electrode and a grid electrode by adopting an electron beam evaporation deposition method. Bombarding the metal target material by using electron beams, and heating, vaporizing and depositing the target metal. Depositing Ti/Al/Ni/Au metal on a p-GaN cap layer, forming an electrode through a metal stripping process, and then adopting a rapid annealing process, wherein argon is selected as a protective gas, the annealing temperature is 900-1000 ℃, the annealing time is 30-40 s, and a grid electrode is formed, wherein the thickness of Ti is 10nm, the thickness of Al is 50nm, the thickness of Ni is 10nm, and the thickness of Au is 20 nm. And then depositing metal Ni/Au on the AlGaN/GaN heterojunction by an electron beam evaporation method under the vacuum condition, and stripping the metal to form a contact electrode on the surface of the AlGaN. Vacuum degree less than 2.0 × 10-6Pa, power range of 150-200W, evaporation rate of 2-3 angstroms/second.
Continuously adopting PECVD to deposit the SiN passivation layer, and setting the power to be 20-30W, N2O/N2Flow rate is 800-900 sccm, SiH4The flow rate is 100-150 sccm, the temperature and pressure are 250 ℃ and 1000mT respectively, the thickness is 30-60 nm, wherein the nitrogen source and SiH4The ratio of Si and N elements tends to be averaged when the gas flow rate ratio is 10. The passivation layer covers a region between the source electrode and the gate electrode, and a region between the gate electrode and the drain electrode.The SiN passivation layer near the grid can be thickened according to the actual process requirement to gradually adjust the electric field distribution nearby, and is in a convex shape and is higher than the source electrode and the drain electrode. After passivation, an ellipsometer can be used for monitoring parameters of the passivation layer, and the parameters of thickness, electric leakage and the like of the passivation layer can meet requirements.
And then growing a symmetrical step-shaped air bridge field plate structure. Firstly, a composite colloid structure consisting of stripping glue and photoresist is adopted to grow a door-opening-shaped sacrificial layer with a flat-top section, wherein the upper layer uses photoresist (660 type and the like), the soft baking temperature is 80-90 ℃, the lower layer uses stripping glue, the soft baking temperature is 140-160 ℃, the composite glue ratio of the photoresist and the stripping glue is 40-60%, and therefore bridge pier displacement and short circuit of bridge bottom metal and bridge piers are avoided. As shown in fig. 1, a gate hole-shaped sacrificial layer having a flat top-shaped cross section (the shape is the same as that of the air dielectric region 72) is formed, and then annealed at room temperature.
Then, O is used2Plasma is used for coating a bottom film, and then an electron beam evaporation table is used for depositing a thin coating (electroplating conductive layer). An electron beam evaporation table is used for depositing a layer of Ti easy to corrode on the surface of a source electrode and the surface of a passivation layer between a grid electrode and a drain electrode, and then Au is deposited on the Ti by the same method to enhance the adhesion and the reliability of a device, wherein the deposition rate is 0.1nm/s, the thickness of the Ti is 1-5 nm, and the thickness of the Au is 4-20 nm. And (3) carrying out exposure and development by using a photoetching plate to obtain an electroplating thickened area, namely the primary form of the air bridge field plate structure.
Then, a mask pattern of the plating region is formed, and a plating solution of a cyanide-free Au plating solution is selected to perform thickening plating to form a bridge floor. And removing the photoresist part which is completely developed to ensure that the electroplating area is as flat as possible. The electroplating temperature is kept constant at 35-45 ℃ as far as possible, and the electroplating speed is 1-5 nm/min.
And finally, removing the mask layer photoresist by adopting an exposure, development and corrosion method. And performing flood exposure treatment, and then removing the photoresist by using a developing solution to remove the electroplated mask layer.
Then, the plating layer is etched. The corrosion Au solution adopts KI solution with the corrosion rate of 1-2 nm/s, and the corrosion Ti solution adopts HF solution with the solution concentration of 5-10% and the corrosion rate of 0.1-0.2 nm/s.
And then removing the door-opening-shaped sacrificial layer. And removing the photoresist by using an acetone solution to initially form a bottom bridge surface of the symmetrical step-shaped air bridge, wherein the bridge surface is a flat-top door-opening-shaped metal layer.
And then, symmetrical rectangular sacrificial layers with the width equal to that of the source electrode are respectively formed on two end sides of the surface of the formed door-opening-shaped metal layer and are used for forming a top metal electroplating area of the special-shaped air bridge. The sacrificial layer in this step may be selected from photoresist.
Then, O is used2And (3) coating the base film by using plasma, and then depositing a thin plating layer (electroplating conductive layer) by using an electron beam evaporation table, wherein the deposition of the plating layer is consistent with the deposition process of the plating layer. And then, selecting cyanide-free electroplating solution for electroplating Au to perform thickening electroplating again until the plating solution is as high as the sacrificial layer, so as to form a top deck of the symmetrical stepped air bridge, namely the thickened deck. And then removing the photoresist again, treating the stripping glue solution at 50-60 ℃, and washing with deionized water. The high-temperature treatment time is 3-5 min, and the washing time is 5-10 min. The air bridge field plate structure with the cross section in a symmetrical step shape is formed.
Using N2And (3) drying the device, thinning the back surface of the semi-insulating substrate, and finally finishing the manufacture of the device shown in the figure 1.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (10)

1. GaN HEMT radio frequency device with air bridge field plate structure, its characterized in that includes: the buffer layer, the GaN channel layer, the AlN insertion layer and the AlGaN barrier layer are sequentially stacked on the substrate; a source and a drain on the AlGaN barrier layer; the p-type GaN cap layer is positioned between the source electrode and the drain electrode, and the grid electrode is positioned on the p-type GaN cap layer;
the passivation layer continuously spans and covers the region between the source electrode and the grid electrode, the grid electrode and the region between the grid electrode and the drain electrode;
one end of the air bridge field plate structure with the symmetrical step-shaped section extends across the region between the source electrode and the grid electrode, the grid electrode and the partial region between the grid electrode and the drain electrode along the surface of the source electrode, and the other end of the air bridge field plate structure is positioned on the passivation layer of the partial region between the grid electrode and the drain electrode;
an air region is arranged between the passivation layer and the symmetrical step-shaped air bridge field plate structure.
2. The GaN HEMT radio frequency device of claim 1, wherein said air-bridge field plate structure has a thickened metal layer across the region of the gate; the width of the end face of the air bridge field plate structure, which is contacted with the source electrode, is equal to the width of the source electrode.
3. The GaN HEMT radio-frequency device of claim 1 or 2, wherein said air-bridge field plate structure has a symmetry axis in the horizontal direction with a vertical bisector of the gate cross-section.
4. The GaN HEMT radio-frequency device of claim 1 or 2, wherein the cross section of the air region between the passivation layer and the air bridge field plate structure is in a shape of a flat-topped gate.
5. The GaN HEMT radio-frequency device according to claim 1 or 2, wherein the AlN insert layer has a thickness of 1-2 nm; the thickness of the AlGaN barrier layer is preferably 10-20 nm, and the Al component is 0.25-0.3; the thickness of the GaN channel layer is 10-20 nm.
6. The GaN HEMT radio-frequency device according to claim 5, wherein the thickness of the p-type GaN cap layer region is 2-2.5 nm, and the doping concentration is 1-2 x 1018cm-3。
7. The GaN HEMT radio frequency device of claim 5, wherein the buffer layer is a GaN buffer layer, and further comprising an AlN nucleation layer disposed on the substrate and a GaN transition layer disposed on the AlN nucleation layer between the substrate and the GaN buffer layer; the thickness of the GaN transition layer is 150-250 nm, and the thickness of the GaN buffer layer is 1.5-2 mu m.
8. The GaN HEMT radio frequency device of claim 1 or 2, wherein said passivation layer is preferably SiN, and the thickness of the passivation layer near the gate is at least equal to the thickness of the passivation layer in the region between the source or drain and the gate.
9. The preparation method of the GaN HEMT radio frequency device with the air bridge field plate structure is characterized by comprising the following steps of:
sequentially epitaxially growing a GaN buffer layer, a GaN channel layer, an AlN insert layer and an AlGaN barrier layer on a substrate;
depositing a passivation layer on the AlGaN barrier layer, and etching the passivation layer to form a source electrode window, a grid electrode window and a grid electrode window positioned between the source electrode and the grid electrode window;
epitaxially growing a p-type GaN cap layer in the gate window, forming a gate on the GaN cap layer, and forming a source electrode and a drain electrode in the source electrode and drain electrode windows;
depositing a passivation layer to cover the region between the source electrode and the grid electrode and the region between the grid electrode and the drain electrode;
photoetching the surface of the passivation layer to form a gate hole-shaped sacrificial layer with a flat-top section;
depositing a metal layer on the surface of the source electrode and the surface of a part of the passivation layer between the grid electrode and the drain electrode to form a flat-top gate-opening-shaped metal layer;
removing the gate-hole-shaped sacrificial layer;
symmetrical rectangular sacrificial layers with the width equal to that of the source electrode are formed on the two end sides of the surface of the door-opening-shaped metal layer respectively, thickened metal layers are deposited among the sacrificial layers, and then the sacrificial layers are removed to form an air bridge field plate structure with a symmetrical step-shaped cross section.
10. The method of claim 9, wherein the thickness of the passivation layer near the gate is at least equal to the thickness of the passivation layer in the region between the source or drain and the gate.
CN202110182884.7A 2021-02-08 2021-02-08 GaN HEMT radio frequency device with air bridge field plate structure and preparation method thereof Pending CN112993019A (en)

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