CN115662885A - GaN Schottky diode grown based on full HVPE process and preparation method thereof - Google Patents

Abstract

The invention provides a GaN Schottky diode grown based on a full HVPE process and a preparation method thereof, wherein the preparation method comprises the following steps: adopting HVPE process, using liquid metal gallium as Ga source, ammonia gas as N source and SiH ₄ An n-type doping source is adopted, the temperature gradient is strictly controlled, and an n-type GaN epitaxial layer grows on the double-polished GaN monocrystal self-supporting substrate; photoetching, exposing and developing the n-type GaN epitaxial layer, and then performing ion implantation to form a heavily doped P-type region; and removing the photoresist, and preparing an ohmic electrode and a Schottky electrode to obtain the GaN Schottky diode. The epitaxial layer of the invention contains C impurityThe amount is obviously reduced, and the carrier mobility of the material is effectively improved; the growth rate is high, and the method is suitable for the growth of the GaN thick film; low cost and is suitable for industrial large-scale production.

Description

GaN Schottky diode grown based on full HVPE process and preparation method thereof

Technical Field

The invention relates to the technical field of semiconductor materials, in particular to a GaN Schottky diode grown based on a full HVPE process and a preparation method thereof.

Background

Gallium nitride (GaN) is an important third-generation semiconductor material, and has excellent application prospect and market potential value in the fields of solid-state light sources, power electronics, microwave radio-frequency devices and the like due to the superior performances of large forbidden band width, high breakdown electric field, large heat conductivity, high electron saturation drift rate, strong radiation resistance and the like.

The vertical GaN diode has attracted great attention and is widely used because of its advantages of high voltage resistance, high temperature resistance, small size, etc. Common vertical GaN diodes are schottky diodes (SBDs), PN diodes (PNDs) and junction barrier schottky diodes (JBSs). Junction barrier schottky diodes (JBS) combine the advantages of schottky diodes and PN diodes, have high breakdown voltage and low reverse leakage, and are one of the indispensable components in GaN power devices. The conventional GaN schottky diode (JBS) is a device fabricated on an epitaxial layer (drift layer) grown on the basis of Metal Organic Chemical Vapor Deposition (MOCVD), and the method becomes one of the most popular methods in GaN epitaxial layer growth due to advantages such as precise doping precision and thickness control, and is also a poor choice for enterprise production. However, limited by the technology, this approach presents some significant problems:

(1) The MOCVD method easily introduces unintentionally doped carbon atoms associated with deep energy levels within the bandgap of the epitaxial layer during epitaxial growth.

(2) MOCVD has a slow growth rate, and cannot grow thicker (> 20 um) GaN epitaxial layers, so that the preparation of devices with high requirements on withstand voltage cannot be met.

(3) In the process of growing GaN by the MOCVD process, organic gallium source trimethyl gallium (TMGa) or triethyl gallium (TEGa) is used as a precursor of gallium, so that the production cost is high, and the method is not beneficial to enterprise-level large-scale production.

The prior art adopts Hydride Vapor Phase Epitaxy (HVPE) method to prepare epitaxial layer still has the problem that the carrier concentration is difficult to drop, and the control to the carrier is inferior to MOCVD, so that the epitaxial layer is difficult to prepare by adopting full HVPE in practical application.

In view of the above, there is a need for an improved GaN schottky diode grown based on the full HVPE process and a method for fabricating the same to solve the above problems.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide a GaN Schottky diode grown based on a full HVPE process and a preparation method thereof, wherein the content of C impurities in an epitaxial layer is obviously reduced, and the carrier mobility of the material is effectively improved; the growth rate is high, the theoretical growth speed is more than 100um/h, and the method is suitable for the growth of the GaN thick film; low cost and is suitable for industrial large-scale production.

In order to realize the aim, the invention provides a preparation method of a GaN Schottky diode based on full HVPE process growth, which comprises the following steps:

s1, growing an n-type GaN epitaxial layer on a double-polished GaN single crystal self-supporting substrate by adopting an HVPE (high voltage vapor phase epitaxy) process; the HVPE process comprises the following steps: liquid metal gallium is used as Ga source, ammonia gas is used as N source, siH ₄ As an n-type doping source, HCl-containing gas is flowed through liquid metal gallium by using inert gas to generate GaCl at 600-900 ℃; conveying the n-type doping source into an HVPE reaction chamber by using inert gas, wherein the temperature of the reaction chamber is 300-1000 ℃, and decomposing into Si and H; followed by reaction of GaCl with NH at 900-1200 deg.C ₃ Reacting with Si to obtain a GaN film doped with Si, and depositing the GaN film on the GaN monocrystal self-supporting substrate;

s2, photoetching, exposing and developing the n-type GaN epitaxial layer obtained in the step S1, then performing ion implantation, and forming two heavily doped P-type regions at two ends of the n-type GaN epitaxial layer;

and S3, removing the photoresist, and then preparing an ohmic electrode and a Schottky electrode to obtain the GaN Schottky diode.

Further, in step S1, the thickness of the n-type GaN epitaxial layer is 30-50 μm, and the carrier concentration of the n-type GaN epitaxial layer is controlled to be 0.5E16-2E16cm ^-3 To (c) to (d); the carrier concentration of the double-polished GaN single crystal self-supporting substrate is 2E18cm ^-3 。

Further, in step S1, the growth rate of the GaN thin film is controlled to be 5-20 μm/h, preferably 15 μm/h.

Furthermore, the growth mode of the double-polished GaN single crystal self-supporting substrate is to rapidly grow 800um massive GaN single crystal on a heterogeneous sapphire substrate by adopting HVPE, strip the substrate from the sapphire substrate by adopting a laser stripping mode, and finally thin the substrate to 500um by grinding and polishing.

Further, in step S2, photoresist is used as a barrier layer, three barrier regions are formed at two ends and in the middle of the surface of the n-type GaN epitaxial layer, and the width of the middle barrier region is greater than that of the barrier regions at the two ends.

Further, in step S2, the implanted ions are Mg ions, and are implanted into the P-type region uncovered by the photoresist, and the implantation depth is 500nm.

Furthermore, the ion implantation comprises two stages, the implantation energy of the first stage is 400KeV, and the implantation Dose is 1 × 10 ¹⁵ cm ^-3 (ii) a The second stage has an implantation energy of 50KeV and an implantation Dose of 1 × 10 ¹⁵ cm ^-3 The implantation angle was 7 °.

Further, in step S2, the photoresist removal is dry photoresist removal, and the processing method is O ₂ plasma, the gas used is O ₂ The gas flow rate was 100sccm, the power was 500W, the bias power was 100W, and the processing time was 10min.

Further, after photoresist removal is completed, the device is subjected to acid cleaning, and the used solution is dilute hydrochloric acid.

Further, in step S3, the metal adopted by the ohmic electrode is Ti, al, ni and Au in sequence, the thicknesses of the metal are 20nm, 100nm, 25nm and 40nm respectively, and the metal is subjected to rapid thermal annealing at 800 ℃ for 1min; the Schottky electrode is formed by sequentially plating Ni and Au metal films as Schottky electrodes of the device through a metal thermal evaporation coating instrument, and the thicknesses of the Schottky electrodes are respectively 25nm and 40nm.

The invention has the beneficial effects that:

according to the GaN Schottky diode grown based on the full HVPE process and the preparation method thereof, the preparation of the high-performance GaN Schottky diode is realized by strictly controlling the growth temperature of the epitaxial layer and simultaneously performing ion implantation. Compared with the traditional MOCVD process, the epitaxial layer has low content of C impurities in the growth process of the HVPE process, so that the carrier mobility of the material is effectively improved; the growth rate is high, the theoretical growth speed is more than 100um/h, and the method is suitable for the growth of the GaN thick film; low cost and is suitable for industrial large-scale production.

Drawings

FIG. 1 is a schematic structural view of a double-parabolic GaN self-supporting substrate.

FIG. 2 is a schematic view of a preparation structure of an n-type GaN epitaxial layer.

FIG. 3 is a schematic structural diagram of a target device after photolithography.

FIG. 4 is a schematic structural diagram of a target device after Mg ion implantation.

FIG. 5 is O ₂ The plasma processing process is shown schematically.

FIG. 6 is O ₂ And (5) a structural schematic diagram of the target device after plasma photoresist stripping.

Fig. 7 is a flow chart of a device etching process.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in detail below with reference to specific embodiments. It should be noted that, in order to avoid obscuring the present invention with unnecessary details, only the structures and/or processing steps closely related to the scheme of the present invention are shown in the specific embodiments, and other details not closely related to the present invention are omitted.

In addition, it is also to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.

The preparation method of the GaN Schottky diode based on the full HVPE process growth provided by the invention comprises the following steps:

as shown in FIG. 1, the device substrate is a double-polished GaN single crystal self-supporting substrate, which is grown by rapidly growing 800um bulk GaN single crystal on a heterogeneous sapphire substrate by HVPE, then peeling the bulk GaN single crystal from the sapphire substrate by laser peeling, and finally thinning the substrate to 500um by grinding and polishing, because the part of the bottom in contact with the sapphire is in large lattice mismatch. The substrate has a carrier concentration greater than 1E18cm ^-3 The carrier concentration of the substrate adopted by the invention is 2E18cm ^-3 . The thickness of the substrate of the vertical GaN diode is 150-400 um, and the thickness of the substrate is 300um (secondary thinning after epitaxy).

Then, an N-type GaN epitaxial layer grows on the GaN self-supporting substrate, the adopted growth equipment is HVPE, liquid metal gallium is used as a Ga source, ammonia gas is used as an N source, and the reaction process of the GaN self-supporting substrate comprises the following two steps:

Ga(l)+HCl(g)→GaCl(g)+H ₂ (g) (1)

firstly, liquid metal gallium reacts with HCl (g) to generate intermediate reactant GaCl, in the process, HCl-containing gas flows through metal Ga by using inert gas, the intermediate reactant with GaCl as a gallium source is generated at 600-900 ℃, and the reaction temperature is preferably 850 +/-30 ℃ (real-time adjustment is made according to the detection environment). And then transferred to the HVPE reaction chamber. The flow rate of the inert gas is usually 100 to 1000sccm, and the flow rate of the HCl-containing gas is usually 50 to 500sccm.

Next, an n-type dopant source is delivered into the HVPE reaction chamber using an inert gas. Typically, the n-type dopant source is SiH ₄ 。SiH ₄ Can be decomposed at high temperature to form n-type doping agent Si and waste gas H ₂ So that the HVPE reaction chamber is filled with the Si doping agent. In the process, the temperature of the HVPE reaction chamber is controlled at 300-1000 ℃ and SiH is controlled ₄ The decomposition is started at 300 ℃, the decomposition is accelerated at 600 ℃, the decomposition is completely decomposed into Si and H at 1000 ℃, and the actual temperature is determined according to the detection of the growth rate and the requirement of the carrier concentration. SiH ₄ The flow rate of the gas is generally 100-300sccm.

Finally, intermediate reactants GaCl and NH ₃ GaN is generated through reaction, the reaction temperature is between 900 and 1200 ℃, and the preferable temperature is 1050 +/-30 ℃ (because the HVPE reaction chamber is a quartz tube, si can be thermally decomposed due to too high temperature, and the carrier concentration is influenced). According to the thickness monitoring system, the growth speed and the thickness of the homoepitaxial gallium nitride film are fed back in real time, and the flow of the gallium source, the N-type doping source and the N source are adjusted, so that the growth speed of the homoepitaxial gallium nitride film is controlled to be 5-20 mu m/h, and the actual growth speed is 15 mu m/h. The carrier concentration of the n-GaN epitaxial layer is controlled to be 0.5E16-2E16cm-3, the thickness is 40um, and the concentration is 1E16 cm-3. The structure behind the GaN epitaxial layer is shown in fig. 2.

By the operation, the epitaxial layer HVPE method can be grown by strictly controlling the temperature gradient, and the thickness is controllable.

After the steps are completed, the target device is subjected to photoetching, exposure and development, a required pattern is left on the epitaxial layer, and then photoresist is used as a barrier layer to form a required shape on the epitaxial layer. The detailed steps of the photoetching are as follows: spin coating, baking, exposing and developing. The rotation speed is 5000r/min during glue homogenizing, the glue drying temperature is 100 ℃, and the time is 3min. The photoresist formed is about 1um thick. Exposure time 10s, development time 20s. The structure is shown in fig. 3.

After the photoetching step is finished, ion implantation is carried out on the device, and the purpose is to form a P-GaN terminal at the edge of an electrode, raise the potential, inhibit the concentration of a peak electric field and improve the withstand voltage of the device. The implantation ions used in the step are Mg ions and are implanted in two stages, the implantation energy of the first stage is 400KeV, the implantation Dose of the second stage is 1 multiplied by 1015cm < -3 >, and the implantation angle is 7 degrees. The depth of ion implantation is 500nm, and the two-stage implantation is performed to make the implantation uniform. The structure of the device after implantation is shown in fig. 4.

And after the ion implantation step is completed, carrying out photoresist removing treatment on the target device. Because the photoresist is used as a barrier layer in the ion implantation process, the photoresist is denatured under the bombardment of high-energy He ion beams, and a dry photoresist removing mode is adopted. The treatment method is O ₂ plasma as shown in fig. 5. The apparatus used is ICP, and the gas used is O ₂ The gas flow rate was 100sccm, the ICP source power was 500W, the bias power was 100W, and the processing time was 10min. The structure of the device after the photoresist stripping is completed is shown in fig. 6. After the photoresist is removed, the device is acid-washed with dilute hydrochloric acid (HCl: H) ₂ O =1:10 For the main purpose of removing O ₂ Impurities generated by the plasma process clean the device.

After all the steps are completed, ohmic electrode (Ohmic) and Schottky electrode (Anode) preparation is carried out on the target device. 1. Ohmic electrode: the ohmic electrode is made of metals such as Ti, al, ni and Au in sequence, the thicknesses of the metals are respectively 20nm, 100nm, 25nm and 40nm, and the metals are subjected to rapid thermal annealing at 800 ℃ for 1min; the Schottky electrode is formed by sequentially plating Ni and Au metal films as Schottky electrodes of the device through a metal thermal evaporation coating instrument, and the thickness of the Schottky electrode is 25nm and 40nm respectively. As shown in fig. 7.

In summary, according to the GaN schottky diode grown based on the full HVPE process and the method for manufacturing the same provided by the invention, the high-performance GaN schottky diode is manufactured by strictly controlling the temperature of the epitaxial layer growth and simultaneously performing ion implantation. Compared with the traditional MOCVD process, the epitaxial layer has low content of C impurities in the growth process of the HVPE process, so that the carrier mobility of the material is effectively improved; the growth rate is high, the theoretical growth speed is more than 100um/h, and the method is suitable for the growth of the GaN thick film; low cost and is suitable for industrial large-scale production.

Although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention.

Claims (10)

1. A preparation method of a GaN Schottky diode based on full HVPE process growth is characterized by comprising the following steps:

s1, growing an n-type GaN epitaxial layer on a double-polished GaN single crystal self-supporting substrate by adopting an HVPE (high voltage polyethylene) process; the HVPE process comprises the following steps: liquid metal gallium is used as Ga source, ammonia gas is used as N source, siH ₄ As an n-type doping source, HCl-containing gas is flowed through liquid metal gallium by using inert gas to generate GaCl at 600-900 ℃; conveying the n-type doping source into an HVPE reaction chamber by using inert gas, wherein the temperature of the reaction chamber is 300-1000 ℃, and decomposing into Si and H; followed by reaction of GaCl with NH at 900-1200 deg.C ₃ Reacting with Si to obtain a GaN film doped with Si, and depositing the GaN film on the GaN monocrystal self-supporting substrate;

s2, photoetching, exposing and developing the n-type GaN epitaxial layer obtained in the step S1, then performing ion implantation, and forming two heavily doped P-type regions at two ends of the n-type GaN epitaxial layer;

and S3, removing the photoresist, and then preparing an ohmic electrode and a Schottky electrode to obtain the GaN Schottky diode.

2. The method for preparing GaN Schottky diode grown based on full HVPE process according to claim 1, wherein in step S1, the thickness of the n-type GaN epitaxial layer is 30-50 μm, and the carrier concentration of the n-type GaN epitaxial layer is controlled to be 0.5E16-2E16cm ^-3 To (c) to (d); the carrier concentration of the double-polished GaN single crystal self-supporting substrate is 2E18cm ^-3 。

3. The method for preparing a GaN schottky diode grown based on the full HVPE process according to claim 1, wherein the growth rate of the GaN thin film is controlled to 5-20 μm/h, preferably 15 μm/h in step S1.

4. The method for preparing GaN Schottky diode grown based on full HVPE process according to any one of claims 1-3, wherein the double-polished GaN single crystal self-supporting substrate is grown by rapidly growing 800um bulk GaN single crystal on a heterogeneous sapphire substrate by HVPE, then peeling off the bulk GaN single crystal from the sapphire substrate by laser peeling, and finally thinning the substrate to 500um by grinding and polishing.

5. The method according to claim 1, wherein in step S2, a photoresist is used as a barrier layer, three barrier regions are formed at two ends and in the middle of the surface of the n-type GaN epitaxial layer, and the width of the middle barrier region is greater than that of the barrier regions at the two ends.

6. The method for preparing a GaN schottky diode grown based on the full HVPE process of claim 1, wherein in step S2, the implanted ions are Mg ions and are implanted in the P-type region uncovered by the photoresist to a depth of 500nm.

7. The method as claimed in claim 6, wherein the ion implantation comprises two stages, the first stage has an implantation energy of 400KeV and the Dose of implantation is 1 x 10 ¹⁵ cm ^-3 (ii) a The second stage has an implantation energy of 50KeV and an implantation Dose of 1 × 10 ¹⁵ cm ^-3 The implantation angle was 7 °.

8. The method for preparing GaN Schottky diode grown based on full HVPE process according to claim 1, wherein in step S2, the photoresist removal is dry photoresist removal, and the processing method is O ₂ plasma, the gas used is O ₂ The gas flow rate was 100sccm, the power was 500W, the bias power was 100W, and the processing time was 10min.

9. The method of claim 8, wherein the device is acid-washed after the photoresist is removed, and the solution is diluted hydrochloric acid.

10. The method for preparing the GaN schottky diode grown based on the full HVPE process according to claim 1, wherein in step S3, the metals adopted by the ohmic electrode are Ti, al, ni and Au in sequence, the thicknesses of which are 20nm, 100nm, 25nm and 40nm, respectively, and the rapid thermal annealing is performed at 800 ℃ for 1min; the Schottky electrode is formed by sequentially plating Ni and Au metal films as Schottky electrodes of the device through a metal thermal evaporation coating instrument, and the thicknesses of the Schottky electrodes are respectively 25nm and 40nm.

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