CN101162695A - Process for gallium nitride HEMT device surface passivation and improving device electric breakdown strength - Google Patents

Abstract

The manufacturing process of passivating the surface of gallium nitride HEMT device and increasing the electric breakdown strength of device is as follows: the gallium nitride HEMT device takes polycrystal carborundum or sappire (0001) or silicon (111) as the underlay, an aluminum nitride nucleating layer grows on the underlay by adopting MOCVD, a high resistance gallium nitride cushion breaker grows on the nucleating layer, a gallium and aluminum nitride layer with concentration gradient grows on the cushion breaker, one or multiple layer of nitride with surface passivation, photoetching and etching by dry method as well as metal vapor deposition are adopted to form ohmic electrodes, photoetching and etching by dry method are adopted to cut a groove between ohmic electrodes, and a grid is deposited in the groove. The device treated by the process is of small loss of drain radio-frequency current and increased electric breakdown strength of device as well as delivered power.

Description

The technology of gallium nitride HEMT device surface passivation and raising device electric breakdown strength

Technical field:

This invention relates to the broad stopband gallium nitride HEMT device surface passivation and handles the technology making that improves device electric breakdown strength with the utmost point.

Background technology:

1. wide bandgap semiconductor resembles gallium nitride (GaN) and carborundum (SiC) has than first generation semiconductor Si or the much higher saturated electrons mobility of second generation semiconductor GaAs (GaAs), this means that wide bandgap semiconductor can provide much higher power density and operating efficiency under high-frequency.The superelevation puncture voltage of GaN and SiC also makes the electronic device based on them can be operated in very high voltage and current, thereby greatly raises the efficiency.At last, in the much higher environment of the extremely outstanding thermal conductivity of the semiconductor material with wide forbidden band temperature that makes device to be operated in to bear than general semiconductor device.

2. exhausted most gallium nitride device adopts certain distortion of HFET (HFET).Its basic structure is that growth skim aluminum gallium nitride (AlGaN) forms heterojunction on the GaN channel layer.This layer AlGaN keeps apart conducting channel and control grid to reduce grid leakage current, finally improves the output radio-frequency power thereby increase gate breakdown voltage.The frequency of device depends on that grid are long.The grid length of typical case's gallium nitride device is about 0.5-1.5um (micron).

3. the most frequently used distortion is an AlGaN/GaN high electron mobility field effect transistor (HEMT).The channel current density of gallium nitride HEMT can reach GaAs or more than 2.5 times of indium phosphide (InP) device.Device architecture: the AlGaN that one deck silicon mixes up forms the heterojunction raceway groove with it on GaN, again with the extremely thin GaN protection surface of one deck.

4. the high electron mobility of gallium nitride HEMT makes it to become the desirable device that is applicable to the high-frequency high power applications.The electric current of flowing through wherein is also very high, gives the credit to the ability that the AlGaN/GaN heterojunction is kept the raceway groove high charge density.This is main because GaN is a kind of strong polar material, and the self poling electric field that it has has been assembled a layer charge automatically at the end face of crystal.The polarity of AlGaN is stronger, then form the polarization sudden change at interface with GaN, thus produce and the proportional interface charge of polarization difference.

5. further, the lattice of AlGaN and GaN does not match and produce piezoelectric effect in the AlGaN layer, the extra electron of One's name is legion is provided for the HEMT raceway groove.The result causes the total charge density in the raceway groove to surpass 10 ¹³Every square centimeter, be 4 to 5 times of GaAs HEMT.At this moment, the interface of AlGaN/GaN must precisely controlledly could guarantee the optimized electronic mobility under the piezoelectric effect.So high current density adds the high-breakdown-voltage of GaN, and gallium nitride HEMT becomes the electronic device of suitable high power applications.

6. to reliably realize the good characteristic of GaN HEMT, designs, the growth of material, technology making etc. plays crucial effects.

Summary of the invention

1. material is prepared (Fig. 1): carborundum is adopted in the making of GaN HEMT, high resistant (111) silicon, or (0001) prison jewel is made substrate (1), (AlN) nucleating layer (2) of employing MOCVD epitaxial growth one deck nitrogen aluminium on substrate; The GaN layer (3) that growth one deck is not intended to mix up on nucleating layer; The AlGaN layer (4) that growth one deck has concentration gradient on gallium nitride layer.The layer of surface passivation layer (5) at least of on the AlGaN layer, growing.Surface passivation layer adopts AlN, GaN and/or SiN.The thickness of passivation layer is at 100-3000 .

2. make Ohmic electrode (Fig. 2): at first adopt photoetching and dry etch process on passivation layer, to open the Ohmic electrode window; then the Ohmic electrode window is arrived in Ohmic electrode metal material (Ti/Al/Ni/Au) vacuum evaporation; on the ohmic metal material, cover layer protective layer again; after quick thermal annealing process, form Ohm contact electrode (10).

3. making platform isolates: utilization photoetching and dry etching are made the device platform and are isolated.

4. make the grid groove: (Fig. 3): adopt photoetching and dry etching, between Ohmic electrode, make the grid groove.The gradient and the degree of depth of groove are controlled meticulously by etching technics.The dry etching of grid groove adopts low damage ICP/RIE technology.In after groove is made device being carried out/process annealing handles, and repairs etch damage.

5. make grid (Fig. 4): the utilization photoetching, metal vacuum evaporation and metal are lifted separating process grid material (Ni/Au, Pt/Au, Ni/Pt/Au, Ni/Pd/Au, Pt/Ni/Au etc.) are deposited in grid (20) groove.

6. make dielectric layer (Fig. 5): after grid is made, the one dielectric layer (30) of on device, growing.Open on source drain with photoetching and dry etching then and connect the metal window.

7. electroplate gas bridge (Fig. 6): after grid completed, the source electrode of device connect (40) by electroplating the gas bridging.Drain electrode, source electrode and gate pads also improve thickness by electroplating, and strengthen conductive capability.

Description of drawings

Fig. 1: the material framework of making gallium nitride HEMT device

Fig. 2: make Ohmic electrode

Fig. 3: dry etching grid groove

Fig. 4: make grid

Fig. 5: growth dielectric layer, photoetching/dry etching dielectric layer

Fig. 6: conductive metal deposition, electroplate the gas bridge

Claims (6)

1. adopting carborundum/High Resistivity Si/sapphire is substrate, and growth contains the nucleating layer of AlN on substrate, the gallium nitride layer that growth is not intended to mix up on nucleating layer, the AlGaN layer of growth gradient concentration on gallium nitride layer.

2. growing surface passivation layer on gradient AlGaN layer, passivation layer be by GaN, AlN, and/or SiN constitutes.

3. adopt Ti/Al/Ni/Au to make Ohmic electrode.

4. after Ohmic electrode is made, make the grid groove.

5. gate deposition is in the grid groove.

6. grid material adopts Ni/Au, Pd/Au, Pt/Au, Ni/Pt/Au, Ni/Pd/Au, Pt/Ni/Au.

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