CN115565856A - A SiC power device ohmic contact, preparation method and application - Google Patents

Abstract

The invention discloses an ohmic contact of a SiC power device, a preparation method and application, comprising the steps of preprocessing the back surface of a 4H-SiC substrate, including the processes of etching and removing water vapor; preparing a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate; and finally, depositing a metal layer on the surface of the 3C-SiC crystal to prepare ohmic contact. The method simplifies the manufacturing process of ohmic contact, reduces specific contact resistance and power loss, and improves the reliability of the SiC power device.

Description

A SiC power device ohmic contact, preparation method and application

technical field

The invention relates to an ohmic contact, a preparation method and an application of a SiC power device, and belongs to the technical field of semiconductor power devices.

Background technique

Silicon devices are important electronic devices in the process of technological development. Since silicon devices are difficult to apply in high temperature, high frequency, high power, and strong radiation environments, there is an urgent need for high temperature applications such as aerospace, oil exploration, nuclear energy, and communications. For electronic devices working in the harsh environment of radiation, seeking a new generation of semiconductor materials has become one of the research hotspots in this field.

Silicon carbide has become the third-generation semiconductor material after silicon, germanium, and gallium arsenide due to its good physical and electrical properties. Since the first commercial silicon carbide substrate and epitaxial materials were reported in 1991, the process of manufacturing silicon carbide devices has made significant progress. However, some key manufacturing process problems of silicon carbide devices still need to be solved and improved. Among them, ohmic contact has always been the focus and difficulty in the preparation of silicon carbide devices. The level of specific contact resistance determines the performance of the device, and there are many factors affecting the specific contact resistance. , such as wafer surface carrier concentration, metal type and thickness, wafer surface pretreatment, metal high temperature annealing conditions, etc. In the prior art, the preparation of ohmic contacts in silicon carbide power devices is mainly through the ohmic contacts formed by alloying and annealing of various metals. There are technical problems such as large differences in process parameters, poor repeatability, complex and uncontrollable reaction mechanisms.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies in the prior art, provide a SiC power device ohmic contact, preparation method and application, simplify the manufacturing process of the ohmic contact, reduce the complexity of the metal annealing process, and reduce the specific contact resistance and power loss , Improve the reliability of SiC power devices.

In order to achieve the above object, the technical scheme adopted in the present invention is:

The invention provides a method for preparing an ohmic contact of a SiC power device, comprising the following steps:

Pretreatment of the back of the 4H-SiC substrate, including etching and dehydration;

A material with a 3C-SiC crystal structure is prepared on the back of the pretreated 4H-SiC substrate;

Deposit a metal layer on the surface of 3C-SiC crystal to make ohmic contact.

Further, the etching includes treating the back of the silicon carbide substrate with hydrofluoric acid and/or hydrochloric acid to remove the oxide layer, organic matter, and particle contamination on the back of the substrate, and then remove the water vapor on the back of the substrate.

Further, preparing a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate includes the following steps:

5×10 ¹⁸ ~5×10 ²⁰ cm ^-3 Al ions are implanted into the back of the 4H-SiC substrate at a temperature of 0°C~100°C;

Use carbon film sputtering equipment to sputter a carbon film with a thickness of 10nm~30nm on the back of the 4H-SiC substrate after ion implantation;

Under the temperature condition of 1700 ℃ ~ 1900 ℃, the 4H-SiC substrate with the carbon film sputtered on the back of the substrate is activated and annealed for 3 ~ 10 minutes to obtain the 3C-SiC crystal material;

Oxidize and remove the carbon film sputtered on the back of the 4H-SiC substrate;

The back of the 4H-SiC substrate after removing the carbon film is placed in a high-temperature furnace for thermal oxidation at 500-800A, and then etched in a CI ₂ -Ar gas RIE etching system.

Further, preparing a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate includes the following steps:

Select monosilane, propane or ethylene as the epitaxial precursor, select hydrogen and/or argon as the carrier gas to pass in advance, and the flow rate of the carrier gas is 300-600sccm;

In the chemical vapor deposition system, the epitaxial precursor deposits a 3C-SiC crystal structure with a thickness of 2-5 μm on the back of the pretreated 4H-SiC substrate.

Further, the deposition pressure in the chemical vapor deposition system is 800Pa-1400Pa, the growth temperature of the 3C-SiC crystal structure is 1500-1650° C., and the growth rate is 3-15 μm/h.

Further, preparing a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate includes the following steps:

Connect the pretreated 4H-SiC substrate and the surface to be bonded to the 3C-SiC wafer;

Activation annealing is performed at a temperature of 1600°C-1900°C in an Ar atmosphere to bond the contact surface;

Put the unbonded side of the 3C-SiC wafer into a high-temperature furnace for thermal oxidation of 500A-800A, and then perform etching in a CI ₂ -Ar gas RIE etching system.

Further, the metal layer is any one or more of Ni, Ti, W, Al, Ta, TaC, TiN, TiW, NiSi ₂ , CoSi ₂ .

In the second aspect, the present invention relates to an ohmic contact of a SiC power device, and the ohmic contact of the SiC power device is prepared by any one of the above preparation methods.

Further, the ohmic contact of a SiC power device of the present invention can be applied to Schottky barrier diodes, metal oxide field effect transistors, MOS controlled thyristors, electron injection enhanced gate transistors, ultra-high power thyristors or insulated gate bipolar transistors .

Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

The invention provides a SiC power device ohmic contact, preparation method and application, which effectively simplifies the manufacturing process of the ohmic contact on the back of the power device, and the obtained contact resistivity can reach the order of 10e ^-6 Ω·cm ² , effectively reducing the ratio contact resistance and power loss;

The present invention forms 3C-SiC material on the back of the 4H-SiC substrate by means of ion implantation or growing epitaxy or bonded wafers, without the need for high-temperature annealing process, and continues to deposit metal on the back of the pretreated silicon carbide substrate. Ohmic contact can be formed.

Description of drawings

Fig. 1 is a flow chart of a method for preparing an ohmic contact of a SiC power device provided by Embodiment 1 of the present invention;

Fig. 2 is a flowchart of a method for preparing an ohmic contact of a SiC power device provided by Embodiment 2 of the present invention;

Fig. 3 is a flowchart of a method for preparing an ohmic contact of a SiC power device provided by Embodiment 3 of the present invention;

Fig. 4 is a schematic diagram of an ion implantation method provided by an embodiment of the present invention;

Fig. 5 is a schematic diagram of a growth epitaxy method provided by an embodiment of the present invention;

FIG. 6 is a schematic diagram of a wafer bonding method provided by an embodiment of the present invention.

detailed description

The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

The present invention provides a SiC power device ohmic contact and its preparation method, which is suitable for the back ohmic contact of SiC junction barrier Schottky diodes and SiC MOSFETs, and the preparation of other back ohmic contacts similar to SiC devices, including metal oxides Field effect transistors, MOS controlled thyristors, electron injection enhanced gate transistors, ultra-high power thyristors, insulated gate bipolar transistors, etc.

A flow chart of a method for preparing an ohmic contact of a SiC power device provided by the present invention mainly includes processes such as processing the back of the 4H-SiC substrate, etching and removing moisture, and then preparing 3C-SiC on the back of the 4H-SiC substrate. crystal structure material, and finally deposit a metal layer on the back of the pretreated silicon carbide substrate to form an ohmic contact.

Wherein, the deposited metal layer is any one or more of Ni, Ti, W, Al, Ta, TaC, TiN, TiW, NiSi ₂ , CoSi ₂ .

The present invention will be further described below in conjunction with the accompanying drawings.

Embodiment one

As shown in FIG. 1 , it is a flow chart of a method for preparing an ohmic contact of a SiC power device provided in this embodiment, which specifically includes the following steps:

Step 1: Perform hydrofluoric acid etching on the back of the 4H-SiC substrate to remove the oxide layer, organic matter, and particle contamination on the back of the 4H-SiC substrate, and then remove the water vapor on the back of the substrate in a high-temperature _N2 atmosphere.

Step 2: Prepare a material with a 3C-SiC crystal structure by ion implantation, as shown in Figure 4, and the specific steps are as follows:

a. The ion implantation condition is 0°C~100°C, and 5×10 ¹⁸ ~5×10 ²⁰ cm ^-3 Al ions are implanted into the back surface of the 4H-SiC substrate;

b. using carbon film sputtering equipment to prepare a carbon film with a thickness of 10nm~30nm on the substrate 1;

c. Using high-temperature activation annealing equipment under the condition of 1700 ° C ~ 1900 ° C, perform a high-temperature activation annealing process for 3 ~ 10 minutes, and obtain 3C-SiC crystal materials;

d. The carbon film sputtered on the back is removed by oxygen plasma oxidation;

e. Put the back of the pretreated silicon carbide substrate into a high-temperature furnace for thermal oxidation of 500~800A, and then perform etching in a CI ₂ -Ar gas RIE etching system to remove the oxide layer.

Step 3: Depositing a Ni/Si metal layer, depositing Ni and Si with a thickness of 10-50nm and 40-80nm successively as contact metal electrodes.

Embodiment two

FIG. 2 is a flow chart of a method for preparing an ohmic contact of a SiC power device provided in this embodiment, which specifically includes the following steps:

Step 1: Perform hydrofluoric acid etching on the back of the 4H-SiC substrate to remove the oxide layer, organic matter, and particle contamination on the back of the substrate, and finally remove the water vapor on the back of the substrate in a high-temperature N2 atmosphere.

Step 2: Adopt the method of growth epitaxy, as shown in Figure 5, the specific steps are as follows:

a. Any one or more of monosilane, propane, and ethylene is selected as the epitaxial precursor, and hydrogen or argon is selected as the carrier gas. The flow rate of the carrier gas is 300-600sccm, the carrier gas and the epitaxial precursor should be introduced 5 minutes in advance before the deposition, and the 4H-SiC substrate is selected;

b. In the chemical vapor deposition system, the deposition pressure is 800Pa-1400Pa, and the 3C-SiC film is deposited on the back of the 4H-SiC substrate. The deposition thickness is about 2-5μm, and the growth temperature and growth rate of 3C-SiC are about 1500-1650℃ And 3-15μm/h.

Step 3: Depositing a Ni/Si metal layer, successively depositing Ni with a thickness of 10-50nm and Si with a thickness of 40-80nm as a contact metal electrode to form an ohmic contact.

Embodiment Three

FIG. 3 is a flow chart of a method for preparing an ohmic contact of a SiC power device provided in this embodiment, which specifically includes the following steps:

Step 1: Perform hydrofluoric acid etching on the back of the 4H-SiC substrate to remove the oxide layer, organic matter, and particle contamination on the back of the substrate, and finally remove the water vapor on the back of the substrate in a high-temperature _N2 atmosphere.

Step 2: Use the method of bonding wafers, as shown in Figure 6, the specific steps are as follows:

a. Connect the 4H-SiC substrate to the surface to be bonded to the 3C-SiC wafer;

b. Perform activation annealing at a high temperature of 1600-1900°C for 10-60min in an Ar atmosphere to obtain a bonded composite substrate;

c. Put the unbonded side of the 3C-SiC wafer into a high-temperature furnace for thermal oxidation of 500-800A to obtain an oxidized composite substrate, and then etch it in a CI ₂ -Ar gas RIE etching system.

Step 3: Depositing a Ni/Si metal layer, depositing Ni and Si with a thickness of 10-50nm and 40-80nm successively as contact metal electrodes.

The present invention also provides an ohmic contact of a SiC power device, and the ohmic contact of the SiC power device is prepared by any one of the above preparation methods.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. It should also be regarded as the protection scope of the present invention.

Claims (9)

1. A method for preparing an ohmic contact of a SiC power device, comprising the steps of: Pretreatment of the back of the 4H-SiC substrate, including etching and dehydration; A material with a 3C-SiC crystal structure is prepared on the back of the pretreated 4H-SiC substrate; Deposit a metal layer on the surface of 3C-SiC crystal to make ohmic contact. 2. A method for preparing an ohmic contact of a SiC power device according to claim 1, wherein the etching comprises treating the back side of the silicon carbide substrate with hydrofluoric acid and/or hydrochloric acid, and then removing the back side of the substrate. vapor. 3. A method for preparing an ohmic contact of a SiC power device according to claim 1, characterized in that, preparing a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate comprises the following steps: 5×10 ¹⁸ ~5×10 ²⁰ cm ^-3 Al ions are implanted into the back of the 4H-SiC substrate at a temperature of 0°C~100°C; Use carbon film sputtering equipment to sputter a carbon film with a thickness of 10nm~30nm on the back of the 4H-SiC substrate after ion implantation; Under the temperature condition of 1700 ℃ ~ 1900 ℃, the 4H-SiC substrate with the carbon film sputtered on the back of the substrate is activated and annealed for 3 ~ 10 minutes to obtain the 3C-SiC crystal material; Oxidize and remove the carbon film sputtered on the back of the 4H-SiC substrate; The back of the 4H-SiC substrate after removing the carbon film is placed in a high-temperature furnace for thermal oxidation at 500-800A, and then etched in a CI ₂ -Ar gas RIE etching system. 4. The method for preparing an ohmic contact of a SiC power device according to claim 1, wherein the preparation of a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate comprises the following steps: Select monosilane, propane or ethylene as the epitaxial precursor, select hydrogen and/or argon as the carrier gas to pass in advance, and the flow rate of the carrier gas is 300-600sccm; In the chemical vapor deposition system, the epitaxial precursor deposits a 3C-SiC crystal structure with a thickness of 2-5 μm on the back of the pretreated 4H-SiC substrate. 5. The preparation method of a SiC power device ohmic contact according to claim 4, characterized in that, the deposition pressure in the chemical vapor deposition system is 800Pa-1400Pa, and the growth temperature of the 3C-SiC crystal structure is 1500-1650 °C, the growth rate is 3-15 μm/h. 6. A method for preparing an ohmic contact of a SiC power device according to claim 1, characterized in that, preparing a material with a 3C-SiC crystal structure on the back of the pretreated 4H-SiC substrate comprises the following steps: Connect the pretreated 4H-SiC substrate and the surface to be bonded to the 3C-SiC wafer; Activation annealing is performed at a temperature of 1600°C-1900°C in an Ar atmosphere to bond the contact surface; Put the unbonded side of the 3C-SiC wafer into a high-temperature furnace for thermal oxidation of 500A-800A, and then perform etching in a CI ₂ -Ar gas RIE etching system. 7. A method for preparing an ohmic contact of a SiC power device according to claim 1, wherein the metal layer is Ni, Ti, W, Al, Ta, TaC, TiN, TiW, NiSi ₂ , CoSi ₂ any one or more of them. 8. A SiC power device ohmic contact, characterized in that the SiC power device ohmic contact is prepared by any one of the preparation methods of claims 1-7. 9. A SiC power device ohmic contact according to claim 8, characterized in that it is used in Schottky barrier diodes, metal oxide field effect transistors, MOS controlled thyristors, electron injection enhanced gate transistors, ultra-high power thyristors or insulated gate bipolar transistors.

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