CN105118853A - MgO substrate-based gallium oxide thin film and growing method thereof - Google Patents

Abstract

The invention discloses an MgO substrate-based gallium oxide thin film and the growing method thereof, and mainly solves the problem of poor surface appearance and small crystal grain size of conventional gallium oxide thin films. The gallium oxide thin film comprises an MgO substrate(1) and a gallium oxide epitaxial layer (3), and is characterized in that a 5-10nm gallium oxide buffer layer (2) is arranged between the MgO substrate(1) and the gallium oxide epitaxial layer (3), and the crystallization quality of the gallium oxide buffer layer is improved through thermal annealing. The surface roughness of a Ga2O3 is reduced, the surface appearance of the Ga2O3 is improved, and the crystal grain size of the Ga2O3 is increased. The MgO substrate-based gallium oxide thin film can be used to manufacture a semiconductor power device.

Description

Gallium Oxide Thin Film Based on MgO Substrate and Its Growth Method

technical field

The invention belongs to the technical field of microelectronics, and relates to a method for growing semiconductor materials, in particular to a Ga2O3 thin film manufacturing method, which can be used for manufacturing semiconductor power devices.

Background technique

In recent years, the third-generation semiconductors represented by SiC and GaN have been widely used due to their characteristics such as large band gap, high breakdown electric field, high thermal conductivity, high saturation electron velocity and high concentration of two-dimensional electron gas at the heterojunction interface. focus on. Although the third-generation semiconductor materials and devices have made significant progress and have entered the stage of practical application, their wide-ranging applications are still limited due to many defects in SiC and GaN materials. For this reason, on the basis of the growth of SiC and GaN materials, device manufacturing and promotion and application, people are also constantly looking for semiconductor materials with homogeneous substrates, excellent material properties, and low prices that can make up for the shortcomings of the above two materials. Wider forbidden band width and larger breakdown field strength are suitable for manufacturing power devices.

Ga2O3 semiconductor materials are particularly interesting. Ga2O3 semiconductor materials have a large band gap, high breakdown field strength, and low on-resistance. They can be used for homoepitaxial growth and are the best choice for the development of power devices. Ga2O3 is a monoclinic crystal with a forbidden band width of about 4.8eV-4.9eV. At present, 2-inch and 4-inch Ga2O3 single crystal substrates have been obtained by the floating zone method and the guided mode method. The method of homoepitaxially growing Ga2O3 thin films on the Ga2O3 single crystal substrate can obtain few defect dislocations and a lattice structure. Relatively complete, high-quality film with carrier concentration continuously changing from 10 ¹⁷ cm ^-3 to 10 ¹⁹ cm ^-3 , has excellent optical properties and stable physical and chemical properties, and can be used to make high-performance power electronic devices and ultraviolet sensors , solar-blind detectors, etc., have broad application prospects.

In order to make better use of the advantages of materials, a lot of research has been done on the growth of Ga2O3 thin films. The growth methods used mainly include: pulsed laser deposition method PLD, sol-gel method, chemical vapor deposition method CVD, metal organic chemical vapor deposition method MOCVD and magnetron sputtering method, etc.

Pulsed laser deposition PLD is the most widely used and most promising film-making technology developed in recent years. To put it simply, pulsed laser deposition PLD means that the pulsed laser beam is focused on a solid target surface, and the super-power of the laser makes the target material rapidly plasmaized, and then sputtered onto the target. It has the following advantages: 1. Due to the high energy of laser photons, many difficult coatings can be prepared by sputtering: such as high-temperature superconducting films, ceramic oxide films, multi-layer metal films, etc.; PLD can be used to synthesize nanotubes and nanopowders wait. 2. PLD can precisely control the film thickness by controlling the laser energy and pulse number. 3. Easy to obtain multi-component films with desired stoichiometric ratios. 4. The deposition rate is high, the test period is short, and the substrate temperature requirement is low. 5. Process parameters can be adjusted arbitrarily. 6. It is easy to clean and handle, and can prepare a variety of film materials.

However, at present, Ga2O3 thin films deposited by PLD adopt a single growth method, that is, the same process parameters are used during the growth process, including oxygen pressure, laser energy, substrate temperature, etc., so that PLD technology can be used on MgO substrates. Ga2O3 films obtained by heteroepitaxy have poor surface morphology and small grain size.

Contents of the invention

The purpose of the present invention is to address the shortcomings of the above-mentioned existing pulsed laser deposition method PLD, to propose a gallium oxide film based on MgO substrate and its growth method, so as to reduce the surface roughness of the film and improve the process parameters by adjusting and optimizing the process parameters. Ga2O3 thin film surface morphology, to obtain high-quality Ga2O3 wide bandgap semiconductor materials.

Technical scheme of the present invention is realized like this:

1. The gallium oxide film based on the MgO substrate, comprising the MgO substrate and the gallium oxide epitaxial layer, is characterized in that: a gallium oxide buffer layer of 5-10nm is arranged between the MgO substrate and the gallium oxide epitaxial layer.

2. the growth method of the gallium oxide film based on MgO substrate, comprises the steps:

(1) MgO substrate is cleaned, and blow dry with nitrogen;

(2) Using PLD equipment to grow a gallium oxide buffer layer of 5-10nm on the MgO substrate, the process parameters are:

Substrate temperature 550℃～600℃,

Oxygen partial pressure 0.008mbar～0.015mbar,

Laser energy 430mJ～470mJ,

Laser frequency 2Hz ~ 3Hz;

(3) Carry out thermal annealing to gallium oxide buffer layer in oxygen atmosphere;

(4) Changing the process parameters of the PLD to grow a gallium oxide epitaxial layer on the gallium oxide buffer layer. Its process parameters are:

Substrate temperature 650℃～700℃,

Oxygen partial pressure 0.045mbar～0.055mbar,

Laser energy 320mJ～350mJ,

Laser frequency 2Hz ~ 3Hz;

In the present invention, a Ga2O3 buffer layer is provided between the MgO substrate and the Ga2O3 epitaxial layer, which improves the coverage of the reactant atoms on the substrate when the Ga2O3 thin film is initially grown, and increases the seed crystal nucleation density. Heat treatment improves the crystallization quality of the buffer layer; in addition, the Ga2O3 epitaxial layer is grown by adjusting the epitaxial growth process parameters, which not only increases the Ga2O3 grain size, reduces the surface roughness of the film, but also improves the surface shape of the entire Ga2O3 film. appearance.

Description of drawings

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

Fig. 2 is a schematic diagram of the process flow of the present invention.

detailed description

Referring to FIG. 1 , the present invention includes a MgO substrate 1 , a buffer layer 2 and an epitaxial layer 3 . The crystal plane orientation of the MgO substrate 1 is (100), the epitaxial layer 3 adopts a Ga2O3 material with a thickness of 100-150 nm, and the buffer layer 2 adopts a Ga2O3 material with a thickness of 5-10 nm, and is located between the MgO substrate 1 and the epitaxial layer 3. between.

With reference to Fig. 2, preparation method of the present invention provides following three kinds of embodiments:

Example 1, making a gallium oxide thin film with a buffer layer thickness of 5 nm.

Step 1, cleaning the MgO substrate.

(1a) Clean the MgO substrate with acetone and absolute ethanol for 5 min respectively;

(1b) Soak the MgO substrate in a mixture of sulfuric acid and phosphoric acid at 160°C for 15 minutes, the ratio of sulfuric acid and phosphoric acid is 3:1;

(1c) Rinse the soaked MgO substrate with deionized water and dry it with dry nitrogen.

Step 2, growing a gallium oxide buffer layer with a thickness of 5 nm.

(2a) Put the cleaned MgO substrate into the pulsed laser deposition PLD chamber, pump the vacuum of the pulsed laser deposition PLD chamber to 10 ^-6 mbar, and adjust the distance between the substrate and the gallium oxide target to 50mm, the speed of the target is kept at 30rpm;

(2b) Heating the MgO substrate to 550°C, adjusting the oxygen partial pressure in the pulsed laser deposition PLD chamber to 0.008mbar, setting the laser energy to 430mJ, the laser frequency to 2Hz, and the number of pulses to 800 to grow the Ga2O3 buffer layer;

(2c) After the growth of the buffer layer is completed, 200 mbar of oxygen is filled into the pulsed laser deposition PLD chamber, and then the grown gallium oxide buffer layer film is allowed to cool naturally.

Step 3, performing thermal annealing on the gallium oxide buffer layer in an oxygen atmosphere, the annealing temperature is 700° C., and the annealing time is 70 minutes.

Step 4, growing a gallium oxide epitaxial layer with a thickness of 100 nm.

(4a) Put the gallium oxide buffer layer after thermal annealing into the pulse laser deposition PLD chamber, pump the vacuum degree of the chamber to 10 ^-6 mbar, adjust the distance between the substrate and the target to 50 mm, and the target The rotation speed is maintained at 30rpm;

(4b) Set the process parameters of pulsed laser deposition PLD epitaxial growth: substrate temperature 650 ° C, oxygen partial pressure 0.045 mbar, laser energy 320 mJ, laser frequency 3 Hz, laser pulse number 8000 epitaxial growth gallium oxide film;

(4c) After the growth of the epitaxial layer is completed, fill the chamber with 200 mbar of oxygen, then allow the gallium oxide epitaxial layer film to cool naturally, and complete the fabrication of a gallium oxide film with a gallium oxide buffer layer thickness of 5 nm.

Example 2, making a gallium oxide thin film with a buffer layer thickness of 8 nm.

Step 1, cleaning the MgO substrate.

This step is the same as Step 1 of Example 1.

Step 2, growing a gallium oxide buffer layer with a thickness of 8 nm.

2.1) Put the cleaned MgO substrate into the pulsed laser deposition PLD chamber, pump the vacuum of the pulsed laser deposition PLD chamber to 10 ^-6 mbar, and adjust the distance between the substrate and the gallium oxide target to 50mm , the speed of the target is kept at 30rpm;

2.2) Heat the MgO substrate to 570°C, adjust the oxygen partial pressure in the pulsed laser deposition PLD chamber to 0.01mbar, set the laser energy to 450mJ, the laser frequency to 3Hz, and the number of pulses to 1200 to grow the Ga2O3 buffer layer;

2.3) After the growth of the buffer layer is completed, the pulsed laser deposition PLD chamber is filled with 200 mbar of oxygen, and then the grown gallium oxide buffer layer film is naturally cooled.

Step 3: Thermally anneal the gallium oxide buffer layer at 800° C. for 60 minutes in an oxygen atmosphere.

Step 4, growing a gallium oxide epitaxial layer with a thickness of 150 nm.

4.1) Put the gallium oxide buffer layer after thermal annealing into the pulsed laser deposition PLD chamber, pump the vacuum of the chamber to 10 ^-6 mbar, adjust the distance between the substrate and the target to 50 mm, and the target Keep the speed at 30rpm;

4.2) Using pulsed laser deposition PLD method to epitaxially grow gallium oxide film on the gallium oxide buffer layer, the process parameters of the epitaxial growth are:

Substrate temperature 675°C,

Oxygen partial pressure 0.05mbar,

Laser energy 340mJ,

Laser frequency 3Hz,

The number of laser pulses is 12000 times;

4.3) After the growth of the epitaxial layer is completed, the chamber is filled with 200 mbar of oxygen, and then the gallium oxide epitaxial layer film is naturally cooled to complete the fabrication of a gallium oxide film with a gallium oxide buffer layer thickness of 8 nm.

Example 3, making a gallium oxide thin film with a buffer layer thickness of 10 nm.

Step A, cleaning the MgO substrate.

The implementation of this step is the same as step 1 in Embodiment 1.

Step B, growing a gallium oxide buffer layer with a thickness of 10 nm.

(B1) Put the cleaned MgO substrate into the pulsed laser deposition PLD chamber, pump the vacuum of the pulsed laser deposition PLD chamber to 10 ^-6 mbar, and adjust the distance between the substrate and the gallium oxide target to 50mm, the speed of the target is kept at 30rpm;

(B2) Heating the substrate to 600°C, adjusting the oxygen partial pressure in the pulsed laser deposition PLD chamber to 0.015mbar, setting the laser energy to 470mJ, the laser frequency to 2Hz, and the number of pulses to 1500 to grow a Ga2O3 buffer layer;

(B3) After the growth of the buffer layer is completed, 200 mbar of oxygen is filled into the pulsed laser deposition PLD chamber, and then the grown gallium oxide buffer layer film is naturally cooled.

In step C, the annealing temperature is set to 900° C., and the gallium oxide buffer layer is thermally annealed for 50 minutes in an oxygen atmosphere.

Step D, growing a gallium oxide epitaxial layer with a thickness of 125 nm.

(D1) Put the gallium oxide buffer layer after thermal annealing into the pulse laser deposition PLD chamber, pump the vacuum degree of the chamber to 10 ^-6 mbar, adjust the distance between the substrate and the target to 50mm, and the target The rotation speed is maintained at 30rpm;

(D2) Set the process parameters of pulsed laser deposition PLD, and epitaxially grow gallium oxide film on the gallium oxide buffer layer. The process parameters of epitaxial growth are: substrate temperature 700°C, oxygen partial pressure 0.055mbar, laser energy 350mJ, laser frequency 2Hz , the number of laser pulses is 10000 times;

(D3) After the growth of the epitaxial layer is completed, fill the chamber with 200 mbar of oxygen, and then allow the gallium oxide epitaxial layer film to cool naturally, and complete the fabrication of a gallium oxide film with a gallium oxide buffer layer thickness of 10 nm.

The above descriptions are only three specific examples of the present invention, and do not constitute any limitation to the present invention. Obviously, for professionals in the field, after understanding the content and principles of the present invention, it is possible without departing from the principles of the present invention. In the case of , structure, various parameter amendments and changes in form and details are carried out, but these amendments and changes based on the idea of the present invention are still within the protection scope of the claims of the present invention.

Claims (6)

1. based on the gallium oxide film of MgO substrate, comprise MgO substrate (1) and gallium oxide epitaxial layer (3), it is characterized in that: be provided with 5 between MgO substrate (1) and gallium oxide epitaxial layer (3) - 10 nm gallium oxide buffer layer (2). 2. The gallium oxide thin film based on MgO substrate according to claim 1, characterized in that: the epitaxial layer (3) is made of Ga2O3 material with a thickness of 100-150 nm. 3. The gallium oxide thin film based on MgO substrate according to claim 1, characterized in that: the crystal plane orientation of the MgO substrate (1) is (100). 4. the growth method of the gallium oxide thin film based on MgO substrate, comprises the steps: (1) MgO substrate is cleaned, and blow dry with nitrogen; (2) Using pulsed laser deposition PLD equipment to grow a 5-10nm gallium oxide buffer layer on the MgO substrate, the process parameters are: Substrate temperature 550℃～600℃, Oxygen partial pressure 0.008mbar～0.015mbar, Laser energy 430mJ～470mJ, Laser frequency 2Hz ~ 3Hz; (3) Carry out thermal annealing to gallium oxide buffer layer in oxygen atmosphere; (4) Change the process parameters of pulsed laser deposition PLD to grow gallium oxide epitaxial layer on the gallium oxide buffer layer after annealing, and its process parameters are: Substrate temperature 650℃～700℃, Oxygen partial pressure 0.045mbar～0.055mbar, Laser energy 320mJ～350mJ, Laser frequency 2Hz ~ 3Hz. 5. The method for growing a gallium oxide thin film based on MgO substrate according to claim 4, characterized in that: the process conditions of thermal annealing in an oxygen atmosphere are: annealing temperature 700°C-900°C, annealing time 50-70min. 6. the growth method of the gallium oxide thin film based on MgO substrate according to claim 4 is characterized in that: the cleaning to MgO substrate is carried out in the mixed solution of sulfuric acid and phosphoric acid, the sulfuric acid and phosphoric acid in the mixed solution The ratio is 3:1, and the cleaning time is 15 minutes.