JP7540187B2 - Gallium oxide semiconductor manufacturing method - Google Patents

Description

This disclosure relates to a method for producing a gallium oxide semiconductor.

Currently, there is a demand for the development of power saving technologies, and hopes are high for reducing loss in power devices. Power devices are installed in all kinds of power converters, such as inverters installed in hybrid and electric vehicles.

In order to realize low-loss power devices, new wide-gap semiconductor materials such as SiC and GaN, which are expected to realize power devices with even higher voltage resistance and lower loss than current silicon (Si), have attracted attention and are being actively researched and developed. Among these, gallium oxide has physical properties such as an even larger band gap compared to SiC and GaN, and is expected to provide excellent device characteristics such as even higher voltage resistance and lower loss when applied to power devices.

For this reason, recently, a method of doping impurities into gallium oxide single crystals using ion implantation has been proposed for the application of gallium oxide to power devices. Patent Document 1 proposes a manufacturing method in which Mg ions are implanted into gallium oxide single crystals, followed by activation annealing to form a high resistance region.

JP 2016-039194 A

When impurities are doped into a gallium oxide single crystal layer using ion implantation to form a high resistance region, the crystal structure of the gallium oxide single crystal layer may be destroyed and become amorphous. If the degree of amorphization of the gallium oxide single crystal layer is large, the crystal structure cannot be fully restored even after subsequent activation annealing treatment.

As a result, conventional manufacturing methods had the problem that the resulting gallium oxide semiconductor was prone to crystal defects.

The present disclosure aims to provide a method for producing a gallium oxide semiconductor with reduced crystal defects.

The present inventors have found that the above object can be achieved by the following means:
A method for producing a gallium oxide semiconductor, comprising: implanting ions into a gallium oxide single crystal layer and then performing an activation annealing treatment;
The temperature of the gallium oxide single crystal layer during the ion implantation is 300° C. to 800° C.
A method for producing gallium oxide semiconductors.

The present disclosure provides a method for producing a gallium oxide semiconductor with reduced crystal defects.

FIG. 1 is a graph showing evaluations of the crystallinity of each of the samples of Example 1 and Comparative Example 1 before and after ion implantation, and after activation annealing treatment.

The following describes in detail the embodiments of the present disclosure. Note that the present disclosure is not limited to the following embodiments, and can be modified in various ways within the scope of the disclosure.

The manufacturing method disclosed herein is a method for manufacturing a gallium oxide semiconductor, which includes implanting ions into a gallium oxide single crystal layer and then performing an activation annealing treatment, and includes a method for manufacturing a gallium oxide semiconductor, in which the temperature of the gallium oxide single crystal layer during the ion implantation is 300°C to 800°C.

Although not limited by the principle, the manufacturing method disclosed herein can produce a gallium oxide semiconductor with reduced crystal defects according to the following principle.

As described above, in conventional methods for manufacturing gallium oxide semiconductors, when impurities are doped into a gallium oxide single crystal layer using ion implantation, the crystal structure of the gallium oxide single crystal layer is destroyed and becomes amorphous, and even when a subsequent activation annealing process is performed, the crystal structure may not be fully restored.

In this regard, in the manufacturing method disclosed herein, the temperature of the gallium oxide single crystal layer during ion implantation is 300°C to 800°C, thereby suppressing destruction of the crystal structure of the gallium oxide single crystal layer when doping the gallium oxide single crystal layer with impurities using the ion implantation method.

By setting the temperature of the gallium oxide single crystal layer at 300°C during ion implantation, the gallium atoms and oxygen atoms in the gallium oxide single crystal layer, as well as the atoms of the implanted impurities, tend to remain in stable positions, suppressing the occurrence of crystal defects. In addition, by setting the temperature of the gallium oxide single crystal layer at 800°C or less during ion implantation, the occurrence of crystal defects due to electrical properties such as oxygen vacancies is suppressed.

As a result, in the manufacturing method disclosed herein, the crystal structure of the gallium oxide single crystal layer is less likely to be destroyed even after ion implantation, and the crystal structure is sufficiently restored by the subsequent activation annealing treatment.

Gallium oxide single crystal layer
The gallium oxide single crystal layer used in the manufacturing method of the present disclosure can be a gallium oxide single crystal layer produced by any method. The gallium oxide single crystal layer can be a layer of α-Ga ₂ O ₃ single crystal, β-Ga ₂ O ₃ single crystal, or Ga ₂ O ₃ single crystal having other crystal structure, and is preferably a layer of β-Ga ₂ O ₃ single crystal.

Ion Implantation
The ion implantation method used in the manufacturing method of the present disclosure can be the same as the conventional method, except that the temperature of the gallium oxide single crystal layer during ion implantation is 300°C to 800°C.

The temperature of the gallium oxide single crystal layer during ion implantation may be 300°C or more, 350°C or more, 400°C or more, or 450°C or more. It may also be 800°C or less, 750°C or less, 700°C or less, or 600°C or less.

The thickness of the high-resistance layer formed by ion implantation, i.e., the diffusion depth of the impurities, can be controlled by changing the energy of the ion implantation.

The dose of the impurity may be, for example, 1×10 ¹⁰ /cm ² to 1×10 ²⁰ /cm ² .

The dose of the impurity may be 1×10 ¹⁰ /cm ² or more, 1×10 ¹¹ /cm ² or more, 1×10 ¹³ /cm ² or more, or 1×10 ¹⁵ /cm ² or more, and may be 1×10 ²⁰ /cm ² or less, 1×10 ¹⁹ /cm ² or less, 1×10 ¹⁸ /cm ² or less, or 1×10 ¹⁷ /cm ² or less.

The manufacturing method of the present disclosure can be particularly effective when the impurity dose is large, for example, when the impurity dose is 1×10 ¹⁵ /cm ² or more, i.e., can achieve a greater reduction in crystal defects than when the manufacturing method of the present disclosure is not used.

The atomic species of the impurity doped into the gallium oxide single crystal layer by ion implantation may be any atomic species capable of forming a high resistance layer in the gallium oxide single crystal layer, for example, at least one species selected from the group consisting of N, Mg, Be, Zn, or Fe.

The manufacturing method of the present disclosure is particularly effective when the atomic number of the doped impurity is large, i.e., it can reduce crystal defects more effectively than when the manufacturing method of the present disclosure is not used.

Activation annealing treatment
In the manufacturing method of the present disclosure, activation annealing is performed after ion implantation into the gallium oxide single crystal layer.

In the manufacturing method of the present disclosure, the heating temperature in the activation annealing treatment is not particularly limited, but may be 700°C or higher. The upper limit of the heating temperature is not particularly limited, but may be 1200°C.

The heating temperature in the activation annealing treatment may be 700°C or more, 750°C or more, 800°C or more, 850°C or more, 900°C or more, or 950°C or more, and may be 1200°C or less, 1150°C or less, 1100°C or less, or 1050°C or less.

In the method of the present disclosure, the time for performing the activation annealing treatment may preferably be 5 to 30 minutes.

The atmosphere in the activation annealing process can be a nitrogen atmosphere.

Gallium oxide semiconductor
The gallium oxide semiconductor obtained by the manufacturing method of the present disclosure has at least a gallium oxide single crystal layer having a high resistance layer.

Example 1 and Comparative Example 1
Example 1
A commercially available β-Ga ₂ O ₃ single crystal substrate with a length of 5 mm, a width of 5 mm, and a thickness of 0.5 mm was prepared as the gallium oxide single crystal used as the base material. The Ga ₂ O 3 single crystal substrate prepared had a (−201) main surface and was an n-type Ga ₂ O ₃ single crystal with a Si concentration of 2× ₁₀ ¹⁷ /cm ³ .

N was ion-implanted into the main surface of the prepared β-Ga ₂ O ₃ single crystal substrate with a 500 nm thick box profile with an N density of 1×10 ²⁰ /cm ³ , and then activation annealing was performed at 800° C. for 30 minutes to obtain a gallium oxide semiconductor. The temperature of the β-Ga ₂ O ₃ single crystal substrate during ion implantation was 300° C.

_The crystallinity of _each of _the β-Ga ₂ O _{3 single} crystal substrates before ion implantation, after ion implantation, and after activation annealing was evaluated by the channeling method of _Rutherford backscattering spectrometry ( _RBS ).

Comparative Example 1
Except for the fact that the temperature of the β-Ga ₂ O ₃ single crystal substrate during ion implantation was room temperature, the crystallinity was evaluated for each of the β-Ga ₂ O ₃ single crystal substrate before ion implantation, the β-Ga ₂ O ₃ single crystal substrate after ion implantation, and the β-Ga ₂ O ₃ single crystal substrate after activation annealing treatment in the same manner as in Example 1.

<result>
The evaluation results are shown in Figure 1. In Figure 1, χmin (%) indicates the scattering intensity, and the smaller this value is, the higher the crystallinity is.

As shown in FIG. 1, the crystallinity of the β-Ga ₂ O ₃ single crystal substrate before ion implantation was equal in Example 1 and Comparative Example 1 (χmin = about 15% in both cases).

In contrast, the crystallinity of the β-Ga ₂ O ₃ single crystal substrate after ion implantation was higher in Example 1 (χmin = about 43%) than in Comparative Example 1 (χmin = about 67%). This magnitude relationship was also true for the β-Ga ₂ O ₃ single crystal substrate after activation annealing treatment, and the crystallinity was higher in Example 1 (χmin = about 11%) than in Comparative Example 1 (χmin = about 21%).

Claims (1)

A method for producing a gallium oxide semiconductor, comprising: implanting ions into a gallium oxide single crystal layer and then performing an activation annealing treatment;
The temperature of the gallium oxide single crystal layer during the ion implantation is 300° C. to 350 ° C.,
The atomic species of the impurity doped into the gallium oxide single crystal layer by the ion implantation is N.
A method for producing gallium oxide semiconductors.

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