JP7741539B2 - Semiconductor device and method for manufacturing the same - Google Patents

Description

The present invention relates to semiconductor devices using diamond and methods for manufacturing semiconductor devices.

Diamond has the characteristics of a large band gap, high carrier mobility, high breakdown field, and high thermal conductivity. Therefore, semiconductor elements using diamond are expected to operate at high voltages and stably in high-temperature, extreme environments with high temperatures and radiation levels. However, while it is possible to create p-type semiconductors using diamond, it is difficult to create n-type semiconductors using diamond alone, as the donor level is deep and the activation rate at room temperature is low.

Patent Document 1 discloses a semiconductor device bonded using a surface activated bonding method in which the surfaces of an n-type gallium-based semiconductor and a p-type diamond substrate are cleaned and activated with an argon beam or plasma, and then pressure is applied to bond the surfaces together. By directly bonding a gallium-based semiconductor with low thermal conductivity to a diamond substrate with high thermal conductivity without using a material with low thermal conductivity in between, heat dissipation performance is improved.

Japanese Patent Application Laid-Open No. 2021-13007

However, in Patent Document 1, defects are formed on the surface of the diamond substrate due to the process using an argon beam or plasma, making it difficult to stably form a heterojunction with good electrical properties such as rectification, and there is room for further improvement.

The present invention therefore aims to provide a semiconductor element that uses diamond and has good electrical properties, as well as a method for manufacturing such a semiconductor element.

The semiconductor element of the present invention comprises, at least in part, a first semiconductor substrate containing an oxide of gallium in its composition, a second semiconductor substrate containing diamond in its composition, and a heterojunction in which a surface of the first semiconductor substrate and a surface of the second semiconductor substrate are bonded to each other by gallium-oxygen-carbon bonding, wherein the first semiconductor substrate contains an n-type dopant at a concentration of 1×10 ¹⁵ cm ^-3 to 1×10 ¹⁹ cm ^-3 , the second semiconductor substrate contains a p-type dopant at a concentration of 1×10 ¹⁵ cm ^-3 to 1×10 ¹⁸ cm ^-3 , and the heterojunction has a rectification characteristic with a rectification ratio of 1×10 ⁸ or more.

The method for manufacturing a semiconductor device of the present invention includes a first hydroxylation step of introducing OH groups into at least a part of the surface of a first semiconductor substrate containing an oxide of gallium in its composition; a second hydroxylation step of introducing OH groups into at least a part of the surface of a second semiconductor substrate containing diamond in its composition; a contact step of bringing the surface of the first semiconductor substrate into contact with the surface of the second semiconductor substrate into which OH groups have been introduced; and a dehydration step of applying activation energy to the contacted first semiconductor substrate and second semiconductor substrate to cause a dehydration reaction, thereby forming a heterojunction between the surfaces of the first semiconductor substrate and the second semiconductor substrate, wherein the first semiconductor substrate contains an n-type dopant, and the concentration of the n-type dopant is 1×10 ¹⁵ cm ^-3 to 1×10 ¹⁹ cm ^-3 , and the second semiconductor substrate contains a p-type dopant, and the concentration of the p-type dopant is 1×10 ¹⁵ cm ^-3 to 1×10 ¹⁸ cm ^-3 , and the second hydroxylation step introduces OH groups by treating the surface of the second semiconductor substrate with an oxidizing liquid, and the oxidizing liquid contains at least aqueous ammonia and hydrogen peroxide .

The present invention makes it possible to provide semiconductor elements that use diamond and have excellent electrical properties.

FIG. 1 is an explanatory diagram showing the configuration of a main part of a semiconductor device according to an embodiment of the present invention; 1 is a flow diagram of a method for manufacturing a semiconductor device according to an embodiment of the present invention; 1 is an explanatory diagram of a manufacturing process of a semiconductor device according to an embodiment of the present invention; FIG. 1 is an explanatory diagram showing a configuration of a main part of a modified example of a semiconductor element according to an embodiment of the present invention; FIG. 1 is a diagram showing main parameters of an example and a comparative example of a semiconductor device according to the present invention. 1 is a diagram showing the current-voltage characteristics of the semiconductor element of Example 1. 1 is a graph showing the current-voltage characteristics of a semiconductor element according to Comparative Example 2.

One embodiment of the present invention will be described in detail below using the drawings. The configurations, shapes, etc. described below are examples for explanatory purposes and can be modified as appropriate depending on the specifications of the semiconductor device. Furthermore, the drawings used in the following description may be partially enlarged, and the dimensions and proportions of each component may not be the same as in reality. Below, corresponding elements in all drawings will be given the same reference numerals, and duplicate explanations will be omitted.

First, the configuration of the semiconductor element 1 will be described with reference to Figure 1. The semiconductor element 1 comprises a p-type diamond semiconductor 2 and an n-type gallium oxide semiconductor 3. The p-type diamond semiconductor 2, the n-type gallium oxide semiconductor 3, and a heterojunction 11 formed between the p-type diamond semiconductor 2 and the n-type gallium oxide semiconductor 3 constitute a heterojunction structure 10. Furthermore, the semiconductor element 1 comprises an anode electrode 4 electrically connected to the p-type diamond semiconductor 2, and a cathode electrode 5 electrically connected to the n-type gallium oxide semiconductor 3.

The p-type diamond semiconductor 2 is made of single-crystal diamond and has a (100) or (110) surface. The p-type diamond semiconductor 2 is formed to a thickness of 0.5 μm to 1 mm (preferably 500 μm or less), which is necessary to form the heterojunction structure 10.

The p-type diamond semiconductor 2 contains boron (B) as a p-type dopant. The concentration of the p-type dopant is set to 1×10 ¹⁵ cm ^-3 to 1×10 ¹⁸ cm ^-3 at which the p-type diamond semiconductor 2 exhibits semiconductor properties. The upper limit of the p-type dopant concentration is determined based on the reverse breakdown voltage required for the semiconductor element 1, within the range at which the p-type diamond semiconductor 2 exhibits semiconductor properties. Furthermore, the lower limit of the p-type dopant concentration is determined based on the carrier density (hole density) and resistivity (parasitic resistance value) excited in the p-type diamond semiconductor 2 within the operating temperature range of the semiconductor element 1. In this way, the p-type diamond semiconductor 2 is a second semiconductor substrate whose composition contains diamond (carbon) containing a p-type dopant.

1, the n-type gallium oxide semiconductor 3 is made of gallium oxide (β-Ga ₂ O ₃ ). The n-type gallium oxide semiconductor 3 is formed to a film thickness of 0.5 μm to 100 μm, which is necessary for forming the heterojunction structure 10. In addition, a film thickness of 1 μm to 10 μm is preferable in view of the allowable parasitic resistance value.

The n-type gallium oxide semiconductor 3 contains silicon (Si), magnesium (Mg), zinc (Zn), or the like as an n-type dopant. The concentration of the n-type dopant is set to 1×10 ¹⁵ cm ⁻³ to 1×10 ¹⁹ cm ⁻³ at which the n-type gallium oxide semiconductor 3 exhibits semiconductor properties. The upper limit of the n-type dopant concentration is determined based on the reverse breakdown voltage required for the semiconductor device 1, within the range at which the n-type gallium oxide semiconductor 3 exhibits semiconductor properties. The lower limit of the n-type dopant concentration is determined based on the carrier density (electron density) and resistivity (parasitic resistance value) excited in the n-type gallium oxide semiconductor 3 within the operating temperature range of the semiconductor device 1. In this way, the n-type gallium oxide semiconductor 3 is a first semiconductor substrate whose composition includes an oxide of gallium (Ga) containing an n-type dopant.

In Figure 1, where the p-type diamond semiconductor 2 and the n-type gallium oxide semiconductor 3 contact each other, a gallium-oxygen-carbon bond (Ga-O-C bond) is formed, in which at least some of the carbon (C) on the surface of the p-type diamond semiconductor 2 is bonded to at least some of the gallium (Ga) on the surface of the n-type gallium oxide semiconductor 3 via oxygen (O). The gallium-oxygen-carbon bond is a heterojunction 11. In this way, the heterojunction 11 is formed by the gallium-oxygen-carbon bond between the surface of the n-type gallium oxide semiconductor 3 (first semiconductor substrate) and the surface of the p-type diamond semiconductor 2 (second semiconductor substrate).

The heterojunction 11 is formed by a manufacturing method including a first hydroxylation step (ST1) of introducing OH groups into at least a part of the surface of the n-type gallium oxide semiconductor 3, which will be described later; a second hydroxylation step (ST2) of introducing OH groups into at least a part of the surface of the p-type diamond semiconductor 2; a contacting step (ST3) of bringing the surface of the n-type gallium oxide semiconductor 3 onto which OH groups have been introduced into contact with the surface of the p-type diamond semiconductor 2 onto which OH groups have been introduced; and a dehydration step (ST4) of applying activation energy to the contacted n-type gallium oxide semiconductor 3 and p-type diamond semiconductor 2 to cause a dehydration reaction.

In FIG. 1, the anode electrode 4 is connected to the p-type diamond semiconductor 2 (anode) of the heterojunction structure 10 by forming an ohmic junction. The anode electrode 4 may be, for example, a metal laminate such as titanium (Ti)/molybdenum (Mo)/gold (Au), titanium (Ti)/platinum (Pt)/gold (Au), or titanium (Ti)/gold (Au).

The cathode electrode 5 is electrically connected to the n-type gallium oxide semiconductor 3 (cathode) of the heterojunction structure 10 by forming an ohmic junction. The cathode electrode 5 may be, for example, a metal laminate such as titanium (Ti)/molybdenum (Mo)/gold (Au), titanium (Ti)/gold (Au), nickel (Ni)/aluminum (Al)/gold (Au), or nickel (Ni)/gold (Au). In this way, the semiconductor element 1 includes the cathode electrode 5 (first electrode) electrically connected to the n-type gallium oxide semiconductor 3 (first semiconductor substrate), and the anode electrode 4 (second electrode) electrically connected to the p-type diamond semiconductor 2.

Next, a method for manufacturing the semiconductor device 1 will be described with reference to FIG. 3, following the flow chart of FIG. 2. First, an n-type gallium oxide semiconductor 3 (first semiconductor substrate) containing an n-type dopant-containing gallium oxide (gallium oxide β-Ga ₂ O ₃ ) is prepared. Next, OH groups are introduced into at least a portion of the surface 3a of the n-type gallium oxide semiconductor 3 (ST1: first hydroxylation step) (left side of FIG. 3( a)). The introduction of OH groups into the surface 3a of the n-type gallium oxide semiconductor 3 is achieved, for example, by irradiating the surface 3a of the n-type gallium oxide semiconductor 3 with oxygen plasma. The n-type gallium oxide semiconductor 3 is processed to a predetermined thickness by a processing method such as polishing or delamination before the first hydroxylation step (ST1) or after the dehydration step (ST4) described below.

In Fig. 2, next, OH groups are introduced into at least a part of the surface 2a of the prepared p-type diamond semiconductor 2 (second semiconductor substrate) (ST2: second hydroxylation step) (right side of Fig. 3(a)). The introduction of OH groups into the surface 2a of the p-type diamond semiconductor 2 is realized, for example, by treating the surface 2a of the p-type diamond semiconductor 2 with an oxidizing liquid. As _the oxidizing liquid, for example, a mixture of ammonia water ( _NH3 ) and hydrogen peroxide ( _{H2O2 )} ( _NH3 / _{H2O2 /H2O )} or a mixture of sulfuric acid ( _H2SO4 ) _and hydrogen peroxide ( _H2O2 ) _{( H2SO4} / _H2O2 / _{H2O )} can be used.

Next, the surface 3a of the n-type gallium oxide semiconductor 3 (first semiconductor substrate) on which OH groups have been introduced and the surface 2a of the p-type diamond semiconductor 2 (second semiconductor substrate) on which OH groups have been introduced are brought into contact (arrow a in Figure 3(b)), and the two are brought into contact (ST3: contacting step) (arrow b in Figure 3(b)). Activation energy is then applied to the contacted n-type gallium oxide semiconductor 3 and p-type diamond semiconductor 2 to cause a dehydration reaction (ST4: dehydration step) (Figure 3(c)).

Examples of activation energy include thermal energy, light energy, electrical energy, and chemical energy. In the case of thermal energy, for example, heating at 150 to 250°C for 2 to 24 hours causes a dehydration reaction. This dehydration reaction forms a heterojunction 11 in which at least a portion of the carbon (C) on the surface 2a of the p-type diamond semiconductor 2 and at least a portion of the gallium (Ga) on the surface 3a of the n-type gallium oxide semiconductor 3 form a gallium-oxygen-carbon bond (Ga-O-C bond) via oxygen (O) (Ga-OH + C-OH → Ga-O-C + H ₂ O).

The order in which the first hydroxylation step (ST1) and the second hydroxylation step (ST2) are performed is not limited to the above example. For example, the first hydroxylation step (ST1) may be performed after the second hydroxylation step (ST2), or they may be performed in parallel. In other words, it is sufficient that the first hydroxylation step (ST1) and the second hydroxylation step (ST2) are completed within a specified time before the contact step (ST3).

In Figure 2, next, an anode electrode 4 and a cathode electrode 5 are formed on the semiconductor element 1 (ST5: wiring step) (see Figure 1). The wiring step (ST5) includes a first wiring step of forming a cathode electrode 5 (first electrode) electrically connected to the n-type gallium oxide semiconductor 3 (first semiconductor substrate), and a second wiring step of forming an anode electrode 4 (second electrode) electrically connected to the p-type diamond semiconductor 2. In the first and second wiring steps, metal laminates that make up the electrodes are layered using vapor deposition or sputtering, and then processed into the desired shape using lift-off or etching.

Next, a modified semiconductor element will be described with reference to Figure 4. The modified semiconductor element 20 differs from the semiconductor element 1 shown in Figure 1 in that an anode electrode 24 (second electrode) is formed on the surface of a p-type diamond semiconductor 21 (second semiconductor substrate). The p-type diamond semiconductor 21 and the n-type gallium oxide semiconductor 22 (first semiconductor substrate) that form a heterojunction 31 with the p-type diamond semiconductor 21 have the same configurations as the p-type diamond semiconductor 2 and n-type gallium oxide semiconductor 3 of the semiconductor element 1, and detailed description thereof will be omitted. Furthermore, the configuration and manufacturing method of the heterojunction 31 are the same as the heterojunction 11 of the semiconductor element 1, and detailed description thereof will be omitted. The p-type diamond semiconductor 21, heterojunction 31, and n-type gallium oxide semiconductor 22 form a heterojunction structure 30. The configuration and manufacturing method of the cathode electrode 23 (first electrode) electrically connected to the n-type gallium oxide semiconductor 22 are the same as the cathode electrode 5 of the semiconductor element 1, and detailed description thereof will be omitted.

The area of the n-type gallium oxide semiconductor 22 is smaller than that of the p-type diamond semiconductor 21, and a portion of the p-type diamond semiconductor 21 is exposed and not in contact with the n-type gallium oxide semiconductor 22. The anode electrode 24 (second electrode) is electrically connected to the exposed portion of the p-type diamond semiconductor 21 by an ohmic junction. In the wiring step (ST5) of the manufacturing method of the semiconductor element 20, the anode electrode 24 (second electrode) electrically connected to the p-type diamond semiconductor 21 (second semiconductor substrate) and the cathode electrode 23 can be formed in the same step. In other words, by simultaneously processing the anode electrode 24 and cathode electrode 23, it is possible to eliminate either the first wiring step or the second wiring step.

As explained above, the semiconductor elements 1, 20 of the present embodiment at least partially comprise a heterojunction structure 10, 30 including a first semiconductor substrate (n-type gallium oxide semiconductor 3, n-type gallium oxide semiconductor 22) containing gallium oxide in its composition, a second semiconductor substrate (p-type diamond semiconductor 2, 23) containing diamond in its composition, and a heterojunction 11, 31 where the surface of the first semiconductor substrate and the surface of the second semiconductor substrate are bonded to each other by gallium-oxygen-carbon bonding. The semiconductor elements 1, 20 of the present embodiment, which use diamond, have excellent rectification characteristics, as will be explained in the examples described below. Examples of semiconductor elements partially comprising the heterojunction structures 10, 30 (heterojunctions 11, 31) of the present embodiment include power devices, temperature sensors, radiation sensors, and nuclear batteries.

Next, examples and comparative examples of the semiconductor element of the present invention will be described with reference to Figures 5 to 7. The table shown in Figure 5 lists the impurity concentrations of the n-type gallium oxide semiconductor, the impurity concentrations of the p-type diamond semiconductor, and the rectification ratios of samples of semiconductor element Example 1, Comparative Example 1, and Comparative Example 2. The impurity concentration of the n-type gallium oxide semiconductor is the concentration of the n-type dopant in the n-type gallium oxide semiconductor 3. The impurity concentration of the p-type diamond semiconductor is the concentration of the p-type dopant in the p-type diamond semiconductor 2. The rectification ratio is the ratio of the forward current measured when a voltage of 4 V is applied in the forward direction to the reverse current measured when a voltage of 4 V is applied in the reverse direction (rectification ratio = forward current/reverse current).

Example 1
Next, a manufacturing method of Example 1 of the semiconductor element 1 will be described. The p-type diamond semiconductor 2 is a CVD substrate of single-crystal diamond with a thickness of 400 μm and a (100) surface containing 1×10 ¹⁷ cm ^-3 of boron as a p-type dopant. The n-type gallium oxide semiconductor 3 is a gallium oxide (β-Ga ₂ O ₃ ) substrate with a (100) surface containing 1×10 ¹⁷ cm ^-3 of an n-type dopant and processed to a thickness of 10 μm.

In the first hydroxylation step (ST1), surface 3a of n-type gallium oxide semiconductor 3 was irradiated for 30 seconds with high-purity oxygen plasma at a pressure of 60 Pa and an output of 200 W, thereby introducing OH groups into surface 3a of n-type gallium oxide semiconductor 3. In the second hydroxylation step (ST2), p-type diamond semiconductor 2 was immersed for 10 minutes in a mixed solution at 75° _C consisting of 10 ml of 28% aqueous ammonia ( _NH3 ), 10 ml of 35% hydrogen peroxide ( _H2O2 ), and 50 ml of pure water, thereby introducing OH groups into surface 2a of p-type diamond semiconductor 2.

After the surface 3a of the n-type gallium oxide semiconductor 3 and the surface 2a of the p-type diamond semiconductor 2 were brought into contact in the contacting step (ST3), the dehydration step (ST4) involved heating at 250°C for 24 hours to cause a dehydration reaction.

In the wiring process (ST5) (first wiring process, second wiring process), a 10 nm thick titanium (Ti), 10 nm thick molybdenum (Mo), and 30 nm thick gold (Au) were sequentially layered by vapor deposition to form a titanium (Ti)/molybdenum (Mo)/gold (Au) laminate as the anode electrode 4 and cathode electrode 5.

6 shows the current-voltage characteristics of the semiconductor device 1 of Example 1, with the anode electrode 4 serving as the reference potential. The semiconductor device 1 of Example 1 exhibits very good rectification characteristics, with a reverse saturation current of approximately 1×10 ⁻⁹ (A/cm ² ) and a rectification ratio (forward current/reverse current) of approximately 1×10 ⁸ .

(Comparative Example 1)
Next, a description will be given of Comparative Example 1 of the semiconductor device 1. Comparative Example 1 is the same as Example 1 except that the p-type diamond semiconductor 2 contains 1×10 ¹⁹ cm ⁻³ of boron as a p-type dopant.

(Comparative Example 2)
Next, a description will be given of Comparative Example 2 of the semiconductor device 1. Comparative Example 2 is the same as Example 1 except that the p-type diamond semiconductor 2 contains 1×10 ²⁰ cm ⁻³ of boron as a p-type dopant.

Figures 7(a) and 7(b) show the current-voltage characteristics of the semiconductor element 1 of Comparative Example 2, with the anode electrode as the reference potential. In Figure 7(a), the anode electrode was connected to the surface of the p-type diamond semiconductor 2, and measurements were taken in a configuration similar to that of the modified semiconductor element shown in Figure 4. In Figure 7(b), the anode electrode was connected to the back surface of the p-type diamond semiconductor 2, and measurements were taken in a configuration similar to that of the semiconductor element 1 shown in Figure 1. In the semiconductor element 1 of Comparative Example 2, whether the anode electrode was connected to the surface of the p-type diamond semiconductor 2 (Figure 7(a)) or the back surface (Figure 7(b)), the reverse direction exhibited ohmic characteristics, and the rectification ratio (forward current/reverse current) was approximately 10, indicating that normal rectification characteristics were not obtained.

The semiconductor element and semiconductor element manufacturing method of the present invention can provide a semiconductor element using diamond with excellent electrical properties.

1, 20 Semiconductor element 2, 21 p-type diamond semiconductor (second semiconductor substrate)
2a Surface (surface of second semiconductor substrate)
3, 22 n-type gallium oxide semiconductor (first semiconductor substrate)
3a Surface (surface of first semiconductor substrate)
4, 24 Anode electrode (second electrode)
5, 23 Cathode electrode (first electrode)
11, 31 heterozygous

Claims (8)

a first semiconductor substrate having a composition containing an oxide of gallium;
a second semiconductor substrate containing diamond in its composition;
a heterojunction at least partially formed between the surface of the first semiconductor substrate and the surface of the second semiconductor substrate, where the heterojunction is formed by gallium-oxygen-carbon bonding;
the first semiconductor substrate comprises an n-type dopant;
the concentration of the n-type dopant is 1×10 ¹⁵ cm ⁻³ to 1×10 ¹⁹ cm ⁻³ ;
the second semiconductor substrate comprises a p-type dopant;
the concentration of the p-type dopant is 1×10 ¹⁵ cm ⁻³ to 1×10 ¹⁸ cm ⁻³ ;
The heterojunction has a rectification characteristic with a rectification ratio of 1×10 ⁸ or more. a first electrode electrically connected to the first semiconductor substrate;
The semiconductor device of claim 1 , further comprising: a second electrode electrically connected to the second semiconductor substrate. 3. The semiconductor device according to claim 1 , wherein the second semiconductor substrate has a thickness of 0.5 μm to 1 mm. 4. The semiconductor device according to claim 1, wherein the first semiconductor substrate has a thickness of 0.5 μm to 100 μm. a first hydroxylation step of introducing OH groups onto at least a portion of a surface of a first semiconductor substrate containing an oxide of gallium;
a second hydroxylation step of introducing OH groups onto at least a portion of the surface of the second semiconductor substrate containing diamond as a composition;
a contacting step of contacting a surface of the first semiconductor substrate having OH groups introduced therein with a surface of the second semiconductor substrate having OH groups introduced therein;
a dehydration step of applying activation energy to the first semiconductor substrate and the second semiconductor substrate that have been brought into contact with each other to cause a dehydration reaction, thereby forming a heterojunction between the surface of the first semiconductor substrate and the surface of the second semiconductor substrate, whereby a gallium-oxygen-carbon bond is formed;
the first semiconductor substrate comprises an n-type dopant;
the concentration of the n-type dopant is 1×10 ¹⁵ cm ⁻³ to 1×10 ¹⁹ cm ⁻³ ;
the second semiconductor substrate comprises a p-type dopant;
the concentration of the p-type dopant is 1×10 ¹⁵ cm ⁻³ to 1×10 ¹⁸ cm ⁻³ ;
the second hydroxylation step includes treating the surface of the second semiconductor substrate with an oxidizing liquid to introduce OH groups;
The method for manufacturing a semiconductor device , wherein the oxidizing liquid contains at least aqueous ammonia and hydrogen peroxide . The method for manufacturing a semiconductor device according to claim 5 , wherein the heterojunction has a rectifying property. 7. The method for manufacturing a semiconductor device according to claim 5 , wherein the first hydroxylation step introduces OH groups by irradiating the surface of the first semiconductor substrate with oxygen plasma. a first wiring step of forming a first electrode electrically connected to the first semiconductor substrate;
The method for manufacturing a semiconductor device according to claim 5 , further comprising a second wiring step of forming a second electrode electrically connected to the second semiconductor substrate.