Epitaxial structure

Abstract

To provide an epitaxial configuration with the ability to regulate stress and increase breakdown voltage.SOLUTION: An epitaxial configuration includes a substrate, a first buffer layer, a second buffer layer, and a channel layer, the first buffer layer is located above the substrate and includes a first portion, the first portion contains a ternary or ternary or larger nitride and a concentration of aluminum atoms in the nitride of 25 at% or less and has doping elements that are 1x1018 cm-3 or more, the second buffer layer is located above the first buffer layer and does not contain aluminum but has doping elements, and the channel layer is located above the second buffer layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an epitaxial structure, and more particularly to an epitaxial structure having the ability to adjust stress to increase breakdown voltage.

Background Art

[0002] A known high electron mobility transistor (HEMT) is a transistor having a two-dimensional electron gas (2-DEG). The two-dimensional electron gas is close to the hetero-junction surface in two types of materials having different band gaps. Since the high electron mobility transistor uses the two-dimensional electron gas with high electron mobility as the carrier channel of the transistor without using the doping region as the carrier channel of the transistor, it has characteristics such as a high breakdown voltage, a high electron mobility, a low conduction resistance, and a low input capacitance, and is widely applied to high-power semiconductor devices.

Summary of the Invention

Problems to be Solved by the Invention

[0003] In general, for a high electron mobility transistor, a buffer layer that is not doped and contains aluminum is installed above the substrate so as to adjust stress. However, since there is a problem that a known buffer layer that is not doped and contains aluminum has a poor breakdown voltage effect, how to provide an epitaxial structure having the ability to adjust stress to increase breakdown voltage becomes a problem that should be solved at an early stage.

Means for Solving the Problems

[0004] In view of this, an object of the present invention is to achieve the effect of being able to provide an epitaxial structure having the ability to adjust stress to increase the breakdown voltage.

[0005] To achieve the above object, the epitaxial structure provided by the present invention includes a substrate, a first buffer layer, a second buffer layer, and a channel layer. The first buffer layer is located above the substrate. The first buffer layer includes a first portion. The first portion includes a ternary or higher nitride, and the concentration of aluminum atoms in the nitride is 25 at% or less. The first portion has a doping element with a doping concentration of 1x10 18 cm -3 or more. The second buffer layer is located above the first buffer layer. The second buffer layer does not contain aluminum but has a doping element. The channel layer is located above the second buffer layer.

[0006] Among them, the first portion is in contact with the second buffer layer.

[0007] Among them, the first buffer layer includes a second portion. The second portion is located between the substrate and the first portion. The substrate and the first portion are in contact with both opposite sides of the second portion, respectively. The concentration of aluminum atoms in the second portion is greater than 25 at%.

[0008] Among them, the thickness ratio of the first buffer layer to the second buffer layer is 1.5 or more and 10 or less.

[0009] Among them, the doping element in the first portion is carbon, iron, or magnesium.

[0010] The epitaxial structure includes a central buffer layer. The central buffer layer is located between the first buffer layer and the second buffer layer. The first buffer layer and the second buffer layer are in contact with both opposite sides of the central buffer layer, respectively. The concentration of aluminum atoms in the central buffer layer is 50 at% or more and the thickness is 10 nm or less.

[0011] Among them, the first portion has at least one nitride film structure having the nitride.

[0012] Among them, the first part includes a superlattice layer, and the superlattice layer includes at least one ternary or higher nitride film and at least one binary nitride film that are overlapped with each other. The at least one ternary or higher nitride film contains the nitride.

[0013] Among them, the first part includes at least one central layer. The concentration of aluminum atoms in the central layer is 50 at% or more while the thickness is 10 nm or less, and the central layer and the nitride film structure are overlapped.

[0014] Among them, when the breakdown voltage value of the epitaxial structure is 1x10 -4 A / cm 2 , the vertical breakdown voltage value is 900 V or more.

[0015] Among them, in the ternary or higher nitride in the first buffer layer, the concentration distribution of aluminum atoms gradually decreases in the direction away from the substrate from the side in contact with the substrate in the first buffer layer.

Advantages of the Invention

[0016] The effect of the present invention is that the first part contains the ternary or higher nitride and the concentration of aluminum atoms in the nitride is 25 at% or less, and the doping concentration in the first part is 1x10 18 cm -3 or more. By being arranged to have a doping element, not only can the stress be adjusted, but also the breakdown voltage capacity of the epitaxial structure can be significantly increased.

Brief Description of the Drawings

[0017]

Figure 1

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Embodiments for Carrying out the Invention

[0018] To explain the present invention more clearly, preferred embodiments will be given and described in detail below with reference to the drawings. As shown in FIG. 1, the epitaxial structure 1 according to the preferred embodiment of the present invention is applied to a high electron mobility transistor, and the epitaxial structure 1 according to the present invention may be formed by deposition by metalorganic chemical vapor deposition (MOCVD).

[0019] Referring to FIG. 1, the epitaxial structure 1 includes a substrate 10, a first buffer layer 20, a second buffer layer 30, and a channel layer 40. The first buffer layer 20 is located above the substrate 10. The first buffer layer 20 includes a first portion 21. The first portion 21 includes a ternary or higher nitride and the concentration of aluminum atoms in the nitride is 25 at% or less. Also, the first portion 21 has a doping concentration of 1x10 18 cm -3It has the doping elements as described above. The second buffer layer 30 is located above the first buffer layer 20. The second buffer layer 30 does not contain aluminum but has doping elements. Further, the channel layer 40 is located above the second buffer layer 30. And the first portion 21 contains the nitride of a ternary system or a quaternary system or higher, and the concentration of aluminum atoms in the nitride is 25 at% or less, and the doping concentration in the first portion 21 is 1x10 18 cm -3 By being installed so as to have the doping elements, not only can the stress be adjusted, but also the breakdown voltage capability of the epitaxial structure 1 can be significantly enhanced.

[0020] Among them, for the first buffer layer 20 and the second buffer layer 30, the ratio of the thicknesses D1 and D2 is 1.5 or more and 10 or less, more preferably 3 or more and 5 or less, and most preferably 5. In this embodiment, the thickness D1 of the first buffer layer 20 is 4.5 um and the thickness D2 of the second buffer layer 30 is 1.5 um will be taken as an example for explanation.

[0021] In this embodiment, the case where the substrate 10 is a silicon substrate will be taken as an example for explanation. In other embodiments, the substrate 10 may be, for example, a silicon carbide substrate or a sapphire substrate. In this embodiment, the case where the nitride of a ternary system or a quaternary system or higher is gallium aluminum nitride will be taken as an example for explanation. Also, the doping element in the first portion 21 is carbon, but actually, the doping element may be a doping element such as iron or magnesium. etc., what is to be explained is that in this embodiment, the case where the second buffer layer 30 is a gallium nitride layer doped with carbon will be taken as an example for explanation. The second buffer layer may be a superlattice structure layer. In other embodiments, the nitride of a quaternary system or higher may be indium gallium aluminum nitride.

[0022] Next, referring to FIG. 1, in this embodiment, the first portion 21 is in contact with the second buffer layer 30. In other words, when the first portion 21 is grown, the second buffer layer 30 is then grown. The first buffer layer 20 includes a second portion 22. The second portion 22 is located between the substrate 10 and the first portion 21, and the substrate 10 and the first portion 21 are in contact with opposite sides of the second portion 22, respectively. That is, the second portion 22 is grown above the substrate 10 first and then the first portion 21 is continuously grown. Among them, the concentration of aluminum atoms in the second portion 22 is greater than 25 at%. Taking the configuration including aluminum gallium nitride as an example for the second portion 22. Also, the second portion 22 does not have a doping element.

[0023] Among them, the first portion 21 includes at least one nitride film structure having the ternary or higher nitride. In this embodiment, as shown in FIG. 1, the first portion 21 and the second portion 22 are each a single-layer nitride film structure. In other embodiments, the first portion 21 or the second portion 22 may each be a nitride film structure having a plurality of layers. For example, in the first portion 21, the nitride film structure of only a plurality of layers with the aluminum concentration of 25% or less is at least one layer or more. For example, it may be three layers (25%, 18%, 7%). As shown in FIG. 2, for the epitaxial structure 2, the first portion 21 includes only three nitride film structures, which are the first aluminum gallium nitride film structure 211 with the aluminum atom concentration of 25 at%, the second aluminum gallium nitride film structure 212 with the aluminum atom concentration of 18 at%, and the third aluminum gallium nitride film structure 213 with the aluminum atom concentration of 7 at%, respectively. Also, the carbon doping concentrations of the first aluminum gallium nitride film structure 211, the second aluminum gallium nitride film structure 212, and the third aluminum gallium nitride film structure 213 are all 1x10 18 cm -3The above is the case. As shown in FIG. 2, the second part 22 may include a structure of only two layers. Each is a gallium aluminum nitride film structure 221 with a gallium aluminum nitride film having a concentration of aluminum atoms of 75 at% and a gallium aluminum nitride film structure 222 with a concentration of aluminum atoms of 50 at%.

[0024] Otherwise, the first part 21 or the second part 22 may each include a superlattice structure. Thereby, the ability to adjust stress can be enhanced. As shown in FIG. 3, the epitaxial structure 3 includes a superlattice layer 214 in the first part 21. The superlattice layer 214 includes at least one ternary or higher nitride film and at least one binary nitride film stacked on top of each other. The at least one ternary or higher nitride film includes the ternary or higher nitride. The ternary nitride film may be a gallium aluminum nitride film with a concentration of aluminum atoms of 25 at%, and the binary nitride film may be an aluminum nitride film.

[0025] Next, continuing to refer to FIG. 3, the epitaxial structure 3 includes two superlattice layers, namely a first superlattice layer 223 and a second superlattice layer 224, in the second part 22. The first superlattice layer 223 includes a plurality of gallium aluminum nitride films and aluminum nitride films stacked on top of each other, and the concentration of aluminum atoms in the gallium aluminum nitride film is 75 at%. The second superlattice layer 224 includes a plurality of gallium aluminum nitride films and aluminum nitride films stacked on top of each other, and the concentration of aluminum atoms in the gallium aluminum nitride film is 50 at%.

[0026] In other embodiments, the epitaxial structure 4 further includes at least one central layer 215 in addition to the single-layer nitride film structure of the first portion 21. The central layer 215 has a thickness of 10 nm or less while the concentration of aluminum atoms is 50 at% or more. The central layer 215 and the single-layer nitride film structure are overlapped. Among them, as shown in FIG. 4, the central layer 215 may be a single layer of aluminum nitride film sandwiched between two single-layer nitride film structures. Actually, the number of the central layers 215 may be plural and may be arranged to be staggeredly overlapped with a plurality of single-layer nitride film structures.

[0027] In other embodiments, as shown in FIG. 5, the epitaxial structure 5 further includes a central buffer layer 50 located between the first buffer layer 20 and the second buffer layer 30, and the first buffer layer 20 and the second buffer layer 30 are respectively in contact with both opposite sides of the central buffer layer 50. The central buffer layer 50 has a thickness of 10 nm or less while the concentration of aluminum atoms is 50 at% or more. The central buffer layer 50 may contain aluminum nitride and have a concentration of aluminum atoms of 50 at% or more, and has a role of adjusting stress.

[0028] It should be noted that in each of the above embodiments, for the ternary or higher nitride in the first buffer layer 20, the concentration distribution of aluminum atoms gradually decreases in the direction away from the substrate 10 from the side in contact with or close to the substrate 10 in the first buffer layer 20. The "gradually decreasing" may be gradually decreasing step by step or continuously decreasing step by step.

[0029] In the above embodiment, when the breakdown voltage value of the epitaxial structure 3 is 1×10 -4 A / cm 2 the vertical breakdown voltage value in the epitaxial structure 3 is 900 V or more. Hereinafter, it will be further described based on Comparative Example 1, Example 1, and Example 2.

[0030] Among them, the epitaxial structure according to Comparative Example 1 is substantially the same as the epitaxial structure 3 shown in FIG. 3 in the above-described embodiment. However, the difference lies in that the first part 21 according to Comparative Example 1 has no doping. The epitaxial structure 3 according to Example 1 is the same as the structure shown in FIG. 3, and the first part 21 has carbon doping of 1×10 18 cm -3 or more. Further, as shown in FIG. 6, the epitaxial structure according to Example 1 has better withstand voltage capability, and the absolute value of the current value according to Example 1 is smaller than the absolute value of the current value according to Comparative Example 1, whether it is the voltage scanned in the positive direction or the voltage scanned in the negative direction. As can be seen therefrom, by having carbon doping of 1×10 18 cm -3 or more in the first part 21, the withstand voltage capability of the epitaxial structure can be effectively enhanced.

[0031] It should be noted that, as shown in FIG. 7, the epitaxial structure 6 according to Example 2 is substantially the same as the epitaxial structure 3 shown in FIG. 3 in the above-described embodiment. However, the difference is that the epitaxial structure 6 according to Example 2 has a gallium nitride aluminum film structure 216 with an aluminum atom concentration of 18 at% and a gallium nitride aluminum film structure 217 with an aluminum atom concentration of 7 at% in addition to the superlattice layer 214 in the first part 21. As shown in FIG. 6, the epitaxial structure 6 according to Example 2 has better withstand voltage capability, and the absolute value of the current value according to Example 2 is smaller than the absolute value of the current value according to Comparative Example 1 and Example 1, whether it is the voltage scanned in the positive direction or the voltage scanned in the negative direction. In other words, by increasing the thickness of the first part 21, the withstand voltage capability of the epitaxial structure can be effectively enhanced.

[0032] From the above, the first part according to the present invention contains a ternary or higher nitride, the concentration of aluminum atoms in the nitride is 25 at% or less, and the doping concentration in the first part is 1×10 18 cm-3 By being arranged to have the doping elements as described above, not only can the stress be adjusted, but also the breakdown voltage capability of the epitaxial structure can be significantly enhanced.

[0033] The above are only preferred practicable embodiments of the present invention, and it goes without saying that any equivalent substitutions based on the description of the present invention and the scope of the patent are included in the scope of the patent of the present invention.

Description of Reference Numerals

[0034] 1, 2, 3, 4, 5, 6 Epitaxial structures 10 Substrate 20 First buffer layer 21 First part 211 First aluminum gallium nitride film structure 212 Second aluminum gallium nitride film structure 213 Third aluminum gallium nitride film structure 214 Superlattice layer 215 Central layer 216, 217 Aluminum gallium nitride film structures 22 Second part 221 Fourth aluminum gallium nitride film structure 222 Fifth aluminum gallium nitride film structure 223 First superlattice layer 224 Second superlattice layer 30 Second buffer layer 40 Channel layer 50 Central buffer layer D1, D2 Thickness

Claims

1. A substrate, It is located above the substrate and includes a first portion. The first portion includes a ternary or higher nitride, and the concentration of aluminum atoms in the nitride is 25 at% or less, and has a doping element with a doping concentration of 1x10 18 cm -3 and a first buffer layer A second buffer layer located above the first buffer layer, containing no aluminum but having a doping element, A channel layer located above the second buffer layer, A central buffer layer, and including, The central buffer layer is located between the first buffer layer and the second buffer layer, and the first buffer layer and the second buffer layer are in contact with each other on both opposite sides. The concentration of aluminum atoms in the central buffer layer is 50 at% or more. An epitaxial structure characterized by this.

2. The first buffer layer includes a second portion, The second portion is located between the substrate and the first portion, and the substrate and the first portion are in contact with each other on both opposite sides. The concentration of aluminum atoms in the second portion is greater than 25 at%. The epitaxial structure according to claim 1, characterized by this.

3. The thickness ratio of the first buffer layer to the second buffer layer is 1.5 or more and 10 or less. The epitaxial structure according to claim 1, characterized by this.

4. The doping element in the first portion is carbon, iron, or magnesium, characterized The epitaxial structure according to claim 1.

5. The thickness of the central buffer layer is 10 nm or less. The epitaxial structure according to claim 1, characterized by this.

6. The first portion includes at least one nitride film structure having the nitride. The epitaxial structure according to claim 1 or 2, characterized by this.

7. The first portion includes a superlattice layer, The superlattice layer includes at least one ternary or higher nitride film and at least one binary nitride film stacked on top of each other, The at least one ternary or higher nitride film has the nitride. The epitaxial structure according to claim 1 or 2, characterized by this.

8. The first portion includes at least one central layer, The concentration of aluminum atoms in the central layer is 50 at% or more and the thickness is 10 nm or less, and the central layer and the nitride film structure are stacked. The epitaxial structure according to claim 6, characterized by this.

9. The epitaxial structure has a breakdown voltage value of 1 x 10 -4 A / cm 2 and when this is the case, the vertical breakdown voltage value is 900 V or more. The epitaxial structure according to claim 1, characterized in that.

10. In the ternary or higher nitride in the first buffer layer, the concentration distribution of aluminum atoms gradually decreases in a direction away from the substrate from the side in contact with the substrate in the first buffer layer. The epitaxial structure according to any one of claims 1 to 5 and claim 9, characterized in that.

11. In the ternary or higher nitride in the first buffer layer, the concentration distribution of aluminum atoms gradually decreases in a direction away from the substrate from the side in contact with the substrate in the first buffer layer. The epitaxial structure according to claim 6, characterized in that.

12. In the ternary or higher nitride in the first buffer layer, the concentration distribution of aluminum atoms gradually decreases in a direction away from the substrate from the side in contact with the substrate in the first buffer layer. The epitaxial structure according to claim 7, characterized in that.

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