A substrate with a protective layer and its manufacturing method, and a group III nitride laminate and its manufacturing method.

Abstract

This invention provides a technique for suppressing Si accumulation at the interface when regrowing a second group III nitride on a first group III nitride in a manner other than continuous growth. [Solution] The protective layer substrate comprises a substrate in which at least the surface layer is composed of a group III nitride, and a protective layer composed of carbon formed directly above the surface layer, and is used as a growth substrate for growing a group III nitride directly above the surface layer in a state in which the protective layer has been removed.

Description

[Technical Field]

[0001] The present invention relates to a substrate with a protective layer, a method for manufacturing the same, and a group III nitride laminate, and a method for manufacturing the same. [Background technology]

[0002] Group III nitrides such as gallium nitride (GaN) are used as materials for manufacturing semiconductor devices such as light-emitting devices and transistors. Nitride laminates, in which a GaN layer is epitaxially grown on a GaN substrate, are attracting attention because of the high quality of the GaN layer.

[0003] When growing a GaN layer on a GaN substrate, the GaN substrate is brought in from the outside into the processing chamber of the crystal growth apparatus where the GaN layer is grown, and the GaN layer is grown on the GaN substrate. In other words, the GaN layer is regrowthed on the GaN substrate in a manner that is not continuous growth.

[0004] Typically, a second group III nitride may be regrown on a first group III nitride that serves as the growth substrate, in a manner that is not continuous growth, such as when regrowing a GaN layer on a GaN substrate. In such cases, due to the removal of the first group III nitride from the crystal growth apparatus after its growth, silicon (Si)-containing contaminants adhere to the surface of the first group III nitride. Conventional techniques have not been able to adequately remove the Si resulting from these contaminants.

[0005] When a second group III nitride is regrown on a first group III nitride in a manner other than continuous growth, Si due to contaminants accumulates at the interface between the first and second group III nitrides during regrowth (see, for example, Figure 4 in Non-Patent Literature 1). Such Si accumulation regions adversely affect the operation of the fabricated semiconductor device, as will be described in detail later. [Prior art documents] [Non-patent literature]

[0006]

Non-Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0007] An object of the present invention is to provide a technique for suppressing Si accumulation at the interface when regrowing a second group III nitride on a first group III nitride in a mode that is not continuous growth.

Means for Solving the Problem

[0008] According to one aspect of the present invention, a substrate having at least a surface layer composed of a group III nitride, and a protective layer formed directly on the surface layer and composed of carbon, are provided, the substrate with a protective layer being used as a growth substrate for growing a group III nitride directly on the surface layer in a state where the protective layer is removed, substrate with protective layer is provided.

[0009] According to another aspect of the present invention, a step of preparing a substrate having at least a surface layer composed of a group III nitride, a step of carrying the substrate into a processing chamber and removing the outermost layer of the surface layer, a step of forming a protective layer composed of carbon directly on the surface layer from which the outermost layer has been removed, continuously with the removal processing of the outermost layer in the processing chamber, a method for manufacturing a substrate with a protective layer having is provided.

[0010] According to yet another aspect of the present invention, A substrate whose surface layer is composed of a group III nitride, A protective layer made of carbon is formed directly above the aforementioned surface layer, A step of preparing a substrate with a protective layer having, The process involves transporting the substrate with the protective layer into the processing chamber and removing the protective layer, The process of growing a group III nitride directly on the surface layer after the protective layer has been removed, in the same processing chamber as the protective layer removal process, Method for manufacturing a group III nitride laminate having It will be provided.

[0011] According to yet another aspect of the present invention, A substrate in which at least the surface layer is composed of a group III nitride, and the surface layer has an uneven structure, A group III nitride layer formed directly above the uneven structure of the surface layer, It has, In the region within a thickness of 50 nm from the interface between the surface layer and the group III nitride layer of the substrate, the maximum silicon concentration of the group III nitride layer is 1 × 10⁻⁶. 17 / cm 3 Less than, Group III nitride laminate It will be provided. [Effects of the Invention]

[0012] A technique is provided for suppressing Si accumulation at the interface when a second group III nitride is regrown on a first group III nitride in a manner other than continuous growth. [Brief explanation of the drawing]

[0013] [Figure 1] Figure 1(a) is a schematic cross-sectional view showing a substrate 10 with a protective layer according to an embodiment of the present invention, and Figure 1(b) is a schematic cross-sectional view showing a nitride laminate 20 according to an embodiment of the present invention. [Figure 2]Figure 2 is a schematic cross-sectional view of the substrate 11 (prepared in the stage before forming the protective layer 15). [Figure 3] Figures 3(a) and 3(b) are schematic diagrams illustrating a manufacturing apparatus 100 for a substrate with a protective layer, which continuously performs the steps of removing the outermost layer of the surface layer 12 of the substrate 11 and forming the protective layer 15. [Figure 4] Figures 4(a) and 4(b) are schematic diagrams illustrating a crystal growth apparatus 200 for continuously performing the steps of removing the protective layer 15 and growing (re-growing) a group III nitride (group III nitride layer 21). [Figure 5] Figures 5(a) and 5(b) are schematic cross-sectional views showing a first and second example of a modified nitride laminate 20, respectively. [Figure 6] Figure 6 is Figure 4 from Non-Patent Document 1, and is an example of a SIMS profile showing the thickness-direction distribution of impurity concentrations such as silicon in a conventional nitride laminate. [Modes for carrying out the invention]

[0014] The manufacturing technology for a group III nitride laminate (hereinafter also simply referred to as a nitride laminate) according to an embodiment of the present invention will be described. First, as preliminary information, the manufacturing technology for conventional nitride laminates will be described. Figure 6 (Figure 4 of Non-Patent Literature 1) is an example of a secondary ion mass spectrometry (SIMS) profile showing the thickness-direction distribution of impurity concentrations such as silicon (Si) in a conventional nitride laminate, and shows the concentration distribution of Si, oxygen (O), and carbon (C).

[0015] The sample illustrated in Figure 6 is a nitride laminate in which a GaN layer is epitaxially grown on a gallium nitride (GaN) substrate; in other words, a nitride laminate in which GaN constituting the GaN layer is regrowthed on the GaN constituting the GaN substrate. The interface between the GaN substrate and the GaN layer is shown by a dashed line. The GaN substrate was grown by hydride vapor deposition (HVPE), and the GaN layer was grown by metal-organic chemical vapor deposition (MOCVD).

[0016] The GaN substrate is brought into the processing chamber of the crystal growth apparatus where the GaN layer is grown (re-grown) from outside the chamber. In other words, before being brought into the processing chamber, the GaN substrate is prepared by being removed from the crystal growth apparatus in which the GaN constituting the substrate was grown. Consequently, contaminants containing silicon adhere to the surface of the GaN substrate.

[0017] In conventional techniques, although the attached Si is cleaned with hydrofluoric acid, etc., it is not sufficiently removed, and Si accumulates on the interface between the GaN substrate and the GaN layer, and the GaN layer is regrowthed with Si in this state, resulting in a Si concentration of 1 × 10⁻¹⁶ at the regrowth interface. 17 / cm 3 It was not possible to reduce it to less than 10. In the example shown in Figure 6, the Si concentration in the GaN substrate and the GaN layer is 10. 15 / cm 3 Although the level is on the order of , the Si concentration at the interface is 1 × 10⁻⁶ 18 / cm 3 It has risen to a level that is exceptionally high, close to that of [another level].

[0018] For example, when fabricating GaN-based high-electron-mobility transistors (HEMTs), a GaN layer may be regrown on a semi-insulating GaN substrate, or an aluminum gallium nitride (AlGaN) layer may be regrown on a GaN layer. The Si accumulation region formed on the regrowth interface can, for example, become a leak path when forming a GaN / AlGaN HEMT structure on a semi-insulating GaN substrate, causing pinch-off failure in the device. Alternatively, when forming an HEMT by regrowing AlGaN on a GaN channel, it can cause the two-dimensional electron gas concentration at the GaN / AlGaN interface to deviate from the design value, leading to adverse effects that alter the device threshold.

[0019] In this embodiment, we propose a manufacturing technique for nitride laminates that can suppress the formation of Si accumulation regions at such regrowth interfaces. Specifically, as will be described in detail later, the formation of Si accumulation regions can be suppressed by performing regrowth of a group III nitride using a substrate with a protective layer having a protective layer for suppressing Si accumulation.

[0020] Referring to Figure 1(a), the protective layer substrate 10 according to this embodiment will be described. Figure 1(a) is a schematic cross-sectional view showing the protective layer substrate 10. The protective layer substrate 10 has a substrate 11 in which at least the surface layer 12 is composed of a group III nitride, and a protective layer 15 composed of carbon (C) formed directly on the surface layer 12, and is used as a growth substrate for growing (regrowing) group III nitride directly on the surface layer 12 (surface 13a) in a state in which the protective layer 15 has been removed.

[0021] The substrate 11 may be a substrate whose entire thickness is made of a group III nitride (for example, a GaN freestanding substrate, a laminated substrate in which a group III nitride layer such as a GaN layer is laminated on a GaN freestanding substrate, etc.), or it may be a laminated substrate in which a group III nitride layer is laminated on a component made of a material other than a group III nitride (a dissimilar material) (for example, a laminated substrate in which a group III nitride layer such as a GaN layer is laminated on a SiC substrate, etc.).

[0022] In this embodiment, the protective layer 15 is not formed on the surface (back surface) of the substrate 11 opposite to the surface layer 12 that serves as the base for regrowing the group III nitride, that is, on the side opposite to the protective layer 15, and the material constituting the back surface of the substrate 11 may be exposed.

[0023] The group III nitride constituting the surface layer 12 of the substrate 11 is typically GaN, but is not particularly limited, and may be a group III nitride containing aluminum (Al) or a group III nitride containing indium (In). In addition, the type of impurity contained in the group III nitride constituting the surface layer 12 of the substrate 11 is not particularly limited, and may be a donor-type impurity such as Si, germanium (Ge), or O, or may be an acceptor-type or semi-insulating impurity such as magnesium (Mg), C, iron (Fe), or manganese (Mn). The concentration of the impurity contained in the group III nitride constituting the surface layer 12 of the substrate 11 is also not particularly limited, and may be appropriately selected as needed.

[0024] As typical embodiments of the group III nitride constituting the surface layer 12 of the substrate 11, the following two are exemplified. As the first embodiment, an n-type group III nitride is exemplified in which the total concentration of donor-type impurities such as Si, Ge, and O is 1×10 17 / cm 3 or less, and the total concentration of acceptor-type and semi-insulating impurities such as Mg, C, Fe, and Mn is lower than the total concentration of the above donor-type impurities. As the second embodiment, a p-type or semi-insulating group III nitride is exemplified in which the total concentration of acceptor-type and semi-insulating impurities such as Mg, C, Fe, and Mn is higher than the total concentration of donor-type impurities. In the second embodiment, the total concentration of donor-type impurities such as Si, Ge, and O may be 1×10 17 / cm 3 or more.

[0025] The protective layer 15 is formed on the entire surface directly above (the surface 13a of) the surface layer 12 of the substrate 11, and is composed of C. The thickness of the protective layer 15 is, for example, 10 nm or more and 1000 nm or less. Since the protective layer 15 covers the surface 13a of the surface layer 12 of the substrate 11, contamination of the surface 13a due to exposure to the atmosphere or the like can be prevented.

[0026] As will be described in detail later, the protective layer 15 is formed on the surface 13a after the Si-containing contaminants 14 have been removed from the surface 13a. This suppresses Si accumulation on the surface 13a, which is the interface between the surface layer 12 of the substrate 11 and the protective layer 15. Specifically, the maximum Si concentration of the protective layer 15 in the region 16 within a thickness of 50 nm from the interface (surface 13a) between the surface layer 12 of the substrate 11 and the protective layer 15 (hereinafter referred to as the vicinity of the protective layer 15 interface region 16) is 1 × 10⁻¹⁶. 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 It is less than.

[0027] A method for measuring the Si concentration in the region 16 near the interface of the protective layer 15 will be described. The Si concentration will be measured by secondary ion mass spectrometry (SIMS) on the substrate 10 with the protective layer. First, a method for defining the interface between the protective layer 15 and the surface layer 12 of the substrate 11 will be described. The surface layer 12 of the substrate 11 is composed of a group III nitride, and the group III element that has the highest composition in the group III nitride will be referred to as the main group III element, representing the constituent elements of the surface layer 12. If the surface layer 12 is composed of GaN, for example, the main group III element is Ga.

[0028] The protective layer 15 is composed of carbon (C), and the C ion strength is strong in the protective layer 15. The surface layer 12 of the substrate 11 is (typically) composed of the main group III elements, and the ionic strength of the main group III elements is strong in the surface layer 12. For both the protective layer 15 and the surface layer 12 of the substrate 11, the composition is constant in the main part in the thickness direction (the part excluding the interface with adjacent layers, hereinafter simply referred to as the main part). Therefore, the C ion strength is constant in the main part of the protective layer 15, and the ionic strength of the main group III elements is constant in the main part of the surface layer 12. In addition, at the interface between the protective layer 15 and the surface layer 12 of the substrate 11, the C ion strength decreases from the protective layer 15 side towards the surface layer 12 side, and the ionic strength of the main group III elements decreases from the surface layer 12 side towards the protective layer 15 side.

[0029] For both the protective layer 15 and the surface layer 12 of the substrate 11, the ionic strength is normalized so that the ionic strength in the main part is 1. The interface between the protective layer 15 and the surface layer 12 of the substrate 11 is defined as the depth at which the C ionic strength and the ionic strength of the main group III element become equal.

[0030] From the interface determined in this way, the region 16 on the protective layer 15 side with a thickness of 50 nm or less is defined as the interface vicinity region 16 of the protective layer 15. In this embodiment, the protective layer 15 has a maximum Si concentration of 1 × 10⁻¹⁶ in the interface vicinity region 16, as measured by SIMS. 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 It is suppressed to be less than ). Note that if the thickness of the protective layer 15 is 50 nm or less, "the region 16 with a thickness of 50 nm or less on the protective layer 15 side" refers to the total thickness of the protective layer 15.

[0031] Furthermore, the measured ionic strength in the main part of each layer does not need to be strictly constant (it may vary to some extent in the thickness direction), and the "constant ionic strength" in the main part of a layer may be determined as follows, taking into consideration that the ionic strength is highly constant (compositional constant) near the center in the thickness direction of the layer: The average value of the ionic strength in a range of 1 / 2 the thickness of the layer (from 1 / 4 to 3 / 4 of the thickness direction of the layer), centered on the center in the thickness direction of the layer, can be defined as the "constant ionic strength" in the main part of the layer.

[0032] The quantification of Si concentration will be explained. For the layer composed of Group III nitride (the surface layer 12 of the substrate 11, and the Group III nitride layer 21 described later), SIMS measurement is performed on a sample in which Si is ion-implanted in a GaN layer (the Si concentration can be calculated by calculation), and the Si ion intensity at that time is matched to the calculated Si concentration. For the protective layer 15 composed of C, it would be desirable to quantify the Si concentration based on SIMS measurement of another sample in which Si is ion-implanted in a C layer, but accurate quantification is difficult because the C layer is amorphous and its density is uncertain. Therefore, here, the C layer is also considered as a GaN layer, and the Si concentration is defined using the quantification results for the GaN layer.

[0033] The nitride laminate 20 according to this embodiment will be described with reference to Figure 1(b). Figure 1(b) is a schematic cross-sectional view showing the nitride laminate 20. The nitride laminate 20 has a substrate 11 in which at least the surface layer 12 is composed of a group III nitride, and a group III nitride layer 21 formed directly above the surface layer 12. As will be described later with reference to Figures 5(a) and 5(b), this embodiment is particularly preferred when the surface layer 12 of the substrate 11 has an uneven structure (when the group III nitride layer 21 is formed directly above the uneven structure). Hereinafter, the group III nitride constituting the surface layer 12 of the substrate 11 may be referred to as the first group III nitride, and the group III nitride constituting the group III nitride layer 21 may be referred to as the second group III nitride.

[0034] The second group III nitride constituting the group III nitride layer 21 is typically GaN, but is not particularly limited and may be a group III nitride containing aluminum (Al) or a group III nitride containing indium (In). The composition of the second group III nitride constituting the group III nitride layer 21 may be the same as or different from the composition of the first group III nitride constituting the surface layer 12 of the substrate 11.

[0035] Furthermore, the type of impurities contained in the second group III nitride constituting the group III nitride layer 21 is not particularly limited and may be donor-type impurities such as Si, Ge, and O, or acceptor-type and semi-insulating impurities such as Mg, C, Fe, and Mn. The concentration of impurities contained in the second group III nitride is also not particularly limited and may be appropriately selected as needed. The conductivity type of the second group III nitride may be the same as or different from that of the first group III nitride constituting the surface layer 12 of the substrate 11.

[0036] As will be described in detail later, by growing (re-growing) the group III nitride layer 21 using the substrate 10 with a protective layer, such a nitride laminate 20 can be obtained, and Si accumulation on the surface 13a which is the interface between the surface layer 12 of the substrate 11 and the group III nitride layer 21 is suppressed. Specifically, the maximum Si concentration of the group III nitride layer 21 in the region 22 within a thickness of 50 nm from the interface (surface 13a) of the surface layer 12 of the substrate 11 and the group III nitride layer 21 (hereinafter referred to as the region near the interface of the group III nitride layer 21 22) is 1 × 10⁻¹⁶. 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 It is less than.

[0037] A method for measuring the Si concentration in the region 22 near the interface of the group III nitride layer 21 will be described. The Si concentration will be measured by SIMS measurement on the nitride laminate 20. First, a method for defining the interface between the group III nitride layer 21 and the surface layer 12 of the substrate 11 will be described. Since the second group III nitride constituting the group III nitride layer 21 may be the same as the first group III nitride constituting the surface layer 12 of the substrate 11, the interface between the group III nitride layer 21 and the surface layer 12 will be defined by the difference in impurities, not by the difference in composition.

[0038] At least one of the growth method, growth conditions, and growth direction of the second group III nitride constituting the group III nitride layer 21 will differ from those of the first group III nitride constituting the surface layer 12 of the substrate 11. Consequently, the concentration of at least one of the impurities C, O, Ge, and Mg will differ between the group III nitride layer 21 and the surface layer 12, and the concentration of the impurity will change abruptly at the interface between the two. Among C, O, Ge, and Mg, the impurity whose concentration differs most between the group III nitride layer 21 and the surface layer 12 will be referred to as the principal impurity.

[0039] The interface between the group III nitride layer 21 and the surface layer 12 of the substrate 11 is defined as the depth at which the concentration of the main impurities is exactly midway between the concentration C2 in the group III nitride layer 21 and the concentration C1 in the surface layer 12 ((C1 + C2) / 2).

[0040] From the interface thus determined, the region 22 on the Group III nitride layer 21 side with a thickness of 50 nm or less is defined as the interface vicinity region 22 of the Group III nitride layer 21. In this embodiment, the Si concentration measured by SIMS in the interface vicinity region 22 of the Group III nitride layer 21 is at most 1 × 10⁻⁶ 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 It is suppressed to be less than ). Note that if the thickness of the group III nitride layer 21 is 50 nm or less, "the region 22 with a thickness of 50 nm or less on the group III nitride layer 21 side" refers to the total thickness of the group III nitride layer 21.

[0041] The impurity concentration in each layer may be determined as follows, taking into consideration the high uniformity of impurity concentration near the center in the thickness direction of the layer: The average value of the concentration of the main impurity in the range of 1 / 2 the thickness of the layer (from 1 / 4 to 3 / 4 of the thickness direction of the layer) centered on the center in the thickness direction of the layer can be determined as the concentration of the main impurity in the layer (concentration C2 in the group III nitride layer 21, concentration C1 in the surface layer 12).

[0042] In the case of actual device wafers, the group III nitride layer 21 (the group III nitride layer formed on the surface layer 12) may consist of multiple layers. In such cases, layers having the same group III atom ratio and the same electron or hole concentration are distinguished, and the layer closest to the surface layer 12 is considered to be the group III nitride layer 21.

[0043] A method for manufacturing a substrate with a protective layer 10 will be described with reference to Figures 2, 3(a), and 3(b). The method for manufacturing a substrate with a protective layer 10 includes the steps of: preparing a substrate 11; transporting the substrate 11 into the processing chamber 110 of the manufacturing apparatus 100 for a substrate with a protective layer 10 and removing the outermost layer 12a of the surface layer 12 of the substrate 11; and forming a protective layer 15 made of C directly on the surface layer 12 from which the outermost layer 12a has been removed, in the processing chamber 110, in a manner continuous with the removal of the outermost layer 12a.

[0044] Figure 2 is a schematic cross-sectional view of the substrate 11 (prepared in the stage before forming the protective layer 15). The surface layer 12 of the substrate 11 is composed of a group III nitride as described above, and contaminants 14 containing Si are attached to the surface 13 of the surface layer 12 due to exposure to air, etc.

[0045] Figures 3(a) and 3(b) are schematic diagrams illustrating a manufacturing apparatus 100 for a substrate with a protective layer, which continuously performs the steps of removing the outermost layer of the surface layer 12 of the substrate 11 and forming the protective layer 15. A sputtering apparatus is exemplified as the manufacturing apparatus 100.

[0046] The manufacturing apparatus (sputtering apparatus) 100 for the substrate 10 with a protective layer has a processing chamber 110. Inside the processing chamber 110, there are electrodes 120 and 130 facing each other, and the voltage applied between electrodes 120 and 130 is controlled by a power supply 140. A target 150 made of C is placed on the side of one electrode 120, and the substrate 11 is placed on the side of the other electrode 130.

[0047] Figure 3(a) shows a process for removing the outermost layer 12a of the surface layer 12 of the substrate 11. In this process, reverse sputtering is performed by setting the voltage so that the sputtering gas 160 collides with the substrate 11, thereby removing the outermost layer 12a of the surface layer 12 of the substrate 11. For example, the outermost layer 12a with a thickness of 1 nm to 1 μm is removed from the entire surface layer 12. As a result, along with the outermost layer 12a, the attached contaminants 14 are also removed, and a substrate 11 having a surface 13a with suppressed Si accumulation is obtained.

[0048] Figure 3(b) shows the process of forming the protective layer 15. In this process, sputtering is performed by setting the voltage so that the sputtering gas 160 collides with the target 150, scattering C particles 150a from the target 150, and depositing the C particles 150a on the surface 13a of the substrate 11 to a thickness of, for example, 10 nm to 1000 nm. As a result, a protective layer 15 made of C is formed on the entire surface directly above the surface 13a of the substrate 11.

[0049] In this way, the substrate 10 with a protective layer is manufactured. The process of forming the protective layer 15 is carried out in the processing chamber 110, continuously with the removal of the outermost layer 12a of the surface layer 12 of the substrate 11, that is, without removing the substrate 11 from the processing chamber 110 after the removal of the outermost layer 12a. As a result, the protective layer 15 can be formed without contamination of the surface 13a, which is the interface between the surface layer 12 of the substrate 11 and the protective layer 15, and thus Si accumulation at the interface is suppressed (the Si concentration in the region 16 within 50 nm thickness from the surface 13a is 1 × 10⁻¹⁶). 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 A protective layer 15 that is less than can be obtained.

[0050] A method for manufacturing a nitride laminate 20 using a substrate 10 with a protective layer will be described with reference to Figures 4(a) and 4(b). The method for manufacturing the nitride laminate 20 includes the steps of: preparing a substrate 10 with a protective layer; transporting the substrate 10 with a protective layer into the processing chamber 210 of a crystal growth apparatus 200 and removing the protective layer 15; and growing (re-growing) a group III nitride (group III nitride layer 21) directly on the surface layer 12 of the substrate 11 in the processing chamber 210, in a state where the protective layer 15 has been removed, in a manner continuous with the removal of the protective layer 15.

[0051] Figures 4(a) and 4(b) are schematic diagrams illustrating a crystal growth apparatus 200 for continuously performing the steps of removing the protective layer 15 and growing (re-growing) a group III nitride (group III nitride layer 21). An MOCVD apparatus is exemplified as the crystal growth apparatus 200.

[0052] The crystal growth apparatus (MOCVD apparatus) 200 has a processing chamber 210. A susceptor 220 on which a substrate 11 is placed is provided inside the processing chamber 210. The susceptor 220 has a heater 230, which heats the substrate 11 to a predetermined processing temperature. A gas supply mechanism 240 supplies processing gas 250 used for each process into the processing chamber 210.

[0053] Figure 4(a) shows the process of removing the protective layer 15. This process is carried out by supplying a gas containing hydrogen and nitrogen as the processing gas 250 and heating the substrate 10 with the protective layer in an atmosphere containing the hydrogen and nitrogen gas. Ammonia is an example of a gas containing hydrogen and nitrogen. The heating temperature is preferably, for example, 800°C to 1100°C. The heating time is preferably, for example, 1 minute to 1 hour. Furthermore, the internal pressure of the apparatus during this process is preferably 0.1 atmospheres to 1 atmosphere, and the partial pressure of ammonia is preferably 0.01 times to 0.5 times the internal pressure of the apparatus.

[0054] The carbon (C) constituting the protective layer 15 reacts with a gas containing hydrogen and nitrogen to form hydrogen cyanide (HCN), etc., thereby removing the protective layer 15. This process is carried out until the protective layer 15 is completely removed. As a result, a substrate 11 is obtained in which the entire surface 13a, free from Si accumulation on the surface layer 12, is exposed.

[0055] Figure 4(b) shows the process for growing (re-growing) a group III nitride (group III nitride layer 21). In this process, group III raw material gas and group V raw material gas are supplied as the processing gas 250, and if necessary, donor type, acceptor type, or semi-insulating type impurity raw material gas is also supplied to grow (re-grow) the group III nitride.

[0056] For the aluminum (Al) raw material gas among the Group III raw material gases, for example, trimethylaluminum (Al(CH3)3, TMA) gas is used. For the gallium (Ga) raw material gas among the Group III raw material gases, for example, trimethylgallium (Ga(CH3)3, TMG) ​​gas is used. For the indium (In) raw material gas among the Group III raw material gases, for example, trimethylindium (In(CH3)3, TMI) gas is used. For the nitrogen (N) raw material gas among the Group V raw material gases, for example, ammonia (NH3) is used. As the carrier gas, for example, at least one of nitrogen gas (N2 gas) and hydrogen gas (H2 gas) is used. The growth temperature can be selected, for example, in the range of 700°C to 1400°C, and the V / III ratio, which is the flow rate ratio of Group V raw material gas to Group III raw material gas, can be selected, for example, in the range of 10 to 5000. The ratio of the supply amount of each raw material gas is adjusted according to the composition of the Group III nitride layer 21 to be grown.

[0057] In this way, the nitride laminate 20 is manufactured by growing (re-growing) a group III nitride (group III nitride layer 21) directly on the surface layer 12 (surface 13a) of the substrate 11. The process of growing (re-growing) the group III nitride layer 21 is carried out in the processing chamber 210, continuously with the removal of the protective layer 15, that is, without removing the substrate 11 from the processing chamber 210 after the removal of the protective layer 15. As a result, the group III nitride layer 21 can be grown (re-grown) without contamination of the surface 13a, which is the interface between the surface layer 12 of the substrate 11 and the group III nitride layer 21, and thus Si accumulation at the interface is suppressed (the Si concentration in the region 22 within a thickness of 50 nm from the surface 13a is 1 × 10⁻¹⁶ 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 A group III nitride layer 21 (less than) can be obtained.

[0058] The composition, impurities, etc. of the second group III nitride constituting the group III nitride layer 21 may be appropriately selected according to the specifications of the semiconductor device to be manufactured using the nitride laminate 20, and may be the same as or different from the composition, impurities, etc. of the first group III nitride constituting the surface layer 12 of the substrate 11.

[0059] Specifically, the following embodiments are exemplified: The first and second Group III nitrides may both be n-type (e.g., in a vertical power device). The first and second Group III nitrides may be p-type and n-type, or n-type and p-type, respectively (in a pn diode). The first and second Group III nitrides may both be p-type. The first and second Group III nitrides may both be semi-insulating (e.g., in a GaN-on-GaN HEMT with stacking up to the GaN channel). As an embodiment where the compositions of the first and second Group III nitrides differ, for example, the first Group III nitride may be GaN and the second Group III nitride may be AlGaN (e.g., in a HEMT with regrowing of an AlGaN layer). In addition, InAlGaScN may be used as the second Group III nitride containing Al (e.g., in a current aperture vertical electron transistor (CAVET)).

[0060] Next, a modified nitride laminate 20 will be described with reference to Figures 5(a) and 5(b). The surface layer 12 of the substrate 11 does not necessarily have to be flat over its entire surface; in this modified example, the surface layer 12 of the substrate 11 has an uneven structure. In this modified nitride laminate 20, the group III nitride layer 21 is formed directly on the uneven structure of the surface layer 12 of the substrate 11. Here, the uneven structure is intentionally provided, and the height difference of the uneven structure is, for example, at least 200 nm or more.

[0061] In this modified example, first, a process is performed to form an uneven surface structure on the surface layer 12 of the substrate 11. Since this process is performed outside the crystal growth apparatus, in the configuration where the surface layer 12 has an uneven surface structure, it is not possible to continuously grow (re-grow) a group III nitride layer 21 on the surface layer 12. After forming the uneven surface structure on the surface layer 12, the substrate 11 is loaded into the manufacturing apparatus 100 for the protective layer substrate 10 and processed to produce a protective layer substrate 10 in which a protective layer 15 is formed on the surface 13a of the surface layer 12 having an uneven surface structure, where Si accumulation is suppressed. Then, the protective layer substrate 10 is loaded into the crystal growth apparatus 200 and processed to produce a nitride laminate 20 in which a group III nitride layer 21 is grown (re-grow) on the surface 13a of the surface layer 12 having an uneven surface structure, where Si accumulation is suppressed. According to this modified example, the protective layer 15 can protect the uneven structure, the surface layer 12 has the desired uneven structure, and Si accumulation at the interface is suppressed (the Si concentration in the region 22 within 50 nm thickness from the surface 13a is 1 × 10⁻¹⁰ 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 A nitride laminate 20 having a group III nitride layer 21 (less than) can be obtained.

[0062] Figure 5(a) is a schematic cross-sectional view showing a first example of a configuration in which the surface layer 12 of the substrate 11 has an uneven structure. In the first example, the surface layer 12 has recesses (trenches) 31. This example assumes, for example, a trench MOS, in which the first group III nitride constituting the surface layer 12 of the substrate 11 is, for example, GaN, and the second group III nitride constituting the group III nitride layer 21 is, for example, AlGaN.

[0063] Figure 5(b) is a schematic cross-sectional view showing a second example in which the surface layer 12 of the substrate 11 has an uneven structure. In the second example, the surface layer 12 has protrusions (mesas) 32. This example is assumed to be a FINFET, for example, and the first group III nitride constituting the surface layer 12 of the substrate 11 is, for example, n-type GaN, and the second group III nitride constituting the group III nitride layer 21 is, for example, p-type GaN.

[0064] <Preferred Embodiments of the Invention> Preferred embodiments of the present invention are described below.

[0065] (Note 1) A substrate whose surface layer is composed of a group III nitride, A protective layer made of carbon is formed directly above the aforementioned surface layer, It has, Used as a growth substrate for growing a group III nitride directly on the surface layer after the protective layer has been removed. A substrate with a protective layer.

[0066] (Note 2) In the region within a thickness of 50 nm from the interface between the surface layer and the protective layer of the substrate, the maximum silicon concentration of the protective layer is 1 × 10⁻¹⁰ 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3 A substrate with a protective layer as described in Appendix 1, which is less than (

[0067] (Note 3) A protective layered substrate as described in Appendix 1, used as a growth substrate for growing a group III nitride on the surface layer in which the aforementioned protective layer has been completely removed.

[0068] (Note 4) A protective layer substrate as described in Appendix 1, used as a growth substrate for continuously growing a group III nitride on the surface layer in the same processing chamber as the protective layer removal process, after the protective layer has been removed.

[0069] (Note 5) The aforementioned substrate is a substrate whose entire thickness is composed of a group III nitride. The protective layered substrate according to Appendix 1, wherein a group III nitride is exposed on the surface of the substrate opposite to the protective layer.

[0070] (Note 6) The substrate is a laminated substrate in which a layer composed of a group III nitride is laminated on a component composed of a material other than a group III nitride, as described in Appendix 1, with a protective layer.

[0071] (Note 7) A substrate with a protective layer as described in Appendix 1, wherein the thickness of the protective layer is 10 nm or more and 1000 nm or less.

[0072] (Note 8) A step of preparing a substrate in which at least the surface layer is composed of a group III nitride, The process involves transporting the substrate into the processing chamber and removing the outermost layer of the surface layer, The process of forming a protective layer made of carbon directly on the surface layer from which the outermost layer has been removed, while continuously performing the removal of the outermost layer within the processing chamber (that is, without removing the substrate from the processing chamber after the removal of the outermost layer), A method for manufacturing a substrate with a protective layer having the following characteristics.

[0073] (Note 9) The aforementioned processing chamber is the processing chamber for the sputtering apparatus, In the step of removing the outermost layer of the surface, the outermost layer is removed by reverse sputtering. In the step of forming the protective layer, the protective layer is formed by sputtering. The method for manufacturing a substrate with a protective layer as described in Appendix 8.

[0074] (Note 10) The method for manufacturing a substrate with a protective layer as described in Appendix 8, wherein the step of removing the outermost layer of the surface layer involves removing the outermost layer with a thickness of 1 nm or more and 1 μm or less.

[0075] (Note 11) The method for manufacturing a substrate with a protective layer according to Appendix 8, wherein the step of forming the protective layer involves forming a protective layer having a thickness of 10 nm or more and 1000 nm or less.

[0076] (Note 12) A substrate whose surface layer is composed of a group III nitride, A protective layer made of carbon is formed directly above the aforementioned surface layer, A step of preparing a substrate with a protective layer having, The process involves transporting the substrate with the protective layer into the processing chamber and removing the protective layer, The process of growing a group III nitride directly on the surface layer from which the protective layer has been removed, in the processing chamber, continuously with the removal of the protective layer (that is, without removing the substrate from the processing chamber after the removal of the protective layer), A method for producing a group III nitride laminate having the following characteristics.

[0077] (Note 13) The method for manufacturing a nitride laminate according to Appendix 12, wherein in the step of removing the protective layer, the substrate with the protective layer is heated in an atmosphere containing a gas containing hydrogen and nitrogen (preferably ammonia gas).

[0078] (Note 14) The method for producing a nitride laminate according to Appendix 12, wherein in the step of growing a group III nitride directly above the surface layer, a group III nitride with the same composition as the group III nitride constituting the surface layer is grown.

[0079] (Note 15) The method for producing a nitride laminate according to Appendix 12, wherein in the step of growing a group III nitride directly above the surface layer, a group III nitride with a different composition from the group III nitride constituting the surface layer is grown.

[0080] (Note 16) A substrate in which at least the surface layer is composed of a group III nitride, and the surface layer has an uneven structure, A group III nitride layer formed directly above the uneven structure of the surface layer, It has, In the region within a thickness of 50 nm from the interface between the surface layer and the group III nitride layer of the substrate, the maximum silicon concentration of the group III nitride layer is 1 × 10⁻⁶. 17 / cm 3 Less than (preferably 5 × 10) 16 / cm 3A group III nitride laminate that is less than (

[0081] (Note 17) The group III nitride laminate described in Appendix 16, wherein the group III nitride layer is composed of a group III nitride containing Al. [Explanation of Symbols]

[0082] 10…Substrate with protective layer, 11…Substrate, 12…Surface portion, 13…Surface, 13a…Surface, 14…Contaminants, 15…Protective layer, 16…Near-interface region (of protective layer 15), 20…Nitride laminate, 21…Group III nitride layer, 22…Near-interface region (of Group III nitride layer 21), 31…Recess (trench), 32…Convex portion (mesa), 100…Manufacturing apparatus (for substrate with protective layer 10), 110…Processing chamber, 120…Electrode, 130…Electrode, 140…Power supply, 150…Target, 160…Sputtering gas, 200…Crystal growth apparatus, 210…Processing chamber, 220…Susceptor, 230…Heater, 240…Gas supply mechanism, 250…Processing gas

Claims

1. A substrate whose surface layer is composed of Group III nitrides, A protective layer made of carbon is formed directly above the aforementioned surface layer, It has, It is used as a growth substrate for growing a group III nitride directly on the surface layer after the protective layer has been removed. A substrate with a protective layer.

2. In the region within a thickness of 50 nm from the interface between the surface layer and the protective layer of the substrate, the maximum silicon concentration of the protective layer is 1 × 10⁻¹⁶. １７ / cm ３ A substrate with a protective layer according to claim 1, wherein the value is less than [value missing].

3. A step of preparing a substrate in which at least the surface layer is composed of a group III nitride, The process involves transporting the substrate into the processing chamber and removing the outermost layer of the surface layer, The process of forming a protective layer composed of carbon directly above the surface layer from which the outermost layer has been removed, in the same process as the removal of the outermost layer within the processing chamber, A method for manufacturing a substrate with a protective layer having the following characteristics.

4. The aforementioned processing chamber is the processing chamber for the sputtering apparatus, In the step of removing the outermost layer of the surface, the outermost layer is removed by reverse sputtering. In the step of forming the protective layer, the protective layer is formed by sputtering. A method for manufacturing a substrate with a protective layer as described in claim 3.

5. A substrate whose surface layer is composed of Group III nitrides, A protective layer made of carbon is formed directly above the aforementioned surface layer, A step of preparing a substrate with a protective layer having, The process involves transporting the substrate with the protective layer into the processing chamber and removing the protective layer, The process of growing a group III nitride directly on the surface layer after the protective layer has been removed, in the same processing chamber as the protective layer removal process, A method for producing a group III nitride laminate having the following characteristics.

6. The method for manufacturing a nitride laminate according to claim 5, wherein in the step of removing the protective layer, the substrate with the protective layer is heated in an atmosphere containing a gas containing hydrogen and nitrogen.

7. A substrate in which at least the surface layer is composed of a group III nitride, and the surface layer has an uneven structure, A group III nitride layer formed directly above the uneven structure of the surface layer, It has, In the region within a thickness of 50 nm from the interface between the surface layer and the group III nitride layer of the substrate, the maximum silicon concentration of the group III nitride layer is 1 × 10⁻¹⁶. １７ / cm ３ Less than, Group III nitride laminate.

8. The group III nitride laminate according to claim 7, wherein the group III nitride layer is composed of a group III nitride containing Al.

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