GaN substrate wafer and method for producing same

Abstract

To provide a GaN substrate wafer that has an appropriate crystallinity as a substrate for a semiconductor device and an improved productivity and a method for manufacturing the same. A GaN substrate wafer with (0001) orientation that has a first region provided on the N-polarity side and a second region provided on the Ga-polarity side, with the re-growth interface interposed, wherein: the minimum thickness of the second region is 20 μm or greater; in the first region, the concentration of at least one element selected from among Li, Na, K, F, Cl, Br and I is equal to or higher than 1×1015 atoms / cm3; and the second region satisfies one or more requirements selected from the following (a) to (c). (a) The Si concentration is equal to or higher than 5×1016 atoms / cm3. (b) The O concentration is equal to or lower than 3×1016 atoms / cm3. (c) The H concentration is equal to or lower than 1×1017 atoms / cm3.

Description

[Technical field]

[0001] The present invention relates to a substrate wafer made of GaN (gallium nitride) and a manufacturing method thereof. TECHNICAL FIELD The present invention relates to a substrate wafer made of GaN (gallium nitride) and a manufacturing method thereof. [Background technology]

[0002] Attempts have been made to use GaN crystals grown by the ammonothermal method as seeds to grow bulk GaN crystals that are not intentionally doped or that are doped with various impurities by HVPE (Hydride Vapor Phase Epitaxy) (Non-Patent Document 1). The GaN substrate is doped with 1×10 dopants to increase the conductivity or carrier concentration, or to increase the resistivity. 18 atoms / cm 3 It is often necessary to add more than this amount. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] M. Bockowski, et al., Journal of Crystal Growth 499 (2018) 1-7 Summary of the Invention [Problem to be solved by the invention]

[0004] According to the ammonothermal method, since the growth environment is close to an equilibrium state, it is possible to grow GaN crystals with high crystallinity. However, from the viewpoint of production efficiency, it is not advisable to use a GaN wafer sliced ​​from a bulk GaN crystal grown by the ammonothermal method as a substrate wafer for manufacturing semiconductor devices as is. For example, bulk GaN crystals grown by ammonothermal methods often have high impurity concentrations due to unintentional doping, and therefore are subject to large variations in dopant concentration from growth lot to growth lot. In addition, in the ammonothermal method, GaN crystal grows while consuming raw materials in a sealed container, so the ratio of the GaN raw material concentration to the dopant raw material concentration in the growth environment is not constant from the start to the end of crystal growth. Therefore, it is not easy to grow bulk GaN crystal with a uniform internal dopant concentration distribution. For these reasons, the electrical properties of GaN wafers produced by slicing bulk GaN crystals grown by the ammonothermal method vary widely among wafers, resulting in many products that are not acceptable for use in the manufacture of the intended semiconductor devices because their electrical properties do not meet the required specifications.

[0005] On the other hand, HVPE makes it possible to grow GaN crystals with lower impurity concentrations than the ammonothermal method. In addition, since each raw material can be continuously supplied from the outside to the growth vessel at a constant supply rate throughout the growth of the GaN crystal, it is possible to grow bulk GaN crystals with dopants uniformly added at a specified concentration. Therefore, if a GaN wafer sliced ​​from a bulk GaN crystal grown by the ammonothermal method is used as a seed to grow a bulk GaN crystal by HVPE, the GaN wafer sliced ​​from the seed will have good crystallinity and little variation in electrical properties, making it ideal as a substrate wafer for semiconductor devices. However, this substrate wafer is manufactured through a process of slicing bulk GaN crystals grown by HVPE, so the production efficiency is not necessarily good. GaN crystals are hard, so slicing takes a long time to prevent cracks from occurring. Furthermore, kerf loss is unavoidable during the slicing process. [Means for solving the problem]

[0006] Generally, in the manufacturing process of semiconductor devices, most of the substrate wafer used is removed by processing, and therefore the inventors realized that it is sufficient for the GaN substrate wafer to have a region formed of crystals with small variations in electrical properties only partially on the front surface side. The present invention has been made based on this idea, and embodiments thereof include the following.

[0007] [1] A (0001) oriented GaN substrate wafer, A first region is provided on the N-polarity side and a second region is provided on the Ga-polarity side across a regrowth interface, The second region has a minimum thickness of 20 μm or more; The concentration of at least one element selected from Li, Na, K, F, Cl, Br, and I in the first region is 1×10 15 atoms / cm 3 And, A GaN substrate wafer, wherein the second region satisfies one or more conditions selected from the following (a) to (c): (a) Si concentration is 5×10 16 atoms / cm 3 That's all. (b) O concentration is 3 × 10 16 atoms / cm 3 The following is the result. (c) H concentration is 1×10 17 atoms / cm 3 The following is the result. [2] The GaN substrate wafer according to [1] above, which satisfies any one of the conditions selected from the following (1) to (3): (1) Having a diameter of 50 mm or more and 55 mm or less and a thickness of 250 μm or more and 450 μm or less. (2) Having a diameter of 100 mm or more and 105 mm or less and a thickness of 350 μm or more and 750 μm or less. (3) Having a diameter of 150 mm or more and 155 mm or less and a thickness of 450 μm or more and 800 μm or less. [3] The GaN substrate wafer according to [1] or [2] above, wherein the second region has a minimum thickness of 300 μm or less. [4] A GaN substrate wafer according to any one of [1] to [3] above, wherein a main surface on the Ga-polar side is a flat surface. [5] The GaN substrate wafer according to [4] above, wherein the regrowth interface is inclined with respect to the Ga-polar primary surface. [6] The GaN substrate wafer according to [5] above, wherein a difference in thickness between one end and the other end in a direction in which the regrowth interface in the second region is inclined does not exceed 200 μm. [7] In the first region, the H concentration is 1×10 17 atoms / cm 3 The GaN substrate wafer according to any one of the above [1] to [6]. [8] In the first region, the O concentration is 1×10 17 atoms / cm 3 The GaN substrate wafer according to any one of the above [1] to [7]. [9] In the first region, the F concentration is 1×10 15 atoms / cm 3 The GaN substrate wafer according to any one of the above [1] to [8].

[10] In at least a portion of the second region, the total concentration of compensating impurities is 1×10 17 atoms / cm 3 The GaN substrate wafer according to any one of the above [1] to [9].

[11] The second region has a main doped region including at least a Ga-polar main surface, and a total concentration of compensating impurities in the main doped region is 1×10 17 atoms / cm 3 The GaN substrate wafer according to

[10] above.

[12] The total concentration of compensating impurities in the primary doped region is 1×10 18 atoms / cm 3 The GaN substrate wafer according to

[11] above.

[13] The GaN substrate wafer according to

[11] or

[12] above, wherein in the primarily doped region, a total concentration of compensating impurities is at least twice as high as a total concentration of donor impurities.

[14] The GaN substrate wafer according to any one of

[11] to

[13] above, wherein the primarily doped region contains one or more elements selected from carbon and transition metal elements.

[15] The GaN substrate wafer according to any one of

[11] to

[14] above, wherein the impurity contained in the primary doped region at the highest concentration is Fe, Mn or C.

[16] The GaN substrate wafer according to any one of

[11] to

[15] above, wherein the primarily doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 20 μm or more.

[17] The GaN substrate wafer according to any one of

[11] to

[16] , wherein in the primarily doped region, the variation in the total concentration of compensating impurities along the c-axis direction is within a range of ±25% from the median value.

[18] The GaN substrate wafer according to any one of

[11] to

[17] , wherein the primarily doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 50% or more of a minimum thickness of the second region.

[19] The total concentration of compensating impurities in the second region is 5×10 19 atoms / cm 3 The GaN substrate wafer according to any one of the above

[10] to

[18] , which is as follows:

[20] In at least a portion of the second region, the total concentration of donor impurities is 1×10 18 atoms / cm 3 The GaN substrate wafer according to any one of the above [1] to [9].

[21] The second region has a primary doped region including at least a Ga-polar primary surface, and a total concentration of donor impurities in the primary doped region is 1×10 18 atoms / cm 3 The GaN substrate wafer according to

[20] above.

[22] The total concentration of donor impurities in the primary doped region is 2×10 18 atoms / cm 3 The GaN substrate wafer according to

[21] above.

[23] The GaN substrate wafer according to

[21] or

[22] above, wherein the impurity contained in the primarily doped region at the highest concentration is Si or Ge.

[24] The GaN substrate wafer according to

[21] or

[22] , wherein in the primarily doped region, a total concentration of donor impurities other than Si is 10% or less of a Si concentration.

[25] In the main doped region, the concentrations of donor impurity elements other than Si and O are independently 1×10 15 atoms / cm 3 The GaN substrate wafer according to

[24] , wherein the GaN substrate wafer has a thickness of less than 100 nm.

[26] In the main doped region, the Ge concentration is 1×10 18 atoms / cm 3 or more, and the Si concentration is 4×10 17 atoms / cm 3 The GaN substrate wafer according to

[23] above.

[27] The GaN substrate wafer according to any one of

[21] to

[26] above, wherein the primarily doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 20 μm or more.

[28] The GaN substrate wafer according to

[27] , wherein the variation in total concentration of donor impurities along the c-axis direction in the primarily doped region is within a range of ±25% from the median value.

[29] The GaN substrate wafer according to any one of

[21] to

[28] , wherein the primarily doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 50% or more of a minimum thickness of the second region.

[30] The total concentration of donor impurities in the second region is 5×10 19 atoms / cm 3 The GaN substrate wafer according to any one of the above

[20] to

[29] , which is as follows:

[31] An epitaxial wafer comprising the GaN substrate wafer according to any one of the above [1] to

[30] , and one or more nitride semiconductor layers epitaxially grown on a Ga-polar main surface of the GaN substrate wafer.

[32] A method for producing an epitaxial wafer, comprising the steps of: preparing a GaN substrate wafer according to any one of the above [1] to

[30] ; and epitaxially growing a nitride semiconductor layer on a Ga-polar primary surface of the GaN substrate wafer.

[33] A method for manufacturing a nitride semiconductor device, comprising the steps of: preparing a GaN substrate wafer according to any one of the above [1] to

[30] ; growing a nitride semiconductor layer on a Ga-polar main surface of the GaN substrate wafer to obtain an epitaxial wafer; and removing at least a portion of the first region of the GaN substrate wafer.

[34] A method for producing a GaN substrate wafer having an N-polarity region and a Ga-polarity region sandwiching a regrowth interface, comprising the steps of: A first step of preparing a c-plane GaN wafer comprising an ammonothermally grown GaN crystal; and a second step of growing a (0001) oriented GaN film with a thickness of 20 μm or more on the c-plane GaN wafer by HVPE to obtain a laminated structure wafer.

[35] The method for producing a GaN substrate wafer according to

[34] , wherein the GaN substrate wafer satisfies any one of the conditions selected from the following (1) to (3): (1) Having a diameter of 50 mm or more and 55 mm or less and a thickness of 250 μm or more and 450 μm or less. (2) Having a diameter of 100 mm or more and 105 mm or less and a thickness of 350 μm or more and 750 μm or less. (3) Having a diameter of 150 mm or more and 155 mm or less and a thickness of 450 μm or more and 800 μm or less.

[36] In the c-plane GaN wafer, the concentration of at least one element selected from Li, Na, K, F, Cl, Br, and I is 1×10 15 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to

[34] or

[35] .

[37] c-plane GaN wafers are treated with H at 1×10 17 atoms / cm 3 The method for producing a GaN substrate wafer according to any one of

[34] to

[36] , wherein the element is contained in a concentration of at least one of these elements.

[38] In the c-plane GaN wafer, the O concentration is 1×10 17 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to any one of the above

[34] to

[37] .

[39] In the c-plane GaN wafer, the F concentration is 1×10 15 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to any one of the above

[34] to

[38] .

[40] In at least a portion of the GaN film, the total concentration of compensating impurities is 1×10 17 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to any one of the above

[34] to

[39] .

[41] The GaN film has a region length in the c-axis direction of 1 μm or more, and a total concentration of compensation impurities in the region is 1×10 17 atoms / cm 3 The method for producing a GaN substrate wafer having a specifically doped region according to

[40] above.

[42] The total concentration of compensating impurities in the specific doped region is 1×10 18 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to the above

[41] .

[43] The method for producing a GaN substrate wafer according to

[41] or

[42] above, wherein in the specific doped region, a total concentration of compensating impurities is at least twice as high as a total concentration of donor impurities.

[44] The method for producing a GaN substrate wafer according to any one of

[41] to

[43] above, wherein the variation in the total concentration of compensation impurities in the specific doped region along the c-axis direction is within a range of ±25% from the median value.

[45] The method for producing a GaN substrate wafer according to any one of

[41] to

[44] above, wherein the region length is 50% or more of the thickness of the GaN film.

[46] The method for producing a GaN substrate wafer according to any one of

[41] to

[45] above, wherein the length from a lower end of the specifically doped region to an interface between the GaN film and the second c-plane GaN wafer is 1 μm or more.

[47] The method for producing a GaN substrate wafer according to any one of

[41] to

[46] above, wherein the specifically doped region contains one or more elements selected from carbon and transition metal elements.

[48] ​​The method for producing a GaN substrate wafer according to

[47] above, wherein the impurity contained in the specific doped region at the highest concentration is Fe, Mn or C.

[49] The total concentration of compensating impurities in the GaN film is 5×10 19 atoms / cm 3 A method for producing a GaN substrate wafer according to any one of the above

[40] to

[48] , which is as follows:

[50] In at least a portion of the GaN film, a total concentration of donor impurities is 1×10 18 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to any one of the above

[34] to

[49] .

[51] In the GaN film, in a specific doped region having a length of 20 μm or more in the c-axis direction, the total concentration of donor impurities is 1×10 18 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to the above

[50] .

[52] The total concentration of donor impurities in the specific doped region is 2×10 18 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to the above

[51] .

[53] A method for producing a GaN substrate wafer according to

[51] or

[52] , wherein the variation in total concentration of donor impurities in the specific doped region along the c-axis direction is within a range of ±25% from the median value.

[54] The method for producing a GaN substrate wafer according to any one of

[51] to

[53] above, wherein the length of the specifically doped region in the c-axis direction is 50% or more of the thickness of the GaN film.

[55] The method for producing a GaN substrate wafer according to any one of

[51] to

[54] above, wherein the length from a lower end of the specifically doped region to an interface between the GaN film and the second c-plane GaN wafer is 1 μm or more.

[56] The method for producing a GaN substrate wafer according to any one of

[51] to

[55] above, wherein the dopant contained at the highest concentration in the specific doped region is Si or Ge.

[57] The method for producing a GaN substrate wafer according to any one of

[51] to

[55] above, wherein in the specifically doped region, a total concentration of donor impurities excluding Si is 10% or less of a Si concentration.

[58] In the specific doped region, the concentration of donor impurity elements other than Si and O is independently 1×10 15 atoms / cm 3 The method for producing a GaN substrate wafer according to

[57] above,

[59] In the specific doped region, the Ge concentration is 1×10 18 atoms / cm 3 or more, and the Si concentration is 4×10 17 atoms / cm 3 The above is a method for producing a GaN substrate wafer according to the above

[56] .

[60] The total concentration of donor impurities in the GaN film is 5×10 19 atoms / cm 3 A method for producing a GaN substrate wafer according to any one of the above

[50] to

[59] , which is as follows:

[61] The method for producing a GaN substrate wafer according to any one of

[34] to

[60] above, further comprising, after the second step, a thinning step of thinning the laminated structure.

[62] The method for producing a GaN substrate wafer according to

[61] above, wherein a difference in thickness of the GaN film before and after the thinning step is 50 μm or more.

[63] The method for producing a GaN substrate wafer according to

[61] or

[62] above, wherein a difference in thickness of the GaN film before and after the thinning step is 200 μm or less.

[64] The method for producing a GaN substrate wafer according to any one of

[61] to

[63] above, wherein an offcut orientation of the GaN substrate wafer is different from an offcut orientation of the c-plane GaN wafer. Effect of the Invention

[0008] A GaN substrate wafer having crystallinity suitable for use as a substrate for semiconductor devices and improved productivity, and a method for manufacturing the same, are provided. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view showing a GaN substrate wafer according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a GaN substrate wafer according to the embodiment. [Diagram 3] FIG. 3 is a cross-sectional view showing a GaN substrate wafer according to an embodiment. [Figure 4] 4A to 4C are cross-sectional views illustrating steps of a manufacturing process for a nitride semiconductor device using a GaN substrate wafer according to the embodiment. [Diagram 5] 5A to 5C are cross-sectional views illustrating the steps of a GaN substrate wafer manufacturing method according to an embodiment. [Figure 6] FIG. 6 is a schematic diagram showing the basic configuration of a crystal growth apparatus used in the ammonothermal method. [Figure 7] FIG. 7 is a schematic diagram showing the basic configuration of an HVPE apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The following is a detailed description of the embodiments of the present invention. The following description of the components is an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist of the present invention. In this specification, when expressed as "X to Y" (X and Y are any numbers), unless otherwise specified, it includes the meaning of "X or more and Y or less", as well as "preferably greater than X" and "preferably smaller than Y". In addition, in this specification, the term "independently" used when describing two or more objects together means that the two or more objects may be the same or different.

[0011] 1. GaN substrate wafer One embodiment of the present invention relates to a GaN substrate wafer. The GaN substrate wafer according to the embodiment is a (0001) oriented GaN substrate wafer, and has a first region provided on the N-polarity side and a second region provided on the Ga-polarity side across a regrowth interface. The second region has a minimum thickness of 20 μm or more. The first region contains at least one of Li (lithium), Na (sodium), K (potassium), F (fluorine), Cl (chlorine), Br (bromine) and I (iodine) at a concentration of 10 15 atoms / cm 3 The impurity concentration in the second region satisfies one or more of the following conditions (a) to (c): (a) Si (silicon) concentration is 5×10 16 atoms / cm 3 End (b) O (oxygen) concentration is 3×10 16 atoms / cm 3 below (c) H (hydrogen) concentration is 1×10 17 atoms / cm 3 below A (0001) oriented GaN wafer is a GaN wafer having a main surface (large area surface) parallel or approximately parallel to the (0001) crystal plane, that is, the c-plane, and is also called a c-plane GaN wafer. In this specification, the term "impurities" refers to components other than Ga and N contained in the GaN substrate.

[0012] An example of a GaN substrate wafer according to an embodiment is shown in Figures 1 and 2. Figure 1 is a perspective view, and Figure 2 is a cross-sectional view. 1 and 2 is a free-standing substrate wafer made only of GaN crystals, one of its two main surfaces being an N-polar surface 101 and the other being a Ga-polar surface 102. The N-polar surface 101 and the Ga-polar surface 102 are parallel to each other. The GaN substrate wafer 100 has a (0001) orientation, and the inclination of the Ga polar surface 102 with respect to the (0001) crystal plane is 10 degrees or less, preferably 5 degrees or less, and more preferably 2.5 degrees or less. The inclination can be 0.2 degrees or more and less than 1 degree, 1 degree or more and 2.5 degrees or less, etc.

[0013] The diameter of the GaN substrate wafer 100 is usually 45 mm or more, and may be 95 mm or more, or 145 mm or more, and is typically 50 to 55 mm (about 2 inches), 100 to 105 mm (about 4 inches), 150 to 155 mm (about 6 inches), etc. The preferred range of thickness of the GaN substrate wafer 100 varies depending on the diameter. When the diameter is about 2 inches, the thickness is preferably 250 μm or more, more preferably 300 μm or more, and preferably 450 μm or less, more preferably 400 μm or less. When the diameter is about 4 inches, the thickness is preferably 350 μm or more, more preferably 400 μm or more, and preferably 750 μm or less, more preferably 650 μm or less. When the diameter is about 6 inches, the thickness is preferably 450 μm or more, more preferably 550 μm or more, and preferably 800 μm or less, more preferably 700 μm or less.

[0014] As described above, the GaN substrate wafer 100 is usually disk-shaped, but in modified examples, the shape of the main surface may be a square, rectangle, hexagon, octagon, ellipse, or an irregular shape. In such modified examples, the above-mentioned diameter can be read as "the shortest length of a straight line passing through the center of gravity on the main surface."

[0015] The N-polar surface 101 of the GaN substrate wafer 100 is the "backside" surface and may be mirror-finished or may be roughened or matte-finished. The Ga polar surface 102 of the GaN substrate wafer 100 is the “front surface”, and when a semiconductor device is manufactured using the GaN substrate wafer 100, a semiconductor layer is typically epitaxially grown on the Ga polar surface 102. The Ga polar surface 102 may be an as-grown surface, but is usually planarized by processing. The processing performed to planarize the Ga polar surface 102 and make it a flat surface may include one or more selected from polishing and CMP (Chemical Mechanical Polishing). In addition to these processing, etching may be performed for the purpose of removing a damaged layer. The roughness of the flat surface is not limited, but for example, the root mean square (RMS) roughness of the Ga polar surface 102 measured by an atomic force microscope (AFM) is preferably less than 5 nm, more preferably less than 2 nm, and even more preferably less than 1 nm in a measurement range of 2 μm×2 μm, and may be less than 0.5 nm. The Ga polar surface 102 may be a surface formed by cutting, but is preferably a surface that has been subjected to only planarization such as polishing, CMP, or etching without cutting.

[0016] GaN substrate wafer 100 has a regrowth interface 103 between its two main surfaces, with a first region 110 on the N-polarity side and a second region 120 on the Ga-polarity side across the regrowth interface 103. The "regrowth interface" refers to a boundary surface that occurs when GaN crystals grow on any substrate, and its existence can be confirmed, for example, by observing a cross section of the GaN substrate wafer with a scanning electron microscope, cathodoluminescence observation, or fluorescence microscope. The regrowth interface 103 is preferably parallel to the Ga polar surface 102. When the regrowth interface 103 is inclined from the Ga polar surface 102, the thickness of the second region 120 is usually minimum at one end in the inclination direction and maximum at the other end. It is preferable that the difference between the thickness of the second region 120 at the one end and the thickness of the second region 120 at the other end does not exceed 200 μm. In the process of manufacturing a nitride semiconductor device using the GaN substrate wafer 100, it is assumed that the first region 110 will be removed eventually. In other words, it is assumed that a nitride semiconductor device chip manufactured using the GaN substrate wafer 100 will not include a portion derived from the first region 110. In such a usage mode, there are no particular restrictions on the electrical properties of the GaN crystal that constitutes the first region 110.

[0017] Since the first region 110 is usually made of ammonothermally grown GaN crystal, at least one element selected from Li (lithium), Na (sodium), K (potassium), F (fluorine), Cl (chlorine), Br (bromine) and I (iodine) is added at a concentration of 1×10 15 atoms / cm 3 The first region usually contains H (hydrogen) and O (oxygen) at a concentration of 1×10 17 atoms / cm 3 Contains at a concentration of or above. The first region 110 contains alkali metal elements such as Li, Na, and K when compounds containing alkali metals, such as LiNH, NaNH, and KNH, are used as mineralizers to ammonothermally grow the GaN crystals that make up the first region. On the other hand, the first region 110 contains halogen elements such as F, Cl, Br and I when compounds containing halogen elements, such as NH4F, NH4Cl, NH4Br and NH4I, are used as mineralizers to ammonothermally grow the GaN crystal that constitutes the region.

[0018] The second region 120 is grown by HVPE on the first region 110. The reason why a regrowth interface 103 exists between the first region 110 and the second region 120 is that the process of growing the first region 110 and the process of growing the second region 120 are not continuous. In this specification, HVPE stands for hydride vapor phase epitaxy. The second region 120 is made of a GaN crystal grown by HVPE, and therefore satisfies one or more of the following conditions (a) to (c) regarding the impurity concentration. (a) Si concentration is 5×10 16 atoms / cm 3 That's all. (b) O concentration is 3 × 10 16 atoms / cm 3 The following is the result. (c) H concentration is 1×10 17atoms / cm 3 The following is the result. Since the first region 110, which acts as a seed for the growth of the second region 120, is made of ammonothermally grown GaN crystal with good crystallinity, the GaN crystal constituting the second region 120 also has good crystallinity. The minimum thickness of the second region 120 is 20 μm or more. The reason for this is that, in the process of manufacturing a nitride semiconductor device chip using the GaN substrate wafer 100, after the first region 110 is removed from the substrate wafer 100, the remaining second region 120 can play a role as a substrate that supports the structure of the semiconductor device chip. The minimum thickness means the thickness at the point where the thickness is smallest. The minimum thickness of second region 120 may be 50 μm or more, 75 μm or more, even 100 μm or more, or even 150 μm or more. The minimum thickness of the second region 120 is preferably 350 μm or less, more preferably 300 μm or less, and may be 250 μm or less, such as 200 μm or less. When the Ga-polar surface 102 and the regrowth interface 103 are parallel and the thickness of the second region 120 is uniform, the thickness of the second region is considered to be at its minimum thickness everywhere.

[0019] Intentional doping of second region 110 is not required. When using conventional HVPE techniques, the total concentration of donor impurities is 1×10 18 atoms / cm 3 It is easy to grow GaN crystals with less than 1000 times the doping concentration. Note that "intentional doping" means that the target element is added as a raw material during the GaN crystal growth process. The total concentration of donor impurities is the sum of the concentrations of all types of donor impurities. The elements that act as donors in GaN crystals are group 14 elements such as Si, Ge (germanium), and Sn (tin), and group 16 elements such as O, S (sulfur), Se (selenium), and Te (tellurium). Of these, Si and O are present in GaN crystals grown by HVPE at concentrations of 1×10 16atoms / cm 3 In contrast, donor impurities other than Si and O, such as group 14 elements other than Si and group 16 elements other than O, can be contained at concentrations of 1×10 or more in GaN crystals grown by HVPE independently unless intentionally added. 15 atoms / cm 3 It is not contained in concentrations greater than this.

[0020] In one example, the second region 110 may be at least partially doped with a compensating impurity. Compensating impurities are impurities that act to compensate for n-type carriers in GaN crystals, and well-known examples are C (carbon) and transition metal elements. Representative transition metal elements are Fe (iron) and Mn (manganese), with other known elements including Co (cobalt), Cr (chromium), V (vanadium), Ni (nickel), and Cu (copper). In GaN crystals grown by HVPE, the total concentration of compensating impurities is about 1×10 unless intentionally doped. 17 atoms / cm 3 The total concentration of compensating impurities is usually less than 1×10 17 atoms / cm 3 It can be more than that. In another example, the second region 110 may be at least partially doped with a donor impurity.

[0021] In a preferred embodiment, a region of the second region 120 that includes at least the Ga polarity principal surface, specifically a region within a specific length L from the Ga polarity surface 102 of the GaN substrate wafer 100, is defined as the primary doped region 120a. When the second region 120 is doped with compensating impurities, the total concentration of compensating impurities in the primary doped region 120a is 1×10 17 atoms / cm 3 More than that, and even 2×10 17 atoms / cm 3 More than that, and 5x10 17 atoms / cm 3or more, preferably 1×10 18 atoms / cm 3 More preferably, 2×10 18 atoms / cm 3 That's 5 x 10. 18 atoms / cm 3 The above may be possible. When the second region 120 is doped with compensating impurities, in the primary doped region 120, the total concentration of the compensating impurities is preferably at least two times, more preferably at least five times, even more preferably at least ten times, and may be at least 50 times, the total concentration of the donor impurities. When the second region 120 is doped with compensating impurities, the GaN crystal forming the primary doped region 120 is semi-insulating, i.e., its room temperature resistivity is greater than 1×10 5 The resistivity may be Ω·cm or more. The compensating impurity contained in the primary doped region 120 at the highest concentration is preferably Fe, Mn or C.

[0022] When the second region 120 is doped with donor impurities, the total concentration of the donor impurities in at least a portion of the second region, for example, the main doped region 120a, is about 1×10 18 cm -3 More than that, and even 2×10 18 cm -3 It is preferable that the value is 5×10 or more. 18 cm -3 It may be more than that. When the second region 120 is doped with a donor impurity, the donor impurity that the primary doped region 120a contains at the highest concentration is preferably Si or Ge, mainly for the following two reasons. First, Si and Ge are donor impurities that exhibit high activation ratios along with O. The activation ratio is the ratio of the carrier concentration to the donor impurity concentration in GaN doped with a donor impurity. Second, O to 1 × 10 18 atoms / cm 3To obtain GaN with these concentrations, facet growth is required, whereas GaN with the same Si or Ge concentrations can be obtained by c-plane growth.

[0023] Facet growth is a technique in which (0001)-oriented GaN films are grown with a pitted growth surface, in contrast to c-plane growth, in which such films are grown with a flat growth surface. Since threading dislocations have the tendency to gather at the bottom of pits, when the primary doped region 120a is formed by facet growth, the uniformity of the threading dislocation density in the Ga polarity surface 102 decreases. However, semiconductor device manufacturers prefer GaN substrate wafers with a high uniformity of threading dislocation density. Forming the primary doped region 120a by facet growth is also disadvantageous in terms of productivity of the substrate wafer 100, because a facet-grown GaN film requires more processing time to flatten the surface than a c-plane-grown GaN film.

[0024] In one example, by setting the total concentration of donor impurities excluding Si in the main doped region 120a to 10% or less of the Si concentration, or even 5% or less, or even 1% or less, it becomes possible to control the carrier concentration in this region by adjusting the Si concentration. In another example, the primary doped region 120a is doped with Ge at 10 18 atoms / cm 3 The Si concentration in the region may be preferably 4×10 17 atoms / cm 3 That's all.

[0025] The specific length L is usually 1 μm or more, and can be arbitrarily determined within a range not exceeding the minimum thickness of the second region 120 . In a preferred embodiment, in the process of manufacturing a nitride semiconductor device chip using the GaN substrate wafer 100, even when the second region 120 is partially removed in addition to the first region 110 from the GaN substrate wafer 100 to expose the primarily doped region 120a, the specific length L is determined so that the GaN substrate consisting only of the remaining primarily doped region 120a can support the structure of the semiconductor device chip. In this preferred embodiment, the specific length L is at least 1 μm, preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 25 μm or more, and may be 50 μm or more, 75 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, etc. In addition, the length from the lower end (the end on the N-polar surface 101 side) of the specific length L to the regrowth interface is preferably 1 μm or more, more preferably 5 μm or more, or 10 μm or more, and the length from the lower end to the interface is preferably 50 μm or less, more preferably 30 μm or less. In this preferred embodiment, the specific length L is preferably 50% or more of the minimum thickness of the second region 120, more preferably 75% or more, and even more preferably 90% or more. In this preferred embodiment, it is desirable for the variation in electrical properties within the primary doped region 120a to be small along the c-axis direction, which is the thickness direction of the GaN substrate wafer 100. Therefore, when compensation impurities are added to the region 120a, the variation in the total concentration of compensation impurities along the c-axis direction within the region 120a is preferably within ±25% from the median, more preferably within ±20%, even more preferably within ±15%, and even more preferably within ±10%. Furthermore, when donor impurities are added to the region 120a, the variation in the total concentration of donor impurities along the c-axis direction in the region 120a is preferably within ±25% from the median, more preferably within ±20%, even more preferably within ±15%, and even more preferably within ±10%.

[0026] When the second region 120 is doped with compensating impurities, the total concentration of compensating impurities in the second region 120, including the primary doped region 120a, is preferably less than 5×10 to avoid significant degradation of crystal quality due to overdoping. 19 atoms / cm 3 The following is further 2×10 19 atoms / cm 3 Below, and further 1×10 19 atoms / cm 3 It can be as follows. When the second region 120 is doped with a donor impurity, the total concentration of the donor impurity in the second region 120, including the main doped region 120a, is preferably less than 5×10 to avoid a significant deterioration in crystal quality due to overdoping. 19 atoms / cm 3 The following is further 2×10 19 atoms / cm 3 Below, and further 1×10 19 atoms / cm 3 It can be as follows. At the bottom of the second region 120, i.e., the portion adjacent to the first region 110, the concentration of the same type of impurity as the impurity intentionally added to the main doped region 120a may increase continuously or stepwise with increasing distance from the first region 110.

[0027] Since the second region 120 is usually grown by HVPE, its impurity concentration satisfies one or more conditions selected from the following (a') to (c'). (a') Si concentration is 5×10 16 atoms / cm 3 End (b') O concentration is 3×10 16 atoms / cm 3 below (c') H concentration is 1×10 17 atoms / cm 3 below

[0028] 3, the regrowth interface 103 may be rough. For example, when the surface of the first region 110 is roughened by etching before the second region 120 is grown, the regrowth interface 103 may be rough. When the direction perpendicular to the regrowth interface 103 from the first region 110 toward the second region 120 is defined as the height direction and the height difference between the highest point and the lowest point at the regrowth interface is defined as the roughness r of the regrowth interface, the roughness r may be, for example, 0.3 μm or more and 12 μm or less. 1 to 3, the edges of the GaN substrate wafer 100 may be chamfered. In addition, the GaN substrate wafer 100 may be provided with various markings as necessary, such as an orientation flat or a notch that indicates the crystal orientation, and an index flat that makes it easy to distinguish between the front and back surfaces.

[0029] When the second region 120 is doped with a compensating impurity, the GaN substrate wafer 100 may be preferably used for the manufacture of nitride semiconductor devices with lateral device structures such as GaN-HEMTs. A nitride semiconductor device is a semiconductor device in which the main part of the device structure is formed from a nitride semiconductor. Nitride semiconductors are also called nitride III-V group compound semiconductors, group III nitride compound semiconductors, GaN-based semiconductors, etc., and include GaN as well as compounds in which part or all of the gallium in GaN is replaced with other group 13 elements of the periodic table (B, Al, In, etc.). The lateral device structure can also be adopted in electronic devices other than high electron mobility transistors (HEMTs), such as bipolar transistors, and in light-emitting devices, such as light-emitting diodes (LEDs) and laser diodes (LDs).

[0030] When the second region 120 is doped with a donor impurity, the GaN substrate wafer 100 may be favorably used for the manufacture of various nitride semiconductor devices having vertical device structures. The vertical device structure can be adopted in light emitting devices such as laser diodes (LDs) and light emitting diodes (LEDs), as well as in electronic devices such as rectifiers, bipolar transistors, field effect transistors, and HEMTs.

[0031] When a nitride semiconductor device is manufactured using the GaN substrate wafer 100, the GaN substrate wafer 100 is prepared as shown in FIG. 4(a), and then an epitaxial film 200 including at least a first nitride semiconductor layer 210 and a second nitride semiconductor layer 220 is grown on the Ga polar face 102 by metal-organic vapor phase epitaxy (MOVPE) as shown in FIG. 4(b), thereby forming an epitaxial wafer. For example, when the nitride semiconductor device is a HEMT, the first nitride semiconductor layer 210 and the second nitride semiconductor layer 220 can be an undoped GaN channel layer and an undoped AlGaN carrier supply layer, respectively. For example, when the nitride semiconductor device is a pn diode, the first nitride semiconductor layer 210 and the second nitride semiconductor layer 220 can be an n-type GaN layer and a p-type GaN layer, respectively.

[0032] After semiconductor processes that may include etching, ion implantation, electrode formation, protective film formation, and the like are performed, the epitaxial wafer is divided into nitride semiconductor device chips. However, in order to thin the epitaxial wafer before division, at least a portion of the first region 110 of the GaN substrate wafer 100 is usually removed by a method such as grinding or etching, as shown in FIG. 4(c). This thinning process can be performed so that a ring-shaped thick portion remains on the outer periphery of the epitaxial wafer, that is, the first region 110 of the GaN substrate wafer 100 can be removed only in the portion excluding the outer periphery of the epitaxial wafer. In FIG. 4(c), the second region 120 has also been partially removed from the GaN substrate wafer 100 such that the primarily doped region 120a is exposed on the N-polar face side of the thinned epitaxial wafer. When the second region 120 is doped with a donor impurity, an electrode may be formed on the surface of the second region 120 exposed by removing the first region 110, and then the epitaxial wafer may be divided. It should be noted that semiconductor devices using the GaN substrate wafer 100 are not limited to nitride semiconductor devices.

[0033] 2. GaN substrate wafer manufacturing method Next, a method for producing a GaN substrate wafer according to another embodiment of the present invention will be described. The method for producing the GaN substrate wafer described below is a preferred embodiment for producing the GaN substrate wafer described above. A preferred embodiment of the GaN substrate wafer obtained by the method for producing the GaN substrate wafer described below is the GaN substrate wafer described above. The above-described GaN substrate wafer 100 according to the embodiment can be preferably manufactured by the method described below. This method is applied to the manufacture of a GaN substrate wafer having an N-polarity region and a Ga-polarity region sandwiching a regrowth interface, and includes the following steps. (i) The first step is to prepare a c-plane GaN wafer consisting of ammonothermally grown GaN crystals. (ii) In the second step, a (0001)-oriented GaN film with a thickness of 20 μm or more is grown by HVPE on the c-plane GaN wafer prepared in the first step to obtain a stacked structure. In this specification, "on the wafer" is synonymous with "on the surface of the wafer."

[0034] The above first and second steps are described in detail below. The structures and characteristics of the first and second regions described above can be applied to the c-plane GaN wafer obtained in the first step and the GaN film obtained in the second step, respectively. In the first step, a c-plane GaN wafer 1, the cross-sectional view of which is shown in FIG. 5(a), is prepared. The c-plane GaN wafer 1 consists of ammonothermally grown GaN crystal. FIG. 6 is a schematic diagram showing a typical configuration of a crystal growth apparatus used for ammonothermal growth of GaN crystals constituting the c-plane GaN wafer 1. Referring to Fig. 6, the crystal growing apparatus includes an autoclave, in which a dissolution zone and a growth zone are provided, which are separated from each other by a baffle. When growing GaN crystals, a feedstock is placed in the dissolution zone together with a mineralizer (not shown), and a seed is suspended by a wire in the growth zone. The feedstock is preferably polycrystalline GaN.

[0035] A gas line connected to a vacuum pump, an ammonia cylinder, and a nitrogen cylinder is connected to the autoclave via a valve. When NH3 (ammonia) is added to the autoclave, the amount of NH3 supplied from the ammonia cylinder can be checked with a mass flow meter. The amount of NH3 placed in the autoclave determines the pressure inside the autoclave when it is heated to a given temperature. After the seeds, feedstock, mineralizer, and NH3 are added, the autoclave is sealed and heated from the outside by a heater (not shown) to achieve a supercritical state inside. The upper and lower parts of the autoclave are heated separately by multiple heaters to provide a temperature gradient between the dissolution zone and the growth zone. In the dissolution zone the feedstock dissolves and in the growth zone GaN recrystallizes on the seeds.

[0036] The mineralizer may be either a basic mineralizer or an acidic mineralizer. Preferred basic mineralizers are compounds containing an alkali metal element, representative examples of which include alkali metal amides such as LiNH2, NaNH2, and KNH2. Preferred acidic mineralizers are compounds containing halogen elements, representative examples of which include ammonium halides such as NH4F, NH4Cl, NH4Br, and NH4I, and gallium halides such as GaF3, GaCl3, GaBr3, and GaI3. The most preferred mineralizers are fluorine-containing compounds such as NHF and GaF3, particularly NHF, because they allow GaN crystals with low impurity concentrations to grow at a high rate. NHF may be prepared in advance and charged into the autoclave, or it may be synthesized by reacting NH3 with HF (hydrogen fluoride) in the autoclave or in a reaction vessel connected to the autoclave. In one example, NH4F or GaF3 may be used in combination with NH4Cl, NH4Br or NH4I.

[0037] When a compound containing an alkali metal element is used as a mineralizer, the GaN recrystallized on the seed contains the alkali metal element derived from the mineralizer. For example, when KNH2 is used as the mineralizer, the GaN recrystallized on the seed contains K. When a compound containing a halogen element is used as a mineralizer, the GaN recrystallized on the seed contains a halogen element derived from the mineralizer. For example, when NHF is used as the mineralizer, the GaN recrystallized on the seed contains F. Whatever mineralizer is used, GaN crystals grown on seeds typically have 1×10 H (hydrogen) and 1×10 O (oxygen) atoms. 17 atoms / cm 3 Contains at a concentration of or above.

[0038] Referring again to FIG. 5(a), the c-plane GaN wafer 1 has, as its major surfaces, an N-polar plane and a Ga-polar plane which are parallel to each other. When manufacturing the above-described GaN substrate wafer 100 according to the embodiment, it is preferable, but not essential, that the inclination angle (offcut angle) and inclination direction (offcut direction) of the Ga polarity plane of the c-plane GaN wafer 1 with respect to the (0001) crystal plane be the same as the offcut angle and offcut direction that the GaN substrate wafer 100 should have. The offcut orientation that the GaN substrate wafer 100 should have varies depending on the requirements of the manufacturer of the semiconductor device that uses the GaN substrate wafer 100, but preparing c-plane GaN wafers 1 having various offcut orientations may lead to a decrease in the production efficiency of the GaN substrate wafer 100. It should also be noted that the optimal conditions for growing the GaN film 2 on the c-plane GaN wafer 1 by HVPE in the next second step may change depending on the offcut orientation of the c-plane GaN wafer 1.

[0039] The initial thickness t of the c-plane GaN wafer 1 1i may be thinner than the usual thickness of a GaN substrate wafer used in the manufacture of nitride semiconductor devices, because, unlike a GaN substrate wafer that must withstand a semiconductor process consisting of multiple steps, the c-plane GaN wafer 1 only needs to be undamaged before the next second step. For example, when the diameter of the c-plane GaN wafer 1 is about 2 inches, its initial thickness t 1i is preferably 300 μm or less, and may be 250 μm or less, or even 200 μm or less.

[0040] In the second step, as shown in Fig. 5(b), a (0001)-oriented GaN film 2 having a thickness of 20 μm or more is grown by HVPE on the Ga polarity plane of the c-plane GaN wafer 1 to obtain a stacked structure. At this time, a regrowth interface is formed between the c-plane GaN wafer 1 and the GaN film 2. Typically, the Ga polar surface of the c-plane GaN wafer 1 is flattened by appropriate techniques such as grinding, polishing, CMP, etc. before the GaN film 2 is grown (flattening process). In one example, the flattened Ga polar surface may be roughened by etching (roughening process) before the GaN film 2 is grown. When HCl (hydrogen chloride) is used as an etching gas, the Ga polar surface of GaN can be roughened without using an etching mask. If an HCl supply line for etching is provided in the HVPE apparatus used to grow the GaN film 2, the Ga polar surface of the c-plane GaN wafer 1 can be roughened in the reactor of the HVPE apparatus immediately before the growth of the GaN film 2.

[0041] The GaN film 2 may be grown without any intentional doping, or may be at least partially doped with compensating or donor impurities. In a preferred example, a specifically doped region 2a may be provided in the GaN film 2. The specifically doped region 2a has a region length in the c-axis direction of, for example, 1 μm or more, and can be 10 μm or more, 20 μm or more, 25 μm or more, 50 μm or more, 75 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, etc. The upper end (the end on the <0001> side) of the specifically doped region 2 a is preferably within 10 μm, more preferably within 5 μm, from the upper surface of the GaN film 2 . The length from the lower end (the end on the [000-1] side) of the specifically doped region 2a to the interface between the c-plane GaN wafer 1 and the GaN film 2 is preferably 1 μm or more, more preferably 5 μm or more, or 10 μm or more, and the length from the lower end to the interface is preferably 50 μm or less, more preferably 30 μm or less. Furthermore, the length of the specifically doped region 2a in the c-axis direction is preferably 50% or more of the thickness of the GaN film 2, more preferably 75% or more, and even more preferably 90% or more.

[0042] When the GaN film 2 is doped with compensating impurities, the total concentration of the compensating impurities in the specific doped region 2a is at least 1×10 17 atoms / cm 3 , which is 2 × 10 17 atoms / cm 3 That's it, 5 x 10 17 atoms / cm 3 That's it, 1×10 18 atoms / cm 3 That's it, 2 x 10 18 atoms / cm 3 That's it, 5 x 10 18 atoms / cm 3 The above may be possible. When the GaN film 2 is doped with compensating impurities, in the specifically doped region 2a, the total concentration of the compensating impurities is preferably at least two times, more preferably at least five times, and even more preferably at least ten times, and may be at least 50 times, the total concentration of the donor impurities. When the GaN film 2 is doped with compensating impurities, the GaN crystal becomes semi-insulating in the specific doped region 2a, i.e., its room temperature resistivity is 1×10 5 It may be Ω·cm or more.

[0043] When the GaN film 2 is doped with donor impurities, the total concentration of the donor impurities in the specific doped region 2a is at least 1×10 18 atoms / cm 3 and preferably 2 × 10 18 atoms / cm 3 More preferably, 5×10 18 atoms / cm 3 That's all. When the GaN film 2 is doped with a donor impurity, the donor impurity that is doped most heavily in the specific doped region 2a is preferably Si or Ge. For example, the total concentration of donor impurities excluding Si in the specifically doped region 2a may be set to 10% or less of the Si concentration, further 5% or less, or even 1% or less. In another example, Ge is added to the specific doped region 2a at 1×10 18 atoms / cm 3 The Si concentration in the region may be preferably 4×10 17 atoms / cm 3 That's all.

[0044] In the specially doped region 2a, it is desirable that the variation in electrical characteristics along the c-axis direction is small. Therefore, when compensating impurities are added to the region 2a, the variation in the total concentration of the compensating impurities along the c-axis direction in the region 2a is preferably within ±25% from the median, more preferably within ±20%, even more preferably within ±15%, and even more preferably within ±10%. Furthermore, when donor impurities are added to the region 2a, the variation in the total concentration of the donor impurities along the c-axis direction in the region 2a is preferably within ±25% from the median, more preferably within ±20%, even more preferably within ±15%, and even more preferably within ±10%.

[0045] When the GaN film 2 is doped with compensating impurities, the total concentration of the compensating impurities in the GaN film 2, including the specific doped region 2a, is preferably 5×10 19 atoms / cm 3 The following is further 2×10 19 atoms / cm 3 Below, and further 1×10 19 atoms / cm 3 It can be as follows. When the GaN film 2 is doped with donor impurities, the total concentration of the donor impurities in the GaN film 2, including the specific doped region 2a, is preferably 5×10 19 atoms / cm 3 The following is further 2×10 19 atoms / cm 3 Below, and further 1×10 19 atoms / cm 3 It can be as follows.

[0046] The lowermost portion of the GaN film 2, i.e., the portion adjacent to the c-plane GaN wafer 1, may be doped with the same type of compensating impurity as the specific doped region 2a, so that the concentration of the compensating impurity increases continuously or stepwise with increasing distance from the c-plane GaN wafer 1. Growth thickness t of GaN film 2 2g may be set according to the design thickness of the Ga-polarity side region of the GaN substrate wafer to be manufactured. Specifically, it may be 20 μm or more, 50 μm or more, 75 μm or more, 100 μm or more, 150 μm or more, or 500 μm or less, 350 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, etc.

[0047] When manufacturing the above-mentioned GaN substrate wafer 100, the growth thickness t 2g may be the same as the design thickness of the second region 120 in the GaN substrate wafer, but is preferably larger than the design thickness, which allows the surface of the GaN film 2 to be flattened in the subsequent thinning process. 2g In order to ensure a processing margin for planarization, the thickness of the second region 120 is preferably 50 μm or more larger than the maximum design thickness of the second region 120, and more preferably 100 μm or more larger. A processing margin exceeding 200 μm is usually not required. In other words, it is preferable that the difference in thickness of the GaN film 2 before and after the thinning step is 200 μm or less. For example, the growth thickness t of the GaN film 2 2g is 50 μm or more larger than the designed maximum thickness of second region 120, the thickness of GaN film 2 is reduced by 50 μm or more in the subsequent thinning step. In other words, the difference in thickness of GaN film 2 before and after the thinning step is 50 μm or more.

[0048] When manufacturing the above-mentioned GaN substrate wafer 100, even if the wafer has a large diameter, for example, a wafer with a diameter of 6 inches, the growth thickness t 2g It is possible to keep the thickness below 500 μm. Growth thickness t 2g Since the size of the GaN film 2 is small, the GaN film 2 can be formed in a relatively short time, and therefore it is possible to grow the GaN film 2 on many c-plane GaN wafers 1 at once without worrying about the by-product NH4Cl (ammonium chloride) clogging the exhaust system of the HVPE apparatus. This allows the throughput in the second step to be extremely high. Furthermore, the shorter time required to form the GaN film 2 can also contribute to reducing costs associated with cleaning and maintenance of the HVPE reactor. In general, the shorter the time required for a single growth step, the slower the degradation of the HVPE reactor will be, and the longer the service life will be.

[0049] Growth thickness t 2gThe small size of the dopant is extremely advantageous in preventing a decrease in yield due to abnormal growth, particularly when the GaN film 2 is doped at a high concentration. 18 atoms / cm 3 This is because, when attempting to grow a GaN crystal containing such a high concentration to a thickness exceeding 1 mm, abnormal growth frequently occurs.

[0050] After the second step, if necessary, a thinning step is performed to thin the laminated structure obtained in the second step, as shown in FIG. 5(c). In FIG. 5(c), the thickness of the c-plane GaN wafer 1 is the initial thickness t 1i to final thickness t 1f and the thickness of the GaN film 2 is reduced to the initial thickness t 2i to final thickness t 2f However, in the thinning step, only either the c-plane GaN wafer 1 or the GaN film 2 may be processed. When manufacturing the above-described GaN substrate wafer 100 according to the embodiment, in the thinning process, the thicknesses of the c-plane GaN wafer 1 and the GaN film 2 are reduced until they match the designed thicknesses of the first region 110 and the second region 120 in the GaN substrate wafer, respectively. When the offcut orientation of the GaN substrate wafer 100 to be manufactured is the same as the offcut of the c-plane GaN wafer 1, the back surface of the c-plane GaN wafer 1 (the N-polarity surface of the laminated structure) can be used as the reference for the plane orientation during thinning. When the offcut orientation of the GaN substrate wafer 100 to be manufactured differs from the offcut of the c-plane GaN wafer 1, i.e., when at least either the offcut angle or the offcut direction differs, the crystal orientation of the laminated structure is confirmed by an X-ray diffraction device before thinning processing. The processing technique used in the thinning step can be appropriately selected from grinding, lapping, CMP, dry etching, wet etching, and the like.

[0051] An HVPE apparatus that can be used in the second step included in the above-mentioned manufacturing method will be described below with reference to FIG. 7 includes a hot-wall type reactor 11, a gallium reservoir 12 and a susceptor 13 disposed within the reactor, and a first heater 14 and a second heater 15 disposed outside the reactor. The first heater 14 and the second heater 15 each surround the reactor 11 in an annular shape. The reactor 11 is a quartz tube chamber. Inside the reactor 11, there are a first zone Z1 that is mainly heated by a first heater 14, and a second zone Z2 that is mainly heated by a second heater 15. An exhaust pipe P E is connected to the reactor end on the second zone Z2 side. The gallium reservoir 12 located in the first zone Z1 is a quartz vessel having a gas inlet and a gas outlet. The susceptor 13 disposed in the second zone Z2 is made of, for example, graphite. A mechanism for rotating the susceptor 13 can be provided as desired.

[0052] To grow GaN in the HVPE apparatus 10, a seed is placed on the susceptor 13, and the inside of the reactor 11 is heated by the first heater 14 and the second heater 15. At the same time, NH3 (ammonia) diluted with a carrier gas is supplied to the second zone Z2 through the ammonia inlet pipe P1, and HCl (hydrogen chloride) diluted with a carrier gas is supplied to the gallium reservoir 12 through the hydrogen chloride inlet pipe P2. This HCl reacts with the metallic gallium in the gallium reservoir 12, and the resulting GaCl (gallium chloride) is transported to the second zone Z2 through the gallium chloride inlet pipe P3. In the second zone Z2, NH3 and GaCl react, and the resulting GaN crystallizes on a seed placed on a susceptor 13. When the growing GaN is to be intentionally doped, a doping gas diluted with a carrier gas is introduced into the second zone Z2 in the reactor 11 through a dopant introduction pipe P4. The portions of the ammonia introduction pipe P1, the hydrogen chloride introduction pipe P2, the gallium chloride introduction pipe P3 and the dopant introduction pipe P4 that are disposed within the reactor 11 are made of quartz. As a carrier gas for diluting NH3, HCl and the doping gas, H2 (hydrogen gas), N2 (nitrogen gas) or a mixed gas of H2 and N2 is preferably used.

[0053] The preferred conditions for growing GaN using the HVPE apparatus 10 are as follows. The temperature of the gallium reservoir is, for example, 500 to 1000°C, preferably 700°C or higher, and preferably 900°C or lower. The susceptor temperature is, for example, 900 to 1100° C., preferably 930° C. or higher, more preferably 950° C. or higher, and preferably 1050° C. or lower, more preferably 1020° C. or lower. The V / III ratio, which is the ratio of NH3 partial pressure to GaCl partial pressure in the reactor, is, for example, 1 to 20, preferably 2 or more, more preferably 3 or more, and is preferably 10 or less. If the V / III ratio is too large or too small, the morphology of the growth surface of GaN deteriorates, which can cause a decrease in crystal quality.

[0054] The incorporation efficiency of certain dopants into GaN crystals strongly depends on the crystal orientation of the growth surface. The uniformity of the concentration of such dopants decreases inside GaN crystals grown under conditions with poor growth surface morphology. This is because the growth surface with poor morphology has facets with various orientations. A typical example of a dopant whose incorporation efficiency into GaN crystals clearly differs depending on the crystal orientation of the growth surface is O (oxygen), but the inventors have found that a similar tendency is observed for Ge (germanium). As will be described later, this is related to the fact that it is better not to lower the molar ratio of H2 in the carrier gas too much when doping Ge. Since both O and Ge are donor impurities, a decrease in the uniformity of their concentrations leads to a decrease in the uniformity of the resistivity and carrier concentration.

[0055] In addition, using too low a V / III ratio increases the concentration of nitrogen vacancies in the growing GaN crystal. Although the effect of nitrogen vacancies on GaN crystals, GaN substrates using such crystals, or nitride semiconductor devices formed on such GaN substrates is not yet clear, the concentration of nitrogen vacancies should be as low as possible because they are point defects. The growth rate of GaN is preferably 40 to 200 μm / h, and can be controlled by using the product of the NH3 partial pressure and the GaCl partial pressure in the reactor as a parameter. An excessively high growth rate deteriorates the surface morphology of the grown GaN. When doping the GaN film 2 in the second step described above, in order to prevent deterioration of the morphology of the growth surface, it is preferable to gradually increase the supply rate of the doping gas to a predetermined value over a period of several minutes to several tens of minutes from the start of supply. For the same reason, it is preferable to start supplying the doping gas when the GaN film 2 has grown to at least several μm.

[0056] Although there is no particular limitation on the method for doping the GaN film 2 with compensating impurities, a method of introducing a doping gas into the HVPE apparatus is usually adopted. The doping gas for C doping can be a hydrocarbon gas such as CH4 (methane). For example, vaporized iron chloride can be used as the doping gas for Fe doping. Iron chloride vapor can be generated by contacting HCl with metallic iron heated under a carrier gas flow, or by reacting ferrocene (bis(cyclopentadienyl)iron) vaporized by heating under a carrier gas flow with HCl in a dopant introduction tube. Here, ferrocene may be replaced with other organic compounds containing iron. The doping gas for Mn doping can be, for example, metallic Mn placed in an inlet tube, which is heated and used with a flow of a carrier gas or the like. When other transition metal elements are added to GaN, the vapor of the transition metal element or the vapor of the chloride of the transition metal element can be used as the doping gas.

[0057] As a doping gas for Si doping, SiH4 (silane), SiH3Cl (monochlorosilane), SiH2Cl2 (dichlorosilane), SiHCl3 (trichlorosilane) or SiCl4 (tetrachlorosilane) can be preferably used. As the doping gas for Ge doping, GeH4 (germane), GeH3Cl (monochlorogermane), GeH2Cls (dichlorogermane), GeHCl3 (trichlorogermane) or GeCl4 (tetrachlorogermane) can be preferably used.

[0058] The molar ratio of H2 in the carrier gas can affect the impurity concentration of the grown GaN. The molar ratio of H2 in the carrier gas is calculated based on the flow rate of each gas species supplied as a carrier gas from outside the reactor to inside the reactor. Table 1 below shows how the impurity concentration of Si- or Ge-doped GaN grown by HVPE at approximately the same growth rate with the same V / III ratio on the Ga polarity surface of a c-plane GaN wafer cut from a GaN crystal grown by HVPE on a sapphire substrate changes depending on the molar ratio of H2 in the carrier gas.

[0059] [Table 1]

[0060] As can be seen from Table 1, the O concentration of Si-doped GaN is 10% or less of the Si concentration when the carrier gas is only N2. Since the donor other than Si is essentially only O, this is equivalent to the total concentration of donors other than Si being 10% or less of the Si concentration. If the molar ratio of H2 in the carrier gas is increased, the O concentration of Si-doped GaN becomes even lower, and is less than 1% of the Si concentration when the molar ratio is 0.7.

[0061] On the other hand, in Ge-doped GaN, when the molar ratio of H2 in the carrier gas is 0 (zero), the Ge concentration is more than 10 times higher than when the molar ratio is 0.7, and the ratio of Ge concentration to Si concentration is also higher. Therefore, at first glance, a lower molar ratio of H2 in the carrier gas seems preferable. However, when the molar ratio of H2 in the carrier gas is 0.7, the O concentration is one order of magnitude higher in the former case than in the latter case, and the inventors have confirmed that this is the reason why the GaN growth surface morphology is worse and the Ge concentration is higher when the former condition is used. When the molar ratio of H2 in the carrier gas is too low, GaN crystals with low uniformity of Ge concentration are grown.

[0062] Therefore, when growing Ge-doped GaN, it is preferable to set the molar ratio of H2 in the carrier gas to about 0.3 to 0.7. In the Ge-doped GaN grown in this way, the Ge concentration is 1×10 18 atoms / cm 3 When the Si concentration is 4×10 17 atoms / cm 3 That's all. The O concentration in GaN grown by HVPE, whether doped with Si or Ge, tends to decrease with increasing H molar ratio in the carrier gas, decreasing by 2×10 16 atoms / cm 3 Below, and further 1×10 16 atoms / cm 3 This is due to the improved surface morphology during growth.

[0063] GaN grown using the HVPE apparatus 10 may contain O and Si at concentrations detectable by SIMS (secondary ion mass spectrometry) even when not intentionally doped. The Si source is the quartz (SiO2) used in the reactor and the piping within the reactor, and the O source is either or both of the quartz and moisture remaining or penetrating into the reactor. The components arranged in the reactor 11, including those not shown in FIG. 7, are made of quartz and carbon, as well as silicon carbide (SiC), silicon nitride (SiNx (silicon nitride), BN (boron nitride), alumina, W (tungsten), Mo (molybdenum), etc. can be used. In this way, the concentration of each impurity except for Si, O, and H in GaN grown using the HVPE apparatus 10 is 5×10 15 atoms / cm 3 It can be the following:

[0064] Although the present invention has been described above with reference to specific embodiments, each embodiment is presented as an example and does not limit the scope of the present invention. Each embodiment described in this specification can be modified in various ways without departing from the spirit of the invention, and can be combined with features described in other embodiments within the scope of feasibility. [Explanation of symbols]

[0065] 1 c-plane GaN wafer 2 GaN film 2a Specific doped region 10 HVPE Equipment 11. Reactor 12 Gallium reservoir 13 Susceptor 14 First Heater 15 Second Heater 100 GaN substrate wafer 101 N polar plane 102 Ga polar surface 103 Regrowth interface 110 First area 120 Second area 120a Main doped region 200 Epitaxial film 210 First nitride semiconductor layer 220 Second nitride semiconductor layer

Claims

1. A (0001) oriented GaN substrate wafer, A first region is provided on the N-polarity side of a regrowth interface, and a second region is provided on the Ga-polarity side of the regrowth interface, The second region has a minimum thickness of 20 μm or more; The concentration of at least one element selected from Li, Na, K, F, Cl, Br, and I in the first region is 1×10 １５ atoms / cm ３ And, The second region satisfies one or more conditions selected from the following (a) to (c): In at least a portion of the second region, a total concentration of donor impurities is 1×10 18 atoms / cm 3 or more; GaN substrate wafer: (a) Si concentration is 5×10 １６ atoms / cm ３ That's all. (b) O concentration is 3×10 １６ atoms / cm ３ The following is the result. (c) H concentration is 1×10 １７ atoms / cm ３ The following is the result.

2. 2. The GaN substrate wafer according to claim 1, which satisfies any one of the following conditions (1) to (3): (1) Having a diameter of 50 mm or more and 55 mm or less and a thickness of 250 μm or more and 450 μm or less. (2) Having a diameter of 100 mm or more and 105 mm or less and a thickness of 350 μm or more and 750 μm or less. (3) Having a diameter of 150 mm or more and 155 mm or less and a thickness of 450 μm or more and 800 μm or less.

3. 3. The GaN substrate wafer according to claim 1, wherein the second region has a minimum thickness of 300 μm or less.

4. 4. The GaN substrate wafer according to claim 1, wherein a main surface on the Ga polarity side is a flat surface.

5. The GaN substrate wafer according to claim 4 , wherein the regrowth interface is inclined with respect to a Ga-polar primary surface.

6. 6. The GaN substrate wafer according to claim 5, wherein a difference in thickness between one end and the other end in a direction in which the regrowth interface in the second region is inclined does not exceed 200 μm.

7. In the first region, the H concentration is 1×10 １７ atoms / cm ３ The GaN substrate wafer according to any one of claims 1 to 6.

8. In the first region, the O concentration is 1×10 １７ atoms / cm ３ The GaN substrate wafer according to any one of claims 1 to 7.

9. In the first region, the F concentration is 1×10 １５ atoms / cm ３ The GaN substrate wafer according to any one of claims 1 to 8.

10. In at least a portion of the second region, the total concentration of the compensating impurities is 1×10 １７ atoms / cm ３ The GaN substrate wafer according to any one of claims 1 to 9.

11. The second region has a main doped region including at least a Ga-polar main surface, and the total concentration of the compensating impurities in the main doped region is 1×10 １７ atoms / cm ３ The GaN substrate wafer according to claim 10 .

12. The total concentration of compensating impurities in the main doped region is 1×10 １８ atoms / cm ３ The GaN substrate wafer according to claim 11 .

13. 13. The GaN substrate wafer according to claim 11, wherein in said primarily doped region, the total concentration of compensating impurities is at least twice the total concentration of donor impurities.

14. 14. The GaN substrate wafer according to claim 11, wherein the primary doped region contains one or more elements selected from the group consisting of carbon and transition metal elements.

15. 15. The GaN substrate wafer according to claim 11, wherein the impurity contained in the primary doped region at the highest concentration is Fe, Mn or C.

16. 16. The GaN substrate wafer according to claim 11, wherein the primary doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 20 μm or more.

17. 17. The GaN substrate wafer according to claim 11, wherein in the primary doped region, the variation in total concentration of compensating impurities along the c-axis direction is within a range of ±25% from a median value.

18. The GaN substrate wafer according to any one of claims 11 to 17, wherein the primary doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 50% or more of the minimum thickness of the second region.

19. The total concentration of the compensating impurities in the second region is 5×10 １９ atoms / cm ３ 19. The GaN substrate wafer according to claim 10, wherein:

20. The second region has a main doped region including at least a Ga-polar main surface, and the total concentration of donor impurities in the main doped region is 1×10 １８ atoms / cm ３ That's all. A GaN substrate wafer according to any one of claims 1 to 19.

21. The total concentration of donor impurities in the primary doped region is 2×10 １８ atoms / cm ３ The GaN substrate wafer according to claim 20 .

22. 22. The GaN substrate wafer according to claim 20, wherein the impurity contained in the primary doped region at the highest concentration is Si or Ge.

23. 22. The GaN substrate wafer according to claim 20, wherein in said primarily doped region, the total concentration of donor impurities excluding Si is 10% or less of the Si concentration.

24. In the main doped region, the concentrations of donor impurity elements other than Si and O are independently 1×10 １５ atoms / cm ３ 24. The GaN substrate wafer of claim 23, wherein the GaN substrate wafer has a thickness of less than 100 nm.

25. In the main doped region, the Ge concentration is 1×10 １８ atoms / cm ３ or more, and the Si concentration is 4×10 １７ atoms / cm ３ The GaN substrate wafer according to claim 22 .

26. The GaN substrate wafer according to any one of claims 20 to 25, wherein the primary doped region is a region within a specific length from a main surface on the GaN polarity side, and the specific length is 20 μm or more.

27. 27. The GaN substrate wafer according to claim 26, wherein the variation in total concentration of donor impurities along the c-axis direction in said primarily doped region is within a range of ±25% from a median value.

28. The GaN substrate wafer according to any one of claims 20 to 27, wherein the primary doped region is a region within a specific length from the main surface on the GaN polarity side, and the specific length is 50% or more of the minimum thickness of the second region.

29. The total concentration of donor impurities in the second region is 5×10 １９ atoms / cm ３ 29. A GaN substrate wafer according to any one of claims 1 to 28, wherein:

30. 30. An epitaxial wafer comprising: the GaN substrate wafer according to claim 1; and a nitride semiconductor layer epitaxially grown on a Ga-polar main surface of the GaN substrate wafer.

31. A method for producing an epitaxial wafer, comprising the steps of: preparing a GaN substrate wafer according to any one of claims 1 to 29; and epitaxially growing a nitride semiconductor layer on a Ga-polar main surface of the GaN substrate wafer.

32. 30. A method for manufacturing a nitride semiconductor device, comprising: preparing the GaN substrate wafer according to any one of claims 1 to 29; growing a nitride semiconductor layer on a Ga-polar main surface of the GaN substrate wafer to obtain an epitaxial wafer; and removing at least a portion of the first region of the GaN substrate wafer.

33. 1. A method for producing a GaN substrate wafer having an N-polarity region and a Ga-polarity region separated by a regrowth interface, comprising: The method includes a first step of preparing a c-plane GaN wafer made of ammonothermally grown GaN crystal, and a second step of growing a (0001)-oriented GaN film having a thickness of 20 μm or more on the c-plane GaN wafer by HVPE to obtain a stacked structure wafer; In at least a portion of the GaN film, the total concentration of donor impurities is 1×10 18 atoms s / cm 3 or more. A method for manufacturing a GaN substrate wafer.

34. 34. The method for producing a GaN substrate wafer according to claim 33, wherein the GaN substrate wafer satisfies any one of the conditions selected from the following (1) to (3): (1) Having a diameter of 50 mm or more and 55 mm or less and a thickness of 250 μm or more and 450 μm or less. (2) Having a diameter of 100 mm or more and 105 mm or less and a thickness of 350 μm or more and 750 μm or less. (3) Having a diameter of 150 mm or more and 155 mm or less and a thickness of 450 μm or more and 800 μm or less.

35. In the c-plane GaN wafer, the concentration of at least one element selected from the group consisting of Li, Na, K, F, Cl, Br, and I is 1×10 １５ atoms / cm ３ The method for producing a GaN substrate wafer according to claim 33 or 34.

36. A c-plane GaN wafer is exposed to 1×10 １７ atoms / cm ３ The method for producing a GaN substrate wafer according to any one of claims 33 to 35, wherein said GaN substrate wafer is contained at a concentration of at least one of said first and second elements.

37. In the c-plane GaN wafer, the concentration of O is 1×10 １７ atoms / cm ３ The method for producing a GaN substrate wafer according to any one of claims 33 to 36, as described above.

38. In the c-plane GaN wafer, the concentration of F is 1×10 １５ atoms / cm ３ The above is the method for producing a GaN substrate wafer according to any one of claims 33 to 37.

39. In at least a portion of the GaN film, the total concentration of compensating impurities is 1×10 １７ atoms / cm ３ The method for producing a GaN substrate wafer according to any one of claims 33 to 38.

40. The GaN film has a region length in the c-axis direction of 1 μm or more, and a total concentration of compensation impurities in the region is 1×10 １７ atoms / cm ３ The method for producing a GaN substrate wafer according to claim 39 , having a specifically doped region.

41. The total concentration of the compensation impurities in the specific doped region is 1×10 １８ atoms / cm ３ The method for producing a GaN substrate wafer according to claim 40.

42. 42. The method for producing a GaN substrate wafer according to claim 40 or 41, wherein in the specific doped region, a total concentration of compensating impurities is at least twice as high as a total concentration of donor impurities.

43. The method for producing a GaN substrate wafer according to any one of claims 40 to 42, wherein the variation in the total concentration of compensation impurities in the specific doped region along the c-axis direction is within a range of ±25% from a median value.

44. The method for producing a GaN substrate wafer according to any one of claims 40 to 43, wherein the region length is 50% or more of the thickness of the GaN film.

45. The method for producing a GaN substrate wafer according to any one of claims 40 to 44, wherein a length from a lower end of the specific doped region to an interface between the GaN film and the c-plane GaN wafer is 1 μm or more.

46. The method for producing a GaN substrate wafer according to any one of claims 40 to 45, wherein the specific doped region contains one or more elements selected from carbon and transition metal elements.

47. 47. The method for producing a GaN substrate wafer according to claim 46, wherein the impurity contained in the specific doped region at the highest concentration is Fe, Mn or C.

48. The total concentration of compensating impurities in the GaN film is 5×10 １９ atoms / cm ３ The method for producing a GaN substrate wafer according to any one of claims 39 to 47, wherein:

49. In the GaN film, in a specific doped region having a region length of 20 μm or more in the c-axis direction, the total concentration of donor impurities is 1×10 １８ atoms / cm ３ The method for producing a GaN substrate wafer according to any one of claims 33 to 48.

50. The total concentration of donor impurities in the specific doped region is 2×10 １８ atoms / cm ３ The method for producing a GaN substrate wafer according to claim 49.

51. 51. The method for producing a GaN substrate wafer according to claim 49 or 50, wherein the variation in total concentration of donor impurities in the specific doped region along the c-axis direction is within a range of ±25% from a median value.

52. The method for producing a GaN substrate wafer according to any one of claims 49 to 51, wherein the region length in the c-axis direction of the specific doped region is 50% or more of the thickness of the GaN film.

53. 53. The method for producing a GaN substrate wafer according to any one of claims 49 to 52, wherein a length from a lower end of the specific doped region to an interface between the GaN film and the c-plane GaN wafer is 1 μm or more.

54. The method for producing a GaN substrate wafer according to any one of claims 49 to 53, wherein the dopant contained at the highest concentration in the specific doped region is Si or Ge.

55. The method for producing a GaN substrate wafer according to any one of claims 49 to 53, wherein in the specific doped region, a total concentration of donor impurities excluding Si is 10% or less of a Si concentration.

56. In the specific doped region, the concentration of donor impurity elements other than Si and O is independently 1×10 １５ atoms / cm ３ 56. The method of claim 55, wherein the GaN substrate wafer is less than 1000 nm thick.

57. In the specific doped region, the Ge concentration is 1×10 １８ atoms / cm ３ or more, and the Si concentration is 4×10 １７ atoms / cm ３ The method for producing a GaN substrate wafer according to claim 54.

58. The total concentration of donor impurities in the GaN film is 5×10 １９ atoms / cm ３ The method for producing a GaN substrate wafer according to any one of claims 33 to 57, wherein:

59. The method for producing a GaN substrate wafer according to any one of claims 33 to 58, further comprising a thinning step of thinning the laminated structure wafer after the second step.

60. 60. The method for producing a GaN substrate wafer according to claim 59, wherein a difference in thickness of the GaN film before and after the thinning step is 50 μm or more.

61. 6. The method of claim 5, wherein the thickness difference of the GaN film before and after the thinning step is 200 μm or less. 9 or 60. A method for producing a GaN substrate wafer according to claim 9 or 60.

62. The method for producing a GaN substrate wafer according to any one of claims 59 to 61, wherein an offcut orientation of the GaN substrate wafer is different from an offcut orientation of the c-plane GaN wafer.

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