Patent Description:
Semiconductor wafers used for light emitting diodes or the like are generally manufactured by growing an element layer or the like for exhibiting a desired function on a base substrate by chemical vapor deposition methods such as a metal organic chemical vapor deposition method (MOCVD method), a molecular beam epitaxy method (MBE method), or a halide vapor phase epitaxy method (HVPE method). Among these, when the element layer is made of, for example, group III nitride single crystal layers containing a mixed crystal of, for example, indium nitride (InN), gallium nitride (GaN), aluminum nitride (AIN), a highly efficient light emitting device in a wavelength range from the infrared region to the ultraviolet region corresponding to the respective band gap energies (<NUM> eV (InN), <NUM> eV (GaN), and <NUM> eV (AIN)) can be produced by controlling the mixed crystal composition of In, Ga, Al which are group III elements. Therefore, a blue light emitting diode using a group III nitride semiconductor is used as a white light emitting diode combined with phosphors in a wide variety of applications including lighting applications or the like.

In recent years, development of ultraviolet light emitting diodes has been progressed, and development of ultraviolet light emitting diodes having an emission peak wavelength at short wavelength, for example, an emission peak wavelength at <NUM> or less has also been progressed. Many attempts have been made to use a sapphire substrate as a base substrate in the ultraviolet light emitting diodes in view of the ability of growing the III group nitride crystal and transmittance of ultraviolet light (see phys. (a) <NUM>, (<NUM>) <NUM>).

<CIT> discloses a light-emitting diode package configured such that the surface of a base on which the light-emitting diodes are to be attached is curved, wherein the light-emitting diodes are die-bonded to the curved surface so as to enable the light-emitting diodes to be bent by the curvature of the curved surface. Thus, stresses are applied to the light-emitting diodes, thereby causing changes in a band structure of a quantum well layer. In the thus-produced light-emitting diode package, efficiency droop, which occurs in response to the injection of high current, is reduced to achieve the high output and high efficiency of the package.

<CIT> describes a sapphire/gallium nitride laminate having reduced bending deformation for an electronic device. Such bending deformation results from interfacial strain caused by the differences in the lattice parameter and thermal expansion coefficient between sapphire and gallium nitride. Because such bending deformation adversely affects the quality and productivity of an electronic device comprising the laminate, <CIT> suggests to provide the laminate with a curvature, wherein resulting curvatures are indicated to be between around <NUM>-<NUM> to <NUM>-<NUM>.

<CIT> discloses a GaN compound semiconductor having a thickness around <NUM> placed on a sapphire substrate. The sapphire substrate warps due to a difference in thermal expansion coefficient between the sapphire and the nitride III-V compound semiconductor such as GaN. This warpage measures as large as <NUM> and adversely effects the manufacturing process of a GaN compound with a semiconductor laser and the polishing of the bottom surface of the sapphire substrate. <CIT> tries to solve this problem by balancing out the thickness of the substrate vs. the thickness of the nitride III-V compound semiconductor layers with curvatures of the substrate of around <NUM>-<NUM> to <NUM>-<NUM>.

However, when a dissimilar material substrate different from the group III nitride, such as a sapphire substrate, is used as the base substrate, because of a large difference of lattice constant between the group III nitride single crystal layer (element layer) and the base substrate (sapphire substrate), there is a problem that high density defects (dislocation density) occurs in the group III nitride single crystal layer at an interface between the group III nitride single crystal layer and the base substrate. As a result, the defect density in the element layer is also increased, and the optical output is lowered.

The problem of dislocation density caused by the large lattice constant difference between the group III nitride single crystal layer (element layer) and the base substrate (sapphire substrate) is inherently an inevitable problem. Therefore, it is very difficult to grow a group III nitride single crystal layer (element layer) with a reduced dislocation density on the sapphire substrate.

Accordingly, an object of the present invention is to provide a semiconductor wafer with high output and finally a semiconductor light emitting device obtained from the semiconductor wafer when a sapphire substrate is used as a base substrate.

In order to solve the above problems, the inventors of the present invention have conducted intensive studies. In a case of using a sapphire substrate, various growth conditions have been examined, and attempts have been made to produce a semiconductor wafer having high optical output even if the dislocation density of the element layer cannot be reduced. As a result, it is found that a high output can be obtained even if the dislocation density cannot be reduced when the obtained semiconductor wafer is bent in a specific direction at a specific ratio, and thus the present invention has been completed.

That is, the present invention relates to a semiconductor wafer according to claim <NUM> and to a respective production method according to claim <NUM>.

According to the present invention, a high output semiconductor wafer and a semiconductor chip can be obtained. The semiconductor wafer exhibits high output even if an element layer made of a group III nitride single crystal layer is formed on a sapphire substrate which is a substrate of dissimilar material, even though the effect of reducing the dislocation density is low. Therefore, since a semiconductor wafer having an emission peak wavelength at the ultraviolet region can be manufactured using a general-purpose sapphire substrate, the semiconductor wafer has a high industrial utility value.

<FIG> shows a representative example of a semiconductor chip obtained by the method of the present invention. It will be appreciated that the semiconductor wafer has a plurality of configurations of the semiconductor chip in <FIG>, and the layer constitution and the like are the same for the semiconductor wafer and the semiconductor chip.

A semiconductor wafer <NUM> of the present invention includes an element layer <NUM> including an n-type layer <NUM>, an active layer <NUM>, and a p-type layer <NUM> on one surface of a sapphire substrate <NUM>. The element layer has a characteristic in that a surface thereof is bent in a convex way (<FIG>).

(Characteristics of Semiconductor Wafer) The semiconductor wafer of the present invention has a characteristic in that the surface of the element layer <NUM> is bent in a convex way. The curvature indicating the degree of bending is <NUM>-<NUM> to <NUM>-<NUM>. The curvature can be measured by X-ray diffraction (XRD), a laser displacement meter, and an interference microscope. In the present invention, the curvature is a value measured with a laser displacement meter. The curvature is a value obtained from the surface of the element layer <NUM> in the semiconductor wafer before forming an electrode. That is, the curvature means a curvature of the outermost surface of the p-type layer <NUM>, and when the p-type layer <NUM> includes a p-type contact layer <NUM>, the curvature means a curvature of the surface of the p-type contact layer <NUM>. In addition, when the curvature of the surface varies depending on the measurement site, the curvature means an average value of curvatures at three or more measurement points.

When the element layer <NUM> is formed on the sapphire substrate <NUM>, for example, when the element layer <NUM> is made of group III nitride single crystal layers, dislocation occurs in the element layer <NUM> due to the difference in lattice constant. Many attempts have been made to reduce this dislocation by improving the production method or by providing a buffer layer <NUM> or the like, but at present this dislocation cannot be reduced sufficiently. According to the present invention, a high output semiconductor wafer can be obtained even if the dislocation is present to a certain extent. Not particularly limited, the dislocation density of the element layer <NUM> in the present invention is <NUM> × <NUM><NUM> [cm-<NUM>] to <NUM> × <NUM><NUM> [cm-<NUM>]. The dislocation density is a value measured by a transmission electron microscope and is a value obtained by confirming the dislocation density of the n-type layer <NUM>.

If the surface of the element layer <NUM> of the sapphire substrate <NUM>, contrary to the invention, is not bent or is bent into a recessed shape, the optical output is lowered. As for the reason why that the advantageous effect is attained when the curvature of the convex surface of the element layer <NUM> is <NUM>-<NUM> to <NUM>-<NUM>, the inventors of the present invention presume as follows.

The inventors of the present invention have found that when an n-type AlGaN layer is grown on the sapphire substrate <NUM> under various conditions, X-ray rocking curves of the (<NUM>) plane are about the same (<NUM> to <NUM> [arcsec]; indicating that the dislocation density does not change), but the PL intensity of the n-type AlGaN layer can be increased by increasing the curvature of the obtained laminate (surface of the n-type AlGaN layer) to a certain extent (see <FIG>). From this result, it is suggested that if the surface of the element layer <NUM> can be bent to a certain extent in a convex shape, the dislocation density in the active layer or the like will not be increased, and incorporation of impurities and point defects will be suppressed. In addition, the inventors of the present invention have found that the optical output can be efficiently increased by setting the curvature of the surface of the element layer <NUM> to <NUM>-<NUM> to <NUM>-<NUM>, and thus complete the present invention.

If the curvature of the surface of the element layer <NUM>, contrary to the invention, is less than <NUM>-<NUM>, the effect of improving the optical output is small. Also, if the curvature of the surface of the element layer <NUM>, contrary to the invention, is more than <NUM>-<NUM>, the semiconductor wafer is bent too largely to be subjected to post processing such as polishing and is difficult to be used as a product. In addition, it is difficult to produce a semiconductor wafer having a curvature more than <NUM>-<NUM>. Considering improvement of optical output, handling property, productivity or the like, the curvature is preferably <NUM>-<NUM> to <NUM>-<NUM>, and more preferably <NUM>-<NUM> to <NUM>-<NUM>.

Hereinafter, the substrate and each layer will be described in turn. (Sapphire Substrate) The sapphire substrate <NUM> is not particularly limited, and a known substrate produced by a known method can be used. A thickness of the sapphire substrate <NUM> is not particularly limited and is usually <NUM> to <NUM>.

The sapphire substrate <NUM> preferably has a (<NUM>) plane as a growth plane (a plane on which the element layer is grown).

In the semiconductor wafer <NUM> of the present invention, the element layer <NUM> is formed on the sapphire substrate <NUM>. According to the present invention, the element layer <NUM> comprises group III nitride single crystal layers, and more specifically AlGaInN layers satisfying a composition represented by AlxInyGazN (x, y, and z are rational numbers satisfying <NUM> ≤ x ≤ <NUM>, <NUM> ≤ y < <NUM>, and <NUM> ≤ z ≤ <NUM>, and x + y + z = <NUM>). The reason is that the group III nitride single crystal layer, particularly an AlxInyGazN layer having the above composition, particularly has a large lattice constant difference from the sapphire substrate and tends to cause dislocation, and as a result, the optical output tends to be lowered easily. Unlike a conventional layer constitution of a semiconductor wafer in which dislocation occurs at a high density and the output is lowered, the optical output can be increased without changing the layer constitution by the present invention. Therefore, the present invention can exhibit an excellent effect when the element layer <NUM> contains Al. Specifically, the present invention is suitable for an ultraviolet light emitting diode (wafer) having an emission peak wavelength at the ultraviolet region, specifically in a range of <NUM> to <NUM>.

In the present invention, the element layer <NUM> may be directly formed on the sapphire substrate <NUM>, or as shown in <FIG>, the element layer <NUM> is preferably formed after the buffer layer <NUM> is formed. Next, the buffer layer <NUM> will be described.

In the present invention, when a buffer layer is provided, the buffer layer <NUM> is preferably made of a group III nitride single crystal layer and is preferably an AlGaInN layer satisfying a composition represented by AlX1InY1GaZ1N (X1, Y1, and Z1 are rational numbers satisfying <NUM> ≤ X1 ≤ <NUM>, <NUM> ≤ Y1 ≤ <NUM>, and <NUM> ≤ Z1 ≤ <NUM>, and X1 + Y1 + Z1 = <NUM>). Among them, when the semiconductor wafer <NUM> of the present invention is used for an ultraviolet light emitting diode, it is preferably that <NUM> ≤ X1 ≤ <NUM>, <NUM> ≤ Y1 ≤ <NUM>, and <NUM> ≤ Z1 ≤ <NUM>, and it is most preferably that a buffer layer <NUM> made of AlN is adopted considering the productivity.

A thickness of the buffer layer <NUM> is not particularly limited and is preferably <NUM> to <NUM>. The buffer layer <NUM> may be a single layer or may be a plurality of layers of two or more as described in detail below. The plurality of layers may be layers having different compositions or may be layers having the same composition but different growth conditions. The layers having the same composition but different growth conditions mean the layers that are grown while changing a ratio (V/III ratio) of the number of moles of nitrogen source gas to the number of moles of a group III raw material gas, the ratio being one of the growth conditions. Most preferred is two or more layers of AlN grown while changing the V/III. In addition, the buffer layer <NUM> may be a gradient layer whose composition continuously changes.

In the present invention, it is preferable to form the element layer <NUM> on the buffer layer <NUM>. Next, each layer constituting the element layer <NUM> will be described.

In the present invention, the n-type layer <NUM> is formed on the sapphire substrate <NUM> via the buffer layer <NUM> as required. The n-type layer <NUM> is a layer doped with an n-type dopant. Although the n-type layer <NUM> is not particularly limited, for example, it is preferable that the n-type layer <NUM> exhibits n-type conductivity by containing Si as a dopant in a range where the impurity concentration is <NUM> × <NUM><NUM> [cm-<NUM>] to <NUM> × <NUM><NUM> [cm-<NUM>]. The dopant material may be a material other than Si.

As described above, the present invention can be conveniently applied to an ultraviolet light emitting diode having an emission peak wavelength at the range of <NUM> to <NUM>. Therefore, the n-type layer <NUM> is made of a group III nitride single crystal layer, and more specifically is made of an AlGaInN layer satisfying a composition represented by AlX2InY2GaZ2N (X2, Y2, and Z2 are rational numbers satisfying <NUM> ≤ X2 ≤ <NUM>, <NUM> ≤ Y2 ≤ <NUM>, and <NUM> ≤ Z2 ≤ <NUM>, and X2 + Y2 + Z2 = <NUM>). The n-type layer <NUM> may be a gradient layer whose composition continuously changes. In addition, the thickness of the n-type layer <NUM> is preferably <NUM> to <NUM>.

The active layer <NUM> is formed on the n-type layer <NUM>. The active layer <NUM> may be composed of, for example, one or more well layers and barrier layers. The number of wells composed of the well layers and the barrier layers may be one, or two or more. In the case of two or more, although not particularly limited, the number is preferably <NUM> or less considering the productivity of the nitride semiconductor light emitting device. In addition, the layer in contact with the n-type layer <NUM> may be either a well layer or a barrier layer.

The active layer <NUM> is made of a well layer and a barrier layer. In general, a band gap of the barrier layer is larger than that of the well layer. That is, the barrier layer is formed of an AlGaInN layer having an Al composition ratio higher than that of the well layer. As described above, the semiconductor wafer of the present invention can be conveniently applied to an ultraviolet light emitting diode. Therefore, the barrier layer is made of an AlGaInN layer satisfying a composition represented by AlX3InY3GaZ3N (X3, Y3, and Z3 are rational numbers satisfying <NUM> ≤ X3 ≤ <NUM>, <NUM> ≤ Y3 ≤ <NUM>, and <NUM> ≤ Z3 ≤ <NUM>, and X3 + Y3 + Z3 = <NUM>). In addition, the thickness of the barrier layer <NUM> is preferably <NUM> to <NUM>.

The band gap of the well layer is smaller than that of the barrier layer. That is, the well layer is formed of an AlGaN single crystal having an Al composition ratio lower than that of the barrier layer. As described above, the semiconductor wafer of the present invention can be conveniently applied to an ultraviolet light emitting diode. Therefore, the well layer is preferably made of an AlGaInN layer satisfying a composition represented by AlX4InY4GaZ4N (X4, Y4, and Z4 are rational numbers satisfying <NUM> ≤ X4 ≤ <NUM>, <NUM> ≤ Y4 ≤ <NUM>, and <NUM> ≤ Z4 ≤ <NUM>, and X4 + Y4 + Z4 = <NUM>. Wherein, X3 > X4 and Z3 ≤ Z4. In addition, a thickness of the well layer <NUM> is preferably <NUM> to <NUM>.

In the present invention, the p-type layer <NUM> may be formed directly on the active layer <NUM>, but the p-type layer <NUM> is preferably formed via the electron blocking layer <NUM>. The electron blocking layer <NUM> suppresses leakage of a part of electrons injected from the n-type layer <NUM> into the active layer <NUM> to a p-type layer <NUM> side due to application of an electric field. Therefore, the electron blocking layer <NUM> can be substituted by a p-type clad layer <NUM> to be described later, but by providing the electron blocking layer <NUM>, an Al composition of the p-type clad layer can be lowered, and a film thickness can be reduced, and as a result, a driving voltage can be reduced.

When the electron blocking layer <NUM> is provided, a band gap of the electron blocking layer <NUM> is preferably larger than the band gap of the active layer <NUM> (a barrier layer having the maximum band gap in the active layer (having the maximum Al composition)) and that of a layer forming the p-type layer <NUM> to be described later. Therefore, the electron blocking layer <NUM> is preferably formed of a single crystal made of AlInGaN having an Al composition ratio higher than that of the above layers. That is, the electron blocking layer <NUM> is preferably formed of an AlInGaN single crystal layer having an Al composition higher than any of the other layers. Therefore, the electron blocking layer <NUM> is preferably made of an AlInGaN layer satisfying a composition represented by AlX5InY5GaZ5N (X5, Y5, and Z5 are rational numbers satisfying <NUM> ≤ X5 ≤ <NUM>, <NUM> ≤ Y5 ≤ <NUM>, and <NUM> ≤ Z5 ≤ <NUM>, and X5 + Y5 + Z5 = <NUM>), and is particularly preferably made of an AlN single crystal layer. The electron blocking layer <NUM> may be a gradient layer whose composition continuously changes.

In addition, the electron blocking layer <NUM> may be an undoped layer or a p-type layer. In the case of a p-type layer, it is preferable that the p-type layer contains p-type dopant such as Mg in a range where the impurity concentration is <NUM> × <NUM><NUM> [cm-<NUM>] to <NUM> × <NUM><NUM> [cm-<NUM>]. A thickness of the electron blocking layer <NUM> is preferably <NUM> to <NUM>.

In the present invention, the p-type layer <NUM> is formed on the active layer <NUM> or on the electron blocking layer <NUM> provided as required. The p-type layer <NUM> is not particularly limited and is preferably made of the p-type clad layer <NUM> and the p-type contact layer <NUM> on which a p-electrode <NUM> is formed.

As described above, the semiconductor wafer <NUM> of the present invention can be conveniently applied to an ultraviolet light emitting diode in the range of <NUM> to <NUM>. Therefore, the p-type clad layer <NUM> is preferably made of an AlInGaN layer satisfying a composition represented by AlX6InY6GaZ6N (X6, Y6, and Z6 are rational numbers satisfying <NUM> ≤ X6 ≤ <NUM>, <NUM> ≤ Y6 ≤ <NUM>, and <NUM> ≤ Z6 ≤ <NUM>, and X6 + Y6 + Z6 = <NUM>).

It is preferable that the p-type clad layer <NUM> contains Mg as a dopant in a range where the impurity concentration is <NUM> × <NUM><NUM> [cm-<NUM>] to <NUM> × <NUM><NUM> [cm-<NUM>]. A thickness of the p-type clad layer <NUM> is not particularly limited and is preferably <NUM> to <NUM>.

In the present invention, the p-type contact layer <NUM> in contact with the p-electrode is preferably provided on the p-type clad layer <NUM>. By forming the p-type contact layer <NUM>, ohmic contact with the p-electrode <NUM> can be easily realized and reduction in contact resistance can be easily realized.

When the p-type contact layer <NUM> is provided, a band gap of the p-type contact layer <NUM> is preferably lower than a band gap of the p-type clad layer <NUM>. That is, the p-type contact layer <NUM> preferably has an Al composition ratio lower than an Al composition of the p-type clad layer <NUM>. Therefore, the p-type contact layer <NUM> is preferably made of an AlInGaN layer satisfying a composition represented by AlX7InY7GaZ7N (X7, Y7, and Z7 are rational numbers satisfying <NUM> ≤ X7 ≤ <NUM>, <NUM> ≤ Y7 ≤ <NUM>, and <NUM> ≤ Z7 ≤ <NUM>, and X7 + Y7 + Z7 = <NUM>). Most preferably, the p-type contact layer <NUM> is formed of a single crystal made of GaN. In addition, it is preferable that the p-type contact layer <NUM> contains Mg a dopant in a range where the impurity concentration is <NUM> × <NUM><NUM> [cm-<NUM>] to <NUM> × <NUM><NUM> [cm-<NUM>]. A thickness of the p-type contact layer <NUM> is not particularly limited and is preferably <NUM> to <NUM>. When the p-type contact layer <NUM> is provided as described above, in the present invention, the curvature of the surface of the p-type contact layer <NUM> is measured.

The n-electrode <NUM> is formed on the exposed surface of the n-type layer <NUM>. Materials used for the n-electrode <NUM> can be selected from various known materials. For example, Ti, Al, Rh, Cr, V, In, Ni, Pt, Au, or the like can be used. Among these, it is preferable to use Ti, Al, Rh, Cr, V, Ni, and Au. These negative electrodes may have a single layer or multi-layer structure having a layer containing an alloy or an oxide of these metals, and a preferred combination is Ti/Al/Au from the viewpoint of ohmic property and reflectance. A thickness thereof is not particularly limited and is preferably <NUM> or more considering the stability of production, and an upper limit thereof is <NUM>.

The p-electrode <NUM> is formed on the p-type contact layer <NUM>. The p-electrode <NUM> preferably has a high transparency to ultraviolet light. Specifically, the transmittance thereof is <NUM>% or more, and preferably <NUM>% or more, to the light of <NUM>. Although not particularly limited, an upper limit thereof is preferably <NUM>%, and industrially preferably <NUM>% or more.

Metal materials used for the p-electrode <NUM> can be selected from various known materials. For example, Ni, Cr, Au, Mg, Zn, Pd or the like can be used. In addition, the light-transmissive positive electrode may be a single layer or multi-layer structure having a layer containing an alloy or an oxide of these metals and a preferred combination is Ni/Au.

When it is necessary for the p-electrode <NUM> to have translucency, the film thickness is preferably as small as possible. Specifically, the film thickness is <NUM> or less, and more preferably <NUM> or less, and a lower limit thereof is <NUM>. When it is not necessary for the p-electrode <NUM> to have a light-transmission property, the above is not the limit and the film thickness may be thick. Specifically, the film thickness is <NUM> or less, and more preferably <NUM> or less, and a lower limit thereof is <NUM>.

In the present invention, a semiconductor light emitting device having an n-electrode and a p-electrode on a semiconductor wafer is used, and the semiconductor wafer is cut to obtain a semiconductor chip. Next, a preferred method for producing the semiconductor wafer <NUM> of the present invention will be described.

In the present invention, the semiconductor wafer <NUM> is produced by forming the element layer <NUM> on the sapphire substrate <NUM>. The sapphire substrate <NUM> to be used preferably has (<NUM>) plane on which the element layer is grown. The (<NUM>) plane may have an off angle, and it is preferable to form an element layer on the (<NUM>) plane inclined at <NUM>° to <NUM>°. Further, the (<NUM>) plane is preferably inclined to an m-axis direction.

In addition, it is preferable that the (<NUM>) plane is smooth, and it is preferable that the (<NUM>) plane has a surface roughness of about <NUM> or less. It is preferable that a bending amount (radius of curvature) of the sapphire substrate <NUM> before growing the element layer <NUM> is <NUM> or more. An upper limit of the radius of curvature is not particularly limited.

In the present invention, the element layer <NUM> is formed on the sapphire substrate <NUM>. Conditions for producing the semiconductor wafer of the present invention are not particularly limited, and the growth is preferably performed by a metal organic chemical vapor deposition (MOCVD) method. According to the study of the inventors of the present invention, it is found that in order to bend the element layer <NUM> so as to satisfy the range of the present invention, the conditions just before growing the buffer layer or the element layer on the sapphire substrate <NUM> are important. Specifically, it is preferable to introduce a certain amount of oxygen into a MOCVD apparatus before growing the buffer layer or the element layer on the sapphire substrate <NUM>. However, the amount of oxygen introduced cannot be unconditionally limited since the optimum value varies depending on the capacity, shape, etc. of each apparatus. For a general MOCVD apparatus, it is preferable to introduce oxygen (air) into the apparatus by opening for about <NUM> minutes to about <NUM> minutes before setting a sapphire substrate into the apparatus. After this operation, the sapphire substrate <NUM> is set in the MOCVD apparatus, and thermal cleaning or the like may be performed by a known method, thereafter the buffer layer <NUM> or the element layer <NUM> is formed. Although the reason why the effect can be obtained by introducing oxygen is unclear, it is considered that a small amount of remaining oxygen influences the growth of the layer initially formed on the sapphire substrate <NUM>, and thereby the finally obtained element layer <NUM> can be bent in a convex way.

In the MOCVD method, the element layer <NUM> can also be bent in a convex way by growing the buffer layer provided as required and the n-type layer under a pressure. Specifically, it is preferable to grow the above layers on the sapphire substrate <NUM> under a pressure of <NUM> Torr to <NUM> Torr. Although the reason is unclear, it is thought that at the early stage of growth, the growth of the layer to be formed is influenced by the pressure, and thereby the finally obtained element layer <NUM> can be bent in a convex way.

Moreover, it will be appreciated that both the oxygen introduction method and the growth method under a pressure can be adopted.

In the present invention, the element layer <NUM> may be directly formed on the (<NUM>) plane of the sapphire substrate <NUM> but is preferably formed via the buffer layer <NUM>, as described above. Next, the growth of the buffer layer <NUM> will be described.

In the present invention, when the buffer layer <NUM> is provided, the preferred composition is as described above. In the present invention, although not particularly limited, the growth is preferably performed by a metal organic chemical vapor deposition (MOCVD) method.

In the semiconductor wafer <NUM> of the present invention, in order to obtain the curvature of the element layer <NUM> within the range of the present invention, it is preferable to adopt the oxygen introduction method and/or the growth method under a pressure of <NUM> Torr to <NUM> Torr, and to control the V/III ratio under the growth conditions of the buffer layer <NUM>. That is, it is preferable to control the ratio (V/III ratio) of the number of moles of the nitrogen source gas to the number of moles of the group III raw material gas. The curvature after growth becomes high when the V/III ratio high, and the more the element layer <NUM> is bent convexly. The range of the V/III ratio under the production conditions is not particularly limited and is preferably <NUM> to <NUM>. It is presumed that, when the V/III ratio is within the above range, nucleation sizes are different at the early stage of growth, and thus the subsequent association process of growth nuclei is different, so that a bent semiconductor wafer can be obtained.

As a particularly preferable method, it is preferable to grow the buffer layer <NUM> in at least two stages. As a particularly preferable condition, it is preferable to adjust a flow rate of the raw material gas such that the V/III ratio is <NUM>,<NUM> to <NUM>,<NUM> so as to form a first buffer layer made of an AlN single crystal as a first growth step, and then to adjust the flow rate of the raw material gas supplied on the first buffer layer such that the V/III ratio is <NUM> to <NUM> so as to further form an AIN single crystal layer, as a first growth step. After the first growth step, an AlN single crystal layer can be grown in multiple stages with the V/III ratio in a range of <NUM> to <NUM>. However, considering operability, it is preferable to form the buffer layer (second buffer layer) by two stages including a second growth step, after the first growth step. In this case, it is preferable that a thickness of the second buffer layer is larger than that of the first buffer layer. Specifically, the thickness of the first buffer layer is preferably <NUM> to <NUM>, and the thickness of the second buffer layer is preferably <NUM> to <NUM>.

In addition, as for the condition for forming the buffer layer <NUM>, a known method can be adopted, and the nitrogen source gas (for example, ammonia) and the group III raw material gas (for example, trimethylaluminum gas, trimethylgallium gas, and trimethylindium gas) may be supplied to the sapphire substrate <NUM> under a flow of hydrogen or nitrogen gas at <NUM> to <NUM> so as to obtain a desired composition and thickness.

The method for growing the n-type layer <NUM> is also not particularly limited, and it is preferable to grow the n-type layer <NUM> by the MOCVD method. When the buffer layer <NUM> is not provided, the n-type layer <NUM> is directly laminated on the sapphire substrate <NUM>. As for a condition for growing the n-type layer <NUM>, a known method can be adopted. The growth conditions of the n-type layer <NUM> on the sapphire substrate <NUM> can be the same as those of the buffer layer <NUM>.

As for other conditions, for example, the n-type layer <NUM> may be grown by supplying an n-type dopant in addition to the Al and Ga raw material gas and ammonia. Although known elements such as Si and O can be used as an element of the n-type dopant, Si is preferably used from the viewpoint of easy control or the like. As the Si raw material, monosilane (SiH<NUM>), tetraethylsilane (TESi) or the like can be used.

A growth temperature at the time of growing the n-type layer <NUM> is not particularly limited, and is preferably <NUM> to <NUM>. A growth rate is preferably <NUM>/h to <NUM>/h. The V/III ratio is not particularly limited, and is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>, in order to satisfy the growth rate in the above temperature range.

Then, same as the buffer layer <NUM> and the n-type layer <NUM>, the active layer <NUM> can also be grown by the MOCVD method so as to satisfy a desired composition. As for a condition for forming the active layer <NUM>, a known method can be adopted.

As for other conditions, a growth temperature of the active layer <NUM> is not particularly limited and is preferably more than <NUM> to <NUM> or lower, and preferably more than <NUM> to <NUM> or lower. The V/III ratio at growing the active layer <NUM> is not particularly limited, and is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>. A growth rate of the active layer <NUM> is preferably <NUM>/h to <NUM>/h, and more preferably <NUM>/h to <NUM>/h. The growth rate of the active layer is preferably in the range of <NUM>/h to <NUM>/h for all layers of the quantum well layer and the barrier layer.

The electron blocking layer <NUM> formed as required can also be grown by the MOCVD method. As for a condition for forming the electron blocking layer <NUM>, a known method can be adopted.

As for other conditions, a growth temperature of the electron blocking layer <NUM> is not particularly limited and is preferably higher than <NUM> to <NUM> or lower, and more preferably higher than <NUM> to <NUM> or lower. A growth rate is preferably <NUM>/h to <NUM>/h, and more preferably <NUM>/h to <NUM>/h. The V/III ratio is not particularly limited, and is preferably in a range of <NUM> to <NUM>, and more preferably in a range of <NUM> to <NUM>. The electron blocking layer <NUM> can also be a p-type by adding a p-type impurity.

The electron blocking layer <NUM> is produced by supplying a p-type impurity in addition to the Al and Ga raw material gas and ammonia. As the p-type impurity, a known material can be used without limitation, and Mg is preferably used considering the activation energy of the p-type impurity or the like.

The p-type clad layer <NUM> can also be grown by the MOCVD method. Specifically, the p-type clad layer <NUM> is produced by supplying a p-type impurity in addition to the Al and Ga raw material gas and ammonia. As the p-type impurity, a known material can be used without limitation, and Mg is preferably used considering the activation energy of the p-type impurity or the like.

As for a condition for forming the p-type clad layer <NUM>, a known method can be adopted. As for a growth temperature, a growth rate, and a V/III ratio thereof, it is preferable to adopt the conditions described for the electron blocking layer <NUM>.

Similarly, the p-type contact layer <NUM> can also be grown by the MOCVD method, and the same impurity as of the p-type clad layer <NUM> can be added.

As for a condition for forming the p-type contact layer <NUM>, a known method can be adopted. A growth temperature is not particularly limited, and is preferably <NUM> to <NUM>, and more preferably <NUM> to <NUM>. A growth rate is also not particularly limited, and is preferably <NUM>/h to <NUM>/h. The V/III ratio is preferably set within a range of <NUM> to <NUM>, more preferably <NUM> to <NUM>, and most preferably <NUM> to <NUM>.

The n-electrode <NUM> is formed on the exposed surface of the n-type layer <NUM>.

The exposed surface of the n-type layer <NUM> is formed by means such as etching. Preferred etching methods include dry etching such as reactive ion etching and inductively coupled plasma etching. In order to remove etching damages after forming the exposed surface of the n-type layer <NUM>, the exposed surface is preferably subject to surface treatment with an acid or alkaline solution. In addition, patterning of the n-electrode can be performed using a lift-off method.

Examples of a method for depositing a metal forming the n-electrode include vacuum evaporation, sputtering, chemical vapor deposition or the like, and the vacuum evaporation is preferred in order to eliminate impurities in the electrode metal. The material used for the n-electrode is as described above.

Patterning of the p-electrode <NUM> is preferably performed using a lift-off method. The metal material used for the p-electrode <NUM> is as described above. Examples of a method for depositing a metal of the p-electrode <NUM> include vacuum evaporation, sputtering, chemical vapor deposition or the like, and the vacuum evaporation is preferred in order to eliminate impurities in the electrode metal.

Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to these examples.

A sapphire C plane ((<NUM>) plane) single crystal substrate (Φ2 inches × thickness <NUM>) was used as a crystal growth substrate. <NUM> minutes after opening an MOCVD apparatus, the sapphire substrate was placed on a susceptor in the MOCVD apparatus, and then the sapphire substrate was heated to <NUM> for <NUM> minutes while flowing hydrogen at a flow rate of <NUM> slm (heat treatment step).

Then, the temperature of the sapphire substrate was set to <NUM>, the flow rate of trimethylaluminum was set to <NUM> pmol / min, and the flow rate of ammonia was set to <NUM> slm. The flow rate of the raw material gas was adjusted such that the V/III ratio at this time was <NUM>. An AlN single crystal layer was formed as a first buffer layer in a thickness of <NUM> under conditions of a total flow rate of <NUM> slm and a pressure of <NUM> Torr (a first growth step: growth of the first buffer layer).

Subsequently, the temperature of the substrate on which the AlN single crystal layer of the first buffer layer was deposited on the sapphire substrate was set to <NUM>, the flow rate of trimethylaluminum was set to <NUM>µmol/min, and the flow rate of ammonia was set to <NUM> slm. The flow rate of the raw material gas was adjusted such that the V/III ratio at this time was <NUM>. An AlN single crystal layer of <NUM> was formed as a second buffer layer under conditions of a total flow rate of <NUM> slm and a pressure of <NUM> Torr (second growth step; growth of the second buffer layer).

Next, under conditions of a substrate temperature of <NUM>, a flow rate of trimethylaluminum of <NUM>µmol/min, a flow rate of trimethylgallium of <NUM>µmol/min, a flow rate of tetraethylsilane of <NUM>µmol/min, and a flow rate of ammonia of <NUM> slm, an n-type layer <NUM> having an Al composition of <NUM>%, a Ga composition of <NUM>% and an In composition of <NUM>% was formed in a thickness of <NUM>. Meanwhile, the pressure in the apparatus was <NUM> Torr. At this time, a half-value width of an X-ray rocking curve of (<NUM>) plane was <NUM> arcsec.

Then, the substrate temperature was set to <NUM>, and after the temperature was constant, an Al<NUM>Ga<NUM>N barrier layer of <NUM> was formed under the same growth conditions as those for growing the n-type layer, except that the flow rate of tetraethylsilane was <NUM>µmol/min, the flow rate of trimethylaluminum was <NUM>µmol/min, and the flow rate of trimethylgallium was <NUM>µmol/min.

Next, an Al<NUM>Ga<NUM>N well layer of <NUM> was formed under the same conditions as those for growing the n-type layer, except that the flow rate of trimethylgallium was <NUM>µmol/min, and the flow rate of trimethylaluminum was <NUM>µmol/min. The growth of the well layer and the barrier layer was repeated for three times to form a triple quantum well layer. Meanwhile, the pressure in the apparatus was <NUM> Torr.

Thereafter, the supply of trimethylgallium and tetraethylsilane was stopped and the substrate temperature was set to <NUM>. After the temperature was constant, an electron blocking layer <NUM> of <NUM> was formed under the same conditions as those for growing the n-type layer, except that bicyclopentadienyl magnesium was supplied at <NUM>µmol/min. At this time, the Al composition is <NUM>%. Meanwhile, the pressure in the apparatus was <NUM> Torr.

Next, with the substrate temperature as it was, a p-type clad layer <NUM> of <NUM> was formed under the same conditions as those for growing the n-type layer, except that bicyclopentadienyl magnesium was supplied at <NUM>µmol/min. At this time, the Al composition was <NUM>%, the Ga composition was <NUM>%, and the In composition was <NUM>%. Meanwhile, the pressure in the apparatus was <NUM> Torr.

Subsequently, the substrate temperature was changed to <NUM> and the pressure was changed to <NUM> Torr, and thereafter a GaN layer of <NUM> was formed as the p-type contact layer <NUM> under conditions of a flow rate of trimethylgallium of <NUM>µmol/min, a flow rate of ammonia of <NUM> slm, a flow rate of bicyclopentadienyl magnesium of <NUM>µmol/min, and a flow rate of carrier gas (hydrogen) of <NUM> slm. Meanwhile, the pressure in the apparatus was <NUM> Torr. Accordingly, a semiconductor wafer was produced.

The curvature of the surface of the element layer <NUM> (p-type contact layer <NUM>) of the obtained semiconductor wafer was measured by a laser displacement meter method. The curvature of the semiconductor wafer was <NUM>-<NUM>, and the results were shown in Table <NUM>.

The obtained semiconductor wafer was subject to heat treatment in a nitrogen atmosphere at <NUM> for <NUM> minutes. Thereafter, a predetermined resist pattern was formed on the surface of the p-type contact layer <NUM> by photolithography, and a window portion without forming a resist pattern was etched by reactive ion etching until the surface of the n-type layer <NUM> was exposed. Thereafter, a Ti (<NUM>) / Al (<NUM>) /Au (<NUM>) electrode (negative electrode) was formed as the n-electrode <NUM> on the surface of the n-type layer <NUM> by a vacuum evaporation method, and heat treatment was performed under a condition of <NUM> for <NUM> minute in a nitrogen atmosphere.

Subsequently, an Ni (<NUM>) / Au (<NUM>) electrode (positive electrode) was formed as the p-electrode <NUM> on the surface of the p-type contact layer <NUM> by a vacuum evaporation method, and thereafter heat treatment was performed in an oxygen atmosphere at <NUM> for <NUM> minutes to produce a nitride semiconductor light emitting device.

As for the obtained semiconductor light emitting device, the optical output and the wavelength at a driving current of <NUM> mA were <NUM> mW and <NUM>. The results were summarized in Table <NUM>.

A semiconductor wafer and a semiconductor light emitting device were produced under the same conditions as in Example <NUM>, except that the flow rate of trimethylaluminum when forming the buffer layer <NUM> (the first growth step) was <NUM>µmol/min, and the V/III ratio at that time was <NUM>. When the evaluation was performed in the same manner as in Example <NUM>, the optical output and the wavelength at a driving current of <NUM> mA were <NUM> mW and <NUM>, and the curvature of the semiconductor wafer was <NUM>-<NUM>. The results were shown in Table <NUM>.

The buffer layer <NUM> was grown to <NUM> under the conditions same as the second growth step of Example <NUM>, except that the opening time of MOCVD apparatus before introduction of the sapphire substrate was <NUM> minute and the first growth step was not performed.

(Formation of n-type Layer <NUM> and Layers after n-type Layer <NUM>) Growth conditions for the n-type Layer <NUM> and the layers after the n-type layer <NUM> are the same as those in Example <NUM>, then a semiconductor wafer and a semiconductor light emitting device were produced. Further, the half-value width in the (<NUM>) plane of the X-ray rocking curve when the n-type layer was formed under this condition was measured.

As for the obtained semiconductor light emitting device, the optical output and the wavelength at a driving current of <NUM> mA were <NUM> mW and <NUM>, and the curvature of the semiconductor wafer was <NUM>-<NUM>. The results were summarized in Table <NUM>.

Claim 1:
A semiconductor wafer (<NUM>) comprising an element layer (<NUM>) including an n-type layer (<NUM>), an active layer (<NUM>), and a p-type layer (<NUM>) on one surface of a sapphire substrate (<NUM>),
wherein a surface of the element layer (<NUM>) is bent in a convex way,
characterized in that a curvature of said surface of said element layer (<NUM>) is <NUM>-<NUM> to <NUM>-<NUM>, and
the element layer (<NUM>) comprises group III nitride single crystal layers, which are made of AlGaInN layers satisfying a composition represented by AlxInyGazN, wherein x, y, and z are rational numbers satisfying <NUM> ≤ x ≤ <NUM>, <NUM> ≤ y ≦ <NUM>, and <NUM> ≤ z ≤ <NUM>, and x + y + z = <NUM>.