Nitride semiconductor wafer and manufacturing method thereof

Abstract

To provide a nitride semiconductor wafer in which warpage is suppressed.SOLUTION: The nitride semiconductor wafer includes: a silicon-based substrate; a buffer layer formed of a nitride semiconductor which is laminated on the silicon-based substrate; and a functional layer including at least a GaN layer which is laminated on the buffer layer. The buffer layer is doped with Fe. An Fe concentration distribution in the laminating direction in the buffer layer has a point at which the Fe concentration is maximum, and is a concentration distribution in which the Fe concentration decreases from the point at which the Fe concentration is maximum toward the functional layer. The Fe concentration at the point at which the Fe concentration is maximum is 2.5×1018atoms / cm3 or more and 6.0×1018atoms / cm3 or less, and the Fe concentration of the upper surface of the buffer layer on the functional layer side is 4.0×1017atoms / cm3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a nitride semiconductor wafer, and more particularly to a nitride semiconductor wafer with reduced warpage. [Background technology]

[0002] Nitride semiconductor wafers, which have an initial AlN layer, a buffer layer, and a GaN-HEMT structure epitaxial layer stacked in that order on a silicon single crystal substrate, are used as epitaxial substrates for power devices and RF devices.

[0003] Wafers in which nitride semiconductors are epitaxially grown on SOI substrates are also used, but epitaxial growth on SOI substrates results in greater wafer warpage than silicon single crystal substrates. To suppress warpage, it is necessary to devise a buffer layer and reduce warpage while monitoring in-situ warpage data (Patent Document 1).

[0004] Although silicon single crystal substrates can be made to have relatively little warping, it is difficult to suppress warping when epitaxially growing nitride semiconductors on SOI substrates. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6473017 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made to solve the above problems, and has an object to provide a nitride semiconductor wafer in which warpage is suppressed. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides: A nitride semiconductor wafer comprising: a silicon-based substrate; a buffer layer made of a nitride semiconductor laminated on the silicon-based substrate; and a functional layer including at least a GaN layer laminated on the buffer layer, the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction of the buffer layer has a point where the Fe concentration is maximum and decreases from the point where the Fe concentration is maximum toward the functional layer; The Fe concentration at the point where the Fe concentration is maximum is 2.5×10 18 atoms / cm 3 Over 6.0 x 10 18 atoms / cm 3 and the Fe concentration in the upper surface of the buffer layer on the functional layer side is 4.0 × 10 17 atoms / cm 3 The present invention provides a nitride semiconductor wafer having the following:

[0008] Doping with Fe at such a concentration distribution can suppress warpage without changing the structure of the nitride semiconductor wafer. The highest Fe concentration in the buffer layer is 2.5 × 10 18 atoms / cm 3 If the value is 6.0×10 or more, warpage can be significantly suppressed. 18 atoms / cm 3 By adjusting the Fe concentration on the top surface of the buffer layer to 4.0×10 17 atoms / cm 3 The Fe concentration on the top surface of the buffer layer can be reduced to 4.0×10 or less. 17 atoms / cm 3 If the content is equal to or less than this, it is possible to prevent the Fe concentration on the device surface from becoming high due to the memory effect of Fe, which would otherwise deteriorate the device characteristics.

[0009] The silicon-based substrate is preferably a silicon single crystal substrate or an SOI (silicon-on-insulator) substrate.

[0010] In the present invention, such silicon-based substrates can be used, but the present invention is particularly effective when an SOI substrate is used, since it is prone to large warpage.

[0011] Preferably, the buffer layer is made up of an AlGaN layer and a superlattice layer in which GaN layers and AlN layers are alternately stacked.

[0012] Such a structure is more effective in suppressing warpage.

[0013] The present invention also provides a method for producing a nitride semiconductor wafer, comprising the steps of: (1) forming a buffer layer made of a nitride semiconductor on a silicon-based substrate; and (2) A step of manufacturing a nitride semiconductor wafer by stacking a functional layer including at least a GaN layer on the buffer layer. and In the step (1), a doping gas for doping with Fe is supplied, and a flow rate of the doping gas is adjusted to make the Fe concentration distribution in the stacking direction in the buffer layer have a point where the Fe concentration is maximum and decrease from the point of maximum Fe concentration toward the functional layer; The Fe concentration at the point where the Fe concentration is maximum is 2.5 × 10 18 atoms / cm 3 Over 6.0 x 10 18 atoms / cm 3 or less, and the Fe concentration in the upper surface of the buffer layer on the functional layer side is 4.0 × 10 17 atoms / cm 3 The present invention provides a method for producing a nitride semiconductor wafer as follows.

[0014] The nitride semiconductor wafer of the present invention with suppressed warpage can be produced in this manner.

[0015] In the step (1), the silicon-based substrate is preferably a silicon single crystal substrate or an SOI (silicon-on-insulator) substrate.

[0016] In the present invention, such silicon-based substrates can be used, but the present invention is particularly effective when an SOI substrate is used, since it is prone to large warpage.

[0017] In the step (1), the buffer layer preferably comprises an AlGaN layer and a superlattice layer in which GaN layers and AlN layers are alternately stacked.

[0018] Such a structure is more effective in suppressing warpage. [Effects of the Invention]

[0019] As described above, the present invention can provide a nitride semiconductor wafer in which a nitride semiconductor is epitaxially grown on a silicon single crystal substrate or an SOI substrate, and in which warpage is suppressed without changing the structure of the buffer layer, etc., and a method for manufacturing the same. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a schematic diagram showing an example of a nitride semiconductor wafer of the present invention. [Figure 2] 1 shows the results of measuring the Fe concentration distribution in the stacking direction of the nitride semiconductor wafers (silicon-based substrates: silicon single crystal substrates) produced in Examples 1 and 2 by SIMS. [Figure 3] 1 shows the results of measuring the Fe concentration distribution in the stacking direction of the nitride semiconductor wafers (silicon-based substrates: SOI substrates) produced in Examples 1 and 2 by SIMS. DETAILED DESCRIPTION OF THE INVENTION

[0021] As described above, there has been a demand for the development of nitride semiconductor wafers with reduced warpage.

[0022] As a result of extensive research into the above-mentioned problems, the inventors have found that warpage of a nitride semiconductor wafer can be suppressed by appropriately controlling the Fe concentration distribution in the buffer layer of the nitride semiconductor wafer, and have completed the present invention.

[0023] That is, the present invention provides a nitride semiconductor wafer including a silicon substrate, a buffer layer made of a nitride semiconductor stacked on the silicon substrate, and a functional layer including at least a GaN layer stacked on the buffer layer, wherein the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction in the buffer layer has a point where the Fe concentration is maximum, and the Fe concentration decreases from the point where the Fe concentration is maximum toward the functional layer, and the Fe concentration at the point where the Fe concentration is maximum is 2.5 × 10 18 atoms / cm 3 Over 6.0 x 10 18 atoms / cm 3 and the Fe concentration in the upper surface of the buffer layer on the functional layer side is 4.0 × 10 17 atoms / cm 3 The nitride semiconductor wafer is as follows:

[0024] The present invention will be described in detail below, but the present invention is not limited thereto.

[0025] [Nitride semiconductor wafers] The nitride semiconductor wafer of the present invention will be described with reference to Fig. 1. Note that the structure of the nitride semiconductor wafer in Fig. 1 is an example, and the present invention is not limited to this.

[0026] 1 includes a silicon substrate 1, a buffer layer 3 made of a nitride semiconductor layered on the silicon substrate 1, and a functional layer 4 including at least a GaN layer layered on the buffer layer 3. The functional layer 4 is composed of, for example, a channel layer (C-GaN) made of GaN and a barrier layer (not shown) made of AlGaN having a band gap different from that of the channel layer. It is also preferable to form a high-resistivity GaN layer (breakdown layer: R-GaN) between the buffer layer 3 and the channel layer.

[0027] Here, the silicon-based substrate 1 is not particularly limited, but is preferably a silicon single crystal substrate or an SOI (silicon-on-insulator) substrate, for example, a 150 mmφ, 675 μm, (111) Si substrate or a 150 mmφ, 675 μm, (111) SOI substrate.

[0028] An initial layer 2 made of AlN and having a thickness of 100 to 200 nm may be provided between the silicon substrate 1 and the buffer layer 3 .

[0029] The buffer layer 3 is not particularly limited, but is preferably composed of an AlGaN layer and a superlattice layer in which GaN layers and AlN layers are alternately stacked. For example, the buffer layer 3 may be composed of superlattice layers (SLs) in which, for example, 23 pairs of GaN layers each having a thickness of 5 to 30 nm and AlN layers each having a thickness of 3 to 10 nm are alternately stacked on an AlGaN layer having a thickness of 100 to 200 nm.

[0030] In the nitride semiconductor wafer of the present invention, the buffer layer 3 is doped with Fe, and the Fe concentration distribution in the stacking direction in the buffer layer 3 has a point where the Fe concentration is maximum, and the Fe concentration decreases from the point where the Fe concentration is maximum toward the functional layer 4, and the Fe concentration at the point where the Fe concentration is maximum is 2.5 × 10 18 atoms / cm 3 Over 6.0 x 10 18 atoms / cm 3 or less, and the Fe concentration on the upper surface of the buffer layer 3 on the functional layer 4 side is 4.0 × 10 17 atoms / cm 3In the present invention, the Fe concentration distribution can be determined from the results of SIMS measurements.

[0031] The Fe concentration distribution in the buffer layer will be explained in more detail with reference to Figures 2 and 3, which show the results of an example described later. Figure 2 shows the Fe concentration distribution by SIMS of a nitride semiconductor wafer epitaxially grown on a silicon single crystal substrate. Figure 3 shows the Fe concentration distribution when epitaxially grown on an SOI substrate under similar conditions. In both Figures 2 and 3, there is a point in the buffer layer where the Fe concentration is maximum (near a depth of 1.2 μm on the horizontal axis in the figure), and from this point the Fe concentration decreases (gradually decreases) toward the functional layer side, reaching an Fe concentration of 4.0 × 10 at the top surface of the buffer layer on the functional layer side (near a depth of 0.55 μm on the horizontal axis in the figure). 17 atoms / cm 3 As can be seen, the Fe concentration peaks in the buffer layer and decreases (gradually decreases) toward the device layer.

[0032] The maximum Fe concentration was 2.5 × 10 18 atoms / cm 3 If the value is lower than 6.0 × 10, no significant suppression effect on warpage is observed. 18 atoms / cm 3 When the concentration of the buffer layer is over 4.0×10 17 atoms / cm 3 It becomes difficult to achieve a concentration of 4.0×10 or less on the top surface of the buffer layer. 17 atoms / cm 3 If the temperature exceeds this value, the Fe concentration on the device surface increases due to the Fe memory effect, deteriorating the device characteristics.

[0033] To achieve this Fe concentration distribution, a doping gas such as Cp2Fe (biscyclopentadienyl iron) can be introduced into the MOCVD apparatus during epitaxial growth of the lower third of the superlattice layer and the underlying AlGaN layer, and the flow rate can be adjusted to achieve the desired Fe doping concentration. Doping with Fe in this way can suppress warpage without changing the buffer layer structure, not only when an SOI substrate is used, but also when a silicon single crystal substrate is used, but the effect is more pronounced when an SOI substrate is used.

[0034] As the functional layer 4, a high-resistivity GaN layer (breakdown layer) having a thickness of 300 to 900 nm is preferably provided on the buffer layer 3. By providing such a high-resistivity layer between the device layer and the buffer layer, it is possible to more reliably suppress the deterioration of the current collapse phenomenon and lateral leakage current at high temperatures, and it is also possible to more reliably suppress the incorporation of Fe into the channel layer, thereby preventing degradation of forward characteristics such as a decrease in mobility. A channel layer made of a GaN layer, which serves as the device layer, is formed on the high-resistivity GaN layer. Although not shown in FIG. 1, a barrier layer made of an AlGaN layer can be formed on the channel layer made of the GaN layer, and by providing a source electrode, a drain electrode, and a gate electrode, for example, a high electron mobility transistor (HEMT) can be formed.

[0035] [Method for manufacturing nitride semiconductor wafers] The present invention also provides a method for producing a nitride semiconductor wafer, comprising: (1) a step of stacking a buffer layer made of a nitride semiconductor on a silicon-based substrate; and (2) a step of stacking a functional layer including at least a GaN layer on the buffer layer to produce a nitride semiconductor wafer, wherein in the step (1), a doping gas for doping with Fe is flowed and a flow rate of the doping gas is adjusted to make the Fe concentration distribution in the stacking direction in the buffer layer a concentration distribution having a point where the Fe concentration is maximum and decreasing from the point where the Fe concentration is maximum toward the functional layer, and the Fe concentration at the point where the Fe concentration is maximum is 2.5×10 18 atoms / cm 3Over 6.0 x 10 18 atoms / cm 3 or less, and the Fe concentration in the upper surface of the buffer layer on the functional layer side is 4.0 × 10 17 atoms / cm 3 The method for producing a nitride semiconductor wafer is as follows.

[0036] The nitride semiconductor wafer of the present invention can be produced in this manner. The method for producing the nitride semiconductor wafer of the present invention will be described in detail below.

[0037] [Process (1)] Step (1) is a step of depositing a buffer layer made of a nitride semiconductor on a silicon-based substrate.

[0038] In this process, first, a silicon-based substrate such as a silicon single crystal substrate or an SOI (silicon-on-insulator) substrate is prepared. Next, a buffer layer made of a nitride semiconductor is epitaxially grown on the silicon-based substrate in an MOCVD apparatus. Alternatively, an initial layer made of AlN may be epitaxially grown on the silicon-based substrate, and then a buffer layer made of a nitride semiconductor may be epitaxially grown on top of that. As described above, the buffer layer is preferably made of an AlGaN layer and a superlattice layer in which GaN and AlN layers are alternately stacked.

[0039] During epitaxial growth, trimethylaluminum (TMAl) can be used as an Al source, TMGa can be used as a Ga source, and NH can be used as an N source, but these are not limited to these. The carrier gas can be N and / or H, and the process temperature is preferably set to, for example, about 900 to 1200°C.

[0040] In the present invention, the Fe concentration distribution in the stacking direction in the buffer layer has a point where the Fe concentration is maximum, and the Fe concentration decreases from the point where the Fe concentration is maximum toward the functional layer, and the Fe concentration at the point where the Fe concentration is maximum is 2.5 × 10 18 atoms / cm 3Over 6.0 x 10 18 atoms / cm 3 or less, and the Fe concentration on the upper surface of the buffer layer on the functional layer side is 4.0 × 10 17 atoms / cm 3 The following applies.

[0041] To achieve such an Fe concentration distribution, a doping gas such as CpFe (biscyclopentadienyl iron) is introduced into the MOCVD apparatus during epitaxial growth of, for example, the lower third of the superlattice layer and the underlying AlGaN layer, and the flow rate is adjusted to achieve the desired Fe doping concentration.

[0042] [Process (2)] Step (2) is a step of manufacturing a nitride semiconductor wafer by stacking a functional layer including at least a GaN layer on a buffer layer.

[0043] In this process, appropriate functional layers may be epitaxially grown depending on the intended use of the nitride semiconductor wafer. For example, in an MOCVD apparatus, a high-resistivity GaN layer as described above may be epitaxially grown, a GaN layer to serve as the device layer may be epitaxially grown on top of that, and a barrier layer made of an AlGaN layer may be epitaxially grown on top of that. By providing a source electrode, a drain electrode, and a gate electrode on top of that, a high electron mobility transistor (HEMT), for example, may be formed.

[0044] The nitride semiconductor wafer produced in this manner has an Fe concentration distribution in the buffer layer that is appropriately controlled, and thus warpage is suppressed. [Example]

[0045] EXAMPLES The present invention will be specifically explained below using examples and comparative examples, but the present invention is not limited to these.

[0046] Example 1 As silicon-based substrates, the following silicon single crystal substrates and SOI substrates were prepared. (1) Single crystal silicon substrate 150mmφ p-Type(111) 675μm Oi:25.6ppmaASTM79 5000Ωcm (2) SOI substrate 150mmφ SOI layer: 100nm / Box layer: 200nm / Si substrate: 675μm SOI layer: (111) CZ 1kΩcm N (nitrogen): 5e14 atoms / cm 3 Oi:25.6ppm ASTM79 Si substrate:(100) 8mΩcm Oi:16ppmaASTM79

[0047] Next, these two wafers were subjected to epitaxial growth in the same batch in an MOCVD apparatus to produce nitride semiconductor wafers under the following conditions.

[0048] First, a 150-nm-thick initial layer of AlN was grown, followed by a 160-nm-thick AlGaN layer. Fe doping was initiated by flowing Cp2Fe at a flow rate of 50 sccm. Next, 25-nm-thick GaN layers and 4.2-nm-thick AlN layers were grown alternately. The supply of Cp2Fe was stopped after eight pairs of GaN and AlN layers had been grown. Alternating GaN and AlN layers were then grown, forming a total of 23 pairs of superlattice layers (SLs), forming a buffer layer consisting of an AlGaN layer and a superlattice layer. Next, a 670-nm-thick high-resistivity GaN layer was grown, followed by a 200-nm-thick GaN layer, which would become the channel layer.

[0049] After that, the two wafers were taken out and the amount of warpage was measured. The results are shown in Table 1. In addition, the Fe concentration in the depth direction was measured by SIMS. The Fe concentration distribution in the wafer using a silicon single crystal substrate is shown in Figure 2, and the Fe concentration distribution in the wafer using an SOI substrate is shown in Figure 3. The maximum Fe concentration in the buffer layer of both wafers was 6.0 x 10 18 atoms / cm 3 The Fe concentration on the top surface of the buffer layer is 4.0×10 17 atoms / cm 3As is clear from Table 1, it can be seen that the amount of warpage was suppressed in all wafers in Example 1 compared to Comparative Examples 1 and 2, which will be described later.

[0050] In the present invention, a flat silicon single crystal substrate was placed on a three-point support stage as a reference, and the horizontal plane was set out, and the amount of warpage was measured by the difference from this plane.

[0051] Example 2 Nitride semiconductor wafers were produced under the same conditions as in Example 1, except that the flow rate of Cp2Fe was set to 20 sccm. As shown in Figures 2 and 3, the maximum Fe concentration in the buffer layer of each wafer was 2.5 × 10 18 atoms / cm 3 The Fe concentration on the top surface of the buffer layer is 2.5×10 17 atoms / cm 3 As shown in Table 1, it can be seen that in Example 2, the warpage of all wafers was suppressed compared to Comparative Examples 1 and 2, although not as much as in Example 1.

[0052] (Comparative Example 1) The flow rate of Cp2Fe was further reduced to a maximum Fe concentration of 2.0 × 10 18 atoms / cm 3 Nitride semiconductor wafers were manufactured in the same manner as in Example 1, except that: As shown in Table 1, in Comparative Example 1, all wafers had improved warpage compared to Comparative Example 2, but the effect was not as significant as in Examples 1 and 2.

[0053] (Comparative Example 2) Except for not flowing Cp2Fe, nitride semiconductor wafers were produced under the same conditions as in Example 1. As shown in Table 1, it can be seen that all wafers in Comparative Example 2 had larger warpage than those in Examples 1 and 2.

[0054] [Table 1]

[0055] As described above, it has become clear that the present invention can provide a nitride semiconductor wafer in which a nitride semiconductor is epitaxially grown on a silicon single crystal substrate or an SOI substrate, and in which warpage is suppressed without changing the structure of the buffer layer, etc., and a method for manufacturing the same.

[0056] The present invention is not limited to the above-described embodiments. The above-described embodiments are merely examples, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits similar effects is included within the technical scope of the present invention. [Explanation of symbols]

[0057] 1...silicon substrate, 2...initial layer, 3...buffer layer, 4...functional layer, 10...Nitride semiconductor wafer.

Claims

1. A nitride semiconductor wafer comprising: a silicon-based substrate; a buffer layer made of a nitride semiconductor laminated on the silicon-based substrate; and a functional layer including at least a GaN layer laminated on the buffer layer, the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction of the buffer layer has a point where the Fe concentration is maximum and decreases from the point where the Fe concentration is maximum toward the functional layer; The Fe concentration at the point where the Fe concentration is maximum is 2.5×10 １８ atoms / cm ３ Above 6.0 x 10 １８ atoms / cm ３ and the Fe concentration in the upper surface of the buffer layer on the functional layer side is 4.0 × 10 １７ atoms / cm ３ is less than or equal to: The nitride semiconductor wafer is characterized in that the silicon-based substrate is an SOI (silicon-on-insulator) substrate.

2. 2. The nitride semiconductor wafer according to claim 1, wherein the buffer layer comprises an AlGaN layer and a superlattice layer in which GaN layers and AlN layers are alternately stacked.

3. A method for manufacturing a nitride semiconductor wafer, comprising: (1) forming a buffer layer made of a nitride semiconductor on a silicon-based substrate; and (2) A step of manufacturing a nitride semiconductor wafer by stacking a functional layer including at least a GaN layer on the buffer layer. and In the step (1), a doping gas for doping with Fe is supplied, and a flow rate of the doping gas is adjusted to make the Fe concentration distribution in the stacking direction in the buffer layer have a point where the Fe concentration is maximum and decrease from the point where the Fe concentration is maximum toward the functional layer; The Fe concentration at the point where the Fe concentration is maximum is set to 2.5×10 １８ atoms / cm ３ Above 6.0 x 10 １８ atoms / cm ３ or less, and the Fe concentration in the upper surface of the buffer layer on the functional layer side is 4.0 × 10 １７ atoms / cm ３ and A method for producing a nitride semiconductor wafer, wherein in the step (1), the silicon-based substrate is an SOI (silicon-on-insulator) substrate.

4. 4. The method for producing a nitride semiconductor wafer according to claim 3, wherein in the step (1), the buffer layer comprises an AlGaN layer and a superlattice layer in which GaN layers and AlN layers are alternately stacked.

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