TW202406142A - Nitride semiconductor wafer and manufacturing method thereof - Google Patents

Abstract

The present invention is a nitride semiconductor wafer, which is provided with: a silicon-based substrate; a buffer layer laminated on the silicon-based substrate and containing a nitride semiconductor; and a functional layer laminated on the buffer layer and containing at least GaN layer; the nitride semiconductor wafer is characterized in that the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction in the buffer layer is a concentration distribution having a maximum Fe concentration, and the Fe concentration is from The point where the Fe concentration is the maximum decreases toward the functional layer, the Fe concentration at the point where the Fe concentration is the maximum is 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the function of the buffer layer is The Fe concentration of the top surface on the layer side is 4.0×10 ¹⁷ atoms/cm ³ or less. This provides a nitride semiconductor wafer in which warpage is suppressed.

Description

Nitride semiconductor wafer and manufacturing method thereof

The present invention relates to a nitride semiconductor wafer, and in particular to a nitride semiconductor wafer in which warpage is suppressed.

The nitride semiconductor wafer obtained by sequentially stacking an initial AlN layer, a buffer layer, and a GaN-high electron mobility transistor (HEMT) structure epitaxial layer on a single crystal silicon substrate is used as an epitaxial substrate for power devices. Epitaxial substrates for radio frequency (RF) components.

In addition, wafers obtained by epitaxial growth of nitride semiconductors on silicon (SOI) substrates covered with insulating layers are also used. When epitaxial growth is performed on SOI substrates, compared with single crystal silicon substrates, the warpage of the wafers is smaller. The distortion is large. In order to suppress warpage, it is necessary to design a buffer layer and reduce warpage while observing in-situ warpage data (Patent Document 1).

Although a single crystal silicon substrate can make warpage relatively small, when a nitride semiconductor is epitaxially grown on an SOI substrate, it is difficult to suppress warpage. [Prior technical literature] (patent document)

Patent Document 1: Japanese Patent No. 6473017

[Problem to be solved by the invention]

The present invention has been made to solve the above problems, and an object thereof is to provide a nitride semiconductor wafer in which warpage is suppressed. [Technical means to solve problems]

In order to solve the above problems, the present invention provides a nitride semiconductor wafer, which includes: a silicon-based substrate; a buffer layer laminated on the silicon-based substrate and including a nitride semiconductor; and a functional layer laminated on the buffer layer and at least includes a GaN layer; wherein, the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction in the buffer layer is a concentration distribution that has a point where the Fe concentration is maximum, and the Fe concentration changes from the Fe concentration The maximum point decreases toward the functional layer, the Fe concentration at the point with the maximum Fe concentration is 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the buffer layer on the functional layer side The Fe concentration on the top surface is 4.0×10 ¹⁷ atoms/cm ³ or less.

By doping Fe with such a concentration distribution, warpage can be suppressed without changing the structure of the nitride semiconductor wafer. If the maximum concentration of Fe in the buffer layer is 2.5×10 ¹⁸ atoms/cm ³ or more, warpage can be significantly suppressed. Furthermore, by setting it to 6.0×10 ¹⁸ atoms/cm ³ or less, the Fe concentration on the top surface of the buffer layer can be set to 4.0×10 ¹⁷ atoms/cm ³ or less. If the Fe concentration on the top surface of the buffer layer is 4.0×10 ¹⁷ atoms/cm ³ or less, it can prevent the Fe concentration on the device surface from becoming high due to the memory effect of Fe, thereby degrading the device characteristics.

Furthermore, preferably, the silicon-based substrate is a single crystal silicon substrate or a silicon on insulating layer (SOI) substrate.

In the present invention, it is possible to use a silicon-based substrate in which warpage is large when an SOI substrate is used, so the present invention is particularly effective.

Furthermore, preferably, the buffer layer includes an AlGaN layer and a superlattice layer formed by alternately stacking GaN layers and AlN layers.

By adopting such a structure, warpage can be suppressed more effectively.

Furthermore, the present invention provides a method for manufacturing a nitride semiconductor wafer, which is a method for manufacturing a nitride semiconductor wafer, which includes the following steps: Step (1), stacking a buffer layer containing a nitride semiconductor on a silicon substrate; and, step (2), laminating a functional layer including at least a GaN layer on the buffer layer to manufacture a nitride semiconductor wafer; and, in the aforementioned step (1), flowing in a doping gas for doping Fe, The flow rate of the doping gas is adjusted to set the Fe concentration distribution in the stacking direction in the buffer layer to a concentration distribution having a maximum Fe concentration point, and the Fe concentration moves from the maximum Fe concentration point toward the aforementioned function The layer is reduced, the Fe concentration at the point with the maximum Fe concentration is set to 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the top surface of the buffer layer on the functional layer side is The Fe concentration is set to 4.0×10 ¹⁷ atoms/cm ³ or less.

In this manner, the nitride semiconductor wafer of the present invention with suppressed warpage can be manufactured.

Furthermore, preferably, in the aforementioned step (1), the silicon-based substrate is a single crystal silicon substrate or a silicon-on-insulating layer (SOI) substrate.

In the present invention, it is possible to use a silicon-based substrate in which warpage is large when an SOI substrate is used, so the present invention is particularly effective.

Furthermore, preferably, in the aforementioned step (1), the buffer layer includes an AlGaN layer and a superlattice layer formed by alternately stacking GaN layers and AlN layers.

By adopting such a structure, warpage can be suppressed more effectively. [Efficacy of the invention]

As described above, the present invention can provide a nitride semiconductor wafer obtained by epitaxially growing a nitride semiconductor on a single crystal silicon substrate or an SOI substrate, and a manufacturing method thereof, and Warpage is suppressed without changing the buffer layer and other structures.

As described above, development of a nitride semiconductor wafer in which warpage is suppressed is sought.

The present inventors conducted intensive research on the above-mentioned problems and found that warpage of the nitride semiconductor wafer can be suppressed by appropriately controlling the Fe concentration distribution in the buffer layer of the nitride semiconductor wafer, leading to the completion of the present invention.

That is, the present invention is a nitride semiconductor wafer provided with: a silicon-based substrate; a buffer layer laminated on the silicon-based substrate and containing a nitride semiconductor; and a functional layer laminated on the buffer layer. At least a GaN layer is included; wherein the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction in the buffer layer is a concentration distribution that has a point where the Fe concentration is maximum, and the Fe concentration is from the point where the Fe concentration is maximum The points are reduced toward the functional layer, the Fe concentration at the point with the maximum Fe concentration is 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the top surface of the buffer layer on the side of the functional layer The Fe concentration is 4.0×10 ¹⁷ atoms/cm ³ or less.

The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[Nitride semiconductor wafer] The nitride semiconductor wafer of the present invention will be described using FIG. 1 . In addition, the structure of the nitride semiconductor wafer in FIG. 1 is an example, and the present invention is not limited thereto.

The nitride semiconductor wafer 10 shown in FIG. 1 has: a silicon-based substrate 1; a buffer layer 3 laminated on the silicon-based substrate 1 and containing a nitride semiconductor; and a functional layer 4 laminated on the buffer layer 3. Contains at least a GaN layer. The functional layer 4 is composed of, for example, a channel layer containing GaN (C-GaN) and a barrier layer (not shown) containing AlGaN. The energy gap of the barrier layer is different from that of the channel layer. Furthermore, it is preferable to form a high-resistance GaN layer (withstand voltage layer: R-GaN) between the buffer layer 3 and the channel layer.

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

An initial layer 2 containing AlN with a thickness of 100 to 200 nm can be provided between the silicon substrate 1 and the buffer layer 3 .

The buffer layer 3 is not particularly limited, but preferably includes an AlGaN layer and a superlattice layer in which a GaN layer and an AlN layer are alternately laminated; for example, it can be made to include, for example, 23 nm on an AlGaN layer with a thickness of 100 to 200 nm. Superlattice layers (SLs) are formed by alternately stacking GaN layers with a thickness of 5 to 30 nm and AlN layers with a thickness of 3 to 10 nm.

Here, 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 is a concentration distribution that has a point where the Fe concentration is maximum, and the Fe concentration is from The point where the Fe concentration is the maximum decreases toward the functional layer 4, the Fe concentration at the point where the Fe concentration is the maximum is 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the functional layer 4 of the buffer layer 3 The Fe concentration on the top surface of the side is 4.0×10 ¹⁷ atoms/cm ³ or less. Furthermore, in the present invention, the Fe concentration distribution can be obtained based on the measurement results of SIMS. In addition, the lower limit of the Fe concentration on the top surface of the buffer layer on the functional layer side is not particularly limited, but it can be set to 2.5×10 ¹⁷ atoms/cm ³ or more, for example.

The Fe concentration distribution in the buffer layer will be described more specifically with reference to FIGS. 2 and 3 showing the results of Examples described below. FIG. 2 shows the Fe concentration distribution obtained by SIMS of a nitride semiconductor wafer obtained by epitaxial growth on a single crystal silicon substrate. In addition, FIG. 3 shows the Fe concentration distribution when epitaxial growth is performed on an SOI substrate under the same conditions. In both Figures 2 and 3, there is a point where the Fe concentration is maximum in the buffer layer (near the depth of the horizontal axis in the figure is 1.2 μm), and the Fe concentration decreases (gradually decreases) from this point toward the functional layer side. The Fe concentration on the top surface of the functional layer side of the buffer layer (near the depth of the horizontal axis in the figure is 0.55 μm) is 4.0×10 ¹⁷ atoms/cm ³ or less. From this, it can be seen that the Fe concentration reaches a peak in the buffer layer and decreases (gradually decreases) toward the element layer.

When the highest value of the Fe concentration is less than 2.5×10 ¹⁸ atoms/cm ³ , no significant inhibitory effect on warpage is observed, and if it exceeds 6.0×10 ¹⁸ atoms/cm ³ , it becomes difficult to separate the buffer layer The concentration of the top surface is set to 4.0×10 ¹⁷ atoms/cm ³ or less. If the concentration on the top surface of the buffer layer exceeds 4.0×10 ¹⁷ atoms/cm ³ , the Fe concentration on the device surface becomes high due to the memory effect of Fe, resulting in deterioration of device characteristics.

To achieve such an Fe concentration distribution, a metal organic vapor deposition (MOCVD) device can be used, for example, to flow Cp ₂ Fe into approximately the lower 1/3 of the superlattice layer and the AlGaN layer below it during epitaxial growth. (dicyclopentadienyl iron) and other doping gases, and adjust its flow rate to dope Fe at a desired concentration. By doping Fe in this way, warpage can be suppressed without changing the structure of the buffer layer not only when using an SOI substrate but also when using a single crystal silicon substrate, but when using an SOI substrate, a better Remarkable effect.

It is preferable to provide a high-resistance GaN layer (withstand voltage layer) with a thickness of 300 to 900 nm as the functional layer 4 on the buffer layer 3 . By providing such a high-resistance layer between the element layer and the buffer layer, it is possible to more reliably suppress the worsening of the current collapse phenomenon and the lateral leakage current at high temperatures, and to more reliably suppress Fe from being mixed into the channel layer, so that it is possible to Prevents deterioration of forward characteristics such as mobility decrease. A channel layer including a GaN layer serving as an element layer is formed on the high-resistance GaN layer. Although not shown in FIG. 1 , by forming a barrier layer including an AlGaN layer on a channel layer including a GaN layer, and providing a source, a drain, and a gate, it is possible to produce, for example, a high electron mobility transistor ( HEMT).

[Method for manufacturing a nitride semiconductor wafer] In addition, the present invention is a method for manufacturing a nitride semiconductor wafer. It is a method for manufacturing a nitride semiconductor wafer, which includes the following steps: Step (1): A buffer layer including a nitride semiconductor is laminated on the buffer layer; and, step (2), a functional layer including at least a GaN layer is laminated on the buffer layer to produce a nitride semiconductor wafer, and, in the aforementioned step (1), an inflow The doping gas used to dope Fe is adjusted to the flow rate of the doping gas, thereby setting the Fe concentration distribution in the lamination direction in the buffer layer to a concentration distribution having a maximum Fe concentration, and the Fe concentration is From the point of maximum Fe concentration to the functional layer, the Fe concentration at the point of maximum Fe concentration is set to 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the buffer is The Fe concentration of the top surface of the layer on the functional layer side is 4.0×10 ¹⁷ atoms/cm ³ or less.

The nitride semiconductor wafer of the present invention can be manufactured in this manner. Hereinafter, the method for manufacturing a nitride semiconductor wafer of the present invention will be described in detail.

[Step (1)] Step (1) is a step of laminating a buffer layer containing a nitride semiconductor on a silicon substrate.

In this step, first, a silicon-based substrate such as a single crystal silicon substrate and a silicon on insulating layer (SOI) substrate is prepared. Then, it is only necessary to epitaxially grow a buffer layer including a nitride semiconductor on the silicon substrate in the MOCVD device. Alternatively, an initial layer including AlN may be epitaxially grown on a silicon substrate, and a buffer layer including a nitride semiconductor may be epitaxially grown thereon. As described above, the buffer layer preferably includes an AlGaN layer and a superlattice layer in which GaN layers and AlN layers are alternately laminated.

During epitaxial growth, trimethylaluminum (TMAl) as an aluminum (Al) source, TMGa as a gallium (Ga) source, and NH ₃ as a nitrogen (N) source can be used, but are not limited to these. In addition, the carrier gas can be N ₂ and H ₂ , or any one of them, and the process temperature is preferably about 900 to 1200°C, for example.

In the present invention, the Fe concentration distribution in the stacking direction in the buffer layer is a concentration distribution that has a point where the Fe concentration is the maximum, and the Fe concentration decreases from the point where the Fe concentration is the maximum toward the functional layer, so that the Fe concentration is the maximum The Fe concentration in the dot is 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the Fe concentration on the top surface of the functional layer side of the buffer layer is 4.0×10 ¹⁷ atoms/ cm ³ or less.

To achieve such an Fe concentration distribution, a metal organic vapor deposition (MOCVD) device can be used, for example, to flow Cp ₂ Fe into approximately the lower 1/3 of the superlattice layer and the AlGaN layer below it during epitaxial growth. (dicyclopentadienyl iron) and other doping gases, and adjust its flow rate to dope Fe at a desired concentration.

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

In this step, appropriate functional layers may be stacked by epitaxial growth according to the application of the nitride semiconductor wafer. For example, the high-resistance GaN layer as described above can be epitaxially grown in a MOCVD device, a GaN layer as an element layer can be epitaxially grown thereon, and a barrier layer including an AlGaN layer can be epitaxially grown thereon. By arranging a source electrode, a drain electrode, and a gate electrode thereon, a high electron mobility transistor (HEMT), for example, can be made.

In the nitride semiconductor wafer produced in this manner, the Fe concentration distribution in the buffer layer is appropriately controlled, thereby suppressing warpage. [Example]

Hereinafter, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited to these examples.

(Example 1) The following single crystal silicon substrate and SOI substrate were prepared as silicon-based substrates. (1) Single crystal silicon substrate 150mmφ p-type (111) 675μm Oi: 25.6ppma (ASTM79) 5000Ωcm (2) SOI substrate 150mmφ SOI layer: 100nm/buried oxide (BOX) layer: 200nm/Si substrate: 675μm SOI layer: ( 111) CZ 1kΩcm N (nitrogen): 5e14atoms/cm ³ Oi: 25.6ppma (ASTM79) Si substrate: (100) 8mΩcm Oi: 16ppma (ASTM79)

Next, epitaxial growth was performed on these two wafers in the same batch using a MOCVD apparatus, and nitride semiconductor wafers were produced under the following conditions.

An initial layer containing AlN is initially formed with a thickness of 150 nm, followed by growth of an AlGaN layer with a thickness of 160 nm. At this time, Fe doping was started by flowing in Cp ₂ Fe at a flow rate of 50 sccm. Then, a GaN layer with a thickness of 25 nm and an AlN layer with a thickness of 4.2 nm were grown alternately. When eight pairs of GaN layers and AlN layers have grown, the supply of Cp ₂ Fe is stopped. Then, GaN layers and AlN layers are grown alternately to form a total of 23 pairs of superlattice layers (SLs), and a buffer layer including an AlGaN layer and a superlattice layer is formed. Then a 670nm high-resistance GaN layer is grown, and then a 200nm GaN layer as a channel layer is grown.

Then, two wafers were taken out and the amount of warpage was measured. The results are shown in Table 1. Furthermore, the Fe concentration in the depth direction was measured using SIMS. The Fe concentration distribution of the wafer using the single crystal silicon substrate is shown in Figure 2, and the Fe concentration distribution of the wafer using the SOI substrate is shown in Figure 3. The maximum Fe concentration in the buffer layer of any wafer is 6.0×10 ¹⁸ atoms/cm ³ , and the Fe concentration on the top surface of the buffer layer is 4.0×10 ¹⁷ atoms/cm ³ . As can be seen from Table 1, compared with Comparative Examples 1 and 2 described below, the amount of warpage of any wafer in Example 1 is suppressed.

Furthermore, in the present invention, a flat single crystal silicon substrate as a reference is placed on a three-point support platform to expose a horizontal surface, and the amount of warpage is measured based on the difference from the flat surface.

(Example 2) A nitride semiconductor wafer was produced under the same conditions as in Example 1, except that the flow rate of Cp ₂ Fe was 20 sccm. As shown in Figures 2 and 3, the maximum Fe concentration in the buffer layer of any wafer is 2.5×10 ¹⁸ atoms/cm ³ , and 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, although none of the wafers is inferior to the level of Example 1, compared with Comparative Examples 1 and 2, warpage is suppressed.

(Comparative Example 1) A nitride semiconductor wafer was produced in the same manner as in Example 1, except that the flow rate of Cp ₂ Fe was further reduced to set the maximum Fe concentration in the buffer layer to 2.0×10 ¹⁸ atoms/cm ³ . As shown in Table 1, although the warpage of any wafer of Comparative Example 1 was improved compared to Comparative Example 2, the significant effect of Examples 1 and 2 was not observed.

(Comparative Example 2) A nitride semiconductor wafer was produced under the same conditions as in Example 1 except that Cp ₂ Fe was not flowed. As shown in Table 1, it can be seen that compared with Examples 1 and 2, the warpage of any wafer in Comparative Example 2 is larger.

[Table 1]

As described above, it can be seen that the present invention can provide a nitride semiconductor wafer obtained by epitaxially growing a nitride semiconductor on a single crystal silicon substrate or an SOI substrate, and a manufacturing method thereof. And warpage is suppressed without changing the buffer layer and other structures.

In addition, the present invention is not limited to the above-mentioned embodiment. The above-mentioned embodiments are only examples, and anything that has substantially the same structure as the technical idea described in the patent application scope of the present invention and performs the same effect is included in the technical scope of the present invention.

1: Silicon substrate 2: Initial layer 3: Buffer layer 4: Functional layer 10:Nitride semiconductor wafer

FIG. 1 is a schematic diagram showing an example of the nitride semiconductor wafer of the present invention. FIG. 2 is a result obtained by measuring the Fe concentration distribution in the stacking direction of the nitride semiconductor wafer (silicon-based substrate: single crystal silicon substrate) produced in Examples 1 and 2 using secondary ion mass spectrometry (SIMS). FIG. 3 is the result of measuring the Fe concentration distribution in the stacking direction of the nitride semiconductor wafer (silicon-based substrate: SOI substrate) produced in Examples 1 and 2 using secondary ion mass spectrometry (SIMS).

Domestic storage information (please note in order of storage institution, date and number) without Overseas storage information (please note in order of storage country, institution, date, and number) without

1: Silicon substrate

2: Initial layer

3: Buffer layer

4: Functional layer

10:Nitride semiconductor wafer

Claims (6)

A nitride semiconductor wafer, which is provided with: a silicon-based substrate; a buffer layer that is laminated on the silicon-based substrate and includes a nitride semiconductor; and a functional layer that is laminated on the buffer layer and includes at least a GaN layer; the The nitride semiconductor wafer is characterized in that the buffer layer is doped with Fe, and the Fe concentration distribution in the stacking direction in the buffer layer is a concentration distribution having a point where the Fe concentration is maximum, and the Fe concentration changes from the Fe concentration The maximum point decreases toward the functional layer, the Fe concentration at the point with the maximum Fe concentration is 2.5×10 ¹⁸ atoms/cm ³ or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the buffer layer on the functional layer side The Fe concentration on the top surface is 4.0×10 ¹⁷ atoms/cm ³ or less. The nitride semiconductor wafer according to claim 1, wherein the silicon-based substrate is a single-crystal silicon substrate or a silicon-on-insulation (SOI) substrate. The nitride semiconductor wafer according to claim 1 or 2, wherein the buffer layer includes an AlGaN layer and a superlattice layer formed by alternately stacking GaN layers and AlN layers. A method for manufacturing a nitride semiconductor wafer is a method for manufacturing a nitride semiconductor wafer, which is characterized by including the following steps: step (1), stacking a buffer layer containing a nitride semiconductor on a silicon substrate; and, step (2), laminate a functional layer including at least a GaN layer on the buffer layer to produce a nitride semiconductor wafer; and, in the aforementioned step (1), flow in the doping gas for doping Fe, and adjust the doping The flow rate of the impurity gas is used to set the Fe concentration distribution in the stacking direction in the buffer layer to a concentration distribution that has a point where the Fe concentration is the maximum, and the Fe concentration decreases from the point where the Fe concentration is the 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 or more and 6.0×10 ¹⁸ atoms/cm ³ or less, and the Fe concentration on the top surface of the buffer layer on the functional layer side is set to It is 4.0×10 ¹⁷ atoms/cm ³ or less. The method for manufacturing a nitride semiconductor wafer according to claim 4, wherein in the step (1), the silicon substrate is a single crystal silicon substrate or a silicon on insulating layer (SOI) substrate. The method for manufacturing a nitride semiconductor wafer according to claim 4 or 5, wherein in the aforementioned step (1), the aforementioned buffer layer is configured to include an AlGaN layer and a superstructure formed by alternately stacking a GaN layer and an AlN layer. lattice layer.

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