JP2016154221A - Semiconductor substrate and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor substrate and a semiconductor device, which achieve less warpage.SOLUTION: A semiconductor substrate is formed by setting a rocking curve half width of a (002) plane of an AlN layer 12 measured by X-ray diffraction at not greater than 1500 seconds when a GaN-based semiconductor layer 14 is formed via the AlN layer 12 formed on top of a SiC substrate 10, and by forming the GaN-based semiconductor layer 14 on the AlN layer 12 to make compression stress occur on the GaN-based semiconductor layer 14 on the AlN layer 12 which has improved crystallinity.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a semiconductor substrate and a semiconductor device, for example, a semiconductor substrate and a semiconductor device in which an AlN layer is formed on a Si substrate.

  A semiconductor device using a gallium nitride (GaN) -based semiconductor is used as a power element that operates at a high frequency and a high output, a light emitting diode or a laser diode that emits light at a short wavelength. Of these semiconductor devices, FETs such as high electron mobility transistors (HEMTs) and laser diodes as light emitting devices are suitable for performing amplification in high frequency bands such as microwaves, quasi-millimeter waves, and millimeter waves. (LD) and light emitting diodes (LEDs) are being developed.

  In general, a sapphire substrate, a SiC (silicon carbide) substrate, or the like is used as a substrate for growing a GaN-based semiconductor layer. Since sapphire substrates and SiC substrates are expensive, a technique for growing a GaN-based semiconductor layer on a Si (silicon) substrate has been developed. Since Si and Ga easily react, an AlN (aluminum nitride) layer is provided as a barrier layer between the Si substrate and the GaN-based semiconductor layer. (For example, patent document 1). It is known that when forming a GaN layer on an AlN layer, the AlGaN layer is formed between the AlN layer and the GaN layer, thereby improving the crystallinity of the GaN layer and reducing warpage (for example, , Patent Document 1)

JP 2008-166349 A

  However, it has been found that even if an AlGaN layer is provided on the AlN layer, the warpage may not be reduced. An object of the present invention is to provide a semiconductor substrate and a semiconductor device with small warpage.

  According to the present invention, an AlN layer having a rocking curve half-value width of (002) plane by X-ray diffraction formed in contact with a Si substrate of 1500 seconds or less, and a GaN-based semiconductor layer formed on the AlN layer, A semiconductor substrate and a semiconductor device are provided. According to the present invention, it is possible to provide a semiconductor substrate and a semiconductor device with small warpage.

  The said structure WHEREIN: The curvature radius of the curvature of the said semiconductor substrate can be set as the structure which is more than +/- 25m. In the above configuration, the warp amount of the semiconductor substrate may be ± 50 μm or less when the size of the semiconductor substrate is 4 inches.

The said structure WHEREIN: The said GaN-type semiconductor layer can be set as the structure which receives compressive stress from the said AlN layer. In the above structure, the GaN-based semiconductor layer is composed includes an _Al x _{Ga 1-x} N layer and GaN layer formed on the _Al x _{Ga 1-x} N layer, the _Al x _{Ga 1-x} N layer The a-axis length may be configured such that A <0.0077x + 0.3189, where the a-axis length is A nm.

The said structure WHEREIN: The film thickness of the said AlN layer can be set as the structure which is 100 nm or more. In the above structure, the GaN-based semiconductor layer is _Al x _{Ga 1-x} N layer, x may be a configuration is 0.3 to 0.6.

  According to the present invention, it is possible to provide a semiconductor substrate and a semiconductor device with small warpage.

FIG. 1A to FIG. 1C are cross-sectional views illustrating a method of manufacturing a semiconductor substrate according to the first embodiment. FIG. 2 is a view of the wafer showing the amount of warpage of the wafer. FIG. 3 is a diagram showing SORI with respect to the half-value width of the rocking curve of the AlN (002) plane. FIG. 4 is a diagram showing the a-axis length with respect to the Al composition ratio of the AlGaN layer. FIG. 5 is a cross-sectional view of the semiconductor device according to the second embodiment.

  Embodiments of the present invention will be described with reference to the drawings.

Example 1 is an example of a semiconductor substrate for HEMT (High Electron Mobility Transistor). FIG. 1A to FIG. 1C are cross-sectional views illustrating a method of manufacturing a semiconductor substrate according to the first embodiment. A Si substrate 10 that is a Si wafer having a thickness of 625 μm and 4 inches is prepared. An Al material is supplied to the surface of the Si substrate 10 without supplying an N material. This is called pre-flow of Al raw material. As shown in FIG. 1A, an AlN layer 12 is formed as a buffer layer in contact with the (111) plane of the Si substrate 10 by using a MOCVD (Metal Organic Chemical Vapor Deposition) method. Each condition is as follows.
Al material pre-flow conditions Pre-flow gas: TMA (trimethylaluminum)
Pre-flow total amount: 20 μmol
Heat treatment temperature: 1050 ° C
Gas pressure: 100 torr
Conditions for forming the AlN layer 12 Source gas: TMA, NH ₃ (ammonia)
Growth temperature: 1150 ° C
Gas pressure: 100 torr
Growth film thickness: 300 nm

As shown in FIG. 1B, an AlGaN layer 14 is formed on the AlN layer 12 as a GaN-based semiconductor layer by MOCVD. The growth conditions for the AlGaN layer 14 are as follows.
Conditions for forming the AlGaN layer 14 Source gas: NH ₃ , TMA, TMG (trimethylgallium)
Growth temperature: 1100 ° C
Gas pressure: 100 torr
Doping: undoped Al composition ratio: 0.5
Film thickness: 100nm

  As shown in FIG. 1C, a GaN layer 16 is formed on the AlGaN layer 14 as an electron transit layer by MOCVD. The film thickness of the GaN layer 16 is 1000 nm. An AlGaN layer 18 is formed on the GaN layer 16 as an electron supply layer. The film thickness of the AlGaN layer 18 is 20 nm, and the Al composition ratio is 0.2. A GaN layer 20 is formed on the AlGaN layer 18 as a cap layer. The film thickness of the GaN layer 20 is 2 nm and is n-type. The growth plane of each layer is the (0001) plane. Thus, a semiconductor substrate for HEMT is completed.

  The film quality of the AlN layer 12 can be controlled by controlling the growth temperature, growth rate, and the like when the AlN layer 12 is grown. Therefore, the growth conditions of the AlN layer 12 were changed, and the half width of the rocking curve of the (002) plane of AlN by X-ray diffraction was measured in the state of FIG. Using the wafer on which the AlN layer 12 was grown under the same conditions, the semiconductor substrate of FIG. 1C was prepared, and the amount of warpage of the wafer was measured. FIG. 2 is a view of the wafer showing the amount of warpage of the wafer. As shown in FIG. 2, with the epitaxial layer facing upward and the edge of the wafer 30 in contact with the flat surface 32, the distance between the most convex portion 34 and the flat surface 32 is defined as the warpage amount SORI. As shown in FIG. 2, the amount of warpage when convex downward is positive, and the amount of warpage when convex upward is negative.

  FIG. 3 is a diagram showing the warping amount SORI with respect to the half width of the rocking curve of the AlN (002) surface. As shown in FIG. 3, when the half-value width of the rocking curve is reduced, the warpage amount SORI is reduced. The full width at half maximum of the rocking curve represents the crystallinity of the AlN layer 12. When the half width of the rocking curve is large, it indicates that the grains of the AlN layer 12 are small and the variation in crystal orientation of each grain is large. On the other hand, when the full width at half maximum of the rocking curve is small, the AlN layer 12 has a large grain and is closer to a single crystal.

  As described in Patent Document 1, it is considered that the amount of warpage is reduced by the AlGaN layer 14 as follows. That is, since the growth temperature of each layer is around 1000 ° C., warping occurs due to the difference in coefficient of linear thermal expansion. Since the linear thermal expansion coefficient of the GaN layer 16 is larger than that of Si or AlN, the wafer is warped so as to protrude downward only with the GaN layer 16. That is, the GaN layer 16 generates tensile stress. In particular, in order to manufacture a good semiconductor device, the thickness of the layer containing GaN (for example, the GaN layer 16) on the AlGaN layer 14 is 0.8 μm or more. For this reason, the amount of warpage of the wafer becomes very large. Therefore, by providing the AlGaN layer 14 having an a-axis length longer than that of the AlN layer 12 on the AlN layer 12, a stress that protrudes upward due to a difference in lattice constant is generated. That is, compressive stress is generated by the AlN layer 12 in the AlGaN layer 14. Thus, it is considered that the amount of warpage can be reduced by compensating the stress caused by the GaN layer with the stress caused by the AlGaN layer 14.

  However, the results of FIG. 3 are considered that when the crystallinity of the AlN layer 12 is poor, no compressive stress is generated in the AlGaN layer 14 and the warpage of the entire wafer is increased. When wafers having different half-value widths of the rocking curve on the AlN (002) plane were formed, when the half-value width of the rocking curve was about 3000 seconds, almost no compressive stress was generated in the AlGaN layer 14. On the other hand, when the half width of the rocking curve on the AlN (002) surface is 1500 seconds or less, sufficient compressive stress is generated in the AlGaN layer 14. The full width at half maximum of the rocking curve is more preferably 1300 seconds or less, and more preferably 1200 seconds or less.

  Furthermore, the warpage amount of the semiconductor substrate is preferably ± 50 μm or less (the radius of curvature is ± 25 m or more) when the size of the semiconductor substrate is 4 inches. If the amount of warpage exceeds ± 50 μm, it becomes impractical in the wafer process step of the semiconductor device. In addition, cracks are likely to occur in the semiconductor substrate. More preferably, the amount of warpage is ± 40 μm or less and the radius of curvature is ± 20 m or more. Further, it is more preferable that the warpage amount is ± 30 μm or less and the curvature radius is ± 15 m or more.

  Although the AlGaN layer 14 has been described as an example of the GaN-based semiconductor layer formed on the AlN layer 12, the GaN-based semiconductor layer may be a layer that receives compressive stress from the AlN layer 12. That is, the GaN-based semiconductor layer may be a layer that generates tensile stress in the AlN layer 12. The GaN-based semiconductor layer is a layer containing GaN, for example, a GaN layer, an InGaN layer, an AlGaN layer, an InAlGaN layer, or a stacked layer thereof.

FIG. 4 is a diagram showing the relationship of the a-axis length with respect to the Al composition ratio of the AlGaN layer 14 in the structure in which the GaN layer 16 is provided on the AlGaN layer 14 as the GaN-based semiconductor layer. In FIG. 4, the a-axis length of unstressed AlN is 0.3112 nm, and the a-axis length of unstressed GaN is 0.3189 nm. Therefore, the a-axis length of the AlGaN layer not subjected to stress is A = −0.0077x + 0.3189 in FIG. Therefore, since the AlGaN layer 4 is subjected to compressive stress, when the AlGaN layer 14 is an Al _x Ga _1-x N layer and the a-axis length of the AlGaN 14 layer is A nm,
A <0.0077x + 0.3189
It becomes.

In order to obtain the crystallinity of the AlN layer 12, the thickness of the AlN layer 12 is preferably 100 nm or more. The film thickness of the AlN layer 12 is more preferably 150 nm or more. The AlN layer 12 is preferably 400 nm or less in order to suppress cracks and the like. In order to apply compressive stress to the AlN layer 12, the Al composition ratio of the AlGaN layer 14, that is, _{x of} Al _x Ga _1-x N is preferably 0.3 or more and 0.6 or more. x is more preferably 0.35 or more and 0.55 or less.

  The second embodiment is an example in which a semiconductor device is formed using the semiconductor substrate of the first embodiment. FIG. 5 is a cross-sectional view of the semiconductor device according to the second embodiment. As shown in FIG. 4, the source electrode 24, the drain electrode 26, and the gate electrode 28 are formed on the GaN layer 20 of the semiconductor substrate of FIG. The source electrode 24 and the drain electrode 26 are ohmic electrodes in which, for example, Ti / Au is stacked from the side closer to the GaN layer 20. The gate electrode 28 is formed by stacking, for example, Ni / Au from the side closer to the GaN layer 20. Thus, the semiconductor device according to Example 2 is completed.

  In the first and second embodiments, the HEMT has been described as an example. However, a transistor other than the HEMT, or an optical semiconductor device such as a laser diode or a photodiode may be used.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

Si substrate 10
AlN layer 12
AlGaN layer 14
GaN layer 16
AlGaN layer 18
GaN layer 20

Claims (13)

An AlN layer having a (002) plane rocking curve half-width of 1500 seconds or less formed by X-ray diffraction in contact with a Si substrate;
A GaN-based semiconductor layer formed on the AlN layer;
A semiconductor substrate comprising:   2. The semiconductor substrate according to claim 1, wherein a curvature radius of warpage of the semiconductor substrate is ± 25 m or more.   2. The semiconductor substrate according to claim 1, wherein the amount of warpage of the semiconductor substrate is ± 50 [mu] m or less when the size of the semiconductor substrate is 4 inches.   The semiconductor substrate according to claim 1, wherein the GaN-based semiconductor layer receives compressive stress from the AlN layer. The GaN-based semiconductor layer is composed includes GaN layer formed on _Al x _{Ga 1-x} N layer and said _Al x _{Ga 1-x} N layer, a-axis length of the _Al x _{Ga 1-x} N layer When the a-axis length is A nm,
A <0.0077x + 0.3189
The semiconductor substrate according to claim 1, wherein the semiconductor substrate is a semiconductor substrate.   6. The semiconductor substrate according to claim 1, wherein the thickness of the AlN layer is 100 nm or more. The semiconductor substrate according to claim 1, wherein the GaN-based semiconductor layer is an Al _x Ga _1-x N layer, and x is 0.3 or more and 0.6 or less. An AlN layer having a (002) plane rocking curve half-width of 1500 seconds or less formed by X-ray diffraction in contact with a Si substrate;
A GaN-based semiconductor layer formed on the AlN layer;
A semiconductor device comprising:   9. The semiconductor device according to claim 8, wherein a curvature radius of warpage of the Si substrate is ± 25 m or more.   The semiconductor device according to claim 8, wherein the GaN-based semiconductor layer receives compressive stress from the AlN layer. The GaN-based semiconductor layer is composed includes GaN layer formed on _Al x _{Ga 1-x} N layer and said _Al x _{Ga 1-x} N layer, a-axis length of the _Al x _{Ga 1-x} N layer When the a-axis length is A nm,
A <0.0077x + 0.3189
The semiconductor device according to claim 8, wherein the semiconductor device is a semiconductor device.   The semiconductor device according to claim 8, wherein the thickness of the AlN layer is 100 nm or more. The semiconductor device according to claim 8, wherein the GaN-based semiconductor layer is an Al _x Ga _1-x N layer, and x is 0.3 or more and 0.6 or less.

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