JP4447344B2 - Semiconductor device, ultraviolet light emitting element using semiconductor structure in semiconductor device, and manufacturing method thereof - Google Patents

Description

  The present invention uses a semiconductor device having a semiconductor structure formed on a heterogeneous substrate excluding AlGaN and including a layer made of AlGaN, which is a nitride semiconductor layer with few crystal defects, and the semiconductor structure in the semiconductor device. The present invention relates to an ultraviolet light emitting device and a method for manufacturing the same.

  Currently, elements that generate ultraviolet light, such as light emitting diodes (LEDs), are being applied in fields such as phosphor excitation, illumination detection, bacteria detection, photocatalysis, and medical use in lighting and displays.

  AlGaN (Al composition x: 0 ≦ x ≦ 1), which is a nitride semiconductor, is taken up as the most promising material for realizing the above-mentioned ultraviolet LED element. Since it is difficult, it is usually formed by applying a crystal growth method such as MOVPE (metalorganic phase epitaxy) to a substrate different from AlGaN. In the present specification, it is assumed that the x value of the Al composition is 0 ≦ x ≦ 1 unless otherwise specified for AlGaN.

  However, any substrate except AlGaN has a large lattice mismatch compared to AlGaN, and therefore, dislocations are likely to occur in AlGaN due to strain stress caused by the lattice mismatch during crystal growth. Reduction is a major issue.

Conventionally, as a method for growing AlGaN, periodic processing is performed so that growth starts from a part of the substrate every several μm, for example, every 2 μm to 3 μm, and the selective growth process and the lateral direction are performed on the substrate. It is proposed that a growth method called ELO (Epitaxial Lateral Overgrowth) combined with growth processes is applied to obtain GaN having a dislocation density of about 1 × 10 ⁷ cm ⁻² , and the same method is also used in the case of AlGaN. (For example, see Patent Document 1).

  FIG. 13 is a side view of a principal part showing a semiconductor structure including a GaN layer grown by ELO. In the figure, 1 is a semiconductor substrate, 2 is a mask, and 3 is a GaN layer.

  As is apparent from the figure, the surface of the semiconductor substrate 1 is uneven, the concave portion is covered with the mask 2, and the convex portion is exposed to the semiconductor substrate 1 itself. The substrate 1 has a structure in which periodic processing is performed so that the growth starts from a part of the substrate under ELO conditions, that is, every 2 μm to 3 μm, and the GaN layer 3 is grown thereon.

  In addition to the above-described problem of dislocations, AlGaN has a problem with high quality. That is, there is a difference in thermal expansion coefficient between the substrate and the AlGaN layer, and the AlGaN layer is grown at a high temperature of 1000 ° C. to 1300 ° C. This is because cracks occur due to the difference in lattice shrinkage with the AlGaN layer.

  There have been proposals to solve this problem by confining the growth region of the AlGaN layer. However, from a practical point of view, if a flat AlGaN layer with no cracks can be obtained in a wide region, it will exceed that. Never.

  Also, when growing GaN, which is a semiconductor single crystal having no cracks or polycrystalline lumps, on the Si substrate, the entire surface of the Si substrate is covered with an uneven reaction preventing layer and a buffer layer, and a GaN layer is grown thereon. It is known (see, for example, Patent Document 2).

However, according to the invention disclosed in Patent Document 2, since the buffer layer also exists in the concave portion, when growing GaN, GaN is attached not only to the convex portion but also to the concave portion. Stable growth of ELO does not occur, and crack generation is attempted to be suppressed by the concavo-convex structure. Therefore, the effect is the same as that of normal ELO and cannot be said to be sufficient.
JP 2001-168042 A JP 2002-293698 A

  In the present invention, it is intended to easily and easily realize a large-area AlGaN layer having low dislocations, no cracks, and maintaining high quality, and an ultraviolet light emitting device using the AlGaN layer.

In the semiconductor device according to the present invention, the ultraviolet light emitting element using the semiconductor structure in the semiconductor device, and the manufacturing method thereof, an amorphous (for example, Si substrate 11) formed on a single crystal substrate ( For example, one or more strain relaxation layers (for example, strain relaxation layer 12) made of SiO ₂ ) or metal (for example, Ti, Ni, Cr, etc.), and unevenness formed by covering a part of the strain relaxation layer. AlGaN formed by covering the unevenness generated by forming a single crystal layer (for example, Si (111) semiconductor layer 13) that is different from AlGaN and forming a single crystal layer that is different from AlGaN. A semiconductor device including an (Al composition x: 0 ≦ x ≦ 1) layer (for example, an AlGaN layer 14) and a manufacturing method thereof are fundamental.

  By adopting the above means, the AlGaN layer growth substrate has a strain relaxation layer made of amorphous or metal. Therefore, the AlGaN layer grown on the AlGaN layer has no crack and has a large area. In addition, the dislocation generated in the AlGaN layer is reduced by growing by applying ELO utilizing the unevenness in the growth substrate. Therefore, if AlGaN according to the present invention is used, a high-performance ultraviolet light emitting device can be realized.

  In the semiconductor device according to the present invention, the ultraviolet light emitting element using the semiconductor structure in the semiconductor device, and the manufacturing method thereof, thermal strain that causes cracks in the AlGaN layer is not applied to the AlGaN layer. It is fundamental to introduce the strain relaxation layer to be introduced into the substrate, but various improvements are required for the introduction.

The thermal expansion coefficient of AlGaN is 4.2 to 5.6 × 10 ⁻⁶ K ⁻¹ , and considering the case where Si is used for the substrate, the thermal expansion coefficient of the substrate is 3.5 × 10 6. ^-6 K ^-1 .

  In general, the crystal growth temperature suitable for the formation of the AlGaN layer is 1000 ° C. to 1300 ° C. Therefore, when the AlGaN layer is grown and then cooled to room temperature, the difference in lattice contraction between the AlGaN layer and the Si substrate is about 0. 0. The AlGaN layer is subjected to a stress due to thermal strain in the plane, and the Si substrate is subjected to thermal strain in the compression direction.

  The thickness of the Si substrate is 300 μm to 600 μm, and the thickness of the AlGaN layer is about two orders of magnitude compared to the thickness of 1 μm to 2 μm. The stress caused by the thermal strain is released by cracks in the AlGaN. Is done.

  The amorphous layer has a density lower than that of a semiconductor and a bond between atoms is weaker than that of a crystal. Therefore, the amorphous layer can be plastically deformed with a stress smaller than a stress applied to the crystal.

  The metal layer can qualitatively be plastically deformed with a stress of 1/100 or less of the shear stress in a complete crystal.

  Therefore, when a thermal strain relaxation layer made of amorphous or metal is introduced into the substrate on which the AlGaN layer is to be grown, the stress caused by the thermal strain is relaxed by the plastic deformation of the thermal strain relaxation layer, and the AlGaN layer Since a stress that is large enough to cause cracks is not applied, a high-quality AlGaN layer can be realized.

  Further, in the present invention, the part where the growth of the AlGaN layer is started is a convex part of the semiconductor surface having irregularities, and the concave part is made of an amorphous or metal having a mask effect in which AlGaN is difficult to grow. Since the strain relaxation layer to be formed is formed with the surface exposed, it is possible to suppress the deposition of AlGaN in the concave portion, and therefore, ELO can be performed reliably.

  Furthermore, since Si can be used as the semiconductor substrate without any restrictions, an inexpensive and large-diameter AlGaN layer can be easily realized in that case.

  FIG. 1 is a cutaway side view showing a principal part of a semiconductor device having a semiconductor structure including an AlGaN layer, which is an embodiment of the present invention. In FIG. 1, 11 is a Si substrate, and 12 is titanium (Ti). A strain relaxation layer, 13 is a Si (111) semiconductor layer, 13A is a recess, and 14 is an AlGaN layer.

  FIGS. 2 to 7 are side sectional views showing the main part of the substrate at the process points for explaining the manufacturing process of the concavo-convex substrate used for the growth of the AlGaN layer which is an embodiment of the method of the present invention. The symbols used in FIG. 1 represent the same parts or have the same meaning.

Refer to FIG. 2 (1) A Ti strain relaxation layer 12 having a thickness of, for example, 100 nm is formed on the Si substrate 11 by applying a vacuum deposition method.

Refer to FIG. 3 (2) The Si (111) semiconductor layer 13 is placed on the Ti strain relaxation layer 12, and high-speed heating at about 1000 ° C. is performed, so that the Ti strain relaxation layer 12 and the Si (111) semiconductor layer 13 are formed. A substrate having a three-layer structure is manufactured by bonding.
(3) Since the bonded Si (111) semiconductor layer 13 is initially about 50 μm to 150 μm thick from the viewpoint of easy handling, it is better to call it “plate” than “layer”. Although suitable, the Si (111) semiconductor layer 13 is effective when it is thin compared to the thickness of the AlGaN layer. Therefore, it is preferable that the Si (111) semiconductor layer 13 be polished to a thickness of about 100 nm to 500 nm after bonding.

Refer to FIG. 4 (4) By applying a resist process in lithography technology, a resist film 15 having a line width of 2 μm and a period of 4 μm is formed on the Si (111) semiconductor layer 13 through spin coating of the resist and lithography. To do.

5 and 6 (5) The Si (111) semiconductor layer 13 is etched using the resist film 15 as a mask to form a recess 13A, and then the resist film 15 is removed.
(6) Accordingly, a substrate having a three-layer structure in which the surface has irregularities and a part of the Ti strain relaxation layer 12 is exposed in the recess 13A is realized.

See FIG. 7 (7) By applying the MOVPE method, an AlGaN layer 14 having a thickness of 1 μm to 2 μm is grown on a substrate having a three-layer structure. In this case, for example, trimethylaluminum (TMAl: Al (CH ₃ ) ₃ ), triethylgallium (TEGa: Ga (C ₂ H ₅ ) ₃ ), and ammonia (NH ₃ ) can be used as the growth raw material. The ratio of the group III raw material (sum of TMA and TEG) and the group V raw material (NH ₃ ), that is, the V / III ratio is a high V / III ratio that promotes lateral growth, ie, 500 The growth temperature is preferably 1000 ° C. to 1300 ° C.

In the embodiment of the above method, the case of using Ti as the material of the strain relaxation layer 12 has been described. However, nickel (Ni) or chromium (Cr) can be used as another metal, and an amorphous material is used. If so, SiO ₂ or SiN may be used.

  In addition to Si (111), SiC or sapphire can be used as the material for the semiconductor layer 13, and the substrate surface has not only a line shape but also a large number of square protrusions or a large number of hexagons. It may be a projection.

  FIGS. 8 to 10 are sectional side views of the main part showing the substrate at the process points for explaining the manufacturing process of the concavo-convex substrate used for the growth of the AlGaN layer which is another embodiment of the method according to the present invention. The symbols used in FIGS. 1 to 7 represent the same parts or have the same meaning.

8 and 9 (1) Oxygen ions 16 are injected while the Si (111) substrate 11A is heated to a temperature of 500 ° C. In this case, the ion implantation energy was 180 keV, and the implantation amount was 1 × 10 ¹⁸ cm ⁻² . FIG. 9 shows a Si (111) substrate 11A ion-implanted under the above conditions.

10 In the in the reference (2) a hydrogen atmosphere, the strain relaxation temperature 1000 ° C., the time and was heat-treated for 10 minutes, made of SiO ₂ and oxygen ions 16 and Si (111) substrate 11A is reacted A substrate having a three-layer structure is realized by generating the layer 12A and restoring crystallinity on the surface of the Si (111) substrate 11A.
(3) Thereafter, the surface of the Si (111) substrate 11A is processed in the same manner as in Example 2 to form irregularities.

  An ultraviolet LED device having excellent performance can be manufactured using the semiconductor structure including the AlGaN layer according to the present invention manufactured as described above. Next, this will be described in detail.

  FIG. 11 is a cut-away side view of an essential part showing an ultraviolet LED element manufactured using a semiconductor structure including an AlGaN layer according to the present invention. The same reference numerals as those used in FIGS. Express or have the same meaning.

In the figure, 17 is an n-side contact layer made of n-Al _0.35 Ga _0.65 N, 18 is a barrier layer made of Al _0.30 Ga _0.70 N, 19 is a well layer made of Al _0.15 Ga _0.85 N, and 20 is Al _0.30 Ga. _A barrier layer made of _0.70 N, 21 an electron barrier layer made of p-Al _0.4 Ga _0.6 N, 22 a p-side cladding layer made of p-Al _0.35 Ga _0.65 N, and 23 made of p-Al _0.2 Ga _0.8 N p The side contact layer, 24 is a transparent electrode, 25 is a p-side electrode, and 26 is an n-side electrode.

In order to fabricate this ultraviolet LED element, n-Al _0.35 Ga _0.65 having a thickness of 1 μm in which Si is doped to about 5 × 10 ¹⁸ cm ⁻³ on the AlGaN layer 14 in the semiconductor structure including the AlGaN layer according to the present invention. An n-side contact layer 17 made of N is grown, and then a barrier layer 18 made of Al _0.30 Ga _0.70 N having a thickness of 20 nm, a well layer 19 made of Al _0.15 Ga _0.85 N having a thickness of 3 nm, and a thickness of 20 nm An active layer composed of a barrier layer 20 made of Al _0.30 Ga _0.70 N is grown, and then an electron barrier made of p-Al _0.35 Ga _0.65 N having an impurity concentration of 5 × 10 ²⁰ cm ⁻³ and a thickness of 10 nm. The layer 21 is grown, and then the p-side cladding layer 22 made of p-Al _0.35 Ga _0.65 N having an impurity concentration of 1 × 10 ²⁰ cm ⁻³ and a thickness of 100 nm is grown. ²¹ c A p-side contact layer 23 made of p-Al _0.2 Ga _0.8 N having a thickness of m ⁻³ and 10 nm is grown.

  As described above, after each semiconductor layer is grown, a lithography technique is applied, and etching reaching from the part of the surface of the p-side contact layer 23 into the n-side contact layer 17 is performed to form an n-side electrode formation scheduled region. .

  A transparent electrode 24 is formed on the p-side contact layer 23, and a p-side electrode 25 and an n-side electrode 26 are formed to complete. In addition, Ni (10 nm) / Au (1000 nm) is used for the p-side electrode 25, and Ti (10 nm) / Al (10 nm) / Ti (10 nm) / Au (1000 nm) is used for the n-side electrode 26, for example, by vacuum evaporation. The film can be formed by applying a method and patterned by applying a lithography technique.

  FIG. 12 is a cut-away side view of the essential part showing an ultraviolet LED element different from Example 4 manufactured by using a semiconductor structure including an AlGaN layer according to the present invention, and the symbols used in FIGS. The same symbol represents the same part or has the same meaning.

  The ultraviolet LED element of Example 5 is configured so that the concavo-convex substrate is finally removed, and the AlGaN layer 14 on the concavo-convex substrate described with reference to FIG. 1 is doped with n-type impurities. Except for the above, the growth of each semiconductor layer is exactly the same as in the case of Example 4 from the n-side contact layer 17 to the p-side contact layer 23.

  Thereafter, Ni (10 nm) / Au (1000 nm) is vacuum-deposited to form the p-side electrode 25, the p-side electrode 25 and the conductive stem 27 are joined, and then wet etching or polishing Is applied to peel off the concavo-convex substrate to expose the n-AlGaN layer 14, and then Ti (10 nm) / Al (10 nm) is formed on the n-AlGaN layer 14 by applying a vacuum deposition method and a lithography technique. ) / Ti (10 nm) / Au (1000 nm) n-side electrode 26 is formed and completed.

  As for the structure of the ultraviolet LED element, in addition to the structures described as Example 4 and Example 5, it can be applied to various conventionally known structures, and also for semiconductor light emitting elements such as lasers. Can be applied.

  In the present invention, the present invention can be implemented in many forms including the above-described embodiment, which will be exemplified below as supplementary notes.

(Appendix 1)
One or more strain relaxation layers made of amorphous or metal formed on a single crystal substrate, and a single crystal layer different from AlGaN formed by covering a part of the strain relaxation layer and generating irregularities A semiconductor comprising: an AlGaN layer (Al composition x: 0 ≦ x ≦ 1) formed by covering unevenness generated by forming a single crystal layer that is different from AlGaN. apparatus.

  (Supplementary note 2) The semiconductor device according to supplementary note (1), wherein the single crystal substrate is a Si substrate and the single crystal layer different from AlGaN is a Si layer having a plane orientation (111).

(Appendix 3)
A step of forming one or more strain relaxation layers made of amorphous or metal on a semiconductor substrate; a step of bonding a semiconductor layer to the strain relaxation layer made of amorphous or metal; and A step of removing a part to expose a portion of the underlying amorphous or metal strain relief layer, and a portion of the underlying amorphous or metal strain relief layer being exposed. And a step of forming an AlGaN layer on the semiconductor layer.

(Appendix 4)
The step of forming one or more strain relaxation layers made of amorphous or metal on the semiconductor substrate is replaced with the step of forming the strain relaxation layer in the semiconductor substrate by ion implantation, and one of the strain relaxation layers is formed. The method of manufacturing a semiconductor device according to appendix (3), wherein an MOCVD method or an HVPE method is applied when forming the AlGaN layer on the semiconductor layer in which the portion is exposed.

(Appendix 5)
An ultraviolet light emitting element comprising an n-type nitride semiconductor layer and a p-type nitride semiconductor layer formed on a semiconductor structure including an AlGaN layer in the semiconductor device according to attachment 1.

(Appendix 6)
An ultraviolet light emission comprising a step of forming an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a semiconductor structure including an AlGaN layer manufactured by the method for manufacturing a semiconductor device according to attachment 3. Device manufacturing method.

(Appendix 7)
A step of forming an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a semiconductor structure including an AlGaN layer manufactured by the method of manufacturing a semiconductor device according to attachment 3, and then, the semiconductor structure including the AlGaN layer. And a step of removing the others while leaving the AlGaN layer.

It is a principal part cutting side view showing the semiconductor device containing the AlGaN layer which is an Example of the thing in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is an Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is an Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is an Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is an Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is an Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is an Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is another Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is another Example of the method in this invention. It is a principal part cutting side view showing the board | substrate in the process important point for demonstrating the manufacturing process of the uneven | corrugated board | substrate used for the growth of the AlGaN layer which is another Example of the method in this invention. It is a principal part cutting side view showing the ultraviolet LED element produced using the semiconductor structure containing the AlGaN layer by this invention. It is a principal part cutting side view showing the ultraviolet LED element different from Example 4 produced using the semiconductor structure containing the AlGaN layer by this invention. It is a principal part cutting side view showing the semiconductor structure containing the GaN layer grown by ELO.

Explanation of symbols

11 Si substrate 12 Titanium (Ti) strain relaxation layer 13 Si (111) semiconductor layer 13A Recess 14 AlGaN layer 15 Resist film

Claims (5)

Amorphous SiO _2, SiN formed on a single crystal substrate or a metal of Ti, Ni, and one or more layers of the strain reducing layer made of any of Cr,
A single crystal layer that is different from AlGaN that is formed by covering a part of the strain relaxation layer and generates irregularities,
A semiconductor device comprising: an AlGaN (Al composition x: 0 ≦ x ≦ 1) layer formed by covering unevenness generated by forming a single crystal layer different from AlGaN . Amorphous SiO _2, SiN on a semiconductor substrate, or forming metals Ti, Ni, one or more layers of the strain reducing layer made of any of Cr,
Bonding a semiconductor layer to the amorphous or metal strain relaxation layer;
Removing a part of the bonded semiconductor layer to expose a part of the underlying amorphous or metal strain relaxation layer;
And a step of forming an AlGaN layer on the semiconductor layer on which a part of the underlying amorphous or metal strain relaxation layer is exposed. 2. An ultraviolet light-emitting element comprising an n-type nitride semiconductor layer and a p-type nitride semiconductor layer formed on a semiconductor structure including an AlGaN layer in the semiconductor device according to claim 1. An ultraviolet ray comprising a step of forming an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a semiconductor structure including an AlGaN layer produced by the method of manufacturing a semiconductor device according to claim 2. Manufacturing method of light emitting element. Forming an n-type nitride semiconductor layer and a p-type nitride semiconductor layer on a semiconductor structure including an AlGaN layer manufactured by the method for manufacturing a semiconductor device according to claim 2;
Next, a part of or all of the semiconductor substrate including the AlGaN layer, the other semiconductor substrate, the one or more strain relaxation layers made of amorphous or metal, and the semiconductor layer of the semiconductor structure including the AlGaN layer. And a step of removing the ultraviolet light emitting element.

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