Method of producing 3-5 group compound semiconductor and semiconductor element

Method for manufacturing group 3-5 compound semiconductor and semiconductor element

Scope of invention

The present invention relates to a method of manufacturing a gallium nitride (GaN) type group 3-5 compound semiconductor, and to a semiconductor element using the group 3-5 compound semiconductor.

Background of the invention

From the general formula In_XGa_yAl_ZN(x+y+z=1,0x1,Oy1 and 0z1) GaN type 3-5 group compound semiconductors can be used for luminescence ranging from ultraviolet light region to visible light The materials used for efficient light-emitting devices in the region, because the direct transition type band gap energy can be adjusted by changing the composition of group 3 elements, it can correspond to red to ultraviolet wavelengths. Furthermore, these Group 3-5 compound semiconductors have a larger energy band gap than conventional typical semiconductors such as Si and GaAs, and thus can maintain their semiconductor properties even at high temperatures at which conventional semiconductors cannot operate. Therefore, the group 3-5 compound semiconductor can mainly make electronic device products have excellent environmental resistance.

However, because the compound semiconductor has an extremely high vapor pressure around the melting point, it is difficult for these compound semiconductors to grow into large crystals. Therefore, up to now, it has not been possible to obtain large-scale compound semiconductor crystals that can be used as substrates for semiconductor device products. Therefore, in general, this type of compound semiconductor is manufactured by epitaxially growing the compound semiconductor on a matrix of a material, such as sapphire or SiC, which has a crystal structure similar to the compound semiconductor and can produce large crystals . Nowadays, higher-quality crystals of the compound semiconductor can be obtained by this method. Even in this case, it is difficult to reduce crystal defects caused by the difference in the lattice constant or the coefficient of thermal expansion between the substrate and the compound semiconductor. The final compound semiconductor usually has about 10⁸cm^-2Or greater defect density. In order to manufacture high-efficiency GaN devices, compound semiconductor crystals with low dislocation density are highly desired.

Generally speaking, methods to reduce dislocation density have been developed to produce crystals by hetero-epitaxial growth methods, which use sapphire or the like as a substrate, where once a mask pattern is formed on the crystal surface, then further The compound semiconductor grows again. The feature of this method is that the compound semiconductor is grown to the side of the mask, and this method is called epitaxial lateral overburden (ELO) method.

According to the above method, in the early re-growth, for example, in SiO₂Crystal growth does not occur on the isostatic mask, but only through the opening, so-called selective growth. If the crystal growth continues further, the crystal growth through the opening portion will also spread to the mask. As a result, an embedding structure for embedding the mask is formed, and a flat crystal surface can be finally obtained. Compared with the dislocation density in the base crystal, the dislocation density in the regrown layer can be greatly reduced by forming the above-mentioned embedding structure.

In the example of gallium nitride type 3-5 group compound semiconductor, if the above-mentioned ELO method is applied, generally speaking, the crystal growth is performed by using the c-plane as the surface. Generally speaking, the stripe direction of the strip mask is set to <1-100> direction, for the effective realization of lateral growth on the mask. However, although it depends on the material used for the mask, when using the ELO method, it is known that the c-axis direction of the crystal growth on the mask is offset from the c-axis of the base crystal. In addition, in the coalescence part of the offset c-axis zone, a so-called small-angle inclined boundary will generate a dislocation concentration part.

Therefore, if the mask fringe is set in the conventional ELO in the <1-100> direction, the c-axis direction of the GaN crystal growth on the mask will be offset from the c-axis of the base crystal and grow in the Many dislocations occur in the GaN layer of the mask. This is one of the major reasons for the deterioration of the quality of the obtained Group 3-5 compound semiconductor.

Summary of the invention

The purpose of the present invention is to provide a method for manufacturing group 3-5 compound semiconductors and a semiconductor device that can solve the above-mentioned conventional technical problems.

The present invention provides: a method for manufacturing 3-5 group compound semiconductors, in which a stripe mask is used for lateral selective growth to produce the 3-5 group compound semiconductor, and the small-angle oblique boundary produced by the 3-5 group compound semiconductor is reduced to produce high-quality and low-level Error density of 3-5 group compound semiconductors. In order to understand the above content, the c-axis variation of the group 3-5 compound semiconductor growing on the strip mask is reduced by slightly rotating the mask stripe direction of the mask pattern for lateral selective growth from the predetermined direction. Lower the sloping boundary at a small angle.

That is to say, the 3-5 group compound semiconductor is manufactured to form the desired GaN type 3-5 group compound semiconductor on the c-plane of the basic crystal containing the GaN type 3-5 group compound semiconductor by a strip mask. In the method of lateral selective growth, a stripe mask is formed on the base crystal so that the stripe is rotated from the <1-100> direction by 0.095° or less and less than 9.6°0. Use this strip mask to perform The lateral selective growth of the GaN type 3-5 group compound semiconductor layer.

As mentioned above, the stripe direction of the strip mask for lateral selective growth is rotated from the predetermined <1-100> direction by an angle within the above range, and the base crystal is selectively elongated to the side on the c-plane The c-axis variation of the desired compound semiconductor layer will be reduced. Therefore, the small-angle oblique boundary generated in the desired compound semiconductor layer is reduced, and a high-quality Group 3-5 compound semiconductor layer can be formed on the base crystal.

Detailed description of the invention

For example, by the metal organic vapor phase epitaxy method or the hydride-vapor-phase-epitaxial method, the desired compound-semiconductor layer can also be formed by other suitable vapor growth methods.

According to the present invention, it is disclosed that the method for manufacturing Group 3-5 compound semiconductor includes the following steps: including the general formula In_aGa_bAl_cN (0a1, 0b1, 0c1, a+b+c=1) represented by the group 3-5 compound semiconductor surface is c-plane on the basic crystal layer to form a strip Mask, and then grow the general formula In on the above-mentioned basic crystal layer_XGa_yAl_ZThe 3-5 group compound semiconductor layer represented by N(0x1, 0y1, 0z1, x+y+z=1), wherein the strip mask is based on the above-mentioned base crystal The layer is formed by rotating the stripe direction from the <1-100> direction by 0.095° or more and less than 9.6°.

Preferably, the group 3-5 compound semiconductor layer is grown by a metal organic vapor phase epitaxy method or a hydride vapor phase epitaxy method.

The Group 3-5 compound semiconductor manufactured by the method of the present invention is preferably used for semiconductor devices.

Hereinafter, specific embodiments of the present invention will be explained in detail with reference to the drawings.

Fig. 1 schematically shows a cross-sectional view of an embodiment of a Group 3-5 compound semiconductor structure manufactured by the method of the present invention. In the group 3-5 compound semiconductor 1, the first group 3-5 compound semiconductor layer 3 serving as the basic crystal is grown on the sapphire substrate by the MOVPE method (metal organic vapor phase epitaxy) to serve as the shield SiO of cover layer 4₂The layer system is deposited on the first group 3-5 compound semiconductor layer 3 by, for example, an RF sputtering method. Here, the first 3-5 group compound semiconductor layer 3 is 3 to 4 (micrometers). In order to produce a good basic crystal, a two-stage growth method using conventional buffer layers, such as GaN, AlN, GaAlN, and SiC, is effective.

As shown in Figure 2, the mask layer 4 is a strip mask with a window portion 4A formed on the c-plane 3A of the first 3-5 group compound semiconductor layer 3, and the The mask layer 4 is formed on the c-plane 3A, so that the stripe direction is slightly rotated from the <1-100> direction by the rotation angle θ, as described later. In Figure 1, the direction perpendicular to the cross section is the <1-100> direction.

As for the method of forming the mask layer 4 to slightly rotate the stripe direction from the <1-100> direction, a mask containing the stripe pattern can be used to rotate from the <1-100> direction to transfer the pattern to the first 3-5 Group compound semiconductor layer 3 method.

Instead, it is possible to use a method in which adjacent stripes in a mask with a stripe pattern are formed without being parallel, but the pattern must be transferred at a desired angle in advance. Another method is to use a method in which adjacent stripes in a mask with a stripe pattern are formed and parallel, but the pattern is transferred in a zigzag direction at a desired angle. Of course, these methods can be combined appropriately.

In Figure 1, the first group 3-5 compound semiconductor layer 3 is composed of the general formula In_aGa_bAl_cN (here 0a1, 0b1, 0c1, a+b+c=1) represents a GaN type group 3-5 compound semiconductor crystal. On the other hand, the mask layer 4 is formed by depositing an appropriate thickness of SiO₂Layers are formed, and a plurality of elongated window portions 4A are formed by photolithography. For example, a strip pattern with a width of 5 (micrometers) is used to form the window portion 4A.

On the group 3-5 compound semiconductor layer 3 and the mask layer 4, the general formula In is formed by regrowth_XGa_yAl_ZThe second 3-5 group compound semiconductor layer 5 represented by N (0x1, 0y1, 0z1, x+y+z=1).

The second group 3-5 compound semiconductor layer 5 is formed as follows. In the early growth stage of the second group 3-5 compound semiconductor layer 5, crystal growth does not occur on the mask layer 4, but selective growth only occurs on the window portion 4A. Therefore, when the crystal growth progresses, the crystal growth of the window portion 4A will also rapidly spread to the mask layer 4 as the thickness increases, and the growing crystalline region extending from both sides of the pattern to the side direction will be close to The central part of the pattern of the mask layer 4 is joined together and forms an embedded structure.

As in the above-mentioned growth process of the second group 3-5 compound semiconductor layer 5, generally speaking, the c-axis direction of the second group 3-5 compound semiconductor layer 5 and the c-axis direction of the first group 3-5 compound semiconductor layer 3 -The axis will be shifted, and a small angle inclined boundary 6 may occur in the merged part of the growth crystalline region extending from the two sides of the mask layer 4 pattern to the side direction.

However, because the mask layer 4 is formed so that the stripe direction is rotated from the <1-100> direction to the rotation angle θ, the c-axis variation of the second group 3-5 compound semiconductor layer 5 is selectively elongated The side direction on the first 3-5 group compound semiconductor layer 3, therefore, the generation of the small-angle oblique boundary can be effectively stopped at the coalescing part.

In the embodiment of FIG. 1, the second group 3-5 compound semiconductor layer 5 is formed by the above-mentioned lateral selective growth. Therefore, among the many dislocations generated in the first 3-5 group compound semiconductor layer 3, only the line dislocation D will not be terminated by the mask layer 4, but the penetrated window portion 4A will be the second Group 3-5 compound semiconductor layer 5 is included. As mentioned above, by forming the second group 3-5 compound semiconductor layer 5, the mask layer 4 in the second group 3-5 compound semiconductor layer 5, the mask layer 4 will terminate the first group 3-5 compound semiconductor layer 5 The dislocation of the compound semiconductor layer 3, and the dislocation will not occur in the second group 3-5 compound semiconductor layer 5 on the mask layer 4. Therefore, the dislocation in the second group 3-5 compound semiconductor layer 5 can be reduced The dislocation density. When the second group 3-5 compound semiconductor layer 5 is grown, a plane is formed, and the growth of the linear dislocation D of the second group 3-5 compound semiconductor layer 5 is controlled according to the formation mode of the plane, so , Line dislocations D will also be formed but will not reach the surface of the second group 3-5 compound semiconductor layer 5.

As for the method for manufacturing the thin film of the group 3-5 compound semiconductor 1, for example, molecular beam epitaxy (hereinafter referred to as MBE) method, MPVPE method, and HVPE method are cited. The MBE method is important because it is suitable for manufacturing multilayer structures with sharp interfaces. Because the MOVPE method is suitable for forming a layered structure with a sharp interface, and also for manufacturing a large-area uniform film, it is important. The HVPE method can produce crystals with a small amount of impurities at a high film-forming speed, so it is important. If the HVPE method is used to grow the second group 3-5 compound semiconductor layer 5, a high growth rate can be obtained, and good crystals can be produced in a short time.

As mentioned above, the stripe direction of the mask layer 4 is slightly rotated from the <1-100> direction. The rotation angle θ is preferably set at an angle, wherein the ratio in the <11-20> direction perpendicular to the mask pattern direction is every 6 to 600 times the a-axis length to a segment (a-axis length). In other words, the generation of the small-angle oblique boundary can be effectively stopped by setting the rotation angle θ of the mask layer 4 to be 0.095° or less and less than 9.6° from the <1-100> direction. More specifically, the rotation angle is 1° or less and less than 5° or less, preferably 1° or less and less than 5° or less.

If the stripe direction of the mask layer 4 is slightly rotated as described above, the c-axis of the second group 3-5 compound semiconductor layer 5 changes, and it is selected on the c-plane 3A of the first group 3-5 compound semiconductor layer 3 Sexually grows laterally and will decrease. Thereby, the generation of the small-angle inclined boundary 6 in the coalescence portion of the second 3-5 group compound semiconductor layer 5 directly above the mask layer 4 can be stopped, and high-quality second 3-5 group compound can be manufactured Semiconductor layer 5.

According to various experimental research results, if the rotation angle θ of the stripe direction of the mask layer 4 from the <1-100> direction is less than 0.095°, the small-angle tilt boundary can be reduced. Furthermore, if the rotation angle θ is 9.6° or more, a good embedding structure cannot be obtained. In other words, it can be confirmed by experiments that the rotation angle θ of the stripe direction of the mask layer 4 from the <1-100> direction should be 0.095° or more and less than 9.6°.

The following experiment is performed to test the improvement of the small-angle oblique boundary generated by rotating the stripe direction of the mask layer 4 from the <1-100> direction.

A 3 micron thick GaN layer is formed on a 2 inch sapphire wafer by the MOVPE method, and a 5 micron wide stripe pattern and a 5 micron gap pattern are formed on the entire surface. Further, by the MOVPE method, the GaN layer is formed on a substrate of 6 microns at 1020° C. and 1/2 atmospheric pressure, and an embedded structure is obtained. Evaluate the rocking curve of the (0004) plane when the stripe direction of the mask layer is slightly rotated from the <1-100> direction.

Evaluating the above-mentioned measurement results when the rotation angle θ of the mask layer is 1°, 3°, and 5°, the rotation angle θ of the comparative example is 0°. Figures 3, 4, and 5 show the measurement results when the rotation angle θ is 1°, 3°, and 5°, respectively. Figure 6 shows the measurement results of the comparative example when the rotation angle θ is 0°.

In each case, the X-rays were incident in the fringe direction of the mask layer, showing a single peak pattern, and the half-height width was about 250 arc seconds. On the other hand, if X-rays are incident in a direction perpendicular to the fringe direction of the mask layer, in the various embodiments performed here, if the rotation angle θ is 0°, the main peaks on the two sides and two The peak of the side. The half-width of the main peak is about 250 arc seconds, which is almost the same as the half-width of the base matrix. When the direction of the fringe is gradually from the <1-100> direction, the peak on the high-angle side will become weaker than the non-rotating example. It is particularly significant when the rotation angle θ is 1° and 3°. Because rotating the fringe direction will reduce the intensity of the side peaks, it is believed that the generation of the small-angle oblique boundary will be suppressed. Good semiconductor devices can be obtained using these substrates.

According to the present invention, as described above, the small-angle oblique boundary can be laterally directed only by rotating the strip mask formed on the c-plane of the base crystal from a predetermined direction <1-100> by 0.095° or more and less than 9.6° Selective growth, while obtaining extremely effective reduction. Therefore, a GaN compound semiconductor with good crystallinity can be manufactured without a significant increase in cost. Furthermore, semiconductor devices with good electrical properties can be manufactured at low cost by this manufacturing method.

<p>The symbols used in each drawing are as follows.</p><p>1: Group 3-5 compound semiconductor</p><p>2: Sapphire matrix</p><p>3: The first 3-5 group compound semiconductor layer</p><p>4: Mask layer</p><p>5: The second group 3-5 compound semiconductor layer</p><p>6: Small angle sloping boundary</p><p>D: Line misalignment</p><p>θ: rotation angle</p><p>3A: c-plane</p><p>4A: Window part</p>

Fig. 1 schematically shows an embodiment of a group 3-5 compound semiconductor structure manufactured by the method of the present invention.

Fig. 2 is a diagram for explaining the rotation of the mask layer of the group 3-5 compound semiconductor shown in Fig. 1 from a predetermined direction.

Figure 3 shows the measurement result of the rocking curve when the rotation angle of the stripes of the mask layer is 1°.

Figure 4 shows the measurement result of the rocking curve when the rotation angle of the stripes of the mask layer is 3°.

Figure 5 shows the measurement result of the rocking curve when the rotation angle of the stripes of the mask layer is 5°.

Figure 6 shows the measurement result of the rocking curve when the rotation angle of the stripes of the mask layer is 0°.