Method for manufacturing a radiation-emitting semiconductor chip

Abstract

Method for manufacturing a radiation-emitting semiconductor chip comprising the following steps: - Providing a growth substrate (1), - epitaxial growth of a buffer layer (3) onto the growth substrate (1), wherein a plurality of V-pits (4) are generated in the buffer layer (3), - epitaxial growth of a radiation-generating active semiconductor layer sequence (5) onto the buffer layer (3), wherein the structure of the V-pits (4) continues into the active semiconductor layer sequence (5), - epitaxial growth of a further electron-blocking layer sequence (9) onto the active semiconductor layer sequence (5), wherein the structure of the V-pits (4) continues into the further electron-blocking layer sequence (9) and wherein the further electron-blocking layer sequence (9) is formed from alternatingly arranged AlGaN layers (10) and InGaN layers (11) or from alternatingly arranged InGaN layers and GaN layers and wherein the aluminum content and / or indium content of the further electron-blocking layer sequence (9) applied to facets (8) of the V-pits (4) is reduced compared to the aluminum content and / or indium content of the further electron-blocking layer sequence (9) applied to a main surface (12) of the active semiconductor layer sequence (5), - selective removal of the further electron-blocking layer sequence (9) from the facets (8) of the V-pits (4) by etching in situ in the epitaxial reactor, wherein the further electron-blocking layer sequence (9) remains on the main surface (12) of the active semiconductor layer sequence (5), and - epitaxial growth of a p-doped semiconductor layer (15) that completely or partially fills the V-pits (4).

Description

[0001] A method for producing a radiation-emitting semiconductor chip and a radiation-emitting semiconductor chip are specified.

[0002] A method for producing a radiation-emitting semiconductor chip is described, for example, in the document WO 2011 / 080 219 A1.

[0003] The following publications also describe methods for producing a radiation-emitting semiconductor chip and / or radiation-emitting semiconductor chips: US 2014 / 0 225 059 A1, US 2015 / 0 115 223 A1, US 2013 / 0 037 779 A1, Quan, Z. et al., Journal of Applied Physics, Vol. 116, 2014, 183107, US 2011 / 0 121 357 A1, US 2012 / 0 033 444 A, and Bell A. et al., Applied Physics Letters, Vol. 85, 2004, No 16, pp. 3417-3419.

[0004] An object of the present application is to provide a method for producing such a semiconductor chip with increased efficiency.

[0005] This object is achieved by a method comprising the steps of patent claim 1.

[0006] Advantageous embodiments and further developments of the method are specified in the dependent claims.

[0007] In a method for producing a radiation-emitting semiconductor chip, a growth substrate is first prepared. The growth substrate can, for example, comprise sapphire, SiC, GaN, AlN, or silicon, or consist of one of these materials.

[0008] According to one embodiment of the method, a buffer layer is epitaxially grown on the growth substrate. A plurality of V-pits are created in the buffer layer.

[0009] For example, the buffer layer has a thickness between 1 micrometer and 15 micrometers inclusive.

[0010] V-pits or V-defects are recesses in an epitaxially grown layer that are shaped like a pyramid or a truncated pyramid. The pyramid or truncated pyramid is preferably a straight pyramid or a straight truncated pyramid. Such defects have the shape of a V in a sectional view, which is where the name of the defects comes from. V-pits particularly preferably have a hexagonal base and a lateral surface composed of six facets. Furthermore, it is also possible for the V-pits to have a lateral surface with, for example, 12 facets. The number of facets in a V-pit can be a multiple of six.

[0011] According to a further embodiment, the facets of a V-pit are each formed not only from a single continuous surface, but from at least two surfaces that are at an angle to each other, so that the respective facet has at least one bend. Such V-pits have a sectional view in which at least one leg of the V has at least two sections with different gradients.

[0012] For example, the base area of ​​the V-pits, preferably when the V-pit is maximally open, has a diameter between 20 nanometers and 1000 nanometers.

[0013] The height of the V-pits is preferably between 15 nanometers and 800 nanometers, particularly preferably between 100 nanometers and 400 nanometers.

[0014] According to one embodiment of the method, a radiation-generating active semiconductor layer sequence is grown epitaxially on the buffer layer. The structure of the V-pits continues into the active semiconductor layer sequence. The facets of the V-pits are generally covered with the material of the further radiation-generating active semiconductor layer sequence. However, the radiation-generating active semiconductor layer sequence on the facets of the V-pits preferably has a significantly smaller thickness than on a main surface of the buffer layer. For example, the active semiconductor layer sequence on the facets of the V-pits has a thickness that, perpendicular to a surface of the facets, is less than 50% of its thickness on the main surface of the buffer layer. Alternatively or additionally, the active semiconductor layer sequence on the facets of the V-pits can further have a different composition than on the main surface of the buffer layer.

[0015] According to a further embodiment, a further layer sequence is epitaxially grown on the active semiconductor layer sequence, in which the structure of the V-pits is also continued. Here, too, the facets of the V-pits are generally covered with the material of the further layer sequence. However, here, too, the further layer sequence on the facets of the V-pits preferably has a significantly smaller thickness and / or a different composition than on a main surface of the active semiconductor layer sequence.

[0016] The remaining layer sequence is designed as an electron-blocking layer sequence. In other words, the further layer sequence is intended to form a barrier for electrons and thus prevent electrons from being lost from the radiation-generating layer sequence into the subsequent layer sequence in the finished semiconductor chip.

[0017] According to a particularly preferred embodiment, in a next step, the further layer sequence is selectively removed from the facets of the V-pits, wherein the further layer sequence remains on the main surface of the active semiconductor layer sequence. Particularly preferably, the further layer sequence completely covers the main surface of the active semiconductor layer sequence even after removal. However, it is possible for a substantially uniform material removal to occur across the main surface of the further layer sequence during the selective removal of the further layer sequence from the facets. Particularly preferably, the material of the further layer sequence is completely removed from the facets of the V-pits, such that the semiconductor material of the radiation-generating active semiconductor layer sequence is exposed.

[0018] In the next step, a p-doped semiconductor layer is epitaxially grown, which can completely or partially fill the V-pits. The material of the p-doped semiconductor layer is particularly preferably in direct contact with the material of the active semiconductor layer sequence within the V-pits.

[0019] The p-doped semiconductor layer is particularly preferably grown epitaxially in such a way that it completely covers the main surface of the further layer sequence and forms a certain thickness starting from the further layer sequence. For example, the p-doped layer has a thickness of between 1 nanometer and 500 nanometers, starting from the main surface of the further layer sequence.

[0020] Particularly preferably, the buffer layer, the radiation-generating active semiconductor layer sequence, the further layer sequence, and the p-doped semiconductor layer comprise or consist of a nitride compound semiconductor material. Nitride compound semiconductor materials are compound semiconductor materials that contain nitrogen, such as the materials from the system In x Al y Ga 1-x-y N with 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and x+y ≤ 1. For example, the following materials are nitride compound semiconductor materials: GaN, InGaN, AlGaN.

[0021] According to one embodiment, the active semiconductor layer sequence comprises a plurality of quantum films separated from one another by barrier layers. The quantum films and the barrier layers are preferably arranged alternately. Particularly preferably, the quantum films comprise InGaN or consist of InGaN, while the barrier layers comprise GaN or consist of GaN. Alternatively, the barrier layers can also comprise AlGaN or consist of AlGaN.

[0022] The quantum films preferably have radiation-generating quantum structures such as quantum dots, quantum wires or quantum wells.

[0023] According to one embodiment, the further layer sequence is formed from alternatingly arranged AlGaN layers and InGaN layers or from alternatingly arranged AlGaN layers and GaN layers or from alternatingly arranged InGaN layers and GaN layers.

[0024] According to a particularly preferred embodiment of the method, the thickness of the further layer sequence on the facets of the V-pits is thinner than on a main surface of the active semiconductor layer sequence. Particularly preferably, the further layer sequence on the facets of the V-pits has a thickness between 5 nanometers and 200 nanometers. On the main surface of the active semiconductor layer sequence, the further layer sequence has a thickness between 10 nanometers and 400 nanometers after epitaxial growth and before selective removal.

[0025] As a rule, it is possible to form the subsequent layer sequence on the facets of the V-pits thinner, as these have a different morphology and surface reconstruction than the main surface of the active semiconductor layer sequence. For example, the epitaxial layers are grown on the main surface of a sapphire substrate, which has a (0001) orientation. Such a main surface of a sapphire substrate is also referred to as a c-face. Accordingly, the main surfaces of the subsequently epitaxially grown layers formed thereon, such as the main surface of the active semiconductor layer sequence, also have a (0001)-oriented main surface.The different morphology and surface reconstruction of the facets usually leads to the material of the further layer sequence being formed thinner and / or with a different composition on the facets of the V-pits during epitaxy than on a main surface of the active semiconductor layer sequence.

[0026] The (0001) main faces of a nitride compound semiconductor material are generally polar due to the crystal structure of such semiconductor materials. The facets of V-pits in such a grown nitride compound semiconductor material typically exhibit a {1-101} orientation and are thus semipolar.

[0027] According to one embodiment, each V-pit is bounded by six facets formed by a non-polar or semi-polar face, preferably by a semi-polar {10-11} face.

[0028] Due to the difference in morphology and surface reconstruction between the main surface and facets of the V-pits, it is possible that the aluminum content and / or the indium content of the further layer sequence applied to the facets of the V-pits is changed, preferably reduced, compared to the aluminum content of the further layer sequence applied to the main surface of the active layer sequence.

[0029] For example, the value of the indium content on the facets of the V-pits has a value between 0.1% and 60% inclusive, preferably a value between 0.5% and 10% inclusive, while the indium content of the further layer sequence on the main surface of the active semiconductor layer sequence preferably has a value between 1% and 30% inclusive.

[0030] For example, the value of the aluminum content on the facets of the V-pits has a value between 1% and 100% inclusive, preferably a value between 5% and 25% inclusive, while the aluminum content of the further layer sequence on the main surface of the active semiconductor layer sequence preferably has a value between 1% and 100% inclusive.

[0031] According to a particularly preferred embodiment of the method, the further layer sequence is selectively removed from the facets of the V-pits by etching in the epitaxial reactor in situ. In other words, the growth substrate with the grown buffer layer and the grown active semiconductor layer sequence, as well as the grown further layer sequence, is removed by etching in the epitaxial reactor. Particularly preferably, the workpiece remains in the epitaxial reactor between the growth processes and the etching process. This simplifies the production of the semiconductor chip.

[0032] To achieve material removal from the subsequent layer sequence in the epitaxial reactor during the etching process, the process parameters in the epitaxial reactor are modified accordingly compared to the growth process. For example, the hydrogen content during etching is increased compared to the hydrogen content during epitaxial growth within the epitaxial reactor. For example, the hydrogen content during epitaxial growth within the epitaxial reactor has a value between 0 and four times the sum of the hydrides that do not correspond to hydrogen, while the hydrogen content within the epitaxial reactor during etching is, for example, at least one-tenth of the sum of the hydrides that do not correspond to hydrogen.

[0033] For the epitaxial deposition of nitride compound semiconductor materials, the epitaxial reactor typically contains gaseous precursor materials, one of which comprises nitrogen, and another of which comprises an element from Group III of the Periodic Table, such as gallium, aluminum, or indium. According to one embodiment of the method, the ratio of nitrogen to a Group III element is reduced during the etching process compared to the growth process. For example, the ratio of nitrogen available for growth to a Group III element available for growth on the surface during the epitaxial process has a value greater than 0.2, preferably greater than 1, whereas during etching it has a value less than 1, preferably less than 0.1.

[0034] Adjusting temperature and pressure can also change the conditions in the epitaxial reactor in such a way that the further layer sequence is removed instead of growing.

[0035] Furthermore, it is possible that regions of the further layer sequence which directly adjoin the edges of the openings of the V-pits in the further layer sequence are removed obliquely during the selective removal of the further layer sequence from the semiconductor facets of the V-pits, so that the facets of the V-pits in the region formed by the further layer sequence have a greater inclination relative to a normal of the main surface of the active semiconductor layer sequence than the rest of the facet.

[0036] For example, a radiation-emitting semiconductor chip comprises an epitaxial growth substrate, an active radiation-generating layer sequence and a further layer sequence.

[0037] Furthermore, the semiconductor chip preferably comprises a p-doped semiconductor layer, wherein a plurality of V-pits extend from the further layer sequence through the further layer sequence and the radiation-generating semiconductor layer sequence. The V-pits taper from the further layer sequence through the radiation-generating layer sequence.

[0038] The material of the p-doped semiconductor layer particularly preferably fills the V-pits completely or partially and is in direct contact with the radiation-generating semiconductor layer sequence at the facets of the V-pits.

[0039] Particularly preferably, the main surface of the growth substrate onto which the buffer layer is epitaxially grown is structured. The structuring of the growth substrate can, for example, comprise structural elements formed as dome-shaped domes. The dome-shaped domes particularly preferably have a base with a diameter between 0.4 micrometers and 3.9 micrometers. The height of the domes is particularly preferably between 0.5 micrometers and 3 micrometers.

[0040] For example, the buffer layer is n-doped at least in the area adjacent to the active semiconductor layer sequence.

[0041] One idea of ​​the present application is to completely remove the additional layer sequence, which is usually arranged between the p-doped layer and the radiation-generating semiconductor layer sequence to block electrons but also hinders the injection of holes, from the facets of the V-pits, thus enabling better injection of holes from the p-doped semiconductor layer into the radiation-generating zone. In this way, the quantum wells of the active semiconductor layer sequence are more evenly supplied with holes perpendicular to their main extension direction. In particular, quantum wells that are further apart from the p-doped layer are better supplied with holes. In this way, the current densities required to achieve a specific radiation yield of the semiconductor chip are advantageously reduced.In particular, the current density in the individual quantum wells is reduced, resulting in a reduction in the probability of non-radiative loss processes of charge carriers in the active radiation-generating semiconductor layer sequence at nominal current. The nominal current, for example, has current densities of at least 5 A / cm. 2 This leads to increased efficiency of the semiconductor chips.

[0042] Furthermore, removing the further layer sequence from the facets of the V-pits leads to a lower serial resistance for injection of holes into the quantum wells and consequently to a lowering of the forward voltage.

[0043] Features and embodiments which are described here only in connection with the method can also, to the extent technically reasonable, be formed in the semiconductor chip and vice versa.

[0044] Further advantageous embodiments and developments of the invention will become apparent from the embodiments and examples described below in conjunction with the figures. Based on the schematic sectional views of the Fig. 1 to 6 an embodiment of a method is explained in more detail. Fig. 7 shows a schematic sectional view of a semiconductor chip according to an example. Fig. Figure 8 shows an exemplary schematic representation of an atomic force microscopy image of an etched surface of a further layer sequence. Fig. 9 shows an example of a height profile of the image from Fig. 8 along line AA'.

[0045] Identical, similar, or functionally identical elements are provided with the same reference numerals in the figures. The figures and the relative sizes of the elements depicted in the figures are not to be considered to scale. Rather, individual elements, particularly layer thicknesses, may be exaggerated for clarity and / or clarity.

[0046] In the method according to the embodiment of the Fig. 1 to 6, in a first step, a growth substrate 1 is provided, for example made of sapphire ( Fig. 1). The first main surface of the sapphire substrate 1 is structured, for example, with dome-like structural elements 2, as already described in the general part of the description.

[0047] In a next step, which is shown schematically in Fig. As shown in Figure 2, a buffer layer 3 is epitaxially deposited on the growth substrate 1. The buffer layer 3 comprises GaN or is formed from GaN. A plurality of V-pits 4 are formed in the buffer layer 3 during the epitaxial growth. For the sake of clarity, Fig. 2 only a V-Pit 4 is shown as an example in cross-section.

[0048] The buffer layer 3 is n-doped at least in the region facing away from the growth substrate 1. The V-pits 4 can extend through the buffer layer 3 to the growth substrate 1 or, as in the present case, Fig. 2 schematically shown, only penetrate a partial area of ​​the buffer layer 3.

[0049] In a next step, a radiation-generating active semiconductor layer sequence 5 is epitaxially deposited on the buffer layer 3 (not shown). The radiation-generating semiconductor layer sequence 5 is formed in this case from alternatingly arranged barrier layers 6 and quantum wells 7. The barrier layers 6 are formed from GaN, AlGaN, InGaN, or AlInGaN, or comprise one of these materials, while the quantum wells 7 comprise InGaN or consist of InGaN.

[0050] During the epitaxial growth of the active radiation-generating semiconductor layer sequence 5, the V-pits 4 extend into the radiation-generating semiconductor layer sequence 5. The facets 8 of the V-pits are also completely covered with the quantum films 6 and the barrier layers 7 of the active semiconductor layer sequence 5.

[0051] In a subsequent step, which is shown schematically in Fig. As shown in Figure 3, a further layer sequence 9 is epitaxially deposited on the radiation-generating semiconductor layer sequence 5. The further layer sequence 5 is formed in this case from alternating AlGaN layers 10 and InGaN layers 11. GaN layers can also be used instead of the AlGaN or InGaN layers 11. The further layer sequence 9 is an electron-blocking layer sequence in this case.

[0052] The further layer sequence 9 is also deposited during epitaxial growth on the facets 8 of the V-pits 4. However, the further layer sequence 9 on the facets 8 of the V-pit 4 has a lower aluminum content and a smaller thickness than on a main surface 12 of the active radiation-generating semiconductor layer sequence 5.

[0053] In a next step, which is shown schematically in Fig. 4, the further layer sequence 9 is removed again from the facets 8 of the V-pits 4, while the further layer sequence 9 remains on the main surface 12 of the radiation-generating semiconductor layer sequence 5. In this case, it is possible that the thickness of the further layer sequence 9 on the main surface 12 of the radiation-generating semiconductor layer sequence 5 decreases.

[0054] The removal of the further layer sequence 9 from the facets 8 of the V-pits 4 can, for example, be carried out in situ within the epitaxial reactor by changing the process parameters in the reactor.

[0055] Furthermore, it is possible, as shown schematically in Fig. 5 shows that the regions 13 of the further layer sequence 9 which directly adjoin the edges of the opening of the V-pits 4 in the further layer sequence 9 are removed to a greater extent during the selective removal of the further layer sequence from the facets 8 of the V-pits 4, so that the facets 8 of the V-pits 4 in the region 14 formed by the further layer sequence 9 have a greater inclination relative to a normal of the main surface 12 of the active semiconductor layer sequence 5 than the rest of the facet 8.

[0056] In a next step, which is shown schematically in Fig. As shown in Figure 6, a p-doped semiconductor layer 15 is epitaxially grown on the further semiconductor layer sequence 9. The p-doped semiconductor layer 15 completely fills the V-pits 4. Since the material of the further layer sequence 9 has been removed from the facets 8 of the V-pits 4, the material of the p-doped semiconductor layer 15 is in direct contact with the radiation-generating semiconductor layer sequence 5. Furthermore, the p-doped semiconductor layer 15 has a certain thickness above the radiation-generating layer sequence 5.

[0057] The semiconductor chip according to the example of Fig. 7 comprises a growth substrate 1, which is made of sapphire, for example. A buffer layer 3 comprising GaN is applied to a main surface 16 of the growth substrate 1, which can be structured as described above. The buffer layer 3 is n-doped, at least in the region facing away from the main surface 16 of the growth substrate 1.

[0058] A radiation-generating active semiconductor layer sequence 5 with alternating quantum wells 6 and barrier layers 7 is formed on the buffer layer 3. The barrier layers 7 are formed, for example, from GaN, while the quantum wells 6 are formed from InGaN.

[0059] On the active radiation-generating semiconductor layer sequence 5, a further layer sequence 9 is arranged, which is formed from alternating AlGaN layers 10 and InGaN or GaN layers 11.

[0060] The semiconductor chip according to the example of Fig. 7 comprises a plurality of V-pits 4 and a p-doped semiconductor layer 15, the material of which completely fills the V-pits 4. In this case, the V-pits 4 completely penetrate the further layer sequence 9 and the radiation-generating layer sequence 5, as well as partially penetrate the buffer layer 3, wherein the cross section of the V-pits 4 tapers continuously from the p-doped layer 15 toward the buffer layer 3.

[0061] The material of the p-doped semiconductor layer 15 is in direct contact with the radiation-generating semiconductor layer sequence 5 at the facets 8 of the V-pits 4. The arrows in Fig. 7 are intended to schematically symbolize the better supply of the quantum films 6 in the active semiconductor layer sequence 5 with holes + from the p-doped layer 15.

[0062] Fig. Figure 8 shows an exemplary schematic representation of an atomic force microscopy image of the surface of another layer sequence 9 in the area of ​​several V-pits 4, while Fig. 9 shows an example of a height profile along the line AA' of the Fig. 8. The arrows in Fig. 8 indicate the same locations on the surface of the atomic force microscopy image as the arrows in the height profile of the Fig. 9. The bright circled area in the photo of the Fig. 8 shows laterally removed areas of the further layer sequence 9 around the V-pit 4 as already shown in the Fig. 5 was described. List of reference symbols 1 growth substrate 2 structural elements 3 Buffer layer 4 V-pits 5 radiation-generating semiconductor layer sequence 6 Quantum film 7 Barrier layer 8 facets of the V-pits 9 further layer sequence 10 AlGaN layer 11 InGaN layer 12 Main surface of the active layer sequence 13 areas of the further layer sequence 14 areas of facets 15 p-doped semiconductor layer 16 Main surface of the substrate + holes

Claims

[1] Method for producing a radiation-emitting semiconductor chip comprising the following steps: - providing a growth substrate (1), - epitaxial growth of a buffer layer (3) on the growth substrate (1), wherein a plurality of V-pits (4) are produced in the buffer layer (3), - epitaxial growth of a radiation-generating active semiconductor layer sequence (5) on the buffer layer (3), wherein the structure of the V-pits (4) continues into the active semiconductor layer sequence (5), - epitaxial growth of a further electron-blocking layer sequence (9) on the active semiconductor layer sequence (5), wherein the structure of the V-pits (4) continues into the further electron-blocking layer sequence (9), and wherein the further electron-blocking layer sequence (9) is formed from alternatingly arranged AlGaN layers (10) and InGaN layers (11) or from alternatingly arranged InGaN layers and GaN layers, and wherein the aluminum content and / or indium content of the further electron-blocking layer sequence (9) applied to facets (8) of the V-pits (4) is reduced compared to the aluminum content and / or indium content of the further electron-blocking layer sequence (9) applied to a main surface (12) of the active semiconductor layer sequence (5), - selectively removing the further electron-blocking layer sequence (9) from the facets (8) of the V-pits (4) by etching in the epitaxial reactor in situ, wherein the further electron-blocking layer sequence (9) remains on the main surface (12) of the active semiconductor layer sequence (5), and - epitaxial growth of a p-doped semiconductor layer (15) which completely or partially fills the V-pits (4). [2] Method according to the preceding claim, in which - the active semiconductor layer sequence (5) comprises a plurality of quantum films (6) which are separated from one another by barrier layers (7), and - the quantum films (6) comprise InGaN and the barrier layers (7) comprise GaN or AlGaN. [3] Method according to one of the above claims, in which the further electron-blocking layer sequence (9) is completely removed from the facets (8) of the V-pits (4), so that the p-doped semiconductor layer (15) at the facets (8) is in direct contact with the active semiconductor layer sequence (5). [4] Method according to one of the above claims, in which the thickness of the further electron-blocking layer sequence (9) on the facets (8) of the V-pits (4) is made thinner than on a main surface (12) of the active semiconductor layer sequence (5). [5] A method according to any one of the above claims, wherein a hydrogen content during the etching process is increased compared to a hydrogen content during the epitaxial growth process within the epitaxial reactor. [6] Method according to one of the above claims, in which a main surface (16) of the growth substrate (1) on which the buffer layer (3) is epitaxially grown is structured. [7] Method according to one of the above claims, wherein the growth substrate (1) comprises sapphire, SiC, GaN, AlN or silicon. [8] Method according to one of the above claims, in which - each V-pit (4) is bounded by the facets (8), the number of which is a multiple of six, and - each facet (8) is formed by a non-polar or semi-polar surface. [9] Method according to one of the above claims, in which the buffer layer (3) is formed n-doped at least in the region adjacent to the active semiconductor layer sequence (5).

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