Abstract
In an embodiment a method for structuring a semiconductor surface includes providing the semiconductor surface, wherein the semiconductor surface is part of a GaN-semiconductor layer, irradiating the semiconductor surface with an electron beam in order to produce an irradiated section and anisotropic wet-chemical etching of the semiconductor surface, wherein an etching rate in the irradiated section is less than that in an unirradiated section of the semiconductor surface, and wherein no etching mask is applied to the semiconductor surface before anisotropic wet-chemical etching.
Claims
1.-17. (canceled)
18. A method for structuring a semiconductor surface, the method comprising: providing the semiconductor surface, wherein the semiconductor surface is part of a GaN-semiconductor layer; irradiating the semiconductor surface with an electron beam in order to produce an irradiated section; and anisotropic wet-chemical etching of the semiconductor surface, wherein an etching rate in the irradiated section is less than that in an unirradiated section of the semiconductor surface, and wherein no etching mask is applied to the semiconductor surface before anisotropic wet-chemical etching.
19. The method of claim 18, wherein the semiconductor layer comprises a III/V semiconductor.
20. The method of claim 19, wherein the semiconductor layer comprises a nitride semiconductor.
21. The method of claim 18, wherein energy of the electron beam is between 1 keV and 200 keV inclusive.
22. The method of claim 18, wherein an irradiation duration of irradiating the semiconductor surface with the electron beam is greater than or equal to 10 ms.
23. The method of claim 18, wherein wet-chemical etching of the semiconductor surface comprises wet-chemical etching with an alkaline solution.
24. The method of claim 18, wherein wet-chemical etching of the semiconductor surface comprises wet-chemical etching with KOH, NaOH, NH.sub.3 or TMAH.
25. The method of claim 18, wherein wet-chemical etching of the semiconductor surface comprises wet-chemical etching with an acid.
26. The method of claim 18, wherein a plurality of parallel sections of the semiconductor surface are irradiated with the electron beam, and wherein the parallel sections have a common main direction of extent.
27. The method of claim 18, wherein at least one ring-shaped section of the semiconductor surface is irradiated with the electron beam.
28. The method of claim 27, wherein at least two ring-shaped sections of the semiconductor surface are irradiated with the electron beam, and wherein radii of the irradiated ring-shaped sections differ from one another.
29. The method of claim 28, wherein at least two concentric ring-shaped sections of the semiconductor surface are irradiated with the electron beam.
30. The method of claim 18, wherein a punctiform irradiation of the semiconductor surface is carried out with the electron beam.
31. A semiconductor body comprising: a semiconductor surface having at least one structure, wherein the semiconductor surface is part of a GaN-semiconductor layer, wherein the at least one structure comprises a material of a topmost layer of the semiconductor surface, wherein the at least one structure is embodied along a curve or as a point, and wherein the at least one structure is produced by anisotropic wet-chemical etching without using an etching mask.
32. The semiconductor body of claim 31, wherein at least two structures are arranged as linear and/or parallel structures.
33. The semiconductor body of claim 31, wherein at least two structures are arranged as concentric ring-shaped structures.
34. The semiconductor body of claim 31, wherein a plurality of structures are arranged along a regular or quasi-regular grid and the structures comprise individual pyramidal structures.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0077] Further advantages and advantageous configurations and developments of the method for structuring a semiconductor surface and the semiconductor body will become apparent from the following exemplary embodiments illustrated in association with the figures.
[0078] FIGS. 1A to 1D show a schematic illustration of the method for structuring a semiconductor surface in accordance with one embodiment;
[0079] FIGS. 2A and 2B show a schematic illustration of parallel structures on a semiconductor surface of a semiconductor body in accordance with one embodiment;
[0080] FIGS. 3A and 3B show a schematic illustration of ring-shaped structures on a semiconductor surface of a semiconductor body in accordance with one embodiment;
[0081] FIG. 4 shows a schematic illustration of pyramidal structures on a semiconductor surface of a semiconductor body in accordance with one embodiment;
[0082] FIGS. 5A-5E and 6 show scanning electron microscopy (SEM) micrographs of structures on a semiconductor surface of a semiconductor body in accordance with various embodiments;
[0083] FIGS. 7, 8A-8F and 9A-9G show SEM micrographs of linear and parallel structures on a semiconductor surface of a semiconductor body in accordance with various embodiments;
[0084] FIG. 8G shows an SEM micrograph of a semiconductor surface of a semiconductor body in accordance with one embodiment;
[0085] FIG. 10 shows an SEM micrograph of a ring-shaped structure on a semiconductor surface of a semiconductor body in accordance with one embodiment; and
[0086] FIGS. 11A-11H, 12, 13 and 14A-C show SEM micrographs of pyramidal structures on a semiconductor surface of a semiconductor body in accordance with various embodiments.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0087] Elements that are identical, of identical type or act identically are provided with the same reference signs in the figures. The figures and the size relationships of the elements illustrated in the figures among one another should not be regarded as to scale. Rather, individual elements may be illustrated with exaggerated size in order to enable better illustration and/or in order to afford a better understanding.
[0088] In the method in accordance with the exemplary embodiment in FIGS. 1A to 1D, firstly a semiconductor layer 1 comprising a semiconductor surface 2 is provided. The semiconductor layer 1 can be grown epitaxially and can comprise or consist of a III/V semiconductor, for example a nitride semiconductor such as GaN. It can be a constituent part of an optoelectronic component and comprise an active region used for generating and/or detecting radiation. The semiconductor surface 2 is formed by the exposed outer surface or a part of the exposed outer surface of the semiconductor layer 1. The semiconductor surface 2 can have in particular an n-conducting region, a nominally undoped region or a p-conducting region and can be embodied as a light exit and/or light entrance surface. This arrangement is shown schematically in FIG. 1A.
[0089] FIG. 1B schematically shows the process of irradiating the semiconductor surface 2 with an electron beam 3. The irradiation of the semiconductor surface 2 produces an irradiated section 4. The irradiated section 4 comprises at least the area corresponding to the extent of the electron beam 3. Sections that are not irradiated by the electron beam 3 are unirradiated sections 5.
[0090] FIG. 1C shows the wet-chemical etching of the semiconductor surface 2. For this purpose, the surface 2 is brought into direct contact with an etching liquid 6, for example an alkaline solution.
[0091] FIG. 1D shows the semiconductor layer 1 after the semiconductor surface 2 has been irradiated with the electron beam 3 and the semiconductor surface 2 has been etched with an etching liquid 6. The etching rate in the irradiated section 4 is significantly less than that in the unirradiated sections 5. This gives rise to a structure 7 that differs from the random roughening of the semiconductor surface 2 by virtue of a greater accentuation vis-à-vis the unirradiated sections 5, which were etched to a greater extent.
[0092] FIGS. 2A and 2B show a schematic illustration of parallel structures 8 on a semiconductor surface 2 of a semiconductor body in accordance with one embodiment. The parallel structures 8 have a common main direction of extent. The parallel structures 8 are embodied linearly in the main direction of extent and arranged in such a way that the prism-shaped linear and parallel structures 8 on the semiconductor surface 2 touch one another (FIG. 2A).
[0093] FIGS. 3A and 3B show a schematic illustration of ring-shaped structures 9 on a semiconductor surface 2 of a semiconductor body in accordance with one embodiment. The ring-shaped structures 9 are arranged concentrically and have different radii and a common centroid corresponding to the center point of the ring-shaped structures 9.
[0094] FIG. 4 shows a schematic illustration of pyramidal structures 10 on a semiconductor surface 2 of a semiconductor body in accordance with one embodiment. The pyramidal structures 10 have a polygon, in particular a symmetrical polygon, as base area. By way of example, the pyramidal structures 10 can have a hexagonal or dodecagonal base area. In particular, etching with an alkaline solution such as KOH, TMAH or NH.sub.3 can result in pyramidal structures 10 having a hexagonal base area and etching with an acid such as H.sub.3PO.sub.4 can result in pyramidal structures 10 having a dodecagonal base area. The pyramidal structures 10 are arranged along a regular grid having at least two directions of extent. In particular, the directions of extent are arranged perpendicular to one another. The distances between the pyramidal structures 10 can be identical within a direction of extent. The distances between pyramidal structures 10 within different directions of extent can differ from one another. In particular, the pyramidal structures 10 can be arranged quasi-regularly within the grid.
[0095] FIGS. 5A to 5E show scanning electron microscopy (SEM) micrographs of irradiated sections 4, unirradiated sections 5 and a structure 7 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The semiconductor surface 2 was etched for 6 minutes in 30% by weight KOH at 80° C.
[0096] FIGS. 5A and 5B show a semiconductor surface 2 of a GaN semiconductor body and FIG. 5C shows a magnified view of FIG. 5A. The semiconductor surface 2 was partly irradiated with an electron beam 3 before etching. Less roughening of the semiconductor surface 2 and also a linear structure 7 can be discerned in the irradiated section 4.
[0097] FIG. 5D shows the magnified view of the irradiated section 4 of the GaN semiconductor surface 2 from FIG. 5A. Acceleration and deacceleration of the electron beam 3 during irradiation is visualized in this figure. In this case, the electron beam 3 moved from the left edge on a horizontal line to the right edge of the irradiated section 4. The speed of the electron beam 3 initially increased during the movement on the horizontal line and decreased again before reaching the right edge of the irradiated section 4. The electron beam 3 momentarily remained stationary on the points at the left edge of the irradiated section 4 in order to store the recorded emission signal. The more slowly the electron beam 3 was moved over the semiconductor surface 2, the smaller the pyramid sizes that can be observed on the semiconductor surface 2. The linear structure 7—illustrated in a magnified view in FIG. 5E—at the left edge of the irradiated section 4 arises from the semiconductor surface 2 being removed to a particularly small extent at the location of the semiconductor surface 2 at which the electron beam 3 was momentarily stationary.
[0098] FIG. 6 shows an SEM micrograph of structures 7 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The irradiation of the irradiated sections 4 of the semiconductor surface 2 was carried out with an energy of the electron beam 3 of 8 keV and an irradiation duration of 100 ms per pixel. The subsequent etching process comprises etching the semiconductor surface 2 for 6 minutes in 30% by weight KOH at 80° C. The structures 7 have the shape of circles (top) or a sector of an annulus (bottom).
[0099] FIG. 7 shows an SEM micrograph of linear and parallel structures 8 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The irradiation of the linear and parallel sections 4 of the semiconductor surface 2 was carried out with an irradiation duration of 100 ms per pixel. Per linear section, 100 pixels were irradiated over a length of 15 μm. The subsequent etching process comprises etching the semiconductor surface 2 for 6 minutes in 30% by weight KOH at 80° C. The linear and parallel structures 8 have a common horizontal main direction of extent. The distances between the linear and parallel structures 8 perpendicular to the main direction of extent are 1.5 μm, as a result of which they touch one another at an etching depth of approximately 3 μm on account of the angles of the sidewalls of the resulting pyramids of 61° on the semiconductor surface 2. A reduced random roughening of the semiconductor surface 2 in and between the irradiated sections 4 can be discerned. Smaller etching depths and smaller distances between the pyramids may be expedient in the case of a thinner semiconductor layer.
[0100] FIGS. 8A to 8F show SEM micrographs of linear and parallel structures 8 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The irradiation of the linear and parallel sections 4 was carried out with 100 ms per pixel and with different electron energies. An electron energy of 5 keV was used in FIG. 8A, 8 keV in FIG. 8B, 10 keV in FIG. 8C and 12 keV in FIG. 8D. The subsequent etching process comprised etching the semiconductor surface 2 for 6 minutes in 30% by weight KOH at 80° C. The SEM micrographs show that the electron energy does not influence the formation of the linear and parallel structures 8.
[0101] FIGS. 8E and 8F show SEM micrographs of the samples from FIGS. 8C and 8B, which were recorded by way of in-lens detection. The dark contrasts with this type of detection indicate a material having low conductivity that has been deposited on the GaN of the linear and parallel structures 8 and the semiconductor surface 2. During the structuring of the semiconductor surface, deposition of organic material on the surface may possibly occur. The origin of these deposits is not known. By way of example, this material may be carbon.
[0102] FIG. 8G shows an SEM micrograph of a semiconductor surface 2 of a GaN semiconductor body directly after irradiation of a point pattern. The irradiated sections 4 were irradiated with an electron energy of 8 keV and an irradiation duration of 5 seconds per pixel. White contrasts are evident in the irradiated sections 4. This may be an indication of an electronic effect that changes the conductivity or charge of the material. By way of example, the irradiation with the electron beam may result in an activation of passivated point defects of the semiconductor layer. In particular, FIG. 8G shows that there are no deposits on the semiconductor surface 2 before etching. The deposits that were observed after etching as shown in FIGS. 8E and 8F must therefore have arisen during or after the etching process.
[0103] FIGS. 9A to 9G show SEM micrographs of linear and parallel structures 8 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The irradiation of the linear and parallel sections 4 was carried out with an electron energy of 8 keV and an irradiation duration of 100 ms per pixel. The subsequent etching process was carried out with 30% by weight KOH at 80° C. and the etching duration was varied. The semiconductor surface 2 was etched for 1 min in FIG. 9A, for 2 min in FIG. 9B, for 3 min in FIG. 9C, for 4 min in FIG. 9D, for 5 min in FIG. 9E, for 6 min in FIG. 9F and for 7 min in FIG. 9G. In all the figures, the linear and parallel structures 8 are clearly discernible and correspond approximately to the preferred target roughness in the productive application. An increase in the etching duration results in an intensified random roughening of the semiconductor surface 2 in the unirradiated sections 5.
[0104] FIG. 10 shows an SEM micrograph of a ring-shaped structure 9 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The ring-shaped section 4 was irradiated with an electron energy of 8 keV and an irradiation duration of 100 ms per pixel. The subsequent etching process comprised etching the semiconductor surface 2 for 6 min with 30% by weight KOH at 80° C. The ring-shaped structure 9 approximately has the shape of an annulus.
[0105] When producing concentric ring-shaped structures 9, the entire circle pattern can have a radius of 500 μm with a chip diameter of 1 mm. In particular, the ring-shaped structures 9 on the semiconductor surface 2 should touch one another. Given an etching depth of approximately 3.5 μm, a distance of 2 μm may then be expedient. Otherwise sections with a random roughening are situated between the ring-shaped structures 9.
[0106] FIGS. 11A to 11H show SEM micrographs of pyramidal structures 10 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The punctiform irradiation of circular sections 4 with the extent of the electron beam 3 on the semiconductor surface 2 was carried out along a regular grid comprising 5×5 sections with an electron energy of 8 keV and the irradiation duration per pixel was varied. The subsequent etching process comprised etching the semiconductor surface 2 for 6 min with 30% by weight KOH at 80° C. FIG. 11A shows an overview micrograph of the pyramidal structures 10 with an irradiation duration of 2 s (bottom right), 3 s (bottom left), 4 s (top right) and 5 s (top left). The pyramidal structures 10 are arranged along regular 5×5 grids. FIGS. 11B to 11H show magnified views of the irradiated grids (left and bottom boundaries marked in each case) with various irradiation durations. The irradiation duration was 0.1 s in FIG. 11B, 1 s in FIG. 11C, 2 s in FIG. 11D, 3 s in FIG. 11E, 4 s in FIG. 11F, 5 s in FIG. 11G and 10 s in FIG. 11H. The pyramidal structures 10 are evident starting from an irradiation duration of 0.1 s, the manifestation of said pyramidal structures increasing as the irradiation duration increases.
[0107] FIG. 12 shows an SEM micrograph of a magnified view of a pyramidal structure 10 from FIG. 11G. The pyramidal structure 10 has a split and finely roughened vertex. In particular, the vertex of the pyramidal structure 10 has a diameter approximately 400 nm wide. It is thus possible to observe a larger top area of the pyramidal structure 10 than the area of the irradiated circular section having a diameter of 20 nm.
[0108] FIG. 13 shows an SEM micrograph of pyramidal structures 10 on a semiconductor surface 2 of a GaN semiconductor body in accordance with one embodiment. The punctiform irradiation of circular sections 4 was carried out with an electron energy of 8 keV and an irradiation duration of 100 ms per pixel. The distance between the lines is 1.5 μm. The length of the lines is 45 μm with 100 pixels over the entire length. The subsequent etching process comprised etching the semiconductor surface 2 for 6 min with 30% by weight KOH at 80° C. In the horizontal direction of extent the individual pyramidal structures caused touch one another on the semiconductor surface 2, whereas they are at a distance from one another in the vertical direction of extent.
[0109] FIGS. 14 A-C show SEM micrographs of pyramidal structures 10 on a semiconductor surface of a GaN semiconductor body in accordance with one embodiment. The punctiform irradiation of 6×6 circular sections 4 with distances of 1.5 μm was carried out with an irradiation duration of 10 s per pixel and an electron energy of 8 keV. The subsequent etching process comprised etching the semiconductor surface 2 for 5 min with 85% by weight H.sub.3PO.sub.4 at 150° C. FIG. 14A shows that almost the entire semiconductor was etched away. The magnified views in FIGS. 14B and 14C show that pyramidal structures 10 are present at the irradiated locations.
[0110] This method can find potential application in the separation of individual semiconductor chips. By means of targeted exposure it is possible to produce surface structures, such as alignment marks, which are attacked during the etching process to a lesser extent than the semiconductor material of the unirradiated sections.
[0111] The invention is not restricted to the exemplary embodiments by the description on the basis thereof. Rather, the invention encompasses any novel feature and also any combination of features, which in particular includes any combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.
