Semiconductor lens, production method for same, and light-receiving element

Abstract

A substrate (101) that has a principal surface in the (100) plane is etched using a first mask pattern (201) that has an opening (201a) that is an ellipse for which the major axis direction is the [0-11] direction of InP to form a plano-convex lens (103) that has a convex surface that is a spherical surface for which the major axis direction is the [0-11] direction. The plano-convex lens (103) is formed at a bottom surface of a recess (102).

Description

Semiconductor lens, its manufacturing method, and light receiving element

[0001] The present invention relates to a semiconductor lens, a method for manufacturing the same, and a light-receiving element.

[0002] Photodiodes for communication applications are becoming increasingly miniaturized to reduce element capacitance and improve operating bandwidth. However, miniaturization of surface-type photodiodes reduces the light-receiving area and reduces the coupling efficiency with incident light. To address this issue, there is a technology for monolithically forming a lens on the semiconductor substrate on which the photodiode is formed, in order to improve the optical coupling efficiency of small photodiodes (Non-Patent Document 1).

[0003] In Non-Patent Document 1, a lens is formed monolithically on an InP substrate using a wet etching technique. This technique takes advantage of the fact that the etching rate is faster around the masked area, and the area close to the periphery of the masked area is etched more deeply to form a convex lens shape. In Non-Patent Document 1, an InP substrate is etched using a mask with a deformed opening in plan view.

[0004] SR Cho et al., "Enhanced Optical Coupling Performance in an InGaAs Photodiode Integrated With Wet-Etched Microlens", IEEE Photonics Technology Letters, vol. 14, no. 3, pp. 378-380, 2002.

[0005] However, the above-mentioned technique has the problem that the radius of curvature of the formed lens varies depending on the lens position, resulting in a distorted lens. In InP, facets are formed according to the surface orientation by wet etching. Therefore, the etching rate varies depending on the direction of the facet, resulting in a different radius of curvature depending on the lens position.

[0006] The present invention has been made to solve the above problems, and has as its object to enable the formation of lenses with a uniform radius of curvature by etching an InP substrate.

[0007] A method for manufacturing a semiconductor lens according to the present invention includes a first step of forming a mask pattern having an elliptical opening on a substrate made of single-crystal InP and having a main surface formed in a (100) plane, and a second step of wet-etching the substrate using the mask pattern as a mask to form a recess in the substrate and a plano-convex lens having a convex surface at the bottom of the recess, the mask pattern having an elliptical opening with its major axis oriented in the [0-11] direction of the InP.

[0008] A semiconductor lens according to the present invention includes a substrate made of single-crystal InP and having a (100) plane as its main surface, a recess formed in the substrate, and a plano-convex lens having a convex surface formed on the bottom of the recess.

[0009] The light receiving element according to the present invention has the above-described semiconductor lens formed on one surface and a photodiode formed on the other surface.

[0010] As described above, according to the present invention, a plano-convex lens is formed on a substrate made of single crystal InP and having a main surface formed in the (100) plane using a mask pattern having an elliptical opening whose major axis is oriented in the [0-11] direction of InP. Therefore, lenses with a uniform radius of curvature can be formed by etching the InP substrate.

[0011] FIG. 1A is a cross-sectional view showing a state of an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1B is a plan view showing a state of an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1C is a cross-sectional view showing a state of a semiconductor lens in an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1D is a cross-sectional view showing a state of a semiconductor lens in an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1E is a plan view showing a state of a semiconductor lens in an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1F is a cross-sectional view showing a state of a semiconductor lens in an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1G is a cross-sectional view showing a state of a semiconductor lens in an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 1H is a cross-sectional view showing a state of a semiconductor lens in an intermediate step in explaining a method for manufacturing a semiconductor lens according to an embodiment of the present invention. FIG. 2 is a structural diagram showing a configuration of a light-receiving element according to an embodiment of the present invention.

[0012] A method for manufacturing a semiconductor lens according to an embodiment of the present invention will be described below with reference to FIGS. 1A to 1H.

[0013] First, as shown in FIGS. 1A and 1B, a first mask pattern 201 having an elliptical opening 201a is formed on a substrate 101 made of single-crystal InP and having a (100) major surface (first step). The shape of the opening 201a in the first mask pattern 201 can be an ellipse whose major axis is oriented in the [0-11] direction of InP. The opening 201a can be an ellipse whose major axis is 5% to 50% longer than its minor axis. The first mask pattern 201 can be made of an inorganic material such as silicon oxide.

[0014] Next, the substrate 101 is wet-etched using the first mask pattern 201 as a mask, thereby forming a recess 102 having an elliptical shape in plan view from the normal direction of the substrate 101, as shown in FIGS. 1C, 1D, and 1E, and forming a plano-convex lens 103 having a convex surface on the bottom surface of the recess 102 (second step). For example, a plano-convex lens 103 having a substantially spherical convex surface can be formed. Note that FIG. 1C shows a cross section of the ellipse in the minor axis direction, and FIG. 1D shows a cross section in the major axis direction. The shape of the recess 102 in plan view is substantially the same as the shape of the opening 201a, with the major axis oriented in the [0-11] direction of InP. For example, the substrate 101 can be etched by wet etching using an etching solution such as Br.

[0015] As described above, the plano-convex lens 103 having a convex surface can be formed by wet etching the substrate 101 using the first mask pattern 201 having the elliptical opening 201 a. For example, the plano-convex lens 103 having a spherical convex surface can be formed.

[0016] As described above, the first mask pattern 201 having the elliptical opening 201a with the major axis oriented in the [0-11] direction of InP is used to etch the substrate 101 whose main surface is the (100) plane, thereby forming the plano-convex lens 103 having a convex surface. The plano-convex lens 103 is formed on the bottom surface of the recess 102.

[0017] According to the above-described etching process, as shown in Non-Patent Document 1, the etching rate is higher in regions closer to the periphery of opening 201a. Here, the distance from the periphery of opening 201a to the center of the ellipse is different in the long axis direction of opening 201a compared to the short axis direction. Therefore, at positions equidistant from the center of elliptical opening 201a, the etching rate is lower in the long axis direction than in the short axis direction.

[0018] In the above-described state, by orienting the facet with the faster etching rate in the direction of the longer axis of the ellipse and the facet with the slower etching rate in the direction of the shorter axis of the ellipse, the etching rate can be made equal at positions equidistant from the center of the ellipse in both the longer and shorter axis directions. As a result, by appropriately setting the dimensions of the ellipse of the opening 201a, a plano-convex lens 103 with a spherical surface and a uniform radius of curvature can be formed. The plano-convex lens 103 can have a perfectly circular cross section parallel to the plane of the substrate 101.

[0019] Next, as shown in Fig. 1F, a second mask pattern 202 is formed to cover the plano-convex lenses 103. Next, the substrate 101 is etched using the second mask pattern 202 as a mask, thereby bringing the height of the periphery 101a of the recess 102 closer to the height of the plano-convex lenses 103, as shown in Fig. 1G (third step). For example, by etching the substrate 101 by wet etching using hydrochloric acid or the like, the height of the periphery 101a of the recess 102 can be brought closer to the height of the plano-convex lenses 103.

[0020] Next, after removing the second mask pattern 202, an anti-reflection coating 104 is formed to cover the surface of the plano-convex lens 103, as shown in FIG. 1H (step 4). The anti-reflection coating 104 can be composed of layers of SiO and TiO. If the height of the periphery 101a of the recess 102 is higher than the plano-convex lens 103, it is not easy to form the anti-reflection coating 104 uniformly on the plano-convex lens 103. By bringing the height of the periphery 101a closer to the height of the plano-convex lens 103, it becomes easier to form the anti-reflection coating 104 uniformly on the plano-convex lens 103.

[0021] The semiconductor lens according to the above-described embodiment can be provided on a substrate on which a photodiode is formed. For example, as shown in Fig. 2, a light receiving element can be formed in which the semiconductor lens according to the embodiment including a plano-convex lens 103 is formed on one surface of a substrate 101 and a photodiode 105 is formed on the other surface of the substrate 101.

[0022] As described above, according to the embodiment of the present invention, a plano-convex lens is formed on a substrate made of single crystal InP and having a main surface formed in the (100) plane using a mask pattern having an elliptical opening whose major axis is oriented in the [0-11] direction of InP. Therefore, lenses with a uniform radius of curvature can be formed by etching the InP substrate.

[0023] Some or all of the above-described embodiments may also be described as, but are not limited to, the following supplementary notes.

[0024] [Supplementary Note 1] A method for manufacturing a semiconductor lens, comprising: a first step of forming a mask pattern having an elliptical opening on a substrate made of single crystal InP and having a main surface formed as a (100) plane; and a second step of wet etching the substrate using the mask pattern as a mask, thereby forming a recess in the substrate and forming a plano-convex lens having a convex surface on a bottom surface of the recess, wherein the mask pattern has an elliptical opening with the major axis oriented in the [0-11] direction of InP.

[0025] [Appendix 2] The method for manufacturing a semiconductor lens according to Appendix 1, further comprising a third step of making the height of the periphery of the recess closer to the height of the plano-convex lens, and a fourth step of forming an anti-reflection film covering the surface of the plano-convex lens.

[0026] [Supplementary Note 3] The method for manufacturing a semiconductor lens according to Supplementary Note 1 or 2, wherein the plano-convex lens is formed from a spherical convex surface.

[0027] [Appendix 4] A semiconductor lens comprising: a substrate made of single-crystal InP and having a main surface formed as a (100) plane; a recess formed in the substrate; and a plano-convex lens having a convex surface formed on the bottom surface of the recess.

[0028] [Supplementary Note 5] The semiconductor lens according to Supplementary Note 4, further comprising an anti-reflection film covering the surface of the plano-convex lens.

[0029] [Supplementary Note 6] The semiconductor lens according to Supplementary Note 4 or 5, wherein the recess is formed in an elliptical shape with the direction of the major axis aligned with the [0-11] direction of InP.

[0030] [Supplementary Note 7] In the semiconductor lens described in any one of Supplementary Notes 4 to 6, the plano-convex lens is configured with a spherical convex surface.

[0031] [Supplementary Note 8] A light-receiving element having the semiconductor lens according to any one of Supplementary Notes 4 to 6 formed on one surface and a photodiode formed on the other surface.

[0032] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention.

[0033] 101...substrate, 101a...periphery, 102...recess, 103...plano-convex lens, 104...anti-reflection film, 105...photodiode.

Claims

1. A method for manufacturing a semiconductor lens, comprising: a first step of forming a mask pattern with an elliptical opening on a substrate made of single crystal InP and having a (100) main surface; and a second step of wet etching the substrate using the mask pattern as a mask to form a recess in the substrate and a plano-convex lens with a convex bottom surface in the recess, wherein the mask pattern has an elliptical opening with its major axis oriented in the [0-11] direction of InP.

2. A method for manufacturing a semiconductor lens according to claim 1, further comprising a third step of adjusting the height of the periphery of the recess to approximate the height of the plano-convex lens, and a fourth step of forming an anti-reflection film covering the surface of the plano-convex lens.

3. A method for manufacturing a semiconductor lens according to claim 1 or 2, wherein the plano-convex lens is formed from a spherical convex surface.

4. A semiconductor lens comprising a substrate made of single crystal InP with a (100) plane as its main surface, a recess formed in the substrate, and a plano-convex lens consisting of a convex surface formed on the bottom surface of the recess.

5. A semiconductor lens according to claim 4, further comprising an anti-reflection coating covering the surface of said plano-convex lens.

6. A semiconductor lens according to claim 4, wherein the recess is formed in an elliptical shape with the direction of the major axis aligned with the [0-11] direction of InP.

7. A semiconductor lens according to claim 4 or 5, wherein the plano-convex lens is composed of a spherical convex surface.

8. A light-receiving element having the semiconductor lens according to claim 4 or 5 formed on one surface and a photodiode formed on the other surface.

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