Semiconductor device and method for manufacturing the same

Abstract

To provide a semiconductor device in which a deposition film in an uneven structure can be suitably separated, and a manufacturing method of the semiconductor device.SOLUTION: A semiconductor device 1A includes: a semiconductor layer 2 having, on one surface 2a side, an uneven structure K constituted while containing a recess section 4; a first electrode film (first deposited film) 3A arranged on one surface 2a of the semiconductor layer 2; and a second electrode film (second deposited film) 3B arranged on a bottom surface 4c of the recess section 4. An enlarged section J having an enlarged cross section is arranged to an opening section 4b side of the recess section 4.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to semiconductor devices and methods for manufacturing semiconductor devices. [Background technology]

[0002] An example of a conventional semiconductor device is a photodiode described in Patent Document 1. This conventional photodiode has a comb-shaped periodic uneven structure formed on the surface of a semiconductor layer. In the periodic uneven structure, a first electrode is disposed on the top surfaces of the protrusions, and a second electrode is disposed on the bottom surfaces of the recesses. In this photodiode, surface plasmon resonance based on incident light is excited by the first electrode and the second electrode. The excited surface plasmon excites photons, including near-field light, at the interface between the semiconductor and at least one of the first electrode and the second electrode. The near-field light generates electron-hole pairs in a depletion layer in the semiconductor layer near the first electrode and the second electrode, thereby generating a photocurrent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-273832 Summary of the Invention [Problem to be solved by the invention]

[0004] In the manufacture of semiconductor devices such as those described above, a method of forming a vapor-deposited film of metal or the like on a semiconductor layer having a concave-convex structure may be employed. In this case, it is important to electrically separate the vapor-deposited film on one surface of the semiconductor layer from the vapor-deposited film on the bottom of the recess, for purposes such as forming a pair of electrodes. However, in actual vapor deposition, the vapor-deposited film may adhere not only to the intended positions of the one surface of the semiconductor layer and the bottom surface of the recess, but also to the inner wall surface of the recess, resulting in electrical connection between the vapor-deposited films.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a semiconductor device and a method for manufacturing the semiconductor device that can suitably separate a vapor-deposited film in a concave-convex structure. [Means for solving the problem]

[0006] A semiconductor device according to one aspect of the present disclosure comprises a semiconductor layer having an uneven structure including a recess on one side thereof, a first vapor-deposited film provided on one side of the semiconductor layer, and a second vapor-deposited film provided on the bottom surface of the recess, and the recess is provided with an enlarged portion whose cross-sectional area is enlarged relative to the portion on the opening side of the recess.

[0007] In this semiconductor device, the recess has an enlarged portion whose cross-sectional area is larger than that of the opening of the recess. In a recess having such an enlarged portion, a portion on the inner wall of the recess can be formed that is not hit by atoms entering the recess from the opening during deposition of a vapor-deposited film. Therefore, the first vapor-deposited film formed on one surface of the semiconductor layer and the second vapor-deposited film formed on the bottom of the recess can be effectively separated.

[0008] The inner wall surface of the recess may be provided with a narrowed portion that narrows the middle portion of the recess relative to the opening portion of the recess. At the narrowed portion, the cross-sectional area of the recess is first reduced and then expanded. Therefore, during the formation of the vapor-deposited film, a portion on the inner wall surface of the recess that is not hit by atoms entering the recess from the opening portion can be reliably formed.

[0009] The narrowed portion may be composed of a first inclined surface that gradually reduces the cross-sectional area of the recess toward the bottom of the recess, and a second inclined surface that is continuous with the first inclined surface and gradually increases the cross-sectional area of the recess toward the bottom. In this case, the second inclined surface can function as a surface that is not hit by atoms entering the recess from the opening. This allows for more reliable separation of the first vapor-deposited film on the top surface of the protrusion and the second vapor-deposited film on the bottom of the recess.

[0010] The first inclined surface may be continuous with the opening of the recess. In this case, since the narrowed portion is continuous with the opening of the recess, the separation position between the first and second deposited films can be brought closer to the opening of the recess. This ensures a sufficient distance between the first and second deposited films, ensuring more reliable separation between them. In particular, when a semiconductor device is designed for surface incidence (light incidence from one side of the semiconductor layer), the continuous change in refractive index at the opening reduces reflection loss.

[0011] The first inclined surface may be spaced apart from the opening of the recess. In this case, the narrowed portion is spaced apart from the opening of the recess, so that the separation position between the first vapor-deposited film and the second vapor-deposited film can be spaced apart from the opening of the recess. This reduces light leakage from the opening and improves light absorption efficiency, particularly when the semiconductor device is back-illuminated (light incident from the other surface of the semiconductor layer).

[0012] The first and second deposited films may be metal films, in which case they can be used as various functional films such as electrodes, scatterers, reflective films, and near-field excitation sources to form an MSM photodetector or a photodetector utilizing the near-field excitation effect.

[0013] An insulating film or a dielectric film may be provided between the semiconductor layer and the metal film on one side of the semiconductor layer. With this configuration, for example, when the metal film is used as an electrode, dark current can be suppressed.

[0014] The semiconductor layer may include a first conductivity type semiconductor layer and a second conductivity type semiconductor layer, the recess may extend through the second conductivity type semiconductor layer into the first conductivity type semiconductor layer, and the narrowed portion may be located in the second conductivity type semiconductor layer. In this case, by using the second evaporated film as a near-field excitation source, a photodetector utilizing the near-field excitation effect can be configured.

[0015] A method for manufacturing a semiconductor device according to one aspect of the present disclosure includes a processing step of forming a concave-convex structure including a recess on one side of a semiconductor layer, and a deposition step of depositing a film by vapor deposition on one side of the semiconductor layer to form a first vapor-deposited film on one side of the semiconductor layer and a second vapor-deposited film on the bottom surface of the recess, wherein the processing step includes a first step using anisotropic etching and a second step including isotropic etching subsequent to the first step.

[0016] In this semiconductor device manufacturing method, a processing step is performed to form a relief structure on one side of a semiconductor layer by combining a first step using anisotropic etching and a second step including subsequent isotropic etching. In anisotropic etching, the width of the recess formed remains constant or gradually narrows as the process progresses. On the other hand, in isotropic etching, the width of the recess gradually increases early in the process, forming an enlarged portion in the recess whose cross-sectional area is larger than the portion on the opening side of the recess. After the enlarged portion is formed, etching may be continued vertically so that the width of the recess remains within a constant range.

[0017] The first step may use reactive ion etching as anisotropic etching, and the second step may use the Bosch process, which includes isotropic etching. The combination of reactive ion etching and the Bosch process allows the enlarged portion to be formed easily and accurately. [Effects of the Invention]

[0018] According to the present disclosure, the deposited film in the concave-convex structure can be suitably separated. [Brief explanation of the drawings]

[0019] [Figure 1] 1A is a schematic cross-sectional view showing the configuration of a semiconductor device according to a first embodiment of the present disclosure, and FIG. 1B is a plan view thereof. [Figure 2] 10(a) and 10(b) are flowcharts showing an example of a manufacturing process for a semiconductor device. [Figure 3]4(a) and 4(b) are flowcharts showing an example of subsequent steps of FIG. 3. [Figure 4] 5(a) and 5(b) are schematic cross-sectional views showing a vapor deposition process for a semiconductor layer according to one embodiment of the comparative example. [Figure 5] 10(a) and 10(b) are schematic cross-sectional views showing a vapor deposition process for a semiconductor layer according to another embodiment of the comparative example. [Figure 6] 1A and 1B are schematic cross-sectional views showing a vapor deposition process for a semiconductor layer according to one embodiment of the present invention. [Figure 7] 10(a) and 10(b) are schematic cross-sectional views showing a vapor deposition process for a semiconductor layer according to another embodiment of the present invention. [Figure 8] 1A is a schematic cross-sectional view showing the configuration of a semiconductor device according to a second embodiment of the present disclosure, and FIG. 1B is a plan view thereof. [Figure 9] 10(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a third embodiment of the present disclosure, and FIG. 10(b) is a plan view thereof. [Figure 10] 10A is a schematic cross-sectional view showing the configuration of a semiconductor device according to a fourth embodiment of the present disclosure, FIG. 10B is a plan view thereof, and FIG. 10C is a schematic cross-sectional view showing a modified example of FIG. [Figure 11] 10(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a fifth embodiment of the present disclosure, and FIG. 10(b) is a plan view thereof. [Figure 12] 10(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a sixth embodiment of the present disclosure, and FIG. 10(b) is a plan view thereof. [Figure 13] 10(a) and 10(b) are schematic plan views showing deformation modes of the recessed portion. [Figure 14] 1A is a schematic cross-sectional view showing the configuration of a semiconductor device according to a modified example of the present disclosure, and FIG. 1B is a plan view thereof. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, preferred embodiments of a semiconductor device and a method for manufacturing a semiconductor device according to one aspect of the present disclosure will be described in detail with reference to the drawings. In each of the embodiments and drawings of the semiconductor device shown below, a single main component is shown, but in an actual semiconductor device, these component components may be arrayed at a predetermined pitch. [First embodiment]

[0021] FIG. 1(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a first embodiment of the present disclosure. FIG. 1(b) is its plan view. The semiconductor device 1A according to the first embodiment is configured as a vertical MSM (metal-semiconductor-metal) photodetector having a comb-shaped electrode pair. As shown in the figure, the semiconductor device 1A is configured to include a semiconductor layer 2, a first electrode film (first evaporated film) 3A, and a second electrode film (second evaporated film) 3B.

[0022] In this embodiment, for convenience, one surface 2a of the semiconductor layer 2 is defined as the front surface, and the other surface 2b of the semiconductor layer 2 is defined as the back surface. The semiconductor device 1A may be a front-illuminated photodetector in which incident light is incident from the front surface side, or a back-illuminated photodetector in which incident light is incident from the back surface side.

[0023] The semiconductor layer 2 is made of, for example, Si. The semiconductor layer 2 has, for example, a rectangular shape in a plan view. The semiconductor layer 2 has one surface 2a and another surface 2b opposite to the one surface 2a. The one surface 2a of the semiconductor layer 2 is provided with a concave-convex structure K including recesses 4. The concave-convex structure K is formed, for example, by processing the one surface 2a of the semiconductor layer 2 by etching or the like. The portions processed by etching or the like constitute the recesses 4 in the concave-convex structure K, and the portions not processed by etching or the like (the one surface 2a of the semiconductor layer 2) constitute the protrusions 5 in the concave-convex structure K. The protrusions 5 may also include a structure in which recesses 4 are formed on a flat surface.

[0024] In a plan view of the semiconductor layer 2, the recess 4 extends linearly in one in-plane direction of the surface 2a of the semiconductor layer 2, from one side on the surface 2a side to the other side (see FIG. 1(b)). The recess 4 has an enlarged portion J whose cross-sectional area is enlarged relative to the portion on the opening 4b side of the recess 4. The cross-sectional area here is the cross-sectional area in a plane perpendicular to the depth direction of the recess 4 (a plane extending in the width direction of the recess 4 in FIG. 1(a)). In this embodiment, in forming the enlarged portion J, a narrowed portion F is provided on the inner wall surface 4a of the recess 4, which narrows an intermediate portion relative to the opening 4b of the recess 4. The intermediate portion is a portion located between the opening 4b and the bottom surface 4c in the depth direction of the recess 4. The narrowed portion F is provided on the inner wall surface 4a of the recess 4, in a portion between the opening 4b and the bottom surface 4c.

[0025] The narrowed portion F is composed of a first inclined surface 6A that gradually reduces the cross-sectional area of the recess 4 toward the bottom surface 4c of the recess 4, and a second inclined surface 6B that is continuous with the first inclined surface 6A and gradually increases the cross-sectional area of the recess 4 toward the bottom surface 4c of the recess 4. The recess 4 having the narrowed portion F can be formed, for example, by two-stage dry etching. The portion from the opening portion 4b to the first inclined surface 6A can be formed by anisotropic etching such as reactive ion etching. The portion from the second inclined surface 6B to the bottom surface 4c can be formed by etching including isotropic etching such as the Bosch process.

[0026] There are no particular limitations on the inclination angle θ1 of the first inclined surface 6A relative to the bottom surface 4c of the recess 4 and the inclination angle θ2 of the second inclined surface 6B relative to the bottom surface 4c of the recess 4. The inclination angle θ1 of the first inclined surface 6A and the inclination angle θ2 of the second inclined surface 6B may be equal to or different from each other. The inclination angle θ1 of the first inclined surface 6A may be greater than the inclination angle θ2 of the second inclined surface 6B or may be smaller than the inclination angle θ2 of the second inclined surface 6B.

[0027] In this embodiment, the first inclined surface 6A is continuous with the opening portion 4b of the recess 4. The cross-sectional area of the recess 4 gradually decreases from the position of the opening portion 4b along the first inclined surface 6A and is smallest at the boundary portion R between the first inclined surface 6A and the second inclined surface 6B. In this embodiment, the second inclined surface 6B forms an enlarged portion J. The cross-sectional area of the recess 4 gradually increases from the boundary portion R to the second inclined surface 6B and is constant between the second inclined surface 6B and the bottom surface 4c. Due to this configuration of the recess 4, the second inclined surface 6B cannot be seen from the one surface 2a side of the semiconductor layer 2 in a plan view of the semiconductor layer 2.

[0028] The Bosch process described above is a type of dry etching technique that forms recesses by repeating the steps of isotropic etching, forming a protective film, and anisotropic etching (removing the protective film). SF6 can be used as the etching gas for processing the Si semiconductor layer 2. For the protective film, for example, C4F8 can be used.

[0029] When the Bosch process is used, the inner wall surface 4a of the recess 4 may become wavy in response to the repetition of the above steps. However, the unevenness caused by the wavy inner wall surface 4a due to the Bosch process is sufficiently small compared to the amount of narrowing of the cross-sectional area of the recess 4 caused by the narrowed portion F (i.e., the amount of protrusion toward the central axis of the recess 4 caused by the first inclined surface 6A and the second inclined surface 6B). Therefore, the inner wall surface 4a between the second inclined surface 6B and the bottom surface 4c can be regarded as a flat surface, and its influence on the formation of the narrowed portion F can be ignored.

[0030] The first electrode film 3A and the second electrode film 3B are both metal films formed by vapor deposition of a metal material such as gold (Au), silver (Ag), copper (Cu), or aluminum (Al). The first electrode film 3A and the second electrode film 3B may also be formed by vapor deposition of a compound material containing these metals. The first electrode film 3A and the second electrode film 3B are both Schottky junctioned to the semiconductor layer 2 and are electrically connected to an external circuit (not shown) by wirings 7A and 7B that are independent of each other.

[0031] In the concave-convex structure K, the first electrode film 3A is located on the top surfaces 5a of the convex portions 5, and the second electrode film 3B is located on the bottom surfaces 4c of the concave portions 4. Here, the first electrode film 3A is formed over the entire top surfaces 5a of the convex portions 5, and the second electrode film 3B is formed over the entire bottom surfaces 4c of the concave portions 4 (see FIG. 1(b)).

[0032] The first electrode film 3A and the second electrode film 3B are separated from each other at least at the narrowed portion F of the recess 4. In the example of FIG. 1(a), on the inner wall surface 4a of the recess 4, the first electrode film 3A located on the top surface 5a of the protrusion 5 also extends to the first inclined surface 6A, but the tip of this extended portion 3Aa stops at the boundary portion R between the first inclined surface 6A and the second inclined surface 6B. The second electrode film 3B is located below the lower end of the second inclined surface 6B. As a result of the narrowed portion F being formed on the inner wall surface 4a of the recess 4, the second electrode film 3B has a trapezoidal cross section that widens toward the bottom surface 4c when viewed from the extending direction of the recess 4.

[0033] Next, a method for manufacturing a semiconductor device will be described. Here, the manufacturing steps for the above-described semiconductor device 1A will be described, but these manufacturing steps can also be applied mutatis mutandis to semiconductor devices 1B to 1F and modified examples according to second to sixth embodiments described later.

[0034] In manufacturing the semiconductor device 1A, first, a processing step is carried out to form a relief structure K including recesses 4 on one surface 2a of the semiconductor layer 2. In the processing step, first, the semiconductor layer 2 is prepared as shown in FIG. 2(a). Next, a resist V is patterned on the one surface 2a of the semiconductor layer 2, in areas excluding the positions where the recesses 4 are to be formed. For example, an electron beam lithography device or the like can be used to pattern the resist V. The resist V can be made of a material such as a non-chemically amplified positive electron beam resist.

[0035] The processing step includes a first step using anisotropic etching and a second step including isotropic etching following the first step. In the first step, the semiconductor layer 2 with the resist V formed on its first surface 2a is placed in an etching chamber, and isotropic etching such as reactive ion etching is performed to process the first surface 2a of the semiconductor layer 2 to a predetermined depth. As a result, as shown in FIG. 2(b), an opening 4b of the recess 4 is formed on the first surface 2a of the semiconductor layer 2, and a first inclined surface 6A continuous with the opening 4b is formed on the inner wall surface 4a of the recess 4.

[0036] In the second step, etching including isotropic etching such as the Bosch process is performed in the etching chamber used in the first step to further deepen the surface 2a of the semiconductor layer 2. As a result, as shown in FIG. 3(a), a second inclined surface 6B is formed that is continuous with the first inclined surface 6A, and a narrowed portion F is formed on the inner wall surface 4a of the recess 4. After the narrowed portion F is formed, the recess 4 is completed by further digging in the thickness direction of the semiconductor layer 2 until it reaches a predetermined depth, and a concave-convex structure K is formed on the surface 2a of the semiconductor layer 2. After the recess 4 is formed, the resist V on the surface 2a of the semiconductor layer 2 is removed.

[0037] After the processing step, a vapor deposition step is carried out in which a film is formed by vapor deposition on the one surface 2a of the semiconductor layer 2. In the vapor deposition step, the semiconductor layer 2 with the recesses 4 formed therein is placed in a vapor deposition chamber, and a metal material is vacuum-deposited on the one surface 2a of the semiconductor layer 2. As a result, as shown in FIG. 3(b), a first electrode film 3A is formed on the one surface 2a of the semiconductor layer 2 (here, the top surfaces 5a of the protrusions 5), and a second electrode film 3B is formed on the bottom surfaces 4c of the recesses 4. An extended portion 3Aa of the first electrode film 3A is formed on the first inclined surface 6A.

[0038] 4(a), in a configuration in which the narrowed portion F is not formed in the recess 4, atoms P entering the recess 4 from the opening 4b may collide with the inner wall surface 4a of the recess 4 during the deposition process. Therefore, as shown in FIG. 4(b), a metal film 104 may be formed on the inner wall surface 4a of the recess 4, and the first electrode film 3A on the surface 2a of the semiconductor layer 2 and the second electrode film 3B on the bottom surface 4c of the recess 4 may be electrically connected to each other via the metal film 104.

[0039] In addition, the etching chamber and the deposition chamber are typically separate, and when performing the deposition process after the processing step, a process of transferring the semiconductor layer with the recesses formed therein to another chamber is required. Therefore, as shown in FIG. 5(a), it is conceivable that the orientation of the semiconductor layer 2 placed in the deposition chamber may be tilted relative to the deposition head. In this case, as shown in FIG. 5(b), atoms P entering the recesses 4 through the openings 4b are more likely to strike the inner wall surfaces 4a of the recesses 4, and the first electrode film 3A on the surface 2a of the semiconductor layer 2 and the second electrode film 3B on the bottom surface 4c of the recesses 4 may be easily connected by the thicker metal film 104.

[0040] In contrast, in the manufacturing method of the semiconductor device 1A, a narrowed portion F is formed in the recess 4 in the processing step. In the recess 4 having the narrowed portion F, when a vapor-deposited film is formed, a portion that is not hit by atoms P entering the recess 4 from the opening portion 4b can be formed on the inner wall surface of the recess, as shown in FIG. 6(a). Here, in a plan view of the semiconductor layer 2, the second inclined surface 6B is an enlarged portion J whose cross-sectional area is enlarged relative to the portion on the opening portion 4b side of the recess 4, and the second inclined surface 6B is not visible from the one surface 2a side of the semiconductor layer 2. Therefore, the second inclined surface 6B can function as a portion that is not hit by atoms P.

[0041] 6(b), although a metal film is formed on the first inclined surface 6A and the first electrode film 3A extends into the recess 4, the tip of this extending portion 3Aa can be terminated at the boundary portion R between the first inclined surface 6A and the second inclined surface 6B. Therefore, it is possible to suitably separate the first electrode film 3A on the one surface 2a of the semiconductor layer 2 and the second electrode film 3B on the bottom surface 4c of the recess 4, and electrical connection between them can be prevented.

[0042] The effect of the narrowing portion F is also effective when the semiconductor layer 2 is tilted relative to the deposition head, as shown in FIG. 7(a). In this case, as shown in FIG. 7(b), the second electrode film 3B on the bottom surface 4c of the recess 4 may be biased to one side due to the tilt of the semiconductor layer 2. However, in a plan view of the semiconductor layer 2, the second inclined surface 6B can be kept obscured from the first surface 2a of the semiconductor layer 2, allowing the second inclined surface 6B to function as a portion that is not hit by the atoms P. Therefore, as in the case of FIG. 6(b), it is possible to separate the first electrode film 3A on the first surface 2a of the semiconductor layer 2 from the second electrode film 3B on the bottom surface 4c of the recess 4, preventing electrical connection between them.

[0043] As described above, in the semiconductor device 1A, the recess 4 has an enlarged portion J whose cross-sectional area expands relative to the portion on the opening 4b side of the recess 4. In the semiconductor device 1A, the enlarged portion J is formed by providing a narrowed portion F on the inner wall surface 4a of the recess 4, which narrows the middle portion relative to the opening 4b of the recess 4. In the recess 4 having the narrowed portion F, the cross-sectional area of the recess 4 first decreases and then expands. Therefore, during the formation of the vapor-deposited film, a portion can be formed on the inner wall surface 4a of the recess 4 that is not hit by atoms P entering the recess 4 from the opening 4b. This allows for the first electrode film 3A provided on the top surface 5a of the protrusion 5 and the second electrode film 3B provided on the bottom surface 4c of the recess 4 to be suitably separated.

[0044] Furthermore, when the semiconductor device 1A is configured as a vertical MSM photodetector as in this embodiment, the process of removing the metal film on the inner wall surface 4a of the recess 4 by wet etching or the like can be omitted when separating the first electrode film 3A and the second electrode film 3B. Therefore, there is no need to adjust the film thicknesses of the first electrode film 3A and the second electrode film 3B, simplifying the manufacturing process.

[0045] In the semiconductor device 1A, the narrowed portion F is composed of a first inclined surface 6A that gradually reduces the cross-sectional area of the recess 4 toward the bottom surface 4c of the recess 4, and a second inclined surface 6B that is continuous with the first inclined surface 6A and gradually increases the cross-sectional area of the recess 4 toward the bottom surface 4c of the recess 4. This allows the second inclined surface 6B to function as a surface that is not hit by atoms P entering the recess 4 from the opening portion 4b. Therefore, the first electrode film 3A provided on the top surface 5a of the protrusion 5 and the second electrode film 3B provided on the bottom surface 4c of the recess 4 can be more reliably separated.

[0046] In the semiconductor device 1A, the first inclined surface 6A is continuous with the opening 4b of the recess 4. With this configuration, the narrowed portion F is continuous with the opening 4b of the recess 4, so the separation position between the first electrode film 3A and the second electrode film 3B can be brought closer to the opening 4b of the recess 4. This ensures a sufficient distance between the first electrode film 3A and the second electrode film 3B, ensuring a more reliable separation between them. In particular, when the semiconductor device 1A is designed for surface incidence (light incidence from the one surface 2a of the semiconductor layer 2), the continuous change in refractive index at the opening 4b reduces reflection loss.

[0047] In the semiconductor device 1A, the first and second evaporated films are both metal films and form the first and second electrode films 3A and 3B, respectively, making the semiconductor device 1A suitable for use as an MSM photodetector.

[0048] In the semiconductor device manufacturing method according to this embodiment, the processing steps are performed by combining a first step using anisotropic etching and a second step using etching including subsequent isotropic etching. In anisotropic etching, the cross-sectional area of the recess 4 formed gradually narrows as the process progresses. On the other hand, in isotropic etching, the cross-sectional area of the recess 4 gradually widens in the early stage of the process, and an enlarged portion J is formed in the recess 4, whose cross-sectional area expands relative to the portion on the opening portion 4b side of the recess 4. Thereafter, the recess 4 can be formed with a constant cross-sectional area.

[0049] Therefore, a narrowed portion F is formed on the inner wall surface 4a of the recess 4 that is finally formed, narrowing the middle portion relative to the opening portion 4b of the recess 4. The narrowed portion F allows the formation of a portion on the inner wall surface 4a of the recess 4 that is not hit by the atoms P entering the recess 4 from the opening portion 4b during the vapor deposition process. Therefore, the first electrode film 3A provided on the one surface 2a of the semiconductor layer 2 and the second electrode film 3B provided on the bottom surface 4c of the recess 4 can be suitably separated.

[0050] In this embodiment, reactive ion etching is used as anisotropic etching in the first processing step, and the Bosch process is used as etching including isotropic etching in the second processing step. The combination of reactive ion etching and the Bosch process allows the narrowed portion F to be formed easily and accurately. [Second embodiment]

[0051] 8(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a second embodiment of the present disclosure. 8(b) is a plan view thereof. As shown in FIGS. 8(a) and 8(b), the semiconductor device 1B according to the second embodiment differs from the semiconductor device 1A according to the first embodiment in that an insulating film 11 is provided between the metal film and the surface 2a of the semiconductor layer 2.

[0052] That is, in the semiconductor device 1B, an insulating film 11 is provided between the top surfaces 5a of the protrusions 5 and the first electrode film 3A on the one surface 2a side of the semiconductor layer 2. The insulating film 11 can be formed, for example, by not removing the resist V (see FIG. 2(a) etc.) used in the processing step after the processing step is completed, but by performing a vapor deposition step in a state in which the resist V remains on the one surface 2a side of the semiconductor layer 2. Instead of the resist V, an inorganic material such as SiO2 or SiN may be used as the insulating film. Also, instead of the insulating film 11, a dielectric film 12 may be provided between the metal film and the one surface 2a side of the semiconductor layer 2.

[0053] In this semiconductor device 1B configuration, as in the first embodiment, during deposition of the deposited film, a portion can be formed on the inner wall surface 4a of the recess 4 that is not hit by atoms P entering the recess 4 through the opening 4b. This allows for effective separation between the first electrode film 3A provided on the top surface 5a of the protrusion 5 and the second electrode film 3B provided on the bottom surface 4c of the recess 4. Furthermore, in the semiconductor device 1B, the insulating film 11 or dielectric film 12 is disposed between the top surface 5a of the protrusion 5 and the first electrode film 3A, thereby suppressing dark current at the Schottky junction of the first electrode film 3A. This improves the detection performance of the semiconductor device 1B as a photodetector. [Third embodiment]

[0054] Fig. 9(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a third embodiment of the present disclosure. Fig. 9(b) is a plan view thereof. As shown in Figs. 9(a) and 9(b), the semiconductor device 1C according to the third embodiment differs from the semiconductor device 1A according to the first embodiment, in that the first inclined surface 6A is spaced apart from the opening 4b of the recess 4.

[0055] In the semiconductor device 1C, the cross-sectional area of the recess 4 is constant from the opening 4b to a certain depth. The first inclined surface 6A and the second inclined surface 6B are located closer to the bottom surface 4c than the portion where the cross-sectional area is constant, and the cross-sectional area is again constant between the second inclined surface 6B and the bottom surface 4c. To form such a recess 4, in the processing step, first, the one surface 2a side of the semiconductor layer 2 is processed to a certain depth by anisotropic etching such as the Bosch process, and then the first and second steps described above are performed.

[0056] In the semiconductor device 1C having such a configuration, similar to the first embodiment, during the formation of the vapor-deposited film, a portion can be formed on the inner wall surface 4a of the recess 4 that is not hit by atoms P entering the recess 4 through the opening portion 4b. Therefore, the first electrode film 3A provided on the top surface 5a of the protrusion 5 and the second electrode film 3B provided on the bottom surface 4c of the recess 4 can be suitably separated. Furthermore, in the semiconductor device 1C, the narrow portion F is spaced apart from the opening portion 4b of the recess 4, so that the separation position between the first electrode film 3A and the second electrode film 3B can be spaced apart from the opening portion 4b of the recess 4. This allows the back-incident light that has passed through the second electrode film 3B to be reflected by the first electrode film 3A and directed toward the second electrode film 3B, particularly when the semiconductor device 1C is rear-incident (light incident from the other surface 2b of the semiconductor layer 2). Therefore, light leakage from the opening portion 4b is suppressed, improving light absorption efficiency. [Fourth embodiment]

[0057] Fig. 10(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a fourth embodiment of the present disclosure. Fig. 10(b) is a plan view thereof. As shown in Figs. 10(a) and 10(b), the semiconductor device 1D according to the fourth embodiment differs from the semiconductor device 1A according to the first embodiment in that a pair of recesses 4,4 is provided in the recessed-recess structure K per unit.

[0058] The semiconductor device 1D is configured as, for example, a back-illuminated lateral MSM photodetector. In the semiconductor device 1D, a metal film (second vapor-deposited film) provided on the bottom surface 4c of one of the recesses 4 constitutes a first electrode film 3A, and a metal film (second vapor-deposited film) provided on the bottom surface 4c of the other recess 4 constitutes a second electrode film 3B. The metal film (first vapor-deposited film) on the top surface 5a of the protrusion 5 functions as a reflective film 13.

[0059] In this configuration of the semiconductor device 1D, as in the first embodiment, when forming a vapor-deposited film, a portion can be formed on the inner wall surface 4a of the recess 4 that is not hit by atoms P entering the recess 4 through the opening portion 4b. This allows for suitable separation between the reflective film 13 provided on the top surface 5a of the protrusion 5 and the first electrode film 3A and the second electrode film 3B provided on the bottom surface 4c of the recess 4. Furthermore, in the semiconductor device 1D, components of incident light incident on the back surface that have passed through the first electrode film 3A and the second electrode film 3B can be reflected by the reflective film 13 and made to enter the first electrode film 3A and the second electrode film 3B. This improves the detection performance of the semiconductor device 1D as a photodetector.

[0060] The semiconductor device 1D can also be configured as, for example, a back-illuminated vertical MSM photodetector. In this case, as shown in FIG. 10(c), the metal film (first vapor-deposited film) on the top surfaces 5a of the protrusions 5 functions as the second electrode film 3B, while the metal film (second vapor-deposited film) on the bottom surfaces 4c of the recesses 4 functions as the second electrode film 3B, and the metal film (first vapor-deposited film) on the top surfaces 5a of the protrusions 5 located between the recesses 4 functions as the reflective film 13. [Fifth embodiment]

[0061] Fig. 11(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a fifth embodiment of the present disclosure. Fig. 11(b) is a plan view thereof. The semiconductor device 1E shown in Figs. 11(a) and 11(b) is configured as a back-illuminated photodetector using the near-field excitation effect.

[0062] In semiconductor device 1E, when light with a wavelength longer than the absorption edge wavelength (wavelength having band gap energy) of the semiconductor is incident, the incident light excites surface plasmons. Utilizing the localized inhomogeneous electric field generated by the resonance of this surface plasmon enables direct optical transition within the semiconductor, resulting in sufficient optical absorption within the semiconductor. In semiconductor device 1E, the optical absorption generated within the semiconductor is extracted externally as a photocurrent, enabling the detection of light with wavelengths longer than the absorption edge wavelength of the semiconductor.

[0063] In the semiconductor device 1E, the semiconductor layer 2 has a first layer (first conductivity type semiconductor layer) 2A of n-type conductivity, a second layer (second conductivity type semiconductor layer) 2B of p-type conductivity, and a third layer (second conductivity type semiconductor layer) 2C of p+ type conductivity. The first layer 2A is located on the other surface 2b side of the semiconductor layer 2, and the third layer 2C is located on the one surface 2a side of the semiconductor layer 2. The second layer 2B is located between the first layer 2A and the second layer 2B. A semiconductor pn junction is formed at the interface between the first layer 2A and the second layer 2B.

[0064] The configuration of the recess 4 formed on the one surface 2a side of the semiconductor layer 2 is the same as in the first embodiment. The recess 4 extends into the first layer 2A, penetrating the third layer 2C and the second layer 2B. The narrowed portion F of the recess 4 is located in the second conductive type semiconductor layer. In the example of FIG. 11(a), the boundary portion R between the first inclined surface 6A and the second inclined surface 6B is located in the third layer 2C. This prevents the extending portion 3Aa of the first electrode film 3A located on the first inclined surface 6A from contacting the first layer 2A. The boundary portion R between the first inclined surface 6A and the second inclined surface 6B may be located in the second layer 2B, as long as the extending portion 3Aa does not contact the first layer 2A.

[0065] In the semiconductor device 1E, a metal film (first vapor-deposited film) provided on the top surfaces 5a of the convex portions 5 in the concave-convex structure K constitutes a first electrode film 3A, and a metal film provided on the other surface 2b of the semiconductor layer 2 constitutes a second electrode film 3B. The first electrode film 3A functions as one contact electrode of the pn junction. The metal film (second vapor-deposited film) provided on the bottom surfaces 4c of the concave portions 4 in the concave-convex structure K functions as a near-field excitation source 15.

[0066] Near-field excitation source 15 is a metal nanostructure that generates surface plasmons near the interface between near-field excitation source 15 and semiconductor layer 2 when incident light is incident on it. Near-field excitation source 15 is provided with a width equal to or less than the wavelength of the incident light so as to be in contact with first layer 2A. This makes it possible to make the position where the localized inhomogeneous electric field is generated coincident with or close to the position of the depletion layer in semiconductor layer 2, thereby enabling the effect of the localized inhomogeneous electric field to be fully exerted.

[0067] In the semiconductor device 1E having this configuration, similar to the first embodiment, a portion on the inner wall surface 4a of the recess 4 is formed that is not hit by atoms P entering the recess 4 through the opening 4b during deposition. Therefore, the first electrode film 3A provided on the top surface 5a of the protrusion 5 and the near-field excitation source 15 provided on the bottom surface 4c of the recess 4 can be suitably separated. By reliably separating the first electrode film 3A and the near-field excitation source 15, the near-field excitation source 15 does not contribute to the extraction of photocurrent but only functions to generate a localized inhomogeneous electric field. Therefore, compared to when the first electrode film 3A and the first layer 2A are in contact or when the near-field excitation source 15 itself serves as a photocurrent extraction electrode, the generation of dark current due to the Schottky junction can be suppressed.

[0068] In this embodiment, the extension portion 3Aa of the first electrode film 3A is located on the first inclined surface 6A in the narrowed portion F. The extension portion 3Aa enhances the scattering effect of incident light. The enhanced scattering effect of incident light increases the absorption rate of broadband light, thereby broadening the detection band of the photodetector. Furthermore, since the opening width of the recess 4 in the region where the extension portion 3Aa is formed is narrower than the width of the near-field excitation source 15, a new surface plasmon resonance mode can be formed. This allows for a new light absorption band to be obtained, enabling the construction of a photodetector with multiple detection bands. Furthermore, the spatial nonuniformity of the localized nonuniform electric field generated by the incidence of incident light becomes more pronounced, improving the near-field excitation effect. [Sixth embodiment]

[0069] Fig. 12(a) is a schematic cross-sectional view showing the configuration of a semiconductor device according to a sixth embodiment of the present disclosure. Fig. 12(b) is a plan view thereof. The semiconductor device 1F shown in Figs. 12(a) and 12(b) is configured as a photodetector using the near-field excitation effect, similar to the fifth embodiment. The semiconductor device 1F differs from the semiconductor device 1E according to the fifth embodiment in that a metal film is not formed on the top surfaces 5a of the convex portions 5 in the concave-convex structure K.

[0070] In the semiconductor device 1F, instead of the configuration in which the first electrode film 3A is formed on the top surface 5a of the convex portion 5, the first electrode film 3A is formed on the one surface 2a side of the semiconductor layer 2 at a position away from the concave-convex structure K. In the example of FIGS. 12(a) and 12(b), the first electrode film 3A is formed in a rectangular shape on one edge portion in a direction perpendicular to the extension direction of the concave portion 4 on the one surface 2a side of the semiconductor layer 2. Like the semiconductor device 1E, the semiconductor device 1F can be configured as a photodetector using the near-field excitation effect. The semiconductor device 1F is not limited by the incident direction of incident light and can accommodate both front-side incidence and back-side incidence.

[0071] In this semiconductor device 1F configuration, as in the first embodiment, a portion on the inner wall surface 4a of the recess 4 is formed that is not hit by atoms P entering the recess 4 through the opening 4b during deposition. This allows for a suitable separation between the first electrode film 3A provided on the one surface 2a of the semiconductor layer 2 and the near-field excitation source 15 provided on the bottom surface 4c of the recess 4. This reliable separation between the first electrode film 3A and the near-field excitation source 15 means that the near-field excitation source 15 does not contribute to photocurrent extraction and only functions to generate a localized inhomogeneous electric field. This reduces the generation of dark current due to the Schottky junction compared to when the first electrode film 3A and the first layer 2A are in contact or when the near-field excitation source 15 itself serves as a photocurrent extraction electrode. [Variations]

[0072] The present disclosure is not limited to the above-described embodiments. For example, in each of the above-described embodiments, the recesses 4 are linearly formed from one side to the other side of the one surface 2a of the semiconductor layer 2 in a plan view of the semiconductor layer 2. However, the planar shape of the recesses 4 is not limited to this. For example, as shown in FIG. 13(a), the planar shape of the recesses 4 may be square. The planar shape of the recesses 4 is not limited to a square, but may be other shapes such as a rectangular, polygonal, circular, or elliptical shape. Furthermore, as shown in FIG. 13(b), the recesses 4 may be arranged in a lattice pattern in the in-plane direction of the one surface 2a of the semiconductor layer 2. The arrangement pattern of the recesses 4 is not limited to the lattice pattern shown in FIG. 13(b), but may be other patterns such as a ring, a concentric circle, a staggered pattern, or a random pattern.

[0073] In the above-described embodiments, both the first and second vapor-deposited films are metal films. However, the first and second vapor-deposited films are not limited to metal films and may be films formed of materials other than metal, such as resin films. For example, as shown in FIGS. 14(a) and 14(b), a semiconductor device 1G may have a first dielectric film 16A, which is a first vapor-deposited film, formed on the top surface 5a of the protrusion 5, and a second dielectric film 16B, which is a second vapor-deposited film, formed on the bottom surface 4c of the recess 4. In the semiconductor device 1G, a first electrode film 3A is formed on a portion of the top surface 5a of the protrusion 5, and a second electrode film 3B is formed on the other surface 2b of the semiconductor layer 2.

[0074] This semiconductor device 1G, like the semiconductor device 1E, can be configured as a photodetector using, for example, the near-field excitation effect. The second dielectric film 16B on the bottom surface 4c of the recess 4 acts as a scatterer that generates wavenumber components, just like a metal film. The second dielectric film 16B acts as a scatterer, generating a near-field near the interface with the semiconductor layer 2, thereby generating the near-field excitation effect.

[0075] In each of the above embodiments, a narrowed portion F is provided that narrows the middle portion of the recess 4 relative to the opening 4b, but the expanded portion J, whose cross-sectional area expands relative to the portion of the recess 4 on the opening 4b side, does not necessarily have to be formed by a narrowed portion F. For example, the recess 4 may be provided with only an inclined surface corresponding to the second inclined surface 6B, and the cross-sectional area of the opening 4b may be maintained from the opening 4b of the recess 4 to the portion corresponding to the second inclined surface 6B.

[0076] In the above embodiments, a photodetector is exemplified as an application of the semiconductor device, but the semiconductor device according to the present disclosure can be applied to other applications. Another application example of the semiconductor device is a SERS (Surface-Enhanced Raman Spectroscopy) substrate. The SERS substrate amplifies the intensity of weak Raman scattered light and can be used for Raman spectroscopic analysis, etc.

[0077] For example, when the semiconductor device 1A shown in FIGS. 1(a) and 1(b) is used as a SERS substrate, the metal film (corresponding to the extended portion 3Aa of the first electrode film 3A in the semiconductor device 1A) located on the first inclined surface 6A constituting the constriction portion F enhances surface Raman scattering. Furthermore, because the constriction portion F separates the metal film on the top surface 5a of the convex portion 5 from the metal film on the bottom surface 4c of the concave portion 4, the gap between the metal films can be reduced by adjusting the thickness of the metal film. This gap can function as a hot spot (surface Raman scattering) on the SERS substrate. [Explanation of symbols]

[0078] Reference Signs List 1A to 1G... semiconductor device, 2... semiconductor layer, 2a... one surface, 2A... first layer (first conductivity type semiconductor layer), 2B... second layer (second conductivity type semiconductor layer), 2C... third layer (second conductivity type semiconductor layer), 3A... first electrode film (first evaporated film), 3B... second electrode film (second evaporated film), 4... recess, 4a... inner wall surface, 4b... opening portion, 6A... first inclined surface, 6B... second inclined surface, 11... insulating film, 12... dielectric film, 13... reflective film (first evaporated film), 15... near-field excitation source (second evaporated film), 16A... first dielectric film (first evaporated film), 16B... second dielectric film (second evaporated film), F... narrowed portion, J... expanded portion, K... uneven structure.

Claims

1. a semiconductor layer having a concave-convex structure including a concave portion on one surface thereof; a first vapor-deposited film provided on the one surface of the semiconductor layer; a second vapor-deposited film provided on a bottom surface of the recess, The recess has an enlarged portion whose cross-sectional area is enlarged relative to a portion of the recess on the opening side, A semiconductor device in which the start position of the enlarged portion is located between the opening of the recess and the bottom surface of the recess in the depth direction of the recess.

2. a semiconductor layer having a concave-convex structure including a concave portion on one surface thereof; a first vapor-deposited film provided on the one surface of the semiconductor layer; a second vapor-deposited film provided on a bottom surface of the recess, The recess has an enlarged portion whose cross-sectional area is enlarged relative to a portion of the recess on the opening side, A semiconductor device in which a narrowed portion is provided on the inner wall surface of the recess, narrowing the middle portion of the recess relative to the opening portion of the recess.

3. 3. The semiconductor device according to claim 2, wherein the narrowed portion is composed of a first inclined surface that gradually reduces the cross-sectional area of the recess toward the bottom side of the recess, and a second inclined surface that is continuous with the first inclined surface and gradually increases the cross-sectional area of the recess toward the bottom side of the recess.

4. 4. The semiconductor device according to claim 3, wherein the first inclined surface is continuous with the opening of the recess.

5. 4. The semiconductor device according to claim 3, wherein the first inclined surface is spaced apart from an opening of the recess.

6. 6. The semiconductor device according to claim 1, wherein the first vapor-deposited film and the second vapor-deposited film are metal films.

7. 7. The semiconductor device according to claim 6, wherein an insulating film or a dielectric film is provided between the metal film and the one surface of the semiconductor layer.

8. the semiconductor layer includes a first conductive type semiconductor layer and a second conductive type semiconductor layer, the recess extends through the second conductive type semiconductor layer into the first conductive type semiconductor layer; The semiconductor device according to any one of claims 1 to 6, wherein the enlarged portion is located in the second conductivity type semiconductor layer.

9. A method for manufacturing a semiconductor device used in the manufacture of the semiconductor device according to claim 1 or 2, comprising: a processing step of forming a concave-convex structure including a concave portion on one surface of the semiconductor layer; a vapor deposition step of depositing a film by vapor deposition on one surface of the semiconductor layer to form a first vapor-deposited film on the one surface of the semiconductor layer and a second vapor-deposited film on a bottom surface of the recess, The method for manufacturing a semiconductor device includes a first process using anisotropic etching and a second process including isotropic etching subsequent to the first process.

10. In the first step, reactive ion etching is used as the anisotropic etching, 10. The method for manufacturing a semiconductor device according to claim 9, wherein the second step including the isotropic etching uses a Bosch process.

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