Method for manufacturing semiconductor device

Abstract

In the present invention, a space (123) is formed between a substrate (121) and an optical element in a first region (151). The space (123) is formed in the first region (151) between the substrate (121) and a device layer (101) supported on the substrate (121) by a support part (122a) of a third region (153). The space (123) is formed by selectively etching and removing a sacrificial layer (122) of the first region (151) and a second region (152) via an opening (110) while leaving the support part (122a).

Description

Semiconductor device manufacturing method

[0001] The present invention relates to a method for manufacturing a semiconductor device.

[0002] The integration of compound optical semiconductors and silicon photonics optical circuits is progressing toward higher speeds, larger capacities, and smaller sizes of optical transceivers for optical communications. For example, low-loss optical coupling is achieved between compound semiconductors (especially InP-based semiconductors) used to fabricate lasers and optical modulators and silicon photonics by adiabatically transitioning the optical mode using a tapered waveguide structure. This heterogeneous integration technology, which combines compound semiconductors and silicon photonics, has attracted attention and is enabling the realization of compact, high-performance optical integrated circuits.

[0003] In particular, among heterogeneous integration technologies, the transfer printing method (also known as the microtransfer printing method) has attracted attention as a technology that can integrate completed compound optical semiconductors and silicon photonics optical circuits with high positional accuracy, high throughput, and low cost (Non-Patent Document 1).

[0004] In the transfer printing method, as shown in Non-Patent Document 1, a sacrificial layer and a device layer are laminated on an original substrate by epitaxial crystal growth, the device layer is processed by known photolithography and etching techniques to form a device structure, the sacrificial layer is then removed by selective wet etching, and the resulting structure is transferred onto a destination substrate using a resin stamp. Therefore, the transfer printing method has attracted attention as a technology that allows target devices to be inspected on the original substrate, selected as non-defective, and then integrated onto a heterogeneous substrate.

[0005] Meanwhile, optical devices made of InP-based compound semiconductors formed on a Si substrate have attracted attention as low-power, highly efficient III-V compound semiconductor devices. As shown in Figure 2, this optical device includes a core-shaped active region 302 formed in a compound semiconductor layer 301, such as InP, with an n-type region 303 and a p-type region 304 sandwiching the active region 302. A first electrode 307 and a second electrode 308 are formed on the n-type region 303 and the p-type region 304, with contact layers 305 and 306 interposed therebetween. A SiO2 layer 309 is formed on the compound semiconductor layer 301 between the first electrode 307 and the second electrode 308.

[0006] The compound semiconductor layer 301 in which the optical device is formed is transferred onto the silicon substrate 321 via the SiO2 layer 322. In this way, the region in which the active section 302, which guides light, is located is sandwiched between the low-refractive-index SiO2 layers 309 and 322. This type of optical device is sometimes called a thin-film optical device because it is formed in a thin compound semiconductor layer 301 with a thickness of 1 μm or less.

[0007] Camiel Op de Beeck et al., "Heterogeneous III-V on silicon nitride amplifiers and lasers via microtransfer printing", Optica, vol. 7, issue 5, pp. 386-393, 2020.

[0008] In the transfer printing method, inspections for selecting non-defective products are performed before transfer, as described above. As shown in FIG. 3 , the optical device before transfer has a semiconductor layer 301 formed on an original InP substrate 311 via a sacrificial layer 312, with the sacrificial layer 312 present underneath. As described above, the layer structure around the active section 302, which guides light, differs before and after transfer in the optical device described above, and the state of optical confinement in the light-guiding region where the active section 302 is located changes significantly. For this reason, it was not possible to perform inspections to select non-defective products before transfer, when the optical device is formed on the original substrate.

[0009] The present invention has been made to solve the above problems, and has as its object to make it possible to inspect optical devices in a state before transfer.

[0010] a fourth step of processing a second region of the device layer surrounding the first region of the device layer to form an opening that penetrates the device layer to reach the sacrificial layer and a connecting portion that bridges the first region and a third region surrounding the second region other than the opening; a fifth step of selectively etching and removing the sacrificial layer in the first and second regions through the opening to form a space between the substrate and the optical element in the first region; a sixth step of irradiating inspection light onto the optical element to perform an inspection; a seventh step of forming a tether resist layer that covers the optical element; and an eighth step of removing the device structure from the substrate using a transfer stamp.

[0011] As described above, according to the present invention, a space is formed between the optical element of the device structure and the substrate, inspection light is irradiated onto the optical element to perform inspection, and then the device structure is removed from the substrate using a transfer stamp, so that inspection of the optical device can be performed in a state before transfer.

[0012] FIG. 1A is a cross-sectional view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1B is a cross-sectional view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1C is a cross-sectional view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1D is a cross-sectional view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1E is a plan view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1F is a cross-sectional view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1G is a cross-sectional view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 1H is a plan view showing a state of a semiconductor device in an intermediate step for explaining a method for manufacturing a semiconductor device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a configuration of a conventional semiconductor device. FIG. 3 is a cross-sectional view showing a configuration of a conventional semiconductor device.

[0013] 1A to 1G, a method for manufacturing a semiconductor device according to an embodiment of the present invention will be described. This method for manufacturing a semiconductor device involves inspecting optical elements of the semiconductor device before transfer during the process of manufacturing the semiconductor device by transfer printing.

[0014] First, as shown in FIG. 1A , a sacrificial layer 122 made of a compound semiconductor is formed on a substrate 121 (first step). The substrate 121 is a transfer source substrate for performing the transfer printing method. The substrate 121 can be made of InP with its main surface in the (100) plane. The sacrificial layer 122 can have a layered structure of a layer made of InAlAs and a layer made of InGaAs. For example, the sacrificial layer 122 can be formed by crystal growth (epitaxial growth) of the above-mentioned compound semiconductor on the substrate 121.

[0015] 1B, a device layer 101 made of a compound semiconductor is formed on the sacrificial layer 122 (step 2). The device layer 101 can be made of a layer of a compound semiconductor used to form a waveguide-type optical element made of a compound semiconductor. The device layer 101 can be made of a layer of a compound semiconductor such as InP, InGaAs, InGaAlAs, or InGaAsP.

[0016] Next, the first region 151 of the device layer 101 is processed to form a device structure including a waveguide-type optical element made of a compound semiconductor in the device layer 101 (step 3). The first region 151 is a rectangular region in a plan view normal to the plane of the substrate 121. For example, as shown in FIG. 1C , a device structure is formed including a core-shaped active region 102, an n-type region 103 and a p-type region 104 sandwiching the active region 102, contact layers 105 and 106, a first electrode 107, and a second electrode 108. The first electrode 107 and the second electrode 108 are electrically connected to the active region 102 via the contact layers 105 and 106, the n-type region 103, and the p-type region 104. An insulating layer 109 made of a low-refractive-index material such as SiO can be formed on the device layer 101 between the first electrode 107 and the second electrode 108.

[0017] For example, this optical element may be a distributed feedback semiconductor laser having a diffraction grating (not shown) in the active layer 102. In this case, a current is applied to the active layer 102 via the first electrode 107, the second electrode 108, the contact layer 105, the contact layer 106, the n-type region 103, and the p-type region 104. This optical element may also be an optical modulator. In this case, a modulation signal is applied to the active layer 102 via the first electrode 107, the second electrode 108, the contact layer 105, the contact layer 106, the n-type region 103, and the p-type region 104. This optical element may also be an optical receiver.

[0018] Next, as shown in FIGS. 1D and 1E , the second region 152 surrounding the first region 151 of the device layer 101 is processed to form an opening 110 and a connecting portion 111 (step 4). For example, the second region 152 is an annular region surrounding the first region 151 in a plan view from the normal direction to the plane of the substrate 121. The opening 110 penetrates the device layer 101 and reaches the sacrificial layer 122. The connecting portion 111 is provided between the first region 151 and a third region 153 surrounding the second region 152, other than the opening 110. For example, the third region 153 is an annular region surrounding the second region 152 in a plan view from the normal direction to the plane of the substrate 121. Note that FIG. 1D shows a cross section taken along line aa' in FIG. 1E . By forming the opening 110 , the first electrode 107 and the second electrode 108 in the second region 152 are removed, and a first electrode pad 107 a and a second electrode pad 108 a are formed in the third region 153 .

[0019] 1E, in addition to the optical element, an optical waveguide 112 connected to the optical element and an input section 113 for inspection light can be formed in the third step. The optical waveguide 112 is led out from the first region 151 through the connecting section 111 to the third region 153. The input section 113 is optically connected to the optical element via the optical waveguide 112. The input section 113 can be formed, for example, by a grating coupler.

[0020] Next, as shown in FIG. 1F , a space 123 is formed between the substrate 121 and the optical element in the first region 151 (step 5). The space 123 is formed in the first region 151 between the device layer 101, which is supported on the substrate 121 by the support portions 122 a in the third region 153, and the substrate 121. The space 123 can be formed by selectively etching and removing the sacrificial layer 122 in the first region 151 and the second region 152 through the opening 110, leaving the support portions 122 a. For example, the sacrificial layer 122 made of InAlAs and InGaAs can be selectively etched and removed using FeCl 3 (iron (III) chloride) as an etchant. By forming the space 123, the layer on the substrate 121 side of the active region 102, where light is guided, becomes the space 123 with a low refractive index.

[0021] 1G and 1H, a first wiring 114 that connects the first electrode 107 and the first electrode pad 107a, and a second wiring 115 that connects the second electrode 108 and the second electrode pad 108a are formed. Note that Fig. 1G shows a cross section taken along line aa' in Fig. 1H.

[0022] After the optical element, optical waveguide 112, and input section 113 are formed as described above, and the space 123 is further formed, inspection is performed by irradiating inspection light onto the optical element (step 6). For example, the inspection can be performed by irradiating inspection light onto the optical element via the input section 113. Alternatively, for example, the inspection can be performed by irradiating inspection light onto the optical element and applying a predetermined inspection signal to the first electrode pad 107 a and the second electrode pad 108 a.

[0023] In this inspection, the layer on the substrate 121 side of the active section 102 where light is guided is the low refractive index space 123, so that it will be transferred to the destination substrate later and will be in the same state as being arranged on a low refractive index layer. Therefore, the state of light confinement in the region where the active section 102 is arranged and where light is guided is almost the same as when it is transferred, and it is possible to perform inspection before transfer and select non-defective products.

[0024] After the inspection is performed as described above, a tether resist (tether) layer (not shown) is formed to cover the device structure having the optical element (step 7), and the device structure covered with the tether resist layer is removed from the substrate 121 using a transfer stamp (not shown) (step 8) and transferred onto the mounting substrate.

[0025] As described above, according to an embodiment of the present invention, a space is formed between the optical element of the device structure and the substrate, inspection light is irradiated onto the optical element to perform inspection, and then the device structure is removed from the substrate using a transfer stamp, making it possible to inspect the optical device in a state before transfer.

[0026] 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.

[0027] 101...device layer, 102...active portion, 103...n-type region, 104...p-type region, 105...p-type region, 106...contact layer, 107...first electrode, 107a...first electrode pad, 108...second electrode, 108a...second electrode pad, 109...insulating layer, 110...opening, 111...connecting portion, 112...optical waveguide, 113...input portion, 121...substrate, 122...sacrificial layer, 151...first region, 152...second region, 153...third region.

Claims

a third step of processing a first region of the device layer to form a device structure in the device layer, the device structure comprising a waveguide-type optical element made of compound semiconductor; a fourth step of processing a second region surrounding the first region of the device layer to form an opening that penetrates the device layer to reach the sacrificial layer and a connecting portion that connects the first region to a third region surrounding the second region other than the opening; a fifth step of selectively etching and removing the sacrificial layer in the first and second regions through the opening to form a space between the substrate and the optical element in the first region; a sixth step of irradiating the optical element with inspection light to perform an inspection; a seventh step of forming a tether resist layer that covers the optical element; and an eighth step of extracting the device structure from the substrate using a transfer stamp.

2. A method for manufacturing a semiconductor device according to claim 1, wherein the optical element comprises a core-shaped active portion and an electrode connected to the active portion, and the sixth step comprises irradiating inspection light onto the optical element and applying a signal to the electrode to carry out the inspection.

3. A method for manufacturing a semiconductor device according to claim 1 or 2, further comprising an input section for the inspection light formed in the third region and optically connected to the optical element, and wherein the sixth step involves directing the inspection light into the optical element via the input section.

4. A method for manufacturing a semiconductor device according to claim 3, wherein the input section is composed of a grating coupler.

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