Micro-transfer printing method of laser chip and photonic integrated chip

Abstract

The invention provides a micro-transfer printing method of a laser chip and a photonic integrated chip. The micro-transfer printing method comprises the following steps: forming a release layer and a laser device layer on a substrate; etching to form a laser unit; forming an anti-reflection layer, wherein the outer side of the anti-reflection layer corresponding to the coupling surface is a coupling end surface; manufacturing a photoresist pattern which has a retraction distance relative to the coupling end face; etching the anti-reflection layer and the release layer, and completely removing the anti-reflection layer and the release layer outside the edge of the coupling end face; forming an anti-separation layer; removing the release layer; and the laser device chip is subjected to micro-transfer printing into the target substrate, and the coupling end face faces the optical waveguide. According to the invention, the alignment precision between the laser chip and the optical waveguide in the direction of the optical propagation axis in the optical waveguide can be greatly improved, the accumulated tolerance is reduced, and the consistency of the distance between the laser chip and the optical waveguide is improved. The distance between the coupling end face of the laser chip and the optical waveguide can be reduced, the optical coupling efficiency is improved, and the light emitting loss is reduced.

Description

Technical Field

[0001] The present invention relates to the field of photon integrated chip design and manufacturing, and particularly to a micro-transfer printing method for a laser chip and a photon integrated chip. Background Art

[0002] In the field of silicon photonics, many applications such as telecommunications, data communication, and sensing devices require integrated light sources to avoid using large and expensive discrete lasers. Since silicon has an indirect bandgap, it is challenging to fabricate a native light source in silicon. One way to solve this problem is to fabricate a hybrid integrated device by integrating a laser chip based on III-V (or compound semiconductor) materials onto a silicon photonics device. Usually, the flip-chip bonding technology is adopted, that is, III-V devices are bonded to the silicon photonics device one by one by using eutectic gold / tin solder. Although this is a mature technology, in mass production, its process speed may be too slow to achieve cost-effectiveness. In addition, due to the possible solder reflow phenomenon in the packaging process, it is necessary to prevent the movement of the III-V gain device after bonding to ensure meeting the maximum alignment accuracy and reducing the cumulative tolerance standard (which reduces the overall alignment accuracy).

[0003] As an alternative, micro-transfer printing (micro-transfer) is gradually becoming an innovative method. By using a viscoelastic stamp to pick up the prepared III-V devices (here called micro-transfer chips or grains), multiple micro-transfer chips can be bonded to the target silicon wafer simultaneously.

[0004] However, in the existing micro-transfer printing process, when transferring and printing the III-V devices into the accommodation cavities reserved on the target silicon optical integration wafer, the gap between the coupling end face of the III-V laser chip and the collimated and aligned silicon waveguide end face is large, which may lead to a decrease in the alignment accuracy between the optical waveguide end faces contained in the two end faces, thus resulting in a large loss of the optical path.

[0005] It should be noted that the above introduction of the technical background is only for the convenience of clearly and completely explaining the technical solution of the present application and facilitating the understanding of those skilled in the art. It cannot be considered that the above technical solutions are well-known to those skilled in the art just because these solutions are described in the background art part of the present application. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a micro-transfer printing method for a laser chip and a photon integrated chip, which is used to solve the problems of low alignment accuracy between the laser chip and the optical waveguide of the accommodation cavity of the target chip and large optical path loss in the prior art.

[0007] To achieve the above and other related objectives, the present invention provides a micro-transfer printing method for a laser chip. The micro-transfer printing method includes: providing a substrate, forming a release layer and a laser device layer on the substrate; forming a patterned hard mask on the laser device layer, etching the laser device layer based on the patterned hard mask to form laser units, with the release layer exposed between adjacent laser units, and each laser unit having a coupling surface for docking with an optical waveguide; depositing an anti-reflection layer on the top surface, side surface of the laser unit, and the exposed surface of the release layer, and the outer side of the anti-reflection layer corresponding to the coupling surface is the coupling end face; fabricating a photoresist pattern, the photoresist pattern having an etching window surrounding the laser unit, and the photoresist pattern having a retraction distance relative to the coupling end face so that the etching window completely exposes the coupling end face; etching the anti-reflection layer and the release layer respectively based on the photoresist pattern to remove the anti-reflection layer and the release layer exposed by the lithography window, and the anti-reflection layer and the release layer outside the edge of the coupling end face are completely removed; forming an anti-detachment layer between the laser chip and the substrate; removing the release layer at the bottom of the laser unit to separate the laser device layer from the substrate, obtaining an independent laser chip, and fixing and supporting the laser chip on the substrate through the anti-detachment layer; separating the laser device chip from the substrate by a micro-transfer printing tool and micro-transfer printing it onto a target substrate, where the target substrate has an optical waveguide structure formed thereon, and the coupling end face of the laser chip faces the optical waveguide.

[0008] Optionally, the substrate includes an indium phosphide substrate, the release layer includes an aluminum indium arsenide layer, the laser device layer includes an N-type doped indium phosphide layer, a multi-quantum well layer, and a P-type doped indium phosphide layer stacked in sequence, and the patterned hard mask includes a silicon dioxide layer.

[0009] Optionally, the anti-reflection layer includes an aluminum oxide layer.

[0010] Optionally, the retraction distance of the photoresist pattern relative to the coupling end face is 0.5 micrometers to 2 micrometers.

[0011] Optionally, a wet chemical etchant is used to etch and remove the release layer at the bottom of the laser chip, and the chemical etchant includes a ferric chloride solution (FeCl3).

[0012] Optionally, the coupling end face of the laser chip is collinearly arranged with the end face of the optical waveguide within the alignment error range of the micro-transfer printing tool.

[0013] Optionally, the distance between the laser chip and the optical waveguide is 0.5 micrometers to 1.5 micrometers.

[0014] Optionally, the anti-detachment layer includes a fixing portion covering the laser chip, an anchoring portion provided on the surface of the substrate, and a bridging portion connecting the fixing portion and the anchoring portion, where the width of the bridging portion is smaller than the widths of the fixing portion and the anchoring portion.

[0015] Optionally, the laser unit includes a coupling surface for docking with an optical waveguide and the remaining non-coupling surfaces, and a photoresist pattern covers and extends to the outside of the non-coupling surfaces, such that after etching the anti-reflection layer and the release layer based on the photoresist pattern, the anti-reflection layer and the release layer have a length exceeding the non-coupling surfaces to form a ledge structure.

[0016] Optionally, the anti-detachment layer includes a plurality of anti-detachment portions, the plurality of anti-detachment portions are spaced apart and distributed on the non-coupling surface, and the release layer is exposed between the plurality of anti-detachment portions.

[0017] Optionally, forming an anti-detachment layer between the laser chip and the substrate includes: forming a photoresist layer on the substrate; patterning the photoresist layer through an exposure and development process to form a plurality of anti-detachment portions; wherein, no anti-detachment portion is provided on the coupling end face, and the patterned photoresist layer has a retraction distance relative to the coupling end face so as to keep the coupling end face clean.

[0018] Optionally, a receiving groove is provided in the target substrate, one side wall of the receiving groove exposes the end face of the optical waveguide, and the laser chip is micro-transfer printed into the receiving groove and the coupling end face of the laser chip faces the optical waveguide.

[0019] Optionally, it further includes the step of filling a planarization coating in the gap between the laser chip and the side wall of the receiving groove and the optical waveguide, and the refractive index of the planarization coating is higher than the refractive index of air and less than the refractive index of the anti-reflection layer.

[0020] Optionally, the material of the planarization coating includes benzocyclobutene.

[0021] The present invention also provides a photonic integrated chip, including: a target substrate, on which an optical waveguide is formed; a laser chip, the laser chip includes a laser device layer and an anti-reflection layer covering the surface and side walls of the laser device layer, the laser chip has a coupling end face for docking with the optical waveguide, the bottom and the side wall of the coupling end face are flush in the vertical direction, and the laser chip is disposed on the target substrate and its coupling end face faces the optical waveguide.

[0022] Optionally, the coupling end face of the laser chip is disposed in contact with the optical waveguide within the alignment error range of the micro-transfer printing tool, and the distance between the laser chip and the optical waveguide is 0.5 micrometer to 1.5 micrometers.

[0023] Optionally, the laser chip includes a coupling end face for docking with the optical waveguide and the remaining non-coupling surfaces, and the anti-reflection layer has a length exceeding the non-coupling end face to form a ledge structure.

[0024] Optionally, a receiving groove is provided in the target substrate, one side wall of the receiving groove exposes the end face of the optical waveguide, and the laser chip is micro-transfer printed into the receiving groove and the coupling end face of the laser chip faces the optical waveguide.

[0025] Optionally, the gap between the laser chip, the side wall of the accommodating groove, and the optical waveguide is filled with a planarization coating, and the refractive index of the planarization coating is higher than that of air and lower than that of the anti-reflection layer.

[0026] Optionally, the target substrate includes a silicon substrate, the laser device layer includes an N-type doped indium phosphide layer, a multi-quantum well layer, and a P-type doped indium phosphide layer stacked in sequence, a pattern hard mask is further provided on the laser device layer, the pattern hard mask includes a silicon dioxide layer, and the anti-reflection layer includes an aluminum oxide layer.

[0027] As described above, the micro-transfer printing method of the laser chip and the photonic integration chip of the present invention have the following beneficial effects:

[0028] In the present invention, by setting the photoresist pattern to have a retraction distance relative to the coupling end face, the ledge structure at the bottom of the coupling end face of the laser chip is completely removed, so as to obtain a coupling end face that is flush in the vertical direction, which can greatly improve the alignment accuracy between the laser chip and the optical waveguide in the light propagation axis direction of the optical waveguide and reduce the cumulative coupling tolerance. With the design of the present invention, the consistency of the distance between the laser chip and the optical waveguide can be greatly improved, and the stability and overall performance of the photonic integration chip can be improved.

[0029] The laser chip of the present invention with no ledge structure at the coupling end face can greatly reduce the distance between the coupling end face of the laser chip and the optical waveguide. For example, the distance between the laser chip and the optical waveguide can be made less than 1 micron, thereby increasing the coupling efficiency between the laser chip and the optical waveguide and reducing the light output loss of the laser chip. Description of the Drawings

[0030] The included drawings are used to provide a further understanding of the embodiments of the present application, which form a part of the specification, are used to illustrate the implementation manners of the present application, and are used to explain the principles of the present application together with the text description. Obviously, the drawings in the following description are only some embodiments of the present application.

[0031] Figures 1 to 14 It shows a schematic structural diagram presented by each step of the micro-transfer printing method of the laser chip according to the embodiment of the present invention. Among them, Figures 6 to 9 、 Figure 12 The left figure in is a cross-sectional structural diagram of the non-coupling end face, and the right figure is a cross-sectional structural diagram of the coupling end face.

[0032] Figure 15 For Figure 13 It is a simulation result diagram of the coupling light efficiency of different lateral offsets and gaps (D2) between the laser chip and the optical waveguide in.

[0033] Description of Component Numbers

[0034] 10 Laser chip

[0035] 101 Substrate

[0036] 102 Release layer

[0037] 103 Buffer layer

[0038] 104 N-type doped indium phosphide layer

[0039] 105 Multi-quantum well layer

[0040] 106 P-type doped indium phosphide layer

[0041] 107 Patterned hard mask

[0042] 108 Patterned photoresist

[0043] 109 Anti-reflection layer

[0044] 110 Coupling end face

[0045] 111 Non-coupling end face

[0046] 112 Photoresist pattern

[0047] 113 Bracket structure

[0048] 114 Anti-lifting layer

[0049] 1141 Fixing part

[0050] 1142 Bridging part

[0051] 1143 Anchoring part

[0052] 201 Target substrate

[0053] 202 Optical waveguide

[0054] 203 Receiving groove

[0055] 204 Planarization coating Detailed implementation manners

[0056] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0057] It should be emphasized that the term "including / comprising" when used herein refers to the presence of features, wholes, steps or components, but does not exclude the presence or addition of one or more other features, wholes, steps or components.

[0058] Features described and / or illustrated for one embodiment can be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments.

[0059] When detailing the embodiments of the present invention, for ease of illustration, sectional views showing the device structure are enlarged locally out of the general scale, and the schematic diagrams are only examples and should not limit the scope of protection of the present invention here. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in actual production.

[0060] For convenience of description, spatial relationship terms such as "under", "below", "beneath", "underneath", "above", "on" etc. may be used herein to describe the relationship of one element or feature shown in the drawings with other elements or features. It will be understood that these spatial relationship terms are intended to encompass other directions of the device in use or operation in addition to the directions depicted in the drawings. Further, when a layer is referred to as being "between" two layers, it can be the only layer between the two layers, or there can be one or more intervening layers.

[0061] In the context of the present application, the structure in which the first feature is "above" the second feature as described may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, such that the first and second features may not be in direct contact.

[0062] It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention schematically. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape and size of the components in actual implementation. The type, quantity and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0063] As Figures 1 to 14 shown, this embodiment provides a micro-transfer printing method for a laser chip, and the micro-transfer printing method includes:

[0064] As Figure 1 shown, first, step 1) is performed, a substrate 101 is provided, and a release layer 102 and a laser device layer are formed on the substrate 101.

[0065] In one embodiment, the substrate 101 can be a silicon substrate, a silicon carbide substrate, a group III-V compound substrate (such as indium phosphide, gallium arsenide, gallium nitride), etc. In this embodiment, the substrate 101 is an indium phosphide (InP) substrate suitable for growing indium phosphide-based lasers.

[0066] In one embodiment, the release layer 102 may be a material with a lattice constant close to that of the substrate 101 (such as an indium phosphide substrate) and the laser device layer (such as an indium phosphide-based laser), and having a high etching selectivity ratio with both the substrate 101 (such as an indium phosphide substrate) and the laser device layer (such as an indium phosphide-based laser). For example, the etching selectivity ratio of the release layer 102 to the substrate 101 (such as an indium phosphide substrate) and the laser device layer (such as an indium phosphide-based laser) is preferably greater than 50:1. In this embodiment, when the substrate 101 is an indium phosphide substrate and the laser device layer is an indium phosphide-based laser, the release layer 102 is preferably an aluminum indium arsenide layer to have a high etching selectivity ratio with both the substrate 101 and the laser device layer. The aluminum indium arsenide layer can be prepared on the indium phosphide substrate by processes such as atomic layer deposition (ALD), chemical vapor deposition (CVD), etc. Its thickness can be determined according to actual needs, such as 10 nanometers to 1000 nanometers, etc., and is not limited to the examples listed here.

[0067] In one embodiment, a buffer layer 103 is further provided between the release layer 102 and the laser layer. The material of the buffer layer 103 can be, for example, undoped indium phosphide to improve the growth quality of the laser device layer. The buffer layer 103 can also prevent damage to the laser layer during the subsequent removal process of the release layer 102 and ensure the stability of the device performance.

[0068] In one embodiment, the laser device layer includes an N-type doped indium phosphide layer (N-InP) 104, a multi-quantum well layer (MQW) 105, and a P-type doped indium phosphide layer (P-InP) 106 stacked in sequence. The above N-type doped indium phosphide layer 104, multi-quantum well layer 105, and P-type doped indium phosphide layer 106 can be prepared by methods such as atomic layer deposition (ALD), chemical vapor deposition (CVD), etc. This lists a structure of the laser device layer. In fact, the laser device layer can also be prepared based on other materials and is not limited to the examples listed here.

[0069] As Figures 1 to 4 shown, then step 2) is carried out. A patterned hard mask 107 is formed on the laser device layer, and the laser device layer is etched based on the patterned hard mask 107 to form laser units. The release layer 102 is exposed between adjacent laser units. Each laser unit has a coupling surface for docking with the optical waveguide 202.

[0070] In one embodiment, the patterned hard mask 107 can be a silicon dioxide layer, which can be formed on the laser device layer by processes such as chemical vapor deposition (CVD). The patterned hard mask 107 can be patterned through processes such as photolithography. Specifically, a patterned photoresist 108 can be formed through processes such as spin-coating a photoresist layer, exposure, and development, and then the photolithography pattern is transferred to the patterned hard mask 107 through a dry etching process.

[0071] In one embodiment, the laser device layer can be etched by a dry etching process (such as an RIE etching process or an ICP etching process) to form a laser unit. The etching can be set to stop at the surface of the release layer 102. The laser unit has a coupling surface for docking with the optical waveguide 202.

[0072] As Figure 5 shown, then step 3) is carried out. An antireflection layer 109 is formed on the top surface, side surface of the laser unit and the exposed surface of the release layer 102. The outer side of the antireflection layer 109 corresponding to the coupling surface is the coupling end face 110.

[0073] In one embodiment, the antireflection layer 109 is a material with a refractive index less than that of indium phosphide and greater than that of air, so as to improve the light output rate of the indium phosphide-based laser unit. Preferably, the antireflection layer 109 can be an aluminum oxide layer (Al 2 O 3 ), which can be prepared by processes such as atomic layer deposition (ALD), chemical vapor deposition (CVD), etc. Chemical vapor deposition (CVD) can be, for example, a plasma-enhanced chemical vapor deposition process (PECVD). Annealing and other treatments can also be added to increase the density and light transmission uniformity of the aluminum oxide layer.

[0074] As Figure 6 shown, then step 4) is carried out. A photoresist pattern 112 is fabricated. The photoresist pattern 112 has an etching window surrounding the laser unit, and the photoresist pattern 112 has a retraction distance D1 relative to the coupling end face 110, so that the etching window completely exposes the coupling end face 110.

[0075] In one embodiment, the photoresist pattern 112 is used to determine the positions where the antireflection layer 109 and the underlying release layer 102 will be etched. Taking a rectangular laser unit as an example, the laser unit includes a coupling end face 110 and three non-coupling end faces 111. Figure 6 The left figure shows that at the non-coupling end face 111, the photoresist pattern 112 extends beyond the non-coupling end face 111 by a distance to create a ledge structure 113. The photoresist pattern 112 extending beyond the non-coupling end face 111 by a distance can effectively protect the non-coupling end face 111 and completely avoid its being affected by subsequent etching. Figure 6The right figure shows that at the coupling end face 110, the photoresist pattern 112 has a retraction distance relative to the coupling end face 110, so that the coupling end face 110 has no ledge structure 113 and has a flush end face. Removing the ledge structure 113 from the coupling end face 110 can ensure that there is no ledge structure 113 between the coupling end face 110 and the optical waveguide 202 during subsequent micro-transfer printing, which can greatly reduce the distance between the coupling end face 110 and the optical waveguide 202, increase the coupling efficiency between the laser chip 10 and the optical waveguide 202, and reduce the light output loss of the laser chip 10. For multiple laser chips 10, it can greatly improve the alignment accuracy between the laser chip 10 and the optical waveguide 202 in the light propagation axis direction of the optical waveguide 202 and also reduce the cumulative coupling tolerance.

[0076] On the one hand, the coupling end face 110 must be completely exposed in the etching window. In one embodiment, the retraction distance of the photoresist pattern 112 relative to the coupling end face 110 is 0.5 μm to 2 μm. Preferably, the retraction distance of the photoresist pattern 112 relative to the coupling end face 110 is 1 μm.

[0077] As Figures 7 to 8 shown, then step 5) is carried out. Based on the photoresist pattern 112, the anti-reflection layer 109 and the release layer 102 are etched in sequence to remove the anti-reflection layer 109 and the release layer 102 exposed in the lithography window. The anti-reflection layer 109 and the release layer 102 outside the edge of the coupling end face 110 are completely removed. In this embodiment, the anti-reflection layer 109 and the release layer 102 are removed in two steps of dry etching. However, the anti-reflection layer 109 of the coupling end face is retained because the dry (plasma-based) etching has high directionality and anisotropy, that is, the etching of the anti-reflection layer 109 on the sidewall is very little.

[0078] As Figure 7 and Figure 8 shown, the laser unit includes a coupling surface for docking with the optical waveguide 202 and the remaining non-coupling surfaces. The photoresist pattern 112 covers and extends to the outside of the non-coupling surfaces, so that after the anti-reflection layer 109 and the release layer 102 are etched based on the photoresist pattern 112, the anti-reflection layer 109 and the release layer 102 have a length exceeding the non-coupling surfaces to form a ledge structure 113. The ledge structure 113 can ensure that the non-coupling surface of the laser does not collide with the side wall of the receiving groove and cause damage to the laser chip.

[0079] In one embodiment, first, a chlorine-based chemical is used to etch the anti-reflection layer 109 in the area not protected by the photoresist pattern 112 through an ICP etching process. As Figure 7 shown in the left figure, a certain width of the anti-reflection layer 109 is retained at the non-coupling end face 111 to form a ledge structure 113. As Figure 7As shown in the right figure, at the coupling end face 110, the anti-reflection layer 109 exposed on the top of the laser chip 10 is also removed. In this embodiment, through optimized chlorine-based chemicals and etching time, it can be ensured that after the anti-reflection layer 109 is removed, the etching of the underlying pattern hard mask 107 (such as a silicon dioxide layer) is minimized, and the integrity of its morphology is ensured, thereby avoiding the influence caused by the exposure of the laser chip 10 to the etching environment.

[0080] Then, after removing the photoresist pattern 112 by an oxygen plasma ashing process, using the anti-reflection layer 109 and the exposed pattern hard mask 107 as an etching mask, the exposed release layer 102 is further etched by a dry etching or wet etching process, as Figure 8 shown.

[0081] As Figures 9 to 11 shown, then step 6) is carried out to form an anti-separation layer 114 between the laser chip 10 and the substrate 101.

[0082] The material of the anti-separation layer 114 can use a conventional positive photoresist (such as based on novolak resin). Other types of photoresists can also be used, such as polyimide (PI) or SU-8, etc. In this embodiment, the anti-separation layer 114 uses a novolak resin-based positive photoresist.

[0083] In one embodiment, forming the anti-separation layer 114 between the laser chip 10 and the substrate 101 includes:

[0084] forming a photoresist layer on the substrate 101;

[0085] patterning the photoresist layer through an exposure and development process to form a plurality of anti-separation parts; wherein, no anti-separation part is provided at the coupling end face 110, and the patterned photoresist layer has a retraction distance relative to the coupling end face 110 to keep the coupling end face 110 clean, so as not to interfere with the optical alignment with the silicon photonics integrated chip (PIC), as Figure 9 shown. Specifically, the anti-separation layer 114 includes a plurality of anti-separation parts, the plurality of anti-separation parts are spaced apart and distributed on the non-coupling surface, and the release layer 102 is exposed between the plurality of anti-separation parts, as Figure 10 shown.

[0086] Figure 11 For Figure 10 the partial structure enlarged view of, as Figure 11As shown, the anti - detachment layer 114 includes a fixing portion 1141 covering the laser chip 10, an anchoring portion 1143 disposed on the surface of the substrate 101, and a bridging portion 1142 connecting the fixing portion 1141 and the anchoring portion 1143. Among them, the width of the bridging portion 1142 is smaller than the widths of the fixing portion 1141 and the anchoring portion 1143. On the one hand, the widths of the fixing portion 1141 and the anchoring portion 1143 are set to a larger area, which can ensure the support strength between the fixing portion 1141 and the anchoring portion 1143 and the laser chip 10 and the substrate 101. On the other hand, the bridging portion 1142 is set to a smaller area and serves as a subsequent fracture zone, which can ensure that the subsequent laser chip 10 and the substrate 101 can be fully detached more easily.

[0087] As Figure 12 shown, then step 7) is carried out to remove the release layer 102 to separate the laser device layer from the substrate 101, obtaining an independent laser chip 10, and the laser chip 10 is fixedly supported on the substrate 101 through the anti - detachment layer 114.

[0088] In one embodiment, a wet chemical etchant can be used to etch and remove the release layer 102. For example, when the release layer 102 is an aluminum indium arsenide layer, the chemical etchant can be ferric chloride solution (FeCl 3 )), and this chemical etchant can ensure the etching selectivity ratio between the release layer 102 and the substrate 101 (such as an indium phosphide substrate) and the laser device layer (such as an indium phosphide - based laser), avoiding damage to the substrate 101 and the laser device layer when etching the release layer 102.

[0089] As Figures 13 to 14 shown, finally step 8) is carried out to separate the laser device chip from the substrate 101 through a micro - transfer printing tool and micro - transfer print it into the target substrate 201, where the target substrate 201 is formed with an optical waveguide 202, the coupling end face 110 of the laser chip 10 faces the optical waveguide 202, and light is generated and emitted in the laser device layer and coupled into the optical waveguide 202.

[0090] In one embodiment, the coupling end face 110 of the laser chip 10 is collinearly arranged and aligned with the end face of the optical waveguide 202 within the alignment error range of the micro-transfer printing tool. Since the lug structure 113 is completely removed, ideally, the distance D2 between the coupling end faces 110 of the laser chip 10 can be close to 0 microns. However, it is preferable to retain a small distance (preferably 1 micron) between the coupling end face 110 of the laser and the end face of the optical waveguide within the receiving groove 203 to avoid damage to the coupling end face 110 of the laser or the end face of the optical waveguide caused by physical contact or fitting. At the same time, the distance D2 between the laser chip 10 and the optical waveguide 202 after micro-transfer printing depends on the alignment accuracy of the micro-transfer printing tool, which is usually within ±0.5 microns. Therefore, in this embodiment, the distance between the laser chip 10 and the optical waveguide 202 can be 0.5 microns to 1.5 microns (i.e., 1 ± 0.5 microns).

[0091] As Figure 13 shown, a receiving groove 203 is provided in the target substrate 201. One side wall of the receiving groove 203 exposes the end face of the optical waveguide 202. The laser chip 10 is micro-transferred into the receiving groove 203 and the coupling end face 110 of the laser chip 10 faces the optical waveguide 202. On the one hand, the structure of the receiving groove 203 can more accurately position the laser chip 10 and improve the alignment accuracy. On the other hand, the laser chip 10 is embedded in the receiving groove 203, which can improve the flatness of the photonic integrated chip.

[0092] In one embodiment, an anti-reflection layer 109 is formed on the end face of the optical waveguide 202 opposite to the laser chip 10 to minimize the back reflection at the interface.

[0093] Due to the back reflection at the air interface, it is disadvantageous to have an air gap between the micro-transferred laser chip 10 and the optical waveguide 202. Therefore, in this embodiment, it further includes the step of filling a planarization coating 204 in the gap between the laser chip 10, the side wall of the groove, and the optical waveguide 202. The refractive index of the planarization coating 204 is higher than that of air and lower than that of the anti-reflection layer 109 to ensure low back reflection in the optical path, as Figure 14 shown. In this embodiment, the material of the planarization coating 204 can be benzocyclobutene (BCB). The refractive index of benzocyclobutene (BCB) matches the requirements well, and it also has a planarization effect. At the same time, in the case of a multi-layer metal structure, benzocyclobutene (BCB) has a sufficient breakdown voltage to provide good electrical isolation for the multi-layer metal structure.

[0094] Removing the ledge structure on the coupling end face of the laser can bring the optical waveguide closer to the waveguide of the III-V compound laser. This shorter spacing can minimize the diffraction when the optical field is transmitted from the waveguide of the III-V compound laser to the optical waveguide, thereby improving optical coupling. This is because there is a better overlap integral between the electric fields on one side of the III-V compound laser and one side of the optical waveguide. Another advantage of the ledge-free structure design is that it can minimize the wavelength dependence of coupling. This is because the smaller gap can avoid the formation of wavelength-related interference patterns at the silicon / III-V compound laser interface.

[0095] Figure 15 For Figure 13 the simulation result diagram of the coupled optical efficiency for different lateral offsets and gaps (D2) between the laser chip and the optical waveguide in Figure 15 It shows the results of three-dimensional time-domain finite-difference (3D-FDTD) transmission simulations at the III-V compound laser / optical waveguide interface for three different gaps (plotted as a function of lateral offset). For the case of zero lateral offset (the III-V compound laser waveguide and the optical waveguide are aligned), the coupling efficiency of the 0.5-μm gap is improved by approximately 0.4 dB compared to the 1.5-μm gap. This means that the round-trip loss is reduced by 0.8 dB. The reduction of the laser cavity loss can bring benefits such as a lower threshold current, an increased output power, an improved efficiency, an improved beam quality, and an extended lifetime.

[0096] As Figure 14 shown, this embodiment also provides a photonic integrated chip, including: a target substrate 201, on which an optical waveguide 202 is formed; a laser chip 10, the laser chip 10 includes a laser device layer and an antireflection layer 109 covering the surface and sidewalls of the laser device layer, the laser chip 10 has at least one coupling end face 110 for docking with the optical waveguide 202, the bottom of the coupling end face 110 is flush with the sidewall in the vertical direction, and the laser chip 10 is disposed on the target substrate 201 and its coupling end face 110 faces the optical waveguide 202.

[0097] In one embodiment, the target substrate 201 can be a silicon substrate (such as a silicon wafer), on which optical structures such as the optical waveguide 202 can be formed. The laser device layer includes an N-type doped indium phosphide layer (N-InP) 104, a multiple quantum well layer (MQW) 105, and a P-type doped indium phosphide layer (P-InP) 106 stacked in sequence. A patterned hard mask 107 is also provided on the laser device layer. The patterned hard mask 107 includes a silicon dioxide layer, and the antireflection layer 109 includes an aluminum oxide layer (Al 2 O 3 ).

[0098] In one embodiment, the coupling end face 110 of the laser chip 10 is disposed in contact with the optical waveguide 202 within the alignment error range of the micro-transfer printing tool. Since the convex shelf structure 113 is completely removed, the bottom and the side wall of the coupling end face 110 are flush in the vertical direction. Ideally, the spacing between the coupling end faces 110 of the laser chip 10 can be 0 micrometers. However, the alignment gap between the laser chip 10 and the optical waveguide 202 after micro-transfer printing depends on the alignment accuracy of the micro-transfer printing tool, which is typically within ±0.5 micrometers. Therefore, in this embodiment, the spacing between the laser chip 10 and the optical waveguide 202 can be 0.5 micrometers to 1.5 micrometers.

[0099] In one embodiment, the laser chip 10 includes a coupling end face 110 for docking with the optical waveguide 202 and the remaining non-coupling faces. The anti-reflection layer 109 has a length extending beyond the non-coupling end face 111 to form a convex shelf structure 113.

[0100] In one embodiment, a receiving groove 203 is provided in the target substrate 201. One side wall of the receiving groove 203 exposes the end face of the optical waveguide 202. The laser chip 10 is micro-transfer printed into the receiving groove 203 and the coupling end face 110 of the laser chip 10 faces the optical waveguide 202. On the one hand, the structure of the receiving groove 203 can more accurately position the laser chip 10 and improve the alignment accuracy. On the other hand, the laser chip 10 is embedded in the receiving groove 203, which can improve the flatness of the photonic integrated chip.

[0101] In one embodiment, the gap between the laser chip 10, the side wall of the receiving groove, and the optical waveguide 202 is filled with a planarization coating 204. The refractive index of the planarization coating 204 is higher than that of air and lower than that of the anti-reflection layer 109 to ensure low back reflection in the optical path. In this embodiment, the material of the planarization coating 204 can be benzocyclobutene (BCB). The refractive index of benzocyclobutene (BCB) matches the requirements well, and it has a planarization effect. At the same time, in the case of a multi-layer metal structure, benzocyclobutene (BCB) has a sufficient breakdown voltage to provide good electrical isolation for the multi-layer metal structure.

[0102] As described above, the micro-transfer printing method of the laser chip and the photonic integrated chip of the present invention have the following beneficial effects:

[0103] In the present invention, by setting the photoresist pattern to have a retraction distance relative to the coupling end face, the ledge structure at the bottom of the coupling end face of the laser chip is completely removed, so as to obtain a coupling end face that is flush in the vertical direction, which can greatly improve the alignment accuracy between the laser chip and the optical waveguide in the direction of the optical propagation axis in the optical waveguide and reduce the cumulative coupling tolerance. By adopting the design of the present invention, the consistency of the distance between the laser chip and the optical waveguide can be greatly improved, and the stability and overall performance of the photonic integrated chip can be improved.

[0104] The laser chip with no ledge structure at the coupling end face of the present invention can greatly reduce the distance between the coupling end face of the laser chip and the optical waveguide. For example, the distance between the laser chip and the optical waveguide can be made less than 1 micrometer, thereby increasing the coupling efficiency between the laser chip and the optical waveguide and reducing the light output loss of the laser chip.

[0105] Therefore, the present invention effectively overcomes various disadvantages in the prior art and has high industrial utilization value.

[0106] The above embodiments are only illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A micro-transfer printing method for a laser chip, characterized in that: The micro-transfer printing method comprises: providing a substrate, and forming a release layer and a laser device layer on the substrate; Forming a pattern hard mask on the laser device layer, etching the laser device layer based on the pattern hard mask to form a laser unit, wherein the release layer is exposed between adjacent laser units, and the laser unit has a coupling surface for docking with an optical waveguide; An anti-reflection layer is formed on the top surface and the side surface of the laser unit and the exposed surface of the release layer, and the outer side of the anti-reflection layer corresponding to the coupling surface is a coupling end surface; Manufacturing a photoresist pattern, wherein the photoresist pattern has an etching window surrounding the laser unit, and the photoresist pattern has a retraction distance relative to the coupling end face, so that the etching window completely exposes the coupling end face; Etching the anti-reflection layer and the release layer based on the photoresist pattern to remove the anti-reflection layer and the release layer exposed by the photolithography window, and the anti-reflection layer and the release layer outside the edge of the coupling end face are completely removed; forming an anti-detachment layer between the laser chip and the substrate; Removing the release layer to separate the laser device layer from the substrate to obtain an independent laser chip, and fixing and supporting the laser chip on the substrate through the anti-detachment layer; The laser device chip is separated from the base by a micro-transfer printing tool and micro-transfer printed into a target substrate, wherein an optical waveguide layer is formed on the target substrate, and the coupling end face of the laser chip faces the optical waveguide.

2. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The substrate comprises an indium phosphide substrate, the release layer comprises an aluminum indium arsenide layer, the laser device layer comprises an N-type doped indium phosphide layer, a multi-quantum well layer and a P-type doped indium phosphide layer stacked in sequence, and the graphic hard mask comprises a silicon dioxide layer.

3. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The anti-reflection layer includes an aluminum oxide layer.

4. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The retraction distance of the photoresist pattern relative to the coupling end surface is 0.5 micrometer to 2 micrometers.

5. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The release layer is removed by etching with a wet chemical etchant, wherein the chemical etchant comprises a ferric chloride solution.

6. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The coupling end face of the laser chip is aligned with the end face of the optical waveguide within the alignment error range of the micro-transfer printing tool.

7. The micro-transfer printing method of a laser chip according to claim 6, characterized in that: The distance between the laser chip and the optical waveguide is 0.5 microns to 1.5 microns.

8. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The anti-detachment layer includes a fixing portion covering the laser chip, an anchoring portion arranged on a surface of a substrate, and a bridging portion connecting the fixing portion and the anchoring portion, wherein a width of the bridging portion is smaller than a width of the fixing portion and the anchoring portion.

9. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The laser unit includes a coupling surface for docking with the optical waveguide and the remaining non-coupling surfaces, and the photoresist pattern covers and extends to the outside of the non-coupling surface, so that after the anti-reflection layer and the release layer are etched based on the photoresist pattern, the anti-reflection layer and the release layer have a length exceeding the non-coupling surface to form a protrusion structure.

10. The micro-transfer printing method of laser chip according to claim 9, characterized in that: The anti-separation layer includes a plurality of anti-separation parts, the plurality of anti-separation parts are distributed at intervals on the non-coupling surface, and the release layer is exposed between the plurality of anti-separation parts.

11. The micro-transfer printing method of laser chip according to claim 10, characterized in that: Forming an anti-separation layer between the laser chip and the substrate comprises: forming a photoresist layer on the substrate; The photoresist layer is patterned by exposure and development process to form a plurality of anti-detachment parts; wherein the anti-detachment part is not provided on the coupling end face, and the patterned photoresist layer has a retraction distance relative to the coupling end face to keep the coupling end face smooth.

12. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The target substrate is provided with a receiving groove, a side wall of the receiving groove exposes the end face of the optical waveguide, the laser chip is micro-transfer printed into the receiving groove and the coupling end face of the laser chip faces the optical waveguide.

13. The micro-transfer printing method of a laser chip according to claim 1, characterized in that: The method further includes a step of filling a gap between the laser chip and the sidewall of the receiving groove and the optical waveguide with a planarization coating, wherein the refractive index of the planarization coating is higher than the refractive index of air and lower than the refractive index of the anti-reflection layer.

14. The micro-transfer printing method of a laser chip according to claim 13, characterized in that: The material of the planarization coating layer includes benzocyclobutene.

15. A photonic integrated chip, characterized in that: include: a target substrate having an optical waveguide formed thereon; A laser chip, comprising a laser device layer and an anti-reflection layer covering the surface and sidewalls of the laser device layer, wherein the laser chip has a coupling end face for docking with an optical waveguide, wherein the bottom of the coupling end face is flush with the sidewall in a vertical direction, and the laser chip is disposed on the target substrate with its coupling end face facing the optical waveguide.

16. The micro-transfer printing method of laser chip according to claim 15, characterized in that: The coupling end face of the laser chip is aligned with the optical waveguide within the alignment error range of the micro-transfer printing tool, and the spacing between the laser chip and the optical waveguide is 0.5 microns to 1.5 microns.

17. The micro-transfer printing method of a laser chip according to claim 15, characterized in that: The laser chip comprises a coupling end face for docking with an optical waveguide and other non-coupling faces, and the anti-reflection layer has a length exceeding the non-coupling end face to form a convex frame structure.

18. The micro-transfer printing method of a laser chip according to claim 15, characterized in that: The target substrate is provided with a receiving groove, a side wall of the receiving groove exposes the end face of the optical waveguide, the laser chip is micro-transfer printed into the receiving groove and the coupling end face of the laser chip faces the optical waveguide.

19. The micro-transfer printing method of a laser chip according to claim 15, characterized in that: The gap between the laser chip and the groove sidewall and the optical waveguide is filled with a planarization coating, and the refractive index of the planarization coating is higher than the refractive index of air and lower than the refractive index of the anti-reflection layer.

20. The micro-transfer printing method of a laser chip according to claim 15, characterized in that: The target substrate includes a silicon substrate, the laser device layer includes an N-type doped indium phosphide layer, a multi-quantum well layer and a P-type doped indium phosphide layer stacked in sequence, a graphic hard mask is also arranged on the laser device layer, the graphic hard mask includes a silicon dioxide layer, and the anti-reflection layer includes an aluminum oxide layer.

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