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

Abstract

The application provides a micro-transfer printing method of a laser chip and a photonic integrated chip, and 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, and the anti-reflection layer outside a coupling surface is a coupling end surface; manufacturing a photoresist pattern, and the photoresist pattern has a retraction distance relative to the coupling end surface; etching the anti-reflection layer and the release layer, and the anti-reflection layer and the release layer outside the edge of the coupling end surface are all removed; forming an anti-separation layer; removing the release layer; and micro-transfer printing the laser device chip into a target substrate, and the coupling end surface faces the optical waveguide. The application can greatly improve the alignment accuracy between the laser chip and the optical waveguide in the direction of the optical propagation axis of the optical waveguide, reduce the cumulative tolerance, and improve the consistency of the spacing between the laser chip and the optical waveguide. The application can reduce the spacing between the coupling end surface of the laser chip and the optical waveguide, increase the optical coupling efficiency, and reduce the light emission loss.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of photonic integrated chip design and manufacturing, in particular to a micro-transfer printing method of laser chip and a photonic integrated chip. BACKGROUND

[0002] In the field of silicon photonics, numerous applications such as telecom, datacom and sensing devices require integrated light sources to avoid the use of bulky and expensive discrete lasers. Since silicon has an indirect bandgap, it is challenging to fabricate a native light source in silicon. One of the solutions to this problem is to fabricate hybrid integrated devices by integrating III-V (or compound semiconductor) based laser chips onto silicon photonic devices. Flip-chip bonding techniques are usually employed, i.e. by using eutectic gold / tin solder, the III-V devices are bonded one by one onto the silicon photonic devices. Although this is a mature technology, the process speed can be too slow for high volume production to be cost effective. Furthermore, due to the solder reflow phenomenon that can occur in the packaging process, the III-V gain devices must be prevented from moving after bonding to ensure that the maximum alignment accuracy is met and the cumulative tolerance standards are reduced (which reduces the overall alignment accuracy).

[0003] As an alternative solution, micro-transfer printing (micro-transfer) is emerging as an innovative approach. By using a viscoelastic stamp to pick up the prepared III-V devices (herein referred to as micro-transfer chips or dies), multiple micro-transfer chips can be bonded simultaneously on the target silicon wafer.

[0004] However, the existing micro-transfer printing process has a large gap between the coupling end face of the III-V laser chip and the end face of the silicon waveguide that is collimated and aligned, which can cause a decrease in the alignment accuracy between the two end faces containing the optical waveguide end faces, thus resulting in a large optical path loss.

[0005] It should be noted that the above introduction to the technical background is only to facilitate a clear and complete description of the technical solutions of the present application, and to facilitate the understanding of those skilled in the art. The above technical solutions cannot be considered as known to those skilled in the art merely because they are described in the background section of the present application. SUMMARY

[0006] In view of the above-mentioned shortcomings of the prior art, the present application aims to provide a micro-transfer printing method of laser chip and a photonic integrated chip, which solves the problems of low alignment accuracy and large optical path loss between the laser chip and the optical waveguide of the target chip cavity in the prior art.

[0007] To achieve the above object and other related objects, the present application provides a micro-transfer printing method of a laser chip, which comprises the following steps: 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, and exposing the release layer between adjacent laser units, wherein the laser units have a coupling surface for being connected with an optical waveguide; depositing an anti-reflection layer on the top surface and side surface of the laser units and the surface of the exposed release layer, and the anti-reflection layer outside the coupling surface is a coupling end surface; making a photoresist pattern, wherein the photoresist pattern has an etching window surrounding the four sides of the laser units, and the photoresist pattern has a retracted distance relative to the coupling end surface, so that the etching window completely exposes the coupling end surface; 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 etching window, and the anti-reflection layer and the release layer outside the edge of the coupling end surface are completely removed; forming an anti-disengagement layer between the laser chip and the substrate; removing the release layer at the bottom of the laser units to separate the laser device layer from the substrate, and obtaining an independent laser chip, and fixing and supporting the laser chip on the substrate through the anti-disengagement layer; separating the laser device chip from the substrate by a micro-transfer printing tool, and micro-transfer printing the laser device chip onto a target substrate, wherein the target substrate has formed an optical waveguide structure, and the coupling end surface of the laser chip faces the optical waveguide.

[0008] Optionally, the substrate comprises an indium phosphide substrate, the release layer comprises an aluminum indium arsenide layer, and 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 which are stacked in sequence, and the patterned hard mask comprises a silicon dioxide layer.

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

[0010] Optionally, the retracted distance of the photoresist pattern relative to the coupling end surface is 0.5 microns to 2 microns.

[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 comprises a ferric chloride solution (FeCl3).

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

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

[0014] Optionally, the anti-disengagement layer comprises a fixed portion covering the laser chip, an anchoring portion arranged on the surface of the substrate, and a bridging portion connecting the fixed portion and the anchoring portion, wherein the width of the bridging portion is smaller than the width of the fixed portion and the anchoring portion.

[0015] Optionally, the laser chip includes a coupling end face for interfacing with the optical waveguide and a remaining non-coupling end face, the photoresist pattern covers and extends to outside of the non-coupling end face, so 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 beyond the non-coupling end face to form a ledge structure.

[0016] Optionally, the anti-disengagement layer includes a plurality of anti-disengagement portions, the plurality of anti-disengagement portions are distributed on the non-coupling end face at intervals, and the release layer is exposed between the plurality of anti-disengagement portions.

[0017] Optionally, forming the anti-disengagement layer between the laser chip and the substrate includes: forming a photoresist layer on the substrate; and patterning the photoresist layer through an exposure and development process to form a plurality of anti-disengagement portions; wherein the coupling end face is not provided with an anti-disengagement portion, and the patterned photoresist layer has a retraction distance relative to the coupling end face, so that the coupling end face remains smooth.

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

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

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

[0021] The application also provides a photonic integrated chip, including: a target substrate, the target substrate being provided with an optical waveguide; and a laser chip, the laser chip including a laser device layer and an anti-reflection layer covering the surface and side wall of the laser device layer, the laser chip having a coupling end face for interfacing with the optical waveguide, the bottom of the coupling end face being flush with the side wall in the vertical direction, and the laser chip being arranged on the target substrate with the coupling end face facing the optical waveguide.

[0022] Optionally, the coupling end face of the laser chip is arranged in abutment with the optical waveguide within a micro-transferring tool alignment error range, and the distance between the laser chip and the optical waveguide is 0.5 microns to 1.5 microns.

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

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

[0025] Optionally, the gap between the laser chip and the sidewall of the receiving slot and the optical waveguide is filled with a planarization coating, the refractive index of which 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 multiple quantum well layer and a P-type doped indium phosphide layer stacked sequentially, and a patterned hard mask is also disposed on the laser device layer, the patterned 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 for laser chips and the photonic integrated chip of the present invention have the following beneficial effects:

[0028] This invention achieves a flush coupling end face by setting the photoresist pattern to have a retraction distance relative to the coupling end face, thus completely eliminating the protrusion structure at the bottom of the laser chip coupling end face. This results in a significantly improved alignment accuracy between the laser chip and the optical waveguide along the optical propagation axis, while reducing accumulated coupling tolerance. The design of this invention greatly improves the consistency of the spacing between the laser chip and the optical waveguide, enhancing the stability and overall performance of the photonic integrated chip.

[0029] The laser chip of the present invention, which has a non-protruding 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 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. Attached Figure Description

[0030] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the embodiments of this application and to illustrate the implementation of this application, together with the textual description, to explain the principles of this application. Obviously, the drawings described below are merely some embodiments of this application.

[0031] Figures 1-14 The diagram shows the structural schematics of each step in the micro-transfer printing method for laser chips according to an embodiment of the present invention. Figures 6-9 , Figure 12 The left image shows a schematic diagram of the cross-sectional structure of the uncoupled end face, and the right image shows a schematic diagram of the cross-sectional structure of the coupled end face.

[0032] Figure 15 In response to Figure 13 Simulation results of coupling optical efficiency for laser chip and optical waveguide with different lateral offsets and gaps (D2).

[0033] Component designation explanation

[0034] 10 Laser Chips

[0035] 101 base

[0036] 102 Release Layer

[0037] 103 Buffer Layer

[0038] 104 N-type doped indium phosphide layer

[0039] 105 Multiple quantum well layers

[0040] 106 P-type doped indium phosphide layer

[0041] 107 Graphical Hard Mask

[0042] 108 Forming patterned photoresist

[0043] 109 Anti-reflective layer

[0044] 110 Coupling end face

[0045] 111 Uncoupled end face

[0046] 112 Photoresist pattern

[0047] 113 convex structure

[0048] 114 Anti-detachment layer

[0049] 1141 Fixing part

[0050] 1142 Bridging section

[0051] 1143 Anchoring section

[0052] 201 Target Substrate

[0053] 202 Optical Waveguide

[0054] 203 Receptacle

[0055] 204 planarization coating Detailed Implementation

[0056] The following specific examples illustrate the implementation 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 embodiments, and 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 / comprises" as used herein refers to the presence of a feature, whole, step, or component, 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 may 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] In the detailed description of embodiments of the present invention, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged and not to scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of the present invention. In actual fabrication, the three-dimensional spatial dimensions of length, width, and depth should be included.

[0060] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0061] In the context of this application, the structure described above the first feature may include embodiments in which the first and second features are formed in direct contact, or 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 illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0063] like Figures 1-14 As shown, this embodiment provides a micro-transfer printing method for laser chips. The micro-transfer printing method includes:

[0064] like Figure 1 As shown, step 1) is performed first, 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 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 can 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 has a high etching selectivity 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 of the release layer 102 with 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, so that it has a high etching selectivity 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) and chemical vapor deposition (CVD), and its thickness can be determined according to actual needs, such as 10 nanometers to 1000 nanometers, and is not limited to the examples listed herein.

[0067] In one embodiment, a buffer layer 103 is further disposed between the release layer 102 and the laser layer. The material of the buffer layer 103 may 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, ensuring the stability of device performance.

[0068] In one embodiment, the laser device layer comprises 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 sequentially. The N-type doped indium phosphide layer 104, the multiple quantum well layer 105, and the P-type doped indium phosphide layer 106 can be fabricated, for example, by atomic layer deposition (ALD), chemical vapor deposition (CVD), or other methods. This embodiment illustrates one structure of a laser device layer; however, the laser device layer can also be fabricated based on other materials and is not limited to the examples listed herein.

[0069] like Figures 1-4 As shown, then step 2) is performed, 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, and a release layer 102 is exposed between adjacent laser units. The 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 a process such as chemical vapor deposition (CVD). The patterned hard mask 107 can be patterned by a process such as photolithography. Specifically, the patterned photoresist 108 can be formed by spin coating a photoresist layer, exposure and development, etc., and then the photolithographic pattern can be transferred to the patterned hard mask 107 by a dry etching process.

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

[0072] As shown in FIG. 2B, then step 3) is performed to form an anti-reflective layer 109 on the top surface and side surfaces of the laser unit and the exposed surface of the release layer 102, and the anti-reflective layer 109 outside the corresponding coupling facet is the coupling end facet 110. Figure 5

[0073] In one embodiment, the anti-reflective layer 109 is a material with a refractive index less than that of InP and a refractive index greater than that of air, to improve the light extraction efficiency of the InP-based laser unit. Preferably, the anti-reflective layer 109 can be an aluminum oxide layer (Al2O3), which can be prepared by processes such as atomic layer deposition (ALD), chemical vapor deposition (CVD), etc. The chemical vapor deposition (CVD) can be, for example, a plasma-enhanced chemical vapor deposition process (PECVD), and additional processes such as annealing can be added to increase the density and light transmission uniformity of the aluminum oxide layer.

[0074] As shown in FIG. 2C, then step 4) is performed to make a photoresist pattern 112, which has an etching window around the laser unit, and the photoresist pattern 112 has a retracted distance D1 relative to the coupling end facet 110, so that the etching window completely exposes the coupling end facet 110. Figure 6

[0075] In one embodiment, the photoresist pattern 112 is used to determine the position of the anti-reflective layer 109 and the underlying release layer 102 to be etched. For example, for a rectangular laser unit including a coupling end facet 110 and three non-coupling end facets 111, Figure 6 The left drawing shows that at the non-coupling end facet 111, the photoresist pattern 112 exceeds the non-coupling end facet 111 by a distance to create a ledge structure 113, and the photoresist pattern 112 exceeding the non-coupling end facet 111 by a distance can effectively protect the non-coupling end facet 111 from being affected by subsequent etching, Figure 6 ​​The right figure shows that at the coupling end face 110, the photoresist pattern 112 has a recessed distance relative to the coupling end face 110, so that the coupling end face 110 has no protrusion structure 113 and has a flush end face. The removal of the protrusion structure 113 from the coupling end face 110 allows for a significant reduction in the distance between the coupling end face 110 and the optical waveguide 202 during subsequent micro-transfer printing. This increases the coupling efficiency between the laser chip 10 and the optical waveguide 202 and reduces the light output loss of the laser chip 10. For multiple laser chips 10, this can greatly improve the alignment accuracy between the laser chip 10 and the optical waveguide 202 along the optical propagation axis and also reduce the cumulative coupling tolerance.

[0076] On the one hand, the coupling end face 110 must be fully 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 micrometers to 2 micrometers. Preferably, the retraction distance of the photoresist pattern 112 relative to the coupling end face 110 is 1 micrometer.

[0077] like Figures 7-8 As shown, step 5) is then performed, where the anti-reflective layer 109 and the release layer 102 are sequentially etched based on the photoresist pattern 112 to remove the anti-reflective layer 109 and the release layer 102 exposed by the photolithography window. All anti-reflective layers 109 and 102 outside the edge of the coupling end face 110 are removed. In this embodiment, the anti-reflective layer 109 and the release layer 102 are removed in two dry etching steps. However, the anti-reflective layer 109 on the coupling end face is retained because dry (plasma-based) etching is used, which has high directionality and anisotropy, meaning that very little etching is performed on the anti-reflective layer 109 on the sidewall.

[0078] like Figure 7 and Figure 8 As 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, such that after etching the anti-reflection layer 109 and the release layer 102 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 protrusion structure 113. The protrusion structure 113 can ensure that the non-coupling surfaces of the laser will not collide with the sidewalls of the receiving slot, thus preventing damage to the laser chip.

[0079] In one embodiment, the antireflective layer 109 in areas not protected by the photoresist pattern 112 is first etched away using a chlorine-based chemical via an ICP etching process. For example... Figure 7 As shown in the left figure, a certain width of anti-reflective layer 109 is retained on the non-coupled end face 111 to form a protruding frame structure 113, as shown in the figure. Figure 7As shown in the right figure, the anti-reflection layer 109 exposed on the top of the laser chip 10 at the coupling end face 110 is also removed. In this embodiment, by optimizing the chlorine-based chemical and etching time, the etching of the underlying pattern hard mask 107 (such as a silicon dioxide layer) can be minimized after the anti-reflection layer 109 is removed, ensuring the integrity of the topography, thereby avoiding the impact of the laser chip 10 exposed to the etching environment.

[0080] Then, the photoresist pattern 112 is removed by an oxygen plasma ashing process, and the anti-reflection layer 109 and the exposed pattern hard mask 107 are used as etching masks to further etch by dry etching or wet etching process to remove the exposed release layer 102, as shown in Figure 8

[0081] As shown in Figures 9-11 , then step 6) is performed to form a detachment prevention layer 114 between the laser chip 10 and the substrate 101.

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

[0083] In one embodiment, forming the detachment prevention 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 by exposure and development to form a plurality of detachment prevention portions; wherein the coupling end face 110 is not provided with a detachment prevention portion, and the patterned photoresist layer has a retraction distance relative to the coupling end face 110, so that the coupling end face 110 remains smooth to avoid interfering with the optical alignment with the silicon photonics integrated chip (PIC), as shown in Figure 9 . Specifically, the detachment prevention layer 114 includes a plurality of detachment prevention portions, and the plurality of detachment prevention portions are spaced apart on the non-coupling face, and the release layer 102 is exposed between the plurality of detachment prevention portions, as shown in Figure 10

[0086] Figure 11 The partial structure enlargement of Figure 10 is shown in Figure 11 ​​As shown, the anti-disengagement layer 114 includes a fixed 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 fixed portion 1141 and the anchoring portion 1143, wherein the width of the bridging portion 1142 is smaller than the width of the fixed portion 1141 and the anchoring portion 1143. On the one hand, the width of the fixed portion 1141 and the anchoring portion 1143 is set to be large, which can ensure the support strength between the fixed portion 1141 and the anchoring portion 1143 and the laser chip 10 and the substrate 101. On the other hand, the width of the bridging portion 1142 is set to be small, and as a subsequent fracture zone, it can ensure that the subsequent laser chip 10 and the substrate 101 are easily and fully disengaged.

[0087] As shown, Figure 12 Then, step 7) is performed, the release layer 102 is removed to separate the laser device layer from the substrate 101, and the independent laser chip 10 is obtained, which is fixed and supported on the substrate 101 by the anti-disengagement 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 a ferric chloride solution (FeCl3). The chemical etchant can ensure the etching selectivity ratio of the release layer 102, 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 during etching of the release layer 102.

[0089] As shown, Figures 13-14 Finally, step 8) is performed, the laser device chip is separated from the substrate 101 by micro-transfer printing, and is micro-transfer printed into a target substrate 201, wherein 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, light is generated and emitted in the laser device layer, and is coupled to the optical waveguide 202.

[0090] In one embodiment, the coupling end face 110 of the laser chip 10 is aligned and aligned with the end face of the optical waveguide 202 within the alignment error range of the micro-transfer printing tool. Since the protrusion structure 113 is completely removed, ideally, the spacing D2 between the coupling end faces 110 of the laser chip 10 can be close to 0 micrometers. However, it is preferable to maintain a small spacing (preferably 1 micrometer) between the laser coupling end face 110 and the end face of the optical waveguide within the receiving groove 203 to avoid damage to the laser coupling end face 110 or the optical waveguide end face caused by physical contact or bonding. Simultaneously, the spacing 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 typically ±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 (i.e., 1 ± 0.5 micrometers).

[0091] like Figure 13 As 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-transfer printed into the receiving groove 203, with the coupling end face 110 of the laser chip 10 facing the optical waveguide 202. The structure of the receiving groove 203 can, on the one hand, more accurately position the laser chip 10 and improve the alignment accuracy; on the other hand, the embedding of the laser chip 10 into the receiving groove 203 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 back reflection at the interface.

[0093] Due to back reflection at the air interface, the air gap between the micro-transfer laser chip 10 and the optical waveguide 202 is unfavorable. Therefore, in this embodiment, the method further includes filling the gap between the laser chip 10 and the recess sidewall and the optical waveguide 202 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. Figure 14 As shown. In this embodiment, the planarization coating 204 can be made of benzocyclobutene (BCB). Benzocyclobutene (BCB) has a refractive index that matches the requirements well, while also having a planarization effect. Furthermore, in the case of a multilayer metal structure, benzocyclobutene (BCB) has sufficient breakdown voltage to provide good electrical isolation for the multilayer metal structure.

[0094] Removing the ledge structure of the coupling facet of the laser enables the optical waveguide and the waveguide of the III-V compound laser to be closer. This shorter separation minimizes the diffraction of the optical field from the waveguide of the III-V compound laser to the optical waveguide, thereby improving the optical coupling. This is because there is a better overlap integral between the electric field of the III-V compound laser side and the optical waveguide side. Another advantage of the ledge-free design is that it minimizes the wavelength dependence of the coupling. This is because the smaller gap avoids the formation of wavelength-dependent interference patterns at the silicon / III-V compound laser interface.

[0095] Figure 15 For the coupling of laser chips and optical waveguides with different lateral offsets and gaps (D2), the simulated results of the coupling optical efficiency are shown. Figure 13 For the coupling of laser chips and optical waveguides with different lateral offsets and gaps (D2), the simulated results of the coupling optical efficiency are shown. Figure 15 The results of the three-dimensional finite-difference time-domain (3D-FDTD) transmission simulation at the III-V compound laser / optical waveguide interface are shown for three different gaps as a function of lateral offset. For the case of zero lateral offset (III-V compound laser waveguide and optical waveguide are aligned), the coupling efficiency for a 0.5 micron gap is about 0.4 decibels better than for a 1.5 micron gap. This means a 0.8 decibel reduction in round-trip loss. A reduction in laser cavity loss can result in benefits such as a reduction in threshold current, an increase in output power, an increase in efficiency, an improvement in beam quality, and an increase in lifetime.

[0096] As shown in Figure 14 The embodiment further provides a photonic integrated chip, comprising: a target substrate 201, wherein an optical waveguide 202 is formed on the target substrate 201; and a laser chip 10, wherein the laser chip 10 comprises a laser device layer and an anti-reflection layer 109 covering a surface and a sidewall of the laser device layer, the laser chip 10 has at least one coupling facet 110 for butt joint with the optical waveguide 202, a bottom of the coupling facet 110 is flush with the sidewall in a vertical direction, and the laser chip 10 is arranged on the target substrate 201 and the coupling facet 110 of the laser chip 10 faces the optical waveguide 202.

[0097] In one embodiment, the target substrate 201 can be a silicon substrate (for example, a silicon wafer), which can be formed with the optical waveguide 202 and other optical structures, the laser device layer comprises 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 which are sequentially stacked, and the laser device layer is further provided with a patterned hard mask 107, the patterned hard mask 107 comprises a silicon dioxide layer, and the anti-reflection layer 109 comprises an aluminum oxide layer (Al2O3).

[0098] In one embodiment, the coupling end face 110 of the laser chip 10 is arranged to abut the optical waveguide 202 within the alignment error range of the micro-transfer printing tool, and since the ledge structure 113 is completely removed, the bottom of the coupling end face 110 is flush with the sidewall in the vertical direction, and in an ideal case, the spacing between the coupling end faces 110 of the laser chip 10 can be 0 microns, however, the alignment gap between the laser chip 10 and the optical waveguide 202 after micro-transfer printing needs to depend on the alignment accuracy of the micro-transfer printing tool, which is usually +-0.5 microns, therefore, in this embodiment, the spacing between the laser chip 10 and the optical waveguide 202 can be 0.5 microns to 1.5 microns.

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

[0100] In one embodiment, the target substrate 201 is provided with a receiving groove 203, one sidewall of the receiving groove 203 exposes the end face of the optical waveguide 202, and the laser chip 10 is micro-transfer printed into the receiving groove 203 with the coupling end face 110 of the laser chip 10 facing the optical waveguide 202. The structure of the receiving groove 203 can on the one hand more accurately position the position of the laser chip 10 to improve the alignment accuracy, and 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 sidewall 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), which has a refractive index that matches the requirements well, and at the same time has a planarization effect, and 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 application have the following beneficial effects:

[0103] The present application sets the photoresist pattern to have a retracted distance relative to the coupling end face, so as to completely remove the ledge structure at the bottom of the coupling end face of the laser chip, thereby obtaining a coupling end face 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 of the optical waveguide and reduce the cumulative coupling tolerance. With the design of the present application, the consistency of the spacing 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 a coupling end face without a ledge structure of the present application can greatly reduce the spacing between the coupling end face of the laser chip and the optical waveguide, such as less than 1 micrometer, thereby increasing the coupling efficiency of the laser chip and the optical waveguide and reducing the light loss of the laser chip.

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

[0106] The above embodiments only exemplarily illustrate the principles and effects of the present application, and are not used to limit the present application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A micro-transfer printing method of a laser chip, characterized by, The micro-transfer printing method comprises: 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, the release layer being exposed between adjacent laser units, the laser units having a coupling surface for interfacing with an optical waveguide; forming an anti-reflection layer on the top surface and side surface of the laser units and the exposed surface of the release layer, the anti-reflection layer outside the coupling surface being a coupling end surface; making a photoresist pattern, the photoresist pattern having an etching window surrounding the laser units, and the photoresist pattern having a retracted distance relative to the coupling end surface so that the etching window completely exposes the coupling end surface; 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 etching window, the anti-reflection layer and the release layer outside the edge of the coupling end surface being completely removed; forming an anti-disengagement layer between the laser chip and the substrate; removing the release layer 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-disengagement layer; separating the laser chip from the substrate by a micro-transfer printing tool and micro-transfer printing the laser chip into a target substrate, wherein the target substrate is formed with an optical waveguide layer, and the coupling end surface of the laser chip faces the optical waveguide.

2. The micro-transfer printing method of a laser chip according to claim 1, wherein: 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 multiple quantum well layer and a P-type doped indium phosphide layer which are stacked in sequence, and the patterned hard mask comprises a silicon dioxide layer.

3. The micro-transfer printing method of laser chips according to claim 1, wherein: The anti-reflection layer comprises an aluminum oxide layer.

4. The micro-transfer printing method of laser chips according to claim 1, wherein: The retracted distance of the photoresist pattern relative to the coupling end surface is 0.5 microns to 2 microns.

5. The micro-transfer printing method of laser chips according to claim 1, wherein: The release layer is removed by wet chemical etching, and the chemical etching agent comprises an iron trichloride solution.

6. The micro-transfer printing method of laser chips according to claim 1, wherein: The coupling end surface of the laser chip is aligned and arranged with the end surface 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, wherein: The spacing between the laser chip and the optical waveguide is 0.5 microns to 1.5 microns.

8. The micro-transfer printing method of laser chips according to claim 1, wherein: The anti-disengagement layer comprises a fixed portion covering the laser chip, an anchoring portion arranged on the surface of the substrate, and a bridging portion connected between the fixed portion and the anchoring portion, wherein the width of the bridging portion is smaller than the width of the fixed portion and the anchoring portion.

9. The micro-transfer printing method of laser chips according to claim 1, wherein: The laser unit comprises a coupling surface for interfacing with an optical waveguide and a remaining non-coupling surface, the photoresist pattern covers and extends to the outside of the non-coupling surface, so 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 beyond the non-coupling surface to form a shelf structure.

10. The micro-transfer printing method of a laser chip according to claim 9, wherein: The anti-disengagement layer comprises a plurality of anti-disengagement portions, and the plurality of anti-disengagement portions are distributed on the non-coupling surface, and the release layer is exposed between the plurality of anti-disengagement portions.

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

12. The micro-transfer printing method of laser chips according to claim 1, wherein: The target substrate is provided with a receiving groove, a side wall of the receiving groove exposes an end face of the optical waveguide, and the laser chip is micro-transferred and 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 12, wherein: The step of filling a gap between the laser chip and the side wall of the receiving groove and the optical waveguide with a planarization coating layer is further included, the planarization coating layer has a refractive index higher than that of air and lower than that of the anti-reflection layer.

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

15. A photonic integrated chip prepared by a micro-transfer printing method based on the laser chip according to any one of claims 1 to 14. The target substrate is provided with an optical waveguide formed thereon. The laser chip includes a laser device layer and an anti-reflection layer covering the surface and side wall of the laser device layer, the laser chip has a coupling end face for interfacing with the optical waveguide, the bottom of the coupling end face is flush with the side wall in the vertical direction, and the laser chip is arranged on the target substrate with the coupling end face facing the optical waveguide. The coupling end face of the laser chip is arranged in collimation with the optical waveguide within the alignment error range of the micro-transferred printing tool, and the distance between the laser chip and the optical waveguide is 0.5-1.5 microns.

16. The photonic integrated chip of claim 15, wherein: The laser chip includes a coupling end face for interfacing with the optical waveguide and the remaining non-coupling faces, and the anti-reflection layer has a length extending beyond the non-coupling faces to form a ledge structure.

17. The photonic integrated chip of claim 15, wherein: The target substrate is provided with a receiving groove, a side wall of the receiving groove exposes an end face of the optical waveguide, and the laser chip is micro-transferred and printed into the receiving groove, and the coupling end face of the laser chip faces the optical waveguide.

18. The photonic integrated chip of claim 15, wherein: The gap between the laser chip and the side wall of the receiving groove and the optical waveguide is filled with a planarization coating layer, the planarization coating layer has a refractive index higher than that of air and lower than that of the anti-reflection layer.

19. The photonic integrated chip of claim 18, wherein: 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, and the laser device layer is further provided with a patterned hard mask, the patterned hard mask includes a silicon dioxide layer, and the anti-reflection layer includes an aluminum oxide layer.

20. The photonic integrated chip of claim 15, wherein: ​

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