Method for improving grating uniformity of SGDBR laser based on process optimization

Abstract

The invention provides a method for improving grating uniformity of an SGDBR laser based on process optimization. The method comprises the following steps: performing epitaxial growth of an epitaxial layer on a substrate for the first time to obtain a grating layer; grating pattern photoetching is carried out on the grating layer, and etching of a grating structure is completed through dry etching; performing secondary epitaxy on the substrate subjected to grating etching, and growing a quantum well structure on the whole substrate until a preset waveguide etching stop layer is reached; defining a passive waveguide butt joint area through photoetching, and completely etching and removing the grown quantum well structure in the passive waveguide butt joint area by adopting dry etching and wet etching processes to expose the grating layer; performing butt-joint epitaxial growth on the etched passive waveguide butt-joint area to form a passive waveguide structure; and carrying out three times of epitaxial growth on a material required by the ridge waveguide on the passive waveguide structure, and forming the ridge waveguide structure through photoetching and dry etching processes. According to the invention, the uniformity of the grating is obviously improved, the process stability is enhanced, the device performance is optimized, and the compatibility is good.

Description

Technical Field

[0001] This invention relates to the technical field of semiconductor optoelectronic device manufacturing, to the fabrication process technology of SGDBR (sampled grating distributed Bragg reflection) semiconductor tunable lasers, and particularly to a method for fabricating SGDBR laser gratings based on process optimization. Background Technology

[0002] SGDBR semiconductor tunable lasers have important applications in optical communication, spectral analysis, and lidar due to their wide-range wavelength tuning and stable output power. The core structure of an SGDBR laser achieves tuning through the wavelength selectivity of a bottom grating, and the uniformity of the grating directly affects the laser's tuning accuracy, side-mode rejection ratio, and output stability.

[0003] In the fabrication process of traditional SGDBR lasers, key steps are involved in the docking growth of passive waveguides and quantum well regions and grating etching. The specific process is as follows: First, the docking region of the passive waveguide is etched (i.e., docking etching). After completion, grating photolithography and etching processes are performed in the docking region. Finally, the grating region and the quantum well region are docked and epitaxially grown.

[0004] However, this process has a significant drawback: during the docking etching process, compounds containing semiconductor materials (such as compounds of group III-V elements) are generated. These compounds are difficult to completely remove during the extraction process of dry etching, and tend to precipitate and remain on the surface of the grating to be etched. When subsequent grating photolithography and etching are performed, the residual compounds cause uneven photoresist adhesion and inconsistent etching rates, ultimately resulting in deviations in the linewidth and depth of the grating fringes and poor uniformity. This grating uniformity defect directly leads to distortion of the laser's reflection spectrum, decreased wavelength tuning accuracy, and even mode switching, severely affecting device performance and production yield. Summary of the Invention

[0005] To address the technical problem of poor grating etching uniformity and impacted device performance caused by residual compound contamination during docking etching in the existing fabrication process of SGDBR semiconductor tunable lasers, this invention proposes a method for improving grating uniformity in SGDBR lasers based on process optimization. By adjusting the order of grating etching and epitaxial growth, interference from residual compounds on grating etching is avoided, ensuring the consistency of the grating layer and improving process stability and device performance.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a method for improving the uniformity of SGDBR laser gratings based on process optimization, comprising the following steps: Initial epitaxy and grating fabrication: Initial epitaxial growth is performed on the substrate until the epitaxial layer required for the grating is formed, thus obtaining the grating layer; photolithography of the grating pattern is performed on the grating layer, and dry etching is used to complete the etching of the grating structure; Secondary epitaxy and quantum well growth: Secondary epitaxy is performed on the substrate after grating etching to grow a quantum well structure on the whole substrate until the preset waveguide etching stop layer is reached; Etching of the passive docking region: The passive waveguide docking region is defined by photolithography, and the quantum well structure that has been grown in the passive waveguide docking region is completely etched away by dry etching and wet etching processes to expose the grating layer. Passive waveguide docking growth: Docking epitaxial growth is performed in the etched passive waveguide docking area to form a passive waveguide structure, achieving optical matching with the surrounding structure; Tertiary epitaxy and ridge waveguide fabrication: The material required for the ridge waveguide is grown on a passive waveguide structure through tertiary epitaxy, and the ridge waveguide structure is formed by photolithography and dry etching processes.

[0007] Preferably, the first epitaxial growth, the second epitaxial growth, the docking epitaxial growth, and the third epitaxial growth are all implemented using MOCVD.

[0008] Preferably, the waveguide etching stop layer is made of InGaAsP material with a PL spectrum of 1.3 μm; the etching stop layer is used for wet selective etching.

[0009] Preferably, the quantum well structure comprises, from top to bottom, an InP grating capping layer, an InGaAsP quantum well active region, and an InP upper confinement layer, which are dry etched to the InP grating capping layer.

[0010] Preferably, the method for defining the passive waveguide docking region is to transfer the pattern on the mask of the passive waveguide docking region to the wafer by photolithography.

[0011] Preferably, the passive waveguide structure changes the effective refractive index through electrical injection, thereby changing the effective refractive index of the grating and shifting the reflection spectrum of the grating.

[0012] Preferably, the passive waveguide structure comprises, from top to bottom, an InGaAsP passive waveguide core layer and an InP cladding layer, the thicknesses of which are the same as the thicknesses of the InGaAsP quantum well active region and the InP upper confinement layer of the quantum well structure, respectively.

[0013] Preferably, the ridge waveguide structure is an InP top cladding layer, first epitaxially layered with an InP layer, and then epitaxially layered with a highly doped InGaAs layer; the width of the ridge waveguide is 2-5 μm.

[0014] Preferably, the substrate is n-type InP, and an InP buffer layer and an InGaAsP grating layer are epitaxially grown on the substrate for the first time; photoresist is coated on the surface of the InGaAsP grating layer, and a grating pattern with a period of 240-260nm is defined by electron beam lithography. The remaining thickness is etched to the InP buffer layer by ICP dry etching and wet etching to form a grating structure.

[0015] Preferably, the thickness of the InGaAsP grating layer is 20-100nm, and the etching depth of the ICP dry etching is 15nm-80nm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: Significantly improved grating uniformity: By advancing the grating etching step before the docking etching, the contamination of the grating surface by the compound residue generated during docking etching is avoided. The photoresist adheres more uniformly, the etching process is more stable, the linewidth and depth of the grating stripes are more consistent, and the reflection spectral lines are more regular.

[0017] Enhanced process stability: By adjusting the sequence of processes, the interference of residual compounds on key processes is eliminated, making the process parameters of steps such as grating etching and docking growth easier to control, and improving the consistency of device performance in mass production.

[0018] Device performance optimization: The uniform grating structure enhances the mode stability of the laser and reduces mode switching phenomena.

[0019] Excellent compatibility: The epitaxial growth, dry etching, and photolithography technologies used in the process are all mature semiconductor manufacturing processes, requiring no special equipment and easily compatible with existing production lines. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a flowchart illustrating the implementation of the present invention.

[0022] Figure 2 This is a structural diagram of the grating after etching according to the present invention.

[0023] Figure 3 This is a structural diagram of the quantum well growth of the present invention.

[0024] Figure 4 This is a structural diagram of the passive docking region quantum well after etching and removal, as per the present invention.

[0025] Figure 5 This is a structural diagram of the completed passive waveguide docking growth according to the present invention.

[0026] Figure 6 This is a structural diagram of the present invention after three extensions.

[0027] Figure 7 This is a simulation diagram of the data obtained by testing the grating etching of the device using an atomic force microscope.

[0028] In this diagram, 1 is the substrate, 2 is the grating layer, 3 is the active region, 4 is the passive waveguide structure, and 5 is the InP top cladding. Detailed Implementation

[0029] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1 A method for improving grating uniformity in SGDBR lasers based on process optimization is presented. By adjusting the sequence of key processes, the influence of etching residues on grating etching is avoided. This process route is clear, highly controllable, and can significantly improve grating uniformity and process stability. Figure 1 As shown, the steps of the present invention include: First epitaxy and grating fabrication: The first epitaxial growth is performed on substrate 1 using MOCVD until the epitaxial layer required for the grating is formed, resulting in grating layer 2; then the grating pattern is photolithographically etched on the grating layer, and the grating structure is etched using a dry etching process. The dry etching process can ensure that the grating morphology perpendicularity is >89 degrees, ensuring that the grating morphology meets the requirements.

[0031] Secondary epitaxy and quantum well growth: Secondary epitaxy is performed on the substrate after grating etching using MOCVD to grow a quantum well structure across the entire substrate until a predetermined waveguide etch stop layer is reached. The etch stop layer uses InGaAsP material with a PL spectrum of 1.3 μm. This serves as a confinement layer for specific compositions. The quantum well structure acts as the light-emitting region after electrical injection, increasing luminescence efficiency. The etch stop layer is used for wet selective etching, removing the material layers above it. The secondary epitaxy produces the active region 3, i.e., the quantum well structure.

[0032] Etching of the passive docking region: The passive waveguide docking region is defined by photolithography. That is, the pattern on the mask of the passive waveguide docking region is transferred to the wafer by photolithography. The quantum well structure that has been grown in the passive waveguide docking region is completely etched away by dry etching and wet etching processes, exposing the underlying grating layer.

[0033] Passive waveguide mating growth: MOCVD is used to perform mating epitaxial growth in the etched passive waveguide mating region to form passive waveguide structure 4, i.e., the passive waveguide core layer, achieving optical matching with the surrounding structure. The function of the passive waveguide structure is to change the effective refractive index through electrical injection, thereby changing the effective refractive index of the grating and shifting the reflection spectrum of the grating.

[0034] Three-stage epitaxy and ridge waveguide fabrication: On the monolithic structure after passive waveguide docking growth, the materials required for the ridge waveguide were grown using MOCVD in three stages. First, an InP layer was epitaxially grown, followed by a layer of highly doped InGaAs. After growth, the ridge waveguide structure was formed by photolithography and dry etching processes.

[0035] The resulting SGDBR laser has good grating uniformity and no other compound residues.

[0036] Example 2 like Figure 1 As shown, a method for improving the grating uniformity of an SGDBR laser based on process optimization is described, and its specific operation steps are as follows: Initial Epitaxy and Grating Fabrication: Using n-type InP as a substrate, initial epitaxy was performed using metal-organic chemical vapor deposition (MOCVD) to grow an InP buffer layer and an InGaAsP grating layer. The InGaAsP grating layer had a thickness of 20-100 nm. The InGaAsP grating layer was used to fabricate the grating structure, while the InP buffer layer was used for lattice matching transition. Photoresist was coated on the surface of the InGaAsP grating layer, and a grating pattern with a period of 240-260 nm was defined by electron beam lithography. ICP dry etching was used to etch to a depth of 15 nm-80 nm, and then wet etching was used to etch the remaining thickness down to the buffer layer to form the grating structure. Figure 2 As shown, the black layer represents the raster layer.

[0037] Secondary epitaxy and quantum well growth: Secondary epitaxy is performed on the surface of the grating structure using MOCVD to sequentially grow an InP grating capping layer, an InGaAsP quantum well active region, and an InP confinement layer. For example... Figure 3 As shown, the red area represents the quantum well structure.

[0038] Etching of the passive docking region: The passive waveguide docking region is defined by photoresist. ICP dry etching is used to etch the active region of the InGaAsP quantum well down to the InP grating capping layer. Then, wet etching is used to completely remove the quantum well structure of the passive waveguide docking region, exposing the underlying InGaAsP grating layer. For example... Figure 4 As shown, Figure 4 The middle layer only extends to the InP grating cover layer.

[0039] Passive waveguide mating growth: Selective MOCVD is used to epitaxially grow an InGaAsP passive waveguide core layer and an InP cladding in the passive waveguide mating region to achieve refractive index matching with the surrounding structure. For example... Figure 5 As shown, the pink layer represents the InGaAsP passive waveguide core. The thickness of both layers corresponds to the thickness of the quantum well structure, ensuring that the core is highly consistent with the quantum well region after docking. The InGaAsP passive waveguide core is used for effective refractive index modulation, which is achieved by electrical injection. The InP cladding is used to confine light, forming a ridge waveguide structure.

[0040] Three-stage epitaxy and ridge waveguide fabrication: A three-stage MOCVD epitaxial growth of the InP top cladding was performed; the ridge waveguide pattern was defined by photolithography, and a ridge waveguide with a width of 2-5 μm was formed by ICP dry etching, completing the fabrication of the device's core structure, such as... Figure 6 As shown.

[0041] The above process improves the uniformity of grating linewidth and depth in the fabricated SGDBR laser, resulting in a more regular reflection spectrum, significantly outperforming devices fabricated using traditional methods. Simulation data after grating etching was obtained using atomic force microscopy. Figure 7 As shown, from Figure 7 As can be seen, the peak height is approximately 0.012 μm, the valley height is approximately -0.021 μm, and the single groove depth is approximately 33 nm. Fluctuations are minimal across multiple cycles, and the height variation patterns at different locations are highly consistent, with no obvious abrupt changes in peak height or valley depth. The contour morphology of each groove (the changing trends of the rising and falling edges) is almost identical across different cycles, demonstrating good consistency in the results.

[0042] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for improving the grating uniformity of an SGDBR laser based on process optimization, characterized in that, The steps are as follows: Initial epitaxy and grating fabrication: Initial epitaxial growth is performed on the substrate until the epitaxial layer required for the grating is formed, thus obtaining the grating layer; photolithography of the grating pattern is performed on the grating layer, and dry etching is used to complete the etching of the grating structure; Secondary epitaxy and quantum well growth: Secondary epitaxy is performed on the substrate after grating etching to grow a quantum well structure on the whole substrate until the preset waveguide etching stop layer is reached; Etching of the passive docking region: The passive waveguide docking region is defined by photolithography, and the quantum well structure that has been grown in the passive waveguide docking region is completely etched away by dry etching and wet etching processes to expose the grating layer. Passive waveguide docking growth: Docking epitaxial growth is performed in the etched passive waveguide docking area to form a passive waveguide structure, achieving optical matching with the surrounding structure; Tertiary epitaxy and ridge waveguide fabrication: The material required for the ridge waveguide is grown on a passive waveguide structure through tertiary epitaxy, and the ridge waveguide structure is formed by photolithography and dry etching processes.

2. The method for improving the grating uniformity of SGDBR lasers based on process optimization according to claim 1, characterized in that, The initial epitaxial growth, secondary epitaxial growth, docking epitaxial growth, and tertiary epitaxial growth are all implemented using MOCVD.

3. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 1 or 2, characterized in that, The waveguide etching stop layer is made of InGaAsP material with a PL spectrum of 1.3 μm; the etching stop layer is used for wet selective etching.

4. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 3, characterized in that, The quantum well structure, from top to bottom, includes an InP grating capping layer, an InGaAsP quantum well active region, and an InP upper confinement layer, which is dry etched to the InP grating capping layer.

5. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 4, characterized in that, The method for defining the passive waveguide docking region is to transfer the pattern on the mask of the passive waveguide docking region to the wafer by photolithography.

6. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 4 or 5, characterized in that, The passive waveguide structure changes the effective refractive index through electrical injection, thereby changing the effective refractive index of the grating and shifting the reflection spectrum of the grating.

7. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 6, characterized in that, The passive waveguide structure comprises, from top to bottom, an InGaAsP passive waveguide core layer and an InP cladding layer. The thicknesses of the InGaAsP passive waveguide core layer and the InP cladding layer are the same as the thicknesses of the InGaAsP quantum well active region and the InP upper confinement layer of the quantum well structure, respectively.

8. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 1 or 7, characterized in that, The ridge waveguide structure is an InP top cladding layer, first epitaxially layered with an InP layer, and then epitaxially layered with a highly doped InGaAs layer; the width of the ridge waveguide is 2-5 μm.

9. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 8, characterized in that, The substrate is n-type InP. An InP buffer layer and an InGaAsP grating layer are epitaxially grown on the substrate for the first time. Photoresist is coated on the surface of the InGaAsP grating layer. A grating pattern with a period of 240-260nm is defined by electron beam lithography. The remaining thickness is etched to the InP buffer layer by ICP dry etching and wet etching to form a grating structure.

10. The method for improving the grating uniformity of an SGDBR laser based on process optimization according to claim 9, characterized in that, The thickness of the InGaAsP grating layer is 20-100nm, and the etching depth of the ICP dry etching is 15nm-80nm.

Images