Method for manufacturing a dfb laser and dfb laser

Abstract

This application provides a method for fabricating a DFB laser and a DFB laser. A ridge waveguide structure is etched on an epitaxial wafer; different dielectric materials are sequentially deposited in the vertical direction of the ridge waveguide structure to form a grating structure; surface electrodes are fabricated in the vertical directions of the ridge waveguide structure and the grating structure, respectively, to obtain the DFB laser. Therefore, this application uses a method of sequential deposition of dielectric materials instead of direct etching to fabricate the grating structure, which reduces the dependence of the fabrication method on growth processes and equipment, lowers the process threshold, and thus improves the fabrication efficiency and yield of the DFB laser.

Description

Technical Field

[0001] This application relates to the field of semiconductor laser technology, and in particular to a method for fabricating a DFB laser and a DFB laser. Background Technology

[0002] A distributed feedback laser (DFB laser) is a type of laser that uses a grating structure (such as a Bragg grating) inside a semiconductor to provide optical feedback, thereby achieving single-mode selection. DFB lasers can compress spectral linewidth, improve the stability of wavelength as a function of temperature, and enhance the selection of longitudinal modes. They possess high-speed, narrow-linewidth, and dynamic single-mode operation characteristics, making them widely applicable in optical communication.

[0003] In related technologies, DFB lasers etch grating structures onto the active layer or waveguide layer. For DFB lasers with grating structures etched onto the active layer, the fabrication process requires secondary epitaxial growth, placing high demands on the growth process and easily introducing defects in the active region, affecting the performance of the DFB laser. For DFB lasers with gratings etched onto the waveguide layer, the gratings are nanoscale, making the fabrication process more complex and imposing stringent requirements on the etching depth. Too low an etching depth leads to weak feedback intensity and poor single-mode characteristics; too high an etching depth causes the etching interface at the edge to extend into the active layer, resulting in numerous surface states and defects, thereby increasing the laser emission threshold, reducing power, and causing mode hopping.

[0004] However, the fabrication process of the aforementioned DFB lasers with built-in grating structures all suffer from problems such as cumbersome fabrication processes, low yield, and high fabrication costs. Summary of the Invention

[0005] This application provides a method for fabricating a DFB laser and a DFB laser, which can reduce the process threshold and fabrication cost.

[0006] On the one hand, this application provides a method for fabricating a DFB laser, comprising:

[0007] Etching a ridge waveguide structure on an epitaxial wafer;

[0008] Different dielectric materials are sequentially deposited in the vertical direction of the ridge waveguide structure to form a grating structure;

[0009] Surface electrodes are fabricated in the vertical direction of the ridge waveguide structure and the grating structure, respectively.

[0010] In one possible implementation, the ridge waveguide structure is etched on the epitaxial wafer, including:

[0011] Photolithographic patterns of ridge waveguides are fabricated on epitaxial wafers;

[0012] Based on the photolithography pattern, a ridge waveguide structure is etched on the epitaxial wafer.

[0013] In one possible implementation, different dielectric materials are sequentially deposited in the vertical direction of the ridge waveguide structure to form a grating structure, including:

[0014] Fabricate a first patterned structure perpendicular to the ridge waveguide structure;

[0015] A silicon oxide thin film of a first predetermined thickness is prepared by atomic layer deposition (ALD) on top of the first patterned structure to form a second patterned structure;

[0016] A silicon nitride thin film of a second predetermined thickness is prepared by stacking it on the second patterned structure using ALD technology to form a third patterned structure;

[0017] Multiple stacked second and third patterned structures are repeatedly fabricated to form a grating structure with the target number of periods.

[0018] In one possible implementation, before fabricating the first patterned structure perpendicular to the ridge waveguide structure, the method further includes:

[0019] In the vertical direction of the ridge waveguide structure, silicon nitride material is deposited using plasma-enhanced chemical vapor deposition (PECVD) to form a passivation layer.

[0020] In one possible implementation, after repeatedly preparing multiple stacked second and third graphic structures, the method further includes:

[0021] Plasma etching technology is used to selectively etch the sidewalls of the silicon oxide film in the second patterned structure and to etch through the silicon nitride film in the third patterned structure to the surface of the epitaxial wafer.

[0022] Silicon oxide material was deposited using plasma-enhanced chemical vapor deposition (PECVD) to fill the etched pores, thereby forming a grating structure on the epitaxial wafer surface with alternating silicon oxide and silicon nitride.

[0023] In one possible implementation, the method further includes, prior to fabricating the photolithographic pattern of the ridge waveguide on the epitaxial wafer:

[0024] The epitaxial wafer is ultrasonically cleaned using cleaning materials; the cleaning materials include at least one of acetone, alcohol, and deionized water.

[0025] In one possible implementation, surface electrodes are fabricated in the vertical directions of the ridge waveguide structure and the grating structure, respectively, including:

[0026] The upper surface of the ridge waveguide structure is exposed using overlay and plasma etching techniques.

[0027] The upper electrode of a DFB laser is deposited on the upper surface of a ridge waveguide structure using electron beam evaporation technology.

[0028] In one possible implementation, the epitaxial wafer includes a substrate; surface electrodes are fabricated in the vertical directions of the ridge waveguide structure and the grating structure, respectively, and the method further includes:

[0029] The lower electrode of the DFB laser is deposited on the back side of the substrate using electron beam evaporation technology.

[0030] In one possible implementation, the method further includes:

[0031] Ohmic contacts are formed between the upper electrode and the upper surface of the ridge waveguide structure, and between the lower electrode and the back surface of the substrate.

[0032] On the other hand, this application provides a DFB laser, which is prepared by the above-described DFB laser preparation method.

[0033] The technical solution provided in this application can achieve at least the following beneficial effects:

[0034] The DFB laser fabrication method and DFB laser provided in this application involve etching a ridge waveguide structure on an epitaxial wafer; depositing a dielectric material in the direction perpendicular to the ridge waveguide structure to form a grating structure; and fabricating surface electrodes in the directions perpendicular to both the ridge waveguide structure and the grating structure to obtain the DFB laser. Therefore, this application uses a method of sequentially depositing different dielectric materials instead of direct etching to fabricate the grating structure, which reduces the dependence of the fabrication method on growth processes and equipment, lowers the process threshold, and thus improves the fabrication efficiency and yield of the DFB laser. Attached Figure Description

[0035] Figure 1 This is a schematic flowchart illustrating an exemplary embodiment of the present application of a method for fabricating a DFB laser;

[0036] Figure 2 This is a front view of a DFB laser shown in an exemplary embodiment of this application;

[0037] Figure 3 This is a left view of a DFB laser shown in an exemplary embodiment of this application;

[0038] Figure 4 This is a top view of a DFB laser shown in an exemplary embodiment of this application. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0040] Before explaining the DFB laser fabrication method provided in the embodiments of this application, we will first introduce the common fabrication methods of DFB lasers and the inventive concept of the embodiments of this application.

[0041] Information transmission requires stable single-mode lasers, a demand that has driven the research and development of semiconductor lasers. When semiconductor lasers are used as light sources in communication systems, spectral broadening due to dispersion reduces the transmission bandwidth, thus limiting the signal transmission rate. Methods to improve the wavelength stability of semiconductor lasers mainly include external cavity methods and internal cavity methods.

[0042] The external cavity method uses specific external optical elements, such as fiber gratings or volume holographic gratings, to compress the output spectrum and then reflect the output light back into the semiconductor laser. However, the external cavity method requires extremely high grating sensitivity and alignment accuracy of the optical elements, and the external collimation system is large and expensive, making it unsuitable for pumping solid-state lasers.

[0043] The internal cavity method integrates a Bragg grating into the semiconductor laser, eliminating the difficulty of adjusting external grating elements. This type of laser with an integrated Bragg grating is called a distributed feedback semiconductor laser, or DFB laser. Specifically, the Bragg grating is etched onto the active layer or waveguide layer of the DFB laser, and optical feedback is achieved through the Bragg grating to compress the spectral linewidth, thereby improving the stability of wavelength as a function of temperature and enhancing the longitudinal mode of the light wave.

[0044] For DFB lasers with gratings etched on the active layer, the fabrication process requires secondary epitaxial growth, which places high demands on the growth process and easily introduces defects into the active region, affecting the performance of the DFB laser. For DFB lasers with gratings etched on the waveguide layer, the fabrication process is more complex due to the nanoscale grating structure. Furthermore, achieving single-mode lasing with high feedback intensity requires stringent requirements on the etching depth. Insufficient etching depth leads to weak feedback intensity and poor single-mode characteristics; excessive etching depth causes the etching interface at the edge to extend into the active layer region, resulting in numerous surface states and defects, which in turn increases the emission threshold, reduces power, and causes mode hopping.

[0045] Furthermore, a method for surface-mounted gratings on epitaxial wafers has been proposed. This involves directly etching Bragg gratings onto the surface after epitaxial growth of each layer of a DFB laser structure, thereby modulating the output light to achieve single-mode selection. The grating period is approximately 100 nanometers, and the fabrication method is typically electron beam lithography. However, this method produces grating structures with relatively small areas. For large-area grating structures at the epitaxial wafer level, electron beam lithography is time-consuming, and the accuracy of field stitching is difficult to guarantee, leading to excessively high fabrication costs. When fabricating short-period grating structures using deep ultraviolet laser dual-beam interference lithography, after exposure and development, the grating pattern needs to be transferred to the semiconductor material using chemical etching or reactive ion etching. Moreover, deep ultraviolet lithography places high demands on the performance of the lithography machine, further increasing fabrication costs.

[0046] In summary, DFB lasers with embedded gratings face the challenge of material regrowth, while DFB lasers with surface gratings suffer from high equipment requirements and the inability to fabricate large areas, both resulting in low yields and high manufacturing costs.

[0047] Based on this, this application provides a method for fabricating a DFB laser and a DFB laser, which uses dielectric material deposition and selective etching to replace traditional direct etching to fabricate a surface grating. Among these methods, there are many deposition methods with atomic layer thickness precision, which are easy to implement; and selective etching can avoid the strict requirements of etching parameters on single-material etching, thereby improving the morphology quality after etching.

[0048] In one exemplary embodiment, such as Figure 1 As shown, this application provides a method for fabricating a DFB laser, comprising the following steps:

[0049] Step 110: Etch a ridge waveguide structure on the epitaxial wafer.

[0050] The epitaxial wafer can be selected based on the fabrication requirements of the DFB laser, choosing a laser epitaxial wafer with the target excitation wavelength. For example, the target excitation wavelength could be 1310 nm.

[0051] In some embodiments, the epitaxial wafer needs to be ultrasonically cleaned with a cleaning material before etching in order to remove impurities attached to the surface of the epitaxial wafer.

[0052] The cleaning materials include at least one of acetone, alcohol, and deionized water.

[0053] As an example, the epitaxial wafer is first cleaned with acetone, then cleaned a second time with alcohol, and finally rinsed with deionized water. The above cleaning steps are repeated three times to obtain a clean epitaxial wafer.

[0054] In one possible implementation, step 110 can be implemented as follows: fabricating a ridge waveguide photolithography pattern on an epitaxial wafer; and etching a ridge waveguide structure on the epitaxial wafer according to the photolithography pattern.

[0055] Specifically, a photoresist mask is first spin-coated onto the cleaned epitaxial wafer surface. After spin coating and baking, a ridge waveguide pattern is fabricated on the epitaxial wafer using photolithography. Then, the ridge waveguide structure is etched onto the epitaxial wafer according to the photolithographic pattern using inductively coupled plasma (ICP) etching technology. Further, after etching the ridge waveguide structure, the epitaxial wafer is cleaned with acetone to remove residual photoresist.

[0056] Step 120: Different dielectric materials are deposited sequentially in the vertical direction of the ridge waveguide structure to form a grating structure.

[0057] The dielectric materials include silicon oxide and silicon nitride, and the resulting grating structure can be a Bragg grating.

[0058] It should be noted that the ridge waveguide structure is the protruding portion on the laser epitaxial wafer after etching. The surface on which the grating structure is formed in the vertical direction includes the side perpendicular to the laser epitaxial wafer and the side extending to the surface of the laser epitaxial wafer. In other words, except for the upper surface of the ridge waveguide structure, the grating structure covers all surfaces in the protruding direction of the ridge waveguide structure.

[0059] In one possible implementation, step 120 can be implemented as follows: a first patterned structure perpendicular to the ridge waveguide structure is prepared; a silicon oxide thin film of a first predetermined thickness is prepared by stacking the first patterned structure and using atomic layer deposition (ALD) technology to form a second patterned structure; a silicon nitride thin film of a second predetermined thickness is prepared by stacking the second patterned structure and using ALD technology to form a third patterned structure; multiple stacked second and third patterned structures are prepared repeatedly to form a grating structure with a target number of periods.

[0060] As an example, the first patterned structure is a rectangular patterned structure with a width of 3.1 μm; the first patterned structure can be fabricated using photolithography. The second patterned structure is a 164 nm silicon oxide thin film, and the third patterned structure is a 164 nm silicon nitride thin film.

[0061] It should be understood that the specific width (or thickness) of the first, second, and third graphic structures mentioned above can be adjusted according to actual needs and is not limited to the dimensions listed above.

[0062] Optionally, when preparing the first patterned structure, the second patterned structure, and the third patterned structure, the photoresist needs to be removed with acetone after each layer is prepared.

[0063] As an example, if the target number of cycles is 30, then 10 silicon oxide films of 164 nm and 10 silicon nitride films of 164 nm need to be prepared.

[0064] In some embodiments, before fabricating a first patterned structure perpendicular to the ridge waveguide structure, silicon nitride material needs to be deposited in the vertical direction of the ridge waveguide structure using plasma-enhanced chemical vapor deposition (PECVD) to form a passivation layer.

[0065] The passivation layer can also be used as part of the grating structure in the later stages.

[0066] Furthermore, after forming the above-mentioned grating structure, in order to improve the morphological quality of the grating structure, selective etching can be performed on the stacked first pattern structure and second pattern structure.

[0067] In one possible implementation, plasma etching technology is used to selectively etch the sidewalls of the silicon oxide film in the second patterned structure and etch through the silicon nitride film in the third patterned structure to the surface of the epitaxial wafer; PECVD technology is used to deposit silicon oxide material to fill the etched hole structure, so as to form a grating structure with silicon oxide and silicon nitride spaced apart on the surface of the epitaxial wafer.

[0068] In this way, the sidewalls of the silicon oxide film in the second patterned structure are etched clean, preventing material fusion between the second and third patterned structures, so as to form a grating structure that meets the requirements.

[0069] In another possible implementation, plasma etching technology is used to selectively etch the sidewalls of the silicon nitride thin film in the third patterned structure and etch through the silicon nitride thin film in the third patterned structure to the surface of the epitaxial wafer; PECVD technology is used to deposit silicon nitride material to fill the etched hole structure, so as to form a grating structure with silicon oxide and silicon nitride spaced apart on the surface of the epitaxial wafer.

[0070] In this way, the sidewalls of the silicon nitride film in the third patterned structure are etched clean, preventing material fusion between the second and third patterned structures, so as to form a grating structure that meets the requirements.

[0071] Step 130: Surface electrodes are fabricated in the vertical directions of the ridge waveguide structure and the grating structure, respectively.

[0072] The surface electrode includes an upper electrode and a lower electrode.

[0073] In one possible implementation, step 130 can be performed by: exposing the upper surface of the ridge waveguide structure using overlay and plasma etching techniques; and depositing the upper electrode of the DFB laser on the upper surface of the ridge waveguide structure using electron beam evaporation. Similarly, the lower electrode of the DFB laser is deposited on the back side of the substrate using electron beam evaporation.

[0074] It should be noted that since the grating structure is formed by depositing dielectric material in the vertical direction of the ridge waveguide structure, the protruding part of the ridge waveguide structure may be covered with dielectric material. In this case, the dielectric material covering the protruding part of the ridge waveguide structure can be removed by overlay technology and plasma etching technology to expose the protruding structure, which is convenient for subsequent electrode fabrication.

[0075] Furthermore, after fabricating the surface electrode, ohmic contacts need to be formed between the surface electrode and the contact material. That is, ohmic contacts need to be formed between the electrode and the upper surface of the ridge waveguide structure, and between the lower electrode and the back surface of the substrate.

[0076] In this embodiment, a ridge waveguide structure is etched on an epitaxial wafer; a dielectric material is deposited in the direction perpendicular to the ridge waveguide structure to form a grating structure; surface electrodes are fabricated in the directions perpendicular to both the ridge waveguide structure and the grating structure to obtain a DFB laser. Therefore, using dielectric material deposition instead of direct etching to fabricate the grating structure reduces the dependence of the fabrication method on growth processes and equipment, lowers the process threshold, and thus improves the fabrication efficiency and yield of DFB lasers.

[0077] In one exemplary embodiment, such as Figure 2 As shown, this application also provides a DFB laser fabricated by the above-described DFB laser fabrication method. The DFB laser comprises, from bottom to top, the following layers stacked sequentially: a lower electrode, a substrate, a lower confinement layer, an active layer, an upper confinement layer, a grating structure, a ridge waveguide structure, and an upper electrode;

[0078] The grating structure is formed by sequentially depositing different dielectric materials and selectively etching them.

[0079] It should be noted that the process of sequentially depositing different dielectric materials and selectively etching to prepare the grating structure can be found in the above method embodiments, and will not be repeated here.

[0080] In addition, the structure of the fabricated DFB laser can also be found in [reference needed]. Figure 3 The left view shown, and Figure 4 The top view shown.

[0081] In the embodiments of this application, there are many deposition methods with atomic layer thickness precision, which are easy to implement; and selective etching can avoid the strict requirements of etching parameters on single-material etching, thus improving the morphology quality after etching. Therefore, using dielectric material deposition and selective etching instead of direct etching to fabricate the grating structure improves the fabrication efficiency and yield of DFB lasers.

[0082] The above detailed embodiments further illustrate the purpose, technical solution, and beneficial effects of the embodiments of this application. It should be understood that the above are merely specific embodiments of the embodiments of this application and are not intended to limit the protection scope of the embodiments of this application. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solutions of the embodiments of this application should be included within the protection scope of the embodiments of this application.

Claims

1. A method for fabricating a DFB laser, characterized in that, The method includes: Etching a ridge waveguide structure on an epitaxial wafer; A first patterned structure perpendicular to the ridge waveguide structure is fabricated; A silicon oxide thin film of a first predetermined thickness is prepared by atomic layer deposition (ALD) on the first patterned structure to form a second patterned structure; A silicon nitride thin film of a second predetermined thickness is prepared by stacking it on the second patterned structure using the ALD technology to form a third patterned structure; Multiple stacked second and third patterned structures are repeatedly fabricated to form a grating structure with a target number of periods, the grating structure covering all surfaces except the top surface in the convex direction of the ridge waveguide structure; Plasma etching technology is used to selectively etch the sidewalls of the silicon oxide film in the second patterned structure and to etch through the silicon nitride film in the third patterned structure to the surface of the epitaxial wafer. Silicon oxide material is deposited using plasma-enhanced chemical vapor deposition (PECVD) technology to fill the etched hole structure, thereby forming a grating structure of silicon oxide and silicon nitride alternating on the surface of the epitaxial wafer. Surface electrodes are fabricated in the vertical directions of the ridge waveguide structure and the grating structure, respectively.

2. The method according to claim 1, characterized in that, The etching of the ridge waveguide structure on the epitaxial wafer includes: A photolithographic pattern of a ridge waveguide is fabricated on the epitaxial wafer; The ridge waveguide structure is etched on the epitaxial wafer according to the photolithography pattern.

3. The method according to claim 1, characterized in that, Before fabricating the first patterned structure perpendicular to the ridge waveguide structure, the method further includes: In the vertical direction of the ridge waveguide structure, silicon nitride material is deposited using plasma-enhanced chemical vapor deposition (PECVD) to form a passivation layer.

4. The method according to claim 2, characterized in that, Before fabricating the photolithographic pattern of the ridge waveguide on the epitaxial wafer, the method further includes: The epitaxial wafer is ultrasonically cleaned using a cleaning material, which includes at least one of acetone, alcohol, and deionized water.

5. The method according to claim 1 or 2, characterized in that, The step of fabricating surface electrodes in the perpendicular directions of the ridge waveguide structure and the grating structure includes: The upper surface of the ridge waveguide structure is exposed using overlay and plasma etching techniques. The upper electrode of the DFB laser is deposited on the upper surface of the ridge waveguide structure using electron beam evaporation technology.

6. The method according to claim 5, characterized in that, The epitaxial wafer includes a substrate; the fabrication of surface electrodes in the perpendicular directions of the ridge waveguide structure and the grating structure includes: The lower electrode of the DFB laser is deposited on the back side of the substrate using electron beam evaporation technology.

7. The method according to claim 6, characterized in that, The method further includes: An ohmic contact is formed between the upper electrode and the upper surface of the ridge waveguide structure, and between the lower electrode and the back surface of the substrate.

8. A DFB laser, characterized in that, The DFB laser is prepared by the DFB laser preparation method according to any one of claims 1 to 7.

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