A method for preventing oxidation of an active region in a DFB laser

Abstract

The application discloses a kind of oxidation prevention processing method of active region in DFB laser, comprising: first, on the etching surface exposed to AlInGaAs active region side wall, sulfide passivation protective layer is formed by treating ammonium polysulfide solution;Subsequently, mixed gas of organic silicon precursor vapor and ozone is applied to carry out gas phase treatment, and siloxane-based crosslinking network is constructed on the surface and edge of protective layer, to form mechanically reinforced composite protective layer;Finally, in phosphorus source atmosphere, near-infrared laser pulse of specific wavelength is scanned and background resistance heating is simultaneously carried out, and the composite protective layer is decomposed by light-heat synergistic desorption, to expose clean AlInGaAs etching surface, and to complete selective epitaxial growth of InGaAsP material layer.The application realizes mechanical reinforcement by the composite structure of sulfide passivation protective layer and siloxane-based crosslinking network, and accurately controls thermal decomposition process by combining light-heat synergistic desorption treatment, to solve the problem of active region sidewall oxidation and desorption thermal stress.

Description

Technical Field

[0001] This invention relates to the field of DFB laser fabrication technology, and in particular to a method for preventing oxidation of the active region in a DFB laser. Background Technology

[0002] Distributed feedback (DFB) laser chips are precise light sources on the information superhighway. With the explosive growth of data traffic, the performance requirements for laser chips are becoming increasingly stringent. Among them, the active region using the aluminum indium gallium arsenide (AlInGaAs) material system has become a key technology route for realizing high-speed and long-distance transmission due to its excellent high-temperature performance and high-speed characteristics.

[0003] However, aluminum is chemically extremely reactive. When the dry etching process in chip manufacturing exposes the sidewalls of the active region of the AlInGaAs quantum well, this etched surface reacts with oxygen and water vapor in the air to generate a layer of amorphous aluminum oxide. This oxide layer not only absorbs light signals and increases device losses, but also, especially in the necessary metal-organic chemical vapor deposition (MOCVD) regrowth step, acts as a heterogeneous interface, severely damaging the crystal quality of the newly formed epitaxial layer, introducing a large number of defects, and ultimately leading to an increase in laser threshold current and a decrease in efficiency. In long-term operation, it becomes a hidden danger of performance degradation, making it difficult to meet reliability standards.

[0004] To address this challenge, the industry has explored various methods. One typical approach involves treating the etched surface with an ammonium polysulfide solution. For example, Chinese patent CN113078553B, entitled "An Aluminum Quantum Trap Laser and Its Fabrication Method," discloses a method that uses a chemical reaction to transform unstable natural oxides into a relatively stable sulfide protective layer, allowing it to be briefly exposed to the atmosphere. However, the sulfide protective layer itself has inherent defects: it is porous and has poor mechanical strength. During the process from solution treatment to transfer to the MOCVD equipment, any slight physical vibration or airflow can cause localized damage or peeling, leading to protective failure. More importantly, in the subsequent MOCVD chamber, the sulfide protective layer needs to be removed through high-temperature heat treatment. Traditional global resistance heating methods generate significant thermal stress at the interface due to the large difference in thermal expansion coefficients between the sulfide protective layer and the underlying AlInGaAs material, easily inducing nanoscale microcracks. These microcracks are also a fatal source of defects for subsequent epitaxial growth. Therefore, existing technologies have always been unable to achieve a balance between effective protection and perfect removal, severely limiting the robustness of the process and the yield of the products. Summary of the Invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defects of poor mechanical strength of sulfide protective layer in the prior art and easy damage to AlInGaAs interface during high temperature desorption. The present invention provides an anti-oxidation treatment method for the active region of DFB laser. Mechanical strengthening is achieved through the composite structure of sulfide passivation protective layer and siloxane crosslinked network. Combined with photothermal synergistic desorption treatment, the thermal decomposition process is precisely controlled, which effectively solves the problems of active region sidewall oxidation and desorption thermal stress.

[0006] To address the aforementioned technical problems, this invention provides a method for preventing oxidation of the active region in a DFB laser, comprising the following steps:

[0007] After the grating fabrication of the DFB laser epitaxial wafer is completed, the epitaxial wafer is etched by a dry etching process until the active region sidewall containing AlInGaAs material is exposed, forming an etched surface. After cleaning the etched surface, it is immersed in an ammonium polysulfide solution for treatment, forming a sulfide passivation protective layer on the surface of the AlInGaAs material.

[0008] An epitaxial wafer with a sulfide passivation protective layer is subjected to a gaseous treatment of a mixture of organosilicon precursor vapor and ozone. Under conditions ranging from room temperature to 60°C, a siloxane cross-linked network is formed on the surface and edge regions of the sulfide passivation protective layer, thereby obtaining a mechanically strengthened composite protective layer.

[0009] In a protective atmosphere containing a phosphorus source, a near-infrared laser is used to irradiate the entire surface of the epitaxial wafer in a pulse scanning manner. The wavelength of the near-infrared laser is configured to have a high absorption rate for the composite protective layer and a low absorption rate for the underlying AlInGaAs material. Simultaneously, background resistance heating is used to perform photothermal synergistic desorption treatment, causing thermal decomposition of the composite protective layer and exposing a clean AlInGaAs etched surface.

[0010] After the photothermal desorption step is completed, an InGaAsP material layer is selectively epitaxially grown on the clean AlInGaAs etched surface to cover and protect the active region sidewalls, forming a complete waveguide structure.

[0011] In one embodiment of the present invention, the dry etching process for etching the epitaxial wafer includes:

[0012] Inductively coupled plasma etching was employed, with chlorine and boron trichloride as the main etching gases, and a trace amount of nitrogen gas was introduced.

[0013] During the etching process, the wafer stage temperature is controlled within a low temperature range of -10℃ to 10℃;

[0014] When the etching endpoint monitoring system detects a signal change, it switches the main etching gas to a mixture containing only boron trichloride and nitrogen, and performs soft landing etching for 5 to 15 seconds.

[0015] In one embodiment of the present invention, the treatment by immersion in an ammonium polysulfide solution includes:

[0016] The epitaxial wafer is slowly immersed in the ammonium polysulfide solution at an angle of 70° to 85° relative to the liquid surface;

[0017] During the soaking process, the solution temperature is controlled at 30℃~50℃, and low-frequency ultrasound with a frequency of 25kHz~40kHz is applied.

[0018] After soaking, the epitaxial wafer is removed from the solution in a step-by-step manner, pausing for 1 to 3 seconds above the liquid surface after each step.

[0019] In one embodiment of the present invention, the organosilicon precursor vapor and ozone are introduced in stages, wherein:

[0020] The first stage involves introducing ozone-rich gas to activate the surface of the sulfide passivation protective layer.

[0021] In the second stage, a mixture of organosilicon precursor vapor and low-concentration ozone is introduced to carry out a cross-linking reaction. The partial pressure of the organosilicon precursor vapor is controlled to gradually increase, starting from an initial low partial pressure and linearly increasing to a target partial pressure within a set time. At the same time, the partial pressure of ozone is controlled to be maintained at a constant low level.

[0022] In the third stage, after reaching the target partial pressure, the introduction of organosilicon precursor vapor is stopped, and a mixed gas containing ozone is continued to be introduced. At the same time, the temperature of the epitaxial wafer is increased by 5°C to 15°C from the original level to complete the final curing of the crosslinked network and promote the volatilization of unreacted precursors and by-products.

[0023] In one embodiment of the invention, the weather treatment is carried out in a reaction chamber. Before the weather treatment, the reaction chamber is evacuated and backfilled with high-purity nitrogen to near atmospheric pressure. This process is repeated at least three times.

[0024] In one embodiment of the present invention, after applying a mixture of organosilicon precursor vapor and ozone for gas treatment, a heated inert carrier gas is introduced to purge the epitaxial wafer; the temperature of the inert carrier gas is 10°C to 20°C higher than the temperature of the gas phase treatment.

[0025] In one embodiment of the present invention, during the vapor phase processing, the change in the quality of the epitaxial wafer is monitored in real time, and the vapor phase processing is terminated when the rate of increase in quality drops to less than 10% of the initial rate.

[0026] In one embodiment of the present invention, the photothermal synergistic desorption process includes:

[0027] Start background resistance heating to uniformly raise the ambient temperature to the target desorption temperature and maintain it stably at this temperature, so that the epitaxial wafer and its surface composite protective layer reach thermal equilibrium as a whole.

[0028] The near-infrared laser emitter is activated, and its initial output power is set to a preheating power that is much lower than the target desorption power. The epitaxial wafer is then subjected to the first pulse scan at this preheating power. Subsequently, the laser output power is linearly increased to the target desorption power in multiple steps.

[0029] Once the laser power reaches the target desorption power, the laser power is kept constant, and the scanning path of the laser beam covers the entire surface of the epitaxial wafer.

[0030] After the desorption process is completed, the near-infrared laser emitter is turned off, and the background resistance heating and phosphorus-containing source atmosphere are maintained to perform in-situ thermal stabilization treatment on the exposed clean AlInGaAs etched surface.

[0031] In one embodiment of the present invention, when irradiating with a near-infrared laser in a pulse scanning manner, the pulse scanning adopts an overlapping scanning path, and the overlap rate between adjacent scanning paths is 50% to 70%; the pulse frequency of the laser is matched with the scanning speed, so that at any point on the surface of the epitaxial wafer, the action time of three or more consecutive laser pulses is reached.

[0032] In one embodiment of the present invention, in the photothermal desorption step: the characteristic peak intensity of sulfur dioxide in the tail gas of the reaction chamber is monitored in real time by mass spectrometry; when the characteristic peak intensity of sulfur dioxide drops to 5% of its peak intensity and remains stable, it is determined that the composite protective layer has been completely desorbed, and laser irradiation and background resistance heating are stopped.

[0033] The technical solution of the present invention has the following advantages compared with the prior art:

[0034] The anti-oxidation treatment method for the active region of a DFB laser described in this invention fundamentally solves the dual problems of vulnerability of the protective layer and damage introduced during the desorption process. First, after preparing the sulfide protective layer, a gas-phase treatment with organosilicon precursor vapor and ozone is applied, constructing a robust siloxane cross-linked network on the surface and edges of the sulfide protective layer at room temperature. This is equivalent to weaving a flexible yet robust composite protective layer in situ outside the original sulfide protective layer. This composite protective layer greatly enhances the overall mechanical strength, enabling it to easily withstand the physical stress during subsequent process transmission, ensuring that the protective layer remains intact before entering the MOCVD chamber.

[0035] Next, the desorption process within the MOCVD chamber employs a photothermal synergy strategy. A specific wavelength of near-infrared laser is selected, which is efficiently absorbed by the upper composite protective layer but penetrates the underlying AlInGaAs active region with almost no loss. While a gentle base temperature field is provided by background resistance heating, the laser delivers energy precisely and selectively to the composite protective layer to be removed via pulse scanning, achieving localized and efficient heating. The composite protective layer rapidly heats up and decomposes due to the absorption of laser energy, while the underlying AlInGaAs etched surface retains its original properties due to its extremely low absorptivity. This fundamentally avoids thermal stress and microcracks caused by overall thermal expansion mismatch, achieving cold peeling of the protective layer.

[0036] In summary, this solution, through the synergistic innovation of constructing a composite protective layer and implementing photothermal synergistic desorption, not only successfully solves the oxidation problem of AlInGaAs materials, but also achieves mechanical strengthening through the composite structure and precisely controls the thermal decomposition process, effectively solving the problems of sidewall oxidation and desorption thermal stress in the active region. Attached Figure Description

[0037] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein:

[0038] Figure 1 This is a process flow diagram of the anti-oxidation treatment method for the active region of a DFB laser according to the present invention;

[0039] Figure 2 This is a process flow diagram of the gas phase treatment process of the present invention;

[0040] Figure 3 This is a process flow diagram of the photothermal synergistic desorption process of the present invention. Detailed Implementation

[0041] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0042] Reference Figure 1 As shown, the present invention proposes a method for preventing oxidation of the active region in a DFB laser, comprising the following steps:

[0043] After the grating fabrication of the DFB laser epitaxial wafer is completed, the epitaxial wafer is etched by a dry etching process until the active region sidewall containing AlInGaAs material is exposed, forming an etched surface. After cleaning the etched surface, it is immersed in an ammonium polysulfide solution for treatment, forming a sulfide passivation protective layer on the surface of the AlInGaAs material.

[0044] An epitaxial wafer with a sulfide passivation protective layer is subjected to a gaseous treatment of a mixture of organosilicon precursor vapor and ozone. Under conditions ranging from room temperature to 60°C, a siloxane cross-linked network is formed on the surface and edge regions of the sulfide passivation protective layer, thereby obtaining a mechanically strengthened composite protective layer.

[0045] In a protective atmosphere containing a phosphorus source, a near-infrared laser is used to irradiate the entire surface of the epitaxial wafer in a pulse scanning manner. The wavelength of the near-infrared laser is configured to have a high absorption rate for the composite protective layer and a low absorption rate for the underlying AlInGaAs material. Simultaneously, background resistance heating is used to perform photothermal synergistic desorption treatment, causing thermal decomposition of the composite protective layer and exposing a clean AlInGaAs etched surface.

[0046] After the photothermal desorption step is completed, an InGaAsP material layer is selectively epitaxially grown on the clean AlInGaAs etched surface to cover and protect the active region sidewalls, forming a complete waveguide structure.

[0047] In practical applications, dry etching can be understood as a technique that uses plasma to bombard the surface of an epitaxial wafer to remove material. For example, it can be achieved through reactive ion etching or electron cyclotron resonance etching. Its main purpose is to precisely control the etching depth and ensure that the exposed etched surface meets the requirements of subsequent processing. Furthermore, the treatment process of ammonium polysulfide solution can be achieved by using different combinations of chemical reagents, such as using solutions containing thiosulfate or other sulfide precursors to form a stable sulfide layer on the surface of AlInGaAs material.

[0048] Specifically, the gas-phase treatment of a mixture of organosilicon precursor vapor and ozone can be achieved in various ways. For example, different organosilicon compounds can be selected as precursors, such as methyltrimethoxysilane or vinyltriethoxysilane, and the formation of the cross-linked network can be optimized by adjusting the ozone concentration and introduction time. Furthermore, the temperature conditions for gas treatment can be flexibly adjusted between room temperature and 60°C to meet the needs of different material systems.

[0049] Furthermore, the wavelength configuration of the near-infrared laser can be selected based on the optical properties of the composite protective layer and the AlInGaAs material. For example, a laser with a wavelength range of 800 nm to 1500 nm can be selected to ensure that the composite protective layer can efficiently absorb light energy while minimizing its impact on the underlying material. Background resistance heating can also be replaced by other uniform heating techniques, such as infrared radiation heating or hot plate heating, to provide a stable thermal environment.

[0050] This embodiment addresses the oxidation problem of exposed AlInGaAs active region sidewalls and the insufficient mechanical strength and microcracks caused by thermal stress during desorption of traditional sulfide protective layers by constructing a composite protective layer that combines high mechanical strength and controllable desorption characteristics. Specifically, the siloxane crosslinking network formed through low-temperature vapor phase treatment significantly improves the mechanical properties of the sulfide protective layer, avoiding the risk of breakage during transfer or operation. Simultaneously, the photothermal synergistic desorption technology combines selective heating with near-infrared laser and a uniform thermal environment created by background resistance heating, effectively reducing interfacial thermal stress and eliminating the risk of microcracks. Finally, the selective epitaxial growth of InGaAsP material layers achieves the construction of a defect-free waveguide structure, completely resolving the device performance degradation problem caused by oxide interfaces.

[0051] The working principle of this application embodiment is as follows: After the grating fabrication of the DFB laser epitaxial wafer is completed, the epitaxial wafer is etched using a dry etching process until the active region sidewalls containing AlInGaAs material are exposed, forming an etched surface. In this step, dry etching can precisely control the etching depth, ensuring that the active region sidewalls are completely exposed, providing a foundation for subsequent processing. After cleaning the etched surface, it is immersed in an ammonium polysulfide solution for treatment, forming a sulfide passivation protective layer on the AlInGaAs material surface. The chemical conversion effect of the ammonium polysulfide solution converts the potential oxides on the etched surface into a sulfide layer, providing an initial anti-oxidation barrier and preventing the formation of alumina due to air exposure.

[0052] Furthermore, the epitaxial wafer with the sulfide passivation protective layer is subjected to gas phase treatment with a mixture of organosilicon precursor vapor and ozone. Under conditions ranging from room temperature to 60°C, a siloxane crosslinking network is formed on the surface and edge regions of the sulfide passivation protective layer, thereby obtaining a mechanically strengthened composite protective layer. Specifically, the reaction between the organosilicon precursor and ozone selectively acts on the surface and edge of the sulfide layer, significantly improving the overall mechanical strength of the protective layer through the crosslinking network structure, preventing damage caused by physical vibration during transfer or operation, while avoiding thermal damage under low temperature conditions.

[0053] In a protective atmosphere containing a phosphorus source, a near-infrared laser is used to irradiate the entire surface of the epitaxial wafer in a pulsed scanning manner. The wavelength of the near-infrared laser is configured to have high absorption of the composite protective layer and low absorption of the underlying AlInGaAs material. Simultaneously, background resistance heating is employed for photothermal synergistic desorption, causing thermal decomposition of the composite protective layer and exposing a clean AlInGaAs etched surface. Thus, by precisely matching the laser wavelength with the material absorption characteristics, the composite protective layer efficiently absorbs light energy while the underlying AlInGaAs absorbs almost nothing. Combined with the uniform thermal environment of background heating, selective thermal decomposition of the composite protective layer is achieved, avoiding interfacial thermal stress caused by differences in thermal expansion coefficients, thereby eliminating the potential for microcracks.

[0054] After the photothermal synergistic desorption step is completed, an InGaAsP material layer is selectively epitaxially grown on the clean AlInGaAs etched surface to cover and protect the active region sidewalls, forming a complete waveguide structure. As a preferred implementation method, direct regeneration based on a clean etched surface ensures the integrity of the epitaxial layer crystal quality, forming a defect-free waveguide structure and completely solving the device performance degradation problem caused by oxide interfaces. The entire scheme achieves seamless integration of protection and desorption stages through the synergistic effects of sulfide layer transformation, mechanical strengthening, photothermal synergistic desorption, and selective epitaxy, effectively addressing the oxidation risk and protective layer treatment challenges after the AlInGaAs active region sidewalls are exposed.

[0055] This application further proposes specific steps for etching epitaxial wafers using a dry etching process: inductively coupled plasma etching is employed, with chlorine and boron trichloride as the main etching gases and a trace amount of nitrogen introduced; during the etching process, the wafer stage temperature is controlled within a low-temperature range of -10℃ to 10℃; when the etching endpoint monitoring system detects a signal change, the main etching gas is switched to a mixed gas containing only boron trichloride and nitrogen, and soft landing etching is performed for a duration of 5 to 15 seconds.

[0056] Inductively coupled plasma etching (ICP-E) is a dry etching technique that uses a high-frequency electromagnetic field to excite gas and generate high-density plasma. It can be implemented using radio frequency (RF) power supplies of different frequencies. The combination of chlorine and boron trichloride as the main etching gases provides excellent etching selectivity for AlInGaAs materials, aiming to achieve efficient and anisotropic material removal through synergistic effects. The introduction of trace amounts of nitrogen is to suppress the oxidation tendency of aluminum during etching; this can be optimized by adjusting the flow rate ratio. Maintaining the wafer stage temperature in the low-temperature range of -10℃ to 10℃ reduces thermal stress accumulation, which can be achieved using cooling devices or temperature control systems. Soft-landing etching refers to using mild etching conditions near the etching endpoint to avoid over-etching, aiming to protect the integrity of the exposed surface.

[0057] Specifically, this scheme ensures high-quality etching results through multifaceted and precise control: First, inductively coupled plasma etching combined with a specific gas combination achieves highly selective etching of AlInGaAs material based on the characteristics of high-density plasma, while the introduction of trace amounts of nitrogen effectively suppresses the formation of surface oxides. Furthermore, the low-temperature environment significantly reduces stress accumulation caused by differences in thermal expansion coefficients, preventing the formation of microcracks. More importantly, the real-time response of the etching endpoint monitoring system triggers a gas switching mechanism immediately upon detecting signal changes. This dynamic adjustment method avoids the over-etching or under-etching problems that may occur with traditional fixed-time etching. The subsequent soft-landing etching process utilizes a gentle gas combination to perform precise processing within a limited time, removing surface residues while avoiding damage to the sidewall structure. These measures work together to ensure that the exposed AlInGaAs active region sidewall surface is smooth, clean, and free of structural damage, providing ideal substrate conditions for subsequent anti-oxidation treatment.

[0058] This application further proposes specific steps for processing by immersion in a polysulfide solution: the epitaxial wafer is slowly immersed in the polysulfide solution at an angle of 70° to 85° relative to the liquid surface; during the immersion process, the solution temperature is controlled at 30° to 50°, and low-frequency ultrasound with a frequency of 25 kHz to 40 kHz is applied; after immersion, the epitaxial wafer is removed from the solution in a step-by-step lifting manner, pausing above the liquid surface for 1 to 3 seconds after each step.

[0059] Specifically, the tilt angle refers to the angle between the epitaxial wafer and the normal to the surface of the ammonium polysulfide solution. This angle can be achieved using a robotic arm or angle adjustment device to avoid air bubble retention during vertical immersion, thus ensuring gradual and uniform contact between the solution and the etched surface. Solution temperature refers to the thermodynamic state of the ammonium polysulfide solution during processing. This temperature can be maintained using a constant-temperature water bath or heating plate to ensure the activity of the sulfidation reaction while preventing excessive corrosion or side reactions. Low-frequency ultrasound refers to mechanical vibration waves in the frequency range of 25kHz to 40kHz, which can be generated by an ultrasonic generator. Its purpose is to enhance reactant diffusion and remove surface particulate impurities, thereby reducing the porosity and defect density of the protective layer. Stepped lifting refers to the operation method of gradually removing the epitaxial wafer from the solution in stages. This can be achieved using a stepper motor-driven lifting mechanism to release surface tension in stages, allowing the residual solution to flow smoothly and preventing microcracks or localized peeling caused by uneven drying.

[0060] In detail, the above-mentioned scheme effectively improves the structural integrity and adhesion stability of the sulfide passivation protective layer by precisely controlling the physical operation parameters during the solution treatment process. First, the epitaxial wafer is slowly immersed in the ammonium polysulfide solution at an angle of 70° to 85°. This method avoids the retention of air bubbles that occurs during vertical immersion, ensuring gradual and uniform contact between the solution and the etched surface, thereby reducing interfacial stress concentration and promoting continuous deposition of the sulfide layer. Subsequently, during the immersion process, the solution temperature is controlled within the range of 30°C to 50°C. This temperature range maintains the appropriate activity of the sulfidation reaction to avoid excessive corrosion and prevents side reactions caused by high temperatures. At the same time, low-frequency ultrasound of 25kHz to 40kHz is applied. The mechanical vibration effect of its specific frequency can effectively disturb the solution boundary layer, enhance the diffusion of reactants, and remove surface particulate impurities, thereby reducing the porosity and defect density of the protective layer. Finally, the epitaxial wafer is removed from the solution using a stepped lifting method, pausing for 1-3 seconds at each step. This operation releases surface tension in stages, allowing the residual solution to flow smoothly under gravity, avoiding liquid film rupture or stress abrupt changes caused by rapid removal. This prevents microcracks or localized peeling of the protective layer due to uneven drying, ultimately ensuring the sulfide layer maintains its complete protective capability during subsequent process transfers. Furthermore, combining this approach with the aforementioned dry etching process and subsequent organosilicon precursor vapor treatment further optimizes the overall anti-oxidation process, significantly improving the quality and reliability of the sulfide passivation protective layer on the AlInGaAs material surface.

[0061] Reference Figure 2 As shown, this application further proposes that the organosilicon precursor vapor and ozone are introduced in stages, wherein: in the first stage, an ozone-rich gas is introduced to activate the surface of the sulfide passivation protective layer; in the second stage, a mixture of organosilicon precursor vapor and low-concentration ozone is introduced to carry out a cross-linking reaction, wherein the partial pressure of the organosilicon precursor vapor is controlled to gradually increase, starting from an initial low partial pressure and linearly increasing to a target partial pressure within a set time, while the partial pressure of ozone is controlled to be maintained at a constant low level; in the third stage, after the target partial pressure is reached, the introduction of organosilicon precursor vapor is stopped, and the ozone-containing mixed gas is continued to be introduced, while the temperature of the epitaxial wafer is increased by 5°C to 15°C from the original level to complete the final curing of the cross-linked network and promote the volatilization of unreacted precursors and by-products.

[0062] Specifically, the phased introduction refers to the process of introducing organosilicon precursor vapor and ozone into the reaction chamber according to a preset time sequence and conditions. This can be achieved using a multi-channel gas control system to ensure precise control of the reaction environment at each stage. The ozone-rich gas refers to a gas mixture with an ozone concentration significantly higher than that of ordinary air, which can be generated through corona discharge or ultraviolet irradiation. Gradually increasing the partial pressure of the organosilicon precursor vapor means adjusting the evaporation source temperature or carrier gas flow rate to linearly increase the vapor pressure over time, aiming to optimize the synchronicity between the crosslinking reaction rate and network growth. Maintaining the ozone partial pressure at a constant low level means stabilizing the ozone supply through a flow controller, aiming to prevent excessive oxidation and damage to the crosslinked network structure. Temperature enhancement of the epitaxial wafer refers to the controlled heating of the epitaxial wafer using a heating device after the target partial pressure is achieved, aiming to accelerate the curing of the crosslinked network and promote the volatilization of residues.

[0063] Specifically, this embodiment achieves high-quality formation of the composite protective layer through a staged gas introduction strategy. First, ozone-rich gas is introduced separately to activate the sulfide passivation protective layer. This process effectively removes surface-adsorbed impurities and activates sulfur atom sites, constructing a highly active substrate for subsequent crosslinking reactions. Then, in the second stage, by controlling the partial pressure of the organosilicon precursor vapor to linearly increase from an initial low pressure to the target partial pressure, while maintaining the ozone partial pressure at a constant low level, this gradual pressure control mechanism ensures the uniformity and controllability of the siloxane crosslinking reaction, avoiding local overreaction or reaction stagnation. Finally, in the third stage, by stopping the precursor supply and increasing the temperature, combined with the continuous introduction of ozone-containing gas, not only is deep curing of the crosslinked network achieved, but the thermally driven effect also promotes the complete volatilization of unreacted precursors and byproducts. The entire process is closely integrated with the aforementioned steps, forming a complete processing flow. This solves the key defect problems that may occur during the formation of the cross-linked network, significantly improves the mechanical strength and damage resistance of the composite protective layer, and provides a reliable guarantee for the exposure of the clean AlInGaAs etched surface.

[0064] This application further proposes that the meteorological treatment be carried out in a reaction chamber. Before the meteorological treatment, the reaction chamber is evacuated and backfilled with high-purity nitrogen to near atmospheric pressure. This process is repeated at least three times.

[0065] The vacuuming process involves removing gases from the reaction chamber using mechanical or molecular pumps. This reduces the residual concentration of oxygen and water vapor, preventing these impurities from interfering with the chemical reaction between the organosilicon precursor and ozone during subsequent gas treatment. In practice, the degree of vacuuming can be adjusted according to process requirements, typically reaching millitor levels to ensure sufficient purification. Backfilling with high-purity nitrogen involves introducing nitrogen gas with a purity of 99.999% or higher into the chamber after vacuuming. This replaces residual air, maintains stable chamber pressure, and prevents external contamination. The choice of high-purity nitrogen is based on its chemical inertness and lack of interference with the reaction system. Repeating this process at least three times is designed to significantly reduce impurity concentration through multiple gas replacements. The specific number of repetitions can be optimized based on actual process verification results; fewer than three repetitions may result in insufficient purification, while more repetitions are unlikely to provide additional benefits.

[0066] Specifically, the aforementioned technical solution creates a highly clean environment for the reaction chamber by implementing a purification process involving multiple vacuuming and high-purity nitrogen backfilling before meteorological processing. Based on this, the vacuuming operation effectively removes oxygen and water vapor from the chamber, preventing these impurities from reacting with the organosilicon precursor or inhibiting ozone activation. Backfilling with high-purity nitrogen not only isolates external contaminants but also ensures a smooth transition for subsequent gas introduction operations through a pressure setting close to atmospheric pressure. The repeated purification process, repeated three times, significantly reduces impurity concentration through a cumulative effect, allowing a uniform and dense siloxane cross-linked network to form on the surface and edge areas of the sulfide passivation protective layer. This overall design ensures the mechanical stability of the composite protective layer, enabling it to effectively resist physical vibration or airflow impact during subsequent transfer or processing, thereby solving the problem of protective failure caused by uneven or locally weakened cross-linked networks.

[0067] Furthermore, this approach, combined with the aforementioned weathering process, provides a clean reaction environment, further enhancing the structural integrity and adhesion of the siloxane crosslinking network and ensuring the reliability of the composite protective layer in subsequent processes. This design not only optimizes the effectiveness of the weathering process but also lays the foundation for improved robustness and yield of the entire anti-oxidation treatment method.

[0068] This application further proposes to perform gas treatment by applying a mixture of organosilicon precursor vapor and ozone, followed by the introduction of heated inert carrier gas to purge the epitaxial wafer; the temperature of the inert carrier gas is 10°C to 20°C higher than the temperature of the gas phase treatment.

[0069] Specifically, the inert carrier gas refers to a chemically stable gas, which can be nitrogen, argon, or helium. In practical applications, the heated inert carrier gas reduces the surface adhesion of residues by increasing the temperature, thereby promoting the desorption and volatilization of residues from the surface of the siloxane crosslinked network. The purpose is to remove organosilicon precursors and byproducts that may adhere to the epitaxial wafer surface after gas-phase treatment, preventing these residues from decomposing and contaminating the AlInGaAs etched surface during subsequent high-temperature desorption. Furthermore, the temperature increment is set within a range of 10℃ to 20℃, a range optimized for the physical properties of the residues to ensure sufficient volatilization without damaging the formed crosslinked network structure.

[0070] In detail, immediately after the vapor phase treatment, a heated inert carrier gas is introduced for purging. This process utilizes the chemical stability of the inert gas to avoid the risk of oxidation. Simultaneously, the heating significantly reduces the surface adhesion of residues, making them easier to desorb and volatilize from the epitaxial wafer surface. Precise temperature control is crucial in this process: too low a temperature may result in incomplete residue removal, while too high a temperature may cause thermal deformation or premature decomposition of the cross-linked network. Therefore, selecting a temperature increment of 10℃ to 20℃ enables efficient cleaning while maintaining the integrity of the protective layer, providing a clean etching surface foundation for subsequent photothermal synergistic desorption. Furthermore, this approach is closely integrated with the aforementioned vapor phase treatment steps, ensuring the cleanliness of the epitaxial growth interface and crystal quality by removing residues, thereby effectively solving the defect problem caused by residue decomposition.

[0071] This application further proposes to monitor the changes in the quality of the epitaxial wafer in real time during the vapor phase processing, and to terminate the vapor phase processing when the rate of increase in quality drops to less than 10% of the initial rate.

[0072] Specifically, real-time monitoring refers to the continuous tracking and recording of the mass changes of the epitaxial wafer during the vapor phase processing using high-precision mass sensors. Its purpose is to capture the dynamic changes during the crosslinking reaction. In practical applications, the mass increase rate can be obtained by differential calculation of the mass difference between adjacent time points, aiming to accurately reflect the real-time state of the crosslinked network construction. The initial rate refers to the mass change rate at the beginning of the vapor phase processing, typically measured within the first 5-10 seconds after the reaction starts, serving as a benchmark for subsequent rate comparisons.

[0073] In detail, during the vapor-phase processing stage, as the organosilicon precursor vapor reacts with ozone, a siloxane cross-linked network gradually forms on the surface of the epitaxial wafer, leading to a continuous increase in wafer mass. The system can precisely grasp the evolution of the reaction rate by monitoring mass changes in real time. In the initial stage of the reaction, due to the high reactant concentration, the cross-linking reaction rate is rapid, resulting in a significant increase in mass. As the cross-linked network gradually becomes more complete, the reaction rate naturally decays, and the mass increase slows down accordingly. When the mass increase rate drops to less than 10% of the initial rate, it indicates that the cross-linking reaction has entered the saturation stage. Timely termination of the process at this point ensures the integrity of the network structure to provide the necessary mechanical strength while avoiding material stress accumulation or waste of process resources due to over-processing. This mechanism, based on reaction kinetics, closely links the termination timing with the actual reaction progress, effectively overcoming the problems of incomplete cross-linking or over-processing caused by reaction rate fluctuations in fixed-time processing, thereby ensuring the quality stability and process controllability of the composite protective layer.

[0074] Reference Figure 3 As shown, this application further proposes a method for photothermal synergistic desorption treatment, including the following steps: starting background resistance heating to uniformly raise the ambient temperature to the target desorption temperature and maintain it stably at this temperature, so that the epitaxial wafer and its surface composite protective layer reach thermal equilibrium; starting a near-infrared laser emitter, with its initial output power set to a preheating power much lower than the target desorption power, and performing the first pulse scan on the epitaxial wafer with this preheating power; subsequently, linearly increasing the laser output power in multiple steps to the target desorption power; after the laser power reaches the target desorption power, maintaining the laser power constant, and the scanning path of the laser beam covering the entire surface of the epitaxial wafer; after the desorption treatment is completed, turning off the near-infrared laser emitter, and maintaining background resistance heating and a phosphorus-containing source atmosphere to perform in-situ thermal stabilization treatment on the exposed clean AlInGaAs etched surface.

[0075] Specifically, background resistance heating refers to a method of uniformly heating the environment surrounding the epitaxial wafer using resistance heating elements. This can be achieved using a multi-zone temperature-controlled resistance heating plate. The purpose is to ensure that the epitaxial wafer and its surface composite protective layer heat up synchronously, avoiding localized thermal expansion differences caused by temperature gradients. Preheating power refers to the initial low power level applied, which can be achieved by adjusting the laser drive current or pulse duty cycle to avoid thermal shock caused by sudden laser power application. Furthermore, the design of linearly increasing laser output power in multiple steps is to achieve a gradual power increase, which can be achieved through programmed control of laser output parameters to prevent thermal stress concentration and material damage.

[0076] In detail, the above method effectively alleviates the problem of thermal stress concentration and ensures surface stability after desorption by finely controlling the thermal management process of photothermal synergistic desorption. First, the introduction of background resistance heating enables the epitaxial wafer and composite protective layer to reach thermal equilibrium as a whole, reducing the local thermal expansion differences caused by temperature gradients and thus suppressing the formation of interface microcracks. Second, the initial output power is set to the preheating power for the first pulse scan, avoiding thermal shock caused by sudden laser power application. The subsequent laser output power is designed to increase linearly in multiple steps to the target desorption power, ensuring a smooth temperature transition through gradual power increase. Once the laser power reaches the target desorption power, a constant power is maintained and the scanning path covers the entire epitaxial wafer surface, ensuring the uniformity and integrity of the desorption process. Finally, after the desorption process is completed, the laser emitter is turned off while background resistance heating and a phosphorus-containing source atmosphere are maintained for in-situ thermal stabilization. The protective environment of the phosphorus-containing source atmosphere immediately stabilizes the exposed AlInGaAs etched surface, while the continuous effect of background resistance heating promotes surface atomic rearrangement and enhances interface stability.

[0077] The above technical solution not only solves the problem of nanoscale microcracks caused by thermal stress concentration at the interface between the composite protective layer and AlInGaAs material, but also ensures timely and stable treatment of the etched surface after desorption, thereby significantly improving the integrity of the waveguide structure and the reliability of the device.

[0078] This application further proposes that when using near-infrared laser to irradiate in a pulse scanning manner, the pulse scanning adopts an overlapping scanning path, and the overlap rate between adjacent scanning paths is 50% to 70%; the laser pulse frequency is matched with the scanning speed, so that any point on the epitaxial wafer surface is within the action time of three or more consecutive laser pulses.

[0079] Specifically, an overlapping scanning path refers to a design scheme that precisely controls the laser scanning trajectory to ensure partial overlap between adjacent scanning areas. This can be achieved using a galvanometer system or a mechanical moving platform. The overlap rate between adjacent scanning paths is defined as the ratio of the overlap width between two scanning areas to the width of a single scan. The purpose is to ensure seamless coverage of the laser's active area while avoiding localized overheating due to excessive overlap. Furthermore, the matching relationship between the laser pulse frequency and the scanning speed can be achieved by adjusting the laser's repetition frequency and the scanning platform's movement speed. The aim is to ensure sufficient energy accumulation at each point, thereby achieving uniform desorption.

[0080] In detail, the aforementioned anti-oxidation treatment method effectively solves the problems of uniformity and energy accumulation during desorption by optimizing the geometric layout and timing control of the pulse scanning. Specifically, the design of the overlapping scanning path, especially the 50% to 70% overlap between adjacent scanning paths, ensures continuous coverage of the laser scanning trajectory, avoids desorption blind zones caused by path gaps, and limits the risk of local overheating caused by excessive overlap, thereby maintaining a uniform distribution of thermal stress and preventing microcracks from forming at the AlInGaAs material interface due to differences in thermal expansion. Furthermore, the precise matching of the laser pulse frequency and scanning speed ensures that any position on the epitaxial wafer surface is continuously subjected to three or more consecutive laser pulses during movement. This timing arrangement guarantees sufficient desorption energy accumulation at each point, avoids material damage caused by excessive energy in a single pulse, effectively promotes the uniform decomposition of the composite protective layer, and ultimately achieves clean exposure of the AlInGaAs etched surface, providing a high-quality interface foundation for subsequent selective epitaxial growth. Based on this, the scheme, combined with the aforementioned photothermal synergistic desorption step, further improves desorption efficiency and interface quality, significantly enhancing process robustness and product yield.

[0081] This application further proposes that in the photothermal desorption step: the characteristic peak intensity of sulfur dioxide in the exhaust gas of the reaction chamber is monitored in real time by mass spectrometry; when the characteristic peak intensity of sulfur dioxide drops to 5% of its peak intensity and remains stable, it is determined that the composite protective layer has been completely desorbed, and laser irradiation and background resistance heating are stopped.

[0082] In practical applications, a mass spectrometer is an instrument capable of precise analysis of gaseous components. It can be implemented using a quadrupole mass spectrometer or a time-of-flight mass spectrometer, aiming to provide high sensitivity and high resolution in real-time monitoring. The characteristic peak intensity of sulfur dioxide can be understood as the signal intensity corresponding to the molecular weight position of sulfur dioxide in the mass spectrum. Its detection accuracy can be optimized by adjusting the ion source parameters and detector gain of the mass spectrometer. Specifically, the peak intensity refers to the characteristic peak intensity corresponding to the moment when the sulfur dioxide release rate is highest during the desorption reaction, serving as a key reference benchmark for judging the desorption process.

[0083] In detail, this embodiment introduces a mass spectrometer to monitor the intensity of the characteristic peak of sulfur dioxide in the exhaust gas of the reaction chamber in real time, transforming the control of the desorption process from an empirical time-dependent mechanism to a precise feedback mechanism based on the concentration of chemical reaction products. During execution, photothermal synergistic desorption treatment is initiated first. As the composite protective layer decomposes, the sulfide passivation protective layer gradually transforms into sulfur dioxide and is released into the exhaust gas. The mass spectrometer continuously collects characteristic peak intensity data in the exhaust gas. When the characteristic peak intensity of sulfur dioxide drops to 5% of its peak intensity and remains stable, it indicates that the desorption reaction is essentially complete, at which point laser irradiation and background resistance heating are immediately stopped. This judgment logic based on reaction kinetics not only avoids the problem of incomplete desorption caused by premature termination but also effectively prevents the risk of thermal stress accumulation caused by overheating. Furthermore, this approach, combined with the aforementioned anti-oxidation treatment method for the active region of the DFB laser, significantly reduces the exposure time of AlInGaAs material in a high-temperature environment by timely terminating the energy input. This reduces the probability of interfacial microcracks and provides a clean and undamaged etching surface for subsequent selective epitaxial growth, ensuring the integrity of the waveguide structure and the stability of device performance.

[0084] To further verify the beneficial effects of the present invention, the following comparative experiment was designed:

[0085] Comparative Example 1: The DFB laser epitaxial wafer, after dry etching to expose the AlInGaAs active region sidewalls, was directly subjected to subsequent MOCVD epitaxial regrowth after cleaning.

[0086] Comparative Example 2: The epitaxial wafer that has been dry-etched was cleaned and then immersed in an ammonium polysulfide solution to form a sulfide passivation protective layer. Subsequently, MOCVD thermal desorption and epitaxial regrowth were performed directly.

[0087] Example: The method of the present invention is adopted, that is, based on Comparative Example 2, a gas phase mechanical strengthening step is added to form a composite protective layer, and a photothermal synergistic desorption step is used for interface activation, followed by epitaxial regrowth.

[0088] Characterization of interface quality after desorption: After the desorption process was completed and the AlInGaAs etched surface was exposed, the integrity of the crystal structure of the etched surface was immediately observed using a high-resolution transmission electron microscope (HR-TEM), and the oxygen atom content and chemical state of aluminum on the surface were quantitatively analyzed using X-ray photoelectron spectroscopy (XPS).

[0089] Epitaxial layer quality and device performance testing: After all samples completed the full InGaAsP waveguide layer regeneration, the non-radiative recombination defect density of the interface region of the epitaxial regeneration was measured by cathodoluminescence; the wafers were fabricated into DFB laser chips, and their threshold current and operating lifetime at 85°C and 100mA constant current were tested.

[0090] The test results are shown in Table 1:

[0091] Table 1

[0092]

[0093] The results of Comparative Example 1 confirm that the AlInGaAs etched surface without any protection will be severely oxidized, resulting in extremely poor epitaxial layer quality and the device will not be able to function properly.

[0094] Comparative Example 2 shows that while traditional sulfide protection methods can provide some oxidation protection (reducing oxygen content from >15% to 5%), their protective layer performs poorly during subsequent global thermal desorption. The microcracks and high defect density observed by HR-TEM confirm the existence of thermal stress damage. This directly leads to a higher device threshold current, and interface defects proliferate rapidly under long-term high-temperature operation, resulting in a shorter device lifespan.

[0095] The data in this embodiment fully demonstrates the comprehensive advantages of the present invention:

[0096] The extremely low oxygen content and perfect HR-TEM interface demonstrate that the vapor-phase mechanical strengthening step ensures the integrity of the protective layer during transport, while the successful photothermal desorption avoids thermal stress damage, thus achieving an atomically clean and damage-free etched surface.

[0097] The resulting extremely low interface defect density is the fundamental reason why the final device achieves a lower threshold current and a significantly extended operating life. This verifies the core beneficial effect of the present invention, which is to ensure atomic-level cleanliness and no damage to the etched surface after desorption while achieving effective oxidation prevention throughout the process. Ultimately, this is reflected in a huge improvement in device performance and reliability.

[0098] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preventing oxidation of an active region in a DFB laser, characterized by, The method comprises the following steps: After the grating preparation of the DFB laser epitaxial wafer is completed, the epitaxial wafer is etched by a dry etching process until the active region sidewall containing AlInGaAs material is exposed to form an etching surface; after the etching surface is cleaned, the epitaxial wafer is immersed in a thiopshate solution for treatment, and a sulfide passivation protection layer is formed on the surface of the AlInGaAs material; The epitaxial wafer with the formed sulfide passivation protection layer is subjected to a gas treatment by mixing a vapor of an organosilicon precursor and ozone, and the organosilicon precursor vapor and ozone are introduced in stages, wherein: in the first stage, ozone-rich gas is introduced to activate the surface of the sulfide passivation protection layer; in the second stage, a mixed gas of the organosilicon precursor vapor and low-concentration ozone is introduced for cross-linking reaction, wherein the partial pressure of the organosilicon precursor vapor is gradually increased, and the partial pressure is linearly increased from an initial low partial pressure to a target partial pressure within a set time, and the partial pressure of ozone is maintained at a constant low level; in the third stage, after the target partial pressure is reached, the introduction of the organosilicon precursor vapor is stopped, and the mixed gas containing ozone is continuously introduced, and the temperature of the epitaxial wafer is increased by 5-15℃ based on the original temperature, so as to complete the final curing of the cross-linking network and promote the volatilization of unreacted precursors and by-products; under the condition of room temperature to 60℃, a siloxane-based cross-linking network is formed on the surface and edge region of the sulfide passivation protection layer, so as to obtain a mechanically reinforced composite protection layer; In a protective atmosphere containing a phosphorus source, a near-infrared laser is used to irradiate the entire surface of the epitaxial wafer in a pulse scanning mode, wherein the wavelength of the near-infrared laser is configured to have a high absorption rate for the composite protection layer and a low absorption rate for the underlying AlInGaAs material; simultaneously, background resistance heating is used for photothermal synergistic desorption treatment, so that the composite protection layer is thermally decomposed to expose a clean AlInGaAs etching surface; After the photothermal synergistic desorption step is completed, an InGaAsP material layer is selectively epitaxially grown on the clean AlInGaAs etching surface to cover and protect the active region sidewall, thereby forming a complete waveguide structure.

2. The method of claim 1, wherein the method is characterized by: The dry etching process for etching the epitaxial wafer comprises: Inductively coupled plasma etching is adopted, and chlorine and boron trichloride are used as main etching gases, and a small amount of nitrogen is introduced; During the etching process, the wafer stage temperature is controlled in a low temperature range of -10℃ to 10℃; When the etching endpoint monitoring system detects a signal change, the main etching gas is switched to a mixed gas containing only boron trichloride and nitrogen, and soft landing etching is performed for a time of 5-15 seconds.

3. The method of claim 1, wherein the method is characterized by: The immersion in the thiopshate solution for treatment comprises: The epitaxial wafer is slowly immersed in the thiopshate solution at an inclination angle of 70-85° relative to the liquid surface; During the immersion process, the solution temperature is controlled at 30-50℃, and low-frequency ultrasonic waves with a frequency of 25-40 kHz are applied; After the immersion is completed, the epitaxial wafer is taken out of the solution in a stepwise manner, and each stepwise lifting is paused for 1-3 seconds above the liquid surface.

4. The method of claim 1, wherein the method is performed on a DFB laser. The gas-phase treatment is performed in a reaction chamber, which is vacuumized and backfilled with high-purity nitrogen to near atmospheric pressure before the gas-phase treatment, and the process is repeated at least three times.

5. The method of claim 1, wherein the method is performed on a DFB laser. After the gas-phase treatment of the mixed gas of the organic silicon precursor vapor and ozone, a heated inert carrier gas is introduced to purge the epitaxial wafer; the temperature of the inert carrier gas is 10-20 DEG C higher than the temperature of the gas-phase treatment.

6. The method of claim 1, wherein the method is performed on a DFB laser. During the gas-phase treatment, the change of the mass of the epitaxial wafer is monitored in real time, and when the mass increase rate drops to within 10% of the initial rate, the gas-phase treatment is terminated.

7. The method of claim 1, wherein the method is performed on a DFB laser. The photothermal synergistic desorption treatment comprises: starting the background resistance heating to uniformly raise the ambient temperature to the target desorption temperature and stably maintain the temperature, so that the epitaxial wafer and the composite protective layer on the surface thereof reach thermal equilibrium as a whole; starting the near-infrared laser emitter, with the initial output power being set to a preheating power much lower than the target desorption power, and performing a first pulse scan on the epitaxial wafer at the preheating power; subsequently, the laser output power is linearly increased to the target desorption power in multiple steps; when the laser power reaches the target desorption power, the laser power is maintained constant, and the scanning path of the laser beam covers the entire surface of the epitaxial wafer; after the desorption treatment is completed, the near-infrared laser emitter is turned off, and the background resistance heating and the phosphorus-containing source atmosphere are maintained to perform in-situ thermal stabilization treatment on the exposed clean AlInGaAs etching surface.

8. The method of claim 1, wherein the method is performed on a DFB laser. When the near-infrared laser is irradiated in a pulse scanning mode, the pulse scanning uses overlapping scanning paths, and the overlapping rate between adjacent scanning paths is 50-70%; the pulse frequency of the laser is matched with the scanning speed, so that at any point on the surface of the epitaxial wafer, the action time of three or more laser pulses is continuous.

9. The method of claim 1, wherein the method is a method of preventing oxidation of an active region of a DFB laser. In the photothermal desorption step: the characteristic peak intensity of sulfur dioxide in the tail gas of the reaction chamber is monitored in real time by a mass spectrometer; when the characteristic peak intensity of sulfur dioxide drops to 5% of the peak intensity and remains stable, it is determined that the composite protective layer has been completely desorbed, and the laser irradiation and the background resistance heating are stopped.

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