Alloying layer-by-layer control method for multilayer metal thin film of dbr laser

Abstract

The application belongs to the technical field of DFB laser, and relates to a method for alloying and layer-by-layer control of a multilayer metal film of a DFB laser, comprising the following steps: determining alloying reaction activation energy of each layer of metal film; determining a first heating temperature and a first holding time according to the activation energy of a bottom layer, determining a second heating temperature and a second holding time according to the activation energy of a middle layer, and calculating a temperature difference value of the two; generating an initial thermal energy layer-by-layer control sequence in the order from the bottom layer to the middle layer; simulating heating based on the sequence, and measuring a bottom layer diffusion depth and a middle layer diffusion depth; when the bottom layer diffusion depth is greater than a critical depth, reducing the first heating temperature and prolonging the first holding time according to the temperature difference value; and when the middle layer diffusion depth is less than a standard depth, increasing the second heating temperature and shortening the second holding time according to the temperature difference value. The method prevents the bottom layer from penetrating a safety interface due to excessive diffusion, ensures that the middle layer is fully diffused to form a low-resistance contact, and improves the reliability and electrical performance of the DFB laser.

Description

Technical Field

[0001] This invention relates to the field of DFB laser technology, and in particular to a method for layer-by-layer control of alloying of multilayer metal thin films in DFB lasers. Background Technology

[0002] The electrode contact layer of a distributed feedback laser (DFB laser) is usually composed of thin films of different metals such as titanium, platinum, and gold stacked in a specific order on the surface of a semiconductor substrate. The alloying process aims to induce controlled diffusion at the metal-semiconductor interface through thermal activation, forming an ohmic contact with low resistance and high adhesion.

[0003] Ideally, each metal layer should be fully fused vertically to reduce contact resistance, while strictly preventing diffusion depth from exceeding a safety threshold and intruding into the underlying active region; otherwise, current leakage or device failure will occur. However, because the bottom metal is in direct contact with the semiconductor, its atomic bonding characteristics result in a significantly lower activation energy for the alloy reaction compared to the middle metal. For example, titanium layers diffuse rapidly at lower temperatures, while platinum layers require higher thermal energy to initiate a full reaction. This inherent energy threshold difference makes it difficult for traditional global isothermal heating strategies to coordinate multilayer reaction kinetics: when the heating temperature is set to meet the needs of the middle metal, the bottom metal often excessively penetrates the safety interface due to an excessively fast reaction rate, directly contacting the active region material and causing structural damage; conversely, if the temperature is only suitable for the bottom metal, the middle metal diffusion is insufficient, leaving unreacted areas that form a high-barrier layer. Even with stepped heating or temperature-monitored feedback control schemes, the fundamental misalignment in reaction initiation time and diffusion rate between different metal layers cannot be eliminated, ultimately leading to uneven interface morphology, local protrusions or voids, obstructed current transmission paths, and decreased device reliability. Summary of the Invention

[0004] Therefore, the purpose of this invention is to address the problem that the inherent difference in energy thresholds between the bottom and middle metal layers leads to excessive fusion of the bottom layer penetrating the safety depth and insufficient diffusion of the middle layer forming unreacted areas under uniform heating conditions, resulting in rough and uneven contact interfaces and obstructed current transmission in DFB lasers. This invention provides a layer-by-layer alloying control method for multilayer metal films in DFB lasers to prevent excessive diffusion of the bottom metal film penetrating the safety interface and ensure sufficient diffusion of the middle metal film to form low-resistance contacts, thereby effectively improving the reliability and electrical performance of DFB lasers.

[0005] To solve the above-mentioned technical problems, the present invention provides a method for layer-by-layer control of alloying of multilayer metal thin films in DFB lasers, comprising: Determine the activation energy for alloying reactions in each layer of the metal thin film; The first heating temperature and the first holding time are determined based on the activation energy of the bottom metal film; the second heating temperature and the second holding time are determined based on the activation energy of the middle metal film; and the temperature difference between the two is calculated. Following the order from the bottom layer to the middle layer, the first heating temperature and the first holding time, and the second heating temperature and the second holding time are combined to generate the initial thermal energy layer-by-layer control sequence. Simulated heating was performed based on the initial thermal energy layer-by-layer control sequence, and the diffusion depth of the bottom layer and the middle layer after simulated heating were measured. In response to the bottom diffusion depth being greater than the critical diffusion depth, the first heating temperature is reduced based on the temperature difference, and the first holding time is extended based on the reduced heating temperature, to obtain the bottom heating temperature and the bottom holding time; in response to the middle diffusion depth being less than the standard diffusion depth, the second heating temperature is increased based on the temperature difference, and the second holding time is shortened based on the increased heating temperature, to obtain the middle heating temperature and the middle holding time.

[0006] Preferably, determining the activation energy for the alloying reaction of each metal thin film includes: preparing test samples of the same batch and thickness as the metal thin film to be tested, wherein the test samples contain a semiconductor substrate identical to that of the DFB laser to be tested and a single-layer test metal thin film deposited on the semiconductor substrate; performing isothermal annealing on the test samples at multiple heating temperatures, with each heating temperature corresponding to a set of test samples; measuring the sheet resistance of each test sample after different annealing times, and using the reciprocal of the time required for the sheet resistance to decrease to 50% of the initial sheet resistance as the reaction rate at that temperature. Rate constant; according to the Arrhenius equation, a relationship curve is plotted with the natural logarithm of the reaction rate constant at each heating temperature as the ordinate and the reciprocal of the thermodynamic temperature as the abscissa. The relationship curve is then linearly fitted, and the slope of the fitted line is multiplied by the gas constant and the absolute value is taken as the activation energy of the alloy reaction of the metal thin film. The Arrhenius equation is: k = A·exp(-Ea / RT); k is the reaction rate constant; Ea is the activation energy; R is the gas constant, with a value of 8.314 J / (mol·K); T is the thermodynamic temperature; A is the pre-exponential factor.

[0007] Preferably, determining the first heating temperature based on the activation energy of the underlying metal film includes: solving for the first heating temperature using the inverse function of the Arrhenius equation; the inverse function of the Arrhenius equation is: ; T1 is the first heating temperature; Ea1 is the activation energy of the alloy reaction of the bottom metal film; k1 is the target reaction rate constant of the bottom metal film; the method for determining the second heating temperature is the same as the method for determining the first heating temperature.

[0008] Preferably, the method for determining the pre-exponential factor includes: performing isothermal annealing treatment on test samples of the same batch and thickness as the metal thin film to be tested at multiple different heating temperatures, measuring the reaction rate constant at each heating temperature; performing linear fitting with the natural logarithm of the reaction rate constant at each heating temperature as the ordinate and the reciprocal of the thermodynamic temperature as the abscissa, and taking the exponent of the intercept of the fitted line as the pre-exponential factor of the metal thin film.

[0009] Preferably, adjusting the heating temperature based on the temperature difference includes: configuring an adjustment coefficient η, where 0.05≤η≤0.3; The bottom heating temperature T1' is determined as: T1' = T1 - η × ΔT; the middle heating temperature T2' is determined as: T2' = T2 + η × ΔT; ΔT is the temperature difference; T1 is the first heating temperature; T2 is the second heating temperature.

[0010] Preferably, extending the first holding time according to the reduced heating temperature includes: ; t1' is the bottom layer heat preservation time; t1 is the first heat preservation time; Ea1 is the activation energy of the bottom metal film alloy reaction; R is the gas constant, with a value of 8.314 J / (mol·K); The second holding time is shortened based on the increased heating temperature, including: t2' is the middle layer heat preservation time; t2 is the second heat preservation time; Ea2 is the activation energy of the middle layer metal thin film alloy reaction.

[0011] Preferably, the simulation heating is performed using an initial thermal energy layer-by-layer control sequence, including: establishing a thermal-diffusion coupled finite element simulation model of the multilayer metal film during the heating process, wherein the finite element simulation model includes the geometric dimensions, material thermal properties, and interface diffusion coefficients of each layer of the metal film; and sequentially inputting the first heating temperature, first holding time, second heating temperature, and second holding time from the bottom layer to the middle layer in the initial thermal energy layer-by-layer control sequence as thermal boundary conditions into the finite element simulation model, and solving for the distribution curves of element concentration along the depth direction inside and at the interface of each layer of the metal film after simulated heating.

[0012] Preferably, measuring the bottom layer diffusion depth and the middle layer diffusion depth after simulated heating includes: extracting characteristic element concentration data of the bottom layer metal film from the element concentration distribution curve along the depth direction, in a direction perpendicular to the metal film interface, and taking the depth position corresponding to the decrease of the characteristic element concentration to 5% of its peak concentration as the bottom layer diffusion depth; extracting characteristic element concentration data of the middle layer metal film, and taking the depth position corresponding to the decrease of the characteristic element concentration to 5% of its peak concentration as the middle layer diffusion depth.

[0013] Preferably, determining the critical diffusion depth includes: using test samples of the same batch and structure as the DFB laser under test, performing alloying treatment at multiple different heating temperatures with gradually increasing temperatures; scanning each treated test sample with a cross-sectional electron microscope, recording the diffusion depth at which the bottom metal film first penetrates the safety interface and comes into contact with the active material below, and obtaining the critical diffusion depth.

[0014] Preferably, determining the standard diffusion depth includes: preparing multiple test samples of the same batch and structure as the DFB laser under test, performing alloying treatment under multiple different heating conditions, and measuring the contact resistivity of each test sample; selecting a group of test samples whose contact resistivity meets the requirements, and measuring the diffusion depth of the group of test samples to obtain the standard diffusion depth.

[0015] Compared with the prior art, the above-described technical solution of the present invention has the following advantages: The alloying layer-by-layer control method for multilayer metal thin films in DFB lasers described in this invention generates a differentiated heating sequence executed sequentially from the bottom layer to the middle layer by identifying the activation energy of each layer. Based on the diffusion depth feedback after simulated heating, the bottom layer is cooled and delayed to suppress excessive fusion penetration to a safe depth, while the middle layer is heated and the heating time is shortened to promote sufficient diffusion and eliminate unreacted areas. This achieves decoupled independent correction between the bottom and middle layers, effectively avoiding damage to the active region caused by excessive diffusion of the bottom metal thin film, while ensuring sufficient alloying of the middle metal thin film. Ultimately, a flat, low-resistance ohmic contact interface is formed, ensuring current transmission efficiency and laser stability. Attached Figure Description

[0016] 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.

[0017] Figure 1 This is a flowchart of the alloying layer-by-layer control method in a preferred embodiment of the present invention; Figure 2 This is a flowchart for determining the activation energy in a preferred embodiment of the present invention; Figure 3 This is a flowchart of the simulated heating process in a preferred embodiment of the present invention. Detailed Implementation

[0018] 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.

[0019] Example

[0020] Traditional alloying processes for multilayer metal films in DFB lasers employ global isothermal heating or stepped heating strategies, failing to fundamentally address the asynchronous reaction problem caused by misaligned energy thresholds (activation energies) across different metal layers. When uniform heating conditions are used, the bottom metal layer with a lower energy threshold is prone to excessive fusion with the semiconductor, damaging the laser's active region; while the middle metal layer with a higher energy threshold may fail to diffuse sufficiently due to inadequate heat distribution, resulting in rough and uneven contact interfaces and obstructed current transmission paths.

[0021] Based on this, embodiments of the present invention provide a method for layer-by-layer control of alloying in multilayer metal thin films for DFB lasers, achieving precise layer-by-layer control of the alloying process of multilayer metal thin films to overcome the aforementioned technical problems. (Refer to...) Figure 1 As shown, it includes the following steps: S100, Determine the activation energy for the alloying reaction of each metal thin film layer; S200. Determine the first heating temperature and the first holding time based on the activation energy of the bottom metal film; determine the second heating temperature and the second holding time based on the activation energy of the middle metal film; and calculate the temperature difference between the two. S300: In the order from bottom layer to middle layer, combine the first heating temperature with the first holding time and the second heating temperature with the second holding time to generate the initial thermal energy layer-by-layer control sequence. S400: Simulated heating is performed based on the initial thermal energy layer-by-layer control sequence, and the diffusion depth of the bottom layer and the middle layer after simulated heating are measured. S500: In response to the bottom layer diffusion depth being greater than the critical diffusion depth, the first heating temperature is reduced according to the temperature difference, and the first holding time is extended according to the reduced heating temperature, to obtain the bottom layer heating temperature and the bottom layer holding time; In response to the middle layer diffusion depth being less than the standard diffusion depth, the second heating temperature is increased according to the temperature difference, and the second holding time is shortened according to the increased heating temperature, to obtain the middle layer heating temperature and the middle layer holding time.

[0022] The technical solution of this embodiment will be described in detail below with reference to a specific DFB laser manufacturing scenario. Taking a typical DFB laser electrode contact layer as an example, its bottom metal film is titanium with a thickness of 80 nanometers, which is in direct contact with the indium phosphide semiconductor substrate; the middle metal film is nickel with a thickness of 150 nanometers, which is deposited on the bottom metal film.

[0023] This method first determines the activation energy for the alloying reaction of each metal thin film layer, that is, obtains the initial energy threshold corresponding to each metal thin film layer; specifically, it determines the activation energy for the alloying reaction between the bottom metal thin film and the semiconductor, and the activation energy for the alloying reaction between the middle metal thin film and the bottom metal thin film.

[0024] Reference Figure 2 As shown, for the underlying metal thin film, test samples of the same batch and thickness as the metal thin film to be tested are prepared. For example, on the same indium phosphide semiconductor substrate as the DFB laser to be processed, a titanium metal thin film with a thickness of 80 nanometers is deposited under the same deposition conditions as the device process to form the underlying test sample. The prepared underlying test sample is placed in a rapid thermal annealing furnace, and four different heating temperatures are selected, such as 623K, 648K, 673K, and 698K, with each heating temperature corresponding to a set of test samples. At each heating temperature, the test samples are subjected to isothermal annealing, and the samples are taken out at different annealing time points (such as 10 seconds, 30 seconds, 60 seconds, 120 seconds, and 240 seconds). The sheet resistance of each test sample after different annealing times is measured by the four-probe method. The change of sheet resistance of each test sample over time is recorded. For each heating temperature, the annealing time required for the sheet resistance to decrease from the initial value to 50% of the initial value is determined, and the reciprocal of this time is taken as the reaction rate constant k at that temperature. Thus, four heating temperatures T and their corresponding reaction rate constants k are obtained.

[0025] According to the Arrhenius equation k = A·exp(-Ea / RT), where k is the reaction rate constant, Ea is the activation energy, R is the gas constant (8.314 J / (mol·K), T is the thermodynamic temperature, and A is the pre-exponential factor, taking the natural logarithm of both sides of the equation yields ln(k) = ln(A) - (Ea / R)·(1 / T). A curve is plotted with the natural logarithm of the reaction rate constant ln(k) at each heating temperature on the ordinate and the reciprocal of the thermodynamic temperature (1 / T) on the abscissa. A linear fit is then performed on this curve, resulting in a straight line. The slope of this line is multiplied by the gas constant R, and the absolute value is taken to obtain the activation energy Ea1 of the reaction between the titanium and indium phosphide semiconductor alloy in the underlying metal film, expressed in joules per mole. The intercept of the fitted line is then exponentially calculated to obtain the pre-exponential factor A1 of the underlying metal film.

[0026] For the intermediate metal thin film, a test sample containing a three-layer structure of semiconductor substrate, bottom metal, and intermediate metal is prepared. Specifically, the preparation method is as follows: First, an 80 nm titanium metal thin film of the same batch and thickness as the bottom metal thin film of the device is deposited on an indium phosphide semiconductor substrate identical to that of the DFB laser to be processed. Then, a 150 nm nickel metal thin film of the same batch and thickness as the intermediate metal thin film of the device is deposited on top of this titanium metal thin film to form the intermediate metal test sample.

[0027] The same testing method as the underlying metal film was used, namely, isothermal annealing at multiple heating temperatures. The sheet resistance change was measured using the four-probe method to obtain the reaction rate constant at each temperature. A curve showing the relationship between ln(k) and 1 / T was plotted and linearly fitted. The slope of the fitted line was multiplied by the gas constant R, and the absolute value was taken to obtain the activation energy Ea2 for the reaction between the nickel intermediate metal film and the titanium underlying metal film. Simultaneously, the pre-exponential factor A2 of the fitted line was obtained by taking the exponent from the intercept.

[0028] Furthermore, the first heating temperature and the first holding time are determined based on the activation energy of the bottom metal film; the second heating temperature and the second holding time are determined based on the activation energy of the middle metal film; and the temperature difference between the two is calculated.

[0029] In this scheme, the first heating temperature T1 and the second heating temperature T2 are obtained by solving the inverse function of the Arrhenius equation; the inverse function of the Arrhenius equation is: Ea is the activation energy; A is the pre-exponential factor; k is the target reaction rate constant, the value of which is set according to the desired alloying treatment time. For example, if the desired characteristic reaction time is about 100 seconds, then k can be set to 0.01 seconds; R is the gas constant, with a value of 8.314 J / (mol·K).

[0030] When solving for the first heating temperature T1: ; When solving for the second heating temperature T2: ; Ea1 is the activation energy for the reaction between the bottom metal film titanium and the indium phosphide semiconductor alloy; A1 is the pre-exponential factor of the bottom metal film. Ea2 is the activation energy for the reaction between the middle metal film nickel and the bottom metal film titanium alloy; A2 is the pre-exponential factor of the middle metal film.

[0031] Substitute Ea1, Ea2, A1, A2 obtained in step S100 and the preset k into the formula to solve for the first heating temperature T1 and the second heating temperature T2.

[0032] The first heat preservation time t1 and the second heat preservation time t2 are determined as follows: the time required to complete the preset reaction progress at the first heating temperature T1 is taken as the first heat preservation time t1, and the time required to complete the preset reaction progress at the second heating temperature T2 is taken as the second heat preservation time t1.

[0033] For example, when the preset reaction progress is 95% complete in the alloying reaction: t1 = -ln(1-0.95) / k(T1), where k(T1) = A1·exp(-Ea1 / RT1); t2 = -ln(1-0.95) / k(T2), where k(T2) = A2·exp(-Ea2 / RT2).

[0034] After obtaining T1, t1, T2, and t2, calculate the temperature difference ΔT between the first heating temperature T1 and the second heating temperature T2: .

[0035] Based on this, the first heating temperature T1 and the first holding time t1 are used as the first heat energy distribution data for the bottom metal film, and the second heating temperature T2 and the second holding time t2 are used as the second heat energy distribution data for the middle metal film. Following the physical stacking order of the DFB laser's multilayer metal films from the bottom to the middle layer, the first and second heat energy distribution data are combined to generate an initial layer-by-layer heat energy control sequence. This sequence can be represented, for example, as follows: first heating at the first heating temperature T1 and holding for the first holding time t1, then heating at the second heating temperature T2 and holding for the second holding time t2.

[0036] Subsequently, referring to Figure 3 As shown, the initial thermal energy is used to control the layer-by-layer heating sequence for simulation heating, and the diffusion depth of the bottom layer and the middle layer after the simulated heating are measured. In this method, a thermal-diffusion coupled finite element simulation model of the multilayer metal thin film during the heating process is first established.

[0037] Specifically, the first step is to establish a geometric model: based on the actual structure of the multilayer metal thin film on the DFB laser chip to be processed, a one-dimensional or two-dimensional axisymmetric geometric model is established. Taking the one-dimensional model as an example, coordinate axes are established along the direction perpendicular to the thin film interface, and the following regions are set sequentially: semiconductor substrate region (thickness is usually 300 to 500 micrometers, but the heat-affected zone is mainly concentrated in the range of a few micrometers near the interface, so 10 micrometers near the substrate interface can be taken as the calculation region when modeling), bottom metal thin film region (thickness is 80 nanometers), and middle metal thin film region (thickness is 150 nanometers). The regions are connected through interface nodes to ensure the continuity of the temperature field and concentration field at the interface.

[0038] The second step is to set the temperature field control equations and boundary conditions: The distribution of the temperature field is governed by the Fourier heat conduction equation: ρ is the material density, in kilograms per cubic meter; c pSpecific heat capacity is expressed in joules per kilogram per Kelvin; T is thermodynamic temperature in Kelvin; t is time in seconds; λ is thermal conductivity in watts per meter per Kelvin; x is the spatial coordinate perpendicular to the interface in meters; Q is the heat of reaction released by the alloying reaction in watts per cubic meter.

[0039] The boundary conditions are set as follows: an isothermal boundary condition is set at the bottom of the semiconductor substrate, with a temperature of room temperature (298 K); a heat flux boundary condition is set on the surface of the multilayer metal film, applying periodic heat flux according to the heating temperature and holding time in the layer-by-layer control sequence based on the initial thermal energy. Specifically, when performing bottom layer heating, a heat flux density corresponding to the first heating temperature T1 is applied to the film surface; when switching to middle layer heating, a heat flux density corresponding to the second heating temperature T2 is applied to the film surface; the initial temperature of each metal film layer is set to room temperature (298 K).

[0040] The third step is to set the governing equations and boundary conditions for the diffusion field: The distribution of the elemental concentration field is governed by Fick's second law: C is the concentration of the diffusing element, expressed as atomic percentage or kilograms per cubic meter; D is the diffusion coefficient, expressed as square meters per second; t is time, expressed as seconds; x is the spatial coordinate perpendicular to the interface, expressed as meters.

[0041] For the bottom metal film (titanium), when it diffuses into the semiconductor substrate (indium phosphide), a concentration jump boundary condition is set at the titanium / indium phosphide interface, meaning the concentration at the interface satisfies the distribution coefficient relationship. For the middle metal film (nickel), when it diffuses into the bottom metal film (titanium), a concentration jump boundary condition is also set at the nickel / titanium interface; a zero flux boundary condition is set at the bottom of the semiconductor substrate and at the film surface.

[0042] Step 4, thermal-diffusion coupling treatment: The temperature field and the concentration field are coupled through the diffusion coefficient D; the relationship between the diffusion coefficient D and the temperature T follows the Arrhenius equation: D0 is the pre-exponential diffusion factor, measured in square meters per second; E d The diffusion activation energy is expressed in joules per mole; R is the gas constant. During the simulation, the temperature field is solved at each time step to obtain the temperature distribution at each node at the current moment. Then, the diffusion coefficient of each node is updated based on the temperature distribution, and finally the concentration field is solved. This sequential coupling method accurately reflects the driving effect of temperature on the diffusion process.

[0043] Step 5, Finite Element Solution: Finite element software (such as the heat transfer module and rare matter transport module of COMSOL Multiphysics) was used to discretize and solve the above governing equations. The backward Euler method was used for time discretization to ensure numerical stability, and linear elements were used for spatial discretization. The time step was set to an adaptive step size with an initial step size of 0.001 seconds and a maximum step size of 1 second. After the solution was completed, the element concentration C(x,t) of each node at each time step was output, thereby obtaining the distribution curve of element concentration along the depth direction.

[0044] From the obtained element concentration distribution curves along the depth direction, the characteristic element concentration data of titanium in the bottom metal film is extracted along the direction perpendicular to the metal film interface. The depth position corresponding to the decrease of this characteristic element concentration to 5% of its peak concentration is taken as the bottom diffusion depth D1. Similarly, the characteristic element concentration data of nickel in the middle metal film is extracted, and the depth position corresponding to the decrease of this characteristic element concentration to 5% of its peak concentration is taken as the middle diffusion depth D2.

[0045] After determining the bottom diffusion depth D1 and the middle diffusion depth D2, the bottom diffusion depth D1 is compared with the critical diffusion depth, and the middle diffusion depth D2 is compared with the standard diffusion depth to generate a reaction misalignment representation. Specifically, in the process of measuring diffusion depth, the critical diffusion depth is determined by experimental verification to be the maximum allowable diffusion depth of the bottom metal film without damaging the underlying active region structure. The standard diffusion depth is determined by analyzing a DFB laser with good electrical performance and stability to determine the diffusion depth range that the middle metal film should reach to form an ideal ohmic contact.

[0046] Specifically, the critical diffusion depth is determined as follows: Test samples of the same batch and structure as the DFB laser under test are alloyed at several gradually increasing heating temperatures, for example, one set of samples is treated at each of 623K, 648K, 673K, 698K, and 723K. Cross-sectional electron microscopy is performed on each treated test sample to observe the diffusion of the underlying titanium thin film. The diffusion depth at which the underlying titanium thin film first penetrates the predetermined safety interface and contacts the underlying indium phosphide active region material is recorded. This depth is taken as the critical diffusion depth D. C .

[0047] The standard diffusion depth is determined as follows: multiple test samples of the same batch and structure as the DFB laser under test are prepared, and alloyed under multiple different heating conditions. The contact resistivity of each test sample is measured. A contact resistivity that meets the device design requirements (e.g., less than 1 × 10⁻⁶) is selected. -6 Ω·cm 2A set of test samples was used to measure the diffusion depth of the test samples, and the measured diffusion depth was used as the standard diffusion depth D. S .

[0048] The aforementioned determination of the bottom diffusion depth D1 and the critical diffusion depth D C If D1 > D C If so, it is determined that the bottom metal film has undergone excessive fusion under the current initial thermal energy layer-by-layer control sequence, generating the first reaction misalignment marker.

[0049] Similarly, the aforementioned determined mid-layer diffusion depth D2 is compared with the standard diffusion depth D. S Compare, if D2 <D S If the diffusion of the intermediate metal film is insufficient under the current initial thermal energy layer-by-layer control sequence, and the predetermined state has not been reached, a second reaction misalignment marker is generated.

[0050] When implementing step S500, the heating temperature and holding time are adjusted according to the reaction misalignment indicator.

[0051] Specifically, firstly, the adjustment coefficient η is configured, and 0.05≤η≤0.3; then, the following corrections are made based on the aforementioned generated reaction misalignment representation.

[0052] When a first reaction misalignment indicator is present, it indicates that the first heating temperature T1 of the underlying metal film is too high and needs to be reduced. The underlying heating temperature T1' is determined according to the formula T1'=T1-η×ΔT, where ΔT is the temperature difference calculated in step two. Since a decrease in temperature will lead to a decrease in the reaction rate, the first holding time needs to be extended accordingly. The underlying holding time t1' is calculated according to the formula: .

[0053] When a second reaction misalignment indicator is present, it indicates that the second heating temperature T2 of the intermediate metal film is insufficient and needs to be increased. The intermediate heating temperature T2' is determined according to the formula T2'=T2+η×ΔT. Since increasing the temperature accelerates the reaction rate, the second holding time needs to be shortened accordingly to avoid excessive diffusion. The intermediate holding time t2' is calculated according to the formula: .

[0054] By configuring the adjustment coefficient η to proportionally scale the temperature difference ΔT, and in conjunction with the time compensation formula based on Arrhenius dynamics, a precise quantitative correction is achieved: the cooling amplitude of the bottom layer is proportional to the temperature difference; the extension of the bottom layer's heat preservation time is proportional to the cooling amplitude; the heating amplitude of the middle layer is proportional to the temperature difference; and the reduction of the middle layer's heat preservation time is also proportional to the heating amplitude. This ensures that the correction step size matches the inherent energy threshold difference between the two metal layers, avoiding under-correction or over-correction.

[0055] When the first reaction misalignment flag and the second reaction misalignment flag exist simultaneously, the above-mentioned cooling delay correction for the bottom metal film and heating delay correction for the middle metal film are executed independently and do not interfere with each other; the corrected T1', t1', T2', and t2' are used as the target thermal energy layer-by-layer control sequence.

[0056] As a preferred implementation, an iterative correction process is adopted: After the first round of correction, T1', t1', T2', and t2' are obtained. Steps S400 and S500 are repeated using the corrected parameters. If the bottom layer diffusion depth is still greater than the critical diffusion depth and / or the middle layer diffusion depth is still less than the standard diffusion depth, then the heating temperature and holding time obtained in the previous round of correction are used as a reference to continue the correction operation of reducing the first heating temperature and extending the first holding time, and increasing the second heating temperature and shortening the second holding time, until D1 ≤ D C And D2 ≥ D S .

[0057] Finally, following the target thermal energy layer-by-layer control sequence obtained in step S500, the actual heating operation is performed on the DFB laser chip to be processed. The DFB laser chip to be processed is placed in a rapid thermal annealing furnace, and the corresponding heating power is output sequentially from the bottom layer to the middle layer: first, the temperature of the rapid thermal annealing furnace is raised to the bottom layer heating temperature T1' and held at the bottom layer for a holding time t1'; then, the furnace temperature is automatically switched to the middle layer heating conditions, adjusted to the middle layer heating temperature T2', and held at the middle layer for a holding time t2'. After all layers are processed, the chip is naturally cooled to room temperature, thereby obtaining a flat, uniform, and depth-controllable target alloy depth in the electrode contact layer of the DFB laser.

[0058] In summary, the alloying layer-by-layer control method for multilayer metal thin films in DFB lasers described in this invention generates a differentiated heating sequence executed sequentially from the bottom layer to the middle layer by identifying the energy threshold of each layer. Based on the diffusion depth feedback after simulated heating, the bottom layer is cooled and delayed to suppress excessive fusion penetration to a safe depth, while the middle layer is heated and the heating time is shortened to promote sufficient diffusion and eliminate unreacted areas. This achieves decoupled independent correction between the bottom and middle layers, effectively avoiding damage to the active region caused by excessive diffusion of the bottom metal thin film, while ensuring sufficient alloying of the middle metal thin film. Ultimately, a flat, low-resistance ohmic contact interface is formed, ensuring current transmission efficiency and laser stability.

[0059] 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 layer-by-layer control of alloying in multilayer metal thin films for DFB lasers, characterized in that, include: Determine the activation energy for alloying reactions in each layer of the metal thin film; The first heating temperature and the first holding time are determined based on the activation energy of the underlying metal film. The second heating temperature and the second holding time are determined based on the activation energy of the middle metal film; and the temperature difference between the two is calculated. Following the order from the bottom layer to the middle layer, the first heating temperature and the first holding time, and the second heating temperature and the second holding time are combined to generate the initial thermal energy layer-by-layer control sequence. Simulated heating was performed based on the initial thermal energy layer-by-layer control sequence, and the diffusion depth of the bottom layer and the middle layer after simulated heating were measured. In response to the bottom diffusion depth being greater than the critical diffusion depth, the first heating temperature is reduced according to the temperature difference, and the first holding time is extended according to the reduced heating temperature, thereby obtaining the bottom heating temperature and the bottom holding time. In response to the middle layer diffusion depth being less than the standard diffusion depth, the second heating temperature is increased according to the temperature difference, and the second holding time is shortened according to the increased heating temperature, thereby obtaining the middle layer heating temperature and the middle layer holding time. Determine the activation energies for alloying reactions in each metal thin film layer, including: Test samples of the same batch and thickness as the metal thin film to be tested are prepared. The test samples include a semiconductor substrate identical to that of the DFB laser to be tested and a single-layer test metal thin film deposited on the semiconductor substrate. The test samples were subjected to isothermal annealing at multiple heating temperatures, with each heating temperature corresponding to a set of test samples. The sheet resistance of each test sample was measured after different annealing times, and the reciprocal of the time required for the sheet resistance to drop to 50% of the initial sheet resistance was taken as the reaction rate constant at that heating temperature. According to the Arrhenius equation, a relationship curve was plotted with the natural logarithm of the reaction rate constant at each heating temperature as the ordinate and the reciprocal of the thermodynamic temperature as the abscissa. The relationship curve was then linearly fitted, and the slope of the fitted line was multiplied by the gas constant and the absolute value was taken as the activation energy of the alloy reaction of the metal thin film. The Arrhenius equation is: k = A·exp(-Ea / RT); k is the reaction rate constant; Ea is the activation energy; R is the gas constant, with a value of 8.314 J / (mol·K); T is the thermodynamic temperature; A is the pre-exponential factor. Determining the first heating temperature based on the activation energy of the underlying metal thin film includes: solving for the first heating temperature using the inverse function of the Arrhenius equation; the inverse function of the Arrhenius equation is: ； T1 is the first heating temperature; Ea1 is the activation energy of the alloy reaction of the bottom metal film; k1 is the target reaction rate constant of the bottom metal film; The method for determining the second heating temperature is the same as the method for determining the first heating temperature.

2. The method for layer-by-layer alloying control of multilayer metal thin films in DFB lasers according to claim 1, characterized in that... The methods for determining the pre-exponential factor A include: On test samples of the same batch and thickness as the metal thin film to be tested, isothermal annealing was performed at multiple different heating temperatures, and the reaction rate constant at each heating temperature was measured. A linear fit was performed with the natural logarithm of the reaction rate constant at each heating temperature as the ordinate and the reciprocal of the thermodynamic temperature as the abscissa. The intercept of the fitted line was then exponentially used as the pre-exponential factor of the metal thin film.

3. The method for layer-by-layer alloying control of multilayer metal thin films in DFB lasers according to claim 1, characterized in that... Adjusting the heating temperature based on the temperature difference includes: Configure the adjustment coefficient η, where 0.05≤η≤0.3; The bottom heating temperature T1' is determined as: T1' = T1 - η × ΔT; The heating temperature T2' of the middle layer is determined as: T2' = T2 + η × ΔT; ΔT is the temperature difference; T1 is the first heating temperature; T2 is the second heating temperature.

4. The method for layer-by-layer alloying control of multilayer metal thin films in a DFB laser according to claim 3, characterized in that... The first holding time is extended based on the reduced heating temperature, including: ; t1' is the bottom layer heat preservation time; t1 is the first heat preservation time; Ea1 is the activation energy of the bottom metal film alloy reaction; R is the gas constant, with a value of 8.314 J / (mol·K); The second holding time is shortened based on the increased heating temperature, including: t2' is the middle layer heat preservation time; t2 is the second heat preservation time; Ea2 is the activation energy of the middle layer metal thin film alloy reaction.

5. The method for layer-by-layer alloying control of multilayer metal thin films in a DFB laser according to claim 1, characterized in that... Simulated heating is performed using an initial thermal energy layer-by-layer control sequence, including: A thermal-diffusion coupled finite element simulation model of the multilayer metal thin film during the heating process is established. The finite element simulation model includes the geometric dimensions, material thermal properties, and interface diffusion coefficients of each metal thin film layer. The first heating temperature, first holding time, second heating temperature, and second holding time in the initial thermal energy layer-by-layer control sequence are sequentially input into the finite element simulation model as thermal boundary conditions from the bottom layer to the middle layer. The distribution curves of element concentration along the depth direction inside and at the interface of each layer of metal film after simulated heating are obtained.

6. The method for layer-by-layer alloying control of multilayer metal thin films in a DFB laser according to claim 5, characterized in that... The diffusion depths of the bottom and middle layers after simulated heating were measured, including: From the distribution curve of the element concentration along the depth direction, the characteristic element concentration data of the bottom metal film is extracted in the direction perpendicular to the metal film interface, and the depth position corresponding to when the concentration of the characteristic element drops to 5% of its peak concentration is taken as the bottom diffusion depth. The concentration data of characteristic elements in the middle metal film are extracted, and the depth position corresponding to the decrease of the concentration of the characteristic element to 5% of its peak concentration is taken as the diffusion depth of the middle layer.

7. The method for layer-by-layer alloying control of multilayer metal thin films in a DFB laser according to claim 1, characterized in that... Determining the critical diffusion depth includes: Test samples of the same batch and structure as the DFB laser under test were alloyed at several different heating temperatures with gradually increasing temperatures. Each processed test sample was scanned by cross-sectional electron microscopy to record the diffusion depth at which the bottom metal film first penetrated the safety interface and came into contact with the active material below, thus obtaining the critical diffusion depth.

8. The method for layer-by-layer alloying control of multilayer metal thin films in a DFB laser according to claim 1, characterized in that... Determining the standard diffusion depth includes: Multiple test samples of the same batch and structure as the DFB laser under test were prepared and alloyed under multiple different heating conditions. The contact resistivity of each test sample was measured. A set of test samples with contact resistivity meeting the requirements were selected, and the diffusion depth of the set of test samples was measured to obtain the standard diffusion depth.

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