Method for controlling laser sealing and surface roughness by controlled solidification cooling speed

Abstract

To provide a method for laser-sealing a vent hole of a membrane and controlling surface roughness.SOLUTION: The method controls surface roughness during laser sealing of a vent hole of a membrane. The method includes a process in which a main pulse from main laser is applied to a vent hole 16 of a membrane at a first time point. The main pulse has a main pulse sectional shape, a main pulse output profile, and a main pulse duration time. The method further includes a process in which one or more auxiliary pulses from one or more auxiliary lasers are applied to the vent hole of the membrane at a second time point after the first time point. One or more auxiliary pulses have an auxiliary pulse sectional shape, an auxiliary pulse output profile, and an auxiliary pulse duration time. In the first application process and the second application process, a seal 20 covering the vent hole of the membrane is formed. The seal includes a seal surface having controlled surface roughness characteristics.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present disclosure relates to pulsed laser irradiation techniques, and more particularly to a method for laser sealing and controlling surface roughness for laser sealing vent holes in a membrane, in which the membrane may be formed from silicon and the method uses a controlled solidification cooling rate.

[0002] background A pulsed laser irradiation technique has been proposed to seal vent openings within an inertial measurement unit (IMU) to capture the critical pressure of the sensor cavity within the device. The vents are formed by deep reactive ion etching of a silicon membrane. Beneath the silicon membrane is a device chamber housing a vacuum-dependent microelectromechanical system (MEMS) sensor. During the laser irradiation process, the seal zone quality can be significantly affected by complex process physics, such as Marangoni flow and / or silicon phase change. The surface topography of the solidified silicon can be problematic for IMU devices. For example, surface roughness can result in the formation of rough edges on the seal zone surface. Removal of such structures can potentially compromise device quality.

[0003] overview According to one embodiment, a method for controlling surface roughness during laser sealing of a membrane vent hole is disclosed. The method includes applying a main pulse from a main laser to the membrane vent hole at a first time point. The main pulse has a main pulse cross-sectional shape, a main pulse power profile, and a main pulse duration. The method further includes applying one or more auxiliary pulses from one or more auxiliary lasers to the membrane vent hole at a second time point later than the first time point. The one or more auxiliary pulses have an auxiliary pulse cross-sectional shape, an auxiliary pulse power profile, and an auxiliary pulse duration. The first applying step and the second applying step form a seal over the membrane vent hole. The seal includes a sealing surface having controlled surface roughness characteristics. In one or more embodiments, the one or more auxiliary pulses can include a first auxiliary pulse, a second auxiliary pulse, a third auxiliary pulse, and a fourth auxiliary pulse. The main pulse power profile can be a non-steady-state main pulse power profile. The auxiliary pulse power profile can be a non-steady-state auxiliary pulse power profile. [Brief explanation of the drawings]

[0004] [Figure 1A] 1 is a cross-sectional view of a device formed from a silicon membrane. [Figure 1B] FIG. 1 is an isolated cross-sectional perspective view showing a portion of a vent in the device. [Figure 1C] 10 is a schematic side view of a laser irradiation process performed on the vent hole opening in a molten state. FIG. [Figure 1D] FIG. 10 is a schematic side view of a laser irradiation process performed on the opening of the vent hole in a solidified state. [Figure 2A] 1 is a schematic cross-sectional view of a melted region of a substrate (e.g., a silicon substrate) when a primary laser is applied. [Figure 2B] 1 is a schematic cross-sectional view illustrating the solidification path of solidified material of a substrate. [Figure 2C] FIG. 10 is a schematic cross-sectional view showing a coagulation path caused by application of an auxiliary laser. [Figure 3A]1 is a schematic top view of a silicon substrate having a melt zone formed by a primary laser (e.g., a Gaussian laser) to seal a vent hole in the silicon substrate. [Figure 3B] 1 is a graph showing the power of the main laser as a function of time step. [Figure 3C] FIG. 1 is a schematic top view of a silicon substrate having a melt zone formed by a primary laser and an auxiliary laser. [Figure 3D] 1 is a graph showing the output of a main laser and the output of an auxiliary laser. [Figure 4A] 3B is a schematic cutaway view of a substrate having a vent hole and a melt pool formed above the vent hole using the primary laser of FIG. 3A. [Figure 4B] 4B is a schematic cross-sectional view of the substrate of FIG. 4A. [Figure 4C] 3D is a schematic cutaway view of a substrate having a vent hole and a melt pool formed above the vent hole using the primary and auxiliary lasers of FIG. 3C. [Figure 4D] 4D is a schematic cross-sectional view of the substrate of FIG. 4C. [Figure 4E] FIG. 4D is a schematic perspective view of the substrate of FIGS. 4A and 4C showing the conformal solidification path indicated by the arrows at time stage 1.5. [Figure 4F] FIG. 4D is a schematic perspective view of the substrate of FIGS. 4A and 4C showing conformal solidification paths indicated by arrows at time step 2.0. [Figure 4G] FIG. 4E is a schematic perspective view of the substrate of FIGS. 4B and 4D showing the conformal solidification path indicated by the arrows at time stage 1.5 with a relative SCR value of 0.64. [Figure 4H] FIG. 4E is a schematic perspective view of the substrate of FIGS. 4B and 4D showing the conformal solidification path indicated by the arrows at time step 2.0 with a relative SCR value of 0.2. [Figure 4I] FIG. 4E is a schematic perspective view of the substrate of FIGS. 4B and 4D showing the conformal solidification path indicated by the arrows at time step 2.7 with a relative SCR value of 0.15. [Figure 4J]FIG. 4E is a schematic perspective view of the substrate of FIGS. 4B and 4D showing the conformal solidification path indicated by the arrows at time step 3.0 with a relative SCR value of 0.4. [Figure 5A] FIG. 4D is a schematic cross-sectional view of the substrate of FIGS. 4A and 4C showing 100% peak height for the final solidified surface morphology. [Figure 5B] FIG. 4D is a schematic cutaway view of the substrate of FIGS. 4A and 4C showing the final solidified surface morphology. [Figure 5C] FIG. 4E is a schematic cross-sectional view of the substrate of FIGS. 4B and 4D showing a 50% peak height for the final solidified surface morphology. [Figure 5D] FIG. 4E is a schematic cutaway view of the substrate of FIGS. 4B and 4D showing the final solidified surface morphology. [Figure 6A] 1 is a graph plotting power as a function of time steps for a main laser to obtain a main power curve. [Figure 6B] 6B is an image showing an end view of the primary laser of FIG. 6A. [Figure 6C] 6B is a graph plotting power as a function of time step for the main laser and one or more auxiliary lasers of FIG. 6A to obtain main and auxiliary power curves; [Figure 6D] 10 is an image showing the relative intensity of an auxiliary laser with dark areas having stronger intensity than light areas. [Figure 6E] 10 is an image showing the relative intensities of the main and auxiliary lasers with dark areas having stronger intensities than bright areas. [Figure 7A] FIG. 11 is a first perspective view showing the results of the vent closure process using the first simulation case. [Figure 7B] FIG. 10 is a second perspective view showing the results of the vent closure process using the first simulation case. [Figure 7C] FIG. 10 is a first perspective view showing the results of the vent closure process using the second simulation case. [Figure 7D] FIG. 10 is a second perspective view showing the results of the vent closure process using the second simulation case. [Figure 8A]FIG. 1 is a top view of six auxiliary lasers spaced equally around the periphery of the main laser above a substrate. [Figure 8B] 8B is a top view of three auxiliary lasers equally spaced around the periphery of the main laser above the substrate shown in FIG. 8A. [Figure 8C] FIG. 1 is a top view of six auxiliary lasers unequally spaced around the periphery of the main laser. [Figure 8D] FIG. 1 is a top view of six auxiliary lasers with different diameters unequally spaced around the periphery of the main laser. [Figure 9A] 10 is a graph showing a main laser profile and an auxiliary laser profile, where the auxiliary laser profile may overlap with or be spaced apart from the main laser profile. [Figure 9B] 1 is a graph showing a main laser profile and an auxiliary laser profile with non-constant power output over time. [Figure 9C] FIG. 1 is a top view of six auxiliary lasers spaced around the periphery of the main laser and having different shapes.

[0005] Detailed Description Embodiments of the present disclosure will now be described. However, it should be understood that the disclosed embodiments are merely examples, and that other embodiments may take various alternative forms. The figures are not necessarily to scale, and some configurations may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein should not be construed as limiting, but merely as representative basis for teaching those skilled in the art to variously employ the embodiments. As those skilled in the art will understand, various configurations illustrated and described with reference to any one of the drawings can be combined with configurations shown in one or more other drawings to create embodiments not explicitly illustrated or described. Combinations of the illustrated configurations provide representative embodiments for typical applications. However, various combinations and modifications of configurations consistent with the teachings of the present disclosure may be desirable for particular applications or implementations.

[0006] Except in the examples, or unless otherwise indicated, all numerical values ​​used herein to indicate amounts of materials or reaction and / or use conditions should be understood to be modified by the word "about" in describing the broadest scope of the invention. Generally, practice within the stated numerical ranges is preferred. Also, unless otherwise specified, percents, "parts," and ratios are by weight; the term "polymer" includes "oligomer," "copolymer," "terpolymer," etc.; the description of a group or type of material as suitable or preferred for a particular purpose in connection with this invention suggests that mixtures of any two or more members of that group or type are equally suitable or preferred; the molecular weight of any polymer is the number average molecular weight; descriptions of components in chemical terms refer to the components at the time they are added in any combination specified in the specification but do not necessarily exclude chemical interactions between the components in a mixture once mixed; an acronym or other abbreviation originally defined applies to all subsequent uses of the same abbreviation in this specification and applies mutatis mutandis to normal grammatical variations of the abbreviation originally defined; and unless otherwise specified, measurements of properties are determined by the same techniques referenced earlier or later for the same property.

[0007] The present invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may, of course, vary. Further, the terminology used herein is used only for the purpose of describing embodiments of the present invention and is not intended to be limiting in any way.

[0008] As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, a reference to a singular component is meant to include plural components.

[0009] The term "substantially" may be used herein to describe disclosed or claimed embodiments. The term "substantially" may modify a value or relative property disclosed or claimed in this disclosure. In such instances, "substantially" may mean that the value or relative property it modifies is within ±0%, ±0.1%, ±0.5%, ±1%, ±2%, ±3%, ±4%, ±5%, or ±10% of the value or relative property.

[0010] In one or more embodiments, a method for reducing the surface roughness of a seal zone in laser sealing of a silicon film is disclosed. One or more embodiments rely on a computational fluid dynamics (CFD) model to simulate the laser used in the silicon film sealing process. The CFD model accounts for complex process physics such as surface tension and / or solidification volume shrinkage. Temperature-dependent material properties, such as density, conductivity, specific heat, and / or surface tension coefficients, can be included in the CFD model to improve simulation accuracy.

[0011] In one or more embodiments, multiphysics numerical simulations are used to study the laser irradiation and melting of silicon materials with the goal of optimizing process parameters to reduce or eliminate solidification surface roughness. One or more embodiments thereby present a novel laser irradiation method or mechanism for reducing or eliminating solidification surface roughness in inertial measurement unit (IMU) fabrication processes.

[0012] The multiphysics CFD model characterizes the complex thermo-fluid phenomena in the vent sealing process. In one or more embodiments, the model includes a fixed laser irradiation heat source, solid-liquid phase transformation, solidification volume change, surface tension induced by Marangoni flow, evaporation pressure, and / or temperature-dependent thermo-fluid properties. Geometric information of the IMU silicon membrane with the vent (e.g., the region of interest in FIG. 1B) can also be included.

[0013] Pulsed laser irradiation techniques can be utilized to seal vent openings in IMUs. The IMUs are configured to capture the critical pressure of a sensor cavity within the device. FIG. 1A is a cross-sectional view of a device 10 formed from a material 12 (e.g., a silicon membrane). The material 12 defines a device chamber 14 and a vent 16. The vent 16 has a vent opening 18 at its distal end. The vent 16 extends between the device chamber 14 and the vent opening 18. FIG. 1B is an isolated cross-sectional perspective view of a portion of the vent 16 within the device 10. FIG. 1B shows a seal 20 configured to seal the vent opening 18. The seal zone 18 is formed by a laser irradiation process.

[0014] When material 12 is a silicon membrane, vent holes 16 are formed by chemical etching of the silicon (Si) membrane. Beneath the silicon membrane, device chamber 14 houses a pressure-sensitive microelectromechanical system (MEMS) sensor. During the laser irradiation process, the silicon in the sealing zone melts, flows, and resolidifies, during which the seal quality can be significantly affected by complex process physics, such as Marangoni flow and Si phase change. As the molten silicon solidifies, its volume increases, which reduces its density and creates peak-shaped surface roughness.

[0015] FIG. 1C is a schematic side view of the laser irradiation process performed on the vent opening 18 in a molten state. FIG. 1D is a schematic side view of the laser irradiation process performed on the vent opening 18 in a solidified state. The laser irradiation process forms a seal 20 with the surface anomalies shown in FIG. 1D. As shown in FIG. 1C, a laser pulse 24 having a pulse duration is used to irradiate the top surface 26 of the silicon film adjacent to the vent hole 16. The material under the irradiation area 28 begins to melt and flow, filling the vent hole 16. After the laser pulse 24 is turned off, the molten silicon solidifies, sealing the vent hole 16, as shown in FIG. 1D. However, as shown in FIG. 1D, a surface roughness 22 is formed on the seal 20.

[0016] One or more embodiments relate to a method for reducing surface roughness while closing vent holes. The surface morphology of a laser sealed film (e.g., a silicon film) may be correlated, at least in part, with the material solidification cooling rate ("SCR"). In one or more embodiments, the SCR may refer to the temperature drop over a period of time after the temperature drops below the material solidus point, and the SCR in a molten pool (e.g., a liquid material) is set to zero. In one or more embodiments, the surface morphology can be adjusted by controlling the SCR (e.g., via an externally applied heat source).

[0017] FIG. 2A is a schematic cross-sectional view of a melted region 100 of a substrate 102 (e.g., a silicon substrate) upon application of a first laser beam 104. FIG. 2B is a schematic cross-sectional view of a solidification path 106 of solidified material 108 of the substrate 102. As shown in FIG. 2B, the melted region 100 first solidifies from the boundary region 110 and then gradually solidifies toward the center. FIG. 2C is a schematic cross-sectional view of a solidification path 112 upon application of a second laser beam 114. Upon further application of the second laser beam 114, the area 118 away from the laser beam cools first, while the melted region 116 maintains a lower SCR (e.g., remains liquid) in the area irradiated by the second laser beam 114. Using the second laser beam 114 changes the surface morphology as shown in FIG. 2B (central ridge morphology) and FIG. 2C (side ridge morphology). In one or more embodiments, a combination of the spatial and temporal characteristics of the lasers, the number of lasers, the laser incidence angle, and / or other configurations of the lasers can produce the desired surface morphology.

[0018] In one or more embodiments, one or more lasers in addition to the first laser are used to control the SCR at the boundary of the melt zone. This method allows for a higher SCR in the center of the melt pool and a lower SCR at the melt pool boundary. In one or more embodiments, after the final cooling zone is extended around the melt pool boundary, the peak height at the center of the melt region surface is reduced.

[0019] 3A is a schematic top view of a silicon substrate 200 having a melt zone formed by a primary laser 202 (e.g., a Gaussian laser) to seal a vent hole in the silicon substrate 200. Once the material in the melt zone melts and flows to seal the vent hole, the first laser is turned off. FIG. 3B is a graph showing the power of the primary laser 202 as a function of time step. As shown in FIG. 3B, during the first time step, the power of the primary laser 202 is at 100%. The length of the time step may be 1 millisecond or more, 1 microsecond or more, or 1 nanosecond or more, or may be a range selecting any two of these values.

[0020] 3C is a schematic top view of a silicon substrate 210 having a melt zone formed from a primary laser 212 and an auxiliary laser 214. The diameter of each auxiliary laser 214 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90% smaller than the diameter of the primary laser 212, or a range between any two of these percentages. The power output of each auxiliary laser 214 can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, and 60% smaller than the power output of the diameter of the primary laser 212, or a range between any two of these percentages. 3D is a graph showing the power of the primary laser 212 and the power of each auxiliary laser 214 as a function of time phase. As shown in FIG. 3D, the power of the primary laser 212 is 100% in the first time phase and 0% thereafter, while the power of each auxiliary laser 214 is 0% in the first time phase and 16.7% in the second and third time phases. The configuration shown in FIG. 3C can enable slower SCR at the melt pool boundary. The first primary time phase and the second auxiliary time phase may vary depending on the embodiment. For example, the first major time step may be 100% of the time step, and the second minor time step may be any of the following time steps relative to the first time step: 50%, 75%, 100%, 125%, 150%, 175%, 200%, 225%, 250%, 275%, 300%, 325%, 350%, 375%, and 400%, or a range between any two of these.

[0021] 4A-4J show SCR values ​​for a first and second simulation case for closing a vent hole in a substrate. In the first simulation case, primary laser 202 is used to form a melt pool that resolidifies to close the vent hole. In the second simulation case, primary laser 212 and auxiliary laser 214 are used to form a melt pool that resolidifies to close the vent hole. In these embodiments, relative SCR values ​​are used to compare the results of the first and second simulation cases. The maximum SCR for the first and second simulation cases is defined as 1.0, and lower SCR values ​​are defined as fractions of 1.0. The relative SCRs of the solidification paths for the first and second simulation cases are determined and compared.

[0022] Figure 4A is a schematic perspective cutaway view of a substrate 300 having a vent hole 302 and a melt pool 304 formed above the vent hole 302 using the primary laser 202 in a first simulation case. Figure 4B is a schematic cross-sectional view of the substrate 300 having a vent hole 302 and a melt pool 304 formed above the vent hole 302. As shown in Figures 4A and 4B, the substrate 300 includes a solid region 306 and a re-solidified region 308 located between the melt pool 304 and the solid region 306. Figures 4A and 4B show the substrate 300 with the primary laser 202 applied after time step 1.5 shown in Figure 3B.

[0023] 4C is a schematic perspective cutaway view of a substrate 310 having a vent hole 312 and a melt pool 314 formed above the vent hole 312 using the primary laser 212 and the auxiliary laser 214 in a second simulation case. FIG. 4D is a schematic cross-sectional view of the substrate 310 having a vent hole 312 and a melt pool 314 formed above the vent hole 312. As shown in FIGS. 4C and 4D, the substrate 310 includes a solid region 316 and a re-solidified region 318 located between the melt pool 314 and the solid region 316. FIGS. 4C and 4D show the substrate 310 with the primary laser 212 and the auxiliary laser 214 applied after time step 1.5 shown in FIG. 3D.

[0024] In a first simulation case, the relative SCR along the path indicated by arrow 320 is 0.75, and the relative SCR along the path indicated by arrows 324 and 326 is 1.0. In a second simulation case, the relative SCR along the paths indicated by arrows 328, 330, 332, and 334 is 0.64. FIG. 4E is a schematic perspective view of substrate 300 illustrating the conformal solidification path indicated by arrows 336 and 338 at time step 1.5. FIG. 4F is a schematic perspective view of substrate 300 illustrating the conformal solidification path indicated by arrows 340 and 342 at time step 2.0. In the first simulation case, the relative SCR along the path indicated by arrows 336 and 338 is 1.0. In the second simulation case, the relative SCR along the path indicated by arrows 340 and 342 is 1.0. Figure 4G is a schematic perspective view of substrate 310 showing a conformal solidification path indicated by arrows 344 and 346 at time step 1.5, where the relative SCR value is 0.64. Figure 4H is a schematic perspective view of substrate 310 showing a conformal solidification path indicated by arrows 348 and 350 at time step 2.0, where the relative SCR value is 0.2. Figure 41 is a schematic perspective view of substrate 310 showing a conformal solidification path indicated by arrows 352 and 354 at time step 2.7, where the relative SCR value is 0.15. Figure 4J is a schematic perspective view of substrate 310 showing a conformal solidification path indicated by arrows 356 and 358 at time step 3.0, where the relative SCR value is 0.4.

[0025] From the data shown in FIGS. 4A-4J, it can be seen that the relative SCR for the second simulation case is slower than that for the first simulation case because the additional laser heat input from the auxiliary laser 214 slows the SCR. From the data shown in FIGS. 4E-4J, it can be seen that the coagulation path changes between the first simulation cases because a higher SCR exists around the auxiliary laser spot of the auxiliary laser 214, and the location where the auxiliary laser spot is applied is the final coagulation region. Comparing FIGS. 4E and 4F with FIGS. 4G-4J shows the change in the coagulation path (e.g., from a peripheral-to-central coagulation path in FIGS. 4E and 4F to a central-to-peripheral coagulation path to the location of the laser spot in FIGS. 4G-4J).

[0026] 5A-5D show a comparison of the final solidified surface morphology of substrate 300 and substrate 310. FIG. 5A is a schematic cross-sectional view of substrate 300 showing a 100% peak height 400 for the final solidified surface morphology. FIG. 5B is a schematic cut-away view of substrate 300 showing the final solidified surface morphology. FIG. 5C is a schematic cross-sectional view of substrate 310 showing a 50% peak height 402 for the final solidified surface morphology. FIG. 5D is a schematic cut-away view of substrate 310 showing the final solidified surface morphology. A reduction in surface peak height is observed in the second simulation.

[0027] FIG. 6A is a graph plotting power as a function of time for a primary laser (e.g., main laser 212) to produce a primary power curve 500. The primary power curve 500 includes a first segment 502 where the power increases abruptly, a second segment 504 where the power decreases abruptly, and a third segment 506 where the power gradually decreases. FIG. 6B is an image showing an end view of the main laser. FIG. 6B shows the relative intensity of the main laser 212, with darker areas having greater intensity than lighter areas.

[0028] FIG. 6C is a graph plotting the power of a primary laser (e.g., main laser 212) and one or more secondary lasers (e.g., one or more auxiliary lasers 214) as a function of time step to obtain a primary power curve 500 and a secondary power curve 508. The secondary power curve 508 includes a first segment 510 of gradually increasing power, a second segment 514 of constant power, a third segment 516 of abruptly decreasing power, and a fourth segment 518 of gradually decreasing power. FIG. 6D is an image showing the relative intensity of the auxiliary laser 214, with darker areas having higher intensity than lighter areas. FIG. 6E is an image showing the relative intensity of the primary laser 212 and the auxiliary laser 214, with darker areas having higher intensity than lighter areas. As shown in FIG. 6E, the laser irradiation areas and / or laser pulse durations of the primary laser 212 and the auxiliary laser 214 overlap.

[0029] Applying the laser power using the power graphs of Figures 6A and 6C results in sufficient sealing of the vent hole. However, applying the laser power according to Figure 6C does not produce the sharp peaks on the surface that are produced by the laser power of Figure 6A. The experiments shown in Figures 6A-6E confirm that a laser spot around the primary laser can advantageously control the surface morphology (e.g., potentially promoting reduced peak height in the melted and solidified regions).

[0030] FIG. 7A is a first perspective view showing the results of the vent hole closing process using the first simulation case. FIG. 7B is a second perspective view showing the results of the vent hole closing process using the first simulation case. FIG. 7C is a first perspective view showing the results of the vent hole closing process using the second simulation case. FIG. 7D is a second perspective view showing the results of the vent hole closing process using the second simulation case. The notches shown around the centers of the melted and solidified regions in FIGS. 7A-7D are used for calibration of the measurement device and do not substantially affect the experimental results.

[0031] In one or more embodiments, one or more characteristics of one of the lasers can be adjusted to reduce surface morphology roughness during the vent sealing process. While the embodiment shown in FIGS. 6C-6E includes four auxiliary lasers, other embodiments can use a different number of auxiliary lasers (e.g., 3, 5, 6, 7, 8, or more, or a range therebetween). For example, FIG. 8A shows a top view of six auxiliary lasers 700A-700F spaced evenly around the periphery of a primary laser 702 above a substrate 704. As shown in FIG. 8A, a portion of each auxiliary laser 700A-700F overlaps with a portion of the primary laser 702. While the overlap is the same for each auxiliary laser, in other embodiments, the overlap may be different (e.g., the center-to-center distance between a pair of auxiliary lasers and the primary laser may be different). As shown in FIG. 8A, the size (e.g., diameter) of each auxiliary laser 700A-700F is the same, but in other embodiments, the size (e.g., diameter) may be different. As another example, FIG. 8B is a top view of three auxiliary lasers 706A-706C spaced evenly around the periphery of the primary laser 702 above the substrate 704. As shown in FIG. 8B, a portion of each auxiliary laser 706A-706C overlaps with a portion of the primary laser 702. FIG. 8C is a top view of six auxiliary lasers 708A-708F spaced unevenly around the periphery of the primary laser 702 above the substrate 704. This uneven spacing can be applied to three or more auxiliary lasers. FIG. 8D is a top view of six auxiliary lasers 710A-710F with different diameters spaced unevenly around the periphery of the primary laser 702. Two or more auxiliary lasers may have different diameters.

[0032] Other characteristics of the one or more lasers that can be adjusted to reduce surface morphology roughness during the vent sealing process include varying the laser's temporal and / or energy profiles. In one or more embodiments, the power of the primary and / or auxiliary lasers may be constant, while the power may vary between the primary and auxiliary lasers. In one or more embodiments, the auxiliary laser's temporal profile may overlap or be separated from the primary laser's temporal profile. FIG. 9A is a graph illustrating a primary laser profile 800 and an auxiliary laser profile 802, where the auxiliary laser profile 802 may overlap or be separated from the primary laser profile 800, as indicated by arrow 804. The time overlap may be between 0% and 100% (e.g., full overlap). In one or more embodiments, 100% overlap means that the auxiliary laser profile is longer than the primary laser profile and fully overlaps with the primary laser profile for the entire time step duration of the primary laser profile. The time separation may be between 0% and 100% of the primary laser's time step duration.

[0033] In one or more embodiments, the power profiles of the primary and auxiliary lasers are not constant. For example, FIG. 9B is a graph illustrating a primary laser profile 806 and an auxiliary laser profile 808 that do not have constant power over time. As indicated by arrow 804 in FIG. 9B, the auxiliary laser profile 808 may overlap or be spaced apart from the primary laser profile 806. The primary laser profile 806 has a triangular shape in which the power increases and then decreases along the time steps of power application by the primary laser profile 806. In other embodiments, the power may start from a higher value and decrease along the time steps, while in yet other embodiments, the power may start from a lower value and increase along the time steps. The increase and / or decrease in power may follow a linear trajectory, a sinusoidal trajectory, a stepped trajectory, a sawtooth trajectory, or a curved trajectory. As shown in FIG. 9C, the auxiliary laser profile 806 has a curved trajectory.

[0034] One or more auxiliary lasers may have different shapes and need not be limited to a circular illumination. By way of non-limiting example, the illumination pattern may be elliptical, approximately square, or irregular. FIG. 9C is a top view of six auxiliary lasers 810A-810F arranged around the periphery of primary laser 812 and having different shapes. For example, auxiliary laser 810C has an irregular shape, auxiliary laser 810D has an approximately square shape, and auxiliary laser 810F has an elliptical shape.

[0035] The following applications are related to the present application: U.S. Patent Application No. 17 / 863,659 (filed July 13, 2022), U.S. Patent Application No. 17 / 863,665 (filed July 13, 2022), and U.S. Patent Application No. 17 / 863,669 (filed July 13, 2022), each of which is incorporated by reference in its entirety herein.

[0036] The processes, methods, or algorithms disclosed herein can be delivered to / implemented in a processing device, controller, or computer, which may include any existing programmable or dedicated electronic control unit. Similarly, the processes, methods, or algorithms can be stored as data and instructions executable by a controller or computer in many forms, including, but not limited to, information permanently stored on non-writable storage media such as ROM devices, and information revocably stored on writable storage media such as floppy disks, magnetic tape, CDs, RAM devices, and other magnetic and optical media. The processes, methods, or algorithms can also be implemented in software-executable objects. Alternatively, the processes, methods, or algorithms can be embodied in whole or in part using suitable hardware components, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), state machines, controllers, or other hardware components or devices, or a combination of hardware, software, and firmware components.

[0037] While exemplary embodiments have been described above, these embodiments are not intended to describe all possible configurations encompassed by the scope of the claims. For example, while certain disclosed embodiments describe simulations and experiments involving laser sealing of vent holes to reduce surface sharpness, one or more embodiments may be applied to reducing sharpness on flat substrate surfaces (e.g., substrates without vent holes) and / or slightly sloped substrate surfaces. It is understood that the terms used herein are descriptive rather than limiting, and that various modifications are possible without departing from the spirit and scope of the present disclosure. As noted above, configurations of various embodiments can be combined to form additional embodiments of the present invention, even if not explicitly described or illustrated. While various embodiments may be described as offering advantages or being more preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those skilled in the art will recognize that, depending on the particular application and implementation, compromises may be made in one or more configurations or characteristics to achieve overall desired system attributes. These attributes may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc. Thus, even if any embodiments are described as less desirable with respect to one or more characteristics as compared to other embodiments or prior art implementations, these embodiments are not outside the scope of this disclosure and may be desirable for particular applications.

Claims

1. 1. A method for controlling surface roughness during laser sealing of a membrane vent, comprising: applying a main pulse from a main laser to the membrane vent at a first time, the main pulse having a main pulse cross-sectional shape, a main pulse power profile, and a main pulse duration; and applying one or more auxiliary pulses from one or more auxiliary lasers to the membrane vent hole at a second time later than the first time, the one or more auxiliary pulses having an auxiliary pulse cross-sectional shape, an auxiliary pulse power profile, and an auxiliary pulse duration; Including, The method, wherein a first said applying step and a second said applying step form a seal over a vent hole in the membrane, the seal including a sealing surface having a controlled surface roughness characteristic.

2. 2. The method of claim 1, wherein the main pulse cross-sectional shape is circular with a major diameter, and the auxiliary pulse cross-sectional shape is circular with a minor diameter smaller than the major diameter.

3. The method of claim 2 , wherein the secondary diameter is between 5% and 90% smaller than the major diameter.

4. The method of claim 1 , wherein the primary pulse power profile has a primary peak power and the auxiliary pulse power profile has an auxiliary peak power that is less than the primary peak power.

5. 5. The method of claim 4, wherein the auxiliary peak power is between 5% and 60% less than the main peak power.

6. The method of claim 1 , wherein the one or more auxiliary pulses are located along the periphery of a main laser pulse.

7. The method of claim 6 , wherein the one or more auxiliary pulses overlap the main laser pulse around the periphery of the main laser pulse.

8. The method of claim 6 , wherein the one or more auxiliary pulses comprise two or more auxiliary pulses equally spaced around the periphery of the main pulse.

9. The method of claim 1 , wherein the second time point overlaps with the main pulse duration.

10. The method of claim 1 , wherein the second point in time is after the main pulse duration.

11. The method of claim 1 , wherein there is a time interval between the main pulse duration and the auxiliary pulse duration.

12. The method of claim 1 , wherein the primary pulse power profile comprises a constant primary power and the auxiliary pulse power profile comprises a constant auxiliary power.

13. The method of claim 1 , wherein the one or more auxiliary pulses include a first auxiliary pulse having a circular shape and a second auxiliary pulse having a non-circular shape.

14. The method of claim 1 , wherein the one or more auxiliary pulses are non-overlapping.

15. The method of claim 1 , wherein the controlled surface roughness characteristic is a reduced surface roughness height.

16. 1. A method for controlling surface roughness during laser sealing of a membrane vent, comprising: applying a main pulse from a main laser to the membrane vent at a first time, the main pulse having a main pulse cross-sectional shape, a main pulse power profile, and a main pulse duration; and applying one or more auxiliary pulses from one or more auxiliary lasers to the membrane vent hole at a second time point that is later than the first time point, the one or more auxiliary pulses having an auxiliary pulse cross-sectional shape, an auxiliary pulse power profile, and an auxiliary pulse duration, the one or more auxiliary pulses including a first auxiliary pulse, a second auxiliary pulse, a third auxiliary pulse, and a fourth auxiliary pulse; Including, The method, wherein a first said applying step and a second said applying step form a seal over a vent hole in the membrane, the seal including a sealing surface having a controlled surface roughness characteristic.

17. 17. The method of claim 16, wherein the first auxiliary pulse, the second auxiliary pulse, the third auxiliary pulse, and the fourth auxiliary pulse are equally spaced around a periphery of the main pulse.

18. 17. The method of claim 16, wherein the first auxiliary pulse, the second auxiliary pulse, the third auxiliary pulse, and the fourth auxiliary pulse have a circular shape.

19. 1. A method for controlling surface roughness during laser sealing of a membrane vent, comprising: applying a main pulse from a main laser to the membrane vent at a first time, the main pulse having a main pulse cross-sectional shape, a main pulse non-steady power profile, and a main pulse duration; and applying one or more auxiliary pulses from one or more auxiliary lasers to the membrane vent hole at a second time later than the first time, the one or more auxiliary pulses having an auxiliary pulse cross-sectional shape, an auxiliary pulse non-steady power profile, and an auxiliary pulse duration; Including, The method, wherein a first said applying step and a second said applying step form a seal over a vent hole in the membrane, the seal including a sealing surface having a controlled surface roughness characteristic.

20. 20. The method of claim 19, wherein the main pulse non-stationary power profile has a triangular shape.

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