Laser sealing and surface micro-bulge control method using discontinuous laser pulses

Abstract

A method for controlling surface dimples during laser sealing of film vents. The method includes applying a laser having a spatial distribution of laser intensity to the film vent to form a seal over the film vent. The seal has a sealing surface. The laser pulse comprises a primary laser pulse region and a secondary pulse region which is later than the primary laser pulse region in time; and a time interval between the primary laser pulse region and the secondary laser pulse region. The primary laser pulse region and / or the secondary pulse region includes a first discontinuous laser pulse and a second discontinuous laser pulse with a first time interval therebetween and / or a third discontinuous laser pulse and a fourth discontinuous laser pulse with a second time interval therebetween. The sealing surface has controlled surface dimpling characteristics.

Description

Technical Field

[0001] The present disclosure relates to pulsed laser irradiation techniques, and more particularly, to laser sealing and surface asperity control methods for laser sealing of membrane vents, wherein the membrane may be formed of silicon, and the methods may use discontinuous laser pulses. Background Art

[0002] A pulsed laser irradiation technique has recently been proposed for sealing vent openings to form a seal zone in an inertial measurement unit (IMU) to capture critical sensor chamber pressure within the device. The vent is formed by deep reactive ion etching of a silicon membrane, beneath which is the device chamber containing a vacuum-dependent micro-electromechanical system (MEMS) sensor. During the laser irradiation process, the seal zone quality may be significantly affected by complex process physics such as Marangoni flow and / or silicon phase changes. For IMU devices, the cured silicon morphology may be problematic. For example, surface micro-protrusions may form rough edges on the surface of the seal zone. Removing such structures may potentially damage the quality of the device. Summary of the invention

[0003] According to one embodiment, a method for controlling surface micro-convexities during laser sealing of a membrane vent is disclosed. The method includes applying a laser having a spatial distribution of laser intensity to the membrane vent to form a seal over the membrane vent. The seal has a sealing surface. The laser pulse includes: a primary laser pulse region and a secondary pulse region that is later in time than the primary laser pulse region; and a time interval between the primary laser pulse region and the secondary laser pulse region. The primary laser pulse region and / or the secondary pulse region include a first discontinuous laser pulse and a second discontinuous laser pulse with a first time interval therebetween and / or a third discontinuous laser pulse and a fourth discontinuous laser pulse with a second time interval therebetween. The sealing surface has controlled surface micro-convexity characteristics.

[0004] According to another embodiment, a method for controlling surface micro-convexities during laser sealing of a membrane vent is disclosed. The method includes applying a laser pulse having a spatial distribution of laser intensity to the membrane vent to form a seal over the membrane vent. The seal has a sealing surface. The laser pulse includes: a primary laser pulse region and a secondary laser pulse region that is later in time than the primary laser pulse region; and a time interval between the primary laser pulse region and the secondary laser pulse region. The primary laser pulse region has a primary laser power, and the secondary laser pulse region has a secondary laser power. The secondary laser power is less than the primary laser power. The sealing surface has controlled surface micro-convexity characteristics.

[0005] According to yet another embodiment, a method for controlling surface micro-asperities during laser sealing of a membrane vent is disclosed. The method includes applying a laser pulse having a spatial distribution of laser intensities to the membrane vent to form a seal over the membrane vent. The seal has a sealing surface. The laser pulse includes a primary laser pulse region and a secondary laser pulse region that is later in time than the primary laser pulse region. The sealing surface has a controlled solidification path, wherein the secondary laser pulse region applies heat to a molten zone formed by the primary laser pulse region, thereby moving molten material from the center of the membrane vent outward therefrom. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1A A cross-sectional view of a device formed with a silicon film is depicted.

[0007] Figure 1B A cutaway perspective isolated view of a portion of a vent within a device is depicted.

[0008] Figure 1C and Figure 1D Accordingly, a schematic side view of a laser irradiation process performed on the vent opening in a molten state and in a solidified state is shown.

[0009] Figure 2 A graph of the density of silicon versus temperature is plotted.

[0010] Figure 3A Power ratio is plotted against time (μs) to depict the laser pulse duration (ie, the length of the top of the curve).

[0011] Figure 3B is a graph depicting the Gaussian distribution of laser intensity.

[0012] Figure 4A Depicted is an image of a vent seal simulated using a computational fluid dynamics (CFD) model.

[0013] Figure 4B The magnitudes (μm) of the simulation results are plotted in comparison with the experimental results for melt depth, melt width, and asperity height.

[0014] Figure 5A Depicted is a plan view of the spatial distribution of laser intensity according to one embodiment.

[0015] Figure 5B Depicted is a graph plotting normalized intensity as a function of normalized spatial distance.

[0016] Figure 5C and Figure 5Dis a graph depicting laser pulse duration distributions for first and second cases with modified laser pulse characteristics.

[0017] Fig.6A1 and Fig.6A2 Depicted are cross-sectional views of a solidification path of a first material after application of a laser heat source according to a first scenario, taken at a first time and a second, later time.

[0018] Figure 6A3 and Figure 6A4 Depicted are cross-sectional views of a second material solidification path after application of a laser heat source according to a second scenario, taken at a first time and a second, later time.

[0019] Fig.6B1 Depicted is an enlarged cross-sectional view of a solidification path of a first material after solidification according to a first condition, taken at a third time.

[0020] Figure 6B2 Depicted is a cross-sectional perspective view of a first material solidification path after application of a laser heat source according to a first scenario, taken at a third time.

[0021] Figure 6B3 Depicted is an enlarged cross-sectional view of a second cure path after cure according to a second scenario, taken at a third time.

[0022] Figure 6B4 Depicted is a cross-sectional perspective view of a second material solidification path after application of a laser heat source according to a second scenario, taken at a third time.

[0023] Fig. 7A Depicted is a graph plotting normalized intensity as a function of normalized spatial distance.

[0024] Figure 7B and Figure 7C is a graph depicting laser pulse duration distributions for first and second cases with modified laser pulse characteristics.

[0025] Fig.7D Depicted is an enlarged cross-sectional view of a solidification path of a first material after solidification according to a first condition, taken at a first time.

[0026] Fig. 7E Depicted is an enlarged cross-sectional view taken at a first time of a second material solidified after solidification according to a second condition.

[0027] Fig. 8A A plan view of the spatial distribution of laser intensity having an elliptical shape with a rectangular cross-section (eg, formed between two concentric ellipses) is depicted.

[0028] Figure 8BDepicted is a plan view of the spatial distribution of laser intensity having a square shape with rounded edges.

[0029] Figure 8C A plan view of the spatial distribution of laser intensity having an octagonal shape is depicted.

[0030] Fig.8D Depicted is a plan view of the spatial distribution of laser intensity with spaced-apart discontinuities in the peripheral direction.

[0031] Fig. 8E Depicted is a plan view of the spatial distribution of laser intensity with spaced-apart discontinuities in the radial direction.

[0032] Figure 8F Depicted is a plan view of the spatial distribution of laser intensity with spaced-apart peripheral discontinuities and spaced-apart radial discontinuities.

[0033] Fig.9A , Fig. 9B and Fig. 9C Depicted is a graph plotting the power ratio as a function of time (μs) for first, second and third cases associated with separate laser pulses for asperity reduction.

[0034] Fig. 10A , Fig. 10B and Fig. 10C Depicted are enlarged cross-sectional views of first, second and third solidifications of silicon material according to first, second and third situations, respectively taken at a first time.

[0035] Fig.11A and Fig. 11B Depicted is a diagram of the position of the secondary laser pulse at its initiation for the second and third cases.

[0036] Fig. 12A , Fig. 12B , Fig. 12C , Fig.12D , Fig.12E and Fig.12F Accordingly, graphs plotting power ratio as a function of time (μs) for first, second, third, fourth, fifth, and sixth cases associated with laser pulses having multiple laser pulse regions (eg, 2 or more) to reduce surface asperities are depicted.

[0037] Fig.13A Depicted is a membrane material defining a vent having a constant diameter along the length of the vent.

[0038] Fig. 13B Depicted is a membrane material defining vents having variable diameters along the length of the vents.

[0039] Fig.14A and Fig. 14BAccordingly, the Fig.13A and Fig. 13B Magnified cross-sectional views of the first and second solidifications of the silicone membrane of the first and second cases, showing the variable diameter vent holes with reduced surface asperities.

[0040] Fig.15A Depicted are cross-sectional views of first, second and third vent holes having first, second and third diameters, respectively, in an upper region of a silicon membrane.

[0041] Fig. 15B A cross section AA' taken at the height of the silicon membrane is depicted.

[0042] Fig. 15C , Fig.15D and Fig.15E Various AA' cross-sectional shapes of vent holes formed according to one or more embodiments are depicted. DETAILED DESCRIPTION

[0043] Embodiments of the present disclosure are described herein. However, it is to be understood that the disclosed embodiments are merely examples, and other embodiments may take various and alternative forms. The drawings are not necessarily drawn to scale; some features may be enlarged or minimized to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as restrictive, but only as a representative basis for teaching those skilled in the art to adopt the embodiments in various ways. As will be understood by those of ordinary skill in the art, the various features illustrated and described with reference to any of the figures may be combined with the features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combination of features shown provides representative embodiments of typical applications. However, for specific applications or embodiments, various combinations and modifications of features consistent with the teachings of the present disclosure may be desired.

[0044] Except where expressly indicated in the examples or otherwise, all numerical quantities in this specification indicating the amount of materials or conditions for reaction and / or use should be understood as modified by the word "about" when describing the broadest scope of the invention. Practice within the stated numerical limits is generally preferred. In addition, unless expressly stated to the contrary: percentages, "parts" and ratio values ​​are all by weight; the term "polymer" includes "oligomers", "copolymers", "terpolymers", etc.; the description of a group or class of materials suitable or preferred for a given purpose in conjunction with the present invention means that any mixture of two or more of the members in the group or class is equally suitable or preferred; the molecular weight provided for any polymer refers to the number average molecular weight; the description of the components in chemical terms refers to the components when added to any combination specified in this specification, and once mixed, chemical interactions between the components of the mixture are not necessarily excluded; the first definition of an abbreviation or other abbreviation applies to all subsequent uses of the same abbreviation in this article, and applies to ordinary grammatical changes of the initially defined abbreviation after mutatis mutandis in detail; and unless expressly stated to the contrary, the measurement of the property is determined by the same technology as previously or later mentioned for the same property.

[0045] The present invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may of course vary. Furthermore, 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.

[0046] 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, reference to a component in the singular is intended to include a plurality of components.

[0047] The term "substantially" may be used herein to describe the disclosed or claimed embodiments. The term "substantially" may modify a value or relative property disclosed or claimed in the present disclosure. In this case, "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.

[0048] In one or more embodiments, a method for reducing surface micro-asperities in a sealing zone in a laser seal of a silicon membrane is disclosed. One or more embodiments rely on a computational fluid dynamics (CFD) model to simulate the laser used in the silicon membrane sealing process. Complex process physics such as surface tension and / or solidification volume shrinkage are considered in the CFD model. Temperature-dependent material properties such as density, conductivity, specific heat, and / or surface tension coefficient can be included in the CFD model to improve simulation accuracy.

[0049] In one or more embodiments, continuous laser pulses with defined primary and secondary pulse regions are used to promote the reduction of surface asperities. The spatial distribution of laser intensity in the primary and / or secondary pulse regions may be annular with a rectangular or Gaussian profile. The power of the secondary laser pulse region may be a certain percentage lower than that of the primary laser pulse region (e.g., in the range of 10% to 60%).

[0050] In one or more embodiments, in a system using first and second discrete and time-separated laser pulse regions, the secondary laser pulses can be applied with an appropriate time interval (e.g., the time value between the primary and supplemental laser pulses) to reduce surface asperities. The surface asperity reduction effect can be enhanced by reducing the time interval. Conversely, the surface asperity reduction effect can be reduced by increasing the time interval.

[0051] In one or more embodiments, variable vent diameter or perimeter may be used to reduce surface asperities.

[0052] Pulsed laser irradiation techniques can be used to seal vent openings in inertial measurement units (IMUs) that are constructed to capture critical sensor chamber pressures within the device. Figure 1A A cross-sectional view of a device 10 formed of a material 12 (eg, a silicon film) is depicted. The material 12 defines a device chamber 14 and a vent 16. The vent 16 terminates at a vent opening 18. The vent 16 extends between the device chamber 14 and the vent opening 18. Figure 1B A cutaway perspective isolated view of a portion of vent 16 within device 10 is depicted. Figure 1B Depicted is a seal 20 configured to seal the vent opening 18. The seal area 18 is formed via a laser irradiation process.

[0053] When the material 12 is a silicon membrane, the vent 16 is formed by chemical etching of the silicon (Si) membrane, beneath which is the device chamber 14 containing a pressure sensitive micro-electromechanical system (MEMS) sensor. During the laser irradiation process, the silicon in the sealing area melts, flows and re-solidifies, during which the seal quality may be significantly affected by complex process physics such as Marangoni flow and Si phase changes. When the molten silicon solidifies, the volume increases, thereby reducing the density, resulting in the formation of peak-shaped surface micro-asperities. For IMU devices, where adjacent devices are built on top of the IMU, the peak-shaped surface micro-asperities may be problematic.

[0054] Figure 1C and Figure 1D Accordingly, a schematic side view of the laser irradiation process performed on the vent opening 18 in the molten state and the solidified state is shown. The laser irradiation process forms a seal 20 having Figure 1D The surface anomaly shown in Figure 1C As shown in FIG. 1 , a laser pulse 24 having a certain pulse duration is used to irradiate the top surface 26 of the silicon membrane adjacent to the vent 16. The material below the irradiated area 28 begins to melt and flow to fill the vent 16. After the laser pulse 24 is turned off, as shown in FIG. Figure 1D As shown in FIG, the molten silicon solidifies and seals the vent 16. However, as Figure 1D As shown in FIG. 1 , surface asperities 22 are formed on the seal 20. The reason for the formation of the surface asperities may be based on the specific physical properties of the silicon material (eg, the silicon material has a liquid density greater than a solid density near its melting temperature).

[0055] Figure 2 A graph of the density of silicon versus temperature is plotted. Figure 2 As shown in , silicon has a liquid density greater than solid density near its melting temperature. Volume contraction and expansion of silicon material during melting and solidification can ultimately contribute to the formation of surface micro-asperities.

[0056] One suggestion involves mechanical removal of the cured silicon micro-asperities. However, mechanical removal may risk failure of the brittle hermetic seal created by sealing the silicon vent holes.

[0057] In one or more embodiments, multi-physics numerical simulation is used to study the laser irradiation and melting of silicon materials for the optimization of process parameters to reduce or eliminate solidified surface micro-protrusions. Thus, one or more embodiments present a novel laser irradiation method or mechanism to reduce or eliminate solidified surface micro-protrusions during IMU manufacturing.

[0058] The multi-physics CFD model characterizes the complex thermal fluid phenomena in the vent sealing process. In one or more embodiments, the model includes a stationary laser irradiation heat source, solid to liquid phase transformation, solidification volume change, surface tension caused by Marangoni flow, vapor pressure and / or temperature-dependent thermal fluid properties. It may also include a vent (e.g., Figure 1B The geometric information of the IMU silicon membrane (the area of ​​interest in the figure) is obtained.

[0059] The validation simulation of the CFD model may be performed using one or more of the following process conditions: (1) laser irradiation power to the material surface; (2) silicon film thickness; (3) film temperature; and (4) vent hole diameter, 10 μm. The laser irradiation power to the material surface may be 15 W to 500 W. The silicon film thickness may be in the range of 50 μm to 300 μm. The vent hole diameter may be 4 μm to 25 μm.

[0060] Figure 3A and Figure 3B Characterization of laser irradiation collected from the laser sealed device is depicted. Figure 3APower ratio is plotted against time (μs) to depict the laser pulse duration (ie, the length of the top of the curve). Figure 3B A graph of normalized intensity as a function of normalized spatial distance is plotted. Figure 3B is a graph depicting the Gaussian distribution of laser intensity.

[0061] Figure 4A An image of a vent seal 50 simulated using a CFD model of an embodiment is depicted. The vent seal 50 includes a seal vent 52. The vent seal 50 includes a melt depth D, a melt width W, and a micro-asperity height H. Figure 4B The comparison of the simulation results (μm) with the experimental results of melt depth, melt width and micro-asperity height is depicted. Figure 4B As shown in Figure 4A The simulated curing characteristics of the molten-salt hydrate are in reasonable agreement with experimental measurements. Figure 4A and Figure 4B The CFD model of one or more embodiments can be used to characterize the formation of surface micro-asperities during laser sealing. The CFD model can also be used to investigate and optimize the sealing quality.

[0062] In one or more embodiments, the laser shot shape and pulse duration may be optimized to reduce surface asperities. The laser shot shape may be an annular shape (eg, formed between two concentric circles) with a laser intensity distribution having a rectangular cross-section. Figure 5A A plan view of a laser intensity spatial distribution 100 is depicted according to one embodiment. Figure 5A The dashed line 102 indicates that Figure 5B The graph shows the normalized spatial distance along the x-axis and Figure 5A The spatial distribution of the laser intensity intercepted by the dotted line 102. For example, in the laser irradiation area, in the annular shape formed between two concentric circles, it shows the shape of a rectangular cross section. The normalized spatial distance is -1 at the left side of the dotted line 102 and extends to +1 at the right side of the dotted line 102. Figure 5B A graph is depicted that plots the normalized intensity as a function of the normalized spatial distance. As can be seen, Figure 5B Rectangular intensities between -0.5 and -0.6 and between 0.5 and 0.6 are shown.

[0063] In one or more embodiments, modification of one or more laser pulse characteristics of the annular rectangular cross-section laser intensity profile may result in a reduction in surface asperities. Figure 5C and Figure 5D FIG. 4 is a graph depicting the laser pulse duration distribution for the first and second cases with modified laser pulse characteristics. Figure 5C and Figure 5DAs shown, although the first and second cases have the same laser pulse duration for the primary laser pulses 150 and 152 respectively, the laser intensity distributions of the first and second cases are different, wherein the secondary laser pulse 154 has a smaller power.

[0064] Fig.6A1 and Fig.6A2 Depicted are cross-sectional views of a solidification path of a first material after application of a laser heat source according to a first situation, taken at a first time and a later second time. Dashed line 200 indicates the center of symmetry of the vent hole of the first situation. Reference numeral 202 indicates the vent hole at the first and second times. Region 204 indicates a first region above the melting point of the silicon material at the first time. Region 206 indicates a second region above the melting point of the silicon material at the second time. Region 208 indicates a first region below the melting point of the silicon material at the first time. Region 210 indicates a second region below the melting point of the silicon material at the second time. Fig.6A1 and Fig.6A2 As shown by the arrows in , when the silicon material solidifies, the second region above the melting point has a smaller area than the first region above the melting point, and when the silicon material solidifies, the first region below the melting point has a smaller area than the second region below the melting point. The arrows indicate the solidification path of the silicon material.

[0065] Figure 6A3 and Figure 6A4 Depicted are cross-sectional views of a second material solidification path after application of a laser heat source according to a second situation, taken at a first time and a later second time. Dashed line 212 indicates the center of symmetry of the vent hole for the second situation. Reference numeral 214 indicates the vent hole at the first and second times. Region 216 indicates a first region above the melting point of the silicon material at the first time. Region 218 indicates a second region above the melting point of the silicon material at the second time. Region 210 indicates a first region below the melting point of the silicon material at the first time. Region 212 indicates a second region below the melting point of the silicon material at the second time. Fig.6A1 and Fig.6A2 As shown by the arrows in , when the silicon material solidifies, the second region above the melting point has a smaller area than the first region above the melting point, and when the silicon material solidifies, the first region below the melting point has a smaller area than the second region below the melting point. The arrows indicate the solidification path of the silicon material.

[0066] from Fig.6A1 , Fig.6A2 , Figure 6A3 and Figure 6A4, it is observed that the first case follows an outside-to-center solidification path relative to the top surface of the silicon material, while the second case follows a center-to-outside solidification path relative to the top surface of the silicon material. The energy input from the secondary laser pulse contributes to the change in the solidification path of the second case. The addition of the secondary laser pulse input creates a high temperature zone around the periphery of the molten pool, which causes the peripheral area of ​​the molten pool to cool more slowly than the central area. The different types of solidification paths for the first and second cases result in completely different surface morphologies. Fig.6A2 The surface peak 224 of the second case is significantly reduced. Figure 6A4 This significant reduction can be in the range of 20% to 90%.

[0067] Fig.6B1 Depicted is an enlarged cross-sectional view of a solidification path of a first material after solidification according to a first condition, taken at a third time. Figure 6B2 Depicted is a cross-sectional perspective view of a first material solidification path after application of a laser heat source according to a first scenario, taken at a third time. Fig.6B1 and Figure 6B2 Region 226 is a melted and fully solidified region (eg, the material has gone through the entire melting and solidification process). Fig.6B1 Region 228 shows a portion of the fully cured area representing the first surface asperities. Figure 6B3 Depicted is an enlarged cross-sectional view of a second material solidification path after solidification according to a second condition, taken at a third time. Figure 6B4 Depicted is a cross-sectional perspective view of a second material solidification path after application of a laser heat source according to a second scenario, taken at a third time.

[0068] Figure 6B3 and Figure 6B4 The region 230 is a melted and fully solidified region. Figure 6B3 The area 232 shows a portion of the fully cured area representing the second surface asperities. The height of the second surface asperities is significantly less than the height of the first surface asperities.

[0069] In another embodiment, the laser irradiation shape may be a ring-shaped laser intensity distribution with a Gaussian profile. Fig. 7A A graph is depicted that plots the normalized intensity as a function of the normalized spatial distance. As can be seen, Fig. 7A Gaussian shaped profiles between approximately -0.9 and -0.4 and between approximately 0.4 and 0.9 are shown. Fig. 7A The normal distribution of the normalized laser intensity with respect to each Gaussian-shaped profile is shown.

[0070] In one or more embodiments, modification of one or more laser pulse characteristics of a circular Gaussian profile laser intensity distribution may result in a reduction in surface asperities. Figure 7B and Figure 7CFIG. 4 is a graph depicting the laser pulse duration distribution for the first and second cases with modified laser pulse characteristics. Figure 7B and Figure 7C As shown, while the first case uses only the primary laser pulse, the second case uses a secondary laser pulse having a smaller power than the primary laser pulse.

[0071] Fig.7D Depicted is an enlarged cross-sectional view of a solidification path of a first material after solidification according to a first condition, taken at a first time. Fig. 7E Depicted is an enlarged cross-sectional view taken at a first time of a second material solidified after solidification according to a second condition. Fig.7D Region 250 is a melted and fully solidified region in the first case (eg, the material has gone through the entire melting and solidification process). Fig. 7E The region 252 is a melted and completely solidified region in the second case. Fig.7D Region 254 shows the portion of the fully cured area representing the first surface asperities (ie, the area above line 255). Fig. 7E Region 256 shows the portion of the fully cured area representing the second surface asperities (ie, the area above line 257). The height of the second surface asperities is significantly less than the height of the first surface asperities. This significant reduction may be in the range of 20% to 90%.

[0072] Although Figure 5A An annular laser intensity profile configured to reduce surface asperities is depicted, but one or more other embodiments may include a different laser intensity profile shape. Fig. 8A A plan view of a laser intensity spatial distribution 260 having an elliptical shape (e.g., formed between two concentric ellipses) with a rectangular cross-section is depicted. The elliptical shape has a major axis and a minor axis. In one or more embodiments, the length of the major axis and the length of the minor axis differ by one or both of the following values: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, or 20%. Figure 8B A plan view of the laser intensity spatial distribution 262 is depicted having a square shape with rounded edges. Other rectangular shapes are contemplated in one or more embodiments. Other polygons may also be used as the shape of the laser intensity spatial distribution. For example, Figure 8C A plan view of a laser intensity spatial distribution 264 having an octagonal shape is depicted. Fig. 8A , Figure 8B and Figure 8C The shaded area on the graph indicates the laser energy.

[0073] Although Figure 5A , Fig. 8A , Figure 8B and Figure 8C A continuous distribution of laser energy is depicted, but in other embodiments, the distribution of laser energy may be discontinuous. Fig.8D , Fig. 8E and Figure 8F Depicted is a discontinuous distribution of laser energy in accordance with one or more embodiments. Fig.8D A plan view of a laser intensity spatial distribution 266 having spaced apart discontinuities 268 in a peripheral direction is depicted. The spaced apart discontinuities 268 may be equally spaced; orderly, unequally spaced; randomly, unequally spaced, or a combination thereof. Fig. 8E A plan view of a laser intensity spatial distribution 270 having spaced apart discontinuities 272 in a radial direction is depicted. The spaced apart discontinuities 272 may be equally spaced; orderly, unequally spaced; randomly, unequally spaced; or a combination thereof. Figure 8F A plan view of a laser intensity spatial distribution 274 having spaced-apart peripheral discontinuities 276 and spaced-apart radial discontinuities 278 is depicted. Fig.8D , Fig. 8E and Figure 8F The shaded area on indicates the laser energy. Any of the discontinuous laser energy profiles may be used with any of the laser profile shapes disclosed in one or more embodiments.

[0074] In one or more embodiments, the laser energy spatial distribution is fixed (e.g., fixed in the x, y, and z directions). In other embodiments, the laser energy spatial distribution (e.g., primary and / or secondary pulses) may have movement (e.g., radial movement in the x and y directions). The movement distance may be limited to a certain offset percentage relative to the measurement result of the laser distribution shape. For example, the movement distance may be an offset percentage of one of the following values ​​or within the range of any two of the following values: 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, and 10%. For example, the movement distance may be equal to or less than 10% of the laser ring radius. Figure 8G A top view of the laser intensity spatial distribution 280 is depicted, with arrows 282 depicting the magnitude of the shift in the radial direction.

[0075] One or more of the above embodiments demonstrates that continuous laser pulses with defined primary and secondary pulse regions promote asperity reduction. In another embodiment, two or more separate laser pulses can reduce asperities. Any of the laser spatial distribution shape and continuous / intermittent can be applied to embodiments utilizing two or more separate laser pulses. Fig.9A , Fig. 9B and Fig. 9CDepicted is a graph plotting the power ratio as a function of time (μs) for first, second and third cases associated with separate laser pulses for asperity reduction. Fig.9A The primary pulse region is shown and there is no secondary pulse region. Fig. 9B A primary pulse region and a secondary pulse region are shown with a first interval therebetween. Fig. 9B As shown in , the primary pulse region has a shorter duration than the secondary pulse region, and the primary pulse region has a higher power than the secondary pulse region. Fig. 9C The primary pulse region and the secondary interval therebetween are shown. Fig. 9C As shown in , the primary pulse region has a shorter duration than the secondary pulse region, and the primary pulse region has a higher power than the secondary pulse region. The second interval is longer than the first interval.

[0076] Fig. 10A , Fig. 10B and Fig. 10C Depicted are enlarged cross-sectional views of first, second and third solidifications of silicon material according to first, second and third situations, respectively taken at a first time.

[0077] Fig. 10A Region 300 is a melted and fully solidified region in the first case (eg, the material has gone through the entire melting and solidification process). Fig. 10B The region 302 is a melted and completely solidified region in the second case. Fig. 10C The region 304 is the melted and completely solidified region of the third case. Fig. 10A Region 306 shows the portion of the fully cured area representing the first surface asperities (ie, the area above line 312). Fig. 10B Region 308 shows the portion of the fully cured area representing the second surface asperities (ie, the area above 314). Fig. 10C The area 310 shows the portion of the fully cured zone representing the third surface micro-protrusions. The height of the second surface micro-protrusions can be significantly less than the height of the first and third surface micro-protrusions. The significant reduction can be in the range of 20% to 90%.

[0078] If through Fig. 10B and Fig. 10C It can be seen that the secondary pulse region separated from the primary pulse region reduces the height of the surface asperities. Fig. 9B The time interval shown in Fig. 10C The time interval shown in Fig. 10B Compared with the time interval Fig. 10C In one or more embodiments, the time interval between the primary laser pulse and the secondary laser pulse is carefully selected, because a relatively large time interval can reduce the reduction of surface asperities. Fig. 10B In the second case shown in FIG, when the secondary laser pulse is started, the secondary laser pulse is applied to the molten zone of the silicon material. Fig. 10C In the third case shown in FIG. 1 , due to the longer cooling period (e.g., at least twice as long), the secondary laser pulse is applied within the resolidified region of the silicon material when the secondary laser pulse is activated. Therefore, it has minimal effect on the reduction of the micro-asperity height.

[0079] Fig.11A and Fig. 11B Depicted is a diagram of the position of the secondary laser pulse at its start for the second and third cases. Fig.11A As shown in FIG. 1 and related to the second case, when the secondary laser pulse 350 is activated, the secondary laser pulse 350 is applied to the molten zone 352 of the silicon material. The laser irradiation position is at the edge of the molten zone 352, thereby moving the molten material from the center of the molten zone 352 to the edge. The movement of the molten material reduces the surface micro-asperities. Fig. 11B As shown in FIG. 3 and in relation to the third case, when the secondary laser pulse 354 is initiated, the secondary laser pulse 354 is applied outside the melt zone 356, but instead is applied in the resolidified zone. This not only does not reduce the asperities by irradiation of the melt zone, but may also result in the generation of additional surface asperities at the location of the secondary laser pulse 354 outside the melt zone 356.

[0080] The time interval may also be expressed as a ratio between the duration of the primary laser pulse and the time interval. In one or more embodiments, the ratio of the time interval to the duration of the primary laser pulse may be any one of the following ratios or within a range of any two of the following ratios: 0.01:1, 0.1:1, 0.2:1, 0.3:1, 0.4:1, 0.5:1, and 0.6:1. As another ratio associated with one or more embodiments, the ratio of the secondary laser pulse to the primary laser pulse may be any one of the following ratios or within a range of any two of the following ratios: 8:1, 7:1, 6:1, 5:1, 4:1, 3:1, 2.5:1, or 2:1.

[0081] In one or more embodiments, multiple continuous or discontinuous laser pulses (eg, 2 or more) with defined pulse areas may be used to reduce surface asperities. Fig. 12A , Fig. 12B , Fig. 12C , Fig.12D , Fig.12E and Fig.12FAccordingly, a graph plotting the power ratio as a function of time (μs) for the first, second, third, fourth, fifth, and sixth cases of laser pulses having multiple pulse regions (e.g., 2 or more) to reduce surface micro-asperities is depicted. In one embodiment, the initial laser pulse region may include multiple discrete laser pulses having the same laser power (e.g., 100% laser power) with relatively short time intervals between consecutive laser pulses (e.g., about 1% to 2% per time interval relative to the entire duration of the initial laser pulse region). The multiple discrete laser pulses may also have different durations. Fig. 12A A primary laser pulse region with multiple discrete laser pulses is shown. In another embodiment, a secondary laser pulse region may include multiple discrete laser pulses with the same laser power (e.g., 25% laser power) or different laser powers, with relatively short time intervals between consecutive laser pulses (e.g., about 1% to 2% per time interval relative to the entire duration of the secondary laser pulse region). Fig. 12B A secondary laser pulse region having multiple discrete laser pulses is shown. In yet another embodiment, both the primary and secondary laser pulse regions may have multiple discrete laser pulses, such as Fig. 12C as shown in .

[0082] In certain embodiments, the plurality of discrete laser pulses may have different laser power levels and / or durations. Fig.12D A primary laser pulse region comprising a plurality of discrete laser pulses having varying power levels is shown. Fig.12E A secondary laser pulse region is shown that includes multiple discrete laser pulses having varying power levels. Fig.12F Both primary and secondary laser pulse regions are shown with multiple discrete laser pulses having varying power levels. The laser power level variation may vary by any of the following values ​​or within a range of any two of the following values: 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, 100%, 101%, 10 7%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59% and 60%.

[0083] In one or more embodiments, variable vent diameters may be used to mitigate surface asperities. Figure 5D A second case is disclosed wherein the laser pulse is a ring shape with primary and secondary pulses. Either continuous or discontinuous shaped laser profiles may be used in accordance with the variable vent diameter embodiment.

[0084] Fig.13A and Fig. 13B Schematic diagrams depicting first and second cases of laser sealing of a vent hole in conjunction with a silicon membrane. Fig.13A Depicted is a film material 400 defining a vent 402 having a constant diameter along the length of the vent 402 . Fig. 13B Depicted is a film material 404 defining a vent 406 having a variable diameter along the length of the vent 408. The vent 406 includes a first diameter section 408 and a second diameter section 410. The first diameter section 408 extends between the vent opening 412 and the second diameter section 410. The second diameter section 410 extends between the first diameter section 408 and a device chamber (not shown). The transition between the first diameter section 408 and the second diameter section 410 forms a shoulder section 414 that is cylindrical in shape and has a width that is the difference between the diameters of the first diameter section 408 and the second diameter section 410. The first diameter section 408 is a percentage larger than the second diameter section 410. The percentage may be any one of the following values ​​or within the range of any two of the following values: 30%, 35%, 40%, 45%, 50%, and 55%. The length of the first diameter section 408 may be equal to the diameter of the first diameter section 408. In another embodiment, the enlarged section of the vent may taper from a larger diameter to the diameter of the base diameter vent portion.

[0085] Fig.14A and Fig. 14B Accordingly, the Fig.13A and Fig. 13B Magnified cross-sectional views of the first and second solidifications of the silicone membrane of the first and second cases, showing the variable diameter vent holes with reduced surface asperities. Fig.14A Region 450 is a melted and fully solidified region of the first case (eg, the material has gone through the entire melting and solidification process). Fig. 14B The region 452 is a melted and completely solidified region in the second case. Fig.14A Region 454 shows the portion of the fully cured area representing the first surface asperities (ie, the area above line 456 having a height depicted by arrow 458). Fig. 14BThe area 460 of the fully solidified region shows the portion of the second surface asperities (i.e., the area above the line 462 having a height depicted by arrow 464). The height of the second surface asperities is less than the height of the first surface asperities, thereby supporting the enlarged diameter portion adjacent to the vent opening to accommodate additional molten material and to reduce the surface asperities upon solidification. The reduction may be in the range of 15% to 30%.

[0086] In one or more embodiments, two or more vent holes with varying diameters may be employed to reduce surface asperities. Fig.15A A cross-sectional view of a first vent 500, a second vent 502, and a third vent 504 having first, second, and third diameters, respectively, in an upper region of a silicon membrane 506 is depicted. The first vent 500, the second vent 502, and the third vent 504 are configured to create a volume for containing a cured material under direct laser irradiation. The first, second, and third diameters may be greater than the original vent diameter (e.g., diameter 508) by any of the following percentages or within the range of any two of the following percentages: 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, 145%, and 150%. The original vent diameter may be any one of the following values ​​or within the range of any two of the following values: 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, and 20 μm. The total height of all vents may be any one of the following values ​​or within the range of any two of the following values: 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, and 25 μm.

[0087] The cross-section of the vent hole formed into the silicon membrane at the height of the silicon membrane may have a substantially circular shape. Fig. 15B A cross section AA′ taken at the height of the silicon membrane 506 is depicted. Fig. 15C , Fig.15D and Fig.15E Various AA' cross-sectional shapes of vent holes formed according to one or more embodiments are depicted. Fig. 15C An elliptical shape 510 (eg, a substantially elliptical shape) is depicted. Fig.15D A square shape 512 (eg, a substantially square shape with rounded corners) is depicted. Fig.15E A rectangular shape 514 (eg, a substantially rectangular shape) is depicted.

[0088] In one or more embodiments, a CFD model is used to simulate a laser silicon membrane sealing process for an IMU sensor. The CFD model takes into account process physics such as surface tension and solidification volume shrinkage. In addition, temperature-dependent material properties such as density, conductivity, specific heat, and surface tension coefficient are considered in the CFD model for accurate simulation.

[0089] As shown in one or more embodiments above with respect to continuous laser pulses, the combination of a primary laser pulse and a secondary laser pulse can reduce the height of the surface micro-asperities. The spatial intensity distribution can be annular with a rectangular or Gaussian profile. The power of the secondary laser power can be a certain percentage lower than the power of the primary laser source. The percentage can be in the range of 20% to 60%.

[0090] In one or more embodiments utilizing continuous laser pulses, a supplemental (e.g., secondary) laser pulse may reduce the surface asperity height. The laser intensity spatial distribution may be annular with a rectangular or Gaussian profile (or other laser shapes as described herein). The supplemental laser power may be lower than the primary laser power, for example, 10% to 60%.

[0091] In one or more embodiments, two separate laser pulses may be utilized, wherein applying a supplemental laser pulse with an appropriate time interval (time value between the primary laser pulse and the supplemental laser pulse) may help reduce the surface asperity height. However, the greater the time interval, the smaller the surface asperity height reduction effect. The primary and secondary laser pulses may include several discrete laser shots.

[0092] In one or more embodiments, a variable vent diameter configuration may be used to reduce surface asperity height. In one or more embodiments, multiple vents with different diameters may help reduce surface asperities, and the vent cross-section may not have a perfectly circular shape.

[0093] The following applications are related to the present application: U.S. patent application serial number 17 / 863659 (RBPA0386PUS) filed on July 13, 2022 and U.S. patent application serial number 17 / 863669 (RBPA0396PUS) filed on July 13, 2022, each of which is incorporated herein by reference in its entirety.

[0094] The processes, methods or algorithms disclosed herein may be delivered to / implemented by a processing device, a controller or a computer, which may include any existing programmable electronic control unit or a dedicated electronic control unit. Similarly, these processes, methods or algorithms can be stored as data and instructions that can be executed by a controller or a computer in many forms, including but not limited to information permanently stored on non-writable storage media such as ROM devices, and information that can be modified and stored on writable storage media such as floppy disks, tapes, CDs, RAM devices, and other magnetic and optical media. These processes, methods or algorithms may also be implemented in software executable objects. Alternatively, these processes, methods or algorithms may be implemented 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 combinations of hardware, software, and firmware components.

[0095] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms covered by the claims. The terms used in the specification are descriptive rather than restrictive terms, and it is understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of the various embodiments can be combined to form other embodiments of the present invention that may not be explicitly described or illustrated. Although various embodiments can be described as providing advantages or being superior to other embodiments or prior art embodiments with respect to one or more desired characteristics, it is preferred that one or more features or characteristics can be compromised to achieve the desired overall system properties, depending on the specific application and implementation. These properties 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, in any embodiment described as less desirable than other embodiments or prior art embodiments with respect to one or more characteristics, these embodiments do not exceed the scope of the present disclosure and may be desirable for a specific application.

Claims

1. A method for controlling surface asperities during laser sealing of a membrane vent, the method comprising: A laser with a spatial distribution of laser intensity is applied to the membrane vent to form a seal above the membrane vent, wherein the seal has a sealing surface, the laser pulse includes: a primary laser pulse region and a secondary pulse region that is later in time than the primary laser pulse region; and a time interval between the primary laser pulse region and the secondary laser pulse region, the primary laser pulse region and / or the secondary pulse region include a first discontinuous laser pulse and a second discontinuous laser pulse with a first time interval therebetween and / or a third discontinuous laser pulse and a fourth discontinuous laser pulse with a second time interval therebetween, and the sealing surface has controlled surface micro-convexity characteristics.

2. The method according to claim 1, wherein: The initial laser pulse region includes a first discontinuous laser pulse region and a second discontinuous laser pulse region, the initial laser pulse region has an initial pulse duration, and the first time interval has a first time interval duration, which is 1% to 2% of the initial pulse duration.

3. The method according to claim 1, wherein: The initial laser pulse region includes a first discontinuous laser pulse region and a second discontinuous laser pulse region, the first discontinuous pulse region has a first discontinuous pulse laser power, and the second discontinuous pulse region has a second discontinuous pulse laser power, and the first discontinuous pulse power and the second discontinuous pulse power are not equal.

4. The method according to claim 1, wherein: The secondary laser pulse region includes a third discontinuous laser pulse region and a fourth discontinuous laser pulse region, the secondary laser pulse region has a secondary pulse duration, and the second time interval has a second time interval duration that is 1% to 2% of the secondary pulse duration.

5. The method according to claim 1, wherein: The secondary laser pulse region includes a third discontinuous laser pulse region and a fourth discontinuous laser pulse region, the third discontinuous pulse region has a third discontinuous pulse laser power, and the fourth discontinuous pulse region has a fourth discontinuous pulse laser power, and the third discontinuous pulse power and the fourth discontinuous pulse power are not equal.

6. The method according to claim 1, wherein: The primary laser pulse region has a primary laser power, and the secondary laser pulse region has a secondary laser power, which is less than the primary laser power.

7. The method according to claim 6, wherein: The secondary laser power is 10% to 60% smaller than the primary laser power.

8. The method according to claim 1, wherein: The controlled surface asperity characteristic is reduced surface asperity height.

9. A method for controlling surface asperities during laser sealing of a membrane vent, the method comprising: A laser pulse having a spatial distribution of laser intensity is applied to the membrane vent to form a seal above the membrane vent, wherein the seal has a sealing surface, the laser pulse comprising: a primary laser pulse region and a secondary laser pulse region that is later in time than the primary laser pulse region; and a time interval between the primary laser pulse region and the secondary laser pulse region, the primary laser pulse region having a primary laser power, and the secondary laser pulse region having a secondary laser power, the secondary laser power being less than the primary laser power, and the sealing surface having a controlled surface micro-convexity characteristic.

10. The method according to claim 9, wherein: The initial laser pulse region has an initial pulse duration, and the time interval has a time interval duration, and a ratio of the time interval duration to the initial pulse duration is 0.01:1 to 0.6:

1.

11. The method according to claim 10, wherein: The ratio of the time interval duration to the initial pulse duration is 0.2:1 to 0.6:

1.

12. The method according to claim 9, wherein: The primary laser pulse region has a primary pulse duration, and the secondary laser pulse region has a secondary pulse duration, and a ratio of the secondary pulse duration to the primary pulse duration is 8:1 to 2:

1.

13. The method according to claim 9, wherein: The secondary laser power is 10% to 60% smaller than the primary laser power.

14. The method according to claim 9, wherein: The controlled surface asperity characteristic is reduced surface asperity height.

15. The method according to claim 9, wherein: The laser intensity spatial distribution is an annular laser intensity distribution, an elliptical laser intensity distribution and a polygonal laser intensity distribution.

16. The method according to claim 9, wherein: The laser intensity spatial distribution in the laser irradiation area formed between the first circle and the second circle or the first ellipse and the second ellipse exhibits a shape having a rectangular cross section or a Gaussian cross section.

17. The method according to claim 9, wherein: The laser intensity spatial distribution has spaced-apart discontinuities.

18. The method according to claim 17, wherein: The laser intensity spatial distribution includes peripheral discontinuities and / or radial discontinuities.

19. The method according to claim 9, wherein: The membrane vents are silicon membrane vents.

20. A method for controlling surface asperities during laser sealing of a membrane vent, the method comprising: A laser pulse having a spatial distribution of laser intensity is applied to the membrane vent to form a seal above the membrane vent, the seal having a sealing surface, the laser pulse comprising a primary laser pulse region and a secondary laser pulse region that is later in time than the primary laser pulse region, and the sealing surface having a controlled solidification path, wherein the secondary laser pulse region applies heat to a molten zone formed by the primary laser pulse region, thereby moving molten material from the center of the membrane vent outward therefrom.

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