Laser sealing method for closing vent hole of micromechanical device

Abstract

A method of sealing a vent of a micromechanical device. The vent hole leads to the chamber of the containing device. A first laser pulse is applied to a vent of a substrate of a micromechanical device for a first time period. The first laser pulse has a first laser intensity spatial distribution. Thereafter, a second laser pulse is applied to the vent for a second period of time. The second laser pulse has a second laser intensity spatial distribution different from the first laser intensity spatial distribution. The second laser pulse may be applied at a different time than the first laser pulse.

Description

Technical Field

[0001] The present disclosure relates to laser sealing methods for closing vent holes of micromechanical devices.In some specific embodiments, the laser applies multiple separate laser profiles at different times. Background Art

[0002] Various micromechanical devices (e.g., microelectromechanical systems (MEMS), inertial measurement units (IMUs), etc.) include vent openings leading to a chamber containing a packaged device. In recent years, pulsed laser irradiation techniques have been utilized to seal the vent openings. The technique includes sealing the vent openings to encapsulate a gas and a critical pressure within a device chamber of the micromechanical device. Summary of the invention

[0003] According to one embodiment, a method of sealing a vent of a micromechanical device includes applying a first laser pulse to a vent of a substrate of the micromechanical device during a first time period, wherein the first laser pulse has a first laser intensity spatial distribution, and wherein the vent leads to a chamber configured to accommodate the device; and then applying a second laser pulse to the vent during a second time period, wherein the second laser pulse has a second laser intensity spatial distribution that is different from the first laser intensity spatial distribution.

[0004] According to one embodiment, a method for sealing a vent of a micromechanical device includes: providing a micromechanical device having a substrate, the substrate having an upper surface, and the substrate defining a vent leading to a chamber configured to accommodate the device; applying a first laser pulse to the substrate at the vent during a first time period, wherein the first laser pulse has a first laser intensity spatial distribution having a first laser pulse intensity at a center of the first laser pulse; and applying a second laser pulse to the substrate at the vent during a second time period, wherein the second laser pulse has a second laser intensity spatial distribution different from the first laser intensity spatial distribution, and wherein the second laser intensity spatial distribution has a second laser pulse intensity at the center of the second laser pulse that is less than the first laser pulse intensity at the center of the first laser pulse.

[0005] According to one embodiment, a method of controlling surface roughness during laser sealing of a vent includes: applying a first laser pulse to the vent of a substrate, wherein the first laser pulse has a first laser intensity spatial distribution; and applying a second laser pulse to the vent, wherein the second laser pulse has a second laser intensity spatial distribution different from the first laser intensity spatial distribution. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 A cross-sectional view depicting the pulsed laser irradiation technique used to seal the vent opening of a micromechanical device.

[0007] Figure 2 Depicted in Figure 1 Cross-sectional view of the sealed vent hole after pulsed laser irradiation technique.

[0008] Figure 3A A laser pulse having a Gaussian or "bell curve" shaped spatial distribution of laser intensity is illustrated according to one embodiment. Figure 3B The diagram shows a method according to an embodiment Figure 3A The time at which the laser pulse is applied.

[0009] FIG. 4 illustrates a pulsed laser irradiation technique in which two different laser pulses are applied, wherein Figure 4A illustrates the laser intensity spatial distribution of a Gaussian-shaped first pulse according to one embodiment, and Figure 4B The laser intensity spatial distribution of a doughnut-shaped second pulse according to one embodiment is illustrated. Figure 4C The diagram shows a method according to an embodiment Figures 4A-4B The two laser pulses are applied at the same time.

[0010] Figure 5A The diagram shows the use of Figure 3A-3B A cross-sectional view of the sealing portion formed by the laser irradiation process of the laser intensity spatial distribution, and Figure 5B The diagram shows the use of Figures 4A-4C Cross-sectional view of the sealing portion formed by the laser irradiation process showing the spatial distribution of laser intensity.

[0011] Fig. 6A Pictured Figure 5A The stress levels at various areas of the seal, and Figure 6B Pictured Figure 5B The stress levels at various areas of the seal.

[0012] FIG. 7 illustrates a pulsed laser irradiation technique in which two different laser pulses are applied, wherein Fig. 7A illustrates the spatial distribution of laser intensity of a top-hat shaped first pulse according to one embodiment, and Figure 7B The laser intensity spatial distribution of a doughnut-shaped second pulse according to one embodiment is illustrated.

[0013] FIG8 illustrates a pulsed laser irradiation technique in which two different laser pulses are applied, wherein Fig. 8A illustrates the spatial distribution of laser intensity of a top-hat shaped first pulse according to one embodiment, and Figure 8B An illustration of the laser intensity spatial distribution of a volcano-shaped second pulse according to one embodiment.

[0014] FIG. 9 illustrates a pulsed laser irradiation technique in which two different laser pulses are applied, wherein Fig. 9Aillustrates the spatial distribution of laser intensity of a volcano-shaped first pulse according to one embodiment, and Fig. 9B The laser intensity spatial distribution of a doughnut-shaped second pulse according to one embodiment is illustrated.

[0015] FIG. 10 illustrates a pulsed laser irradiation technique in which two different laser pulses are applied, wherein Fig. 10A illustrates the spatial distribution of laser intensity of a volcano-shaped first pulse according to one embodiment, and Fig. 10B The spatial distribution of laser intensity of second pulses of different volcano shapes according to one embodiment is illustrated.

[0016] Fig.11 A schematic diagram of first and second lasers with respect to a vent hole is illustrated according to one embodiment. DETAILED DESCRIPTION

[0017] 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 exaggerated or minimized to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as limiting, but merely 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 of the 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 expected.

[0018] As used herein, "a", "an", and "the" refer to both the singular and the plural, unless the context clearly indicates otherwise. For example, a "processor" programmed to perform various functions refers to one processor programmed to perform each function, or more than one processor programmed together to perform each of the various functions.

[0019] The terms "substantially" or "approximately" may be used herein to describe disclosed or claimed embodiments. The terms "substantially" or "approximately" may modify a numerical value or relative property disclosed or claimed in the present disclosure. In this case, "substantially" or "approximately" 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.

[0020] Various micromechanical devices (e.g., microelectromechanical systems (MEMS), inertial measurement units (IMUs), etc.) include vent openings leading to a chamber containing a packaged device. In recent years, pulsed laser irradiation techniques have been used to seal the vent openings. These techniques seal the vent openings to encapsulate gases and critical pressures within the device chamber of the micromechanical device. For example, Figure 1 An example of a micromechanical device 10 sealed according to these techniques is illustrated. The micromechanical device 10 includes a substrate 12, such as silicon or other materials commonly used for integrated circuits in micromechanical devices. The term "substrate" may also refer to a film or layer of one or more layers of other materials (e.g., polysilicon, silicon dioxide, etc.) stacked above an underlying material (e.g., silicon). The substrate 12 is formed with a chamber 14, also referred to as a cavity or recess. The chamber 14 houses or encapsulates a device 16, which may be any type of MEMS device or IMU, such as an accelerometer, gyroscope, temperature sensor, pressure sensor, etc. The substrate 12 is also formed with a vent 18 that allows initial air or gas communication between the chamber 14 and the environment outside the micromechanical device 10 until it is sealed. The vent 18 and / or the chamber 14 may be formed in a layer or material above the base substrate, and unless otherwise specified, these layers should be included as part of the term "substrate." Sealing the vent hole 18 can prevent the gas or external environmental factors from affecting the gas or vacuum within the chamber 14. To seal the vent hole 18, laser irradiation is used, wherein a laser beam 20 is directed to the surface above the vent hole 18. This causes some of the material of the substrate 12 above the vent hole 18 to melt, thereby producing a seal 22 formed by the melt of the substrate 12.

[0021] However, this approach often leaves the surface rough. For example, Figure 2 Shows the laser irradiation process after completion Figure 1 As can be seen here, the resulting seal 22 (which is a solidified melt of the material of the substrate 12) includes surface roughness 24, which is high spots or bumps on the upper surface 26 of the seal 22. This surface roughness 24 may be undesirable in some applications because, for example, it may come into contact with an opposing surface when the micromechanical device 10 is assembled to another component.

[0022] Many laser irradiation processes typically use Figure 3A-3B Laser pulse profile shown. Figure 3A The diagram shows a Gaussian (or "bell curve") distribution of laser intensity, with increased laser intensity at or near the center of the vent and decreasing intensity away from the vent center. This may be referred to as a Gaussian laser intensity spatial distribution. Figure 3A The distribution shown in is a cross section relative to the substrate, such as Figure 1-2The laser pulse profile can therefore be referred to as a Gaussian shape or Gaussian cross section. Figure 3B As shown, the laser pulse is given a single, constant power or intensity throughout its application as shown by the flat line from time step 0 to time step 1. Each time step may be a number of nanoseconds, milliseconds, microseconds, etc., depending on the application.

[0023] Several solutions have been proposed to improve the laser irradiation process to eliminate or at least improve the presence of surface roughness. For example, U.S. Patent Application No. 17 / 973,217, filed on October 25, 2022, entitled "Laser Sealing Method for Closing Vent Holes of Micromechanical Devices" (the entire contents of which are incorporated herein by reference) relates to a method for sealing vent holes by applying laser pulses to grooves offset from a substrate. While this is a viable method for removing or reducing surface roughness for many applications, it is not perfect for all applications.

[0024] Thus, the present disclosure provides various embodiments for further improving the laser irradiation process to further reduce or eliminate the presence of any surface roughness. In some embodiments, for a single vent sealing process, the laser pulse profile varies over time. Various laser pulse profiles are disclosed that, when combined, can reduce surface roughness. In addition, the combination of two (or more) different laser pulse profiles reduces the stress magnitude at or around the vent, thereby improving the structural rigidity and reliability of the seal for the vent.

[0025] A laser pulse profile, also referred to as a laser intensity spatial distribution, refers to the intensity of a laser pulse with respect to the distance from the center of the laser pulse, relative to a cross-sectional view of a substrate acted upon by the laser pulse. As will be described below, a first laser pulse can have a first laser intensity spatial distribution, and a subsequent second laser pulse can have a second laser intensity spatial distribution that is different from the first laser intensity spatial distribution. For example, the second laser intensity spatial distribution can take one of a variety of shapes having a laser pulse intensity at its center that is less than the center of the first laser intensity spatial distribution.

[0026] An example of this is in Figures 4A-4C In this embodiment, again, a Gaussian laser intensity spatial distribution is used for the first time (e.g., from time step 0 to time step 1). Thereafter, a second laser intensity spatial distribution is applied. In this embodiment, a "ring" shaped laser intensity spatial distribution is used, such as Figure 4BThis donut shape can include laser intensity applied in an annular region around the center, with little or no laser applied at the center. The result is a donut-shaped laser intensity spatial distribution when looking down at the laser-irradiated substrate.

[0027] A second laser pulse having a second laser intensity spatial distribution (in this case, a donut shape) can be applied to the substrate immediately after or immediately after applying the first laser pulse having a first intensity spatial distribution (in this case, a Gaussian shape). Figure 4C . Also shown here is an embodiment in which the second laser pulse is applied for a longer time than the first laser pulse. The second laser pulse having the second laser intensity spatial distribution is shown as being applied from time step 1 to time step 3, which is twice as long as the first laser pulse having the first laser intensity spatial distribution. In other embodiments, the length of time for which the second laser pulse is applied is greater or less than the amount of time shown.

[0028] Although Figure 4C The second laser pulse is shown to be applied immediately or immediately after the first laser pulse, but in other embodiments, there may be a small time interval between the first and second laser pulses. For example, a Gaussian shaped pulse may be applied first, followed by a short period of time without applying a laser pulse, and then a donut shaped pulse may be applied. This temporal relationship between the first and second pulses may apply to any and all embodiments described herein.

[0029] Figure 4B The shape of the laser intensity spatial distribution of the circular ring shape shown can be different from the shape shown. For example, although Figure 4B The laser intensity spatial distribution shown in shows two different Gaussian shapes spaced from the center where no laser is applied, but these two Gaussian shapes can be square (i.e., flat on the top and flat on the sides), or these two Gaussian shapes can be steeper or flatter than shown here.

[0030] In short, two different laser pulses with two different laser intensity spatial distributions are used to seal the vent hole. The result is a seal with reduced surface roughness. Figure 5A The diagram shows the use of Figure 3A-3B A cross-sectional view of the sealing portion formed by the laser irradiation process of the laser intensity spatial distribution, and Figure 5B The diagram shows the use of Figures 4A-4C The cross-sectional view of the sealed part formed by the laser irradiation process shows the spatial distribution of the laser intensity. Figure 5A In the embodiment, the sealing portion 22 is formed to have a width W base and depth D base , and having a height H base The surface is rough 24. Figure 5B The formed sealing portion 22' has a width W test and depth D test , and having a height H test The surface roughness 24' of the sealing portion 22' is test and depth D test Similar in width and depth to seal portion 22 (e.g., within 3%), but Figure 5A The surface roughness is 24 degrees. base compared to, Figure 5B Surface roughness 24' height H test The use of two different laser pulses with two different laser intensity spatial distributions has reduced the size of the surface roughness compared to when only one laser pulse with a single laser intensity spatial distribution was utilized.

[0031] Using two different laser pulses can also significantly influence the stress level in the micromechanical device. Fig. 6A Shown with Figure 5A The stress levels associated with the seals shown, and Figure 6B Shown with Figure 5B The dashed box in each figure represents the high stress area of ​​the seal. In this area, the seal is used with Figures 4A-4C Two different laser pulses with the same laser intensity spatial distribution reduced the stress by a range of 10% to 30%. Although not shown, the use of other laser intensity spatial distributions disclosed herein also reduced the stress in this area of ​​the seal.

[0032] Figures 7-10 illustrate additional embodiments of laser intensity spatial distributions that may be used in a laser irradiation process for sealing a vent. For each figure, the "A" figure represents the laser intensity spatial distribution of a first laser, and the "B" figure represents the laser intensity spatial distribution of a second laser. The second laser is delivered after the first laser, either immediately or after a short delay in which no laser is applied.

[0033] FIG. 7 illustrates the first and second laser pulses used to seal the vent, wherein Fig. 7A illustrates a first laser pulse having a "top hat" shaped spatial distribution of laser intensity, and Figure 7B A second laser pulse having a donut-shaped spatial distribution of laser intensity is illustrated. Fig. 7AThe top-hat shape may include a platform 70 of laser pulse intensity at or near the center of the pulse. In this case, the platform is at or near 1 on a normalized pulse intensity scale (e.g., Y-axis). Additionally, the top hat shape tapers downward from the platform to zero on either side 72 of the platform. These tapers or sidewalls 72 are substantially vertical. The steep, substantially vertical sidewalls provide a very small transition between the substrate area that is not acted upon by the laser pulse and the substrate area that is acted upon by the laser pulse. 100% of the laser power may be provided in the platform area, in the center of the laser, and no laser power may be provided outside the area. In other words, the laser pulse intensity may be binary, where the laser is either at full power or at zero power at any spatial distance from the center of the laser. The annular shape of the second laser pulse may be similar to the annular shape described above, in which two Gaussian regions are separated by the space at the center of the laser pulse, in which no laser power is provided. In other embodiments, each of these Gaussian regions may be replaced with a consistent (e.g., rectangular, top-hat shaped) laser power.

[0034] FIG. 8 illustrates the first and second laser pulses used to seal the vent, wherein Fig. 8A The diagram shows a Fig. 7A The "top hat" shape of the laser intensity spatial distribution of the first laser pulse, and Figure 8B A second laser pulse having a volcano-shaped spatial distribution of laser intensity is illustrated. The volcano shape may be defined by a crater 80 located at or near the center of the second laser pulse and a pair of sidewalls 82 away from the center of the second laser pulse. Each sidewall may have, for example, a Gaussian shape, and the laser pulse intensity (e.g., 100% laser power) may be higher than the central crater region 82 (e.g., 20% laser power).

[0035] FIG. 9 illustrates the first and second laser pulses used to seal the vent, wherein Fig. 9A illustrates a first laser pulse having a volcano-shaped spatial distribution of laser intensity, and Fig. 9B A second laser pulse having a donut-shaped spatial distribution of laser intensity similar to the donut shape described above is illustrated. Fig. 9A The shape of the volcano is similar to Figure 8B The shape of the volcano, except Fig. 9A The laser power or intensity ratio at the laser center Figure 8B This produces a volcano-shaped spatial distribution of laser intensity with a Figure 8B The crater area at the bottom of the volcano is 90 higher.

[0036] The various shapes of laser intensity spatial distributions described herein can be used for either the first laser pulse or the second laser pulse. As an example, FIG. 10 illustrates the first and second laser pulses used to seal the vent, wherein Fig. 10A The diagram shows a Fig. 9A The first laser pulse has a volcano-shaped laser intensity spatial distribution, and Fig. 10B The diagram shows a Figure 8B FIG. 1 is a diagram showing a second laser pulse having a volcano-shaped laser intensity spatial distribution of the shape shown. In other embodiments, a donut shape may be used for the first laser pulse and a top hat shape may be used for the second laser pulse. The present disclosure should not be limited to the combinations of laser pulses shown in the figures. Furthermore, the present disclosure should not be limited to the shapes of the laser intensity spatial distribution disclosed herein.

[0037] The center of the first laser pulse may not be at the same location as the center of the second laser pulse. Fig.11 A first laser pulse having a first laser center and a second laser pulse having a second laser center are illustrated. Here, the first laser center does not overlap with the second laser center. For example, the second laser center is closer to the wall of the vent than the first laser center. In other embodiments, the first laser center is closer to the wall of the vent than the second laser center. In addition, both laser centers can be offset from the center of the vent. The distance between the vent center and the first laser center can be different from (e.g., greater than or less than) the distance between the first laser center and the second laser center.

[0038] Although exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive words, not restrictive, and it should be 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 further embodiments of the present invention that may not be explicitly described or illustrated. Although various embodiments may have been described as providing advantages or being superior to other embodiments or prior art implementations in terms of one or more desired characteristics, it is recognized by those of ordinary skill in the art 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, applicability, weight, manufacturability, ease of assembly, etc. Therefore, in terms of one or more characteristics, to the extent that any embodiment is described as less desirable than other embodiments or prior art implementations, these embodiments are not outside the scope of the present disclosure and may be desirable for specific applications.

Claims

1. A method for sealing a vent hole of a micromechanical device, the method comprising: applying a first laser pulse to a vent of a substrate of a micromechanical device for a first time period, wherein the first laser pulse has a first laser intensity spatial distribution, and wherein the vent leads to a chamber configured to receive the device; and A second laser pulse is then applied to the vent for a second period of time, wherein the second laser pulse has a second spatial distribution of laser intensity that is different from the first spatial distribution of laser intensity.

2. The method according to claim 1, wherein: The second time period is different from the first time period.

3. The method according to claim 1, wherein: The first laser intensity spatial distribution has a Gaussian shape.

4. The method according to claim 3, wherein: The second laser intensity spatial distribution has a ring shape.

5. The method according to claim 4, wherein: No laser light is applied at the center of the second laser pulse.

6. The method according to claim 1, wherein: The first laser intensity spatial distribution has a top-hat shape.

7. The method according to claim 6, wherein: The top hat shape includes a plateau of laser pulse intensity at or near the center of the pulse and a pair of side walls leading from the plateau to zero laser intensity, wherein each side wall is substantially vertical.

8. The method according to claim 6, wherein: The second laser intensity spatial distribution has a ring shape.

9. The method according to claim 6, wherein: The second laser intensity spatial distribution has a volcano shape.

10. The method according to claim 9, wherein: The volcano shape includes a crater-shaped laser pulse intensity at or near a center of the second laser pulse, and a pair of sidewalls away from the center, whose laser pulse intensity exceeds that of the crater.

11. The method according to claim 1, wherein: The first laser intensity spatial distribution has a volcano shape having a first laser intensity magnitude at a center of the first laser pulse.

12. The method according to claim 11, wherein: The second laser intensity spatial distribution has a second volcano shape having a second laser intensity magnitude at a center of the second laser pulse, wherein the second laser intensity magnitude is different from the first laser intensity magnitude.

13. The method according to claim 1, wherein: The center of the first laser pulse is offset from the center of the vent by a first distance, and the center of the second laser pulse is offset from the center of the vent by a second distance, the second distance exceeding the first distance.

14. A method for sealing a vent hole of a micromechanical device, the method comprising: providing a micromechanical device having a substrate having an upper surface and defining a vent opening to a chamber configured to receive the device; applying a first laser pulse to the substrate at the vent for a first time period, wherein the first laser pulse has a first laser intensity spatial distribution having a first laser pulse intensity at a center of the first laser pulse; and A second laser pulse is applied to the substrate at the vent during a second time period, wherein the second laser pulse has a second laser intensity spatial distribution that is different from the first laser intensity spatial distribution, and wherein the second laser intensity spatial distribution has a second laser pulse intensity at a center of the second laser pulse that is less than the first laser pulse intensity at the center of the first laser pulse.

15. The method according to claim 14, wherein: The second time period is different from the first time period.

16. The method according to claim 14, wherein: The first laser intensity spatial distribution has a Gaussian shape.

17. The method according to claim 16, wherein: The second laser intensity spatial distribution has a ring shape.

18. The method of claim 14, wherein a center of the first laser pulse is offset from a center of the second laser pulse.

19. A method of controlling surface roughness during laser sealing of a vent hole, the method comprising: applying a first laser pulse to a vent hole of a substrate, wherein the first laser pulse has a first laser intensity spatial distribution; and A second laser pulse is applied to the vent, wherein the second laser pulse has a second laser intensity spatial distribution that is different from the first laser intensity spatial distribution.

20. The method according to claim 19, wherein: The first laser intensity spatial distribution has a first laser pulse intensity at a center of the first laser pulse, and wherein the second laser intensity spatial distribution has a second laser pulse intensity at a center of the second laser pulse, the second laser pulse intensity being less than the first laser pulse intensity.

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