Structures and process to prevent the laser reseal structure from protruding beyond the wafer surface

Abstract

Method for producing a micromechanical component (1) with a substrate (3) and with a cap (7) connected to the substrate (3) and enclosing a first cavern (5) with the substrate (3), wherein a first pressure prevails in the first cavern (5) and a first gas mixture with a first chemical composition is enclosed, wherein -- in a first process step (101) an access opening (11) connecting the first cavern (5) with a surrounding (9) of the micromechanical component (1) is formed in the cap (7), wherein -- in a second process step (102) the first pressure and / or the first chemical composition is set in the first cavern (5), wherein -- in a third process step (103) the access opening (11) is closed by introducing energy or heat into an absorbing part (21) of the cap (7) using a laser, wherein -- in a fourth process step (104), which takes place before the third process step (103), a recess (17) is formed in one of the surfaces (19) of the cap (7) facing away from the first cavern (5) in the area of ​​the access opening (11) to receive a material area (13) of the cap (7) that has been converted into a liquid state in the third process step (103), wherein the recess (17) is designed such that the material region (13) transformed into a solid state is arranged between a plane extending substantially along the surface (19) and the first cavern (5), wherein the recess (17) is etched anisotropically into the surface (19).

Description

State of the art

[0001] The invention relates to a method according to the preamble of claim 1.

[0002] Such a method is known from WO 2015 / 120939 A1. If a specific internal pressure is desired in a cavity of a micromechanical component, or if a gas mixture with a specific chemical composition is to be enclosed in the cavity, the internal pressure or chemical composition is often adjusted during the capping of the micromechanical component or during the bonding process between a substrate wafer and a cap wafer. During capping, for example, a cap is bonded to a substrate, whereby the cap and the substrate together enclose the cavity. By adjusting the atmosphere or the pressure and / or the chemical composition of the gas mixture present in the environment during capping, the desired internal pressure and / or chemical composition in the cavity can thus be set.

[0003] The method known from WO 2015 / 120939 A1 allows for the targeted adjustment of internal pressure in a cavity of a micromechanical component. In particular, this method makes it possible to produce a micromechanical component with a first cavity, in which a first pressure and a first chemical composition can be set that differ from a second pressure and a second chemical composition at the time of capping.

[0004] In the method for precisely controlling the internal pressure in a cavity of a micromechanical component according to WO 2015 / 120939 A1, a narrow access channel to the cavity is created in the cap or cap wafer, or in the substrate or sensor wafer. The cavity is then flooded with the desired gas and internal pressure via the access channel. Finally, the area around the access channel is locally heated using a laser, causing the substrate material to liquefy locally and, upon solidification, hermetically seal the access channel.

[0005] Further disclosures are found in the publications DE 102014202801 A1, US 2013 / 0265701 A1 and US 2013 / 0074596 A1. Disclosure of the invention

[0006] The object of the present invention is to provide a method for manufacturing a mechanically robust and long-life micromechanical component in a manner that is simpler and more cost-effective than those found in the prior art. Furthermore, the object of the present invention is to provide a compact, mechanically robust, and long-life micromechanical component compared to those found in the prior art. According to the invention, this applies in particular to a micromechanical component with a (first) cavity. With the method and micromechanical component according to the invention, it is also possible to realize a micromechanical component in which a first pressure and a first chemical composition can be set in the first cavity and a second pressure and a second chemical composition can be set in a second cavity.For example, such a method is provided for the production of micromechanical components, for which it is advantageous if a first pressure is enclosed in a first cavity and a second pressure in a second cavity, wherein the first pressure is to differ from the second pressure. This is the case, for example, when a first sensor unit is incorporated into a micromechanical component.

[0007] Rotation rate measurement and a second sensor unit for acceleration measurement are to be integrated into a micromechanical component.

[0008] The task is solved by the fact that -- in a fourth process step, a recess is formed in one of the surfaces of the substrate or cap facing away from the first cavern in the area of ​​the access opening to receive a material area of ​​the substrate or cap that was converted into a liquid state in the third process step.

[0009] This provides a simple and cost-effective method for manufacturing a micromechanical component, with which the solidified material region, or the material region transformed into a solid state, can be recessed into the substrate or cap relative to the surface. Compared to a method without forming the recess, the method according to the invention has the advantage, for example, that the solidified material region protrudes less far above the surface, thus offering less surface area for mechanical impacts. This makes the solidified material region and / or the interfaces between the solidified material region and the remaining substrate or cap, and / or the area around the interfaces, less susceptible to cracking.In other words, the solidified material area is less susceptible to damage and unintentional contact, for example during the production flow, thanks to the inventive method, and is therefore less of a cause and starting point for cracks. Furthermore, the inventive method makes it less problematic if the substrate material is only heated locally and contracts relative to its surroundings during both solidification and cooling. The fact that a very high tensile stress can thus arise in the sealing area is also less problematic, since lowering the solidified material area minimizes the surface area exposed to mechanical impacts. Consequently, spontaneous cracking, which can occur depending on the stress and material, is also less likely.Cracking due to thermal or mechanical stress on the micromechanical component during further processing or in the field is also less likely, since the area of ​​the sealed access opening is better protected. In particular, with the method according to the invention, it is less critical if, during solidification of the material area, a tip or protrusion of the tip forms in the middle of the molten zone or in the middle of the solidified material area above the surface of the substrate or cap due to recrystallization dynamics. The probability of damage to such a tip or unintentional contact with it during the further manufacturing process can be effectively reduced by using the recess. In particular, it is advantageous according to the invention for the tip to be located below an otherwise (i.e., except for the area of ​​the access opening) substantially flat surface of the cap or substrate.Thus, the method according to the invention is an effective way to reduce the probability that the tip is the cause or starting point of cracks. It therefore provides a simple and cost-effective method for manufacturing a micromechanical component that is mechanically robust and has a long service life compared to the prior art.

[0010] In the context of the present invention, the term “micromechanical component” is to be understood as encompassing both micromechanical components and microelectromechanical components.

[0011] The present invention is preferably intended for the manufacture of a micromechanical component with one cavity. However, the present invention is also intended, for example, for a micromechanical component with two cavities or with more than two, i.e., three, four, five, six or more than six, cavities.

[0012] Preferably, the access opening is closed by introducing energy or heat into an energy- or heat-absorbing part of the substrate or cap using a laser. Preferably, energy or heat is introduced sequentially into the absorbing part of the substrate or cap of several micromechanical components, which are, for example, manufactured together on a wafer. Alternatively, however, simultaneous introduction of energy or heat into the respective absorbing part of the substrate or cap of several micromechanical components is also possible, for example, using multiple laser beams or laser devices.

[0013] Advantageous embodiments and further developments of the invention can be found in the dependent claims and in the description with reference to the drawings.

[0014] According to a preferred embodiment, the cap with the substrate encloses a second cavern, wherein a second pressure prevails in the second cavern and a second gas mixture with a second chemical composition is enclosed.

[0015] A further object of the present invention is a method for manufacturing a micromechanical component comprising a substrate and a cap connected to the substrate and enclosing a first cavity and a second cavity with the substrate, wherein a first pressure prevails in the first cavity and a first gas mixture with a first chemical composition is enclosed, wherein a second pressure prevails in the second cavity and a second gas mixture with a second chemical composition is enclosed, wherein -- in a first process step, an access opening connecting the first cavern with an environment of the micromechanical component is formed in the substrate or in the cap, wherein -- in a second process step the first pressure and / or the first chemical composition is set in the first cavern, wherein -- in a third process step, the access opening is closed by introducing energy or heat into an absorbing part of the substrate or cap using a laser, wherein -- in a fourth process step, a recess is formed in one of the surfaces of the substrate or cap facing away from the first cavern in the area of ​​the access opening to receive a material area of ​​the substrate or cap that was converted into a liquid state in the third process step.

[0016] According to a preferred embodiment, the recess is designed such that the solidified material region is situated between a plane extending substantially along the surface and the first cavity. This advantageously prevents the solidified material region from projecting beyond the surface, thus further reducing its exposure to mechanical impacts. Consequently, the solidified material region and / or the interfaces between the solidified material region and the remaining substrate or cap, and / or the area around the interfaces, are even less susceptible to cracking.

[0017] According to a preferred embodiment, the recess is designed such that a first area of ​​a projection of the recess onto a plane extending substantially along the surface is larger than a second area of ​​a projection of the solidified material region or the absorbing part of the substrate or cap onto the plane. This advantageously prevents the solidified material region from protruding above the surface if the recess is recessed over a surface area by at least the height of the material region's expected overhang in a process without a recess.

[0018] According to a preferred embodiment, the recess is designed such that a first area of ​​a projection of the recess onto a plane extending substantially along the surface is smaller than a second area of ​​a projection of the solidified material region or the absorbing part of the substrate or cap onto the plane. This advantageously allows the amount of the substrate or cap material region that has been converted into the liquid state to be reduced, thus enabling a melt pool generated by the energy input to flow more freely without requiring an unnecessarily large area of ​​the surface for the recess's formation.

[0019] According to a preferred embodiment, the recess is formed in a plane extending substantially parallel to the surface and is rotationally symmetrical to the access channel, the material area, or the absorbing part of the substrate or cap. This allows the melt pool to flow particularly advantageously.

[0020] According to a preferred embodiment, the recess is etched anisotropically into the surface. This advantageously allows the recess to be designed anisotropically or elongated, with a larger extent essentially perpendicular to the surface rather than parallel to it, or with a smaller extent essentially perpendicular to the surface rather than parallel to it.

[0021] According to a preferred further development, the fourth process step is carried out after the first process step. This advantageously allows the recess to be created in the surface using the existing access channel.

[0022] According to a preferred further training plan, it is intended that -- in the fourth process step, a further recess or preferably a plurality of further recesses is formed in the surface in the area of ​​the access opening to receive a material area of ​​the substrate or the cap that was converted into a liquid state in the third process step.

[0023] According to a preferred further development, it is intended that the exclusion or the further exclusion or the multitude of further exclusions be structured using a hard mask.

[0024] Furthermore, another object of the present invention is a micromechanical component comprising a substrate and a cap connected to the substrate and enclosing a first cavity with the substrate, wherein a first pressure prevails in the first cavity and a first gas mixture with a first chemical composition is enclosed, wherein the substrate or the cap comprises a closed access opening, and wherein the substrate or the cap comprises a surface of the substrate or the cap facing away from one of the first caverns and a recess arranged in the region of the access opening for receiving a material region of the substrate or the cap that has been converted into a liquid state during the closing of the access opening.

[0025] According to a preferred embodiment, the cap with the substrate encloses a second cavern, wherein a second pressure prevails in the second cavern and a second gas mixture with a second chemical composition is enclosed.

[0026] Furthermore, another object of the present invention is a micromechanical component comprising a substrate and a cap connected to the substrate and enclosing a first cavity and a second cavity, wherein a first pressure prevails in the first cavity and a first gas mixture with a first chemical composition is enclosed, wherein a second pressure prevails in the second cavity and a second gas mixture with a second chemical composition is enclosed, wherein the substrate or the cap comprises a sealed access opening, and wherein the substrate or the cap comprises a surface of the substrate or the cap facing away from one of the first cavities and a recess arranged in the region of the access opening for receiving a material region of the substrate or the cap that has been converted into a liquid state during the sealing of the access opening.This advantageously provides a compact, mechanically robust, and cost-effective micromechanical component with preset first and second pressures. The aforementioned advantages of the method according to the invention also apply accordingly to the micromechanical component according to the invention.

[0027] According to a preferred embodiment, the recess is designed such that the solidified material area is arranged between a plane extending substantially along the surface and the first cavity. This advantageously provides a micromechanical component that is particularly robust against mechanical impacts.

[0028] According to a preferred embodiment, the first pressure is lower than the second pressure, with a first sensor unit for measuring the angular rate being arranged in the first cavern and a second sensor unit for measuring the acceleration being arranged in the second cavern. This advantageously provides a mechanically robust micromechanical component for measuring angular rate and acceleration, with optimal operating conditions for both the first and second sensor units. Brief description of the drawings Fig. Figure 1 shows a schematic representation of a micromechanical component with an open access opening according to an exemplary embodiment of the present invention. Fig. Figure 2 shows a schematic representation of the micromechanical component according to Fig. 1 with a closed access opening. Fig. Figure 3 shows a schematic representation of a method for manufacturing a micromechanical component according to an exemplary embodiment of the present invention. Fig. Figure 4 shows a schematic representation of a material area of ​​a substrate or a cap of a micromechanical component according to a further exemplary embodiment of the present invention. Fig. Figure 5 shows a schematic representation of a micromechanical component according to a third exemplary embodiment of the present invention at different times during the inventive method. Fig. Figure 6 shows a schematic representation of a micromechanical component according to a fourth exemplary embodiment of the present invention at different times during the inventive method. Fig. Figure 7 shows a schematic representation of a micromechanical component according to a fifth exemplary embodiment of the present invention at different times during the inventive method. Embodiments of the invention

[0029] In the various figures, identical parts are always marked with the same reference symbols and are therefore usually only named or mentioned once.

[0030] In Fig. 1 and Fig. Figure 2 is a schematic representation of a micromechanical component 1 with an open access opening 11 in Fig. 1 and with closed access opening 11 in Fig. Figure 2 shows an exemplary embodiment of the present invention. Here, the micromechanical component 1 comprises a substrate 3 and a cap 7. The substrate 3 and the cap 7 are connected to each other, preferably hermetically, and together enclose a first cavity 5. For example, the micromechanical component 1 is configured such that the substrate 3 and the cap 7 additionally enclose a second cavity. The second cavity is in Fig. 1 and in Fig. 2, however, is not shown.

[0031] For example, in the first cavern 5, especially in situations like those in Fig. Figure 2 shows a sealed access opening 11, and a first pressure is present. Furthermore, a first gas mixture with a first chemical composition is enclosed in the first cavity 5. Additionally, for example, a second pressure prevails in the second cavity, and a second gas mixture with a second chemical composition is enclosed in the second cavity. Preferably, the access opening 11 is arranged in the substrate 3 or in the cap 7. In the present embodiment, the access opening 11 is arranged in the cap 7 by way of example. However, according to the invention, it can alternatively be provided that the access opening 11 is arranged in the substrate 3.

[0032] For example, it is planned that the initial pressure in the first cavern 5 will be lower than the second pressure in the second cavern. It is also planned, for example, that a [missing text] will be installed in the first cavern 5. Fig. 1 and Fig. 2 not shown first micromechanical sensor unit for measuring rotation rate and in the second cavern a in Fig. 1 and Fig. 2 second micromechanical sensor units for acceleration measurement are arranged, not shown.

[0033] In Fig. Figure 3 shows a schematic representation of a method for manufacturing the micromechanical component 1 according to an exemplary embodiment of the present invention. In this process, -- in a first process step 101 the access opening 11 connecting the first cavern 5 with an environment 9 of the micromechanical component 1, in particular narrow, is formed in the substrate 3 or in the cap 7. Fig. Figure 1 shows, as an example, the micromechanical component 1 after the first process step 101. Furthermore, -- in a second process step 102, the first pressure and / or the first chemical composition is set in the first cavern 5, or the first cavern 5 is flooded with the desired gas and the desired internal pressure via the access channel. Furthermore, for example -- in a third process step 103, the access opening 11 is closed by introducing energy or heat into an absorbing part 21 of the substrate 3 or the cap 7 using a laser. Alternatively, for example, it is also provided that -- in the third process step 103, the area around the access channel is preferably heated locally by a laser and the access channel is hermetically sealed. Thus, it is advantageously possible to provide the process according to the invention with energy sources other than a laser for sealing the access opening 11. Fig. Figure 2 shows, by way of example, the micromechanical component 1 after the third process step 103.

[0034] After the third procedural step 103, in a Fig. Mechanical stresses occur in the lateral region 15 of the micromechanical component 1, as illustrated by example in Figure 2, both on the surface 19 and in depth perpendicular to a projection of the lateral region 15 onto the surface 19, i.e., along the access opening 11 and in the direction of the first cavern 5. These mechanical stresses, in particular local mechanical stresses, prevail especially at and near an interface between a material region 13 of the cap 7 that transitions into a liquid state in the third process step 103 and into a solid state after the third process step 103, closing the access opening 11, and a residual region of the cap 7 that remains in a solid state during the third process step 103. Fig. 2 the material area 13 of the cap 7 closing the access opening 11 is to be regarded as merely schematic or is shown schematically, in particular with regard to its lateral extent or shape, especially parallel to the surface 19, and in particular with regard to its extent or configuration perpendicular to the lateral extent, especially perpendicular to the surface 19.

[0035] As in Fig. 3 is shown as an example; additionally, -- in a fourth process step 104, a recess 17 is formed in one of the surfaces 19 of the substrate 3 or the cap 7 facing away from the first cavern 5 in the area of ​​the access opening 11 for receiving or partially receiving a material area 13 converted into a liquid state in the third process step 103, or at least partially converted into a liquid state of absorbing part 21 of the substrate 3 or the cap 7. As in Fig. As illustrated by example in Figure 3, the fourth process step 104 is carried out, for instance, after the first process step 101 and before the second process step 102. However, it is also alternatively provided that the fourth process step 104 is carried out before the first process step 101 or after the second process step 102. Thus, the process according to the invention can be advantageously adapted to different manufacturing processes in a simple manner.

[0036] In particular, it is provided that before the laser resealing or before the first process step 101, structures or the recess 17 or a plurality of recesses 17 in the area of ​​the access channel or the access opening 11 are introduced into the surface 19 or silicon surface in order to sink or lower the sealing plane or the material area 13, so that the protrusion resulting from the solidification of the melt pool lies below the wafer surface or surface 19.

[0037] In Fig. Figure 4 shows a schematic representation of an already solidified material region 13 of the substrate 3 or the cap 7 according to a further exemplary embodiment. Here, the solidified material region 13 or the tip protrudes beyond the surface 19 of the cap 7. Fig. 5, Fig. 6 and Fig. Figure 7 schematically depicts micromechanical components 1 according to a third, fourth, and fifth exemplary embodiment at different points in time of the inventive method. Several different structures or structures of recesses 17 are proposed, wherein the structures are preferably etched anisotropically into the surface 19 or silicon surface. For example, the cap 7 comprises a recess 17 arranged in the surface 19 of the cap 7 facing away from the first cavity 5. In the Fig. In the embodiment shown in Figure 7, the cap 7 comprises a plurality of recesses 17. Furthermore, the recess 17 or the plurality of recesses 17 are arranged in the area of ​​the access opening 11 to receive a material region 13 of the cap 7 that has been converted into a liquid state during the closing of the access opening 11. In all of the embodiments shown in Figure 7, the recess 17 is arranged in the area of ​​the access opening 11 to receive a material region 13 of the cap 7 that has been converted into a liquid state. Fig. 5, Fig. 6 and Fig. In the embodiments shown in Figure 7, the recess 17 or the plurality of recesses 17 is designed such that the solidified material area 13 is arranged between a plane extending substantially along the surface 19 and the first cavern 5.

[0038] Fig. Figure 5 shows a micromechanical component 1 at different times during a method according to the invention, wherein the recess 17 is configured such that a first area of ​​a projection of the recess 17 onto a plane extending substantially along the surface 19 is larger than a second area of ​​a projection of the solidified material region 13 or the absorbing part 21 of the substrate 3 or the cap 7 onto the plane. For example, it is additionally or alternatively provided that, to recess the reseal overhang, an area larger than the melting area is advantageously etched around the access channel by means of anisotropic etching. Here, the etching depth is, for example, at least the height of the expected overhang. Furthermore, the size of the area is selected, for example, such that the melting area, taking all tolerances into account, always lies within it.

[0039] Furthermore, it shows Fig. 6 a micromechanical component 1 at different times during a method according to the invention, wherein the recess 17 is formed such that a first surface of a projection of the recess 17 onto a plane extending substantially along the surface 19 is smaller than a second surface of a projection of the solidified material region 13 or of the absorbing part 21 of the substrate 3 or of the cap 7 onto the plane.

[0040] Furthermore, it shows Fig. 7 a micromechanical component 1 at different times during a method according to the invention, wherein the recess 17 is formed in a plane extending substantially parallel to the surface 19 and is rotationally symmetrical to the access channel 11 or to the material region 13 or to the absorbing part 21 of the substrate 3 or the cap 7. In particular, in the Fig. In the embodiment shown in Figure 7, the recess 17 or the plurality of recesses 17 is etched anisotropically into the surface 19.

[0041] In Fig. 6 and Fig. Figure 7 illustrates that the amount of material melted during laser resealing can be reduced by one or more etched individual structures to such an extent that the melt pool can flow and, after solidification, no longer protrudes above the wafer surface 19. The depth that the structures extend into the silicon surface 19 can be adjusted to the proportion of the etched area within the melting zone. The more material is removed, the shallower the etching depth needs to be. However, it must be ensured that the remaining material is sufficient to seal the access channel 11.

[0042] Finally, it is preferably provided that an area larger than the melting zone is recessed over a surface by at least the height of the expected overhang, or that the amount of melting material in the melting zone is reduced by one or more individual structures etched into the surface 19, so that the melt pool can flow. In this case, the depth to which the structures extend into the silicon surface 19 can range from a few micrometers to exceeding the melting depth of the cap 7, the substrate 3, or the silicon. For example, it is also provided that the recess 17 or the plurality of recesses 17 or structures are combined with stress-release structures.

Claims

[1] Method for producing a micromechanical component (1) with a substrate (3) and with a cap (7) connected to the substrate (3) and enclosing a first cavern (5) with the substrate (3), wherein a first pressure prevails in the first cavern (5) and a first gas mixture with a first chemical composition is enclosed, wherein -- in a first process step (101) an access opening (11) connecting the first cavern (5) with a surrounding (9) of the micromechanical component (1) is formed in the cap (7), wherein -- in a second process step (102) the first pressure and / or the first chemical composition is set in the first cavern (5), wherein -- in a third process step (103) the access opening (11) is closed by introducing energy or heat into an absorbing part (21) of the cap (7) using a laser, wherein -- in a fourth process step (104), which takes place before the third process step (103), a recess (17) is formed in one of the surfaces (19) of the cap (7) facing away from the first cavern (5) in the area of ​​the access opening (11) to receive a material area (13) of the cap (7) that has been converted into a liquid state in the third process step (103), wherein the recess (17) is designed such that the material region (13) transformed into a solid state is arranged between a plane extending substantially along the surface (19) and the first cavern (5), wherein the recess (17) is etched anisotropically into the surface (19). [2] Method according to claim 1, wherein the cap (7) with the substrate (3) encloses a second cavern, wherein a second pressure prevails in the second cavern and a second gas mixture with a second chemical composition is enclosed. [3] Method according to one of the preceding claims, wherein the recess (17) is designed such that a first surface of a projection of the recess (17) onto a plane extending substantially along the surface (19) is larger than a second surface of a projection of the material region (13) transformed into a solid state or of the absorbing part (21) of the cap (7) onto the plane. [4] Method according to claim 1, wherein the recess (17) is designed such that a first surface of a projection of the recess (17) onto a plane extending substantially along the surface (19) is smaller than a second surface of a projection of the material region (13) converted into a solid state or of the absorbing part (21) of the cap (7) onto the plane. [5] Method according to one of the preceding claims, wherein the recess (17) is formed in a plane extending substantially parallel to the surface (19) and is rotationally symmetric to the access channel (11) or to the material region (13) transformed into a solid state or to the absorbing part (21) of the cap (7). [6] Micromechanical component (1) comprising a substrate (3) and a cap (7) connected to the substrate (3) and enclosing a first cavity (5) with the substrate (3), wherein a first pressure prevails in the first cavity (5) and a first gas mixture with a first chemical composition is enclosed, wherein the cap (7) comprises a closed access opening (11), wherein the cap (7) comprises a recess (17) located on a surface (19) of the cap (7) facing away from one of the first cavity (5) and in the region of the access opening (11) for receiving a material region (13) of the cap (7) that has been converted into a liquid state during the closing of the access opening (11), wherein the recess (17) is configured such that the material region (13) converted into a solid state is arranged between a plane extending substantially along the surface (19) and the first cavity (5), wherein the recess (17) is etched anisotropically into the surface (19). [7] Micromechanical component (1) according to claim 6, wherein the cap (7) encloses a second cavern with the substrate (3), wherein a second pressure prevails in the second cavern and a second gas mixture with a second chemical composition is enclosed.

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