METHOD FOR WELDING A COMPONENT

Description

[0001] The invention relates to a method for welding a component comprising at least a first and / or a second component section, wherein, in particular, a cavern is formed between the first and the second component section, wherein the first and / or the second component section has an opening for pressure connection of the cavern with an environment of the component. State of the art

[0002] German patent application DE 10 2014 210 857 A1 discloses a component and method in which the angular rate sensors and accelerometers are configured as two adjacent micromechanical structures. To selectively control the internal pressure within a cavity between two components of a single component, a getter material or an outgassing material is arranged in an additional cavity between the two components. After the bonding process, in which the two components are joined, this additional cavity is connected to the main cavity via a connection opening. The getter material or outgassing material is then activated, causing gases to be bound in the additional cavity and the connected cavity, or resulting in outgassing. Only when the desired internal pressure has been established in the connected cavity is the connection opening to the additional cavity closed.In this way, the getter material or the outgassing material is used solely to set a defined internal pressure. However, the use of a getter material requires an additional cavity or additional installation space. DE 10 2017 125140 A1 discloses a method for manufacturing a hermetically sealed housing containing a semiconductor component. The method comprises inserting a housing with a housing body and a housing cover into a process chamber, wherein the housing cover closes a cavity of the housing body and is gas-tightly attached to the housing body, wherein at least one opening is formed in the housing, and wherein at least one semiconductor component is arranged in the cavity. The method further comprises applying sealing material to the at least one opening while a predetermined gas atmosphere prevails in the process chamber. Glass frit can be used as a sealing material to seal the opening.The subsequent melting of the sealing material can include irradiating the sealing material with a laser beam. Disclosure of the invention

[0003] A method for welding a component with the features of claim 1 is proposed. Preferred, advantageous and / or further embodiments of the invention will become apparent from the dependent claims, the following description and / or the figures.

[0004] A method for welding a component, in particular a component with a microelectromechanical system (a so-called MEMS component), is proposed. The component to be welded is preferably configured as a gyroscope, pressure sensor, or accelerometer. The component is constructed in layers. The component has at least one first and / or one second component section, which form the layered structure of the component. The first and / or second component section is preferably configured as a semiconductor device and / or as a semiconductor layer (substrate layer). For example, the component sections are each configured on a wafer, with several first and several second component sections arranged side by side on the respective wafer.

[0005] The first and / or second component section preferably comprises a microelectromechanical structure. The microelectromechanical structure is preferably configured as a microelectronic circuit, actuator, or sensor. For example, the microelectromechanical structure forms the gyroscope or the accelerometer and / or is a component thereof.

[0006] The component has at least one cavity, which is formed, in particular, between the first and second component sections. The cavity forms a recess within the component, preferably having an arbitrary shape. The cavity is preferably suitable for accommodating the microelectromechanical structure of the first and / or the second component section. The cavity is preferably created during the joining of the first and second component sections, the first and second component sections preferably being joined together using a bonding process. For example, one of the component sections is designed as a cap wafer and the other component section as a MEMS wafer, wherein the cap wafer and the MEMS wafer are bonded together using a bonding process, e.g., wafer bonding, for encapsulation, so that the cavity is formed inside the component.The microelectromechanical structure of the MEMS wafer and / or the cap wafer is encapsulated in the cavity using bonding processes. This makes it possible to create the cavities necessary for the operation of the respective microelectromechanical structure, e.g., a sensor structure. For example, a specific internal pressure, e.g., a vacuum, is applied in the cavity for the sensor structure to minimize its damping. For example, a low internal pressure is set for a gyroscope, preferably less than 50 mbar and / or at least 1 mbar. In contrast, a higher internal pressure is preferably provided for an accelerometer, preferably less than 800 mbar and / or at least 500 mbar.

[0007] Furthermore, it is provided that the first and / or the second component section has an opening for pressure bonding of the cavity to the surrounding area of ​​the component. The opening in one of the component sections is preferably designed as a rounded opening, e.g., a bore, wherein the opening is preferably positioned perpendicular to the layer structure of the component in one of the component sections. Alternatively, the opening has any basic shape, e.g., a slit or slot, wherein the opening is preferably arranged at a contact point of the two component sections, e.g., at a bonding point.

[0008] The opening is connected to the cavern, in particular via fluid and / or pressure, so that the pressure and / or atmosphere prevailing in the vicinity of the component is maintained within the cavern. The adjustment of the cavern conditions by the ambient conditions of the component preferably occurs before the welding process and / or is preferably designed as a preceding step of the process. The process is designed to close the opening in the first and / or second component section.

[0009] In the process for welding the component, in particular a MEMS component, a filler piece made of a filler material is arranged on the respective component section with the opening, so that the opening is at least covered and / or filled by the filler piece.

[0010] The filler element is preferably adapted in its basic shape to the opening, so that it is suitable for overlapping and / or closing the opening. For example, the filler element is designed in its basic shape as a cylinder, a cone, a sphere, or a disc. Alternatively, the filler element is shapeless, for example, as a powder or a paste. The filler element is preferably applied to the component section with the opening in an application step, preferably temporarily attached to the respective component section. Preferably, in the application step, the filler element is connected to the corresponding component section, in particular by a positive locking connection, so that the filler element is held within the opening.Alternatively or optionally, in the application step, the filler is positioned on the component section so that the opening and / or an access area of ​​the opening is covered. Preferably, the filler is held on the component section by adhesion. For example, the filler adheres with a contact surface to a component surface of the component section that surrounds the opening. This alternative application step is preferably provided when the filler is designed as a disc or as a layer in the component's layer structure. Preferably, the filler is positioned on the component section such that at least a portion of the filler is located outside the opening. For example, this portion of the filler protrudes beyond the component surface.

[0011] The subsequent procedure for welding the component involves welding the filler piece to the respective component section using a laser welding process, so that the opening in the component section is closed by the filler material of the filler piece to hermetically seal the cavity.

[0012] In the laser welding process and / or the laser welding step, at least the filler piece is thermally treated, in particular by a laser beam, so that the filler material of the filler piece is at least partially melted. Preferably, the laser beam heats the filler piece at least to the melting temperature of the filler material. In a variant outside the scope of the claimed invention, the filler material has a lower melting temperature than a material of the component sections, so that only the filler piece is melted during welding. This prevents material from the component section from being removed. According to the invention, both have a common melting temperature, so that both are melted.

[0013] In this process step, the cavity is hermetically sealed from the component's surroundings. The conditions within the cavity are thus maintained at a constant level. A key advantage is that the filler material acts as a welding filler when welding the component section to the filler piece, meaning that only a small volume of the component section needs to be melted. As the molten metal and / or weld pool cools, the filler material reduces residual stresses, preventing microcracks at the weld point. This results in a particularly high weld tightness. This advantageous welding process reduces component failure rates due to leaking cavities. Because of the additional filler material, a smaller volume of material, or virtually no material at all, needs to be melted to close the opening.This also protects the component or component section from damage caused by material removal and / or from excessive thermal stress during laser welding.

[0014] According to the invention, the filler piece, which is welded to the first or second component section, is made of a filler material of the same type as the respective component section. According to the invention, the first component section and / or the second component section and the filler piece consist of silicon or a silicon-containing semiconductor material. ParticularlyPreferably, the first or second component section and the filler are made of a common material. This has the advantage that the materials bond sufficiently strongly to one another during welding, and residual stresses in the weld pool are reduced during cooling. According to the invention, the similar materials have a common melting temperature, e.g., the melting temperature of silicon (1410 °C), so that a uniform weld point and / or weld seam is produced in a transition area between the component section and the filler during laser welding.

[0015] In a preferred embodiment of the method, the cavity is filled with gas, and the gas is introduced through the opening in one of the component sections. The filling piece is then welded to the respective component section to create a gas-tight seal. The gas filling in the cavity is preferably generated by flooding the area surrounding the component with a gas, whereby pressure equalization causes the gas to flow from the area surrounding the component into the cavity through the opening. This gas filling step is preferably carried out before the filling piece is attached to the component section with the opening. Thus, after the cavity is filled with the gas, the filling piece is attached to the corresponding component section, and these are subsequently welded together by laser welding to create a gas-tight seal.The advantage is that the gas filling creates the necessary cavern conditions for sensor operation, e.g., a pressure sensor, while filling through the opening ensures that each component, e.g., each component of a wafer array, is filled with the same amount of gas. Furthermore, the advantageous method for welding the component ensures that the gas filling cannot escape through the opening or weld point, as the filling material of the filler piece creates a particularly robust seal for the opening.

[0016] In a further preferred embodiment of the method, the cavity is provided to have a specific internal pressure, which is applied to the cavity via the opening in one of the component sections. The filler piece is welded to the respective component section to create a pressure-tight seal of the cavity. Preferably, the cavity has a negative pressure, in particular a pressure of less than 500 mbar, preferably less than 300 mbar, and specifically less than 100 mbar. The specific internal pressure is preferably determined based on the microelectromechanical structure or the respective sensor structure. For example, to minimize damping of the sensor structure (rotation rate sensor), the lowest possible internal pressure, e.g., 1 mbar, is set. This allows the rotation rate sensor to be operated with a relatively low excitation voltage.In contrast, a significantly higher internal pressure, e.g., 500 mbar, is applied to sensor structures, such as accelerometers, to prevent them from vibrating. This process step is preferably performed before the filler piece is placed on the corresponding component section. The advantage is that the filler piece, acting as a welding filler, reliably seals the opening pressure-tight, thus ensuring sufficient stability of the weld. Generally, such openings are sealed with surrounding molten material from the component, which flows into the opening. As the molten material hardens, it contracts within the opening area, creating a trough-like depression, resulting in a weld with an unknown material thickness. Consequently, a high failure rate occurs because the welds have varying degrees of pressure tightness.The filler piece ensures a fixed amount of material is used during welding, guaranteeing a consistent weld thickness. Furthermore, the geometry of the filler piece, e.g., as a "plug" or "cork," is advantageous because it creates a tighter seal at the opening / weld, particularly in the presence of negative pressure within the cavern.

[0017] In a preferred embodiment of the method, the first and / or second component section has a welded joint for connection to the filler piece, the weld being produced by laser welding. The weld is particularly designed as a metallurgical bond. The weld between one of the component sections and the filler piece is suitable for attaching the filler piece, e.g., as a disc or layer, to the respective component section. For example, these are temporarily joined together in a first step of the laser welding process, so that the opening is then welded and / or sealed in a second step of the laser welding process.

[0018] In a preferred embodiment of the method, the laser welding process involves melting at least the filler material of the filler piece by a laser beam to create the weld between the first and / or second component section and the filler piece. Specifically, the weld is created by melting a portion of the filler piece, preferably in a position where the filler piece protrudes beyond the opening. For example, the filler piece protrudes at least 0.1 mm beyond the opening and / or extends from the opening onto the surrounding component surface. In particular, the portion or protrusion of the filler piece is melted by the laser beam during laser welding and welded to its surroundings. In this context, the filler piece is to be understood as a sealing element that is welded to the component section.Consequently, the filler piece can have additional functions for the component. For example, one or more bond wires for the electrical connection of the component are held by the filler piece and / or fixed to the component surface. Alternatively or optionally, a bond wire is embedded in the filler piece so that it is guided into the component via the weld point.

[0019] In an alternative embodiment of the process, the laser welding process involves completely melting at least the filler material of the infill piece with a laser beam to create a molten pool consisting of at least the infill material for sealing the opening. The infill material thus acts as a welding filler that is completely melted. The advantage of completely melting the infill piece is that the molten pool spreads throughout the opening, ensuring a seamless seal. This prevents and / or eliminates fit errors caused by manufacturing tolerances and / or deviations in the geometry of the infill piece relative to the opening.

[0020] In a further embodiment of the method, it is provided that the component forms a microelectromechanical system component (MEMS component), specifically an SI-MEMS component, wherein the first and / or the second component section has a microelectromechanical structure, the microelectromechanical structure being arranged within the cavern.

[0021] In the method for welding the MEMS component, as described above, the filler piece made of a filler material, in particular silicon-containing filler material, is arranged on the respective component section with the opening, so that the opening is at least covered and / or filled by the filler piece, wherein the filler piece is welded to the respective component section by the laser welding process for the hermetic sealing of the microelectromechanical structure within the cavern.

[0022] Further features, advantages, and effects of the invention will become apparent from the following description of preferred embodiments of the invention. These include: Figure 1 a sectional view of a component with a first and a second component section with an opening and with a filler piece for arrangement at the opening as a preferred embodiment of a process step; Figure 2 A detailed representation of the opening in the first or second component section with a laser-welded filler piece as a preferred embodiment of a further process step.

[0023] One application example for the components manufactured using the method described below are so-called MEMS components (microelectromechanical system components). MEMS components feature microscopically small electromechanical structures that form microelectronic circuits, actuators, or sensors. For example, the electromechanical sensors are configured as angular rate sensors or accelerometers.

[0024] The electromechanical structure is formed within the layered structure of the MEMS component. These layers are encapsulated by a component to protect the sensor structures and ensure a defined pressure for the respective sensor operation. For this purpose, a cavity is formed inside the MEMS component, which houses the sensor structures and maintains the defined pressure. MEMS sensors, which typically operate under vacuum, are therefore hermetically sealed. To ensure reliable sensor operation throughout the entire lifetime of the MEMS component, it is necessary to maintain the pressure in the cavity. Preferably, a hole is incorporated into the component, connecting the inner cavity to the surrounding environment. This hole allows the pressure in the cavity to be determined by reference to the ambient pressure of the component or by flooding the cavity with a gas.

[0025] In the Figure 1A cross-sectional view shows a component 1 with a layered structure. Component 1 has dimensions of a few millimeters; for example, it has a base area of ​​at least 2 mm² and a layer thickness of at least 0.5 mm. Component 1 is designed as a MEMS (micro-electro-mechanical system) component. Component 1 has a first and a second component section 2a, b, which form the layered structure of component 1. The component sections 2a, b are formed, for example, in a manufacturing process on a silicon wafer, whereby several wafer-level layers are arranged one above the other and bonded together in a bonding process. The stacked component sections 2a, b are in contact with each other with their inner surfaces 4a, b, and a bonding frame 3 connects the inner surfaces 4a, b.The bonding frame 3 is used, for example, in the bonding process during the manufacture of component 1 between the component sections 2a, b. The second component section 2b is designed as a cap component and / or as a so-called cap or cap wafer, wherein the second component section 2b has a cap recess 5a, which is formed as a notch and / or protrusion in the material of the second component section 2b. The first component section 2a has a microelectromechanical structure 6, which is formed on an inner surface of the first component section 2a. The microelectromechanical structure 6 forms, for example, a microelectromechanical component of a sensor, actuator, circuit, or oscillator and is designed depending on its operation. These can have any structure and different configurations. Therefore, the microelectromechanical structure 6 is in the . Figure 1only presented in a highly schematic way.

[0026] The two component sections 2a, b are arranged one above the other such that the cap recess 5a of the second component section 2b faces the microelectromechanical structure 6 of the first component section 2a, thus forming a cavity 5 for the microelectromechanical structure 6. The bonding frame 3 is formed around the cavity 5 and is fundamentally suitable for connecting the two component sections 2a, b and hermetically sealing the cavity 5.

[0027] The second component section 2b, or cap component, is generally placed on top of the first component section 2a to protect the microelectromechanical structure 6. The cavity 5 is designed to control the operating conditions of the microelectromechanical structure 6. For example, a specific internal pressure is generated in the cavity 5 for the operation of the microelectromechanical structure 6, e.g., a sensor structure. Alternatively or optionally, the cavity 5 is filled with a gas that surrounds the microelectromechanical structure 6. The pressure or gas filling can be generated by a getter material or an outgassing material. However, there is a risk that the getter material will generate different pressures within the components, resulting in varying conditions for the microelectromechanical structure 6, which could, for example, lead to measurement errors in one of the MEMS sensors.Furthermore, these materials require additional installation space, which increases the dimensions of the component and the manufacturing costs, e.g. due to fewer component sections on an "expensive" wafer.

[0028] To adjust the cavern conditions in cavern 5, component 1 has an opening 7. The opening 7 is formed on the first and / or the second component section 2b. According to the exemplary embodiment, the opening 7 is formed on the second component section 2b, the cap component. The opening 7 is designed as a pressure connection. The opening 7 connects cavern 5 to an environment U of component 1. Pressure equalization takes place through the opening 7 between the environment U and cavern 5, so that the desired internal pressure and / or gas filling in cavern 5 is set by the environment U.

[0029] The term opening 7 refers to any opening and / or hole suitable for fluidically connecting the cavern 5 to the environment U. According to the exemplary embodiment, opening 7 is designed as a bore. Opening 7 is, for example, drilled into the respective component section 2a, b. For example, opening 7 has a channel or labyrinth that is connected to an inlet on a component surface and an outlet at the cap recess.

[0030] To hermetically seal the cavity 5, a filler piece 8 is arranged on the respective component section 2a, b with the opening 7 in one step of the welding process for component 1. According to the exemplary embodiment, the filler piece is designed in its basic form as a "plug" or "cork" and is arranged on the second component section 2b. Alternatively, the filler piece 8 has any other basic form suitable for covering and / or closing the opening 7. The filler piece 8 is arranged on the respective component section 2a, b, for example, in an application step. For instance, the filler piece 8 is inserted into the opening 7 by a manipulator, e.g., a robot arm. Alternatively or optionally, the filler piece 8 is arranged by applying another layer, similar to wafer-level layer fabrication.For example, in a subsequent step, excess material of the filler piece 8 that is not required to close the opening 7 can be removed. According to the exemplary embodiment, the filler piece 8 is arranged so that it protrudes from the second component section 2b. A section 8a of the filler piece 8 extends out of the opening 7. Section 8a has a protruding edge so that it rests against the surrounding surface of component section 2b.

[0031] In the Figure 2 A detailed view shows a section of component 1 from the Figure 1The component 1 has the first or second component section 2a, b, which is formed with the opening 7. The component 1 has the filler piece 8, which is made of a filler material, e.g. silicon. In its unwelded state, the filler piece 8 has a conical shape, which is positively inserted into the bore-like opening 7. The filler piece 8 is arranged on the component section 2a, b in a previous step of the process, as described above.

[0032] By arranging the filler piece 8, the opening 7 is already closed. To hermetically seal this "closure," in a further step of the process, the filler piece 8 is welded to the respective component section 2a, b by a laser welding process and / or laser welding. The laser welding process comprises, for example, a laser welding device with a laser welding head 20, wherein the laser welding device generates a laser beam L which exits via the laser welding head 20 for welding. In the Figure 2 The laser welding process is shown in a simplified manner, with the laser beam L directed onto a welding area 9 between the filler piece 8 and the respective component section 2a, b. The laser welding head 20 is, for example, designed to be movable, and is moved along the welding area 9 by the laser welding device during welding.

[0033] The laser beam L melts a portion of the filler material of the filler piece 8 as well as a portion of the material of the respective component section 2a, b, thus producing a circumferential weld bead 10. For example, only or predominantly the section 8a of the filler piece 8, which protrudes beyond the component surface, is melted. The weld bead 10 seals the weld area 9, so that the opening 7 is completely closed, thereby hermetically sealing the cavity 5 located inside the component 1 from the environment U. In the laser welding process, a weld joint is created by the material bond of the weld bead 10. The weld joint attaches the filler piece 8 to the respective component section 2a, b.The described welding process for component 1 melts a very small volume of material in the respective component section 2a, b, since the filler piece 8 acts as a welding filler. This prevents damage caused by melting of the respective component section 2a, b and reduces the thermal stress on component 1.

Claims

1. Method for welding a component (1) comprising at least one first and / or one second component portion (2a, b), wherein a cavity (5) is formed in particular between the first and the second component portion (2a, b), wherein the first and / or the second component portion (2a, b) has an opening (7) for connecting the cavity (5) to a surrounding area (U) of the component (1) in pressure terms, - in which method a filling piece (8) of a filling material is arranged on the respective component portion (2a, b) that has the opening (7), so that the opening (7) is at least covered and / or filled by the filling piece (8), - in which method the filling piece (8) is welded to the respective component portion (2a, b) by a laser welding process, so that the opening (7) in the component portion (2a, b) is closed by the filling material of the filling piece (8) to hermetically seal the cavity (5), wherein the filling piece (8) that is welded to the first or the second component portion (2a, b) is made from a filling material which is of the same type as the respective component portion (2a, b) and has a common melting temperature, wherein the first component portion (2a) and / or the second component portion (2b), and the filling piece (8) consist of silicon or a silicon-containing semiconductor material.

2. Method according to Claim 1, characterized in that the cavity (5) is filled with gas, the cavity (5) being filled with the gas via the opening (7) in one of the component portions (2a, b), wherein the filling piece (8) is welded to the respective component portion (2a, b) to gas-tightly seal the cavity (5).

3. Method according to either of the preceding claims, characterized in that the cavity (5) has a determined internal pressure, the internal pressure in the cavity (5) being applied via the opening (7) in one of the component portions (2a, b), wherein the filling piece (8) is welded to the respective component portion (2a, b) to pressure-tightly seal the cavity (5).

4. Method according to any of the preceding claims, characterized in that the first and / or the second component portion (2a, b) has a welded connection for connection to the filling piece (8), the welded connection being established by the laser welding process.

5. Method according to Claim 4, characterized in that the laser welding process involves using a laser beam to melt at least the filling material of the filling piece (8), in order to establish the welded connection between the first and / or the second component portion (2a, b) and the filling piece (8).

6. Method according to Claims 1 to 3, characterized in that the laser welding process involves using a laser beam to completely melt at least the filling material of the filling piece (8), in order to create a melt pool from at least the filling material of the filling piece (8) to close the opening (7).

7. Method according to any of the preceding claims, characterized in that the component (1) forms a microelectromechanical system component (MEMS component), wherein the first and / or the second component portion (2a, b) has a microelectromechanical structure (6), wherein the microelectromechanical structure (6) is arranged within the cavity (5), wherein the filling piece (8) is welded to the respective component portion (2a, b) to hermetically seal the microelectromechanical structure (6) inside the cavity (5).