MEMS getter structure for wafer level packaging and activation and preparation method thereof

Abstract

The invention provides an MEMS getter structure for wafer level packaging and an activation and preparation method of the MEMS getter structure. The structure comprises a support body arranged on the readout circuit wafer, a low-melting-point material layer arranged on the support body, and a suspended getter structure anchored on the support body through the low-melting-point material layer. The activation method comprises the following steps: inverting a device integrated with the structure, electrifying and heating to melt the low-melting-point material, so that the suspended getter structure is separated from the support body to realize thermal isolation, and then heating to activate the getter layer; the device can also be heated for the second time after being placed uprightly, so that the low-melting-point material is re-melted and solidified to re-anchor the suspended structure. The preparation method comprises the steps of forming the support body on the readout circuit, depositing the low-melting-point material layer, and sequentially forming the getter electric heating layer and the getter layer. Through the fusible anchoring design, a heat conduction path is cut off when the getter is activated so as to protect a sensitive circuit and a pixel, and the mechanical reliability of the structure is enhanced through re-anchoring after the getter is activated.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems (MEMS) design and manufacturing in semiconductor technology, specifically relating to a MEMS getter structure for wafer-level packaging and its activation and preparation method. Background Technology

[0002] Infrared detection technology is widely used in various fields due to its all-weather capability (day and night), good environmental adaptability, and ability to obtain richer background and target information compared to visible light. In the military field, infrared detection technology is used for remote sensing reconnaissance, missile guidance, missile defense early warning, and individual soldier night vision systems. In the industrial field, infrared detection technology is mainly used for the detection of various equipment and systems, and the detection of gas leaks such as methane, enabling faster identification of equipment malfunctions, improving production efficiency, and ensuring the safety of personnel within factories. The most common type is the uncooled infrared focal plane array detector, a core component of an infrared detection system responsible for converting infrared radiation light signals into electrical signals and outputting them. The performance of the infrared focal plane array directly affects the performance of the entire infrared detection system.

[0003] To improve detector performance, vacuum encapsulation is necessary. The third-generation detectors developed to date have clearly prioritized further reducing detector size as a key research direction. To achieve this, the most advanced and commercially viable packaging method in the field is wafer-level packaging. This method abandons traditional concepts, using MEMS fabrication methods to produce the package on a wafer basis. The infrared focal plane detector wafer is then bonded to the package wafer, completing the encapsulation of all dies on the entire wafer in a single process. This significantly improves production efficiency, and the MEMS-fabricated package offers a significant advantage in reducing package size, making this packaging method highly regarded and accepted.

[0004] Wafer-level packaging offers significant advantages in reducing the size of detector chips and packages, but it still faces many technical challenges. Maintaining the vacuum level within the package is crucial to the detector's performance. Current methods involve preparing a getter within the package and activating it during or after vacuum packaging. This allows the getter to absorb gases from within the package, thereby increasing the vacuum level.

[0005] For example, patent CN116768141A describes an infrared detector getter module and vacuum packaging structure, in which getter material is placed on a suspended support structure, arranged in parallel with functional module 8, and completely covered within a sealed microcavity. Patent CN119263192A describes an area-array pixel-packaged uncooled infrared detector and its fabrication method, in which a getter film is prepared on the structural cavity, and the getter material is deposited through release holes onto the getter region composed of second microbridges, thus fully utilizing the chip area.

[0006] Despite various optimizations to the getter within a smaller wafer-level package, risks remain, including small getter area and insufficient getter capacity; high temperatures during getter activation that can easily be transmitted to pixels or readout circuits, causing pixel or readout circuit failure; and insufficient support for the getter layer, making it prone to breakage during vibration and impact. Summary of the Invention

[0007] The purpose of this invention is to provide a MEMS getter structure for wafer-level packaging, as well as its activation and preparation method, to solve the technical problems in the prior art where getter activation at high temperatures easily damages sensitive circuits and pixels, and where insufficient support of the getter structure leads to poor reliability.

[0008] To achieve the above objectives, the first technical solution adopted by the present invention is: a MEMS getter structure for wafer-level packaging, characterized in that it comprises: The support is mounted on the readout circuit wafer; A low-melting-point material layer is disposed on the support; A suspended getter structure is anchored to the support body through the low-melting-point material layer; the suspended getter structure includes at least a getter electric heating layer disposed on the low-melting-point material layer and a getter layer disposed on the getter electric heating layer; The melting point of the low-melting-point material layer is lower than the activation temperature of the getter layer.

[0009] Furthermore, the suspended getter structure also includes a second dielectric layer and a third dielectric layer as insulating layers, the second dielectric layer covering the low melting point material layer, and the third dielectric layer covering the getter electrically heating layer.

[0010] Furthermore, the support includes a low-melting-point material support located directly below the pixel area and a total getter support located around the array periphery, wherein the low-melting-point material support and the total getter support are made of the same material.

[0011] Furthermore, the getter electric heating layer is interconnected in the region corresponding to the pixel array, and its electrode leads extend to the edge of the array and are connected to the pre-set pads on the readout circuit wafer to form a complete current loop.

[0012] The second technical solution adopted in this invention is: the activation method of the MEMS getter structure described in the first technical solution, comprising the following steps: The first step is to invert the device integrating the MEMS getter structure so that the getter electric heating layer is located below the support. The second step is to heat the getter heating layer by applying electricity to melt the low melting point material layer, thereby causing the suspended getter structure to detach from the support under the action of gravity, so as to form thermal isolation from the readout circuit wafer. The third step is to continue heating to the activation temperature of the getter layer to activate the getter layer.

[0013] Furthermore, the process includes a fourth step: placing the device upright and energizing the getter heating layer again, causing the low-melting-point material layer to remelt and then cool and solidify, thereby re-anchoring the suspended getter structure to the support.

[0014] The third technical solution proposed in this invention: a method for preparing the MEMS getter structure described in the first technical solution, comprising the following steps: S1, a first sacrificial layer is prepared on the readout circuit wafer and a hole structure is etched to form a low melting point material support in the hole structure of the pixel area and a full getter support is formed around the array. S2, depositing a low-melting-point material layer on a low-melting-point material support, with the low-melting-point material layer encapsulating the low-melting-point material support; S3, an electric heating layer for getter and a getter layer are sequentially formed on the low melting point material layer to form a suspended getter structure.

[0015] Furthermore, in step S1, after the hole structure is formed, a first dielectric material is deposited on the readout circuit wafer 1. This material fills the hole structure and covers the first sacrificial layer. After removing part of the first dielectric material, the remaining first dielectric material forms a low-melting-point material support located directly below the pixel area and a full getter support located on the periphery of the array at the hole structure.

[0016] Furthermore, in step S3, a second dielectric layer is deposited covering the low-melting-point material layer 4. The second dielectric layer is thickened with a full getter support at the array edge position, and the getter electric heating layer is formed on the second dielectric layer. A third dielectric layer and a getter layer are sequentially deposited on the getter electric heating layer.

[0017] Furthermore, following step S3 are the following subsequent steps: S4, On the getter layer, a second sacrificial layer is prepared, and a pixel structure is prepared on it; S5, remove the first sacrificial layer, the second sacrificial layer and the sacrificial layer used in the formation of the pixel structure, so that the pixel structure and the suspended getter structure are released and suspended.

[0018] The beneficial effects of the present invention are as follows: 1. The present invention adopts a low-melting-point metal anchored suspension getter structure. During the heating and activation process of the getter, the detector is inverted, the low-melting-point metal melts, and the suspension getter structure is detached from the low-melting-point metal anchor, cutting off the channel for high temperature to be transmitted to the center of the readout circuit and the array pixels, thus avoiding the impact of high temperature on the function of the readout circuit and the array pixels.

[0019] 2. After the getter is activated, the detector is positioned upright, and the suspended getter structure comes into contact with the low-melting-point material support again under the action of gravity. By applying a small current to the getter electric heating layer, the low-melting-point material layer is melted. After the low-melting-point material cools and solidifies again, the low-melting-point material support and the suspended getter structure are re-anchored, forming a stable and reliable suspended getter structure support structure under each pixel. This avoids the large area of ​​unsupported structure caused by the suspended getter structure only being supported at the edge of the array area, which can greatly improve the impact and vibration reliability of the detector.

[0020] 3. The low-melting-point material described in this invention can achieve a set melting point through material formulation adjustments, forming a temperature-controllable switching effect. Specifically, after reaching the set melting point during inverted heating, the switch between the low-melting-point material support and the suspended getter structure is opened, cutting off the temperature transfer channel. Similarly, during upright low-current heating, after reaching the set melting point again, the low-melting-point material support and the suspended getter structure are solidified and anchored, closing the switch.

[0021] 4. The present invention places the getter below the pixel, rather than on the same plane as the pixel, which significantly improves the miniaturization of the chip and detector, and is particularly suitable for wafer-level packaging and pixel-level packaging of infrared focal plane detector chips.

[0022] 5. The fabrication process of the getter support structure of this invention is integrated with the MEMS process of infrared detectors, which further reduces the difficulty of cross-platform processing of infrared detectors. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the fabrication of a low-melting-point material support on a readout circuit wafer in the preparation method of the present invention; Figure 2 This is a schematic diagram of the low-melting-point material layer after preparation in an embodiment of the present invention; Figure 3 This is a schematic diagram showing the second dielectric layer and the getter electric heating layer after preparation in an embodiment of the present invention; Figure 4This is a schematic diagram of the structure of the suspended getter in an embodiment of the present invention; Figure 5 This is a schematic diagram of the infrared focal plane pixel structure containing the second and third polyimide layers in an embodiment of the present invention; Figure 6 This is a schematic diagram of the polyimide layer after being released using a plasma release process in an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating the working principle of activating the getter by inverting the device in an embodiment of the present invention; Figure 8 This is a schematic diagram illustrating the working principle of re-anchoring the getter structure by placing the device upright in an embodiment of the present invention; Figure 9 This is a top view of the getter structure layout in an embodiment of the present invention, taking a 3×3 pixel array as an example; The diagram is labeled as follows: 1. Readout circuit wafer, 2. First polyimide layer, 3. Low melting point material support, 4. Low melting point material layer, 5. Second dielectric layer, 6. Getter heating layer, 7. Third dielectric layer, 8. Getter layer, 9. Second polyimide layer, 10. Third polyimide layer, 11. Pixel structure, 12. PI-1 hole, 13. Full getter support. Detailed Implementation

[0024] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the invention in any way.

[0025] Generally, MEMS uncooled infrared focal plane array detector arrays are rectangular or square arrays composed of neatly arranged effective pixels in X rows and Y columns.

[0026] This invention proposes an innovative MEMS getter structure and its integration scheme. For example... Figure 6 As shown, this scheme ultimately forms a two-layer structure: the upper layer is an infrared focal plane pixel structure, and the lower layer is a getter assembly. The manufacturing and activation processes, along with the accompanying drawings, are described in detail below.

[0027] Example 1 This embodiment describes a MEMS getter structure manufacturing process compatible with MEMS uncooled infrared focal plane detector technology for wafer-level packaging, ultimately obtaining the following... Figure 6The structure shown includes a support body disposed on the readout circuit wafer 1; a low-melting-point material layer 4 disposed on the support body; and a suspended getter structure anchored to the support body via the low-melting-point material layer 4. The suspended getter structure includes at least a getter electric heating layer 6 disposed on the low-melting-point material layer 4 and a getter layer 8 disposed on the getter electric heating layer 6. The melting point of the low-melting-point material layer 4 is lower than the activation temperature of the getter layer 8.

[0028] The support includes a low-melting-point material support 3 located directly below the pixel area and a total getter support 13 located around the array periphery. The low-melting-point material support 3 and the total getter support 13 are made of the same material, such as SiO2 or SiN.

[0029] The suspended getter structure also includes a second dielectric layer 5 and a third dielectric layer 7 as insulating layers. The second dielectric layer 5 covers the low melting point material layer 4, and the third dielectric layer 7 covers the getter electric heating layer 6.

[0030] The getter electric heating layer 6 is interconnected in the region corresponding to the pixel array, and its electrode leads extend to the edge of the array and are connected to the preset pads on the readout circuit wafer 1 to form a complete current loop.

[0031] The specific preparation method involves the following steps: S1, as Figure 1 As shown, the readout circuit wafer 1 (i.e., the ROIC wafer) is cleaned and dried. Then, a first polyimide layer 2 (PI-1 layer) is fabricated on the readout circuit wafer 1 as a first sacrificial layer. PI-1 holes 12 are formed on the first polyimide layer 2 by photolithography. Next, a first dielectric material is deposited on the wafer, which fills the PI-1 holes 12 and covers the surface of the first polyimide layer 2. A portion of the first dielectric material is removed, and the remaining first dielectric material forms a low-melting-point material support 3 (located directly below the pixel area) in the PI-1 holes 12 and a full getter support 13 (such as...) in the array periphery region. Figure 9 (As shown).

[0032] In this structure, the middle part of the low-melting-point material support 3 contacts the readout circuit wafer 1 within the PI-1 hole 12, and its outer edge dimension is larger than that of the PI-1 hole 12. A contact surface is formed on the first polyimide layer 2 protruding from the readout circuit wafer, which can remelt after activation with the low-melting-point material layer, thus forming a concave structure for the low-melting-point material support 3 as a whole. Simultaneously, it can also serve as a storage pool for the molten liquid during the activation process of the low-melting-point material in the suspension getter structure.

[0033] S2, as Figure 2As shown, a low-melting-point material layer 4 is deposited on the formed low-melting-point material support 3. The low-melting-point material layer 4 completely covers and encapsulates the low-melting-point material support 3. The shape of the low-melting-point material layer 4 matches the shape of the low-melting-point material support 3 to ensure that the low-melting-point material support 3 is not exposed. The low-melting-point material layer 4 also forms a concave structure.

[0034] By designing a low-melting-point material formulation, the melting point of the low-melting-point material is adjusted, that is, the separation temperature and re-anchoring temperature of the low-melting-point material support 3 from the suspended getter structure are adjusted when the low-melting-point material melts.

[0035] S3, as Figure 3 As shown, a second dielectric layer 5 is deposited on the wafer, serving as an insulating layer covering the low-melting-point material layer 4. The second dielectric layer is thickened at the array edge positions to form a fully getter support 13. Then, a conductive material is deposited and patterned to form a getter electroheating layer 6. The patterned getter electroheating layer 6 is applied in the region corresponding to the pixel array (e.g., ...). Figure 9 The electrodes are interconnected in a mesh or serpentine pattern to achieve uniform heating. Their electrode leads extend to the outside of the getter support 13 region at the edge of the array and are connected to the pre-set pads on the readout circuit wafer 1 to form a complete current loop.

[0036] S4, such as Figure 4 As shown, a third dielectric layer 7 and a getter layer are sequentially deposited on the getter electrically heated layer 6. The third dielectric layer 7 forms an insulating layer between the getter electrically heated layer 6 and the getter layer 8 within the array region, and the getter support is thickened at the edge of the array region. Thus, the composite structure consisting of the second dielectric layer 5, the getter electrically heated layer 6, the third dielectric layer 7, and the getter layer 8 forms the getter structure. This structure will subsequently release suspension, and is therefore defined as a suspended getter structure.

[0037] The getter layer 8 is disposed below each pixel in the array area. All the getter layers 8 below the pixels constitute a full getter structure. The edge of the full getter structure is supported above the readout circuit by the full getter support 13.

[0038] S5, such as Figure 5 As shown, a second polyimide layer 9 (PI-2 layer) is prepared on the getter layer 8 as a second sacrificial layer, and a pixel structure containing a third polyimide layer 10 (PI-3 layer) is prepared on it.

[0039] S6, such as Figure 6As shown, the wafer, after completing the above steps, is placed in a vacuum reaction chamber, and a plasma release process is used to remove the three sacrificial layers: the third polyimide layer 10, the second polyimide layer 9, and the bottom first polyimide layer 2. After release, the pixel structure 11 is completely suspended; simultaneously, the suspended getter structure, composed of the second dielectric layer 5, the getter electrically heated layer 6, the third dielectric layer 7, and the getter layer 8, is also released and suspended. At this time, the suspended getter structure is firmly fixed to the readout circuit wafer 1 by the edge full getter support 13, while its main body is "separably" anchored to each low-melting-point material support 3 by the solidified low-melting-point material layer 4.

[0040] The materials used in the second dielectric layer 5 and the third dielectric layer 7 are generally composed of SiO2 or SiN, just like the first dielectric material.

[0041] This manufacturing process is highly integrated with existing infrared detector MEMS technology. By simultaneously releasing two suspended layers—the pixel and the getter—in a single operation, the process is greatly simplified. Placing the getter below the pixel, rather than on the same plane, significantly saves chip area and strongly promotes the miniaturization of wafer-level packaging.

[0042] Example 2 This embodiment describes how to safely activate and finally harden a getter on a device manufactured in Embodiment 1 above that has undergone wafer-level vacuum packaging (i.e., the package cover has been bonded to form a sealed cavity). Reference Figure 7 and Figure 8 It demonstrates two key states in the activation process.

[0043] Step 1, as follows Figure 7 As shown, the packaged infrared detector device is inverted, so that the pixel structure 11 is at the bottom, the getter layer 8 is in the middle, and the readout circuit wafer 1 is at the top. The getter heating layer 6 is heated by an external pin, and the heat is gradually transferred to the low-melting-point material layer 4. As the temperature gradually increases, the low-melting-point material layer 4 melts first and flows downwards into the second dielectric layer 5. Simultaneously, the suspended getter structure, having lost its solid anchoring, moves downwards under its own gravity, detaching from the low-melting-point material support 3. This prevents the temperature from being directly transferred to the center of the readout circuit and the array pixels via solid-state heat transfer, effectively avoiding failure of the readout circuit and array pixels due to the high temperature required for getter activation.

[0044] Step 2: Under thermal isolation, the temperature of the suspended getter structure continues to rise until it reaches the activation temperature of the getter and is maintained for a period of time. The getter layer 8 is fully activated and can efficiently absorb residual gas molecules in the encapsulation cavity, thereby significantly improving and maintaining the vacuum level in the encapsulation cavity.

[0045] Step 3, as Figure 8 As shown, after activation is complete and the low-melting-point material cools and solidifies, the detector is placed upright. At this time, the suspended getter structure comes into contact with the low-melting-point material support 3 again under gravity. A small current is applied again through the getter's electric heating layer to melt the low-melting-point material, but the temperature is low and does not affect the readout circuit and array pixel functions. After the low-melting-point material cools and solidifies again, the low-melting-point material support 3 and the suspended getter structure are re-anchored, forming a stable and reliable support structure for the suspended getter structure under each pixel. This avoids the situation where the suspended getter structure is only supported at the edge of the array area, resulting in a large area of ​​unsupported suspension, which can greatly improve the detector's shock and vibration reliability.

[0046] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the specific implementation of the present invention with reference to the above embodiments. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the protection scope of the pending claims.

Claims

1. A MEMS getter structure for wafer-level packaging, characterized in that, include: The support is mounted on the readout circuit wafer; A low-melting-point material layer is disposed on the support; A suspended getter structure is anchored to the support body through the low-melting-point material layer; the suspended getter structure includes at least a getter electric heating layer disposed on the low-melting-point material layer and a getter layer disposed on the getter electric heating layer; The melting point of the low-melting-point material layer is lower than the activation temperature of the getter layer.

2. The MEMS getter structure for wafer-level packaging according to claim 1, characterized in that, The suspended getter structure further includes a second dielectric layer and a third dielectric layer as insulating layers, the second dielectric layer covering the low melting point material layer, and the third dielectric layer covering the getter electrically heating layer.

3. The MEMS getter structure for wafer-level packaging according to claim 1, characterized in that, The support structure includes a low-melting-point material support located directly below the pixel area and a total getter support located around the array periphery. The low-melting-point material support and the total getter support are made of the same material.

4. The MEMS getter structure for wafer-level packaging according to claim 1, characterized in that, The getter electric heating layer is interconnected in the region corresponding to the pixel array, and its electrode leads extend to the edge of the array and are connected to the pre-set pads on the readout circuit wafer to form a complete current loop.

5. A method for activating a MEMS getter structure as described in any one of claims 1 to 4, characterized in that, Includes the following steps: The first step is to invert the device integrating the MEMS getter structure so that the getter electric heating layer is located below the support. The second step is to heat the getter heating layer by applying electricity to melt the low melting point material layer, thereby causing the suspended getter structure to detach from the support under the action of gravity, so as to form thermal isolation from the readout circuit wafer. The third step is to continue heating to the activation temperature of the getter layer to activate the getter layer.

6. The activation method for the MEMS getter structure according to claim 5, characterized in that, The process also includes a fourth step: placing the device upright and energizing the getter heating layer again to remelt the low-melting-point material layer and then cool and solidify it, thereby re-anchoring the suspended getter structure to the support.

7. A method for preparing a MEMS getter structure as described in any one of claims 1 to 4, characterized in that, Includes the following steps: S1, a first sacrificial layer is prepared on the readout circuit wafer and a hole structure is etched to form a low melting point material support in the hole structure of the pixel area and a full getter support is formed around the array. S2, depositing a low-melting-point material layer on a low-melting-point material support, with the low-melting-point material layer encapsulating the low-melting-point material support; S3, an electric heating layer for getter and a getter layer are sequentially formed on the low melting point material layer to form a suspended getter structure.

8. The manufacturing method according to claim 7, characterized in that, In step S1, after the hole structure is formed, a first dielectric material is deposited on the readout circuit wafer 1. The material fills the hole structure and covers the first sacrificial layer. After removing part of the first dielectric material, the remaining first dielectric material forms a low-melting-point material support located directly below the pixel area and a full getter support located on the periphery of the array at the hole structure.

9. The manufacturing method according to claim 7, characterized in that, In step S3, a second dielectric layer is deposited covering the low-melting-point material layer 4. The second dielectric layer is thickened with a full getter support at the array edge position, and the getter electric heating layer is formed on the second dielectric layer. A third dielectric layer and a getter layer are sequentially deposited on the getter electric heating layer.

10. The manufacturing method according to claim 7, characterized in that, The following steps are included after step S3: S4, On the getter layer, a second sacrificial layer is prepared, and a pixel structure is prepared on it; S5, remove the first sacrificial layer, the second sacrificial layer and the sacrificial layer used in the formation of the pixel structure, so that the pixel structure and the suspended getter structure are released and suspended.

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