A high-reliability wafer-level packaged thin-film bulk acoustic wave device structure and its fabrication method

Abstract

This invention belongs to the field of chip packaging, specifically relating to a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure and its fabrication method. The structure includes a functional wafer and a capping wafer. The functional wafer has opposing first and second surfaces and a communicating first sidewall surface. The capping wafer has opposing third and fourth surfaces and a communicating second sidewall surface. The capping wafer has metallized vias penetrating the third and fourth surfaces and metal pillars completely filling the metallized vias. The edge of the third surface is bonded to the edge of the second surface via a sealing ring of a certain thickness. A communicating metal deposition layer is provided on the first surface, the first sidewall surface, and part of the second sidewall surface, covering the outer sidewall of the sealing ring. An electroplated thickening layer is provided on the surface of the metal deposition layer. This invention encapsulates the wafer-level packaged thin-film bulk acoustic wave device, blocking gas from entering and exiting from the side, thus improving the hermeticity of the wafer-level package.

Description

Technical Field

[0001] This patent belongs to the field of chip packaging, specifically relating to a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure and its fabrication method. Background Technology

[0002] Thin-film bulk acoustic wave (BAS) devices are devices based on bulk acoustic wave theory and utilize acoustic resonance to achieve electrical frequency selection. Frequency selection is achieved by resonating the piezoelectric thin film between the electrodes of the thin-film bulk acoustic wave filter in a direction perpendicular to the filter. They are characterized by small size, low cost, high quality factor (Q), and strong power handling capability.

[0003] With the development of technology, the data transmission speed between global systems is accelerating, and film bulk acoustic wave (FBAR) devices are being widely used in an increasing number of applications, such as in the field of wireless communication. As wireless communication systems and terminals are trending towards miniaturization, this requires miniaturized components within the system. Currently, most FBAR filter packaging products adopt wafer-level packaging (WLP) technology, such as... Figure 1 As shown, it includes a functional wafer 11 and a capping wafer 12. A metal pillar 14 is disposed inside the capping wafer 12, and an outer pad 13 is disposed on the outer surface of the metal pillar 14. A sealing ring is disposed at the edge of the functional wafer 11 and the capping wafer 12. When performing wafer-level packaging of thin-film bulk acoustic wave devices, a sealing ring is generally made at the edge of the device, and a gas-tight structure is formed by gold-gold bonding. However, as the device size becomes smaller and smaller, the width of the sealing ring is further compressed, which leads to a reduction in the gas-tight effect. Summary of the Invention

[0004] Addressing the problems of existing technologies, this invention employs a semi-dicing process, combined with a metal deposition layer and an electroplated thickening layer, to adequately encapsulate the wafer-level packaged thin-film bulk acoustic wave (TFT-AS) device. This prevents gas from entering or exiting from the side, further improving the hermeticity of the wafer-level package. In the wafer-level packaging of the TFT-AS filter, a semi-dicing process is first used to expose the sealing ring. Then, a seed layer is established using magnetron sputtering, followed by electroplating to grow a metal layer on the top and sidewalls. This metal layer covers the sealing ring on the sidewall of the wafer-level package. Even when the sealing ring is narrow and there is a risk of leakage, a metal isolation layer is formed, preventing moisture and other substances from intruding into the filter cavity along the bonding interface. This significantly improves the wafer-level reliability of the TFT-AS filter.

[0005] The present invention provides the following technical solutions to achieve the above-mentioned technical objectives:

[0006] In a first aspect, the present invention provides a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure, comprising a functional wafer and a capping wafer. The functional wafer has opposing first and second surfaces, and a first sidewall surface connecting the first and second surfaces. The capping wafer has opposing third and fourth surfaces, and a second sidewall surface connecting the third and fourth surfaces. The capping wafer is provided with metallized vias penetrating the third and fourth surfaces and metal pillars completely filling the metallized vias. The edge of the third surface of the capping wafer is bonded to the edge of the second surface of the functional wafer through a sealing ring of a certain thickness. A communicating metal deposition layer is provided on the first surface and the first sidewall surface of the functional wafer, and on a portion of the second sidewall surface of the capping wafer. The metal deposition layer covers the outer sidewall of the sealing ring of a certain thickness. An electroplated thickening layer is provided on the surface of the metal deposition layer.

[0007] In a second aspect, the present invention also provides a method for fabricating a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure, the method comprising:

[0008] A functional wafer is provided, the functional wafer having opposing first and second surfaces, and a first sidewall surface connecting the first and second surfaces;

[0009] A capped wafer is provided, the capped wafer having opposing third and fourth surfaces, and a second sidewall surface connecting the third and fourth surfaces;

[0010] The capping wafer is provided with metallized vias penetrating the third and fourth surfaces and metal pillars that completely fill the metallized vias;

[0011] The edge of the third surface of the capping wafer and the edge of the second surface of the functional wafer are bonded together by a sealing ring of a certain thickness.

[0012] Half-cutting is performed on the bonded functional wafer and cap wafer. The functional wafer above the sealing ring is cut through, and the cap wafer below the sealing ring is cut into a groove to expose the outer wall of the sealing ring.

[0013] A connected metal deposition layer is deposited on the first surface and the first sidewall surface of the functional wafer, and on a portion of the second sidewall surface of the capping wafer by magnetron sputtering, and covers the outer sidewall of the sealing ring.

[0014] An electroplated thickening layer is formed on the surface of the metal deposition layer by electroplating, and covers the outer wall of the sealing ring with a certain thickness.

[0015] A full cut is performed on the electroplated functional wafer and the capping wafer to penetrate through the functional wafer and the capping wafer.

[0016] The beneficial effects of this invention are:

[0017] 1. The present invention employs a structure of metal deposition layer and electroplated thickening layer to encapsulate the wafer-level packaged thin-film bulk acoustic wave device, blocking gas from entering or exiting from the side, thereby further improving the hermeticity of the wafer-level package.

[0018] 2. The metal deposition layer and electroplated thickening layer of the present invention use metal layers of different thicknesses, which can maximize the reliability of the metal sealing ring. A metal sealing ring of a certain height and thickness is formed on the sidewall of the functional wafer and the cap wafer. Even if there is a risk of leakage, a metal isolation layer can be formed to prevent water vapor and other substances from entering the cavity of the filter along the bonding interface. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of a thin-film bulk acoustic wave device structure using traditional wafer-level packaging technology.

[0020] Figure 2 This is a half-cut schematic diagram of the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention;

[0021] Figure 3 This is a deposition schematic diagram of the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention;

[0022] Figure 4 This is a schematic diagram of the electroplating of the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention;

[0023] Figure 5 This is a schematic diagram of the fully cut structure of the wafer-level packaged thin-film bulk acoustic wave device of the present invention;

[0024] Figure 6 This is a schematic diagram of the full cutting process of the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention;

[0025] Figure 7 This is a flowchart illustrating the fabrication method of the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention.

[0026] In the figure: 20, half-cut kerf; 11, 21, functional wafer; 12, 22, capping wafer; 13, 23, outer pad; 14, 24, metal pillar; 15, 25, sealing ring; 26, metal deposition layer; 27, electroplated thickening layer. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] like Figures 2-6 As shown, the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention includes a functional wafer 21 and a capping wafer 22. The functional wafer 21 has opposing first and second surfaces, and a first sidewall surface connecting the first and second surfaces. The capping wafer 22 has opposing third and fourth surfaces, and a second sidewall surface connecting the third and fourth surfaces. The capping wafer 22 is provided with metallized vias penetrating the third and fourth surfaces and metal pillars 24 completely filling the metallized vias. The edge of the third surface of the capping wafer is bonded to the edge of the second surface of the functional wafer through a sealing ring 25 with a certain thickness. The first surface and the first sidewall surface of the functional wafer, and part of the second sidewall surface of the capping wafer are provided with a communicating metal deposition layer 26. The metal deposition layer 26 covers the outer sidewall of the sealing ring with a certain thickness. An electroplated thickening layer 27 is provided on the surface of the metal deposition layer 26.

[0029] The metal pillar 24 extends from the fourth surface of the capping wafer 22 to form an outer pad 23.

[0030] In this embodiment of the invention, the thickness of the metal deposition layer 26 is greater than or equal to 500 nm, and the electroplated thickening layer 27 is greater than or equal to 5 μm. This is to ensure that electroplating costs are saved as much as possible while improving the reliability of the metal layer.

[0031] In order to set the metal deposition layer 26, the functional wafer 21 and the capping wafer 22 need to be half-cut, so that the first surface and the first sidewall surface of the functional wafer, as well as part of the second sidewall surface of the capping wafer, are exposed. Therefore, the height of the half-cut is the depth of the first sidewall surface and the depth of part of the second sidewall surface, and the height of part of the second sidewall surface of the metal deposition layer is greater than or equal to 15 μm.

[0032] In this embodiment of the invention, the parameters of the entire electroplating process are adjusted according to the chip size and the distance between chips. The distance between chips cannot be less than 50μm, otherwise side half cutting is difficult to achieve, and electroplating is prone to electroplating abnormalities such as pore formation. Therefore, the spacing of the functional pattern of the functional wafer can be set to be greater than or equal to 50μm.

[0033] Figure 7This is a flowchart illustrating the fabrication method of the wafer-level packaged thin-film bulk acoustic wave device structure of the present invention, as shown below. Figure 7 As shown, the method includes:

[0034] 101. A functional wafer is provided, the functional wafer having opposing first and second surfaces, and a first sidewall surface connecting the first surface and the second surface;

[0035] 102. A capped wafer is provided, the capped wafer having opposing third and fourth surfaces, and a second sidewall surface connecting the third and fourth surfaces;

[0036] 103. The capping wafer is provided with metallized vias penetrating the third and fourth surfaces and metal pillars completely filling the metallized vias;

[0037] 104. The edge of the third surface of the capping wafer and the edge of the second surface of the functional wafer are bonded together by a sealing ring of a certain thickness.

[0038] 105. Perform half-cutting on the bonded functional wafer and cap wafer, cut through the functional wafer above the sealing ring, and cut a groove in the cap wafer below the sealing ring to expose the outer wall of the sealing ring.

[0039] like Figure 2 As shown, a half-dicing is performed on the bonded functional wafer and capping wafer to form a half-dicing slit 20. The thickness of the half-dicing slit 20 includes not only the thickness penetrating the functional wafer 21 but also a portion of the thickness of the capping wafer 22, and the thickness of the capping wafer 22 is greater than or equal to 15 μm. Therefore, the thickness of the half-dicing exceeds the thickness of the functional wafer 22, and the thickness of the capping wafer exceeds 15 μm.

[0040] 106. A connected metal deposition layer is deposited on the first surface and the first sidewall surface of the functional wafer, and on a portion of the second sidewall surface of the capping wafer, by magnetron sputtering, and covers the outer sidewall of the sealing ring.

[0041] like Figure 3 As shown, after obtaining the half-cut slit 20, a connected metal deposition layer 26 is deposited on the surface of the half-cut slit 20 and the first surface of the functional wafer. This metal deposition layer 26 can effectively cover the sealing ring of the wafer-level package sidewall, forming a metal isolation layer inside the sealing ring, which can prevent moisture and other substances from intruding into the filter cavity along the bonding interface. This greatly improves the wafer-level reliability of the thin-film bulk acoustic wave filter.

[0042] In a preferred embodiment of the present invention, considering the stress influence between the wafer surface and the metal layer, in order to stably fix the metal layer on the wafer surface, the surface of the metal layer is also heated by laser radiation during the deposition of the metal layer. The surface heat diffuses into the interior through thermal conduction, which can release most of the stress as much as possible; this avoids the high-temperature deformation stress between the wafer surface and the metal layer. Due to the difference in the coefficient of thermal expansion between the wafer and the metal layer, large residual stress is easily generated at the cut, which leads to a decrease in the sealing performance at the cut edge. The present invention uses laser radiation heat conduction to alleviate the residual stress at the cut edge, and can also reduce the temperature and pressure at the cut.

[0043] 107. An electroplated thickened layer is formed on the surface of the metal deposition layer by electroplating, and covers the outer wall of the sealing ring with a certain thickness;

[0044] like Figure 4 As shown, after forming a metal deposition layer 26 on the first surface and first sidewall surface of the functional wafer, and part of the second sidewall surface of the capping wafer, an electroplated thickening layer 27 is needed to reinforce the surface. Therefore, the electroplated thickening layer 27 has the same shape as the metal deposition layer 26. Considering the difficulty of the deposition and electroplating processes, the present invention sets the thickness of the metal deposition layer 26 to be greater than or equal to 500 nm and the thickness of the electroplated thickening layer 27 to be greater than or equal to 5 μm. By using two metal layers to wrap the wafer-level packaged thin-film bulk acoustic wave device, gas is blocked from entering and exiting from the side, further improving the hermeticity of the wafer-level package.

[0045] Understandably, by depositing material before electroplating, damage to the wafer surface caused by impurities during the electroplating process can be avoided. This creates a metallic insulating layer inside the sealing ring, preventing moisture and other substances from entering the filter cavity along the bonding interface. This significantly improves the wafer-level reliability of the thin-film bulk acoustic wave filter.

[0046] 108. Perform a full cut on the electroplated functional wafer and the capping wafer to penetrate through the functional wafer and the capping wafer.

[0047] like Figure 6 As shown, after forming the electroplated thickened layer 27, full dicing is continued along the half-cut slit 20 on the electroplated functional wafer 21 and the capping wafer 22, which can form multiple independent device structures.

[0048] In a preferred embodiment of the present invention, after heating the surface of the metal layer with laser radiation, the laser can also be used to perform a full cut on the half-cut slit 20, such as... Figure 5As shown, the laser is used along the direction indicated by the arrow to completely separate the half-cut slits 20, forming multiple independent device structures. Then, a grinding wheel is used to divide the entire device, which can further improve reliability, ensure that the metal layer is not torn by the grinding wheel, and ensure its integrity. This further improves the reliability of the metal sealing ring and ultimately improves the airtightness of the thin-film bulk acoustic wave device structure.

[0049] In a preferred embodiment of the present invention, the method further includes the metal pillar 24 extending an outer pad 23 from the fourth surface of the capping wafer; preferably, the outer pad 23 can be welded to the metal pillar 24 by electroplating and chemical plating, and the welding stress can be released by loading.

[0050] In a preferred embodiment of the present invention, the spacing between the functional patterns on the functional wafer exceeds 50 μm.

[0051] In the description of this invention, it should be understood that the terms "coaxial," "bottom," "one end," "top," "middle," "other end," "upper," "side," "top," "inner," "outer," "front," "center," "both ends," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0052] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "setting," "connection," "fixing," "rotation," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components or the interaction between two components. Unless otherwise explicitly limited, those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0053] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-reliability wafer-level packaged thin-film bulk acoustic resonator, characterized in that, The device includes a functional wafer and a capping wafer. The functional wafer has opposing first and second surfaces, and a first sidewall surface connecting the first and second surfaces. The capping wafer has opposing third and fourth surfaces, and a second sidewall surface connecting the third and fourth surfaces. The capping wafer has metallized vias penetrating the third and fourth surfaces and metal pillars completely filling the metallized vias. The edge of the third surface of the capping wafer is bonded to the edge of the second surface of the functional wafer through a sealing ring of a certain thickness. The first surface and the first sidewall surface of the functional wafer, as well as a portion of the second sidewall surface of the capping wafer, are provided with a communicating metal deposition layer. The metal deposition layer covers the outer sidewall of the sealing ring of a certain thickness. An electroplated thickening layer is provided on the surface of the metal deposition layer.

2. The high-reliability wafer-level packaged thin-film bulk acoustic resonator according to claim 1, characterized in that, The metal pillar extends from the fourth surface of the capping wafer to form an outer pad.

3. The high-reliability wafer-level packaged thin-film bulk acoustic resonator according to claim 1, characterized in that, The thickness of the metal deposition layer is greater than or equal to 500 nm, and the electroplated thickening layer is greater than or equal to 5 μm.

4. A high-reliability wafer-level packaged thin-film bulk acoustic resonator according to claim 1, characterized in that, The height of the second sidewall surface of the metal deposition layer is greater than or equal to 15 μm.

5. A high-reliability wafer-level packaged thin-film bulk acoustic resonator according to claim 1, characterized in that, The spacing of the functional patterns on the functional wafer exceeds 50 μm.

6. A method for fabricating a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure, characterized in that, The method includes: A functional wafer is provided, the functional wafer having opposing first and second surfaces, and a first sidewall surface connecting the first and second surfaces; A capped wafer is provided, the capped wafer having opposing third and fourth surfaces, and a second sidewall surface connecting the third and fourth surfaces; The capping wafer is provided with metallized vias penetrating the third and fourth surfaces and metal pillars that completely fill the metallized vias; The edge of the third surface of the capping wafer and the edge of the second surface of the functional wafer are bonded together by a sealing ring of a certain thickness. Half-cutting is performed on the bonded functional wafer and cap wafer. The functional wafer above the sealing ring is cut through, and the cap wafer below the sealing ring is cut into a groove to expose the outer wall of the sealing ring. A connected metal deposition layer is deposited on the first surface and the first sidewall surface of the functional wafer, and on a portion of the second sidewall surface of the capping wafer by magnetron sputtering, and covers the outer sidewall of the sealing ring. An electroplated thickening layer is formed on the surface of the metal deposition layer by electroplating, and covers the outer wall of the sealing ring with a certain thickness. A full cut is performed on the electroplated functional wafer and the capping wafer to penetrate through the functional wafer and the capping wafer.

7. The method for fabricating a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure according to claim 6, characterized in that, The method also includes the metal pillar extending from the fourth surface of the capping wafer to form an outer pad.

8. The method for fabricating a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure according to claim 6, characterized in that, The thickness of the half-cut exceeds the thickness of the functional wafer, and the depth of the cut cap wafer exceeds 15 μm.

9. The method for fabricating a high-reliability wafer-level packaged thin-film bulk acoustic wave device structure according to claim 6, characterized in that, The spacing of the functional patterns on the functional wafer exceeds 50 μm.

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