Glass through-vias utilizing a conductive barrier layer
A conductive barrier layer applied between copper and gold layers in MEMS components addresses copper diffusion issues, enhancing reliability and performance by preventing copper migration and contamination in copper glass through vias.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- MENLO MICROSYSTEMS INC
- Filing Date
- 2023-06-07
- Publication Date
- 2026-06-24
Smart Images
Figure 2026520714000001_ABST
Abstract
Description
Background Art
[0001] Copper-based electrical vias can be used to transmit electrical signals to microelectromechanical system (MEMS) components. Copper-based vias can provide an effective electrical interface to MEMS devices and / or external devices or systems encapsulated by conductive metal pads. Under certain conditions, the conductive metal pads can exhibit corrosion, which can adversely affect the performance of the MEMS components.
Summary of the Invention
Problems to be Solved by the Invention
[0002] Embodiments described herein are directed to a conductive barrier layer applied between a copper glass through via (TGV) and any associated gold layer to reduce or eliminate the movement of copper through the gold layer, and as a result, reduce or eliminate the formation of contaminants (e.g., CuO) on the surface of the gold layer.
[0003] In one aspect, the invention can be a method of preventing corrosion associated with a conductive glass through via (TGV). The method can include forming a TGV in a glass substrate for use in a microelectromechanical system (MEMS) device. The TGV can have a first end and a second end and can at least partially include copper. The method can further include applying a conductive barrier layer on the first end of the TGV and / or on the second end of the TGV.
[0004] The method may further include applying a metal layer on top of the conductive barrier layer. The method may also include extending the conductive barrier layer over the first end of the TGV and over at least a portion of the glass substrate surrounding the end of the TGV, such that the conductive barrier layer overlaps the boundary between the TGV and the glass substrate. The method may further include applying the conductive barrier layer using an electroless plating process. The electroless plating technique may be electroless palladium-gold immersion (EPIG). The electroless plating technique may be gold-electroless palladium-gold immersion (IGEPIG). The electroless plating technique may be electroless nickel-gold immersion (ENIG).
[0005] In one embodiment, forming a TGV in a glass substrate may further include forming a planar TGV in a glass substrate. Forming a TGV in a glass substrate may further include forming a constricted TGV in a glass substrate.
[0006] In another embodiment, the present invention may be a conductive glass through-via (TGV) structure comprising a TGV formed in a glass substrate for use in microelectromechanical systems (MEMS) devices. The TGV may have a first end and a second end and may contain at least partially copper. The structure may further comprise a conductive barrier layer applied on the first end and / or the second end of the TGV.
[0007] The structure may further comprise a metal layer disposed on top of the conductive barrier layer. The conductive barrier layer may extend over the first end of the TGV and over at least a portion of the glass substrate surrounding the end of the TGV, such that the conductive barrier layer overlaps the boundary between the TGV and the glass substrate. The conductive barrier layer may be applied using an electroless plating process. The electroless plating technique may be electroless palladium-gold immersion (EPIG). The electroless plating technique may be gold-electroless palladium-gold immersion (IGEPIG). The electroless plating technique may be electroless nickel-gold immersion (ENIG). The TGV may be a planar TGV. The TGV may be a constricted TGV.
[0008] In another embodiment, the present invention may be a micro-electromechanical system (MEMS) component comprising a glass substrate for hosting a MEMS device, a glass lid disposed on the glass substrate and enclosing the MEMS device within a cavity, and glass through-vias (TGVs) formed within the glass lid. The TGV may have a first end on the outside of the glass lid and a second end electrically coupled to the MEMS device. The TGV may contain at least partially copper. The MEMS component may further comprise a conductive barrier layer applied on the first end of the TGV and / or on the second end of the TGV.
[0009] The conductive barrier layer may extend above the first end of the TGV and above at least a portion of the outer surface of the glass lid, such that the conductive barrier layer overlaps the boundary between the TGV and the glass lid.
[0010] A patent or application file must include at least one drawing made in color. A copy of this patent or patent application publication accompanied by the color drawing will be provided by the Office upon request and payment of the necessary fees.
[0011] The above will become clear from the following more specific description of exemplary embodiments, as shown in the attached drawings, where similar reference numerals throughout the drawings refer to the same parts. The drawings are not necessarily to scale, and instead the focus is on illustrating embodiments. [Brief explanation of the drawing]
[0012] [Figure 1A] This diagram shows the components of a MEMS (Mechanical Energy Management System) part. [Figure 1B] This diagram shows the components of a MEMS (Mechanical Energy Management System) part. [Figure 2] This figure shows an example of a barrier layer arrangement according to an embodiment of the present invention. [Figure 3A] This is a cross-section of a constricted via. [Figure 3B] This is a top view of a constricted via. [Figure 4A] This is a cross-sectional view of a planar via. [Figure 4B] This is a cross-sectional view of a planar via. [Figure 4C] This is a top view of a planar via. [Figure 5] This diagram shows the details of the barrier layer at the top of the via. [Figure 6] This figure shows the barrier layer thickness and coverage characteristics at a selected depth for a constricted via. [Figure 7A] This figure shows the via corrosion characteristics when there is no barrier layer in the designated location. [Figure 7B] This figure shows the via corrosion characteristics when a barrier layer is present in a predetermined location. [Modes for carrying out the invention]
[0013] The following is a description of exemplary embodiments.
[0014] A microelectromechanical system (MEMS) component may have a two-part structure, as shown in Figure 1A. The first part comprises a MEMS device structure 10 built on a glass substrate 12, and the second part comprises a glass lid or cap 14 surrounding and covering the MEMS device structure 10, as shown in Figure 1B, forming a hermetically sealed cavity 16 in which the MEMS device structure 10 resides. One or more conductors may pass through the glass lid 14 to reach the MEMS device structure 10, thereby enabling electrical access to the MEMS device structure 10 from outside the sealed cavity 16. These conductors may be in the form of glass through-vias (TGVs) 18 that facilitate the transmission of electrical signals through the glass lid 14 while maintaining the hermetically sealed cavity 16.
[0015] The conductive material within the TGV18 may be copper, with a gold layer 20a bonded to the lower end of the TGV18 (i.e., facing the substrate) and a gold layer 20b (outer bonding pad) bonded to the upper end of the TGV18. A gold layer 20c is disposed on the substrate 12 and electrically coupled to the MEMS device structure 10. The gold layer 20a at the bottom of the TGV18 is bonded to the gold layer 20c on the substrate 12 by thermocompression bonding, thereby forming a hermetically sealed cavity 16 as shown in Figure 1B.
[0016] Copper is known to diffuse readily through gold, especially at high temperatures. When copper from TGV18 diffuses through the gold layer 20a into the oxygen-containing cavity of the MEMS device 10, there is a significant risk of contaminants (e.g., cupric oxide, CuO) forming on the cavity-facing surface of the gold layer 20a. These contaminants can adversely affect the performance of the MEMS device 10. Furthermore, copper may migrate through the outer gold layer 20b to form copper contaminants on the outer bonding pad, thereby increasing the likelihood of inadequate external electrical connections to the MEMS component.
[0017] The embodiments described herein are directed to one or more conductive barrier layers applied between (i) copper (Cu) glass through vias (TGVs) and (ii) each of one or more gold (Au) layers associated with the TGVs. The barrier layer is configured to reduce or eliminate the movement of Cu from the TGV through one or more associated Au layers.
[0018] FIG. 2 shows an example of a barrier layer arrangement according to the described embodiments. The example of FIG. 2 is not necessarily drawn to scale and is used to present a conceptual explanation. Similar to the structure shown in FIG. 1A, the cap 14 includes a copper-based TGV 18 disposed within the glass lid 14, the gold layer 20b is coupled to the upper end of the TGV 18, and the gold layer 20a is coupled to the lower end of the TGV 18. Although the TGV 18 in this exemplary embodiment is described as being copper-based, it should be understood that in some embodiments, the TGV may include copper, or a material that is mostly copper (e.g., more than 95 percent copper), or a material that contains less copper (e.g., more than half copper), or a material that contains less than half copper.
[0019] The barrier layer 202a is disposed between the TGV 18 and the Au layer 20a at the lower end of the TGV 18 (i.e., facing the substrate). The barrier layer 202b is disposed between the TGV 1� and the Au layer 20b at the upper end of the TGV 18.
[0020] In the exemplary embodiments described herein, the barrier layer includes palladium (Pd). In alternative embodiments, the barrier layer may include a material such as nickel (Ni) or a composite including Pd and / or Ni, or other materials suitable for blocking the movement of Cu. The barrier layer must be thick enough to prevent the movement of Cu to an adjacent metal layer (e.g., gold) at high temperatures (e.g., 300 °C to 400 °C for 1 to 2 hours). The sufficient thickness of the barrier layer may depend on the characteristics and physical parameters of the device and can be determined empirically, but the sufficient thickness is generally at least 250 nm for Pd and at least 175 nm for Ni.
[0021] The process of deploying the barrier layer described in this specification may be integrated into the procedures for manufacturing microelectromechanical system (MEMS) components. In an exemplary embodiment, the TGVs may be manufactured during MEMS component fabrication and filled with copper. The TGVs can take several forms, including several versions of constricted vias (as shown in the cross-sectional view of FIG. 3A, the top view of FIG. 3B, and FIGS. 5(A), 5(B), and 6), or planar vias (shown in FIGS. 4A, 4B, and 4C). Here, "planar" refers to the fact that the metallized top 402 of the via 404 is substantially in the same plane as the glass surface 406 (up to the manufacturing specifications). Other variations to these designs are also possible.
[0022] After the Cu-based vias are formed in the glass wafer, the glass wafer undergoes a metal surface treatment step where a conductive barrier layer is deposited or plated on top of the Cu-based vias. This can include a pre-treatment of the Cu surface, followed by the use of a catalyst, a barrier layer, and a final Au layer. In some cases of EPIG, for example, a thin Ni or Au layer may be incorporated between Cu and Pd, and in other cases, Pd may be plated directly on Cu along with some pre-treatment (such as etching of Cu).
[0023] There are several processes available for applying a conductive barrier layer, such as (i) electroless nickel-immersion gold plating (ENIG), (ii) electroless palladium-immersion gold plating (EPIG), (iii) immersion gold-electroless palladium-immersion gold plating (IGEPIG), and other types of barrier layer processes.
[0024] An important characteristic is the presence of a barrier material (e.g., nickel (Ni) or palladium (Pd) in the above example) covering the entire exposed via surface, and that the barrier material is thick enough to prevent the migration of Cu to Au at high temperatures (e.g., 350-400°C for 1-2 hours). This also includes a continuous layer of this metallic finish across the entire outer surface of the TGV. An annealing step may also be used to remove embedded hydrogen from the coating.
[0025] Once the conductive barrier layer is deposited, an additional layer (e.g., Au) is deposited on the lid wafer, and then the lid wafer is bonded to the MEMS substrate in a specific oxygen environment. The barrier layer provides reliable performance across a range of process and operating environment parameters (%O2, humidity, temperature, etc.).
[0026] Figure 5(A) shows a cross-sectional view of an exemplary constricted via, viewed near the glass substrate surface at the top of the via. As shown, the conductive Pd barrier layer is positioned on the outside of the Cu via, covering the glass-to-copper interface around the via. It is important that the Pd barrier layer completely covers the entire TGV surface and has a uniform thickness. Achieving complete coverage is challenging for constricted via designs. The thickness of the barrier layer tends to be greater at the top / outside of the constricted via than inside the cavity. See, for example, Figure 6, which shows the coverage of the Pd barrier layer at various depths of a constricted via into the glass substrate. Figure 6 shows that the coverage near the top of the constricted via is complete or near complete, while the coverage to the deeper parts of the via cavity can be significantly reduced. Techniques such as sonication may be used to deliver Pd into the via cavity, thereby obtaining a thicker and more uniform barrier layer to the deeper parts of the via cavity. On the other hand, when the barrier layer described herein is applied to a planar via, a barrier layer of uniform thickness tends to be obtained, resulting in complete or near-complete coverage across the entire planar via.
[0027] Figure 7A shows an exemplary top view of a via without a Pd barrier (or with insufficient Pd barrier placement), and Figure 7B shows an exemplary top view of a via with considerable Pd barrier layer coverage. In both Figures 7A and 7B, the dark circle in the center of the via represents the via cavity (see, for example, Figure 3A). Figure 7A shows a considerable amount of cupric oxide (CuO) corrosion 702 formed around the via surface due to copper migration through the gold layer, whereas Figure 7B shows relatively little CuO corrosion on the via surface due to the presence of the Pd barrier layer.
[0028] The arrangement of conductive barrier layers described herein can be achieved using a variety of techniques, particularly electroless plating (e.g., ENIG, EPIG, or IGEPIG), sputtering, atomic layer growth (ALD), chemical vapor deposition (CVD), and physical vapor deposition (PVD). Chemical-based techniques such as electroless plating tend to yield better results for cavity-based vias (e.g., constricted vias) because they facilitate the propagation of the barrier material into the via cavity. Furthermore, as described herein, ultrasonic treatment techniques may be used to further enhance the distribution of the barrier material into the via cavity.
[0029] While exemplary embodiments are specifically shown and described, it will be understood by those skilled in the art that various modifications can be made in form and detail without departing from the scope of embodiments contained in the appended claims.
Claims
1. A method for preventing corrosion related to conductive glass through vias (TGVs), Forming a TGV in a glass substrate for use in a microelectromechanical system (MEMS) device, wherein the TGV has a first end and a second end and contains at least a portion of copper. Applying a conductive barrier layer on the first end of the TGV and / or on the second end of the TGV, A method that includes this.
2. The method according to claim 1, further comprising applying a metal layer on the conductive barrier layer.
3. The method according to claim 1, further comprising extending the conductive barrier layer over the first end of the TGV and over at least a portion of the glass substrate surrounding the end of the TGV, such that the conductive barrier layer overlaps the boundary between the TGV and the glass substrate.
4. The method according to claim 1, further comprising applying the conductive barrier layer using an electroless plating process.
5. The method according to claim 4, wherein the electroless plating technique is electroless palladium-immersion gold plating (EPIG).
6. The method according to claim 4, wherein the electroless plating technique is immersion gold-electroless palladium-immersion gold plating (IGEPIG).
7. The method according to claim 4, wherein the electroless plating technique is electroless nickel-gold immersion plating (ENIG).
8. The method according to claim 1, further comprising forming the TGV in the glass substrate by forming a planar type TGV in the glass substrate.
9. The method according to claim 1, further comprising forming the TGV in the glass substrate by forming a constricted TGV in the glass substrate.
10. A TGV formed in a glass substrate for use in a microelectromechanical system (MEMS) device, wherein the TGV has a first end and a second end and contains at least a portion of copper, A conductive barrier layer applied to the first end and / or the second end of the TGV, A conductive glass through-via (TGV) structure comprising [a specific feature].
11. The structure according to claim 10, further comprising a metal layer disposed on the conductive barrier layer.
12. The structure according to claim 10, wherein the conductive barrier layer extends over the first end of the TGV and over at least a portion of the glass substrate surrounding the end of the TGV, such that the conductive barrier layer overlaps the boundary between the TGV and the glass substrate.
13. The structure according to claim 10, wherein the conductive barrier layer is applied using an electroless plating process.
14. The structure according to claim 13, wherein the electroless plating technology is electroless palladium-immersion gold plating (EPIG).
15. The structure according to claim 13, wherein the electroless plating technology is immersion gold-electroless palladium-immersion gold plating (IGEPIG).
16. The structure according to claim 13, wherein the electroless plating technology is electroless nickel-gold immersion plating (ENIG).
17. The structure according to claim 10, wherein the TGV is a planar type TGV.
18. The structure according to claim 10, wherein the TGV is a constricted TGV.
19. A glass substrate that holds a microelectromechanical system (MEMS) device, A glass cover is disposed on the glass substrate and surrounds the MEMS device within the cavity, A glass through-via (TGV) formed within the glass lid, wherein the TGV has a first end located outside the glass lid and a second end electrically coupled to the MEMS device, and comprises at least a portion of copper, A conductive barrier layer applied to the first end and / or the second end of the TGV, A MEMS component equipped with the following features.
20. The MEMS component according to claim 19, wherein the conductive barrier layer extends over the first end of the TGV and over at least a portion of the outer side of the glass lid, such that the conductive barrier layer overlaps the boundary between the TGV and the glass lid.