1. Field of the Invention
The present invention generally relates to a multi-layer via structure, and more particularly to a multi-layer via structure applied for a flexible semiconductor device or a flexible multi-layer substrate.
2. Description of Prior Art
A multi-layer substrate can be utilized for manufacturing a package substrate, a printed circuit board, a flexible package substrate or a flexible printed circuit for realizing miniaturization of all electronic products is an inevitable trend in this modern world. Particularly, constant researches in the related industry are held for developing lighter, thinner, more flexible semiconductor devices or multi-layer substrates to create kinds of flexible and bendable electronic products. These flexible semiconductor devices or flexible multi-layer substrates can be applied in kinds of flexible and bendable electronic products more efficiently and can meet miniaturization demands of these electronic products. As the thicknesses of the flexible multi-layer substrates get thinner, the routing densities of the integrated circuits and the multi-layer substrates become higher.
Please refer to FIG. 1, which depicts a diagram of a multi-layer via structure with multi-layer buried vias formed for raising the routing density of the integrated circuit and the multi-layer substrate according to stacked via skill of prior art. As shown in FIG. 1, the idea of the stacked via structure is to locate the metal layers 10, 20 and 30 (metal line or bond pad) of different layers in the same perpendicular position. After the respective dielectric layers 80 and 90 are formed, the perpendicular vias are formed at the positions of the metal layers 10 and 20. Then, conducting metal material is offered to form via metals 60, 70 to eclectically connect the different metal layers 10, 20 and 30 (metal line or bond pad) higher and lower. It is an effective skill of decreasing the routing density of the integrated circuit and the multi-layer substrate. However, such skill can be merely applicable to the hard integrated circuit or the hard substrate but not applicable to the flexible integrated circuit and the flexible multi-layer substrate. The main reason is that the property of such stacked via structure leads to gather a large amount of metal materials in a via area and therefore, such stacked via structure has no flexibility almost. If such stacked via structure according to prior art is applied in the flexible integrated circuits and flexible multi-layer substrates and bent. The bending action can easily damage the stacked via structure.
Please refer to FIG. 2, which depicts a diagram of a multi-layer via structure with a cross-layer via (blind via) formed for raising the routing density of the integrated circuit and the multi-layer substrate according to stacked via skill of prior art. The idea of such stacked via structure is also to locate the metal layers 10 and 20 (metal line or bond pad) of different layers in the same perpendicular position. The respective dielectric layers 80 and 90 are employed to insulate the metal layers 10 and 20 from other metals. A single perpendicular via is formed for penetrating the aforesaid all layers. Then, the via metal 60 shown in FIG. 2 is formed by an etching process or a build up process to electrically connect the different metal layers 10 and 20. However, such skill still can merely be applicable to the hard integrated circuit or the hard substrate. The property of such stacked via structure remains to lead to gather a large amount of metal materials in a via area and therefore, such stacked via structure has no flexibility almost. Accordingly, such stacked via structure is not applicable to the flexible integrated circuit and the flexible multi-layer substrate.
Please refer to FIG. 3, which depicts a diagram of a multi-layer via structure with a cross-layer via having an inclined wall and formed according to stacked via skill of another prior art. Similarly as described in prior art shown in FIG. 2, the idea of such multi-layer via structure is to locate the metal layers 10 and 20 (metal line or bond pad) of different layers in the same perpendicular position roughly. The respective dielectric layers 80 and 90 are employed to insulate the metal layers 10 and 20 from other metals. A single perpendicular via is formed for penetrating the aforesaid all layers. Then, the via metal 60 shown in FIG. 3 is formed by an etching process or a build up process to electrically connect the different metal layers 10 and 20. However, the wall of the single perpendicular via is tilted and must have an angle with certain degrees. Consequently, the occupied area of the metal layers 20, 60 (bond pad) in the multi-layer substrate becomes larger and results in low routing density.
Please refer to FIG. 4, which depicts a diagram of a multi-layer via structure with multi-layer buried vias formed according to staggered via skill of prior art. As shown in FIG. 4, the via metal 60 is formed on the metal layer 10 in advance and extends outwards on the surface of the dielectric layer 80 with a certain position and a certain area (for connecting with the via metal 70). Then, the dielectric layer 90 is formed and an open is formed at the aforesaid certain area and the via metal 70 is formed at the aforesaid certain area. As shown in FIG. 4, the vertical line 99 passing through the edge of the via metal 70 falls on the aforesaid certain position of the via metal 60. This is a general arrangement in prior art that the via metal 70 is not overlapped with the via metal except the aforesaid certain area as much as possible. Such multi-layer via structure is the most common and the most widely used structure in prior art but it cannot decrease the size of the integrated circuit and multi-layer substrate as much as the stacked via structure shown in FIG. 3. Therefore, such multi-layer via structure still has inherent limitations for decreasing the routing density of the integrated circuit and the multi-layer substrate. Although, the flexibility of such multi-layer via structure is better than the flexibility of the stacked via structure, it is beyond the staggered via skill of prior art's reach to satisfy the further demands of the routing density for the flexible integrated circuit and the flexible multi-layer substrate nowadays.
Consequently, there is a need to develop a multi-layer via structure to solve the aforesaid drawbacks of prior arts and to break through the limitations to satisfy the thinner, more flexible demands of the flexible integrated circuits and flexible multi-layer substrates as increasing the routing densities of the flexible integrated circuits and flexible multi-layer substrates further.