TWI404150B - Bonding pad flatten method for bumping structure package feasibility improvement - Google Patents

Abstract

A bonding pad flatten method for bumping structure package feasibility improvement includes etching of a thick metal layer after it is formed above a pad to form a flatten metal film, and bumping on the flatten metal film above the pad. This process can extremely improve the flatness of the bump and thereby enhance the feasibility and yield of the subsequent packaging.

Description

Bond pad flattening process to improve the feasibility of bump structure packaging

This invention relates to a wafer process, and more particularly to a bumping process for a wafer level package.

At the wafer level, the coplanarity after plating is not good due to the topography of the wafer surface or the re-passivation layer coating, and the poor coplanarity will cause subsequent wire bonding. Or the difficulty of pressing the package. As shown in FIG. 1, the conventional bump process directly grows the bumps 16 on the aluminum pad 10, and the edge of the aluminum pad 10 has a cliff formed by the wafer passivation layer 12 and the back passivation layer 14, so that after plating, The edges of the bumps 16 have raised protrusions 18. When the bump 16 is applied to the wire bonding package, as shown in FIG. 2, the protrusion 18 affects the wire drawing window, so that the bonding wire 20 cannot be firmly bonded to the bump 16, thereby reducing the yield. When the bumps 16 are applied in the press-fit package, as shown in FIG. 3, the bumps 16 are pressed to crush the conductive particles in the conductive paste 24 on the panel 22 to achieve electrical connection with the wires on the panel 22. However, the poor surface flatness of the bumps 16 causes the ratio of the conductive particles to be crushed to be lowered, thereby lowering the yield. Known solutions include modifying the top metal layout, changing the process before the wafer passivation layer 12, changing the SPICE model of the top layer metal, increasing the area of the aluminum pad 10, and using finer joints. Line 20, but these all have other shortcomings or insurmountable difficulties. For example, increasing the area of the aluminum pad 10 increases the area of the die, and the thinner bonding wire 20 cannot withstand large currents and cannot be applied to the power pad.

In the case of a product having a thick metal (greater than 3 μm), the thickness of the bump 16 is increased in order to lower the resistance value, resulting in a worse surface flatness of the bump 18, so that the difficulty of subsequent packaging is also higher.

The rear passivation layer 14 is thick, so that it is difficult to reduce the problems caused by the uneven surface of the aforementioned bumps 16. A product having a Re-Distribution Layer (RDL) has more than 99% requiring a post-passivation layer 14, and thus it is also difficult to avoid the difficulty caused by the uneven surface of the aforementioned bump 16.

One of the objects of the present invention is to provide a bump process for wafer level fabrication.

One of the objects of the present invention is to provide a bond pad planarization process that improves the feasibility of bump structure packaging.

According to the present invention, a bonding pad planarization process for improving the feasibility of a bump structure package includes sequentially sputtering a barrier layer and a seed layer on a pad, forming a thick metal layer on the seed layer, and grinding the thick metal layer to form a flat a metal film, the planarized metal film over the solder pad covers the photoresist, and the seed layer and the barrier layer are sequentially etched by using the photoresist as an etching mask, and the photoresist is removed and grown on the planarized metal film. Bump.

According to the present invention, a bonding pad planarization process for improving the feasibility of a bump structure package includes sequentially sputtering a barrier layer and a seed layer on a pad, forming a thick metal layer on the seed layer, and grinding the thick metal layer to form a flat a metal film covering the photoresist on the planarized metal film, but exposing a region above the pad, growing a bump in the exposed region, removing the photoresist, and sequentially etching the bump as an etch mask Seed layer and barrier layer.

After forming the planarized metal film, the present invention further grows the bumps thereon, thereby greatly improving the flatness of the bumps, and contributing to the feasibility and yield of the packaging process.

4A to 4H are flowcharts of the first embodiment. After the wafer front-end process is completed, as shown in FIG. 4A, the wafer passivation layer 12 and the post-passivation layer 14 are overlaid on the wafer, and only the pad 10 is exposed. The pad 10 is typically aluminum. When the bonding pad is to be formed, as shown in FIG. 4B, the barrier layer 262 and the seed layer 264 are sequentially sputtered. The barrier layer 262 may be titanium (Ti), titanium tungsten (TiW) or chromium (Cr), and has a thickness of 250A to 4000A. The seed layer 264 can be copper (Cu) or gold (Au) with a thickness between 1000A and 5000A. So far, it is the same as the conventional technology. Next, a thick metal layer 30 of copper or gold is plated on the seed layer 264 to have the structure shown in Fig. 4C. Preferably, the thickness of the thick metal layer 30 is greater than 3 μm. Then, the surface of the thick metal layer 30 is chemically mechanically polished (CMP) to form the planarized metal film 32 shown in FIG. 4D. Next, as shown in FIG. 4E, a photoresist 34 is formed on the planarization metal film 32 above the pad 10 as an etching mask by a yellow light process, and the residual seed layer 28 is removed by a copper etching or gold etching process, followed by titanium, The titanium oxide or chromium etching process removes the barrier layer 262 to form the structure shown in FIG. 4F. After the photoresist 34 is removed, as shown in FIG. 4G, the bump 36 is grown from the planarization metal film 32 as shown in FIG. 4H. The bump process is a well-known technique and will not be described in detail.

When the bump 36 is applied to the wire bonding package, as shown in FIG. 5, since the surface of the bump 36 is relatively flat, a wider window is provided for wire bonding, which increases the feasibility of the wire bonding package.

When the bump 36 is applied to the press-fit package, as shown in FIG. 6, since the surface of the bump 36 is relatively flat, the conductive particles in the conductive paste 24 can be sufficiently crushed to increase the feasibility and yield of the press-fit package.

7A to 7H are flowcharts of the second embodiment, wherein the first four steps are the same as the steps of FIGS. 4A to 4D, but the present embodiment covers the photoresist 34 by a yellow light process after CMP and directly performs gold bumps. The pattern of the copper bump or the post-passivation layer conductor is redistributed. As shown in FIG. 7E, the photoresist 34 exposes only the planarization metal film 32 over the bonding pad 10, as shown in FIG. 7F, in the planarization metal film. 32 copper or gold bumps 36 are grown. Preferably, the thickness of the bump 36 is greater than 3 μm. Then, the photoresist 34 is removed, and as shown in FIG. 7G, the etching process is performed by using the bump 36 as an etching mask to remove the residual seed layer 28 and the barrier layer 262, and the structure shown in FIG. 7H is obtained. The surface of the bump 36 is relatively flat, thus increasing the feasibility and yield of the packaging process, as shown in FIGS. 5 and 6.

As shown in the above process, the method of the present invention does not require special modification of the top metal layout, and it is not necessary to change the process model of the wafer passivation layer 12 or the top metal model. It is not necessary to particularly increase the pad for the bonding pad application supporting high current. 10 size.

The above description of the preferred embodiments of the present invention is intended to be illustrative, and is not intended to limit the scope of the invention to the disclosed embodiments. It is possible to make modifications or variations based on the above teachings or learning from the embodiments of the present invention. The embodiments are described and illustrated in the practical application of the present invention in various embodiments, and the technical idea of the present invention is intended to be equivalent to the scope of the following claims. Decide.

10. . . Solder pad

12. . . Wafer passivation layer

14. . . Post passivation layer

16. . . Bump

18. . . Bulge

20. . . Bonding wire

twenty two. . . panel

twenty four. . . Conductive plastic

262. . . Barrier layer

264. . . Seed layer

30. . . Thick metal layer

32. . . Flattening metal film

34. . . Photoresist

36. . . Bump

Figure 1 is a conventional bump structure;

2 is a schematic view showing the application of the bump of FIG. 1 in a wire bonding package;

3 is a schematic view showing the application of the bump of FIG. 1 in a press-fit package;

4A to 4H are flowcharts of a first embodiment of the present invention;

5 is a schematic view showing the application of the bump of the present invention in a wire bonding package;

Figure 6 is a schematic view showing the application of the bump of the present invention to a press-fit package;

7A through 7H are flowcharts of a second embodiment of the present invention.

10. . . Solder pad

12. . . Wafer passivation layer

14. . . Post passivation layer

20. . . Bonding wire

262. . . Barrier layer

32. . . Flattening metal film

36. . . Bump

Claims (8)

A bonding pad planarization process for improving the feasibility of a bump structure package includes the steps of: (A) sequentially sputtering a barrier layer and a seed layer on the pad; (B) forming a thick metal layer on the seed layer; Grinding the thick metal layer to form a planarization metal film; (D) the planarization metal film over the pad covers the photoresist; (E) sequentially etching the seed layer and the barrier layer with the photoresist as an etch mask (F) removing the photoresist; and (G) growing bumps on the planarized metal film. The bonding pad planarization process of claim 1, wherein the step B comprises electroplating copper or gold to form the thick metal layer. The bonding pad planarization process of claim 1, wherein the thick metal layer formed in the step B has a thickness greater than 3 μm. The bonding pad planarization process of claim 1, wherein the step C comprises chemical mechanical polishing of the thick metal layer. A bonding pad planarization process for improving the feasibility of a bump structure package includes the steps of: (A) sequentially sputtering a barrier layer and a seed layer on the pad; (B) forming a thick metal layer on the seed layer; Grinding the thick metal layer to form a planarized metal film; (D) covering the photoresist on the planarized metal film but exposing a region above the pad; (E) growing a bump in the exposed region; Removing the photoresist; and (G) sequentially etching the seed layer and the barrier layer with the bump as an etch mask. The bonding pad planarization process of claim 5, wherein the step B comprises electroplating copper or gold to form the thick metal layer. The bonding pad planarization process of claim 5, wherein the step B forms a thick metal layer having a thickness greater than 3 μm. The bonding pad planarization process of claim 5, wherein the step C comprises chemical mechanical polishing of the thick metal layer.