1. Field of the Invention
The present invention relates to a semiconductor device with projection electrodes (bumps) which can be connected electrically and mechanically to a circuit substrate, a method of fabricating a semiconductor device for the same, and a structure for mounting the semiconductor device which electrically and mechanically connect the semiconductor device to the circuit substrate.
For the above-mentioned circuit substrate, a resin substrate made of a fiber glass reinforced epoxy or the like, a ceramic substrate, or a glass substrate or the like for constituting a liquid crystal display panel can be used.
2. Description of the Related Art
Conventionally, there exists a semiconductor device with bumps which can be connected electrically and mechanically to a circuit substrate, for example a semiconductor device 71 as shown in FIG. 15.
In the semiconductor device 71, multiple electrode pads 74 are formed on an upper surface 72a of a semiconductor chip 72, and the upper surface 72a is covered with an insulating film 76 leaving only the upper surfaces of the electrode pads 74 not covered. Lower electrodes 79 are formed above respective electrode pads 74. Bumps 82 formed in a substantially vertical straight-walled shape with respect to the upper surface 72a of the semiconductor chip 72 are provided above respective lower electrodes 79.
Next, a method of fabricating the semiconductor device 71 shown in FIG. 15 will be described with reference to FIG. 16 to FIG. 18 as well.
For fabricating the semiconductor device 71, the insulating film 76 is first formed over the entire surface of the semiconductor substrate 70 on which plural electrode pads are placed in lines in the direction perpendicular to the upper surface of the semiconductor substrate and thereby plural semiconductor chips are to be formed, as shown in FIG. 16.
Thereafter, the insulating film 76 is patterned to expose the upper surface of the electrode pads 74 with a photolithography treatment and an etching treatment.
Next, a common electrode film 78 is formed on the entire surface of the surface 70a of the semiconductor substrate 70, including on the insulating film 76 and on the electrode pads 74 with a sputtering process.
Incidentally, the common electrode film 78 is made by sequentially forming aluminum in a thickness of 0.8 .mu.m, chromium at 0.01 .mu.m, and copper at 0.8 .mu.m, respectively, from the side of the semiconductor substrate 70.
The common electrode film 78 having such a multi-layered structure serves as a connecting layer to the electrode pads 74 and a barrier layer for preventing interdiffusion, as well as an electrode used for forming bumps with a plating process.
Next, as shown in FIG. 17, a photoresist 80 is formed over the entire surface of the common electrode film 78 in a thickness of 17 .mu.m with a spin coating process. The photoresist 80 is patterned with a photolithography treatment by using a predetermined photomask to expose the photoresist 80 in an exposure apparatus and then performing a development treatment. By the patterning, the photoresist 80 exposes the common electrode film 78 to open each area in which a bump 82 is designed to be formed later.
Next, the bump 82, in straight-walled shape and having a thickness ranging from 10 .mu.m to 15 .mu.m, is formed in each opening of the photoresist 80 above the common electrode film 78 with a gold plating treatment which uses the common electrode film 78 as an electrode for plating.
After the photoresist 80 is removed, each of the bumps 82 is used as a mask and the common electrode film 78 is etched with a wet etching process to form the lower electrodes 79 in areas aligned with the bumps 82 as shown in FIG. 18.
Finally, the semiconductor substrate 70 is processed by cutting (dicing) at the boundary parts between the adjacent semiconductor chips of semiconductor substrate 70 into single pieces of a semiconductor chip 72 as shown in FIG. 15, thus obtaining plural semiconductor devices 71.
Incidentally, the wet etching is performed when the common electrode film 78 is etched to form the lower electrodes 79 as described in FIG. 18 and FIG. 19 for the following reasons.
Specifically, since the common electrode film 78 is formed in a three-layered structure consisting of aluminum in a thickness of 0.8 .mu.m, chromium at 0.01 .mu.m, and copper at 0.8 .mu.m, respectively, from the side of the semiconductor substrate 72, the use of a dry etching process would need to use a composite etching gas as an etching gas used to obtain an etching selectivity of a layer being etched with respect to the other layers, thereby complicating the selection of the composite etching gas.
Also, the dry etching process is disadvantageous in industrial manufacturing since it takes a very long time for the etching. Furthermore, the dry etching process has a disadvantage in that expensive apparatuses used for the etching treatment are required.
According to the wet etching process however, an etchant allowing for good etching selectivity can be selected to conveniently perform the etching treatment without requiring large-scale equipments.
Next, an example of a conventional structure for mounting a semiconductor device to connect the semiconductor device 71 formed in accordance with the above-mentioned fabricating method to a circuit substrate will be described with reference to FIG. 19, with a liquid crystal display panel taken as an example.
In FIG. 19, portions other than the semiconductor device 71, glass substrates 86a, 86b of liquid crystal display panel 86, and a flexible printed circuit board (FPC) 68 are shown as a sectional view.
In a liquid crystal display panel 86 shown in FIG. 19, a liquid crystal 96 is filled between glass substrates 86a and 86b. A plurality of transparent electrodes 88a, 88b are provided on the opposite surface of the glass substrate 86a so as to run perpendicular with each other.
To mount the semiconductor device 71 above the glass substrate 86a which is the circuit substrate of the liquid crystal display panel 86, the semiconductor device 71 is disposed upside down with respect to the orientation shown in FIG. 15. The semiconductor device 71 is disposed with the bumps 82 thus located on the lower positions in alignment with the transparent electrode 88a on the glass substrate 86a.
At this point, an anisotropic conductive adhesive 54 is interposed between the bumps 82 and the glass substrate 86a.
Incidentally, the anisotropic conductive adhesive 54 is formed by mixing conductive particles 52 into an insulating adhesive.
In this manner, while the semiconductor device 71 is set on the glass substrate 86a of the liquid crystal display panel 86, concurrently with the semiconductor device 71 being pressed on the liquid crystal panel substrate 86a, a heating is performed therefor to connect each bump 82 electrically to the respective transparent electrodes 88a on the glass substrate 86a.
Furthermore, an FPC 68 is also disposed above the terminal electrode 88c formed on the right side in FIG. 19 on the glass substrate 86a such that an anisotropic conductive adhesive 54 having the conductive particles 52 mixed therein is interposed between the FPC 68 and the terminal electrode 88c. While the FPC 68 is pressed on the glass substrate 86a, heating is performed therefor.
The FPC 68 is a film patterned with a copper wiring electrode for transmitting electrical power and providing an input signal to the semiconductor device 71.
The above-mentioned structure holds the conductive particles 52 of the anisotropic conductive adhesive 54 between the bumps 82 and the transparent electrodes 88a and between the FPC 68 and the terminal electrode 88c, respectively, which provides an electrical connection between the bumps 82 and the transparent electrodes 88a and between the copper wiring electrode on the FPC 68 and the terminal electrode 88c as well as a mechanical connection thereof using the insulating adhesive.
Thereafter, as shown in FIG. 19, a mold resin 62 is applied onto the semiconductor device 71, the upper surface of the flexible film 68, and the periphery thereof. The mold resin 62 prevents moisture from entering each of the connections between the bumps 82 and the transparent electrodes 88a and the connection between the copper wiring electrode on the FPC 68 and the terminal electrode 88c, and also provides mechanical protection, thereby improving reliability.
However, the above-mentioned conventional semiconductor device and the structure for mounting the same on the circuit substrate have a disadvantage in that a large area is occupied to mount the semiconductor device on the circuit substrate.
Thus, it is difficult to reduce the circuit substrate to which the semiconductor device is connected, in size.
For example, a connecting area 8 for connecting the semiconductor device 71 above the glass substrate 86a of the liquid crystal display panel 86 to the FPC 68 as shown in FIG. 19 is required to have a width of approximately 5 mm since the semiconductor device 71 has a width of 2 mm and requires a margin for connection of 1 mm and the flexible film 68 requires a margin for connection of 2 mm.
The portion of the glass substrate 86a at which the semiconductor device 71 and the flexible film 68 are connected is a portion which serves as a non-displaying region of the liquid crystal panel. Thus, the above-mentioned conventional structure has a disadvantage in that the area of the non-displaying region is very large with respect to the area of the displaying region.
In other words, a larger area is occupied to mount the semiconductor device and the FPC onto the liquid crystal display panel.