This invention relates to a semiconductor device comprising bumps that are suitable for mounting on a circuit board with an anisotropic conductive film therebetween.
Recently, a semiconductor device for surface mounting comprising bumps (projecting terminals) capable of electrically and mechanically connecting to a circuit board has been often used.
The structure of the bump in such a conventional semiconductor device and a fabricating method thereof will be briefly described with reference to FIG. 14A to FIG. 14D. Incidentally, these drawings are sectional views, but oblique lines showing sections are omitted.
FIG. 14D shows a section of the bump and thereabout of a complete semiconductor device.
On the surface of a silicon wafer 213 which is cut into semiconductor chips, a selective oxide (LOCOS) film 204 which is a layer necessary for fabricating a semiconductor device is provided, and an aluminum layer 702 is provided on the selective oxide (LOCOS) film 204. This aluminum layer 702 is a layer necessary to input and output a power supply or a signal to/from interconnections in the semiconductor device and an integrated circuit from/to the outside.
On top of that, a passivation film 703 which is an insulation protection film covering the entire face of the silicon wafer 213 is provided, and an opening portion 703a is formed in the passivation film 703 on the aluminum layer 702. A gold bump 701 which is mushroom shaped is provided from the aluminum layer 702 within the opening portion 703a extending onto the passivation film 703 around the opening portion 703a with a noble metal film 705 therebetween.
In this drawing, only one bump is shown, but many bumps are provided in a real semiconductor chip.
FIG. 14A to FIG. 14C are views showing the mid-steps of the fabrication of this semiconductor device.
As shown in FIG. 14A, the selective oxide film 204 is formed on the silicon wafer 213, and the aluminum layer 702 which is connected to the internal integrated circuit is formed at a necessary position on the selective oxide film 204. The passivation film 703 which covers the entire face of the silicon wafer 213 including the aluminum layer 702 is formed, and the opening portion 703a for establishing connection with the outside is formed on the aluminum layer 702.
Then, as shown in FIG. 14B, the noble metal film 705 is formed on the entire faces of the passivation film 703 and the aluminum layer 702, and further a photosensitive resist 710 is selectively (except for a bump formation region) formed on the noble metal film 705.
The noble metal film 705 is a noble metal layer such as an alloy of titanium and tungsten, or the like and has a function as an electrode for producing the gold bump 701, which is formed on the aluminum layer 702 in a subsequent step, by electro-plating, and another function of improving the connection between the aluminum layer 702 and the gold bump 701.
This noble metal film 705 is formed by being laminated on the entire surface in a vacuum apparatus.
Next, as shown in FIG. 14C, a gold layer is produced in a portion in which the resist 710 is not formed by the electro-plating step to form the gold bump 701 which is the mushroom shaped bump electrode.
Then, after the resist 710 is removed, the noble metal layer 705 is removed with the gold bump 701 as a mask with only a portion thereof under the gold bump 701 left. FIG. 14D is a sectional view of this state.
Through such process steps, the bump electrodes of the gold bumps 701 are formed on the silicon wafer 213, and the silicon wafer 213 is cut into discrete semiconductor chips to complete semiconductor devices.
However, in the semiconductor device comprising such conventional bumps, since a plating process which is hard to manage is employed for making up the bumps, the bumps are prone to be nonuniform in height, and additionally, the use of costly gold for the material of the bumps results in a high cost of production.
The present invention is made to solve such problems and its object is to make it possible to easily fabricate bump electrodes of a semiconductor device at low cost and to make the height of the bumps uniform.
Moreover, another object is to make it possible that the height of a most projecting end face of the bump is sufficiently higher than those of projecting faces of any other parts of the semiconductor device in order that the bump can be surely electrically connected to an interconnection on a circuit board when such a semiconductor device is mounted on the circuit board with an anisotropic conductive film therebetween, and that an effective area of the end face is made large to catch a plurality of conductive particles.
To achieve the above object of the present invention, a semiconductor device comprising a polysilicon layer used for an interconnection and a gate of a transistor, an insulation layer covering thie polysilicon layer, an interconnection conductor layer formed on the insulation layer, and a bump for inputting and outputting a power supply or a signal to an integrated circuit, on the surface of a semiconductor chip in which the integrated circuit is formed, is structured as follows.
A polysilicon film and an insulation film made of the same materials as those of said polysilicon layer and said insulation layer are provided at a region at which the bump is formed, on the surface of the semiconductor chip; a first conductor which covers the insulation film and is electrically connected to the interconnection conductor layer is made of the same material as that of the interconnection conductor layer by sputtering; a protection insulation film which covers the surfaces of the first conductor, the interconnection conductor layer, and the semiconductor chip and in which an opening portion is provided on the first conductor is formed; a second conductor which conducts to the first conductor through the opening portion is formed on the protection insulation film by sputtering.
Further, the bump is composed of the polysilicon film, the insulation film, the first conductor, and the second conductor, and is formed so that a height of a most projecting end face thereof from the surface of the semiconductor chip is higher than those of projecting faces of any other parts.
Also in this case, each of the aforesaid first conductor and the second conductor can be made of aluminum.
Moreover, it is preferable that the most projecting end face of the bump is covered with a conductive film for preventing surface oxidation, that is, a conductive oxidation film or a noble metal film.
In the case where the aforesaid bump is composed of the aforesaid first conductor and the second conductor which conducts to the first conductor through the opening portion formed in the protection insulation film covering the first conductor, the film thickness of the protection insulation film at the region under the second conductor is formed thicker than that of the other region, thereby increasing the bump""s height.
Further, in the present invention, a semiconductor device comprising a bump, on the surface of a semiconductor chip in which an integrated circuit is formed, for inputting and outputting a power supply or a signal to the integrated circuit and mounted on a substrate with an anisotropic conductive film containing a large number of conductive particles therebetween is structured as follows.
On the surface of the semiconductor chip, a first conductor which is electrically connected to the integrated circuit; a protection insulation film which covers the surfaces of the first conductor and the semiconductor chip and in which a through hole is formed on the first conductor; and a second conductor which is formed on the protection insulation film by sputtering and conducts to the first conductor through the through hole, are provided, wherein the bump is composed of the first conductor and the second conductor, and is formed so that a height of a most projecting end face thereof from the surface of the semiconductor chip is higher than those of projecting faces of any other parts by an error in diameter of the large number of conductive particles contained in the anisotropic conductive film or more.
It is desirable that a maximum opening dimension of the through hole formed in the protection insulation film is within 1.5 times a minimum diameter of the large number of conductive particles contained in the anisotropic conductive film.
Moreover, it is acceptable that the through hole formed in the protection insulation film is composed in shape of a square, a rectangle, a polygon, a circle, or an ellipse, or a plurality of through holes in these different shapes.
The second conductor is formed in an area larger than a region within which a step is formed at the protection insulation film caused by a step of the first conductor, thereby increasing an effective area of the most projecting end face of the bump.