The present invention relates to the structure of a passivation film in a semiconductor device such as a VLSI and a method of manufacturing the semiconductor device.
In a conventional semiconductor device such as a VLSI, a semiconductor element such as a transistor and metal wires are formed on an interlayer insulating film, and a passivation film is formed on the metal wires for the purpose of preventing the invasion of moisture and impurities such as heavy metals or alkaline metals into the metal wires and the insulating film.
Such a conventional semiconductor device will be described as follows with reference to FIG. 19. As shown in FIG. 19, an interlayer insulating film 12 made from silicon oxide is formed on a semiconductor substrate 11, whereas metal wires 13 and a metal electrode 14 which are made from aluminum or an aluminum alloy that is mainly composed of aluminum are formed on the interlayer insulating film 12. In reality, a semiconductor element such as a transistor is formed on the interlayer insulating film 12; however, it is not illustrated for the sake of convenience of the drawing.
A silicon oxide film 15 and a silicon nitride film 16 are formed on the metal wires 13 and the metal electrode 14 by means of a CVD process or the like. The silicon oxide film 15 and the silicon nitride film 16 compose a passivation film 17. The passivation film 17 has an opening portion 17a on the top surface of the metal electrode 14 so as to conduct a wire-bonding.
In the conventional semiconductor device such as a VLSI, a distance between the metal wires 13 and the distance between the metal wire 13 and the metal electrode 14 become smaller as the device is miniaturized. This causes the following problems.
When the passivation film 17 is deposited by means of the CVD process, the film 17 is overhung at the corners on the top surfaces of the metal wires 13 and the metal electrode 14 because the film 17 becomes thicker at the corners than the other portions. This causes the passivation film 17 to be deposited insufficiently or to suffer pin holes in an area between the metal wires 13 and the area between the metal wire 13 and the metal electrode 14.
When the passivation film 17 is formed thinly or has pin holes, the passivation film 17 may suffer a crack 18 in the vicinity of the junction of either a metal wire 13 or the metal electrode 14 and the interlayer insulating film 12 due to a stress such as a heat treatment after the formation of the passivation film 17. The crack 18 allows entrance of impurities or moisture, which corrode the metal wires 13 and the metal electrode 14, increase the relative permittivity of the interlayer insulating film 12, or decrease the insulation of the interlayer insulating film 12. As a result, the properties and the reliability of the semiconductor device are deteriorated.
In addition, in the vicinity of the junction of either a metal wire 13 or the metal electrode 14 and the interlayer insulating film 12, the passivation film 17 becomes the interface of the film which is deposited on the top surface the interlayer insulating film 12 and the film which is deposited on a side surface of a metal wire 13 or the metal electrode 14, so that the passivation film 17 has a lower density than in the other area. This low-density area, which is the vicinity of the junction of the metal wires 13 or the metal electrode 14 and the interlayer insulating film 12, facilitates the invasion of impurities or moisture into the metal wires 13 and the metal electrode 14, so that the properties and the reliability of the semiconductor device are further deteriorated.
These problems have been so far coped with by enlarging the thickness of the silicon nitride film 16 which is a component of the passivation film 17. However, the thickened silicon nitride film 16 causes the overhangs of the passivation film 17 at the corners on the top surfaces of the metal wires 13 and the metal electrode 14 to get in contact with each other. Thus, it remains unsolved that the thickness of the passivation film 17 is insufficient at the junction of either a metal wire 13 or the metal electrode 14 and the interlayer insulating film 12, and there is a new problem that the capacitance becomes larger if the thickness of the passivation film 17 is enlarged.