Semiconductor Integrated Circuit Device

The present invention relates to a semiconductor integrated circuit device, and more particularly to a semiconductor integrated circuit device having a device-protecting insulating film of 1.0 .mu.m or more in thickness on a device.

The progress in insulated gate field effect transistor integrated circuits (hereinafter called MOS IC) towards the realization of a high degree of circuit integration and high operation speed has been remarkable, and these operation speeds are gradually approaching the range of bipolar IC's.

Generally in a MOS IC, operational speed is largely governed by channel lengths L and dissipated currents of individual MOS transistors forming the integrated circuit, and as the lengths L are shorter and the operation currents are larger, it becomes operable at a higher speed. This implies that upon design and manufacture of a MOS IC operable at a high speed, a finer pattern should be formed, and ground or power supply wirings having larger current capacities, that is, ground or power supply wirings having broad widths, are necessitated.

In the case where an IC is constructed of MOS transistors having short channel lengths (4 .mu.m or less) for the purposes of realizing high speed and large-scale integration, it was discovered that in addition to the fact that a slight error in patterning would result in variations of characteristics, the reliability of the device, as compared to that of a transistor having a longer channel length L (5 .mu.m or more), is extremely sensitive to minute amounts of contamination ions.

Variations in characteristics caused by external contamination also arise in the process of assembling a MOS IC. The mechanism by which these variations in characteristics occur can be explained in the following manner.

Among the materials generally used for assembly are low-melting-point glass and plastics. Since these materials consist of various compounds, they are of high impurity as compared to the materials used in a diffusion manufacturing process of a MOS IC chip, and thus contain contamination substances which cause variations in characteristics. On the other hand, it is a common practice to provide an insulating film over the surface of an integrated circuit device for the purpose of protecting the device from contamination as well as from undesirable mechanical forces. However, in the event that this insulating film consists of a silicon dioxide (SiO.sub.2) film of about 0.5.about.1 .mu.m in thickness, if a contamination substance should be deposited onto the surface of such an insulating film, during the heat treatment in the assembly process, heavy ions emanating from the contamination substance diffuse through the insulating film and reach the gate region of the MOS transistor, resulting in variations in the threshold voltage, and attendant unacceptable characteristics in the MOS IC. In a MOS IC which has become unacceptable due to the above-mentioned cause, since the contamination ions move at a high temperature, the environmental condition of use will determine the extent of threshold voltage variations, thereby lowering the overall reliability of the device.

With regard to a method for obviating the problem in reliability caused by the above-described mechanism, it has been discovered that if phospho-silicate glass of several mol% in concentration is used as an insulator for protecting the device, and the thickness of the insulating film is selected to be 1 .mu.m or more, the resulting insulating film will protect the device from the contamination ions. This is caused by the fact that since the phosphorus contained in phospho-silicate glass serves as a getter for the contamination ions applied externally, the contamination ions are not mobile under the subsequent influence of heat or an electric field. In other words, if a phospho-silicate glass film of 1 .mu.m or more in thickness is used as a protective film, the resulting MOS IC will have a high reliability against external contamination. However, phospho-silicate glass has an extremely large grain size when it is grown on wiring metals such as on aluminum (Al) or aluminum-silicon alloy, and if the surface of the metal is large, the stress between grains will also become unacceptably high. If the film thickness becomes 1.about.1.5 .mu.m or more, cracks or faults are generated in the phospho-silicate glass or silicon dioxide film. These faults do not occur when the width of a metallic wiring is narrow, but they are generated on a broad wiring such as a ground or power supply wiring. Moreover, in the contemplated MOS IC operable at a high speed, since the current capacity is to be great due to the large operating current requirements as described previously, a power supply or ground wiring having such a broad width is necessitated, thereby enhancing the possibility of incurring such faults.

The ground or power supply wiring layer extends from the bonding pad to about 50.about.250 .mu.m distance in the broad width state, and separates to narrower width wiring layers for connecting to the circuit elements such as MOS transistors. The above-described faulting problem occurs in the area between the bonding pad and a point remoted from the bonding pad of about 50.about.250 .mu.m.

It is an object of the present invention to provide an effective semiconductor integrated circuit device in which the above-mentioned shortcomings of the prior art are eliminated.

It is another object of the present invention to provide an effective semiconductor integrated circuit device having high reliability, a high operational speed, and a high degree of circuit integration. The present invention employs a phospho-silicate glass film of 1 .mu.m or more in thickness as a device-protecting insulating film, in which faults are prevented by dividing the ground or power supply wirings into two or more narrow wirings. This eliminates the surface on which large grain size phospho-silicate glass forms, while maintaining the greater wiring widths needed for high speed MOS IC operation.

According to one embodiment of the present invention, a semiconductor integrated circuit device comprises a semiconductor substrate; an insulation layer, formed onto said semiconductor substrate; a metallic wiring layer formed onto the insulator layer for providing a power supply or a ground potential to the circuit elements in the chip, which is divided into at least two substantially parallel wiring sections; and a protecting insulation film of 1 .mu.m or more in thickness formed onto said wiring sections.

According to another embodiment of the present invention, a semiconductor integrated circuit device comprises a semiconductor substrate; an insulation layer, formed onto said semiconductor substrate; a bonding pad formed onto said insulation layer; a metallic electrode wiring layer for providing a power supply or a ground potential formed onto said insulation layer and extending inwardly from said bonding pad; and a protecting insulation film covering said wiring layer, disposed such that an effective area of said bonding pad is exposed, said wiring layer being divided in the vicinity of said exposed area of said bonding pad into at least two substantially parallel wiring layer sections.

The protecting insulation film may be made of either phospho-silicate glass or silicon dioxide of 1 .mu.m or more thickness. Generally, aluminum or aluminum-silicon alloy can be used in the metallic electrode layer. The widths of the wiring sections are preferably not more than 50 .mu.m, and the distance between the exposed area of the bonding pad and the divided portion of the wiring layer is also preferably not more than 50 .mu.m.

FIG. 1 is a planar view showing a semiconductor integrated circuit device according to a prior art technique,

FIG. 2A is a planar view showing a encircled portion 100 in FIG. 1 in an enlarged scale,

FIG. 2B is a cross-sectional view taken along line A--A' in FIG. 2A as viewed in the direction of the arrows,

FIG. 3 is a planar view showing a preferred embodiment of the present invention,

FIG. 4A is a planar view-showing a encircled portion 200 in FIG. 3 in an enlarged scale,

FIG. 4B is a cross-sectional view taken along line B--B' in FIG. 4A as viewed in the direction of arrows, and

FIG. 5 is a graph showing an experimental data of the fault generation ratio of a protecting insulating film as a function of width of the metallic wiring layer.

FIGS. 1, 2A and 2B show a semiconductor integrated circuit device (chip) 20 constructed according to the methods in the prior art, in which an insulation layer 6 such as silicon dioxide is formed onto a semiconductor substrate 7, and both a plurality of bonding pads 11 for input or output signal wiring layers 2 of aluminum and twin bonding pads 9 for grounding or power supply wiring layer 1, of aluminum are formed onto insulation layer 6 so as to locate at a peripheral portion of the substrate. Each wiring layer 2 extends inwardly to connect to each circuit element (not shown), including the MOS transistor, provided in the chip. A broad wiring layer 1 of 90 .mu.m in width for grounding or power supply extends from the bonding pad 9 to a separating point 30 which is about 50.about.250 .mu.m away from the bonding pad 9. At the separating point 30, the broad wiring layer is separated into narrower wiring layers 12, to connect to circuit element (not shown) including MOS transistors provided in the chip. In FIG. 2B, a protecting insulation film of phospho-silicate glass 5 covers the wiring layers, the insulating layer 6 and the circuit elements, but does not cover an effective area 10 of about 100 .mu.m square of the bonding pads 9 and 11 as seen in FIG. 2A. On the broad metallic wiring layer 1, the grain size of the phosphorus silicate glass 5 becomes larger than that on the narrower metallic wirings and the resulting grain stresses are such that if the protecting insulation film is of 1.about.1.5 .mu.m or more in thickness, as seen in FIGS. 2A and 2B, faults 4 develop which give rise to the afore-mentioned reliability problems.

Accordingly, an examination was made into the relationship between the width of the aluminum metallic wiring layer and the fault generation ratio of phospho-silicate glass of 1.5 .mu.m in thickness. The results of such an examination, as shown in FIG. 5, teach that a metallic wiring layer such as of aluminum or aluminum-silicon alloy, when maintained at a width of 50 .mu.m or less, will not produce any faults in the phospho-silicate glass protecting insulation layer grown above it.

FIGS. 3, 4A and 4B show one preferred embodiment of the present invention. In these Figs., component parts are enumerated as they were in FIGS. 1, 2A and 2B. The broad aluminum wiring layer 1 of 90 .mu.m in width for grounding or power supply is divided at dividing position 40 into three narrower wiring layer sections 8 of aluminum. The divided position is 50 .mu.m or less away from the edge 10' of the exposed bonding area 10. Each of the divided wiring sections is of 30 .mu.m in width, and extend in parallel, with a distance between them of 10 .mu.m to the separating point 30 50.about.200 .mu.m away from the dividing position 40.

Since the wiring layer of large current capacity is divided into narrower wiring layers 8, even if phospho-silicate glass 5 is grown on the metallic wiring layer up to a thickness of 1 .mu.m or more, the stresses between the grains are not sufficient to generate faults 4.

In accordance with the present invention, a MOS IC having a high operation speed and a high degree of circuit integration can be manufactured with a high degree of reliability not heretofore possible.