Semiconductor device including power supply pad and trunk wiring which are arranged at the same layer level

A semiconductor device includes a semiconductor substrate which includes a functional circuit, a trunk wiring which passes through a portion near a position immediately above a center portion of the functional circuit, a power supply pad which is connected to an end of the trunk wiring and placed at a layer level which is same as a layer level where the trunk wiring is placed, and a connection wiring which connects a substantially center portion of the functional circuit and the trunk wiring.

INCORPORATION BY REFERENCE

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2008-241987 which was filed on Sep. 22, 2008, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device.

2. Description of Related Art

In a semiconductor device, a plurality of wiring layers are formed on a semiconductor substrate on which a functional circuit with high power consumption, such as a CPU (Central Processing Unit), a ROM (Read Only Memory), or a RAM (Random Access Memory), is formed. A power supply wire is formed at each wiring layer, and the power supply wires of the wiring layers are electrically connected to each other through vias. The power supply wire at the wiring layer serving as the bottom layer is electrically connected to the functional circuit via a contact hole. A power supply pad is electrically connected to the power supply wire at the wiring layer serving as the top layer. Power is supplied from the power supply pad to the functional circuit through the power supply wires of the wiring layers. In this case, a voltage drop tends to increase with an increase in the distance from the power supply pad when viewed from a planar perspective. In other words, the semiconductor device has, e.g., the problem of a low capability for supplying power to a substantially center portion of the functional circuit which is far from the power supply pad when viewed from the planar perspective.

For this reason, the semiconductor devices in Patent Documents 1 and 2 each have a reinforcement power supply wire to reinforce a portion where the semiconductor device has a large voltage drop and has a low power supply capability. More specifically, in the semiconductor device of each of Patent Documents 1 and 2, a power supply pad is electrically connected to a ring wire. One end of the reinforcement power supply wire is electrically connected to the ring wire. The other end of the reinforcement power supply wire extends to, e.g., a substantially center portion of a functional circuit which is the portion where the semiconductor device has a low power supply capability and is electrically connected to the substantially center portion. The ring wire and the power supply pad are formed at different layers. The ring wire and the power supply pad are connected through a via.

Note that the semiconductor device in Patent Document 2 is configured such that the width dimension of the reinforcement power supply wire is changed depending on the distance from the power supply pad to a portion where the semiconductor device has a low power supply capability when viewed from a planar perspective.[Patent Document 1] Japanese Patent Application Laid Open No. 61-193467[Patent Document 2] Japanese Patent Application Laid Open No. 2006-313765

SUMMARY

In the semiconductor device in each of Patent Documents 1 and 2 described above, the power supply pad and the ring wire are connected to each other through the via. The via is of high resistance, and the power supply capability significantly decreases.

A semiconductor device includes a semiconductor substrate including a functional circuit, a trunk wiring which passes through a portion near a position immediately above a center portion of the functional circuit, a power supply pad which is connected to an end of the trunk wiring and placed at a layer level which is same as a layer level where the trunk wiring is placed, and a connection wiring which connects a substantially center portion of the functional circuit and the trunk wiring.

With this configuration, the semiconductor device is capable of efficiently supplying power to a portion near the center portion of the functional circuit of the semiconductor substrate and has a high power supply capability.

According to the present invention, it is possible to provide a semiconductor device with a high power supply capability.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

First Exemplary Embodiment

A semiconductor device1of an exemplary embodiment includes a semiconductor substrate2, a wiring layer3, and a power supply pad4, as shown inFIGS. 1 and 2.

The semiconductor substrate2is a semiconductor substrate on which a functional circuit21with high power consumption, such as a CPU, a ROM, or a RAM, that is a type of transistor is formed. Note that although the semiconductor substrate is shown to have only one functional circuit21in the exemplary embodiment, for illustrative simplicity, a large number of functional circuits and a circuit with low power consumption are formed on the semiconductor substrate, as will be described later.

A plurality of the wiring layers3are stacked on the functional circuit21of the semiconductor substrate2. Distribution wires31through which power is supplied to the semiconductor substrate2are formed at each wiring layer3. Each distribution wire31extends in a transverse direction or a longitudinal direction when viewed from a planar perspective. As for ends of the distribution wires31, adjacent distribution wires31are connected to each other through an end wire32.

The distribution wires31extending in the transverse direction and the distribution wires31extending in the longitudinal direction are stacked in order in a vertical direction and are arranged in a grid when viewed from the planar perspective. The distribution wires31of the exemplary embodiment are stacked in four layers, as shown inFIG. 2. An interlayer dielectric film is formed between sets of the distribution wires31which are arranged vertically adjacent to each other. The sets of the distribution wires31arranged vertically adjacent to each other are electrically connected through vias5formed in the interlayer dielectric film. An interlayer dielectric film is also formed between the distribution wires31of the wiring layer3serving as the bottom layer and the functional circuit21of the semiconductor substrate2. The distribution wires31of the wiring layer3serving as the bottom layer and the functional circuit21of the semiconductor substrate2are electrically connected through contact holes6formed in the interlayer dielectric film.

Trunk (main) wires33are formed at the wiring layer3serving as the top layer. Each trunk wire33passes through a portion where a voltage drop remains large until the functional circuit21becomes inoperable or malfunctions. That is, the trunk wire33passes through a portion near a position immediately above a center portion O of the functional circuit21. The trunk wires33of the exemplary embodiment extend in the transverse direction and the longitudinal direction and are formed to cross when viewed from the planar perspective. An intersection of the trunk wires33is arranged near the position immediately above the center portion O of the functional circuit21. Note that the trunk wire33extending in one of the transverse direction and the longitudinal direction may be formed to be divided at the intersection with the trunk wire33extending in the other direction.

The distribution wires31are formed in a region T which is demarcated by adjacent ones of the trunk wires33at the wiring layer3when viewed from the planar perspective.

The connection relationship between the trunk wire33and the distribution wires31formed at the same layer as the trunk wire33will be described. In the exemplary embodiment, the trunk wire33extending in the longitudinal direction is electrically connected to the distribution wires31extending in the transverse direction at the same layer as the trunk wire33. That is, the trunk wire33is electrically connected to the end wires32for the distribution wires31through connection wires34at the same layer. A connection between each end wire32(the trunk wire33) and the distribution wires31is located near a position immediately above the center portion O of the functional circuit21of the semiconductor substrate2. The width dimension of the trunk wire33is made larger than the width dimensions of the connection wires34and the distribution wires31.

The connection relationship between the trunk wire33and the distribution wires31formed at the wiring layer3serving as the second layer from the top will be described. In the exemplary embodiment, the trunk wire33extending in the transverse direction is electrically connected to the distribution wires31extending in the longitudinal direction at the wiring layer3serving as the second layer from the top. That is, each connection wire34extending to a position immediately below the trunk wire33is electrically connected to the corresponding end wire for the distribution wires31at the wiring layer3serving as the second layer from the top. The trunk wire33is electrically connected to the connection wires34through the vias5. A connection between the trunk wire33and the distribution wires31is located near the position immediately above the center portion O of the functional circuit21of the semiconductor substrate2. The distribution wires31,32, which are provided at the top layer and the second layer from the top may be arranged in a ring shape to supply the power supply voltage to all wires31,32at each of layer level, respectively.

Note that directions in which the trunk wires33and the distribution wires31extend and the connection relationships between the trunk wires33and the distribution wires31are not limited to the above-described ones and are appropriately modified.

In this case, some of the vias5connecting the sets of the distribution wires of the wiring layers3serving as the third and subsequent layers from the top are formed near a position immediately above the center portion O of the functional circuit21of the semiconductor substrate2. Some of the contact holes6connecting the distribution wires31of the wiring layers3serving as the bottom layer and the functional circuit21of the semiconductor substrate2are also formed near a position immediately above the center portion O of the functional circuit21. As a result, the trunk wires33are connected to the functional circuit21near the position of the center portion O using, as connection wiring between the trunk wires33and the functional circuit21, the connection wires34connecting the trunk wires33and the distribution wires31, the vias5connecting the sets of the distribution wires, and the contact holes6connecting the distribution wires31and the functional circuit21.

The power supply pads4formed at the same layer as each trunk wire33are electrically connected to two ends of the trunk wire33. That is, the trunk wire33and the power supply pads4are formed at the same layer and are connected without the mediacy of high-resistance vias. For this reason, the resistance is low, and power supply can be efficiently performed. In this case, the width dimension of each trunk wire33is preferably made larger than those of the power supply pads4. This configuration makes it possible to reduce the drawing resistance from each power supply pad4into the trunk wire33and more efficiently perform power supply.

Generally, in the case of a semiconductor device configured such that each power supply pad is arranged outside, before current is drawn to a center portion of the semiconductor substrate2at the top layer, the current is drawn into the wiring layer serving as a lower layer, and power cannot be efficiently supplied to the center portion O of the functional circuit21, depending on the balance in wiring resistance between wiring layers or within the same layer. In contrast, in the semiconductor device1of the present invention, the power supply pads4are formed at the ends of the trunk wire33extending in the transverse direction or the longitudinal direction. That is, since the power supply pads4are formed on an axis L of each trunk wire33, the distance from each power supply pad4to the portion near the position immediately above the center portion O of the functional circuit21is the shortest distance. For this reason, in the semiconductor device1, current is satisfactorily drawn to the center portion O of the functional circuit21, as shown inFIG. 2. Accordingly, the semiconductor device1is capable of efficiently performing power supply.

With the above-described configuration, the semiconductor device1of the present invention is capable of efficiently supplying power to a portion near the center portion of the functional circuit21of the semiconductor substrate2, as shown inFIG. 3, and has a high power supply capability.

Note thatFIG. 3shows a region covered by supply of power from the trunk wires33(a region surrounded by a broken line inFIG. 3is the covered region). The remaining regions are covered by supply of power from the power supply pads4electrically connected to the distribution wires31at the top layer, as shown inFIG. 4.

In the semiconductor device1of the exemplary embodiment, only portions near the position immediately above the center portion O of the functional circuit21of the semiconductor substrate2in each trunk wire33are connected to the distribution wires31. The present invention, however, is not limited to this structure. Other portions of the trunk wire33may be connected to the distribution wires31to the extent that the resistance balance within each wiring layer is not lost, as shown inFIG. 5.

Although the power supply pads4are formed at the two ends of each trunk wire33in the semiconductor device1of the exemplary embodiment, the present invention is not limited to this structure. As shown inFIG. 6, the power supply pad4may be formed at one end of the trunk wire33. Additionally, the number of power supply pads4is not particularly limited, and a plurality of (two in the shown example) power supply pads4may be formed at each end of the trunk wire33, as shown inFIG. 7. In this case, although each power supply pad4is off the axis L of the trunk wire33, the power supply pad4only has to be formed on an extension of the trunk wire33.

Second Exemplary Embodiment

A semiconductor device100of a second exemplary embodiment is configured to be almost the same as the semiconductor device1of the first exemplary embodiment described above. However, the semiconductor device100is different in layout of a trunk wire33, a distribution wire31, and the like. For this reason, a description of same components will be omitted.

In the semiconductor device100of the second exemplary embodiment, the trunk wire33is formed only in a transverse direction, as shown inFIG. 8. In this case as well, the trunk wire33passes through a portion near a position immediately above a center portion O of a functional circuit21of a semiconductor substrate2. Distribution wires31are formed on two sides of the trunk wire33at a wiring layer3when viewed from a planar perspective. The trunk wire33is electrically connected to the distribution wires31at the portion near the position immediately above the center portion O of the functional circuit21of the semiconductor substrate2. The trunk wire33is electrically connected, through a via5, to a connection wire34which is connected to the distribution wires31at the second layer from the top. Note that power supply pads4are electrically connected to the distribution wires31at the top layer.

With the above-described configuration, it is possible to efficiently supply power to the center portion O of the functional circuit21of the semiconductor substrate2, as in the semiconductor device1of the first exemplary embodiment.

In the semiconductor device100as well, only a portion near the position immediately above the center portion0of the functional circuit21of the semiconductor substrate2in the trunk wire33is connected to the distribution wires31. The present invention, however, is not limited to this structure. Other portions of the trunk wire33may be connected to the distribution wires31to the extent that the resistance balance within each wiring layer is not lost, as shown inFIG. 9.

Although the power supply pads4are formed at two ends of the trunk wire33in the semiconductor device100of the above-described exemplary embodiment, the present invention is not limited to this structure. As shown inFIG. 10, the power supply pad4may be formed at one end of the trunk wire33. Additionally, the number of power supply pads4is not particularly limited, and a plurality of (two in the shown example) power supply pads4may be formed at each end of the trunk wire33, as shown inFIG. 11. In this case, although each power supply pad4is off an axis L of the trunk wire33, the power supply pad4only has to be formed on an extension of the trunk wire33.

Third Exemplary Embodiment

In each of the semiconductor devices of the first and second exemplary embodiments described above, only one functional circuit is formed on the semiconductor substrate2. The present invention, however, is not limited to this structure.

As shown inFIG. 12, a plurality of functional circuits21ato21c, such as a CPU and a RAM, may be formed. In this case as well, a trunk wire33is formed to pass through a portion near a position immediately above a center portion of each of the functional circuits21ato21c.

Exemplary embodiments of a semiconductor device according to the present invention have been described above. The present invention, however, is not limited to the above-described exemplary embodiments, and various changes may be made without departing from the scope of the present invention.