Semiconductor device with fuse wires and connection wires

1. Field of the Invention

The present invention relates to a semiconductor device, and more particularly to a fuse circuit.

2. Related Background Art

A semiconductor memory such as a DRAM has a redundant circuit for replacing a defective memory with a redundant memory. The circuit has a program circuit for storing an address of the redundant memory. If any defective cell exists, the address of the defective cell is programmed in the LSI, so that the redundant cell is accessed at the time of access with the address during the LSI operation. The redundant circuit has a program element (fuse) formed of polysilicon or aluminum wiring. The replacement address programming is conducted by blowing the fuse using a laser device.

There has been suggested a fuse circuit having an arrangement wherein circuit blocks for determining a replacement address are disposed on one side of a fuse area and return wires are used, for example, in Japanese Laid-Open Patent Publication (Kokai) No. 2003-142582.

Referring to FIG. 7 , there is shown a pattern diagram of a fuse circuit described in the patent publication.

Circuit blocks 101 are disposed on one side of a fuse region. A plurality of fuses 106 are arranged symmetrically about a common wire 107 . Fuses 106 b , 106 d , and 106 f arranged relatively distant from the circuit blocks 101 are connected to the corresponding circuit blocks, respectively, via return wires 103 .

Referring to FIG. 8 , there is shown a layout plan view of the fuse circuit shown in FIG. 7 .

A plurality of fuse wires 201 are arranged perpendicularly to a common wire 203 . A return wire 202 is connected at one end of each of the fuse wires 201 , with the fuse wires 201 and the corresponding return wires 202 arranged alternately.

Referring to FIG. 9 , there is shown a cross-sectional view taken on line D-D of the fuse circuit shown in FIG. 8 . The fuse wires 201 are formed by upper-layer wiring and the return wires 202 are formed by lower-layer wiring.

The fuse wires 201 are arranged so as to satisfy the positional relation of preventing a short circuit between the return wires and the fuse wires caused by scattering of material 300 of the fuse wires due to irradiation with a laser beam as shown in FIG. 10 . In other words, the fuse wires 201 are arranged at a pitch A so as not to be damaged by a laser beam at the time of fuse cutting as shown in FIG. 8 .

In addition, Japanese Laid-Open Patent Publication (Kokai) No. 2002-368094 discloses a technology of an arrangement of return wires just under a fuse element.

In a semiconductor memory device, there are various fuses on the current chip and the number of fuses thereon is increasing. Therefore, the ratio of the fuse area to the chip area is increasing. The layout, however, as shown in Japanese Laid-Open Patent Publication (Kokai) No. 2003-142582 has problems of a wide fuse pitch and a large fuse area.

Furthermore, in Japanese Laid-Open Patent Publication (Kokai) No. 2002-368094, it is necessary to cut a fuse layer surely in actual laser trimming. Therefore, wiring just under the fuse layer is irradiated with a laser beam immediately after the cutting, and thus there is an extremely high risk. Moreover, a fuse wire has such a problem that it spatters breaking a part of the surrounding insulating layer in the instant of being blown at a high temperature, thus adversely affecting return wires just under and close to it.

It is a main object of the present invention to provide a semiconductor device for reducing a fuse area and preventing an effect of laser trimming.

According to one aspect of the present invention, there is provided a semiconductor device, wherein wires corresponding to a plurality of fuse wires are arranged collectively in one place. Furthermore, the wires are arranged in multiple layers.

In the semiconductor device according to the present invention, the fuse wires are arranged at the first pitch in a region where the foregoing wires are arranged between adjacent fuse wires, and the fuse wires are arranged at a pitch narrower than the first pitch in a region where the foregoing wires are not arranged between adjacent fuse wires.

As set forth hereinabove, according to the semiconductor device of the present invention, the wires connected to the plurality of fuse wires are arranged collectively, thereby enabling the fuse wires to be arranged at the minimum wiring pitch. Furthermore, if the connected wires are arranged in two or more layers, the wires can be further collectively arranged.

With these features, the fuse pitch can be narrowed while preventing the connection wires from being damaged by a laser beam, thereby permitting a reduction in area of a fuse circuit.

FIG. 1 is a diagram showing a semiconductor device according to the first embodiment of the present invention.

FIG. 2 is a diagram showing a cross section of the semiconductor device according to the first embodiment.

FIG. 3 is a diagram showing a semiconductor device according to the second embodiment of the present invention.

FIG. 4 is a diagram showing a cross section of the semiconductor device according to the second embodiment.

FIG. 5 is a diagram showing a semiconductor device according to the third embodiment of the present invention.

FIG. 6 is a diagram showing a cross section of the semiconductor device according to the third embodiment.

FIG. 7 is a diagram showing circuit blocks of a conventional semiconductor device.

FIG. 8 is a diagram showing a plan layout of the conventional semiconductor device.

FIG. 9 is a diagram showing a cross section of the conventional semiconductor device.

FIG. 10 is a diagram for explaining a positional relation on the layout of the conventional semiconductor device.

FIG. 11 is a diagram showing a cross section of the semiconductor device according to the fourth embodiment.

The preferred embodiments of the present invention will now be described in detail hereinafter with reference to the accompanying drawings in order to clarify the foregoing and other objects, features, and effects of the present invention.

Referring to FIG. 1 and FIG. 2 , there are shown diagrams of the first embodiment of the present invention.

FIG. 1 is a diagram showing a plan layout of a fuse circuit according to the first embodiment. FIG. 2 is a diagram showing a cross section taken on line A-A of FIG. 1 .

Fuse wires 1 are arranged perpendicularly to a common wire 2 extending in a horizontal direction. The common wire 2 and the fuse wires 1 are formed by upper-layer aluminum or other metal wiring. The fuse wires 1 a to 1 d are connected at one end to corresponding circuit blocks (not shown) provided in a circuit block area 10 disposed on the side of one end. At the other end of the fuse wires 1 a to 1 d , they are correspondingly connected to return wires 4 a to 4 d , which are extending perpendicularly to the fuse wires 1 and arranged in such a way as to be located in parallel with the fuse wires and substantially centrally between the fuse wires. The return wires 4 a to 4 d are connection wires, which are connected to the corresponding circuit blocks provided in the circuit block area 10 . The return wires are also the second wires formed from metal.

The return wires 4 a and 4 c are formed by the first lower-layer wiring underlying the upper-layer. The return wires 4 b and 4 d are formed by the second lower-layer wiring underlying the first lower-layer wiring. The return wires 4 b and 4 d are arranged just under the return wires 4 a and 4 c.

The return wires 4 a and 4 b are arranged in the same region between the adjacent fuse wires 1 a and 1 b and between 1 c and 1 d shown in FIG. 11 . The return wires 4 c and 4 d are arranged in a region between the adjacent fuse wires 1 c and 1 d . The first and second lower-layer wires are embedded in insulating layers 6 a to 6 c . The fuse wires 1 a to 1 d are connected to the return wires 4 a to 4 d by plugs (not shown) embedded in corresponding contact holes.

A surface of the fuse region is covered with a cover film 3 , with the fuses exposed from an opening 5 in the cover film 3 . In other words, both ends of the fuse wires and both cross sections of the return wires are covered with the cover film 3 . At the time of programming, the corresponding fuses are cut by irradiating circular portions indicated by a dotted line in FIG. 1 with a laser beam. In FIG. 1 , 12 fuses are provided in one opening.

Due to no return wire provided between the fuse wires 1 b and 1 c , they can be arranged at the minimum wiring pitch B. On the other hand, a return wire is disposed between the fuse wires 1 a and 1 b and therefore they are arranged at a pitch A wider than the pitch B.

In this manner, the semiconductor device according to the first embodiment has the plurality of return wires arranged in the same region. This creates regions where no return wire is disposed and fuses can be arranged at the minimum fuse pitch. Moreover, the return wires are arranged in multiple layers.

Therefore, for example, if the current fuse pitch B is assumed to be 1, the pitch A for an arrangement in which the return wires are disposed inside the fuse cover need be approx. 1.6 to prevent a laser damage at fuse cutting. When adopting the fuse pitches like those in this embodiment, value 2.6 of the pitch A plus the pitch B is obtained. Considering that the conventional fuse pitch 3.2 obtained from pitch A*2, the fuse pitch can be narrowed by approx. 20%.

Furthermore, in this embodiment, the return wires are arranged not just under the fuse wires, but between the fuse wires, thereby securing an enough distance from the fuses. On the other hand, if the return wires are arranged just under the fuse wires, fuse wires need be cut surely in actual laser trimming and a laser beam immediately after the cutting involves a risk of directly impinging on the wires just under the fuse wires. Moreover, at the instant of being blown at a high temperature, the fuse wires may spatter breaking a part of the surrounding insulating layer, thereby involving a risk of adversely affecting the wires close to and just under the fuse wires.

The return wires are adopted in the present invention. This arrangement enables circuit regions to be put together in one place, thereby permitting a generation of common control signals and a reduction in wiring parasitic capacitance load and thus enabling a contribution to an acceleration in speed and a reduction in power.

Referring to FIG. 3 and FIG. 4 , there are shown diagrams of the second embodiment of the present invention.

FIG. 3 is a diagram showing a plan layout of a fuse circuit according to the second embodiment. FIG. 4 is a diagram showing a cross section taken on line B-B of FIG. 3 .

In the second embodiment, return wires 8 a to 8 d corresponding to fuse wires 7 a to 7 d are arranged between the fuse wires 7 b and 7 c.

According to this embodiment, the four return wires 8 a to 8 d are arranged collectively in one place, thereby permitting an increase in area of the minimum pitch B and a reduction in area of the entire fuse in comparison with the first embodiment.

In the second embodiment, a plurality of (two in FIG. 3 ) fuses are arranged in one string and the strings are arranged in a plurality of stages (four stages in FIG. 3 ), with connection wires (wires 8 a and 8 b ) for other fuse strings passing between adjacent fuse strings (between the fuse wires 7 b and 7 c ). Moreover, other signal wires can be arranged in a region where the fuse wires 7 b and 7 c are arranged. For example, a signal wire supplied to another circuit can also be arranged just under or just over the wires 8 a and 8 b.

Referring to FIG. 5 and FIG. 6 , there are shown diagrams of the third embodiment of the present invention.

FIG. 5 is a diagram showing a plan layout of a fuse circuit according to the third embodiment. FIG. 6 is a diagram showing a cross section taken on line C-C of FIG. 5 .

In the third embodiment, return wires 10 a to 10 d corresponding to fuse wires 9 a to 9 d are arranged between the fuse wires 9 b and 9 c and further the return wires 10 a to 10 d are arranged in four layers.

According to the third embodiment, the pitch of the return wire section is smaller than in the second embodiment, thereby permitting a further reduction in area of the entire fuse.

It is to be understood that the present invention is not limited to those specific embodiments. On the contrary, it is apparent that the embodiments can be appropriately modified within the technical scope of the present invention.

For example, while the return wires are formed in different layers from the layer of the fuse wires in the embodiments, they can be formed in the same layer as the fuse wires. For example, in FIG. 2 , the return wires 4 a and 4 c can be formed in the same layer as the fuse wires and between the fuse wires 1 a and 1 b , and the return wires 4 b and 4 d can be arranged in the places of the return wires 4 a and 4 c . The fuse wires and the return wires 4 a and 4 c are formed by using the same wiring layer. According to this arrangement, a difference in height between the return wires and the fuse wires is reduced, thereby permitting a reduction in effect of defocusing and spreading of a laser beam.

Moreover, two return wires 4 a and 4 b are arranged vertically in the first embodiment. They, however, can be arranged in parallel using the same underlying wiring layer, for example, like the return wires 8 a and 8 d in FIG. 4 . In addition, the fuse wires need not be limited to metal wires, but, can be, for example, polysilicon wires. In other words, the fuse wiring only need be a conductive film that can be laser-trimmed. Furthermore, regarding the order of the return wire layers shown in FIG. 2 , FIG. 4 , and FIG. 6 , no importance need be attached to the order shown in the foregoing embodiments.