JPH06104338A - Fuse element for memory cell repair - Google Patents

Abstract

PURPOSE:To obtain a fuse element for repairing memory cells used for a redundancy circuit constituted by adding a standby bit for repair to a memory cell array by making the width of the element at its central part boarder than that at its both end sections. CONSTITUTION:By forming a fuse element 1 used for a redundancy circuit constituted by adding a standby bit for repair to a memory cell array in such a way that the width W of the element 1 at its central part is broader than that D at its both end sections, it is contrived that the damage to the substrate, etc., of the element 1 can be suppressed when the element 1 is blown by means of a laser beam and, at the same time, the blowing of the element 1 can be easily recognized. Therefore, the reliability of the circuit can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuse element for memory cell repair.

[0002]

2. Description of the Related Art In recent years, elements of semiconductor devices have been miniaturized,
As the number of elements included in one integrated circuit chip increases, the level of defect density also increases, but the yield is often low at the development stage and the beginning of mass production. Redundant circuit technology has been proposed and put into practical use as one of means for solving such a problem.

That is, in the redundant circuit technique, when a defective row or column or memory cell exists in the memory array, some rows or columns of spare bits are prepared and an address signal corresponding to the defective portion is prepared. When a mark is entered, a row or column of spare bits is selected instead, so that it can be used as a non-defective product even if it contains a defect. As a method of switching to the spare bit, a fuse blowing method using a laser is widely used because it has advantages such as a small occupied area of a programming circuit and easy alignment of a laser beam as a trimming device. (For example, "Memory Repair Technology and Its Equipment (Monthly Semiconductor World, 1989.7, P60-6
8) ")).

By the way, in such a laser fuse cutting method, polysilicon is used as a fuse element. As the shape of this fuse element, for example, the fuse element 1a having a parallel width as shown in FIG. 4 (a) or the fuse element having a narrow central portion as shown in FIG. 4 (b). 1b (see, for example, Shin Kayama's "Ultra High Speed MOS Device (February 1986, published by Baifukan, P.331)") and the like. Further, as the waveform / intensity distribution of the laser beam used for blowing the fuse, a Gaussian distribution G as shown in FIG. 5 (a) or a rectangular distribution H as shown in FIG. 5 (b) is generally used.

[0005]

However, in the fuse element 1a or 1b having the above-mentioned shape,
When a laser beam having a Gaussian distribution G or a rectangular distribution H is applied, there is a problem that in the case of the Gaussian distribution G, if the irradiation width of the laser beam is too narrow, the fuse remains on the side surface of the fuse and the fuse cannot be completely blown. In the case of the rectangular distribution H, there is a defect that the base of the fuse is damaged if the irradiation width of the laser beam is too wide.

Further, as the direction of the conventional way of thinking,
In order to make the fuse area as small as possible, there is an electric fuse method in addition to the laser method for fusing the fuse, but it was necessary to make the fuse width narrower than general wiring and to concentrate Joule heat generation. For this reason, there is a tendency that the fuse width of the fuse element 1b shown in FIG. 4 (b) is made narrower, so that the shape of the fuse element cannot be accurately recognized and the base is damaged. There was a risk that the problem would increase.

It is an object of the present invention to provide a fuse for memory cell repair that solves the above problems of the prior art.

[0008]

SUMMARY OF THE INVENTION The present invention is a fuse element used in a redundant circuit in which spare bits for repair are added in a memory cell array, the width of the central portion of which is larger than that of both ends. A fuse element for a memory cell repair, which has a shape.

[0009]

[Operation] According to the present invention, since the fuse element used for the redundant circuit has a medium-thick shape, it is possible to easily recognize the fuse element, and it is possible to suppress damage to the base or the like during fusing by the laser beam. .

[0010]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the fuse element 1 of the present invention has a so-called medium-thick shape in which the width of the central portion is larger than the width of both end portions. Width W of this central part
Is preferably within √2 times the effective irradiation radius r of the Gaussian distribution laser beam R used for fusing, that is, W ≦ √2r. Specifically, for example, the width D of both ends of the fuse element 1 is 2 μm, r. A width W of about 4 μm is suitable for 3 μm.

As described above, by making the shape of the fuse element 1 of the present invention medium and thick, it becomes possible to easily recognize the fuse alignment when positioning the laser beam. That is, if the peripheral portion S of the fuse element 1 shown in FIG. 2 is registered as an image recognition pattern, for example, when positioning is performed by laser scanning, the longitudinal direction on both sides of the middle thick portion is scanned along the dotted line T. Then, it will be easy to recognize.

[0012] FIG. 3 shows an example in which the fuse window 2,2 constructed on both sides of the fuse element 1 SOG or SiO ₂ or the like, and registers the peripheral portion S 'of the fuse window 2,2 It is also possible to recognize by scanning the longitudinal directions on both sides of the convex portion along the dotted line T ′. By providing the fuse windows 2 and 2, the base of the fuse is not damaged.

[0013]

According to the present invention, since the fuse element used in the redundant circuit has a medium-thick shape, it is possible to easily recognize the fuse element, and it is possible to suppress damage to the underlayer due to fusing by the laser beam. Contribute to the improvement of the circuit reliability.

[Brief description of drawings]

FIG. 1 is a plan view showing an example of the shape of a fuse element of the present invention.

FIG. 2 is a diagram illustrating an example of a method of recognizing a fuse element of the present invention.

FIG. 3 is a diagram illustrating another example of the method for recognizing a fuse element of the present invention.

4 (a) and 4 (b) are plan views illustrating the shape of a conventional fuse element.

5A and 5B are characteristic diagrams illustrating the waveform / intensity distribution of a laser beam used for fusing a fuse element.

[Explanation of symbols]

 1 fuse element 2 fuse window

Claims (1)

[Claims] 1. A fuse element used in a redundant circuit in which spare bits for repair are added in a memory cell array, wherein a width of a central portion of the fuse element is thicker than both end portions thereof. Fuse element for memory cell repair.