JPS60136333A - Laser fuse device - Google Patents

Abstract

PURPOSE:To enable to reduce in size of a highly integrated device by a method wherein steppings are provided on the thermally oxided film located under a laser fuse, thereby enabling to reduce the damage given to a silicon substrate by a laser beam. CONSTITUTION:A fuse 3 consisting of polysilicon and other conductor is formed on the thermally oxided film 2 located on a silicon substrate 1. When a stepping 1a is provided on the upper surface of said silicon substrate 1, the thermally oxided film 2 to be formed on the upper surface of the stepping 1a has a stepping 7 as a matter of course, and the fuse 3 which will be formed thereon also formed in such a manner that it has a stepping. The fuse 3 is covered by a protective film 4 consisting of phosphorus glass and a thermally oxided film. When a laser beam is made to irradiate, the fuse 3 is heated up to a high temperature by the given energy, it is fused, an aperture part 8 is formed, the protective film is flown off, and the fuse 3 is burnt out. The generation of damage on the silicon substrate 1 is suppressed due to the existence of the heavy stepping 7 on the thermally oxided film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a laser fuse device used in a redundant circuit of a semiconductor device.

(Prior Art) Conventionally, a laser fuse for redundant circuit switching disposed on a semiconductor device is configured as shown in FIG. 1(a). In FIG. 1 (-), a fuse 3 made of polysilicon or other conductor formed on a thermal oxide film 2 on a silicon substrate 1 is surrounded by a protective film 4 such as phosphor glass or a thermal oxide film. In the conventional radar fuse configured as described above, when a defective circuit is to be switched out, when a laser beam is irradiated as shown by arrow A1, the fuse is heated to a high temperature by the energy given to the fuse. The protective film 4 is then blown away to form a melted part 5, as shown in FIG. 1(b).
). If the Lede beam energy is appropriate and stable and the thermal oxide film 2 is sufficiently thick, defects 6 will not occur on the silicon base &1 due to laser irradiation, but if the Lede beam energy is inappropriate (general ),
Alternatively, if the energy is unstable even if the energy is appropriate, or if the thermal oxide film has become thinner due to the miniaturization of devices, laser irradiation as shown in defect 6 in Figure 1(b) There were several drawbacks such as defects occurring in the silicon substrate.

Here, the specifications of a typical conventional laser fuse will be outlined. # film such as polysilicon is -3000□N,
The total thickness is around 2μ, the width is around 10μ, the thickness of the thermal oxide film is 5000A to 1μ, and the thickness of the protective film is 5000A.
A-1μ, Radhe beam irradiation energy is in the form of a spot, around 2μ units, spot diameter is 6μφ to 4μφ, N
When the dYAG laser is used for an irradiation time of 40 ns, the temperature of polysilicon and the like reaches approximately 1400° C., and is heated to, for example, 2 Joules, melting and cutting.

For example, 2μ joules is appropriate, and 3μ joules is too much (this is caused by variations in the laser beam and laser fuse parameters).The underlying silicon to which the laser beam is applied will be excessively heated, leading to transitions. defects occur, increasing leakage current to adjacent devices, and deteriorating the quality and reliability of the device.

Furthermore, as the density of devices increases, the thermal oxide film 2 must be made thinner. In that case, the above-mentioned effects will be even greater.

(Purpose of the Invention) The present invention can reduce the damage caused by a laser to a silicon substrate, thereby contributing to improving the quality and reliability of semiconductor devices, as well as increasing the degree of integration and reducing device dimensions. Our aim is to provide laser fuse equipment that can.

(Summary of the Invention) The key point of this invention is that a step of thermal oxide film is provided in the fuse portion where the laser is irradiated.

(Embodiments) Hereinafter, embodiments of the laser fuse device of the present invention will be described based on the drawings. FIG. 2(a) is a sectional view showing the configuration of one embodiment. In this Figure 2 (a),
The same parts as in FIGS. 1(a) and 1(b) will be described with the same reference numerals.

As shown in FIG. 2(a), a fuse 3 made of polysilicon or other conductor is formed on a thermal oxide film 2 on a silicon substrate 1. A step 1a is formed on the upper surface of this silicon substrate 1.
Therefore, the thermal oxide film 2 formed on the upper surface also inevitably has a step 7. The fuse 3 formed above this also has a step.

The fuse 3 is protected by a protective film 4 made of phosphor glass or a thermal oxide film. The step 7 of the thermal oxide film 2 can be formed before the thermal oxide film 2 is formed as described above. The above can be easily manufactured using current silicon semiconductor technology.

Next, as shown in Figure 2(a), attach the fuse part to the
When the laser beam shown by arrow A1 is irradiated as shown in
The fuse 3 is heated to a high temperature by the applied energy and melted, forming an opening 8. Then, the protective film 4 is blown away, and the fuse 3 is cut as shown in FIG. 2(b).

By doing this, the thickness of the thermal oxide film 2 under the fuse 3 becomes thicker like the step 7 in the portion irradiated with the laser beam, compared to the conventional method.

Therefore, damage to the silicon substrate 1 by the laser beam is less likely to occur because the step 7 of the thermal oxide film 2 is apparently thicker by the difference in step of the thermal oxide film 2.

Finally, compared to the conventional structure, the structure of the laser fuse device of the present invention is designed to prevent excessive energy of the laser beam, instability of the laser beam, or thinning of the thermal oxide film 2 due to miniaturization of the device. This structure allows damage to the silicon substrate 1 to be extremely small.

Here, an example of the process for forming the step 7 will be described. A photoresist is applied to the silicon substrate 1, and holes are formed in a predetermined pattern by dry or wet etching to form the above-mentioned step 1a on the silicon substrate 1. This step 1a
The height of the awn is about 5000A.

Next, by aging the silicon substrate 1, a thermal oxide film 2 is formed. The thickness of this thermal oxide film 2 is 5000
~10.0OOA. .

Next, polysilicon is grown to a thickness of about 3000λ on this thermal oxide film 2 by the COD method to form a fuse 3 having a step. Protective film 4f on this fuse 3: thickness 5
000~10.000A is formed.

Furthermore, the laser beam used for irradiation conventionally used 2 μjoules, but in the embodiment of the present invention, it can be reduced to about 1.5μjoules. The reason for this decrease in irradiation energy is considered to be due to the following two reasons.

fl) This is because the polysilicon becomes substantially thinner at the step 70 portion.

(2) This is because the underlying thermal oxide film 2 becomes thicker at the step portion 7, so that the amount of energy absorbed by the polysilicon at the step portion increases.

In this way, by reducing the irradiation energy of the laser beam and increasing the thickness of the thermal oxide film at the stepped portion, damage to the silicon substrate when the fuse blows can be reduced.

Furthermore, by using the fuse of the present invention, for example, in a redundant circuit of a large-capacity semiconductor memory, it will contribute to improving the quality and reliability of the semiconductor memory, and the underlying oxide film can be designed to be thinner, resulting in higher integration. , which contributes to the reduction of device dimensions.

(Effects of the Invention) As explained above, in this invention, since a step is provided in the thermal oxide film under the Radhe fuse, damage to the silicon substrate by the Radhe beam can be reduced, and it can be applied to semiconductor memories etc. Second, there are advantages in that the quality reliability of semiconductor elements can be improved and the dimensions of highly integrated devices can be reduced.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of a conventional laser fuse device, FIG. 1(b) is a cross-sectional view showing the same laser fuse device irradiated with a laser beam, and FIG. 2(a) is a cross-sectional view of the laser fuse device of the present invention. FIG. 2(b) is a cross-sectional view showing the structure of an embodiment of the apparatus, and FIG. 2(b) is a cross-sectional view showing the state in which the laser fuse device of FIG. 2(a) is irradiated with a laser beam. DESCRIPTION OF SYMBOLS 1... Silicon substrate, 2... Thermal oxide film, 3... Fuse, 4... Protective film, 7... Step difference in thermal oxide film, 8
...opening area. Patent applicant Oki Electric Industry Co., Ltd.

Claims (1)

[Claims] A laser fuse device kJ characterized in that a step is formed in the thermal oxide film below a portion of the fuse formed on the thermal oxide film on a silicon substrate where the laser beam is irradiated.