The above and other objects, features and advantages of this invention will become more apparent by reference to the following detailed description of the invention taken in conjunction with the accompanying drawings, wherein:
Preferred embodiment of the present invention will now be explained in detail with reference to the drawings.
As shown in
The fuse element 20 has a tubular shape with a hollow portion 20a therein, as shown in
A more specific explanation is given of the structure of the fuse element 20. The fuse element 20 includes a first tubular portion 21 that passes through the insulating film 31, a second tubular potion 22 that passes through the insulating film 32, and a third tubular portion 23 that passes through the insulating film 33. In the present embodiment, a diameter d22 at the second tubular potion 22 is set to be smaller than a diameter d21 at the first tubular portion 21 and a diameter d23 at the third tubular portion 23. Accordingly, a thermal capacity of the second tubular potion 22 is smaller than the other portions. As are result, when the second tubular portion 22 is irradiated with a laser beam, the fuse element 20 is easily cut.
The insulating film 32 is made of mainly of a material different from those of the insulating films 31 and 33, and uses a material of which the absorptivity of light is larger in a wavelength range of the laser beam to be irradiated than those of the insulating films 31 and 33. The use of such a material is to effectively concentrate energy of the laser beam to be irradiated onto the second tubular potion 22.
Although not particularly limited, it is preferable to select, as main components of the insulating films 31 and 33, silicon oxide (SiO2), and it is preferable to select, as a main component of the insulating film 32, silicon nitride (Si3N4). The reason for this selection is that in silicon oxide (SiO2), the absorptivity of light in a wavelength range of 300 nm to 1000 nm is 10%, whereas in silicon nitride (Si3N4), the absorptivity is about 90%, so that it is possible to effectively concentrate the energy of the laser beam to be irradiated onto the second tubular potion 22. The refractive index of silicon oxide (SiO2) in the above-described wavelength area is about 3.9, whereas the refractive index of silicon nitride (Si3N4) in the above-described wavelength area is about 7.9. In this light, too, it is possible to concentrate the energy onto the second tubular portion 22.
The film thickness of the insulating film 32 is preferably thinner than those of the insulating films 31 and 33. The reason for these film thicknesses is that when the film thickness of the insulating film 32 is set to be thinner, it becomes possible to concentrate the energy of the laser beam as much as possible. More specifically, the film thickness of the insulating film 32 is preferably set to be 200 nm or less. The reason for this is that when the film thickness of the insulating film 32 is set to be more than 200 nm, it is not possible to obtain an effect in concentrating the energy of the laser beam. In particular, when silicon nitride (Si3N4) is used as the material for the insulating film 32, hydrogen permeability significantly decreases, so that it becomes difficult to execute a process for restoring a defect occurring on a silicon substrate with hydrogen.
On the other hand, when the film thickness of the insulating film 32 is too thin, it becomes impossible to sufficiently absorb the energy of the laser beam by the second tubular portion 22, and when the film thickness is set to be less than 10 nm, it becomes difficult to retain evenness of the film. Taking into account these points, it is preferable that the film thickness of the insulating film 32 is set to be 10 nm or more and 200 nm or less. In particular, it is preferable that the film thickness is set to be about 50 nm to 100 nm.
The lower electrode 11 is connected to a diffused layer 51 provided in a semiconductor substrate 50 via a through-hole electrode 41 provided in an insulating film 40. The material for the lower electrode 11 is not particularly limited, but tungsten (W) or the like is preferably used.
The upper electrode 12 is a wiring of the top layer, for example, and is covered with a passivation film 60. The material for the upper electrode 12 is not particularly limited, but aluminum (Al) or the like is preferably used.
As shown in
While a specific numerical value of the height H of the fuse element 20 is not particularly limited, the numerical value is preferably larger than the depth of focus of the laser beam to be irradiated, and more preferably at least two times larger than the depth of focus. With such value, even when the focal point of the laser beam slightly deviates in the up and down directions, the focal point is almost always at the fuse element 20. Further, it becomes possible to greatly reduce components of energy, out of the energy of the irradiated laser beam, that leak below the fuse element 20.
The depth of focus (DOF) can be represented by the following equation (1), where λ is the wavelength of the laser beam to be irradiated, and NA is the numerical aperture of an objective lens that converges the laser beam.
Accordingly, when the wavelength of the laser beam to be irradiated is 300 nm and the numerical aperture of the objective lens is 0.548, the depth of focus (DOF) is nearly 1 μm. When the fuse element 20 is cut by using such optical system, the height H of the fuse element 20 can be set to 1 μm or more. In this case, the height H of the fuse element 20 is preferably about 3 μm.
On the other hand, although a specific numerical value of the average diameter D of the fuse element 20 is not particularly limited, the numerical value is preferably smaller than a diffraction limit of the laser beam to be irradiated, and more preferably, half or less than the diffraction limit. With such value, it becomes possible to more surely cut the fuse element 20, and enhance the packaging density of the fuse element 20.
When the average diameter D of the fuse element 20 is set smaller than the diffraction limit, a certain component of the energy with which the fuse element 20 is not irradiated leaks below the fuse element 20. However, the intensity of the laser beam is imparted with a Gaussian distribution, which means that the inner the area on the Gaussian distribution, the higher the intensity, and thus, the leaking energy in the edge portions is not so high. Further, the fuse element 20 has a vertically long shape, and a large portion of the energy is absorbed by the fuse element 20, as explained above. As a result, the component of the energy that leaks below the fuse element 20 is very small.
The diffraction limit (DL) can be represented by the following equation (2), where λ is the wavelength of the laser beam to be irradiated, and NA is the numerical aperture of an objective lens that converges the laser beam.
Accordingly, similar to the above, when the wavelength of the laser beam to be irradiated is 300 nm and the numerical aperture of the objective lens is 0.548, the diffraction limit (DL) is about 330 nm. When such optical system is used to cut the fuse element 20, the diameter D of the fuse element 20 can be set to 300 nm or less. In this case, the average diameter D of the fuse element 20 is preferably about 200 nm.
Although the material for the fuse element 20 is not particularly limited, tungsten (W) is preferably used because tungsten (W) is excellent as a conductive material forming a tubular shape, and tungsten (W) also has high absorptivity of light in an ultraviolet range.
A program circuit 70 shown in
With this configuration, when the fuse element 20 is cut, a potential of the connection point A is a low level, so that the connection point B, which is the output terminal, is connected to the power supply potential VDD via the transistor 72. Thus, an output Out is fixed at a high level. In contrast, when the fuse element 20 is not cut, the potential of the connection point A is a high level, so that the connection point B, which is the output terminal, is connected to the ground potential GND via the transistor 73. Thus, the output Out is fixed at a low level.
Accordingly, when the fuse element 20 is used to configure such program circuit 70, a logical value of the output Out is determined according to whether the fuse element 20 is cut. Thus, the use of a plurality of such program circuits 70 enables storing of defective addresses, for example.
The cutting of the fuse element 20 is performed by irradiating a laser beam via the passivation film 60. That is, the tubular fuse element 20 having the hollow portion 20a therein is irradiated with a laser beam from an axial direction.
The laser beam passes through an objective lens (not shown) and is converged in a region where the fuse element 20 is formed. The diffraction limit of the laser beam is determined by the equation (1). When the wavelength of the laser beam is 300 nm and the numerical aperture of the objective lens is 0.548, the diffraction limit (DL) is about 330 nm, as explained above. On the other hand, the average diameter D of the fuse element 20 can be scaled down to ¼ of an exposure wavelength by a super resolution technology in which a phase shift mask or the like is used. Accordingly, as shown in
However, when an optical system in which the depth of focus (DOF) is equal to or less than the height H of the fuse element 20 is used, or preferably, an optical system in which the depth of focus (DOF) is half or less than the height H of the fuse element 20 is used, energy of which the main components have high intensity is absorbed by the fuse element 20. Thus, energy that leaks below the fuse element 20 is very small. As a result, only a thin laser beam of which intensity is weak leaks below the fuse element 20, as indicated by a dotted line L1 in
As for the energy of the laser beam that leaks below the fuse element 20, the greater the height H of the fuse element 20, the weaker. More specifically, when the height H of the fuse element 20 is at least three times greater than the average diameter D, an effective attenuation can be secured. In particular, when the height H of the fuse element 20 is set to at least five times greater than the average diameter D, the attenuation of the laser beam is sufficient. When the height H of the fuse element 20 is set to about 10 to 20 times greater than the average diameter D, the attenuation of the laser beam is even more sufficient. However, when a ratio between the height H and the average diameter D of the fuse element 20 is extremely large, the aspect ratio becomes large. Thus, it becomes difficult to manufacture the fuse element 20.
When the fuse element 20 is irradiated with the laser beam, it is preferable that focal positions in the up and down directions is adjusted such that the second tubular potion 22 of the fuse element 20 remains within the DOF, as shown in
When the fuse element 20 is irradiated with the laser beam, the tubular structure of the fuse element 20 is collapsed, and the fuse element 20 is separated into upper and bottom portions, as shown in
To cut the fuse element 20 more surely, the volume of the hollow portion 20a is preferably sufficiently large. More specifically, the volume of the hollow portion 20a is preferably equal to or larger than that of the fuse element 20. The reason for this is that the larger the volume of the hollow portion 20a, the more easier for the fuse element 20 to be separated into the upper and bottom portions when the fuse element 20 is destructed by laser beam irradiation. Another reason for this is that the larger the volume of the hollow portion 20a, the less likely a crack occurs in the insulating films 31 to 33 because even when an instantaneous cubical expansion occurs due to laser beam irradiation, stress occurring resulting from the expansion is alleviated by the hollow portion 20a.
Thus, in the semiconductor device according to the present embodiment, the fuse element 20 has the hollow portion 20a therein, so that when the fuse element 20 is irradiated with the laser beam, an internal destruction of only the fuse element 20 can selectively occur, without greatly damaging the surrounding areas of the fuse element 20.
In the semiconductor device according to the present embodiment, the height H of the fuse element 20 is greater than the DOF of the laser beam, so that it is possible to effectively absorb the energy of the laser beam to be irradiated. In the semiconductor device according to the present embodiment, the insulating film 32 of which the absorptivity of light is large is arranged between the insulating films 31 and 33, and in the area where the insulating film 32 is penetrated, the diameter of the second tubular potion 22 of the fuse element 20 is small. Thus, the energy of the laser beam effectively concentrates onto the second tubular potion 22. This means that it is possible to greatly decrease the power of the laser beam to be irradiated, compared to the conventional case. Further, the height H of the fuse element 20 is greater than the depth of focus DOF of the laser beam, so that it is possible to sufficiently secure the margin of the focal positions in the upper and down directions. This means that it is possible to use an object lens having a large numerical aperture (NA).
That is, in the semiconductor device according to this embodiment, it is possible to cut the fuse element 20 by using the objective lens having a large numerical aperture and the laser beam of which power is weak. Therefore, the energy density rapidly decreases in an area distant from the focal position even within a beam spot of the laser beam. As a result, the damage imposed on a member located above the fuse element 20 as in the case of the passivation film 60 shown in
Thus, it becomes possible to cut the fuse element 20 without substantially destructing the passivation film 60. As explained above, the destruction of the passivation film occurring at the time of trimming often gives rise to moisture penetration or the like, which is a cause of a decrease in reliability of the semiconductor device. However, according to this embodiment, such problem is solved, and thus, the reliability of the semiconductor device can be enhanced. Further, the passivation film is not substantially destructed, so that almost no debris occurs at the time of trimming. For these reasons, even when the focal distance is short because the numerical aperture of the objective lens is set large, debris hardly adheres to the objective lens.
Since the objective lens having a large numerical aperture is used, even when dust adheres to the surface of the passivation film 60, it is possible to suppress the attenuation of the laser beam, which occurs due to the adhesion of the dust. That is, when an objective lens having a relatively small numerical aperture as shown in
where La is a diameter in
62a>62b.
This proves that the shadow is smaller when the objective lens having a relatively large numerical aperture is used. Accordingly, when the objective lens having a large numerical aperture is used as in this embodiment, the influence of the dust 61 is reduced.
According to this embodiment, the damage imposed on the member located above or below the fuse element 20 is very small, so that it is possible to arrange another wiring or the like below or above the fuse element 20.
In the example shown in
As for the material for the wiring 81 shown in
By taking advantage of the fact that the energy density in the area distant from the focal position is very low, it is possible to greatly narrow the distance between the adjacent fuse elements compared to the conventional case. Although a specific distance between the adjacent fuse elements is not particularly limited, the distance can be set shorter than the height H of each fuse element 20.
In the example shown in
That is, as shown in
When it is necessary to further reduce the energy attenuation caused by the irradiation of the upper electrode 12 or the like with the laser beam L, the fuse element 20 can be irradiated with the laser beam L slightly obliquely with respect to an axial direction to avoid an area in which the upper electrodes 12 are closely arranged, as much as possible.
Accordingly, when a laser trimming is performed on an array of such fuse elements 20, for example, the passivation film 60 that covers the fuse elements can remain seamless and continuous whereas some portions of the fuse elements are cut as shown in
In this embodiment, by taking advantage of the fact that the passivation film 60 is not substantially destructed, it becomes possible to irradiate the fuse element with a laser beam by a so-called immersion method, in which liquid is interposed between the objective lens and the passivation film 60. When this method is used, it becomes possible to further increase an effective numerical aperture of the objective lens.
That is, the numerical aperture (NA) is given by the following equation (3), where n is the refractive index of a medium existing on an optical path, and θ is the convergent angle of a laser beam.
NA=n×sin θ (3)
In general trimming, the medium is air, so that n=1. However, when liquid, for example pure water of n=1.44, is used as the medium, the numerical aperture becomes 1.44 times greater. Thus, the energy density imposed on the member located above or below the fuse element 20 is not only further decreased, but also the power itself of the laser beam to be irradiated can be set as low as possible. Further, since heat generated by the irradiation with the laser beam is efficiently cooled by the pure water, which is the medium, it is possible to further decrease the damage imposed on the member near the fuse element 20.
A method of manufacturing the semiconductor device according to this embodiment is explained next.
As shown in
As shown in
Thereby, as shown in
The photoresist 35 is then removed. Subsequently, a conductor that serves as a material for the fuse element 20 is grown by using a film formation method of example CVD, excellent in coverage, as shown in
As a result, materials of the fuse element 20 are deposited on inner walls of the through-holes 31a, 32a and 33a. The through-hole 33a, which serves as an entrance of the material gas, is firstly caped before the interior of the through-holes 31a, 32a and 33a are filled with the conductor, as shown in
Thereafter, an unnecessary conductor formed on the surface of the insulating film 33 is removed, the upper electrode 12 contacting the fuse element 20 is formed, and the passivation film 60 covering the upper electrode 12 is formed, to complete the semiconductor device according to this embodiment. According to the method explained above, it is possible to surely form the fuse element 20 having the hollow portion 20a.
The method of forming the fuse element 20 having the hollow portion 20a is not limited to the above-described method, and another method can be used. When it is difficult to cap the through-hole 33a, which functions as the entrance of the material gas, it is also possible to form the fuse element 20 by growing a conductor that becomes the fuse element 20 on inner walls of the through-holes 31a, 32a, 33a using a film forming method that is excellent in coverage, such as a CVD method, and thereafter, as shown in
As explained above, according to this embodiment, the energy of the laser beam is efficiently absorbed by the fuse element 20, and the margin of the focal position in the up and down directions is sufficiently secured. Thus, it becomes possible to perform a trimming that uses the objective lens having a large numerical aperture and the laser beam having a weak power.
Thus, it becomes possible to perform a laser trimming without substantially destructing the passivation film, so that it is possible to prevent a decrease in reliability, which is caused by the destruction of the passivation film, of the semiconductor device. In addition, since almost no debris occurs at the time of the trimming, almost no debris adheres to the objective lens.
Since it is possible to perform the trimming by using the objective lens having a large numerical aperture and the laser beam having a weak power, it becomes not only possible to arrange another wiring below or above the fuse element, but also possible to set the distance between the adjacent fuse elements narrow. Therefore, it is also possible to increase an integration density.
A second embodiment of the present invention is explained next.
As shown in
The added insulating film 34 is an insulating film located on top of the insulating film 33, and as a material for the insulating film 34, a material different from that of the insulating film 33 is selected. For example, when the main component of the insulating film 33 is silicon oxide (SiO2), for the main component of the insulating film 34, silicon nitride (Si3N4) or silicon oxynitride (SiON) or the like can be used. The film thickness of the insulating film 34 is preferably set to be thinner than that of the insulating film 33.
As shown in
As shown in
Thereafter, an unnecessary conductor formed on the surface of the insulating film 34 is removed, the upper electrode 12 contacting the fuse element 20 is formed, and the passivation layer 60 covering the upper electrode 12 is formed, whereby the semiconductor device according to the second embodiment is completed.
Thus, according to this embodiment, it becomes possible to more surely form the fuse element 20 having the hollow portion 20a.
The present invention is in no way limited to the aforementioned embodiments, but rather various modifications are possible within the scope of the invention as recited in the claims, and naturally these modifications are included within the scope of the invention.
For example, in each of the first and second embodiments, the semiconductor device has the structure in which the insulating film 32 of which the absorptivity of light is high is sandwiched by the two insulating films 31 and 33. However, the present invention is not limited thereto, and it suffices when at least an insulating film of which the absorptivity of light is relatively low and an insulating film of which the absorptivity of light is relatively high are stacked, and a fuse element is arranged such that it penetrates these insulating films. However, as in each of the embodiments, when the structure in which the insulating film of which the absorptivity of light is high is sandwiched by the two insulating films is employed, the second tubular portion that is easily cut can be located at the central portion of the fuse element. Thus, it becomes possible to enhance the reliability of the fuse element.
In the embodiment, the fuse element 20 having the hollow portion 20a is used. However, the hollow portion 20a is not necessarily arranged as long as the lower electrode 11 and the upper electrode 12 can be insulated by the laser trimming. However, the presence of the hollow portion permits cutting of the fuse element more surely, and functions to drastically decrease damage imposed on surrounding areas of the fuse element, so that it is highly preferable that such a hollow portion is formed. Further, even when the through-hole is partially buried, it is particularly preferable that an area where the insulating film 32 of which the absorptivity of light is high is penetrated have at least a hollow portion.
In the embodiment, the lower electrode 11 is connected to the diffused layer 51 via the through-hole electrode 41. However, the diffused layer 51 itself can be used as the lower electrode.
Number | Date | Country | Kind |
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2006-079412 | Mar 2006 | JP | national |