JPH07183109A - Trimming element - Google Patents

Abstract

PURPOSE:To decrease a fusing current while the resistance of a fuse for trimming is kept low. CONSTITUTION:A polysilicon fuse 3 is formed on a first insulating film 2 and is insulated from an aluminium wiring 5 by a second insulating film 4. Such a first opening part 8 as a part of the fuse 3 and a part of the film 2 are exposed is formed in the film 4 and moreover, such an exposed part is etched also in the film 2 and a hollow part 7 is formed. A space to encircle the fuse 3 is formed of the parts 7 and 8. Accordingly, a heat diffusion in the space is suppressed by the existence of such the part formed of the parts 7 and 8 and the fuse 3 is cut even by a low fusing current.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to integrated circuits having trimming fuses, and more particularly to fuse structures.

[0002]

2. Description of the Related Art In an integrated circuit, particularly an analog integrated circuit, trimming by a fuse element is necessary for adjusting characteristic variations in a manufacturing process. For example, the resistance of patterned resistance is difficult to obtain the accuracy of resistance value ± 30%.
It also becomes. Therefore, the resistance that requires high precision is made slightly lower, and the resistance value is adjusted by blowing the fuse.

FIG. 4 is an example of a circuit for resistance trimming using two fuse elements.

Resistors R, r1 and r2 are connected in series between BB '. In the initial state, the resistances r1 and r2
Is short-circuited by the fuses 1 and 2, the resistance between BB 'is R.

When resistance adjustment is required, for example, a resistance value can be set to R + r1 by flowing a fusing current between the terminals T1 and T2 to fuse the fuse 1.

Similarly, the fuse 2 can be adjusted in r2, and eventually R, R + r1, R + r2, R + r1 +.
A combination of r2 is possible.

Finer adjustment is possible by changing the number and combination of fuses and resistors.

[0008]

The fusing of the polysilicon fuse 3 is performed by Joule heat generated by the fusing current, and the fusing current is 200 mA to 300 mA.
A relatively large current of mA is due to the fact that the insulating film in contact with the polysilicon fuse 3 has a thermal conductivity of about 0.65 W.
This is because the heat is relatively well transferred to / mK, so that the heat easily diffuses, and the temperature at which the polysilicon fuse 3 is blown does not easily reach the temperature.

On the other hand, the melting of the polysilicon fuse 3 is
Generally, this is done by an LSI tester at the wafer stage, but normally the power capacity of an LSI tester is 10
Since it is about 0 mA, there is a problem that it cannot be blown out by such a tester.

As a solution to this problem, there is a method of narrowing the width of the polysilicon fuse 3.

This is a method of increasing the current density by narrowing the width of the polysilicon fuse 3 and concentrating the Joule heat generated by the fusing current. However, the resistance which is not blown must be short-circuited. Therefore, the resistance of the polysilicon fuse 3 must be sufficiently low, while if it is too thin, the polysilicon fuse 3
Becomes a parasitic resistance and makes the resistance value in an unmelted state inaccurate, so it cannot be made too thin.

Therefore, an object of the present invention is to provide a trimming element which can be blown by a normal LSI tester without reducing the width of the polysilicon fuse 3.

[0013]

In the trimming element of the present invention, at least a part of the insulating film adjacent to the polysilicon fuse is removed by etching so as to form a space surrounding the polysilicon fuse. It has a portion that does not contact with.

As a result, the Joule heat from the polysilicon fuse generated by the fusing current is less likely to diffuse in the portion not in contact with the insulating film.

[0015]

EXAMPLE A trimming element shown in an example of the present invention uses a polysilicon fuse having a portion which is not in contact with an insulating film.

Since heat hardly diffuses in such a portion, the temperature can easily reach a temperature at which the fuse is blown, and the fusing current can be reduced without narrowing the width of the polysilicon fuse.

First, this embodiment will be described with reference to the drawings. FIG. 1 is a plan view of a trimming element shown in this embodiment, and FIG. 2 is a sectional view showing an AA ′ section in FIG.

In this embodiment, the upper and lower insulating films in contact with the polysilicon fuse are partially removed by etching, and the polysilicon fuse and the insulating film are not in contact with each other in such a portion.

Next, a manufacturing process of the trimming element shown in FIGS. 1 and 2 will be described.

The same parts as those in the conventional example are designated by the same reference numerals. First, the first insulating film 2 made of silicon oxide is formed on the silicon substrate 1.

The insulating film is a field oxide film,
It is formed simultaneously during the so-called LOCOS process.

Next, a polysilicon wiring layer is formed on the first insulating film 2 by the CVD method and patterned into a predetermined shape to form a polysilicon fuse 3.

This step is also carried out at the same time as the formation of the polysilicon wiring which becomes the wiring between elements such as transistors.

Subsequently, a phosphorus glass film (P
The second insulating film 4 made of SG) is formed, and the second insulating film on the polysilicon fuse 3 is formed at the time of forming a contact hole for connecting the polysilicon wiring and the aluminum wiring further formed thereon. At the same time, the contact hole 6 is also formed in 4.

Next, an aluminum film is formed by the sputtering method and patterned into a predetermined shape to form the aluminum wiring 5.

The structure in the above steps is the same as that of the conventional example.

Next, the second insulating film 4 is etched so that a part of the polysilicon fuse 3 is exposed, and a first opening 8 is formed.

At this time, the first opening 8 is formed to have a size larger than the width of the polysilicon fuse 3.

Therefore, as shown in FIG. 1, not only a part of polysilicon fuse 3 but also a part of first insulating film 2 is exposed by first opening 8.

Next, the photoresist used as the mask during the etching of the first opening 8 is used as it is,
The first insulating film 2 which is partially exposed is etched with a fluorine-based chemical (for example, hydrofluoric acid).

As a result, the etching progresses not only in the vertical direction but also in the horizontal direction, and a hollow portion 7 is formed between the first insulating film 2 and the polysilicon fuse 3.

The second insulating film 4 is used in this embodiment.
Since the phosphorus glass film that is etched by the fluorine-based chemical is used as the above, the formation of the first opening 8 and the formation of the hollow portion 7 can be performed simultaneously.

FIGS. 1 and 2 show the trimming element formed through the above steps. Since the hollow portion 7 and the first opening 8 are formed, a space surrounding the polysilicon fuse 3 exists. Is different from the conventional example.

According to this embodiment, the polysilicon fuse 3 and the first insulating film 2 are not in contact with each other in the hollow portion 7, and the second insulating film 4 is not in contact with each other in the first opening 8. The contact area between the polysilicon fuse 3 and the first and second insulating films 2 and 4 is significantly reduced without changing the width or other shape of the polysilicon fuse 3. As a result, thermal diffusion is less likely to occur in the non-contact portion of the polysilicon fuse 3, so that the fusing current can be set to 100 mA or less while keeping the resistance in the unfused state sufficiently low.

As shown in FIG. 1, when the size of the first opening 8 is about twice the width of the polysilicon fuse 3, the polysilicon fuse 3 and the second insulating film are not in contact with each other. If the opening has a shape close to a square as shown in FIG. 1, it is sufficient if one side has a length about twice the width of the polysilicon fuse 3. However, the first opening 8 may be smaller than the above size as long as the heat diffusion from the polysilicon fuse 3 can be suppressed.

It goes without saying that the first opening 8 may be larger than this.

Further, although the shape of the first opening 8 is shown as a square in FIG. 1, it may be another shape (for example, circular).

Further, since a part of the polysilicon fuse 3 is left exposed by the first opening 8, impurities may enter from here when the package is carried out by a method such as resin sealing, but the passivation film. Since the exposed portion is eliminated by forming the passivation film after trimming and adjusting the resistance value before forming the film, there is no concern that impurities may enter.

In the case of packaging by the airtight sealing method, it is not necessary to perform trimming before forming the passivation film.

In this case, after forming the passivation film 9 as shown in FIG.
By forming the second opening 10 in a portion corresponding to the opening 8, the contact between the polysilicon fuse 3 and the passivation film 9 can be eliminated.

The formation of the second opening 10 can be performed in the same process as the opening of the pad portion.

[0042]

As described above, according to the present invention, a part of the insulating film in contact with the polysilicon fuse is opened, and a part of the insulating film has a hollow structure. Is reduced and heat dissipation from the polysilicon fuse during trimming is prevented, so that the fusing current can be 100 mA or less.

As a result, a specially designed L for trimming is used.
Trimming can be performed by an ordinary LSI tester without using an SI tester, and since a large current is not used for trimming, the life of the measuring probe is not shortened.

The present invention can also be applied to the case of trimming with a laser beam or the like, because it is blown by heat even when trimming with a laser beam or the like.

[Brief description of drawings]

FIG. 1 is a plan view of a trimming element showing an embodiment of the present invention.

FIG. 2 is a sectional view of FIG.

FIG. 3 is another cross-sectional view of the trimming element showing the embodiment of the present invention.

FIG. 4 is a diagram showing an example of a circuit using a trimming element.

FIG. 5 is a plan view of a trimming element showing a conventional example.

6 is a sectional view of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 1st insulating film 3 Polysilicon fuse 4 2nd insulating film 5 Aluminum wiring 6 Contact hole 7 Hollow part 8 1st opening 9 Passivation film 10 2nd opening

Claims (5)

[Claims] 1. A first insulating film formed on a silicon substrate, a polysilicon fuse formed on the first insulating film and patterned into a predetermined shape, the first insulating film and the first insulating film. A trimming element including a second insulating film formed on a polysilicon fuse and a wiring layer connected to the polysilicon fuse through a contact hole formed in the second insulating film A trimming element, wherein at least a part of the first and second insulating films which are in contact with each other is removed by etching so as to form a space surrounding the polysilicon fuse. 2. The trimming device according to claim 1, further comprising a passivation film formed on the entire surface of the chip having the trimming element according to claim 1, wherein the passivation film is removed by etching without making contact with the polysilicon fuse. element. 3. The space is a space for preventing the polysilicon fuse and the first and second insulating films from being in contact with each other over a length that is at least twice the width of the polysilicon fuse. The trimming element according to claim 1. 4. The trimming element according to claim 1, wherein the first insulating film is an oxide film. 5. The trimming element according to claim 4, wherein the second insulating film is an oxide film.