JPS6059678B2 - Programmable read-only memory device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a programmable read-only memory device (hereinafter referred to as a PROM device).

), and particularly relates to shoot-type PROM elements. <Prior Art> In recent years, as semiconductor LSIs including PROM elements have progressed, their demand has been increasing.

In the case of PROM elements, they are being used not only as PROM-ISI but also as so-called redundancy circuits of memory Li and logic LSI, that is, defect relief circuits. Typical secondary PROM elements include those of the junction short type in which writing is performed by shorting the PN junction by passing an excessive current through the PN junction of one diode, and those of the junction short type in which writing is performed by shorting the PN junction by passing an excessive current through the PN junction of one diode. There are two types: a current phase type that performs writing by cutting the three-phase element, and a laser fuse type that performs writing by cutting a three-phase element with a laser beam.

Among these, 1 junction short type PROM element and 2
Current phasing PROM devices require very large currents to program together.

For example, the specific value of the required programming current is approximately 100 [Wl, A] in the junction short method of 1.
In the current phase method of No. 2, several 10 CmA] is required. Driving such a large current typically requires a bipolar transistor with high amplification. Also,
In order to apply a PROM element for SI on MOS, a current driving MOS transistor with a very large channel width is required, and therefore a large area is occupied. For this reason, it has been difficult to achieve high integration with the PROM elements of the above-mentioned methods 1 and 2. On the other hand, in the case of the laser fuse type PROM element (3), programming is done by cutting off a predetermined program position using a laser beam, but the positions to which the laser beam is applied are very close together, so the high An expensive programming device such as a highly accurate automatic position detection device is required.

Under such circumstances, the current phase type PROM element, which is the most typical PROM element, has the above-mentioned drawbacks, but programming and processing is the simplest, and its merits are significant when it comes to utilizing PROM elements. It is well worth the evaluation.

Therefore, we will consider the current phase method. FIG. 1 is a diagram showing a phase element section of a conventional current phase system, in which a is an equivalent circuit thereof, and b is a structural diagram viewed from above. In the equivalent circuit of a, when a current is passed between terminals 1 and 2, phase element F is fused, and programming is performed by this fusion. In the structural diagram of b, the phase element F is formed of, for example, a polycrystalline silicon layer.
The ends 5 and 6 of the phase element F are made of aluminum (hereinafter referred to as
It is abbreviated as N. ) In order to make contact with the wirings 7 and 8, it is provided so as to be spread out relative to the phase element F. Contact holes 3 and 4 are provided at the ends 5 and 6, and are connected to Al wirings 7 and 8 through these holes. In addition to the above-mentioned drawbacks (difficulty in achieving high integration), such conventional PROM elements also have problems with the designability, processability, and reliability of the phase element F due to the fact that B fuses out due to energization. be.

In other words, these problems are, firstly, that the fusing mechanism of the phase element has not been fully elucidated, and secondly, that it is necessary to heat the phase element above its melting point. This is caused by thermal damage to the area around the phase element. Furthermore, since the phase element cannot be covered with a passivation film (protective film) at the time of fusing, there is also a drawback that reliability becomes poor. It is an object of the present invention to provide a PROM element that eliminates the drawbacks, has excellent high density, can reduce the current required for programming, has excellent reliability, and has a high degree of design margin.

<Summary of Structure of the Invention> In order to achieve the above object, a PROM element according to the present invention includes a conductive first wiring layer made of a first material and a conductive wiring layer made of a second material with an insulating film interposed therebetween. 2 wiring layers are arranged facing each other, and further, the first wiring layer is placed in contact with the second wiring layer.
A third wiring layer made of a third material is provided with a disconnection in a portion opposite to the second wiring layer.

The second substance and the third substance have a eutectic temperature of the first substance.
By supplying electricity to the first wiring layer, the first wiring layer is made to act as a heating element, and the heat generated causes the second wiring layer to heat up in the opposing portion.
By eutecticization of the material and the third material, the electrical resistance between both ends of the disconnected portion of the third wiring layer is lowered, so that programming can be performed.

According to such a configuration, the phase element is formed in the second and third wiring layers, and its conductivity changes instead of being blown out by a programming operation (that is, energization).

The phase element and the heating element (first wiring layer) to which the programming current is applied are insulated and separated by an insulating film. The heat generated by the first wiring layer, which serves as a heating element, is transferred to the second wiring layer.
It is sufficient to locally eutectic the gap between the current and the third wiring layer (phase element), and therefore the current required for programming can be significantly reduced. In addition, since less heat is generated, thermal damage to the surroundings can be reduced, and higher density is possible.In addition, since the current is small, the transistor that drives the program current can also be made smaller. contribute to the promotion of In addition, the eutectic process progresses relatively statically as a physical phenomenon, and programming can be performed while the PROM element is covered with a passivation insulating film. A PROM element with high reliability can be provided.

Examples of the invention The present invention will be explained below based on illustrative embodiments.

〔composition〕

FIG. 2 is a plan view showing essential parts of the first embodiment of the PROM element according to the present invention, and FIG. is a cross-sectional view along ■-■, and FIG. 4 is a cross-sectional view taken along ■-■.

An insulating film 20 made of, for example, a silicon oxide film or a silicon nitride film is grown on the semiconductor substrate 10 (
Figures 3 and 4).

On the insulating film 20, a conductive first wiring layer 30 having a thickness of about 5000 Å is patterned into a band shape.

As the material used for the first wiring layer 30, low-resistance cup-shaped or tomoe-shaped polycrystalline silicon is used, but other high-melting point metals (MO, .Pt..w, Ta, etc.) or high-melting point metals are used. Silicide, n+ type or p+ type polycrystalline silicon, etc. can be used. First wiring layer 30
An insulating film 40 made of, for example, a silicon oxide film or a silicon nitride film with a thickness of several hundred angstroms is grown on a part or all of the film (FIGS. 3 and 4).

A layer having a thickness of about 5 mm is formed on the first wiring layer 30 via this insulating film 40.
A second wiring layer 50 of 000A is provided intersecting with the first wiring layer 30.

Therefore, the first wiring layer 30 and the second wiring layer 50 are placed opposite each other with the insulating film 40 interposed therebetween. As the material used for the second wiring layer 50, high resistance q-polycrystalline silicon or n-type polycrystalline silicon is used. Note that the first wiring layer 30 and the second wiring layer 50 do not need to intersect perpendicularly, and may intersect obliquely; however, orthogonal arrangement is most rational in terms of manufacturing. On the second wiring layer 50, there is a third wiring layer in contact with it.
A wiring layer 60 is provided.

This third wiring layer 60 is composed of the first wiring layer 30 and the second wiring layer 5.
The wire is disconnected by a predetermined gap (approximately 1 μm) on the opposing portion 70 with
) is used. In this way, the first
A protective film 80 for a patch is grown on the second and third wiring layers 30, 50, and 60 to completely cover them.

The protective film 80 is formed of phosphor glass with a thickness of 1 μm, for example. 1. [Programming Operation] Next, the programming operation of the PROM element having the above configuration will be explained.

- Programming is performed by passing a current of about several WLA through the first wiring layer 30. That is, the first wiring layer 3
By passing a current through the first wiring layer 30, the first wiring layer 30 acts as a heating element (heater). The generated heat heats the second wiring layer 50 via the insulating film 40. What should be noted here is controlling the current so that it does not reach the melting point (for example, 1420° C.) of the first wiring layer 30 itself. Due to such heating by the first wiring layer 30, the second wiring layer 50 and the third wiring layer in the opposing portion 70 are
It is possible to raise the temperature of the wiring layer 60 to a temperature higher than the eutectic temperature (for example, 580° C.).

As shown in FIG. 5, by performing the above-described programming operation, a eutectic region 90 is formed in the second wiring layer 50 and the third wiring layer 60 in the vicinity of the opposing portion 70.

Due to the formation of this eutectic region 90, the resistivity of the third wiring layer 60, which was almost disconnected before programming, is reduced to approximately 10
The resistance decreases from 10Ω to approximately 100Ω or less and becomes conductive. In other words, the resistance ratio before and after programming is about 103 or more, and the third wiring layer 6 as a phase element
0 is effectively programmed from a non-conducting open state to a conducting short-circuit state. Next, equivalent circuits of the above PROM element are shown in FIGS. 6A and 6B.

A shows a PROM element in an open state before programming, and b shows a PROM element in a short-circuited state after programming. H indicates a heating element corresponding to the first wiring layer 30, and F indicates a phase element corresponding to the second and third wiring layers 50 and 60. In the above description, a single PROM element has been described, but a memory cell array can be constructed by using a plurality of PROM elements.

FIG. 7 shows an example of a memory cell array in which PROM elements are arranged in rows and columns. Heater Hll arranged in matrix,・
・, Hij are matrix lines Rl, . . . , R,; Cl, . . . , C
, are placed at each intersection of .

These matrix lines Rl, R, :Cl, C, are made of a material that does not generate heat, such as aluminum metal, and are connected to the heaters Hll, . . . , Hij via contacts.

To program, matrix lines Rl,...,RJ;Cl,...
・,C, and select the selected matrix line R, and Cm
This is done by short-circuiting any phase element Flm by applying a voltage between them to cause the heater HIm to generate heat. Terminal 1j191j2 of each phase element Fij is matrix line Rl9
゜゜9Rj'SCl9゜゜9C,, heater Hll,...
, Hij through wiring and contacts that are three-dimensionally configured so as not to come into contact with each other. These wirings are respectively connected to other LSI circuit sections, and the phase element Fjj is used as a memory element. Next, other embodiments of the present invention will be described.

FIG. 8 is a cross-sectional structural diagram showing another embodiment. The difference from the PROM element shown in the above-mentioned embodiments (FIGS. 2 to 4) is that the disconnected portion of the opposing portion 70 of the third wiring layer 60 is in contact with the second wiring layer 50 via the insulating film 100. That's true. This is to ensure accurate shaping of the disconnected portion and ensure insulation in a non-conducting state. <Effects of the Invention> As described above, according to the present invention, the phase elements (second and third wiring layers) and the heating element (first
(wiring layer)) and are placed opposite to each other while being insulated and separated from each other via an insulating film.

Therefore, the phase element can be programmed without energizing the phase element itself while connected to the LSI circuit that utilizes it. In this respect, the degree of freedom in utilizing the PROM element is increased, unlike the conventional current phase method in which programming is performed by directly supplying current to the phase element. In addition, as a programming current, it is sufficient to flow enough heat into the heating element to generate the heat necessary to cause a eutectic state between the second and third wiring layers constituting the phase element, and this value is generally several It should be below MA.

This value is approximately 1 in the case of the conventional current phase method.
The value is 110. Furthermore, the temperature required for the heating element itself is low, and thermal damage to the surroundings due to the generated heat can be significantly reduced compared to the conventional current phase type. Suitable for miniaturization and high density of current drive elements that drive. In addition, the eutectic process between the second wiring layers progresses statically due to the physical mechanism compared to the fusing process of the current phase method, so it is highly designable.

Furthermore, the PROM element of the present invention can be programmed while covered with a passivation protective film, that is, an insulating film, and in this respect as well, it has higher reliability than conventional current phase elements. It is.

[Brief explanation of the drawing]

Figure 1 shows a conventional current-fused phase element.
is its equivalent circuit diagram, b is its plan view, FIG. 2 is a plan view showing the main structure of the PROM element according to the present invention, FIG. 3 is a sectional view taken along the line ■-■ in FIG. 2, and FIG. ■ in the diagram
5 is a sectional view showing the state of the PROM element according to the present invention after programming, and FIG. 6 is a cross-sectional view showing the state of the PROM element according to the present invention
FIG. 7 is an equivalent circuit diagram of a ROM element, in which a is a circuit diagram showing a state before programming, b is a circuit diagram showing a state after programming, and FIG. 7 is an equivalent circuit diagram showing an example of a matrix memory cell array using PROM elements according to the present invention. The circuit diagram and FIG. 8 are cross-sectional views showing another embodiment of the present invention. 30...First wiring layer, 40...Insulating film, 50...Second wiring layer, 60...Third
Wiring layer, 70... Opposing part.

Claims (1)

[Scope of Claims] 1. A first wiring layer that is made of a conductive first substance and generates heat when energized; and a second substance that is disposed opposite to the first wiring layer with an insulating film interposed therebetween. a second wiring layer consisting of;
a third wiring layer made of a third material, which is disposed in contact with the second wiring layer and is disconnected at or near an opposing portion of the first and second wiring layers; Second,
A programmable lead characterized in that the third substance is a substance that becomes eutectic with the heat generated by the first wiring layer, and that the eutectic temperature is sufficiently lower than the melting point of the first substance.・Only memory element. 2. A programmable read-only memory device according to claim 1, wherein the first material is low-resistance polycrystalline silicon. 3. The device according to claim 1, wherein the first substance is a high melting point metal or a silicide of a high melting point metal.
memory element. 4. A programmable read-only memory device according to claim 1, wherein the first material is N-type or P-type polycrystalline silicon. 5 Claims 1, 2, 3, or 4
A programmable read-only memory device according to item 1, characterized in that the second material is a high-resistance polycrystalline silicon, and the third material is an aluminum metal. 6 Claims 1, 2, 3, or 4
3. A programmable read-only memory device according to item 1, characterized in that the second material is N-type polycrystalline silicon, and the third material is aluminum metal. 7 Claims 1, 2, 3, 4,
In the device according to item 5 or 6, the first wiring layer and the second wiring layer are arranged to face each other in a crossing state. memory element.