JPS5914834B2 - read-only semiconductor storage device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a read-only semiconductor memory device, and particularly to a read-only semiconductor memory device having a structure that is advantageous for writing information.

9 Read-only semiconductor memory device (ReadOnlyM)
memory) (hereinafter abbreviated as ROM) has a phase type P
-ROM (Fused Programmable ROM)
).

Then, a so-called polycrystalline silicon resistor, which has a desired resistance value by ion-implanting impurities into polycrystalline silicon or by doping impurities during growth, is used as a phase for this 1, and a diode is connected in series with this. There is a connecting body connected to the terminals at both ends thereof near each intersection of a plurality of row lines and a plurality of column lines substantially perpendicular to the row lines. The above is illustrated in FIG. 1. That is, in the figure, 1, 1', 1''...
. is a row line, 2, 7, 2'', . . . are column lines, 3a is a phase of a polycrystalline silicon resistor, and 3b is a diode connected in series with the phase to form a connected body. 4
a and 4b are the terminals at both ends of the connecting body and the row lines 1 and 1.
', 1''..., column lines 2, Z, 2''...

In the above-mentioned IC, writing to a specific position is accomplished by applying a forward current to the phase and the diode, cutting off the o phase and completing the writing. Second
Figure a shows the state before writing, Figure b shows the state after writing,
3a' is the disconnected phase. According to the above-mentioned conventional writing method, the phase is fused due to temperature rise due to energization. Effects such as migration are superimposed due to the action of the electric field, leading to disconnection. Therefore, if the applied voltage exceeds a certain value, It has the disadvantage of requiring a current. In addition, writing of the phase is completed by destruction, but there is also the disadvantage that the heat generated at the time of destruction has an adverse effect when a plastic envelope is used. The present invention provides a structure of a semiconductor memory device that eliminates the above-mentioned conventional drawbacks.

The read-only semiconductor memory device of the present invention connects a plurality of row lines and a plurality of column lines substantially perpendicular to the row lines by a connected body consisting of a series connection of a semiconductor active element and a polycrystalline silicon resistor in the vicinity of their intersections. In a read-only semiconductor memory device that performs a write operation by connecting the polycrystalline silicon resistor and reducing its resistance value by supplying current to the polycrystalline silicon resistor according to write information, the polycrystalline resistor is connected to aluminum wiring at both ends. The resistance value is reduced by the diffusion of aluminum from the aluminum wiring into the polycrystalline silicon resistor due to the temperature rise associated with current flow.

Next, the present invention will be described in detail with reference to the drawings for an embodiment of a semiconductor memory device.

Both FIGS. 3 and 4 show the structure of an exemplary coupling body of the present invention, with FIG. 3A showing the state before writing and FIG. 4B showing the state after writing. In Figure 3, the resistance value is 100KΩ before writing.
The above-mentioned connected body I of the resistor 13a and the diode 13b connected in series thereto becomes a connected body 13' of the series connected body of the resistor 13a' and the diode 13b whose resistance value is 0 when energized for writing. This shows the state that has changed. The following figure 4 shows a type of P-R that uses the semiconductor element's VcE (SAT) (collector-emitter saturation voltage) as the threshold.
In the OM, for example, by applying a forward current between the base and the collector, the polysilicon resistor 23a is brought to a short-circuited polysilicon resistor 23a'. The structure and writing of the polysilicon resistor will be described next. FIG. 5 shows the change in resistance value of a polysilicon resistor doped with impurities by ion implantation with respect to heat treatment time at 500°C. That is, in the case shown in FIG. 6, the polysilicon film 15 is exposed to Va by ion implantation.
Impurities of Q:2X1014/Cd were introduced at cc:40KeV, the film thickness was 5000mm, and the planar dimensions were (150mm).
μX75μ), the Al wiring layer 16 was formed with a layer thickness of 1.2μ and the planar dimensions as shown in the figure (two parallel strips of length 140μ×width 15μ (spaced 25μ) deposited) in N2 gas. 5000CX 10 minutes Anneal
g) It is a variation in resistance value when the vertical axis is the subsequent resistance value as 100 and the horizontal axis is the heating time in units of minutes. From this figure, it can be seen that by performing heat treatment at a certain temperature for a certain period of time, Al atoms of the wiring metal diffuse into polysilicon and have the effect of lowering the resistance value. In fact, by supplying power to the polysilicon resistor, the temperature of the polysilicon increases and the applied electric field causes Al atoms to diffuse into the polysilicon in a short period of time, resulting in a short circuit state. In one example, the width is about 2μ or less, the length is about 8μ or less, and the thickness is about 0.
A forward voltage of 6 is applied to a shotgun diode connected in series to a polysilicon resistor with a resistance of 5μ and a resistance of several hundred kilohms.
By applying ~7V and flowing a current of several tens to hundreds of micrometers for several tens of microseconds to several tens of milliseconds, the short-circuit of the fuse was possible. The point to be noted in this writing method is that in the above embodiment, if the supplied power is quite large and the power is supplied in a pulsed manner within several tens of microseconds, the polysilicon resistor will disappear before the diffusion of Al atoms becomes noticeable. Since this may lead to destruction, an appropriate write voltage (current) waveform is required. Next, FIGS. 7a to 7c show an example of a process for forming a polysilicon resistor according to the present invention.

First, a SiO2 film 32 is formed on one main surface of a silicon substrate 31, a polysilicon layer 33 (UndOped shape) is formed on the entire surface of the substrate (Figure a), and then impurities are injected by ion implantation and then heat treatment is performed. After that, patterning for forming phase portions is performed (Figure b). Note that 33' in figure b
is a patterned doped polysilicon layer. Next, an Al layer as an example of wiring metal is deposited and patterned to form a patterned Al layer 34 (FIG. c). According to the present invention, conduction is achieved by applying doping to the metal layer deposited on the polysilicon resistor, so there is no need for fusing, excessive temperature rise, etc. as in the prior art.

Therefore, it is possible to prevent the adverse effects caused by the scattering of the phase body, and it is also effective in preventing damage and deformation of the envelope, which has poor heat resistance such as plastic, due to heat generated by high temperatures.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the wiring of a conventional ROM, and FIG. 2 is a diagram showing changes due to writing in a concatenated body of a conventional phase-type ROM. FIGS. 3 and 4 are diagrams showing changes in the coupling body in a ROM according to an embodiment of the present invention. FIG. a shows the state before writing, FIG. b shows the state after writing, and FIG. A diagram showing changes in values; FIG. 6 is a plan view of a doped polysilicon film on which Al wiring is formed; FIGS. Both are cross-sectional views. Note that the same reference numerals in the drawings indicate the same or corresponding parts, respectively. 13...
Connecting body, 13a, 23a... Resistor in the connecting body, 13b... Diode, 15, 33...
... Polysilicon layer, 16, 34 ... Wiring metal layer, 31 ... Silicon substrate, 32 ...
...SiO2 film.

Claims (1)

[Claims] 1 Multiple row lines and multiple column lines that are almost orthogonal to these,
A semiconductor active element and a polycrystalline silicon resistor are connected in the vicinity of the intersection by a series connection body, and the polycrystalline silicon resistor is energized according to written information,
In a read-only semiconductor memory device that performs a write operation by decreasing its resistance value, the polycrystalline resistor is in contact with aluminum wiring at both ends, and the decrease in resistance value is due to the aluminum wiring due to temperature rise due to energization. A read-only semiconductor memory device characterized in that it is produced by diffusion of aluminum into a polycrystalline silicon resistor.