JPS60117769A - Semiconductor memory device - Google Patents

Abstract

PURPOSE:To obtain a PROM, which is made conductive or non-conductive only by the radiation of laser after the completion of the device so as to form a program, has a simple structure, and can accomplish high integration, by using the shift of a flat band voltage into the negative direction due to the radiation of the laser, and inverting the interface between the semiconductor and an oxide film. CONSTITUTION:A pair of N<+> type contact regions, i.e., the first contact region 4 and the second contact region 5, having the reverse conductive type with respect to a substrate 1, is formed in a P type silicon substrate, with an interval being provided. An oxide film 2, which strides on the part between the contact regions, is formed on the surface of the substrate 1. Electrode wirings 6 and 7 comprising Al are formed on the contact regions 4 and 5, respectively. At first, the part between the electrode wirings 6 and 7 is not conducted. Then, laser 3 is projected through a PSG8. The substrate is P type, but Qss is moved to the positive side by the radiation of the laser. As a result, the surface of the substrate is inverted to (n). Thus, the part between the contact regions 4 and 5 is conducted. In this way, the P-ROM is made conductive by projecting the laser, and writing is performed.

Description

[Detailed Description of the Invention] Technical Field The present invention relates to flat band portage V by laser irradiation.
5i-sto using negative direction/\ shift of FR.

It relates to a programmable ROM (FROM) that is programmed by inverting the interface and establishing conduction.

BACKGROUND OF THE INVENTION The present inventor irradiated St with an oxide film on it using an Ar laser, and the result was 5t-8in as shown in FIG.

It was found that Qss, which is the charge at the interface, changes.

FIG. 1 shows this in terms of the flat band voltage VF'B of the MOS diode, with the horizontal axis representing the laser power and the vertical axis representing the flat band voltage shift ΔVvB. As shown in the figure (from about 8'w), Δv?B increases monotonically with respect to the laser power.In other words, as the laser power increases, vyn shifts in the negative direction.In other words, Qss is normal pressure, but it becomes positive. This indicates that the n-channel MO8) transistor shifts to the depletion mode side, and the P-channel MOS transistor shifts to the enhancement mode side. The present invention provides S
This is obtained from FROM' by using the inversion of the t-sto2 interface.

BACKGROUND TECHNOLOGY Conventionally, FROMs include fuse type and diode pair type. The fuse type uses an electric current to blow out the fuse.
In the diode pair type, reverse voltage destroys one diode and causes it to conduct. In such a conventional FROM, the structure is complicated because fuses and diode pairs are formed in the device, and there is a problem in increasing the degree of integration.

OBJECTS OF THE INVENTION An object of the present invention is to obtain a programmable ROM (PROM) which has a simple structure and can be highly integrated by utilizing the inversion of the semiconductor-oxide film interface by laser irradiation.

Structure and operation of the invention First, the effects of laser irradiation, which are utilized in the present invention and which were discovered by the present inventor and outlined in the technical background section above, will be described in detail. In FIG. 2, 1 is a silicon substrate;
A St (h2) film with a thickness of 420× is formed on the surface. Now, heat the substrate 1 to 100° C. and place the laser spot 3 on the oxide film 2 shown in Figure A at 5 cfn/
Scan as shown in Figure B at a speed of s. Its pitch is 6
It was set to 0μ/step. Under the above conditions, a relationship between Ar laser power and ΔV7B (shift of flat band voltage) as shown in Fig. 1 occurs, and Ar laser power is 8
A phenomenon in which ΔVFB monotonically increases in the negative direction above w is observed. In addition, in Figure 1, △v with a laser power of 8W
yn has started to change, but this changes depending on the oxide film thickness and the focus of the laser throttle, and in some cases it may rise at 4W, but eventually (C) When the laser power is increased, ΔvPB becomes monotonous. increases in the negative direction, that is, Sl
-810! Qo, which is the charge on the interface, is normally positive, but it increases in the direction of the cuff.

The present invention makes use of this, and the present invention will be described in detail below with reference to Examples. FIG. 3 shows an embodiment of the present invention, in which a pair of n+ type contact regions, a first contact region 4 and a second contact region, which are of the opposite conductivity type to the substrate 1, are spaced apart from each other on a p-type silicon substrate 1. A contact region 5 is formed, and an oxide film (SiO, . . . ) spanning between the contact regions of each part is formed.
2 is formed on the surface of the substrate 10. In each contact region 4, 5, ionized wiring 6.7 made of At
is formed. To illustrate the dimensions of each part in the figure, the thickness 4 of the surface protection film 8 (PSG) is 1 μm, the depth t of the contact region! + is 3000X. beginning,
There is no conduction between the electrode wirings 6 and 7 in FIG. 6A. Next, Figure B
As a result of irradiating the laser 3 through P8G8Y, conduction occurs between the contact regions 4.5. In this way, as shown in FIGS. This is a P-ROM that is written in the state, and its top view is shown in Figure 4A.
, shown in B. For simplicity, only the relationship between the contact area 4.5 and the laser spot 9 is shown. In reality, the details are worked on after the device is completed, so there are At electrode beads 6 and 7 and a protective layer PSG B that covers the entire surface.
G8 is about 1 μm, and since PSG itself is transparent to visible light, it is possible to irradiate a laser onto the Si-5 lot structure using JIJ1. As shown in Figure B, a large number of elements are actually formed on the substrate 1, and the laser spot needs to be tied so that it does not cover other elements.
Since the laser beam can be easily confined within topmφ (15 μm or less), it is possible to achieve a sufficiently high degree of integration.

Although the case in which a p-type substrate is used has been described above, the surrounding areas between each contact region 4.5 on the substrate are initially non-conducting, and are made conductive by this laser, so there is no need to isolate the elements. However, when using an n-type substrate, the periphery is in a conductive state, so there is no point in cutting only part of the channel with a laser to make it non-conductive. Therefore, it is necessary to separate each element as shown in FIG. 10 is an isolation region, and the elements formed therein have the same structure as in FIG. 3A, except that the substrate 1 is of n type and the contact region 4.
The difference is that they are mold regions (denoted as contact regions 4', 5'). First contact area 4'.

A channel is formed around the contact area 5' and the contact area is in a constant state of electrical conductivity, but when the laser spot 9 is irradiated as shown in FIG. 5, the contact area between the contact areas a1 and 51 becomes non-conductive.

As described in the detailed description of the invention, the present invention has the advantage that after the device is completed, it is possible to program the device by making it conductive or non-conductive using only laser irradiation.

In addition, the structure is simple, and the laser beam is 0.5 to 1μ.
According to the present invention, it is easy to achieve a high degree of integration because the device can be packed into the m order.

[Brief explanation of drawings]

Figure 1 is a graph showing the change in ΔVFB when 81-5 lot, which is the premise of the present invention, is irradiated with laser, Figure 2 A, B
are explanatory diagrams of the laser irradiation state for St -5l (h, respectively. Figures 6A and B are explanatory diagrams of the configuration before and after laser irradiation of the embodiment of the present invention, respectively. Figure 4 is an explanatory diagram of the configuration of the embodiment of the present invention. In this embodiment, A is an explanatory diagram of the laser irradiation state for one element, B is an explanatory diagram of the laser irradiation state for a substrate on which multiple elements are formed, and FIG. 5 is a top view of another embodiment of the present invention. Figure. 1... Silicon substrate, 2 ・= 5 lots, 4, 5
・=Contact area, 6, 7... Electrode wiring, 8...
・PEG, 9...shi-TheSpot Patent Applicant Fujitsu Limited Agent Patent Attorney Gobe Tamamushi (one other person) Figure 1 Figure 2 Figure 3 Figure 4 Figure A Figure 5

Claims (1)

[Claims] a pair of contact regions of conductivity type opposite to that of the substrate formed on a p- or n-type semiconductor substrate at a distance; an oxide film formed on the surface of the semiconductor substrate between the contact regions;
and electrode wiring formed in each of the pair of contact regions, and the half-body-oxide film interface is reversed by shifting the flat band voltage in the negative direction/＼ by laser irradiation to connect the pair of contact regions. What is claimed is: 1. A programmable read-only semi-integrated memory device, characterized in that the space between the two is electrically conductive or non-conductive.