JPS6350857B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device, and more particularly to a semiconductor device in which circuit characteristics are adjusted by cutting a polycrystalline silicon resistor or fuse.

Insulated gate field effect integrated circuit device (hereinafter referred to as
MOS ICs (MOS ICs) were originally developed for use in digital circuits, and are still mostly used in digital circuits today. However, in recent years MOS
With the remarkable progress in IC technology, research has begun on the application of MOS ICs to analog circuits. When a MOS IC is used as a digital circuit, its various circuit characteristics are determined by the relative ratios of the threshold voltages and characteristics of the individual MOS transistors that make up the circuit, whereas when used as an analog circuit, In this case, the circuit characteristics are determined by the threshold voltage and the absolute value of the characteristics.

Additionally, MOS ICs usually consist of transistors with two to several types of characteristics, and
The threshold voltages of transistors constituting MOS ICs are normally distributed within a range of 20% to 30% of the set value. Therefore, in digital MOS ICs, circuits are designed with a margin in anticipation of these fluctuations. However, in analog circuits, if the variation range is the same as that in digital circuits, circuit design would be extremely difficult due to the nature of analog, and could be said to be virtually impossible.

Therefore, in analog circuits, it becomes necessary to somehow correct the variation in circuit characteristics during the MOS IC manufacturing process to a point close to the design value.

Circuit characteristics such as system gain, frequency characteristics, and reference voltage source voltage are subject to correction.
After fabricating the IC, the values of the correction circuit will be set using a laser or pulsed current. As this correction circuit, a method using selective cutting of a polycrystalline silicon resistor or a polycrystalline silicon fuse has been developed.

The problem with blowing out polycrystalline silicon using constant voltage or constant current pulses is that the resistance of the polycrystalline silicon or the point at which the fuse blows cannot be determined, so other elements must be placed nearby. This makes it difficult to conduct the process, which increases layout constraints, and reduces reliability due to deterioration of moisture resistance due to melting or cracking of the insulating film cover on the polycrystalline silicon at the fused part, and moisture infiltration from there. It is to cause

In order to solve this problem, polycrystalline silicon resistors or fuses of various shapes were fused using pulses, and experiments were conducted to determine changes in the fused area and the insulating film cover over it, and the following results were obtained. .
That is, if the shape of the polycrystalline silicon is linear, the point where the polycrystalline silicon is fused is not determined, but if it is L-shaped, it is always fused at the bent point. In addition, if there is no polycrystalline silicon thermally oxidized film on the melted area and only an insulating film cover made by vapor phase growth (CVD), there will be no change in the insulating film cover even if the polycrystalline silicon melts. unacceptable.

In other words, the difference in the location of fusing due to the shape is that when polycrystalline silicon is made into an L shape, when a pulse is applied, the current density at the bent location becomes larger, and heat is generated locally compared to other locations. On the other hand, the difference between different insulating film covers is that the thermal oxide film has a more dense structure than the insulating film cover made by vapor phase growth, or the difference between polycrystalline silicon and its thermal oxidation. It was found that this was due to the difference in the expansion coefficient during heat generation due to the difference in the degree of adhesion between the film and the insulating film formed by vapor phase growth and the polycrystalline silicon. Note that the pulse was applied to the polycrystalline silicon resistor or fuse using the circuit shown in FIG.

In the circuit shown in FIG. 1, a capacitor 2 is charged by a DC constant voltage power supply, and the charge stored in the capacitor 2 is applied to a sample 3.

From the above, if the shape of the polycrystalline silicon resistor or fuse is L-shaped and there is no thermal oxidation film of polycrystalline silicon on this folded angle, it is possible to reliably determine the melting point. Moreover, damage to the insulating film cover due to melting can be avoided.

The present invention proposes an L-shaped polycrystalline silicon resistor or fuse that is intended to be cut after the IC is manufactured, in order to adjust various circuit characteristics with high precision, for example, in an analog circuit MOS IC composed of MOS transistors. By removing the polycrystalline silicon thermal oxide film especially on the bent parts, highly reliable and high-precision analog circuits can be created.
This is an attempt to realize a MOS IC.

An embodiment of the present invention will be described using FIGS. 2 and 3. FIG. 2a shows a linear polycrystalline silicon resistor or fuse, FIG. 2b shows an L-shaped polycrystalline silicon resistor or fuse. A voltage is applied between both electrodes 9. When the shape of the polycrystalline silicon resistor or fuse 5 is L-shaped, the melting point is limited to the bent portion 6, but when it is straight, the melting point is limited to the one end 7 and the other end 8. It is not determined which part between the two will be fused. Therefore, if the shape of the polycrystalline silicon is L-shaped, the melting point can be easily determined, and the damage to the surrounding area will not be caused as compared to the case where the polycrystalline silicon is straight. Here, a wiring 11 to another circuit is connected to the electrode 9. The fact that the polycrystalline silicon resistor melts at the bent portion 6 was discovered through experiments by the inventor of the present invention, and theoretically this means that the electric field tends to concentrate at the bent portion. This is thought to be due to the

FIG. 3 shows the state of the insulating film cover according to the present invention, with FIG. 3a showing a top view and FIG. 3b showing a cross-sectional view of the portion indicated by the broken line c-c' in FIG. 3a. It is. The thermal oxide film 12 of polycrystalline silicon is removed on the bent portion 6 of the L-shaped polycrystalline silicon 5 formed on the insulating film 14 on the main surface of the semiconductor substrate 15, and the polycrystalline silicon thermal oxide film 12 is removed. Only the insulating film 13 formed by phase growth is used as a cover. With this structure, since the melting point is only at the bent portion 6, the polycrystalline silicon can be melted off without causing any damage to the insulating film cover 12 above it, thereby reducing reliability due to damage to the insulating film cover. It does not cause a decrease in sexuality.

In other words, according to the present invention, the melting point can be determined with high accuracy, and since no damage is caused to the insulating film cover, there is no effect on other active elements due to polycrystalline silicon melting, and deterioration of moisture resistance due to scratches on the insulating film cover can be avoided. It has become possible to manufacture highly accurate and highly reliable semiconductor devices without causing a decrease in reliability.

[Brief explanation of drawings]

FIG. 1 is a pulse application circuit diagram used in a polycrystalline silicon resistor or fuse blowing experiment. FIG. 2a is a plan view showing a conventional linear polycrystalline silicon resistor or fuse, FIG. 2b is a plan view showing an L-shaped polycrystalline silicon resistor or fuse according to an embodiment of the present invention, and FIG. Figure 3b is a plan view showing how the polycrystalline silicon thermal oxide film on the bent part of the resistor or fuse has been removed and only the insulating film cover formed by the vapor phase growth method covers the bent part. is the third
3A and 3B are cross-sectional views taken along line c-c' in FIG. In the figure, 1... DC constant voltage power supply, 2... Capacitor, 3... Sample, 4... Mercury relay, 5... Polycrystalline silicon resistor or fuse, 6... Bent part of L-shaped polycrystalline silicon resistor or fuse, 7
...One end of a linear polycrystalline silicon resistor or fuse, 8... The other end of a linear polycrystalline silicon resistor or fuse, 9... Pulse input electrode for cutting the polycrystalline silicon resistor or fuse, 10... Pulse input electrode and Connection portion with polycrystalline silicon, 11... Wiring of circuit for correcting analog circuit characteristics, 12... Polycrystalline silicon thermal oxide film, 13... Insulating film for cover by vapor phase growth, 14... Field insulating film, 15... Semiconductor substrate.

Claims (1)

[Scope of Claims] 1. A semiconductor device in which various circuit characteristics are adjusted by cutting a resistor or fuse made of polycrystalline silicon, in which the shape of the polycrystalline silicon resistor or fuse is distorted. A semiconductor device characterized by: 2. Claim 1, characterized in that the polycrystalline silicon thermal oxide film on the twisted portion of the polycrystalline silicon resistor or fuse is removed.
The semiconductor device described in .