JPS5949685B2 - Ion implantation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ion implantation method that does not cause dielectric breakdown of an insulating film in a semiconductor device.

In recent years, ion implantation has become important as one of various techniques applied when manufacturing semiconductor devices. However, when this ion implantation method is carried out, it has become a problem that dielectric breakdown of the insulating film occurs.

Normally, there is no need to implant ions into the insulating film itself, but in some types of semiconductor devices, for example, a polycrystalline silicon film is grown on an insulating film such as silicon dioxide, and after patterning it into the desired shape. It is necessary to perform ion implantation to convert the polycrystalline silicon film into a resistive film. In this case, when the polycrystalline silicon film is patterned, a portion of the insulating film is exposed, so if ion injection is performed, ions will also be injected into the insulating film. There is no problem if the dose of this ion injection is small, but for example, 1×
If the dose is as high as 1015 [cln-2] or more, the surface potential of the insulating film will increase, causing various types of deterioration.
A particular problem is dielectric breakdown. Therefore, let us consider the mechanism of dielectric breakdown caused by this ion injection. That is, as seen in FIG. 1, when an insulating film 2 made of micronized silicon is formed on a semiconductor substrate 1 and ions 3 are implanted into it, a part of the charge is transferred through a bus as indicated by an arrow P1. Then, it passes straight into the semiconductor substrate 1. Further, when scanning is performed by swinging an ion beam, a portion of the charge leaks through the bus as indicated by arrow P2, that is, through the surface of the insulating film 2. However, among these buses, bus P2 is high impedance;
When the bus P2 is dominant, it is not possible to eliminate all the charges, so charges gradually accumulate on the surface of the insulating film 2. If, for example, there is a floating electrode on the insulating film 2, eventually The insulation of the insulating film 2 is broken and charges are released from the electrode to the semiconductor substrate 1. In that case, the insulating film 2 will be in a state where a crater has been formed. Figure 2 shows how the bus P becomes more dominant and the bus P2 becomes more dominant and charges are accumulated in the insulating film 2.
It is explained with the aid of a diagram. That is, when the ions 3 are press-injected into the insulating film 2, electron e/hole pairs are generated on the surface thereof. The charge of the ions 3 generates a strong electric field in the direction of the substrate 1 against the hole leakage, so normally, the hole leakage will reach the substrate 1 along the bus P1 depending on the electric field. However, the remaining electrons e are neutralized by the ions 3, and the surface charge is supposed to disappear. However, in reality, when ions 3 are implanted into the insulating film 2, the structure is destroyed and many traps for holes are formed, and the hole leakage is shown in Figure 2. As shown in the figure, it can be seen that it is trapped and unable to move.
That is, during high-dose ion implantation into an insulating film, bus P does not exist, and ion charges are expected to be released only through bus P2. Due to the above-mentioned mechanism, the surface of the insulating layer 2 becomes highly tilted in the positive direction. For example, by setting it as shown in FIG. The surface potential at a distance L from the electrode 4. As shown in FIG. 3b, it will be understood from this that as the size of the semiconductor wafer increases, its potential increases rapidly. In addition, W1 in Fig. 3b is 5 (ni) (2 [inches]) and W2 is 7.5.
[C! ! L) (3 [inches]), W, is 10C-(4 [inches]
[inch]) represents each wafer. The conditions for obtaining the data in Figure 3 are: ion ribon (B+), implantation energy: 80 [Ke], 11:8 [μA] (1.4 [μA])
]), and the thickness of the insulating film 2 was 1.0 [μm]. The present invention prevents dielectric breakdown due to retention of ion charges even when ions are implanted into a semiconductor wafer having an insulating film.This will be explained in detail below. In this manner, holes trapped near the surface of the insulating film 2 during ion implantation are eliminated.

Specifically, an ultraviolet source is placed near the target, that is, a semiconductor wafer to be ion-implanted, and ions are implanted while irradiating the semiconductor wafer with ultraviolet rays.

In this way, no ionic charge is accumulated near the surface of the insulating film 2, and therefore no dielectric breakdown occurs. This is the fourth
This will be explained with reference to the energy band diagram shown in the figure.

Now, as described above, electron e/hole h pairs are generated on the surface by ion implantation, but electron e/hole h pairs are also generated by ultraviolet irradiation.

Moreover, unlike the case of ion intrusion, in the case of ultraviolet rays, it occurs throughout the insulating film 2, that is, in deep parts. Therefore, most of the generated holes h reach the substrate 1 and are released without being affected by the traps near the surface of the insulating film 2. The remaining electrons e move to the surface of the insulating film 2 and act to neutralize the implanted ions 3.
In order to eliminate the above-mentioned positive charge on the surface of the insulating film 2, for example, it may be considered to implant hot electrons, but in that case, the amount of ions injected and the amount of electrons injected If they are not balanced, the resolution may be incomplete or, conversely, negative charges may accumulate. However, in the present invention, this difficulty is eliminated by using pairs of electrons e and holes h. In other words, if the positive charges existing on the surface of the insulating film 2 are eliminated and the potential there is lowered, the electric field will not act strongly on the electron e/hole h pairs generated by ultraviolet irradiation, and the As a result, many things disappear almost immediately on the spot due to recombination. In this way, the present invention always
Actions are automatically taken to maintain neutrality. As can be seen from the above explanation, according to the present invention, even if ion implantation is performed at a high dose into a semiconductor wafer having an insulating film,
There is no possibility of dielectric breakdown occurring in the insulating film.

This can be easily carried out by simply irradiating the semiconductor wafer with an ultraviolet lamp or the like during ion implantation.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of charge accumulation by ion implantation, Figure 2 is an energy band diagram to explain hole trapping, and Figure 3 is an illustration of charge accumulation on the surface of an insulating film of a semiconductor wafer by ion implantation. FIG. 4 shows data explaining that the potential increases when applied, a is a schematic diagram explaining the settings at that time, b is a line diagram, and FIG. 4 is an energy band diagram when the present invention is implemented. In the figure, 1 is a substrate, 2 is an insulator, 3 is an ion, 4 is a power source, e is an electron, and h is a hole.

Claims (1)

[Claims] 1. An ion implantation method characterized in that when ions are injected into a semiconductor wafer having an insulating film on the surface, the semiconductor wafer is irradiated with ultraviolet rays.