JPH0517699B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor ion implantation method for forming a highly concentrated impurity region in a semiconductor device.

In recent years, ion implantation methods have become very widely used. For example, in MOS semiconductor devices, ion implantation has traditionally been used primarily to control the threshold voltage of channels, but recently it has been used to form highly concentrated impurity regions such as sources and drains. I'm getting used to it.

When implanting charged ions at such a high concentration, there are the following problems.

The implanted ion dose is N (pieces/m ² ), the number of charges is n,
Assuming that the elementary charge q=1.6×10 ^-19 C and that the injection is made into the insulating layer, its dielectric constant is ε (F/m).

Now, if ion implantation is uniform and the charges create an electric field E at both ends of the insulator, then E (V/m)
The size of is E=nqN/ε.

Using the example of diffusion of the source and drain of a MOS semiconductor device as specific values for this formula, and assuming SiO ₂ as the insulator, n = 1, N = 2 × 10 ¹⁹
/m ² , ε=ε _px =3.5×10 ⁻¹¹ F/m, and by substituting this into the above equation, E=1×10 ¹¹ V/m.

By the way, the dielectric strength field of SiO ₂ is said to be about 10 ⁹ V/m, and if this electric field is applied as it is, the insulating film will be destroyed, so it is necessary to release the charged charges. Furthermore, when ion implantation is performed into semiconductors, a photoresist is normally used as a master, but this photoresist has low conductivity, and there may be areas without photoresist or isolated islands, so the surface The amount of charge that leaks out and escapes is smaller than the amount of charge that is injected, and a large charge gradually builds up, often resulting in dielectric breakdown.

The present invention has been made in view of these problems, and provides a semiconductor ion implantation method that prevents breakdown of the insulating film, enables large current ion implantation, and is effective in forming a high concentration impurity region. This is what I am trying to do.

That is, the method of the present invention, when implanting charged ions of 2×10 ^{17 or} more/m ^{2 or} more into a semiconductor, simultaneously implants the ions into the semiconductor through a conductive thin film filter and irradiates the surface of the semiconductor with ultraviolet rays. This is a characteristic feature.

Examples of the charged particles to be ion-implanted into the semiconductor include B, As, P, Si, Ga, In, and Sn.

The above ion dose is effective when performing large current ion implantation at a high concentration of 2×10 ¹⁷ ions/m ² or more, and when the dose is less than the above, the electric field applied to the insulating film is low and the problem of dielectric breakdown is eliminated. few.

The conductive thin film filter is disposed in front of an electrode for scanning the charged ion beam, and has a function of neutralizing the charged ions and implanting them in an atomic state into the semiconductor. As such a conductive thin film filter, for example, a thin film of Al, C, Au, etc. is used. The neutralization effect of charged particles by the conductive thin film filter varies depending on the ion implantation conditions and film thickness, and is difficult to control. Therefore, it is effective to use it in combination with ultraviolet irradiation as described above.

When irradiating the above ultraviolet rays, use one with an energy of 3 eV or more to release the charges trapped on the substrate surface as secondary electrons into the vacuum or toward a conductor, neutralizing the substrate. It is something to do. Note that the charged particles that emit secondary electrons when irradiated with ultraviolet light are limited to negative ions, and cannot be applied to positive ions such as As and P.

Further, in addition to the above method, in the present invention, a conductive thin film filter may be provided in front of the scanning electrode of the charged ion beam, and the electric charge may be absorbed there, and only the ions may be transmitted therethrough to be implanted into the semiconductor substrate. . In this case, as a conductive thin film filter,
Although thin films of Al, C, Au, etc. are used, the effect of charge absorption by these thin films varies depending on the ion implantation conditions and film thickness and is difficult to control, so it is effective to use them in combination with the above-mentioned ultraviolet irradiation.

Next, examples of the present invention will be described.

Boron B was ion-implanted into a silicon wafer under the following implantation conditions. Boron ions were implanted at 50 keV at a dose of 2×10 ¹⁹ ions/m ² for an irradiation time of 20 minutes into ten 4-inch silicon wafers.

At the same time as the ion implantation, the sample surface was irradiated with ultraviolet rays from a Xe lamp through the Safeye window. In this case, ultraviolet rays were irradiated over the entire surface of the wafer using a 500 watt Xe lamp using a lens.

As a result, no scattering of polysilicon or destruction of the oxide film on the wafer surface was observed, and a good high concentration impurity region could be formed.

As explained above, according to the semiconductor ion implantation method according to the present invention, breakdown of the insulator can be prevented, large current ion implantation can be performed, and a high concentration impurity region can be formed satisfactorily. .

Claims (1)

[Claims] 1. A semiconductor characterized in that when 2×10 ¹⁷ or more charged ions/m ^{2 or} more are implanted into a semiconductor, the ion implantation into the semiconductor is performed through a conductive thin film filter, and at the same time, the surface of the semiconductor is irradiated with ultraviolet rays. ion implantation method.