Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Patent
1995-11-27
1997-04-29
Anderson, Bruce C.
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
250423R, 31511181, H01J 37317
Patent
active
056251955
DESCRIPTION:
BRIEF SUMMARY
The invention relates to low- or medium-current ion implantation, especially in microelectronics.
The first uses of high-energy ion implantation in microelectronics concerned the fabrication of CCD (Charge Coupled Device) sensors and the programming of read-only memories, for example for electronic games.
High-energy ion implantation (of the order of 600 to 700 keV of phosphorus ions into silicon) has since found other applications, for example for improving lateral isolation in CMOS circuits having a high density of integration.
High-energy ion implantation also has many advantages in the fabrication of semiconductor components. It thus makes it possible to effect a field isolation ("channel stopper") which, in addition to better lateral isolation, offers a reduction in the n.sup.+ /p.sup.+ distance between NMOS and PMOS transistors and in the diffusion of the dopants into the active zones of the semiconductor component during oxidation.
Another advantage resides in the production of thin and localized buried collectors in bipolar technologies. Such an ion implantation requires doses of a few 10.sup.14 ions of phosphorus per cm.sup.2 with an energy of 1.5 MeV or else of boron at 800 keV.
Mention may be also made of the production of buried layers in order to decrease leakage currents via the substrate. Currently, such production is generally carried out by epitaxy, which is a delicate and expensive technique in an industrial environment. It is therefore preferable to carry out the ion implantations at doses [lacuna] 10.sup.15 ions per cm.sup.2 of phosphorus at 1.5 MeV or else of boron at 800 keV.
However, energies of the order of 1 MeV (mega-electron-volt) currently require recourse to the costly solution of conventional linear-type accelerators. Such machines exist but they are very costly and remain laboratory machines since industrialists reproach them for their lack of reliability and of flexibility and, above all, hesitate to invest in a machine meeting the requirements of only a small number (one, or perhaps two) technological steps.
In order for high-energy implantation to become a relatively approachable technique for industrialists, one solution consists in using multiply-charged ions. However, the ion sources used are generally hot-filament sources which have an operating lifetime of about twenty hours or so and furthermore only allow low available currents to be obtained, resulting in the production of multiply-charged ion doses which barely exceed 10.sup.13 /cm.sup.2 (see in particular the article by A. GROUILLET et al., "Device performances and parametric studies of high energy implantations with multiple charged ion beams" ION IMPLANTATION TECHNOLOGY--92, p. 417-420).
Moreover, another type of multiply-charged ion source exists which combines, at the same time, two high magnetic fields (one axial and the other radial) as well as injection of a microwave electromagnetic field into an ionization chamber, the dimensions of which are calculated so that the source works in the electron cyclotron resonance condition, making it possible to produce, from a gas admitted into the ionization chamber, an ionized gaseous plasma containing highly charged ions.
This type of ion source was initially developed in order to be applied to nuclear fusion. Thus it has been possible to obtain multiply-charged ions such as Ar.sup.13+, Kr.sup.20+ or Xe.sup.20+. However, such sources are extremely heavy and bulky, without counting the volume of the power-supply unit which they require, and these constraints mean that adapting them to conventional industrial implanters is totally out of the question.
It is true that a small-sized electron cyclotron resonance (ECR) source is known from European Patent Application No. 0,527,082. Nevertheless, the source described in this prior document, associated with a microwave supply producing the microwave energy necessary to generate the ionized plasma, cannot be arranged in a conventional implanter especially because of the dimensional constraints of the source/microwave supply a
REFERENCES:
patent: 5327475 (1994-07-01), Golovanivsky et al.
patent: 5355399 (1994-10-01), Golovanivsky et al.
patent: 5449920 (1995-09-01), Chan
patent: 5483077 (1996-01-01), Glavish
Production of Milliampere Class Mass-Separate Multiply Charged Ion Beam J. Vac. Sci. Tech. vol. 9, No. 2 published Apr. 1991, pp. 307-311.
Patent Abstract of Japan, vol. 18, Number 252 JP, A, 06 036 235, Mar. 1994.
Anderson Bruce C.
France Telecom
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