Kourosh Saadatmand

Measurement and analysis of deposition-etch characteristics of BF3 plasma immersion ion implantation

The deposition-etch characteristics of BF3 plasmas were quantitatively measured and analyzed using a deposition monitor, and were correlated with plasma parameters. It was found that by controlling pressure and rf power, the source could be operated in regimes which were either deposition or etch dominant. This data was then applied to a −2 kV plasma immersion ion implantation BF3 process to explain retained dose characteristics. A good qualitative agreement between the deposition-etch data and implanted retained dose data was obtained.

Measurements of secondary electron emission and plasma density enhancement for plasma exposed surfaces using an optically isolated Faraday cup

We present secondary electron yield and plasma enhancement factor data for silicon surfaces exposed to Ar, He, N2, O2, H2, and BF3 plasmas, for incident ion energies from 0.5–10 keV. A fiber-optic isolated Faraday cup was used to directly measure the ion current Jion, allowing a direct measurement of the secondary electron yield. This method automatically accounted for the effect of pulse-induced plasma density enhancement due to the ionization of neutral gas by accelerated secondary electrons, which we observed and measured quantitatively. The values of the secondary electron yields measured by this method were higher than published values measured by the conventional (ultraclean surface and ultrahigh vacuum) methods but lower than published values measured by previous plasma immersion ion implantation methods.

Ion beam technologies in the semiconductor world (plenary)

Ion beam technologies, in particular ion implantation, have had a profound effect on the development of Si integrated circuits. We review the pertinent history of ion source and machine development within the constraints of Moore’s law. For ion sources, the critical roles of hot cathode and rf sources are discussed. Novel applications such as sources for finely focused beams for lithography and cluster beams for doping (decaborane) or smoothing (Ar) will be discussed. Future trends in terms of the next generation of devices and the required implantation machines will be reviewed.

Spatial distributions of the emitting species in a Penning surface‐plasma source

Using optical spectroscopy we study the spatial and temporal distributions of the Hα, Cs i(4555 A), Cs ii(4604 A), and Mo i(3903 A) emission lines in a Penning surface‐plasma source (SPS). A diagnostic slit exposes the entire SPS discharge gap either parallel or perpendicular to the magnetic field. The spatial and temporal distributions of the emitting species are recorded using a 1‐m monochromator. In addition, the visible light and the Hα and Cs ii(4604 A) spatial distributions are recorded with a video camera. The cesium atomic and ionic light, and the molybdenum atomic light, is strongly concentrated near the cathodes; the visible light and the Hα light is almost uniform in both directions. Electron‐impact ionization of atoms sputtered from the cathodes and the return of the ions to the cathodes by residual plasma fields is probably the mechanism which concentrates cesium near the cathodes. The Cs0 mean free path is estimated to be 16 and 0.43 mm for 2 and 400 A discharges, respectively.

Ion depletion effects in sheath dynamics during plasma immersion ion implantation-models and data

In plasma immersion ion implantation, the wafer is negatively pulsed while immersed in a dc ambient plasma. During this high voltage pulse, the sheath expands, and plasma ions are accelerated to the wafer. The essential character of this plasma sheath expansion can be described by a simple mathematical model, first proposed by Lieberman. In this article, we build on Lieberman’s model, extending it to describe the ion current before and after the pulse. We find that a dip in ion current is predicted immediately after the pulse, due to the depletion of ions within the sheath. This simple model is tested using Faraday cup data, and is also compared to a particle-in-cell simulation.

Negative ions for heavy ion fusion and semiconductor manufacturing applications

Radio frequency driven multicusp source was set up to run chlorine plasma and the source performance was compared between positive and negative chlorine ion production. A maximum Cl− current density of 45 mA/cm2 was achieved at 2.2 kW of rf power with electron to negative ion ratio of 7 and positive to negative ion ratio of 1.3. 99.8% of the total negative chlorine beam was atomic Cl−. To produce negative boron ions for semiconductor manufacturing applications, a noncesiated, sputtering-type surface production ion source was constructed. An external rf antenna geometry and large LaB6 converter were implemented in the source design. Maximum B2− ion current density of 1 mA/cm2 was achieved at 800 W of rf power and −600 V converter voltage. Total B2− ion current was 1.8 mA.

Particle trapping and annihilation within the extraction system of ion sources

Many applications of ion sources (e.g., ion implantation in the semiconductor industry) are very sensitive to particles and have tight specifications on allowable particle number and size. Among the sources of particles are the ion source itself (due to either nucleation in the plasma, or ion bombardment of the surfaces), and the extraction electrodes (due to ion bombardment). This article investigates the processes to which such particles are subjected during their flight through the extraction electrodes. They travel at much lower velocity than the accelerated ions due to their much larger mass, and so are bombarded by these increasingly energetic ions. The processes considered during the trajectory of the particle are: charging, acceleration in the electrode fields, entrapment within the suppression gap, heating from ion bombardment, radiation cooling, melting, vaporization, and Coulomb explosion. These processes are all modeled simultaneously as the trajectory of the particle is followed. A general co...