Hidemi Koike

Microwave ion source for high-current implanter.

A long-life, high-current, microwave ion source for an electromagnetic mass separator is described. Ionization takes place due to the 2.45-GHz microwave discharge at a magnetic field intensity which is higher than the electron cyclotron resonance magnetic field. The discharge chamber is a ridged circular waveguide. The discharge region is restricted to a rectangular volume between the ridged electrodes by filling the remaining portions with dielectric. This source operates under low pressure (10(-2)-10(-3) Torr) and with high power efficiency. The incident microwave power is only several hundred watts at maximum output. When PH(3) gas is introduced, the total extracted current is about 40 mA with a 2x40-mm extraction slit. A P(+) ion implantation current of more than 10 mA is obtained by combining the source with a 40-cm radius, 60 degrees deflection magnetic mass separator.

High‐current ion implanter using a microwave ion source

A new ion implanter has been designed for high‐dose predeposition in a semiconductor production line. It incorporates a microwave ion source, a 90° magnetic mass separator, and a rotating disk target chamber. Mass peak variations of PH3 gas are shown as a function of the incident microwave power. The ion energy level can be varied from 10 to 50 keV. It makes 10 mA P+ implantation (maximum 15 mA) possible. After beam adjustment, implantation is automatically carried out with a microcomputer. The operation rate of the implanter is remarkably improved due to the long lifetime of the modified microwave ion source and the low gas consumption. The dose nonuniformity of a 3‐in. wafer implanted with this implanter has a standard deviation (σ) of 0.5%. This small nonuniformity results in a small σ in the transistor current gain (less than 3.5%).

Microwave ion source for high current metal beams

Abstract A high current, metal ion source has been developed for application to materials modification in metals and insulators. In a microwave discharge type ion source, even highly reactive materials such as metal halides, as well as oxygen, can be used for source feed materials. The microwave ion source originally developed for conventional semiconductor fabrication has been modified to provide several mA of mass-separated metal ions. So far, ions of Al + , Ga + , Ti + , Hf + and Sc + have been obtained.

Ion beam acceleration using variable frequency RFQ

Abstract To develop a high-current MeV ion implanter, a beam acceleration feasibility study using a variable frequency RFQ system was carried out. The RFQ system consists of an LC tank circuit and conventional RFQ electrodes 60 cm in length. The resonance frequency was varied by changing the electrical capacity in the circuit. Experimental results show that injected N+ beams of 1.3 keV were accelerat frequency in the range of 12–15 MHz. The Q-value obtained was over 1500. Results show that a variable frequency RFQ system is suitable for application in MeV ion implantation.

New microwave ion source for high energy ion implanter

Abstract A new high current multiply-charged ion source, which is used for a high energy ion implanter, was designed to produce a mA-class multiply-charged ion beam. The discharge chamber is approximately four times larger than that of a conventional coaxial-type source and has a multipole magnetic field. An ion beam of a several mA is extracted from the new source and mass-analyzed. The extracted ion beam has an Ar 2+ beam of approximately 1 mA. The Ar 2+ /Ar + ratio obtained from this new source is 80%, which is a large improvement over the 10% of the conventional source. This ratio increases with absorbed microwave power.

Beam extraction experiments from microwave ion sources

With the aim of designing a new ion source for ampere‐class beams, the beam extraction characteristics of standard coaxial‐type microwave ion sources were investigated in detail at energies lower than 10 keV. It was found that this source has the capability of providing Ar+ beams of 200 mA at the acceleration voltage of 7.0 kV and the microwave power of 850 W. The obtainable beam current increases with a decrease of gap width between positive and negative electrodes. Moreover, it is shown that the microwave ion source is suitable for obtaining high‐current beams of single‐charged ions. Both the plasma source and extraction electrode diameters for 1‐A beam are estimated to be about 13 cm. The required microwave power is about 6 kW.

Emittances of a microwave ion source for implantation

Abstract A new apparatus was developed to study the performance of a microwave ion source as a means to improve a high-current ion implanter. The apparatus consists of an emittance measuring device, a mass separator and a beam profile monitor. It can handle beams of high current (several 10 mA) and high power (up to 2 kW). By studying emittances of the ion source, conditions for improved matching of the ion source and the mass separator in the ion implanter were obtained.

New microwave ion source for multiply charged ion beam production

Abstract To obtain high-current beams of rather lower-charge-state multiply charged ions, a new microwave ion source is designed. Ion beams of a few mA are extracted from the plasma and mass-analysed. The extracted beams have large quantities of multiply charged Ar ions at relatively lower gas pressures of 10 −4 −10 −3 Pa. In addition, these quantities tend to effectively increase with microwave power. The microwave power necessary for mA-class implantation current of low-charge-state ions is estimated to be from 3–5 kW.

Non-mass analysed ion implantation using microwave ion source

Abstract To evaluate the usefulness of high-current non-mass-analysed (NMA) ion implantation using a new microwave ion source, the photovoltaic properties of silicon solar cells were studied. When phosphorus vapour is introduced into the ion source, it provides implant current of more than 10 mA for the 5–15 keV energy range. The fraction of neutral phosphorus particles implanted together with ions is typically less than 10% of the total dose. The conversion efficiency of solar cells fabricated by NMA implantation is about 10% without any anti-reflection coating. Changes in implantation energy do not significantly change the values of these efficiencies. Continuous and stable oxygen ion beams of about 110 mA were obtained at 5.0 kV, which is high enough to apply to material modification in metals, insulators and semiconductors.

Beam qualities of a microwave ion source

Beam characteristics of a microwave ion source for implantation were studied with an apparatus that can evaluate the degree of matching between the ion source and mass‐separator optics. The principal cause that limits the beam transmission of mass separator optics was clarified and an approach was taken to eliminate it. The emittance for the length depends on the plasma density distribution along the slit, which was found to be closely related to the vapor inlet system of the plasma chamber. In order to make the plasma density distribution uniform, several vapor inlets were arranged in a line along the slit. This resulted in a lower emittance.