Noriyuki Sakudo

Microwave ion source for ion implantation

Abstract Fundamentals of microwave ion sources used for ion implantation as well as their main features are reviewed and evaluated. Ion sources using plasmas generated by microwave discharge in a magnetic field have many advantageous features. Since they operate even with reactive source materials, they can provide long-life stable ion beams for a variety of ion species. They can provide either multiply-charged ion beams or high-current ion beams of singly-charged ions depending on selected operational conditions. High-current beams of singly-charged ions can be extracted in various sizes and forms. An ion source that extracts an ion beam of 40 mm diameter through a multiaperture lens can provide argon, hydrogen and oxygen ion beams of several hundred mA at 5 kV. The ion current can be further increased by increasing the volume of the discharge chamber and the area of the multiaperture lens. An ion source that extracts a slit-shaped beam suitable for ion implantation can provide mass-separated currents of 10 mA (maximum 15 mA) for As+ and P+ as well as various metal ions of several mA. Due to versatility of beam extraction, this ion source has been modified to a higher voltage (120 kV) by combining a double-stage extraction lens, and to a higher mass-separated current (30 mA) by lengthening the ion exit slit.

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%).

RIKEN 200 KV high current implanter for metal surface modification

Abstract A high current, metal ion implanter was constructed in order to aid the formation of a new metastable surface alloy. This implanter, called a RIKEN 200 kV high current implanter, is a modified Lintott high current machine (Series III), which has the advantages of having its own microwave ion source and an extra target chamber. The microwave discharge ion source without a hot-filament has a comparatively long lifetime because the chloride ions and radicals in a plasma during discharge of metal chlorides might prevent metal to deposit on the inner walls of the discharge chamber by bombarding and chemically cleaning them. An extra target chamber for metal modification is able to control the surface composition by utilizing the sputtering effect of the ion beam during ion implantation. The use of this ion source and the extra target chamber is suggested to be suitable for the production of metallic ions and for the implantation into metals. The case study will be introduced for Ti implantation into Fe.

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.

Quadrupole electrodes with flat faces

A method to analyze multipole fields formed with flat‐face electrodes by using conformal mapping is described. Quadrupole fields of various parameter values which define the electrode shape are analyzed by this method, and the optimum parameter values for making distortion components of the field minimum are obtained. This result is also useful in designing the shapes of magnetic quadrupoles.