A new plasma etching technique using microwave discharge is presented. Silicon wafers are etched by the discharge in a (CF4+O2) gas mixture. Fine patterns with dimensions of 1 µm are etched up to 1 µm in depth without undercutting at a pressure of 5×10-4 Torr with an Al mask having 0.08 µm thickness. Etching is thought to be carried out by chemical reactions. With this technique, the etching rate becomes maximum (2.6×10-2 µm/min) when the mixing ratio γ is 20%. Symbol γ is the partial pressure of O2 divided by the total pressure. The etched depth is proportional to the etching time.
This technique is suitable for etching fine patterns of semiconductor devices.
A coaxial microwave ion source which provides high-current ion beams is presented. The microwave discharge takes place in a magnetic mirror field. The intensity of this field is higher than that of the electron cyclotron resonance at 2.45 GHz over the entire discharge region. The antenna of the discharge chamber is water cooled to protect the ceramic which is used as the vacuum seal as well as the conduit for microwaves into the discharge chamber. The ion beam is extracted through a three-stage multiaperture lens with 124 holes 3 mm in diameter. An electron suppressed Faraday cup is used to collect 200-mA argon and 400-mA hydrogen ion beams.
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.
The fields in circular concave electrodes with both infinitesimal and infinite thickness are analyzed by giving appropriate boundary conditions, and the optimum electrode angles for approximating the ideal quadrupole field best are obtained. These angles are 44° for infinitesimal tliickness and 37° for infinite thickness. These results are verified by field plotting method. The realization of these electrodes is also discussed.
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