Ion implanting system

#1. Field of the Invention

#This invention relates to an ion implanting system, and more particularly to an ion implanting system equiped with a charge neutralizing facility.

#2. Description of the Related Art

#FIG. 1 is a cross-section of an ion implating system according to a basic embodiment of the present invention;

#FIG. 2 is a schematic cross-section of an electron shower shown in FIG. 1;

#FIG. 3 is a partially broken perspective view of an ion implanting system according to a more practical embodiment of the present invention;

#FIG. 1 shows schematically an ion implanting system according to an embodiment of the present invention.

#An ion beam generating unit 11 generates an ion beam 17 of a predetermined ion species and supplies the ion beam 17 to a wafer disk chamber 15 through an ion beam housing 13 formed e.g. of aluminum. At a location in the ion beam housing 13, there is provided an electron shower 25 which includes a filament 21 forming a primary electron source and a target 23 formed of e.g. aluminum and serving as a secondary electron source. The disk chamber contains a wafer disk 31 which is formed of e.g. aluminium and rotates at a very high speed. The wafer disk 31 is equiped, on its front surface, with a plurality of wafer susceptors 33 which may be either metal or insulator, for mounting a plurality of semiconductor wafers 35 thereon. On the front surface of the wafer disk 31, a charge receiving conductor member 41 formed of e.g. aluminum is placed to have a surface level substantially coplanar with the wafer surface near a wafer or a pseudo-wafer while being insulated from the wafer disk 31. On the rear surface of the wafer disk 31, another conductor 43 formed of aluminum etc., and insulated from the disk 31, is disposed and connected with the charge receiving conductor 41 on the front surface through a conducting wire 45 coated with an insulator such as teflon. A stationary capacitor electrode 47 is disposed in the vicinity of the rotating passing of the rear conductor 43 to face the rotating and charge inducing conductor 43 and form a capacitive coupling therwith. The stationary capacitor electrode 47 is connected to a control circuit 50. The control circuit 50 controls the output of the electron shower 25 to reduce the piled-up charge, based on the signal received through the capacitor electrode 47. An evacuating system 60 is connected to the disk chamber 15 for evacuating the disk chamber 15.

#Now, description will be made on the operation of the ion implantation. Wafers 35 are set on the susceptors 33 on the front face of the wafer disk 31. The disk chamber 15 is evacuated by the evacuating system 60. An ion beam 17 is generated by the ion beam generating unit 11 and is irradiated on the wafers 35 located on the rotating wafer disk 31. At this moment, the charge receiving conductor 41 positioned near the wafer susceptors 33 is also irradiated by the ion beam and may be charged up. As stated before, the charge receiving conductor or susceptor conductor 41 is connected with the rear conductor 43 through the conductor member 45, but is isolated from the wafer disk 31. Therefore, the conductors 41, 43, and 45 will be charged by the reception of charge carrying ions. When the rear conductor 43 and the stationary conductor 47 face each other, a capacitance C is established. In dependence with the amount of charge stored on the conductor 43, charge will be induced on the stationary capacitor electrode 47. Since the wafer disk 31 is rotating, the charge induced on the capacitor electrode 47 will change cyclically and increases the peak value when the stored charge becomes high. Such induced amount of charge is detected e.g. as an alternating current signal. The control circuit 50 detects the charge received on the charge-receiving conductor 41. Based on the detection signal, the control circuit 50 controls the electron shower to emit electrons, thereby neutralizing the charge-up due to the ions. Along with the irradiation of electrons on the charge receiving conductor 41, the amount of charge on the conductor 41 is reduced and the signal induced on the capacitor electrode 47 will be reduced. By detecting such change in the detection signal, the control circuit 50 adjusts the output of the electron shower 25 at an optimum level.