Dose monitor for plasma doping system

Abstract

Plasma doping apparatus includes a plasma doping chamber, a platen mounted in the plasma doping chamber for supporting a workpiece such as a semiconductor wafer, a source of ionizable gas coupled to the chamber, an anode spaced from the platen and a pulse source for applying voltage pulses between the platen and the anode. The voltage pulses produce a plasma having a plasma sheath in the vicinity of the workpiece. The voltage pulses accelerate positive ions across the plasma sheath toward the platen for implantation into the workpiece. The plasma doping apparatus includes at least one Faraday cup positioned adjacent to the platen for collecting a sample of the positive ions accelerated across the plasma sheath. The sample is representative of the dose of positive ions implanted into the workpiece. The Faraday cup may include a multi-aperture cover for reducing the risk of discharge within the interior chamber of the Faraday cup. The Faraday cup may be configured to produce a lateral electric field within the interior chamber for suppressing escape of electrons, thereby improving measurement accuracy.

1 . An ion implantation system for causing ions to impact an implantation surface comprising: 
 a process chamber defining a chamber interior into which one or more workpieces can be inserted for ion treatment;    an energy source for setting up an ion plasma within the process chamber;    a support for positioning one or more workpieces within an interior region of the process chamber so that an implantation surface of the one or more workpieces is positioned within the ion plasma;    a pulse generator in electrical communication with the workpiece support for applying electrical pulses for attracting ions to the support;    one or more dosimetry cups including an electrically biased ion collecting surface parallel to the implantation surface; and    an implantation controller for monitoring signals from the one or more dosimetry cups to control ion implantation of the one or more workpieces.    
     
     
         2 . The ion implantation system of  claim 1  wherein the one or more dosimetry cup have generally circular apertures.  
     
     
         3 . The ion implantation system of  claim 1  further including multiple dosimetry cups with apertures forming a sector ring shape.  
     
     
         4 . The ion implantation system of  claim 1  wherein signals from the dosimetry cup that are used by the controller are derived from electric current through the collecting surface of the dosimetry cup.  
     
     
         5 . The ion implantation system of  claim 1  wherein the parameter of the ion implantation process controlled is the duration of the implantation of the workpiece.  
     
     
         6 . The ion implantation system of claim  41  wherein the dosimetry cups are imbedded in the workpiece support to eliminate stray capacitance to ground thereby avoiding displacement current errors.