Servo control for high emittance electron source
First Claim
1. A system for regulating emission current of an electron source comprisinga filament for emitting electrons, a first voltage source for heating said filament, an emission current sensor, a second voltage source for supplying an accelerating voltage and a voltage representing current flow at said second voltage source, detecting means for detecting a difference between emission current detected by said emission current sensor and a set point, means including cascaded feedback loops for controlling said first voltage source responsive to said detecting means and said voltage representing current flow at said second voltage source.
1 Assignment
0 Petitions
Accused Products
Abstract
An automatic control servo system having a number of cascaded loops equal in number to the number of voltage sources applied to elements of a high-emittance electron source provides accurate and stable electron emission current control independently of beam energy and accommodates large differences in thermal mass between the elements of the electron source, as may be encountered in high-emittance, indirectly heated cathode electron sources. Individual loops of the system may be critically tuned independently of each other.
22 Citations
20 Claims
-
1. A system for regulating emission current of an electron source comprising
a filament for emitting electrons, a first voltage source for heating said filament, an emission current sensor, a second voltage source for supplying an accelerating voltage and a voltage representing current flow at said second voltage source, detecting means for detecting a difference between emission current detected by said emission current sensor and a set point, means including cascaded feedback loops for controlling said first voltage source responsive to said detecting means and said voltage representing current flow at said second voltage source.
-
8. A method of controlling current in an accelerated beam in an electron beam tool, said method including steps of
detecting beam current, controlling voltage applied to a filament with two cascaded feedback loops responsive to said beam current detected in accordance with said detecting step, a set point and a current output of an accelerating voltage source.
-
17. A method of controlling current in an accelerated beam in an electron beam tool, said method including steps of
detecting beam current, controlling voltage applied to a filament responsive to said beam current detected in said detecting step, a set point and a current output of an accelerating voltage source, wherein said set point is a desired value for said detected beam current and said voltage is controlled by cascaded feedback loops.
-
20. A method of fabricating a semiconductor device using an electron beam tool comprising
a filament for emitting electrons, a first voltage source for heating said filament, an emission current sensor, a second voltage source for supplying an accelerating voltage and a voltage representing current flow at said second voltage source, detecting means for detecting a difference between emission current detected by said emission current sensor and a set point, means including cascaded feedback loops for controlling said first voltage source responsive to said detecting means and said voltage representing current flow at said second voltage source, said method including steps of accelerating electrons between said filament and an indirectly heated cathode with a bombardment voltage, wherein said voltage applied to said filament is controlled using cascaded feedback loops in accordance with said beam current, said set point, said current output of said accelerating voltage source and a current output of a bombardment voltage source, exposing a resist with said electrons to define an element of said semiconductor device, and completing said semiconductor device.
Specification