Radiant energy – Irradiation of objects or material – Irradiation of semiconductor devices
Reexamination Certificate
2003-04-01
2004-12-07
Wells, Nikita (Department: 2881)
Radiant energy
Irradiation of objects or material
Irradiation of semiconductor devices
C250S491100, C250S492100, C250S492300
Reexamination Certificate
active
06828572
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to semiconductor device fabrication and ion implantation, and, more particularly, to calibrating, detecting and/or modifying an ion beam incident angle during setup or in situ.
BACKGROUND OF THE INVENTION
Ion implantation is a physical process that is employed in semiconductor device fabrication to selectively implant dopant into semiconductor and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and semiconductor material. For ion implantation, dopant atoms/molecules are ionized, accelerated, formed into a beam, analyzed, and swept across a wafer, or the wafer is swept through the beam. The dopant ions physically bombard the wafer, enter the surface and come to rest below the surface, at a depth related to their energy.
An ion implantation system is a collection of sophisticated subsystems, each performing a specific action on the dopant ions. Dopant elements, in gas or solid form, are positioned inside an ionization chamber and ionized by a suitable ionization process. In one exemplary process, the chamber is maintained at a low pressure (vacuum). A filament is located within the chamber and is heated to the point where electrons are created from the filament source. The negatively charged electrons are attracted to an oppositely charged anode also within the chamber. During the travel from the filament to the anode, the electrons collide with the dopant source elements (e.g., molecules or atoms) and create a host of positively charged ions from the elements in the molecule.
Generally, other positive ions are created in addition to desired dopant ions. The desired dopant ions are selected from the ions by a process referred to as analyzing, mass analyzing, selection, or ion separation. Selection is accomplished utilizing a mass analyzer that creates a magnetic field through which ions from the ionization chamber travel. The ions leave the ionization chamber at relatively high speeds and are bent into an arc by the magnetic field. The radius of the arc is dictated by the mass of individual ions, speed, and the strength of the magnetic field. An exit of the analyzer permits only one species of ions, the desired dopant ions, to exit the mass analyzer.
An acceleration system is employed to accelerate or decelerate the desired dopant ions to a predetermined momentum (e.g., mass of an dopant ion multiplied by its velocity) to penetrate the wafer surface. For acceleration, the system is generally of a linear design with annular powered electrodes along its axis. As the dopant ions enter therein, they are accelerated therethrough.
However, a number of potential problems can occur during ion implantation procedures that can damage and/or destroy semiconductor devices being fabricated. One potential problem encountered during ion implantation is an unacceptable degree of electrical charging (wafer charging) of the wafer surface. For example, an ion beam can carry excessive positive charges that charge or buildup on a wafer surface. The positive charge can draw neutralizing electrons from the surface, the bulk, the beam, structures, layers, and the like and degrade or destroy such components. Additionally, excessive charge buildup can cause voltages and/or current to be applied to semiconductor device components in an uncontrolled manner thereby damaging the device components.
Another potential problem encountered during ion implantation is an incorrect angle of implantation. Generally, an ion implantation is performed at a specific angle with respect to a wafer surface. If a calibration error or angular error is present (e.g., process equipment is not calibrated properly) the ion implantation can be performed at a different angle, location and/or depth than intended. Such errors can undesirably modify the implantation profile, fail to dope certain areas, implant dopants into unintended areas, damage device structures, dope to an incorrect depth, and the like.
SUMMARY OF THE INVENTION
The following presents a simplified summary in order to provide a basic understanding of one or more aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention, nor to delineate the scope thereof. Rather, the primary purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
The present invention facilitates semiconductor device fabrication by monitoring and correcting angular errors before and/or during ion implantation procedures. Additionally, the present invention facilitates semiconductor device fabrication by calibrating a process disk with respect to an incident ion beam without requiring measurement of implantation results on wafers.
The present invention employs an ion beam incident angle detector that passes charged ions there through as a function of an incident angle of an ion beam. The charged ions generate a signal (beam current or charge potential) that is a function of the incident angle of the ion beam. The angle detector of the present invention has an aperture with an aspect ratio that facilitates accuracy and can increase a signal to noise ratio. One or more of these angle detectors can be employed prior to ion implantation device fabrication processes in order to calibrate a process disk, wafer, and/or an end station holding a work piece with respect to an incident ion beam. During calibration, the angle detectors provide values for various so-called “alpha and beta” offset angles, which are about orthogonal axes and are typically related to the wafer twist and tilt. Generally, an incident ion beam substantially normal to a wafer or disk surface should yield the largest value. Thus, based on these provided/measured peak values, angular error can be detected and correction values determined.
During ion implantation processes for semiconductor device fabrication, the angle detector may provide values, which can then be compared with previous and/or expected charge values to determine if a correction in situ should be performed. On identifying an angular error during processing, process parameters including angular offset values are modified or adjusted to at least partially correct the identified angular error.
According to one aspect of the present invention, an angle detector comprises a tube portion that passes charged ions as a function of an incident angle of the ions, and a capacitor or detector portion that accumulates charged ions. The tube portion has an aspect ratio that facilitates accuracy and can increase a signal to noise ratio. The angle detectors provide peak charge values for various angular offset angles. Generally, an incident ion beam substantially normal to a wafer or disk surface should yield the largest peak value. Thus, based on these provided/measured peak charge values, angular error can be detected and correction values determined.
According to another aspect of the present invention, an angle detector comprises a tube portion and a profile hole, that pass charged ions as a function of an incident angle of the ions, and a disk faraday that measures beam current according to charged ions that pass through an aperture defined by the tube and profile hole. The aperture has an aspect ratio that facilitates accuracy and can reduce a signal to noise ratio. The angle detectors provide peak beam current values for various angular offset angles. Generally, an incident ion beam substantially normal to a wafer or disk surface should yield the largest measured beam current value. Thus, based on these provided/measured beam current values, angular error can be detected and correction values determined.
To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative asp
Freer Brian S.
Graf Michael A.
Parrill Thomas
Reece Ronald N.
Axcelis Technologies Inc.
El-Shammaa Mary
Eschweiler & Associates LLC
Wells Nikita
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