US 20060145096 A1 Abstract Methods are provided for calibrating an ion beam scanner in an ion implantation system, comprising measuring a plurality of initial current density values at a plurality of locations along a scan direction, where the values individually correspond to one of a plurality of initial voltage scan intervals and one of a corresponding plurality of initial scan time values, creating a system of linear equations based on the measured initial current density values and the initial voltage scan intervals, and determining a set of scan time values that correspond to a solution to the system of linear equations that reduces current density profile deviations. A calibration system is provided for calibrating an ion beam scanner in an ion implantation system, comprising a dosimetry system and a control system.
Claims(20) 1. A method for calibrating an ion beam scanner in an ion implantation system, the method comprising:
measuring a plurality of initial current density values at a plurality of locations along a scan direction, the initial current density values individually corresponding to one of a plurality of initial voltage scan intervals and one of a corresponding plurality of initial scan time values; creating a system of linear equations based on the measured initial current density values and the initial scan time values; and determining a set of scan time values for the voltage scan intervals corresponding to a solution to the system of linear equations that reduces current density profile deviations. 2. The method of 3. The method of 4. The method of forming a matrix A of the measured initial current density values with m rows corresponding to the m locations along the scan direction and n columns corresponding to the n initial voltage scan intervals and time values; forming an initial time vector T _{0 }comprising the n initial scan time values; and computing an initial profile vector P _{0 }comprising m initial current density profile values, wherein the initial profile vector P_{0}=A*T_{0}. 5. The method of computing a profile average value P _{AVG }as the average of the m initial profile values, wherein P_{AVG}=(1/m)*(P_{01}+P_{02}+ . . . +P_{0m}); computing a profile deviation vector ΔP comprising m profile deviation values, wherein ΔP _{j}=P_{0j}−P_{AVG }for j=1 through m; computing an inverse matrix A ^{−1}; multiplying the inverse matrix A ^{−1 }and the profile deviation vector ΔP to obtain a time deviation solution vector ΔT_{SOLUTION }comprising n scan time deviation values, wherein ΔT_{SOLUTION}=A^{−1}*ΔP; and computing a scan time solution vector T _{SOLUTION }as the sum of the time deviation solution vector ΔT_{SOLUTION }and the initial time vector T_{0}, the scan time solution vector T_{SOLUTION }comprising the set of scan time values corresponding to the solution to the system of linear equations that reduces current density profile deviations, wherein T_{SOLUTION}=ΔT_{SOLUTION}+T_{0}. 6. The method of ^{−1 }is computed using singular value decomposition (SVD). 7. The method of selectively truncating the matrix A by eliminating one or more columns having no non-zero entries to form a truncated matrix A _{T }having m rows corresponding to the m locations along the scan direction and n′ columns corresponding to the n′ remaining initial voltage scan intervals and time values, wherein n′ is less than n; and selectively truncating the initial time vector T _{0 }to form a truncated initial time vector T_{0T }comprising n′ initial scan time values; wherein the initial profile vector P _{0 }is computed as P_{0}=A_{T}*T_{0T}; and wherein determining the set of scan time values comprises:
computing the profile average value P
_{AVG }as the average of the m initial profile values, wherein P_{AVG}=(1/m)*(P_{01}+P_{02}+ . . . +P_{0m}); computing a profile deviation vector ΔP comprising m profile deviation values, wherein ΔP
_{j}=P_{0j}−P_{AVG }for j=1 through m; computing an inverse matrix A
_{T} ^{−1}; multiplying the inverse matrix A
_{T} ^{−1 }and the profile deviation vector ΔP to obtain a time deviation solution vector ΔT_{SOLUTION }comprising n′ scan time deviation values, wherein ΔT_{SOLUTION}=A_{T} ^{−1}*ΔP; and computing a scan time solution vector T
_{SOLUTION }as the sum of the time deviation solution vector ΔT_{SOLUTION }and the truncated initial time vector T_{0T}, the scan time solution vector T_{SOLUTION }comprising the set of scan time values corresponding to the solution to the system of linear equations that reduces current density profile deviations, wherein T_{SOLUTION}=ΔT_{SOLUTION}+T_{0T}. 8. The method of selectively truncating the matrix A by eliminating one or more columns having no non-zero entries to form a truncated matrix A _{T }having m rows corresponding to the m locations along the scan direction and n′ columns corresponding to the n′ remaining initial voltage scan intervals and time values, wherein n′ is less than n; and selectively truncating the initial time vector T _{0 }to form a truncated initial time vector T_{0T }comprising n′ initial scan time values; wherein the initial profile vector P _{0 }is computed as P_{0}=A_{T}*T_{0T}. 9. The method of forming a matrix A of the measured initial current density values with an integer number m rows corresponding to the m locations along the scan direction and an integer number n columns corresponding to n initial voltage scan intervals and time values; forming an initial time vector T _{0 }comprising the n initial scan time values; and computing an initial profile vector P _{0 }comprising m initial profile values, wherein the initial profile vector P_{0}=A*T_{0}. 10. The method of computing a profile average value P _{AVG }as the average of the m initial profile values, wherein P_{AVG}=(1/m)*(P_{01}+P_{02}+ . . . +P_{0m}); computing a profile deviation vector ΔP comprising m profile deviation values, wherein ΔP _{j}=P_{0j}−P_{AVG }for j=1 through m; computing an inverse matrix A ^{−1}; multiplying the inverse matrix A ^{−1 }and the profile deviation vector ΔP to obtain a time deviation solution vector ΔT_{SOLUTION }comprising n scan time deviation values, wherein ΔT_{SOLUTION}=A^{−1}*ΔP; and computing a scan time solution vector T _{SOLUTION }as the sum of the time deviation solution vector ΔT_{SOLUTION }and the initial time vector T_{0}, the scan time solution vector T_{SOLUTION }comprising the set of scan time values corresponding to the solution to the system of linear equations that reduces current density profile deviations, wherein T_{SOLUTION}=ΔT_{SOLUTION}+T_{0}. 11. The method of ^{−1 }is computed using singular value decomposition (SVD). 12. The method of selectively truncating the matrix A by eliminating one or more columns having no non-zero entries to form a truncated matrix A _{T }having m rows corresponding to the m locations along the scan direction and n′ columns corresponding to the n′ remaining initial voltage scan intervals and time values, wherein n′ is less than n; and selectively truncating the initial time vector T _{0 }to form a truncated initial time vector T_{0T }comprising n′ initial scan time values; wherein the initial profile vector P _{0 }is computed as P_{0}=A_{T}*T_{0T}; and wherein determining the set of scan time values comprises:
computing the profile average value P
_{AVG }as the average of the m initial profile values, wherein P_{AVG}=(1/m)*(P_{01}+P_{02}+ . . . +P_{0m}); _{j}=P_{0j}−P_{AVG }for j=1 through m; computing an inverse matrix A
_{T} ^{−1}; multiplying the inverse matrix A
_{T} ^{−1 }and the profile deviation vector ΔP to obtain a time deviation solution vector ΔT_{SOLUTION }comprising n′ scan time deviation values, wherein ΔT_{SOLUTION}=A_{T} ^{−1}*ΔP; and computing a scan time solution vector T
_{SOLUTION }as the sum of the time deviation solution vector ΔT_{SOLUTION }and the truncated initial time vector T_{0T}, the scan time solution vector T_{SOLUTION }comprising the set of scan time values corresponding to the solution to the system of linear equations that reduces current density profile deviations, wherein T_{SOLUTION}=ΔT_{SOLUTION}+T_{0T}. 13. The method of _{T }having m rows corresponding to the m locations along the scan direction and n′ columns corresponding to the n′ remaining initial voltage scan intervals and time values, wherein n′ is less than n; and _{0 }to form a truncated initial time vector T_{0T }comprising n′ initial scan time values; wherein the initial profile vector P _{0 }is computed as P_{0}=A_{T}*T_{0T}. 14. The method of 15. A calibration system for calibrating an ion beam scanner in an ion implantation system, the calibration system comprising:
a dosimetry system operable to measure a plurality of initial current density values at a corresponding plurality of locations along a scan direction in a workpiece location of an ion implantation system; and a control system operably coupled with the dosimetry system and a power supply associated with a beam scanner of the ion implantation system, the control system being operable to cause the scanner to scan an ion beam across the workpiece location of the ion implantation system in the scan direction one or more times according to a plurality of initial voltage scan intervals and a corresponding plurality of initial voltage scan time values such that the dosimetry system can measure a plurality of initial current density values at a plurality of locations along a scan direction in a workpiece location of an ion implantation system; wherein the initial current density values individually correspond to one of the plurality of initial voltage scan intervals and to one of the corresponding plurality of initial scan time values; and wherein the control system is further operable to create a system of linear equations based on the measured initial current density values and the initial scan time values, and to determine a set of scan time values for the voltage scan intervals corresponding to a solution to the system of linear equations that reduces current density profile deviations. 16. The calibration system of _{0 }comprising the n initial scan time values, and to compute an initial profile vector P_{0 }comprising m initial profile values, wherein the initial profile vector P_{0}=A*T_{0}. 17. The calibration system of _{AVG }as the average of the m initial profile values, wherein P_{AVG}=(1/m)*(P_{01} 30 P_{02}+ . . . +P_{0m}), to compute a profile deviation vector ΔP comprising m profile deviation values, wherein ΔP_{j}=P_{0j}−P_{AVG }for j=1 through m, to compute an inverse matrix A^{−1}, to multiply the inverse matrix A^{−1 }and the profile deviation vector ΔP to obtain a time deviation solution vector ΔT_{SOLUTION }comprising n scan time deviation values, wherein ΔT_{SOLUTION}=A^{−1}*ΔP, and to compute a scan time solution vector T_{SOLUTION }as the sum of the time deviation solution vector ΔT_{SOLUTION }and the initial time vector T_{0}, the scan time solution vector T_{SOLUTION }comprising the set of scan time values corresponding to the solution to the system of linear equations that reduces current density profile deviations, wherein T_{SOLUTION}=ΔT_{SOLUTION}+T_{0}. 18. The calibration system of ^{−1 }using singular value decomposition (SVD). 19. The calibration system of _{T }having m rows corresponding to the m locations along the scan direction and n′ columns corresponding to the n′ remaining initial voltage scan intervals and time values, wherein n′ is less than n, and to selectively truncate the initial time vector T_{0 }to form a truncated initial time vector T_{0T }comprising n′ initial scan time values;
wherein the control system computes the initial profile vector P _{0 }as P_{0}=A_{T}*T_{0T}; and wherein the control system determines the set of scan time values by computing the profile average value P _{AVG }as the average of the m initial profile values, wherein P_{AVG}=(1/m)*(P_{01}+P_{02}+ . . . +P_{0m}), computing a profile deviation vector ΔP comprising m profile deviation values, wherein ΔP_{j}=P_{0j}−P_{AVG }for j=1 through m, computing an inverse matrix A_{T} ^{−1}, multiplying the inverse matrix A_{T} ^{−1 }and the profile deviation vector ΔP to obtain a time deviation solution vector ΔT_{SOLUTION }comprising n′ scan time deviation values, wherein ΔT_{SOLUTION}=A_{T} ^{−1}*ΔP, and computing a scan time solution vector T_{SOLUTION }as the sum of the time deviation solution vector ΔT_{SOLUTION }and the truncated initial time vector T_{0T}, the scan time solution vector T_{SOLUTION }comprising the set of scan time values corresponding to the solution to the system of linear equations that reduces current density profile deviations, wherein T_{SOLUTION}=ΔT_{SOLUTION}+T_{0T}. 20. The calibration system of _{T }having m rows corresponding to the m locations along the scan direction and n′ columns corresponding to the n′ remaining initial voltage scan intervals and time values, wherein n′ is less than n;
wherein the control system selectively truncates the initial time vector T _{0 }to form a truncated initial time vector T_{0T }comprising n′ initial scan time values; and wherein the control system computes the initial profile vector P _{0 }as P_{0}=A_{T}*T_{0T}.Description The present invention relates generally to ion implantation systems, and more specifically to improved systems and methods for uniformly scanning ion beams across a workpiece. In the manufacture of semiconductor devices and other products, ion implantation is used to dope semiconductor wafers, display panels, or other workpieces with impurities. Ion implanters or ion implantation systems treat a workpiece with an ion beam, to produce n or p-type doped regions or to form passivation layers in the workpiece. When used for doping semiconductors, the ion implantation system injects a selected ion species to produce the desired extrinsic material, wherein implanting ions generated from source materials such as antimony, arsenic or phosphorus results in n-type extrinsic material wafers, and implanting materials such as boron, gallium or indium creates p-type extrinsic material portions in a semiconductor wafer. Low energy implanters are typically designed to provide ion beams of a few thousand electron volts (keV) up to around 80-100 keV, whereas high energy implanters can employ linear acceleration (linac) apparatus (not shown) between the mass analyzer In the manufacture of integrated circuit devices, display panels, and other products, it is desirable to uniformly implant the dopant species across the entire surface of the workpiece The implantation system Referring also to Prior to entering the scanner Also, the geometry and operating voltages of the scanner In general, it is desirable to provide uniform implantation of the surface of the workpiece Although the conventional point-to-point scanner calibration techniques may be adequate where the width of the ion beam Another consideration is the amount of beam overscan, which includes the extent to which the ion beam Accordingly there is a need for improved ion beam scanner calibration techniques by which uniform implantation can be facilitated, and which facilitates improved scan efficiency by determining the minimum overscan required to achieve uniform implantation of a workpiece. The following presents a simplified summary of the invention in order to provide a basic understanding of some 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 of the invention. Rather, the 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 relates to systems and methods for calibrating an ion beam scanner in an ion implantation system, in which the current density contributions of multiple scanner voltage intervals are individually measured for multiple profile points along a beam scan direction to generate a system of linear equations, and a set of scan time values are computed for the voltage scan intervals corresponding to a solution that reduces current density profile deviations. Unlike conventional point-to-point calibration techniques, the invention provides compensation for implant contributions produced by the beam some distance from the beam center, and is thus particularly suitable for use in low energy ion implanters having relatively wide beams and/or in situations where the lateral beam width varies along the scan direction to provide uniform implantation across a workpiece surface. In addition, the invention may be employed to reduce excess overscan, thereby improving system scan efficiency without sacrificing implant uniformity. One aspect of the invention provides a method for calibrating an ion beam scanner in an ion implantation system, comprising measuring a plurality of initial current density values at a plurality of locations along a scan direction, where the initial current density values individually correspond to one of a plurality of initial voltage scan intervals and to one of a corresponding plurality of initial scan time values. The method further comprises creating a system of linear equations based on the measured initial current density values and initial scan time values, and determining a set of scan time values for the voltage scan intervals that correspond to a solution to the system of linear equations that reduces current density profile deviations. Another aspect of the invention provides a calibration system for calibrating an ion beam scanner in an ion implantation system. The calibration system comprises a dosimetry system and a control system operably coupled with the dosimetry system and a power supply associated with a beam scanner, where the dosimetry system measures a plurality of initial current density values at a plurality of locations along a scan direction in a workpiece location of an ion implantation system. The control system causes the scanner to scan an ion beam across the workpiece location of the ion implantation system in the scan direction according to an initial set of voltage scan intervals and corresponding scan time values so that the dosimetry system can measure a plurality of initial current density values at the plurality of locations along the scan direction in a workpiece location of an ion implantation system, where the initial current density values individually correspond to one of the plurality of initial voltage scan intervals and to one of the corresponding plurality of initial scan time values. The control system is further operable to create a system of linear equations based on the measured initial current density values and the initial scan time values, and to determine a set of scan time values for the voltage scan intervals corresponding to a solution to the system of linear equations that reduces current density profile deviations. The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed. The present invention will now be described with reference to the drawings wherein like reference numerals are used to refer to like elements throughout, and wherein the illustrated structures are not necessarily drawn to scale. The invention provides methods and systems for calibrating an ion beam scanner in an ion implantation system, which may be employed to improve implant uniformity and to improve system scan efficiency by reducing excess overscan. The method Computations are then performed at Referring also to As shown in The beamline assembly The beamline assembly Referring also to During initial setup or calibration of the system Referring also to In a measurement operation during system calibration, the control system Referring to With the initial segmentation of the measurement range For the single sensor case in A determination is made at Interval scanning and single position measurements continue in this fashion (at When i becomes equal to n in Referring to In an alternative aspect of the present invention, the data may be collected in accordance with the method Referring now to The control system At After any such truncation, the computations Referring also to At At Referring also to Referring now to Accordingly, such superfluous columns can be truncated from the matrix A, and the corresponding time entries in the initial time vector T In this case, the initial profile vector P Alternatively, the voltage scan intervals may be redefined to include the original number n intervals spread out over a smaller range to exclude the unneeded overscan, and the calibration process may be repeated. Other iterative approaches may be employed as well, such as redefining the measurement locations (profile intervals) to include more measurements in areas experiencing the largest deviations, or according to other criteria, wherein all such alternative approaches are contemplated as falling within the scope of the invention and the appended claims. Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims. In particular regard to the various functions performed by the above described components or structures (blocks, units, engines, assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (e.g., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. Referenced by
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