The present invention relates generally to ion implantation, and particularly to systems and methods for identifying beam energy.
Ion implantation is a physical process, as opposed to diffusion, which is a chemical process that is employed in semiconductor apparatus fabrication to selectively implant dopant into a semiconductor workpiece and/or wafer material. Thus, the act of implanting does not rely on a chemical interaction between a dopant and the semiconductor material. For ion implantation, dopant atoms/molecules are ionized and isolated, sometimes accelerated or decelerated, formed into a beam, and swept across a workpiece or wafer. The dopant ions physically bombard the workpiece, enter the surface and typically come to rest below the workpiece surface in the crystalline lattice structure thereof.
In RF based accelerators, ions are repeatedly accelerated through multiple RF voltage driven acceleration gaps. Due to the time varying nature of RF acceleration fields and the multiple numbers of acceleration gaps (usually greater than 20) there are a large number of parameters which influence the final beam energy. Although it may not be technically impossible, “set and forget” techniques can not be used in setting up the final beam energy and fine adjustments have to be performed on the parameters to maximize beam transmission through a filter with known passband.
An energy filter is used not only as a simple filter to reject unwanted portions of the energy spectrum, but also and more importantly as an energy standard to which all the acceleration parameters are tuned. In this sense, the energy filter plays the ultimate role in determining the final beam energy. However, quite often the design of the energy filter has to be compromised, mostly because of space restrictions or some other imposed conditions limiting proper functioning and as a result, precision in the final beam energy is uncertain. There have been several attempts to develop an independent measurement system of beam energy, but no particular method has been incorporated into production machines.
Accordingly, suitable systems or methods for identifying beam energy are desired, that accurately measures the final beam energy.
The following presents a simplified summary of the invention 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 according to one or more embodiments creates a beam energy identification system utilizing a beam scanner which scans an accelerated ion beam at a frequency to create a wide uniform ion beam in one direction for uniform ion implantation on a workpiece, or a semiconductor wafer. One embodiment of this invention comprises two narrow Faraday cups placed at a distance downstream of scanner and a difference in scanner voltage (or current if the scanner is electromagnetic) to deflect the ion beam into each of the two narrow Faraday cups is used to calculate the energy of ion beam.
According to yet another aspect of the invention, two narrow Faraday cups are placed downstream of a scanner after going through a beam parallelizing lens (e.g., an electromagnetic lens, called an angle corrector magnet) to parallelize the fanning-out beam exiting the scanner. Again, a measured difference in scanner voltage (or current if the scanner is electromagnetic) to deflect the ion beam into each of the two Faraday cups is used to calculate the energy of the ion beam.
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 aspects and implementations of the invention. These are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.
The present invention will now be described with reference to the attached drawings, wherein like reference numerals are used to refer to like elements throughout. It will be appreciated by those skilled in the art that the invention is not limited to the exemplary implementations and aspects illustrated and described hereinafter. For the sake of providing a clear description of the invention, the systems and the methods will be described in connection with scanned pencil ion beam implantation. However, it is to be expressly understood that these descriptions are not intended to be self-limiting in any manner
Referring now to the figures, in accordance with one exemplary aspect of the present invention,
A workpiece and/or substrate 134 is moved orthogonal (shown as moving in and out of the paper) to the ion beam 115 in the hybrid scan scheme to irradiate the entire surface of the workpiece 134 uniformly. As stated above, various aspects of the present invention may be implemented in association with any type of ion implantation system, including, but not limited to the exemplary system 100 of
The exemplary hybrid parallel scan single wafer ion implantation system 100 comprises a source chamber assembly 112 which includes an ion source 102 and an extraction electrode assembly 121 to extract and accelerate ions to an intermediate energy. A mass analyzer 104 removes unwanted ion mass species; the accelerator assembly 113 accelerates the ions to a final energy. The beam scanner 119 scans a pencil beam exiting from the accelerator assembly 113 back and forth at a fast frequency into the angle corrector lens 120 to convert the fanning out scanned beam 111 from the beam scanner 119 to the parallel shifted beam 115 and the workpiece 134 which is housed in a process chamber.
The accelerator assembly 113, for example, can be RF linear particle accelerator (LINAC) in which ions are accelerated repeatedly by an RF field, or a DC accelerator, for example, a tandem electrostatic accelerator, which accelerates ions with a stationary DC high voltage. The beam scanner 119, either electrostatically or electromagnetically scans the ion beam 110 left to right into the angle corrector lens 120, which converts the fanning-out beam 111 into the parallel shifted ion beam 115. The angle corrector lens 120 is most likely to be an electromagnetic magnet as shown, but there is also an electrostatic version, for example. The final parallel shifted ion beam 115 out of the angle corrector lens 120 is directed onto the workpiece 134.
For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam 202 by the electrostatic scanner 204 is a linear function of scan voltage (for an electrostatic scanner) and the inverse of beam energy. The calculation for a deflection angle (Δθ1S) is shown below as Equation 1. In this embodiment of the present invention the angle corrector magnet 220 is deactivated which allows the deflected beam 211, deflected by the scanner to pass through the angle corrector magnet 220 without deflection.
Δθ1S=(K1S)(ΔV1S)/(E/q) (electrostatic equation) (Eq. 1)
wherein:
Rearranging the terms described above can be done to determine the beam energy (E), shown below as Equation 2:
E=(Δθ1S)(q)/((K1S)(ΔV1S)) (electrostatic equation) (Eq. 2)
Now referring to an electromagnetic scanner 215 (as opposed to an electrostatic scanner 204) the change of beam deflection angle (Δθ1M) is shown below as Equation 3. In this embodiment of the present invention the angle corrector magnet 220 is deactivated which allows the scanner deflected beam 211 to pass through the angle corrector magnet 220 without deflection.
Δθ1M=(K1M)(q)(ΔB1M)/(sqrt(Em)) (electromag. eq.) (Eq. 3)
wherein:
Rearranging terms to determine the beam energy (E) is shown below as Equation 4:
E=(K1MΔB1Mq Δθ1M)2/m (electromag. eq.) (Eq. 4)
Yet another embodiment of the present invention is an ion beam energy identification system 300; depicted in
The system 300 can be utilized in an exemplary hybrid parallel scan single wafer ion implantation system 100 (e.g.,
For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam 302 by the electrostatic scanner 304 is a linear function of scan voltage (for an electrostatic scanner) and the inverse of the ion beam energy. The calculation for the shift of beam position (Δθ2S) is shown below as Equation 5. In this embodiment of the present invention the angle corrector magnet 220 is activated which allows the fanned out beam 211 to be converted into a parallel ion beam 315 as illustrated in
Δθ2S=(f2S)(k2S)(ΔV2S)/(E/q) (Eq. 5)
wherein:
Rearranging terms:
E=(Δθ2S)(q)/((f2S)(k2S)(ΔV2S)) (Eq. 6)
Now referring to another embodiment of the present invention is an electromagnetic scanner 315 (as opposed to the electrostatic scanner 204) the shift of beam position (Δθ2M) is shown below as Equation 7. In this embodiment of the present invention the angle corrector magnet 320 is activated which allows the deflected beam by the scanner 311 to pass through the angle corrector magnet 320 and to be deflected into a parallel ion beam 315.
Δθ2M=(f2M)(k2M)q(ΔB2M)/sqrt(Em) (Eq. 7)
wherein:
Rearranging terms:
E=(qK2Mf2MΔB2MΔθ2M)2/m (Eq. 8)
The method 400 begins at 404 with generating an ion beam 202 and scanning the ion beam 202 in a fast scan axis with an ion beam scanner 204 (e.g.,
Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a deflected ion beam 211 (
E=(Δθ1S)(q)/((K1S)(ΔV1S)) (electrostatic equation) (Eq. 2)
wherein:
If it is determined at 408 that the scanner is the electromagnetic scanner 217 the current is varied to obtain the peak of a first deflected ion beam peak 211a (
E=(K1MΔB1Mq Δθ1M)2/m (Eq. 4)
wherein:
The method 500 begins at 504 with generating an ion beam 302 and scanning the ion beam 302 in a fast scan axis with an ion beam scanner 304 (e.g.,
Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a parallel ion beamlets created from the parallel ion beam 315 (
E=(Δθ2S)(q)/((f2S)(k2S)(ΔV2S)) (electrostatic equation) (Eq. 6)
wherein:
Wherein, the method 500 ends if the scanner was the electrostatic scanner 313.
If it is determined at 508 that the scanner 304 (
E=(K2MΔB2Mq Δθ2M)2/m (electromagnetic equation) (Eq. 8)
wherein:
Wherein, the method 500 ends if the scanner is an electromagnetic scanner 317.
Although the invention has been illustrated and described with respect to one or more implementations, equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described components (assemblies, apparatus, 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 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.”
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