System and method of beam energy identification for single wafer ion implantation

The present invention involves a beam energy identification system, comprising an accelerated ion beam, wherein the accelerated ion beam is scanned in a fast scan axis within a beam scanner, wherein the beam scanner is utilized to deflect the accelerated ion beam into narrow faraday cups downstream of the scanner, wherein a difference in scanner voltage or current to position the beam into the Faraday cups is utilized to calculated the energy of ion beam.

FIELD OF INVENTION

The present invention relates generally to ion implantation, and particularly to systems and methods for identifying beam energy.

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

DETAILED DESCRIPTION OF THE INVENTION

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,FIG. 1illustrates a typical hybrid parallel scan single wafer ion implantation system100. The implantation system100is also a type referred to as a post acceleration implanter, since a main accelerator113is placed after a mass analyzer104and before an energy filter130. Most ion implanters of this type have the energy filter130after the accelerator113to remove unwanted energy spectrum in the output of accelerator113. The filtered ion beam goes through a beam scanner119and then through an angle corrector lens120to convert the fanned-out beam111into a parallel shifted ion beam115.

A workpiece and/or substrate134is moved orthogonal (shown as moving in and out of the paper) to the ion beam115in the hybrid scan scheme to irradiate the entire surface of the workpiece134uniformly. 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 system100ofFIG. 1.

The exemplary hybrid parallel scan single wafer ion implantation system100comprises a source chamber assembly112which includes an ion source102and an extraction electrode assembly121to extract and accelerate ions to an intermediate energy. A mass analyzer104removes unwanted ion mass species; the accelerator assembly113accelerates the ions to a final energy. The beam scanner119scans a pencil beam exiting from the accelerator assembly113back and forth at a fast frequency into the angle corrector lens120to convert the fanning out scanned beam111from the beam scanner119to the parallel shifted beam115and the workpiece134which is housed in a process chamber.

The accelerator assembly113, 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 scanner119, either electrostatically or electromagnetically scans the ion beam110left to right into the angle corrector lens120, which converts the fanning-out beam111into the parallel shifted ion beam115. The angle corrector lens120is most likely to be an electromagnetic magnet as shown, but there is also an electrostatic version, for example. The final parallel shifted ion beam115out of the angle corrector lens120is directed onto the workpiece134.

FIG. 2illustrates a beam energy identification system200utilized in an exemplary hybrid parallel scan single wafer ion implantation system100(e.g.,FIG. 1), wherein a stationary pencil ion beam202is scanned with an electrostatic beam scanner204in one axis, the fast scan axis (usually greater than 100 Hz), a fanned out beam211can be converted to a parallel shifted beam215by an angle corrector lens220, typically an electromagnet (e.g., angle corrector magnet) and a wafer or workpiece234is mechanically moved orthogonal to the beam scanning axis. In this type of ion implantation system100the electrostatic beam scanner204is most often positioned after the ion beam202acquires full acceleration energy. The beam scanner204can be either electrostatic or electromagnetic, but for simplicity of discussion, it is assumed that the scanner204is an electrostatic scanner. For an electromagnetic scanner, the mathematical relationship is slightly more complex than for the electrostatic scanner204and it requires knowing the mass of the ions.

For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam202by the electrostatic scanner204is 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 magnet220is deactivated which allows the deflected beam211, deflected by the scanner to pass through the angle corrector magnet220without deflection.
Δθ1S=(K1S)(ΔV1S)/(E/q) (electrostatic equation)  (Eq. 1)

wherein:Δθ1Sis a change of deflection angleK1Sis a constant (of the 1st order) throughout the ranges of the beam energy (E) and scanner voltage (V1S)ΔV1Sis the change in electrostatic scanner voltageE is the beam energyq is the charge value of the ions

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 scanner215(as opposed to an electrostatic scanner204) the change of beam deflection angle (Δθ1M) is shown below as Equation 3. In this embodiment of the present invention the angle corrector magnet220is deactivated which allows the scanner deflected beam211to pass through the angle corrector magnet220without deflection.
Δθ1M=(K1M)(q)(ΔB1M)/(sqrt(Em)) (electromag. eq.)  (Eq. 3)

wherein:Δθ1Mis the change of beam deflection angle;K1Mis constant (of the 1st order) throughout the ranges of the beam energy (E) and a magnetic field in the electromagnetic scanner;ΔB1Mis the change in the electromagnetic scanner magnetic field;E is the beam energy;q is the charge value of the ions; andm is the mass of ions.

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 system300; depicted inFIG. 3that can also be used in a hybrid scan single wafer ion implantation system100. In this kind of system a beam scanner is most often situated after the ion beam302acquires full acceleration energy. The primary angle of deflection of the ion beam202by the scanner204is a linear function shown as Equation 5 that adds an additional correction factor f1M.

The system300can be utilized in an exemplary hybrid parallel scan single wafer ion implantation system100(e.g.,FIG. 1), wherein a stationary pencil ion beam302is scanned (usually at a frequency greater than 100 Hz) with an electrostatic beam scanner304in one axis. In the fast scan axis, a fanned out beam311is converted to a parallel shifted beam315by activating an angle corrector lens320, typically an electromagnet (e.g., angle corrector magnet) and a wafer or workpiece334is mechanically moved orthogonal to the beam scanning axis. In this type of ion implantation system the beam scanner304is most often positioned after the ion beam302acquires full acceleration energy. The beam scanner304can be either electrostatic or electromagnetic, but for simplicity of discussion, it is first assumed that the scanner304is an electrostatic scanner. For an electromagnetic scanner as discussed supra, the mathematical relationship is slightly more complex than for an electrostatic scanner and it requires knowing the mass of the ions.

For small angles (i.e., angles less than about 10 degrees) the angle of deflection of the ion beam302by the electrostatic scanner304is 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 magnet220is activated which allows the fanned out beam211to be converted into a parallel ion beam315as illustrated inFIG. 3.
Δθ2S=(f2S)(k2S)(ΔV2S)/(E/q)  (Eq. 5)

wherein:Δθ2Sis the shift of beam position;f2Sis a correction factor to account for effect of corrector magnet;K2Sis approximately constant throughout ranges of the beam energy and electrostatic scanner voltage;ΔV2Sthe change in electrostatic scanner voltage;E the beam energy; andq is the charge value of the ions.

Now referring to another embodiment of the present invention is an electromagnetic scanner315(as opposed to the electrostatic scanner204) the shift of beam position (Δθ2M) is shown below as Equation 7. In this embodiment of the present invention the angle corrector magnet320is activated which allows the deflected beam by the scanner311to pass through the angle corrector magnet320and to be deflected into a parallel ion beam315.
Δθ2M=(f2M)(k2M)q(ΔB2M)/sqrt(Em)  (Eq. 7)

wherein:Δθ2Mis the shift of beam position;f2Mis a correction factor to account for effect of corrector magnet;K2Mis approximately constant throughout ranges of the beam energy and electromagnetic scanner current;ΔB2Mthe change in magnetic field in the electromagnetic scanner;E the beam energy;m is the mass of ions; andq is the charge value of the ions.

FIG. 4illustrates an exemplary method of beam energy identification400that will be described in detail with respect toFIG. 2. Although the methodology400is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with one or more aspects of the present invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methodologies according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated.

The method400begins at404with generating an ion beam202and scanning the ion beam202in a fast scan axis with an ion beam scanner204(e.g.,FIG. 2), for example. The ion beam202(FIG. 2) is extracted at404and scanned at a frequency of greater than 100 Hz. The ion beam202in this example is a pencil ion beam; however potential ion beams can be a divergent beam, a ribbon beam, and the like. The ion beam scanner204can be an electrostatic ion beam scanner215(FIG. 2) or an electromagnetic ion beam scanner217.

Two or more Faraday cups and/or other type detection mechanism(s) and/or sensors can be employed to detect a deflected ion beam211(FIG. 2) and thus ascertain the ion beam energy associated therewith. At406a first Faraday cup216is located to capture a first deflected ion beam peak211aand a second Faraday cup218is located to capture a second deflected ion beam peak211b. It is determined at408if the scanner is an electrostatic scanner215or an electromagnetic scanner217. If the scanner is the electrostatic scanner215the voltage is varied to obtain peak of a first deflected ion beam211a(FIG. 2) in the first Faraday cup216(FIG. 2) and a second deflected ion beam peak211b(FIG. 2) in the second Faraday cup218(FIG. 2). An angle corrector magnet220(FIG. 2) is deactivated so that the deflected ion beam211by the scanner travels to the Faraday cups216and218un-deflected. The beam energy (E) is calculated at414(FIG. 4) utilizing the change in voltage. Referring to the equation derived previously as Eq. 2.
E=(Δθ1S)(q)/((K1S)(ΔV1S)) (electrostatic equation)  (Eq. 2)

wherein:Δθ1Sis an shift of beam angle;K1Sis a constant (of the 1st order) throughout the ranges of beam energy (E1S) and scanner voltage (V1S);ΔV1Sis the change in electrostatic scanner voltage;E is the beam energy; andq is the charge value of the ions.

If it is determined at408that the scanner is the electromagnetic scanner217the current is varied to obtain the peak of a first deflected ion beam peak211a(FIG. 2) in the first Faraday cup216(FIG. 2) and a second deflected ion beam peak211b(FIG. 2) in the second Faraday cup218(FIG. 2). The angle corrector magnet220(FIG. 2) is deactivated so that the deflected ion beam211by the scanner travels to the cups216and218un-deflected. The beam energy (E) is calculated utilizing the change in magnetic field in the scanner at414. Referring to the equation derived previously as Eq. 4.
E=(K1MΔB1Mq Δθ1M)2/m(Eq. 4)

wherein:Δθ1Mis shift of beam angle;K1Mis a constant (of the 1st order) throughout the ranges of the beam energy (E) and scanner current;ΔB1Mis the change in the magnetic field in electromagnetic scanner;E is the beam energym is the mass of ions; andq is the charge value of the ions.

FIG. 5illustrates yet another exemplary method for beam energy identification500that will be described in detail with respect toFIG. 3. Although the methodology500is illustrated and described hereinafter as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with one or more aspects of the present invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methodologies according to the present invention may be implemented in association with the formation and/or processing of structures illustrated and described herein as well as in association with other structures not illustrated.

The method500begins at504with generating an ion beam302and scanning the ion beam302in a fast scan axis with an ion beam scanner304(e.g.,FIG. 3), for example. The ion beam302(FIG. 3) is extracted at504and scanned at a frequency of greater than 100 Hz. The ion beam302in this example is a pencil ion beam; however potential ion beams can be a divergent beam, a ribbon beam, and the like. The ion beam scanner304can be an electrostatic ion beam scanner315(FIG. 3) or an electromagnetic ion beam scanner317.

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 beam315(FIG. 3) and thus ascertain the ion beam energy associated therewith. At506a first faraday cup322is located to capture a first parallel ion beam peak315aand a second faraday cup324is located to capture a second parallel ion beam peak315b. It is determined at508if the scanner304is an electrostatic scanner313or an electromagnetic scanner317. If the scanner304is an electrostatic scanner313the voltage is varied to obtain a first parallel ion beam peak315a(FIG. 3) in the first Faraday cup322(FIG. 3) and a second parallel ion beam peak315b(FIG. 3) in the second Faraday cup324(FIG. 3). An angle corrector magnet320(FIG. 3) is activated so that the parallel ion beam315travels to the cups322and324. The ion beam energy (E) is calculated at514(FIG. 5) utilizing the change in scanner voltage. Referring to the equation derived previously as Eq. 6.
E=(Δθ2S)(q)/((f2S)(k2S)(ΔV2S)) (electrostatic equation)  (Eq. 6)

wherein:Δθ2Sis the second electrostatic shift of beam position;f2Sis a correction factor to account for effect of corrector magnet;K2Sis approximately constant throughout ranges of the second electrostatic beam energy 2 and electrostatic scanner voltage;ΔV2Sthe second change in electrostatic scanner voltage;E the beam energy; andq is the charge value of the ions.

Wherein, the method500ends if the scanner was the electrostatic scanner313.

If it is determined at508that the scanner304(FIG. 3) is an electromagnetic scanner317the current is varied to obtain a parallel ion beam peak315a(FIG. 3) in the first Faraday cup322(FIG. 3) and a second parallel ion beam peak315b(FIG. 3) in the second Faraday cup324(FIG. 3). The angle corrector magnet320(FIG. 3) is activated so that the parallel ion beam315travels to the cups322and324. The beam energy (E) is calculated utilizing the change in current at514. Referring to the equation derived previously as Eq. 8.
E=(K2MΔB2Mq Δθ2M)2/m(electromagnetic equation)  (Eq. 8)

wherein:Δθ2Mis the shift of beam position;K2Mis a constant (of the 1st order) throughout the ranges of a beam energy (E) and scanner current;ΔB2Mis the change in a magnetic field of the electromagnetic scanner;E is a beam energy; andq is a charge value of the ions.

Wherein, the method500ends if the scanner is an electromagnetic scanner317.