Patent Application
20160172159
The present embodiments relate to ion beam apparatus, and more particularly, to components and methods to control ion beams in beamline ion implanters.
In the present day, ion implanters are often constructed to optimize implantation according to a specific set of applications. In current applications, for example, some beamline ion implanters are configured to generate high current ribbon beams in which the beam cross section that intercepts a substrate is defined by a beam width that is much greater than the beam height.
In the present day it is common to perform ion implantation using ribbon beams in an ion implanter that is dedicated to ribbon beam implantation, where a ribbon beam is directed to the substrate having a beam width sufficient to cover an entire substrate along a first direction of the substrate. The ribbon beam may have a much smaller height than width, where the ribbon beam height along a second direction perpendicular to the first direction is smaller than a substrate dimension along the second direction. In this manner, just a portion of a circular or rectangular substrate is exposed to the ribbon beam at one instance. Consequently, the entire substrate may be exposed to the ribbon beam by scanning the substrate with respect to the ribbon beam along the second direction.
However, if the ribbon beam exhibits non-uniformities in current density, for example, these non-uniformities may be reflected in non-uniform dose that is received by the substrate. For example, small fluctuation in current density may occur locally within portions of a ribbon beam during an ion implantation process, which may result in areas of higher or lower implant dose within a substrate that is exposed to the ribbon beam. It is with respect to these and other considerations that the present improvements have been needed.
This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended as an aid in determining the scope of the claimed subject matter.
In one embodiment an apparatus to control a ribbon ion beam may include a coil assembly comprising a plurality of electromagnetic coils configured to generate a magnetic field proximate the ribbon beam, the magnetic field extending in a first direction that forms a non-zero angle with respect to a direction of propagation of the ribbon ion beam; a current source assembly configured to supply current to the coil assembly; and a controller configured to control the current source assembly to send at least one dithering current signal to the coil assembly responsive to a beam current measurement of the ribbon ion beam, wherein the at least one dithering current signal generates a fluctuation in magnetic field strength of the magnetic field.
In another embodiment, an ion implanter may include an ion source to generate a ribbon ion beam; a beam monitor to perform a beam current measurement of the ribbon ion beam at a first position; a coil assembly comprising a multiplicity of coils configured to generate a magnetic field proximate the ribbon beam at a second position, the magnetic field extending in a first direction that that forms a non-zero angle with respect to a direction of propagation of the ribbon ion beam at the second position; and a current source assembly configured to supply a dithering current to the coil assembly; and a controller configured to control the current source assembly to send at least one dithering current signal to the coil assembly responsive to the beam current measurement, wherein the dithering current generates a fluctuation in magnetic field strength of the magnetic field.
In a further embodiment a method for controlling a ribbon ion beam may include measuring a beam current profile of the ribbon ion beam at a first position, the beam current profile comprising beam current density as a function of position along at least one direction that is perpendicular to a direction of propagation of the ribbon ion beam; determining a non-uniformity in the ribbon ion beam based upon the beam current profile; and sending a control signal to dither current within at least one electromagnetic coil of a coil assembly comprising plurality of electromagnetic coils, the coil assembly being disposed around the ribbon beam at a second position, and configured to generate a magnetic field extending in a first direction that forms a non-zero angle with respect to a direction of propagation of the ribbon ion beam at the second position, wherein the at least one electromagnetic coil generates a fluctuating magnetic field that causes a time-dependent variation in beam current density in the ribbon ion beam.
The present embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which some embodiments are shown. The subject matter of the present disclosure, however, may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the subject matter to those skilled in the art. In the drawings, like numbers refer to like elements throughout.
The embodiments described herein provide novel ion implanters, and novel apparatus and methods to control an ion beam in an ion implanter. In various embodiments a multi-coil assembly is provided in a beamline ion implanter to dither an ion beam while the ion beam is directed to a substrate. The dithering may provide various advantages, including improvements in beam current dose uniformity or reduction in beam current dose variation at a substrate as well as providing control of angular spread of ion trajectories within an ion beam, and control of beam size. In particular a multi-coil assembly may be arranged at a target location in a beamline ion implanter to dither a ribbon ion beam to improve beam properties. The multi-coil assembly may include a plurality of electromagnetic coils that are capable of being driven independently of one another, that is, an electromagnetic coil of the multi-coil assembly is capable of receiving current independently of other electromagnetic coils of the multi-coil assembly. The multi-coil assembly of the present embodiments is arranged proximate to an ion beam in order to locally alter a magnetic field in order to affect the ion beam in a targeted manner.
In various embodiments current may be supplied to the multi-coil assembly by a current source assembly that may include multiple independent current sources. In some embodiments, a given current source is dedicated to provide current to one electromagnetic coil, or to a pair of electromagnetic coils. However, the embodiments are not limited in this context. In the present embodiments, a controller is provided to control the current source assembly to send a dithering signal(s) to the coil assembly. The dithering signal manifests as changing current through an electromagnetic coil as a function of time, which causes a fluctuation of the magnetic field proximate the ion beam that may affect the ion beam in a targeted manner.
As detailed below, further embodiments provide the advantage of tailoring dithering of an ion beam according to a targeted effect on the ion beam, which may include providing a uniform dithering signal that generates sweeping the ion beam as a whole with a time varying dipole field, or individually dithering electromagnetic coils where any combination of dither current amplitude (dither amplitude), frequency, or phase, may vary among different electromagnetic coils. In particular embodiments, a controller is coupled to a beam monitor that may perform beam current measurements on an ion beam. The controller may receive a beam current measurement from the beam monitor and may send at least one dithering current signal to the coil assembly that is responsive to the beam current measurement. In this manner, the ion beam may be adjusted in real-time by dithering a magnetic field that affects the ion beam to correct for a detected beam non-uniformity or other beam property.
For convenience in the discussion to follow, different coordinate systems are employed to describe operation of the present embodiments as shown in
When the ion beam 104 is delivered to the substrate 118, for many applications it may be desirable that the ion beam 104 has a uniform beam current density throughout its cross-section, that is, within the Xs-Y plane. It may also be desirable that the size of the cross-section of the ion beam 104, such as the height or width of the cross-section of the ion beam 104 be accurately controlled. I may further be desirable to control the trajectories of ions. For example, it may be desirable to limit the angular spread of ion trajectories of ions within the ion beam 104 when those ions impact the substrate 118. Accordingly, the ion implanter 100 is provided with a current source assembly 124 that may provide a dithering current signal or group of dithering current signals to the coil assembly 112, in order to adjust beam current density, angular spread of ions, and beam size in either width or height, to name specific characteristics. The ion implanter 100 additionally includes a controller 122 that is configured to control the current source assembly 124 to send the dithering signals to the appropriate electromagnetic coil(s) of the coil assembly 112.
As further illustrated in
Although
Turning now to
As shown in
In various embodiments, the current source assembly 124 may include multiple current sources (not shown) in which a given coil, such as electromagnetic coil 112a, is coupled to a current source to receive current independently of other electromagnetic coils. In some embodiments, each electromagnetic coil of coil assembly 112 may receive current independently of each other electromagnetic coil. In this manner, the electromagnetic coils may be driven individually or in concert with one another depending upon the current signals generated by current source assembly 124. An example of driving electromagnetic coils of the coil assembly 112 in concert involves sending the same dither current signal to all the electromagnetic coils, which may generate a time-dependent magnetic dipole field that generates a dither of the ion beam 104 along the X-axis. In other examples, a dither current signal may be provided to the coil assembly 112 to generate a time varying quadrupole field. On the other hand, a dither current signal may be sent to electromagnetic coil 112a that differs from current signals sent to other electromagnetic coils of the coil assembly 112, which may create a local dither of the ion beam 104 proximate to the electromagnetic coil 112a.
In particular embodiments, the controller 122 may control the current source assembly 124 to send a select dither current signal to a single electromagnetic coil, such as electromagnetic coil 112e, while static current is sent to the other electromagnetic coils of coil assembly 112. In this example the ion beam 104 experiences a local dither in a region that is proximate to the electromagnetic coil 112e, while other parts of the ion beam 104 may pass through the coil assembly 112 experiencing just a static magnetic field. However, the embodiments are not limited in this context.
In additional embodiments, instead of a pair of upper coil assembly and lower coil assembly, a coil assembly to dither an ion beam may comprise a single coil assembly located on one side of an ion beam and similar to the upper coil assembly 202 or lower coil assembly 204, without a corresponding coil located on the other side of the ion beam.
In further embodiments, different dither signals that vary in at least one respect may be provided to different electromagnetic coils of a coil assembly.
The current signal 302 may be provided to a first electromagnetic coil or a first group of electromagnetic coils. As illustrated, a dither current signal shown as the current signal 302 has a first amplitude, which is shown as A1. A dither current signal that is shown as a current signal 304 in
In other scenarios, it may be desirable to change the frequency of a dither current signal provided to a coil assembly in order to more rapidly or more slowly dither the ion beam, depending upon the circumstances. For example, a slowly varying non-uniformity that is detected by the beam monitor 120 may trigger a relatively lower frequency dither current signal (slow dither current signal), than a more rapidly varying non-uniformity, which may trigger a relatively higher frequency dither current signal (fast dither current signal). In some scenarios different dither current signals having different frequencies may be applied simultaneously to different parts of an ion beam, such as ion beam 104 For example, referring also to
In other examples two different dither signals may be provided to different electromagnetic coils of a coil assembly, in which the two different dither signals have a phase offset from one another. This may allow finer control over beam dithering that is produced by the resulting dither magnetic field.
It will be apparent that other combinations of dither current signals may be provided to a coil assembly that involve combinations of variations in amplitude, frequency and phase offset among the dither current signals that are distributed among different electromagnetic coils.
It is further to be noted that the amount of current variation in a dither current signal, that is, the dither current amplitude, may be just a fraction of a current that is provided to an electromagnetic coil. For example, the amplitude A1 may represent 5% 10% or 20%, 50% or 100% of a total current supplied to a given electromagnetic coil. Referring again to
In addition, although the embodiments of
In additional embodiments, a multi-coil assembly may be composed of multiple electromagnetic coils that are wound around a common conducting bar.
The current source assembly 124 may be coupled to the upper coil assembly 404, lower coil assembly 406, first side coil 408 and second side coil 410. Although not explicitly illustrated in
In additional embodiments the conductive material of the member 412 may be removed from the side portions where the first side coil 408 and second side coil 410 are disposed in
It is to be noted that in the embodiments illustrated in
One potential side effect during a dithering operation performed by a coil assembly is the introduction of eddy currents, which may be induced into nearby conductors, such as wave guides (beam guides) or graphite sheets. The eddy currents within a coil assembly itself may be reduced to a low level by the use of laminated steel (transformer steel). However eddy currents may still be induced in a conductive beam guide.
In addition, the frequency of dithering of a dither current signal may be reduced to a level in which eddy current formation is reduced or eliminated. For example if dither frequency is maintained below 100 Hz, eddy current formation may be largely avoided.
The present disclosure is not to be limited in scope by the specific embodiments described herein. Indeed, other various embodiments of and modifications to the present disclosure, in addition to those described herein, will be apparent to those of ordinary skill in the art from the foregoing description and accompanying drawings. Thus, such other embodiments and modifications are in the tended to fall within the scope of the present disclosure. Furthermore, although the present disclosure has been described herein in the context of a particular implementation in a particular environment for a particular purpose, those of ordinary skill in the art will recognize that its usefulness is not limited thereto and that the present disclosure may be beneficially implemented in any number of environments for any number of purposes. Thus, the claims set forth below should be construed in view of the full breadth and spirit of the present disclosure as described herein.
