Methods and apparatus for implanting ions in a workpiece, such as a semiconductor wafer, include generating an ion beam, measuring parallelism of the ion beam, adjusting the ion beam for a desired parallelism based on the measured parallelism, measuring a beam direction of the adjusted ion beam, orienting a workpiece at an implant angle referenced to the measured beam direction and performing an implant with the workpiece oriented at the implant angle referenced to the measured beam direction. The implant may be performed with a high degree of beam parallelism.
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0. 27. A method for implanting ions into a workpiece, comprising:
generating an ion beam;
measuring a beam direction of the ion beam without implanting any workpiece with the ion beam;
tilting a workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction; and
performing an implant with the workpiece tilted at the implant angle.
0. 33. Apparatus for implanting ions into a workpiece, comprising:
means for generating an ion beam;
means for measuring a beam direction of the ion beam without implanting any workpiece with the ion beam;
means for tilting a workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction, wherein the implant is performed with the workpiece tilted at the implant angle.
0. 39. Apparatus for implanting ions into a workpiece, comprising:
an ion beam generator;
a measuring system for measuring a beam direction of the ion beam without implanting any workpiece with the ion beam; and
a tilt mechanism for tilting the workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction, wherein the implant is performed with the workpiece tilted at the implant angle.
0. 45. A method for implanting ions into a workpiece, comprising the steps of:
generating an ion beam;
adjusting the ion beam for a desired measure of parallelism;
measuring a beam direction of the adjusted ion beam without implanting any workpiece with the ion beam;
tilting a workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction; and
performing the implant with the workpiece titled at the implant angle.
1. A method for implanting ions into a workpiece, comprising the steps of:
generating an ion beam;
adjusting the ion beam for a desired measure of parallelism in a plane;
measuring a beam direction of the adjusted ion beam in said plane without implanting any workpiece with the ion beam;
tilting a workpiece about an axis perpendicular to said plane at an implant angle referenced to the measured beam direction; and
performing an the implant with the workpiece tilted at the implant angle.
19. Apparatus for implanting ions into a workpiece, comprising:
an ion beam generator;
an ion optical element for adjusting the ion beam for a desired parallelism in a plane;
a measuring system for measuring a beam direction of the adjusted ion beam in said plane without implanting any workpiece with the ion beam; and
a tilt mechanism for tilting the workpiece about an axis perpendicular to said plane at an implant angle referenced to the measured beam direction, wherein an implant is performed with the workpiece tilted at the implant angle referenced to the measured beam direction.
0. 57. Apparatus for implanting ions into a workpiece, comprising:
an ion beam generator;
an ion optical element for adjusting the ion beam for a desired parallelism;
a measuring system for measuring a beam direction of the adjusted ion beam without implanting any workpiece with the ion beam; and
a tilt mechanism for tilting the workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction, wherein the implant is performed with the workpiece tilted at the implant angle referenced to the measured beam direction.
0. 49. A method for implanting ions into a workpiece, comprising the steps of:
generating an ion beam;
measuring parallelism of the ion beam;
adjusting the ion beam for a desired parallelism based on the measured parallelism;
measuring a beam direction of the adjusted ion beam without implanting any workpiece with the ion beam;
tilting a workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction; and
performing the implant with the workpiece tilted at the implant angle referenced to the measured beam direction.
8. A method for implanting ions into a workpiece, comprising the steps of:
generating an ion beam;
measuring parallelism of the ion beam in a plane;
adjusting the ion beam in said plane for a desired parallelism based on the measured parallelism;
measuring a beam direction of the adjusted ion beam in said plane without implanting any workpiece with the ion beam;
tilting a workpiece about an axis perpendicular to said plane at an implant angle referenced to the measured beam direction; and
performing an implant with the workpiece tilted at the implant angle referenced to the measured beam direction.
0. 53. Apparatus for implanting ions into a workpiece, comprising:
means for generating an ion beam;
means for measuring parallelism of the ion beam;
means for adjusting the ion beam for a desired parallelism based on the measured parallelism;
means for measuring a beam direction of the adjusted ion beam without implanting any workpiece with the ion beam;
means for tilting a workpiece about an axis that is not parallel to the measured beam direction at an implant angle referenced to the measured beam direction; and
means for performing the implant with the workpiece tilted at the implant angle referenced to the measured beam direction.
14. Apparatus for implanting ions into a workpiece, comprising:
means for generating an ion beam;
means for measuring parallelism of the ion beam in a plane;
means for adjusting the ion beam in said plane for a desired parallelism based on the measured parallelism;
means for measuring a beam direction of the adjusted ion beam in said plane without implanting any workpiece with the ion beam;
means for tilting a workpiece about an axis perpendicular to said plane at an implant angle referenced to the measured beam direction; and
means for performing an implant with the workpiece tilted at the implant angle referenced to the measured beam direction.
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This invention relates to systems and methods for ion implantation of semiconductor wafers or other workpieces and, more particularly, to methods and apparatus for adjusting beam parallelism in ion implanters.
Ion implantation is a standard technique for introducing conductivity-altering impurities into semiconductor wafers. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the wafer. The energetic ions in the beam penetrate into the bulk of the semiconductor material and are embedded into the crystalline lattice of the semiconductor material to form a region of desired conductivity.
Ion implantation systems usually include an ion source for converting a gas or a solid material into a well-defined ion beam. The ion beam is mass analyzed to eliminate undesired ion species, is accelerated to a desired energy and is directed onto a target plane. The beam is distributed over the target area by beam scanning, by target movement or by a combination of beam scanning and target movement. An ion implanter which utilizes a combination of beam scanning and target movement is disclosed in U.S. Pat. No. 4,922,106 issued May 1, 1990 to Berrian et al.
The delivery of a parallel ion beam to the semiconductor wafer is an important requirement in many applications. A parallel ion beam is one which has parallel ion trajectories over the surface of the semiconductor wafer. In cases where the ion beam is scanned, the scanned beam is required to maintain parallelism over the wafer surface. The parallel ion beam prevents channeling of incident ions in the crystal structure of the semiconductor wafer or permits uniform channeling in cases where channeling is desired. Typically, a serial ion implanter is utilized when a high degree of beam parallelism is required.
In one approach, the beam is scanned in one dimension so that it appears to diverge from a point, referred to as the scan origin. The scanned beam then is passed through an ion optical element which performs focusing. The ion optical element converts the diverging ion trajectories to parallel ion trajectories for delivery to the semiconductor wafer. Focusing can be performed with an angle corrector magnet or with an electrostatic lens. The angle correction magnet produces both bending and focusing of the scanned ion beam. Parallelism may be achieved with an electrostatic lens, but energy contamination can be a drawback.
The output ion beam from the angle corrector magnet or other focusing element may be parallel or may be converging or diverging, depending on the parameters of the ion beam and the parameters of the focusing element. When an angle corrector magnet is utilized, parallelism can be adjusted by varying the magnetic field of the angle corrector magnet. The angle corrector magnet typically has a single magnetic field adjustment which varies both parallelism and bend angle, or beam direction. It will be understood that the ion implanter is often required to run a variety of different ion species and ion energies. When the beam parameters are changed, readjustment of the angle corrector magnet is required to restore beam parallelism.
In prior art ion implanters, the angle corrector magnet is typically adjusted so that the ion beam has normal incidence on a wafer plane of the ion implanter end station. However, the angle corrector adjustment which achieves normal incidence on the wafer plane may result in less than optimum parallelism. In particular, an ion beam that is adjusted for normal incidence on the wafer plane may be somewhat diverging or converging. As shown in
In another approach, the angle corrector magnet is designed for best parallelism under typical conditions, and the ion implanter end station is positioned for normal incidence of the ion beam on the wafer. However, beam parallelism and normal incidence are not maintained over a wide range of beam parameters, and changing the position of the end station is very difficult.
Accordingly, there is a need for improved methods and apparatus for adjusting beam parallelism in ion implanters.
According to a first aspect of the invention, a method is provided for implanting ions into a workpiece. The method comprises the steps of generating an ion beam, adjusting the ion beam for a desired measure of parallelism, measuring a beam direction of the adjusted ion beam, orienting a workpiece at an implant angle referenced to the measured beam direction, and performing an implant with the workpiece oriented at the implant angle.
The step of adjusting the ion beam may comprise adjusting the ion beam for substantially parallel ion trajectories. In general, the beam direction may differ from the beam axis of the ion implanter. The implant angle may be zero degrees, in which case the workpiece is oriented normal to the measured beam direction.
The workpiece may comprise a semiconductor wafer, and the step of orienting the workpiece may comprise tilting the semiconductor wafer at the implant angle referenced to the measured beam direction.
The method may further comprise the step of measuring an angle of non-parallelism of the ion beam. The step of adjusting the ion beam may be based on the measured angle of non-parallelism. The beam direction and the angle of non-parallelism of the ion beam may be measured with a movable beam profiler and one or more beam detectors.
According to another aspect of the invention, apparatus is provided for implanting ions into a workpiece. The apparatus comprises means for generating an ion beam, means for measuring parallelism of the ion beam, means for adjusting the ion beam for a desired parallelism based on the measured parallelism, means for measuring a beam direction of the adjusted ion beam, means for tilting a workpiece at an implant angle referenced to the measured beam direction, and means for performing an implant with the workpiece tilted at the implant angle referenced to the measured beam direction.
According to a further aspect of the invention, apparatus is provided for implanting ions into a workpiece. The apparatus comprises an ion beam generator, an ion optical element for adjusting the ion beam for a desired parallelism, a measuring system for measuring a beam direction of the adjusted ion beam, and a tilt mechanism for tilting a workpiece at an implant angle referenced to the measured beam direction. An implant is performed with the workpiece tilted at the implant angle referenced to the measured beam direction.
The ion optical element may comprise an angle corrector magnet for adjusting the ion beam for substantially parallel ion trajectories. The measuring system may comprise a movable beam profiler and one or more beam detectors. Where the implant angle is zero degrees, the workpiece is tilted normal to the measured beam direction.
For a better understanding of the present invention, reference is made to the accompanying drawings, which are incorporated herein by reference and in which:
A simplified block diagram of an example of an ion implanter suitable for incorporating the present invention is shown in FIG. 1. An ion beam generator 10 generates an ion beam of a desired species, accelerates ions in the ion beam to desired energies, performs mass/energy analysis of the ion beam to remove energy and mass contaminants and supplies an energetic ion beam 12 having low level of energy and mass contaminants. A scanning system 16, which includes a scanner 20 and an angle corrector 24, deflects the ion beam 12 to produce a scanned ion beam 30 having parallel or nearly parallel ion trajectories. An end station 32 includes a platen 36 that supports a semiconductor wafer 34 or other workpiece in the path of scanned ion beam 30 such that ions of the desired species are implanted into the semiconductor wafer 34. The ion implanter may include additional components well known to those skilled in the art. For example, the end station 32 typically includes automated wafer handling equipment for introducing wafers into the ion implanter and for removing wafers after implantation, a dose measuring system, an electron flood gun, etc. It will be understood that the entire path traversed by the ion beam is evacuated during ion implantation.
The principal components of ion beam generator 10 include an ion beam source 40, a source filter 42, an acceleration/deceleration column 44 and a mass analyzer 50. The source filter 42 is preferably positioned in close proximity to ion beam source 40. The acceleration/deceleration column 44 is positioned between source filter 42 and mass analyzer 50. The mass analyzer 50 includes a dipole analyzing magnet 52 and a mask 54 having a resolving aperture 56.
The scanner 20, which may be an electrostatic scanner, deflects ion beam 12 to produce a scanned ion beam having ion trajectories which diverge from a scan origin 60. The scanner 20 may comprise spaced-apart scan plates connected to a scan generator. The scan generator applies a scan voltage waveform, such as a sawtooth waveform, for scanning the ion beam in accordance with the electric field between the scan plates.
Angle corrector 24 is designed to deflect ions in the scanned ion beam to produce scanned ion beam 30 having parallel ion trajectories, thus focusing the scanned ion beam. In particular, angle corrector 24 may comprise magnetic pole pieces 26 which are spaced apart to define a gap and a magnet coil (not shown) which is coupled to a power supply 28. The scanned ion beam passes through the gap between the pole pieces 26 and is deflected in accordance with the magnetic field in the gap. The magnetic field may be adjusted by varying the current through the magnet coil. Beam scanning and beam focusing are performed in a selected plane, such as a horizontal plane.
In the embodiment of
Examples of operation of angle corrector 24 are shown in
A flow chart of a process for adjusting an ion implanter and performing ion implantation in accordance with an embodiment of the invention is shown in FIG. 4. In step 100, an ion beam is generated and is transported through the beamline of an ion implanter. As shown in
In step 102, the parallelism of the ion beam is measured at or near the plane where the ion beam is incident on the semiconductor wafer or other workpiece. An example of a technique for measuring ion beam parallelism is described below in connection with
In step 104, the ion beam is adjusted for a desired measure of parallelism, typically near zero divergence or convergence. As shown in
The magnetic field which provides the best parallelism is, in general, not the same magnetic field which directs scanned ion beam 30 normal to wafer plane 70 of the ion implanter end station. Instead, parallel ion beam 30 is incident on wafer plane 70 at an angle 120 relative to a normal to wafer plane 70, as shown in FIG. 5. It will be understood that the angle 120 is exaggerated in
In step 106, the direction of the adjusted ion beam is measured. In particular, the angle 120 of the adjusted ion beam relative to the normal to wafer plane 70 is measured. An example of a technique for measuring ion beam direction is described below in connection with
In step 108, the implant angle is set relative to the direction of the adjusted ion beam and, in particular, referenced to angle 120. The implant angle is set by tilting wafer support platen 36 relative to the wafer plane 70 of the implanter using tilt mechanism 84. Where normal incidence of the parallel scanned ion beam 30 on the wafer 34 is desired, wafer support platen 36 is tilted by an angle 122 that is equal to angle 120. Thus, the wafer support surface of platen 36 is normal to parallel scanned ion beam 30. Where non-zero implant angles are desired, wafer support platen 36 is tilted relative to the measured beam direction. The measured beam direction is thus the reference for setting the implant angle. The non-zero implant angle may be set by tilting the wafer in a direction parallel to the plane of scanning and focusing or may be set by tilting the wafer in a direction orthogonal to the plane of scanning and focusing. In each case, the non-zero implant angle is referenced to the measured beam direction.
In step 110, the implant is performed with the wafer support platen at the desired implant angle referenced to the measured beam direction and with the scanned ion beam 30 adjusted for best parallelism. Thus, the best parallelism is achieved at the desired implant angle.
An example of a technique for measuring ion beam parallelism and direction is described with reference to
As shown in
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In general, the ion beam may be converging or diverging and may have a non-zero beam angle relative to the wafer plane. The profiler positions when detector outputs pulses are generated can be analyzed to determine both the parallelism and direction of the ion beam. The parallelism may be specified as the half angle of divergence or convergence, and the beam direction may be specified relative to a normal to a wafer plane 170. Additional details regarding techniques for measuring ion beam parallelism and direction are provided in U.S. application Ser. No. 09/588,419, filed Jun. 6, 2000, which is hereby incorporated by reference.
It will be understood that different techniques may be used for measuring beam parallelism and direction within the scope of the invention. In addition, the invention is not limited to use with a scanned ion beam. For example, the invention may be used with a ribbon ion beam as disclosed in U.S. Pat. No. 5,350,926, issued Sep. 27, 1994 to White et al.
While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.
Renau, Anthony, Olson, Joseph C.
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