Patent Application
20070176123
The present invention concerns ion implanters and more particularly an ion implanter having an analyzer magnet and/or other magnet structure for use in providing an ion beam to implant ions into a workpiece.
Axcelis Technologies, assignee of the present invention, designs and sells products for treatment of workpieces such as silicon wafers during integrated circuit fabrication. Ion implanters create an ion beam that modifies the physical or electrical properties of workpieces such as silicon wafers that are placed into the ion beam. This process can be used, for example, to dope the silicon from which the untreated wafer is made to change the properties of the semiconductor material. Controlled use of masking with resist materials prior to ion implantation, as well as layering of different dopant patterns within the wafer, produce an integrated circuit for use in one of a myriad of applications.
An ion implantation chamber of an ion beam implanter is maintained at reduced pressure. Subsequent to acceleration along a beam line, the ions in the beam enter the implantation chamber and strike the wafer. In order to position the wafer within the ion implantation chamber, wafers are moved by a robot into a load lock from a cassette or storage device that is located at high pressure.
The present invention concerns an ion beam implanter for implanting a workpiece such as a semiconductor wafer. The ion beam implanter includes an ion beam source for generating an ion beam moving along a path of travel directed toward a workpiece. The beam can be delivered to the wafer as a so called “pencil beam”, can be scanned back and forth from an initial trajectory in a raster scan manner, or can be generated as a so-called “ribbon beam”. A workpiece support positions a wafer in an implantation chamber so that the ions that make up the beam strike the workpiece.
An exemplary ion beam implanter includes an ion source for generating an ion beam confined to a beam path and an implantation chamber having an evacuated interior region wherein a workpiece is positioned to intersect the ion beam. The implanter further includes at least one magnet positioned along the beam path between the ion source and the implantation chamber including i) a core material and ii) a superconducting magnet conductor positioned relative to said core material which, when energized creates a magnetic field for bending the ions in the ion beam away from an initial trajectory at which they enter the magnet
Superconducting magnets have several advantages over conventional magnets used in prior art ion implanters. These include, but are not limited to: decreased size, weight, and power consumption; increased temporal and spatial stability of the resulting magnetic field; and ability to produce uniform magnetic fields over a wide area, which may be an enabling technology for steering a “ribbon” beam wide enough to uniformly implant wafers with a diameter as wide as 300 mm, and possibly as high as the 450 mm and 700 mm diameters that are currently being projected for implant technology roadmaps. Superconducting magnets may also be advantageously used to mass analyze high mass species such as In or Sb at extraction energies higher than possible with prior art magnet technology. In addition, superconducting magnets may provide valuable benefits in scanned beam architectures where scanning and parallelizing magnets are utilized along the path of beam travel.
These and other features of the exemplary embodiment of the invention are described in detail in conjunction with the accompanying drawings.
Turning to the drawings,
The ion source 12 includes a plasma chamber defining an interior region into which source materials including an ionizable gas or vaporized source material are injected. Ions generated within the plasma chamber are extracted from the chamber by ion beam extraction assembly 28, which typically includes a number of electrodes for creating an ion accelerating electric field.
Positioned along the beam path is an analyzing magnet 30 having superconducting electromagnetic coils, which when energized bend the ion beam 14 and direct it through a beam shutter 32. As illustrated in
Ions within the fan-shaped beam follow diverging paths along a single plane after they leave the scanning magnet 40. Thereafter, the ions typically enter a parallelizing magnet 42, wherein the ions that make up the beam 14a are again bent by varying amounts so that they exit the parallelizing magnet 42 moving along generally parallel beam paths. Those of skill in the art will recognize that the ions may be directed to enter magnetic structure shown as an energy filter 44 that deflects the ions in a direction transverse to the scan plane, in a downward or upward direction relative to the y-axis direction shown in
The scanned ion beam 14a that exits the parallelizing magnet 42 is an ion beam with a cross-section essentially forming a very narrow rectangle, that is, a beam that extends in one direction, e.g., has a vertical extent that is limited (e.g. approx ½ inch) and has an extent in the orthogonal direction that widens outwardly due to the scanning or deflecting caused by the scanning magnet 40 to completely cover a diameter of a workpiece such as a silicon wafer. Generally, the extent of the scanned ion beam 14a is sufficient, when scanned, to implant an entire surface of the workpiece 24. That is, the scanning magnet 40 will deflect the beam such that a horizontal extent of the scanned ion beam 14a, upon striking the implantation surface of the workpiece 24 within the implantation chamber 22, will be at least the diameter of the workpiece.
A workpiece support structure 50 both supports and moves the workpiece 24 (up and down in the y direction) with respect to the scanned ion beam 14 during implantation such that an entire implantation surface of the workpiece 24 is uniformly implanted with ions. Since the implantation chamber interior region is evacuated, workpieces must enter and exit the chamber through a loadlock 60. A robotic arm 62 mounted within the implantation chamber 22 automatically moves wafer workpieces to and from the loadlock 60. A workpiece 24 is shown in a horizontal position within the load lock 60 in
In a typical implantation operation, undoped workpieces (typically semiconductor wafers) are retrieved from one of a number of cassettes 70-73 by one of two robots 80, 82 which move a workpiece 24 to an orienter 84, where the workpiece 24 is rotated to a particular orientation. A robot arm retrieves the oriented workpiece 24 and moves it into the load lock 60. The load lock closes and is pumped down to a desired vacuum, and then opens into the implantation chamber 22. The robotic arm 62 grasps the workpiece 24, brings it within the implantation chamber 22 and places it on the workpiece support structure 50. After ion beam processing of the workpiece 24, the workpiece support structure 50 returns the workpiece 24 to a horizontal position and the electrostatic clamp is de-energized to release the workpiece. The arm 62 grasps the workpiece 24 after such ion beam treatment and moves it from the support 50 back into the load lock 60. In accordance with an alternate design the load lock has a top and a bottom region that are independently evacuated and pressurized and in this alternate embodiment a second robotic arm (not shown) at the implantation station 20 grasps the implanted workpiece 24 and moves it from the implantation chamber 22 back to the load lock 60 and into one of the cassettes 70-73.
Superconducting Magnet Materials
The various magnets typically used in an ion implantation system, including, but not limited to the exemplary mass analysis magnet 30, scanning magnet 40, parallelizing magnet 42 and/or angular energy deflection magnet 44 described herein above with respect to the implantation system of
In an exemplary embodiment of a mass analyzing magnet in accordance with the present invention, as shown in
In combination with the conductors 144, two core portions are situated in face-to-face orientation to form a magnet entrance so that ions enter a center passageway of the magnet. A singular bottom section of the core 40a is depicted in
Each of the core sections is made up of many individual magnet laminations which are generally thin, planar sheets or ribbons that are wound about a mandrel to form the magnet sections. The exposed planar surface of the center segment of the overall core is made up of a combination of the cut ends of the smaller prongs of each of the ten “U” shaped core sections.
The two halves of the magnet yoke (all ten core sections in the exemplary embodiment) are supported by structure above and below the beamline passageway that includes mounting flanges 150 that support the yoke and saddle coils. In accordance with the present invention, the saddle coils are constructed from hollow superconducting materials through which a coolant fluid is routed during operation of the magnet. The core and coils are supported by flange 150. As seen in
In operation, control electronics coupled to the magnet coils energize the coils to create an alternating magnetic field that deflects the ions entering the magnet by a varying amount that depends on the instantaneous field strength when the ion enters the magnet. The magnetic field has a vector component in generally the positive y direction with one polarity of coil energization and a vector component in generally the negative y direction with the second polarity electrical energization.
While the present invention has been described with a degree of particularity, it is the intent that the invention includes all modifications and alterations from the disclosed design falling with the spirit or scope of the appended claims.
