Patent Number: 063317133
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an ion implanter apparatus 1 is shown. The apparatus comprises an ion source assembly 10 in schematic form only, whose structure will be described in more detail in connection with FIGS. 2-5 below. The ion source assembly includes an ion source 20 which is fed with a supply of atoms or molecules from a gas bottle 12, for example. The ion source has an extraction assembly shown generally at 14 from which an ion beam 16 is produced. The ion beam 16 is directed through an ion mass selector 17 including a magnetic analyser 18. Ions of the chosen mass to charge ratio follow a curved path through the magnetic analyser 18 and pass through an exit slit 15 before impinging upon a target substrate 19 mounted upon a substrate holder 19a. As will be appreciated by the skilled reader, the above elements are all housed in a vacuum housing although this is not shown for clarity. Referring next to FIG. 2a, 2b, 3a and 3b, a schematic plan view of the ion source assembly 10 embodying the present invention is shown in various views. In FIGS. 2a and 3a, the ion source assembly 10 is shown in a first, closed position. FIGS. 2b and 3b show the assembly 10 in a second, open position. The ion source assembly comprises an ion source 20 which may be of any suitable type such as a Freeman or Bernas source, for example. In the example shown in the Figures, the ion source 20 has a base portion 25, and a generally elongate portion upon that base. The end of the generally elongate portion contains an arc chamber 30. As will be familiar to those skilled in the art, the arc chamber 30 has an aperture therein to allow ions generated within the ion source to exit. The ion source assembly also includes an extraction electrode 40, which is mounted immediately adjacent the face plate 35 to allow ions formed within the ion source 20 to be extracted in the form of an ion beam. In order to support the extraction electrode 40 next to the face plate 35, an extraction electrode support member 50 is employed. As seen in FIG. 2a, the extraction electrode support member 50 is U-shaped in section, with the base thereof holding the extraction electrode 40. The ion source 20 is usually at a common potential of a few kV or more. In order to accelerate positive ions away from the arc chamber 30, the extraction electrode 40 needs to be at a net negative potential relative to the potential of the ion source 20. Therefore, both the ion source 20 and the extraction electrode 40 (via the extraction electrode support member 50, which is electrically conducting) are connected to separate voltage supplies (not shown). Furthermore, the extraction electrode support ember 50 is electrically insulated from the base of the ion source 20 by a first high voltage bushing 60, formed from a suitable insulating material. The first high voltage bushing 60 acts not only to separate the extraction electrode support member 50 from the base portion 25 of the ion source 20, but also to support the extraction electrode support member 50 mechanically relative to the ion source base portion 25. The aperture of the arc chamber 30, and the extraction electrode 40, extend into an evacuatable chamber 70. This chamber 70 contains a suppressor electrode 80 at a net negative potential with respect to the extraction electrode 40. Downstream of the suppressor electrode 80 is a fourth, ground electrode 90. The suppressor and ground electrodes 80,90 together form an extraction assembly 100 (shown in perspective view in FIG. 3b). The purpose of the various electrodes in the tetrode structure does not form part of the present invention and will not be described in further detail. The chamber 70 and the ground electrode 90 are typically at a common ground potential relative to the ion source 20 and extraction electrode 40. Therefore, it is again necessary to insulate the chamber 70 from the extraction electrode support member 50, and this is accomplished with a second high voltage bushing 110. As with the first high voltage bushing 60, the second high voltage bushing 110 not only electrically insulates the extraction electrode support member 50 from the chamber 70, but also provides mechanical support for the extraction electrode support member 50. The end face of the second high voltage bushing 110, proximal to the chamber 70, has a bushing flange 120. The ion source 20, extraction electrode 40, extraction electrode support member 50, first high voltage bushing 60, second high voltage bushing 110 and bushing flange 120 together constitute an ion source sub assembly 130, as indicated in FIGS. 2a and 2b. The ion source sub assembly 130 is mounted against an end face 140 of the chamber 70 but movable relative thereto, as will be described in further detail referring in particular to FIGS. 2b and 3b. In use, the bushing flange 120 of the ion source sub assembly 130 abuts against the end face 140 of the chamber 70. The ion source assembly 10 must be evacuated in use and an O-ring seal (not shown) is therefore employed to allow the bushing flange 120 to form a vacuum-tight seal with the end face 140 of the chamber 70. A hinge 150 is attached between an outside wall of the chamber 70, and the bushing flange 120. Previously, in order to access the inside of the chamber 70, or the extraction electrode 40, the ion source 20 first had to be lifted away from the assembly 10 by detaching it from the first high voltage bushing 60 and the extraction electrode support member 50. Even then, to access the inside of the chamber 70, the extraction electrode support member 50 also had to be removed. Using the hinge 150, the ion source sub assembly 130 can be rotated away from the chamber 70 by pivoting about the hinge 150. This is shown in FIGS. 2b and 3b. Not only does the hinge 150 allow ready access to the inside of the chamber 70, but it also supports the weight of the ion source sub assembly 1when in the second position shown in FIGS. 2b and 3b, that is, when the bushing flange 120 does not abut the end face 140 of the chamber 70. The inner walls of the chamber 70 may be lined with a liner 160 which is preferably formed from aluminum sheet. Aluminum is relatively cheap and a liner formed from it may therefore be disposable. Moreover, aluminum is inert to the process. The use of a liner is advantageous because, over time, the walls of the chamber accrue a layer of material formed from the ion beam. As the layer builds up, it deleteriously affects the vacuum pumping rate and introduces the risk of species cross contamination in the wafer to be implanted. By lining the walls of the chamber and then removing the liner and disposing of it on a regular basis, the problems associated with material build up on the chamber wall are alleviated. It will be appreciated that the hinge described herein provides the ready access to the chamber 70 desirable to allow a liner to be used beneficially. FIG. 4 shows a close up perspective view of the hinge 150 of FIGS. 2a, 2b, 3a and 3b, in situ. FIG. 5 shows an exploded view of the hinge 150. As may be seen, the hinge comprises a first hinge part 200 attached in use to the wall of the chamber 70 via screws or bolts (not shown) extending through apertures 205 in the first hinge part. A second hinge part 210 is in use attached in a similar manner to the bushing flange 120. The first and second hinge parts 200, 210 are linked to each other via two hinge linking members 220,230. Each of the two hinge parts 200,210 and hinge linking members 220,230 which together constitute the hinge 150 are connected together via pins or dowels 240 which slide into cooperating needle bearings 260 inserted into holes 265 formed axially in the upper and lower portions of the second hinge part 210 and in the upper and lower portions of both of the hinge linking members 220,230. To assemble the hinge 150, needle bearings are first inserted into the axial holes 265 in the second hinge part 210 and in the hinge linking members 220,230. Next, a plurality of thrust bearing assemblies 250, each comprising a needle thrust race and a thrust washer, are aligned with thrust bearing apertures 275 in the lower portions of each of the first hinge part 200 and the first and second hinge linking members 220,230. The second hinge linking member 230 is aligned with the first hinge part 200 and dowels 240 are inserted through the first hinge part 200 to pivotally connect that first hinge part 200 to the second hinge linking member 230. Next, the first hinge linking member 220 is pivotally attached to the second hinge linking member 230 by inserting dowels 240 through the second hinge linking member 230 into the first hinge linking member 220. Finally, the second hinge part 210 is pivotally connected to the first hinge linking member 220 again by insertion of dowels through the first hinge linking member 220 into the second hinge part 210. It will be appreciated that the ion source sub assembly 130 has significant mass, and the first and second hinge parts 200,210 as well as the first and second hinge linking members 220,230 are therefore preferably formed of a relatively high tensile material such as aluminum. The hinge 150 is also relatively elongate to provide additional strength. Whilst the invention has been described in connection with a fixed axis hinge to connect the source sub assembly 130 with the chamber 70, it will be understood that a number of variations are possible. For example, rather than pivoting about a fixed axis, the hinge may instead move through an arc as the source sub assembly 130 moves relative to the chamber 70. In that case, the sub assembly will move axially away from the chamber as well as rotating relative to it. In other words, upon opening the source sub assembly, all of the bushing flange 120 moves away from the chamber, not just those parts away from the hinge itself. This arrangement may be advantageous if the ion source 20 and extraction electrode 40 extend a long way into the chamber; with a fixed point pivot, the ends of these elements might `catch` upon the wall of the chamber when the source sub assembly 130 is pivoted about the hinge. Likewise, rather than a single hinge, two or more sliders could be employed to connect the source sub assembly to the chamber. This would allow linear sliding of the former relative to the latter. Whilst this arrangement is not preferred as access to the inside of the chamber is more difficult, it does at least allow support for the bulky source sub assembly during disassembly of the ion source assembly. Finally, it is to be appreciated that the hinge need not constrain the source sub assembly to move relative to the chamber in a horizontal plane. However, given the weight of the source sub assembly, if the hinge is to allow movement in a vertical plane as well, then a mechanical energy storage device such as a spring or gas strut is desirably mounted between the source sub assembly and chamber. Thus, the decrease in potential energy when the source sub assembly moves downwards relative to the chamber can be stored in the spring or gas strut. Then, when the source sub assembly is to be moved back upwards against gravity, the energy stored in the spring or gas strut can be utilised to assist the person moving it. Whilst a tetrode structure ion source assembly has been described in the above embodiment, it will of course be understood that the traditional triode structure is also more easily dismantled for cleaning and servicing when a hinge is employed.