Insulator for high current ion implanters

An insulator usable in high current ion implantation systems includes increased surface due to the configuration of an inner cylinder and an outer cylinder coupled to the inner cylinder at one end. A cylindrical cavity extends between the two cylinders increasing the surface area and making the insulator resistant to being coated by a coating that could produce a leakage path.

FIELD OF THE INVENTION

This invention relates to an ion beam source head and extraction assembly used in an ion implantation system used for the implantation of ions into substrates such as semiconductor wafers. More particularly, the invention relates to an improved insulator used in the source head to insulate high voltage components from low voltage components.

BACKGROUND

Ion implantation techniques for modifying the electrical conductivity properties of semiconductor materials are well known. In order to generate the ions necessary for implantation into the semiconductor wafer, an ion source is provided which generates ions of a chosen element. An extraction assembly comprising a plurality of electrodes is provided downstream of the ion source to extract, accelerate and focus the ions before they enter a mass analyzer and selector and reach the wafer.

U.S. Pat. No. 6,777,882 B2 describes such an ion beam generator apparatus. The contents of U.S. Pat. No. 6,777,882 B2 are hereby incorporated by reference as if set forth in their entirety.FIG. 1shows an exemplary extraction assembly11for generating ion beam30and directing the same to a semiconductor wafer disposed in a grounded end station (not shown). Each of extraction, suppression and ground electrodes23,24and25respectively, include apertures through which the ion beam extends in this exemplary arrangement. Each of the apertured electrodes23,24and25comprise a single electrically-conductive plate having an aperture through the plate to allow ion beam30emerging from ion source20to pass through. The ion source head includes ion source20and arc chamber20A and is maintained by a voltage supply at a positive voltage relative to ground for a positive ion beam. The energy of the ion beam emerging from the extraction assembly is determined by the voltage supplied to the ion source. A typical value for this voltage is 20 KV, providing an extracted beam energy of 20 keV. Other extracted beam energies, such as beam energies of 80 keV and higher, may be used in other arrangements. Suppression electrode24is biased by a supplied voltage with a negative potential relative to ground. For a beam of positive ions, extraction electrode23is maintained by a voltage supply at a potential below the potential of the ion source, i.e. source electrode22, so as to extract the positive ions from the ion source. The potential of extraction electrode23would typically be below the potential of the suppression electrode24for a low energy beam, and above the potential of suppression electrode24for a high energy beam.

The biased extraction electrode23is separated from ion source20by insulator44which contacts both the biased extraction electrode23and ion source20which is held at the same potential as source electrode22. In other arrangements, insulators such as insulator44can be used to insulate various other high voltage components from ground or other low voltage components.

Such insulators, including insulator44, can become coated by the gas containing the ion beam and which emanates from ion source20and can migrate throughout the extraction assembly and source head. When the surface of insulator44becomes coated, the resistance of the insulator decreases and a leakage path is produced between the components it is intended to insulate, in the illustrated example, extraction electrode23, and ion source20. This causes the beam current of ion beam30to become unstable and eventually requires replacement of extraction assembly11in order to maintain performance of the overall ion implantation system.

It would therefore be desirable to provide an insulator that is resistant to becoming coated and providing a leakage path such as that necessitates replacement of the source head components.

SUMMARY OF THE INVENTION

To address these and other needs, and in view of its purposes, the present invention provides an improved insulator for an ion implantation system having an ion source maintained at a high electric potential, a grounded end station adapted for holding wafers (i.e., substrates) and a plurality of extraction electrodes accelerating the ions from the source and directing an ion beam onto the wafers of the end station, in one aspect. The improvement comprises the insulator disposed between a first high voltage component and a second component being a lower voltage component or a component maintained at ground. The insulator comprises an inner cylindrical body surrounded by an outer cylindrical body with a gap therebetween. The outer cylindrical body has opposed ends, one of the ends radially coupled to the inner cylindrical body.

In another aspect, the insulator is disposed within an apparatus having a chamber with a first component maintained at a high electric potential and proximate to a second component desirably maintained at a lower potential or ground, and with an ionic gas present therein. The insulator is disposed between and physically contacting each of the first and second components. The insulator comprises an inner cylindrical body concentrically surrounded by an outer cylindrical body with a gap therebetween. The outer cylindrical body has opposed ends, one of the ends radially coupled to the inner cylindrical body by a flange extending circumferentially around the inner cylindrical body.

In another aspect, provided is an insulator for insulating a first component maintained at a high electrical potential from a second component desirably maintained at ground in an ionic gaseous environment. The insulator comprises an inner cylindrical body having opposed ends disposed between and physically contacting each of the first and second components, the inner cylindrical body concentrically surrounded by an outer cylindrical body with a gap therebetween and the outer cylindrical body having opposed ends, one of the ends radially coupled to the inner cylindrical body by a flange extending circumferentially around the inner cylindrical body.

DETAILED DESCRIPTION

Provided is an insulator that insulates a high voltage component bias at a high potential from a further low voltage component maintained at ground or at a significantly lower potential level. The inventive insulator finds particular applicability for use in an ion source head in an ion implantation system, particularly a high current ion implantation system used in the semiconductor manufacturing industry. In this application the inventive insulator may insulate an electrode, electrode bar or high voltage line maintained at a high potential from another electrode or other component desirably maintained at ground, or at a considerably lower potential. The inventive insulator also finds application in various other tools and systems used in various industries and in which a high voltage potential is to be insulated from a ground or low voltage component. The inventive insulator is resistant to becoming coated with a coating that can cause shorting from the high voltage component to ground when the coating completely coats the surface of the insulator.

The insulator may be used, for example, as insulator44in an ion implantation system such as shown inFIG. 1, though the insulator is not limited to use in conjunction with the illustrated exemplary system, or within ion implantation systems in general.

FIG. 2shows a more general assembly within which the inventive insulator may be used.FIG. 2shows an exemplary arrangement of extraction assembly121and source head120within which inventive insulator100may be used. Within source head120is ion source130with G1arc chamber slit140, and G2extraction electrode150. Extraction assembly121includes G3suppression electrode160and G4ground electrode170. In one exemplary embodiment, both G3suppression electrode160and G4ground electrode170are maintained at ground potential. Together, the source head and extraction assembly produce ion beam180. Extraction field190including G1arc chamber slit140and G2extraction electrode150sets the beam current of ion beam180. The beam energy is set by acceleration field200which includes each of G1arc chamber slit140, G2extraction electrode150, G3suppression electrode160, and G4ground electrode170. G1arc chamber slit140may be maintained at a positive electric potential and electric potential of G2extraction electrode150may be held below the potential of the ion source—G1arc chamber slit140so as to extract positive ions from ion source130. In one exemplary embodiment, G2extraction electrode150may be maintained at a potential of about −2 kV to about −30 kV less than G1arc chamber slit140.

Insulator100with opposed ends102and104is disposed between G1arc chamber slit140and G2extraction electrode150in the illustrated arrangement which is exemplary only. Insulator100may be used in various other locations and applications. Arrangements such as shown inFIG. 2may be used in AMAT-Applied Materials, Inc. high current implanters, for example. Applied Materials, Inc. is located in Santa Clara, Calif. Insulator100may alternatively be used in various other tools that require isolation between high voltage and low voltage or ground. For example, other high current implanters and high energy implanters may utilize the insulator of the invention.

FIGS. 3 and 4show perspective views of the exemplary insulator of the invention. The insulator may be formed of conventional materials such as primarily Al2O3but other materials may be used in other exemplary embodiments. In one exemplary embodiment, insulator100may be formed of 99.7% Al2O3. Insulator100includes increased surface area with respect to conventional insulators of a given length such as length112and therefore, when disposed in a gap of a given size between a high voltage and ground or low voltage component, the increased surface area is less likely to be completely coated to form a leakage path. The increased surface area itself decreases the possibility of a continuous coating being formed thereon. Moreover, the design geometry includes surfaces not outwardly exposed to gas in the environment and additionally makes it difficult for a film or coating to be formed continuously from opposed ends of insulator100.

Insulator100includes opposed ends102and104and is formed of inner cylinder106and outer cylinder108. Opposed ends102,104typically are in physical contact with the respective components they are insulating. Referring toFIGS. 3 and 4, inner cylinder106and outer cylinder108are concentric in the illustrated embodiment. Other arrangements may be used in other exemplary embodiments. Concentric cylindrical cavity114extends inwardly to a depth from each of opposed ends102. In other exemplary embodiments, concentric cylindrical cavity114may not be present. Length116of outer cylinder108is less than length112of inner cylinder106. The illustrated exemplary embodiment is intended to be just that—exemplary, and in other arrangements, lengths112and116may be almost the same and in yet other exemplary embodiments, length116may be relatively smaller than length112. Gap110is a cylindrical cavity formed between outer cylinder108and inner cylinder106. Radial thickness of inner cylinder106is greater than that of outer cylinder108. Outer cylinder108includes opposed ends113and115. At end115, inner cylinder106and outer cylinder108are radially joined by a flange disposed between inner cylinder106and outer cylinder108. The flange may be continuous so that inner cylinder106is completely circumferentially joined to outer cylinder108such that the cavity formed within gap110is open at one end (113) and closed at the other end (115). In the illustrated embodiment, outer cylinder108is spaced a fixed distance from inner cylinder106making gap110of uniform distance.

FIGS. 5A and 5Bare engineering schematic diagrams showing side and end views of an exemplary insulator of the invention, respectively. As shown in the side view ofFIG. 5A, length112of inner cylinder106may be 50 centimeters in one exemplary embodiment but may be formed to any of various lengths as determined by the spacing between the components that insulator100will be used to insulate. In one exemplary embodiment, length116may be about 31 centimeters when length112is 50 centimeters, but other relative dimensions and other absolute dimensions may be used depending on the configuration of the system within which insulator100is being used. Length116of outer cylinder108may be at least 60% of length112of inner cylinder106in an advantageous embodiment.

FIG. 5Bis a plan, end view showing relative radial dimensions of inner and outer cylinders106and108, respectively. Radial thickness126of inner cylinder106is greater than corresponding radial thickness128of outer cylinder108of the exemplary embodiment, but in other exemplary embodiments, the relative radial thicknesses may vary. In one exemplary embodiment, radial thickness126may be four times as great as radial thickness128but other relative thickness may be used in other embodiments depending on the design of the source head. Thickness125of gap110is advantageously maintained at a small value making it more difficult for gas present in the source head to enter the cavity of gap110and form a continuous coating on the surfaces that define the cavity. Referring again toFIG. 5A, it can be seen that in order for a leakage path to be formed from one end of insulator100to the other, a continuous coating must be formed on all outer surfaces as well as on inner surfaces122(shown in dashed lines) of gap110. The outer diameter124of insulator100may take on various values and one exemplary embodiment may be around 25 centimeters.

The dimensions of insulator100will vary to accommodate the particular location in which insulator100will be used. Opposed ends102and104of insulator100are advantageously physically coupled to the elements of different electric potential between which the insulator provides insulation. One exemplary arrangement is shown inFIG. 6.

Source head132shown inFIG. 6illustrates another exemplary arrangement in which insulator100may be used. In the illustrated exemplary embodiment, high voltage134is supplied to G2graphite electrode136by means of electrode bar138. In one exemplary embodiment, high voltage134may be the illustrated −20 KV but in other exemplary embodiments other voltages may be used. G2graphite electrode136may be maintained at a greater negative potential than G1arc chamber142, for example G2graphite electrode136may be maintained at a potential −2 kV to −30 kV greater than G1arc chamber142. Arc chamber (G1)142generates plasma that is extracted by electrode136to produce exiting plasma144which will be later focused into an ion beam. Source head132also includes filament electrode148and gas supply piping146. Insulator100is disposed between high potential electrode bar138and any location in the source head held at the G1potential, providing insulation therebetween. In an exemplary embodiment, insulator100may be disposed between high potential electrode bar138and gas supply piping146. According to the illustrated arrangement, end102of insulator100, i.e the end adjacent closed end115of outer cylinder108(as shown inFIGS. 3 and 5A, for example) may be oriented inwardly, contacting gas supply piping146. In other arrangements, insulator100may be positioned such that open end113(seeFIGS. 3 and 5A) is distally positioned with respect to the gas flow anticipated within source head132. This further diminishes the possibility that gas will completely fill gap110for an extended time to form a continuous coating on the surfaces thereof. It is an advantage of the inventive insulator100that electrode bar138is sufficiently insulated from gas supply piping146(and vice versa) with an insulator100that is resistant to having a leakage path formed thereacross. Insulator100therefore prevents leakage between electrode bar138and ground components and extends source head life with no additional costs. The beam current remains stable for improved yield and extensive monitoring of the system, or frequent changing of source head parts, is not necessary.