Extraction bushing breakdown boron implant-EPB1 - Ion implantation ion source - Google Patents

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EPA2 en. In embodiments discussed below, the beam dump is discretely defined and isolated, preferably being removed from direct contact with the ionization chamber, with the electron beam passing through an exit port in the ionization chamber prior to being intercepted by the beam dump. The system of claim 18 in which the monitoring system comprises a temperature detector arranged to detect progress or Extraction bushing breakdown boron implant of an exothermic reaction of the reactive gas with contamination the surfaces. Preferred embodiments of these and other aspects of the invention have one or Extraction bushing breakdown boron implant of the Licking arm pits free features:. Carbon dopant gas and co-flow for implant beam and source life performance improvement. It is preferably a resistance-heated or indirectly heated, planar cathode emitter plate such as plate 33 described above in connection with FIG. Ryding 1 1. The extraction stage serves as an injection stage for the following lens system which comprises collimating lens 84 followed by zoom lens Electron gun: For ionizing the gases within the ionization chamber, electrons of controlled energy and generally uniform distribution are introduced into the ionization chamber by a broad, generally collimated beam electron gun as shown in the illustrative figures described below.

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During transport of the sublimated borohydride vapor to the ionization chamber breamdown surfaces are held at a higher Bukkake teen than that Extraction bushing breakdown boron implant the vaporizer but well below the buhing of dissociationto prevent condensation of the vapor. Method and apparatus for improved ion acceleration in an ion implantation system. Indeed, up to half of the borohydride vapor introduced into the source may Urahara hentai in the ion source as breakdon, condensed material. A temperature detector is arranged to detect substantial termination of an exothermic reaction of the reactive gas with contamination on a surface of the system. The method of claim 30 in which the borohydride material is octa-decaborane, B 18 Extraction bushing breakdown boron implant 22and the reactive gas cleaning system is employed to remove condensed decomposition products of octa-decaborane from the surfaces. Furthermore, in the case of the borohydrides, the total cross section representing all interactions with Pants passed ionizing medium i. The reactive gas cleaning system Extraction bushing breakdown boron implant a conduit from a container of pressurized reactive gas, for instance ClF 3. That is, only a small fraction from a few percent to a few tens of percent of the gas or vapor fed into the ion source is ionized. The system is constructed for use in implanting ions in semiconductor wafers, the ionization chamber having a volume less breakdonw about ml and an internal surface area of less than about cm 2. Instead, as shown in FIG. Solid feed materials 29 such as decaborane or octadecaborane can be vaporized in vaporizer 28and the vapor fed into the ionization chamber 44 through vapor conduit 32 within the source block This has the effect of limiting the amount of unwanted deposits on surfaces of the ion generating system, thus extending the ion source life between cleanings. Aluminum, on the other Extracction, is a column III element like In and B of the periodic table, and therefore offers the advantage of being only a mild Extrcation in implnt it is a P-type dopant in siliconwhile transition metals such as molybdenum are very detrimental to carrier lifetimes in integrated circuits.

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Contact Email sales Email support. Assignee Semequip, Inc. Inventors Thomas N. Horsky , Robert W. Sacco, Jr. Jacobson , Wade A. The service lifetime of an ion source is enhanced or prolonged by the source having provisions for in-situ etch cleaning of the ion source and of an extraction electrode, using reactive halogen gases F or Cl , and by having features that extend the service duration between cleanings.

The latter include accurate vapor flow control, accurate focusing of the ion beam optics, and thermal control of the extraction electrode that prevents formation of deposits or prevents electrode destruction.

An apparatus comprised of an ion source for generating dopant ions for semiconductor wafer processing is coupled to a remote plasma source which delivers F or Cl ions to the first ion source for the purpose of cleaning deposits in the first ion source and the extraction electrode. These methods and apparatus enable long equipment uptime when running condensable feed gases such as sublimated vapor sources, and are particularly applicable for use with so-called cold ion sources.

Methods and apparatus are described which enable long equipment uptime when decaborane and octadecarborane are used as feed materials, as well as when vaporized elemental arsenic and phosphorus are used, and which serve to enhance beam stability during ion implantation. An ion generating system for generating an ion beam comprising: a vaporizer of solid feed material for producing vapor of the material, an ion source and extraction electrode within a vacuum housing, and a reactive gas cleaning system, the ion source comprising an ionization chamber connected to a high voltage power supply and having an inlet for vapor of the material from the vaporizer, an energizeable ionizing system for ionizing the vapor within the ionization chamber and an extraction aperture that communicates with the vacuum housing, the vacuum housing evacuated by a vacuum pumping system,.

The system of claim 2 constructed to produce the reactive cleaning gas flow by a generator that comprises a supplemental plasma chamber, the supplemental plasma chamber arranged to receive a gaseous feed compound capable of being disassociated by plasma within the plasma chamber to produce the flow of reactive cleaning gas through an outlet, and a conduit for transporting the reactive gas from the supplemental plasma chamber to the ionization chamber.

The system of claim 1 in which the source material to be ionized by the ion source comprises a molecule that is subject to producing a material that is condensable on surfaces of the ion generating system during ion source operation and the reactive gas is selected to be capable of reacting with the condensable material to form a volatilized reaction product.

The system of claim 1 in which the ion source is a low temperature ion source, the energizeable device of the ion source being constructed to produce a focused electron beam for electron-impact ionization or constructed to operate as an RF field ion source. The system of claim 1 having a vaporizer constructed to vaporize a solid borohydride source material and supply borohydride vapor to the ionization chamber for ionization.

The system of claim 6 in which the borohydride material is decaborane, B 10 H 14 , and the reactive gas cleaning system is adapted to remove condensed decomposition products of decaborane from the surfaces. The system of claim 7 in which the borohydride material is octa-decaborane, B 18 H 22 , and the reactive gas cleaning system is adapted to remove condensed decomposition products of octa-decaborane from the surfaces.

The system of claim 1 in which the reactive gas cleaning system comprises a supplemental reactive gas generator constructed to disassociate a gaseous compound to atomic fluorine.

The system of claim 1 in which the reactive gas cleaning system comprises a supplemental reactive gas generator constructed and arranged to share a service facility with the ion source. The system of claim 1 combined with a system to direct the extracted ion beam through a mass analyzer, in which the reactive gas cleaning system is a supplemental reactive gas generator constructed and arranged to share a service facility with the mass analyzer.

The system of claim 1 in which the ionization chamber is supported within a vacuum housing via an insulative bushing that enables the ion source, when energized during its operation, to be maintained at a voltage potential substantially different from that of the vacuum housing, and the reactive gas cleaning system is disposed to be maintained at the potential of the ion source, and communicates with the ionization chamber through the insulative bushing.

The system of claim 12 in which the reactive gas cleaning system comprises a supplemental reactive gas generator capable of disassociating a gaseous feed compound to provide reactive gas, the generator operable when the ion source is de-energized to provide a flow of reactive gas into and through the ionization chamber and through the ion extraction aperture to react with and remove the deposits on at least some of the surfaces of the ion generating system.

The system of claim 13 constructed to produce the reactive gas flow by a generator that comprises a supplemental plasma chamber, the supplemental plasma charged to receive a gaseous feed compound capable of being disassociated by plasma within the plasma chamber to produce flow of reactive cleaning gas through an outlet, and a conduit for transporting the reactive gas from the supplemental plasma chamber to the ionization chamber. The system of claim 1 in which the ionization chamber is supported within the vacuum housing via an insulative bushing that enables the ion source, during operation, to be maintained at a voltage potential substantially different from that of the vacuum housing, and the reactive gas cleaning system is disposed to be maintained at the potential of the vacuum housing, an communicates with the ionization chamber through the wall of the housing, thence via a voltage break separate from the insulative bushing to the ionization chamber.

The system of claim 15 in which the reactive gas cleaning system comprises a supplemental reactive gas generator capable of disassociating a gaseous feed compound to provide reactive gas, the generator operable when the ion source is de-energized to provide a flow of reactive gas into and through the ionization chamber and through the ion extraction aperture to react with and remove the deposits on at least some of the surfaces of the ion generating system.

The system of claim 16 constructed to produce the reactive gas flow by a generator that comprises a supplemental plasma chamber, the supplemental plasma chamber arranged to receive a gaseous feed compound capable of being disassociated by plasma within the plasma chamber in produce the flow of reactive cleaning gas through an outlet, and a conduit for transporting the reactive gas from the supplemental plasma chamber to the ionization chamber.

The system of claim 1 in combination with a monitoring system adapted to monitor the progress of cleaning action of the reactive gas on the surfaces. The system of claim 18 in which the monitoring system comprises an end-point detection system adapted to at least assist in detecting substantial completion of reaction of the reactive gas with contamination on the surfaces.

The system of claim 19 in which the end point detection system comprises analysis system for the chemical makeup of gas that has been exposed to the surfaces during operation of the nerve gas cleaning system.

The system of claim 18 in which the monitoring system comprises a temperature detector arranged to detect progress or termination of an exothermic reaction of the reactive gas with contamination the surfaces. The system of claim 1 in which the ion source includes a component within or in communication with the ionization chamber that is susceptible to harm by the reactive gas, and means are provided for protecting the component from the reactive gas.

The system of claim 22 in which said protecting means comprises a conduit for producing a flow of inert gas past the component susceptible to harm.

The system of claim 1 in which the reactive gas is a halogen and surfaces of the ion generating system from which deposits are to be removed by the reactive gas are comprised of material resistant to attack by the halogen.

The system of claim 24 in which the ion source is a low temperature ion source and surfaces of the ion generating system comprising the ion source or an exposed portion of the extraction electrode closest to the ion source, from which deposits are to be removed, are comprised of aluminum or an aluminum-based material that is resistant to attack by the halogen. The system of claim 1 in which the ion source is disposed within a vacuum housing associated with a pumping system, the pumping system comprising a high vacuum pump capable of producing high vacuum and a backing pump capable of producing rough vacuum, the high vacuum pump operable during operation of the ion source, and being capable of being isolated from the vacuum housing during operation of the reactive gas cleaning system, the backing pump operable during operation of the reactive gas cleaning sub-system to remove volatized reaction products.

The system of claim 1 in which the extraction electrode is associated with an electrical heater, the heater adapted, during ion extraction, to maintain the extraction electrode at elevated temperature above the condensation temperature of vapors derived from solid feed material being ionized.

A method of producing an ion beam employing the system of claim 1 , including the steps of operating the ion source and thereafter discontinuing operation of the ion source and subjecting the surfaces to cleaning by flow into the ionization chamber of reactive gas such as atomic fluorine.

The mea of claim 28 including employing the ion source to produce an ion beam that is implanted into a target. The method of claim 29 conducted to vaporize a solid borohydride source material and supply borohydride vapor to the ionization chamber for ionization.

The method of claim 30 in which the borohydride material is decaborane, B 10 H 14 , and the reactive gas cleaning system is employed to remove condensed decomposition products of decaborane from the surfaces.

The method of claim 30 in which the borohydride material is octa-decaborane, B 18 H 22 , and the reactive gas cleaning system is employed to remove condensed decomposition products of octa-decaborane from the surfaces. The method of claim 29 employed to implant ions selected from the group consisting of arsenic-containing compounds , arsine, element arsenic, phosphorus-containing compounds , phosphine, elemental phosphorus, antimony-containing compounds, trimethylantimony, antimony pentafluoride silicon compounds, and germanium compounds.

An ion generating system for generating a ion beam comprising: a source of feed material in gaseous or vaporized form, an ion source and an extraction electrode within a vacuum housing, and a reactive gas cleaning system, the ion source comprising: an ionization chamber connected to a high voltage power supply and having an inlet for gaseous or vaporized feed material,. The system of claim 34 in which the source material to be ionized by the ion source comprises a molecule that is subject to producing a material that is condensable on surfaces of the ion generating system during ion source operation and the reactive gas is selected to be capable of reacting with the condensable material to form a volatilized reaction product.

The system of claim 34 in which the ion source is a low temperature ion source, the energizeable device of the ion source being constructed to produce a focused electron beam for electron-impact ionization or constructed to operate as an RF field ion source. The system of claim 34 having a vaporizer constructed to vaporize a solid borohydride source material and supply borohydride vapor to the ionization chamber for ionization.

The system of claim 38 in which the borohydride material is decaborane, B 10 H 14 and the reactive gas cleaning system is adapted to remove condensed decomposition products of decaborane from the surfaces. The system of claim 38 in which the borohydride material is octa-decaborane, B 18 H 22 , and the reactive gas cleaning system is adapted to remove condensed decomposition products of octa-decaborane from the surfaces. The system of claim 34 in which the reactive gas cleaning system comprises a supplemental reactive gas generator constructed to disassociate a gaseous compound to atomic fluorine.

The system of claim 34 in which the reactive gas cleaning system comprises a supplemental reactive gas generator constructed an arranged to share a service facility with the ion source. The system of claim 34 combined with a system to direct the extracted ion beam tough a mass analyzer, in which the reactive gas clearing system is a supplemental reactive gas generator constructed and arranged to share a service facility with the as analyzer.

The system of claim 34 in which the ionization chamber is supported within a vacuum housing via an insulative bushing the enables the ion source, when energized during its operation, to be maintained at a voltage potential substantially different from that of the vacuum housing, and the reactive gas cleaning system is disposed to be maintained at the potential of the ion source, and communicates with the ionization chamber through the insulative bushing.

The system of claim 34 in which the ionization chamber is supported within the vacuum housing via a insulative bushing that enables the ion source, during operation, to be maintained at a voltage potential substantially different from that of the vacuum housing, and the reactive gas cleaning system is disposed to be maintained at the potential of the vacuum housing, and communicates with the ionization chamber through the wall of the housing, thence via a voltage break separate from the insulative bushing to the ionization chamber.

The system of claim 34 in combination with a monitoring system adapted to monitor at least some aspect of the progress of cleaning action of the reactive gas on the surfaces. The system of claim 46 in which the monitoring system comprises an end-point detection system adapted to at least assist in detecting substantial completion of reaction of the reactive gas with combination on the surfaces.

The system of claim 47 in which the end point detection system comprises an analysis system for chemical makeup of gas that has been exposed to the surfaces during operation of the reactive gas cleaning system. The system of claim 46 in which the monitoring system comprises a temperature detector arranged to detect progress or termination of an exothermic reaction of the reactive gas with communication on the surfaces.

The system of claim 34 in which the ion source includes a component within or in communication with the ionization chamber that is susceptible to harm by the reactive gas, and means are provided to protect the component from the reactive gas. The system of claim 50 in which the means comprises a conduit for producing a flow of inert gas, such as argon, past the component susceptible to harm. The system of claim 34 in which the reactive gas is a halogen and surfaces of the ion generating system from which deposits are to be removed by the reactive gas are comprised of material resistant to attack by the halogen.

The system of claim 52 in which the ion source is a low temperature ion source and surfaces of the ion generating system comprising the ion source or an exposed portion of the extraction electrode closest to the ion source, from which deposits are to be removed, are comprised of aluminum or an aluminum-based material that is resistant to attack by the halogen. The system of claim 34 in which the ion source is disposed within a vacuum housing associated with a pumping system the pumping system comprising a high vacuum pump capable of producing high vacuum and a backing pump capable of producing rough vacuum, the high vacuum pump operable during operation of the ion source, and being capable of being isolated from the vacuum housing during operation of the reactive gas cleaning system, the backing pump operable during operation of the reactive gas cleaning system to remove volatilized reaction products.

The system of claim 34 in which the extraction electrode is associated with an electrical heater, the heater adapted during ion extraction, to maintain the extraction electrode at elevated temperature above the condensation temperature of gaseous or vaporous material leaving the ion source.

A method of producing an ion ea employing the system of claim 34 , including the steps of operating the ion source an thereafter discontinuing operation of the ion source and subjecting the surfaces to cleaning by flow into the ionization chamber of reactive gas. The method of claim 56 including employing the ion source to produce an ion beam that is implanted into a target. The method of claim 57 conducted to vaporize a solid borohydride source material and supply borohydride vapor to the ionization chamber for ionization.

The method of claim 58 in which the borohydride material is decaborane, B 10 H 14 , and the reactive gas cleaning system is employed to remove condensed decomposition products of decaborane from the surfaces. The method of claim 58 in which the borohydride material is octa-decaborane, B 18 H 22 , and the reactive gas cleaning system is adapted to remove condensed decomposition products of octa-decaborane from the surfaces.

The method of claim 57 employed to implant ions selected from the group consisting of arsenic-containing compounds, arsine, elemental arsenic, phosphorus-containing compounds, phosphine , elemental phosphorus, antimony-containing compounds trimethylantimony , an antimony pentafluoride silicon compounds and germanium compounds. A method of producing an ion beam employing an ion implantation system having an ion source and an extraction electrode for extracting ions from the ion source, in which the extraction electrode is associated with an electrical heater, the heater adapted, during ion extraction, to maintain the extraction electrode at elevated temperature above the condensation temperature of gaseous or vaporous material leaving the ion source, the method comprising electrically heating the extraction electrode while extracting ions from the ion source and including the steps of operating the ion source and thereafter discontinuing operation of the ion source and subjecting the extraction electrode surface to cleaning by flow of reactive gas.

Provisional Patent Application No. It also relates to a method and apparatus for operating an ion source to produce an ion beam for ion implantation of semiconductor substrates and substrates for flat panel displays. In particular the invention concerns extension of the productive time i. An ion source typically employs an ionization chamber connected to a high voltage power supply.

The ionization chamber is associated with a source of ionizing energy, such as an arc discharge, energetic electrons from an electron-emitting cathode, or a radio frequency or microwave antenna, for example. A source of desired ion species is introduced into the ionization chamber as a feed material in gaseous or vaporized form where it is exposed to the ionizing energy. Extraction of resultant ions from the chamber through an extraction aperture is based on the electric charge of the ions.

An extraction electrode is situated outside of the ionization chamber, aligned with the extraction aperture, and at a voltage below that of the ionization chamber. The electrode draws the ions out, typically forming an ion beam. Depending upon desired use, the beam of ions may be mass-analyzed for establishing mass and energy purity, accelerated, focused and subjected to scanning forces. The beam is then transported to its point of use, for example into a processing chamber. As the result of the precise energy qualities of the ion beam, its ions may be implanted with high accuracy at desired depth into semiconductor substrates.

The precise qualities of the ion beam can be severely affected by condensation and deposit of the feed material or of its decomposition products on surfaces of the ion beam-producing system, and in particular surfaces that affect ionization, ion extraction and acceleration. The Ion Implantation Process The conventional method of introducing a dopant element into a semiconductor wafer is by introduction of a controlled energy ion beam for ion implantation.

The impurity elements are selected to bond with the semiconductor material to create electrical carriers, thus altering the electrical conductivity of the semiconductor material. The concentration of dopant impurities so introduced determines the electrical conductivity of the doped region. Many such N- and P-type impurity regions must be created to form transistor structures, isolation structures and other such electronic structures, which collectively function as a semiconductor device.

To produce an ion beam for ion implantation, a gas or vapor feed material is selected to contain the desired dopant element. The gas or vapor is introduced into the evacuated high voltage ionization chamber while energy is introduced to ionize it. This creates ions which contain the dopant element for example, in silicon the elements As, P, and Sb are donors or N-type dopants, while B and In are acceptors or P-type dopants.

An accelerating electric field is provided by the extraction electrode to extract and accelerate the typically positively-charged ions out of the ionization chamber, creating the desired ion beam.

When high purity is required, the beam is transported through mass analysis to select the species to be implanted, as is known in the art. The ion beam is ultimately transported to a processing chamber for implantation into the semiconductor wafer. Similar technology is used in the fabrication of flat-panel displays FPD ' s which incorporate on-substrate driver circuitry to operate the thin-film transistors which populate the displays.

The substrate in this case is a transparent panel such as glass to which a semiconductor layer has been applied. Ion sources used in the manufacturing of FPD ' s are typically physically large, to create large-area ion beams of boron, phosphorus and arsenic-containing materials, for example, which are directed into a chamber containing the substrate to be implanted. Most FPD implanters do not mass-analyze the ion beam prior to its reaching the substrate.

Ion Contamination In general, ion beams of N-type dopants such as P or As should not contain any significant portion of P-type dopant ions, and ion beams of P-type dopants such as B or In should not contain any significant portion of N-type dopant ions.

Since the chemical reaction is exothermic, energy is released during the reaction, elevating the chamber temperature. A dedicated endpoint detector , in communication with the vacuum housing , is used to monitor the reactive gas products during chemical cleaning. Apparatus for in-situ chamber cleaning. It contains required facilities for the ion source such as pumping systems, power distribution, gas distribution, and controls. A temperature detector is arranged to detect substantial termination of an exothermic reaction of the reactive gas with contamination on a surface of the system.

Extraction bushing breakdown boron implant. Featured Presentation

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USA1 - Ion implantation ion source, system and method - Google Patents

Effective date : Various aspects of the invention provide improved approaches and methods for efficiently: Vaporizing decaborane and other heat-sensitive materials via a novel vaporizer and vapor delivery system; Delivering a controlled, low-pressure drop flow of vapors, e. Provisional Patent Application No. The invention provides production-worthy ion sources and methods capable of using new source materials, in particular, heat-sensitive materials such as decaborane B 10 H 14 , and hydrides and dimer-containing compounds novel to the ion implantation process, to achieve new ranges of performance in the commercial ion implantation of semiconductor wafers.

The invention enables shallower, smaller and higher densities of semiconductor devices to be manufactured, particularly in Complementary Metal-Oxide Semiconductor CMOS manufacturing.

In addition to enabling greatly enhanced operation of new ion implanter equipment in the manufacture of semiconductor devices, the invention enables the new ion source to be retrofit into the existing fleet of ion implanters with great capital cost savings.

Embodiments of the invention uniquely implant decaborane and the other dopant materials in particularly pure ion beams, enabling a wide range of the needs of a fabrication facility to be met.

Various novel constructional, operational and process features that contribute to the cost-effectiveness of the new technology are applicable as well to prior technology of the industry. As is well known, ion implantation is a key technology in the manufacture of integrated circuits ICs. In the manufacture of logic and memory ICs, ions are implanted into silicon or GaAs wafers to form transistor junctions, and to dope the well regions of the p-n junctions. By selectively controlling the energy of the ions, their implantation depth into the target wafer can be selectively controlled, allowing three-dimensional control of the dopant concentrations introduced by ion implantation.

The dopant concentrations control the electrical properties of the transistors, and hence the performance of the ICs. For those species which are of solid elemental form, many are obtainable in gaseous molecular form, such as fluoride compounds that are ionizable in large quantities at significantly elevated temperatures. The ion implanter is a manufacturing tool which ionizes the dopant-containing feed materials, extracts the dopant ions of interest, accelerates the dopant ions to the desired energy, filters away undesired ionic species, and then transports the dopant ions of interest to the wafer at the appropriate energy for impact upon the wafer.

The presence in the implanter of certain elements, such as the disassociated element fluorine, is detrimental to the implanted wafers, but, despite such drawbacks, trace amounts of such contaminants have been tolerated in many contexts, in the interest of achieving production-worthy throughput volume. Lower contaminant levels from what is now achievable is desired. In a complex relationship, overall, a number of variables must be controlled in order to achieve a desired implantation profile for a given ion implantation process:.

These variables affect the electrical performance, minimum manufacturable size and maximum manufacturable density of transistors and other devices fabricated through ion implantation. A typical commercial ion implanter is shown in schematic in FIG. The ion beam I is shown propagating from the ion source 42 through a transport i. A portion of the beam is focused by the magnet 43 onto a mass resolving aperture The aperture size lateral dimension determines which mass-to-charge ratio ion passes downstream, to ultimately impact the target wafer 55 , which typically may be mounted on a spinning disk The beam current passing aperture 44 can be monitored by a moveable Faraday detector 46 , whereas a portion of the beam current reaching the wafer position can be monitored by a second Faraday detector 47 located behind the disk The ion source 42 is biased to high voltage and receives gas distribution and power through feedthroughs The source housing 49 is kept at high vacuum by source pump 50 , while the downstream portion of the implanter is likewise kept at high vacuum by chamber pump The ion source 42 is electrically isolated from the source housing 49 by dielectric bushing The ion beam is extracted from the ion source 42 and accelerated by an extraction electrode In this case, the ion beam impacts the wafer 55 with ion energy E.

In other implanters, as in serial implanters, the ion beam is scanned across a wafer by an electrostatic or electromagnetic scanner, with either a mechanical scan system to move the wafer or another such electrostatic or electromagnetic scanner being employed to accomplish scanning in the orthogonal direction. A part of the system of great importance in the technology of ion implantation is the ion source.

This type of source is commonly the basis for design of various ion implanters, including high current, high energy, and medium current ion implanters. The ion source a is mounted to the vacuum system of the ion implanter through a mounting flange b which also accommodates vacuum feedthroughs for cooling water, thermocouples, dopant gas feed, N 2 cooling gas, and power. The dopant gas feed c feeds gas, such as the fluorides of a number of the desired dopant species, into the arc chamber d in which the gas is ionized.

Also provided are dual vaporizer ovens e, f inside of the mounting flange in which solid feed materials such as As, Sb 2 O 3 , and P may be vaporized. The ovens, gas feed, and cooling lines are contained within a water cooled machined aluminum block g.

The water cooling limits the temperature excursion of the aluminum block g while the vaporizers, which operate between C and C, are active, and also counteracts radiative heating by the arc chamber d when the ion source is active.

The arc chamber d is mounted to, but designedly is in poor thermal contact with, the aluminum block g. The ion source a employs an arc discharge plasma, which means that it operates by sustaining within a defined chamber volume a generally narrow continuous electric arc discharge between hot filament cathode h, residing within the arc chamber d, and the internal walls of the arc chamber d.

The arc produces a narrow hot plasma comprising a cloud of primary and secondary electrons interspersed with ions of the gas that is present. Since this arc can typically dissipate in excess of W energy, and since the arc chamber d cools only through radiation, the arc chamber in such Bernas ion sources can reach a temperature of C during operation. The gas is introduced to arc chamber d through a low conductance passage and is ionized through electron impact with the electrons discharged between the cathode h and the arc chamber d and, as well, by the many secondary electrons produced by the arc discharge.

To increase ionization efficiency, a substantial, uniform magnetic field i is established along the axis joining the cathode h and an anticathode j by externally located magnet coils, 54 as shown in FIG. This provides confinement of the arc electrons, and extends the length of their paths. The trajectory of the thus-confined electrons results in a cylindrical plasma column between the cathode h and anticathode j. The arc plasma density within the plasma column is typically high, on the order of 10 12 per cubic centimeter; this enables further ionizations of the neutral and ionized components within the plasma column by charge-exchange interactions, and also allows for the production of a high current density of extracted ions.

The ion source a is held at a potential above ground i. The cathode h of such a conventional Bernas arc discharge ion source is typically a hot filament or an indirectly-heated cathode which the thermionically emits electrons when heated by an external power supply. It and the anticathode are typically held at a voltage V c between 60V and V below the potential of the ion source body V a.

Once an arc discharge plasma is initiated, the plasma develops a sheath adjacent the exposed surface of the cathode h within chamber d. This sheath provides a high electric field to efficiently extract the thermionic electron current for the arc; high discharge currents e. In addition to the heat dissipated by the arc, the hot cathode h also transfers power to the walls of the arc chamber d. Thus, the arc chamber d provides a high temperature environment for the dopant arc plasma, which boosts ionization efficiency relative to a cold environment by increasing the gas pressure within the arc chamber d, and by preventing substantial condensation of dopant material on the hot chamber walls.

If the solid source vaporizer ovens e or f of the Bernas arc discharge ion source are used, the vaporized material feeds into the arc chamber d with substantial pressure drop through narrow vaporizer feeds k and l, and into plenums m and n. The plenums serve to diffuse the vaporized material into the arc chamber d, and are at about the same temperature as the arc chamber d.

Radiative thermal loading of the vaporizers by the arc chamber also typically prevents the vaporizers from providing a stable temperature environment for the solid feed materials contained therein below about C. A very significant problem which currently exists in the ion implantation of semiconductors is the limitation of production-worthy ion implantation implanters that prevents effective implanting of dopant species at low e.

One critically important application which utilizes low-energy dopant beams is the formation of shallow transistor junctions in CMOS manufacturing. As transistors shrink in size to accommodate more transistors per IC according to a vital trend, the transistors must be formed closer to the surface of the target wafer.

This requires reducing the velocity, and hence the energy, of the implanted ions, so that they deposit at the desired shallow level. The most critical need in this regard is the implantation of low-energy boron, a p-type dopant, into silicon wafers. Since boron atoms have low mass, at a given energy for which the implanter is designed to operate, they must have higher velocity and will penetrate deeper into the target wafer than other p-type dopants; therefore there is a need for boron to be implanted at lower energies than other species.

Ion implanters are relatively inefficient at transporting low-energy ion beams due to space charge within the ion beam, the lower the energy, the greater the problem. The space charge in low energy beams causes the beam cross-section area i. When the beam profile exceeds the profile for which the implanter's transport optics have been designed, beam loss through vignetting occurs.

For example, at eV transport energy, many ion implanters currently in use cannot transport enough boron beam current to be commercially efficient in manufacturing; i. In addition, known ion sources rely on the application of a strong magnetic field in the source region.

Since this magnetic field also exists to some extent in the beam extraction region of the implanter, it tends to deflect such a low-energy beam and substantially degrade the emittance properties of the beam, which further can reduce beam transmission through the implanter. An approach has been proposed to solve the problem of low-energy boron implantation: molecular beam ion implantation.

The resulting implantation depth and dopant concentration dose of the two methods have been shown to be generally equivalent, with the decaborane implantation technique, however, having significant potential advantages. Since the transport energy of the decaborane ion is ten times that of the dose-equivalent boron ion, and the ion current is one-tenth that of the boron current, the space charge forces responsible for beam blowup and the resulting beam loss can potentially be much reduced relative to monatomic boron implantation.

Decaborane is a solid material which has a significant vapor pressure, on the order of 1 Torr at 20 C, melts at C, and decomposes at C. To be vaporized through preferred sublimination, it must therefore be vaporized below C, and it must operate in a production-worthy ion source whose local environment walls of the ionization chamber and components contained within the chamber is below C to avoid decomposition. Also, the vaporizers of current ion sources cannot operate reliably at the low temperatures required for decaborane, due to radiative heating from the hot ion source to the vaporizer that causes thermal instability of the molecules.

The vaporizer feed lines k, l can easily become clogged with boron deposits from decomposed vapor as the decaborane vapor interacts with their hot surfaces.

Hence, the present production-worthy implanter ion sources are incompatible with decaborane ion implantation. Prior efforts to provide a specialized decaborane ion source have not met the many requirements of production-worthy usage. More broadly, there are numerous ways in which technology that has been common to the industry has had room for improvement. Cost-effective features, presented here as useful in implementing the new technology, are applicable to implementation of the established technology as well.

Various aspects of the invention provide improved approaches and methods for efficiently:. Embodiments of the present invention can enhance greatly the capability of new ion implantation systems and can provide a seamless and transparent upgrade to end-users' existing implanters. In particular, aspects of the invention are compatible with current ion implantation technology, such that an ion source constructed according to the invention can be retrofitted into the existing fleet of ion implanters currently installed in expensive fabrication plants.

Embodiments of the invention are 1 constructed, sized and arranged such that they fit into the existing ion source space of commercial implanters, and 2 employ a novel control system for the ion source which can physically replace the existing ion source controller, without further modification of the implanter controls and qualified production techniques.

According to one aspect of the invention, an ion source capable of providing ions in commercial ion current levels to the ion extraction system of an ion implanter is provided, the ion source comprising an ionization chamber defined by walls enclosing an ionization volume, there being an ion extraction aperture in a side wall of the ionization chamber, the aperture having a length and width sized and arranged to enable the ion current to be extracted from the ionization volume by the extraction system.

The invention features a broad beam electron gun constructed, sized and arranged with respect to the ionization chamber to direct an aligned beam of primary electrons through the ionization chamber to a beam dump maintained at a substantial positive voltage relative to the emitter voltage of the electron beam gun.

Preferably the beam dump is thermally isolated from the ionization chamber or separately cooled. The axis of the beam path of the primary electrons extends in a direction generally adjacent to the aperture, the electron beam having a dimension in the direction corresponding to the direction of the width of the extraction aperture that is about the same as or larger than the width of the aperture, a vaporizer arranged to introduce e.

In preferred embodiments the electron gun is mounted on a support that is thermally isolated from the walls of the ionization chamber. Preferred embodiments of these and other aspects of the invention have one or more of the following features:. A vaporizer is incorporated into the ion source assembly in close proximity to the ionization chamber and communicating with it through a high conductance, preferably along a line of sight path, and is constructed to be controllable over part or all of the range of 20 C to C.

The beam dump has an electron-receiving surface larger than the cross-section of the electron beam entering the ionization chamber. The electron gun produces a generally collimated beam, in many instances, preferably the electron gun being generally collimated while transiting the ionization chamber.

The beam dump is mounted on a dynamically cooled support, preferably a water-cooled support. The electron gun is mounted on a dynamically cooled support, preferably, a water-cooled support. The electron gun cathode is disposed in a position remote from the ionization chamber. The volume occupied by the electron gun cathode is evacuated by a dedicated vacuum pump.

The ion source electron gun includes a cathode and variable electron optics that shape the flow of electrons into a beam of selected parameters, including a general dispersion of the electrons, and a profile matched to the extraction aperture, preferably in many cases the electrons being in a collimated beam within the ionization chamber.

The electron gun comprises a high transmission electron extraction stage capable of extracting at least the majority of electrons from an emitter of the gun, the extraction stage followed by a collimator and further electron optic elements, in preferred embodiments the further electron optics comprising an electron zoom lens or electron optics constructed to have the capability to vary the energy and at least one magnification parameter of the electron beam, preferably both linear and angular magnification of the beam and in preferred embodiments the electron optics comprising a five or more element zoom lens.

The ion source is constructed, sized and arranged to be retrofit into a pre-existing ion implanter, into the general space occupied by the original ion source for which the implanter was designed. The ion source is constructed and arranged to cause the electron beam to have a profile matched to the opening of the ion extraction aperture, preferably the cross-section being generally rectangular.