WO2001006041A1

WO2001006041A1 - Method and apparatus for production of a doped feed rod by ion implantation

Info

Publication number: WO2001006041A1
Application number: PCT/DK2000/000402
Authority: WO
Inventors: Leif Jensen; Jan Vedde
Original assignee: Topsil Semiconductor Materials A/S
Priority date: 1999-07-19
Filing date: 2000-07-14
Publication date: 2001-01-25
Also published as: AU5966600A

Abstract

A method and apparatus for production of a doped feed rod comprising implanting a dopant (17) into or below the surface of a feed rod (1) by impacting an electrically accelerated atomic or molecular species (7) of said dopant on said feed rod; use of a doped feed rod for the production of a doped single crystal, in particular a doped silicon single crystal; methods and apparatus for production of a doped single crystal; a method of producing a doped feed rod having a non-natural abundance of dopant isotopes, and a doped single crystal obtainable therefrom.

Description

METHOD AND APPARATUS FOR PRODUCTION OF A DOPED FEED ROD BY ION IMPLANTATION

DESCRIPTION

BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for production of a doped feed rod by ion implantation.

The Technical Field

Single crystals are typically grown from feed rods by crystal growth methods such as the floating zone (FZ) crystal growth method, or the Czochralski (CZ) crystal growth method.

The FZ method is preferred for production of crystals of silicon for high-power semiconductor devices because a high degree of purity can be achieved. The CZ method is preferred for production of crystals of silicon for semiconductor VLSI devices because very large single crystals can be achieved.

Generally, for the production of a doped single crystal, such as a doped silicon single crystal which is doped with boron or phosphorus, there is a number of ways of incorporating the dopant, or a precursor therefor.

Thus, the single crystal can be doped with the dopant; the feed rod from which the single crystal is produced can be doped with the dopant; or the dopant can be incorporated during the production of the single crystal, typically by introducing the dopant into the molten zone, i.e. either the molten phase of the feed rod, the crystal growing phase of the single crystal, or both.

The dopant or a precursor therefor is incorporated into the growing crystal, primarily controlled by the equilibrium distribution coefficients of the dopant inside or outside of the crystal, to provide a homogeneous distribution, e.g. axial and radial distribution, of dopant m the doped single crystal.

A homogeneous distribution is important for most doped single crystal applications, such as semiconductor applications .

The degree of homogeneity of the dopant depends upon a number of factors including factors such as the dopant itself, the doping method, and the influence of crystal growth parameters .

Ion implantation is a process m which energetic, charged atoms or molecules are directly introduced into a substrate. Specifically, ionic dopants of e.g. B, Al, Sb, P, Ag and Au have been implanted m polycrystallme silicon. Acceleration energies range between 10-200 keV for most ion implanters, although energies as high as several MeV are being utilized m high-energy implant systems .

Known ion implanting techniques include focusing a beam of dopant ions on the surface of a molten semiconductor material in the neighbourhood of a crystal being pulled while being rotated; ion implantation on a polycrystallme, multipass zone refined ingot rod of silicon while being rotated; and ion implanting a desired dopant in a layer of a rotating feed rod close to the surface. Common to these techniques is the requirement of complex equipment to mechanically move and rotate the feed rod.

Alternatively, the feed rod can be fixed and the ion beam moved perpendicularly to the longitudinal axis of the feed rod, which, however, requires even more complex equipment .

Prior Art Disclosures

W. Keller and A. Muhlbauer 'Floating Zone Silicon", Preparation and properties of solid state material, Volume 5, Marcel Dekker, Inc., New York, USA, (1981)

and W. C. O'Mara, R. B. Herring and L. P. Hunt, 'Handbook of Semiconductor Silicon Technology", Noyes Publications, New Jersey, USA, (1990)

disclose various doping techniques and single crystal growing techniques.

GB 1 186 127 discloses a method and apparatus for doping semiconductors wherein a beam of dopant ions is focused on the surface of the molten semiconductor material m neighbourhood of the crystal being pulled while being rotated. Dopant ions such as boron, aluminium, antimony, phosphorous, silver or gold are injected into the molten material. Magnetic deflection can be used to isolate pure dopant ions from impurities m the dopant. Resistivities of 1-100 ohm-cm of the pulled doped silicon crystal are reported .

US 4 094 730 discloses a multipass method of fabricating a doped silicon single crystal from a polycrystallme mgot rod of silicon. A polycrystallme rod is refined by multipass zone refining. Electrical dopants to provide P type and N type material are then ion implanted on the clean rod by conventional ion beam implantation as the rod is rotated. A single crystal zone melt pass is then made by moving a zone heater converting the polycrystallme rod into a single crystal structure and distributing the dopant through the clean region of the crystal. Resistivities of 0.1 - 100 ohm-cm of the produced single crystal material is reported.

DE 24 15 717 discloses a method of doping a semiconductor feed rod by ion implanting a desired dopant concentration m a layer of a rotating feed rod close to the surface and subsequently distributing the dopant a cross the feed rod by zone melting. Alternatively, the feed rod can be fixed and the ion beam can moved perpendicular to the longitudinal axis of the feed rod to provide a zig-zag line type doping layer on a part of the rod. The doped layer of the feed rod can be protected by a protective layer to prevent evaporation of dopant during a subsequent zone melting process. Such a moving ion beam is difficult and expensive to achieve.

Japanese Patent Application Publication No. 63 297 211 discloses a Si-B alloy dopant material for production of

Si-s gle crystals by the pulling up method wherein the dopant material contain B comprising more than 95 wt-%

B and less than 5 wt- B thereby reducing segregation of B dopant and provide uniform electrical characteristics of a wafer of the single crystal. DISCLOSURE OF THE INVENTION

Object of the Invention

It is an object of the present invention to seek to provide an improved method and apparatus for producing a αoped feed rod by ion implantation, particular a simplified method and apparatus for producing a doped silicon feed rod with an accurately assessable amount of dopant.

It is another object of the present invention to seek to provide an improved method and apparatus to produce a doped single crystal, m particular a doped silicon single crystal.

It is a further object of the present invention to seek to provide an improved method and apparatus to produce a αoped feed rod which provides an improved distribution of dopants.

In another aspect, it is the object of the present invention to seek to provide a doped single crystal which can easily be distinguished from known doped single crystals, in particular a doped silicon single crystal.

Further objects appear from the description elsewhere.

Solution According to the Invention

'Doped Feed Rod by Ion Implantation"

In an aspect of the invention, there is provided a method of producing a doped feed rod by ion implantation as claimed m claim 1, said method comprising implanting a dopant into or below the surface of an axially moving, non-rotatmg feed rod by laterally impacting an electrically accelerated atomic or molecular species of said dopant on said feed rod.

It has surprisingly turned out that by implanting a dopant into or below the surface of an axially moving, non-rotatmg feed rod by impacting an electrically accelerated atomic or molecular species of said dopant on said feed rod, doped feed rods which are particularly suited for the production of doped single crystals and which exhibit accurately assessable amounts of dopants can be produced by simplified mechanical feed rod moving equipment .

"Ion implantation by impacting"

The term 'impacting an electrically accelerated atomic or molecular species of said dopant on said feed rod" is intended to mean that the electrically accelerated atomic or molecular species which have been provided with a suitable energy through an electrical acceleration process (typically m an electrostatic field providing an energy of the accelerated specie larger than 10 keV) is directed onto the feed rod, the latter being a suitable state e.g. solid or liquid, for impact therewith and exchange of energy with the feed rod atoms until they come to rest. The electrically accelerated atomic or molecular species of the dopant can both be m a charged state and in an uncharged state at impact.

The amount of implanted dopant can be accurately determined from a measurement of the amount of electrically accelerated atomic or molecular species, or from a derivative thereof. Also, the concentration of dopant can be accurately controlled which is important m designing doped single crystals having desired properties .

"Atomic or molecular species of said dopant"

The expression an 'atomic or molecular species of said dopant" is intended to mean an atom or a molecule, or a composition thereof which comprises the dopant and which can become accelerated to an energy which is sufficient for implanting the dopant into or below the surface of the feed rod. Preferred embodiments of the atomic or molecular species of the dopant are described further nereinbelow .

Acceleration for impacting ionic species is known in the art, e.g. from various ion acceleration techniques, see e.g. S. Wolf and R.N. Tauber "Silicon Processing for the VLSI Era", Volume 1 - Process Technology, Lattice Press, California, USA, (1986) .

"Feed rod"

It is intended that the term "feed rod" designates any suitable preform, or mgot, of a material which is suitable of providing a melt of the material from which a single crystal is grown.

The feed rod may have any shape suitable for the specific method and apparatus used. Especially, the feed rod is not limited to a cylindrical shape which is often associated with a narrow meaning of the word "rod".

Also, generally, the term 'feed rod" should not be interpreted a narrow sense which is often associated with "feeding" of a material in a continuous process, although, in a preferred embodiment, the feed rod is used in a continuous process, the floating zone crystal growth method. The term "feed rod" is also intended to encompass feeding materials for batch, or semi-batch or se i- contmuous process, e.g. the Czochralski crystal growth method .

Iαedlly, as for any melt-dop g method, the feed rod should be pure, i.e. the impurity content should be small compared to the dopant level. However, for very accurate doping, impurities of dopant present the feed rod have to be tal en into account, when calculating the dose of αopant .

Examples of feed rods are cylindrical rods of high resistivity polycrystallme silicon for use float zone silicon crystal growth, e.g. supplied by Advanced Silicon Materials Inc., Washington State, USA.

The feed rod can be any suitable state, liquid or solid at implantation of dopant into or below the surface of the feed rod.

Preferred embodiments

"Acceleration of dopant"

The atomic or molecular species of the dopant can be accelerated by any suitable method known the art, see e.g. S. Wolf and R.N. Tauber "Silicon Processing for the VLSI Era", Volume 1 - Process Technology, Lattice Press, California, USA, (1986) disclosing various ion implanting techniques . In an embodiment, the accelerated atomic or molecular species is accelerated by an electrical field, whereby it is obtained that charged dopants, or dopants which are chargeable, can easily be accelerated to the desired energy which is sufficient to ensure the desired implantation. The electrical field can be constant or variable .

Thus, a skilled person can select the type of charged dopant, e.g. by charge/mass separation of the various isotopes of elemental dopants, e.g. the natural isotopes of B and B of boron, or a precursor e.g. radioactive isotope decaying to a desired dopant, and the dopant can be provided with sufficient energy at impact to be implanted the desired depth of the feed rod, i.e. either on the surface, m the surface, or below the surface of the feed rod. Consequently, the term "into or below the surface" is intended to include dopant conditions providing implantation of dopant on the surface as well as below it.

A slilled person can simply establish a relation between the energy of the dopant of interest and its range m the feed rod material, the latter optionally determined by various chemical or instrumental analysis techniques such as mass spectrometry, see e.g. Schroder, D.K. "Semiconductor Material and Device Characterization", A Wiley-Interscience Publication, John Wiley & Sons, New York, USA (1990) .

It is preferred that the electrically accelerated atomic or molecular species of said dopant is m a charged state at impact on said feed rod whereby known charged particle accelerator can be used to directly impact the desired species of the dopant into or below the surface of the feed rod.

In some applications, however, it may be an advantage to further control the range of the dopant m the feed rod, i.e. the distance an accelerated dopant species travels in the feed rod before co ing to rest. For this purpose, a charge neutral dopant species will generally have a longer range and travel deeper into the feed rod before coming to rest due to less affinity towards the electrons of the feed rod material.

Consequently, in another preferred embodiment, the electrically accelerated atomic or molecular species of said dopant is transformed into a neutral state at impact

"Charge/mass separation - isotope selection"

Generally, electrically accelerated dopant species will follow trajectories m the electric field which depend on the charge/mass ratio of the dopant species. Consequently, the species impacting on the feed rod can be selected with respect to their charge/mass ratio. Specifically, for elemental dopants, they can be selected with respect to their isotopes. This provides a unique method of selecting the isotope of the dopant to be implanted into or below the surface of the feed rod.

Consequently, doped feed rods can be produced which exhibit a specific isotope distribution of dopant elements, particular an improved distribution of dopants which provides a reduced variability of segregation of the dopant during the single crystal growth process. Accordingly, another aspect of the invention, the present invention provides a doped feed rod which has a non-natural abundance of isotopes of at least one element of the dopant.

In an embodiment the non-natural abundance of isotopes consists of at least two isotopes whereby e.g. the segregation of the dopant consisting of more isotopes can be controlled by varying the amounts of isotopes of the dopant .

In another embodiment the non-natural abundance of isotopes essentially consists of one isotope whereby isotopic effects on dopant segregation can be avoided.

Tne method of providing a non-natural abundance of dopant isotope is not limited to doped feed rods. The non-natural abundance of dopant isotopes is also transferred to the doped single crystal grown therefrom.

Also, as disclosed for still another aspect of the invention there is provided a method of producing a doped single crystal wherein an accelerated atomic or molecular species of the dopant is impacted into a melt of feed rod material, into a grown single crystal therefrom, or into both the melt and the grown single crystal, the non- natural abundance of dopant isotopes is also provided.

An embodiment of this method comprises impacting of said atomic or molecular species into the floating zone of a feed rod/growing single crystal produced by the floating zone single crystal growth method. In a preferred embodiment the doped single crystal is a doped silicon crystal.

"Finger prints"

The method according to the invention offers a unique method of providing a specific isotopic dopant implantation "finger print" which can be used to measure and check whether a given doped feed rod or a material derived therefrom, e.g. a doped single crystal, has been produced by implantation of an accelerated atomic or molecular species of the dopant, thereby likely falling within doped feed rods of the present invention.

Thus, it can be established whether a doped feed rod or a doped single crystal is produced according to the present invention .

Of course monoisotopic elements such as Be, Na, Al, P, Sc, Mn, Co, As, Nb, Rh, I, Cs, Pr, Tb, Ho, Au, and Bi cannot be subject to such an isotopic selection, particularly of stable isotopes.

However, the concept of non-natural abundance of isotopes of dopants comprises radioactive isotopes, particular long-lived radioisotopes, which may be present detectable amounts. Radioactive isotopes may be measured by various techniques known in the art, including nuclear track techniques, neutron activation analysis, and mass spectrometry . Also, gamma-ray emitting radioisotopes can be measured directly by gamma-ray spectrometry.

The technique of neutron transmutation could be used to provide a non-natural abundance of isotopes of the dopant, except of course for the cases of monoisotopic elemental dopants like phosphorus (see above) .

"Randomised charge/mass ratio"

Generally, m a preferred embodiment, the electrically dccelerateα atomic or molecular species of the dopant is controlled with respect to its charge/mass ratio.

In some applications, it may not be desired to implant dopant of certain isotopes. Instead the natural abundance of isotopes for a given dopant is desired. This can be achieved by ensuring that all isotopes of the dopant are impacted on the feed rod.

Therefore, m another embodiment, the electrically accelerated atomic or molecular species of said dopant is randomised with respect to its charge/mass ratio.

Various methods of randomising the charge/mass ration can be used. In a simple method the magnetic field the ion analyser is made to sweep the beam of charged dopant species .

"Charged dopant species"

Generally, the atomic or molecular species of the dopant is brought into a suitable state wherein it can be electrostatically accelerated to an energy suitable for ensuring implantation of said dopant on its impact on said feed rod. At the impact of the accelerated atomic or molecular species on the feed rod, however, the species can be a charged state or m a neutral state. Preferably, the atomic or molecular species is in a charged state during acceleration whereby a useful method of measuring the amount of dopant by measuring the current of the accelerated atomic or molecular species, or an equivalent electrical current to neutralise it, including derivatives thereof such as integrated electrical current, electrical voltage, photoelectrons, or the like, can be obtained.

Sources of ions and electrons are known m the art. Examples of types of available ion sources include, but are not limited to, ion sources obtained by surface lomsation, field lonisation, sputtering, laser, electron beam lonisation, arc discharge, plasma beam, and RF plasma. For more details see C.E. Hill, "Ion and Electron sources", CERN, Geneva, Switzerland (1997) the content of which is incorporated by reference.

'Charge neutralisation"

Before impact, the accelerated charged dopant species can be neutralised by any suitable method known m the art.

In a preferred embodiment, the beam of accelerated dopant species is passed at close distance by a glowing filament whereby electrons can easily be exchanged and the dopant be neutralised.

Depending on the application, the advantage of using neutral species at impact is that their range the feed rod can be longer than for charged species. "State of the feed rod"

Generally, according to the present invention, the feed rod can be m any suitable state, liquid, solid, or both liquid and solid, at the time of implanting the dopant.

For some applications it is preferred that the feed rod is m a solid state at impact, e.g. to avoid the cost of energy to liquify the feed rod. Further, when the feed rod is in a solid state, the consequently lower temperatures imply that dopant species implanted into or below the surface of the doped feed rod are not easily evaporated off compared to impact at higher temperatures.

For some applications it is preferred that the feed rod is m a liquid state at impact, e.g. to take advantage of a more easy penetration into the feed rod material of the dopant species at elevated or high temperatures, and of an improved mixing of the dopant species with the feed rod atoms.

Accordingly, m a preferred embodiment, the feed rod is m a molten state at impact of the accelerated atomic or molecular of said dopant.

Protective layer"

In order to ensure as little evaporation of dopant species from the doped feed rod, either during implantation of dopant species on or below the surface of the feed rod, or in a subsequent processing step, e.g. during growth of a doped single crystal therefrom, a protective layer may be provided on the surface, in the surface, or below the surface of the feed rod. Accordingly, in a preferred embodiment, the doped feed rod is protected by a protective layer whereby loss of dopant is reduced or avoided, either during preparation, storage, or a subsequent processing step.

The protective layer and methods of providing a protective layer can be provided according to methods known m the art.

Preferred methods for providing a protective layer for the doped feed rod are selected from the group of processes consisting of annealation of the doped feed rod, oxidation of the doped feed rod, and deposition of a protective material onto the doped feed rod.

The protective layer can consist of any suitable material which is able to prevent the dopant species from being lost from the doped feed rod as discussed above and which does not adversely affect the properties and function of the final single crystal produced therefrom.

Examples of suitable protective materials are known the art.

In a preferred embodiment, the protective layer comprises a protective material which is composed of the same or a similar material as the feed rod material.

Examples of protective layers for doped silicon feed rods are silicon oxide, silicon nitride, silicon carbide, and amorphous or polycrystallme silicon. "Specific feed rod materials, dopants and their properties"

Generally, the dopants are selected according to the particular properties they are intended to impose to the doped single crystal.

Accordingly, m a preferred embodiment, the dopant comprises a material which is able to modify the properties of the feed rod material.

"Semiconducting feed rod materials"

In d preferred embodiment, the feed rod material is a serricorducting material comprising an element or a mixture of elements selected from the group of elements consisting of single elements of group IV, pair of elements chosen from group IV elements, pair of elements chosen from group III and group V elements, pair of elements chosen from group II and group VI elements, and pair of elements chosen from group IV and group VI elements of the Periodic Table of Elements.

More specifically, in a preferred embodiment, the semiconducting material is selected from the group consisting of Si, Ge, C, and SiC, or a combination thereof .

In a most preferred embodiment, the feed rod material essentially comprises silicon.

The term "essentially comprises" is intended to mean that besides the major component, the feed rod material may comprise other components e.g. impurities or additives such as dopants providing other desired properties. Generally, the feed rod material can be m any suitable form.

In preferred embodiments, the feed rod material is either amorphous or polycrystallme.

Also, the feed rod material may itself be a single crystal, or a doped single crystal, doped with one or more further dopants.

Properties'

Generally, the properties to be imposed by the dopant are any suitable property which a dopant can modify.

In preferred embodiments, the dopant modifies the electrical, mechanical, and optical properties of the material .

Electrical properties"

Typical properties are the electrical properties, e.g. resistivity and carrier life time, strain and/or stress properties, crystal structure controlling properties, and light emission properties. However, as mentioned, the method according to the present invention can be used to implant dopants providing other properties to the feed rod, the single crystal grown therefrom, or both.

The dopant for modifying the electrical properties of a semiconducting material can be of either N-type or P- type. In a preferred embodiment, the dopant is selected from the group consisting of N-type doping elements or P-type doping elements.

More specifically, m a preferred embodiment, the N-type doping element is selected from the group consisting of the group 5a elements: N, P, As, Sb, and Bi of the Periodic Table of Elements.

Also, more specifically, in another preferred embodiment, the P-type doping element is selected from the group consisting of the group 3a elements: B, Al , Ga, In, Ti of the Periodic Table of Elements.

"Charge carrier properties"

For many semiconductor applications, it is important to control the life time of the minority carriers which may influence e.g. the leak current and forward voltage drop of the semiconductor, see ASTM "Lifetime Factors m Silicon", American Society for Testing and Materials (1980) .

Consequently, in a preferred embodiment, the dopant comprises an element which is able to modify the life time of charge carriers of a doped single crystal.

It is preferred that the charge carrier life time modifying element is selected from the group consisting of Au and Pt .

Acceleration of dopants of e.g. Au and Pt is known in the art . "Mechanical properties"

For many semiconductor applications, it is important to control the carrier mobility which is influenced by the distance between atoms the crystal lattice.

Consequently, m a preferred embodiment, the dopant comprises an element which is able to modify the strain and/or stress of a doped single crystal whereby lattice distances of the crystal lattice can be controlled.

In a preferred embodiment, the strain and/or stress modifying element is selected from the group consisting of C, Ge, and Sn.

Acceleration of dopants of e.g. C, Ge, and Sn is known in the art.

'Crystal structure"

In many applications of single crystals, the crystal structure is important m the sense that it often comprises various defects such as lattice sites having interstitial atoms, i.e. one or more additional atoms, or lattice sites having vacancies, i.e. one or more atoms are missing m the crystal lattice.

Both types of defects may influence carrier mobility, carrier lifetime, and diffusion rates of species m the lattice, mechanical strength of the lattice, and effects of impurities, See Mikkelsen, Jr. J.C., Pearton, J.S., Corbett, J.W., and Pennycook, S.J. "Oxygen, Carbon, Hydrogen and Nitrogen in Crystalline Silicon", Material Research Society, Pittsburgh, Pennsylvania, USA, (1986) . Consequently, in a preferred embodiment, the dopant comprises an element which is able to control the crystal structure of a doped single crystal whereby carrier mobility, carrier lifetime, and diffusion rates of species m the lattice, mechanical strength of the lattice, and effects of impurities can be controlled.

For example, getter sites for collection of unwanted impurities and diffusion rates of e.g. fast diffusing elements may be introduced the crystal lattice.

Specifically, m a preferred embodiment, the structure controlling element is selected from the group consisting of 0, C, N, and H.

Acceleration of dopants of e.g. 0, C, N, and H is known i tne art.

"Optical properties"

For many applications the optical properties of the single crystal is important.

Consequently, in a preferred embodiment, the dopant comprises an element which is able to control light emission, absorption and guidance of a doped single crystal .

Specifically, m a preferred embodiment, the light emission controlling element is selected from the group consisting of the rare earth metals, preferably Er.

Acceleration of dopants of e.g. Er is known in the art. Further preferred aspects and embodiments of methods for producing doped feed rods and doped single crystals are claimed in the claims 40-42, and 46-50.

Apparatus for producing doped feed rod and doped single crystal

The apparatus for producing a doped feed rod and a doped single crystal essentially comprises an ion implanter, e.g. a particle accelerator for the desired dopant; and a single crystal growing apparatus, e.g. a floating zone crystal growth apparatus, or a Czochralski crystal growth apparatus for growing a single crystal from the produced doped feed roα; both of which ion implanter and single crystal growing apparatus can be realised by a skilled person .

Generally, the apparatus can be operated as m subsequent operation steps, i.e. a doped feed rod is produced a first step, and then a doped single crystal is grown therefrom m a second step. However, the apparatus can be realised m a combination, whereby the implantation of the dopant is provided directly into or below the surface of the longitudinally moving feed rod which is zone melted for growing a single crystal from the thus doped feed rod.

In both aspects, the implantation of dopant by impacting an electrically accelerated atomic or molecular species of the dopant on the feed rod, either m solid or liquid form, or m the form of a single crystal being grown therefrom, is a common technical feature.

Consequently, according to an aspect, the invention relates to an apparatus for producing a doped feed rod, said apparatus comprising means for implanting a dopant into or below the surface of a feed rod, wherein said depart implanting means comprises means for electrically decelerating atomic or molecular species of said dopant for impact thereof on said feed rod.

In a preferred embodiment the dopant implanting means comprises means for electrically accelerating charged atomic or molecular species of said dopant.

In a further preferred embodiment, the dopant implanting means comprises means for providing charged atomic or molecular species of said dopant.

In a still further preferred embodiment, the dopant implanting means comprises means for neutralising the electrically accelerated charged atomic or molecular species of said dopant before impact on the feed rod.

In a another preferred embodiment, the apparatus further comprising means for wholly or partially bringing the feed rod in a molten state at impact of the accelerated atomic or molecular species of said dopant.

In a preferred embodiment, the apparatus further comprising a means for selecting the charge/mass ratio of the atomic or molecular species to be impacted on the feed rod.

In a preferred embodiment, the dopant implanting means comprises means for deflecting the accelerated atomic or molecular species of the dopant for controlling the point of impact thereof. Further preferred aspects and embodiments of apparatus for producing doped feed rods and doped single crystals are claimed in the claims 43-45, and 51-52.

Doped feed rod obtainable by the method

According to another aspect, the invention also relates to a doped feed rod obtainable by the method, such a doped feed rod exhibiting an accurately assessable amount of dopant.

Also, as previously described, such a doped feed rod may exhibit a non-natural abundance of isotopes of at least one element of the dopant.

This effect is particularly useful for providing a doped feed rod which can easily be distinguished through the non-natural isotope abundance "finger print" from doped feed rods produced according to prior art methods.

Use of doped feed rod

Further, according to still another aspect, the invention relates to use of such a doped feed rod for production of doped single crystals.

It is particularly surprising that a doped single crystal exhibiting an accurately controlled amount of dopant, and optionally exhibiting ^" a non-natural isotope abundance "finger print" can be provided.

Simultaneous production and doping of a single crystal

In still a further aspect of the invention, there is provided a method of producing a doped single crystal comprising providing a doped feed rod according to the invention; providing a melt of said feed rod material; and growing a single crystal from said melt while a further dopant, either the same or different from the dopant of the doped feed rod, is implanted into or below the surface of said melt, into or below the surface of said grown single crystal, or into or below the surface both of said melt and of said grown single crystal, by impacting an accelerated atomic or molecular species of said dopant on said melt, on said grown single crystal, or both on said melt and on said grown single crystal whereby it is ensured that particularly well controlled distributions of dopants can be obtained. Also, further dopants can be introduced.

Thus, since m this combination method, the point of impact and the exact dose of dopant can be controlled at any point of the feed rod, at any point of the melted feed rod, at any point of the growing or grown crystal, or any combination of these points of impact, simultaneously or independently of each other, the distribution of dopants can be very accurately controlled.

Preferably, the melt of said feed rod material for the single crystal is provided by an inductive heating which ensures a well defined zone of providing a melt of the feed rod and a growing zone of the single crystal being grown .

Further preferred embodiments and aspects of the present invention are defined in the claims. Doped feed rod having non-natural abundance of isotopes

Generally, ion implantation can provide non-natural abundance of the dopants independent of the relative movement of the feed rod with respect to the ion implanting beam.

Accordingly, m another aspect of the present invention, there is provided a method of producing a doped feed by ion implantation as claimed m claim 55 comprising implanting a dopant having a non-natural abundance of isotopes of at least one of its elements into or below the surface of a feed rod by impacting an electrically accelerated atomic or molecular species of the dopant on the feed rod, whereby various isotopic effects of dopant having elements with more isotopes can be controlled.

Specifically, the relative amounts of dopant isotopes, e.g. B and B, or ^" Sb and Sb, can be controlled, thereby improving the distribution of dopant, see the discussion in section "Charge/mass separation - isotope selection" .

In a preferred embodiment, the dopant can be chosen to essentially consist of the one or the other of such isotopes whereby e.g. isotopic effects on the dopant segregation during single crystal growth can be controlled.

For this aspect of the invention, the disclosure of the previously described method and apparatus also applies without being limited to simplified mechanical feed rod moving equipment. Measuring the distribution of dopant

The axial dopant distribution over the length of a single crystal is usually measured by means of electrical two- or four-point probe measurements, e.g. according to the ASTM standard F374-94a, see "1996 Annual book of ASTM Standards Electrical Insulation and Electronics", Volume 10.05 Electronic (II), ASTM, Pennsylvania, USA, disclosing standard test method for sheet resistance silicon epitaxial, diffused, polysilicon, and ion- implanted layers using an m-line four-point probe.

3. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, by way of examples only, the invention is further disclosed with detailed description of preferred embodiments. Reference is made to the drawings in which

Fig. 1 shows a side view sketch of a preferred embodiment of an apparatus according to the invention comprising means for implanting a dopant into or below the surface of a feed rod;

Fig. 2 shows a side view sketch of another preferred embodiment of an apparatus according to the invention as shown in fig. 1 further comprising means for growing a single-crystal, exemplified by an apparatus used carrying out the floating zone method;

Fig. 3 shows a side view sketch of still another preferred embodiment of an apparatus according to the invention as shown m fig. 2 wherein the means for implanting a further dopant impacts the dopant into or below a melted surface of the feed rod above the heat induction coil;

F g. 4 shows a side view sketch of still another preferred embodiment of an apparatus according to the invention as shown fig. 2 wherein the means for implanting a further dopant impacts the dopant into or below a melted surface of the feed rod below the heat induction coil;

Fig. 5 shows in more details a longitudinal cross sectional view sketch of the floating zone of apparatus snown m fig. 2;

Fig. 6 shows m more details a longitudinal cross sectional view sketch of the floating zone of apparatus shown m fig. 3; and

Figs. 7A-7C show three dimensional sketches of the implanted dopant species along the lines AA, BB, and CC Figs. 5 and 6, respectively.

4. DETAILED DESCRIPTION

Fig. 1 shows a side view sketch of a preferred embodiment of an apparatus according to the invention comprising means for implanting a dopant 17 (see Fig. 5), e.g. boron ions phosphorus ions, into or below the surface of a feed rod 1, e.g. an amorphous silicone rod. Such an ion implant equipment named "GIRAF" has been installed at the Physical & Astronomical Institute, Aarhus University, Denmark, see unpublished Internal Report by Bøgh, E., Dahl, P., Jørgensen, H.E, and Nielsen, K.O. (1965), and Carter, G. and Collmgton, J.S., 'Ion bombardment of Solids", Hememan Educational Books, Ltd., London (1968) for more details of the used particle accelerator. More recent published books about particle accelerators are available with updated technologies.

An example of a commercial apparatus is a modified version of model 350D implanter supplied by Varian Ion Implant Systems, 35 Dory Road, Gloucester, MA 01930, USA.

Means for providing charged atomic or molecular species of the dopant, e.g. exemplified by ions of boron or phosphorus m a plasma state, consists of an ion source 12, e.g. an ion source device supplied by Oxford Applied Research, Crawly Mill, Witney, Oxfordshire 0X8 5TJ, UK.

The charged atomic or molecular species are selected for their charge/mass-ratio by an analysing magnet 11 and are accelerated m an electrical field, here an electrostatic field 10. The beam of charged atomic or molecular species of the dopant is shaped and focused by beam shaping and focusing means, here exemplified by an ion focusing lens 9 forming an ion beam 7.

The ion beam 7 impacts atomic or molecular species of the dopant into or below the surface of the feed rod, here exemplified by ions impacting into or below the surface of the rod 1 m a solid state.

The amount of implanted dopant is measured by the current of the electrically accelerated atomic or molecular species, or by the electrical current of neutralising electron charge required to neutralise the electrically accelerated atomic or molecular species, here exemplified by electrical current measuring equipment 4 , e.g. an ampere meter model 485 Digital Picoammeter supplied from Keithley Instruments, Inc., 28775 Aurora Road, Cleveland, Ohio 44139, USA.

It should be understood that uncharged atomic or moleculdr species of the dopant may impact into or below the surface of the feed rod either a charged state or m an uncharged state. In the latter case, charge neutralisation of the charged state of the respective charged atomic or molecular species can be obtained by introducing a suitable charge conversion thereof, e.g. by introducing a charge stripper such as a glowing filament into or close to the ion beam. In this case the amount of implanted dopant can be measured by measuring the electrical current of neutralising electron charge required to neutralise the electrically accelerated atomic or molecular species.

The feed rod 1 is coupled mechanically to a shaft 2 for axial movement of the feed rod in the directions indicated by the arrow 5 without rotational movement. Suitable means for providing axial movement of the shaft is commercially available in equipment for pulling single crystals by the floating zone method, e.g. a model FZ 16 supplied from Topsil Semiconductor Materials A/S, Denmark, operated in a non-rotational mode.

The arrangement of means for implanting a dopant 17 (see Figs. 5, 7A-7C) into or below the surface of a feed rod 1, and the shaft 5 and feed rod 1 are placed a housing, here an ion implanting chamber 8 connected through a flange 18 to a process chamber 3 which is further connected to vacuum pumping equipment 6. The shaft 5 moves through a vacuum tight seal (not shown) . Vacuum pumping equipment is commercially available, e.g. a turbo molecular pumping unit model TSH 450H from Balzers Aktiengesellschaft, FL-9496 Balzers Furstentum, Liechtenstein .

In order to prevent loss of dopant during storage or shipment, the doped feed rod is provided a protective layer by subjecting it to oxidation, nitπdation or deposition of feed rod material by methods known m the

Fig. 2 shows a side view sketch of another preferred embodiment of an apparatus according to the invention as shown in fig. 1, said apparatus further comprising means for growing d single crystal 13, exemplified by a floating zone apparatus used in carrying out the floating zone method, see above reference to commercial equipment.

In still a further embodiment, the floating zone apparatus comprises means for wholly or partially bringing the doped feed rod m a molten state at impact of the accelerated atomic or molecular species of said dopant, here exemplified by a heating element 14 m a circular shape, e.g. an high RF induction coil supplied from Topsil Semiconductor Materials A/S, Denmark.

For growth of large size single crystals the apparatus may include means for supplying argon at a higher pressure (> 1 bar) thereby reducing the risk of spark over between the feed rod and/or the growth crystal at the induction coils.

Fig. 3 shows a side view sketch of still another preferred embodiment of an apparatus according to the invention as shown fig. 2 wherein the means for implanting the dopant impacts a further dopant into or below a melted surface of the feed rod. This particular embodiment provides the advantage of introducing a further dopant into a molten state of the feed rod whereby less impact energy of the dopant may be required.

Further, the impacting beam can be directed to the floating zone, i.e. the melt on top of the single crystal held together mamly because of its surface tension and magnetic forces (not shown), whereby the implantation of a further dopant m the feed rod can be located m a very well defined region of the melt neck of the doped feed rod during drawing of a single crystal thereof.

Also a more uniform axial and radial distribution of dopant in the single crystal can be obtained by selecting the further dopant to be that of the doped feed rod.

The radial dopant distribution is influenced by the rotation rate of the single crystal, the diameter of the single crystal and the manner the zone is heated by induction by the induction coil. Radial dopant can be influenced by permanent magnetic field which acts like a fluid break which can reduce the velocity of the convection.

By combining all these known techniques with accurate incorporation of further dopants into or below the surface of the molten part of the floating zone of the feed rod and/or the growing zone of the single crystal, the radial dopant distribution can be controlled. Also, further dopants can be introduced.

Fig. 4 shows doping of the molten part m the floating zone, by implanting concentration of dopant species into or below the surface of the molten surface, here below the induction coil 14. Deflection means, here exemplified by electrostatic deflection scanning plates 21 are sweeping the ion beam up and down (e.g. m the region indicated with reference numeral 22) whereby the point of impact 23, here below the induction coil, of the atomic or molecular species of the dopant into or below the molten surface, i.e. either above or below the induction coil, can be selected. The distribution of the dopant is controlled by the scanning frequency and the amplitude of voltage applied to the deflection plates 21.

Due to thermal convection and diffusion of dopant m the molten phase distribution the molten phase can cause a radial dopant distribution in the single crystal. Fig. 4 shows how a controlled radial distribution of dopant can be provided. By knowing the convection and temperature distribution the melt, the radial dopant dose needed to optimise the distribution can be calculated. Melt convection and temperature distribution can be calculated e.g. by using the software "Float Zone Simulation", supplied by CAPE Simulations, Inc., One Bridge Street, Newton, Massachusetts 02158, USA.

Fig. 5 shows in more details a longitudinal cross sectional view sketch of the floating zone of apparatus shown in fig. 2. In particular, the implanted layer of dopant 17 is shown. More details along the line A-A are shown in Fig. 7A.

The profile of the implanted layer is formed by the energetic ions penetrating the target surface. The ions lose their energy due to collisions with atomic nuclei (nuclear collision) and electrons (coulombs interaction) in the target, and eventually come to rest. In the latter mechanism, the energy transferred to the electrons can provide electrons m higher energy levels (excitation) , or provide ejection of free electrons ( lonisation) . Implanting energy below 10 KeV the nuclear collision is the dominant stopping process, and at an implanting energy above 10 KeV the stopping process is dominated by coulomb interaction.

Fig. 6 shows in more details a longitudinal cross sectional view sketch of the floating zone of apparatus shown m fig. 3. In particular, the implanted layer of dopant of the ion beam 7 is shown. More details along the line B-B are shown in Fig. 7B.

Diffusion of dopant m molten silicon is high compared to diffusion in solid silicon. The implanted dopant layer is mixed into rod material due to high large diffusion coefficient. Examples of diffusion coefficients of phosphor m solid silicon is 1*10^" m /s at 1300 °C, and diffusion coefficient of phosphor m molten phase silicon is 3.4 10^" m /s.

Figs. 7A, 7B, and 7C show three dimensional sketches of the implanted dopant species along the lines A-A, B-B, and C-C m Figs. 5 and 6, respectively.

Although, Fig. 7B indicates that identical distributions can be obtained along the lines B-B of the two embodiments of the invention shown m Figs. 5 and 6, this may not be the case. Depending on the point of impact of the ion beam 7, e.g. at the melt neck, no dopant species will appear m line B-B of Fig.6. 5 . EXAMPLES

Preferred embodiments of the invention are further illustrated by examples of production of doped feed rods 5 and doped single crystals.

Example 1 "Phosphorus doped silicon feed rod"

A silicon feed rod (Purity: boron < 0.02 ppb, phosphorus in < 0.03 ppb, carbon < 0.1 ppm, and lifetime > 1500 μs ) supplied by Advanced Silicon Materials Inc., State of Washington, USA was doped with phosphorus by the method and apparatus illustrated m Fig 1. The dopant species, here phosphorus ions produced by an ion source of red 15 pnosphorus (> 99 purity), was implanted into the feed rod using a 400 keV beam m the "GIRAF" research particle accelerator of Aarhus University, Denmark.

The silicon feed rod was moved without rotation with a 20 speed of 0.02 cm/s.

In the vacuum chamber, the pressure was adjusted and kept at sufficient pressure, a low pressure, less than 10^" mbar (10^" Pa), to ensure a stable flow of phosphorus 25 ions to the feed rod surface.

During implanting of the phosphorus ions, the electrical current flow between the rod and the ion implanter was measured. The flow of phosphorus ion was adjusted 30 depending of the speed of the feed rod to provide electrical current values the range 1*10^{"^} to 30*10^"" ampere. Typical values for the exemplified feed rods were electrical current values of about 10*10^"' ampere. The surface concentration of phosphorus ions m or below the surface of the feed rod was calculated as the number of atoms corresponding to the concentration of phosphorus m a doped single crystal which was grown of the feed rod .

Surface concentrations of phosphorus ions can vary with large limits depending on the application, e.g. m the range of 1*10 to 5*10 atoms/cm . Typical values for the feed rods used for growing the single crystals reported m Table 1 were 4*10 atoms/cm .

Similar results were obtained by rotating the longitudinally moving rod during implantation

Example 2 "Phosphorus doped silicon feed rods with protecting layers of silicon oxide, silicon nitride, or silicon"

"Silicon oxide"

A protective layer of silicon oxide was applied onto the surface of a phosphorus doped silicon feed rod produced as described m example 1 by heating doped silicon feed rods to 800 °C for one hour m 1 atmosphere of oxygen supplied at 2 1/mm m a four-stack furnace, Thermco Products Corporation, Orange, California, USA.

Alternatively, a silicon oxide layer was provided on a similar phosphorus doped feed rod by applying water at an elevated temperature of 500-800 °C . "Silicon nitride"

A protected layer was formed by thermally growing a film of silicon nitride on a phosphorus doped silicon feed rod produced as described in example 1. The feed rod was heated pure ammonia at a temperature the range 950- 1200 °C in a similar furnace as described above for silicon oxide.

Alternatively, a silicon nitride layer could be prepared by plasma enhanced CVD using a nitrogen-hydrogen gas mixture in the temperature range of 30 to 400 °C in a model AIX-200RD apparatus supplied by Aixtron AG, Achen, Germany .

'Silicon layer"

Growing a layer of feed rod material can also form a protected layer. The layer can be an amorphous or polycrystallme layer.

A protected layer was formed by chemical vapour deposition (CVD) of a gaseous feed rod material, here silane, on a phosphorus doped silicon feed rod produced as described in example 1.

The gaseous feed rod material was fed into a reaction chamber at an elevated temperature of 650 °C and 1 bar (10 Pa) pressure, and the reactants were allowed to react with the feed rod surface. The reaction process and growth rate is depending on temperature and pressure. A typical deposition rate of 30 nm/min was obtained at 650 °C and 1 bar pressure. Accelerated tests of the prepared doped silicon feed rods at temperatures of about 600 °C to the melting point of about 1400 °C for loss of dopant during heating in the subsequent steps of providing a doped silicon single crystal indicated that a sufficient dopant diffusion barrier could be obtained.

Example 3 "Phosphorus doped silicon single crystal"

0 Phosphorus doped silicon feed rods produced according to examples 1 and 2 were grown into single crystals using the floating zone method and conventional floating zone apparatus model FZ 16 supplied from Topsil Semiconductor Materials A/S, Denmark. c

The single-crystal dopant concentration N-, [atoms/cm^"] was calculated using the formula:

N = I / (v*d*d*π/4) 0 wherein I is the ion dose [atoms/s] measured as the electrical current measured between the feed rod and the ion implanter, i.e. the current measured by the ampere meter 4 shown Fig. 1 during implantation of the 5 dopant, v is the feed rod speed [cm/s], d is the feed rod diameter [cm]. Typical values are shown in Table 1.

It should be noted that this formula is only valid for circular round surface of the feed rod. However, it can 0 be modified according to the shape of the feed rod.

The obtained resistivities measured by the four-point probe ASTM standard test, F 374-94 are presented m Table 1. 5 As seen in Table 1, the three first listed phosphorus doped silicon single crystals (without a protective layer) show a range of dopant concentration calibration factors of 57-58 which implies that a batch-to-batch variability of less than 1 can be obtained.

Example 4 "Boron doped silicon feed rod"

A silicon feed rod similar to that used m example 1 was doped with boron by the method and apparatus illustrated Fig 1 and described in example 1 with the exception that boron ions of B (81.6 ) were implanted into the rod using a 200 KeV beam instead of a 400 keV beam of phosphorus ions .

The conditions of the pressure m the vacuum chamber and flow of phosphorus ions were as described m example 1.

Surface concentrations of boron ^* B ions can vary with large limits depending on the application. Values as indicated example 1 were obtained.

Typical values for the feed rod used for growing the single crystal reported in Table 2 were also as indicated in example 1.

Experiments using ' B (18,4 ) gave similar results.

Example 5 "Phosphorus doped silicon feed rods with protecting layers of silicon oxide, silicon nitride, or silicon"

Similar experiments with protective layers were carried out as described in example 2. Similar long term stability of boron doped silicon feed rods with protective layers can be obtained.

Example 6 "Boron doped silicon single crystal"

A boron doped silicon single crystals was grown by a similar method as described example 3.

The obtained resistivities are shown in Table 2.

A possible explanation of the lower calibration factor for boron doped silicon single crystal is the difference of diffusion coefficient of boron and phosphorus polycrystallme silicon.

Example 7 "Antimony doped silicon feed rod"

A silicon feed rod similar to that used m example 1 was doped with antimony by the method and apparatus illustrated in Fig 1 and described in example 1 with the exception that antimony ions of '^" Sb were implanted into the rod using a 200 KeV beam instead of a 400 keV beam of phosphorus ions .

The conditions of the pressure in the vacuum chamber and flow of phosphorus ions were as described in example 1.

Surface concentrations of antimony ^1_1Sb ions can vary with large limits depending on the application. Similar values as indicated m example 1 were obtained.

Typical values for the feed rod used for growing the single crystal reported in Table 4 were also as indicated in example 1. Experiments using ^L Sb gave similar results.

Example 8 "Antimony doped silicon single crystal"

An antimony doped silicon single crystals was grown by a similar method as described in example 3.

The obtained resistivities are shown Table 4.

A possible explanation of the lower calibration factor for antimony doped silicon single crystal is the difference of diffusion coefficient of antimony and phosphorus in polycrystallme silicon.

Table 1

Phosphorus doped silicon single crystals

CO c

CD (/) H

H C H

CO

X

m m

H

* Measured dose is obtained by measuring four-point resistivity and calculating average c value of all readings. The obtained average resistivity reading is converted to m ι concentration by using ASTM F 723 "Standard Practice for Conversion Between Resistivity and Dopant Density for Boron and Phosphors-Doped Silicon" .

** Crystal was grown from a silicon feed rod with a protective layer of silicon oxide. The silicon oxide layer was made as thermal oxidation in dry oxygen at 800 °C one hour.

Table 2

Boron doped silicon single crystal

CO c

CD CΛ

H

C H

0) * Measured dose is obtained by measuring four-point resistivity and calculating average

X rπ m value of all readings. The obtained average resistivity reading is converted to

H

3 concentration by using ASTM F 723 'Standard Practice for Conversion Between Resistivity and c r- Dopant Density for Boron and Phosphors-Doped Silicon" . m ι

Table 3

Boron doped silicon single crystal

Λ D /> C H

m

0) x m m * Measured dose is obtained by measuring four-point resistivity and calculating average

H value of all readings. The obtained average resistivity reading is converted to c r~ concentration by using ASTM F 723 "Standard Practice for Conversion Between Resistivity and m ιo Dopant Density for Boron and Phosphors-Doped Silicon" .

Table 4

Antimony doped silicon single crystal

O c

CD O H

H C H

m O x m m * Accurate predoping phase at start up end of rod

H

** Measured dose is obtained by measuring four-point resistivity and calculating average ιo value of all readings. The obtained average resistivity reading is converted to en concentration by using ASTM F 723 "Standard Practice for Conversion Between Resistivity and Dopant Density for Boron and Phosphors-Doped Silicon" .

Claims

METHOD AND APPARATUS FOR PRODUCTION OF A DOPED FEED ROD Bϊ' ION IMPLANTATION CLAIMS

1. A method of producing a doped feed rod by ion implantation, the method comprising implanting a dopant (17) into or below the surface of an axially moving, non- rotating feed rod (1) by laterally impacting an electrically accelerated atomic or molecular species (7) of said dopant on said feed rod.

2. method according to claim 1 wherein said electrically accelerated atomic or molecular species of said dopant is in a neutral state at impact on said feed rod.

3. A method according to claims 1-2 wherein said electrically accelerated atomic or molecular species of said dopant is controlled with respect to its charge/mass ratio .

4. A method according to claims 1-3 wherein the amount of said implanted dopant is measured by the current of the electrically accelerated atomic or molecular species, or by the electrical current of neutralising electron charge required to neutralise the electrically accelerated atomic or molecular species.

5. A method according to any of the preceding claims wherein said feed rod is in a molten state at impact of the accelerated atomic or molecular of said dopant.

6. A method according to any of the preceding claims wherein said doped feed rod is protected by a protective laye .

7. A method according to claim 6 wherein the protective layer is a layer obtained by a process selected from the group of processes consisting of annealation of the doped feed rod, oxidation of the doped feed rod, and deposition of a protective material onto the doped feed rod.

ό . A method according to claims 6 or 7 wherein the protective layer comprises a protective material which is composed of the same or a similar material as the feed rod material.

9. A method according to any of the preceding claims wnerem said dopant comprises a material which is able to modify the properties of the material of the feed rod.

10. A method according to claim 9 wherein the feed rod material is a semiconducting material comprising an element or a mixture of elements selected from the group of elements consisting of single elements of group IV, pair of elements chosen from group IV elements, pair of elements chosen from group III and group V elements, pair of elements chosen from group II and group VI elements, and pair of elements chosen from group IV and group VI elements of the Periodic Table of Elements.

11. A method according to claim 10 wherein said semiconducting material is selected from the group consisting of Si, Ge, C, and SiC, or a combination thereof .

12. A method according to claims 9-10 wherein said dopant is selected from the group consisting of N-type doping elements or P-type doping elements.

13. A method according to claim 12 wherein said N-type doping element is selected from the group consisting of the group 5a elements: N, P, As, Sb, and Bi of the Periodic Table of Elements.

14. A method according to claim 12 wherein said P-type dopirg element is selected from the group consisting of tne group 3d elements: B, Al , Ga, In, Ti of the Periodic Table of Elements.

15. A method according to any of the preceding claims wherein said dopant comprises an element which is able to modify the life time of a charge carrier m a doped single crystal.

16. A method according to claim 15 wherein said charge carrier life time modifying element is selected from the group consisting of Au and Pt .

17. A method according to any of the preceding claims wherein said dopant comprises an element which is able to modify the strain and/or stress of a doped single crystal .

18. A method according to claim 17 wherein the strain and/or stress modifying element is selected from the group consisting of C, Ge, and Sn.

19. A method according to any of the preceding claims wherein said dopant comprises an element which is able to control the crystal structure of a doped single crystal.

20. A method according to claim 19 wherein the structure controlling element is selected from the group consisting of 0, C, N, and H.

21. A method according to any of the preceding claims whereir said dopant comprises an element which is able to control light emission of a doped single crystal.

22. A method according to claim 21 wherein the light emission controlling element is selected from the group consisting of the rare earth metals, preferably Er.

23. A me hod according to any of the preceding claims wherein said feed rod essentially comprises a single crystal material or a doped single crystal material.

24. A method according to any of the preceding claims wherein said feed rod essentially comprises a polycrystallme material.

25. A method according to any of the preceding claims wherein said feed rod essentially comprises an amorphous material .

26. A method according to any of the preceding claims wherein the feed rod essentially comprises silicon.

27. A method according to any of the preceding claims wherein the dopant provides a non-natural abundance of isotopes of at least one of its elements.

28. A method according to claim 27 wherein the non- natural abundance of isotopes consists of at least two isotopes.

29. A method according to claim 27 wherein the non- natural abundance of isotopes essentially consists of one isotope .

30. An apparatus for producing a doped feed rod by ion implantation; said apparatus comprising means (2) for axially moving a feed rod without rotation; means (6,7,8,9,10,11,12,21) for laterally implanting a dopant

10 into or below the surface of an axially moving, non- rotatmg feed rod (1); said dopant implanting means comprises means (10) for electrically accelerating atomic or molecular species of said dopant for impact thereof on

- c X o

31. An apparatus according to claim 30 wherein said dopant implanting means comprises means for neutralising the electrically accelerated charged atomic or molecular species of said dopant before impact on the feed rod.

20

32. An apparatus according to any of claims 30-31 further comprising means (14) for wholly or partially bringing the feed rod in a molten state at impact of the accelerated atomic or molecular species of said dopant.

25

33. An apparatus according to any of claims 30-32 further comprising a means (11) for selecting the charge/mass ratio of the atomic or molecular species to be impacted on the feed rod.

30

34. An apparatus according to claim 33 wherein the dopant is an isotope of the atomic or molecular species.

35. An apparatus according to claims 30-34 wherein said 35 dopant implanting means comprises means for deflecting the accelerated atomic or molecular species of the dopant for controlling the point of impact thereof.

36. Use of a doped feed rod as produced by a method as claimed claims 1-29, for the production of a doped single crystal.

37. A method of producing a doped single crystal comprising providing a doped feed rod produced by a method as claimed m claims 1-29, and growing a doped single crystal (13) from a melt of said doped feed rod.

3o. A method according to claim 37 wherein the doped single crystal is a doped silicon single crystal.

39. A method according to any of claims 37 or 38, wherein the doped single crystal is grown from a melt of a feed rod by a method selected from the floating zone method and the Czochralski method.

40. An apparatus for producing a doped single crystal material by ion implantation, said apparatus comprising means (6,7,8,9,10,11,12,21) for providing a doped feed rod as claimed claims 30-35 and means (14) for growing a single crystal (13) from a melt of said doped feed rod.

41. An apparatus according to claim 40 wherein said means for growing a single crystal (13) from a melt of said doped feed rod comprises heating means (14) for generating a molten zone (15) of said feed rod.

42. An apparatus according to claim 40 or 41 wherein said implantation means comprises means for deflecting the means for directing the accelerated atomic or molecular species of the dopant to a point of impact above or below saiα growing means (14) .

43. A method of producing a doped single crystal comprising providing a doped feed rod produced by a method as claimed claims 1-29; providing a melt of said doped feed rod material; and growing a single crystal (13) from said melt while a further dopant (12) is implanted into or below the surface of said melt, into or below the surface of said grown single crystal, or into or below the surface both of said melt and of said grown single crystal, by impacting an electrically accelerated atomic or molecular species (7) of said dopant or said melt, on said grown single crystal, or ooth on said melt and on said grown single crystal, said further dopant being the same or different from the dopant of the feed rod.

44. A method according to claim 43 wherein the melt of said feed rod material for the single crystal is provided by an inductive heating.

45. A method according to claim 44 wherein the inductive heating is applied above, below, or both above and below the point or points of impact of said dopant (12) into or below the surface of said melt, into or below the surface of said grown single crystal, or into or below the surface both of said melt and of said grown single crystal .

46. A method according to any of claims 43-45 wherein the doped single crystal is grown from said melt of said feed rod material by a method selected from the floating zone method and the Czochralski method.

47. A method according to any of claims 43-46 wherein the doped single crystal is a doped silicon single crystal.

48. A method according to any of claims 43-47 wherein the further dopant provides a non-natural abundance of isotopes of at least one of its elements.

49. A method according to claim 48 wherein the non- natural abundance of isotopes consists of at least two isotopes.

50. A method according to claim 48 wherein the non- natural abundance of isotopes essentially consists of one isotope .

51. An apparatus for producing a doped single crystal comprising means (6,7,8,9,10,11,12,21) for proving a doped feed rod as claimed m claims 30-35; means for providing a melt of a feed rod material; means for growing a single crystal (13) from said melt; and means (6,7,8,9,10,11,12,21) for implanting a further dopant into or below the surface of said melt, into or below the surface of said grown single crystal, or into or below the surface both of said melt and of said grown single crystal, by impacting an electrically accelerated atomic or molecular species (7) of said dopant on said melt, on said grown single crystal, or both on said melt and on said grown single crystal, said further dopant being the same or different from the dopant of the doped feed rod.

52. An apparatus according to claim 51 further comprising a means (11) for selecting the charge/mass ratio of the atomic or molecular species of said further dopant to be impacted on the feed rod.

53. An apparatus according to claim 52 wherein the further dopant is an isotope of the atomic or molecular species .

5 . The apparatus according to any of claims 51-53 further comprising deflection means (21) for deflecting said electrically accelerated atomic or molecular species (7) of said dopant for controlling the point of impact on said melt, on said grown single crystal, or both on said melt and on said grown single crystal.

55. A method of producing a doped feed rod by ion implantation, the method comprising implanting a dopant (17) having a non-natural abundance of isotopes of at least one of its elements into or below the surface of a feed rod (1) by impacting an electrically accelerated atomic or molecular species (7) of said dopant on said feed rod.

56. A method according to claim 55 wherein the non- natural abundance of isotopes consists of at least two isotopes .

57. A method according to claim 55 wherein the non- natural abundance of isotopes essentially consists of one isotope .

58. A doped feed rod obtainable by a method according to any of claims 55-57.

59. A doped single crystal obtainable by growing a single crystal from a melt of a doped feed rod as claimed claim 58.