EP2965362A1 - Monolithic silicon wafer having alternating n-doped areas and p-doped areas - Google Patents

Monolithic silicon wafer having alternating n-doped areas and p-doped areas

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Publication number
EP2965362A1
EP2965362A1 EP14713263.3A EP14713263A EP2965362A1 EP 2965362 A1 EP2965362 A1 EP 2965362A1 EP 14713263 A EP14713263 A EP 14713263A EP 2965362 A1 EP2965362 A1 EP 2965362A1
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EP
European Patent Office
Prior art keywords
zones
wafer
doped
type
areas
Prior art date
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EP14713263.3A
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German (de)
French (fr)
Inventor
Jean-Paul Garandet
Sébastien Dubois
Nicolas Enjalbert
Jordi Veirman
Yannick Veschetti
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Publication of EP2965362A1 publication Critical patent/EP2965362A1/en
Withdrawn legal-status Critical Current

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/70—Manufacture or treatment of devices consisting of a plurality of solid state components formed in or on a common substrate or of parts thereof; Manufacture of integrated circuit devices or of parts thereof
    • H01L21/71—Manufacture of specific parts of devices defined in group H01L21/70
    • H01L21/76—Making of isolation regions between components
    • H01L21/761—PN junctions
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
    • H01L31/0352—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions
    • H01L31/035272—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by their shape or by the shapes, relative sizes or disposition of the semiconductor regions characterised by at least one potential jump barrier or surface barrier
    • H01L31/03529—Shape of the potential jump barrier or surface barrier
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/042—PV modules or arrays of single PV cells
    • H01L31/047—PV cell arrays including PV cells having multiple vertical junctions or multiple V-groove junctions formed in a semiconductor substrate
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/18—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof
    • H01L31/1804—Processes or apparatus specially adapted for the manufacture or treatment of these devices or of parts thereof comprising only elements of Group IV of the Periodic Table
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L31/04—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices
    • H01L31/06—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers
    • H01L31/068—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof adapted as photovoltaic [PV] conversion devices characterised by potential barriers the potential barriers being only of the PN homojunction type, e.g. bulk silicon PN homojunction solar cells or thin film polycrystalline silicon PN homojunction solar cells
    • H01L31/0687—Multiple junction or tandem solar cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/547—Monocrystalline silicon PV cells
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the present invention relates to a new monolithic silicon wafer having, in a vertical sectional plane, an alternation of n-doped zones and p-doped zones, and to different process variants for its preparation.
  • Such a wafer is particularly advantageous in the context of the development of photovoltaic cells and modules.
  • PV photovoltaic modules
  • PV modules of reasonable size of the order of the m 2 , the size standard for the wafers (156 x 156 mm) makes the open circuit voltages (V oc in English terminology) of the PV modules are limited. a few tens of volts.
  • a first option could be to use materials other than crystalline silicon (Si), in particular semiconductors with band gap amplitudes exceeding 1, 1 eV (electronvolt).
  • silicon such as an amorphous Si type material on crystalline Si, resulting from the so-called heterojunction technology, or even CdTe type materials (cadmium telluride).
  • CdTe type materials cadmium telluride
  • Pozner et al. [1] have modeled the serialization of cells with vertical p / n junction planes, unlike the configuration of conventional wafers where the junction plane is horizontal.
  • the advantage of this approach is to be able to consider a collective type of treatment, monolithic substrate, for the realization of cells.
  • many technical questions remain open as to the practical realization of such a structure, the cost of which, moreover, may be very high.
  • Gatos et al. [2] propose to take advantage of the heterogeneous incorporation of oxygen during the growth of a silicon crystal by Czochralski directed solidification. The origin of these fluctuations in oxygen concentration is poorly known, but this principle is used by Gatos et al. to obtain structures of alternating conductivity n / p by thermal annealing.
  • thermal anneals at temperatures of 400-500 ° C, allow the formation of thermal donors (DT ), small agglomerates of oxygen (typically formed from the combination of 3 to 20 oxygen atoms) that behave as electron donors in silicon.
  • thermal donors typically formed from the combination of 3 to 20 oxygen atoms
  • these thermal donors can cause compensation of the material and its change in conductivity.
  • an annealing for example at a temperature of 450 ° C for 50 hours of a wafer cut into a Czochralski ingot parallel to the direction of solidification, thus provides structures p / n.
  • the size of the n and p zones typically of the order of one hundred microns [2] can not be controlled. It is therefore not possible to define the output voltage of such a structure, which represents a major obstacle for the integration of these structures in a complete solar system. Moreover, in a configuration where the sub-cells are connected in series to obtain high voltages, it is then impossible to balance the currents, which is a very strong limitation with respect to the energy conversion efficiency of the 'together.
  • the present invention aims to provide a new monolithic silicon wafer to overcome the aforementioned drawbacks, as well as methods for accessing such a wafer.
  • the present invention relates, according to a first of its aspects, to a monolithic silicon wafer, having, in at least one vertical section plane, an alternation of n-doped zones and of p-doped zones, each of the zones extending throughout the thickness of the wafer, characterized in that:
  • said p-doped and p-doped zones each have, in the plane of section, a width (Li, L 2 ) of at least 1 mm; the n-doped zones have a concentration of thermal donors based on interstitial oxygen (DT) distinct from that of the p-doped zones; and
  • n-doped zones and said p-doped zones are separated from one another by zones of electrical insulation.
  • the wafer is characterized when observed in its horizontal position.
  • the wafer is defined as having an alternation of n-doped zones and p-doped zones extending over the entire thickness of the wafer, in a vertical cutting plane of the wafer positioned horizontally.
  • thermal donors or more simply under the abbreviation "DT", the thermal donors based on interstitial oxygen.
  • electrical insulation zone is meant a zone having a high electrical resistivity, in particular greater than or equal to 2 k ⁇ cm and advantageously greater than or equal to 10 k ⁇ cm.
  • the electrical isolation zone may be a so-called intrinsic zone, namely a zone of the wafer in which the electron-type charge carrier and hole-type charge carrier concentrations are similar.
  • the present invention proposes methods making it possible to easily access such a wafer from a p-doped silicon wafer.
  • the present invention thus relates to a method of manufacturing a wafer as defined above, comprising at least the steps consisting in:
  • step (ii) subjecting said wafer of step (i) to an overall heat treatment, conducive to activation of interstitial oxygen-based heat donors and conversion of the entire wafer to n-type; (iii) subjecting areas of the wafer obtained at the end of step (ii), dedicated to forming the p-doped zones, to a localized heat treatment that is favorable for the annihilation of the thermal donors and to the conversion of said zones of type n in type p; and
  • the present invention relates to a method of manufacturing a wafer as defined above, comprising at least the steps consisting in:
  • step (c) subjecting said wafer of step (b) to an overall heat treatment conducive to the activation of the interstitial oxygen-based thermal donors at the hydrogen-doped regions, and to the conversion of said zones (1 1) p-type type n and said zones (13) in electrical isolation zones, to obtain the expected wafer.
  • these methods make it possible, by controlling the local concentrations of thermal donors, to control, with precision, the size of the n and p zones formed, as well as the conductivity and the size of the electrical insulation zones.
  • the present invention relates to a photovoltaic device, in particular a photovoltaic cell, comprising a silicon wafer as defined above.
  • the silicon wafers according to the invention divided into a plurality of sub-cells of controlled sizes, advantageously make it possible to produce PV modules having an increased open circuit voltage, while maintaining a reasonable standard size of the order of 2 m 2. .
  • Other characteristics, advantages and modes of application of the wafers according to the invention and processes for its preparation will become more apparent on reading the detailed description which will follow, examples of embodiments of the invention and the examination annexed drawings, in which:
  • FIG. 1 shows, schematically, in a vertical sectional plane, the structure of a silicon wafer according to the invention
  • FIG. 2 shows schematically the various steps of the method of manufacturing a wafer according to the invention, according to a first embodiment
  • FIG. 3 shows schematically the various steps of the method of manufacturing a wafer according to the invention, according to a second embodiment
  • FIG. 4 represents, in a view from above, for the method of example 1, the zones (12) irradiated with the laser of the wafer during step (iii) for the formation of the p-doped zones (FIG. 4a) and during step (iv) for the formation of the electrical insulation zones (FIG. 4b);
  • FIG. 5 represents, in a view from above, for the method of example 2, the masking in step (b) of the zones (12) of the wafer during the first ion implantation step (FIG. 5a) and the masking the zones (12) and (13) during the second ion implantation step (FIG. 5b); and the distribution of the zones formed at the end of step (c) (FIG. 5c).
  • a wafer according to the invention may have a thickness (e) ranging from 100 to 500 ⁇ , in particular from 150 to 300 ⁇ .
  • L may have a total length (L) ranging from 10 to 30 cm, in particular from 15 to 20 cm.
  • a wafer of the invention comprises an interstitial oxygen concentration of between 10 17 and 2.10 18 cm “3, in particular between 5.1017 and 1,5.1018 cm" 3. This concentration takes into account the content in interstitial oxygen, which are not in the form of agglomerates (thermal donors) in the silicon wafer.
  • the interstitial oxygen concentration may for example be obtained by Fourier Transformed InfraRed Spectroscopy (FTIR) analysis.
  • FTIR Fourier Transformed InfraRed Spectroscopy
  • a silicon wafer according to the invention has an alternation of n-doped zones (1 10) and p-doped zones (120), separated from each other by electrical isolation zones (130).
  • the doped regions n (110) of the wafer may be, independently of each other, an electron type of charge carrier density between 10 14 and 2.10 16 cm “3, in particular from 5.10 14 to 5.10 15 cm “3 .
  • the concentration of electron-type charge carriers can be determined, for example, by measuring the Hall effect (which makes it possible to determine the type of doping).
  • They may have, independently of each other, a width (Li) in the cutting plane ranging from 1 mm to 10 cm, in particular from 5 mm to 5 cm.
  • the p-doped areas (120) of the wafer may have, independently of one another, a hole-type charge carrier density ranging from 10 14 to 2.10 16 cm- 3 , in particular from 5.10 14 to 5.10 15 cm- 3. .
  • the concentration of charge carriers of the hole type can be deduced from a measurement of the resistivity, for example by the Hall effect measurement method.
  • They may have, independently of each other, a width (L 2 ) in the section plane ranging from 1 mm to 10 cm, in particular from 5 mm to 5 cm.
  • the expression "independently of one another” means that the width may differ from one n-doped zone to another n-doped zone, or from one p-doped zone to another p-doped zone.
  • these widths (Li, L 2 ) can be adjusted according to the knowledge of those skilled in the art.
  • the n-type materials are generally less sensitive to metallic impurities than the p-type materials, the photogenerated currents are generally higher in n-doped zones than in p-doped zones.
  • the widths (Li, L 2 ) of the p-doped and n-doped zones can be adapted during the preparation of the wafer, in particular with a view to optimally matching these currents in the final silicon wafer.
  • n-doped zones (110) of the wafer according to the invention have a concentration of oxygen-based thermal donors (DT) distinct from that of the p-doped zones (120).
  • control of the local DT concentration provides access to the alternating electrical conductivity n and p of the wafer.
  • an overall annealing of a wafer according to the invention for example at a temperature greater than or equal to 600 ° C, in particular between 600 and 700 ° C, allows dissolution (also called “annihilation”). ) of all the DTs and leads to finding a platelet of homogeneous conductivity.
  • This characteristic can advantageously be used to distinguish a wafer according to the invention from wafers which would not be obtained by a method according to the invention.
  • the electrical isolation zones (130), separating an n-doped zone (110) and a p-doped zone (120), preferably have a resistivity greater than or equal to 2 k ⁇ cm, in particular greater than or equal to 10 k ⁇ . cm.
  • the resistivity can be measured by any conventional method, such as, for example, by the so-called 4-point measurement method, or by measuring the effect of eddy currents induced by an alternating magnetic field.
  • each of the electrical isolation zones (130) advantageously has a width (L 3 ) in the section plane ranging from 50 ⁇ to 5 mm, in particular from 200 ⁇ to 1 mm.
  • a zone of electrical insulation too long in the final silicon wafer is likely to lead to an active loss and therefore a drop in energy efficiency at the module that will be formed from these wafers.
  • a zone of electrical insulation that is too short may be insufficient to ensure good isolation between the sub-cells (n-doped zones and p-doped zones), which can also lead to a drop in efficiency at the module level. resulting.
  • the zones n and p can be arranged so as to form a two-dimensional pattern.
  • the arrangement of the alternating zones n and p may form a checker pattern.
  • the side of a square (zones n and p) of the checkerboard may be between 1 mm and 10 cm, preferably between 5 mm and 5 cm.
  • the electrical insulation zones (130) then form the perimeter of each of the zones n and the zones p. This configuration is for example implemented in the examples which follow.
  • the invention is not limited to such an arrangement; different configurations, other than a checkerboard pattern, may be envisaged within the context of the present invention (for example rectangular, polygonal patterns, etc.).
  • a wafer (10) according to the invention can be produced, according to various alternative embodiments, from a wafer (1) made of p-doped silicon, comprising a concentration of charge carriers of the hole type (p 0 ) between 10 14 and 2.10 16 cm -3 and an interstitial oxygen concentration [Oi]
  • the p-doped silicon wafer (1) has a concentration of hole-type charge carriers (p 0 ) ranging from 5.10 14 to 10 16 , in particular from 5.10 14 to 5.10 15 cm -3 .
  • the p-doped silicon wafer (1) has an interstitial oxygen concentration [Oi] ranging from 5 ⁇ 10 17 to 1.5 ⁇ 10 18 cm -3 .
  • the relative variation of the interstitial oxygen concentration in the silicon wafer (1) is less than 40%, in particular less than
  • Such a p-doped silicon wafer (1) may for example be obtained by cutting a shaped silicon ingot, according to techniques known to those skilled in the art, by directed solidification of a molten bath, in particular by the technique gradient cooling (also known as "gradient freeze” in English) or by liquid or gaseous epitaxy.
  • the methods according to the invention implement one or more steps of activation or annihilation of DTs.
  • activation is meant the formation of these thermal donors based on interstitial oxygen. They are generally formed during annealing at a temperature of 300-500 ° C. Such annealing allows the association of oxygen atoms to form a species with more complex stoichiometry that has an electron donor behavior in silicon.
  • the thermal donors thus formed are stable at room temperature, but annealing at a temperature above 600 ° C. allows their dissociation, which cancels out the effects of the thermal activation previously carried out. This is called “annihilation” or “dissolution” of DTs.
  • Activation / annihilation treatments used according to the invention can be operated under air or under an inert atmosphere. 1st embodiment
  • a wafer (10) according to the invention can be obtained via a method comprising at least the following steps:
  • step (ii) subjecting said wafer of step (i) to an overall heat treatment, conducive to activation of interstitial oxygen-based heat donors and conversion of the entire wafer to n-type;
  • the overall heat treatment in step (ii) may for example be carried out by thermal annealing of the entire wafer, for example in an oven.
  • the annealing may for example be carried out at a temperature greater than or equal to 300 ° C and strictly less than 600 ° C, in particular ranging from 400 to 500 ° C and more particularly about 450 ° C.
  • the duration of the thermal anneal may be greater than or equal to 30 minutes, in particular be between 1 hour and 20 hours, in particular be approximately 4 hours.
  • the wafer () obtained, in n-doped silicon may have a content of electron-type charge carriers (n 0 ) ranging from 10 14 to 2.10 16 , in particular from 5.10 to 14 to 5.10 15 cm “3 .
  • step (iii) a person skilled in the art is able to adjust the conditions of the localized heat treatment in step (iii) suitable for the annihilation of the thermal donors in the zones (12) of the wafer dedicated to forming p-doped zones and the reconversion of these n-type zones into p-type.
  • localized is meant that the heat treatment affects only the determined areas (12) of the wafer, unlike a global heat treatment that affects the entire wafer.
  • these areas (12) of the wafer subjected to heat treatment, for example laser irradiation, are determined with respect to the architecture of the desired final wafer.
  • the areas (12) of the wafer which are desired to become p-type can be brought to a temperature greater than or equal to 600 ° C, in particular ranging from 600 to 1000 ° C, in particular for at least 10 seconds. It is up to those skilled in the art to use known means for channeling heat fluxes and limiting the lateral propagation of heat to keep n / p zones well defined.
  • the localized heat treatment can be advantageously operated by exposing the zones (12) to be treated to a laser beam, preferably a broad-spot laser if it is desired to irradiate large areas, for example with a spot size of 1. order of the cm.
  • the laser can for example operate at a wavelength greater than or equal to 500 nm, in particular ranging from 500 nm to 1100 nm, which allows a propagation of heat deep in the material.
  • step (iv) The adjustment of the heat treatment conditions in step (iv) to transform the portions (13) of each of the n-type zones contiguous to a p-type zone into electrical insulation zones is also within the competence of the skilled person.
  • Step (iv) can be advantageously carried out by exposure of each portion
  • this additional laser treatment must be more localized than that implemented in step (iii) to achieve the width (L 3 ) of the desired electrical insulation zones, and thus achieve a good compromise between quality insulation and limitation of the size of the compensated zone, inactive from the photovoltaic point of view.
  • the irradiation time and laser power parameters can be adjusted to annihilate a fraction of the thermal donors in the treated areas (13) and convert them into areas of high resistivity electrical insulation.
  • the wafer may be subjected, subsequent to step (iv), to a surface treatment, in particular by etching, to remove any hardened surface regions resulting from the laser treatment.
  • etching can be carried out using a solution formed of a mixture HN0 3 , HF and CH 3 COOH, also known as CP133. 2 ° embodiment
  • a wafer (10) according to the invention can be obtained via a method comprising at least the following steps:
  • step (c) subjecting said wafer of step (b) to an overall heat treatment conducive to the activation of the interstitial oxygen-based heat donors at the hydrogen-doped zones (1 1) and (13), and converting said n-type p-type zones (11) and said zones (13) into electrical isolation zones to obtain the expected wafer (10).
  • step (b) it is up to those skilled in the art to adjust the hydrogen doping levels of the zones (11) and (13) in step (b) to obtain the desired conversion of the zones in step (c), without affecting the zones (12). ) devoid of hydrogen and dedicated to form the areas p of the final wafer.
  • the doping is operated so as to allow a uniform volume distribution of hydrogen in the areas concerned and over the entire thickness of the wafer.
  • the doping in step (b) can be carried out via a first step (bl) of implantation of hydrogen on the surface or sub-surface of the zones to be doped, followed by a second step ( b2) of diffusion of hydrogen over the entire thickness (e) of the wafer.
  • substrate hydrogen implantation means implantation at depths ranging from a few nanometers to a few tens of nanometers.
  • the hydrogen implantation can be carried out by conventional techniques, for example by plasma treatment, in particular by chemical phase deposition.
  • PECVD Plasma assisted vapor
  • MIRHP microwave - induced remote hydrogen plasma
  • the plasma treatment is carried out on both sides of the wafer.
  • the hydrogen implantation zones may be defined using a mask (for example, a metal grid), leaving only the surfaces of the areas to be doped accessible, as illustrated in example 2 which follows, for example by PECVD.
  • a mask for example, a metal grid
  • the hydrogen may be uniformly deposited over the entire surface of the wafer, and the deposit may be etched, for example with hydrofluoric acid (HF), in the zones (12) which it is desired to remain type p.
  • HF hydrofluoric acid
  • the hydrogen doping rate is preferably increased at the zones (11) intended to form the n-doped zones.
  • the implantation of hydrogen at the zones (11) and (13) can thus comprise:
  • the volume doping rate of the zones (11) dedicated to form the doped zones n can be between 1 and 4.10 13 cm -3 .
  • the volume doping rate of the zones (13) dedicated to form the zones of isolation electrical can be between 1 and 4.10 11 cm “3 .
  • the diffusion of hydrogen into the zones to be doped (step (b2)) can be performed, for example, by exposing said zones to ultrasound, in particular using piezoelectric transducers.
  • piezoelectric transducers working between 20 kHz and 1 MHz, preferably between 50 and 500 kHz, acoustic deformations induced between 5.10 “6 and 2.10 " 5 , and treatment times between 5 and 120 minutes, preferentially between 10 and 60 minutes.
  • the diffusion of hydrogen in step (b2) can be carried out by thermal annealing of the wafer, in particular in an oven, in particular at a temperature ranging from 400 ° C. to 1000 ° C., and for a period ranging from 5 seconds to 5 hours.
  • doping with hydrogen will accelerate the activation kinetics of thermal donors in the doped zones.
  • An overall thermal treatment of the wafer can thus be operated under conditions conducive to the privileged activation of thermal donors in the zones provided with hydrogen, and without affecting the areas which are devoid of them.
  • the overall heat treatment in step (c) may for example be carried out by thermal annealing at a temperature greater than or equal to 300 ° C. and strictly less than 600 ° C., in particular from 400 ° to 500 ° C., and more particularly from approximately 450 ° C.
  • the annealing time may be greater than or equal to 30 minutes, in particular between 1 hour and 20 hours, and more particularly about 3 hours.
  • a low temperature technology of heterojunction type (amorphous silicon on crystalline silicon) is used, for the realization of the photovoltaic cell.
  • a first layer of intrinsic amorphous silicon typically of a thickness of the order of 5 nm
  • a p + or n + doped amorphous layer on each of the faces of the wafer
  • metallizations also called “conductive contacts”
  • Formation of one or more metallizations front and / or back of the wafer in particular by screen printing Ag or Ag / Al.
  • a step of annealing the metallizations is then carried out in a passage oven at 800 ° C for a few seconds.
  • the PV cells obtained according to the invention can then be assembled to produce a photovoltaic module of reasonable size, conventionally of dimension of the order of m 2 , and having an increased voltage compared to modules developed from conventional cells.
  • the invention thus relates to a photovoltaic module formed of a set of photovoltaic cells according to the invention.
  • a p-type silicon wafer 220 ⁇ in thickness is used, obtained by cutting an ingot developed by solidification directed by the gradient-freeze technique.
  • This wafer has a content type of charge carriers holes, determined via the measurement of the resistivity of 5.10 15 cm “3, and an interstitial oxygen concentration as determined by FTIR analysis, 1.5x10 18 cm" 3.
  • the wafer is annealed at 450 ° C for 4 hours to activate thermal donors. This annealing allows the conversion of the p-type wafer to n-type, with an electron content, determined by measurement of the Hall effect, of 2.10 15 cm -3 .
  • the wafer is then positioned under a laser beam, shaped according to the pattern shown in FIG. 4a.
  • the non-irradiated areas are those that we want to keep n-type, and the irradiated areas (12) are the areas that we want to re-switch p-type.
  • the reasons are of dimension 4x4 cm 2 .
  • the laser beam uses a wavelength in the red / infrared, in order to bring heat deep down.
  • the laser power is adjusted in order to raise the temperature of the substrate to at least 600 ° C, in order to dissolve the majority of the thermal donors in the presence and convert the zone back to type p, while limiting as much as possible the degradation of the surface of the sample.
  • a power of 30 W for a 100 ⁇ beam diameter is a good example of an operating point, with a zone scan.
  • the duration of the laser treatment is adjusted so as to allow the rise in temperature of all irradiated areas beyond the threshold of 600 ° C for at least 10 minutes. seconds, while limiting the lateral diffusion of heat, in order to obtain a mosaic of types as sharp as possible.
  • the wafer undergoes a second laser step, aiming at the development of highly resistive zones between the different regions of opposite types.
  • the beam is scanned around the perimeter (13) of each n-type sub-element, over a width of 1 mm (in black in FIG. 4b).
  • the parameters of irradiation duration and laser power are adjusted in order to obtain localized zones where only a fraction of the thermal donors has been dissolved, making it possible to obtain an electrical isolation zone, and therefore very resistive .
  • the wafer undergoes a chemical attack type CP133 (HF, HN0 3 , CH3COOH) in order to remove any hardened surface areas resulting from the laser steps.
  • CP133 chemical attack type
  • the surfaces of the wafer are previously polished by a chemical attack type CP133.
  • a first masking step, using a metal grid placed above the substrate, is performed in accordance with the patterns, shown in Figure 5a.
  • the masked areas (12) correspond to the areas of the wafer which will remain of type p.
  • the open areas correspond to the zones (11) and (13) of the wafer intended to form the n-type zones and the electrical insulation zones.
  • This first masking step is followed by an ion implantation of hydrogen, by plasma immersion using a standard equipment, at a surface dose Dl of 4.10 9 cm -2 , which will correspond for the wafer of 200 ⁇ of thickness at a volume dose of 2.10 11 cm -3 .
  • the implantation energy of the hydrogen used for this application is close to 135 keV.
  • This first ion implantation step is then followed by a new masking step, as shown in FIG. 5b.
  • the masked areas are then the areas of the wafer (12) which will remain p-type (non-implanted areas) as well as the areas (implanted at the dose Dl) of the wafer (13) intended to form the areas of electrical insulation.
  • This second masking step is followed by a second step of ion implantation under 135 keV energy at an implantation dose D 2 of 4.10 11 cm -2 , which, in a 200 ⁇ thick wafer, corresponds to at a volume dose of 2.10 13 cm -3 .
  • the wafer is thermally annealed at a temperature in the region of 450 ° C. for a period of 3 hours, in order to transform the p-doped zones comprising hydrogen into n-doped zones, as shown schematically in FIG. 5c.
  • the wafer has an alternation of n-doped zones and p-doped zones, each of the n and p zones being separated by an electrical insulation zone (130) of high resistivity.

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Abstract

The present invention concerns a monolithic silicon wafer (10) having, in at least a vertical cutting plane, alternating n-doped areas (110) and p-doped areas (120), each of the areas extending over the entire thickness (e) of the wafer, characterised in that: - said n-doped areas (110) and p-doped areas (120) each have, in the cutting plane, a width (L1, L2) of at least 1 mm; - the n-doped areas (110) have a concentration of oxygen thermal donors different from that of the p-doped areas (120); and - said n-doped areas (110) and said p-doped areas are separated from each other by electrical insulation areas (130). It also concerns methods of producing such a wafer.

Description

PLAQUETTE DE SILICIUM MONOLITHIQUE PRESENTANT UNE ALTERNANCE DE ZONES DOPEES N ET DE ZONES DOPEES P  MONOLITHIC SILICON WAFER HAVING AN ALTERNATION OF N-DOPED ZONES AND DOPED ZONES
La présente invention se rapporte à une nouvelle plaquette de silicium monolithique présentant, dans un plan vertical de coupe, une alternance de zones dopées n et de zones dopées p, et à différentes variantes de procédé pour sa préparation. The present invention relates to a new monolithic silicon wafer having, in a vertical sectional plane, an alternation of n-doped zones and p-doped zones, and to different process variants for its preparation.
Une telle plaquette est particulièrement avantageuse dans le cadre de l'élaboration de cellules et modules photovoltaïques.  Such a wafer is particularly advantageous in the context of the development of photovoltaic cells and modules.
Actuellement, les modules photovoltaïques (PV) sont majoritairement fabriqués à partir de l'assemblage de cellules en silicium mono- ou multi-cristallin, ces cellules étant généralement réalisées à partir de plaquettes, également appelées « wafers », de conductivité électrique p.  Currently, photovoltaic modules (PV) are mainly made from the assembly of mono- or multi-crystalline silicon cells, these cells being generally made from wafers, also called "wafers", of electrical conductivity p.
Dans des modules PV de taille raisonnable, de l'ordre du m2, le standard de taille pour les plaquettes (156 x 156 mm) fait que les tensions de circuit ouvert (Voc en terminologie anglo-saxonne) des modules PV sont limitées à quelques dizaines de Volts. In PV modules of reasonable size, of the order of the m 2 , the size standard for the wafers (156 x 156 mm) makes the open circuit voltages (V oc in English terminology) of the PV modules are limited. a few tens of volts.
Différentes voies ont été explorées pour tenter d'augmenter la tension Voc des modules PV. Different paths have been explored in an attempt to increase the voltage V oc of the PV modules.
Une première option pourrait consister à utiliser des matériaux autres que le silicium (Si) cristallin, notamment des semi-conducteurs présentant des amplitudes de bande interdite (ou « band gap » en langue anglaise) supérieures au 1, 1 eV (électron- volt) du silicium, comme par exemple un matériau de type Si amorphe sur Si cristallin, issu de la technologie dite à hétéroj onction, ou encore des matériaux du type CdTe (tellurure de cadmium). Malheureusement, l'amélioration en termes de tensions de circuit ouvert est limitée, car l'utilisation de semi-conducteurs à bande interdite trop élevée (> 2 eV) conduit à une baisse significative de la quantité de photons absorbée et à une perte en rendement de conversion énergétique.  A first option could be to use materials other than crystalline silicon (Si), in particular semiconductors with band gap amplitudes exceeding 1, 1 eV (electronvolt). silicon, such as an amorphous Si type material on crystalline Si, resulting from the so-called heterojunction technology, or even CdTe type materials (cadmium telluride). Unfortunately, the improvement in terms of open circuit voltages is limited because the use of bandgap semiconductors that are too high (> 2 eV) leads to a significant decrease in the amount of photons absorbed and a loss in efficiency. energy conversion.
Une autre possibilité serait de réduire la taille des cellules par rapport au standard actuel de 156 x 156 mm, ce qui permettrait, par mise en série d'un plus grand nombre de cellules formant le module, d'accroître la valeur de la tension Voc. Cependant cette solution rendrait plus délicate les opérations de manutention pour l'élaboration des modules. Par ailleurs, la nécessité de garder un espace entre cellules formant le module PV pour la connectique conduit à une perte de surface utile (i.e. permettant la photogénération de porteurs électriques). Cette perte de surface est plus importante avec la mise en œuvre d'un plus grand nombre de cellules de taille réduite. Enfin, sauf à utiliser une technologie de cellule à contacts arrière (RCC, Rear Contact Cell en terminologie anglo saxonne), cette solution pose des problèmes délicats de métallisation et de connectique. Another possibility would be to reduce the size of the cells compared to the current standard of 156 x 156 mm, which would make it possible, by placing a greater number of cells forming the module in series, to increase the value of the voltage V oc . However, this solution would make more difficult handling operations for the development of modules. Moreover, the need to keep a space between the cells forming the PV module to the connector leads to a loss of useful surface (ie allowing photogeneration of electric carriers). This loss of surface is greater with the implementation of a larger number of cells of reduced size. Finally, except using a technology of rear contact cell (RCC, Rear Contact Cell in English terminology), this solution poses delicate problems of metallization and connectivity.
Pour tenter de réduire cette perte de surface utile, il pourrait être envisagé de réaliser une plaquette monolithique de taille standard 156 x 156 mm, et de graver a posteriori des tranchées, par exemple par ablation laser, ce qui aurait pour effet de créer effectivement une pluralité de cellules de plus petite taille. Cependant, le traitement de gravure est susceptible de conduire à une fragilisation de la plaquette, et donc à des problèmes de tenue mécanique. Par ailleurs, le problème de l'isolation entre les sous- cellules est complexe, surtout si une résistance d'isolement importante est nécessaire pour les applications visées. Enfin, comme évoqué ci-dessus, sauf à utiliser une technologie RCC, cette solution pose des problèmes délicats de métallisation et de connectique.  In an attempt to reduce this loss of useful area, it could be envisaged to make a monolithic wafer of standard size 156 x 156 mm, and to subsequently etch trenches, for example by laser ablation, which would have the effect of effectively creating a plurality of smaller cells. However, the etching treatment is likely to lead to embrittlement of the wafer, and therefore to problems of mechanical strength. In addition, the problem of isolation between the sub-cells is complex, especially if a high isolation resistance is required for the intended applications. Finally, as mentioned above, except using an RCC technology, this solution poses delicate problems of metallization and connectivity.
Plus récemment, Pozner et al. [1] ont envisagé par modélisation la mise en série de cellules à plans de jonction p/n verticaux, à la différence de la configuration des wafers classiques où le plan de jonction est horizontal. L'intérêt de cette approche est de pouvoir envisager un traitement de type collectif, sur substrat monolithique, pour la réalisation des cellules. Toutefois, de nombreuses questions techniques restent ouvertes quant à la réalisation en pratique d'une telle structure, dont le coût risque, par ailleurs, d'être très élevé.  More recently, Pozner et al. [1] have modeled the serialization of cells with vertical p / n junction planes, unlike the configuration of conventional wafers where the junction plane is horizontal. The advantage of this approach is to be able to consider a collective type of treatment, monolithic substrate, for the realization of cells. However, many technical questions remain open as to the practical realization of such a structure, the cost of which, moreover, may be very high.
Gatos et al. [2] proposent de tirer parti de l'incorporation hétérogène d'oxygène au cours de la croissance d'un cristal de silicium par solidification dirigée selon le procédé Czochralski. L'origine de ces fluctuations de concentration d'oxygène est mal connue, mais ce principe est utilisé par Gatos et al. pour obtenir des structures de conductivité alternée n/p par recuit thermique.  Gatos et al. [2] propose to take advantage of the heterogeneous incorporation of oxygen during the growth of a silicon crystal by Czochralski directed solidification. The origin of these fluctuations in oxygen concentration is poorly known, but this principle is used by Gatos et al. to obtain structures of alternating conductivity n / p by thermal annealing.
Il est en effet connu de l'état de l'art [3] que, dans des plaquettes de silicium contenant de l'oxygène, des recuits thermiques à des températures de 400-500 °C, permettent la formation de donneurs thermiques (DT), petits agglomérats d'oxygène (typiquement formés de l'association de 3 à 20 atomes d'oxygène) qui se comportent en donneurs d'électrons dans le silicium. Ainsi, lorsque ces donneurs thermiques sont générés dans le silicium de type p, ils peuvent entraîner une compensation du matériau et son changement de conductivité. La libération d'électrons étant fonction de la concentration locale en oxygène, un recuit, par exemple à une température de 450 °C pendant 50 heures d'une plaquette découpée dans un lingot Czochralski parallèlement à la direction de solidification, permet ainsi d'obtenir des structures p/n. It is indeed known from the state of the art [3] that, in silicon wafers containing oxygen, thermal anneals at temperatures of 400-500 ° C, allow the formation of thermal donors (DT ), small agglomerates of oxygen (typically formed from the combination of 3 to 20 oxygen atoms) that behave as electron donors in silicon. Thus, when these thermal donors are generated in the p-type silicon, they can cause compensation of the material and its change in conductivity. The release of electrons depending on the concentration In local oxygen, an annealing, for example at a temperature of 450 ° C for 50 hours of a wafer cut into a Czochralski ingot parallel to the direction of solidification, thus provides structures p / n.
Malheureusement, les fluctuations de concentration n'étant pas maîtrisées, la taille des zones n et p, typiquement de l'ordre de la centaine de microns [2], ne peut être contrôlée. Il n'est donc pas possible de définir la tension de sortie d'une telle structure, ce qui représente un obstacle majeur pour l'intégration de ces structures dans un système solaire complet. Par ailleurs, dans une configuration où les sous-cellules sont connectées en série pour obtenir des tensions élevées, il est alors impossible d'équilibrer les courants, ce qui est une limitation très forte vis-à-vis du rendement de conversion énergétique de l'ensemble.  Unfortunately, as the concentration fluctuations are not controlled, the size of the n and p zones, typically of the order of one hundred microns [2], can not be controlled. It is therefore not possible to define the output voltage of such a structure, which represents a major obstacle for the integration of these structures in a complete solar system. Moreover, in a configuration where the sub-cells are connected in series to obtain high voltages, it is then impossible to balance the currents, which is a very strong limitation with respect to the energy conversion efficiency of the 'together.
En outre, la variation de taille entre les différentes sous-cellules sur la surface d'une plaquette ([2], figure 1) induit une complexité, d'un point de vue technologique, qui représente un inconvénient majeur pour la réalisation des cellules photovoltaïques. Enfin, il n'est pas possible, dans la structure obtenue par Gatos et al. [2], de spécifier une résistance d'isolement entre les sous-cellules. Une telle limitation est préjudiciable au rendement de conversion énergétique de la cellule photovoltaïque.  In addition, the variation in size between the different sub-cells on the surface of a wafer ([2], FIG. 1) induces a complexity, from a technological point of view, which represents a major disadvantage for the production of the cells. PV. Finally, it is not possible in the structure obtained by Gatos et al. [2], to specify an isolation resistance between the sub-cells. Such a limitation is detrimental to the energy conversion efficiency of the photovoltaic cell.
Par conséquent, il demeure un besoin de disposer de plaquettes de silicium, appropriées pour la réalisation de modules PV à haute tension de circuit ouvert et minimisant les surfaces inactives (i.e. ne permettant pas la collecte des porteurs photogénérés). Therefore, there remains a need for silicon wafers, suitable for making high voltage open circuit PV modules and minimizing inactive surfaces (i.e. not allowing the collection of photogenerated carriers).
La présente invention vise précisément à proposer une nouvelle plaquette de silicium monolithique permettant de pallier les inconvénients précités, ainsi que des procédés pour accéder à une telle plaquette.  The present invention aims to provide a new monolithic silicon wafer to overcome the aforementioned drawbacks, as well as methods for accessing such a wafer.
Plus précisément, la présente invention concerne, selon un premier de ses aspects, une plaquette de silicium monolithique, présentant, dans au moins un plan vertical de coupe, une alternance de zones dopées n et de zones dopées p, chacune des zones s'étendant sur toute l'épaisseur de la plaquette, caractérisée en ce que :  More specifically, the present invention relates, according to a first of its aspects, to a monolithic silicon wafer, having, in at least one vertical section plane, an alternation of n-doped zones and of p-doped zones, each of the zones extending throughout the thickness of the wafer, characterized in that:
- lesdites zones dopées n et dopées p présentent chacune, dans le plan de coupe, une largeur (Li, L2) d'au moins 1 mm ; - les zones dopées n présentent une concentration en donneurs thermiques à base d'oxygène interstitiel (DT) distincte de celle des zones dopées p ; et said p-doped and p-doped zones each have, in the plane of section, a width (Li, L 2 ) of at least 1 mm; the n-doped zones have a concentration of thermal donors based on interstitial oxygen (DT) distinct from that of the p-doped zones; and
- lesdites zones dopées n et lesdites zones dopées p sont séparées entre elles par des zones d'isolation électrique.  said n-doped zones and said p-doped zones are separated from one another by zones of electrical insulation.
Dans la suite du texte, et sauf indication contraire, la plaquette est caractérisée lorsqu'elle observée dans sa position horizontale. Ainsi, en particulier, la plaquette est définie comme présentant une alternance de zones dopées n et de zones dopées p s' étendant sur toute l'épaisseur de la plaquette, dans un plan vertical de coupe de la plaquette positionnée horizontalement.  In the rest of the text, and unless otherwise indicated, the wafer is characterized when observed in its horizontal position. Thus, in particular, the wafer is defined as having an alternation of n-doped zones and p-doped zones extending over the entire thickness of the wafer, in a vertical cutting plane of the wafer positioned horizontally.
On parlera indifféremment dans la suite du texte de « plaquette » ou de We will discuss indifferently in the following text "plaquette" or
« wafer ». "Wafer".
On désignera par la suite par « donneurs thermiques », ou plus simplement sous l'abréviation « DT », les donneurs thermiques à base d'oxygène interstitiel.  Thereafter will be designated by "thermal donors", or more simply under the abbreviation "DT", the thermal donors based on interstitial oxygen.
Par « zone d'isolation électrique », on entend une zone présentent une forte résistivité électrique, en particulier supérieure ou égale à 2 kQ.cm et avantageusement supérieure ou égale à 10 kQ.cm. De manière idéale, la zone d'isolation électrique peut être une zone dite intrinsèque, à savoir une zone de la plaquette dans laquelle les concentrations de porteurs de charge de type électrons et de porteurs de charge de type trous sont similaires.  By "electrical insulation zone" is meant a zone having a high electrical resistivity, in particular greater than or equal to 2 kΩ cm and advantageously greater than or equal to 10 kΩ cm. Ideally, the electrical isolation zone may be a so-called intrinsic zone, namely a zone of the wafer in which the electron-type charge carrier and hole-type charge carrier concentrations are similar.
Selon un autre de ses aspects, la présente invention propose des procédés permettant d'accéder, de manière aisée, à une telle plaquette, à partir d'une plaquette en silicium dopé p.  According to another of its aspects, the present invention proposes methods making it possible to easily access such a wafer from a p-doped silicon wafer.
Selon un premier mode de réalisation particulier, la présente invention concerne ainsi un procédé de fabrication d'une plaquette telle que définie précédemment, comprenant au moins les étapes consistant en :  According to a first particular embodiment, the present invention thus relates to a method of manufacturing a wafer as defined above, comprising at least the steps consisting in:
(i) disposer d'une plaquette en silicium dopé p comprenant une concentration en porteurs de charge de type trous (p0) comprise entre 1014 et 2.1016 cm"3 et une concentration en oxygène interstitiel [Oi] comprise entre 1017 et 2.1018 cm"3 ; (i) having a p-doped silicon wafer comprising a hole-type charge carrier concentration (p 0 ) of between 10 14 and 2.10 16 cm -3 and an interstitial oxygen concentration [Oi] between 10 17 and 2.10 18 cm -3 ;
(ii) soumettre ladite plaquette de l'étape (i) à un traitement thermique global, propice à l'activation des donneurs thermiques à base d'oxygène interstitiel et à la conversion de l'ensemble de la plaquette en type n ; (iii) soumettre des zones de la plaquette obtenue à l'issue de l'étape (ii), dédiées à former les zones dopées p, à un traitement thermique localisé propice à l'annihilation des donneurs thermiques et à la reconversion desdites zones de type n en type p ; et (ii) subjecting said wafer of step (i) to an overall heat treatment, conducive to activation of interstitial oxygen-based heat donors and conversion of the entire wafer to n-type; (iii) subjecting areas of the wafer obtained at the end of step (ii), dedicated to forming the p-doped zones, to a localized heat treatment that is favorable for the annihilation of the thermal donors and to the conversion of said zones of type n in type p; and
(iv) transformer, par traitement thermique, la portion de chaque zone de type n, contigue à une zone de type p, en une zone d'isolation électrique, pour obtenir la plaquette (iv) converting, by heat treatment, the portion of each n-type zone, contiguous to a p-type zone, into an electrical isolation zone, to obtain the wafer
(10) attendue. (10) expected.
Selon un seconde mode de réalisation particulier, la présente invention concerne un procédé de fabrication d'une plaquette telle que définie précédemment, comprenant au moins les étapes consistant en :  According to a second particular embodiment, the present invention relates to a method of manufacturing a wafer as defined above, comprising at least the steps consisting in:
(a) disposer d'une plaquette en silicium dopé p comprenant une concentration en porteurs de charge de type trous (p0) comprise entre 1014 et 2.1016 cm"3 et une concentration en oxygène interstitiel [Oi] comprise entre 1017 et 2.1018 cm"3 ; (a) having a p-doped silicon wafer comprising a hole-type charge carrier concentration (p 0 ) of between 10 14 and 2.10 16 cm -3 and an interstitial oxygen concentration [Oi] between 10 17 and 2.10 18 cm -3 ;
(b) doper en hydrogène les zones, dites (1 1) et (13), de la plaquette dédiées à former les zones dopées n et les zones d'isolation électrique ; et  (b) hydrogen doping the so-called (1 1) and (13) zones of the wafer dedicated to form the n-doped zones and the electrical isolation zones; and
(c) soumettre ladite plaquette de l'étape (b) à un traitement thermique global propice à l'activation des donneurs thermiques à base d'oxygène interstitiel au niveau des zones dopées en hydrogène, et à la conversion desdites zones (1 1) de type p en type n et desdites zones (13) en zones d'isolation électrique, pour obtenir la plaquette attendue.  (c) subjecting said wafer of step (b) to an overall heat treatment conducive to the activation of the interstitial oxygen-based thermal donors at the hydrogen-doped regions, and to the conversion of said zones (1 1) p-type type n and said zones (13) in electrical isolation zones, to obtain the expected wafer.
De manière avantageuse, ces procédés permettent, via le contrôle des concentrations locales en donneurs thermiques, de maîtriser, avec précision, la taille des zones n et p formées, ainsi que la conductivité et la taille des zones d'isolation électrique.  Advantageously, these methods make it possible, by controlling the local concentrations of thermal donors, to control, with precision, the size of the n and p zones formed, as well as the conductivity and the size of the electrical insulation zones.
Egalement, il est possible selon l'invention, comme développé dans la suite du texte, de réaliser des structures bidimensionnelles, par exemple avec une disposition des zones n et p alternées en damier, ce qui permet avantageusement d'accroître encore le nombre de sous-cellules en série formées sur la plaquette.  Also, it is possible according to the invention, as developed in the rest of the text, to produce two-dimensional structures, for example with a layout of the n and p zones alternating checkerboard, which advantageously allows to further increase the number of sub series cells formed on the wafer.
Selon encore un autre de ses aspects, la présente invention concerne un dispositif photovoltaïque, en particulier une cellule photovoltaïque, comportant une plaquette de silicium telle que définie précédemment.  According to yet another of its aspects, the present invention relates to a photovoltaic device, in particular a photovoltaic cell, comprising a silicon wafer as defined above.
Les plaquettes de silicium selon l'invention, divisées en une pluralité de sous- cellules de tailles contrôlées, permettent avantageusement de produire des modules PV présentant une tension de circuit ouvert accrue, tout en conservant une taille raisonnable standard de l'ordre du m2. D'autres caractéristiques, avantages et modes d'application des plaquettes selon l'invention et des procédés pour sa préparation, ressortiront mieux à la lecture de la description détaillée qui va suivre, des exemples de réalisation de l'invention et à l'examen des dessins annexés, sur lesquels : The silicon wafers according to the invention, divided into a plurality of sub-cells of controlled sizes, advantageously make it possible to produce PV modules having an increased open circuit voltage, while maintaining a reasonable standard size of the order of 2 m 2. . Other characteristics, advantages and modes of application of the wafers according to the invention and processes for its preparation will become more apparent on reading the detailed description which will follow, examples of embodiments of the invention and the examination annexed drawings, in which:
- la figure 1 représente, de manière schématique, dans un plan vertical de coupe, la structure d'une plaquette de silicium selon l'invention ;  - Figure 1 shows, schematically, in a vertical sectional plane, the structure of a silicon wafer according to the invention;
- la figure 2 représente, de manière schématique, les différentes étapes du procédé de fabrication d'une plaquette selon l'invention, selon un premier mode de réalisation ;  - Figure 2 shows schematically the various steps of the method of manufacturing a wafer according to the invention, according to a first embodiment;
- la figure 3 représente, de manière schématique, les différentes étapes du procédé de fabrication d'une plaquette selon l'invention, selon un second mode de réalisation ;  - Figure 3 shows schematically the various steps of the method of manufacturing a wafer according to the invention, according to a second embodiment;
- la figure 4 représente, en vue de dessus, pour le procédé de l'exemple 1, les zones (12) irradiées au laser de la plaquette lors de l'étape (iii) pour la formation des zones dopées p (figure 4a) et lors de l'étape (iv) pour la formation des zones d'isolation électrique (figure 4b) ;  FIG. 4 represents, in a view from above, for the method of example 1, the zones (12) irradiated with the laser of the wafer during step (iii) for the formation of the p-doped zones (FIG. 4a) and during step (iv) for the formation of the electrical insulation zones (FIG. 4b);
- la figure 5 représente, en vue de dessus, pour le procédé de l'exemple 2, le masquage en étape (b) des zones (12) de la plaquette lors de la première étape d'implantation ionique (figure 5a) et le masquage des zones (12) et (13) lors de la seconde étape d'implantation ionique (figure 5b) ; et la répartition des zones formées à l'issue de l'étape (c) (figure 5c).  FIG. 5 represents, in a view from above, for the method of example 2, the masking in step (b) of the zones (12) of the wafer during the first ion implantation step (FIG. 5a) and the masking the zones (12) and (13) during the second ion implantation step (FIG. 5b); and the distribution of the zones formed at the end of step (c) (FIG. 5c).
Il convient de noter que, pour des raisons de clarté, les différents éléments sur les figures sont représentés en échelle libre, les dimensions réelles des différentes parties n'étant pas respectées.  It should be noted that, for the sake of clarity, the various elements in the figures are represented in free scale, the actual dimensions of the different parts not being respected.
Dans la suite du texte, les expressions « compris entre ... et ... », « allant de ... à ... » et « variant de ... à ... » sont équivalentes et entendent signifier que les bornes sont incluses, sauf mention contraire. In the remainder of the text, the expressions "between ... and ...", "ranging from ... to ..." and "varying from ... to ..." are equivalent and mean to mean that terminals are included unless otherwise stated.
Sauf indication contraire, l'expression « comportant/comprenant un(e) » doit être comprise comme « comportant/comprenant au moins un(e) ». PLAQUETTE Unless otherwise indicated, the expression "comprising / including a" shall be understood as "comprising / including at least one". WAFER
Il est fait référence, dans la description qui suit, à la figure 1 annexée. Reference is made, in the description which follows, to the appended FIG.
Une plaquette selon l'invention peut présenter une épaisseur (e) allant de 100 à 500 μηι, en particulier de 150 à 300 μιη. A wafer according to the invention may have a thickness (e) ranging from 100 to 500 μηι, in particular from 150 to 300 μιη.
Elle peut présenter une longueur totale (L), allant de 10 à 30 cm, en particulier de 15 à 20 cm.  It may have a total length (L) ranging from 10 to 30 cm, in particular from 15 to 20 cm.
Selon un mode de réalisation particulier, une plaquette selon l'invention comporte une concentration en oxygène interstitiel comprise entre 1017 et 2.1018 cm" 3 , en particulier comprise entre 5.1017 et 1,5.1018 cm" 3. Cette concentration prend en compte la teneur en oxygène interstitiel, qui ne sont pas sous forme d'agglomérats (donneurs thermiques) dans la plaquette de silicium. According to a particular embodiment, a wafer of the invention comprises an interstitial oxygen concentration of between 10 17 and 2.10 18 cm "3, in particular between 5.1017 and 1,5.1018 cm" 3. This concentration takes into account the content in interstitial oxygen, which are not in the form of agglomerates (thermal donors) in the silicon wafer.
La concentration en oxygène interstitiel peut être par exemple obtenue par analyse par spectroscopie infrarouge à transformée de Fourier (en langue anglaise « Fourier Transformed InfraRed Spectroscopy » (FTIR)).  The interstitial oxygen concentration may for example be obtained by Fourier Transformed InfraRed Spectroscopy (FTIR) analysis.
Comme décrit précédemment, une plaquette de silicium selon l'invention présente une alternance de zones dopées n (1 10) et de zones dopées p (120), séparées entre elles par des zones d'isolation électrique (130).  As described above, a silicon wafer according to the invention has an alternation of n-doped zones (1 10) and p-doped zones (120), separated from each other by electrical isolation zones (130).
En particulier, les zones dopées n (110) de la plaquette peuvent présenter, indépendamment les unes des autres, une densité de porteurs de charge de type électrons allant de 1014 à 2.1016 cm"3, en particulier de 5.1014 à 5.1015 cm"3. In particular, the doped regions n (110) of the wafer may be, independently of each other, an electron type of charge carrier density between 10 14 and 2.10 16 cm "3, in particular from 5.10 14 to 5.10 15 cm "3 .
La concentration en porteurs de charge de type électrons peut être par exemple déterminée par mesure de l'effet Hall (qui permet de déterminer le type de dopage).  The concentration of electron-type charge carriers can be determined, for example, by measuring the Hall effect (which makes it possible to determine the type of doping).
Elles peuvent présenter, indépendamment les unes des autres, une largeur (Li) dans le plan de coupe allant de 1 mm à 10 cm, en particulier de 5 mm à 5 cm.  They may have, independently of each other, a width (Li) in the cutting plane ranging from 1 mm to 10 cm, in particular from 5 mm to 5 cm.
Les zones dopées p (120) de la plaquette peuvent présenter, indépendamment les unes des autres, une densité en porteurs de charge de type trous allant de 1014 à 2.1016 cm"3, en particulier de 5.1014 à 5.1015 cm"3. The p-doped areas (120) of the wafer may have, independently of one another, a hole-type charge carrier density ranging from 10 14 to 2.10 16 cm- 3 , in particular from 5.10 14 to 5.10 15 cm- 3. .
La concentration en porteurs de charge de type trous peut être par exemple déduite d'une mesure de la résistivité, par exemple par la méthode de mesure d'effet Hall.  For example, the concentration of charge carriers of the hole type can be deduced from a measurement of the resistivity, for example by the Hall effect measurement method.
Elles peuvent présenter, indépendamment les unes des autres, une largeur (L2) dans le plan de coupe allant de 1 mm à 10 cm, en particulier de 5 mm à 5 cm. Par l'expression « indépendamment les unes des autres », on entend signifier que la largeur peut différer d'une zone dopée n à une autre zone dopée n, ou d'une zone dopé p à une autre zone dopée p. They may have, independently of each other, a width (L 2 ) in the section plane ranging from 1 mm to 10 cm, in particular from 5 mm to 5 cm. The expression "independently of one another" means that the width may differ from one n-doped zone to another n-doped zone, or from one p-doped zone to another p-doped zone.
De manière avantageuse, ces largeurs (Li, L2) peuvent être ajustées selon les connaissances de l'homme du métier. En particulier, les matériaux de type n étant généralement moins sensibles aux impuretés métalliques que les matériaux de type p, les courants photogénérés sont généralement plus élevés dans des zones dopées n que dans des zones dopées p. Ainsi, les largeurs (Li, L2) des zones dopées p et dopées n peuvent être adaptées lors de la préparation de la plaquette, en vue notamment d'égaler au mieux ces courants dans la plaquette de silicium finale. Advantageously, these widths (Li, L 2 ) can be adjusted according to the knowledge of those skilled in the art. In particular, since the n-type materials are generally less sensitive to metallic impurities than the p-type materials, the photogenerated currents are generally higher in n-doped zones than in p-doped zones. Thus, the widths (Li, L 2 ) of the p-doped and n-doped zones can be adapted during the preparation of the wafer, in particular with a view to optimally matching these currents in the final silicon wafer.
Les zones dopées n (110) de la plaquette selon l'invention présentent une concentration en donneurs thermiques à base d'oxygène (DT) distincte de celle des zones dopées p (120).  The n-doped zones (110) of the wafer according to the invention have a concentration of oxygen-based thermal donors (DT) distinct from that of the p-doped zones (120).
Comme il ressort des procédés de réalisation de la plaquette décrits ci-dessous, le contrôle de la concentration locale en DT permet d'accéder à la conductivité électrique alternée n et p de la plaquette.  As can be seen from the methods for producing the wafer described below, control of the local DT concentration provides access to the alternating electrical conductivity n and p of the wafer.
Il est à noter qu'un recuit global d'une plaquette conforme à l'invention, par exemple à une température supérieure ou égale à 600 °C, notamment comprise entre 600 et 700 °C, permet la dissolution (encore appelée « annihilation ») de l'ensemble des DT et conduit à retrouver une plaquette de conductivité homogène. Cette caractéristique peut être avantageusement utilisée pour distinguer une plaquette selon l'invention, de plaquettes qui ne seraient pas obtenues par un procédé conforme à l'invention.  It should be noted that an overall annealing of a wafer according to the invention, for example at a temperature greater than or equal to 600 ° C, in particular between 600 and 700 ° C, allows dissolution (also called "annihilation"). ) of all the DTs and leads to finding a platelet of homogeneous conductivity. This characteristic can advantageously be used to distinguish a wafer according to the invention from wafers which would not be obtained by a method according to the invention.
Les zones d'isolation électrique (130), séparant une zone dopée n (110) et une zone dopée p (120), présentent de préférence une résistivité supérieure ou égale à 2 kQ.cm, en particulier supérieure ou égale à 10 kQ.cm.  The electrical isolation zones (130), separating an n-doped zone (110) and a p-doped zone (120), preferably have a resistivity greater than or equal to 2 kΩ cm, in particular greater than or equal to 10 kΩ. cm.
La résistivité peut être mesurée par toute méthode conventionnelle, comme par exemple, par la méthode de mesure dite des 4 pointes, ou encore par mesure de l'effet des courants de Foucault induit par un champ magnétique alternatif.  The resistivity can be measured by any conventional method, such as, for example, by the so-called 4-point measurement method, or by measuring the effect of eddy currents induced by an alternating magnetic field.
Selon un mode de réalisation particulier, chacune des zones d'isolation électrique (130) présente avantageusement une largeur (L3) dans le plan de coupe allant de 50 μπι à 5 mm, en particulier de 200 μπι à 1 mm. En effet, une zone d'isolation électrique trop longue dans la plaquette de silicium finale est susceptible de conduire à une perte de manière active et donc une baisse du rendement énergétique au niveau du module qui sera formé à partir de ces plaquettes. En revanche, une zone d'isolation électrique trop courte peut s'avérer insuffisante pour assurer une bonne isolation entre les sous-cellules (zones dopées n et zones dopées p), ce qui peut également conduire à une baisse de rendement au niveau du module résultant. According to a particular embodiment, each of the electrical isolation zones (130) advantageously has a width (L 3 ) in the section plane ranging from 50 μπι to 5 mm, in particular from 200 μπι to 1 mm. Indeed, a zone of electrical insulation too long in the final silicon wafer is likely to lead to an active loss and therefore a drop in energy efficiency at the module that will be formed from these wafers. On the other hand, a zone of electrical insulation that is too short may be insufficient to ensure good isolation between the sub-cells (n-doped zones and p-doped zones), which can also lead to a drop in efficiency at the module level. resulting.
Selon un mode de réalisation particulier, les zones n et p peuvent être agencées de manière à former un motif bidimensionnel.  According to a particular embodiment, the zones n and p can be arranged so as to form a two-dimensional pattern.
Par exemple, dans une vue de dessus de la plaquette, la disposition des zones n et p alternées peut former un motif de type damier. Le côté d'un carré (zones n et p) du damier peut être compris entre 1 mm et 10 cm, de préférence entre 5 mm et 5 cm. Dans le cadre de ce mode de réalisation particulier, les zones d'isolation électrique (130) forment alors le pourtour de chacune des zones n et des zones p. Cette configuration est par exemple mise en œuvre dans les exemples qui suivent.  For example, in a top view of the wafer, the arrangement of the alternating zones n and p may form a checker pattern. The side of a square (zones n and p) of the checkerboard may be between 1 mm and 10 cm, preferably between 5 mm and 5 cm. In the context of this particular embodiment, the electrical insulation zones (130) then form the perimeter of each of the zones n and the zones p. This configuration is for example implemented in the examples which follow.
Bien entendu, l'invention n'est nullement limitée à une telle disposition ; différentes configurations, autres qu'un motif damier, peuvent être envisagées dans le cadre de la présente invention (par exemple motifs rectangulaires, polygonaux, etc.).  Of course, the invention is not limited to such an arrangement; different configurations, other than a checkerboard pattern, may be envisaged within the context of the present invention (for example rectangular, polygonal patterns, etc.).
FABRICATION DE LA PLAQUETTE MANUFACTURE OF THE PLATE
Comme évoqué précédemment, une plaquette (10) selon l'invention peut être élaborée, suivant différentes variantes de réalisation, à partir d'une plaquette (1) en silicium dopée p, comprenant une concentration en porteurs de charge de type trous (p0) comprise entre 1014 et 2.1016 cm"3 et une concentration en oxygène interstitiel [Oi] As mentioned above, a wafer (10) according to the invention can be produced, according to various alternative embodiments, from a wafer (1) made of p-doped silicon, comprising a concentration of charge carriers of the hole type (p 0 ) between 10 14 and 2.10 16 cm -3 and an interstitial oxygen concentration [Oi]
17 18 3  17 18 3
comprise entre 10 et 2.10 cm" . between 10 cm and 2.10 ".
Selon un mode de réalisation particulier, la plaquette (1) en silicium dopé p présente une concentration en porteurs de charge de type trous (p0) allant de 5.1014 à 1016, en particulier de 5.1014 à 5.1015 cm"3. According to a particular embodiment, the p-doped silicon wafer (1) has a concentration of hole-type charge carriers (p 0 ) ranging from 5.10 14 to 10 16 , in particular from 5.10 14 to 5.10 15 cm -3 .
Selon un mode de réalisation particulier, la plaquette (1) en silicium dopé p présente une concentration en oxygène interstitiel [Oi] allant de 5.1017 à 1,5.1018 cm"3. According to a particular embodiment, the p-doped silicon wafer (1) has an interstitial oxygen concentration [Oi] ranging from 5 × 10 17 to 1.5 × 10 18 cm -3 .
De manière avantageuse, la variation relative de la concentration en oxygène interstitiel dans la plaquette en silicium (1) est inférieure à 40 %, en particulier inférieure à Advantageously, the relative variation of the interstitial oxygen concentration in the silicon wafer (1) is less than 40%, in particular less than
20 % et de préférence inférieure à 10 %. Une telle plaquette (1) en silicium dopé p peut être par exemple obtenue par découpe d'un lingot de silicium formé, selon des techniques connues de l'homme du métier, par solidification dirigée d'un bain fondu, en particulier par la technique de refroidissement sous gradient (encore connue sous l'appellation « gradient freeze » en langue anglaise) ou par épitaxie en voie liquide ou gazeuse. 20% and preferably less than 10%. Such a p-doped silicon wafer (1) may for example be obtained by cutting a shaped silicon ingot, according to techniques known to those skilled in the art, by directed solidification of a molten bath, in particular by the technique gradient cooling (also known as "gradient freeze" in English) or by liquid or gaseous epitaxy.
Les procédés selon l'invention, décrits ci-dessous, mettent en œuvre une ou plusieurs étapes d'activation ou d'annihilation des DT.  The methods according to the invention, described below, implement one or more steps of activation or annihilation of DTs.
On entend par « activation », la formation de ces donneurs thermiques à base d'oxygène interstitiel. Ils se forment généralement lors d'un recuit à une température de 300-500 °C. Un tel recuit permet l'association d'atomes d'oxygène pour former une espèce à la stœchiométrie plus complexe qui a un comportement donneur d'électrons dans le silicium.  By "activation" is meant the formation of these thermal donors based on interstitial oxygen. They are generally formed during annealing at a temperature of 300-500 ° C. Such annealing allows the association of oxygen atoms to form a species with more complex stoichiometry that has an electron donor behavior in silicon.
Les donneurs thermiques ainsi formés sont stables à température ambiante, mais un recuit à une température supérieure à 600 °C permet leur dissociation, ce qui annule les effets de l'activation thermique précédemment réalisée. On parle alors d'« annihilation » ou « dissolution » des DTs.  The thermal donors thus formed are stable at room temperature, but annealing at a temperature above 600 ° C. allows their dissociation, which cancels out the effects of the thermal activation previously carried out. This is called "annihilation" or "dissolution" of DTs.
Les traitements d'activation/annihilation mis en œuvre selon l'invention peuvent être opérés sous air ou sous atmosphère inerte. 1er mode de réalisation Activation / annihilation treatments used according to the invention can be operated under air or under an inert atmosphere. 1st embodiment
Il est fait référence dans la description qui suit de ce premier mode de réalisation, à la figure 2 annexée.  Reference is made in the following description of this first embodiment to the appended FIG. 2.
Selon cette première variante, une plaquette (10) selon l'invention peut être obtenue via un procédé comprenant au moins les étapes suivantes :  According to this first variant, a wafer (10) according to the invention can be obtained via a method comprising at least the following steps:
(i) disposer d'une plaquette (1) en silicium dopé p telle que décrite précédemment ;  (i) having a p-doped silicon wafer (1) as previously described;
(ii) soumettre ladite plaquette de l'étape (i) à un traitement thermique global, propice à l'activation des donneurs thermiques à base d'oxygène interstitiel et à la conversion de l'ensemble de la plaquette en type n ;  (ii) subjecting said wafer of step (i) to an overall heat treatment, conducive to activation of interstitial oxygen-based heat donors and conversion of the entire wafer to n-type;
(iii) soumettre des zones (12) de la plaquette ( ) obtenue à l'issue de l'étape (iii) subject zones (12) of the wafer () obtained at the end of the step
(ii), dédiées à former les zones dopées p, à un traitement thermique localisé propice à l'annihilation des donneurs thermiques et à la reconversion desdites zones (12) de type n en type p ; et (ii), dedicated to forming the p-doped zones, to a localized heat treatment suitable for the annihilation of the thermal donors and the conversion of said n-type zones (12) into p-type; and
(iv) transformer, par traitement thermique, la portion (13) de chaque zone de type n, contigiie à une zone de type p, en une zone d'isolation électrique (130), pour obtenir la plaquette (10) attendue.  (iv) heat-transforming the portion (13) of each n-type zone contiguous to a p-type zone into an electrical isolation zone (130) to obtain the expected wafer (10).
Le traitement thermique global en étape (ii) peut être par exemple réalisé par recuit thermique de la totalité de la plaquette, par exemple dans un four. The overall heat treatment in step (ii) may for example be carried out by thermal annealing of the entire wafer, for example in an oven.
Il appartient à l'homme du métier d'ajuster les conditions de recuit pour la conversion de l'ensemble de la plaquette (1) de départ en type n.  It is up to the person skilled in the art to adjust the annealing conditions for the conversion of the entire wafer (1) to n-type.
Le recuit peut être par exemple opéré à une température supérieure ou égale à 300 °C et strictement inférieure à 600 °C, en particulier allant de 400 à 500 °C et plus particulièrement d'environ 450 °C.  The annealing may for example be carried out at a temperature greater than or equal to 300 ° C and strictly less than 600 ° C, in particular ranging from 400 to 500 ° C and more particularly about 450 ° C.
La durée du recuit thermique peut être supérieure ou égale à 30 minutes, en particulier être comprise entre 1 heure et 20 heures, notamment être d'environ 4 heures.  The duration of the thermal anneal may be greater than or equal to 30 minutes, in particular be between 1 hour and 20 hours, in particular be approximately 4 hours.
A l'issue de l'étape (ii), la plaquette ( ) obtenue, en silicium dopé n, peut présenter une teneur en porteurs de charge de type électrons (n0) allant de 1014 à 2.1016, en particulier de 5.1014 à 5.1015 cm"3. At the end of step (ii), the wafer () obtained, in n-doped silicon, may have a content of electron-type charge carriers (n 0 ) ranging from 10 14 to 2.10 16 , in particular from 5.10 to 14 to 5.10 15 cm "3 .
De même, l'homme du métier est à même d'ajuster les conditions du traitement thermique localisé en étape (iii) propices à l'annihilation des donneurs thermiques dans les zones (12) de la plaquette dédiées à former des zones dopées p et la reconversion de ces zones de type n en type p. Similarly, a person skilled in the art is able to adjust the conditions of the localized heat treatment in step (iii) suitable for the annihilation of the thermal donors in the zones (12) of the wafer dedicated to forming p-doped zones and the reconversion of these n-type zones into p-type.
Par « localisé », on entend que le traitement thermique affecte uniquement les zones déterminées (12) de la plaquette, à la différence d'un traitement thermique global qui affecte la totalité de la plaquette. Bien entendu, ces zones (12) de la plaquette soumises au traitement thermique, par exemple à l'irradiation par laser, sont déterminées au regard de l'architecture de la plaquette finale souhaitée.  By "localized" is meant that the heat treatment affects only the determined areas (12) of the wafer, unlike a global heat treatment that affects the entire wafer. Of course, these areas (12) of the wafer subjected to heat treatment, for example laser irradiation, are determined with respect to the architecture of the desired final wafer.
Les zones (12) de la plaquette dont on souhaite qu'elles deviennent de type p peuvent être portées à une température supérieure ou égale à 600 °C, notamment allant de 600 à 1000 °C, en particulier pendant au moins 10 secondes. Il appartient à l'homme du métier de mettre en œuvre des moyens connus pour canaliser les flux de chaleur et limiter la propagation latérale de la chaleur pour garder des zones n/p bien délimitées. The areas (12) of the wafer which are desired to become p-type can be brought to a temperature greater than or equal to 600 ° C, in particular ranging from 600 to 1000 ° C, in particular for at least 10 seconds. It is up to those skilled in the art to use known means for channeling heat fluxes and limiting the lateral propagation of heat to keep n / p zones well defined.
Le traitement thermique localisé peut être avantageusement opéré par exposition des zones (12) à traiter à un faisceau laser, de préférence un laser à large spot si l'on souhaite irradier des zones de taille importante, par exemple avec une taille de spot de l'ordre du cm.  The localized heat treatment can be advantageously operated by exposing the zones (12) to be treated to a laser beam, preferably a broad-spot laser if it is desired to irradiate large areas, for example with a spot size of 1. order of the cm.
Le laser peut par exemple fonctionner à une longueur d'onde supérieure ou égale à 500 nm, en particulier allant de 500 nm à 1 100 nm, ce qui permet une propagation de la chaleur en profondeur dans le matériau.  The laser can for example operate at a wavelength greater than or equal to 500 nm, in particular ranging from 500 nm to 1100 nm, which allows a propagation of heat deep in the material.
L'ajustement des conditions du traitement thermique en étape (iv) pour transformer les portions (13) de chacune des zones de type n, contigues à une zone de type p, en zones d'isolation électrique, relève également des compétences de l'homme du métier.  The adjustment of the heat treatment conditions in step (iv) to transform the portions (13) of each of the n-type zones contiguous to a p-type zone into electrical insulation zones is also within the competence of the skilled person.
L'étape (iv) peut être avantageusement opérée par exposition de chaque portion Step (iv) can be advantageously carried out by exposure of each portion
(13) à un faisceau laser, en particulier de faible taille de spot, par exemple de 20 à 100 μιη de largeur. (13) to a laser beam, in particular of small spot size, for example from 20 to 100 μιη of width.
En effet, ce traitement laser additionnel doit être plus localisé que celui mis en œuvre en étape (iii) pour atteindre la largeur (L3) des zones d'isolation électrique souhaitée, et parvenir ainsi à un bon compromis entre qualité d'isolation et limitation de la taille de la zone compensée, inactive du point de vue photovoltaïque. Indeed, this additional laser treatment must be more localized than that implemented in step (iii) to achieve the width (L 3 ) of the desired electrical insulation zones, and thus achieve a good compromise between quality insulation and limitation of the size of the compensated zone, inactive from the photovoltaic point of view.
Les paramètres de durée d'irradiation et de puissance laser peuvent être ajustés pour obtenir l'annihilation d'une fraction des donneurs thermiques dans les zones traitées (13) et leur conversion en des zones d'isolation électrique de forte résistivité.  The irradiation time and laser power parameters can be adjusted to annihilate a fraction of the thermal donors in the treated areas (13) and convert them into areas of high resistivity electrical insulation.
Selon un mode de réalisation particulier, la plaquette peut être soumise, ultérieurement à l'étape (iv), à un traitement de surface, en particulier par attaque chimique, pour supprimer les éventuelles régions surfaciques écrouies résultant du traitement par laser. According to a particular embodiment, the wafer may be subjected, subsequent to step (iv), to a surface treatment, in particular by etching, to remove any hardened surface regions resulting from the laser treatment.
Tout type de techniques d'attaque chimique connues peuvent être utilisées. Par exemple, l'attaque chimique peut être effectuée à l'aide d'une solution formée d'un mélange HN03, HF et CH3COOH, également connu sous le nom de CP133. 2° mode de réalisation Any type of known etching techniques can be used. For example, the etching can be carried out using a solution formed of a mixture HN0 3 , HF and CH 3 COOH, also known as CP133. 2 ° embodiment
Il est fait référence dans la description qui suit de ce second mode de réalisation, à la figure 3 annexée.  Reference is made in the following description of this second embodiment to the appended FIG.
Selon cette seconde variante, une plaquette (10) selon l'invention peut être obtenue via un procédé comprenant au moins les étapes suivantes :  According to this second variant, a wafer (10) according to the invention can be obtained via a method comprising at least the following steps:
(a) disposer d'une plaquette (1) en silicium dopé p telle que décrite précédemment ;  (a) having a p-doped silicon wafer (1) as previously described;
(b) doper en hydrogène les zones, dites (11) et (13), de la plaquette dédiées à former les zones dopées n et les zones d'isolation électrique ; et  (b) hydrogen doping the zones, called (11) and (13), of the wafer dedicated to form the n-doped zones and the electrical isolation zones; and
(c) soumettre ladite plaquette de l'étape (b) à un traitement thermique global propice à l'activation des donneurs thermiques à base d'oxygène interstitiel au niveau des zones (1 1) et (13) dopées en hydrogène, et à la conversion desdites zones (11) de type p en type n et desdites zones (13) en zones d'isolation électrique, pour obtenir la plaquette (10) attendue.  (c) subjecting said wafer of step (b) to an overall heat treatment conducive to the activation of the interstitial oxygen-based heat donors at the hydrogen-doped zones (1 1) and (13), and converting said n-type p-type zones (11) and said zones (13) into electrical isolation zones to obtain the expected wafer (10).
Il appartient à l'homme du métier d'ajuster les taux de dopage en hydrogène des zones (11) et (13) en étape (b) pour obtenir la conversion souhaitée des zones en étape (c), sans affecter les zones (12) dépourvues en hydrogène et dédiées à former les zones p de la plaquette finale. It is up to those skilled in the art to adjust the hydrogen doping levels of the zones (11) and (13) in step (b) to obtain the desired conversion of the zones in step (c), without affecting the zones (12). ) devoid of hydrogen and dedicated to form the areas p of the final wafer.
De préférence, le dopage est opéré de manière à permettre une distribution volumique uniforme de l'hydrogène dans les zones concernées et sur toute l'épaisseur de la plaquette.  Preferably, the doping is operated so as to allow a uniform volume distribution of hydrogen in the areas concerned and over the entire thickness of the wafer.
Selon un mode de réalisation particulier, le dopage en étape (b) peut être opéré via une première étape (bl) d'implantation d'hydrogène à la surface ou en sub-surface des zones à doper, suivie d'une seconde étape (b2) de diffusion de l'hydrogène sur toute l'épaisseur (e) de la plaquette.  According to a particular embodiment, the doping in step (b) can be carried out via a first step (bl) of implantation of hydrogen on the surface or sub-surface of the zones to be doped, followed by a second step ( b2) of diffusion of hydrogen over the entire thickness (e) of the wafer.
On entend par l'implantation d'hydrogène en « sub-surface », une implantation à des profondeurs allant de quelques nanomètres à quelques dizaines de nanomètres.  The term "sub-surface" hydrogen implantation means implantation at depths ranging from a few nanometers to a few tens of nanometers.
L'implantation de l'hydrogène peut être effectuée par des techniques classiques, par exemple par traitement plasma, notamment par dépôt chimique en phase vapeur assisté par plasma (PECVD) ou par plasma d'hydrogène distant induit par microondes (MIRHP). The hydrogen implantation can be carried out by conventional techniques, for example by plasma treatment, in particular by chemical phase deposition. Plasma assisted vapor (PECVD) or microwave - induced remote hydrogen plasma (MIRHP).
Elle peut encore être opérée par une technique d'implantation ionique, notamment par une technique de type SmartCut®. It can still be operated by an ion implantation technique, in particular by a SmartCut ® type technique.
Avantageusement, pour limiter le temps de diffusion de l'hydrogène et les risques d'exo-diffusion, le traitement plasma est réalisé sur les deux faces de la plaquette.  Advantageously, to limit the diffusion time of the hydrogen and the risks of exo-diffusion, the plasma treatment is carried out on both sides of the wafer.
Les zones d'implantation d'hydrogène peuvent être définies à l'aide d'un masque (par exemple, une grille métallique), laissant accessibles uniquement les surfaces des zones à doper, comme illustré dans l'exemple 2 qui suit, par exemple par PECVD.  The hydrogen implantation zones may be defined using a mask (for example, a metal grid), leaving only the surfaces of the areas to be doped accessible, as illustrated in example 2 which follows, for example by PECVD.
En alternative, on peut déposer l'hydrogène de façon uniforme sur toute la surface de la plaquette, et graver le dépôt, par exemple avec de l'acide fluorhydrique (HF), dans les zones (12) dont on souhaite qu'elles restent de type p.  Alternatively, the hydrogen may be uniformly deposited over the entire surface of the wafer, and the deposit may be etched, for example with hydrofluoric acid (HF), in the zones (12) which it is desired to remain type p.
Le taux de dopage en hydrogène est de préférence accru au niveau des zones (11) destinées à former les zones dopées n.  The hydrogen doping rate is preferably increased at the zones (11) intended to form the n-doped zones.
Selon un mode de réalisation particulier, l'implantation d'hydrogène au niveau des zones (11) et (13) peut ainsi comprendre :  According to a particular embodiment, the implantation of hydrogen at the zones (11) and (13) can thus comprise:
- une première étape d'implantation d'hydrogène en surface ou sub-surface des zones (11) dédiées à former les zones dopées n et des zones (13) dédiées à former les zones d'isolation électrique, en masquant les zones (12) dédiées à former les zones dopées p ; et  a first step of implantation of hydrogen at the surface or sub-surface of the zones (11) dedicated to form the n-doped zones and zones (13) dedicated to form the zones of electrical insulation, by masking the zones (12); ) dedicated to forming the p-doped zones; and
- une seconde étape d'implantation d'hydrogène en surface ou sub-surface des zones (11) dédiées à former les zones dopées n, en masquant les zones (12) dédiées à former les zones dopées p et les zones (13) dédiées à former les zones d'isolation électrique.  a second step of implantation of hydrogen at the surface or sub-surface of the zones (11) dedicated to forming the n-doped zones, by masking the zones (12) dedicated to forming the p-doped zones and the dedicated zones (13) to form the areas of electrical insulation.
Il appartient à l'homme du métier d'ajuster les taux surfaciques d'hydrogène implanté, notamment au regard de l'épaisseur de la plaquette (1), de manière à obtenir les taux de dopage volumique souhaités, à l'issue de la diffusion de l'hydrogène sur toute l'épaisseur de la plaquette.  It is up to those skilled in the art to adjust the implanted hydrogen surface rates, particularly with regard to the thickness of the wafer (1), so as to obtain the desired volumetric doping levels, at the end of the diffusion of hydrogen over the entire thickness of the wafer.
Par exemple, le taux de dopage volumique des zones (11) dédiées à former les zones dopées n peut être compris entre 1 et 4.1013 cm"3, Le taux de dopage volumique des zones (13) dédiées à former les zones d'isolation électrique peut être compris entre 1 et 4.1011 cm"3. La diffusion de l'hydrogène dans les zones à doper (étape (b2)) peut être par exemple opérée par exposition desdites zones aux ultrasons, en particulier à l'aide de transducteurs piézoélectriques. For example, the volume doping rate of the zones (11) dedicated to form the doped zones n can be between 1 and 4.10 13 cm -3 . The volume doping rate of the zones (13) dedicated to form the zones of isolation electrical can be between 1 and 4.10 11 cm "3 . The diffusion of hydrogen into the zones to be doped (step (b2)) can be performed, for example, by exposing said zones to ultrasound, in particular using piezoelectric transducers.
Par exemple, on peut utiliser des transducteurs piézoélectriques travaillant entre 20 kHz et 1 MHz, de préférence entre 50 et 500 kHz, des déformations acoustiques induites entre 5.10"6 et 2.10"5, et des durées de traitement entre 5 et 120 minutes, préférentiellement entre 10 et 60 minutes. For example, it is possible to use piezoelectric transducers working between 20 kHz and 1 MHz, preferably between 50 and 500 kHz, acoustic deformations induced between 5.10 "6 and 2.10 " 5 , and treatment times between 5 and 120 minutes, preferentially between 10 and 60 minutes.
En alternative, la diffusion de l'hydrogène en étape (b2) peut être opérée par recuit thermique de la plaquette, notamment dans un four, en particulier à une température allant de 400 °C à 1000 °C, et pendant une durée allant de 5 secondes à 5 heures.  As an alternative, the diffusion of hydrogen in step (b2) can be carried out by thermal annealing of the wafer, in particular in an oven, in particular at a temperature ranging from 400 ° C. to 1000 ° C., and for a period ranging from 5 seconds to 5 hours.
De fait, le dopage par l'hydrogène va permettre d'accélérer les cinétiques d'activation des donneurs thermiques dans les zones dopées. Un traitement thermique global de la plaquette peut ainsi être opéré dans des conditions propices à l'activation privilégiée des donneurs thermiques au niveau des zones pourvues en hydrogène, et sans affecter les zones qui en sont dépourvues.  In fact, doping with hydrogen will accelerate the activation kinetics of thermal donors in the doped zones. An overall thermal treatment of the wafer can thus be operated under conditions conducive to the privileged activation of thermal donors in the zones provided with hydrogen, and without affecting the areas which are devoid of them.
Le traitement thermique global en étape (c) peut être par exemple opéré par recuit thermique à une température supérieure ou égale à 300°C et strictement inférieure à 600 °C, en particulier de 400 à 500 °C, et plus particulièrement d'environ 450 °C.  The overall heat treatment in step (c) may for example be carried out by thermal annealing at a temperature greater than or equal to 300 ° C. and strictly less than 600 ° C., in particular from 400 ° to 500 ° C., and more particularly from approximately 450 ° C.
La durée du recuit peut être supérieure ou égale à 30 minutes, en particulier être comprise entre 1 heure et 20 heures, et plus particulièrement d'environ 3 heures.  The annealing time may be greater than or equal to 30 minutes, in particular between 1 hour and 20 hours, and more particularly about 3 hours.
DISPOSITIFS PHOTO VOLTAIOUES VOLTAIVE PHOTO DEVICES
L'homme du métier est à même de mettre en œuvre les traitements adéquats classiques, pour l'élaboration d'une cellule photovoltaïque (PV), à partir d'une plaquette (10) selon l'invention, par exemple des traitements appropriés à la formation des jonctions p/n au sein des zones n ou p, ou encore à la formation des contacts assurant la mise en série des sous-cellules.  The skilled person is able to implement the appropriate conventional treatments, for the development of a photovoltaic cell (PV), from a wafer (10) according to the invention, for example treatments appropriate to the formation of the p / n junctions within the n or p zones, or else the formation of the contacts ensuring the serialization of the sub-cells.
De préférence, à l'issue du procédé de fabrication de la plaquette (10) selon l'invention, on utilise une technologie basse température de type hétéroj onction (silicium amorphe sur silicium cristallin), pour la réalisation de la cellule photovoltaïque. A titre d'exemples, peuvent être opérées, à l'issue de la fabrication de la plaquette (10) selon l'une ou l'autre des variantes de procédé décrites précédemment, une ou plusieurs étapes suivantes : Preferably, at the end of the manufacturing process of the wafer (10) according to the invention, a low temperature technology of heterojunction type (amorphous silicon on crystalline silicon) is used, for the realization of the photovoltaic cell. By way of examples, after the manufacture of the wafer (10) according to one or the other of the method variants described above, it is possible to carry out one or more of the following steps:
- dépôt d'une première couche de silicium amorphe intrinsèque (typiquement d'une épaisseur de l'ordre de 5 nm) et d'une couche amorphe dopée p+ ou n+, sur chacune des faces de la plaquette ;  depositing a first layer of intrinsic amorphous silicon (typically of a thickness of the order of 5 nm) and of a p + or n + doped amorphous layer on each of the faces of the wafer;
- dépôt de couches d'oxyde transparent conducteur, notamment à base d'ITO, en surface desdites couches de silicium amorphe ;  depositing transparent conductive oxide layers, in particular based on ITO, on the surface of said amorphous silicon layers;
- formation d'une ou plusieurs métallisations (également appelées « contacts conducteurs ») en face avant et/ou arrière de la plaquette, notamment par sérigraphie de pâte d'argent, à basse température.  - Formation of one or more metallizations (also called "conductive contacts") on the front and / or back of the wafer, in particular by serigraphy of silver paste, at low temperature.
Il est cependant également possible d'élaborer une cellule photovoltaïque en utilisant la technologie classique, à haute température. Dans le cadre de la mise en œuvre d'une telle technologie, il est nécessaire de réaliser les étapes à haute température (par exemple, de diffusion gazeuse), préalablement aux traitements thermiques d'activation/annihilation des donneurs thermiques.  However, it is also possible to develop a photovoltaic cell using conventional technology, at high temperature. In the context of the implementation of such a technology, it is necessary to carry out the high temperature steps (for example, gas diffusion), prior to heat treatments for activation / annihilation of the thermal donors.
A titre d'exemple, dans le cadre d'une technologie haute température, peuvent être opérées, préalablement aux traitements thermiques d'activation/annihilation des DT mis en œuvre dans l'une ou l'autre des variantes de procédé de préparation de la plaquette, un ou plusieurs étapes suivantes :  For example, in the context of a high temperature technology, can be operated, prior to DT activation / annihilation heat treatments implemented in one or other of the preparation process variants of the platelet, one or more of the following steps:
- dépôt d'une ou plusieurs couches de passivation et/ou anti-reflet ; depositing one or more passivation and / or anti-reflection layers;
- formation d'une ou plusieurs métallisations en face avant et/ou arrière de la plaquette, notamment par sérigraphie Ag ou Ag/Al. Une étape de recuit des métallisations est réalisée ensuite dans un four à passage à 800 °C environ, pendant quelques secondes. - Formation of one or more metallizations front and / or back of the wafer, in particular by screen printing Ag or Ag / Al. A step of annealing the metallizations is then carried out in a passage oven at 800 ° C for a few seconds.
Les cellules PV obtenues selon l'invention peuvent alors être assemblées pour élaborer un module photovoltaïque de taille raisonnable, classiquement de dimension de l'ordre du m2, et présentant une tension accrue par rapport aux modules élaborés à partir de cellules classiques. The PV cells obtained according to the invention can then be assembled to produce a photovoltaic module of reasonable size, conventionally of dimension of the order of m 2 , and having an increased voltage compared to modules developed from conventional cells.
Selon encore un autre de ses aspects, l'invention concerne ainsi un module photovoltaïque formé d'un ensemble de cellules photovoltaïques selon l'invention. L'invention va maintenant être décrite au moyen des exemples suivants, donnés bien entendu à titre illustratif et non limitatif de l'invention. According to yet another of its aspects, the invention thus relates to a photovoltaic module formed of a set of photovoltaic cells according to the invention. The invention will now be described by means of the following examples, given of course by way of illustration and not limitation of the invention.
EXEMPLES EXEMPLE 1 EXAMPLES EXAMPLE 1
(i) Plaquette de silicium dopé p  (i) p-doped silicon wafer
On utilise une plaquette de silicium de type p de 220 μιη d'épaisseur, obtenue par découpe d'un lingot élaboré par solidification dirigée par la technique de refroidissement sous gradient (« gradient freeze »).  A p-type silicon wafer 220 μιη in thickness is used, obtained by cutting an ingot developed by solidification directed by the gradient-freeze technique.
Cette plaquette présente une teneur en porteurs de charge de type trous, déterminée via la mesure de la résistivité, de 5.1015 cm"3, et une concentration en oxygène interstitiel, déterminée par analyse FTIR, de 1,5.1018 cm"3. This wafer has a content type of charge carriers holes, determined via the measurement of the resistivity of 5.10 15 cm "3, and an interstitial oxygen concentration as determined by FTIR analysis, 1.5x10 18 cm" 3.
(ii) Conversion de la plaquette en type n (ii) Conversion of the wafer into type n
La plaquette subit un recuit à 450 °C pendant 4 heures afin d'activer des donneurs thermiques. Ce recuit permet la conversion de la plaquette de type p en type n, avec une teneur en électrons, déterminée par mesure de l'effet Hall, de 2.1015 cm"3. The wafer is annealed at 450 ° C for 4 hours to activate thermal donors. This annealing allows the conversion of the p-type wafer to n-type, with an electron content, determined by measurement of the Hall effect, of 2.10 15 cm -3 .
(iii) Traitement thermique localisé (iii) Localized heat treatment
La plaquette est ensuite positionnée sous un faisceau laser, mis en forme selon le motif représenté en figure 4a. Les zones non irradiées sont celles que l'on veut conserver de type n, et les zones irradiées (12) sont les zones que l'on souhaite refaire basculer de type p. Les motifs sont de dimension 4x4 cm2. The wafer is then positioned under a laser beam, shaped according to the pattern shown in FIG. 4a. The non-irradiated areas are those that we want to keep n-type, and the irradiated areas (12) are the areas that we want to re-switch p-type. The reasons are of dimension 4x4 cm 2 .
Le faisceau laser utilise une longueur d'onde dans le rouge/infrarouge, afin d'apporter de la chaleur en profondeur. La puissance laser est réglée dans le but d'élever la température du substrat au moins à 600°C, afin de dissoudre la majorité des donneurs thermiques en présence et reconvertir la zone en type p, tout en limitant autant que possible la dégradation de la surface de l'échantillon.  The laser beam uses a wavelength in the red / infrared, in order to bring heat deep down. The laser power is adjusted in order to raise the temperature of the substrate to at least 600 ° C, in order to dissolve the majority of the thermal donors in the presence and convert the zone back to type p, while limiting as much as possible the degradation of the surface of the sample.
Une puissance de 30 W pour un diamètre de faisceau de 100 μπι constitue un bon exemple de point de fonctionnement, avec un balayage de zone.  A power of 30 W for a 100 μπι beam diameter is a good example of an operating point, with a zone scan.
La durée du traitement laser est réglée de manière à permettre la montée en température de toutes les zones irradiées au-delà du seuil de 600 °C pendant au moins 10 secondes, tout en limitant la diffusion latérale de chaleur, afin d'obtenir une mosaïque de types aussi nette que possible. The duration of the laser treatment is adjusted so as to allow the rise in temperature of all irradiated areas beyond the threshold of 600 ° C for at least 10 minutes. seconds, while limiting the lateral diffusion of heat, in order to obtain a mosaic of types as sharp as possible.
(iv) Formation des zones d'isolation électrique (iv) Formation of electrical insulation zones
La plaquette subit une deuxième étape laser, visant à l'élaboration de zones très résistives entre les différentes régions de types opposés. Dans ce but, le faisceau est balayé sur le pourtour (13) de chaque sous élément de type n, sur une largeur de 1 mm (en noir sur la figure 4b).  The wafer undergoes a second laser step, aiming at the development of highly resistive zones between the different regions of opposite types. For this purpose, the beam is scanned around the perimeter (13) of each n-type sub-element, over a width of 1 mm (in black in FIG. 4b).
Les paramètres de durée d'irradiation et de puissance laser sont ajustés dans le but d'obtenir des zones localisées où seule une fraction des donneurs thermiques a été dissoute, permettant l'obtention d'une zone d'isolation électrique, et donc très résistive.  The parameters of irradiation duration and laser power are adjusted in order to obtain localized zones where only a fraction of the thermal donors has been dissolved, making it possible to obtain an electrical isolation zone, and therefore very resistive .
Enfin, la plaquette subit une attaque chimique type CP133 (HF, HN03, CH3COOH) afin de supprimer les éventuelles zones surfaciques écrouies, résultant des étapes laser. Finally, the wafer undergoes a chemical attack type CP133 (HF, HN0 3 , CH3COOH) in order to remove any hardened surface areas resulting from the laser steps.
EXEMPLE 2 EXAMPLE 2
(a) Plaquette de silicium dopé p  (a) p-doped silicon wafer
On utilise une plaquette de silicium de type p de 200 μπι d'épaisseur, avec une teneur en porteurs trous de 1015 cm"3, et une concentration en oxygène de 7.1017 cm"3. Using a wafer of p-type silicon 200 μπι thick, with a carrier content holes 10 15 cm "3, and an oxygen concentration of 7.10 17 cm" 3.
Les surfaces de la plaquette sont préalablement polies par une attaque chimique type CP133.  The surfaces of the wafer are previously polished by a chemical attack type CP133.
(b) Dopage en hydrogène (b) Hydrogen doping
Implantation ionique d'hydrogène  Ionic implantation of hydrogen
• Une première étape de masquage, à l'aide d'une grille métallique posée au dessus du substrat, est effectuée conformément aux motifs, présentés sur la figure 5a. Les zones masquées (12) correspondent aux zones de la plaquette qui resteront de type p. Les zones découvertes correspondent aux zones (11) et (13) de la plaquette destinées à former les zones de type n et les zones d'isolation électrique.  • A first masking step, using a metal grid placed above the substrate, is performed in accordance with the patterns, shown in Figure 5a. The masked areas (12) correspond to the areas of the wafer which will remain of type p. The open areas correspond to the zones (11) and (13) of the wafer intended to form the n-type zones and the electrical insulation zones.
Les motifs sont de dimension 4x4 cm2. Cette première étape de masquage est suivie d'une implantation ionique d'hydrogène, par immersion plasma à l'aide d'un équipement standard, à une dose surfacique Dl de 4.109 cm"2, ce qui correspondra pour la plaquette de 200 μιη d'épaisseur à une dose volumique de 2.1011 cm"3. L'énergie d'implantation de l'hydrogène utilisée pour cette application est voisine de 135 keV. The reasons are of dimension 4x4 cm 2 . This first masking step is followed by an ion implantation of hydrogen, by plasma immersion using a standard equipment, at a surface dose Dl of 4.10 9 cm -2 , which will correspond for the wafer of 200 μιη of thickness at a volume dose of 2.10 11 cm -3 . The implantation energy of the hydrogen used for this application is close to 135 keV.
• Cette première étape d'implantation ionique est ensuite suivie d'une nouvelle étape de masquage, comme représenté en figure 5b. Les zones masquées sont alors les zones de la plaquette (12) qui resteront de type p (zones non implantées) ainsi que les zones (implantées à la dose Dl) de la plaquette (13) destinées à former les zones d'isolation électrique. Cette seconde étape de masquage est suivie d'une seconde étape d'implantation ionique sous l'énergie 135 keV à une dose d'implantation D2 de 4.1011 cm"2, ce qui, dans une plaquette de 200 μπι d'épaisseur, correspondra à une dose volumique de 2.1013 cm"3. Diffusion de l'hydrogène This first ion implantation step is then followed by a new masking step, as shown in FIG. 5b. The masked areas are then the areas of the wafer (12) which will remain p-type (non-implanted areas) as well as the areas (implanted at the dose Dl) of the wafer (13) intended to form the areas of electrical insulation. This second masking step is followed by a second step of ion implantation under 135 keV energy at an implantation dose D 2 of 4.10 11 cm -2 , which, in a 200 μπι thick wafer, corresponds to at a volume dose of 2.10 13 cm -3 . Hydrogen diffusion
Les masques sont ensuite enlevés, et la plaquette subit un recuit thermique en four à une température de 700 °C pendant 10 minutes, pour permettre à l'hydrogène issu des couches implantées de se répartir de façon homogène sur l'épaisseur de la plaquette. (c) Traitement thermique global  The masks are then removed, and the wafer is thermally oven-annealed at a temperature of 700 ° C for 10 minutes, to allow hydrogen from the implanted layers to evenly distribute over the wafer thickness. (c) Overall heat treatment
La plaquette subit un recuit thermique à une température voisine de 450 °C pendant une durée de 3 heures, afin de transformer les zones dopées p comprenant l'hydrogène en zones dopées n, comme représenté schématiquement en figure 5c.  The wafer is thermally annealed at a temperature in the region of 450 ° C. for a period of 3 hours, in order to transform the p-doped zones comprising hydrogen into n-doped zones, as shown schematically in FIG. 5c.
A l'issue du traitement thermique, la plaquette présentent une alternance de zones dopées n et de zones dopées p, chacune des zones n et p étant séparées par une zone d'isolation électrique (130) de résistivité élevée. Références : At the end of the heat treatment, the wafer has an alternation of n-doped zones and p-doped zones, each of the n and p zones being separated by an electrical insulation zone (130) of high resistivity. References :
[1] Pozner et al, Progress in Photovoltaics 20 (2012), 197 ;  [1] Pozner et al, Progress in Photovoltaics 20 (2012), 197;
[2] US 4,320,247 ; [2] US 4,320,247;
[3] Wijaranakula, Appl. Phys. Lett. 59 (1991), 1608.  [3] Wijaranakula, Appl. Phys. Lett. 59 (1991), 1608.

Claims

REVENDICATIONS
1. Plaquette de silicium (10) monolithique, présentant, dans au moins un plan vertical de coupe, une alternance de zones (1 10) dopées n et de zones (120) dopées p, chacune des zones s'étendant sur toute l'épaisseur (e) de la plaquette, caractérisée en ce que : Monolithic silicon wafer (10) having, in at least one vertical sectional plane, an alternation of n-doped zones (1 10) and p-doped zones (120), each of the zones extending over the entire thickness (e) of the wafer, characterized in that:
- lesdites zones (1 10) et (120) présentent chacune, dans le plan de coupe, une largeur (Li, L2) d'au moins 1 mm ; - said zones (1 10) and (120) each have, in the cutting plane, a width (Li, L 2 ) of at least 1 mm;
- les zones dopées n (1 10) présentent une concentration en donneurs thermiques à base d'oxygène interstitiel distincte de celle des zones dopées p (120) ; et  the n-doped zones (1 10) have a concentration of thermal donors based on interstitial oxygen distinct from that of the p-doped zones (120); and
- lesdites zones dopées n (110) et lesdites zones dopées p (120) sont séparées entre elles par des zones d'isolation électrique (130). said n-doped zones (110) and said p-doped zones (120) are separated from each other by electrical isolation zones (130).
2. Plaquette selon la revendication 1, ladite plaquette comprenant une concentration en oxygène interstitiel comprise entre 1017 et 2.1018 cm"3, en particulier comprise entre 5.10 17 et 1,5.1018 cm" 3, 2. Plate according to claim 1, said wafer comprising an interstitial oxygen concentration of between 10 17 and 2.10 18 cm "3, in particular between 5.10 and 17 1,5.1018 cm" 3,
3. Plaquette selon la revendication 1 ou 2, dans laquelle lesdites zones dopées n (110) présentent, indépendamment les unes des autres, une largeur (Li) allant de 1 mm à 10 cm, en particulier de 5 mm à 5 cm.  3. A wafer according to claim 1 or 2, wherein said n-doped zones (110) have, independently of each other, a width (Li) ranging from 1 mm to 10 cm, in particular from 5 mm to 5 cm.
4. Plaquette selon l'une quelconque des revendications précédentes, dans laquelle lesdites zones dopées p (120) présentent, indépendamment les unes des autres, une largeur (L2) allant de 1 mm à 10 cm, en particulier de 5 mm à 5 cm. 4. Plate according to any one of the preceding claims, wherein said p-doped zones (120) have, independently of one another, a width (L 2 ) ranging from 1 mm to 10 cm, in particular from 5 mm to 5 mm. cm.
5. Plaquette selon l'une quelconque des revendications précédentes, dans laquelle chacune desdites zones d'isolation électrique (130) présente une largeur (L3) allant de 50 μπι à 5 mm, en particulier de 200 μπι à 1 mm. 5. A wafer according to any one of the preceding claims, wherein each of said electrical insulating areas (130) has a width (L 3 ) ranging from 50 μπι to 5 mm, in particular from 200 μπι to 1 mm.
6. Plaquette selon l'une quelconque des revendications précédentes, dans laquelle la disposition desdites zones n et p alternées forme un motif bidimensionnel, en particulier de type damier, avec le côté d'un carré étant plus particulièrement compris entre 1 mm et 10 cm, lesdites zones d'isolation électrique formant un pourtour de chacune des zones n et p.  6. A wafer according to any one of the preceding claims, wherein the arrangement of said n and p alternating zones form a two-dimensional pattern, in particular of the checkerboard type, with the side of a square being more particularly between 1 mm and 10 cm. said electrical insulation zones forming a periphery of each of the zones n and p.
7. Procédé de fabrication d'une plaquette (10) selon l'une quelconque des revendications 1 à 6, comprenant au moins les étapes consistant en : (i) disposer d'une plaquette (1) en silicium dopé p comprenant une concentration en porteurs de charge de type trous (p0) comprise entre 1014 et 2.1016 cm"3 et une concentration en oxygène interstitiel [Oi] comprise entre 1017 et 2.1018 cm"3 ; A method of manufacturing a wafer (10) according to any one of claims 1 to 6, comprising at least the steps of: (i) having a p-doped silicon wafer (1) comprising a hole-type charge carrier concentration (p 0 ) of between 10 14 and 2.10 16 cm -3 and an interstitial oxygen concentration [Oi] of between 17 and 2.10 18 cm- 3 ;
(ii) soumettre ladite plaquette de l'étape (i) à un traitement thermique global, propice à l'activation des donneurs thermiques à base d'oxygène interstitiel et à la conversion de l'ensemble de la plaquette en type n ;  (ii) subjecting said wafer of step (i) to an overall heat treatment, conducive to activation of interstitial oxygen-based heat donors and conversion of the entire wafer to n-type;
(iii) soumettre des zones (12) de la plaquette ( ) obtenue à l'issue de l'étape (ii), dédiées à former les zones dopées p, à un traitement thermique localisé propice à l'annihilation des donneurs thermiques et à la reconversion desdites zones (12) de type n en type p ; et  (iii) subjecting areas (12) of the wafer () obtained at the end of step (ii), dedicated to forming the p-doped zones, to a localized thermal treatment that is favorable for the annihilation of the thermal donors and to reconverting said n-type zones (12) into p-type; and
(iv) transformer, par traitement thermique, la portion (13) de chaque zone de type n, contigiie à une zone de type p, en une zone d'isolation électrique (130), pour obtenir la plaquette (10) attendue.  (iv) heat-transforming the portion (13) of each n-type zone contiguous to a p-type zone into an electrical isolation zone (130) to obtain the expected wafer (10).
8. Procédé selon la revendication 7, dans lequel ledit traitement thermique en étape (ii) est opéré par recuit à une température supérieure ou égale à 300°C et strictement inférieure à 600 °C, en particulier allant de 400 à 500°C et plus particulièrement d'environ 450 °C.  8. The method of claim 7, wherein said heat treatment step (ii) is carried out by annealing at a temperature greater than or equal to 300 ° C and strictly less than 600 ° C, in particular ranging from 400 to 500 ° C and more particularly about 450 ° C.
9. Procédé selon la revendication 7 ou 8, dans lequel lesdites zones (12) dédiées à former des zones dopées p sont portées en étape (iii) à une température supérieure ou égale à 600°C, notamment allant de 600 à 1000 °C, en particulier pendant au moins 10 secondes.  9. The method of claim 7 or 8, wherein said zones (12) dedicated to form p-doped areas are carried in step (iii) at a temperature greater than or equal to 600 ° C, in particular ranging from 600 to 1000 ° C , especially for at least 10 seconds.
10. Procédé selon l'une quelconque des revendications 7 à 9, dans lequel ledit traitement thermique localisé en étape (iii) est opéré par exposition desdites zones (12) à un faisceau laser, en particulier avec une taille de spot de l'ordre du cm.  The method according to any one of claims 7 to 9, wherein said localized heat treatment in step (iii) is operated by exposing said zones (12) to a laser beam, in particular with a spot size of the order cm.
1 1. Procédé selon l'une quelconque des revendications 7 à 10, dans lequel l'étape (iv) est opérée par exposition de chaque portion (13) à un faisceau laser, en particulier de taille de spot allant de 20 à 100 μιη.  1. Method according to any one of claims 7 to 10, wherein step (iv) is performed by exposing each portion (13) to a laser beam, in particular of spot size ranging from 20 to 100 μιη. .
12. Procédé de fabrication d'une plaquette (10) selon l'une quelconque des revendications 1 à 6, comprenant au moins les étapes consistant en :  A method of manufacturing a wafer (10) according to any one of claims 1 to 6, comprising at least the steps of:
(a) disposer d'une plaquette (1) en silicium dopé p comprenant une concentration en porteurs de charge de type trous (p0) comprise entre 1014 et 2.1016 cm"3 et une concentration en oxygène interstitiel [Oi] comprise entre 1017 et 2.1018 cm"3 ; (b) doper en hydrogène les zones, dites (11) et (13), de la plaquette dédiées à former les zones dopées n et les zones d'isolation électrique ; et (a) having a p-doped silicon wafer (1) comprising a hole-type charge carrier concentration (p 0 ) of between 10 14 and 2.10 16 cm -3 and an interstitial oxygen concentration [Oi] of between 17 and 2.10 18 cm- 3 ; (b) hydrogen doping the zones, called (11) and (13), of the wafer dedicated to form the n-doped zones and the electrical isolation zones; and
(c) soumettre ladite plaquette de l'étape (b) à un traitement thermique global, propice à l'activation des donneurs thermiques à base d'oxygène interstitiel au niveau des zones dopées en hydrogène, et à la conversion desdites zones (11) de type p en type n et desdites zones (13) en zones d'isolation électrique, pour obtenir la plaquette (10) attendue.  (c) subjecting said wafer of step (b) to an overall heat treatment, conducive to the activation of the interstitial oxygen-based heat donors at the hydrogen doped regions, and to the conversion of said zones (11) n-type p type and said zones (13) in electrical insulation zones, to obtain the wafer (10) expected.
13. Procédé selon la revendication 12, dans lequel le dopage en étape (b) comprend une étape (bl) d'implantation d'hydrogène à la surface ou en sub-surface des zones à doper, suivie d'une étape (b2) de diffusion de l'hydrogène sur toute l'épaisseur (e) de la plaquette.  13. The method of claim 12, wherein the step doping (b) comprises a step (bl) of implantation of hydrogen on the surface or sub-surface areas to be doped, followed by a step (b2). diffusion of hydrogen over the entire thickness (e) of the wafer.
14. Procédé selon la revendication précédente, dans lequel l'implantation d'hydrogène en étape (bl) est effectuée par traitement plasma, en particulier par dépôt chimique en phase vapeur assisté par plasma, par plasma d'hydrogène distant induit par micro-ondes, ou par une technique d'implantation ionique.  14. Method according to the preceding claim, wherein the implantation of hydrogen in step (b1) is carried out by plasma treatment, in particular by plasma-enhanced chemical vapor deposition, by microwave-induced remote hydrogen plasma. , or by ion implantation technique.
15. Procédé selon la revendication 13 ou 14, dans lequel l'étape (b2) de diffusion de l'hydrogène dans les zones à doper est opérée par exposition desdites zones aux ultrasons, en particulier à l'aide de transducteurs piézoélectriques ; ou par recuit thermique de la plaquette, en particulier à une température allant de 400 °C à 1000 °C et pendant une durée allant de 5 secondes à 5 heures.  15. The method of claim 13 or 14, wherein the step (b2) of hydrogen diffusion in the areas to be doped is operated by exposure of said zones to ultrasound, in particular using piezoelectric transducers; or by thermal annealing of the wafer, in particular at a temperature ranging from 400 ° C to 1000 ° C and for a time ranging from 5 seconds to 5 hours.
16. Procédé selon l'une quelconque des revendications 12 à 15, dans lequel l'étape (c) est opérée par recuit à une température supérieure ou égale à 300 °C et strictement inférieure à 600 °C, en particulier de 400 à 500 °C et plus particulièrement d'environ 450 °C.  16. A process according to any one of claims 12 to 15, wherein step (c) is carried out by annealing at a temperature greater than or equal to 300 ° C and strictly less than 600 ° C, in particular from 400 to 500 ° C. ° C and more particularly about 450 ° C.
17. Dispositif photovoltaïque, en particulier cellule photovoltaïque, comportant une plaquette de silicium telle que définie selon l'une quelconque des revendications 1 à 6.  Photovoltaic device, in particular a photovoltaic cell, comprising a silicon wafer as defined in any one of claims 1 to 6.
EP14713263.3A 2013-03-08 2014-03-06 Monolithic silicon wafer having alternating n-doped areas and p-doped areas Withdrawn EP2965362A1 (en)

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FR1352096A FR3003089B1 (en) 2013-03-08 2013-03-08 MONOLITHIC SILICON PLATE WITH MULTI-JOINT P / N VERTICAL.
PCT/IB2014/059497 WO2014136082A1 (en) 2013-03-08 2014-03-06 Monolithic silicon wafer having alternating n-doped areas and p-doped areas

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