WO2014083240A1 - Procédé de fabrication d'une structure comprenant une couche de passivation sur une surface d'un substrat - Google Patents

Procédé de fabrication d'une structure comprenant une couche de passivation sur une surface d'un substrat Download PDF

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Publication number
WO2014083240A1
WO2014083240A1 PCT/FI2013/051090 FI2013051090W WO2014083240A1 WO 2014083240 A1 WO2014083240 A1 WO 2014083240A1 FI 2013051090 W FI2013051090 W FI 2013051090W WO 2014083240 A1 WO2014083240 A1 WO 2014083240A1
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precursor
passivation layer
substrate
aluminum
atomic
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PCT/FI2013/051090
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English (en)
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Shuo Li
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Beneq Oy
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    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/44—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating
    • C23C16/455—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the method of coating characterised by the method used for introducing gases into reaction chamber or for modifying gas flows in reaction chamber
    • C23C16/45523—Pulsed gas flow or change of composition over time
    • C23C16/45525—Atomic layer deposition [ALD]
    • C23C16/45553—Atomic layer deposition [ALD] characterized by the use of precursors specially adapted for ALD
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
    • C23C16/30—Deposition of compounds, mixtures or solid solutions, e.g. borides, carbides, nitrides
    • C23C16/40—Oxides
    • C23C16/403—Oxides of aluminium, magnesium or beryllium
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
    • C23C16/56—After-treatment
    • 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
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02109—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates
    • H01L21/02112—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer
    • H01L21/02172—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing at least one metal element, e.g. metal oxides, metal nitrides, metal oxynitrides or metal carbides
    • H01L21/02175—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing at least one metal element, e.g. metal oxides, metal nitrides, metal oxynitrides or metal carbides characterised by the metal
    • H01L21/02178—Forming insulating materials on a substrate characterised by the type of layer, e.g. type of material, porous/non-porous, pre-cursors, mixtures or laminates characterised by the material of the layer the material containing at least one metal element, e.g. metal oxides, metal nitrides, metal oxynitrides or metal carbides characterised by the metal the material containing aluminium, e.g. Al2O3
    • 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
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02225—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer
    • H01L21/0226—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process
    • H01L21/02263—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process deposition from the gas or vapour phase
    • H01L21/02271—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process deposition from the gas or vapour phase deposition by decomposition or reaction of gaseous or vapour phase compounds, i.e. chemical vapour deposition
    • H01L21/0228—Forming insulating materials on a substrate characterised by the process for the formation of the insulating layer formation by a deposition process deposition from the gas or vapour phase deposition by decomposition or reaction of gaseous or vapour phase compounds, i.e. chemical vapour deposition deposition by cyclic CVD, e.g. ALD, ALE, pulsed CVD
    • 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
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02107—Forming insulating materials on a substrate
    • H01L21/02296—Forming insulating materials on a substrate characterised by the treatment performed before or after the formation of the layer
    • H01L21/02299—Forming insulating materials on a substrate characterised by the treatment performed before or after the formation of the layer pre-treatment
    • H01L21/02301—Forming insulating materials on a substrate characterised by the treatment performed before or after the formation of the layer pre-treatment in-situ cleaning
    • 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
    • H01L31/02—Details
    • H01L31/0216—Coatings
    • H01L31/02161—Coatings for devices characterised by at least one potential jump barrier or surface barrier
    • H01L31/02167—Coatings for devices characterised by at least one potential jump barrier or surface barrier for solar cells

Definitions

  • the present invention relates to film deposi tion technology.
  • the present invention relates to method and a structure for passivating a silicon sur face .
  • Photovoltaic cells are gradually becoming an important means of generating electrical energy. Espe ⁇ cially solar cells, photovoltaic cells designed to convert sunlight into electrical energy, are consid- ered as one of the most promising candidates for re ⁇ newable energy production.
  • crystalline silicon (c-Si) solar cells has been the introduction of surface passivation to reduce the charge carrier recombination on the surface of a sili ⁇ con wafer.
  • Surface recombination in semiconductors is a result of possibly many different mechanisms leading to trapping of charge carriers in specific energy states at or close to the surface of a semiconductor.
  • These energy states, or surface states as they are of ⁇ ten called, may originate from different sources, such as impurities at the surface or the inevitable disrup- tion of periodicity of a semiconductor crystal at the surface.
  • the purpose of the invention is to provide a new type of method for fabricating a structure com ⁇ prising a passivation layer on a surface of a substrate comprising crystalline silicon. Further the purpose of the present invention is to provide a structure comprising a passivation layer on a surface of a substrate comprising crystalline silicon.
  • Fig. 1 is a flow-chart illustration of a method according to one embodiment of the present in ⁇ vention.
  • Fig. 2. is a schematic illustration of a structure according to one embodiment of the present invention .
  • the present invention relates to a method for fabricating a structure comprising a passivation layer on a surface of a substrate comprising crystalline silicon for reducing recombination of charge carriers on the surface of the substrate, wherein the method comprises the step of depositing a passivation layer, comprising aluminum oxide, on the surface of the sub ⁇ strate by exposing the deposition surface of the sub ⁇ strate in a reaction space, at a temperature of 90 - 290 °C, to alternately repeated surface reactions of at least one precursor for aluminum and at least one precursor for oxygen, wherein the at least one precursor for aluminum comprises at least one precursor for aluminum including a halogen, and wherein the at least one precursor for oxygen is provided to the deposition surface with a gas flow including 1 - 15 mole-% of the at least one precursor for oxygen.
  • a "flow of gas”, “flow of carrier gas” or a “gas flow” is commonly used for supplying the different precur- sors used during the deposition process.
  • the gas flow may comprise a gas, which is inert towards the precur ⁇ sors used in the process.
  • the gas flow comprises nitrogen or argon .
  • the present invention relates to a method for fabricating a structure comprising a passivation layer on a surface of a substrate comprising crystalline silicon for reducing recombination of charge carriers on the surface of the substrate, wherein the method comprises the step of depositing a passivation layer, comprising aluminum oxide and having halogen, hydro- gen, and carbon incorporated therein, on the surface of the substrate by exposing the deposition surface of the substrate in a reaction space, at a temperature of 90 - 290 °C, to alternately repeated surface reactions of at least one precursor for aluminum and at least one precursor for oxygen, wherein the at least one precursor for aluminum comprises at least one precursor for aluminum including a halogen.
  • the passivation layer further comprises chlorine, io- dine, bromine, and/or fluorine.
  • the present invention further relates to a structure comprising a passivation layer comprising aluminum oxide on a surface of a substrate comprising crystalline silicon, for reducing recombination of charge carriers on the surface of the substrate, ob ⁇ tainable by the method according to the present inven ⁇ tion.
  • the present invention further relates to a structure comprising a passivation layer comprising aluminum oxide on a surface of a substrate comprising crystalline silicon, for reducing recombination of charge carriers on the surface of the substrate, wherein the passivation layer comprises 29 - 38 atom- ic-% of aluminum, 50 - 58 atomic-% of oxygen, 1 - 5 atomic-% of halogen, 4 - 15 atomic-% of hydrogen, and 0,1 - 1 atomic-% of carbon.
  • the passivation layer comprises 31 - 36 atomic-% of aluminum, 52 - 56 atomic-% of oxygen, 1,5 - 2,5 atomic-% of halogen, 8 - 11 atomic-% of hydrogen, and 0,2 - 0,5 atomic-% of carbon.
  • impu ⁇ rities may include halogen, hydrogen, and carbon.
  • the structure to be fabricated is a photovoltaic cell structure.
  • a photovoltaic cell structure can be used to convert incident electromagnetic radiation to elec ⁇ trical energy through a photovoltaic effect.
  • a solar cell structure a specific type of a photovoltaic cell structure, can be used to convert solar radiation into electrical energy.
  • the photovoltaic cell structure is an n-type silicon photovoltaic cell structure.
  • the photovoltaic cell struc ⁇ ture is a p-type silicon photovoltaic cell structure.
  • N-type cells have an re ⁇ type base and a thin p-conductive layer or emitter.
  • N- type silicon can be produced by doping silicon with compounds that contain one more valence electrons than the silicon does. Phosphorus and arsenic can be men ⁇ tioned as examples of such compounds. Since only four electrons are required to bond with the four adjacent silicon atoms, the fifth valence electron is available for conduction.
  • P-type silicon can be produced by doping silicon with a compound containing one less va- lence electrons than silicon.
  • Boron can be mentioned as an example of such a compound.
  • silicon having four valence electrons is doped with atoms that have one less valence electrons, i.e. three valence elec- trons, only three electrons are available for bonding with four adjacent silicon atoms, therefore an incom ⁇ plete bond (hole) exists which can attract an electron from a nearby atom. Filling one hole creates another hole in a different Si atom. This movement of holes is available for conduction.
  • the emit ⁇ ter can be p-doped through boron diffusion or added aluminum .
  • passivation of a surface for reducing surface recombi ⁇ nation, i.e. for reducing the recombination of charge carriers on or in immediate proximity to the passivat- ed surface.
  • a precursor for aluminum including a halogen e.g. chlorine
  • the use of a precursor for aluminum including a halogen affects the concentration of aluminum, oxygen, halogen, hydrogen, and carbon of the formed layer in a manner resulting in good passivation properties.
  • the term "surface of the silicon substrate”, “sur ⁇ face of the substrate comprising silicon”, “surface of the substrate”, “the surface” or “deposition surface” is used to address the surface of the substrate or the surface of the already formed deposit on the sub ⁇ strate.
  • the term “deposition surface” should be understood as including the surface of the substrate, which has not yet been exposed to any precursor as well as the surface, which has been exposed to one or more precursors.
  • the “deposition surface” chang- es during the method of forming a deposit or layer on the substrate when chemicals get adsorbed onto the surface .
  • the passivation layer is fabricated on the surface of the substrate by an ALD-type process.
  • the growth of the passivation layer in the ALD-type process is essentially thermally activated.
  • the passivation layer is fabricated on the surface of sub- strate, in some embodiments of the invention, by an ALD-type process excellent conformality and uniformity is achieved for the passivation layer.
  • plasma activation is employed.
  • the ALD-type process is a method for depositing uniform and conformal deposits or layers over substrates of various shapes, even over complex three dimensional structures.
  • the substrate is alternately exposed to at least two different precursors (chemicals) , usually one precur- sor at a time, to form on the substrate a deposit or a layer by alternately repeating essentially self- limiting surface reactions between the surface of the substrate (on the later stages, naturally, the surface of the already formed layer on the substrate) and the precursors.
  • the deposited material is "grown" on the substrate molecule layer by molecule layer .
  • the distinctive feature of the ALD-type pro ⁇ cess is that the surface to be deposited is exposed to two or more different precursors in an alternate man ⁇ ner with usually a purging period in between the pre- cursor pulses.
  • a purging period the deposition surface is exposed to a flow of gas which does not re ⁇ act with the precursors used in the process.
  • This gas often called the carrier gas is therefore inert to ⁇ wards the precursors used in the process and removes e.g. surplus precursor and by-products resulting from the adsorption reactions of the previous precursor pulse.
  • This purging can be arranged by different means.
  • the basic requirement of the ALD-type process is that the deposition surface is purged between the introduction of a precursor for a metal and a precursor for a non-metal.
  • the purging period ensures that the gas phase growth is limited and only surfaces ex ⁇ posed to the precursor gas participate in the growth.
  • the purging step with an inert gas can, ac- cording to one embodiment of the present invention, be omitted in the ALD-type process when applying two pro ⁇ cess gases, i.e. different precursors, which do not react with each other.
  • the purging period can be omitted between two precursors, which do not react with each other I.e. the purging period can be omitted, in some embodiments of the present invention, e.g. between two different precursors for oxygen if they do not react with each other.
  • the alternate or sequential exposure of the deposition surface to different precursors can be car ⁇ ried out in different manners.
  • the substrate is placed in a reaction space, into which precursor and purge gases are being introduced in a predetermined cycle.
  • Spatial atomic layer deposi ⁇ tion is an ALD-type process based on the spatial sepa- ration of precursors gasses.
  • the different precursor gasses can be confined in specific process areas or zones while the substrate passes by.
  • constant gas flow zones separated in space and a moving substrate are used in order to ob ⁇ tain the time sequential exposure.
  • a continuous coating process is achieved enabling roll- to-roll coating of a substrate.
  • the cycle time depends on the speed of move ⁇ ment of the substrate between the gas flow zones.
  • the thickness of the material or deposit pro- Jerusalem by the ALD-type process can be increased by re ⁇ peating several times a pulsing sequence comprising the aforementioned pulses containing the precursor ma ⁇ terial, and the purging periods.
  • the number of how many times this sequence, called the "ALD cycle" is repeated depends on the targeted thickness of the lay ⁇ er.
  • depos ⁇ iting the passivation layer is terminated before the passivation layer reaches a thickness of 5 nanometers, preferably before the passivation layer reaches a thickness of 3 nanometers.
  • the passivation layer has a thick- ness of below 5 nanometers, preferably below 3 nanome ⁇ ters .
  • the impurity distribution and/or content through the passivation layer is adjusted by exposing the deposition surface of the substrate to precursor pulses of different halogen content.
  • the halogen content of the pulse of the precursor for aluminum including a halogen i s 1 - 75 atomic percentage, and preferably 9 - 21 atomic percentage.
  • the halogen content may be varied between separate pulses resulting in the possibility to pro ⁇ cute a passivation layer with a predetermined impurity distribution.
  • the impurity content of the passivation layer is gradually changed through the passivation layer.
  • the use of an ALD-type process enables easy adjustment of the passivation layer composition by adjusting the amount of a precursor within the carrier gas to which the deposition surface is exposed to.
  • the ALD-type process enables the production of a passivation layer having the impurities, such as halogen, hydrogen, and carbon, uniformly doped or non-uniformly distributed within the passivation layer comprising aluminum ox- ide.
  • the substrate to be deposited according to the method of the present invention comprises crystal ⁇ line silicon (c-Si) .
  • the substrate comprises multi- and/or mono- crystalline silicon or any modification thereof.
  • Mono- like crystalline silicon can be mentioned as an exam ⁇ ple of such a modification.
  • the substrate comprising crystalline silicon is a sub- strate having an essentially planar form.
  • the substrate com- prising crystalline silicon is a substrate having a three-dimensional form.
  • the inventor of the present invention contrary to the general expectation in the art, surpris- ingly found out that by including chlorine as well as other impurities such as hydrogen and carbon, in a passivation layer comprising aluminum oxide, the passivation properties or quality of the layer were sur ⁇ prisingly improved.
  • the firing stability of the pas- sivation layer deposited according to the method of the present invention was likewise improved compared to a passivation layer comprising aluminum oxide and produced without using a halogen containing aluminum precursor.
  • the firing stability of aluminum oxide is mainly affected by the presence of hydrogen in the layer or film and on the silicon interface.
  • the aforementioned improvement is a result of the presence of e.g. chlorine, being a rather large atom or mole ⁇ cule, is able to trap hydrogen that may be released from the aluminum oxide material. It is also to be as ⁇ sumed that chlorine and other impurities present in the aluminum oxide material is able to reduce possible formation of water which usually may develop in the aluminum oxide passivation layer. Possibly released water may cause unwanted blistering of the passivation layer.
  • an advantage of the method according to the present invention is that blistering of the pas ⁇ sivation layer is significantly reduced when using a halogen containing precursor for aluminum for producing the passivation layer comprising aluminum oxide. It is also to be assumed that formed by-products, which contain halogen, such as HC1, can remove loose 3 ⁇ 40 on the deposition surface during the deposition process and decrease blistering formation. It is also to be assumed that the halogen in the aluminum precursor decreases the reactivity of the aluminum precursor compared to the precursor for aluminum without halo ⁇ gen. The inventor of the present invention found out that forming a passivation layer according to the present invention at the specified temperature range, a large amount of impurities can be left in the formed passivation layer. The impurities were found to have a positive impact on the passivation of the silicon sur- face.
  • the aluminum oxide passivation layer formed on the surface of the substrate comprises halogen incorporated in the passivation material.
  • the halogen is present within the passivation layer in ion form.
  • the halogen forms a bond with the silicon of the substrate.
  • the precursor for aluminum including a halogen is selected from a group consisting of a precursor for aluminum including chlorine, a precursor for aluminum including fluorine, a precursor for aluminum including iodine, and a precursor for aluminum including bro- mine.
  • the precursor for aluminum including a halogen is a precursor for aluminum including chlorine.
  • the ALD-type process enables switching between different precursor pulses during the deposition process.
  • the precursor for aluminum including a halogen can be changed to another precursor for aluminum including a halogen such that a passivation layer comprising aluminum oxide and at least two different halogen elements is formed.
  • the precursor for aluminum including a halogen can be changed during the deposition process to a precursor for aluminum not including a halogen.
  • the precursor for aluminum including chlorine is se- lected from a group consisting of AICI 3 , AlMeCl 2 and AlMe 2 Cl .
  • the precursor for aluminum including fluorine is selected from a group consisting of AIF 3 , AlMe 2 F, AlMeF 2 .
  • the precur- sor for aluminum including iodine is selected from a group consisting of AII 3 , AlMeI 2 , AlMe 2 I.
  • the precursor for alu ⁇ minum including bromine is selected from a group con ⁇ sisting of AlBr 3 , AlMeBr 2 , AlMe 2 Br.
  • the precursor for oxygen is a selected from a group consisting of 0 2 , O3, r?OHd, A10-- Et 3 , A10iPr 3 , H 2 0 2 , N 2 0, and N 2 0 4 .
  • the step of exposing the deposition surface of the substrate in a reaction space to the at least one pre ⁇ cursor for oxygen comprises exposing the deposition surface to at least two different precursors for oxy ⁇ gen at least partly simultaneously.
  • the step of exposing the deposition surface of the substrate in a reaction space to the at least one pre ⁇ cursor for oxygen comprises exposing the deposition surface to at least two different precursors for oxy ⁇ gen in a sequential manner without purging the deposi- tion surface in between the exposure of the different precursors for oxygen .
  • the precursor for aluminum including chlorine is Al- Me 2 Cl and the precursor for oxygen is O3.
  • the precursor for alu ⁇ minum including chlorine is AICI 3 and the precursor for oxygen is O3.
  • the deposition is carried out at a temperature of 150 - 250 °C, and preferably at a temperature of 190 - 210 °C . The inventor of the present invention found out that the use of this kind of temperature range result ⁇ ed in a rather high impurity level, and therefore a high carrier lifetime and good thermal stability.
  • the method further comprises the step of heat treating the formed passivation layer. In one embodiment of the present invention the method further comprises the step of annealing the structure. In one embodiment of the present invention the step of annealing the struc ⁇ ture is carried out at a temperature of 300 - 900 °C, preferably 350 - 450 °C, and more preferably 390 - 410 °C . In one embodiment of the present invention the step of annealing the structure is carried out for 0,1 seconds - 120 minutes, preferably 20 - 40 minutes, and more preferably 25 - 35 minutes. In one embodiment of the present invention the method further comprises the step of firing the structure.
  • the step of firing the structure is carried out at a temperature of 650 - 1000 °C, prefer ⁇ ably 700 - 900 °C, and more preferably 750 - 850 °C . In one embodiment of the present invention the step of firing the structure is carried out for 0,1 - 10 sec ⁇ onds, preferably 1 - 5 seconds, and more preferably for 2 - 3 seconds .
  • the structure further comprises a conductive electrode on the passivation layer.
  • the conductive electrode comprises metal.
  • the structure further comprises a layer comprising alumi- num on the passivation layer.
  • the method further comprises the step of forming a conductive electrode on the pas- sivation layer.
  • the method further comprises the step of form ⁇ ing a layer comprising aluminum on the passivation layer .
  • a lay ⁇ er or a conductive electrode when e.g. a lay ⁇ er or a conductive electrode is referred to as being "on" another layer, it can be directly on the other layer, or intervening layers may be present.
  • a barrier layer between the passivation layer and the conductive electrode can be mentioned as one example of such an intervening layer.
  • the structure comprises further layers.
  • further layers may include e.g. an anti- reflection layer or a reflection enhancing layer.
  • both sides of the essentially planar substrate are deposited with a passivation layer.
  • the present invention further relates to the use of chlorine incorporated in a passivation layer comprising aluminum oxide on a surface of a substrate comprising crystalline silicon for reducing recombination of charge carriers on the surface of the sub ⁇ strate.
  • the chlorine present in the passivation layer comprising aluminum oxide can be used for improving the passivation effect or quality of the passivation layer .
  • the present invention further relates to the use of chlorine incorporated in a passivation layer comprising aluminum oxide on a surface of a substrate comprising crystalline silicon for improving the firing stability of the passivaiton layer.
  • the efficient passivation was observed by a significant increase in the efficiency of a solar cell whose surface was passivated with a layer of aluminum oxide deposited by using a precursor for aluminum including a halogen, compared to an otherwise identical- ly produced solar cell structure but during which dep ⁇ osition no halogen containing aluminum precursor has been used.
  • a method, and a structure, to which the invention is related may comprise at least one of the embodiments of the invention described hereinbefore.
  • An advantage of the method according to the present invention is that it enables the inclusion of a desired impurity level into a passivation layer com ⁇ prising aluminum oxide.
  • the inventor of the present invention surprisingly found out that the presence of impurities such as halogen, carbon and hydrogen in the aluminum oxide passivation layer improves the passivation properties of the formed layer on the surface of a silicon substrate.
  • An advantage of the method according to the present invention is that the specific concentration of the at least one precursor for oxygen improves the passivation properties of the formed passivation layer on the surface of the substrate, in particular the carrier lifetime of the passivation properties.
  • An advantage of the passivation layer formed with the method according to the present invention is that the halogen in the aluminum precursor affects in an advantageous manner the negative charge density as well as the interface defect density of the pas ⁇ sivation layer.
  • An advantage of the present invention is that the firing stability of the passivation layer deposit ⁇ ed according to the present invention is likewise im- proved.
  • An advantage of the present invention is that the unwanted delamination of the passivation layer, i.e. blistering formation, is reduced when including e.g. halogen, hydrogen, and carbon into the aluminum oxide material.
  • DMAC1 dimethylaluminum chloride
  • An advantage of especially dimethylaluminum chloride (DMAC1) as a precursor for producing a pas ⁇ sivation layer comprising aluminum oxide is that the production of dimethylaluminum chloride is cheaper than the production of e.g. trimethylaluminum traditionally used for producing a passivation layer of aluminum oxide.
  • the use of cheaper precursors highly affects the final costs for the photovoltaic cell man ⁇ ufacturer .
  • the ALD-type process is a method for depositing uniform and conformal films or layers over substrates of various shapes. Further, as presented above in ALD-type processes the deposit is grown by alternately repeating, essentially self- limiting, surface reactions between a precursor and a surface to be coated.
  • the prior art discloses many different apparatuses suitable for carrying out an ALD-type process.
  • the construction of a processing tool suitable for carrying out the methods in the fol- lowing embodiments will be obvious to the skilled per ⁇ son in light of this disclosure.
  • the tool can be e.g. a conventional ALD tool suitable for handling the pro ⁇ cess chemicals.
  • the method of Fig. 1 and the structure of Fig. 2 illustrate, respectively, a method and the cor ⁇ responding structure according to one embodiment of the invention.
  • the method of Fig. 1 presents how to carry out the method for passivating the silicon substrate 3 with a passivation layer 2 comprising alumi- num oxide and specific impurities incorporated there ⁇ in .
  • Figure 1 illustrates a method according to one embodiment of the present invention for producing a structure 1 comprising a passivation layer 2 on a surface of a substrate 3 comprising crystalline sili ⁇ con, wherein the passivation layer 2 comprises aluminum oxide having specific impurities incorporated therein .
  • the method of Fig. 1 illustrates a method ac- cording to one embodiment of the invention for carrying out efficient surface passivation on a surface of crystalline silicon.
  • This exemplary embodiment of the present invention begins by bringing the silicon substrate 3 into the reaction space (step 1) of a typical reactor tool, e.g. a tool suitable for carrying out an ALD-type process as a batch-type process.
  • the reaction space is subsequently pumped down to a pressure suita- ble for forming a passivation layer 2, using e.g. a mechanical vacuum pump, or in the case of atmospheric pressure ALD systems and/or processes, flows are typi ⁇ cally set to protect the deposition zone from the at- mosphere.
  • the substrate 3 is also heated to a tempera ⁇ ture suitable for forming the passivation layer 2 by the used method.
  • the substrate 3 can be introduced to the reaction space through e.g. an airtight load-lock system or simply through a loading hatch.
  • the sub- strate 3 can be heated by e.g. resistive heating ele ⁇ ments which also heat the entire reaction space.
  • the surface of the sil- icon substrate can be conditioned in step 1 such that the passivation layer 2 may be essentially directly deposited on the silicon surface.
  • This conditioning of the silicon surface commonly includes chemical purifi ⁇ cation of the surface of the silicon substrate 3 from impurities and/or oxidation. Especially removal of ox ⁇ ide is beneficial when the silicon surface has been imported into the reaction space via an oxidizing en ⁇ vironment, e.g. when transporting the exposed silicon surface from one deposition tool to another.
  • the conditioning can be done ex-situ, i.e. outside the tool suitable for ALD-type processes.
  • An example of an ex-situ conditioning process is etching for 1 min in a 1 % HF solution followed by rinsing in Dl-water.
  • a passivation layer 2 comprising aluminum oxide and including impurities such as halogen, hydrogen and carbon, directly on the surface of the silicon substrate 3.
  • the precursors are suitably introduced into the reaction space in their gaseous form. This can be realized by first evaporating the precursors in their respective source containers which may or may not be heated depending on the properties of the precursor chemical itself.
  • the evaporated precursor can be de ⁇ livered into the reaction space by e.g. dosing it through the pipework of the reactor tool comprising flow channels for delivering the vaporized precursors into the reaction space.
  • Controlled dosing of vapor into the reaction space can be realized by valves in ⁇ stalled in the flow channels or other flow control- lers . These valves are commonly called pulsing valves in a system suitable for ALD-type deposition.
  • a reactor suitable for ALD-type deposition comprises a system for introducing carrier gas, such as nitrogen or argon into the reaction space such that the reaction space can be purged from surplus chemical and reaction by-products before introducing the next chemical into the reaction space.
  • carrier gas such as nitrogen or argon
  • This feature togeth- er with the controlled dosing of vaporized precursors enables alternately exposing the surface of the sili ⁇ con film to precursors without significant intermixing of different precursors in the reaction space or in other parts of the reactor.
  • the flow of carrier gas is commonly continuous through the reac ⁇ tion space throughout the deposition process and only the various precursors are alternately introduced to the reaction space with the carrier gas.
  • purging of the reaction space does not necessarily result in complete elimination of surplus precursors or reaction by-products from the reaction space but resi- dues of these or other materials may always be pre ⁇ sent .
  • step a) is carried out; i.e. the surface of the silicon substrate 3 is exposed to a precursor for aluminum including a halogen, such as dimethylaluminumchloride (DMAC1) .
  • a precursor for aluminum including a halogen such as dimethylaluminumchloride (DMAC1) .
  • DMAC1 dimethylaluminumchloride
  • Expo ⁇ sure of the surface to the precursor for aluminum including halogen results in the adsorption of a portion of the introduced precursor, e.g. DMAC1, onto the sur ⁇ face of the silicon substrate.
  • the deposition surface is exposed to at least one precursor for oxygen (step b) ) , such as O3.
  • the precursor for oxygen is provided to the depo- sition surface of the substrate with a gas flow in ⁇ cluding 1 - 15 mole-% of the precursor for oxygen. Subsequently, the reaction space is purged again. Some of the precursor for oxygen in turn gets adsorbed onto the surface resulting from step a) .
  • each exposure of the deposition surface to a precursor in step a) or step b) results in formation of additional deposit on the deposition surface as a result of ad ⁇ sorption reactions of the corresponding precursor with the deposition surface.
  • Thickness of the passivation deposit or layer 2 on the surface of the silicon sub ⁇ strate 3 can be increased by repeating the steps a) and b) , as presented by the flow-chart of Fig. 1.
  • the thickness of the passivation deposit is increased un- til a targeted thickness is reached, after which the alternate exposures are stopped and the process is ended.
  • a pas- sivation layer comprising aluminum oxide and impurities such as halogen, hydrogen and carbon incorporated therein is formed on the surface of the silicon sub ⁇ strate.
  • This passivation layer provides the efficient and advantageous surface passivation discussed above.
  • the passivation deposit also has excellent thickness uniformity and compositional uniformity along the dep ⁇ osition surface.
  • struc- ture comprising a passivation deposit comprising aluminum oxide and including impurities incorporated therein can be fabricated.
  • EXAMPLE 1 Fabricating a structure comprising a pas- sivation layer on a surface of a silicon substrate
  • a passivation layer 3 was formed on the surface of crystalline silicon substrates 2 according to an embodiment of the present invention shown in Fig. 1.
  • the substrates were first inserted inside the reaction space of a P400 ALD batch tool (available from Beneq OY, Finland) . After preparations for load ⁇ ing the substrates into the ALD tool, the reaction space of the ALD tool was pumped down to underpressure and a continuous flow of carrier gas was set to achieve the processing pressure of about 1 mbar (1 hPa) and the substrates 3 were subsequently heated to the processing temperature. The temperature was stabi- lized to the processing temperature of 200 °C inside the reaction space by a computer controlled heating period of six hours.
  • the carrier gas discussed above, and responsible for purging the reac ⁇ tion space was nitrogen (N 2 ) .
  • the processing tempera- ture was sufficient to result in a thermally activated ALD-type growth and no plasma activation was employed in this example.
  • the surface of the crystalline silicon substrates was conditioned. During this step possible impurities can be removed from the exposed surface of the crystalline silicon substrates.
  • the precursor for aluminum including chlorine was introduced to the reaction space according to step a) of Fig. 1, to expose the deposition surface of the silicon substrate 3 to said precursor.
  • the carrier gas purge the reaction space from surplus precursor for aluminum including chlorine and reaction byproducts
  • the result ⁇ ing surface of the substrate was similarly exposed to the precursor for oxygen in step b) .
  • the precursor for oxygen was provided to the deposition surface with a gas flow including 1 - 15 mole-% of the precursor for oxygen.
  • the reaction space was purged again. This pulsing sequence consisting of step a) and step b) was carried out once and then repeated 1 - 1999 times before the process was ended and the sub ⁇ strates were ejected from the reaction space and from the ALD tool.
  • the 2 - 2000 "ALD cycles" resulted in a passivation layer of aluminum oxide having chlorine, hydrogen and carbon incorporated therein with a thick- ness of approximately 1-4,9 nm on the surface of the substrate comprising crystalline silicon.
  • the pas ⁇ sivation layer 2 was measured to be very conformal and uniform over large surface areas.
  • Exposure of the surface of the substrate to a specific precursor was carried out by switching on the pulsing valve of the P400 ALD tool controlling the flow of the precursor chemicals into the reaction space. Purging of the reaction space was carried out by closing the valves controlling the flow of precur- sors into the reaction space, and thereby letting only the continuous flow of carrier gas flow through the reaction space.
  • the pulsing sequence in this example was in detail as follows: 0.6 s exposure to DMAC1, 1.5 s purge, 0.4 s exposure to O3, 2.0 s purge.
  • An expo ⁇ sure time and a purge time in this sequence signify a time a specific pulsing valve for a specific precursor was kept open and a time all the pulsing valves for precursors were kept closed, respectively.
  • a passivation layer comprising aluminum oxide and chlorine, hydrogen, and carbon incorporated there ⁇ in was formed.
  • the passivation layer comprised 33.8 atomic-% of aluminum, 54 atomic-% of oxygen, 2 atomic- % of chlorine, 10 atomic-% of hydrogen, and 0.2 atom ⁇ ic-% of carbon.
  • the precursor for aluminum including chlorine was DMAC1 and the precursor for oxygen was O3, but other precursors can also be used.
  • the other precursors for aluminum including chlorine include e.g. AICI3, and AlMeCl2, and the other precur ⁇ sors for oxygen include e.g. O2, . OHd, AlOEta, A10iPr 3 , H 2 O 2 , 2 O, and N 2 O 4 .
  • the precursor for aluminum as well as the precursor for oxygen can be changed from one to another during the deposition process.
  • a precursor for aluminum including iodine, a precursor for aluminum including bromine, or a precursor for aluminum including fluorine can be used for the production of a passivation layer.
  • the test results showed that the passivation quality of a passivation layer comprising aluminum oxide and having iodine, bromine or fluorine incorporated therein was improved compared to a passivation layer comprising aluminum oxide but no halogen incorporated therein.
  • a passivation layer was formed on the surface of a substrate comprising crystalline sil ⁇ icon by using trimet ylaluminum (IMA) as a precursor for aluminum instead of DMAC1 as in example 1.
  • IMA trimet ylaluminum
  • the precursor for oxygen was the same as in example 1, i.e. 0 . 3. All other parameters were kept as in example 1 above .
  • a passivation layer comprising aluminum oxide was formed.
  • the passivation layer of the comparative example 1 comprised 38 atomic-% of aluminum, 58 atom- ic-% of oxygen, 3 atomic-% of hydrogen, and 0.1 atom ⁇ ic-% of carbon.
  • comparative example 1 was likewise subjected to the step of annealing and to the step of firing under similar conditions as presented above in example 1.
  • example 1 and the compar- ative example 1 were measured, after the step of an ⁇ nealing and also after the step of firing, to identify their carrier lifetimes, respectively.
  • the measure ⁇ ments were carried out by illuminating the surface of the silicon substrate with a pulsing laser and. the rate of change in resistivity was measured after the laser pulse was terminated. The excess carrier life ⁇ time was then calculated from the measurement the higher the lifetime curve is, the slower is the recom ⁇ bination and therefore the better is the passivation.
  • the structure of Fig. 2 further illustrates the presence of a conductive electrode 4, e.g. alumi ⁇ num electrode, formed on the passivation layer 2.
  • the aluminum electrode 4 can be fabricated on the pas ⁇ sivation layer 2 by a screen printing method compris ⁇ ing e.g. printing the aluminum paste on the pas ⁇ sivation layer 2 , drying and curing the paste at high temperature using method steps, which will be obvious to the person, skilled in the art.
  • the structure ac ⁇ cording to the present invention may also comprise further layers.
  • a. barrier layer may be included between the passivation layer and the conductive elec ⁇ trode for efficiently protecting- the passivation layer from effects caused by interaction between the pas ⁇ sivation layer and the conductive electrode 4.

Abstract

L'invention concerne un procédé de fabrication d'une structure comprenant une couche de passivation disposée sur une surface d'un substrat comprenant du silicium cristallin pour réduire une recombinaison de porteurs de charge sur la surface du substrat. Elle concerne une structure correspondante.
PCT/FI2013/051090 2012-11-29 2013-11-21 Procédé de fabrication d'une structure comprenant une couche de passivation sur une surface d'un substrat WO2014083240A1 (fr)

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WO2016079498A1 (fr) * 2014-11-17 2016-05-26 The University Of Liverpool Couche de barrière diélectrique

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